Nice Weekend Alert!

Current Radar

Well, That Was Close

Too much cloud cover this morning, insufficient dew points, and unidirectional wind profiles are among the reasons we didn’t gett tornadic storms today. They were very close. That storm to our SW, then S, was rotating pretty well (it may have dropped a tornado, NWS will confirm later), although it did lose its oomph when it got closer to I-65.

Anyway, the severe weather threat tonight is over. Even our Severe Thunderstorm Watch was cancelled 2 hours early. A cold front will push through tonight while we sleep, and may deliver a few no-worry showers.

Friday – Sunday: Yes, Please

Maybe a little colder than you’d like, but we’ll dry out, with chilly mornings, and nice afternoons.

There are a few chances for rain next week. And, yes, maybe thunderstorms next Thursday, but that forecast is in voo-doo land (and too far away) to be worthy of further comment.

This website supplements @NashSevereWx on Twitter, which you can find here.

Severe Thunderstorm Watch Until 10PM

Current Radar

Severe Thunderstorm Watch – In Effect Until 10:00PM CT

The Storm Prediction Center has issued a Severe Thunderstorm Watch for Davidson and Williamson Counties. Here’s a closer look:

ww0071_radar

severe watch

Probabilities

probs

Stay tuned to @NashSevereWx for updates, as well as multiple other sources (like local TV). We will not post warnings on here, so follow us on Twitter for more frequent, up-to-date information.

Friday: Clearing Out – Wake Up 57° High 68°

Still, some clouds will hang around, but we are dry! Highs will be a bit cooler, with temperatures in the mid-to-upper 60s by afternoon.

Saturday and Sunday: A Much-Needed Break

Highs will only be in the low to mid 60s, but sunshine will be out in full force. This will be a great weekend to get outside!

Extended Outlook:

Screen Shot 2016-03-31 at 7.15.32 AM

This website supplements @NashSevereWx on Twitter, which you can find here.

NEW Mesoscale Discussion - Watch Possible Soon

Current Radar

NEW Mesoscale Discussion – Issued at 3:48PM CT

The Storm Prediction Center has issued a “mesoscale discussion” that borders Davidson and Williamson Counties. Here’s a snippet:

new 1

new 2

In short, our area will likely be placed under some sort of severe weather watch very soon. Damaging winds are the primary risks, although large hail and an isolated tornado cannot be ruled out. Instability is limited and looks to remain that way for the rest of the day.

Stay tuned to @NashSevereWx for updates, as well as multiple other sources (like local TV). We will not post warnings on here, so follow us on Twitter for more frequent, up-to-date information.

Friday: Clearing Out – Wake Up 57° High 68°

Still, some clouds will hang around, but we are dry! Highs will be a bit cooler, with temperatures in the mid-to-upper 60s by afternoon.

Saturday and Sunday: A Much-Needed Break

Highs will only be in the low to mid 60s, but sunshine will be out in full force. This will be a great weekend to get outside!

Extended Outlook:

Screen Shot 2016-03-31 at 7.15.32 AM

This website supplements @NashSevereWx on Twitter, which you can find here.

New Mesoscale Discussion - Watch Possible Soon

Current Radar

Now: Strong/Severe Storms Approaching – As of 3PM 75°

The Storm Prediction Center has issued a “mesoscale discussion” that borders Davidson and Williamson Counties. Here’s a snippet:

Capture

Capture1

In short, our area will likely be placed under some sort of severe weather watch very soon. Winds are close, but not quite where they need to be for a robust tornado threat. However, surface heating and dewpoints continue to rise.

Stay tuned to @NashSevereWx for updates, as well as multiple other sources (like local TV). We will not post warnings on here, so follow us on Twitter for more frequent, up-to-date information.

Friday: Clearing Out – Wake Up 57° High 68°

Still, some clouds will hang around, but we are dry! Highs will be a bit cooler, with temperatures in the mid-to-upper 60s by afternoon.

Saturday and Sunday: A Much-Needed Break

Highs will only be in the low to mid 60s, but sunshine will be out in full force. This will be a great weekend to get outside!

Extended Outlook:

Screen Shot 2016-03-31 at 7.15.32 AM

This website supplements @NashSevereWx on Twitter, which you can find here.

Threat Reduced, But Still There. Hail, Winds Biggest Threat Later.

Current Radar

Today: PM Severe Weather Possible – High 74°

We’ve been covered by clouds this morning, which has prevented storm-making destabilization.

The winds, while strong, are largely unidirectional, which does not support large, tilted updrafts necessary for terrible weather.

We have been writing here (and tweeting @NashSevereWx) about the need for us to destabilize and get some variable wind direction if we are going to believe the models’ argument that we will see severe weather here later today.

So, all morning, we’ve been waiting for this to change, but it hasn’t changed. And, now, even though we expect some storm-making destabilization and more storm-favorable wind fields this afternoon, it may be too little too late to create a significant severe weather event feared by the models (and the Storm Prediction Center) this morning. As you’ll see below, although the tornado risk has been reduced (but not eliminated), the hail and wind risk hasn’t (at least, not that much).

That said, we will see storms later today, and they could be severe. Just, not as bad as the “significant severe” event advertised by the models this morning and in the Storm Prediction Center’s 8 AM outlook. It’s a matter of degree, y’all.

The new Outlook from SPC has been published. We have been removed from the “enhanced risk” area and placed in the next-lowest category, a “slight risk,” which is a 2 on a scale of 0 to 5.

SPC has reduced the probability of a tornado within 25 miles of us from 10% to 5%, and removed the “hatched” (significant severe) threat from all of Tennessee.

The probability of damaging winds within 25 miles of us remains 15%.

The probability of large hail has also been pulled further away from us. The current probability of large hail within 25 miles of us is 15%:

All that said, it’s still going to rain and storm today, and a severe weather threat remains!

The weather does not care about these outlooks. We have had severe thunderstorms and tornadoes under these outlooks before. But, I like the direction the forecast is moving.

Timing

This remains a mess. Models have been little help. This graphic from NWS-Nashville is helpful.

It’s important to not treat the models as truth. Before we start sounding an alarm, we will need to see CAPE and instability, along with helicity and shear values, actually increase, and make itself evident in weather balloon and other observed data. It has to move beyond the theoretical to the actual. Do not assign alarm to model forecasts. Wait for storms on the radar.

We will be updating you throughout the day on Twitter at @NashSevereWx. We will not post warnings on this website. Consult multiple, reliable weather sources for forecast and warning information, and stay weather-aware. 

Rain totals are expected to be around 1-2″. Localized areas (especially in Williamson County) could see up to 3″ of rain with any heavier storms that “train” across a local area.

Screen Shot 2016-03-31 at 7.09.48 AM

Friday: Clearing Out – Wake Up 54° High 67°

Still, some clouds will hang around, but we are dry! Highs will be a bit cooler, with temperatures in the mid-to-upper 60s by afternoon.

Saturday and Sunday: A Much-Needed Break

Highs will only be in the low 60s, but sunshine will be out in full force. This will be a great weekend to get outside!

Extended Outlook:

Screen Shot 2016-03-31 at 7.15.32 AM

This website supplements @NashSevereWx on Twitter, which you can find here.

Hail, Tornadoes, Damaging Winds Possible Late Afternoon/Evening

Current Radar

Today: PM Severe Weather Possible – 9AM 64° High 74°

Today’s Take-Away: Whether you will be at work this afternoon/evening, at an event, or at home, have a severe weather plan ready. Use multiple reliable sources to get any warnings that may be issued and stay up-to-date on any developments later today.

The Storm Prediction Center updated their convective outlook overnight, upgrading us to an “Enhanced Risk” of severe weather for this afternoon’s storm threat.

SPC Outlook as of 800AM CT

Screen Shot 2016-03-31 at 8.19.32 AM

On David’s unofficial SPC outlook translator, this is a “getting concerned” event:

Hazards

The breakdown of each individual hazard is laid out below:

Probability of a Tornado within 25 miles of you: Davidson Co. 5%, Williamson Co. 10%

Nashville-proper is right on the line when it comes to a higher, more significant tornado threat today. Regardless of the lines on the map, both of our counties need to be equally weather-aware. The SPC does include a “10% significant” hatched area, indicating a 10% chance of a strong tornado within 25 miles of any point (inside the black hatch marks). This area includes everyone south of I-40.

Damaging Wind: 15% Chance of Damaging Winds within 25 miles of any (yellow) highlighted point

Severe Hail: 30% Significant Probability for most of Davidson/Williamson Counties

This threat map indicates that both Davidson and Williamson counties face a 30% significant probability of severe hail within 25 miles of any point (inside the 30% black-hatched region). Also, a significant threat area (black hash marks) indicates the potential for larger hailstones, in excess of 2+” diameter hail, within that highlighted zone.

Timing

HRRR Model

image5

10-11AM, Round 1 Ends: The morning rain – containing no severe potential – moves out completely, around 11AM, and we begin a clearing out process. Again, no severe weather is anticipated through this period.

11AM-2PM, Clouds Move Out, Instability Moves In: Morning cloud cover should begin to break up, according to the HRRR. This will lead to a heating and mixing of our atmosphere. Think of it like a convection oven. In other words, our atmosphere will begin destabilize. A destabilized atmosphere makes storms.

HRRR at 2PM — Clouds Breaking Up

hrrr_cloud_nashville_10

2PM-5PM, Storms Develop West: Storms will develop ahead of the cold front in western Tennessee. They will enter a more unstable atmosphere and will likely strengthen, albeit very dependent on how much instability has been created by any sunshine that works in this afternoon. However, even without a lot of sun, there will be so much warm, wet air moving in, that it won’t be difficult to destablize.

5PM-9PM, Storms Arrive: Storms should make their way into the western portions of Davidson/Williamson Counties a little before sunset. The “mode” or structure of these storms looks to be either super-cellular or multi-cellular. What does this mean? Multi-cellular storms usually pose more of a damaging wind/hail threat, whereas supercells are more known for tornadoes and large hail.

David’s Thoughts: As David has mentioned, today’s event is not like the two earlier events that we have seen this year. For those, there was question as to whether or not severe weather would even occur. With this event, severe weather is likely, but we cannot be sure exactly where. We are expected to have all of the necessary ingredients for robust thunderstorm development this afternoon/evening. We hope the storms come much later than early evening because the models think instability will be less then.

If we are going to get a Tornado Watch for the approaching weather, it probably won’t be issued until mid-afternoon.

We will be updating you throughout the day on Twitter at @NashSevereWx. Consult multiple, reliable weather sources and stay weather-aware.

Rain totals are expected to be around 1-2″. Localized areas (especially in Williamson County) could see up to 3″ of rain with any heavier storms that “train” across a local area.

Screen Shot 2016-03-31 at 7.09.48 AM

Friday: Clearing Out – Wake Up 54° High 67°

Still, some clouds will hang around, but we are dry! Highs will be a bit cooler, with temperatures in the mid-to-upper 60s by afternoon.

Saturday and Sunday: A Much-Needed Break

Highs will only be in the low 60s, but sunshine will be out in full force. This will be a great weekend to get outside!

Extended Outlook:

Screen Shot 2016-03-31 at 7.15.32 AM

This website supplements @NashSevereWx on Twitter, which you can find here.

What to Know About the Storm Potential for Tomorrow

Current Radar

With our first round of rain, we could begin to see scattered rain showers as early 10 PM. Most of the heavy constant rainfall won’t begin until after midnight. We expect a wet morning commute:

Thursday: Two Rounds of Rain & Storms – Wake Up 61° High 74°

Summary:

The most recent SPC severe weather outlook has us very close the area alerted to significant severe weather potential.

A more localized view of us on that bubble:

image_full6.gif (960×720) - Google Chrome 2016-03-30 15.24.07

On David’s unofficial SPC outlook translator, this is a “you have my attention” event, right on the border of “getting concerned”:

As David mentioned early, this event is nothing like the two earlier “slight” risk events that we have seen. In both those events, there was question as to whether or not severe weather would occur at all in the region. With this event, severe weather will be happening at some point tomorrow. The exact location of where it will happen is still TBD. We are expected to have all of the ingredients present for severe weather in the afternoon/evening hours. The question is if the moisture from the storms to our West reach our location in time to utilize those ingredients.

We are expecting two rounds associated with this weather event. First, in the early morning, main concern is flash flooding. Then, a break in the action, to allow for the atmosphere to potentially recharge. Second, later in the afternoon/early evening, our main concerns are damaging winds, more localized flash flooding, hail, and a tornado or two. Make note that all our hazard levels have increased through the day.

image_full6.gif (960×720) - Google Chrome 2016-03-30 15.23.50

Round 1 – Early Morning

Timing: Rush hour primarily, expect it to take you a little longer to get to work

Main Concern: Localized Flash Flooding

 

NAM, GFS, and Euro are all taking the stance that we may have a few periods of showers in the early AM, but will get significant heavy downpour during morning rush hours:

hires_ref_nashville_18.png (1000×750) - Google Chrome 2016-03-30 16.06.15

While the models may not agree how, both of the scenarios will lead to localized flash flooding. Be safe and aware of your surroundings. If you see a flooded roadway, “Turn Around Don’t Drown!”

Lunchtime-ish Break in the Action

When the morning rain ends, weather nerds everywhere will be rushing to view the satellite trends (will the sun come out?), special weather balloon data (if NWS launches some), and the SPC’s RAP Mesoanalysis page, all of which will indicate whether the atmosphere is filling back up with instability/CAPE, shear, supportive wind fields, LCL heights, and other ingredients that will have to come together to set us up for severe weather ahead of an approaching cold front expected later in the day.

For example, here’s the NAM4 model for 4 PM Thursday, showing some sunshine, which suggests we’ll be recharging our CAPE/instability.

hires_btop_nashville_40.png (1000×750) - Google Chrome 2016-03-30 07.54.35

Round 2 – The Potential Severe Storms

Timing: Still a little too far out to tell. ETA late afternoon/evening/late

Based on the information from the NWS, estimate times are probably between 4 PM – 10 PM. I really do not see any storms developing much before 5 PM because that is when our atmosphere will be recharging.

image_full5.gif (960×720) - Google Chrome 2016-03-30 15.22.46

All of the models seem to be agreeing that the rain will be here in the evening hours. How early or late is still undetermined and all the models vary at that point.

GFS thinks rain could start around 7 PM with the heavy, potentially severe storms right behind it:

WeatherBELL Models _ Premium Weather Maps - Google Chrome 2016-03-30 15.33.33

The NAM holds off a bit, shows some showers going north of us and the main event not reaching us until after 9 PM.

hires_ref_nashville_33.png (1000×750) - Google Chrome 2016-03-30 16.11.54

Main Concern: Damaging Winds, Hail, Flash Flooding, a Tornado or two.

A lot of our concern about “how bad will it be” is still up in the air. The lull after the morning rain will be the key to our potential severe weather — will the atmosphere recharge? A strong southern wind will shove reinforcing warm air to recharge our atmosphere; however, if pockets of the region remain clouded over, or ongoing storms to the south cut off the good southern moisture transport, the threat will diminish. In addition, the upper level support of severe weather should be higher nearer to the Ohio River. The whereabouts of these gaps in co-located severe weather ingredients present the forecaster with the most uncertainty here — no one knows where they will develop — so absent that certainty SPC did not feel it appropriate to expand its risk area across I-65. I also think our risk is slightly lower because models suggest the storms will show up after dark. If storms show up after dark, less ingredients will be present.

Flooding concerns will remain through the evening hours. If we get one of those supercells “training” over our area, the already-saturated ground from the morning rain could set the stage for localized flooding. Most weather deaths and injuries occur from people in cars around flooded roads.

The majority of the threat does still remain to our west; however, these storms very easily with the right timing could develop and move into our region.

One forecast model, the usually-over-dramatic NAM4, is painting a grim, and frankly scary, severe weather setup tomorrow. The details of that aren’t helpful. It looks way too unrealistic; however, the other models are building a consensus that the storm potential is real. So, stay tuned.

We will be updating you throughout the day on Twitter at @NashSevereWx. Consult multiple reliable weather sources tonight and tomorrow.

When Will It End?

Rain should be gone by your drive to work on Friday.

Rain totals are expected to be around 1′ to 2″ when all is said and done. Local areas (especially in Williamson County) could potentially see up to 3″ of rain through this event.

image_full3.gif (960×720) - Google Chrome 2016-03-30 07.29.09

Extended Outlook:

My Forecast - Google Chrome 2016-03-30 15.16.53

This website supplements @NashSevereWx on Twitter, which you can find here.

Thursday’s Severe Weather Threat Growing, Closer

Current Radar

Updates reflecting new information from this afternoon are written below in blue.

Today: Clouds Rolling In, Windy – High 75°

We’ve already begun to see the clouds moving into our area ahead of the storms we will be seeing tonight into tomorrow. Even with the clouds, temps are expected to climb very quickly into the 70°s.

Visible Satellite Image showing the cloud cover building to our west and moving in:

The winds could be annoying at times today with gusts up to 25 mph. Sustained winds should remain between 5-15 mph the rest of the time.

Tonight: Heavy Rain Late – Temps only Dropping into the 60°s

The HRRR model expects showers beginning as early as 10 PM tonight. Heavier rainfall will not come until the early AM hours tomorrow.

Thursday: Heavy Rain Early, Severe Storms in the Afternoon – Wake Up 61° High 74°

Summary

The lunchtime severe weather outlook from the Storm Prediction Center has arrived. Compared to this morning, this outlook represents a heightened severe weather concern that’s getting closer to us:

This is a “you have my attention” event, right on the border of “getting concerned”:

Let me add something else — this isn’t anything like the last two events we’ve had here, where there was a conditional “slight” risk. In the first event, the condition was instability/CAPE — none developed, nothing happened. In the second event, the condition was shear (and CAPE), we got little of each, not much happened.

In this event, unlike what we’ve seen so far this storm season, SPC expects a significant severe weather event to be ongoing to our west, then racing into Middle Tennessee Thursday late afternoon/evening. This system should have at least twice as much instability/CAPE, and as much, if not a little more, shear, than those previous non-events. In other words, it has a lot more “stuff” to work with. So, while we are not guaranteeing severe weather Thursday (see below to read why), do not dismiss this event, and stay weather aware. 

We expect 2 rounds of rain/storms. First, in the early morning tomorrow, main concern is flash flooding. Then, a break in the action, to allow for the atmosphere to recharge. Second, later in the afternoon/early evening, our main concerns are damaging winds, more localized flash flooding, hail, and a tornado or two.

image_full6.gif (960×720) - Google Chrome 2016-03-30 07.32.10

Round 1 — Early Morning Outlook

Rain will continue through the overnight hours into the early morning hours tomorrow. Our first threat comes around the rush hour time frame. Periods of heavier rainfall will be impacting us then.

hires_ref_nashville_32.png (1000×750) - Google Chrome 2016-03-30 08.02.52

These periods of heavy downfall could cause localized flash flooding. Be advised that your drive to work tomorrow may take longer than usual. Be safe and aware of your surroundings. If you see a flooded roadway, “Turn Around Don’t Drown!”

Lunchtime-ish Break in the Action

When the morning rain ends, weather nerds everywhere will be rushing to view the satellite trends (will the sun come out?), special weather balloon data (if NWS launches some), and the SPC’s RAP Mesoanalysis page, all of which will indicate whether the atmosphere is filling back up with instability/CAPE, shear, supportive wind fields, LCL heights, and other ingredients that will have to come together to set us up for severe weather ahead of an approaching cold front expected later in the day.

For example, here’s the NAM4 model for 4 PM Thursday, showing some sunshine, which suggests we’ll be recharging our CAPE/instability.

hires_btop_nashville_40.png (1000×750) - Google Chrome 2016-03-30 07.54.35

Round 2 — Late Afternoon/Evening/Late

ETA and storm strength is conditional on what happens in the morning. Models vary as to when the next round will arrive.

In the lunchtime update, the Storm Prediction Center emphasized that Thursday morning rain/storms will lay down outflow boundaries and cold pools which can feed and otherwise enhance the storm concern for later in the day. After that morning rain, a strong southern wind will shove reinforcing warm air to recharge our atmosphere; however, if pockets of the region remain clouded over, or ongoing storms to the south cut off the good southern moisture transport, the threat will diminish. In addition, the upper level support of severe weather should be higher nearer to the Ohio River. The whereabouts of these gaps in co-located severe weather ingredients present the forecaster with the most uncertainty here — no one knows where they will develop — so absent that certainty SPC apparently did not feel it appropriate to expand its risk area across I-65. I also think our risk is slightly lower because models suggest the storms will show up after dark.

The Euro and GFS models delivers this rain well before midnight.

However, the NAM4 shows this second round — the “main event” — reaching us around the midnight hour:

hires_ref_nashville_49.png (1000×750) - Google Chrome 2016-03-30 07.47.17

If the storms develop sooner, they should be stronger. This is because as we go through the day, the highest shear will be escaping north, chasing the system’s parent low pressure center racing off to the Great Lakes. But, if the storms can get rolling late afternoon/early evening, there should be sufficient shear and helicity to set off some supercell and quasi-linear thunderstorms. If this verifies – and there remains uncertainty about whether it will – our tornado threat will rise; however, the main threats will be damaging straight-line winds from storms that appear to form a bow on radar. Hail is also a concern.

All that said, it is expected there will be plenty of instability, shear, and upper level support in west Tennessee to develop significant severe potential with large hail and perhaps a strong tornado or two. As a southwesterly low level wind jet intensifies and nears into the evening hours, “storms may congeal [sic] into an eastward propogating bow/mesoscale convective system …. impacting … Middle/Western TN.” (SPC Forecast Discussion).

Perhaps the most dangerous part of these storms may turn out to be flooding during Round 2. If we get one of those supercells “training” over our area, the already-saturated ground from the morning rain could set the stage for localized flooding. Most weather deaths and injuries occur from people in cars around flooded roads.

All that said, we do not expect to be in the epicenter of severe weather activity Thursday, but the expected epicenter has moved much closer to us in this latest outlook. The bigger risk exists to our west, including almost all of Mississippi, extending into west Tennessee (including Memphis), then into W Kentucky and southern Illinois.

One forecast model, the usually-over-dramatic NAM4, is painting a grim, and frankly scary, severe weather setup tomorrow. The details of that aren’t helpful. It looks way too unrealistic; however, the other models are building a consensus that the storm potential is real. So, stay tuned.

We will be updating you throughout the day on Twitter at @NashSevereWx. Consult multiple reliable weather sources. 

When Will It End?

Rain should be gone by your drive to work on Friday.

Rain totals are expected to be around 1′ to 2″ when all is said and done. Local areas (especially in Williamson County) could potentially see up to 3″ of rain through this event.

image_full3.gif (960×720) - Google Chrome 2016-03-30 07.29.09

Friday: Sunny – Wake Up 52° High 66°

After the rain, clouds will be clearing throughout the day and we should see partly cloudy skies through the night. Temps will also stay relatively warm. Very nice start to the weekend.

Weekend Outlook:

My Forecast - Google Chrome 2016-03-30 07.35.39

We are expected to have an amazing weekend with clear skies and warmer temps. Next shot of rain isn’t until the beginning of next week.

This website supplements @NashSevereWx on Twitter, which you can find here.

Thursday’s Severe Weather Threat Growing, Closer

Current Radar

Updates reflecting new information from this afternoon are written below in blue.

Today: Clouds Rolling In, Windy – High 75°

We’ve already begun to see the clouds moving into our area ahead of the storms we will be seeing tonight into tomorrow. Even with the clouds, temps are expected to climb very quickly into the 70°s.

Visible Satellite Image showing the cloud cover building to our west and moving in:

The winds could be annoying at times today with gusts up to 25 mph. Sustained winds should remain between 5-15 mph the rest of the time.

Tonight: Heavy Rain Late – Temps only Dropping into the 60°s

The HRRR Model is still a little too far out for us to see exactly when the non-severe storms will come tonight. We expect to see light showers beginning as early as 10 PM tonight. Heavier rainfall will not come until the early AM hours tomorrow.

hrrr_ref_se_16.png (1024×768) - Google Chrome 2016-03-30 07.42.30

Thursday: Heavy Rain Early, Severe Storms in the Afternoon – Wake Up 61° High 74°

Summary

The lunchtime severe weather outlook from the Storm Prediction Center has arrived. Compared to this morning, this outlook represents a heightened severe weather concern that’s getting closer to us:

 

On David’s unofficial SPC outlook translator, this is a “you have my attention” event, right on the border of “getting concerned”:

Let me add something else — this isn’t anything like the last two events we’ve had here, where there was a conditional “slight” risk. In the first event, the condition was instability/CAPE — none developed, nothing happened. In the second event, the condition was shear (and CAPE), we got little of each, not much happened.

In this event, unlike what we’ve seen so far this storm season, SPC expects a significant severe weather event to be ongoing to our west, then racing into Middle Tennessee Thursday late afternoon/evening. This system should have at least twice as much instability/CAPE, and as much, if not a little more, shear, than those previous non-events. In other words, it has a lot more “stuff” to work with. So, while we are not guaranteeing severe weather Thursday (see below to read why), do not dismiss this event, and stay weather aware. 

We expect 2 rounds of rain/storms. First, in the early morning tomorrow, main concern is flash flooding. Then, a break in the action, to allow for the atmosphere to recharge. Second, later in the afternoon/early evening, our main concerns are damaging winds, more localized flash flooding, hail, and a tornado or two.

image_full6.gif (960×720) - Google Chrome 2016-03-30 07.32.10

Round 1 — Early Morning Outlook

Rain will continue through the overnight hours into the early morning hours tomorrow. Our first threat comes around the rush hour time frame. Periods of heavier rainfall will be impacting us then.

hires_ref_nashville_32.png (1000×750) - Google Chrome 2016-03-30 08.02.52

These periods of heavy downfall could cause localized flash flooding. Be advised that your drive to work tomorrow may take longer than usual. Be safe and aware of your surroundings. If you see a flooded roadway, “Turn Around Don’t Drown!”

Lunchtime-ish Break in the Action

When the morning rain ends, weather nerds everywhere will be rushing to view the satellite trends (will the sun come out?), special weather balloon data (if NWS launches some), and the SPC’s RAP Mesoanalysis page, all of which will indicate whether the atmosphere is filling back up with instability/CAPE, shear, supportive wind fields, LCL heights, and other ingredients that will have to come together to set us up for severe weather ahead of an approaching cold front expected later in the day.

For example, here’s the NAM4 model for 4 PM Thursday, showing some sunshine, which suggests we’ll be recharging our CAPE/instability.

hires_btop_nashville_40.png (1000×750) - Google Chrome 2016-03-30 07.54.35

Round 2 — Late Afternoon/Evening/Late

ETA and storm strength is conditional on what happens in the morning. Models vary as to when the next round will arrive.

In the lunchtime update, the Storm Prediction Center emphasized that Thursday morning rain/storms will lay down outflow boundaries and cold pools which can feed and otherwise enhance the storm concern for later in the day. After that morning rain, a strong southern wind will shove reinforcing warm air to recharge our atmosphere; however, if pockets of the region remain clouded over, or ongoing storms to the south cut off the good southern moisture transport, the threat will diminish. In addition, the upper level support of severe weather should be higher nearer to the Ohio River. The whereabouts of these gaps in co-located severe weather ingredients present the forecaster with the most uncertainty here — no one knows where they will develop — so absent that certainty SPC did not feel it appropriate to expand its risk area across I-65. I also think our risk is slightly lower because models suggest the storms will show up after dark.

The Euro and GFS models delivers this rain well before midnight.

However, the NAM4 shows this second round — the “main event” — reaching us around the midnight hour:

hires_ref_nashville_49.png (1000×750) - Google Chrome 2016-03-30 07.47.17

If the storms develop sooner, they should be stronger. This is because as we go through the day, the highest shear will be escaping north, chasing the system’s parent low pressure center racing off to the Great Lakes. But, if the storms can get rolling late afternoon/early evening, there should be sufficient shear and helicity to set off some supercell and quasi-linear thunderstorms. If this verifies – and there remains uncertainty about whether it will – our tornado threat will rise; however, the main threats will be damaging straight-line winds from storms that appear to form a bow on radar. Hail is also a concern.

All that said, it is expected there will be plenty of instability, shear, and upper level support in west Tennessee to develop significant severe potential with large hail and perhaps a strong tornado or two. As a southwesterly low level wind jet intensifies and nears into the evening hours, “storms may congeal [sic] into an eastward propogating bow/mesoscale convective system …. impacting … Middle/Western TN.” (SPC Forecast Discussion).

Perhaps the most dangerous part of these storms may turn out to be flooding during Round 2. If we get one of those supercells “training” over our area, the already-saturated ground from the morning rain could set the stage for localized flooding. Most weather deaths and injuries occur from people in cars around flooded roads.

All that said, we do not expect to be in the epicenter of severe weather activity Thursday, but the expected epicenter has moved much closer to us in this latest outlook. The bigger risk exists to our west, including almost all of Mississippi, extending into west Tennessee (including Memphis), then into W Kentucky and southern Illinois.

One forecast model, the usually-over-dramatic NAM4, is painting a grim, and frankly scary, severe weather setup tomorrow. The details of that aren’t helpful. It looks way too unrealistic; however, the other models are building a consensus that the storm potential is real. So, stay tuned.

We will be updating you throughout the day on Twitter at @NashSevereWx. Consult multiple reliable weather sources. 

When Will It End?

Rain should be gone by your drive to work on Friday.

Rain totals are expected to be around 1′ to 2″ when all is said and done. Local areas (especially in Williamson County) could potentially see up to 3″ of rain through this event.

image_full3.gif (960×720) - Google Chrome 2016-03-30 07.29.09

Friday: Sunny – Wake Up 52° High 66°

After the rain, clouds will be clearing throughout the day and we should see partly cloudy skies through the night. Temps will also stay relatively warm. Very nice start to the weekend.

Weekend Outlook:

My Forecast - Google Chrome 2016-03-30 07.35.39

We are expected to have an amazing weekend with clear skies and warmer temps. Next shot of rain isn’t until the beginning of next week.

This website supplements @NashSevereWx on Twitter, which you can find here.

New Details On Storms and Severe Weather Potential

Current Radar

Tonight: Crisp, Cool, and “Fresh” – 9PM 57°

Current Satellite

Screen Shot 2016-03-29 at 4.30.39 PM

Only a few high to mid-level clouds will pass overhead tonight, allowing temperatures to drop into the mid 50s by 9PM.

Overnight lows will fall into the middle 40s under mostly clear skies.

Wednesday: Sun to Clouds, Windy, Then Rain Late – Wake Up 45° High 74°

We start off in the 40s, but southerly flow bumps temperatures into the mid-70s by the afternoon. Winds will pick up gradually through the day, starting at 5 to 15 mph, with gusts up to 25 mph.

More clouds and less sun will be the afternoon trend, with the potential for scattered showers and isolated storms arriving by late evening.

4KM NAM at 7PM Wednesday

Screen Shot 2016-03-29 at 4.42.19 PM

No impressive rainfall totals will come from this activity, and chances are good you’ll get your Wednesday evening outdoorsy thing in before the skies open. We will be watching a main line of storms, some strong, that will arrive during the very early hours of Thursday morning.

Thursday: Strong Storms & Flash Flooding: Something to Watch – Wake Up 62° High 75°

Strong to severe thunderstorms are a possibility throughout the day.

SPC Outlook for Thursday

(same thing, only zoomed in)

We are only included in a marginal (“1” on a scale of 0-5) risk for severe weather. This goes for mainly hail and damaging winds.

(Based on the latest model data, I would not be surprised to see our area upgraded to a greater risk of severe weather for Thursday afternoon and evening.)

Timing: Round 1 (Thu. AM), Round 2 (Thu. 5PM – Fri. 3AM)

Threats: Large hail, damaging winds, and an isolated tornado with “Round 2.”

Morning, Round 1:

NAM 4KM at 7AM Thursday

Screen Shot 2016-03-29 at 4.49.07 PM

Conditional Severe Threat: I would not be surprised to see a couple “hailers” Thursday AM as cloud temperatures cool. A small surge of energy overhead (one of many), associated with the larger low pressure system, could help enhance this potential.

This is a conditional threat, meaning *all* ingredients will need to present for this threat to materialize.

Heavy rain and flash flooding is the main threat in the AM, especially during rush hour. Remember, “Turn Around, Don’t Drown!”.

Round 2: Afternoon/Evening (*Primetime*):

Models are agreeing that there will be a lull in the action sometime on Thursday, probably in the middle afternoon.

It looks possible that a new line of showers and thunderstorms will develop ahead of the cold front Thursday afternoon/night. Caveat: This all depends on how much dry time/breaks in the clouds we get Thursday afternoon to destabilize/recharge the atmosphere. Stable air = plain rain and storms; unstable air = potent/severe storms.

4KM NAM at 7PM Thursday

Screen Shot 2016-03-29 at 5.02.22 PM

This line could come through anywhere between 7PM Thursday and the early morning hours of Friday, as outlined below. The main threats with this afternoon-evening line of storms will be large hail, damaging winds, and a tornado cannot be ruled out.

*More model agreement! The GFS, Euro, and NAM are now all saying that our storms will shut down around 4AM Friday morning.*

 

Flash Flooding Potential:

Screen Shot 2016-03-29 at 5.08.58 PM

A total of 1-2″ of rain look likely for both Davidson and Williamson counties; however, some areas (especially in Williamson Co.) could see 3″+ locally.

Of course, we continue to monitor this next weather event on Twitter @NashSevereWx and right here at NashSevereWx.com.

Weekend Preview:

We wouldn’t want you to be caught off guard like this poor wedding crew.

In short, the week’s end looks awesome. Sunny skies will dominate with highs in the 60s. We will dry out, but the ground will remain somewhat soggy from the amount of rain we will see Wednesday and Thursday.

Screen Shot 2016-03-29 at 5.28.51 PM

As the Nashville NWS put it this morning: “Next weekend looks amazing.”

This website supplements @NashSevereWx on Twitter, which you can find here.