March 29: Severe Weather Again Tomorrow


Beautiful weather today, with partly cloudy skies and temperatures topping out near 80° this afternoon (today’s record is 85° set in 1895):

Just a very slight shower chance along the Tennessee River, otherwise we’ll be waiting until tomorrow for rain.

Thunderstorms will move in Thursday morning, weakening as they cross the Tennessee River…but they’ll still possess a marginal severe threat (mainly from damaging winds).  This is the North American Model’s (NAM) radar simulation from midnight through noon:

A break in the storms around midday will set the stage for a significant severe weather threat to develop late in the day Thursday.  Returning to the NAM model’s radar simulation from 3pm through 6am, it shows storms developing in West Tennessee and marching across the Midstate through the evening and overnight:

Don’t put too much faith in the specific placement of the storms on these radar simulations — the pattern is more important, especially since this whole event is still 24 hours away.  All types of severe weather will be possible…tornadoes, straight-line winds, large hail, and frequent lightning:

The Storm Prediction Center has outlined a “Moderate Risk” (level 4 of 5) of severe storms for roughly the western half of the Midstate, with an “Enhanced Risk” (3/5) and “Slight Risk” (2/5) farther east:

That’s ominous.  It’s rare for the SPC to outline a Moderate Risk more than 24 hours in advance — it’s only happened for the Midstate twice in the last five years, as best I can recall.  Even more-ominous, SPC has outlined much of the Midstate for a statistically “significant” severe threat (in the hatched area):

That means a 10%+ chance of an EF2+ tornado, 75mph straight-line winds, or hail 2″+ in diameter, within 25 miles of any point in that zone.

Now that you’re in this mode…

…let’s talk about some of the uncertainties (i.e., the “good news”).  There are two basic ways that this could all fizzle out.  The first is that the moisture doesn’t increase enough to boost the atmospheric instability (“storm fuel”).  I’m not counting on that — our in-house RPM model projects dew points in the low 60s tomorrow afternoon:

That’s good-enough for severe storms, albeit without much margin of error.  The more likely cause for hope is related to the morning storms — if they last long enough, or if the clouds linger long enough, our temperatures might not warm up enough for the storm fuel to build up.  Fingers crossed!

The best advice is to hope for the best and plan for the worst.  The “analog” forecast (comparing tomorrow’s pattern to similar historical patterns) points toward a significant severe weather threat:

And the SPC’s ensemble forecast (a blend of 25+ models) shows a 70+% chance of storms with severe characteristics tomorrow afternoon and evening…and that threat has been inching eastward with every new model run over the last 48 hours:

All of this means you should plan on staying weather-aware throughout the day — follow us on Twitter (Facebook is essentially useless for time-sensitive information), and download the 4WARN mobile app and set it up to alert you if warnings are issued in your area.  That’s not me pushing the company line — it’s a good way to stay up-to-date, especially if you’re going to be out and about.  You can download the mobile app at this link.  Once it’s on your phone/tablet, go to “Settings” under the drop-down menu:
Then turn on the Severe Weather Alerts:

Once tomorrow’s storm threat has moved through, the weather will calm down in time for the weekend, then another storm chance heads our way Sunday night and Monday.

The nerd-links are taking a break the next couple of days, since all of my attention is on this severe weather threat.  (That alone should tell you how significant it is!)

Social media links

Twitter: @WSMVweather, @PaulHeggenWSMV, @WSMVLisaSpencer, @WSMVDanThomas, @daphne_deloren, @NWSNashville

Facebook: 4WARN Weather, Paul Heggen WSMV, Lisa Spencer, Dan Thomas WSMV, Daphne DeLoren, NWS Nashville

Instagram: PaulHeggenWSMV

About paulheggen33

Morning meteorologist for WNCN-TV in Raleigh.
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