February 29: Mild Leap Day, Stormy Tuesday, Daily Links


This weekend’s weather turned out to be VERY nice — a little breezy yesterday, but temperatures climbed into the 60s on Saturday and up to 70 on Sunday!  We’ve got another mild day in store today, with temperatures climbing to the mid 60s this afternoon:

The warm air isn’t here to stay, though…a strong cold front will push into the Midstate late Tuesday, and along with that front we’ll see a good chance of thunderstorms, some of which could be strong or even severe.  The fact that tomorrow is “Super Tuesday” is just coincidence — this system isn’t nearly as organized as the one that brought numerous tornadoes to the Midstate on February 5, 2008.  Nonetheless, it’s something we’ll have to watch carefully.

Two main factors will help to determine the scope and strength of tomorrow’s severe weather threat:
1) How much humidity will be in place as the storms arrive?  Limited moisture equals limited instability — right now the forecast humidity levels are very borderline in terms of their ability to support widespread severe weather.
2) How fast will the storms move in?  A mid- to late-afternoon storm arrival is our worst-case scenario, because it gives the atmosphere more time to get organized — but things are trending in a hopeful direction with the latest forecast model data.

The radar simulation from our two in-house models (RPM on the left, BAMS on the right) shows that they’re in reasonably-good agreement that storms will enter the Midstate by mid-morning on Tuesday, with the strongest storms moving through Nashville around midday, and out of the area by late afternoon:
There are other forecast models that disagree — one of which, the 4km-resolution North American Model (NAM), brings strong storms into the Midstate closer to the “worst-case” time frame…here’s the noon snapshot of that model:

So which model will be right?  Well…none of them.  All forecast models have flaws, so it’s a matter of picking out which one will be less-wrong, and trying to find the consensus points between all of the various versions of “what could happen.”  The fact that the more-reliable short-range data is pointing toward a slightly earlier arrival is a good sign — but we’ll still have to be watching for some strong storms already by mid-morning on Tuesday.  The “analog” forecast (comparing Tuesday’s pattern to similar historical patterns) shows the best chance of severe weather along and east of I-65:
This matches up pretty well with the timing depicted by our Futurecast models — the morning storms west of I-65 won’t have as favorable an environment as what the midday and afternoon storms will find as they move to the east.

The Storm Prediction Center’s Short-Range Ensemble Forecast (SREF) has been depicting a later storm-arrival time, but its latest output speeds things up a little.  It’s still slower than our Futurecast models, showing the best chance of strong/severe thunderstorms moving across the Tennessee River by noon…
…then across the rest of the Midstate in the afternoon:

The SREF’s depiction of the Supercell Composite Parameter (a handy statistic to quickly answer the “how bad?” question) doesn’t show any off-the-charts values:
But those numbers are still high enough that we’ll keep a close eye on every storm that develops on Tuesday.

The Storm Prediction Center has included the entire Midstate in a Slight Risk (level 2 of 5) for severe thunderstorms Tuesday:
The word “slight” can be misleading — basically, it means that severe thunderstorms are likely to occur somewhere in the yellow-shaded area on that map, but the odds of it happening directly in your neighborhood are relatively low.  I’d still plan on staying weather-aware throughout the day Tuesday, and in the meantime stay tuned for further revisions to the forecast today — as I’m typing this, we’re still more than 24 hours away from the first storms moving into the Midstate, so we’ve still got plenty of time for tweaks to the forecast.  Dan and Lisa will post blog updates later today, and I’ll share any new information I find interesting via social media (links at the bottom of this post).

Cold air will crash in on the back edge of this system, but it looks like the moisture will be gone before any changeover to snow could occur (the exception, as always, is along the Cumberland Plateau).  Colder-than-normal temperatures will prevail Wednesday through Friday, with another chance of rain on Thursday:
7 Day PM
At this point, the weekend looks great!  We’ll hope that remains the case as the week progresses…



Social media links

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

Facebook: 4WARN Weather, Paul Heggen WSMV, Lisa Spencer, Dan Thomas WSMV, Nancy Van Camp WSMV, NWS Nashville

Instagram: PaulHeggenWSMV

About paulheggen33

Morning meteorologist for WNCN-TV in Raleigh.
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