March 30: Severe Storms Possible Thursday, Daily Links

WEATHER

A strong storm system will have a big impact on our weather over the next 48 hours — strong to severe thunderstorms will be possible tomorrow, which we’ll get to in a moment.  For today, expect warm and windy conditions…high temperatures will be about 10 degrees above-average:
PAUL RPM 4KM Temperature
With sustained winds out of the south at 15-20 mph and gusts approaching 30 mph:
PAUL RPM WIND GUSTS

Most of the thunderstorm activity will stay to our west today, where a significant severe weather threat will shape up:
PAUL SEVERE RISK REGION 1

Before I get into showing you the Futurecast simulation of when and where the storms will occur tonight and tomorrow, a caveat: I’m just showing one version of one model.  Other models have varying versions of the timing, placement, and strength of the thunderstorms — I’m not showing ALL of those models because we just get into “paralysis by analysis” at that point.  We’re always riding the emotional roller coaster with one model saying “ah, don’t worry” and another one saying “oh that’s NOT good”…and sometimes that’s different runs of the same model!  Everything you’re about to read represents my best attempt to sort through the discrepancies and unravel this riddle.

Futurecast (using the RPM model, for you serious weather nerds) shows storms approaching the Mississippi River by 5pm today:
RPM 5P WED

Showers and a few storms could wet things down this evening to the west of I-65, but the heaviest rain will still be off to our west until midnight:
RPM 8P WED RPM 10P WED

The thunderstorms responsible for the severe weather in the middle of the country today will march our way through the night, but they’ll be losing their intensity as they cross the Tennessee River around and after midnight:
RPM 12A THU RPM 2A THU RPM 4A THU RPM 6A THU RPM 8A THU
It’s certainly possible that these storms could maintain their strength sufficiently for a damaging wind threat in the wee hours of Thursday morning.  I don’t think that’s terribly likely, though — the most likely scenario is that we get some loud storms with heavy rain, but for the most part they remain below severe limits.

Now things get tricky.  As the morning rain moves off to the east, how much will we clear out?  We had the same question facing us just last Thursday — in that case, the morning rain moved slowly enough, and the clouds remained overhead long enough, to eliminate our severe weather potential later in the day.  But every storm system is different, and tomorrow it’s looking like we’ll see faster progression of the early-morning rain, leaving us with a longer time frame for potential clearing overhead.  That’s exactly what Futurecast anticipates around midday Thursday:
RPM 1P THU
IF the rain moves fast enough, and IF the clouds break up, that would set the stage for some nasty storms Thursday afternoon and evening.  IF.  IF IF IF.  (Have I said it enough yet?)  One of the things the forecast models struggle with the most is cloud cover, so our best-case scenario of “cloudy and cooler all day” is very much still a possibility.

That said, let’s hope for the best and plan for the worst, and assume that Futurecast knows what it’s doing with that midday sunshine.  Temperatures warm up to the upper 70s, and we’re off to the races.  Another batch of storms would develop closer to the cold front that’s responsible for this mess, and these would have a much greater severe weather potential.  Futurecast shows the second batch of stronger storms developing by mid-afternoon and marching west-to-east across the Midstate:
RPM 3P THU RPM 5P THU RPM 7P THU

Sticking with the scenario where all of the IFs come together for severe thunderstorms in the afternoon and early evening, what kinds of severe weather are we talking about?  All kinds — damaging winds, large hail, tornadoes, and flash flooding.  Switching computer models, let’s look at the American GFS model (usually a very conservative, storm-squashing model) and its version of what the weather balloon data will look like Thursday afternoon — I’ll explain what you’re seeing below the image:
gfs_2016033006_039_KBNA
That ain’t good.  The circled statistics provide a little elaboration on that basic analysis.
– CAPE (white circle) — that’s storm fuel — values are over 1000, more than sufficient for explosive storm growth.  That’s been the limiting factor with the past few severe-weather chances, but it appears we’ll have enough instability overhead tomorrow for storms to “take off.”
– LCL (yellow circle) — cloud base levels are expected to be less than a kilometer off the ground, which is low enough to be a concern from a tornadic perspective.
– SRH (red circle) — storm-relative helicity measures the wind shear in the lowest levels of the atmosphere.  This might prove to be the limiting factor tomorrow, but this model still points to more than enough wind shear to organize and rotate thunderstorms as they develop.
– Severe weather indices (light blue circle) — the Supercell Composite Parameter is forecast to be over 6, and the Significant Tornado Parameter is forecast to be around 2.  Those numbers basically take all of the instability and wind shear measurements and combine them to show the overall threat.  Those numbers are far from record-setting, but they’re “good enough” from an atmospheric standpoint…which means “bad enough” for us.

All of that sounds pretty ominous.  But the Storm Prediction Center has placed us in a “Slight Risk” area (level 2 of 5) for severe thunderstorms, with the “Enhanced Risk” (level 3 of 5) just off to our southwest:
PAUL SEVERE RISK REGION
Why only a Slight Risk, when all of the current data is pointing to a significant severe weather chance late Thursday?  Because the atmospheric set-up won’t be perfect for severe weather, and there are still numerous ways in which the evolution of this system could prevent the best severe weather ingredients from coming together.

That brings us to the best-case scenario.  Any ONE of these would probably be enough to significantly reduce our severe weather threat tomorrow — if they all happen, well…great!
– Tonight’s storms move in after midnight with no severe weather, and they move more slowly than expected across the Midstate, giving the atmosphere less time to re-charge.- After the morning rain departs, the clouds linger overhead.  We don’t see any sunshine to warm us up, and temperatures hover in the upper 60s.  Instability isn’t sufficient for the second batch of storms to become severe.
– The second batch of storms doesn’t develop as quickly out to our west.  Those storms don’t move into the Midstate until sunset, when the most favorable wind energy has shifted away — even if there’s still enough instability in place, the storms can’t get organized to produce widespread severe weather.

Regardless of whether we get the best-case or worst-case scenario, we’re going to be on the lookout for some flooding issues.  The morning rain will saturate the ground, so the afternoon/evening rain won’t be able to soak in.  Total rainfall amounts will only be around 2″ once you add up both the morning and evening rain, but that’s enough to cause localized flooding if it falls quickly enough.
PAUL RPM 4KM - PRECIP ACCUM

Last week I had a high degree of optimism regarding the best-case scenario playing out in our favor.  I’m less optimistic at this point about tomorrow’s severe weather potential.
PAUL SEVERE RISK GRAPH
Should you panic?  Cry?  Should you stock up on canned goods and barricade yourself in a bunker until sunrise Friday?  Should you flee the country?
gohed

There’s still plenty of time for things to head in a better direction for us!  The forecast can change (and it probably will, to as least some extent), so check back in with us for updates.  I’ll share some thoughts on social media (links below) throughout the day, Dan or Lisa will post a blog update later, and we’ll have our regular weather segments in our newscasts.

Once the last of the lingering showers winds down in the pre-dawn hours of Friday morning, we’ll see decreasing clouds the rest of Friday.  Lots of sunshine in store for us this weekend — temperatures will be a little below-average, with a noticeable chill in the air at night.  We’ll warm up again Monday, before the next chance of showers and non-severe storms moves in Monday night:
WSMV 7 Day AM

 

LINKS

Now that all the severe weather nerdiness has been covered, let’s get to some other geeky stuff…

  • What it’s like to be a weather observer on the tallest mountain in the northeastern U.S. — home of the “world’s worst weather.”
  • Thanks to climate change, cruise ships have another route open — through the Arctic.
  • The global winter (Dec-Jan-Feb) average temperature was 2.03 degrees above the 20th-century average.  2016 is off to a record-setting start.
  • The volcanic eruption in Alaska earlier this week caused some major travel headaches.  Airplanes can fly right through clouds, so why can’t they fly through volcanic ash clouds?
  • Jupiter got whacked with a decent-sized asteroid on St. Patrick’s Day.
  • The regularly-erupting geysers on Saturn’s moon Enceladus now have a more detailed explanation, thanks to computer modeling.
  • The hunt is on for “Planet 9” — a Neptune-size planet waaaaaaaay out there in our solar system.  It hasn’t been confirmed yet, but astronomers are already trying to figure out why it’s so far out there.
  • A new NASA instrument will hunt for planets outside our solar system by more-accurately measuring the “wobble” of distant stars.
  • The jets of material ejected by supermassive black holes (the ones at the centers of galaxies) approach temperatures of ten trillion degrees.  That’s 10,000,000,000,000.  The center of the Sun is “only” 15,000,000,000 degrees.
  • I love love LOVE this idea (especially for summertime around here): a self-filling bottle that converts humid air to drinkable water.

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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

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About paulheggen33

Morning meteorologist for WSMV-TV in Nashville.
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