March 29: Storms Thursday, Daily Links

WEATHER

First, the good news: today’s weather looks nearly perfect!  Lots of sunshine, low humidity, a not-too-strong breeze from the northeast, and mild temperatures.  Temperatures will reach the mid to upper 60s this afternoon:
TUESDAY HIGHS

Breezy and warmer conditions in store for us tomorrow, but we’ll stay dry during the day.  High temperatures should climb to the mid 70s, despite a bit more cloud cover:
WEDNESDAY HIGHS

Now, the not-so-good news: widespread thunderstorms and heavy rain will bring the potential for flash flooding and damaging straight-line winds Wednesday night and Thursday.  The forecast models are still a bit at-odds regarding when the storms will initially move in, with the possibilities ranging from late Wednesday evening to sunrise Thursday.  One of our in-house models, the RPM, shows storms approaching the Mississippi River by sunset Wednesday…but delays the onset of storms in the Midstate until the very early hours of Thursday morning:
RPM 6P WED RPM 12A THU RPM 4A THU RPM 7A THU RPM 10A THU

Those storms could drop an inch or so of rain in a very short amount of time, so we’ll be watching for flash flooding as they move through.  The damaging wind potential isn’t very high with the Thursday morning storms, as the early-morning time frame isn’t conducive to much of a severe weather threat.  The problem is, we’re not done with the storm chances once that first batch moves through.  Futurecast paints an ominous picture, with a break from the rain around midday into the afternoon:
RPM 1P THU RPM 4P THU
That would allow the atmosphere to warm up and “re-charge” for more thunderstorms.  This particular computer model shows a hefty line of storms rolling into western Middle Tennessee around sundown, moving west-to-east across the Midstate throughout Thursday evening:
RPM 7P THU RPM 10P THU RPM 1A FRI
Keep in mind, that’s ONE version of ONE model.  I’m confident in its big-picture presentation, but the details will remain subject to revision as we get more data.

Adding up the rain throughout Wednesday night and Thursday with the same forecast model yields some impressive totals — more than 1.5″ across most of the Midstate, with some spots receiving close to 3″ or rainfall:
PAUL ECMWF RAIN
This far out (48 hours-ish), I don’t put too much faith in the location of the specific “bullseyes” of heavy rainfall — just be aware that localized flooding could be an issue with the heaviest storms.

The evening storms (or afternoon, if things speed up) would have the greatest potential to produce severe weather, mainly in the form of damaging straight-line winds…but I can’t cross large hail or isolated tornadoes off the list of possibilities at this point, either.  Everything hinges on that midday break — if the sun comes out and we warm up to the upper 70s, the atmosphere will be ready to go.  If the clouds stick around and temperatures stay in the low 70s, that will help significantly.  Because of that uncertainty, the Storm Prediction Center has only outlined us in a “Marginal Risk” (level 1 of 5) for severe thunderstorms, with the “Slight Risk” (level 2 of 5) well to our south:
PAUL SEVERE RISK REGION
I think before all is said and done, that Slight Risk area will be expanded farther north, at least to include the southern half of the Midstate.  Why?  Glad you asked…

The SPC’s short-range ensemble forecast (SREF) model — a super-blend of about 20 different models — shows a pretty good chance (50-70%+) that any thunderstorms Thursday will be organized enough to produce severe weather:
SREF_prob_combined_supercell__f057 SREF_prob_combined_supercell__f060 SREF_prob_combined_supercell__f063 SREF_prob_combined_supercell__f066 SREF_prob_combined_supercell__f069 SREF_prob_combined_supercell__f072
As a reminder, “severe weather” is defined as 58+mph wind gusts, 1″+ diameter hail, or a tornado.

The best ingredients for severe weather (i.e. the most favorable combination of instability to fuel the storms, and wind shear to organize them) will take shape Thursday evening, when the Supercell Composite Parameter values approach 6 in the southern half of the Midstate:
SREF_SCCP_MEDIAN_MXMN__f069
That value of 6 is pretty much the threshold of confidence when it comes to differentiating “strong” storms from severe storms.

The Significant Tornado Parameter (that one should be obvious) reaches a forecast value of 2 across much of the Midstate by Thursday evening:
SREF_SIGTOR_MEDIAN_MXMN__f069
Similar to the forecast for the Supercell Composite Parameter, those Significant Tornado Parameter values represent the threshold between “we’re probably fine” and “let’s pay attention to this.”

Finally, the analog forecast (comparing this pattern to similar historical patterns) shows a 25% chance of 5+ severe weather reports in the Midstate Thursday evening, with an even higher chance in Mississippi and Alabama:
SVRall_N5_110km_gfs212F072

Both the SREF and RPM have been remarkably consistent in their depictions, which gives me a little more confidence that they know what they’re doing.  All of that data combined is what prompts me to think the SPC will (or should) expand the Slight Risk region up into at least the southern half of the Midstate (probably all the way up to the TN/KY border), and probably outline an “Enhanced Risk” (level 3 of 5) for parts of Mississippi and Alabama.  I’m sure they’re hesitating because of the uncertainty in how this whole scenario will evolve — plus, they’ve been burned already a couple of times this year by Slight or Enhanced Risk outlooks that didn’t pan out.  There’s still plenty of time for things to change as this system takes shape, so we’ll keep you posted.

Once the Thursday evening/night storms move through, things will settle down for a while.  Just a slight chance of showers late Friday as colder air arrives from the northwest, then lots of sunshine over the weekend and into early next week.  Temperatures will be a little cooler than average for the first weekend in April, but I don’t think we’re going to hear too many complaints!
WSMV 7 Day AM

 

LINKS

Nerdiness.  Mostly weather and space stuff today, but a few other nuggets as well…

  • Atmospheric researcher have discovered a sea-surface temperature pattern in the Pacific Ocean that can be used to predict heat waves in the eastern United States up to 50 days in advance.
  • This winter’s extent of Arctic sea ice reached a record low.  (The record it broke was just set last year.)
  • Climate change is impacting the life cycles of Arctic birds as well.
  • Parts of the Great Barrier Reef are being “fried” by the worst coral bleaching event on record.
  • A volcano has erupted in Alaska’s Aleutian Islands, sending plumes of ash 20,000 feet into the air.
  • If you get up early enough tomorrow morning, you might be able to catch a glimpse of a green comet in the sky.
  • With $30 million on the line, private companies are racing to put a robotic lander on the moon.
  • One astrobiologist claims that Venus was likely home to (simple) life at some point in the past.
  • Technology doesn’t have to be confusing…simple changes could make digital media easier to use.
  • What one snarky facial expression can teach us about the evolution of language.
  • Finally…so you say you want to be a TV news anchor?  You might think again after this…

About paulheggen33

Morning meteorologist for WNCN-TV in Raleigh.
This entry was posted in Uncategorized and tagged , , , . Bookmark the permalink.