Severe WX April 3rd-5th, 2023 (South, Southeast, Ohio Valley)

[warneagle]

Really makes you appreciate the significance of Friday. I remember us discussing if the CAMS were on crack printing that many supercells and UH streaks. Little did we know they were on to something and in agreement on something significant occurring.

I mean yeah Friday was the rare occasion where the worst-case scenario actually verified. Obviously that could still happen tomorrow but there are a lot more clear mitigating factors versus where the models were a few days ago where it looked like this was gonna be the main event and Friday was the prequel.

 

[cincywx]

deja...

 

[Penitentes]

And the SPC drops another double-barrel moderate risk.

...SUMMARY...
A large area of severe potential will exist from Tuesday afternoon
into Wednesday morning, from eastern portions of the Plains into the
Missouri and mid/upper Mississippi Valleys. Strong tornadoes and
particularly damaging winds are expected. Both afternoon and
overnight potential will exist across various regions, including the
risk of dangerous nighttime tornadoes.

 

[cincywx]

new disco draws particular attention to the nocturnal threat...emphasis mine

DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1255 PM CDT MON APR 03 2023

VALID 041200Z - 051200Z

...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS FROM EASTERN
IOWA INTO NORTHWEST ILLINOIS...AND FROM SOUTHERN MISSOURI
SOUTHWESTWARD TOWARD THE ARKLATEX....

..SUMMARY

A LARGE AREA OF SEVERE POTENTIAL WILL EXIST FROM TUESDAY AFTERNOON
INTO WEDNESDAY MORNING, FROM EASTERN PORTIONS OF THE PLAINS INTO THE
MISSOURI AND MID/UPPER MISSISSIPPI VALLEYS. STRONG TORNADOES AND
PARTICULARLY DAMAGING WINDS ARE EXPECTED. BOTH AFTERNOON AND
OVERNIGHT POTENTIAL WILL EXIST ACROSS VARIOUS REGIONS, INCLUDING THE
RISK OF DANGEROUS NIGHTTIME TORNADOES.

..SYNOPSIS

A LARGE UPPER TROUGH WILL MOVE FROM THE ROCKIES INTO THE PLAINS ON
TUESDAY, WITH AN UPPER LOW TRACKING FROM WY TO NORTHERN MN BY
WEDNESDAY MORNING, DEEPENING AFTER 00Z. MEANWHILE, UPPER RIDGING
WILL OCCUR OVER THE EASTERN STATES. A STRONG 100 KT MIDLEVEL JET MAX
WILL BE POSITIONED FROM NM INTO WESTERN KS DURING THE DAY, WITH AN
INTENSIFYING JET CORE TUESDAY NIGHT FROM KS INTO IA. JUST AHEAD OF
THE PRIMARY UPPER TROUGH/JET, A LEADING SPEED MAX WILL STRENGTHEN
FROM OK INTO KS AND MO DURING THE DAY, PERHAPS WITH A SUBTLE LOBE OF
COOLING ALOFT.

AT THE SURFACE, LOW PRESSURE WILL EXIST OVER EASTERN CO TUESDAY
MORNING, AND WILL SHIFT EASTWARD ACROSS KS DURING THE DAY,
TRANSLATING EAST/NORTHEAST ALONG A COLD FRONT. THIS LOW WILL SHIFT
INTO IA BY EVENING, AND INTO WI BY 12Z WEDNESDAY. AHEAD OF THE LOW,
A PROMINENT WARM FRONT WILL MOVE RAPIDLY NORTH, BEGINNING THE DAY
FROM NORTHEAST KS INTO CENTRAL IL, AND REACHING NEAR I-80 FROM IA
INTO NORTHERN IL BY 00Z. THIS BOUNDARY WILL CONTINUE NORTH INTO
SOUTHERN WI AND WESTERN LOWER MI OVERNIGHT, AHEAD OF THE SURFACE
LOW. BEHIND THE LOW, A COLD FRONT WILL MAKE AN EASTWARD PUSH DURING
THE LATE EVENING AND OVERNIGHT ACROSS IA, NORTHWEST MO AND EASTERN
KS.

SOUTH OF THE LOW, A DRYLINE WILL STRETCH FROM EASTERN KS INTO
CENTRAL OK AND NORTH TX AT 00Z, AND MAY BECOME STATIONARY OR EVEN
BACK WESTWARD OVER THE SOUTHERN PLAINS DURING THE LATE EVENING AND
PRIOR TO THE COLD FRONT ARRIVING FROM THE NORTH.

GIVEN RELATIVELY HIGH HEIGHTS OVER THE EASTERN CONUS PRECEDING THE
UPPER TROUGH, A VERY WIDE WARM SECTOR WILL DEVELOP FROM THE SURFACE
LOW AND DRYLINE EASTWARD WELL EAST OF THE MS RIVER, WITH UPPER 60S F
DEWPOINTS COMMON FROM EASTERN OK AND AR SOUTHWARD. THE COMBINATION
OF AN EXPANSIVE WARM SECTOR AND STRONG SHEAR, FOR LONG DURATION AND
IN VARIOUS FORCING REGIMES, SUGGESTS THAT SIGNIFICANT SEVERE WEATHER
IS LIKELY. HOWEVER, SUBTLETIES REGARDING TIMING WITH REGARD TO THE
DIURNAL CYCLE, CAPPING, AND CONFLICTING MODEL OUTPUT WILL MAKE THIS
PREDICTION CHALLENGING, ESPECIALLY WHEN WEIGHING POTENTIAL IMPACTS
TO LIFE AND PROPERTY.

..IA...NORTHERN MO...IL...SOUTHERN WI - DAYTIME

THE AREA NEAR THE WARM FRONT AND LATER IN LATE INTO THE OVERNIGHT
HOURS AHEAD OF THE SURFACE LOW WILL BE A FAVORED AREA FOR SUPERCELLS
AND TORNADOES. STORMS ARE EXPECTED TO FORM FROM NORTHERN MO INTO IA
DURING THE LATE AFTERNOON, SHIFTING NORTHEASTWARD WITH THE WARM.
LOW-LEVEL SHEAR WILL BE EXTREMELY FAVORABLE FOR TORNADOES, AS WITH
OVER 300 M2/S2 SRH AND MUCAPE PERHAPS UP TO 3000 J/KG. THE STEEP
LAPSE RATES ALOFT WILL MAXIMIZE UPDRAFT STRENGTH AS WELL, RESULTING
IN STRONG TORNADOES. THIS THREAT MAY PERSIST FARTHER NORTHEAST INTO
SOUTHERN WI AND NORTHERN IL INTO THE NIGHT AS THE WARM AND UNSTABLE
AIR WITH THE WARM FRONT CONTINUES TO MOVE NORTH WITH THIS STRONG
SYSTEM.

..NORTHEAST TX INTO AR AND INTO MO - OVERNIGHT

CONFIDENCE IS INCREASING IN THE POTENTIAL FOR RARE AND DANGEROUS
OVERNIGHT TORNADOES AND DAMAGING WINDS, AND A MODERATE RISK HAS BEEN
INTRODUCED FOR THIS REGION. THE AIR MASS WILL REMAIN CAPPED DURING
THE DAY, AS BOUNDARY-LAYER MOISTURE BUILDS. STEEP LAPSE RATES WILL
EXIST ABOVE THE CAPPING LAYER, WHICH WILL NOT BE PARTICULARLY STRONG
OVERNIGHT DUE TO ROBUST MOISTURE. AS THE COLD FRONT APPROACHES FROM
THE WEST, THE LOW-LEVEL JET WILL REMAIN STRONG PROVIDING THETA-E
ADVECTION THROUGH THE NIGHT. NOCTURNAL STORMS ARE FORECAST TO ERUPT
AFTER 06Z, AND PERHAPS CLOSER TO 08Z FROM SOUTHWEST MO INTO WESTERN
AR AND INTO NORTHEAST TX. HODOGRAPHS WILL STRONGLY FAVOR TORNADIC
SUPERCELLS WITH EFFECTIVE SRH NEAR 400 M2/S2. FURTHER, STEEP LAPSE
RATES ALOFT AND AMPLE INSTABILITY WILL FAVOR STRONG TORNADOES, AND A
LONG TRACKED TORNADO CANNOT BE RULED OUT. THIS APPEARS TO BE A RARE
CASE WHERE THE FRONT MAY ACT MORE LIKE A DRYLINE DURING THE
OVERNIGHT HOURS, WITH VEERING AT 850 MB BEING MORE GRADUAL. CAPPING
IS MOST LIKELY TO LIMIT THE EASTWARD EXTENT OF THE THREAT FOR
SOUTHERN AREAS NEAR LA.

..JEWELL.. 04/03/2023

 

[TornadoFan]

Oh come on.

 

[CheeselandSkies]

Yes, just came here to post that. Very interesting and rather ominous 1730Z discussion from SPC. Certainly not a setup to "sleep on" (quite literally) just yet!

 

[TornadoFan]

That is some....very strong wording.

 

[CentralKyWeather]

Can't figure out why they didn't expand the risk East for Day 3.

 

[ColdFront]

Yes, just came here to post that. Very interesting and rather ominous 1730Z discussion from SPC. Certainly not a setup to "sleep on" (quite literally) just yet!

100%. Even the word “rare”. I’m not going to lie, compared to yesterdays outlook, this one is very strongly worded.

You would think after Friday I’d learn my lesson and stop guessing or speculating on events lol.

I was expecting Broyles at the bottom

 

[TheSuckZone]

I was expecting Broyles at the bottom

 

[Muwx]

In SWMO the gradient in tornado percentage is about a tight as it can possibly get. Western half of a county is 5% and the eastern half is 15% hatched.

 

[Austin Dawg]

View attachment 19805
Oh come on.

Wow. Mother Nature seems to have it in for these places. She seems to be letting TN, MS, and AL off-the-hook this time but it's going to be a long Spring Tornado season.

 

[warneagle]

I’m a bit surprised the SPC was that aggressive given the various uncertainties around this setup. I wouldn’t have expected them to express that level of confidence but I guess there’s a reason they get paid to do this and I don’t.

The nighttime aspect of it is one thing that really concerned me when I was looking at the 12z NAM; the cap really starts to erode right around the time the LLJ starts to strengthen after 0z, so the main supercell threat (however much of it materializes) would probably be concentrated in the late evening to overnight hours yet again.

 

[ColdFront]

THIS APPEARS TO BE A RARE
CASE WHERE THE FRONT MAY ACT MORE LIKE A DRYLINE DURING THE
OVERNIGHT HOURS

On this above, is this because the front isn’t moving as fast and won’t push the storms into a line, similar to how storms that fire on the dry line are more likely to stay discrete?

Or what mechanism is in play here

 

[Taylor Campbell]

There are a lot of point soundings from north to south with strong to violent tornado potential.

 

[brianc33710]

I’m a bit surprised the SPC was that aggressive given the various uncertainties around this setup. I wouldn’t have expected them to express that level of confidence but I guess there’s a reason they get paid to do this and I don’t.

The nighttime aspect of it is one thing that really concerned me when I was looking at the 12z NAM; the cap really starts to erode right around the time the LLJ starts to strengthen after 0z, so the main supercell threat (however much of it materializes) would probably be concentrated in the late evening to overnight hours yet again.

Yeah the previously mentioned inhibiting factors aren't mentioned in this discussion.

 

[cincywx]

Yeah the previously mentioned inhibiting factors aren't mentioned in this discussion.

this kind of summarizes it, but not nearly in the same manner as the previous outlook:

"HOWEVER, SUBTLETIES REGARDING TIMING WITH REGARD TO THE
DIURNAL CYCLE, CAPPING, AND CONFLICTING MODEL OUTPUT WILL MAKE THIS
PREDICTION CHALLENGING, ESPECIALLY WHEN WEIGHING POTENTIAL IMPACTS
TO LIFE AND PROPERTY."

this is purely conjecture, but with how quickly the models have trended towards a nocturnal threat, i imagine that they used this opportunity to start getting the word out about it now. they make it very clear how dangerous nighttime outbreaks are in the disco itself, and i think they wanted to push across the fact that an overnight event is expected, regardless of the uncertainties.

 

[warneagle]

There are a lot of point soundings from north to south with strong to violent tornado potential.

Yeah I’m not questioning the potential, obviously this event has a very high ceiling, I’m just surprised at the level of confidence they’re expressing at this point given the potential failure modes (capping, LCLs, maybe VBV) that are still evident on the most recent model runs.

 

[UncleJuJu98]

So what's the news I've had a very busy day changing work routes so I haven't been able to keep up with all that's gone on today fo tommorows weather lol. Seems like confidence has increased since a bimodal moderate has been issued

 

[warneagle]

this kind of summarizes it, but not nearly in the same manner as the previous outlook:

"HOWEVER, SUBTLETIES REGARDING TIMING WITH REGARD TO THE
DIURNAL CYCLE, CAPPING, AND CONFLICTING MODEL OUTPUT WILL MAKE THIS
PREDICTION CHALLENGING, ESPECIALLY WHEN WEIGHING POTENTIAL IMPACTS
TO LIFE AND PROPERTY."

this is purely conjecture, but with how quickly the models have trended towards a nocturnal threat, i imagine that they used this opportunity to start getting the word out about it now. they make it very clear how dangerous nighttime outbreaks are in the disco itself, and i think they wanted to push across the fact that an overnight event is expected, regardless of the uncertainties.

That’s plausible, and I’m guessing they’re setting up the same kind of progression they went with on Friday (expand the moderate in the Day 1, upgrade the current moderate(s) to high if obs warrant tomorrow). I just expected them to hold off a bit longer unless they’re seeing something I’m not.