Severe Weather Threat 4/25-4/26, 2024 - (Thursday, Friday)

[andyhb]

Model consensus growing for a multi-day, upper end severe weather episode from Friday 4/27 through next Tuesday.
Looking for a failure mode and can't find one. Ample CAPE everywhere, plenty of shear, favorable LCL heights and limited capping.

That said, there could be two factors that either reduce the ceiling on this system:

1. The highest shear does seem to be displaced from the best CAPE during some the 27th-1st period. But for most of that time frame, some shear is present in most of the warm sector. Otherwise, shear and CAPE are overlapping quite well.

2. Ongoing convection could reduce atmospheric recovery. However, model's don't seem to be concerned with moisture quality. This is a slow moving storm and very moist area will be advecting into the warm sector very efficiently for several days.

Interestingly, NE IL/SE WI (Chicago, Milwaukee, Madison) area might be a good chase target for late evening on April 27th and perhaps again on April 28th.

Early convection/initiation is by far the biggest failure mode with both Friday and Saturday. With Thursday, it's that the wave slows too much or the moisture return is less than advertised.

 

[NorthGaWeather]

While the current threats are over Oklahoma and Texas, there's still gonna be a risk further east. SPC did hint at that in their discussion

I think that at least some severe risk will extend into MS/TN and may clip NW AL. Best upper level support will be lifting away from the rest of us. But that can always change.

 

[tennessee storm chaser]

I think that at least some severe risk will extend into MS/TN and may clip NW AL. Best upper level support will be lifting away from the rest of us. But that can always change.

Looking like Monday will be big threat mid south region . Least the most potent

 

[lake.effect]

Some insane soundings from the 00z GFS:

Eastern OK Friday 4/27



Chicago Suburbs(!) 4/28 (Chicago has been in the crosshairs for several runs now)



4/29 near St. Louis



East-Central Missouri on Tuesday 5/1

 

[lake.effect]

Surprised the SPC is keeping probs at 15% for the forecast period. Maybe they're playing it safe after recent "busts" (their forecast discussion also mentions some uncertainty about timing, placement, mode, etc). I was expecting a 30% area on D5 or D6 after last night's model runs.

CSU MLP models showing a high end event for Friday and Saturday:

 

[cniemczura]

Surprised the SPC is keeping probs at 15% for the forecast period. Maybe they're playing it safe after recent "busts" (their forecast discussion also mentions some uncertainty about timing, placement, mode, etc). I was expecting a 30% area on D5 or D6 after last night's model runs.

CSU MLP models showing a high end event for Friday and Saturday:

View attachment 25562View attachment 25563

I've been watching the SPC closely for about 10 years now. Maybe it's just me, but I've seen a lot more variance in forecast vs. actuals over the last 2-3 years. Someone mentioned there's been a shift in how these forecast are formulated?

Since we've had a lot of over and under performance this year, I'm expecting more than what's forecasted this weekend

 

[jiharris0220]

I think it’s because models have gotten so high res and detailed that it’s easy to put too much thought into every failure mode and favorable parameter. To the point that days that look active ends up being less than expected, and vice versa.
Back then, when models were far less accurate and detailed, only the most volatile looking days got higher end risk.
Which is why there was less variability in verification.
Obviously though there was still massive under and over performances, but definitely not in the numbers we’re seeing now. Which is ironic because it’s not because models have gotten worse, it’s because we have too much to work with now.

 

[JPWX]

Saw this link that Spann had on Weatherbrains website last night. I've included the picture as well.

 

[CheeselandSkies]

Was a bit concerned the first whiff of the NAM might throw cold water on Friday's setup in Iowa but in actuality it has upped the ante, with monster hodographs near the triple point/warm front. It's at 84 hours so not taking it as gospel by any means, but it certainly isn't anything to dissuade me from the idea that it could be a productive chase day.

 

[Clancy]

Was a bit concerned the first whiff of the NAM might throw cold water on Friday's setup in Iowa but in actuality it has upped the ante, with monster hodographs near the triple point/warm front. It's at 84 hours so not taking it as gospel by any means, but it certainly isn't anything to dissuade me from the idea that it could be a productive chase day.

If I remember correctly, the NAM can sometimes over-do wind fields, especially at the end of its forecast range, but considering it's showing solutions even remotely close to what's shown above, definitely cause for concern.

 

[TornadoFan]

Day 3 has just been updated to an enhanced risk.

...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM THE
EASTERN TX PANHANDLE AND WESTERN OK INTO SOUTHWEST/SOUTH-CENTRAL
KS...

AMENDED TO UPDATE FORECAST

...SUMMARY...
Severe thunderstorms are likely from late Thursday afternoon into
Thursday night across parts of the central and southern Great
Plains. Very large hail, severe wind gusts, and strong tornadoes
will all be possible.


Guidance continues to suggest strong buoyancy will be in place ahead
of a negatively tilted shortwave trough ejecting across the southern
High Plains. General forecast expressed in the previous outlook
remains valid, but confidence in an area of greater severe-weather
potential has become more apparent with the most recent guidance.
Late afternoon development is anticipated across the TX Panhandle,
with these storms quickly becoming severe and capable of large to
very large hail up to 3" in diameter. Low-level moisture may be
later to arrive in west-central/southwest KS, delaying convective
initiation to a few hours later than farther south. Large to very
large hail is anticipated with initial development across
west-central/southwest KS as well.

In both of these areas, storms are expected to move
east-northeastward off the dryline, encountering strengthening
low-level southerly flow and environment that is increasingly
favorable for tornadoes. Low-level shear will continue to
strengthening into the early evening, and the overall environment
supports the potential for strong to intense tornadoes if a discrete
mode can be maintained.

 

[TheSuckZone]

D3 upgraded to hatched enhanced. Local weather office says very low tornado chance while SPC wording says strong to intense tornadoes.

 

[TornadoFan]

When's the last time the SPC did an unscheduled Day 3 update?

 

[JPWX]

When's the last time the SPC did an unscheduled Day 3 update?

Give me a few minutes and I'll see what I can find

 

[KCweatherboy]

D3 upgraded to hatched enhanced. Local weather office says very low tornado chance while SPC wording says strong to intense tornadoes.

Seems to be a timing thing like last week's threat. If the more progressive models are right, then it's certainly possible for strong storms. Prominent OKC met Mike Morgan seems to agree with the low tornado threat though.

Of course until weaker than forecasted lapse rates derail any threat again /s

Looking past Friday's threat, I am somewhat nervous for my family and friends around the KC area on the 27-28th. It's been awhile since the last big event in the area (May 2019 Linwood, KS EF4) and there's been a few "false alarms" since then. And there's still the common plains mentality in the area of trying to look for the tornado before taking shelter, which becomes a big problem if any tornado is rain-wrapped

 

[TheSuckZone]

Seems to be a timing thing like last week's threat. If the more progressive models are right, then it's certainly possible for strong storms. Prominent OKC met Mike Morgan seems to agree with the low tornado threat though.

Of course until weaker than forecasted lapse rates derail any threat again /s

Looking past Friday's threat, I am somewhat nervous for my family and friends around the KC area on the 27-28th. It's been awhile since the last big event in the area (May 2019 Linwood, KS EF4) and there's been a few "false alarms" since then. And there's still the common plains mentality in the area of trying to look for the tornado before taking shelter, which becomes a big problem if any tornado is rain-wrapped

I was taking the back way into Lawrence thru Linwood a couple months ago and the path of that tornado is still very visible with the sawed off trees.

 

[JPWX]

When's the last time the SPC did an unscheduled Day 3 update?

April 7th 2021, but that's for just the month of April.

 

[JPWX]

Y'all once I get finished with the Eastern Pacific tropical PowerPoints, I'm gonna go thru and get all the severe weather data/statistics jotted down in a spreadsheet.

It's a pain having to search thru SPC and all that. I like to have everything in one place.

 

[andyhb]

And this is why we don't trust the NAM and its derivatives for thermodynamics this far out.

 

[lake.effect]

18z NAM ups the ante once again, with extreme parameters across a big region from Thursday to early Saturday (when the run ends)

What's even more noteworthy is that multiple rounds look possible, with little to no reduction in instability. Not sure if I buy that.

The average sounding for Eastern OK/Western AR/Southeastern MO/Northeastern TX on late Friday/early Saturday is PDS TOR.

There's 1-2 window for a downward trend, but things are seem to be pointing in one direction. At least for now.