Severe Weather 2025

slenker said:
It's totally understandable to misinterpret this, but yeah, SRH is considered a part of wind shear. Effective shear is technically a different thing, and all I know about it is higher values of effective shear are better for supercellular development/storm development in general. I think it also plays a role in how large supercells for a certain event may end up being. I could be wrong on this because I'm not a met, but I believe effective shear is basically the wind shear through the entire altitude of the atmosphere, while SRH is wind shear measured in the lower levels - at least that's my way of understanding it.
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Did some more research and effective shear (AKA speed sheer and vertical sheer) is basically the magnitude of vertical movement of winds, speed differences with height, and can also be associated with the movement speed of the cell. Changes in wind speed and direction at the 500 mb level can lead to increased vertical wind shear (speed shear), and rotating updrafts (directional sheer and helicity). Basically, we were both right. The modeled windspeeds at 500 mb next week are only enough to produce around 35-40 kt eff (speed) sheer. Most of the really violent, June plains tornadoes have eff shear in the 60-80 kt range.

Lower speed shear values make it easier for storms to get choked off by excess moisture, which will be available in abundance this time of year. A significant increase of wind speed with height (higher speed sheer) will tilt a storm's updraft. This allows the updraft and downdraft to occur in separate regions of the storm, reducing water loading in the updraft. The downdraft will not cut-off the updraft and will even enforce it.

Here are two soundings I pulled from this upcoming system. Directional sheer (helicity) doesn't look like an issue, but speed sheer (eff sheer) could be. When speed shear is weak, the directional shear is not of as much significance. A lot of storms in this environment will move slowly and be short lived, with heavy rainfall for a short time. Wind direction change with height will be high but often unorganized. I'd imagine the reason so many strong tornadoes happen this time of year in the Dakotas, Montana, Wyoming, and Colorado is because there's a lot less moisture to choke the storms off in those areas.



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andyhb said:
Pattern for next week appears to be unraveling with the trough not phasing properly and one of the shortwaves feeling the weakness from the TC in the eastern Pacific. Leads to much less flow over the Plains.
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Grand Poo Bah said:
12z GFS says "just kidding" and brings the flow right back lol. Ryan Hall seems to think any disturbance in the jet streak means bad news this time of year with the moisture and CAPE already in place. Which is probably a solid take mixed with a little hype casting.

The cold front does look like it'll be decently powerful and provide a good bit of forcing. That jet streak is the biggest question mark currently. Lots of tricky interactions happening by the looks of it.
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Tuesday in particular looks to hold some potential in the Midwest (mainly northern MO/southern IA/western IL). However the GFS, especially on the 0Z Friday run that just came in, wants to blow up a lot of precip that wrecks most of the warm sector. Will have to see how that evolves.

There's also some potential further west over portions of KS/OK/western MO, but that's too far for me to reach after work.
 
Can definitely see the reasoning for the 15% risk area for Tuesday.

Moderate shear at 500mb
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Tons of forcing with a strong cold front
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Relative Humidity and PWAT might be low enough to keep the storms from choking themselves out in that low speed sheer too.

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Could be dealing with a sneaky overperformer today. Synoptically-driven threat with a tornado risk on the Eastern Seaboard. SPC considering pulling out a 10% risk for tornadoes in parts of the Mid-Atlantic.
SPC AC 301249

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0749 AM CDT Fri May 30 2025

Valid 301300Z - 311200Z

...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS OVER PORTIONS
OF CENTRAL AND EASTERN NORTH CAROLINA...MUCH OF SOUTH CAROLINA...AND
EAST-CENTRAL GEORGIA...

...SUMMARY...
Scattered to numerous severe storms with wind damage, large hail,
and a few tornadoes will be possible this afternoon and evening
across parts of the Mid Atlantic and Southeast.

...Mid-Atlantic/Carolinas and Southeast...
An Enhanced Risk for damaging thunderstorm winds has been introduced
with this outlook for portions of eastern GA, much of SC and
central/eastern NC.

A mid/upper-level trough is forecast to amplify over the eastern
CONUS today, as a vigorous embedded shortwave trough moves eastward
from the lower Ohio Valley towards VA/NC. In response to this
shortwave trough, a deepening surface cyclone will move eastward
from central KY into the Mid Atlantic by evening. A trailing cold
front will move across parts of the Southeast, Carolinas, and
Virginia. Wind profiles across the warm sector of the deepening
cyclone will be seasonably strong, but instability is expected to be
tempered by weak midlevel lapse rates and substantial cloud cover.

As large-scale ascent with the approaching shortwave trough develops
across the warm sector, thunderstorms are expected to develop along
and near the cold front and move generally east. Latest hi-res
guidance suggests a predominantly linear mode across the Enhanced
Risk area, where confidence regarding greater destabilization is
highest. Damaging winds are expected to be the primary severe
hazard, although a tornado threat will exist primarily with bowing
segments.

Farther north across VA/MD/DE, confidence regarding storm mode is
lower, with some guidance suggesting the potential for
discrete/semi-discrete supercells ahead of the front. These storms
would have the potential for severe wind/hail, and potentially pose
a tornado risk with stronger/more sustained storms. If confidence
increases regarding the expected coverage of severe storms in this
area, then higher severe probabilities may be warranted with the
1630z Convective Outlook.

Along the Gulf Coast from southeast TX into the western FL
Panhandle, moderate/strong buoyancy and 25-30 kts of westerly shear
will be present. Here, scattered clusters of strong/severe storms
posing a risk for mainly damaging winds are expected to develop this
afternoon.

...Eastern WI into northern IL/IN and Lake Michigan...
A mid/upper-level shortwave trough and strong northerly jet will
move southward across parts of the Great Lakes during the afternoon
and evening. Modest low-level moisture will limit buoyancy, but
relatively steep midlevel lapse rates and cold temperatures aloft
will support thunderstorm development during the late afternoon and
evening. Localized damaging gusts and hail could accompany the
strongest storms.

...Eastern NM into Far West TX...
Low-level southeasterly flow will maintain modest boundary-layer
moisture across parts of NM and West TX. Moderate instability and 25
kt midlevel northwest flow could support a few strong storms capable
of isolated hail and strong to severe gusts this afternoon and
evening.

..Bunting/Bentley.. 05/30/2025
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