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Severe Threat May 15-16, 2025

12Z NAM says dangerous environment in place across a lot of the country on Friday evening. Also says a fairly stout cap (hence the very low 3CAPE) could keep much of the Deep South out of the danger zone. However, if it doesn't hold, I wouldn't want to see what an environment like that could spit out. Soundings from near Smithville at the AL/MS border and at the AL/GA line near Haralson County, respectively. Standard fare caveats are 1) this is the NAM at 84 hours, 2) things could change between now and then, 3) the cap could be over-modelled, 4) even without a cap, there may not be much that develops in the way of severe weather, 5) the locations most at risk could change between now and 84 hours from now.

That said, globals remain fairly aggressive about this setup, and both Thursday and Friday look like potentially dangerous days for parts of the country. Middle MSV and Ohio Valley look pretty ripe both days. The GFS also generally corresponds with the NAM on issues like capping. Keep in mind, if you're along/north of Interstate 40, you should definitely be paying attention - my concerns are targeted at the southern extent of the possible risk area. Correspondingly, both FFC and BMX don't sound terribly impressed by the setups for their respective WFOs. Another thing to note is that wind profiles look alright Friday evening, but remain fairly unidirectional in the daytime Friday and Saturday.
.LONG TERM...
(Wednesday night through Monday)
Issued at 230 AM EDT Tue May 13 2025

Key Messages:

- A couple rounds of strong to severe thunderstorms are possible
between Friday and Monday.

- Above average temperatures, by 5 to 10 degrees, are favored
next weekend.

A transient upper level ridge will slide through Georgia on
Thursday. As this occurs mid and upper level subsidence will
increase and an elevated mixed layer will develop. The combination
of these two factors will inhibit afternoon convection and lead to
a dry day with just a few fair weather cumulus in the afternoon.
Temperatures will also increase, leading to widespread highs in
the upper 80s. A couple spots in central Georgia may reach 90
degrees.

Between Friday and Monday strong zonal or near zonal flow will
develop over the Southeastern U.S. Multiple shortwaves may ride
this flow from west to east creating the potential for
thunderstorms. Another feature to watch will be a cold front
sagging south through the Tennessee valley. The potential exists
for this front to stall out over Georgia this weekend, providing
and additional focal point for possible convection. Two other
noteworthy expectations for the weekend include increasing
instability (GEFS & EPS means suggest MUCAPE approaching 2500
J/kg) and strong unidirectional shear profiles (0 to 500 mb shear
over 50 kt at times). These to factors, combined with the front
and shortwaves, suggest the potential for multiple Mesoscale
Convective Systems (MCS) to form and move through Georgia. Several
rounds of thunderstorm activity could occur between Friday and
Monday, with the greatest potential for severe weather expected in
north Georgia between Friday afternoon and Saturday night.
Damaging straight line winds look like the main potential hazard,
but large hail could also occur. Anyone with outdoor events
should monitor the forecast closely.

If thunderstorms don`t screw up any of the diurnal trends, then
above average temperatures (by 5 to 10 degrees) are expected
between Friday and Monday. Translated into tangible values, this
would mean highs in the upper 80s in north Georgia and lower 90s
in central Georgia.

Albright
Click to expand...
.LONG TERM...
(Wednesday night through next Monday)
Issued at 146 AM CDT TUE MAY 13 2025

Upper level ridging and high pressure will be over the area for
Thursday. The area should be dry, with probably the only day of
little to no precip chances in the forecast. By Friday afternoon,
a low pressure system will strengthen over the Ohio Valley, with a
front draped over the area. Models differ on how far south the
boundary will cause convection, but with a minimal amount of
instability and shear increasing along a mid level jet,
thunderstorms are possible, especially across the northern areas.
Saturday and Sunday, a ridge starts to develop over the Gulf with
a couple of shortwaves moving through the south. Showers and
thunderstorms are possible each day, mainly with the day`s heating
in the afternoon through the evening. By Monday, the ridge
strengthens with flow turning to the west. Activity should be
possible around this high, with the bulk of convection basically
skirting our area for now.
Click to expand...
1747147563941.png1747147599310.png1747147689419.png1747147721929.png
 
Clancy said:
12Z NAM says dangerous environment in place across a lot of the country on Friday evening. Also says a fairly stout cap (hence the very low 3CAPE) could keep much of the Deep South out of the danger zone. However, if it doesn't hold, I wouldn't want to see what an environment like that could spit out. Soundings from near Smithville at the AL/MS border and at the AL/GA line near Haralson County, respectively. Standard fare caveats are 1) this is the NAM at 84 hours, 2) things could change between now and then, 3) the cap could be over-modelled, 4) even without a cap, there may not be much that develops in the way of severe weather, 5) the locations most at risk could change between now and 84 hours from now.

That said, globals remain fairly aggressive about this setup, and both Thursday and Friday look like potentially dangerous days for parts of the country. Middle MSV and Ohio Valley look pretty ripe both days. The GFS also generally corresponds with the NAM on issues like capping. Keep in mind, if you're along/north of Interstate 40, you should definitely be paying attention - my concerns are targeted at the southern extent of the possible risk area. Correspondingly, both FFC and BMX don't sound terribly impressed by the setups for their respective WFOs. Another thing to note is that wind profiles look alright Friday evening, but remain fairly unidirectional in the daytime Friday and Saturday.


View attachment 41373View attachment 41374View attachment 41375View attachment 41376
Click to expand...
Thank you @Clancy
 
ColdFront said:
Wow. It’s 84 hours out and the NAM but wow. That speckled broken line look Reminds me of the reanalysis reflectivity of Palm Sunday 1965, only a bit further west.

View attachment 41378
Click to expand...
From some of the soundings I’ve seen posted earlier on this thread, I saw a BNA sounding from 4/3/74 very soon after I posted the MGM 4/4 sounding. This event is trending in a real dangerous direction right now.
 
Kds86z said:
I also noticed the SPC extended outlook mentioned severe wx pattern.
Click to expand...
Wouldn’t be surprised in the slightest to see this enhanced 500 mb flow stick around east of the Mississippi for a while. The globals show the trough behind this one contributing to this same pattern, albeit not as impressive as what it looks like now, for the time being.
 
Jbop said:
Interesting that when most of the posters here agree that the pattern looks dangerous the SPC has more of a conservative forecast compared to a more aggressive forecast when it's the opposite.
Click to expand...
Think you see a different discussion in tomorrow outlooks …. Models starting really turn in a bad direction
 
If you get more aggressive convective coverage Friday afternoon into night, it's going to be a very dangerous day that day. Probably won't be able to figure out how aggressive or conservative convection will be until we get into the HRRR range I would think.
 
Just what I was thinking. it isn't over until it's over. The severe weather season was making us guess think it could be quiet to end the season but nope! Looks like one more big event possibly.

Please Stop No More GIF by LiL Renzo
 
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