2014-04-28 FCST: MO AR LA MS TN IL IN KY AL

[chrisbray]

Kinda surprised no thread up for Monday yet, as SPC issued a moderate risk on their day 3 forecast. Everyone must be pretty focused on this weekend!

The moderate risk covers West Tennessee and West Mississippi, but I am going to discuss the slight risk that reaches up across Eastern Missouri/Illinois/Western Kentucky/Southern Indiana.

NAM and GFS agree that at least 60-65 surface dewpoints will advect into the area, with the GFS returning higher values. Surface winds are backed slightly out of the SSE. Cape ranges from 2500-3000 on the NAM, and 1500-2000 on the GFS, while at the same time the NAM is suggesting bulk shear up to 70 knots remains in only the southern portion of this area, and the GFS has 50-70 knot bulk shear all the way up to the warm front across northern Illinois.

This is because the NAM takes the 500mb wind speed maxima well south into the Moderate risk area, while the GFS seems to think it will turn north and overspread the southern part of Illinois. Location and timing of such impulses could be key. 0-3km EHIs on both models approach 3-4.

Pros: Backed surface winds, decent moisture/cape, strong shear
Cons: Timing and positioning of synoptic scale lift/support may not be conducive for tornadic storms. Wind profiles on forecast soundings who a veer-back-veer which could cause issues with storms that fire.

Feel free to chime in with other details or to discuss other locations in the forecast!

 

[Jeff Wright]

Worse yet, the Birmingham Alabama NOAA weather radio transmitter suffers an outage, and a low power replacement doesn't carry as well.

 

[Dave Gallaher]

The early tor-warned storm in MS is advancing at about 35mph. Wondering if storm motions will remain at that level when they reach AL on Monday. If so, it will be a pleasant change from our normal spring events with 55-60mph storm motions (or faster on 4/27/11).

 

[chrisbray]

Unfortunately I don't really have the ability to chase today. But I have a couple hour window where if a storm fires in my county I can observe it. I'm 50/50 on whether the tornado threat really materializes today across central Il. With every run, models keep the warm front farther south and seem to gradually decrease cape. BUT, there is a narrow window with the warm front to produce some supercells with a tornado threat. Looks like clearing will be moving through most of central IL as daytime heating commences, so there is reason to believe 1000-2000 cape will be realized.

Lack of overall directional shear could be problematic, and storms will be moving perpendicular to the west-east warm front.

Should be interesting to see if this plays out.

 

[Jeff House]

As of 9:45 am Central new thunderstorms already developing on back edge in eastern Arkansas. Delta region atmosphere is pretty worked over; however, by afternoon I expect those to become a broken line of supercells. OFB from morning rain will set up over northern Mississippi. I expect that OFB to be a focal point for stronger/longer supercells and tornadoes this afternoon.