Area Forecast Discussion
Issued by NWS Paducah, KY
Issued by NWS Paducah, KY
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482 FXUS63 KPAH 221332 AFDPAH Area Forecast Discussion National Weather Service Paducah KY 832 AM CDT Wed May 22 2024 .KEY MESSAGES... - Severe thunderstorms possible today, with hail the leading threat. Some wind damage potential may develop in the afternoon. At least some potential that storms are unable to initiate in the afternoon. Heavy rain can be expected with any storms that form. - Scattered to occasionally numerous storms are possible Thursday through Saturday. The tendency will be for peak coverage in the afternoon, but very subtle jet-level waves could spark things any time through the holiday weekend. - Sunday remains the best potential for more organized and widespread severe weather. There are timing and detail discrepancies between models, as you would expect, but we will need to keep a close eye in the coming days. && .UPDATE... Issued at 832 AM CDT Wed May 22 2024 Relatively clear skies to start the morning should allow for strong surface heating through the late morning. Jet-level ascent is increasing over MO/OK/KS this morning, that should time out to arrive over the quad-state by about 20z. The challenge for our area then becomes whether the increased ascent nudges the surface front far enough southeast to lead to more convection forming south of the area. Whichever areas remain to the southeast of the front will likely have 3000-3500 J/kg of MLCAPE to work with by this afternoon amid sufficient deep layer shear for storm organization. Forecast of convection starting by 3-4 pm with severe risk seems on track, but coverage and placement will be a challenge. && .DISCUSSION... Issued at 218 AM CDT Wed May 22 2024 Subsidence from the right front quadrant of an approaching jet maximum seems to be winning the convective coverage game tonight. Widely scattered thunderstorms are trending downward over the quad-state while there is some new development over south central Missouri that appears to be initiating in an area of strong lower-level frontal convergence. Based on observed and model soundings believe this convection is partially elevated with about 1500 J/kg of CAPE rooted at 800mb or so to work with. This activity may pose a hail threat over the next couple of hours. The overall picture though is subsidence increasing a capping inversion through early this morning. Most of the guidance generates enough convection to skew the thermodynamics but I *think* we will see enough sun to warm into the middle 80s as a capping inversion strengthens over the area. If you modify soundings this afternoon to about 84 degrees with a 70-73 degree dewpoint you get about 2500 J/kg of MLCAPE. The cap holds against unforced parcels but there may be just enough frontal convergence to initiate convection this afternoon, helped perhaps by a little bit of height fall via a shortwave passing over IA/IL. Shear is relatively light in the 0-3km layer which may make parcels a little less susceptible to dry air entrainment, but coverage will probably be limited by a pretty neutral jet-level ascent environment. I think what we will probably have is a supercells or nothing scenario. Hail looks to be the headliner threat with wind also accompanying it. Upscaling into more linear features is possible but doesn`t look extremely likely. Tornado threat appears muted given the low level shear environment. Very heavy rainfall will be a threat as storm motion may be fairly slow given the weak shear environment and PWATs remain above 90th percentile climatologically. The front stalls over the area Thursday through Saturday and we will be mostly at the mercy of daytime heating and very small perturbations in the flow aloft which will be extremely difficult to identify and time. Kept a broad shower and thunderstorm chance. Given the moisture and instability present heavy rain and isolated severe weather looks possible each afternoon. Sunday still looks potentially concerning, although some spread in the GFS/ECMWF timing of a subtle lead shortwave trough ahead of a stronger closed low over the intermountain west would likely result in big differences for our total severe threat. the ECMWF merges this leading shortwave with the broader troughing creating a sort of negative tilt longerwave trough from MO to ND which results in a stronger surface low and faster frontal passage. Where the GFS keeps the systems separate, leading to a slower frontal passage. Both models though show strong westerly shear at a sharp angle to the existing front, with 850mb flow ramping up to 35-45 kts in the late morning and afternoon with dewpoints in the 70s. The GFS leading wave scenario opens the possibility for warm sector initiation with MLCAPEs at 3000 J/kg with 0-1km SRH over 250 m2/s2 with a front cutting into slightly less, but still respectably strongly sheared air. The ECMWF initiates convection earlier owing to the faster progression and doesn`t let peak heating quite arrive but still shows a concerningly volatile airmass ahead of the activity that does develop. Lapse rates below 700mb though are pretty weak in GFS soundings owing it looks like to warmer and drier air mixing in from the southwest and it will be important to see how those details develop as well. Once the front clears Monday, which looks dry, another shortwave pulls up on Tuesday which may give us some thunder chances, particularly across the south. && .AVIATION /12Z TAFS THROUGH 12Z THURSDAY/... Issued at 833 AM CDT Wed May 22 2024 Convection will be the primary flight concern today. New thunderstorm development is possible, mainly over the southern half of the area after about 20z. Coverage should be scattered but convection may be slow moving leading to longer periods of terminal impacts. Showers and isolated storms may continue overnight. && .PAH WATCHES/WARNINGS/ADVISORIES... IL...None. MO...None. IN...None. KY...None. && $$ UPDATE...JGG DISCUSSION...JGG AVIATION...JGG