Area Forecast Discussion
Issued by NWS Paducah, KY
Issued by NWS Paducah, KY
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814 FXUS63 KPAH 211738 AFDPAH Area Forecast Discussion National Weather Service Paducah KY 1238 PM CDT Tue May 21 2024 .KEY MESSAGES... - Mostly likely we stay dry until after dark today, but breezy. Then there is a small risk for severe storms (wind) in the overnight Tuesday. - If instability can build Wednesday a respectable severe weather risk will emerge (wind and hail). As will a flash flood risk. - Severe thunderstorm risks currently appear to peak on Wednesday and then again potentially on Sunday. But some type of severe storms may be possible each day Wed-Sun. Flash flooding may also develop any of those days and flash flood watches may be required later today or Wednesday. && .DISCUSSION... Issued at 233 AM CDT Tue May 21 2024 A sprawling low pressure system with 3 separate trough/jet max elements sits over the northern Rocky Mountain region this morning. A double barreled closed low sits over British Columbia and Alberta with a jet max running down the Canadian Pacific coast giving a nudge to everything that lies ahead. With a trough axis over MT/WY and numerous embedded shortwave troughs to the east with 110-120 kt jet maxima to the north and south of a stronger shortwave over SD/NE. To the south of the southern jet max over Texas a fairly strong elevated mixed layer is being pulled in off the Mexican Plateau. While broad southerly flow ahead of lee troughing is advecting mid 60s dewpoints into much of the south central CONUS with 70 and even 80 degree dewpoints along the Texas Gulf Coast. CIRA hourly precipitable water seems to suggest PWAT values in this area, which will eventually head this way, are a little stronger than the GFS has modeled currently. Locally moisture is increasing through the column, although its definitely richer near the surface, with a weak inversion at around 700mb that will likely grow stronger as the day progresses today. As this giant mess moves eastward a surface low will rapidly strengthen over the upper midwest today and our mid- to low-level winds will strengthen which will increase moisture advection and advect the aformentioned TX EML over the region. The net result will be a hot day that should remain mostly precip free despite increasing low level moisture as the capping inversion strengthens. Winds will pick up out of the south at 10-15 mph, enough for enhanced caution on area lakes. Tuesday evening upper diffluence increases as the TX upper jet max approaches. This starts work on lifting out our capping mechanism. The HRRR and NAM seem to have a good grasp on the thermodynamic situation where the GFS appears to be underdoing the EML a little bit. This would result in convection initiating along the cold front in western Missouri in the late afternoon and then upscaling and trekking eastward, approaching the area by late evening. Thermodynamic environment may be supportive for some severe overnight mainly in the form of wind given fairly strong deep and low level shear, but instability will be a big question. New forecast has PoPs increasing after 05z and then slowly tapering through 09z as large scale ascent weakens as the nose of the jet max moves to our northeast. We then get into the right rear quadrant of this jet after 21z Wednesday. I think its possible given the richness of the column moisture we maintain too much convection for surface heating to yield much instability, but the more likely solution at this point appears to be enough of a respite that we heay up into the mid 80s with dewpoints in the upper 60s, particularly from about Paducah southward. This would yield 2000-2500 J/kg of MLCAPE with fairly strong deep layer and sufficient 0-3km shear for a more organized wind threat. The tornado threat appears a little more muted given projected 0-1km shear values. The NAM and ECMWF and to some extent the GFS (although it is more southeast of the area with this forcing) keep jet level lift over the area with low level warm advection increasing though the overnight making at least a few rounds of thunderstorms (although probably only one round of severe potential) possible. Column PWATs are projected at 1.6 to 1.7 and as mentioned before the GFS may be running a little low with the airmass in the western Gulf, so flash flooding may become a headliner concern into the overnight. Its too early for a flood watch but one may be required before all is said and done. A fairly large discrepancy then builds into the guidance between GFS/ECMWF members for Thursday with the GFS a little further south with a shortwave that leaves us more dry on Thursday where the ECMWF paints widespread thunder again. Given the column moisture, rain/thunder looks very likely but the precip magnitude and any flooding potential will rest on exactly how that shortwave moves through. We remain in a stagnant pattern with a front southwest to northeast just northwest of the area in most guidance through Friday before it approaches in current GFS/ECMWF guidance. Keeping rain and thunderstorm chances with dewpoints in the mid 60s to near 70. Severe weather and flooding potential could emerge on either of these days but predictability is very low given the spread in guidance and the fickle convective nature of the systems involved. A stronger shortwave moves towards the area on Sunday spinning up a strong surface low over MO/IL and tracking to our northeast. GFS/ECMWF have been consistent for a couple of days with this system both showing more potent mix of instability and shear with a favorable synoptic scale pattern for a more substantial severe weather threat. PWATs also rise up to 1.6-1.8 inches late in the day. This system as will be the case with everything after tomorrow night though will absolutely be influenced by coverage and intensity of thunderstorms in the days preceding it. Essentially any day Wednesday through Sunday could see both severe thunderstorm or flash flood warnings. I think the flash flood threat has a higher ceiling overall but some decent wind looks possible Wednesday if it comes together and we are going to need to watch Sunday very closely. && .AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/... Issued at 1233 PM CDT Tue May 21 2024 A good midlevel cu field has developed across the area and will persist through the evening hours. Main story is convection that will initiate to the west over central MO this evening and will move eastward through the area and will bring thunderstorms to the terminals overnight. Right now models indicate that convection will diminish by tomorrow morning. MVFR cigs are expected with this convection and through tomorrow morning. Winds today are breezy out of the south at around 10-15 kts with gusts to around 20 kts. Winds will shift overnight to being out of the southwest and will be less breezy. && .PAH WATCHES/WARNINGS/ADVISORIES... IL...Lake Wind Advisory until 6 PM CDT this evening for ILZ075>078- 080>094. MO...Lake Wind Advisory until 6 PM CDT this evening for MOZ076-086- 087-100-107>112-114. IN...Lake Wind Advisory until 6 PM CDT /7 PM EDT/ this evening for INZ081-082-085>088. KY...Lake Wind Advisory until 6 PM CDT this evening for KYZ001>022. && $$ DISCUSSION...JGG AVIATION...SHAWKEY