Area Forecast Discussion
Issued by NWS La Crosse, WI
Issued by NWS La Crosse, WI
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088 FXUS63 KARX 312334 AFDARX Area Forecast Discussion National Weather Service La Crosse WI 634 PM CDT Fri May 31 2024 .KEY MESSAGES... - Showers, a few storms continue tonight into Saturday. Severe weather not expected but locally heavy rains possible into early evening. - More rain chances Sunday night/Mon and again later Tue into Tue night. Some threat for strong/severe storms, moreso Tue evening...but ample uncertainties in timing/placment of responsible weather makers. Heavy rain potential. Something to watch. - End of next week trending cooler with occasional showers. && .DISCUSSION... Issued at 225 PM CDT Fri May 31 2024 TONIGHT/SAT: areas of showers, a few storms A bit of upper level energy with a cold front reflected at the sfc working on a 1000 J/kg pool of SBCAPE to fire areas of showers and storms across parts of IA, MN and northwest WI this afternoon. Some of the CAMS suggest an uptick in intensity by late afternoon/early evening. Instability is marginal with weak shear - so not expecting anything too perky (no severe locally but a strong storm or two not out of the question). The showers will continue into the overnight with a few cracks of thunder but overall coverage should be on the decline with decrease in instability (loss of daytime heating). The pcpn looks to shift east/southeast of the local area toward the noon hour, but recent CAMS runs suggest a thin line of convection could fire in the afternoon, in a ribbon of instability with some lingering convergence along the system`s cold front and/or differential heating between sunny/cloudy region post the morning rains. Here again, very skinny CAPE profile in the vertical and not much shear to work with (limiting/eliminating a strong/severe risk). Enough potential to continue smaller end rain chances (20-40%) through the afternoon. SUN NIGHT/MON: more rain chances Another shortwave trough and attendant cold front will be pushing across the northern plains Sunday. Line of showers/storms should spark along the leading edge of the system, and with ample buoyant, moist air to play with, strong-severe storms appear to be a solid bet. These are progged to slide over western MN Sun evening and continue to the Mississippi River overnight. They should be diminishing in intensity and coverage with loss of daytime heating (instability), increasing near sfc CIN, and some weakening in the low level jet/moisture transport. Showers and a few storms likely persisting over the region Monday as the shortwave/front continues to exit east. Clouds, pcpn will favor holding the greater pool of instability southward, limiting potential for strong storms locally. Of course, all this depends on timing. While the EC and GFS generally favor the aforementioned solution (as do their ensemble members), the NAM does not. The 31.12z NAM is about 12 hours slower, which would end up bringing the front in later in the day - where more instability could/would be available, and raises the specter of stronger storms. For now, will stick with the GFS/EC solution - but keep an eye on evolution as we move into the new work week. TUE/TUE NIGHT: another round of storms, some could be strong Long range guidance has been in good agreement with dropping a more robust upper level shortwave across the northern plains Tue, spinning across the upper mississippi river valley Tue afternoon/evening. Relatively warm, moist air pools ahead of the attendant cold front with PWs currently looking to push upwards of 1 3/4" while MUCAPES could climb 2000+ J/kg. Some wind shear to play with, aiding convective potential/development. Obviously too far out to put any definitive statement on what to expect, but depending on how quickly the system moves, there would be the potential for strong/severe storms across parts of the region. In addition, warm cloud depths progged by the EC and GFS to tickle 4K m...pointing to efficient rain makers...suggesting a heavy rain threat. North-south orientation of any rain band and progressive nature west-east would work against prolonged heavy rain, but a localized concern certainly. Something else to keep an eye on as we move into the new work week. LATTER HALF OF NEW WEEK: blocking pattern? Trending cooler, occasional showers GEFS and EPS runs over the past couple days continue to carve out an upper level trough over the eastern great lakes/new england states while amplifying a ridge along the west coast. They start to disagree with whether this pattern will hold through the weekend, or show some progression east. WPC cluster analysis bears this out suggesting both solutions are possible...with the bulk of the EPS favoring holding the pattern in place while most of the GEFS nudge the ridge eastward. The EPS would bring cool air in, and hold it there, through the weekend along with periodic shower chances. The GEFS also returns cooler air, but suggests some moderation toward week`s end. It would still favor those shower chances. Upshot for sensible weather? Still looking like a return to cooler than normal temps either way, with occasional shower chances. How long the colder air sticks around, and how widespread rain chances would be, remain question marks. && .AVIATION /00Z TAFS THROUGH 00Z SATURDAY/... Issued at 634 PM CDT Fri May 31 2024 Main taf concerns are thunderstorm chances at RST taf site early in the taf period...then MVFR/IFR conditions at both RST/LSE taf sites after 06z Saturday into Saturday morning. Showers and storms have developed along a weak surface front from south central Minnesota into western Wisconsin. The showers/storms are expected to slowly move east across the region this evening into Saturday morning. RST taf site may be impacted the showers/storms early this evening. However most of the storms will stay northwest of the taf site and have introduce a couple hours of tempo group for the potential of a stray storm to impact the RST taf site. Instability weakens this evening and allow storms to diminish to showers late this evening into tonight. Behind surface front...ceilings lower into MVFR conditions at both RST/LSE taf sites after 06z Saturday. There could be a brief period of IFR condition at RST. Have kept mention out of RST taf site. Next concern is how long does the MVFR conditions last at both taf sites Saturday. Though latest trends indicate through early Saturday afternoon and have improving conditions early to mid afternoon at both RST/LSE taf sites. && .ARX WATCHES/WARNINGS/ADVISORIES... WI...None. MN...None. IA...None. && $$ DISCUSSION...Rieck AVIATION...DTJ