Area Forecast Discussion
Issued by NWS La Crosse, WI

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043 FXUS63 KARX 231126 AFDARX Area Forecast Discussion National Weather Service La Crosse WI 626 AM CDT Mon Sep 23 2024 .KEY MESSAGES... - Near normal temps next couple days, then milder regime returns for the rest of the week (5 to 10 degrees above normal). - Trending dry for the new work week. More uncertainty in rain potential for the weekend. && .DISCUSSION... Issued at 200 AM CDT Mon Sep 23 2024 OVERVIEW: weak area of surface high pressure builds across the area today while a spin in the upper layers of the atmosphere tracks east across the central plains. Northern fringes of this feature could glance across parts of northeast IA/southwest WI. A stronger, better developed shortwave trough is progged to drop south/southeast across the northern plains tonight, diving across the MO river valley by 00z Wed. As it does it will lift the weaker ripple northeast across the eastern great lakes - perhaps skimming across far eastern parts of the forecast area Tue. The GFS and EC have been at odds with how to handle the stronger shortwave, but last few deterministic runs of both models lean into what was originally a GFS-centric solution - dropping the trough over the lower mississippi river valley and developing a cutoff low. Comparing to WPC cluster analysis, all 4 of the clusters have this solution with some variety with how strong the cutoff low could be and strength of upper level ridging. Compared to its last several runs, all WPC clusters show a stronger/sharper ridge axis running northeast-southeast across the great lakes at 00z Sat while also strengthening the cutoff low. There is one, somewhat weaker solution of the 4, but this is in the minority with only a handful of the GEFS/EPS ensemble members favoring it. To muddle the picture is a potential tropical system to track northward out of the gulf Thu, looping counter-clockwise around the cutoff low. This could spin remnants of the tropical system across the region before both upper level features merge and get a shove east/northeast from another shortwave trough dropping from western Canada to across the northern plains for the start of next week. A lot more uncertainty with how the weekend with play out with the addition of the tropical system - and probably won`t get too much clarity for a few days. 10- PCPN CHANCES: there could be low end chances (10-20%) across the far south and then far east for Mon/Tue respectively thanks to the aforementioned bit of upper level energy. Latest NBM keeps any influence farther south and east for the time being and will run with that for pcpn chances (thus dry). Looks to stay dry for the rest of the work week with growing uncertainties on the rain potential for the weekend. How the interaction of the possible tropical system and the cutoff low is murky at best. About 1/2 of the EPS members spread at least light QPF over parts of the forecast area with only a handful of support in the GEFS. For now, the grand ensemble of models paints light qpf across the southern portion of the forecast area with the NBM sketching low end pops (20%). This looks reasonable given the setup and development questions. TEMPS: a couple more days of near normal temps for the area before an upper level ridging bends northeast from the plains. A return to a more mild regime has been progged by both the GFS and EPS and the ensemble suites continue to place 75% of their members at or above the normals into the weekend. Very little spread between the 25-75%, which has been a consistent trend and increases confidence in this outcome. More spread creeps into ensembles later in the weekend into the early part of next week with the aforementioned uncertainties of the influences of a possible tropical system. && .AVIATION /12Z TAFS THROUGH 12Z TUESDAY/...
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Issued at 626 AM CDT Mon Sep 23 2024 Predominantly VFR conditions during the day today. Winds will be light and out of the southeast throughout the TAF period. Fog will continue in river valleys for the next couple of hours. Monday night into Tuesday morning looks to be another night where valley fog will be possible as light winds, mostly clear skies, and a low dewpoint depression will aid in potential fog development.
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&& .ARX WATCHES/WARNINGS/ADVISORIES... WI...None. MN...None. IA...None. && $$ DISCUSSION...Rieck AVIATION...Cecava