Area Forecast Discussion
Issued by NWS La Crosse, WI

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000 FXUS63 KARX 181044 AFDARX Area Forecast Discussion National Weather Service La Crosse WI 544 AM CDT Fri Jun 18 2021 .SHORT TERM...
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(Today through Saturday Night) Issued at 219 AM CDT Fri Jun 18 2021 Well, a very long and active severe storm episode this last evening early this morning across the NWS La Crosse forecast area. Very large hail up to the size of baseballs and some 60 mph winds in the most severe storms, along with some intense rainfall. This was all due to a vigorous mid-level trough pushing through and interacting with very muggy airmass in place (precipitable water values in the 1.7-2.0 range). Still some stronger storms mainly south of I-90 around but severe threat appears to have diminished significantly. Expecting any lingering storms to be mostly cleared of the area by daybreak. Otherwise, another very warm but drier airmass filters into the area today as high pressure moves in from the Northern Plains. Under mostly sunny/partly cloudy skies, look for highs in the 80s to lower 90s. Models showing northwest flow aloft ushering in a trough of low pressure and decent packet of 500-300mb pv-advection Friday night. Looks like we could see scattered showers and isolated thunderstorms on a previously dry forecast. Will add some mid-range pops for now to cover this. High pressure rebuilds into the area Saturday for what looks to be a very pleasant day with highs in the mid-70s to mid-80s. Will see showers and thunderstorm chances move into the area after midnight Saturday night in warm air/moisture advection ahead of low pressure heading east across the Plains. .LONG TERM...(Sunday through Thursday) Issued at 219 AM CDT Fri Jun 18 2021 Periodic showers and storms will be seen Sunday as low pressure tracks across the area. Will have to keep an eye on how the warm sector sets up, juxtaposed with bulk shear. NAM and GFS both show nose of higher CAPE edging into our southern area, coupled with 30- 40kt 0-3km bulk shear by afternoon. So, could see a chance for some strong to severe storms -mainly south of I-90. In addition, looks like we could see some heavier rainfall as well associated with the deformation/stronger frontogenesis northwest of the surface low. Will likely have to ramp up messaging as this is becoming an increasingly consistent signal. Fairly significant pattern change behind the aforementioned storm system as GFS/ECMWF carve out a deep longwave trough over us and the eastern CONUS. As a result, looks cooler through Wednesday before a ridges starts to rebuild into the region by Thursday. Could see a few instability showers Monday in the cooler cyclonic flow aloft but looks dry Tuesday and Wednesday. May see a few showers/storms as GFS hints at a trough overtopping the ridge. Look for highs Monday and Tuesday in the mid-60s to mid 70s, 70s/near 80 Wednesday, and mid- 70s to mid-80s Thursday.
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&& .AVIATION...
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(For the 12Z TAFS through 12Z Saturday morning) Issued at 540 AM CDT Fri Jun 18 2021 VFR conditions expected today. Any lingering vicinity valley fog and low stratus near LSE will quickly dissipate after sunrise. Northwest winds behind yesterday`s front will become a little more westerly later this afternoon, with potential for deeper mixing to bring down some gusts around 20 knots. Winds will become light this evening with increasing mid clouds ahead of an approaching disturbance aloft. This feature is expected to trigger isolated to scattered showers overnight that may impact the TAF sites. Instability aloft looks marginal but could be enough to support isolated thunderstorms. Due to low overall confidence in rain potential tonight, just included VCSH for now and will further evaluate with later TAF issuances.
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&& .ARX WATCHES/WARNINGS/ADVISORIES... WI...None. MN...None. IA...None. && $$ SHORT TERM...DAS LONG TERM...DAS AVIATION...Kurz

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