Area Forecast Discussion
Issued by NWS La Crosse, WI
Issued by NWS La Crosse, WI
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779 FXUS63 KARX 310341 AFDARX Area Forecast Discussion National Weather Service La Crosse WI 1041 PM CDT Thu May 30 2024 .KEY MESSAGES... - More showers, a few storms for Friday into Friday night (40-70% chances). Lower end amounts expected (few hundreths to upwards of 1/4"). - More storm chances Sunday night/Monday. Some potential for strong to severe, depending on timing. - Warming as we move into the new month with highs expected to meet/exceed the early June normals. && .DISCUSSION... Issued at 220 PM CDT Thu May 30 2024 OVERVIEW: fairly progressive, quick moving upper level flow into the middle part of next week promising to push shortwave ridges/troughs across the upper mississippi river valley. Periodic rain chances will continue, with no prolonged period to "dry out" in the near term. Some potential for severe storms too - highly dependent on timing/positioning of the upper level features/sfc fronts. Overall height increases a loft support some warming as we move into the weekend/next week - not "hot" per se, but the recent run of highs in the 60s/70s should push to, and a few degrees above, the seasonable normals as we creep into the start of June (mid 70s to around 80). Venturing into the following weekend, long term guidance suggests ridge building will occur over the west coast/plain states. Some differences between the GEFS and EPS here, but the upshot would be to carve out an upper level trough over the great lakes...which could mean more showery and cooler conditions. Something to watch. FRIDAY/FRI NIGHT: rain, storm chances Elongated bit of upper level shortwave energy stretched north-south across the dakotas at early afternoon, per latest upper water vapor satellite imagery. The shortwave, along with an associated cold front at the sfc, were serving to fire shower/storms - fueled by a ribbon of instability/moisture transport. Not too perky as of yet but should see some increase in intensity/areal coverage as the afternoon wears on. The system gradually moves east tonight, but not in a hurry, and short term guidance points to weakening in the overall forcing. CAMS models bring the pcpn to the forecast area`s doorstep (SE MN) by 12z, but questionable on how much further east the chances make through the day. Most of the short term guidance hold the sfc boundary/convergence from northwest WI into northwest IA while the upper level shortwave shears out north and south. Eventually, the sfc front, instability axis and fetch of moisture transport bend across the local area, spreading rain chances eastward but currently on the "lower end" (sub 50%). All in all, the higher chances and greater rainfall amounts continue to be favored from northwest WI into northwest IA. SUN NIGHT/MON: storm chances, strong to severe possibilities Medium/long range guidance remains in solid agreement with tracking an upper level shortwave trough across the northern plains Sunday with some reflection at the sfc. Disparities in how strong the shortwave will/could be, along with the frontogenetic lift with the sfc front. Warm, moist unstable airmass pools over the northern plains to fuel storm chances with PWs upwards of 1 1/4" and SBCAPES of 2500 J/kg. Wind shear enough to aid storm organization. Current GEFS/EPS runs favor tracking the storm system across the local area Monday morning/early afternoon. CAPE pool shifts southeast Monday in this scenario, moreso across IA and northern IL. With the current timing, showers and storms would fire over the northern plains Sunday afternoon, shifting into western MN for the evening. Some severe weather looks like a good bet. As the storms shift east overnight, decreasing instability and increasing sfc based CIN would work to downscale the severe threat. Then on Monday, morning pcpn/clouds will conspire against quick destabilization, which would shift most of a strong/severe threat south/east of the local area. Very timing dependent - so keeping a close eye on evolution, location of the main features. TUE NIGHT/WED: another round of storms? Long range guidance pointing to another, but stouter shortwave trough would drop across the northern plains and then the upper mississippi river valley Tue night into Wed. In this case, instability not looking as robust as Sun night and shifted southward. Low level jet/moisture transport looks to drive northward ahead of the system and PWs could push north of 1 1/2". Another good shot for storms, but uncertainties for any strong/severe storm potential. && .AVIATION /06Z TAFS THROUGH 06Z SATURDAY/... Issued at 1040 PM CDT Thu May 30 2024 Main taf concerns are showers and potential for thunder at both LSE/RST taf sites. A weak surface front slowly moves east across the area Friday. Weak convergence and very limited instability will allow a few showers to develop early Friday afternoon along the front. Due to very little instability...thunderstorm chances are low and will keep mention out of tafs. Latest trends show slower movement of front moving across the region. Have delayed the onset of the possibility of showers into the taf sites...especially the RST taf site. VFR conditions are expected to prevail through the much of the taf period. However...if a stronger shower moves over the taf sites...a brief period of MVFR conditions could occur Friday afternoon/evening. Southerly wind speeds will be around 10 knots or less. && .ARX WATCHES/WARNINGS/ADVISORIES... WI...None. MN...None. IA...None. && $$ DISCUSSION...Rieck AVIATION...DTJ