Area Forecast Discussion
Issued by NWS La Crosse, WI
Issued by NWS La Crosse, WI
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428 FXUS63 KARX 121107 AFDARX Area Forecast Discussion National Weather Service La Crosse WI 607 AM CDT Sun May 12 2024 .KEY MESSAGES... - Warm today! Highs could top out in the mid 80s in warmer valley locations. - Scattered late afternoon showers/storms today into the evening (20- 40%) with pcpn chances shifting south of I-90 Monday. - Seasonable temps for the new work week with the next, better shot for widespread rain chances coming Thu. && .DISCUSSION... Issued at 225 AM CDT Sun May 12 2024 * OVERVIEW: Upper level flow remains fairly progressive as we move through the weekend and next week. Various shortwave troughs/ridging could/will shift west to east across the Upper Mississippi River valley, although long range guidance has been at odds at how this will shake out. The model blend suffers as a result, "smearing" the pcpn chances over a longer period than is likely - while also lowering them. That said, the EPS and GEFS are showing some signs of coming together - at least for pcpn chances Thu. Meanwhile for temps, after a warm one today, trends continue to favor highs topping around around the seasonable norms through the work week. * TODAY/SUNDAY: very warm today, cooler (seasonable) Monday. Scattering of late afternoon/evening showers-storms today (20-40%) with shift in chances to south of I-90 Monday. Southwest-northeast running sfc cold front still set to sink southward across the region, tied to an upper level shortwave trough just north of the great lakes. Weakly convergent in the near sfc layer without much low level thermodynamics to air the lift ahead of it. No help in the upper levels either. GFS and NAM builds 1500+ J/kg of SBCAPE by late afternoon in the warm sector ahead of the front. However, soundings continue to show deep mixing (upwards 7 kft) - which will promote drying along with gusty winds. Thus, GFS and NAM overshooting sfc Td (GFS into the low 60s!) and SBCAPEs are overdone. HRRR more reasonable in the 500 to 750 J/kg range. No wind shear. CAMS models spark scattered showers/storms along and ahead of the front by mid afternoon, persisting into early evening. Again, due to over forecasting moisture concerns, coverage in some of these short term models is likely over done. Still, should be enough to spark a few showers/storms of the pulse variety (20-40% chances). Any storm will produce enhanced wind gusts. Severe storms not anticipated. The front is set to lay up across central IA into southern/northern IL for Monday...a bit more southern compared to some previous model runs. A shortwave trough in the southern portion of the upper level flow will track across the mid mississippi river valley on Monday, while a piece of energy drops southeast from the northern plains. Both will work on the sfc boundary, helping force deformation band of pcpn across IA into southern WI. Shear remains uninteresting while the bulk of the instability shifts south/southeast. Mostly rain with perhaps a clap or two of thunder is the likely outcome...and generally south of I-90 (locally). Still looking like a warm end to the weekend. 850 mb temps on track to warm from around +9 C at 00z last night to +13 C by 21z today. Deep mixing upwards of 700 mb will work to bring that warmer air to the sfc. Latest HREF paints a 70-90% to reach or exceed 80 degrees for highs (lower north of I-94). Valley locations likely the warmest and look to peak in the mid 80s. A taste of summer but minus the humidity. It will cool back to the early May normals Monday with the passage of the cold front. * THURSDAY: next shot for rain Long range guidance is in a bit better agreement with trying to refine timing/placement of the potential pcpn makers for the new work week. Latest EPS and GEFS runs have the preponderance of their ensemble members bringing at least some light QPF across the upper mississippi with an upper level shortwave trough Thu (perhaps as early as the the overnight Wed). Not looking very dynamic at the moment, but should have some fetch to southerly moisture. Latest GFS doesn`t show much for instability nor wind shear. Still way too early to ferret out any stronger storm risk. && .AVIATION /12Z TAFS THROUGH 12Z MONDAY/... Issued at 615 AM CDT Sun May 12 2024 VFR expected across the forecast area from northeast Iowa, southeast Minnesota, and western into central Wisconsin. Limited precipitation chances with cold frontal passage tonight from northwest to southeast. Given low confidence and potential impacts, have continued with VCSH. Could be refined at 12.18Z TAF issuance. Regardless, higher cloud bases expected to keep VFR ceilings. Very minimal thunder chances at both TAF sites (KLSE & KRST) has prevented from introducing TS at either. Otherwise, potential for LLWS at KLSE tonight with frontal passage. Given the increased forecast hour, have opted not to include but again will be further refined in coming forecasts. && .ARX WATCHES/WARNINGS/ADVISORIES... WI...None. MN...None. IA...None. && $$ DISCUSSION...Rieck AVIATION...JAR