Area Forecast Discussion
Issued by NWS La Crosse, WI
Issued by NWS La Crosse, WI
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903 FXUS63 KARX 280920 AFDARX Area Forecast Discussion National Weather Service La Crosse WI 420 AM CDT Fri Jun 28 2024 .KEY MESSAGES... - Periodic showers and thunderstorms will occur through tonight. A severe thunderstorm this afternoon and evening cannot be ruled out, but this appears increasingly doubtful for our forecast area. - A few sprinkles possible Saturday followed by cooler, drier conditions Saturday night into Monday. - More rounds of showers/storms Monday into Tuesday and again next Thursday and Friday. Should details come together, some severe storms could occur Tuesday. && .DISCUSSION... Issued at 418 AM CDT Fri Jun 28 2024 Through Tonight: Periodic Showers and Thunderstorms, Potential Afternoon/Evening Severe 08z WV satellite shows quasi-zonal flow aloft over the upper midwest ahead of an upper low over southern Alberta with multiple perturbations within this flow. An area of showers with sporadic thunder is ongoing from S MN south through IA and a squall line is sweeping east through SD. Today, given increasing 850mb moisture transport as the upper low churns eastward, expect periodic showers and a few thunderstorms as the various shortwave eject downstream. Most favorable times will be this morning as the IA/S MN convection and potential MCV associated with the E SD squall move eastward and again around 4 to 7 PM as a shortwave lifts east northeast out of NE. Primary limiting factor for thunderstorm coverage - and by extension severe thunderstorm potential - looks to be available instability, as insolation looks to be greatly limited by the morning round of activity and mostly cloudy conditions that occur in the wake of this. Time period with a conditional risk for a severe storm looks to be 7 PM to 10 PM in mainly our far west as guidance suggests 750-1000 J/kg of MLCAPE could develop as heights aloft fall ahead of the main upper low. That said, while the mid-levels will cool, am skeptical enough destabilization will occur at the surface. Should sufficient destabilization manage to be realized, with progged sfc-6km bulk shear values of around 40 knots and some turning seen in hodographs, a severe storm could occur. Progged DCAPE does creep toward 1000 J/kg so damaging winds and, given potential for a rotating updraft, hail would be the main concerns. Saturday through Sunday Night: Potential Sprinkles, Cooler Saturday, a few sprinkles could occur in the northeastern half of the CWA as a robust shortwave rotates around the departing upper trough. As a surface high builds over the Dakotas and shifts to the Great Lakes, temperatures should drop Saturday and Sunday nights, with values in the lower 40s possible in Taylor County south to the cranberry bogs of Monroe County. Monday through Tuesday: Next Round of Showers, Storms Long range guidance remains in good agreement that the next upper trough will slowly slide eastward over the northern CONUS Monday into Tuesday. PWATs once again approach 2" as Gulf moisture is transported to the region via 850mb moist advection. While the progressive nature of the system should limit flash flooding risk, another few inches of rain could fall over these two days, keeping rivers swollen. LREF joint CAPE/CIN/shear probabilities suggest some chance for severe storms Tuesday, but would need opportune timing of the main upper trough to coincide with peak heating Tuesday afternoon, and this remains uncertain at this time. Next Thursday through Friday: More Rain Chances The upper wave train rolls on Thursday into Friday as guidance is once again in pretty good agreement that the next upper trough will advance eastward sometime during this period. While the pattern in some guidance would suggest less optimal moist fetch will occur compared to our last several waves - i.e. PWATs remain under 1.5" - still a variety of exact solutions, so will need to monitor this period in the coming days. && .AVIATION /06Z TAFS THROUGH 06Z SATURDAY/... Issued at 1043 PM CDT Thu Jun 27 2024 Active weather through this forecast period will make for a tough forecast and changing aviation conditions. While VFR conditions still linger, this will change as more showers move in from the west in short term as a series of waves bring rounds of convection into Friday night. Will likely see ceilings lower into MVFR range as moisture transport increases with low level jet overnight. Hard to tell if this will mean more scattered shower activity or if we will get breaks. But broad lift will certainly lead to stratus and as decaying storms move in towards morning, could see IFR ceilings (60%) chance overtake parts of the area Friday morning. Questions also arise on how long this will linger and impact later storm development. These details get even tougher past 18 hours but did introduce at least a small period of thunderstorm activity Friday afternoon as moisture axis and related instability climb ahead of boundary. && .HYDROLOGY... Issued at 401 AM CDT Thu Jun 27 2024 While rivers continue to fall below flood stage, most of this water is still on route to the Mississippi River. As a result, the Mississippi River is expected to keep rising through the next 3 to 5 days depending on location and routing of tributary rivers. While official forecasts from the River Forecast Center do take into consideration all of the water that has already fallen and is on its way into the Mississippi River, it only takes the next 24-48 hours of forecast precipitation. The next chance of precipitation returns late tonight lasting through Friday. While widespread amounts of 0.5" to 1.0" are not expected to immediately or substantially affect ongoing flooding concerns, an additional widespread 1" to 2" of rainfall upstream will prolong residence of elevated river levels. As a result, the Mississippi River levels may initially slightly decrease before increasing again as the additional rainfall flows downstream this weekend into next week. Elevated rivers with ongoing minor to moderate flood stages from Lake City through Guttenberg are expected to persist beyond the next 7 to 10 days. && .ARX WATCHES/WARNINGS/ADVISORIES... WI...None. MN...None. IA...None. && $$ DISCUSSION...Ferguson AVIATION...Boyne HYDROLOGY...JAR