Area Forecast Discussion
Issued by NWS La Crosse, WI
Issued by NWS La Crosse, WI
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719 FXUS63 KARX 301047 AFDARX Area Forecast Discussion National Weather Service La Crosse WI 547 AM CDT Tue Apr 30 2024 .KEY MESSAGES... - Severe weather possible mainly west of the Mississippi River between 6 PM and 9 PM. Severe weather threats include hail up 1 inch, damaging winds (wind gusts up to 60-65 mph) and possibly a tornado or two. The greatest risk of tornadoes look to be in northeast Iowa closer to and west of the Interstate 35 corridor. - Heavy rain and maybe another round of severe weather on Thursday. && .DISCUSSION... Issued at 251 AM CDT Tue Apr 30 2024 Late This Afternoon and Evening - Severe weather possible mainly west of the Mississippi River The 30.00z models are in fairly good agreement that a negatively tilted 500 mb shortwave trough will move northeast out of the Central Plains late this afternoon and then moves quickly northeast through the Upper Mississippi River Valley this evening. At the surface, a strengthening low pressure area will move northeast from near Omaha, NE at 30.18z to somewhere between Grand Forks, ND and the Twin Cities by 01.00z and over northern Minnesota by 01.06z. As this occurs, the surface warm front tries to lift northward toward the Interstate 90 corridor during the late afternoon and evening. The HREF 30.00Z spread in the 2 meter dew points is rather tight with the 10th to 90th percentiles only having up to 3F spread (in the mid and upper 50s) in the warm sector. The 25th to 75th percentiles in the HREF are showing surface-based CAPES ranging from 200 to 1000 J/kg across northeast Iowa, southeast Minnesota, and southwest Wisconsin. These differences are due to uncertainties on how far north will the surface warm front will get. This instability weakens rapidly with the loss of diurnal heating this evening. This adds to the uncertainty on the eastern extent of the severe weather later in the evening. Near the surface warm front, the 0-3 km of the hodograph greatly lengthens as the low level jet (which is from the south and southwest) strengthens this evening. The 0-1 km shear climbs to around 30 knots and the deep-layer (0-6 km) shear climbs to around 50 knots. SPC has a slight risk covering Dodge, Mower, and western Fillmore counties in southeast Minnesota, and all but Allamakee and Clayton counties in northeast Iowa. There is a marginal risk east toward Interstate 94 in Wisconsin. CSU is a bit further east with their tornado, wind, and hail threats. Looking at the soundings and CAMs, it looks like the highest threat for severe weather this evening will be from 6 PM through 9 PM and mainly west of the Mississippi River. Skinny CAPES in the soundings suggest that hail will be likely up to CAPES. However, if the CAPES are slower at falling this evening or the storms becomes supercellular, the hail might be a bit larger than that. Other severe weather threats include damaging winds (winds up to 60-65 mph) and possibly a tornado or two. The greatest risk of tornadoes look to be in northeast Iowa closer to and west of the Interstate 35 corridor. Wednesday night into Friday - Heavy rain and maybe another round of severe weather on Thursday On Thursday and Thursday night, another strong 500 mb shortwave will move east out of the Central Plains and move northeast into the Upper Great Lakes. Strong moisture transport ahead of this wave will increase precipitable water into the 1 to 1.5 inch range (LREF 10th to 90th percentiles). With elevated most unstable CAPE up to 750 J/kg, the MCS might be able to produce some marginal severe hail and strong to locally severe hail in the vicinity of the surface warm front. Due to this potential, SPC`s Day 3 (Thursday/Thursday night) has a marginal risk up to Interstate 94. Rainfall amounts look to be mainly in the 1 to 2 inch range with locally higher amounts possible. && .AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/... Issued at 547 AM CDT Tue Apr 30 2024 VFR conditions will prevail through much of the daytime as winds trend SE ahead of a cold front. Some shower/isolated storm potential could occur by 20-21Z at KRST with higher chances for bands/clusters of showers/storms to move west to east through the evening. Erratic, gusty winds and IFR/MVFR conditions could occur with any storms. Skies will gradually clear in the wake of the storms with winds shifting westerly, possibly gusting up to 25 to 35 kts at times, depending on mixing depth. && .ARX WATCHES/WARNINGS/ADVISORIES... WI...None. MN...None. IA...None. && $$ DISCUSSION...Boyne AVIATION...JM