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FXUS63 KARX 240305 AFDARX

Area Forecast Discussion National Weather Service La Crosse WI 1000 PM CDT Tue Apr 23 2024

KEY MESSAGES

- Scattered showers and storms with small hail exit the area this evening.

- Cooler tonight into Wednesday. Low temperatures tonight will fall into the middle 20s to middle 30s.

- Active weather starting Friday with widespread rains through the weekend and some potential for severe storms at times...especially Sunday.

DISCUSSION
Issued at 300 PM CDT Tue Apr 23 2024

Tonight through Thursday

Mid-level trough passing through the western Great Lakes this afternoon with colder air aloft, decent mid-level lapse rates, but limited CAPE to work with was leading to low based, scattered convection. Some small hail reports but activity will wain quickly as this wave passes and with loss of heating.

Passage of wave will lead to a quiet couple days with northwest flow. Dry regime will allow for another chilly night with sub freezing temperatures expected for parts of the area. Winds are expected to remain up overnight so short term freeze risk is about main concern versus frost. Even though temperatures likely to be below freezing for a brief period of time, may need another headline given setup.

With area in between systems next couple days, main concern will be watching for any fire weather risks given continued dry airmass.
Nearly full sun and atmospheric mixing could drop afternoon relative humidity values below 30 percent (and possibly near 20 percent) on Wednesday. The good news is lighter winds and lower fine fuel numbers expected, which should limit overall risk. Winds do increase on Thursday as surface ridge exits, but so does the cloud cover and low level moisture advection, limiting risk. Parts of central Wisconsin would be last to notice these limiting factors so again, will have to watch trends.

Friday through Tuesday

Larger pattern shift taking place late week will lead to a period of more active weather, with widespread rains a given and a window or two where severe storms could impact area. Models have two main waves resolved that will have their biggest impact on our region Friday and again Sunday.

Starting Thursday night we will see impressive moisture advection northward across central CONUS with broad lift ahead of approaching wave. This will lead to dramatic increase in convection coverage that will move into the local areas Friday. Short wave will take on a negative tilt as it ejects into the Plains but still looking like timing will favor warm sector and higher risk of severe storms to the southwest of us. Amount of convection could play into how things evolve after that even as wave is forecast to lift northeast and weaken heading into Saturday. Ensembles continue to suggest lower confidence in surface based instability working into immediate area.

Saturday could be a slight lull in the extent of convection between waves, but given the front could be layed up over area and no big reprise in precipitable water values, redevelopment during daytime is a possibility adding to the overall rainfall threat.

Even though we are talking about Day 6, the setup for Sunday might be the most interesting at this point. Another strong wave progged to eject out of the southwest and approach western Great Lakes.
Corridor of moisture ahead of this wave and previously mentioned front will continue to parade convection. Track and more of a neutral tilt wave suggest a less occluded but well defined frontal structure working across the forecast area. Again, numerous days out and lots of factors to resolve, but even model blends hint at well defined warm and cold fronts leaving us in the warm sector favoring a higher risk for severe storms. Will certainly have to watch trends as we draw closer.

Examining total rainfall from Friday into early Monday via ensembles suggests many areas could be in that 1 to 2 inch range. Convection always makes exact amounts fickle but given we could have several rounds of showers and storms, still feel fairly certain that everyone will see another soaking bout of rain. Rivers and drainage areas handled last event /Tuesday April 16th/ well but would still expect rises on area rivers at the very least, and possibly a few locations getting into action stage.

Looking further ahead, mean heights start to build for the Midwest suggesting we could start another warming trend.

AVIATION /06Z TAFS THROUGH 06Z THURSDAY/
Issued at 1000 PM CDT Tue Apr 23 2024

CIGS: skc/sct through Wed night as high pressure meanders across the region.

WX/vsby: no impacts expected. Next shot for rain will come Fri, with on and off rain chances then for the weekend.

WINDS: generally light northerly becoming light southeast Wed evening.

ARX WATCHES/WARNINGS/ADVISORIES
WI...Freeze Warning from 2 AM to 8 AM CDT Wednesday for WIZ032-033.
MN...Freeze Warning from 2 AM to 8 AM CDT Wednesday for MNZ079- 086>088-094>096.
IA...None.

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