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FXUS63 KMPX 181910 AFDMPX

Area Forecast Discussion National Weather Service Twin Cities/Chanhassen MN 210 PM CDT Sat May 18 2024

KEY MESSAGES

- Showers and thunderstorms, some possibly severe, in WI this afternoon with the best chance near and to the east of Eau Claire, Chippewa, and Rusk counties.

- An active pattern set to begin Sunday night. Multiple chances for rain, possibly heavy, and thunderstorms over the next week. Greatest risk for heavy rain will be on Tuesday.

DISCUSSION
Issued at 210 PM CDT Sat May 18 2024

Today and tonight... A cold front continues to move across Minnesota this afternoon. Ahead of the front has more warm air advection and moisture with drier air behind it. The temperature gradient of this front is not as obvious at this point of the day, as much of the area along and ahead of it has had significant daytime heating and is above 80 degrees. The front is well defined by the cumulus clouds along and ahead of it.
Building instability will allow for these cumulus clouds to start to tower this afternoon. Some have already started to gain some height across Wisconsin as seen on GOES cloud phase RGBs.
This will continue through to the evening as peak heating and convective temperatures are achieved. The timing of where the cold front is will be key, as has been mentioned in all the previous discussions. Currently expecting this timing to work out near or to the east of Rusk, Chip, Eau Claire Counties. Some of these storms as seen in the SPC marginal risk could be strong to severe. This would likely favor hail in the early more discrete phase, but isolated high wind gusts are possible as well with favorable mixing from today's heat.

Sunday through Wednesday... This will be the focus of the week with inches of rain forecast. First on Sunday another LLJ will pick up with a warm front moving in from Iowa. This will provide for a setup not unlike what we saw Friday evening and night. It does look like a better forcing and moisture setup though, so more confident in the occurrence of this rain and totals will be higher as seen in out QPF forecast. This whole period will be supported by an upper low over the Canadian Prairies. Short wave after short wave will pass through the Upper Midwest along the south side of this larger circulation. The strongest of these waves comes on Tuesday. This is helped with surface support as the main low that remains rather stationary on Monday starts to move out to the north towards us on Tuesday. As this moves we will move into the most favorable area of lift. This is where we see the highest QPF, with amounts in ensembles of 2 to 4 inches possible, as mentioned in the previous discussion. The rain part of this forecast looks very likely, but what is less certain is how far north we can see severe weather. SPC has a day 4 outlook across parts of southern Minnesota and western Wisconsin. Good shear and as mentioned before forcing could provide for this. Less certain on the instability front as cloudy and rainy days often do not have the heat needed for large amounts of CAPE and therefore this could be more marginal.
That's why the risk area is to the south where it should be warmer that the higher risk is present. This severe chance is also seen in machine learning outlooks run by CSU. So Tuesday will be the day to keep an eye on for multiple reasons. Rain chances persist into Wednesday as this wave moves out of the Upper Midwest. Wednesday will also be the coolest day of the week with high temperatures in the upper 50s to mid 60s.

Thursday into next weekend... Models get much more dispersive in this period. Still plenty of QPF among ensemble members, but not as clear of a signal and much more spread. Overall it seems a more active period is likely to continue, but confidence on timing of when rain could fall remains low at this time.
Temperatures should be fairly steady this period with near to maybe slightly below normal depending on cloud cover.

AVIATION /18Z TAFS THROUGH 18Z SUNDAY/
Issued at 105 PM CDT Sat May 18 2024

The front at 18Z extended from far east central MN to south central MN with a healthy field of cumulus to its east, and some showers, especially in Wisconsin. In the wake of the front, west to northwest winds were often gusting around 25 knots and this should continue into early evening. A few thunderstorms will develop this afternoon to the east of KEAU, but KEAU could see a brief showers. Not enough of a chance to mention, though.

After that, a surface high will track across Iowa tonight with winds shifting from the west to south overnight. The next wave of incoming mid/high clouds will arrive Sunday morning in western MN and spread into Wisconsin during the afternoon.

KMSP...The main concern will be northwest winds gusting to 25-30 knots this afternoon in the wake of the front. Any showers this afternoon should be well east of the airfield.

/OUTLOOK FOR KMSP/ SUN...VFR. MVFR/SHRA likely late. Wind SE 10-15kts.
MON...MVFR/-TSRA thru mrng. VFR chc SHRA aftn. Wind SE 5-10kts.
TUE...MVFR/-TSRA likely. Wind NE 10-15 kts.

HYDROLOGY
Issued at 253 AM CDT Sat May 18 2024

The heavy rain event for Tuesday currently highlights the potential for a large footprint of 1 to 3 inches of rain, with some locations pushing 4 inches to hit much of the upper MN River Basin. Gauges at Montevideo, Granite Falls, and Morton are still at or near minor flood stage and if the kind of rainfall amounts we are currently seeing were to fall in the upper MN basin, then renewed flooding along the Minnesota River upstream of Mankato will be possible as we head into Memorial Day weekend.

MPX WATCHES/WARNINGS/ADVISORIES
MN...None.
WI...None.

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