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FXUS63 KMPX 172003 AFDMPX

Area Forecast Discussion National Weather Service Twin Cities/Chanhassen MN 303 PM CDT Fri May 17 2024

KEY MESSAGES

- Chance for some isolated thunderstorms across central Minnesota late this afternoon into this evening.

- Low RH values Saturday afternoon could result in areas of elevated fire weather conditions.

- Another round of showers and thunderstorms, some possibly severe, in western WI Saturday afternoon and evening.

- An active pattern set to begin Sunday night. Multiple chances for rain, possibly heavy, and thunderstorms over the next week.



DISCUSSION
Issued at 303 PM CDT Fri May 17 2024

Today and tomorrow... Cumulus clouds starting to build over western Minnesota this afternoon driven by diurnal heating and the LLJ. With inverted V soundings elevated thunderstorms could be a risk later today across eastern Minnesota into western Wisconsin. Some CAMs have been consistently showing this risk, but there is a wide spread among CAMs from nothing to scattered thunderstorms. What is confident is that with dry low level air, heavy rain is not a threat. However, the main concerns would be lighting and based on the soundings some isolated strong gusts.
All the cloud cover is very diurnally driven and it will clear up as the sun sets. Then all attention turns the the cold front moving across the Upper Midwest. This will keep Saturday cooler than what we have seen today. It also will allow for another round of thunderstorms in Wisconsin. It is all about timing here. The instability should build up enough by the late afternoon for the storms to pop. It is all about where the cold front is located when this happens. Current CAMs suggest that it will be near Eau Claire. Question is just west or to the east? That is what is uncertain. Some wind and hail will be both be possible with theses storms. More recent runs have already moved this west as the previous discussion and earlier SPC Outlook kept most of this risk to our east.

Sunday through Thursday...Sunday will start out dry behind Saturday's cold frontal passage. It won't be long before the next system moves in. Another system will move in from the Rockies on Sunday with a warm front draped across the Minnesota/Iowa border region. This system will be slow to depart and give us multiple chances for rain Sunday through Wednesday.
This is all driven synoptically by multiple shortwave disturbances moving along the south side of a fairly stationary upper low over the Canadian Prairies. This will have a fair amount of moisture available with NAEFS percentiles around the 90th during this period. As mentioned in the previous discussion WPC has also recognized this and we are in continuous marginal risks over this period from late Sunday into the middle of the next week. There is also indications of a strong shear environment on Tuesday, especially over Wisconsin. The limiting factor here will be instability as we will be in the middle of a wet cloudy period that could keep temperatures low and CAPE skinny. This was recognized with a day 5 risk by SPC.

Getting past mid week the pattern continues to look busy, but the spread among the ensembles (ENS, GEFS, and GEPS) increases. So we could see continued rain through the end of the week or more of a dry period. It is too soon to tell. There are however fewer members with QPF on Thursday into early Friday before than the previous Sunday to Wednesday period. Bottom line, it will be cooler and wetter from late Sunday through the next week. This should continue to help us recover from the drought and could help restock area lakes and water tables that we weakened with repetitive drought stress.

AVIATION /18Z TAFS THROUGH 18Z SATURDAY/
Issued at 1226 PM CDT Fri May 17 2024

Morning line of showers has all but dissipated in western Wisconsin, with satellite revealing mostly clear skies over the Minnesota terminals. Southerly winds will increase this afternoon as a warm front lifts through the state. Have added/continued the potential for LLWS this evening given the expected strengthening LLJ across the Upper Midwest. EAU is the only site to not feature wind shear concerns at this time, given the the expected weakening of the LLJ with eastern extent tomorrow morning. Also of note, latest CAM guidance has trended upward with the potential for isolated convection on the nose of the LLJ this afternoon and evening. AXN, STC, MSP, and RNH would be the primary terminals to watch for this activity, however the chances appear too low/isolated to include in the 18z TAF set.

KMSP...Eastward approach of the strengthening LLJ has prompted the threat for LLWS overnight, so have opted to include mention in the 18z TAF. Threat for LLWS will decrease by daybreak Saturday, followed by a shift in the winds from southerly to westerly by midday.

/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.

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

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