NWS Forecast Discussion
816 FXUS63 KMPX 191057 AFDMPX Area Forecast Discussion National Weather Service Twin Cities/Chanhassen MN 557 AM CDT Mon May 19 2025 .KEY MESSAGES... - Soaking rain arrives today through Tuesday night. Highest chances for rain in western into southern MN while lowest chances are north of I-94. Severe weather is not expected. - 2.5" to over 3" of rain is expected for western to southern MN today into Wednesday. - Drier and warmer for the second half of the week. && .DISCUSSION... Issued at 321 AM CDT Mon May 19 2025 Cloud cover has spread over nearly all of our entire region early this morning as southerly flow streams in moisture ahead of our next weather system. Only our far northern WI counties have cooled enough to where areas of frost are possible. The forecast for our next system Monday into Wednesday remains mostly on track. Showers and thunderstorms currently over the Central Plains will continue lifting north-northeast tonight within the low-level warm conveyor belt of moisture. The initial surge of precip will reach southwestern MN near sunrise but should be losing steam as it moves away from the synoptic lift and instability. Still, CAMs do show a decaying, weak MCS-like feature moving northeast into southern MN this morning. Questions remain on how far this feature persists but did add in 40-60% PoPs that translate northeast through our southern MN counties. Additional northward moving showers and thunderstorms should focus over southwestern and western MN by early this afternoon as a low pressure center over SD occludes. Precipitation will slowly make its way east into this evening as it advances ahead of an arching cold front. However, did try to delay the rain`s arrival for eastern MN (including MSP) and WI by a few hours. Forecast soundings delay large-scale vertical saturation until at least after 7 PM tonight for these regions. During Monday night, the upper-level trough driving the entire system will become negatively tilted over the central CONUS as a second jetstreak rounds the base. Large amounts of synoptic scale lift and a south-southeasterly LLJ of moisture will focus over the Upper Midwest (with secondary surface cyclogenesis occurring over IA). The result will be the formation of a large stratiform shield of rain across the entire southern halves of MN and WI late Monday night. This feature should remain mostly in place (besides its long axis pivoting counter-clockwise around the low to the south) Tuesday into Wednesday; leading to a long-duration rainfall event. The good news with this event is that MUCAPE will be very low to zero, meaning we won`t have widespread convectively enhanced rainfall. But, the Grand Ensemble still produces at least 1.5" of mean QPF into Wednesday south of I-94. Amounts climb over 2" for western to southern MN with the Twin Cities near the edge of the probabilistic gradient for this amount. Areas near Mankato and south to the MN/IA border currently have the best chance at seeing the most rain. The 50th percentile QPF of the EPS and GEFS both have over 2.5" in this region. Amounts jump to well over 3" when stepping up to the 75th percentile! Currently, have 3.0-3.5" of rain forecast for south-central MN but localized areas could see amounts go even higher if some convection does manage to occur. Widespread flooding will likely not be an issue, but don`t be surprised if ponding of water occurs, especially in low-lying areas. It should also be mentioned that it will be very breezy Monday through Tuesday with the strong LLJ and deepening surface lows. Winds Tuesday morning look to be especially strong, particularly across southeast MN and western WI where gusts could reach 40 MPH. The 00Z HREF has mean wind gusts of 45 to even 50 MPH in this region! Though, this ensemble can be known to over-forecast winds. Still, this will need to be watched in case a wind headline is needed for Tuesday morning. Guidance begins to slightly diverge during Wednesday with regards to how quickly precipitation dissipates as the low pressure system slowly exits east into the Ohio Valley. Each deterministic model keeps a northwest to southeast band of precip draped from the Dakotas through MN and into WI along what seems to be a trailing stationary front. This precip should taper off as we get later into Wednesday but, a few more tenths of an inch of rain may occur if it holds on longer than expected. The forecast finally quiets down by Thursday as northwesterly flow brings in drier air. Guidance suggests this northwest flow to last through the end of this week with temperatures rebounding towards normal. Currently have mid 60s and very low PoPs forecast Thursday through Saturday so it should be a pleasant end to the week. An impulse or two in the upper-level flow could bring back rain chances near the start of next week, but forecast certainty is low at this time due to model spread. && .AVIATION /12Z TAFS THROUGH 12Z TUESDAY/... Issued at 554 AM CDT Mon May 19 2025 We begin VFR with high level CIGS for all but EAU as -SHRA will spread across all TAF sites from SW to NE, beginning in RWF at ~14z and reaching EAU/RNH by 00-02z. Winds will likewise increase as the surface low nears with a consistent 060-090 direction increasing to 20G30kts. -TSRA is possible for a 3-4 hour window, however with such a cool airmass it may just end up being a few rumbles rather than legitimate TS. CIGS are expected to drop to MVFR as -SHRA increases in intensity, roughly 6-8 hours after it arrives at each individual site. KMSP...The main change from the 06z TAF was tightening the window for -TSRA based off the RAP from 00-03z. The confidence in legitimate TS is low, such that a few rumbles are the main expectation due to the cooler airmass. /OUTLOOK FOR KMSP/ WED...MVFR/-SHRA early, then VFR. Wind NE 10-15kts. THU...VFR. Wind N 10-15kts. FRI...VFR. Wind NE 5-10kts. && .MPX WATCHES/WARNINGS/ADVISORIES... MN...None. WI...None. && $$ DISCUSSION...CTG AVIATION...TDH
NWS MPX Office Area Forecast Discussion