NWS Forecast Discussion
300 FXUS63 KMPX 150511 AFDMPX Area Forecast Discussion National Weather Service Twin Cities/Chanhassen MN 1211 AM CDT Mon Sep 15 2025 .KEY MESSAGES... - Occasional chances for showers and thunderstorms throughout the week, with the most active period to be Wednesday through Friday. - Warm and humid conditions continue through Wednesday, then cooling off to near normal. && .DISCUSSION... Issued at 237 PM CDT Sun Sep 14 2025 h5 analysis this afternoon shows a rather blocky pattern over the CONUS, with a blocking high over Michigan, with couple of negatively tilted troughs over the western half of the country, one over Oregon/Washington and the other near the CO/Neb border. With that CO wave, there`s a deep plume of moisture coming out of Mexico and extending up into the Dakotas and the Canadian Prairies. For us, it is the trough coming out of CO that will cause headaches for much of the upcoming week as it becomes cut-off from the main flow within the central North American ridge and slowly meanders across the north central CONUS. For today, that blocking high over Michigan has helped to keep the moisture shunted to the west. In addition, it has kept our surface winds more southeasterly, which has checked up the forward progress of the warm front some, with it roughly along I-94 down into the Cities, then down along the MS River from there. Eventually, this plume of moisture will start coming into MN, though we`re likely looking at after 21z before showers make inroads into western MN. Through the night, we`ll see southerly winds at h85 through h5 work east across MN and into western WI. Usually, a LLJ on the order 30- 35 kts would be a good source of lift for precipitation development thanks to the WAA associated with it. However, when looking at the h85-h7 layer, the temperature advection within these southerly winds is either neutral or even cold. Given the lack of WAA and its associated lift, deterministic, ensemble, and hi-res models are all over the board with if/where we see showers through the night. Given this uncertainty, basically capped PoPs at 30-40% through the night and Monday morning, with the highest PoPs following the path of enhanced h85 and h7 winds and the moisture feed associated with it. This looks to be the type of setup where within this moisture plume, we see isolated to scattered showers come and go through the night and Monday morning wherever we happen to get some mesoscale convergence within the southerly flow. Given the small scale nature of the forcing, confidence on when/where we`ll see precip is low. SPC still has a Marginal Risk over far western MN and this still looks plausible, as any stronger convection we see out there will have the potential to mix down some of the stronger winds we have in that h85-h5 layer. Needless to say though, we aren`t anticipating anything widespread. For Monday and Tuesday, the models are trending drier for the MPX area as the h5 low slowly spins over the Dakotas. We`ll have ample moisture (PWAT over 1.5") for generating precip, but we look to be missing the forcing component for getting any widespread precipitation. Some diurnal showers will be possible both days, but in general, these two days look hot and and humid for mid-September standards, with highs remaining in the 80s and dewpoints in the 60s to low 70s. More active weather looks to finally set in on Wednesday as the cut- off mid-level low begins moving into western MN. This looks like a rather broad and nebulous upper trough that will be working across the upper MS Valley into next weekend. Though by no means a washout at any point, we should see several periods of showers from Wednesday into next weekend as weak vorticity features and diurnal destabilization provide the forcing to get showers going. Given the weak forcing, confidence on precip is relatively low in any period (though chances look best during the late afternoon and evenings), which the NBM covers well with its prolonged period of 30-50 PoPs Wednesday through Friday. PoPs do start coming down over the weekend, but those lower PoPs will be defendant on how long it takes for an incoming Pacific jet to move far enough east to start pushing this upper trough out of the upper MS Valley. Besides the rain chances, all the cloud cover and rain will help hold temperatures down, with highs expected to be back near normal (in the 70s) from Wednesday on, though lows will remain above normal through this period. && .AVIATION /06Z TAFS THROUGH 06Z TUESDAY/... Issued at 1204 AM CDT Mon Sep 15 2025 TSRA associated with the low over the Dakotas has weakened and has made minimal eastward progress. Have removed the PROB30s for KAXN and KRWF. Southeasterly winds around 10kts continue through early this morning before shifting to the south by mid/late morning as a warm front lifts northward. Still some uncertainty on precip chances for tomorrow afternoon, but have opted to leave everyone dry for the time being. VFR conditions throughout the period with winds diminishing after sunset. KMSP...No additional concerns. /OUTLOOK FOR KMSP/ TUE...VFR, chc MVFR/-TSRA late. Wind S 5-10kts. WED...MVFR/SHRA/-TSRA. Wind S 5-10kts. THU...MVFR/SHRA/-TSRA. Wind SE 5-10kts. && .MPX WATCHES/WARNINGS/ADVISORIES... MN...None. WI...None. && $$ DISCUSSION...MPG AVIATION...Dye
NWS MPX Office Area Forecast Discussion