Area Forecast Discussion
Issued by NWS Twin Cities, MN
Issued by NWS Twin Cities, MN
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471 FXUS63 KMPX 010148 AFDMPX Area Forecast Discussion National Weather Service Twin Cities/Chanhassen MN 848 PM CDT Fri May 31 2024 .KEY MESSAGES... - Showers & thunderstorms become more widespread this evening. Localized heavy rainfall possible from south-central Minnesota through western Wisconsin. - Severe thunderstorms & localized heavy rain possible Sunday evening, especially across western and southern Minnesota. - Another chance for widespread rain likely Tuesday night. && .UPDATE... Issued at 848 PM CDT Fri May 31 2024 Recent rain rates have been low enough that the flash flooding threat is decreasing. This is due to lower instability values as daytime heating has come to an end. Rain will continue along the largely stationary boundary tonight, but thunderstorm coverage will continue to decrease as we head into the overnight hours. && .DISCUSSION... Issued at 240 PM CDT Fri May 31 2024 TONIGHT/SATURDAY MORNING...Showers and thunderstorms are becoming more widespread across southern Minnesota this afternoon, as frontogenesis & moisture convergence increase along a slow moving front. This activity will continue to spread north and east along the front this evening, with showers and thunderstorms continuing into tomorrow morning as the front slowly exits the area to the east. Storm motion & low-level moisture return vectors are oriented parallel to the slow moving front, meaning showers & thunderstorms are likely to train over the same areas tonight. Precipitable water values in the 90th percentile are high, but not extreme, so while localized heavy rain & flash flooding fare a potential concern - it does not appear to be a widespread threat. High resolution ensemble guidance continues to highlight a swath of 1-2" of rain from south-central Minnesota, through the southern reaches of the Twin Cities metro, & into west-central Wisconsin. Individual high-res models depict localized pockets of 3-4" where training of the heaviest thunderstorms occur, so while we can`t say exactly where these heaviest amounts may occur, our confidence is fairly high that we will see some localized heavy rain impacts tonight through tomorrow morning. CAPE & shear values are fairly paltry for a severe weather threat, but can`t rule out isolated small hail and/or gusty winds from a few storms this afternoon & evening. SATURDAY-SUNDAY MORNING...The rain will be out of eastern Minnesota by mid-morning & western Wisconsin by early afternoon, with dry weather then expected into Sunday afternoon. Guidance continues to indicate an environment favorable for severe weather developing across western Minnesota by late Sunday afternoon, ahead of a cold front/surface low approaching out of the eastern Dakotas. MLCAPE values around 2000 J/kg & effective bulk shear of 30-40 kts will support all modes of severe weather, although the threat for large hail/tornadoes looks to mainly be limited to discrete supercells early in the event across eastern SD/far-southwest MN. Early long-range CAM guidance suggests that these initial discrete storms will merge into a MCS by the evening, which will move into western & southern Minnesota through the evening. Instability values are forecast to drop off across central Minnesota, so the severe threat is not really anticipated to continue into eastern Minnesota & western Wisconsin Sunday night, but we`ll have to see if this trend continues. Heavy rain could also be a concern given PW values forecast to be above the 90th percentile, but the progressive nature of the MCS & its expected weakening through the night should act to limit rainfall amounts to the 1-2" range. While the severe threat may diminish across central & eastern Minnesota, the thunderstorm complex is still expected to persist as it heads east, with stormy weather continuing into Monday morning across western Wisconsin. MONDAY THROUGH FRIDAY...Monday will be dry in the wake of the departing storm system, however this will be short-lived as another system approaches the area Tuesday. The surface low with this system is actually forecast to be stronger than the one Sunday night, but displaced more to the north over southern Canada. Widespread convection is again expected along the cold front draped to its south, which will bring good chances for another 1" of rain (at least) through Tuesday night. Confidence is still fairly low on the potential for severe weather and heavy rain/flooding concerns, given differences in the timing of the front & uncertainty on the quality of deep shear this far south along the front. Beyond Wednesday, cooler northwest flow develops aloft as a broad & persistent trough lingers over the Great Lakes & eastern CONUS through next weekend. Temperatures will be cooler, with periodic shower chances but lesser chances for organized thunderstorms/heavy rain. && .AVIATION /00Z TAFS THROUGH 00Z SATURDAY/... Issued at 620 PM CDT Fri May 31 2024 Rain showers with isolated thunderstorms will continue to impact most terminals this evening into tonight. The best chance for thunderstorms will be at MKT followed by the Wisconsin TAF sites. Almost no chance at AXN and only slight chance at STC. Winds are light and will remain light through this period. After the rain comes to an end these light winds with lingering humidity will cause some mist to form. Ceilings will also come down with MVFR most likely, but some high IFR will also be possible. After sunrise mist will dissipate and ceilings will rise with a return to VFR by late morning. KMSP... The chance for TS around the airfield has gone down, but it is not zero so have gone down to VCTS in the latest TAFs. Chance for this thunder in the vicinity will be over the next three hours with some lingering rain after that. Ceilings will fall and some fog will form as the rain ends with MVFR most likely, but some IFR possible. Back to VFR late tomorrow morning. Light winds through the period. /OUTLOOK FOR KMSP/ SUN...VFR, MVFR/-RA likely late chc TS. Wind S 10-20 kts. MON...MVFR/-RA early chc TS, then VFR. Wind SW to NW 10-15 kts. TUE...VFR early, then MVFR/SHRA/-TSRA. Wind S 10-20 kts. && .MPX WATCHES/WARNINGS/ADVISORIES... MN...None. WI...None. && $$ UPDATE...NDC DISCUSSION...ETA AVIATION...NDC