textproduct: Twin Cities

KEY MESSAGES

- Widespread steady soaking rain through today.

- Heavy rain and localized flooding threat greatest near the Iowa border this evening.

- Seasonable temperatures with mainly dry conditions expected for the Sunday through next work week.

DISCUSSION

Issued at 231 AM CDT Fri Sep 18 2026

Looking at the h5 analysis early this morning, a ridge of mid-summer strength (600 dm!) is centered over the TX/OK/AR/LA region. Around the periphery of this ridge is a shortwave of southwest monsoon origin moving out of northern Neb and across SoDak. Widespread rainfall has developed with this wave, though it's your classic synoptic setup, with strong WAA at h85 and fgen around h7 combining to create this precip shield. This will all move east across southern MN and into western WI, resulting in several hours of light to moderate rain across the area today. This will result in a fairly widespread 1-2 inches of rain along and south of a roughly Morris to St. Cloud and Chippewa Falls line. MUCAPE will be limited with this round of precipitation, so the excessive rain risk with this first wave is low. It will just be a much needed soaking rain and washout of a Friday.

This evening is when the excessive rain threat begins to show up as the warm front begins to sharpen to the north of I-80 in Iowa, with a persistent LLJ riding up over the front. PWATs will be near 2" with MUCAPE increasing to over 2000 j/kg over northern Iowa. All the ingredients are in place for a heavy rain event tonight to the north of the warm front, but the the HREF/REFS show the LLJ setting up from about Omaha to the I-90/94 split near Tomah in WI. It's along the MN/IA border from I-35 east that the atmosphere looks to have in its crosshairs for producing heavy rain, which means it's the portions of far southeast MN and northeast IA in the La Crosse WFO coverage area that are really under the greatest risk for seeing excessive rainfall. HREF and REFS PMM QPF both show near 8" of rain falling near the MN/IA border east of I-35, which looks reasonable given the synoptic setup with this event. We already have Freeborn County in a Flood Watch for the excessive rainfall potential and this looks to be our one county that has the greatest risk of seeing heavy rainfall, so we maintained the watch for only that county. Besides heavy rain, with that 2000+ j/kg of MUCAPE, HREF/REFS both show some stronger updrafts with some rotation developing with this second round, so the inclusion of a Marginal Risk up toward Rochester from the SPC in their Day 1 convective outlook makes sense. With that said, lapse rates look to be near moist adiabatic in the mid-levels, so this likely puts the hail ceiling for this event at a water coated 1". The timeframe that will have the greatest risk for both excessive rainfall and severe weather in the MPX area will be 00z to 06z this evening (7pm to 1am).

For Sunday through Wednesday, the main feature that shows up on the forecast charts is persistent high pressure to the north of the Great Lakes. This will keep low level flow out of the east for Sunday through Wednesday. These east winds will be very dry below h7, which will help push any rainfall south and west of the MPX area through the middle of next week. We'll continue to see weak disturbances ride around the southern ridge Sunday and Monday, but those look to result in continued mid/upper level cloud cover, but will struggle to produce more than the occasional sprinkles given the dry low level air. These east winds will also keep temperatures seasonable, with lows in the 30s/40s and highs in the 60s. Depending on what cloud cover looks like, it is possible we'll need some frost headlines Monday and Tuesday mornings in western WI.

Beyond Wednesday, the northern stream will have retreated well to the north in Canada, which will keep us dry. The only really change we'll see to the weather for the end of next week is our easterly winds will become southeast, which will allow temperatures to warm up some, with the frost threat going away and highs starting to creep back up into the 70s.

AVIATION /12Z TAFS THROUGH 18Z SATURDAY/

Issued at 547 AM CDT Fri Sep 18 2026

Rain continues to spread across central and southern Minnesota this morning. Not much change from the previous forecast, mainly just tightening up precip timing windows for IFR/LIFR conditions. Prevailing low end MVFR/IFR seems pretty likely through much of the TAF period with occasional dips to LIFR. East winds may gust to around 20-25kts during the afternoon before diminishing after 00z. Once the bulk of the rain comes to an end early Saturday, IFR cigs/vis will persist with fog/drizzle through the end of the forecast period. Winds will eventually turn more northeasterly.

KMSP...Slight adjustments to timing as mentioned above, but otherwise, the forecast remains on track.

/OUTLOOK FOR KMSP/ SAT...MVFR. Chc IFR. Wind NE 10-20 kts. SUN...VFR. Wind NE 10-20 kts. MON...VFR. Wind E 5-10G15 kts.

MPX WATCHES/WARNINGS/ADVISORIES

MN...Flood Watch from this evening through Saturday morning for Freeborn. WI...None.