028 FXUS63 KMPX 222336 AFDMPXArea Forecast Discussion National Weather Service Twin Cities/Chanhassen MN 636 PM CDT Mon Sep 22 2025
.KEY MESSAGES...
- Dense Fog Advisory for portions of central MN tonight through early Tuesday.
- Another round of showers and storms is expected along and south of the I-90 corridor this afternoon and evening.
- Quiet weather for the rest of the week with temperatures in the 70s.
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.DISCUSSION... Issued at 200 PM CDT Mon Sep 22 2025
An upper-level trough situated over Lake Superior will prog slowly to the northeast over the next several hours. A surface low was located over southern MN with a stationary boundary extending over to central Lake Superior and a cold front trailing behind down through Nebraska. These features are expected to track to the east- southeast through this afternoon. Another round of showers and thunderstorms looks most probable to redevelop across extreme southern and southeastern MN this afternoon and evening. Based off of latest cams, isolated CI looks to occur as early as 2 or 3 PM this afternoon with development trailing down along the surface boundary to the southwest into northwestern IA. The SPC does have this region in a marginal (level 1 of 5) risk for severe thunderstorms as the convective environment does look to advertise lapse rates around 7 deg/km and MLCAPE values 1000-2000 J/kg. However, the best support for the strongest storms has seen a noticeable southeastward shift over the last few runs of the hi-Res guidance, thus the overall trend in PoPs appears to have nudged southward over the MN/IA border. In order to keep mentionable PoPs within southern MN, we deviated from the NBM slightly by maintaining a blend of the previous forecast which kept a mention of slight PoPs across southern MN. For any storm that does manage to become severe would pose mainly a large hail and damaging wind threat. But again, the best likelihood of these threats look to be focused across northern Iowa.
Flow aloft veers to northerly with some minor deviations to northwest/northeast over the rest of the week, alongside weak surface high pressure bringing general subsidence across the region. Fair weather cu can still be anticipated daily as dew points remain in the 50s as mixing remains favorable. Which will also maintain chances for overnight fog as temperatures fall to dew points with efficient radiation cooling and a lack of surface winds under high pressure. The fog will be the most dense earlier in the week behind the showers, especially tonight. Visibilities will likely fall below one quarter mile across north-central MN where a Dense Fog Advisory is in effect from midnight tonight through 10 AM Tuesday. Depending on fog development trends overnight, its likely the advisory may need to be extended in coverage farther south across west- central MN. Drying conditions will continue throughout the week which will gradually suppress the fog coverage a bit more each night.
As mentioned in the previous discussion, it looks to be a fairly warm but overall quiet end to September, with predictability lower as we head into October due to a lack of longer scale indicators. For now, enjoy the warm weather while it lasts as October also brings the autumnal equinox, marking the trend of rapidly losing daylight as we slide closer to the winter months.
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.AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/... Issued at 627 PM CDT Mon Sep 22 2025
VFR expected for the next few hours into the early overnight hours. Fog and low stratus will redevelop by Tuesday morning. IFR to LIFR look most likely for south- central MN into west- central WI as cigs fall to near 500 feet and visibilities reduce in fog. Opted to continue the aggressiveness with respect to fog (1/2sm visibilities) developing at RWF and STC where greatest fog occurred this morning. Conditions should improve to MVFR/VFR by late Tuesday morning into early afternoon. Light to calm northeasterly winds overnight and through the day Tuesday.
KMSP...Expecting IFR stratus to develop again overnight. A dip to LIFR conditions is possible by 7AM with ceilings flirting with the 005 threshold. This lowering could last a few hours. Amendments may be needed once again to catch up with the trend as cigs will be right on the LIFR/IFR line. Conditions will improve to VFR by early afternoon. Northeasterly winds near 5 knots throughout the period.
/OUTLOOK FOR KMSP/ WED...VFR. Wind NE 5-10 kts. THU...VFR. Wind NW 5-10 kts. FRI...VFR. Wind SW 5-10 kts.
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.MPX WATCHES/WARNINGS/ADVISORIES... MN...Dense Fog Advisory from midnight tonight to 10 AM CDT Tuesday for Kanabec-Mille Lacs-Morrison-Todd. WI...None.
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DISCUSSION...Dunleavy AVIATION...PV
NWS MPX Office Area Forecast Discussion