106
FXUS63 KMPX 172024
AFDMPX

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
324 PM CDT Sun Aug 17 2025

.KEY MESSAGES...

- Another round of thunderstorms and heavy rain tonight into
  Monday morning. Uncertainty still exists on the exact
  placement of the heaviest rain.

- A few severe thunderstorms also possible this evening, with
  damaging wind gusts the primary threat followed by hail.

- Seasonably cool & dry through the rest of the week.

&&

.DISCUSSION...
Issued at 244 PM CDT Sun Aug 17 2025

One more round of heavy rain & potential flooding is expected
tonight into tomorrow morning, but unfortunately we`re still
dealing with uncertainty on where exactly that chance will be
greatest. In the large scale, we have a very favorable pattern
for widespread thunderstorms tonight, with a stationary front
across southern Minnesota slowly lifting northwards overnight as
a warm front & acting as the main forcing mechanism for storms
tonight. A lobe of vorticity passing over the central half of
Minnesota will provide the upper level forcing, but the exact
location of the heaviest rainfall tonight will depend on two
separate mesoscale forcing mechanisms. The first is the
remnants of a thunderstorm complex over northeast South Dakota,
which is forecast to track across central Minnesota this evening
& tonight. Many of the global ensembles & AI ensembles favor
this placement over central Minnesota & western Wisconsin, where
the upper level forcing is stronger & the mesoscale forcing
from the MCV provides plenty of forcing along the surface
front. However, a second group of high-resolution models favors
a more southerly focus area, across southern Minnesota &
southwest Wisconsin, where the low-level jet becomes the main
mode of forcing & interacts with the surface front & outflow
from this mornign`s storms. Unfortunately it is still not clear
which of these forcing mechanisms will win out, but the trends
of ongoing convection along the South Dakota/Minnesota border
should give us our answer by early evening.

Thunderstorms are expected to become more widespread across
western Minnesota this evening (5-7 PM), congealing into a
cluster of storms through the evening & night across Minnesota &
eventually waning over western Wisconsin early tomorrow
morning. These storms will be slow- moving with storm motions
likely 20 kts or less, which along with rainfall rates near 2"
per hour will result in our flooding threat tonight. As
mentioned earlier, confidence is low on where exactly the most
widespread thunderstorms & heaviest rain will occur, but nearly
all high-resolution models depict localized amounts of 4+ where
they have the heaviest thunderstorms. This leads to higher
confidence in the potential for heavy rain & flooding tonight,
even if we wont know exactly where until storms fire this
evening. So in general, most of the area can expect
thunderstorms and amounts of 1-2" through tomorrow morning, with
higher chances for 3-4" or more wherever that main axis of
thunderstorms sets up tonight. Given how nearly the entire area
has seen 2-3" of rain since Friday & soils are nearly saturated
already, opt to issue an area-wide Flash Flood watch tonight as
anywhere that sees thunderstorms tonight could have the
potential for rapid runoff leading to flooding.

In addition to the heavy rain threat, a few severe storms are
also possible this evening. We`ve seen more clearing than
expected this afternoon, which will allow for surface-based CAPE
values of 2000 J/kg to develop south of the surface front along
southern Minnesota. The mid-level lapse rates are not great and
will probably limit the threat for widespread severe weather,
but it`s likely that at least a few storms will be able to tap
into this higher CAPE and develop into more organized clusters
or lines as the evening progresses. Damaging wind gusts would
be the primary hazards with these storms, but hail is also
possible earlier this evening if any deeper updrafts are able to
tap into the increasing wind shear & become supercellular.

The heaviest rain will end from west to east during the early
morning hours, with lingering lighter rainfall continuing
across southeast Minnesota & western Wisconsin into early
afternoon. Beyond that, we`ll be able to dry out with cooler
and drier weather expected through the rest of the week.

&&

.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 1250 PM CDT Sun Aug 17 2025

Latest radar trends show more notable decaying of showers across
western MN. Stationary boundary draped across south central
MN is the dividing line between VFR conditions across far
southern MN and MVFR or lower cigs across central MN/western
WI. Another round of showers and thunderstorms is forecast to
develop late this afternoon across SD and move across the
region overnight. Have included TEMPOs to try and isolate
windows where thunder is most likely. Uncertainty exists in how
progressive convection will be at any single terminal and given
the going pattern opted to lean on the pessimistic side and
proceed with large precipitation windows. Significant
improvements to the forecast arrive Monday morning and winds
turn northwesterly.

KMSP...Latest forecast data keeps thunder/precipitation impacts
away from the terminal until after ~2z. Have maintained the
TEMPO for -TSRA, which is most likely early in the precipitation
window. Opted to keep visibility reductions from rain in the
TAF through 12z due to uncertainty in how quickly rain chances
will end.

/OUTLOOK FOR KMSP/
TUE...VFR. Wind NE 5-10kts.
WED...VFR. Wind NE 5kts.
THU...VFR. Wind S 5-10kts.

&&

.MPX WATCHES/WARNINGS/ADVISORIES...
MN...Flood Watch from 7 PM CDT this evening through Monday morning
     for Blue Earth-Brown-Chippewa-Douglas-Faribault-Kandiyohi-
     Lac Qui Parle-Martin-McLeod-Meeker-Nicollet-Pope-Redwood-
     Renville-Sibley-Stearns-Stevens-Swift-Todd-Watonwan-
     Yellow Medicine.
     Flood Watch from 10 PM CDT this evening through Monday morning
     for Anoka-Benton-Carver-Chisago-Dakota-Freeborn-Goodhue-
     Hennepin-Isanti-Kanabec-Le Sueur-Mille Lacs-Morrison-
     Ramsey-Rice-Scott-Sherburne-Steele-Waseca-Washington-
     Wright.
WI...Flood Watch from 10 PM CDT this evening through Monday morning
     for Barron-Chippewa-Dunn-Eau Claire-Pepin-Pierce-Polk-
     Rusk-St. Croix.

&&

$$

DISCUSSION...ETA
AVIATION...Strus