485
FXUS63 KMPX 020819
AFDMPX

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
319 AM CDT Wed Jul 2 2025

.KEY MESSAGES...

- Isolated to scattered airmass thunderstorms possible this
  afternoon and evening.

- Hot and humid Thursday into Friday with widespread shower and
  thunderstorm chances late Friday into Saturday.

&&

.DISCUSSION...
Issued at 318 AM CDT Wed Jul 2 2025

Today...Early this morning there are a few areas of
thunderstorms: northern Minnesota and eastern South Dakota.
Based on storm track the more likely storms to impact southern
Minnesota or western Wisconsin are the storms in South Dakota.
If these storms can maintain we could see them move into
southern Minnesota later this morning. Overall the environment
in South Dakota is more favorable with more moisture and
instability. So the most likely setup would be the storms
decaying before reaching into southern Minnesota or just be
decaying storms with little impact in southern Minnesota. The
storms to the north are already on a dissipating trend and
unlikely to impact us down here. Looking ahead to the afternoon
ample instability and moisture should allow for airmass
thunderstorms to form. With a trough across Ontario we could
also see some subtle upper level support. Overall shear is not
impressive, so not expecting much organized convection. There is
enough shear that that we could see a few isolated stronger
storms as indicated by the SPC Marginal Risk. As this is more
of a airmass setup these storms could bubble up just about
anywhere across the region. So QPF is rather uncertain as this
will not be widespread coverage of rain, just widespread chance
for isolated to maybe scattered storms. As expected for airmass
storms, they will fall quickly as heating stops near/after
sunset.

Thursday into Saturday... Hot and moist air will continue
advecting into the Upper Midwest ahead of a frontal passage
Friday into Saturday. This will bring temperatures up slightly,
but more importantly take dew points up into the low 70s. This
will increase WBGT and heat index values to much more
uncomfortable levels. How much we warm up will have a big impact
on the final heat risk, as for example the Twin Cities NBM
deterministic currently has a high of 89. However the NBM
percentiles are much warmer with the 25th at 92 and 75th at 94.
With the forecast dew points in the lower 70s, the 75th
percentile could take us to near the heat index values we saw
for the Extreme Heat Warning a few weeks ago. All of this also
provides us with a lot of instability and precipitable water.
Precipitable water values are generally in the 1.5 to 2 inch
range which is in the top 10 to top percentile of values. This
heat and humidity would also allow for CAPE of 2500 to 3500 J/kg,
which is more than enough to sustain convection. However we
will need some forcing and that is most likely going to be
provided by a cold front. The timing of this frontal passage
will be key, especially for Independence Day celebrations since
this passage looks most likely late on July 4 into July 5. Areas
along and just ahead of this front will likely see rain and
thunder which is not the kind of fireworks people hope for on
July 4th. In general, ensemble timing of the front suggests
overnight Friday into Saturday for much of southern Minnesota
and western Wisconsin. So hopefully people can get their
celebrations in ahead of the rain chances. In addition to the
timing the other question will be how strong thunderstorms will
be? Instability is not the question here, as it is more shear.
As shear remains uncertain SPC has a marginal risk across the
area. In their discussion they said if more favorable warm
sector shear becomes apparent, then higher severe weather
probabilities would be needed. Overall best chances look to be
hot and humid Thursday and Friday with some more airmass storm
chances followed by more widespread rain and thunderstorms
Friday night into Saturday.

Sunday into next week... Sunday and Monday will be cooler and
less humid in the post-frontal airmass. This will likely be
the nicest period of weather over the coming week. The next
system looks to start moving in on Tuesday, but as is common
this far out still a lot of variability in ensemble guidance.
Some members take us right back into another wet period and
other start more a of dry pattern similar to what we have seen
in Julys the past few years.

&&

.AVIATION /06Z TAFS THROUGH 06Z THURSDAY/...
Issued at 1229 AM CDT Wed Jul 2 2025

Mainly VFR and dry through the period. There is a cluster of
storms that has formed over the Dakotas, which some hi-res
models have tracking through southwest MN. Storms are expected
to weaken overtime, however some threat of lightning could
approach RWF should these pass overhead early this morning. A
few other isolated storms are possible again this afternoon
across much of the area. Coverage is low enough to exclude from
any given TAF at this time. In other words, most sites should
not be impacted, but those that do see storms could have a
brief burst of heavy rain and gusty winds.

KMSP...No additional concerns.

/OUTLOOK FOR KMSP/
THU...VFR, chc -TSRA/MVFR late. Wind SE 5-10kts.
FRI...VFR, chc TSRA/IFR pm. Wind S 10-15G25-30kts.
SAT...-SHRA/MVFR, chc IFR. Wind W 5-10kts.

&&

.MPX WATCHES/WARNINGS/ADVISORIES...
MN...None.
WI...None.

&&

$$

DISCUSSION...NDC
AVIATION...BED