761
FXUS63 KMPX 182053
AFDMPX

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
353 PM CDT Wed Sep 18 2024

.KEY MESSAGES...

- More active weather over the next couple of days. Potential
  for very large hail exists with Slight Risk (level 2 of 5)
  Thursday afternoon.

- Uncertainty remains high with rainfall forecast this weekend
  into early next week.

- Cooler air still anticipated next week, with highs retreating
  back into the 60s and 70s (close to normal)

&&

.DISCUSSION...
Issued at 348 PM CDT Wed Sep 18 2024

Upper low on satellite over eastern Montana will be the key player
with our weather over the next couple of days. By Friday morning,
this feature will be near western Hudson Bay in northeast Manitoba.
This will drive the cold front currently over the central
Dakotas across our area on Thursday, moving across western MN
in the morning, crossing the I-35 corridor in the afternoon,
then washing out overnight in western to central WI. We have a
band of cloud cover and a few embedded showers ahead of a lead
shortwave approaching central MN this afternoon that will drive
some virga/shower potential as it works into western WI this
evening. Anything we get out of this lead band is not expected
to be severe. The severe potential for today resides with what,
if anything, we get out ahead of the front in SoDak where
mesoanlysis shows 1500-2000 j/kg of mlCAPE exists. Models
continue to struggle with if/where storms will develop in this
warm sector this afternoon, but given the instability with 30-40
kts of bulk shear, severe storms will be possible with any
activity that develops in that warm sector. The uncertainty in
convective coverage this afternoon carries on through tonight
with CAMs showing anything from nothing happening tonight, to a
shield of showers and storms working across the MPX area tonight
through the morning. Given the uncertainty, held PoPs through
the night at 50% outside of central MN.

Thursday looks to be our turn for severe weather. For mid-
September, we have a higher end severe environment forecast to
be in place. Mid-level lapse rates are forecast to steepen
overnight ahead of the front. By Thursday afternoon, dewpoints
in the upper 60s with these lapse rates will support mlCAPE of
2000-3000+ j/kg. For Thursday it`s not a question of if, but
when/where storms initiate. Storms are expected to develop
between 19z & 21z near the I-35 corridor in an environment
supportive of supercells and the potential for very large hail
in particular. Storms are expected to become more linear as the
threat moves deeper into WI. The Day 2 update did nudge severe
probabilities farther east, but an upgrade to an Enhanced risk
(level 3 of 5) for the severe risk on Thursday is not completely
out of the question given the hail potential in the metro area.

Dry and sunny weather is expected on Friday and that sun is why most
of our area is forecast to see highs nudge up into the low 80s once
again. For the weekend, uncertainty abounds. There will be two waves
to watch, a northern stream wave going across southern Canada on
Saturday, then a wave coming up out of the 4-corners late this
weekend. That northern stream wave will push a cold front across
MN on Saturday. WAA ahead of the front is why Saturday suddenly
has fairly widespread highs in the 80s once again. The forcing
with this front will be well to our north, while the moisture
will be locked up with the southern stream wave coming at us for
the end of the weekend. As for that second wave, uncertainty
abounds for how far north it will track and how quickly it
moves, with the large model spread explaining why the NBM
continues to have 30/40 pops spread out across Sunday and
Monday. With that spread, we`re still in a situation where we
could get very little rain, or a good soaking 1-1.5 inch rain
event. Where there is more confidence is that between the
Saturday front and this system Sunday/Monday, we`ll see highs
dip a little bit below normal to start next week.

&&

.AVIATION /18Z TAFS THROUGH 18Z THURSDAY/...
Issued at 1241 PM CDT Wed Sep 18 2024

VFR conditions continue through this afternoon, with breezy
winds out of the southeast gusting to 20-25 kts. The low-level
jet will strengthen across south central Minnesota tonight,
which will introduce scattered convection to the forecast. Made
slight tweaks to the ongoing PROB30s to keep a 3-4 hour window
of -TSRA potential at each terminal. Confidence is highest in
convection across the western Minnesota terminals, with lower
confidence in whether or not storms will persist into western
Wisconsin Thursday morning. Given the position of the low-level
jet, have included mention of WS at the Minnesota terminals
tonight. Additional chances for -TSRA will likely be added to
the end of the 24-hour TAFs in a forthcoming issuance.

KMSP...Maintained the PROB30 for -TSRA between 8-12z. Latest
guidance remains on the marginal side for wind shear, though
decided to keep it in the TAF after collaborating with ZMP
CWSU. Convection is forecast to redevelop across eastern
Minnesota Thursday afternoon, so have introduced another PROB30
for -TSRA between 20-23z tomorrow.

/OUTLOOK FOR KMSP/
FRI...VFR. Wind WNW 5-10kts.
SAT...VFR. Chc SHRA/TSRA. Wind SE 5-10kts.
SUN...VFR. Chc SHRA/MVFR. Wind NE 5-10 kts.

&&

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

&&

$$

DISCUSSION...MPG
AVIATION...Strus