569
FXUS63 KMPX 171735
AFDMPX

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
1235 PM CDT Tue Sep 17 2024

.KEY MESSAGES...

- Isolated showers and weak storms in western MN today, otherwise
mostly sunny and warm.

- More chances for showers and storms coming up, first round late
Wednesday into Thursday favoring western Minnesota. Better chance
late Thursday into Friday across the area.

- Temperatures cool down through the weekend with highs near 70
  by Sunday and into next week.

&&

.DISCUSSION...
Issued at 306 AM CDT Tue Sep 17 2024

Our quiet night thus far is showing signs of life with a band of
weak showers stretching from Redwood Falls down into central Iowa,
with another line of weak storms entering southwestern Minnesota.
This linear cluster of storms is not expected to pose any kind of
threat besides occasional lightning and rumbles of thunder, ending
up more of a wake up call than anything more. The environment to our
west is more conducive to maintaining storms with instability over
500 J/KG decreasing to less than 100 by the time it reaches the MPX
CWA. Once these storms outrun the instability we should see the
lightning fall off before eventually dissipating as the forcing
stops once they get away from the LLJ over the Dakotas. None of the
CAMs this morning have picked up on this line of storms and thus we
rely on the environmental cues to say the expectation would be to
have them dissipate before reaching the Twin Cities. The main impact
from them could end up being an increase in local cloud cover for a
few hours as they move through, which should have much impact on
temperatures for the day as we are once again looking to reach the
mid 80s on the back of southerly winds advecting warmth to the area.
We will be watching what happens over the next few hours before
sunrise to figure out just how long lived these storms end up being.

After today, the upper level occlusion producing a surface low will
begin to move over the northern CONUS towards the Great Lakes,
resulting in a broad swath of shortwave forcing out ahead of it with
a 1.5-2 PVU anomaly reaching western Minnesota by Wednesday evening
producing scattered showers and storms as it does. The low level jet
will have shifted eastwards due to the movement of the upper level
system, which should give us plenty of moisture and warmth to work
with as well as some lower level shear to get a few storms going.
The main question is just how widespread given the weak overall
forcing in the mid to upper levels, with the better environment
overall arriving on Thursday as the system continues to move
eastwards. The positioning of the surface system drags a broad
frontal boundary across the area Thursday evening into Friday with
continued LLJ warmth and moisture advection with better forcing from
the coupling of the lower level front and upper level system. Given
the environment, strong to severe thunderstorms are on the table
with plenty of shear due to the stacked nature of the system along
the front as well as good lower level lapse rates due to the LLJ.
Overall the current SPC outlooks with a marginal Wednesday night
into a Slight Risk along the front Thursday seems like a safe bet
for now, with greater detail upcoming as more we get into range of
more CAM solutions.

Yet another system arrives over the weekend, this time signaling a
clear end to our stretch of hotter weather with another occluded
upper level system this time diving southwards from Alaska towards
the northern plains bringing colder air with it. Right now, the
second half of Saturday through the first half of Sunday is the
expected time frame for most of the showers with strong winds on the
back end of the system into early next week bringing much cooler
temperatures as highs reach only around 70 by Monday with lows in
the 50s. The longer range ensembles are showing a potential first
day of October in the mid 60s for highs which is right where normal
is for this time of year. Overall given the next week, it is likely
we end September warmer than normal for the month as a whole, with
the degree of precipitation likely being decided over the next 5 to
6 days.

&&

.AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/...
Issued at 1215 PM CDT Tue Sep 17 2024

It will be another 24-30 hours of southerly winds and VFR skies.
Like yesterday, not anticipating storms near the western IA/MN
border to survive the afternoon, with even RWF expected to
remain dry. The big question for tonight is do we see showers
develop again tonight like we have seen the last 2 nights.
Sunday night they were across eastern SoDak & Neb, last night it
was western IA into southwest MN. If we were to see it happen
again tonight, it would likely shift east to be more aligned
with the I-35 corridor. Confidence in them happening again is
too low to include in any of the TAFs at this point, but it is
something to keep an eye on.

KMSP...No weather is expected today. We don`t have any showers
in the TAF for Wednesday morning, but if we repeat what happened
with shower development the last 2 nights to the west, they
would likely form a bit farther east than they did the last 2
nights, meaning MSP would be in line to start Wednesday with
some shra/tsra activity. Nothing shows this happening, so we
don`t have anything in the TAF, but it is something we`ll have
to continuously reconsider through the night.

/OUTLOOK FOR KMSP/
THU...VFR. SHRA/TSRA likely. Wind SSW 15G25 kts.
FRI...VFR. Wind WNW 5-10kts.
SAT...VFR. Chc shra/tsra. Wind SE 5-10 kts.

&&

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

&&

$$

DISCUSSION...MPG
AVIATION...MPG