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615
FXUS63 KMPX 181758
AFDMPX

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
1258 PM CDT Wed Sep 18 2024

.KEY MESSAGES...

- Active weather pattern returns, with a marginal risk (Level
  1/5) for severe thunderstorms across western MN today.

- Slight risk (Level 2/5) for severe weather across eastern
  MN/western WI Thursday. Large hail and damaging winds are the
  main threats, however tornado potential does exist.

- Additional chance for widespread precipitation during the
  second half of the weekend, followed by significantly cooler
  air next week.

&&

.DISCUSSION...
Issued at 438 AM CDT Wed Sep 18 2024

A transition into a more active weather pattern begins today.
Currently temperatures range in the mid to upper 60s and low
70s. A few isolated showers were located over east-central MN
but shouldnt amount to much over the next few hours. Low
pressure over eastern Montana is progged to continue north-
northeastward over the next few days into Saskatchewan and
Manitoba. A stationary boundary that extends off of the occluded
region of this system will be draped across southwestern MN
today. This should act as the lifting mechanism for todays
convective environment. Although not as strong as yesterday, a
LLJ remains in place while bringing up rich Gulf moisture.
Scattered showers and thunderstorms are expected to develop over
western MN this afternoon along a gradient of 1400 j/kg and
25-30kts of effective shear. Todays eastern extent of
thunderstorm coverage depends depend on how well the forecasted
capping inversion can erode to allow for parcel lift. The Storm
Prediction Center has issued a marginal risk (level 1 of 5)
across the Dakotas and Western MN with primary hazards
consisting of damaging wind gusts, and isolated large hail. Any
developed precip will gradually dissipate and move east
overnight.

On Thursday, the first wave of convection has passed. Additional
development is expected across central and eastern MN and
western WI as the cold front proceeds from west to east. This
time, the environment looks to be more conducive for severe
weather thus the SPC has issued a slight (Level 2 of 5) risk of
severe thunderstorms. CAPE in the mixed layer will range between
2000-3000J/kg, steep lapse rates of 7-8 deg C/km, low-level
shear around 35kts which will support the threat of a few
discrete supercells capable of producing large hail, damaging
wind gusts, and possibly a tornado or two across eastern MN and
western WI. As the afternoon/evening progress, these storms may
congeal into clusters before dissipating after sunset.

As we enter the weekend, Friday looks to be the driest day with
mostly clear skies and temperatures near 80 degrees. Saturday
into Sunday features another clipper-type wave which will bring
back widespread rainfall chances that will last into early next
week. As of the latest forecasted QPF from the WPC over the next
several days, 1.5 to 2.0 inches are possible especially across
southern MN and western WI. At the same time though, a few
members of ensemble guidance advertise lesser amounts which does
hinder confidence in precip totals. Now in terms of
temperatures, forecast highs will decrease into the upper 60s
and lows in the lower 50s by early next week. At the same time,
it would behoove mentioning that the warmth isnt over just yet.
Per the CPC Temperature Outlook for the rest of the month points
the northern plains being likely warmer than normal.

&&

.AVIATION /18Z TAFS THROUGH 18Z THURSDAY/...
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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.
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&&

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

&&

$$

DISCUSSION...Dunleavy
AVIATION...Strus