Area Forecast Discussion
Issued by NWS Twin Cities, MN

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857
FXUS63 KMPX 241742
AFDMPX

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
1242 PM CDT Sun Sep 24 2017

.UPDATE...For 18z Aviation discussion below

&&

.SHORT TERM...(Today and tonight)
Issued at 355 AM CDT Sun Sep 24 2017

Late last night, the front made it pretty far east in thanks
eastward moving gravity waves helping push it east. It eventually
reached the metro, but has since began lifting northwest as a warm
front.  As of 3am, the front lied from near Hayward, WI to the
southeast through Redwood Falls, MN. The movement and timing of
the front is the main point of discussion.

The majority of the precipitation continues to be on the cool side
of the front and that will continue.  With the front expected to
continue lifting northwest as a warm front, winds will become
southerly today and expect a dry morning across the entire forecast
area.  Those southerly winds should increase to 10-15 with gusts of
20 MPH during the day.  With the entire forecast area being in the
warm sector, expect highs in the mid 80s to near 90 for most of the
area, except in far western MN and Alexandria, where temps will be
held in the 70s.  The front will be across the eastern Dakotas by
midday, and start pushing west again by this afternoon.  A gradual
re-introduction of pops from west to east through the overnight
period is warranted as the front moves slowly east.  This will be
the final tease from this front, as once it comes through tonight,
we`ll stay on the cool side for the coming days.

As the front moves eastward late this afternoon through tonight,
moderate forcing and modest instability will fuel continuous shower
and thunderstorm development in a SW to NE oriented band
immediately behind the front.  By 12Z tomorrow morning, the front
should be very close to the Twin Cities Metro.  The severe weather
threat for today and tonight is low.  The excessive rainfall outlook
includes southwestern MN in a slight risk, and a marginal risk
farther north. This is mainly due to prolonged training of showers
and storms behind the front, however meager instability will
limit updraft strength, otherwise the threat would be higher.

.LONG TERM...(Monday through Saturday)
Issued at 355 AM CDT Sun Sep 24 2017

Forecast concerns deal with later in the period as a potent short
wave moves south across the western Great Lakes Friday/Saturday per
the latest EC.

Models are very consistent in the evolution of the mean long wave
trough across the western CONUS slowly weakening and lifting
northeast across the Northern Plains/Upper Midwest by mid week. This
would keep the chance of precipitation in the forecast through
Tuesday afternoon. I wouldn`t be surprised to see categorical pops
for most of Minnesota Monday night/Tuesday morning, especially in
the eastern 2/3 of MPX forecast area.  This is based on both ample
deep layer moisture, and upper level support as the right quadrant
of the 25H jet helps with the forcing aloft. As in previous
discussions, PWAT values remain abnormally high for this time of
year, so rainfall amounts will be locally heavy, with some flooding
possible, especially in low lying areas.

Once the mean flow becomes more southwest/west by Tuesday
afternoon/evening, does the precipitation exit the area.

Past Thursday, the mean upper level flow becomes more amplified
across western Canadian. EC/GFS/GEM all support this amplified flow
from a developing ridge, late in the week. Differences occur
downstream as the EC is much more aggressive with a short wave
across the western Great Lakes by Friday. The GEM/GFS are less
aggressive and dampen out this stronger short wave vs. the EC.
Although this doesn`t significantly alter the forecast for
Minnesota, western Wisconsin could have a better chance of
precipitation if the EC is correct. Even if the EC is correct, a
reinforcing shot of Canadian air will keep most of the Upper Midwest
cool through the weekend.

Past next weekend, the weather pattern is dependent on how upstream
energy moves across the eastern Pacific, and interacts with the
upper ridge across the Northern Rockies. There could be another warm
period the first week of October if the upper ridge becomes more
established across the Upper Midwest as some of the longer range
models indicate.

&&

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 1243 PM CDT Sun Sep 24 2017

Expect showers and isolated thunderstorms to gradually spread
eastward across the area this evening and overnight. Have included
VCSH mentions a bit farther east of the main activity for this
afternoon given the potential for isolated showers to spawn in
the somewhat unstable airmass ahead of the front/cloud cover.
Otherwise, the most concentrated and widespread precipitation
looks to expand eastward across central/southern MN after 05z,
reaching WI around/after 12z Monday. Low clouds will also
lower/thicken overnight, with most of MN sites experiencing MVFR
conditions through at least Monday morning.

KMSP...
Could see a few showers in the area as early as 00z, but the main
area of showers looks to hold off until after 06z. Thunder threat will
be fleeting/isolated. MVFR cigs/vsbys look to build in after
daybreak Monday, and persist through most of the day.

/OUTLOOK FOR KMSP/

Mon night...MVFR likely with Likely SHRA and slgt chc TS. Winds NW
5 kts.
Tue...Chc MVFR/TSRA early. Winds NW 5-10 kts.
Wed...VFR. Winds WNW 5-10 kts.
Thu...VFR. Winds W 5 kts.

&&

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

$$


SHORT TERM...SPD
LONG TERM...JLT
AVIATION...LS



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