Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 241152

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
652 AM CDT Mon Sep 24 2018

.SHORT TERM...(Today and tonight)
Issued at 357 AM CDT Mon Sep 24 2018

Water vapor imagery and RAP h5 analysis shows a deep trough working
across the northern Rockies, with a plume of Pacific moisture
(though not from the tropical Pacific) streaming out ahead of this
trough into the northern Plains and northwest Ontario. At the
surface, a low was analyzed at 3am near the MN/SD/ND border, with a
warm front draped across central MN and the cold front trailing
back into the Neb Panhandle.  A sheared out lead shortwave will work
out of the trough today and into northern MN this afternoon, though
the main energy with the trough will hold off until Tuesday morning.
The surface low will move on to Hudson Bay tonight, which will push
the warm front well north of our area through the morning, with the
trailing cold front moving into western MN mid-morning, the Twin
Cities during the early evening, and reaching Eau Claire after

For precip chances, the big thing has been to slow the eastward
advancement of precip across the area through the morning. Forecast
models still show the warm sector remaining capped, with the
majority of the precipitation we see coming within an fgen band
behind the cold front. The kinematic environment certainly looks
favorable for severe weather, but the thermodynamic environment just
isn`t there and the limited CAPE looks to be good enough to generate
a rumble of thunder or two, but no severe weather.

We will have thickening cloud cover throughout the day, so it will
be harder to get temperatures to overachieve like they did on
Sunday, but 925mb temps near 18c and a filtered sunshine ahead of
the cold front will be enough to push highs back into the low to mid
70s from south central into east central MN and western WI. Out in
far western MN, the morning fropa will keep temperatures flat or
even falling through the afternoon.

For tonight, precip chances will be best in the evening, with a
general diminishing trend in precip expected to around midnight. But
late in the night, as the main upper wave pushes across SD/Neb, we
will likely see shower coverage begin to increase across
southern/western MN in response to lift from what will be a system
beginning a strengthening phase in its life cycle.

.LONG TERM...(Tuesday through Sunday)
Issued at 357 AM CDT Mon Sep 24 2018

Confidence remains high in a cooler and active pattern developing
Tuesday and continuing into the weekend. An amplified upper trough
will pivot over the Upper Midwest on Tuesday generating ample ascent
aloft for precipitation to develop during the day on Tuesday. Little
in the way of thunder is expected given surface temperatures in the
upper 50s and paltry MUCAPEs. Most areas can expect scattered
showers and perhaps a few tenths of an inch of rain through
wednesday morning. Flow aloft transitions to zonal as the trough
departs to the east on Wednesday, with a 125+ kt jet developing
overhead. This jet spins up a surface low off to our north which
will provide another chance for showers on Thursday, with again only
light precipitation amounts expected out of this system. Models
agree with a surface low developing somewhere over the plains
towards the end of the weekend and generating a large swath of
precipitation out ahead of it. However confidence is still low in
the track and timing of this feature.

Chilly temepratures will be the other story this week as we stay on
the cool side of the jet and get our first sustained taste of
Canadian air this fall. Highs are expected to remain in the 50s/low
60s with overnight lows generally in the 40s. The coldest air
looks to set up over the weekend as high pressure slides over
Minnesota and Wisconsin. The GFS develops a stronger and drier
high than the Euro and would result in some locations in central
Minnesota and west- central Wisconsin seeing their first below-
freezing temperatures of the year. Have kept lows in the mid-30s
across these areas but some patchy frost potential is certainly
there Friday and especially Saturday morning.


.AVIATION...(For the 12Z TAFS through 12Z Tuesday morning)
Issued at 652 AM CDT Mon Sep 24 2018

Main change from the going TAFs was to start backing away from
precip mention as rapid updating models show only scattered
activity developing along and behind the front as it moves
through. MVFR with some IFR cigs are expected to develop behind
the cold front, with RWF/STC/AXN likely seeing cigs improve
overnight as deeper moisture shifts to the east. Timing wise, only
had some minor delays in their arrival from what we had. It is
beginning to look more likely that our best chance for rain will
come Tuesday morning as the main upper wave moves in.

KMSP...The HRRR has been going back and forth with whether or not
MSP sees any showers with the fropa, though it has settled in on
the 23z-04z window as having the best opportunity for seeing a
brief shower. CIGs overnight may drop into the IFR range, but kept
heights a bit more conservative for now. Confidence is increasing
that Tuesday morning will feature a steady light rain as the main
upper wave moves through.

Tue...Bcmg VFR in aftn. Wind NW 10-15 kts.
Wed...Chc mrng MVFR cigs. Wind W 10G20 kts.
Thu...VFR. Chc -shra. Winds WNW 15G25 kts.




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