Area Forecast Discussion
Issued by NWS Twin Cities, MN

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798
FXUS63 KMPX 220005
AFDMPX

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
705 PM CDT Sat Oct 21 2017

.SHORT TERM...(This evening through Sunday)
Issued at 419 PM CDT Sat Oct 21 2017

A narrow line of thunderstorms has developed along an eastward
advancing cold front in western MN this afternoon.  We got some
clearing ahead of this line this afternoon, which allowed temps in
western MN to sneak up into the low 70s with dewpoints in the low
60s, SPC mesoanalysis has consistently shown 1000-1500 j/kg of
SBCAPE. Other combined parameters, like the supercell composite
parameter and conditional SigTor probability light up in the warm
sector ahead of the front as well, indicating we have an environment
that could at least marginally support surface based severe
weather. However, forecast soundings show us our problem for
getting severe weather and it`s weak low level lapse rates. We
have enough forcing and instability to get storms going, but those
weak lapse rates are resulting in skinny CAPE profiles and weaker
storms. This trend really looks to stay with us through the
duration of the event, so our severe threat will continue to be
low, with really the only threat the possibility of strong wind
gusts if we can get favorable bowing structures to develop in the
line.

CAM agreement on the line has been pretty good, so just used a blend
of those to track pops to the east with the line. Showers may linger
through mid morning out toward Ladysmith/Eau Claire, but otherwise,
Sunday will more than make up for our dreary Saturday. There`s not
really any cold air to speak of behind the front, so we`ll see highs
tomorrow in MN in the low/mid 60s, while WI stays in the 50s thanks
to a little extra cloud cover and cooler 925mb temps. Main concern
Sunday will be the threat for elevated fire weather conditions in
western MN. We currently have afternoon humidities down near 25% out
in west central MN, but sustained winds look to be down around 10-15
mph with gusts to 20-25. As long as winds stay at this level, we
won`t have to worry about fire headlines, and at this point, it`s
unlikely they`ll be much stronger than what we have, so we should
be good.

.LONG TERM...(Sunday night through Saturday)
Issued at 419 PM CDT Sat Oct 21 2017

The main theme for the extended continues to exist, with temperatures
gradually cooling as the upper pattern becomes more amplified
with a ridge west and trough east. Model agreement is decent
through Tuesday, but from Wednesday on, there`s still lots of
model disagreement and run-to-run consistency issues with how the
trough deepens over the center of North America.

Monday/Monday night, we will see a series of short waves move across
the upper MS Valley, but moisture will be lacking, so not expecting
much in the way of precip. This wave will close off over the Great
Lakes though and deepen substantially off to our east. This will
result in windy conditions Monday and Tuesday, with wrap around
moisture possibly impacting western Wisconsin Tuesday.

Next wave arrives Tuesday night in the form of a clipper type wave
coming down on the backside of the Great Lakes upper low. The GFS is
the farther west and most aggressive with this wave, bringing a
quick hit of precip to western WI. Temperatures would be cold enough
on the GFS to support a rain/snow mix, so have that possibility in
the grids, though confidence is low as to if there will be any
precip with this wave at all as it will be in the process of getting
absorbed by the large system over the Great Lakes.

We will get a brief warmup Wednesday, before the next strong wave
impacts the upper Midwest. This wave will result in the development
a large surface cyclone. Models are starting to converge on the idea
of a deep cyclone developing over the northern Great Lakes. The GFS
is the deepest/farthest west with the system and though we stuck
with the blended guidance for PoPs Thu/Fri next week, those PoPs
certainly lean toward the GFS solution, which is wetter for us.
We`ll have low heights with this system and cool temperatures, so
you`ll again see rain/snow mix chances show up in the overnight
periods, but I wouldn`t get too excited about seeing your first
flakes of snow next week just yet.

&&

.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 705 PM CDT Sat Oct 21 2017

Narrow line of storms has weakened substantially, with most
precip as showers now in central MN and some in southern MN. Most
of this in MN is behind the front, but a few storms may continue
to develop ahead of the front. The few storms will be rather
short-lived in any given location. Heftier storms in north central
Iowa were about to enter MN, and these will likely slide up
toward Red Wing and then Wisconsin.

Other issue continue to be gusty south winds this evening ahead
of the front.

Ceilings will be short-lived MVFR behind the front, then mostly
5000-8000 feet agl after the front for a little while.

KMSP...
Looks like most storms will slide by the east of KMSP, though
there is still potential early this evening for a storm until 01z.
Otherwise, it will take a few hours before the showers dissipate
or move east. After that, quiet VFR weather.

/OUTLOOK FOR KMSP/
Mon...VFR. Winds W 20G30 kts.
Tue...Chc MVFR. Wind NW at 20G30 kts.
Wed...Chc MVFR. Wind NW at 15G25 kts.

&&

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

$$

SHORT TERM...MPG
LONG TERM...MPG
AVIATION...TDK



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