Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 241819

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
119 PM CDT Mon Jul 24 2017

.SHORT TERM...(Today and tonight)
Issued at 401 AM CDT Mon Jul 24 2017

Early morning satellite imagery together with surface obs and RAP13
analysis showed an area of high pressure centered over Lake
Superior, with light clockwise flow in place across the Upper
Midwest. Skies were mostly clear except for a few pockets of low
stratus. There was an area of thunderstorms upstream across the
Black Hills of South Dakota.

This area of thunderstorms should dissipate today, but the MCV
associated with it could produce a few showers and thunderstorms
across the far northwest part of the CWA Monday night. The HiRes
models show a few areas of convection, but not too confident in
their existence based on the forecast soundings of the GFS and NAM,
which show a capped environment. Instead it appears that the HiRes
models may be latching onto more of an altocumulus field.
Meanwhile expect today to be mostly sunny and slightly warmer than
yesterday with southeasterly winds.

.LONG TERM...(Tuesday through Sunday)
Issued at 401 AM CDT Mon Jul 24 2017

A few elevated showers and thunderstorms, or possibly accas, may
be ongoing at the start of the period Tuesday morning on the
leading edge of the strongest moisture advection. The strength of
the capping due to a dry boundary layer should prevent widespread
activity from developing. Scattered to broken mid level clouds may
persist for much of the day east of the EML poking into west
central MN, and a dry airmass from the continental high pressure
ridge over the Great Lakes will keep temperatures mild east of
I-35. The degree of sunshine will determine how hot west central
MN will get. Guidance has moderated from the very hot readings
being advertised Saturday night to more reasonable levels in the
mid 90s.

Showers and thunderstorms will fire on a cold front situated from
west central to northeast Minnesota during the very late
afternoon or evening hours. A severe threat continues to be
possible, but should be limited to a lower end event due to
strongest mid level flow confined to the north. Still waiting to
get into more hi-res model windows, but global models seem to
indicate the potential for upscale growth into clusters or a
couple MCSs during the overnight hours.

Perhaps the bigger threat will be heavy rain. A slow moving front
Tuesday night will facilitate a concentrated corridor of heavy
totals. Pwats around 2 inches, MBE velocities less than 10 kts,
and the potential for renewed development all night along this
front could result in several inches locally. Sided a bit more
with the Canadian and the ECMWF for QPF because while I do believe
there will be localized extreme totals which the NAM and GFS
indicate, it is impossible to pinpoint where at this juncture
given complex mesoscale features that aren`t resolvable until
hours before the event. The foreign models portray a bit more of a
generalized picture. Looking at the totality of the guidance,
including ensembles, it appears central MN stands the best chance
for excessive rainfall. Storms will continue into Wednesday across
southern MN into central Wisconsin, albeit in a likely weaker
state and the front beginning to accelerate should provide more
of a conditional heavy rain threat.

Northwest flow will prevail beyond Wednesday with near normal
temperatures and little chance for rain. There may be a front that
sags south next weekend, but some models wash it out before
reaching the area.


.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 110 PM CDT Mon Jul 24 2017

A rather widespread MVFR level stratocu field formed this morning
beneath the inversion across the area and continues to linger
primarily across southern and eastern Minnesota. The dense cloud
cover is located from Mille Lacs through the Twin Cities and south
through southeastern MN, and is in the process of eroding from
both the west and the east. As the day continues, expect a
combination of mixing and subsidence to erode this cloud layer

Expect a decent shot at showers and a few thunderstorms tonight
primarily after 03Z in far western MN, and progressing eastward
overnight. There is some doubt pertaining to the cap in the
Dakotas but as the low level jet increases tonight, so does
theta-e advection which could be enough of a push to overcome the
cap and at least initiate some elevated convection.

KMSP...confidence on placement of precip overnight is relatively
low, hence went the PROB30 route for now until the picture becomes
more clear.

Wed...VFR with TSRA possible early. Wind NW at 05kt
Thu...VFR. Wind NE at 10kt.
Fri...VFR. Wind E at 5kt.




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