Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 121058

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
558 AM CDT Sat Aug 12 2017

.SHORT TERM...(Today and tonight)
Issued at 259 AM CDT Sat Aug 12 2017

We are starting to see moisture return across the Plains this
morning, ahead of a shortwave centered over northeast MT. The
leading edge of this moisture return can be seen with a band of
accas that stretches from a complex of decaying storms west of
Bismark, southeast toward Sioux Falls, SD. This band of accas
lines up well with isentropic lift on the 305/310K surfaces and
fgen in the h85-h7 layer. This zone of ascent will continue east
through the morning and will move into western Minnesota by the
afternoon. This forcing, along with what looks to be a weak MCV
associated with the ND convection will help spark some scattered
showers in western MN this afternoon. Main change here to the
forecast was to keep things dry through the morning.

Though we`ll see scattered showers by the afternoon out west, not
really expecting more widespread and heavier precipitation to
arrive until tonight as the MT shortwave reaches eastern SD.
Associated height falls with this wave will result in a
strengthening of the LLJ from eastern Neb toward southwest MN.
This should result in a shield of showers with embedded
thunderstorms moving into western MN after midnight. These forcing
features are slow to move, so the PoPs don`t move much over
night, with precip chances remaining west of I- 35 through the
short term. Though there is potential we could see things end up a
bit farther east than currently forecast if the MCV near Bismark
ends up stronger than is depicted with the deterministic models.
Half of the 10 NCAR hi-res ensemble members show precip to or east
of the I-35 corridor by 12z Sunday. Current forecast is certainly
leaning on the slower side of the NCAR ensemble, staying closer
to where the ECMWF/GFS/NAM show the better forcing in terms of the
LLJ through the night. Held the thunder mention to a slight
chance as well, as lapse rates and instability look meager,
indicating we will likely see more of the shower with embedded
thunderstorm look.

Rainfall amounts look greatest out in western MN where the nose of
the LLJ will reside. Forcing features look to be moving pretty
slow tonight, so although we aren`t expecting excessive rainfall
rates, a prolonged period of light to moderate could easily put
down amounts between 1 and 1.5 inches out in west central MN.

.LONG TERM...(Sunday through Friday)
Issued at 259 AM CDT Sat Aug 12 2017

A more active, wetter and cooler pattern is expected for much of
the upcoming week, featuring several days of showers/thunderstorms
along with mild daily temperature swings as a few surface and
upper level systems slide through the region.

A meandering upper level low over northeast Montana this morning
will swing across the region Sunday into Sunday night, spreading
showers and a few thunderstorms over much of the coverage area
during this time. Not looking for an overabundance of
precipitation due to the lack of associated surface frontal
features and the compact size of the upper low. That said, a plume
of deep southerly moisture will stream into the region in advance
of the upper level system which will aid in producing rainfall
amounts in the 0.25"-0.50" range for much of the area,
particularly the MN portion of the WFO MPX coverage area.

This system will exit off to the east late Monday, being replaced
by a sharp upper level ridge will will bring a brief respite from
rain. However, a more organized frontal system with an associated
strong upper level trough will in concert shift across the area
Tuesday through Wednesday night. Given the stronger dynamics of
this system, greater coverage of thunderstorms can be expected
along with greater rainfall amounts. Still a little diffuse to
make severe weather a distinct possibility but chances, albeit
non-zero, are rather low. Once this system moves off to the east,
yet another upper level system is progged to drive southeast over
the region Thursday night into Friday, producing additional


.AVIATION...(For the 12Z TAFS through 12Z Sunday morning)
Issued at 557 AM CDT Sat Aug 12 2017

High pressure centered overhead today means the calm winds of this
morning will stick with us through the day today. Moisture will be
increasing to the west this afternoon and AXN/RWF may see some
light rain this afternoon, but better moisture and forcing arrive
tonight, with the NAM/GFS showing a shield of rain moving into
RWF/AXN at 6z. How quickly this spreads east is still in question,
but by 18z Sunday, rain looks to be spreading into the Twin Cites.

KMSP...No fog or stratus to throw a wrench in things this morning,
with forecast soundings showing little in the way for winds all
day today. Biggest question mark is how quickly does rain arrive
Sunday. For now, followed a gfs/nam idea with chances increasing
through the morning Sunday, but the experimental hrrr has precip
moving into MSP as early as 6z Sunday, so rain could move in
earlier than currently forecast.

Sun...SHRA/TSRA likely. Chc MVFR. Wind SE 5 kts.
Mon...VFR. Wind SE at 5 kts.
Tue...VFR. Wind SSE at 5-10 kts.




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