Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 091832

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
132 PM CDT Wed Aug 9 2017



.SHORT TERM...(Today and tonight)
Issued at 335 AM CDT Wed Aug 9 2017

Early morning surface analysis shows an area of low pressure
centered over central South Dakota. 925-850mb moisture transport
ahead of this feature correlates with scattered shower and
thunderstorm activity entering southwestern Minnesota early this
morning. This area will expand eastward and strengthen over central
and south central MN today with reinforcement supplied by the
arrival of a mid/upper trough from the northwest. Therefore expect
shower and thunderstorm development to become more organized over
the area as the day progresses.

After the first surge of precipitation associated with the
moisture/warm air advection moves off, breaks in the precip/clouds
over western MN could provide for modest afternoon destabilization.
MLCAPE progs circa 1500 J/kg combined with steepening lapse rates
could contribute to a brief window of borderline severe storm
development over western MN near the cold front. Shear isn`t very
impressive however, so any hail/wind-producers would be isolated in

By 01Z Thursday, the surface low will have entered central
Minnesota, with continued mid/upper forcing over northern/eastern
areas supplying non-severe storms as the front works eastward. Over
the 24-hour period (12z Wed to 12z Thu), expect one half to one inch
rainfall totals to be common.

Given the cloud cover and precipitation, expect rather cool
temperatures today with highs in the 70s.

.LONG TERM...(Thursday through Tuesday)
Issued at 335 AM CDT Wed Aug 9 2017

Biggest questions for the long term are potential for showers over
the weekend and do we ever get out of this predominately northwest
flow. Other than that, our run of relatively benign weather will
continue, with the long term period looking to have no real threat
for severe weather, heavy rainfall, or extreme heat.

We`ll start the period with the system currently approaching us from
Dakotas working across the Great Lakes Thursday. We will be on the
backside of the system, though in its cyclonic flow, with cool
temperatures aloft. This will set the stage for scattered afternoon
showers/storms on Thursday, with the greatest coverage east, with no
precipitation expected by the time you get to the South Dakota
border. Surface high moves in Thursday night and this combined with
loss of daytime heating will quickly bring and end to precipitation
Thursday evening.  The surface high will be overhead for Friday,
with another very pleasant summer afternoon expected.

For the weekend, we`ll see a wave crest the western ridge and dive
southeast toward us as it runs around the eastern trough, not too
dissimilar to what we will see today. However, where as today`s wave
will be at least maintaining its strength and amplitude, if not
strengthening a little, the wave for this weekend will be shearing
out over the upper MS Valley and will be becoming increasingly less
defined. Beside forcing waning, mid level lapse rates look to be
close to moist adiabatic, so we won`t be seeing much instability
either. We did expand PoPs farther north and east out of southwest
MN for the weekend, with the Canadian and GFS in particular
spreading precip farther northeast with this wave than previous
runs.  Even GEFS QPF plumes at MSP show a few more members
kicking out some light precip over the weekend. Still, the greatest
signal for precip over the weekend continues to be in southwest MN.
No matter where we see it though, it looks to be light and scattered
at best.

As for the question of when do we get out of the predominately
northwest flow, the answer is for the next 10 days is we likely
won`t.  However, we will see a modification to the flow as the
Alaskan low pushes from its current location near the Aleutian
Islands over into western Canada. This will help shove the ridge
into central Canada. Out east though, the trough looks to stay in
place, so we will keep the NW flow through most of next week as
well, but the ridge building into central Canada will allow it to be
a milder northwest flow, with single digit h85 temps no longer
occurring. This will allow temperatures next week to rebound back to
right at normals, while the predominately northwest flow will keep
us in a mainly dry feed as well.


.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 132 PM CDT Wed Aug 9 2017

Widespread shower activity will continue through mid-afternoon
across the area. Visibility & ceilings should mostly remin VFR
with some brief periods of MVFR in the heaviest rain showers.
Expecting a window of clearing later this afternoon before another
round of scattered thunderstorms develops & continues after
sunset. MVFR ceilings along with northerly winds move in tomroow
morning behind a cold front, with some patchy fog possible around

Mostly VFR conditions as showers continue into mid-afternoon,
with brief periods of MVFR possible in the heaviest rain. Showers
expected to move out around 22z with another round of SHRA &
possibly TSRA after sunset

Thu...MVFR Cigs likely early. Chc SHRA/TSRA. Wind W 5-10 kts bcmg NW.
Fri...VFR. Wind N 5-10 kts.
Sat...VFR. Wind N 5 kts.&&



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