Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 142049

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
349 PM CDT Mon Aug 14 2017

.SHORT TERM...(This evening through Tuesday)
Issued at 331 PM CDT Mon Aug 14 2017

Early afternoon satellite imagery together with surface obs and
500mb heights showed an upper level ridge over the Dakotas, with a
shortwave trough over Wisconsin. Beneath these two features was an
area of surface high pressure characterized by light winds, but
boundary layer moisture remained in place which led to overcast
skies. A few breaks in the clouds have started to form over the last
few hours, and this trend should slowly continue into the evening
and overnight. Given the light winds, should see radiation fog
quickly develop in those areas that manage to clear out.

On Tuesday an upper level trough currently located over the Idaho
panhandle will move eastward and develop and area of convection over
the high plains. This precip will reach western MN Tuesday
afternoon. Any storms that develop late Tuesday into Tuesday night
will have the potential to produce heavy rain. Tropopause heights
are still above 150mb with PWATS near 2 inches. It does appear that
the forcing will be distributed over a large area, meaning not
expecting a focused area for ascent which should limit the flooding
potential. Regardless will have to watch the HiRes models and see if
any higher totals appear as they begin to capture this event.

.LONG TERM...(Tuesday night through Monday)
Issued at 331 PM CDT Mon Aug 14 2017

Main focus of the long term period continues to be the expected
rainfall for late Tuesday night through the day Wednesday, and even
lingering Wednesday night across the eastern portion of the area.

By tomorrow evening, a strengthening shortwave will be advancing
northeast across the high plains and pulling in plentiful moisture
from the south, indicated by PWATs increasing to around 2 inches and
surface dewpoints around 70 degrees.  This system does not look to
be much of a severe weather producer, but instead a widespread
moderate rain produces with sub-severe embedded thunderstorms.  So,
main concern with it is potential for heavy rainfall, which lines
up with the slight risk outlook for excessive rain by WPC. Expect
healthy rainfall amounts, with many locations in the 1-3" range,
but over a prolonged period in general as opposed to falling very
quickly. However, there were a few places that received a couple
inches of rainfall last night, making them a little more at risk
for seeing surface runoff develop quickly.

Conditions look to dry out Thursday into Friday, with another
shortwave expected to move in Friday night.  This wave will come
down from our northwest and looks much more meager than the
Wednesday system.  Still, could see some scattered showers and

After that, conditions should be dry with southerly flow developing,
leading to a gradually warming pattern through the end of the


.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 229 PM CDT Mon Aug 14 2017

Low level moisture continues to linger in the form of low stratus.
Forecast soundings show clearing skies later this evening so
should see some breaks expand over the next few hours, but then
fog quickly developing overnight through early Tuesday morning.
Continued with this trend in the taf, but feeling less confident
in the clearing skies, and may just end up with IFR stratus
instead of fog.

Area of MVFR clouds is gradually diminishing so should see VFR
conditions later this afternoon at KMSP. Areas of fog could
develop tonight, but MSP rarely gets IFR/LIFR radiation fog so
continued with 4sm in the TAF. There is still quite a bit of low
level moisture, so could see MVFR/IFR stratus redevelop overnight.

Wed...MVFR/IFR with -TSRA. Wind S-SE at 5-10 kts.
Thu...VFR. Wind N-NW 5-10 kts.
Fri...VFR. Wind W 5 kts.




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