Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 150008

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
708 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 an 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

.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 00Z TAFS through 00Z Tuesday evening)
Issued at 708 PM CDT Mon Aug 14 2017

Concern remains the development of low clouds and fog tonight.
This looks most favorable for southern MN into the KEAU area, but
certainly possible for central MN to KRNH and KRPD as well.

Low clouds lingered all day in much of southern MN into KEAU, with
the last few pockets dissipating only early this evening per
satellite. With lingering moisture and light winds, these areas
should be quickest to redevelop tonight. Confidence is above
average for this area.

Meanwhile in central MN to the Rice lake WI area, diurnal cu are
fading quickly with loss of heating. This area is more
questionable for redevelopment, since light northeast winds were
bringing in slightly drier air. But even this area will be
susceptible to patchy radiational fog, and have indicated such at
KAXN, KSTC, and KRNH, where it is often easy to get radiational
fog. Confidence, however, is only average in this part of the

Once low clouds dissipated early this afternoon, cu formed, but
they are fading quickly with loss of heating. Thus skies should be
mostly clear much of the night. There is some potential for
radiational fog late tonight. However, this is uncertain since
light ne winds were bringing in slightly drier air. Therefore kept
a period of MVFR visibility, but left the clouds as low scattered.
Then for Tuesday, some midday cu are likely, and mid/high clouds
should spread across the area later Tuesday. It is also possible
that some showers might arrive 03z-06z on the 16th, but was too
uncertain to include in the taf. Will certainly need to add it for
the 06z issuance that will go through to 12z on the 16th.

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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