Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 181828
AFDMPX

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
128 PM CDT Fri Aug 18 2017

.SHORT TERM...(Today and tonight)
Issued at 358 AM CDT Fri Aug 18 2017

The short term concern remains what appears to be short waves
affecting the region today into this evening. Then with clearing
trend fog potential remains later tonight.

Latest radar and satellite shows initial short wave moving across
southeast SODAK at the moment. Overall cloud top trends show some
warming as activity moves into more stable airmass over southern MN.
Most CAMs showing acitivity moving across mainly sc MN this morning.
WIll try and hold pops in that region for this wave. The next NODAK
wave moving through central/eastern portions of that state. Will
have to carry some PoPs into that region through the morning as
well. Will have to maintain high chance for now. May have to
increase into the afternoon as the main wave drops over the
southwest CWA. Deterministic models do drive quite a bit of
instability into the areas as the wave drops through. The best or
deeper shear remains across the west and southern cwa into early
evening. Depending on heating and instability, we could see at least
a large hail and damaging wind threat for a time over far southern
MN this afternoon/early evening.

This system exits the area this evening and we should see clearing
during the night. Expect surface ridge to builds east over the area
with winds diminishing as boundary layer decouples. This should
promote good radiational cooling and at least patchy fog development
after 06z Saturday.

.LONG TERM...(Saturday through Thursday)
Issued at 358 AM CDT Fri Aug 18 2017

After patchy fog lifts Saturday morning, a mild day with mostly
clear skies and highs in the 80s is expected.

On Sunday, clouds increase ahead of the next system, which will
bring a prolonged period of shower and thunderstorm chances late
Sunday through Monday night. The main change with the 18.00z
models was to speed up the arrival of our front about 6-9 hours.
This could mean a few showers and storms pop on Sunday afternoon,
although the bulk of the activity is expected to hold off until
Sunday evening/night as a LLJ of 45 knots intersects the boundary.
Precipitable water values are still forecast to be around 2
inches, so in addition to severe weather, heavy rainfall will also
be a hazard to monitor.

Tuesday through the end of the upcoming work week we see cooling
temperatures as a deep trough over northern Ontario sinks to the
Great Lakes. The track of the trough was depicted a bit farther to
the east with the 18.00z runs. Therefore, opportunities for
precip associated with weak impulses traversing the western
periphery of the trough look to be less. Highs in the 70s will
still be common however for Wednesday through Friday under
northwest flow aloft.

&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 128 PM CDT Fri Aug 18 2017

First of two upper waves is moving across southern MN this
afternoon, with a stronger one now over northeast SD. Cold cloud
tops with the MN wave have now pushed off into northern WI, well
north of the precip, so expect this precip shield to continue it`s
weakening trend over the next couple of hours. The SD wave will
be what supplies us with our main TS threat today, but with it
tracking toward northwest IA this afternoon, agree with what the
HRRR shows in that this is a problem for western MN. RWF/AXN have
the greatest threat for thunder, though it can not be completely
ruled out everywhere else. Confidence in thunder occurring
outside of AXN/RWF is to low to include anything more than a vcsh.
Tonight, skies will clear out with a surface high settling over
IA. This, given recent rains will set the stage for dense fog.
Like the TS, FG can`t be completely ruled out at any terminals,
though chances for FG look greatest at RWF/MKT due to their
proximity to the high. Once the fog burns off, there are no
weather concerns for Saturday.

KMSP...Though can`t completely rule out more showers later this
afternoon, confidence is highest in a dry scenario the rest of the
TAF period once the rain at the onset moves off. Fog tonight may
become problematic down in the river valley and parts of the
airport closest to the valley, but out at the ASOS, fog should not
be an issue.

/OUTLOOK FOR KMSP/
Sun...VFR. Chance MVFR/TSRA overnight. Wind SW 5 kts.
Mon...Chc MVFR/-TSRA. Wind SE 5 kts.
TUE...Chc MVFR/-TSRA early, bcmg VFR. Wind N 5-10 kts.

&&

.MPX WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
&&

$$

SHORT TERM...DWE
LONG TERM...LS
AVIATION...mpg



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