Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 181057

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

.updated for the 12z aviation discussion below...

.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 12Z TAFS through 12Z Saturday morning)
Issued at 555 AM CDT Fri Aug 18 2017

Rain showers moving into southern MN could move as far northern as
KRWF-KMSP line through 18z. KRWF-KMKT are the most likely
locations to see the -shra this morning. Should maintain vfr
however. Then the North Dakota wave moves southeast over the
region with thunder threat through about 01z. Mentioned prob30 for
thunder at several locations. We expect clearing thereafter with
mvfr and psbl ifr fog possible 06z-12z Sat across much of the

KMSP...Still thinking main morning light rain should stay south of
the field...but it may be close. Opted for vcsh after 15z. Should
maintain vfr until thunder threat moves in later this afternoon -
after 21z as the secondary wave passes through. Mentioned prob30
21z-24z for now. Then clearing with some fog possible later

Sat nite...VFR. Wind SW 5 kts.
Sun...VFR. Chance TSRA overnight. Wind SW 5 kts.
Mon...Chc MVFR/-TSRA. Wind S 5 kts.




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