Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 271800

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
1200 PM CST Sun Nov 27 2016

.SHORT TERM...(Today and tonight)
Issued at 345 AM CST Sun Nov 27 2016

Concerns are twofold in the short term. First and foremost is the
widespread dense fog event that has ensued with plentiful boundary
layer moisture and light winds in place. The dense fog advisory was
expanded to included the entire forecast area. In addition to the
sub-quarter mile visibility reductions, sub-freezing temps are
likely yielding slick spots on paved surfaces (especially
bridges/overpasses). It could be awhile before visibilities improve
this morning given the low level flow and amount of moisture trapped
in the boundary layer. Will quite possibly need to extend the dense
fog advisory past its current 9 am expiration, particularly across
central MN. Given uncertainty in the areal/temporal extent to which
this would be needed, will hold off to see how things evolve this
morning. Have also gone a bit more pessimistic with cloud cover
given the potential for stratus/stratocu to linger. South/east
central and southeast MN and west central WI will have the highest
potential for sun this afternoon prior to the clouds entering from
the west, and are therefore expected to see high temps a bit warmer
(mid to upper 40s).

By 21z, Hi-res models are in pretty good agreement that the surface
low will be across southwestern SD/NE...with the precipitation
shield entering southwestern MN. Have slowed precip chances down
about 1-2 hours, but in general things look about the same, with
rain reaching the Interstate 94 corridor around 00z Monday. The 00z-
06z timeframe looks to feature the most widespread areal coverage of
rain, with indication of dry slotting moving into southwestern MN
between 06z and 12z Monday. Weak elevated instability still looks
sufficient to favor the inclusion of an isolated thunder mention
tonight as well. Most area should see one half to three quarters of
an inch rainfall by daybreak Monday.

.LONG TERM...(Monday through Saturday)
Issued at 345 AM CST Sun Nov 27 2016

The large scale pattern remains favorable for a continuation of
cloudy skies, light precipitation, and near to slightly above
normal temperatures from Monday through Wednesday. Due to these
conditions, very little diurnal temperature change is expected
with highs and lows within 5 to 10 degrees.

Models are consistent with this pattern so confidence in the
forecast from Monday through Wednesday is fairly high. One of the
main focus in the models is the strength of a large ridge building
across central Canada next week. Although models are again similar
on slowly filling and lifting a cutoff low from the Upper Midwest,
eastward across the Great Lakes by Wednesday/Thursday. The pace of
the eastward progression of this upper low is dependent on the
upper ridge location in central Canada, and the strength or
weakness as the week progresses. The cloud skies and light
precipitation could linger longer this week if the upper ridge
remains strong.

Once the upper low moves off and the upper flow becomes more
progressive, a slight warming trend is expected by next weekend.
These warmer temperatures for the first week of December will
likely be short lived as longer range models have been forecasting
a significant change in the weather pattern with much colder
conditions after December 7th. The latest EC/GFS near 240 hours
out have a very strong high pressure system building north of the
northwest territories of Canada. This air mass is progged to move
southward the week of December 7th into the the northern United
States. Although this forecast is far from perfect, trends in the
pattern change reflect a higher confidence in this air mass
affecting our region the second week of December.


.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 1159 AM CST Sun Nov 27 2016

One of the more impressive dense fog events you are ever going to
see up here is finally start to improve as increasing SE winds
slowly bring better visibilities up from the southeast. A couple
of numbers that stick out from this fog were minimum RVRs this
morning at MSP of just 600-800 ft, but most staggering of all is
what has happened at AXN. AXN has been at 1/4sm or less since 17z
yesterday and will likely spend over 30 hours in dense fog. For
improvements, the HRRR vis forecast has been pretty good today, so
followed it for timing improvements in vis. For AXN, this
basically means its more 1/4sm vis until the rain arrives this
evening. As for the rain, short term models are in good agreement
on when it gets here and only needed to delay the onset in TAFs by
about an hour. Confidence in the forecast diminishes considerably
behind this band of rain as a dry slot works into the area. The
HRRR has clear skies coming into southern MN late tonight, so
tried to hint at some better conditions being possible at RWF and
MSP as the dryslot comes in. For AXN, there is a good chance they
descend back into dense fog behind the rain shield as they will be
closer to the surface low with deeper moisture and less mixing.

KMSP...We are finally getting out from under the fog and we are
done with it the rest of the TAF period. We`ll get a brief period
of VFR clouds, but MVFR cigs are already up to Ames, IA.
Confidence is high in rain moving in between 1z and 2z. We`ll see
continuous rain until 6z, but at that point MSP will start getting
into the influence of the dry slot and confidence in the TAF
decreases considerably at this point.

Tue...MVFR/IFR. Chc -RA. Wind SW 5-10 kts.
Wed...MVFR/IFR. Chc -RA/-SN. Wind NW 5-10 kts.
Thu...MVFR/IFR. Chc -RA/-SN. Wind NW 5-10 kts.


WI...Dense Fog Advisory until 3 PM CST this afternoon for WIZ014-015.

MN...Dense Fog Advisory until noon CST today for MNZ067-069-070-073-

     Dense Fog Advisory until 6 PM CST this evening for MNZ041>043-

     Dense Fog Advisory until 3 PM CST this afternoon for MNZ044-045-



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