Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 271228

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

.UPDATE...For 12z Aviation discussion below


.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 12Z TAFS through 12Z Monday morning)
Issued at 630 AM CST Sun Nov 27 2016

Dense (freezing) fog will plague the sites during the first
several hours of the TAF period, with VLIFR visibilities common.
Improvement will be slow, especially at northern sites (KAXN and
KSTC), but expect visibilities to improve to MVFR between 16z and
18z. Eastern sites have the highest chance to see VFR cigs by
afternoon, including KMSP/KRNH/KEAU. Meanwhile, we will see high
clouds streaming in from the west as the next system approaches.
Associated rain will reach southwest MN (KRWF) around 22z...spread
north/east to reach KAXN/KSTC/KMSP around 00z...and eventually
KRNH/KEAU between 00z and 02z. Isolated thunder is also quite
possible (primarily KRWF-KMSP-KRNH-KEAU), but at this point
confidence/coverage are too low to warrant a mention in the TAFS.
Once the precipitation starts it will continue into the early
morning hours with prevailing LIFR conditions. There are some
indications of a dry slot working into the southwest by
we could see a temporary break in the precip expanding north and
east toward daybreak Monday. Winds will increase from the
southeast today with gusts to 25kts develop in conjunction with
precip onset.

Freezing fog with visibility around one quarter mile will affect
MSP during the first couple hours of the TAF, and then gradually
improvement will occur throughout the morning. VFR conditions
should prevail this afternoon until the rain arrives around 00z.
Will need to monitor the thunderstorm potential, but at this point
the probability is too low to warrant a mention in the TAF. The
wind direction will be around 120 degrees through the majority of
the period, with gusts into the lower 20s (knots) developing this

Mon...MVFR early with -SHRA. Wind S 10-15 kts.
Tue...MVFR/IFR. Chc -RA. Wind SW 5-10 kts.
Wed...MVFR/IFR. Chc -RA/-SN. Wind NW 5-10 kts.


WI...Dense Fog Advisory until 9 AM CST this morning for WIZ014>016-

MN...Dense Fog Advisory until 9 AM CST this morning for MNZ041>045-



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