Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 262014

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
214 PM CST Sat Nov 26 2016

.SHORT TERM...(This evening through Sunday)
Issued at 211 PM CST Sat Nov 26 2016

Subsidence from an upper ridge moving in from the Dakotas has
resulted in a gorgeous late November day...for most.  This
subsidence has trapped some low level moisture and with weak surface
flow to help mix this moisture out, we have seen dense fog remain
across central MN, with another batch of mainly stratus over NW WI.
This central MN fog also coincides with where the greatest snow
cover remains from the blizzard back on the 18th. Even if we see
visibilities at places like Alexandria and Long Prairie improve to
the 2-4 mile range this afternoon, the continued light winds and
moist boundary layer will result in the rapid expansion of dense fog
in the area once again. As a result, have decided to issue a dense
fog advisory in central MN through the rest of tonight. We will
start with where the fog has remained overnight and will expand it
later if need be. Light winds will be in place pretty much area wide
with continued high low level moisture, so this fog will likely
expand overnight, though how far south and east it will build is in
question, which is why for now we have gone with a conservative
dense fog advisory area. Think the HRRR is likely overdoing its fog
depiction (as it did last night), but the SREF has probabilities for
visibilities less than 1 mile greater than 80% along and north of a
Redwood Falls/Twin Cities/Eau Claire line, which would be a good
boundary for the potential southern extent of any fog we see tonight.

Sunday, the deep trough currently coming onshore in California will
be working out into the Plains states. This will eventually lead to
cyclogenesis over Nebraska during the afternoon. Ahead of this
developing low, a significant surge of moisture will be rapidly
pushing north toward MN, with a band of isentropically forced
showers quickly approaching from the south. We will see the first
shots of rain moving into southwest MN around 21z, with the period
ending at 00z (6 pm Sunday evening) with a band of rain from west
central into south central MN that will quickly spread northeast
across the area Sunday evening. 850-500mb differential theta-e is
negative coming up Sunday afternoon on the NAM, indicating the
presence of some weak convective instability, so have a small
thunder mention coming up with the rain as well.

.LONG TERM...(Sunday night through Saturday)
Issued at 211 PM CST Sat Nov 26 2016

Precipitation will continue to overspread the area Sunday evening as
low pressure lifts north from the Nebraska/South Dakota border to
near the border of Minnesota and the Dakotas by 12Z Monday. The
model guidance is actually in good agreement on the track of the
surface low and upper level features through that time frame. As
that occurs, we`ll see rain overspread the area Sunday night, with
the dry slot working in by Monday morning. Still looks to be enough
elevated instability, per layer differential theta-e values of near
or below zero, for a mention of some thunder over most of the area
into Monday morning. Colder air will start to filter in from the
west Monday night, with lingering precipitation transitioning to
some light snow overnight into Tuesday morning. By that point, the
surface low will be slowly filling and should be located somewhere
over Minnesota. It will then move ever so slowly east over the next
couple days, eventually making it to the upper Great Lakes by
Thursday as a secondary low takes shape near New England. This will
result in a  prolonged period of chance PoPs from Tuesday into
Thursday, with mainly light snow potential at night, and mainly
light rain or mixed potential during the daytime as temperatures get
back into the middle 30s each day. By Friday and Saturday we should
see sufficient dry air work into the region for things to dry out,
although enough low level moisture looks to linger for things to
remain mostly cloudy. Overall, will be a fairly gloomy week with
temperatures running a bit above normal, mainly due to lows that
will be well above normal.


.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 1213 PM CST Sat Nov 26 2016

Fog is again the primary forecast concern. Where snowpack is
greatest in central MN, fog has been slow to budge and do not
think this is going anywhere today or tonight. AXN may see the
visibility increase to between 1 and 4 miles this afternoon, but
they will quickly fog back in. Also expect fog to develop again
tonight in western WI where winds will be lightest. There is
potential that fog could develop at RWF/MSP as well given moist
boundary layer and light winds, but will keep the fog mention to
near the snow and lightest winds. Sunday morning will see
increasing southeast winds as the next storm system approaches,
with rain moving into the terminals for the 00z TAF window.

KMSP...Only potential problem will be the treat for fog tonight.
Fog stayed out of MSP last night and expect the same tonight,
with the vis dropping down to 4 or 5 miles. Rain looks to arrive
shortly after 00z Mon, or just beyond the 30 hour window.

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.


MN...Dense Fog Advisory until 9 AM CST Sunday for MNZ041>044-048>050.



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