Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 081815

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
1215 PM CST Fri Dec 8 2017

.SHORT TERM...(Today and tonight)
Issued at 406 AM CST Fri Dec 8 2017

The odd and highly amplified pattern featuring thundersnow in
south Texas and 40 degree temperatures in the Yukon spells
meridional flow here. The wave to watch today is currently located
just west of Hudson Bay. It will dive due south through the day,
bringing a brief round of accumulating snow to the eastern half
of the CWA late this afternoon and early evening. As the snow
begins to arrive, mid and upper levels begin to dry out, leaving a
relatively shallow moist layer. This moist layer, however, is
coincident with the DGZ and the strongest omega which should get
some decent snow showers going. The highest rates should last
maybe an hour or two given the fast motion of the system so 1-1.5
inches can be expected at most.

Further west, the moist layer is even shallower, but again is
coincident with the DGZ while CAA helps steepen lapse rates into
that layer. Such a set up warrants low chance PoPs with little or
no accumulation.

.LONG TERM...(Saturday through Thursday)
Issued at 406 AM CST Fri Dec 8 2017

The trough lifts out Saturday night with temperatures likely
rising overnight into the 20s. Westerly flow will bring a Pacific
airmass in Sunday ahead of another clipper system Sunday night and
Monday. The ECMWF has shifted west again with the stripe of
accumulating snow, favoring the central and eastern CWA
potentially making for a troublesome commute. The rest of the
guidance is further east, more northeastern Minnesota and
Wisconsin. Maintained chance PoPs for most of the forecast area,
highest PoPs in Wisconsin where likelies continue. This one could
bring 2 or 3 inches. Strong CAA on the backside of the system
will likely bring another round of scattered snow showers or
flurries, along with wind gusts of 30 to 40 mph Monday afternoon.

This pattern is expected to persist for at least the next week with
weak disturbances diving southeast across the Upper Midwest. It
remains to be seen whether we will be more on the mild side or
the cold side of these, but with the storm track very nearby most
of the accumulating snow would fall to the north and east.


.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 1214 PM CST Fri Dec 8 2017

Our next system is up in Manitoba and quickly heading for the
MN/WI border. Warm advection out ahead of this wave has helped
clear out MVFR and lower cigs and looks like we will not go sub-
vfr until the cold front with the Manitoba low arrives. Still
looking good for about a 3 or 4 hour window of light snow in WI,
with the west edge of the snow shield swiping MSP. We may see on
and off light snow/flurries through the rest of the night as the
clouds expected in the wake of the cold front will be located
completely withing the dendritic snow growth zone, which is
usually a recipe for easy flurry generation. Right behind the
front there also looks to be a 2-4 hour window of very strong wind
gusts, possible gusting to over 40 kts at AXN/RWF/MKT so do have a
period where winds are quite a bit stronger than guidance. Lower
confidence on how long post frontal clouds stick around, but the
could be with us well into the afternoon Saturday.

KMSP...Confidence is high that CIGS will remain VFR until
basically the snow arrives. Still only expect a half inch, with
that 23z-02z window still looking good for when MSP sees snow. May
see NW winds gust into the 30s from about 3z-6z before slowly
quieting down the rest of the night. Confidence is low on when
MSP will lose the post frontal MVFR cigs. Could be as early as 9z
or wait until as late as 21z, given the time of year, we went the
longer route.

Sun...VFR. Chc IFR/-sn overnight. Wind NW 10G15 kts.
Mon...MFVR with chc IFR/-SN early. Wind NW 15G25 kts.
Tue...VFR. Wind NW 10 kts.




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