Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 170019 AAA

Area Forecast Discussion...UPDATED
National Weather Service Twin Cities/Chanhassen MN
619 PM CST Sat Dec 16 2017

.SHORT TERM...(This evening through Sunday)
Issued at 300 PM CST Sat Dec 16 2017

The main forecast concern is the redevelopment of fog overnight,
especially in areas that cleared this afternoon. An elevated
inversion will continue to strengthen overnight. Thus, with
boundary layer moisture high, some melting snow in southern
Minnesota this afternoon, and leftover fog/stratus, will set the
stage for redevelopment of fog. Little mixing in the boundary
layer is also conducive for fog formation, and with an increasing
mid level dry layer, fog will form. It remains questionable on the
formation of dense fog, but this is still a possibility.
Otherwise, tomorrow highs will depend upon how widespread the low
clouds/fog expand overnight and whether the clouds break up. For
now, 30s, with some 20s where the cloud cover is expected to be
more dense for Sunday highs.

.LONG TERM...(Sunday night through Saturday)
Issued at 315 PM CST Sat Dec 16 2017

The main forecast questions or concerns are next week storm
system which does have the possibility of producing lots of
snowfall somewhere in the central or northern part of the United
States. The question remains on where the storm will track over
the central part of the nation. Although models have been slowly
working on a more consistent output, they are still having some
run to run inconsistency in the northern/southern jet stream
interaction. Plus, due to the phasing of the jets, models will
have some trouble in the initial start of the storm once it moves
out into the plains.

Initially, a warm air advection regime will commence late
Wednesday across central Minnesota where the best potential of a
few inches of snow will fall. The bigger question is the storm
moving out of the Rockies and into the plains late in the week.
The set up is a classic Colorado, or Plains low which does support
a large swath of heavy snow on the northwest side of the surface
low track. Using CIPS analogs, valid around Wednesday afternoon,
does support a swath of warm air advection snowfall across central
Minnesota. The schematic of the CIPS analogs does have a small
but heavy band of snow across west central to central Minnesota
(1st analog is December 9, 2012). However, it looks as though this
could be two systems interacting, and not so much on the initial
warm air advection regime. Looking at stormdata during that
period in 2012, there was a significant blizzard in western
Minnesota, where some areas in west central Minnesota receiving a
foot or more of snow. I don`t want anyone to get excited for a lot
of snow, but the potential is there.

Confidence is fairly high that a cold arctic outbreak will
commence the week of December 25th. The GFS/EC/GEM all support a
deep arctic upper low developing over Hudson Bay, with strong
northerly flow directly from the arctic over the Upper Midwest
during this time period. 850 temperatures are very cold in the
range of -25 to -32C which correlates to surface temperatures in
the subzero range. This could be one of the coldest Christmas
since 1996 where the high was only 9 below zero in the Twin


.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 619 PM CST Sat Dec 16 2017

Cigs will deteriorate to IFR levels this evening at most of the
TAF locations. Given the light, stagnant flow in the low levels,
not anticipating too much of an improvement on Sunday. Some
visibility reductions are also possible, particularly at AXN
overnight with some dense fog freezing fog.

KMSP...MVFR cigs for now, but they will deteriorate to IFR levels
during the late evening and remain there through early Sunday

Mon...VFR, MVFR possible. Wind SW 10-15G25kts.
Tue...VFR. Wind NW 20G35kts.
Wed...MVFR, IFR/-SN possible. Wind E 5-15kts.




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