Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 162121

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
321 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 18Z TAFS through 18Z Sunday afternoon)
Issued at 1125 AM CST Sat Dec 16 2017

Enhanced daytime satellite imagery from the new GOES-East has low
clouds/fog across the Twin Cities metro area, but more patchy for
areas south/southwest toward the Minnesota River Valley. However,
based on satellite trends, low clouds/fog will continue to spread
westward across east central-south central Minnesota by the late
afternoon/early evening. Otherwise, the rest of central/southern
Minnesota should see a period of VFR or MVFR cigs during the
afternoon before more IFR cigs develop as a strong inversion
develops overnight. West central Wisconsin will likely see another
period of MVFR/VFR conditions this afternoon, but the IFR cigs
should begin to spread back across the region by late
afternoon/early evening. Confidence is average for this afternoon,
but much lower tonight/Sunday as the strong inversion develops and
traps the boundary layer moisture over the region. Winds will be
light from the east/southeast, and become more west/southwest


As discussed before, low end MVFR will likely continue this
afternoon before cigs begin to lower once again this evening.
Confidence is low on when this cigs redevelop and how long they
stay. Winds will be light from the northeast/east through most of
the period.


Sun...Possibly BCMG VFR in aftn. Wind variable 5 kts or less.
Mon...VFR. Wind SW 10-15G25 kts.
Tue...VFR. Wind NW 20-25G35 kts.




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