Area Forecast Discussion
Issued by NWS Twin Cities, MN

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346
FXUS63 KMPX 172112
AFDMPX

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
312 PM CST Sun Dec 17 2017

.SHORT TERM...(This evening through Monday)
Issued at 245 PM CST Sun Dec 17 2017

An earlier enhanced area of elevated returns across east central
Minnesota, and into west central Wisconsin, has finally been able
to saturate the boundary layer. Thus, light snow had developed
from the northern suburbs of the Twin Cities, eastward into west
central Wisconsin where a light dusting of snow is likely before
sunset. Otherwise, the main concern overnight is redevelopment of
fog/stratus as the boundary layer mixing is very light. Not until
winds begin to turn more south/southwest, as they are in west
central Minnesota, will the chance of fog begin to lower. Until
then, patchy fog, some locally dense fog, is still possible in
southern Minnesota, eastward into west central Wisconsin. Based on
some clearing tonight, and partly sunny conditions on Monday,
highs will rise above freezing for most areas, the warmest
readings will occur in west central Minnesota where both lack of
snow cover and a downslope component along the Buffalo Ridge will
lead to highs in the 40s.

.LONG TERM...(Monday night through Sunday)
Issued at 310 PM CST Sun Dec 17 2017

...A MAJOR WINTER STORM POSSIBLE LATE NEXT WEEK...

There remains uncertainty in the forecast on the exact track of a
winter storm late next week, but confidence has increased enough
to warrant a headline in the extended period due to several
reasons.

First, both the GFS/EC have been consistent in the past two runs
on the upper level pattern for this week, and nearly the same for
a surface low developing across Colorado, and moving it northeast
across the plains, and into the western Great Lakes region. Only
the GEM has a slight southern track bias which leads to the
uncertain in the exact track.

Secondly, CIPS analogs for late this week (108 hrs) remained
favorable for accumulating snowfall across Minnesota, and northern
Wisconsin. Only subtle differences in the thermal profile and the
jet couplet are noted, but this is for the number one analog and
not necessarily the mean.

Thirdly, this winter storm is forming in the Rockies, and moving
out into the plains near Colorado/Texas/Oklahoma. This is a
classic scenario of a winter storm for the Upper Midwest. Only
differences are the track on the surface low, the amount of
moisture available, and upper level dynamics.

I don`t want to alarm those who are going to be traveling late
next week, but this scenario does support an eye on the weather
front. As always, uncertainties exist, so always check back for
the latest forecast.

Another weaker storm system will bring a band of mainly light snow
across central Minnesota, and west central Wisconsin Wednesday,
as a warm air advection regime develops in advance of a storm
system moving out of the northern Rockies.

Once this storm moves out of the region early in the weekend, a
very cold air mass will begin to surge southward across the United
States. The core of the cold air looks to settle in the Upper
Midwest on Christmas day where daytime highs could possible not go
above zero. It hasn`t been this cold on Christmas since the
Winter of 1996 where the daytime high was 9 below.

Based on current trends of the mean upper level flow developing
off the west coast of British Columbia, and the possibility of a
blocking ridge, the colder than normal temperatures could stay
with us through the end of December.

&&

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 1140 AM CST Sun Dec 17 2017

Continued the same trend with the worst conditions in south
central/east central Minnesota, and into portions of central
Minnesota, and west central Wisconsin. The best conditions will
occur in west central/southwest Minnesota, especially once
south/southwest winds develop later today, tonight. Confidence
remains high that the IFR, MVFR cigs will hold through the next 6
hours for KMKT, KRNH, KEAU, KAXN, KMSP. Elsewhere, a period of
IFR or MVFR cigs are still possible, but confidence is much lower.
After 00z, and once winds shift to the southwest/south,
conditions will improve especially in western/southwestern
Minnesota. Conditions in west central Wisconsin may not become VFR
until Monday afternoon or later.

KMSP...

IFR conditions, with a slow trend toward low end MVFR cigs will
continue through the afternoon with high confidence. Lower
confidence that cigs will lower once again tonight as winds become
more southwest. By morning, MVFR cigs will lift above 1.7k, and
VFR by the afternoon. Confidence still remains low for VFR cigs by
Monday afternoon.

/OUTLOOK FOR KMSP/

Mon evening...VFR. Wind SW 10-15G25kts.
Tue...VFR. Wind NW 20G30kts.
Wed...VFR. Chc IFR/-SN. Wind E 5-15kts.

&&

.MPX WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
&&

$$

SHORT TERM...JLT
LONG TERM...JLT
AVIATION...JLT



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