Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 181150

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
550 AM CST Mon Dec 18 2017

.SHORT TERM...(Today and tonight)
Issued at 413 AM CST Mon Dec 18 2017

Big story for the short term is today looks to be the warmest day
we see locally for at least the next two weeks, and this may be
the last time the Twin Cities makes a run at 40 for several weeks,
so get out there and enjoy it today!

The main weather feature we will see today is shortwave energy
currently over British Columbia that will shoot along the
international border on the south side of strong zonal flow across
southern Canada. This will bring a quick couple of inches to far
northern MN, but will draw mild air north into southern MN. There`s
very little model spread with highs today, so feel confident with
highs ranging from the mid 40s in the upper MN valley, with mid 30s
across central MN into northwest WI.

Tonight, despite a cold front slipping across the area, it will be a
mild night. The system driving this front will be clear up over
Hudson Bay and this front will bring in west winds and a cooler
airmass of still Pacific origin, while a more polar continental
airmass and northwest winds will remain locked up to the north of a
cold front that will be nearing the Canadian border Tuesday morning.
Nudged forecast lows up a bit more toward a blend of the raw models
as opposed to the MOS, which pushed lows up into the mid/upper 20s,
or near to slightly above our normal highs for this time of year.

.LONG TERM...(Tuesday through Sunday)
Issued at 413 AM CST Mon Dec 18 2017

The highlights in the long term are still the snow later this week
followed by frigid temperatures for Christmas.

What hasn`t changed much with the latest model runs is the
anticipated area for moderate to heavy snow on Thursday & Thursday
night, which looks to be generally along and south of a Redwood
Falls to (southern) Twin Cities to Ladysmith line south to
Interstate 90. What does still remain uncertain is snowfall
amounts, especially given the 18.00z ECMWF solution, which
featured less phasing of the northern/southern streams and
therefore less snowfall. If this solution were to pan out then the
bulk of the forecast area would not receive winter storm warning
snowfall amounts. The GFS has wobbled a bit with its depiction of
where the heaviest band will set up, but has held strong with a
solid band of amounts in the 6-12" range. Meanwhile the CIPS
Analogs place the heaviest band in the heart of the CWA (near the
aforementioned line). Therefore, confidence was not quite high
enough yet to issue a headline this morning.

Prior to the main band of snow, the warm advection 1-2" band of
snowfall is still expected to clip the northern part of the
forecast area (I-94 north) on Wednesday.

After the system lifts out Arctic air still looks to filter into
the region. Single digit highs look likely for the 24th, with
even colder readings for Christmas day with highs from zero to 5


.AVIATION...(For the 12Z TAFS through 12Z Tuesday morning)
Issued at 550 AM CST Mon Dec 18 2017

Main concern this period is timing what is left of the LIFR
stratus out of WI. Followed a blend of the HRRR/lamp for this,
which may be a bit long for keeping it in place with south winds
starting mix these clouds out. VFR for the rest of the period,
with the lone exception of up at AXN behind the cold front
tonight. This is a brief window when looking at the NAM sounding
for AXN, so kept them VFR for now.

KMSP...No sub VFR cigs are expected this period. Vis may be a
little slower to improve than advertised as dewpoints are
forecast to rise around 30, which may keep the haze lingering a
bit longer than currently forecast.

Tue...VFR. Wind NW 15G30kts.
Wed...VFR. Chc IFR/-SN. Wind ESE 5-15kts.
Thu...IFR/SN developing. LIFR/+SN possible. Several inches
      possible. Wind NE 10kts.




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