Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 080422

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
1022 PM CST Wed Dec 7 2016

.SHORT TERM...(This evening through Thursday)
Issued at 255 PM CST Wed Dec 7 2016

The main forecast concern through Thursday afternoon is whether any
of the snowfall will accumulate as the last batch of deeper moisture
shifts southward.

The storm system that has affected the Upper Midwest/Northern Plains
over the past two days was centered north of the Great Lakes. A
surface trough was noted across northern Minnesota which will move
south/southeast overnight. Although QPF amounts will be extremely
light in this air mass regime, even a hundredth or two with create a
light dusting, or possibly an inch. This type of snow is very dry,
fluffy, and will be easily blown around. I wouldn`t be surprised to
see some blowing snow problems if an inch of snow develops. This
surface trough and associated area of deeper moisture will move
southeast of Minnesota and limit any accumulating snowfall by
Thursday afternoon. The best time frame is late this evening,
through Thursday morning for any accumulations.

Temperatures will likely hold within a degree or two overnight, and
rise into the 20s Thursday afternoon. Gusty winds will continue
overnight, through Thursday morning before tapering off Thursday

.LONG TERM...(Thursday night through Wednesday)
Issued at 255 PM CST Wed Dec 7 2016

Main forecast issues this period would be the potential snow storm
developing Saturday into Saturday night. Then the overall
amplified northwest flow pattern developing through the end of
the forecast period.

We expect clouds to linger through at least Thursday night...with
perhaps some breaks developing into Friday. Cyclonic flow may
still drop a few flurries into Thursday evening over the far
east. The surface high pressure ridge moves east through
Friday...with a minor shot of arctic air. Temperatures should
range around 10 degrees below normal through Sunday.

The snow threat increases again Saturday into Saturday night over
much of the cwa. The GFS and NAM are most amplified with the
short wave dropping across the rockies from the Pacific Northwest
into the Northern Plains into Saturday. The 12z ECMWF troughs a
wrench in the forecast its trend of weakening the wave as it moves
across the Northern Plains during this period. It produces only
light QPF/snow with this feature and waits for another stronger
short wave dropping in behind this system Sunday afternoon and
Sunday night. There were some issues with upper air soundings
getting into the 12z NAM_WRF and GFS...but believe this should
have very little impact tot eh forecast overall. We will continue
to push the categorical pops spreading across the southern half
of the area through Saturday. 12 hour snow amounts for Saturday
are generally 3-5 inches south of a line from near AXN-STC-MSP. An
additional 1 to 3 inches of accumulation are possible over the
eastern area into Saturday the system moves out...and
would push totals around 7 inches mainly along and south of the
Minnesota River Valley. Still would like to see another model run
before issuing any headlines...due to the discrepancy in the
models handling the potential two waves.

The real arctic plunge follows this system Monday through much of
next week. The ECMWF was more amplified with its northwest flow
pattern and was drawing H85 temperatures of minus 32C over the
area Tuesday into Wednesday. The GFS brings in minus 22C air over
the region. Not quite as cold...but with fresh snow cover and
lighter winds developing into midweek...we may struggle to remain
above zero for highs...and lows should bottom out close to 5 below
to 15 below zero possible. We will trend several degrees colder
than guidance for the Tuesday/Wednesday period for now. Wind
chills will be approaching advisory criteria(minus 25F) during
this period as well...but winds should be trending lighter as the
high pressure ridge moves in.


.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 1020 PM CST Wed Dec 7 2016

Aside from KAXN, which has been IFR/LIFR for around 36 hours due
to blowing snow, most TAF sites will be MVFR/VFR for ceilings with
light snow or flurries through the morning. There will be a
slightly heavier round of snow late tonight that could result in
IFR visibility. Little in the way of accumulation is expected.


MVFR ceilings should have filled back in (but ceilings could vary
from 2500-4000ft for most of the night. Snow will increase
slightly in intensity early in the morning as a light band of
snow drops south from northern MN into the Twin Cities metro. A
dusting to quarter or third of an inch is possible.

Fri...VFR. WNW wind 5-10 kts.
Sat...MVFR with SN and IFR likely. SE wind 5-10 kts.
Sun...IFR/MVFR early with SN. VFR by Afternoon. NW wind 10 kts.




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