Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 091018

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
418 AM CST Sat Dec 9 2017

.SHORT TERM...(Today and tonight)
Issued at 419 AM CST Sat Dec 9 2017

Cyclonic flow and a moist and unstable boundary layer is producing
widespread flurries early this morning. Stratus and flurries
extend north all the way to the international border and beyond.
As the ridge axis pushes overhead later this morning and shifts to
the southeast this evening, drier air will work in and should
break up the cloud cover a bit and end the flurries.

Another short wave will push southeast tonight. This one looks
drier than its predecessors and the moist low levels are warmer
than the -18 to -12C DGZ zone. Therefore, not expecting snow with
this wave, but if the boundary layer destabilizes again toward
Sunday morning to the degree the NAM indicates, then we cannot
rule out some freezing drizzle with the lack of ice present in the
column. This is a low probability scenario, but worth a mention.

.LONG TERM...(Sunday through Friday)
Issued at 419 AM CST Sat Dec 9 2017

If freezing drizzle does develop late Saturday night, it will end
by mid morning Sunday with drier air moving in again. Another
ridge axis will pass through Sunday ahead of the next clipper for
Sunday night. With cloud cover persisting and the mid level ridge
being suppressed a bit to the west, it doesn`t appear we will be
making a run for temperatures above freezing except for the MN
valley and points southwest.

Moisture deepens and the entire column saturates Sunday evening.
A band of snow will develop along the warm front of the clipper
and should spread southeast into central and eastern Minnesota
between 00-03Z and shift into Wisconsin after 06Z. The band of
snow will be transient enough to limit the amount of accumulation
to 2 inches or less, but it may come down moderately for a time
with the degree of moisture and forcing expected. Guidance still
does not show the best consistency with placement of this band,
but for this forecast, I favored the slightly westerly
displacement of the GFS/ECMWF over the eastern NAM/GEM due to the
more suppressed ridge to the west. The 06Z GFS has shifted even
further west. The surface low will track roughly from northern MN
into central WI Monday morning, placing the majority of the CWA in
the warm sector following the band of snow. There`s a better
chance for above freezing temps early Monday before the arctic
front, strong CAA, and gusty winds arrive Monday afternoon.
Therefore, did not include blowing snow mention for now with the
risk of some snowmelt, but should temperatures remain below
freezing the 30 kt wind gusts would be sufficient.

Seasonably cold air returns Tuesday, but the long wave trough
appears to lift out of the eastern U.S. for late week. Milder air
will flow eastward and we should return to near or slightly above
normal temps. Baroclinic zone sets up across Canada during this
time, keeping the predominant storm track up there. There still
aren`t hints at any meaningful snowfall for the next two weeks and
looking at the CFS nothing for the next month and a half.
Obviously this can change quickly, but it is unusual to not see
at least a fantasy storm somewhere in the extended guidance.


.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 1031 PM CST Fri Dec 8 2017

Quick-moving clipper-type system is winding down as the heaviest
batches of light snow have shifted off to the east and
dissipated. In the wake of the main trough aloft, weak bands of
flurries/snow showers will still drift southeast from northeast MN
but mainly be confined to far eastern MN into western WI, and only
over the first 2-4 hours of the 09/06z TAFs. The more complicated
concern will be the barely-MVFR ceilings in their patchwork setup
at initialization. There may be some bouncing between VFR and MVFR
through roughly 12z then VFR conditions are expected to prevail
through the rest of the TAF period. Ceiling will rise to roughly
040-060 through late morning then continue to rise and scatter out
through the afternoon hours. High ceilings are then expected to
re-develop Saturday evening.

KMSP...Have gone the more optimistic route of keeping ceilings as
VFR through this morning per observation and model trends but a
relatively short duration of MVFR ceilings cannot be ruled out. If
any does develop over MSP, expect it to be between 020-030 (and
nothing below 1700ft). Clouds will scatter out around midday and
remain as such through Saturday afternoon.

Sun...VFR. Chc IFR/-SN overnight. Wind NW 10G15 kts.
Mon...MFVR with chc IFR/-SN early. Wind NW 15G25 kts.
Tue...VFR. Wind NW 10 kts.




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