Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 090123
AFDMPX

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
723 PM CST Fri Dec 8 2017

.UPDATE...
Issued at 631 PM CST Fri Dec 8 2017

Updated to include 00z aviation discussion below.

&&

.SHORT TERM...(This evening through Saturday)
Issued at 320 PM CST Fri Dec 8 2017

Quick moving clipper moving into northeast MN this afternoon is
still on track to drop south along the MN/WI border this evening,
with maybe 1.5" of snow coming down for Ladysmith down to Eau
Claire. Models have remained fairly consistent with the handling
of this wave and only change made to the existing forecast for
this snow was to delay its arrival by a couple of hours.

Beside the snow, there also looks to be a 3 or 4 hour period
behind this systems cold front where winds could get a bit
strong, especially for western into south central MN. CAA in the
wake of the front will result in steep lapse rates with a mixed
layer getting up to between 850 and 800 mb. NAM shows top of the
channel winds immediately behind the front getting into the mid 40
kts, so did boost winds above blended guidance, with some 40+ mph
wind gusts not out of the question. Beside the winds, forecast
soundings also show any post frontal stratus being located
directly within the dendritic growth zone, so it shouldn`t be
tough developing flurries/light snow through the night.

Big question for Saturday is how quickly do we loose the low
clouds. Even if we do lose the clouds though, we will be placed
squarely within the temperature gradient between the cold trough
to the east and warm ridge to the west, so any way you slice it,
our Saturday will have more clouds than sun. Not much spread in
guidance for highs tomorrow, so stuck pretty close to a mean of
blended guidance.

.LONG TERM...(Saturday night through Friday)
Issued at 320 PM CST Fri Dec 8 2017

Biggest concern in the long term is the potential for a pretty
healthy clipper Sunday night into Monday morning, with the
potential for a good 3-4 inches north of I-94 in the MPX CWA.
Otherwise the highly amplified pattern we have in place does not
look to begin to break down and change until the 15th of December,
or the last day of the long term period. This means more NW flow
with ample opportunities for quick moving clippers. The coldest of
the temperatures looks to shift east of where it has been this
week, so we look to be a bit milder next week, with high
temperatures near normal.

The biggest change we have seen in the last 24 hours comes with
the clipper for Sunday night. With its 08.00 run, the ECMWF
brought this system quite a bit southwest, bringing snow into the
MPX area. With the 08.12 runs, we saw the GFS come southwest with
the ECMWF, while the ECMWF drifted a little north from it`s
previous run. The result, is the 08.12 ECMWF/GFS are in pretty
good agreement on this low drifting southeast along or just south
of I-94, with a good burst of snow coming down just to the north
of the low track. QPF amounts are forecast to be possibly as high
as a quarter inch, which would work out to over 4 inches of snow,
which also brings in the chance of needing some headlines, so this
system bears some watching.

After Monday, model spread becomes quite large with exactly where
the through and ridge will setup, so stuck with the blended
forecast from Tuesday on. The one thing about the trough/ridge
placement though is we look to be under the influence more of the
ridge than the trough, hence highs next week largely near normal.
There are lots of small chances for snow as well that will be
refined with time as models typically don`t hone in on forecast
with these systems until you get about 3 days out. After Sunday
night, the next weak clipper looks to come through the region
Wednesday, followed by another for Friday.

After Friday, the GEFS and EPS mean h5 height forecasts both show
the western ridge breaking down and shifting west out into the
north Pacific while the Hudson low heads back to the north of
Hudson Bay. This will keep us in near to above normal
temperatures, though the flow pattern looks to become more
conducive to getting stronger and more moist storm systems to
traverse the upper MS valley as we head into the second half of
December.

&&

.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 631 PM CST Fri Dec 8 2017

Quick-moving clipper system will produce flurries to light snow
mainly along and north of the I-94 corridor, thus including KSTC-
KMSP-KRNH-KEAU as sites which may well experience -SN. Regardless,
ceilings are expected to drop to MVFR levels for all TAF sites.
Visibilities will be subject to -SN, thus the aforementioned 4
sites may see MVFR to potentially brief IFR reductions in
visibility mainly through 04z. The low ceilings are then expected
to remain in place through midnight then gradual improvement is
expected overnight through daybreak to lower-end VFR ceilings.
There is still some uncertainty as to the duration of the lower
clouds but latest models indicate a shorter duration of the MVFR
ceilings so have gone that route. VFR conditions with scattering
out of clouds is expected for tomorrow. Northwest winds may
briefly become gusty behind the upper trough responsible for the
snowfall but winds will settle down to around 10 knots close to
daybreak then gradually back to west by late tomorrow afternoon
and to southwest after dark tomorrow.

KMSP...MVFR ceilings look to persist through this evening with a
gradual improvement overnight through tomorrow. Brief rounds of
-SN may drift over the airfield over the first few hours but only
 MVFR visibility is expected, at worst. Potentially, ceilings
 could drop to under 1700ft but this would be short-lived. NW
 gusty winds are then expected for much of the day tomorrow.

/OUTLOOK FOR KMSP/
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.

&&

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

$$

UPDATE...JPC
SHORT TERM...MPG
LONG TERM...MPG
AVIATION...JPC



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