Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 160920

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
320 AM CST Sat Dec 16 2017

.SHORT TERM...(Today and tonight)
Issued at 320 AM CST Sat Dec 16 2017

A weak surface low will slide more or less down the MN River this
morning from west central into south central MN, following a
stationary boundary. The temperature gradient across MN was quite
impressive this morning thanks to that boundary, with temperatures
ranging from near 40 in the warm sector over southwest MN, while a
few stations up in the Boundary Waters have dropped to between 15
and 20 below zero as they are under the influence high pressure
centered to the southwest of Hudson Bay. This baroclinic zone
between the Pacific airmass to the southwest and continental polar
airmass to the northeast has resulted in ample cloud cover across
most of the area, along with a band of light snow from Aitkin down
toward Sheboygan, WI. This snow is diminishing rapidly as the low
shifts southeast and the temepratures gradient and associated
fgen diminish. We may see some light snow linger out toward
Ladysmith into the afternoon, but after sunrise, no additional
accumulations are anticipated.

Main issue really for today into tonight is what will happen with
the stratus. Overnight, we will see a surface ridge axis setup over
the MPX area. We have ample low level moisture out there, which
probably means we are heading toward stratus becoming widespread
again this afternoon into tonight as this moisture becomes trapped
under a subsidence inversion, so you probably shouldn`t count on
there being much in the way of clearing through Saturday night.

For temperatures, we will continue to see the cold airmass get
shunted northeast of the area. However, the cloud cover will keep
diurnal trends in check today. Still based on what we saw yesterday
with this airmass, its looking pretty likely that we will see
temperatures push up into the low 40s along the I-90 corridor. Lows
tonight will be dependent on cloud cover. If we hold extensive cloud
cover through the night, then another night of teens and 20s for
lows is what we`ll see. If we are able to work any clearings in
though, we will likely see places make a run for zero. At this
juncture, playing the cloud route, with confidence on development
and subsequent placement on any clearings being too low to stray
from a model mean for lows tonight.

.LONG TERM...(Sunday through Friday)
Issued at 320 AM CST Sat Dec 16 2017

The biggest question in the long term forecast is centered around
the degree of northern and southern stream phasing, and the impact
that will have on the snowfall potential in the Wednesday to
Thursday time frame.

In the meantime, weak ridging will lead to mild temperatures and
dry weather on Sunday. Temperatures will average around 5 to 10
degrees above normal, generally ranging from the low to mid 30s.
Even warmer highs in the mid 30s to lower 40s are expected on
Monday as southerly flow develops ahead of a weak trough
extending south from northern Manitoba. Associated shortwave
energy could generate light snow (or rain-snow) as far south as
central MN/WI on Monday afternoon and night, but the majority of
the area is expected to stay dry.

Tuesday will be a tad cooler with brisk northwest flow ensuing in
the wake of the trough, although temperatures will still be in
the 30s for highs.

And that brings us to Wednesday, when the forecast becomes a bit
more complicated. The difficulty arises with models resolving the
degree of phasing of streams. The 16.00z solutions trended toward
less phasing, and more of a split flow pattern. This would make
for a healthy snow across the northern half of MN/WI, but wouldn`t
yield much snow for areas south of I-94, other than possibly a
cosmetic touch-up. Will of course continue to monitor trends with
this system, but as of this morning a warning-worthy event looks
less likely for the bulk of the forecast area.

For Friday into the holiday weekend we then look to take a turn
toward frigid temperatures. By Saturday morning, both GFS and
ECMWF 925-850mb temps are unanimously in the -18C to -20C range.
That would likely translate to highs in the teens for Saturday,
with a surge of even colder air looking to arrive by Christmas.


.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 1034 PM CST Fri Dec 15 2017

The fairly wide band of light-moderate snow has shown signs of
shrinking through the evening hours as it as been sliding
southeast across MN and WI. This trend is expected to slowly
continue through the early morning hours but the most persistent
-SN will occur mainly over the WI TAF sites. Ceilings will
 generally run in the MVFR range for all terminals, with KAXN most
 susceptible to IFR ceiling into the early morning hours.
 Visibilities will generally run in the VFR range but isolated
 heavier bursts of snow may well produce brief bouts of IFR
 visibility. Once the main swath of snow diminishes during the
 early morning hours, scattered flurries and snow showers will
 persist mainly over the eastern MN and western WI through

KMSP...Steady -SN has shifted east of MSP in the last couple hours
with only flurries and/or snow showers expected through daybreak.
Ceilings are expected to drop back into MVFR range during the
pre-dawn hours and remain in MVFR range through tomorrow evening.
A period of ceilings sub-1700ft may potentially develop during
the evening push tomorrow but isn`t expected to be long-lasting.

Sun...Mainly VFR. Chc morning MVFR. Wind variable 5 kts or less.
Mon...VFR. Wind SW 10 kts.
Tue...VFR. Wind NW 10-15 kts.




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