Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 161727
AFDMPX

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
1127 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 18Z TAFS through 18Z Sunday afternoon)
Issued at 1125 AM CST Sat Dec 16 2017

Enhanced daytime satellite imagery from the new GOES-East has low
clouds/fog across the Twin Cities metro area, but more patchy for
areas south/southwest toward the Minnesota River Valley. However,
based on satellite trends, low clouds/fog will continue to spread
westward across east central-south central Minnesota by the late
afternoon/early evening. Otherwise, the rest of central/southern
Minnesota should see a period of VFR or MVFR cigs during the
afternoon before more IFR cigs develop as a strong inversion
develops overnight. West central Wisconsin will likely see another
period of MVFR/VFR conditions this afternoon, but the IFR cigs
should begin to spread back across the region by late
afternoon/early evening. Confidence is average for this afternoon,
but much lower tonight/Sunday as the strong inversion develops and
traps the boundary layer moisture over the region. Winds will be
light from the east/southeast, and become more west/southwest
Sunday.

KMSP...

As discussed before, low end MVFR will likely continue this
afternoon before cigs begin to lower once again this evening.
Confidence is low on when this cigs redevelop and how long they
stay. Winds will be light from the northeast/east through most of
the period.

/OUTLOOK FOR KMSP/

Sun...Possibly BCMG VFR in aftn. Wind variable 5 kts or less.
Mon...VFR. Wind SW 10-15G25 kts.
Tue...VFR. Wind NW 20-25G35 kts.

&&

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

$$

SHORT TERM...MPG
LONG TERM...LS
AVIATION...JLT



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