Area Forecast Discussion
Issued by NWS Twin Cities, MN

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157
FXUS63 KMPX 232330
AFDMPX

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
530 PM CST Mon Jan 23 2017

.SHORT TERM...(This evening through Tuesday)
Issued at 416 PM CST Mon Jan 23 2017

Forecast concerns on the short term are on the impending winter
storm to impact southern Minnesota and west-central Wisconsin
Tuesday afternoon into Wednesday. Overnight, continued patchy fog
and general gloominess will continue with lows in the mid-upper 20s
areawide. The upper-Midwest gets in on the incredibly active weather
pattern across the continent as a deep trough that brought drought
busting rains to southern California this weekend spins up a classic
Colorado Low. Model consensus has been increasing in the track of
this low, with the 12Z NAM & GFS solutions moving a little further
south and more in line with the ECMWF which has handled the
evolution of this event well. Current thinking is snowfall will
begin across SW Minnesota late Tuesday morning and spread east
through the afternoon. Juicy PW values of 0.5-0.6 will be near the
climatological maximum for late January and surface temperatures
slightly above freezing suggest snowfall ratios of only 8-9:1. This
will be a heavy, wet snow so roads will especially messy and
shoveling driveways and sidewalks will be extra-strenuous. Well-
defined 850-500 mb frontogenesis and even some slightly negative epv
all suggest that this will be a band-driven snowfall event with a
tight gradient in snowfall amounts. Snowfall will be heaviest
tuesday evening coinciding with the heaviest forcing, with snow
tapering off after sunrise and moving east of the area by Wednesday
afternoon.

The trend towards a more southern track in both the deterministic
models and ensemble spread suggests this band will setup along the I-
90 corridor, where 8-10" is forecast and a Winter Storm warning is
in effect from Tuesday afternoon into Wednesday evening. There is
still some possibility in this heaviest snow band being displaced
further north and a Winter Storm Watch is in effect along and south
of a Canby to Eau Claire line to account for this uncertainty.
Further complicating the forecast is the location of the snowfall
gradient right over the Twin Cities Metro, with 3-4" expected around
Anoka to near 7" possible across the far south metro. Continue to
monitor our forecasts for the latest on snowfall totals and
potential upgrades to the Winter Storm Watch.

As snow tapers off Wednesday with the low departing to the east,
gusty northerly winds will develop in its wake with gusts up to 25
mph possible across southwest MN. As a result, areas of blowing and
drifting snow will develop, especially in rural areas.

.LONG TERM...(Tuesday night through Monday)
Issued at 416 PM CST Mon Jan 23 2017

The extended forecast is mainly dry with perhaps a few snow showers
over the weekend. Temperatures will continue near or slightly above
the seasonal average. No significant storms are expected between now
and early next week.

Early afternoon water vapor imagery with GFS 500mb heights and winds
showed a long wave positive trough over the western CONUS. This
trough will bring our storm system for Tuesday/Wednesday, but then
an upstream upper level ridge will break across Canada leading to
subsidence and high pressure over the Upper Midwest which will
arrive late Sunday.

A few light snow showers will precede this area of high pressure.
Forecast soundings show overcast skies through the rest of the week
so not anticipating much sun this week. However the overcast skies
will keep daily high temperatures in the mid to upper 20s.

&&

.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 530 PM CST Mon Jan 23 2017

MVFR/IFR ceilings at the TAF sites are trapped under a surface
ridge that will be with us into early Tuesday. Hence, the ceilings
are not going anywhere and will likely drop some overnight. BR
will also likely become widespread again tonight, especially for
KRNH and KEAU. Adjusted the start time on the SN for KRWF and
KMSP on Tuesday. Latest short term guidance is slower with the
onset for KRWF around 20z and KMSP at 23z. Visibilities will
deteriorate rather quickly once the snow starts with 1/2 to 3/4sm
likely within an hour or two. Near calm winds overnight becoming
light easterly on Tuesday and then NE 10-15 knots late in the
day/evening.

KMSP...Low MVFR ceilings through the night and Tuesday. There is a
small threat for ceilings under 010 Tuesday morning between 11z
and 15z. Snow expected to arrive by 23z and persist into Wednesday
morning before ending by afternoon. The period of heaviest snow
with rates of 3/4" per hour is most likely from 25/02z-06z.

/OUTLOOK FOR KMSP/
Tue night...IFR. SN. NE wind 10 to 15 kt.
Wed...IFR. SN early. MVFR late. NE wind 10-20G25 kts bcmg NW.
Thu...MVFR. Chc -SN. NW wind 10 to 20 kt.

&&

.MPX WATCHES/WARNINGS/ADVISORIES...
WI...Winter Storm Watch from Tuesday afternoon through Wednesday
     afternoon for WIZ024-026-028.

MN...Winter Storm Watch from Tuesday afternoon through Wednesday
     afternoon for MNZ070-078.

     Winter Storm Watch from Tuesday afternoon through Wednesday
     afternoon for MNZ064-065-067-069-075>077.

     Winter Storm Warning from noon Tuesday to 6 PM CST Wednesday for
     MNZ073-074-082>085-091>093.

&&

$$

SHORT TERM...ETA
LONG TERM...JRB
AVIATION...RAH



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