Area Forecast Discussion
Issued by NWS Duluth, MN

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137
FXUS63 KDLH 052338
AFDDLH

Area Forecast Discussion
National Weather Service Duluth MN
538 PM CST Thu Dec 5 2019

.SHORT TERM...(This evening through Friday night)
Issued at 455 PM CST Thu Dec 5 2019

The short-term forecast period will be bookended by a couple of
clipper systems that will bring some light snow to portions of the
region, mainly along our northern areas.

The current clipper system moving through the region this afternoon
will eventually move out by this evening, with some additional snow
expected over the Minnesota Arrowhead region south along the South
Shore of Lake Superior. This clipper was driven by a subtle
shortwave trough aloft and some 850-700 mb layer frontogenetical
forcing. Any additional accumulations should range between a half
inch up to around 2 inches. This snow could result in some slick
road conditions at times. There was some thought to include freezing
drizzle mixed with the snow, particularly over northern Wisconsin
for this afternoon and evening, but decided to go with all snow for
now as the model soundings indicate that while there could be some
ice loss aloft, the saturated layer in the low-levels appears to be
just too shallow to support freezing drizzle. There certainly is a
marginal possibility for freezing drizzle, but confidence is too low
to add it in the forecast for now. Strong cold air advection will
move in overnight, with 850 mb temperatures in the -9 to -13 degrees
C range. The models are indicating that this will support at least
some lingering lake effect snow showers over the Lake Superior
snowbelt region overnight. Overnight temperatures should become
quite cold tonight, with lows in the single digits above zero over
northeast Minnesota, with single digit and lower teens over
northwest Wisconsin where some lingering cloud cover will help
maintain relatively warmer temperatures.

High pressure will build into the region Friday, leading to dry
conditions with partly to mostly sunny skies for a time. However,
this respite from cloud cover will be short-lived, as increasing
clouds are expected Friday afternoon ahead of the next clipper
system that will bring another round of light snow Friday evening.
There are some differences among the guidance on the location of the
axis of the snow, as the NAM model is a bit farther south than the
GFS, ECMWF, and GEM models. I leaned towards the latter three models
due to the better agreement. In all, another 1 to 2 inches of snow
will be possible, generally north of Highway 2 in northeast
Minnesota.

.LONG TERM...(Saturday through Thursday)
Issued at 455 PM CST Thu Dec 5 2019

Saturday through Sunday a potent low pressure system moves
through the area, bringing some precipitation chances to the area.
On Saturday the models bring a wedge of warm air in here aloft,
with high temperatures at the surface getting into the upper 20s
to mid 30s, and 850mb temps zero to 5 above. This warm air
advection in combination with the warm front that surges up into
Canada is likely to produce a wintry mixture of freezing
rain/drizzle or snow Saturday night and early Saturday. For now it
appears we may manage to miss the worst of it, with the
precipitation up into Canada during the day, then precipitation
not working it`s way back into the area until after the cold air
surges back in from the northwest on Sunday. However, there is
still a lot of uncertainty with this event with significant
differences in the thermal profiles. For now, am anticipating that
Saturday afternoon and night we may get a period of freezing fog
and drizzle in the warm air advection, which then turns to snow as
the cold front moves through the area Saturday night and Sunday.

Sunday night and Monday appears to be interesting as a strong
upper level trough and vort max move across the area, interacting
with the low level front to bring a period of snow to the area.
The models are really struggling with the track of this storm as
previous runs were farther southeast, but the 12z runs have pulled
back to the northwest. We are probably too far out for the models
to have a good handle on this storm, but it does look like it has
the potential to produce an area of 6 or more inches of snow
somewhere in our region. The GEFS plumes have a pretty large
spread as well, so confidence in getting any heavier snowfall
amounts is low at this time. Once this moves through the area, the
models are showing a period of very cold temperatures, with a pool
of 850mb temperatures of -15 or colder that settles over the area
starting Monday night and continuing through Wednesday. Analog and
ensemble data have been showing these cold temperatures for a few
runs now, so it is no surprise to see that the Analog data now
shows a high probability of temperatures of 10 below zero or
colder overnight, probably Tuesday night and Wednesday night. We
may be looking at our first Wind Chill Advisory of the season in
this time range if the current indications work out. Temperatures
moderate through the end of the work week, but it still appears
colder than normal.

&&

.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 538 PM CST Thu Dec 5 2019

A weak area of low pressure will continue to move southeast away
from the region and will be replaced by high pressure. Light snow
continued over northeast Minnesota into northern Wisconsin but
that will come to an end tonight. The exception will be along
portions of the South Shore which may see snow showers continue
overnight due to northerly winds across the lake. Model consensus
is that the stratus over the Northland will decrease overnight.
For this evenings forecast, we did delay transitioning
broken/overcast MVFR ceilings to scattered by 2 to 4 hours.
However, this may need to be delayed further but we`ll keep an eye
on satellite imagery and observations through the evening. A
period of gusty northwest winds will develop this evening as the
gradient tightens between the departing low and incoming high.

&&

.MARINE...
Issued at 455 PM CST Thu Dec 5 2019

Light snow is affecting the lake this afternoon with northeast
winds of 5 to 10 knots with waves of less than 2 feet. Tonight
winds will turn to the northwest and increase to 10 to 15 knots,
and waves may push up into the 2 to 4 foot range along the south
shore, but should stay below Small Craft Advisory criteria. Wind
speeds and waves diminish again for Friday. Friday night winds
turn to the southwest and start building waves along the North
Shore, where a Small Craft Advisory may be needed late Friday
night and Saturday morning.

&&

.PRELIMINARY POINT TEMPS/POPS...
DLH   7  19  13  28 /   0   0  30  10
INL   4  19  15  28 /   0  20  50  10
BRD   5  21  14  31 /   0   0  10   0
HYR  10  21  13  32 /  10   0  10   0
ASX  13  23  16  32 /  20   0  20   0

&&

.DLH WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
LS...None.
&&

$$

SHORT TERM...LE
LONG TERM...JTS
AVIATION...Melde
MARINE...LE



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