Area Forecast Discussion
Issued by NWS Duluth, MN

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FXUS63 KDLH 181201
AFDDLH

Area Forecast Discussion
National Weather Service Duluth MN
601 AM CST Mon Dec 18 2017

.SHORT TERM...(Today through Tuesday)
Issued at 300 AM CST Mon Dec 18 2017

Mild today ahead of a cold front which will bring light snow to much
of the Northland, perhaps mixing with rain at times. Windy Tuesday
with mostly sunny skies for parts of east-central MN and northwest
Wisconsin with temperatures remaining on the mild side.

On the synoptic scale a generally zonal flow aloft across the
Northern Plains and Upper Midwest, though a tightening gradient as
an upper low deepens and descends upon northern Manitoba and far
northwest Ontario today into tomorrow. At low levels an elevated
warm front will briefly build into the Northland today from west to
east before a cold front overtakes it from the north. As warmer air
advects in at low levels, highs will rise to the mid 30s across much
of the Northland, though with at least a few inches of snow on the
ground across the region, the warmer air over the snow pack will
lead to patchy fog through the day. As a cold front and associated
low-level shortwave trough approach from the northwest this
afternoon broad-scale lift will result in a broad area of light
precipitation. Precip should be mainly in the form of snow, but some
drizzle/rain is possible at times given the near-freezing surface
temperatures. Decent lift through the snow growth zone combined with
low levels already being saturated could produce some larger
snowflakes as dendrites collide and aggregate. This could have the
effect of producing slightly more snowfall, so forecast snowfall
amounts for today were raised slightly. Now around 1 to 3 inches are
expected, still generally limited to around the Iron Range and
points north in northern Minnesota. The most intense snowfall rates
will occur during the afternoon/evening commute time along and east
of Highway 53 north of the Iron Range. Some light snow possible for
the Twin Ports in the evening hours, but less than an inch is
expected. Breezy southwest winds at times with a few gusts to around
20-25 mph.

Overnight a brief period of lake enhanced snow showers are possible
for the south shore as colder air advects into the region and low
level winds turn more northwesterly. The window of time will be
brief between when winds turn northwesterly and the drier air moves
in aloft. Low level wind directions would also support the brief
development of the north shore gravity wave, which could cause a
band of snow to impact the Bayfield Peninsula for a period
overnight. Up to an inch of snow is possible for parts of the south
shore due to these local effects, with snowfall possibly lingering
into the Tuesday morning hours. Otherwise mostly cloudy with lows in
the mid 20s and northwest winds remaining breezy at 10 to 15 mph.

On Tuesday skies will be mostly to partly sunny with the possibility
for strato/alto cumulus clouds to bubble up in the afternoon as deep
low level mixing leads to windy conditions. Northwest winds will be
15 to 20 mph with gusts of 30 to 40 mph. Otherwise mild with
temperatures above normal, in the mid 20s to low 30s.

.LONG TERM...(Tuesday night through Sunday)
Issued at 300 AM CST Mon Dec 18 2017

An active extended period is in store across the region with a
period of snow Wednesday and Wednesday night with a winter storm
passing through the region bringing another chance for accumulating
snow to portions of the Northland Thursday into Friday. There will
be lake effect snow as well Wednesday night into the weekend,
including portions of the North Shore, Twin Ports, and South Shore
into Friday shifting to just the South Shore over the weekend. Very
cold air is also still expected to arrive Saturday and continue into
next week.

Increasing warm air advection will cause snow to develop across
portions of the Northland Wednesday, mainly in the afternoon. The
snow will spread across most of the Northland Wednesday night. Low
level winds will become easterly on Wednesday and will lead to
higher snowfall along the North Shore into the Twin Ports due to
lake processes. The snow will become light or end late Wednesday
night into Thursday morning for most areas with the exception at the
head of Lake Superior which will see east/northeast low level winds
continue. Inversion levels are forecast to be around 3000FT or less
which should limit snow intensity. At this time, we expect snowfall
totals from 1 to 2 inches for most areas Wednesday afternoon into
Wednesday night, with higher amounts along the North Shore.

An upper trough will move onto the western CONUS coast late Tuesday
into Tuesday night, then continue into the Northern Rockies to Great
Basin region by 12Z Thursday. Surface low pressure will develop in
response with an extension of the low well north of the center into
the Northland on Thursday. The surface low will move toward the
Nebraska/Missouri/Kansas border by early Thursday evening, then
track toward southern Wisconsin or southern Lake Michigan Friday
afternoon. Snow is expected to develop Thursday and continue into
Friday. Chances will be highest over northwest Wisconsin into far
east central to northeast Minnesota. Lake processes will be ongoing
through this time as well complicating the snowfall forecast. We
expect the highest snowfall totals over northwest Wisconsin with
little snowfall from this second round from Walker to Ely on north.
Confidence is increasing that at least several inches will occur
over northwest Wisconsin, possibly as far west as Mcgregor, the Twin
Ports north toward Silver Bay. This storm is still several days away
so adjustments in the track will likely occur which will alter
expected snowfall amounts. Also, shifts in the low level winds will
have a big impact on which areas see lake enhanced snowfall.

As the low pulls away from the region Friday into Friday night, the
snow will diminish for most areas. Lake effect snow will continue to
be possible along the South Shore with more accumulation possible.
Colder air will be moving into the region Friday behind the low with
a big push of much colder air coming in on Saturday into Sunday. The
GFS has returned to a solution that has a low pressure system in the
vicinity of the Northland Christmas Eve Day into Christmas Day but
the ECMWF shows no sign of the low. Confidence in which solution
ends up being correct is low. The GFS would suggest some light snow
accumulation possible over portions of the Northland Christmas
Eve/Christmas versus a drier ECMWF. Highs Wednesday are expected
from the 10 to 15 along the International Border to around 20 in
northwest Wisconsin. Highs will warm a few degrees Thursday and
Friday then cool over the weekend. By Sunday, highs will only reach
the single digits below zero over far northern Minnesota to the
single digits above over southern areas of the Northland. Even
colder temperatures are expected Christmas Day into next week and
much of the region may see highs remain below zero.

&&

.AVIATION...(For the 12Z TAFS through 12Z Tuesday morning)
Issued at 601 AM CST Mon Dec 18 2017

A trough of low pressure and warm air advection will lead to light
snow today, mainly over far northern Minnesota this afternoon and
evening. Much of the Northland will remain under MVFR or IFR
ceilings but there will be areas of VFR. The VFR conditions are
most likely over western areas and this morning. KBRD is expected
to remain VFR through most of the period. An improvement to VFR is
expected over more areas late tonight as the trough passes and
winds turn to west to northwest. MVFR conditions will remain
through the period over far northern Minnesota.

&&

.PRELIMINARY POINT TEMPS/POPS...
DLH  33  23  28   7 /  50  50   0   0
INL  33  22  24   0 /  80  70  20   0
BRD  35  23  30  12 /  10  20   0  10
HYR  34  25  32  10 /  20  30   0   0
ASX  35  26  32  12 /  30  50  10  10

&&

.DLH WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
LS...Small Craft Advisory until 10 PM CST Tuesday for LSZ140>143-146-
     147.

     Small Craft Advisory from 10 AM this morning to 10 PM CST
     Tuesday for LSZ121-144-145-148.

&&

$$

SHORT TERM...JJM
LONG TERM...Melde
AVIATION...Melde



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