Area Forecast Discussion
Issued by NWS Duluth, MN

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FXUS63 KDLH 092104
AFDDLH

Area Forecast Discussion
National Weather Service Duluth MN
304 PM CST Mon Jan 9 2017

.SHORT TERM...(This evening through Tuesday)
Issued at 304 PM CST Mon Jan 9 2017

Two rounds of snow through the short-term period as temperatures
warm up to near-normal. Today a broad warm front lifting northeast
into the upper Midwest will result in a period of light to moderate
snowfall through the evening, with orographic lift leading to
locally higher totals along the north shore. A break in the snow
late tonight, then another quick round of moderate to potentially
heavy snowfall Tuesday morning as a low matures over the mid-
Mississippi River Valley and a cold front moves from west to east
across the Northland. After a brief warmup today into tomorrow
morning, temperatures take a tumble Tuesday afternoon as another
refreshing arctic airmass builds in behind the front.

This afternoon into tonight...Radar returns and surface observations
have not been especially impressive with common visibility in the
around a mile as the broad area of snowfall moves across the region
associated with warm air advection. Still looking at around 1-3"
snowfall this afternoon into the evening, with southwest winds and
increasing low level moisture late this afternoon into the evening
aiding in higher totals across northwest Wisconsin and the Minnesota
Arrowhead. Low level winds will be favorable for lake and orographic
enhancement of snowfall across the north shore where snowfall is
expected to linger on through much of the night. At around -10 to
-12C, 850mb temps are somewhat marginal for true lake effect with
lake surface water temps around +2 to +4 C, but we`ve seen this type
of pattern produce locally higher snow amounts due to orographic
lift along the steeper terrain of the north shore. For most
locations outside of the north shore, snow should come to an end or
at least diminish in intensity after midnight. Temperatures will not
fall too much, remaining steady in the teens - above zero!

Tuesday...Guidance is coming into very good agreement for a period
of moderate to heavy snowfall Tuesday morning across much of the
Northland. On the synoptic scale, a mid-level shortwave trough
ejects out of the central Rockies into the Great Plains late
tonight, lifting east across the Mississippi River Valley Tuesday. A
resultant surface low will begin to deepen from near Iowa Tuesday
morning into northeast Wisconsin Tuesday afternoon. The evolution of
this rapidly deepening low will lead to very strong broad-scale
lift, with Thaler-QG computed Omega values around -20 mb/hr across
all global guidance, which is fairly strong. With plenty of low-
level moisture already in place, this rapidly deepening low will
likely lead to a period of moderate to heavy snowfall, with broad
lift through the column per model soundings. With the dendritic
growth layer fairly elevated around 600mb, this scenario may lead to
very large flakes as dendrites form large aggregates on their way
down. Guidance is in remarkable agreement for the large-scale
forcing and the resulting QPF output, though think there is more
uncertainty than guidance spread would allow to be believed because
the cold air rushing in from the west mid-day will lead to drying of
upper and mid levels, putting an end to the heaviest snowfall rates.
Still, another 2-4" for northwest Wisconsin and the Minnesota
Arrowhead, with 1-2" for the rest of the northern Minnesota.

Gusty winds in the wake of the low could lead to blowing and
drifting snow on Tuesday afternoon with west-northwest winds gusting
to near 30 mph. Highs Tuesday in the mid teens to mid 20s in
northeast Minnesota and as warm as 30 in northwest Wisconsin.
However, these temperatures will occur early in the day, with
temperatures falling in the afternoon as colder air moves in from
the west.

.LONG TERM...(Tuesday night through Monday)
Issued at 304 PM CST Mon Jan 9 2017

Tuesday night will have chances of light snow winding down as sfc
low pressure moves off to the east. The models are progging a very
brief respite from precipitation late Tuesday/early Wednesday
morning before another 500 mb shortwave trough translates through
the region. The 09.12z NAM/GFS are both showing some good isentropic
lift associated with this shortwave, along with some decent 850-700
mb layer frontogenetical forcing. The soundings from these models
are in a little bit of disagreement regarding the adequacy of
saturation in the dendritic growth zone. The GFS is a bit more
bullish on this compared to the NAM. The models don`t agree on how
far south the positive vorticity advection energy reaches as the GFS
is bringing it farther south than the NAM. However, the 09.18z NAM
is coming into more alignment with the 09.12z GFS. It`s not clear
how quickly this precipitation will move out of the region as the
NAM lingers snow across NW WI Wednesday afternoon, while the GFS and
ECMWF has it pretty well out of the forecast area. The consensus
blend chance PoPs are leaning more towards the GFS/ECMWF solutions,
so will keep them in the forecast for now.

Thursday morning should be dry as sfc high pressure moves in. There
may be some snow showers Thursday developing across the area as a
push of low-level warm air advection grazes the northern sections of
the forecast area, but confidence is not very high at this time.
There might be some lake enhanced snowfall over the Bayfield
Peninsula down to the Gogebic range Thursday evening through Friday
afternoon as 1000-850 mb mean layer winds become more northwesterly
as the warm air advection passes. These two bouts of precipitation
aren`t expected to amount to much in terms of accumulation as both
the GEFS and SREF ensemble plumes are showing only 1 to 2 inches of
new snow for the Duluth area through Thursday, with a bit more
possible in the Bayfield Peninsula due to the lake enhancement.

Thursday morning, and especially Friday morning, are showing a
return to bitterly cold temperatures. The models are progging 925 mb
temperatures to drop as low as the upper teens and lower 20s below
zero Thursday morning, and into the lower to mid 20s below zero
Friday morning. Sfc high pressure will also translate through the
region Friday morning, causing skies to clear, enhancing radiational
cooling. This will allow temperatures to drop into the single digits
and teens below zero Thursday morning, and into the teens and 20s
below zero Friday morning. This is forecast drop wind chill values
into the Wind Chill Advisory levels, and possibly Wind Chill Warning
criteria Friday morning.

A return to more seasonal temperatures are forecast for Saturday and
Sunday as the sfc high pressure moves off to the east, and winds
become more southerly. Some locations next Monday may even reach 30
degrees F.


&&

.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1138 AM CST Mon Jan 9 2017

Mainly MVFR conditions expected early this afternoon, with ceiling
heights between 1-2 kft. The next storm system will then move
through the region this afternoon and evening, which will support
light to moderate snowfall and IFR conditions, including reduced
visibilities down to 1SM at times. There should be a brief break
in the precipitation overnight before another round moves in
Tuesday morning, which will once again bring some reduced
visibilities.


&&

.PRELIMINARY POINT TEMPS/POPS...
DLH  15  22  -2   7 / 100  90  30  50
INL   7  14  -7   0 / 100  80  40  20
BRD  14  18  -4   7 /  50  60  40  40
HYR  19  28   1  12 / 100  90  20  50
ASX  18  29   4  13 / 100  90  20  50

&&

.DLH WATCHES/WARNINGS/ADVISORIES...
WI...Winter Weather Advisory until 3 PM CST Tuesday for WIZ001>004-
     008-009.

MN...Winter Weather Advisory until 3 PM CST Tuesday for MNZ012-020.

     Winter Storm Warning until 3 PM CST Tuesday for MNZ021.

LS...Small Craft Advisory from 2 PM Tuesday to 4 AM CST Wednesday for
     LSZ121-140>148.

&&

$$

SHORT TERM...JJM
LONG TERM...JTS
AVIATION...JTS



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