Area Forecast Discussion
Issued by NWS Duluth, MN

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FXUS63 KDLH 070436
AFDDLH

Area Forecast Discussion
National Weather Service Duluth MN
1036 PM CST Fri Dec 6 2019

.UPDATE...
Issued at 1036 PM CST Fri Dec 6 2019

Updated Marine section below.

&&

.SHORT TERM...(This evening through Saturday night)
Issued at 357 PM CST Fri Dec 6 2019

Another day, another clipper system moving through the Northland
this evening, with light accumulating snow possible.

Chances of light accumulating snow will increase this afternoon,
persisting through the evening, as a clipper system passes through
the region. A subtle mid-level shortwave trough and southerly flow
around a departing high pressure ridge axis will lead to increasing
low-level warm air advection, which will support these chances of
snow. Latest SREF and GEFS ensemble guidance depicts a mean QPF
value of at or below 0.06 inches for this evening, which should
yield only some small accumulation amounts. The 06.12z NAM model
soundings indicate the heaviest snowfall should occur from near
Bigfork, MN, southeast to Hibbing and Two Harbors, as the soundings
show more of an enhanced isentropic lift signature within a
saturated dendritic growth zone, so we did increase the snowfall
amounts slightly. We are still looking at snow accumulations of no
more than 1.5 inches, with lighter amounts to the north and south of
this axis of heaviest snowfall. Overnight lows should remain chilly,
with values in the lower to middle teens.

The clipper system will quickly move out of the region no later than
sunrise Saturday, leading to a dry, but mostly cloudy day across the
Northland. Southerly flow will continue Saturday, leading to high
temperatures slightly warmer than average in the upper 20s to lower
30s - warmest to the south. Another mid-level shortwave trough with
an attendant surface low will bring more chances of precipitation
for Saturday night and early Sunday morning. Precipitation types
will be more of a challenge to pin down as a warm nose develops.
This layer of warm air does appear to be unsaturated, with trapped
moisture under a low-level inversion. This should support some
freezing drizzle, which may mix in with snow. Accumulations from
this precipitation should remain quite light, but the freezing
drizzle may result in some slick road conditions in some spots.

.LONG TERM...(Sunday through Friday)
Issued at 357 PM CST Fri Dec 6 2019

The main concern of the long term is the cold temperatures with only
a few chances for snow.

A cold front will work across the Northland Sunday and bring a first
shot of cold Arctic air into the region. Only light snow chances
with perhaps some freezing drizzle are expected through the day as
drier air filters in behind the front. An upper-level longwave
trough will then move into the Northern Plains Sunday night with a
surface low moving from the Central Plains to the Great Lakes by
midday Monday. An inverted trough associated with this low will
move through the region bringing snow for Sunday night and into
Monday. The 06.12 suite of models have nudged this system a bit
further to the north with snow now expected to impact more of the
Northland. Accumulations of 2 to 5 inches are expected roughly along
and south of MN Highway 210 and through much of northwest Wisconsin
with lesser amounts to the north.

Low pressure will become established across Hudson Bay Sunday night
putting the Northland into northwest flow both aloft and at the
surface. This will result in very cold Arctic air flowing into the
region. Lake effect snows will also persist after the synoptic snow
moves out Monday into Tuesday night with the cold air streaming in.
Some accumulations are expected with this snowfall, but amounts
remain in question. Wind variations may move the areas of snowfall
around as well during this period. Additionally, the entire
Northland will see temperatures fall well below normal, resulting in
daytime highs in the single digits below zero for most areas Tuesday
and Wednesday and overnight lows in the teens below zero Wednesday
and Thursday mornings. Dangerous wind chills will also be possible
with these very cold temperatures.

The upper low over Hudson Bay will move east over the latter half of
the week. A clipper system may bring some light snow during the
Wednesday night into Thursday period with models then diverging on
solutions heading into the weekend. A warmup is expected during this
time, however, as surface winds turn more westerly then
southwesterly as the upper low pulls away allowing warm air
advection to set up.

&&

.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 558 PM CST Fri Dec 6 2019

A fast moving shortwave will bring a period of MVFR visibilities
in light snow and deteriorating ceilings. Ceilings will start out
VFR, but then deteriorate to MVFR, which will then linger through
the remainder of the TAF period. KINL, KHIB and KBRD are likely
to drop into IFR as well, but not until well after the snow ends.
Have some concerns for this stratus as models are well known for
overdoing the amount of low level moisture and whether it will
create clouds or not. Would not be surprised to see a few hours of
VFR at the terminals generally between 12z and 18z before the next
period of snow begins to move toward the area and increases the
potential for lower cloud bases.


&&

.MARINE...
Issued at 1036 PM CST Fri Dec 6 2019

Light snow is moving across western Lake Superior this evening,
associated with breezy southwest winds which are gusting in the 15
to 20 knot range. Nearshore waves remain less than 3 feet, but out
in the open waters waves are larger. These winds will diminish
overnight and Saturday morning, but will increase once again for
Saturday afternoon and night. These will cause building waves
along the North Shore, and we may need a Small Craft Advisory for
portions of the North Shore north of Taconite Harbor late tomorrow
and tomorrow night. The South Shore may also need one depending on
wind speeds. Timing and location are still somewhat uncertain.
Winds will diminish and turn northwest on Sunday, allowing waves
to also diminish.

&&

.PRELIMINARY POINT TEMPS/POPS...
DLH  14  29  26  31 /  60  10  30  20
INL  15  29  18  24 /  50  20  30  30
BRD  15  31  26  29 /  10   0  10  20
HYR  14  33  28  34 /  20  10  20  20
ASX  12  32  29  35 /  70  20  20  40

&&

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

$$

UPDATE...LE
SHORT TERM...JTS
LONG TERM...BJH
AVIATION...LE
MARINE...LE


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