Area Forecast Discussion
Issued by NWS Duluth, MN

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FXUS63 KDLH 042106
AFDDLH

Area Forecast Discussion
National Weather Service Duluth MN
306 PM CST Sun Dec 4 2016

.SHORT TERM...(This evening through Monday)
Issued at 306 PM CST Sun Dec 4 2016

The focus remains on the snow moving through the Northland this
afternoon with the deep low pressure trough lifting through the
region. Earlier this morning, we had increased snowfall amounts
across parts of the Northland after reviewing the latest higher
resolution model guidance, seeing snowfall reports come in with
higher amounts than anticipated, and seeing a period of decent
dendritic growth here in Duluth. The most significant increases
to the snowfall forecast were made for areas from Duluth up the
North Shore, which prompted expanding our earlier winter winter
advisory for the Shore of Cook County down to include the Shore of
Lake County and even the Duluth area. The advisories are in effect
through 6 pm and 9 pm, with the latter time for Cook County. The
snow is continuing to fall along the North Shore, so will
definitely maintain the current advisories for the Shore. As for
Duluth, while there has been a break in the snow, additional bands
of snow are approaching from the west and southwest, which should
bring additional light snow through early this evening. Therefore,
will maintain the advisory for Duluth, too.

The axis of a deep low pressure trough, extending from west
central Manitoba to at least eastern Missouri, will lift through
the Upper Midwest and Great Lakes through the rest of today and
into early Monday. Its synoptic lift, combined with relatively
deep moisture ahead of the trough, will continue to result in
light to moderate snowfall rates across northeast Minnesota and
parts of northwest Wisconsin today and this evening, with the snow
gradually spreading and exiting to the north and east. There will
be widespread snowfall totals, including what fell earlier today,
of 1 to 3 inches across the Northland. The greatest amounts, of
about 3 to 6 inches, will be along the higher terrain of the
Minnesota North Shore, from the eastern outskirts of Duluth to
Grand Portage. This is because of a few factors, including the
moisture lake enhancement from the strong southerly flow over
western Lake Superior, the orographic lift up the higher terrain,
and the good potential dendritic growth because of good vertical
motion within the secondary key thermal layer for dendritic growth
near -2 to -5 degrees Celsius.

The snow will gradually shift north and east later this afternoon
and evening, exiting and tapering off for the Northland. A warmer
air mass will filter into the Northland from the south and
southwest, in the wake of the passing trough. Some clearing of the
skies across the west and south, as well as the fresh snowpack and
light winds, will likely let temperatures to drop to the middle
20s.

The surge of warmer air from the south late tonight and Monday
will likely result in low-level stratus moving into the region.
The soundings are showing a decent inversion by late tonight with
low-level saturation. Some models, such as the HRRR experimental,
are suggesting this will result in fog. Not convinced yet if this
stratus layer will dramatically reduce visibility, but will need
to reevaluate the threat of fog later on. It is certainly possible
if warm enough air overrides the snowpack and results in some
melting of the snowpack and help the boundary layer saturate. If
the skies clear better tonight, then the radiational cooling could
strengthen that inversion and provide a better setup for fog.

A not-so-stacked low will move through the North Dakota region
Monday, likely resulting in light snow across parts of the
Northland, especially northern Minnesota, Monday afternoon.
Temperatures in the lower and middle 30s, though, will limit
accumulation to little amounts until the evening.

.LONG TERM...(Monday night through Sunday)
Issued at 306 PM CST Sun Dec 4 2016

The long-term period will begin with another mid-level shortwave
trough associated with a broad swath of positive vorticity
advection evident in all of the synoptic scale models. A strong
push of a 700- 500 mb layer deformation zone sets up along the
leeward side of the trough. The 04.12z synoptic models have taken
the sfc low pressure center slightly southeast compared to
yesterday`s corresponding runs, but overall uncertainty still
exists on the exact track of the low, but the overall agreement is
to bring the center of the low across North Dakota, and into
southern Manitoba and southwest Ontario, Canada Tuesday morning.
The models are bringing the sfc low pressure over Canada, which
should place the Northland within the cyclonic flow aloft. There
are some questions based on the model QPF as to where exactly an
precipitation that develops will be. The GFS is once again more
bullish than the NAM/ECMWF models. Generally, those in the
furthest north counties will be more likely to see precipitation.
At this time, accumulations look to be steady, but light, with
about a few tenths of an inch of snow expected every six hours. Of
course, this is depending on the low track, so we will keep an eye
on the latest guidance.

This light snow looks to continue through the day Wednesday as
another quick pulse of energy sweeps south through the area. The
low will eventually take its leave late Tuesday, which will result
in veering sfc winds from west to a more northwesterly direction.
This will set up cold air advection on the backside of the low.
Temperatures look to plummet from Wednesday through Friday as 925
mb temperatures drop between -8 and -13 degrees C across the
forecast area on Wednesday, to as low as -19 degrees C Friday
morning in the GFS. Lows during this period will drop into the
teens and single digits during this time, as highs stay in the mid
to upper teens. Wind chill values are likely to drop into the
single digits, above and below freezing, the mornings of Thursday
through Saturday.

Chances of light snow showers will linger through Friday as we
stay within the cyclonic flow. The northwest flow will help to
support some lake enhanced snow in the Snowbelt region of
northwest Wisconsin. I bumped up the PoPs a little bit in Ashland
and Iron counties in Wisconsin to account for the lake
enhancement. This should begin to ramp up Thursday morning and
last through the day Friday before tapering off Saturday morning
as sfc high pressure moves in, which will weaken the on-shore
flow. Isentropic lift in the 1000-850 mb layer reaches up to -10
ubar/s Thursday afternoon into Friday morning, when the lake
enhancement will be maximized and PoPs are at their highest. 850
mb temperatures will also be at their lowest at that time, which
will range between -17 and -20 degrees C. Otherwise, most of the
rest of the forecast area should stay dry.

Chances of light snow looks to return Saturday and Sunday as
another mid-level shortwave and 850-700 mb warm air advection
makes its way back into the area. Temperatures look to rebound
slightly but should still stay below freezing.

&&

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 117 PM CST Sun Dec 4 2016

LIFR and IFR ceilings, with some MVFR and isolated IFR vsbys due
to snowfall continues across the TAF sites this afternoon.
Ceilings should continue to be in the 300-1000 foot range. The
main wave causing the snowfall should move out by this evening and
overnight.

Low cigs are expected to continue this evening and overnight,
however, as model soundings are indicating the development of a
low level inversion, which should trap some moisture in the
boundary layer. NAM soundings are looking fairly dry above 3000
feet or so. Winds are expected to veer more from the southwest
overnight but should stay light. Ceiling heights should improve
Monday morning.

&&

.PRELIMINARY POINT TEMPS/POPS...
DLH  27  35  24  25 /  40  30  30  20
INL  25  34  22  23 /  50  50  60  40
BRD  25  35  22  23 /  10  20  20  20
HYR  26  37  26  28 /  20  20  30  20
ASX  29  39  29  30 /  40  20  30  20

&&

.DLH WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...Winter Weather Advisory until 6 PM CST this evening for MNZ020-
     037.

     Winter Weather Advisory until 9 PM CST this evening for MNZ021.

LS...Small Craft Advisory until 10 AM CST Monday for LSZ140.

&&

$$

SHORT TERM...Grochocinski
LONG TERM...JTS
AVIATION...JTS


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