Area Forecast Discussion
Issued by NWS Duluth, MN

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244
FXUS63 KDLH 022120
AFDDLH

Area Forecast Discussion
National Weather Service Duluth MN
320 PM CST Fri Dec 2 2016

.SHORT TERM...(This evening through Saturday)
Issued at 320 PM CST Fri Dec 2 2016

The Northland`s light northwest flow will continue into tonight,
especially aloft, while the axis of a subtle ridge of high
pressure shifts into Northland from the west. Ample cloud cover
upstream in Canada is giving good confidence the current overcast
cloud cover will continue overnight, as suggested by the HRRR,
local WRF, and 4 km NAM. The cloud cover will bolster the
overnight temperatures, despite the very light winds speeds later
tonight that tend to favor good radiational cooling, so refrained
from the colder model guidance. Leaned on a blend with lows
ranging from the middle 20s over northwest Wisconsin and low 20s
across northeast Minnesota.

There are low chances of very light snow and patchy freezing
drizzle across small portions of the South Shore, mainly along
west/north side of the Bayfield Peninsula, due to the cold flow
over Lake Superior.

Light, southerly return flow will develop Saturday in the wake of
the passing ridge of high pressure. There should be lingering
broken/overcast low-level cloud cover. Highs should reach the
upper 20s to near 30 degrees.

.LONG TERM...(Saturday night through Friday)
Issued at 320 PM CST Fri Dec 2 2016

A shot of snow showers is possible Saturday night and Sunday
morning as a sharp shortwave trough and associated maximum of
positive vorticity advection will move through the forecast area.
Enhanced low- level convergence will also help to provide the lift
to support snow, which should stay fairly light, with
accumulations between 1-2 inches. Most of the snow will fall
Sunday morning between 12-18z. Bumped up PoPs to categorical along
our southern most tier of counties as the mid-level isentropic
lift is maximized in this area. QPF signals in the synoptic models
also appear to be maximized in this area. Chances of snow will
tapper off Sunday evening and overnight as the shortwave
translates to the east.

Monday morning looks to be dry at this point as the 850-500 mb
layer dries up, according to the GFS/NAM model soundings. A low-
level inversion does develop during this time, which will keep the
low levels fairly moist. A sfc low pressure system then moves in
from the west. There is some uncertainty at this point regarding
chances of precipitation from this system as the GFS is lingering
some measurable precipitation from Tuesday through Thursday, while
the ECMWF has the low pivoting north, keeping the moisture further
north. The CMC model seems to be in better agreement with the
ECMWF, so I lowered the PoPs to better match what the guidance is
leaning towards. After this initial wave moves through, cold air
advection plows into the region. Models indicating 925 mb
temperatures aloft as low as -17 degrees C. This should support
temperatures near or below seasonal averages, with lows in the
teens and single digits Thursday through Saturday.

Tuesday night through Wednesday looks to be mostly dry before
another wave sweeps through from the north. This wave looks to
keep a slight chance of snow around through Friday morning before
moving out Friday evening, except for the Lake Superior snowbelt.
GFS soundings indicate some saturation in the dendritic growth
zone, along with steepening low level lapse rates, so expanded the
pops from what the consensus blends were giving.

&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 1138 AM CST Fri Dec 2 2016

The primary concern for the rest of the today and tonight will be
MVFR cigs, with some isolated IFR cigs, across the TAF sites.
Ceiling heights between 1-2 kft will be common during this period.
Northwest winds look to stay fairly light through the forecast
period, with some veering in the winds by Saturday morning as
surface high pressure ridging moves through the region.

&&

.PRELIMINARY POINT TEMPS/POPS...
DLH  25  29  24  33 /  10  10  40  50
INL  23  28  23  33 /  10  10  30  50
BRD  22  29  27  35 /  10  10  40  40
HYR  25  31  24  35 /  10  10  30  70
ASX  29  33  25  36 /  10  10  30  50

&&

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

$$

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



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