Area Forecast Discussion
Issued by NWS Duluth, MN

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FXUS63 KDLH 081541
AFDDLH

Area Forecast Discussion
National Weather Service Duluth MN
941 AM CST Fri Dec 8 2017

.UPDATE...
Issued at 941 AM CST Fri Dec 8 2017

Made some minor adjustments to POPs and snowfall amounts, mainly
to increase POPs when snowfall chances will be greatest this
afternoon and to increase snowfall amounts a bit. There remains a
strong consensus across guidance that the large-scale forcing may
result this clipper producing locally higher snowfall amounts
despite the quick-moving nature. Snowfall amounts were raised
across the board, with a broad 1-3 inches expected for northeast
Minnesota and northwest Wisconsin this afternoon/evening. Also
made some adjustments to slightly lower snowfall amounts west of
Lake Mille Lacs including the Brainerd Lakes region where it looks
like less than a half inch is expected.

With the timing of the snowfall today, the heaviest snowfall rates
will fall during or at least in the early parts of the evening
commute hours for the Iron Range, MN Arrowhead and Twin Ports
which could enhance the impacts of this otherwise low-impact and
seasonal clipper. For the Twin Ports the worst of the snowfall
rates will be between 2pm to 5pm. Trends will continue to be
monitoring through today, but there is a possibility a brief
winter weather advisory may be needed for some areas of the
Northland. For the lake effect snow for Iron/Ashland counties late
today/tonight some minor adjustments were made with snowfall
amounts just slightly nudged up, though we continue to have
confidence this will be a solid "advisory"-level snowfall with 1-3
inches of snow this afternoon, then periodic bands of lake effect
snow tonight leading to another 2-4 inches of accumulation.

UPDATE Issued at 547 AM CST Fri Dec 8 2017

Updated for the new 12Z Aviation Discussion below.

&&

.SHORT TERM...(Today through Saturday)
Issued at 303 AM CST Fri Dec 8 2017

A quick moving clipper system will dive southward over the
Northland from Manitoba today, bringing a burst of light snow
across the region. This system is characterized by a decently
strong mid-level shortwave trough, with a lobe of positive
vorticity advection associated with it. Enhanced moisture
advection will also accompany this system, with some decent
isentropic lift in the mid-levels. RAP/NAM/GFS model soundings all
indicate increased, and fairly deep, saturation within the
dendritic snow growth zone. Thaler QG omega progs are indicating a
fairly strong maxima that should translate across the Northland
this afternoon. Due to the transient nature of the clipper, snow
amounts should be limited despite the robustness of the system.
Some light snow could fall over Koochiching and northern St.
Louis counties late this morning as the wave enters from the
north, but the bulk of the snow will fall this afternoon.
Generally, the forecast continues total snow between 1 to 3
inches across the region. While amounts should be light in nature,
there could still be some slick spots on area roads, especially
for the afternoon commute.

The main concern then turns to lake effect snow along the Lake
Superior snowbelt once the clipper departs late this evening. We
will remain underneath northerly mid-level flow, and cold air
advection will increase overnight. This, coupled with 1000-850 mb
layer winds turning northerly, will increase the lake effect snow
potential. 850 mb layer temperatures will drop between 15 to 20
degree below zero range, so delta-Ts will be very favorable for
lake enhancement. Snow rates will increase this evening,
especially over Iron and Ashland counties in northwest Wisconsin,
and continue through Saturday morning. New snow amounts in these
counties could range between 3 to 7 inches, with perhaps even
higher amounts along the Gogebic Range. The Winter Weather
Advisory remains in effect for Ashland and Iron counties through
Saturday morning. The lake effect should inevitably diminish
Saturday afternoon as drier air moves into the region.
Temperatures will remain chilly today and Saturday, with highs in
the teens and lower 20s, with lows tonight in the single digits
above zero, with perhaps some below zero temperatures over the
Minnesota Arrowhead.

.LONG TERM...(Saturday night through Thursday)
Issued at 258 AM CST Fri Dec 8 2017

Light snow is possible Sunday night and early Monday, but
otherwise there is no sign of any significant snow this week. The
Northland will see a brief return of milder weather early in the
period, but another cold air outbreak is expected early this
upcoming week. The rest of the week will see temperatures near or
below normal.

A weak Canadian Clipper will pass through Ontario and Great Lakes
region Saturday night and Sunday. It will only bring some very light
lake effect snow showers to the South Shore in northern Wisconsin
Sunday. Sunday`s temperatures will be somewhat mild in comparison to
our recent cold weather. Another, more significant Canadian Clipper
will move into the Canadian Prairies and then US Northern Plains
Sunday night and early Monday, and then pass through the southern
Great Lakes later Monday and Monday night. Its passage will bring
light snow to the Northland, with widespread snowfall around 1 to 2
inches. Much colder air will return in its wake, and the northerly
flow Monday into Tuesday could produce lingering light lake effect
snow showers for the South Shore.

An area of high pressure will pass through the Northland Tuesday
afternoon and night, but then another passing weak Clipper will
bring more light snow to the Northland Wednesday. Expect cold
northerly flow into Thursday.

&&

.AVIATION...(For the 12Z TAFS through 12Z Saturday morning)
Issued at 547 AM CST Fri Dec 8 2017

Expect widespread MVFR conditions through much of the period, with
a little break for some areas later this morning and early
afternoon. Snow will spread south through the region this
afternoon and early evening, bringing a period of IFR/MVFR
visibility. Gusty northerly winds will develop in the wake of this
passing Clipper system. There will likely be a transition back to
VFR later tonight.


&&

.PRELIMINARY POINT TEMPS/POPS...
DLH  20   6  15  11 / 100  50   0   0
INL  16   0  13  10 / 100  10  10  10
BRD  24  11  20  16 /  60  30   0   0
HYR  22   9  16   9 / 100 100  10   0
ASX  22  12  17  12 / 100 100  30  10

&&

.DLH WATCHES/WARNINGS/ADVISORIES...
WI...Winter Weather Advisory from 3 PM this afternoon to noon CST
     Saturday for WIZ003-004.

MN...None.
LS...Small Craft Advisory from 10 PM this evening to 10 AM CST
     Saturday for LSZ121-146>148.

&&

$$

UPDATE...JJM
SHORT TERM...JTS
LONG TERM...Grochocinski
AVIATION...Grochocinski



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