Area Forecast Discussion
Issued by NWS Duluth, MN

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192
FXUS63 KDLH 110539
AFDDLH

Area Forecast Discussion
National Weather Service Duluth MN
1139 PM CST Sun Dec 10 2017

.UPDATE...
Issued at 939 PM CST Sun Dec 10 2017

Light snow occurring in northwest Minnesota and moving east.
Current forecast is now on track.

UPDATE Issued at 710 PM CST Sun Dec 10 2017

Slowed down the arrival of the snow by a few more hours again.
Reflectivities seen on North Dakota radars is just starting to
reach the ground. Made some adjustments based on these trends.

UPDATE Issued at 520 PM CST Sun Dec 10 2017

The system due to affect the forecast area tonight is still in
Canada as of 5pm. A warm front was approaching the Red River
Valley with plenty of mid and high clouds ahead of this system.
Best forcing is still off in the western Dakotas and have delayed
the onset of the snow by a few hours. Rest of the forecast is on
track.

&&

.SHORT TERM...(This evening through Monday)
Issued at 356 PM CST Sun Dec 10 2017

The main concern in the short term is the fast moving clipper that
is forecast to move through tonight and early Monday. We can see
this clipper taking shape over northern Saskatchewan on satellite
imagery, producing precipitation there according to the Canadian
radar network. There is a mixture of rain and snow, and where snow
is falling visibilities of less than a mile have been reported.
The surface low is located near La Ronge, well north of Saskatoon
Canada. A warm front extends southeast from the low to eastern
North Dakota before trailing into southwest Minnesota. This front
to ease to the east somewhat tonight, but not enough to bring
temperatures above freezing as the clipper slides southeast across
the forecast area tonight and early Monday. The warm air advection
wing tonight and trailing wrap around precipitation Monday to
bring a short period of snow to the region between midnight
tonight and noon Monday. The heaviest precipitation to fall in
about a 3 hour period mostly tonight ahead of the surface low
where the frontogenesis band is strongest. This is a fairly potent
clipper, but nothing extraordinary and am expecting a quick 1 to 3
inches of snow laid out across the forecast area. The timing of
the snowfall is going to make the Monday morning commute more
difficult. Most of the snow should be on the ground by 6 AM, which
is likely to produce slippery road conditions. Though not
convenient, thresholds are not quite there for a winter weather
advisory and have held off on that for now and am going to beef up
wording in HWO and the weather story, and will be issuing an SPS
for the snowfall to hopefully raise awareness of this clipper.

.LONG TERM...(Monday night through Sunday)
Issued at 356 PM CST Sun Dec 10 2017

Long term forecast remains on track with several periods of light
snow and cool temperatures.

Meridional flow aloft will continue Monday night. Arctic air
advection and clearing skies and fresh snowpack from Monday`s
clipper should yield low temperatures on either side of zero.
Highs on Tuesday will be cool as well with readings in the single
digits northeast to the low 20s southwest. A shortwave trough is
forecast to dive southeastward out of the Canadian Rockies and
into the Central Plains Tuesday night and Wednesday. While that
trough won`t affect the Northland directly, it will change the
upper flow pattern northwesterly. Deterministic guidance is split
in handling the next shortwave which will affect our area
Wednesday. The GFS is a little faster and stronger with the
trough and associated vort max and brings a swath of 1 to 3
inches of snow to northeast Minnesota and northwest Wisconsin.
The GEM and ECMWF are stronger with the western shortwave and
bring lower snow chances to the Northland. A better chance of
light snow arrives Wednesday night into Thursday. All of the long
range models bring some accumulation to the area. GFS brings the
higher amounts once again with several more inches possible.
Another pattern shift to a progressive mode is indicated late
this week into next weekend. While the details differ between
models, the GFS, ECMWF, and GEM all feature a pattern shift. The
GFS and ECMWF bring an Alberta Clipper through the Northland
Friday night and Saturday while the GEM is weaker and farther
north. Given the timing differences, even between the GFS and
ECMWF, continued the earlier trend of chance POPs Friday and
Saturday. The pattern shift late this week will also bring
slightly warmer temperatures to the region. Look for highs on
Friday in the middle teens northeast to the upper 20s southwest.
Highs on Saturday could reach the freezing mark along over our
southern CWA with middle to upper 20s in the north.

&&

.AVIATION...(For the 06Z TAFS through 06Z Monday night)
Issued at 1139 PM CST Sun Dec 10 2017

Light snow will overspread the terminals through the first few
hours of the forecast. This is in response to a powerful vorticity
maxima moving southeast through ND at the start of the forecast.
A mix of VFR and MVFR cigs initially, with MVFR/IFR cigs and
vsbys in the vicinity of band of moderate snow. The snow will end
from north to south after 12Z as the vort max and its associated
surface low move past the terminals. Gusty winds are expected
behind the surface low along with an improvement to VFR.

&&

.PRELIMINARY POINT TEMPS/POPS...
DLH  10  25  -1  14 / 100  90   0   0
INL   3  19  -6  11 /  90  10   0   0
BRD  19  30   6  21 / 100  30   0  10
HYR   9  29   1  14 / 100  70  10   0
ASX   7  28   7  15 /  90  90  10  20

&&

.DLH WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
LS...Gale Watch from Monday afternoon through Monday evening for
     LSZ121-146>148.

     Small Craft Advisory from 10 AM Monday to 4 AM CST Tuesday for
     LSZ121-145>148.

     Small Craft Advisory from 4 PM Monday to 4 AM CST Tuesday for
     LSZ140>144.

&&

$$

UPDATE...GSF
SHORT TERM...LE
LONG TERM...Huyck
AVIATION...GSF



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