Area Forecast Discussion
Issued by NWS Duluth, MN

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FXUS63 KDLH 241733

Area Forecast Discussion
National Weather Service Duluth MN
1133 AM CST Sat Feb 24 2018

Issued at 1130 AM CST Sat Feb 24 2018

Updating Aviation section below for the 18Z TAF update. Added a
little more snow to Wisconsin.


.SHORT TERM...(Today through Sunday)
Issued at 425 AM CST Sat Feb 24 2018

The main concern during the short term continues to focus on a
fast-moving winter storm which will affect the Northland late this
afternoon through Sunday morning.

Dense fog has developed over portions of northwest Wisconsin this
morning. While numerous stations have reported very low
visibility early this morning, think we`ll fluctuate between low
stratus and fog through mid-morning. Low lying areas where winds
have decoupled have the best chance of seeing significantly
reduced visibility. In coordination with MPX and ARX, have opted
for a Dense Fog Advisory through 9 AM.

A potent shortwave trough will eject out of the Colorado Rockies
this morning with lee cyclogenesis forecast. A baroclinic leaf was
in its early stages of development from northeast Colorado to
South Dakota as observed in GOES-16 water vapor imagery with
cirrus spreading into western Minnesota. The trough and associated
surface low will quickly lift from Colorado to Wisconsin by
midnight. Deterministic models feature a diverse range of forecast
trajectories for the system with the GFS and ECMWF farthest
southeast, the NAM faster and farthest north, and the GEM between
the GFS/ECMWF and NAM solutions. Snow moving into the Northland is
a foregone conclusion at this point, the main question is timing
and final totals. With the wide spread in the guidance, confidence
in snow amounts and placement is lower than this time yesterday.
A swath of 7 to 10 inches of snow still seems likely, but has
shifted farther east with this forecast. The main axis of the
heaviest snow stretches from the St. Croix Valley north through
Douglas and Bayfield Counties and up the north shore. Onshore
winds with this system should result in locally enhanced snowfall
amounts along the north shore, where up to 12 inches of snow is
possible. The diverse low trajectories have a knock-on effect on
frontogenetic forcing and potential instability. Still think there
will be one or more FGEN bands of snow associated with this
system, but the orientation in relation to the storm movement is
still uncertain. Periods of 1 inch per hour snowfall seem likely.
Additional adjustments to timing and amounts will likely be needed
this afternoon as the system matures. The strongest omega and
dendritic growth layer will both be well aloft during this storm,
with a warmer layer with less supersaturation below. Given the
thermal and moisture profiles, snow ratios between 13 and 16 to 1
seem favored. With lower confidence in the forecast particulars
than yesterday morning, did not make any adjustments to winter
storm headlines.

Snow will quickly wind down as the system moves through northeast
Ontario on Sunday. Skies will clear from southwest to northeast
during the day as high pressure builds in.

.LONG TERM...(Sunday night through Friday)
Issued at 425 AM CST Sat Feb 24 2018

By Sunday evening the surface low will be north of Lake Superior,
pulling away from the region while high pressure builds into the
region. At this point the upper flow pattern becomes more zonal
and will result in a milder period. It will also be a fairly dry
period with some small chances of precipitation later in the week
as a Canadian short wave trough dips into the northern tier of the
U. S. then merges with the southern stream long wave trough.
Resultant precipitation area will mainly be associated with the
southern system, giving mainly southern areas of the forecast area
the precipitation chances. Warm enough air will be coming into
the region on Thursday to give a chance of rain.


.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 1130 AM CST Sat Feb 24 2018

VFR until a fairly substantial system brings heavy snow and LIFR
conditions after 00Z Sun through about 09Z with 1/4SM vsbys and
low ceilings. Wind may cause a little blowing snow as well. The
system moves through the area quickly with a return to MVFR/VFR
late in the TAF period. Fairly confident in onset timing in TAFs.


DLH  29  21  30  14 /  40 100  20   0
INL  30  18  30  13 /  10 100  60  10
BRD  27  17  29  13 /  90 100   0   0
HYR  34  23  32  13 /  60 100  20  10
ASX  32  25  33  18 /  10 100  30  10


WI...Winter Storm Warning from 6 PM this evening to 9 AM CST Sunday
     for WIZ001>004-006>009.

MN...Winter Storm Warning from 9 PM this evening to noon CST Sunday
     for MNZ011-012-019>021-026.

     Winter Weather Advisory from 6 PM this evening to 9 AM CST
     Sunday for MNZ025-033-034.

     Winter Storm Warning from 6 PM this evening to 9 AM CST Sunday
     for MNZ035>038.

     Winter Weather Advisory from 9 PM this evening to noon CST
     Sunday for MNZ010-018.



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