Area Forecast Discussion
Issued by NWS Duluth, MN

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FXUS63 KDLH 221740 AAA
AFDDLH

Area Forecast Discussion...UPDATED
National Weather Service Duluth MN
1140 AM CST Mon Jan 22 2018

.UPDATE...
Issued at 1140 AM CST Mon Jan 22 2018

Updated forecast to reduce ice accumulation and fine tune the
change over from a freezing drizzle/snow mix to all snow this
afternoon and tonight. Freezing drizzle was reported at DLH and
mixed with snow for the past several hours. Strong wind shear
across the top of the cloud layer should result in increased drop
sizes due to a combination of evaporation and collision/
coalescence (Bergeron) processes. Areas downwind of Lake Superior
where "deeper" convection is occurring seem to favor snow over
freezing drizzle, even with temperatures at the top of the
saturated layer in the -6 to -8 Celsius range. Those temperatures
are evidently cold enough to activate some clay and bacterial ice
nuclei, which has resulted in the snow earlier this morning at
DLH and elsewhere. Convergence over the southwest arm of Lake
Superior and also in the Chequamegon Bay and areas inland is
further enhancing upward vertical motion. Have added a higher
potential for light snow vs freezing drizzle to the southwest of
Chequamegon Bay, based on high-res simulated reflectivity and a
thin stripe of KDLH radar returns in the same area. The convection
is quite shallow and the radar is likely sampling only the very
top of the band. Have high confidence snow vs freezing drizzle is
occurring where the band is located with enhanced snow amounts
expected.

As deeper moisture arrives this afternoon with northward surge of
precipitation from the south, expect seeder/feeder process to
take over from mixing/Bergeron affects of the cloud top
turbulence. As the seeder/feeder process takes over, freezing
drizzle threat will end as snow becomes the dominant precip type.
To the north and west of the snow band, freezing drizzle will
remain possible.

We have lowered ice accumulation amounts with this forecast update
since freezing drizzle rather than freezing rain will be the
dominant icing threat. Ice amounts now range from a light glaze up
to several hundredths of an inch from the I-35 Corridor east
across northwest Wisconsin. The highest ice accumulation will be
found over southern Bayfield, northern Ashland, and northern Iron
Counties.

The forecast was also updated for the latest 18Z Aviation
Discussion below.

&&

.SHORT TERM...(Today through Tuesday)
Issued at 313 AM CST Mon Jan 22 2018

The winter storm system that has been advertised for the last
several days arrives over northwest Wisconsin today, which will
lead to between 6 to 9 inches of new snowfall over our eastern
northwest Wisconsin counties.

For this morning, the main areas of snow will be over Price and
Sawyer counties and points north and west to the Twin Ports. We`ve
had some steady light snow at NWS Duluth for the last several
hours, thanks to a persistent northeast fetch off Lake Superior.
The models have been doing poorly in determining the
precipitation types as the soundings indicate more freezing
drizzle than light snow as there`s not much in the way of ice
production aloft. Moreover, there`s a fairly deep dry layer
between 900-600 mb, with a shallow saturated layer near the
surface, per the latest RAP/NAM model soundings. As the system
approaches, snow should be the dominate p-type, but freezing
drizzle will be possible, especially if ice loss occurs. This
difference in p-types will play a role in the amount of snow
accumulation and ice accretion over northwest Wisconsin. The
latest snowfall forecast for snow amounts will be between 3 to 9
inches southeast of an Ironwood, MI to Spooner, WI line, with the
heaviest snow falling over Price county. With the potential for
freezing drizzle, some higher ice accretion amounts will be
possible this afternoon and evening. Given how snow, instead of
freezing drizzle, is on-going, we are thinking that the ice
accretion amounts will be slightly lower than from the previous
forecast, but still could reach over 0.10" from Cable, WI
northeast towards Ashland and Kimball. The only change to the
Winter Storm Warnings/Winter Weather Advisories was to issue a
Winter Weather Advisory for Bayfield county, keeping all else the
same.

Once the system departs late this evening and overnight, some
light lake enhanced snow should linger over the Lake Superior
snowbelt region from the Bayfield Peninsula southeast towards the
Gogebic Range. Some of the synoptic snow might linger still over
Price county as well. However, amounts should be light, with only
a few tenths of an inch expected in these areas. Otherwise, skies
will decrease from the north as surface high pressure over Hudson
Bay noses into the region, with mid-level ridging to the west.
The best chances of clearing skies will be the north, which should
support some decent radiative cooling as winds decrease. Leaned
towards the colder guidance for overnight lows tonight, with
values ranging from near zero over the BWCAW area, to the low to
middle teens over central Minnesota and northwest Wisconsin.
Tuesday looks to be mostly sunny and dry across the Northland,
with highs in the upper teens to middle 20s. Clouds will be on the
increase from west to east in the afternoon ahead of a mid-level
wave that will translate across the region Tuesday night and
Wednesday morning.

.LONG TERM...(Tuesday night through Sunday)
Issued at 313 AM CST Mon Jan 22 2018

The extended period will feature a couple weak systems that will
bring mainly light chances for precipitation and a warming trend
peaking Friday.

A shortwave will move through the Northland late Tuesday night into
Wednesday evening accompanied by warm air advection. An area of high
pressure will precede this wave and move across northern Ontario.
The high will serve to veer low level winds from east to
southeast Tuesday night then to south to southwest Wednesday
evening. Colder 850MB temperatures, from -12C to -14C, will be
over far western Lake Superior and a chance for lake effect snow
will occur from late Tuesday evening into Wednesday along portions
of the North Shore. Light snow accumulation will be possible.
There will be a chance for light snow over portions of far
northern Minnesota from the shortwave as well with any
accumulation light. An upper level ridge will build over the
Northern Plains into Saskatchewan and Alberta Wednesday night with
increasing warm air advection downstream over the Northland. Dry
conditions are expected Wednesday night into Thursday night. The
upper ridge will continue east during this time passing east of
the area Thursday night. An area of low pressure will move into
the region late Thursday night into Friday passing east Friday
night. High temperatures Wednesday will be in the twenties then
warm into the mid thirties to mid forties on Friday. A chance for
light rain or light snow will occur Friday with mainly chances for
light snow Friday night into Saturday. Most of the forcing with
the low, which will track north of the region, will occur north of
the International Border, so rain/snow accumulation is expected
to be light Friday into Saturday.

High pressure will build over the region next weekend providing most
of the area with dry weather and cooling temperatures. The exception
to the dry weather will be in the snowbelt along Lake Superior`s
south shore which will have a chance for snow showers. High
temperatures are expected to cool into the teens to lower twenties
by Sunday.

&&

.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1140 AM CST Mon Jan 22 2018

Widespread IFR and MVFR conditions across northwest WI and
northeast MN will continue through this evening. A winter storm is
lifting through the Upper Midwest towards the Great Lakes today.
This storm will spread snow and low visibilities into parts of
northwest WI, including KHYR, but most of the Northland will
avoid the snow. KDLH saw some light freezing drizzle this morning,
and there is a low chance of more of it this afternoon. Do not
have enough confidence in it to carry it any longer in the
forecast.

Drier air will filter into the region tonight, bringing the return
to VFR conditions to most areas overnight or by later Tuesday
morning.


&&

.PRELIMINARY POINT TEMPS/POPS...
DLH  26   9  22  10 /  30  20   0  10
INL  24  -1  17   4 /  10   0  10  10
BRD  29  12  24  13 /  10  10  10  10
HYR  30  15  25   8 /  80  70   0  10
ASX  29  17  23   9 /  70  70  10  10

&&

.DLH WATCHES/WARNINGS/ADVISORIES...
WI...Winter Storm Warning until midnight CST tonight for WIZ003-004-
     008-009.

     Winter Weather Advisory until midnight CST tonight for WIZ001-
     002-006-007.

MN...None.
LS...None.
&&

$$

UPDATE...Huyck
SHORT TERM...JTS
LONG TERM...Melde
AVIATION...Grochocinski


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