Area Forecast Discussion
Issued by NWS Duluth, MN

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316
FXUS63 KDLH 200535
AFDDLH

Area Forecast Discussion
National Weather Service Duluth MN
1235 AM CDT Thu Apr 20 2017

.SHORT TERM...(This evening through Thursday)
Issued at 341 PM CDT Wed Apr 19 2017

Upper level ridging was covering a majority of the forecast area at
19Z/2pm. At the surface, ridging was nosing down western Lake
Superior and covered the region. A northeasterly flow was occurring
over the lake and was affecting the rest of the area. This resulted
in precipitable water values of less than one half inch which is
fairly dry. Even though low clouds were initially streaming off of
Lake Superior into northwest Wisconsin and near the Twin Ports. Most
of this cloud cover has eroded, although surface observations
indicate some still exists underneath an expanding, thickening
cirrus shield. This dry air was impeding the expanse/arrival of the
anticipated rain. Have adjusted pops for the rest of the afternoon.

Tonight and Thursday finds the forecast area affected by a fairly
strong surface low. This low is forecast to move through Iowa into
southern Wisconsin tonight, and into lower Michigan Thursday. The
rain will slowly spread across the southern half of the forecast
area in the evening, and northward overnight. Cold air will begin to
be pulled into the higher terrain areas of Lake and Cook counties,
and into the Twin Ports by late evening. The rain will begin to mix
with snow. As the night progresses, the colder air will push
westward and the snow will begin to mix in with the rain. There will
be a few hours of all snow over northeast Minnesota. Some slushy
accumulations are expected up the north shore. The coldest air at
850mb will swing over the region Thursday morning keeping the
rain/snow mix going, especially over northwest Wisconisn into the
afternoon. Diurnal heating will offset snow amounts by Thursday
afternoon. The precipitation ends from west to east late in the
day.

.LONG TERM...(Thursday night through Wednesday)
Issued at 341 PM CDT Wed Apr 19 2017

Wintry mixed precipitation will taper off over the Arrowhead and
northwest Wisconsin Thursday evening, but another chance of mixed
precipitation arrives Sunday night through Tuesday morning.

Surface low pressure will continue to lift away from the Northland
Thursday evening. A wintry mix of rain, snow, and slight chance of
freezing rain will continue through the evening, with only a slight
chance of precip lingering over Ashland and Iron Counties after
midnight. High pressure builds in quickly behind the departing low
with clearing skies expected. Very dry conditions are expected
Friday afternoon and again Saturday afternoon with minimum RH values
in the 25-35% range are expected both days. Wind speeds of 5 to 10
mph on Friday and 5 to 15 mph on Saturday will accompany the dry
conditions, helping to limit the wildfire danger. Temperatures will
top out in the low 50s to low 60s on Friday and middle 50s to middle
60s on Saturday. A cool front will dive south into northern
Minnesota Saturday afternoon, which will keep the fire danger lower
over those areas.

Main attention then shifts to the Sunday night through Tuesday
timeframe. A compact trough of low pressure and associated areas of
cyclonic vorticity advection will result in falling heights and
forcing for ascent as they move out of the Rockies and into northern
Plains by Monday afternoon. Isentropic upglide will develop north of
a warm front with increasing cloud cover and precipitation chances
by late Sunday night. The surface low will lift from western South
Dakota and the Nebraska Panhandle east-northeast through central
Wisconsin and into Upper Michigan by noon Tuesday. This storm track
places the Northland in the best deformation zone with the highest
potential for accumulating snow. As of this afternoon, deterministic
guidance is in good agreement on many of the details and confidence
is higher than average for a system more than 4 days out.
Accumulating snow appears most likely over northern Minnesota,
including the Arrowhead, but a rain/snow mix is favored for much of
the Northland. Given the thermal profiles and precipitation rates,
the location and timing of the snow will be refined through the
weekend. In addition to the precipitation, a tightening pressure
gradient over western Lake Superior will yield increasing northeast
winds and building waves early next week.

&&

.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 1227 AM CDT Thu Apr 20 2017

A low pressure system will move from Iowa late this evening will
move into southern Wisconsin by 12Z Thursday, continuing northeast
during day. IFR and MVFR ceilings will be widespread over the the
southern half of the Northland including KHIB/KHYR/KDLH along with
areas of precipitation. A mix of rain and snow will be possible,
mainly impacting KDLH/KHIB/KBRD and possibly to KINL. The
visibility will drop to 1 to 2 miles in snow at times.

In addition to the precipitation the low will produce strong
winds, especially around Lake Superior.

The precipitation will diminish in coverage/intensity from west
to east through the day lingering longest over the Arrowhead south
into northern Wisconsin.

&&

.PRELIMINARY POINT TEMPS/POPS...
DLH  32  40  32  55 / 100 100  20   0
INL  35  52  32  59 /  30  30  10   0
BRD  36  47  34  60 /  90  80  10   0
HYR  37  40  32  57 /  90  90  30   0
ASX  36  38  32  55 / 100 100  40   0

&&

.DLH WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
LS...Small Craft Advisory until 4 AM CDT early this morning for
     LSZ140>147.

     Gale Warning from 4 AM early this morning to 4 PM CDT this
     afternoon for LSZ140>147.

     Small Craft Advisory until 10 PM CDT this evening for LSZ121-148.

&&

$$

SHORT TERM...GSF
LONG TERM...Huyck
AVIATION...Melde/CLC



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