Area Forecast Discussion
Issued by NWS Duluth, MN

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515
FXUS63 KDLH 250044
AFDDLH

Area Forecast Discussion
National Weather Service Duluth MN
744 PM CDT Mon Apr 24 2017

.UPDATE...
Issued at 744 PM CDT Mon Apr 24 2017

A warm front is draped over the southern half of the forecast area
from near BRD to between OLG/HYR in northwest Wisconsin to near
IWD. An area of light rain was falling from Cass county northeast
to northern St. Louis county. This is in an area of FGEN from the
surface to 850mb and a coupled jet structure. Will see this batch
of rain move off to the northeast along with the coupled jets.
This will lead to a decrease in the overall coverage of rain
tonight. Surface temps are well above freezing and will remain
that way overnight, so no longer expecting a mix of precipitation
types. Made some adjustments based on these trends.

&&

.SHORT TERM...(This evening through Tuesday)
Issued at 339 PM CDT Mon Apr 24 2017

Another shot of short wave every being eject out of the broad
western trough has been keeping the northland on the wet side.
Currently the surface low pressure over far western MN has pushed
the cold front back north with the baroclinic zone right across
northern Minnesota, generally along U. S. Highway 2. There was a
large temperature difference with 30s and 40s north of the front
and 60s south of the front. And temperatures were kept in the 30s
along Lake Superior. Strong isentropic light will be bringing more
rain to the region. The rain areas late this afternoon were in
west central to northwest Minnesota in the cold sector with a
batch of rain over southern MN stream north in the warm sector. by
Tuesday morning the low will be entering Wisconsin, while the
bulk of the snow will be north of the low. But, more rain will be
due in late in the after as another section of short wave moves
through along with a cold front. The precipitation will begin as
rain, but cold air will air with the cold frontal passage and a
mix of precipitation types are likely. Read more in the extended
discussion below.

.LONG TERM...(Tuesday night through Monday)
Issued at 339 PM CDT Mon Apr 24 2017

An ice storm is possible across the Minnesota Arrowhead Tuesday
night into Wednesday...with a wintry mix elsewhere likely to cause
slick roads Wednesday. Lingering light precipitation Thursday, then
dry Friday into Saturday before another chance for rain and snow
arrives Sunday. Temperatures remain on the cool side through the
rest of the month - highs in the 30s to low 40s mid-week, warming up
to the 40s to near 50 into the weekend.

On the synoptically scale a longwave mid-level trough over the desert
southwest will eject into the Great Plains and up the Mississippi
River Valley Wednesday into Thursday. A mid-level shortwave trough
embedded within the longwave trough will organize across the
Dakotas late Tuesday into Wednesday, with an associated surface low
deepening across eastern Iowa Tuesday night into northeast Wisconsin
and into the U.P. on Wednesday...eventually merging with a more
broad low stretching from the Great Lakes south to the lower
Mississippi River Valley that develops in response to the
approaching longwave trough.

While model differences at this point are well within typical for
this time range, just minor variations in the track and low level
temperatures means drastically different precipitation types and
impacts. However, a majority of guidance is now supporting a
freezing rain scenario for much of the north shore/MN Arrowhead. As
the low deepens, colder air air will move in from the north at the
surface. However, above the surface around 850mb warmer air will
melt any snow that falls, and thus if temperatures at the surface
fall below freezing, freezing rain would fall resulting in at least
the possibility for significant ice accumulations, especially for
the higher terrain of the north shore that are likely to cool the
fastest. The 850mb low will track from southern Minnesota towards
northwest Wisconsin Tuesday night, and as it does warm air advection
to the north and northwest of the low will result in moderate
precipitation rates overnight, with a half inch to as much as an
inch of liquid-equivalent precipitation. With the possibility for
even a short period of freezing rain in some locations, there is the
potential for a messy if not dangerous Wednesday morning commute for
some communities. Confidence in precipitation occurring is very high,
but confidence on precipitation type and any resulting snow/ice
accumulation is low at this time. Thus, we will hold off on any kind
of watch at this point. However, a significant ice storm with a
quarter to half inch of ice is a possibly scenario for much of the
Minnesota Arrowhead. For the Twin Ports and other portions of
northern Minnesota more of a wintry mix is expected with a mess of
rain, sleet, freezing rain, and snow possible. In northwest
Wisconsin this main initial round of precipitation should remain all
rain Tuesday night through the day on Wednesday.

As the low exits to the northeast during the afternoon Wednesday the
entire column will finally cool down, though at this point drier air
will also be working in at upper levels which would result in a lack
of ice aloft and thus more of a drizzle/freezing drizzle scenario
lingering into Thursday. However, the light precip rate Wednesday
night into Thursday could add up to a tenth or so of additional ice
for areas of the MN Arrowhead and portions of northwest Wisconsin.

Mainly dry Friday into Saturday as guidance has trended towards a
more southerly storm track, keeping the active weather pattern just
to our south for a short time. Winds out of the north and partly to
mostly cloudy skies will lead to cooler conditions persisting.

Late Saturday into Sunday another longwave trough over the Four
Corners region ejects into the Great Plains and Midwest. However,
this storm takes a track farther east, with the best chances for
light rain/snow across northwest Wisconsin. Light snowfall
accumulations are possible.

&&

.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 635 PM CDT Mon Apr 24 2017

VFR at the start of the forecast. An area of showers was moving
through the BRD/INL terminals and was in the vicinity of HIB at
the outset. With strong warm air advection underway, will see
these showers persist in the vicinity of INL/HIB/BRD/DLH until
near 06Z before subsiding. Next round of precipitation arrives by
late afternoon from near HYR to DLH and BRD. Ceilings will remain
VFR until the arrival of the precipitation and then drop into the
MVFR range with some isolated IFR.


&&

.PRELIMINARY POINT TEMPS/POPS...
DLH  36  54  31  33 /  50  70  90  70
INL  33  40  25  34 /  90  20  60  60
BRD  39  52  33  40 /  40  60  90  60
HYR  47  63  37  41 /  40  80 100  70
ASX  43  61  34  36 /  30  70  90  80

&&

.DLH WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
LS...Small Craft Advisory until 10 PM CDT this evening for LSZ121-
     146>148.

     Small Craft Advisory until 4 AM CDT Tuesday for LSZ144-145.

     Small Craft Advisory until 9 AM CDT Tuesday for LSZ140>143.

&&

$$

UPDATE...GSF
SHORT TERM...CLC
LONG TERM...JJM
AVIATION...GSF



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