Area Forecast Discussion
Issued by NWS Duluth, MN

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257
FXUS63 KDLH 252052
AFDDLH

Area Forecast Discussion
National Weather Service Duluth MN
352 PM CDT Tue Apr 25 2017

.SHORT TERM...(This evening through Wednesday)
Issued at 352 PM CDT Tue Apr 25 2017

Parts of the Minnesota Arrowhead are under an Ice Storm Warning
for tonight and Wednesday, with the threat of substantial tree
damage and power outages. Please read on.

An area of low pressure in the Central Plains, as of this
afternoon, will lift to the Lake Superior region by late Wednesday
afternoon. It will bring a surge of warm and humid air aloft
northward into the Northland, resulting widespread rain by later
this evening. However, cold, sub-freezing air near the surface,
originating from Canada, will work its way into the Northland
overnight and Wednesday. Gusty northerly flow will develop
tonight, of about 10 to 20 mph with gusts of up to 30 mph in some
areas, and temperatures will drop into the 20s and lower 30s for
much of the Northland by Wednesday morning. This complex scenario
is expected to result in a transition from rain this evening to a
wintry mixture of precipitation across the Northland overnight
into Wednesday, with periods of rain, freezing rain, sleet, and
snow. The primary concern is the potential for freezing rain,
followed by sleet, with icing and gusty winds posing a threat to
trees and power lines.

The best potential for freezing rain and icing is in the
Arrowhead, especially closer to the tip of the Arrowhead in Cook
County, where those areas face a full-fledged ice storm.
Widespread icing of a quarter to nearly three quarters of an inch,
combined with gusty northerly winds, will likely result in
substantial tree damage and power outages. Untreated roads will
eventually become difficult, if not impassable, to travel on.
Confidence is relatively high in this forecast for substantial
icing in Cook County. There will be little if any warming
Wednesday, so the iced over trees will remain frozen through the
day.

Other parts of northern Minnesota and northwest Wisconsin are
forecast much lower amounts of icing from freezing rain, but also
some sleet and light snow. Areas around the head of Lake Superior,
including Two Harbors, the Twin Ports, Cloquet, and some inland
areas as far east as Bayfield County, could get up to a couple
tenths of an inch of icing, as well as some sleet accumulation.
This could cause some tree branches to fall with the gusty winds,
and untreated roads could be difficult to travel on Wednesday
morning. Even lighter amounts of freezing rain are forecast for
the Iron Range and areas to its north and west, but there could be
sleet accumulation and up to a few inches of snow to make for
difficult travel conditions. The confidence in the forecast for
these areas is lower, than for the Arrowhead, because of some
model disagreements in the thermal profile aloft and how far north
and west the precipitation will advance into the Northland.

Overall, it looks like the latest model runs have shifted the
total precipitation of this storm system farther east compared to
the models from last night. This resulted in the latest forecast
shifting the total rainfall east and lessening the freezing rain
threat for some areas. The exception was for the eastern
Arrowhead, where the total ice accumulation was increased compared
to the previous forecast. We issued an Ice Storm Warning for the
eastern Arrowhead, as well as flexible Winter Weather Advisories
near the head of Lake Superior and into parts of north-central
Minnesota. We considered having an advisory for areas farther
south, such as into the Brainerd Lakes region, but confidence is
somewhat low on the threat of a wintry mixture of precipitation
for those areas at this point.

The worst conditions of this storm will likely be late tonight
through Wednesday morning. The precipitation will gradually lift
north and east, and exit the Northland, Wednesday afternoon and
evening. Much of northwest Wisconsin will likely see this
precipitation remain mostly rain with the warmer temperatures in
the 30s and lower 40s.

.LONG TERM...(Wednesday night through Tuesday)
Issued at 352 PM CDT Tue Apr 25 2017

Wednesday evening into Thursday a broad area of low pressure will
lift northeastward from the western Great Lakes into Ontario. The
occluded system will continue advecting cold air across northeast
MN and northwest WI. This will gradually change precipitation to
all snow from west to east across eastern MN into northwest WI.
Far northeast MN will remain all snow through Thursday with high
temperatures in the lower 30s. Elsewhere precipitation will
gradually change over to rain as highs warm to the mid 30`s and
low 40`s. Precipitation chances will linger across northern
locations into Friday as the cutoff system rotates across Ontario.

After the system exits, high pressure will build into the Upper
Midwest late Friday night into Saturday as a 500 hPa ridge builds
in from the Northern Plains. This dry period will be short lived
as a longwave trough digs from the Intermountain West on Saturday
into the Central Plains on Sunday. In response to the longwave
trough, a surface low will develop across the Central Plains early
on Sunday and lift northeastward into the Upper Mississippi River
Valley on Monday. This will spread precipitation into the
Northland from the south. The latest GFS/ECMWF and GEM are in good
agreement as with the previous model runs for this system. The
GFS is a bit slower and warmer than the latest ECMWF/GEM. Though
it is still too early to determine specific precipitation types
for this system, a mix of freezing rain/sleet/snow and rain are
possible if the latest guidance holds true late this weekend into
early next week. Those with travel plans on Sunday and Monday
should stay tuned for future updates. Temperatures will fluctuate
through the extended period. The warmest readings will be found on
Saturday with highs ranging from the 40`s along the Lake Superior
Shoreline, to the low 50`s inland. Low temperatures will
generally range from the 20`s to 30`s throughout the Northland.

&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1249 PM CDT Tue Apr 25 2017

An area of low pressure will quickly move northward from the
Central Plains this afternoon into eastern Wisconsin by Wednesday
afternoon. This will move precipitation in from south to north
late this afternoon and evening. Expect VFR/MVFR conditions to
deteriorate to IFR/LIFR tonight and persist until the end of the
TAF period. Expect visibilities to drop to MVFR/IFR as
precipitation spreads in.

The latest GFS/NAM/RAP and DLHWRF forecast soundings show a
change over from rain to sleet or freezing rain then snow at all
northeast MN terminals except for KINL. At KINL precipitation
should remain all snow, however there is a brief period initially
where a wintry mix is possible before changing over to all snow.
As a result, have mentioned a wintry mix at KHIB/KBRD/KDLH.
KHIB/KBRD will see a change over to sleet/snow around 12Z until
the end of the TAF. KDLH may see more in the way of freezing rain
late tonight and Wednesday morning, however confidence was not
high enough at this point to include in the latest TAF set. In
addition to the precipitation, gusty north to northeast winds can
be expected tonight into Wednesday.

&&

.PRELIMINARY POINT TEMPS/POPS...
DLH  31  33  24  34 /  80  90  40  30
INL  26  29  22  34 /  40  70  50  40
BRD  33  36  25  41 /  80  80  30  20
HYR  39  39  28  38 /  90  80  40  30
ASX  35  35  27  37 /  90  90  50  40

&&

.DLH WATCHES/WARNINGS/ADVISORIES...
WI...Winter Weather Advisory from 3 AM to 7 PM CDT Wednesday for
     WIZ001-002.

MN...Winter Weather Advisory from 3 AM to 7 PM CDT Wednesday for
     MNZ037.

     Winter Weather Advisory from 8 PM this evening to 7 PM CDT
     Wednesday for MNZ010-011-018>020-026.

     Ice Storm Warning from 8 PM this evening to 10 PM CDT Wednesday
     for MNZ012-021.

LS...Gale Warning from 7 PM this evening to 10 PM CDT Wednesday for
     LSZ121-140>148.

&&

$$

SHORT TERM...Grochocinski
LONG TERM...WL
AVIATION...WL



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