Area Forecast Discussion
Issued by NWS Duluth, MN

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FXUS63 KDLH 251931
AFDDLH

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

.UPDATE...
Issued at 231 PM CDT Tue Apr 25 2017

The forecast was updated through Wednesday, focusing on the threat
of freezing rain and icing. A surge of warm and humid air aloft
from the south tonight and Wednesday will combine with cold
surface air in Canada, which will be flowing out of Ontario
overnight. This will be a recipe for a complex scenario of rain
transitioning to periods of freezing rain, sleet, and snow tonight
and Wednesday. Confidence has increased in the freezing rain
threat, especially for the eastern Arrowhead, where icing
accumulations could reach three quarters of an inch, enough to be
considered an ice storm. Overall, the amount of precipitation has
shifted east compared to the previous forecast, which lessened
the freezing rain threat for some areas. The exception was the
eastern Arrowhead, including for the Grand Portage and Grand
Marais areas, where the icing was generally increased compared to
the previous forecast. There is still some uncertainty in the
icing threat considering the complex situation and dependency on
temperatures aloft as well as surface temperatures. Some model
disagreements add to the mixture of uncertainty, with the overall
cooler GFS suggesting more snow and sleet compared to the NAM
(which has warmer air aloft than the GFS to more suggest freezing
rain). Another consideration is the relatively warm road
temperatures, which will take some time to cool enough to support
glazing on the roads. The greater threat of any icing is likely to
trees, which could be brought down onto power lines by gusty
northerly winds tonight and Wednesday provided the trees get heavy
enough from the icing. Expect a more thorough discussion soon.

UPDATE Issued at 1249 PM CDT Tue Apr 25 2017

Please see the 18Z Aviation Discussion below.

&&

.SHORT TERM...(Today through Wednesday)
Issued at 431 AM CDT Tue Apr 25 2017

Confidence continues to increase in a possible winter storm
affecting portions of the region. Surface low pressure over the
Oklahoma Panhandle this morning will lift northeast to northern
Ontario by Wednesday evening. A wintry mix of rain, freezing rain,
sleet, and snow is likely over much of the Northland beginning
tonight. An inverted trough was located over north-central
Minnesota this morning with rain showers affecting much of the
Northland. The trough is expected to slide slowly eastward
shifting the focus for showers northeastward through this morning.
Most locations should experience a break in precipitation before
the next round moves in this afternoon and tonight. The surface
low is forecast to move from southwest Iowa and northwest Missouri
to northeast Iowa and southwest Wisconsin overnight. A nose of
warm air aloft will lift northward across Wisconsin and into the
Arrowhead. Southerly cold air advection near the surface will
lower temperatures below freezing beginning in the high terrain
along the North Shore and spreading across the remainder of the
Arrowhead and west to the Iron Range tonight. Temperatures will
dip below freezing near the Twin Ports and Cloquet eastward
through the high terrain of the South Shore by sunrise Wednesday
morning. Much of the Arrowhead has the potential for more than
one-quarter inch of ice accumulation, with lesser amounts expected
farther west and south. However, given continued variability in
the guidance solutions, the axis of heaviest freezing rain may
shift farther west or south with later updates. Have issued a
Winter Storm Watch for the areas most likely to see significant
ice accumulation. Should the warm nose be less intense than
forecast, much of that freezing rain would fall as sleet or snow
with significant snow accumulation possible. In either case,
difficult travel is expected tonight through Wednesday and
continuing into Thursday. Ice and snow amounts will be lower over
north-central and central Minnesota and our southern tier of
Wisconsin counties. Winter Weather Advisories may be needed later
today on the periphery of the watch.

.LONG TERM...(Wednesday night through Monday)
Issued at 431 AM CDT Tue Apr 25 2017

The late April storm will continue to affect the Northland
Wednesday night and Thursday, before gradually moving out of the
area during the latter portion of the work week. Freezing rain,
sleet, and snow will continue to be possible Wednesday night and
early Thursday. Given the wintry mix, travel could continue to be
hampered Wednesday night and Thursday. High pressure will build
into the Northland on Thursday and Friday, from west to east. This
area of high pressure should bring mainly dry conditions from
Friday into Saturday, but another major storm system is looking
more likely starting on Sunday. A major longwave trough is
expected to move out of the Rockies on Saturday, before ejecting
northeastward into the western Great Lakes on Sunday. Rain is
expected to move quickly into the Upper Midwest on Sunday, and
then change over to snow across portions of the region by Sunday
night. Some freezing rain or sleet will also be possible,
potentially hampering travel plans for the end of the weekend and
early in the upcoming work week. The ECMWF and GFS have come into
much better agreement concerning this storm system, although the
GFS is a bit further to the west and not as deep as the ECMWF. The
ECMWF is also a bit warmer than the GFS, adding further
complexity to expected precipitation types during this period.
While it is still way too early to determine any possible snow or
ice accumulations, this system definitely bears watching, as the
ECMWF drops the central pressure of this system to 980 mb.
Temperatures throughout the period will be highly variable, with
the warmest temperatures expected late in the week and into the
weekend. Still, temperatures are expected to be below normal.

&&

.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 4 PM CDT Wednesday for
     LSZ121-146>148.

     Gale Warning from 7 PM this evening to 10 AM CDT Wednesday for
     LSZ140>145.

&&

$$

UPDATE...Grochocinski
SHORT TERM...Huyck
LONG TERM...DAP
AVIATION...WL



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