Area Forecast Discussion
Issued by NWS Duluth, MN

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503
FXUS63 KDLH 190545 AAC
AFDDLH

Area Forecast Discussion...UPDATED
National Weather Service Duluth MN
1245 AM CDT Tue Sep 19 2017

.UPDATE...
Issued at 1245 AM CDT Tue Sep 19 2017

Update for new 06Z Aviation Discussion below.

UPDATE Issued at 1023 PM CDT Mon Sep 18 2017

Low stratus has returned to most of the Northland this evening.
Don`t expect to see any improvement overnight, but will be some
time tomorrow before the sun can get high enough to overturn the
atmosphere and break up the clouds.

&&

.SHORT TERM...(This evening through Tuesday)
Issued at 249 PM CDT Mon Sep 18 2017

Mostly cloudy with light to moderate rain ending in northwest
Wisconsin this evening, and while the large-scale forcing for the
precipitation will exit to the northeast, low level clouds will
advect in from the south late today into tonight resulting in
mainly cloudy skies continuing through much of Tuesday. A warm
sector will advect north across the Upper Midwest on Tuesday which
will lead to warmer temperatures, and there should be some breaks
in the clouds by the afternoon with southeast winds increasing.

On the synoptic scale an upper low will deepen over the Canadian
Rockies early to mid week while some mid-level shortwave riding
develops ahead of this upper low across the Upper Midwest Tuesday,
amplifying and moving northeast into Ontario towards mid-week. At
mid to upper levels the broad flow will become southwesterly in
response to these synoptic-scale features. At the surface an
elongated area of low pressure will develop stretching from
southern Alberta into the western Dakota by Tuesday afternoon,
with a resulting southerly flow pattern across the eastern Dakotas
and Minnesota. This southerly flow will result in low level
warmth and moisture being advected into the Upper Mississippi
River Valley through Tuesday.

Tonight light southeast winds combined with increasing low level
clouds advecting from the south may result in drizzle across
portions of the north shore; otherwise mainly cloudy with lows in
the upper 40s to low 50s.

Tuesday will start off mainly cloudy but the sunshine should be
strong enough to break through the stratus in the afternoon. Deep
mixing will promote increasing south-southeast winds with gusts up
to 30 mph in parts of north-central Minnesota. Highs in the 70s,
except in the 60s along the north shore due to winds off the lake.

.LONG TERM...(Tuesday night through Monday)
Issued at 249 PM CDT Mon Sep 18 2017

An active weather pattern looks to develop for the extended
period, with the potential for strong to severe storms Tuesday
night and Wednesday morning, along with temperatures that are
forecast above normal to well above normal.

The overall pattern for the long-term period generally shows a
broad mid- to upper-level low that develops over the Pacific
Northwest/British Columbia/Alberta region, placing the Northland
underneath strong southwesterly flow aloft. This looks to enhanced
isentropic upglide over the region, providing lift for an active
weather pattern. For Tuesday night and Wednesday, a cold front
boundary will translate eastward over the region, coupled with a
shortwave trough. Strong southerly flow will be supported by a 50
to 60 kt low-level jet as well. There is the potential for strong
to severe storms, mainly Tuesday night/Wednesday morning as an
unseasonably strong instability axis develops over western
Minnesota. MLCAPE values from the 18.12z GFS/NAM range between
1000 to 2000 J/kg, with deep layer shear of 35 to 45 kts. SPC has
a large chunk of the Northland in a Marginal Risk of severe
weather, along with a Slight Risk over Cass and Crow Wing
counties, mainly for large hail and damaging winds.

High pressure will then build briefly across the region late
Wednesday into Thursday, providing a respite from precipitation.
Mostly clear skies Thursday morning will lead to a cool night due
to radiational cooling. Bumped down the low temperatures Thursday
morning a bit to better capture this. Lows Thursday morning could
range from the lower to middle 40s north to the upper 40s to near
50 south. Warm, moist air will return to the region during the day
Thursday, and especially for Friday, where high temperatures
could reach into the upper 70s and lower 80s for much of the
Northland.

The warm frontal zone resulting from the return flow will persist
over the region, placing us within the warm sector of an
approaching low pressure system. The baroclinic zone will continue
over the region from Friday night through the weekend, which
could support the threat for flash flooding. Pwat values of 1.5"
to 1.9" are progged by the 18.12z GFS, which is in the >99% of
climatology, per the NAEFS analysis. This threat of flooding will
need to be watched in subsequent forecasts.

&&

.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 1245 AM CDT Tue Sep 19 2017

Conditions will be mainly MVFR/IFR through the night with CIGS
below ovc010 from KHIB to KDLH and KBRD. CIGS will be hier to the
far north at KINL and the far south at KHYR. Clouds will have a
hard time breaking up tomorrow, so CIGS will likely rise to MVFR
by afternoon. Winds will get very strong tomorrow afternoon with
gusts to 30 kts. There will be wind shear in the evening with
strong winds 1500 to 2000 off the surface of at least 40 kts.

&&

.PRELIMINARY POINT TEMPS/POPS...
DLH  52  63  59  69 /  20  10  70  50
INL  49  68  58  68 /  10   0  80  40
BRD  53  71  59  69 /  10   0  80  20
HYR  53  73  62  73 /  40   0  50  40
ASX  51  70  59  74 /  30   0  50  30

&&

.DLH WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
LS...None.
&&

$$

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



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