Area Forecast Discussion
Issued by NWS Duluth, MN

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FXUS63 KDLH 182346 AAA

Area Forecast Discussion...UPDATED
National Weather Service Duluth MN
646 PM CDT Mon Sep 18 2017

.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 00Z TAFS through 00Z Tuesday evening)
Issued at 642 PM CDT Mon Sep 18 2017

Mainly MVFR ceilings will be seen overnight with cigs from 2k to
3k feet and possibly going below 1k at the MN TAF sites. Winds
will be under 5 kts overnight and the moist airmass could result
in some fog, also. By midday Tuesday the fog will have lifted
abd clouds should be VFR. By then, the southeast winds will have
picked up quite a bit and gusts to 25 kts are expected the
remainder of the TAF period, or til 00Z.


DLH  52  63  59  69 /  30  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




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