Area Forecast Discussion
Issued by NWS Duluth, MN

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263
FXUS63 KDLH 191152 AAA
AFDDLH

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

.UPDATE...
Issued at 652 AM CDT Tue Sep 19 2017

Update for new 12Z Aviation Discussion below.

&&

.SHORT TERM...(Today through Wednesday)
Issued at 349 AM CDT Tue Sep 19 2017

High pressure was over Quebec at 08Z with a ridge axis into the
forecast area. A light easterly flow off of Lake Superior was
helping to produce some patchy drizzle and fog from the Twin
Ports/Cloquet area and along the North Shore. Some patchy fog was
noted elsewhere. This ridge axis should affect the forecast area
through the day. Meanwhile, a surface low center was located in
southeast Montana at 08Z. A warm front extended in a easterly
direction from this low and into southwest Minnesota. The surface
low will become elongated through the day with the main low center
appearing to be in western Nebraska by 00Z Wednesday. Another low
was located over eastern Saskatchewan. An occluded frontal
boundary connected these two lows and will be the focus for storm
development. The warm front appears to remain over southern
Minnesota through the day. With the forecast area ahead of these
lows and the departing ridging, will see plenty of moisture advect
into the region with warm air advection. Showers and storms
should hold off through the day, but see plenty of clouds.

A pair of vigorous short waves will eject eastward from a closed
low over the Canadian Rockies tonight. The first one, which is
weaker than the second, reaches the western edge of the forecast
area by 06Z Wednesday. Not expecting any storms into the western
portion of the area prior to 03Z. However, there are some models
that bring some into this area during this time. Have small pops
to account for these differences. This is supported by the
ARW/NMM/NAM/NAMNest and the NSSL WRF. The storms begin to move
across the western tier through 06Z and possibly into Pine county.
There is potential for some severe storms with MUCAPE values
rising into the 1500-2500 J/kg range over the Brainerd Lakes
region east into Pine county. 40-50kt of shear will accompany
these CAPE values. Better opportunity for severe will be with the
second stronger short wave. The first short wave lifts north into
Canada by 12Z as the second arrives in western Minnesota. It is
with this second wave and an approaching cold front that the
stronger storms will arrive. Will hold off on the mention of
severe for now as there are timing differences, as well as storm
strength advertised by the various short term hires models. Cloud
over will also affect amount of destabilization/severe potential.

A broken line of storms will continue to march east through the
rest of the forecast area Wednesday morning, diminishing by
afternoon. This activity will be aligned with the second wave and
the cold front. The cold front should reach the eastern edge of
the forecast area late Wednesday afternoon as the short wave lifts
northeast into Canada. Dry high pressure will follow behind the
cold front.

.LONG TERM...(Wednesday night through Monday)
Issued at 349 AM CDT Tue Sep 19 2017

An active weather pattern will continue through the long term.
Very warm temperatures are expected for the remainder of the week.
Cooler air will gradually invade the Northland from the
northwest, but areas in northwest Wisconsin will see much above
normal temperatures continue through Sunday. There will be several
opportunities for strong to severe thunderstorms and heavy
rainfall.

The eastern arm of an Omega Block over the eastern Pacific will
loiter over the western half of the continent for much of the
extended. The mid- and upper-level trough will be quite broad
Wednesday evening stretching from Ontario westward into the
eastern Pacific. Surface high pressure and subsidence can be
expected over the Upper Midwest in the wake of a departing
shortwave trough and cold front. Winds aloft will turn southerly
once again by mid-morning Thursday as a warm front lifts northward
into northwest Ontario. That boundary will become quasi-
stationary with areas to the south, including the Northland,
experiencing unseasonable warmth with near record temperatures
forecast. The chance of rain and thunderstorms increases Thursday
night and continues through early next week as the front slowly
migrates eastward each day. The latent baroclinic zone and broad
swath of isentropic ascent in the warm sector should provide ample
chances for strong thunderstorms and heavy rainfall. The
potential for strong to severe thunderstorms will include the
entire CWA Thursday night and Friday morning thanks to moderate
instability and strong deep layer shear of 30 to 45 knots. The
atmosphere will recharge during the day with another round of
strong to potentially severe storms possible Friday afternoon and
evening. That period also holds the best potential for excessive
rainfall with surface low pressure lifting through northern
Minnesota along the stationary front. The thunderstorm risk will
shift farther southeast for Saturday and Sunday, mainly focused
over northwest Wisconisn. Another shortwave trough will move
through the Upper Midwest along the baroclinic zone, which may
lead to a heightened risk of excessive rainfall again on Sunday.
By Sunday night the deep trough will begin moving eastward, taking
on a slightly more progressive character. Rain and thunderstorm
chances remain high Monday before high pressure moves through the
Canadian Prairies and grazes the region bringing quieter
conditions Monday night.

&&

.AVIATION...(For the 12Z TAFS through 12Z Wednesday morning)
Issued at 652 AM CDT Tue Sep 19 2017

Isentropic ascent over the region north of a surface warm front
over southern and western Minnesota will help keep ceilings low
this morning into the afternoon. Look for a gradual improvement in
categories as boundary layer mixing develops. Showers and storms
approach from the west late tonight ahead of an approaching cool
front. Strong southerly winds in the low-levels will increase the
risk of low-level wind shear at all terminals tonight.

&&

.PRELIMINARY POINT TEMPS/POPS...
DLH  65  58  69  49 /  10 100  50  10
INL  67  58  68  45 /   0 100  50  10
BRD  72  60  70  50 /  10  80  20   0
HYR  72  62  74  47 /   0  60  50  10
ASX  72  59  75  47 /  10  60  40  10

&&

.DLH WATCHES/WARNINGS/ADVISORIES...
WI...Beach Hazards Statement through this evening for WIZ001.

MN...Beach Hazards Statement through this evening for MNZ037.

LS...None.
&&

$$

UPDATE...Huyck
SHORT TERM...GSF
LONG TERM...Huyck
AVIATION...Huyck



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