Area Forecast Discussion
Issued by NWS Duluth, MN

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FXUS63 KDLH 180538 AAB
AFDDLH

Area Forecast Discussion...UPDATED
National Weather Service Duluth MN
1238 AM CDT Mon Sep 18 2017

.UPDATE...
Issued at 1238 AM CDT Mon Sep 18 2017

Update for new 06Z Aviation Discussion below.

&&

.SHORT TERM...(This evening through Monday)
Issued at 321 PM CDT Sun Sep 17 2017

A surface ridge will move through the Northland overnight,
developing clear skies and nearly calm wind speeds overnight. The
strong radiational cooling will give the region a cool night and
spotty areas of fog, especially near any areas of water, such
areas with wet soils from recent rains. The temperatures will dip
into the upper 30s and lower 40s over much of the region. Some of
our local cold spots could see a brief freeze, like in Embarrass.

Southerly flow will develop Monday in the wake of the passing
high pressure, which will begin to bring back warmer and more
humid air into the region. However, a shortwave will lift through
the southern and eastern forecast area, which will bring cloud
cover and rain, keeping a lid on the temperatures. The shortwave
will likely bring rain to northwest Wisconsin, which the forecast
has up to around a tenth of an inch, but we may need to increase
in areas when confidence increases on the track and potency of the
shortwave. Light rain is also possible for some areas of nearby
MN, and over the Lake and along the North Shore. High temperatures
are forecast to be in the upper 50s to lower 60s.

.LONG TERM...(Monday night through Sunday)
Issued at 321 PM CDT Sun Sep 17 2017

A general persistence of the western U.S. mean trof/eastern U.S.
mean ridge pattern is expected to persist from the middle part of
this week through next weekend. This will result in the western
Great Lakes region being underneath general southwest flow aloft
during this time. Despite brief intrusions of cooler air after the
departure of individual waves, prevailing low level flow will be
out of the south, which will result in a rather warm and humid
period for mid-late September. Periodic chances for rain and
thunderstorms will also exist with both the northward migration of
the moisture gradient, and also with the cold front and main
forcing with each disturbance that traverses the region.

The first such disturbance is expected to eject northeastward
Tuesday night/Wednesday morning, and should be accompanied by
widespread rain and thunderstorms. While exact details of
placement/timing are difficult to iron out a couple days in
advance, instability and shear parameters appear favorable for at
least a few strong to severe storms, and perhaps a limited heavy
rainfall potential Tuesday night. Although the rapid northeast
movement of the primary forcing lobe as depicted by the current
model consensus would seemingly act to somewhat limit the heavy
rain potential, the presence of a 50+ knot low level jet, copious
moisture return in the surface-850 mb layer and precipitable water
amounts in the moist axis approaching 1.8 inches in the latest
guidance and associated potential for intense precip rates cannot
be ignored.

A brief break in precip chances should follow the departing
system later Wednesday into Thursday, but the return of warm/humid
boundary layer air should not take long as southerly flow
returns. Chances for thunderstorms will then persist from Friday
through Sunday. Initially, the best areal coverage may stay to our
west across the Dakotas and western Minnesota in closer proximity
to the surface boundary and mass convergence axis, but as the
front slowly sags southeastward with time, the primary convergence
axis should shift into central/eastern Minnesota by
Saturday/Sunday. While this is almost a week away, current model
consensus would suggest at least some potential for strong storms,
as well as an increasing heavy rain threat with a slow moving
frontal zone, and the return of precipitable water amounts above
1.5 inches.

&&

.AVIATION...(For the 06Z TAFS through 06Z Monday night)
Issued at 1238 AM CDT Mon Sep 18 2017

High pressure will gradually move off to the east tonight, as an
area of low pressure and upper level system moves in from the west
and southwest. A few sprinkles will be possible in northwest
Wisconsin later tonight, with the chance of showers increasing
throughout the day from KDLH to KHYR. We should generally see VFR
conditions overnight and into Monday evening, although some
localized fog will be possible overnight. This could result in
spotty IFR CIG`s and VSBY`s, especially at KHIB. In addition, some
MVFR CIG`s and VSBY`s will be possible Monday evening, especially
from KDLH into KHYR.

&&

.PRELIMINARY POINT TEMPS/POPS...
DLH  43  60  49  63 /   0  20  10  10
INL  37  64  46  66 /   0  10  10  10
BRD  43  62  48  68 /   0  20  10  10
HYR  41  61  50  68 /  10  50  20  10
ASX  41  63  47  67 /   0  50  20  10

&&

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

$$

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



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