Area Forecast Discussion
Issued by NWS Duluth, MN

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FXUS63 KDLH 110543
AFDDLH

Area Forecast Discussion
National Weather Service Duluth MN
1243 AM CDT Fri Aug 11 2017

.UPDATE...
Issued at 1243 AM CDT Fri Aug 11 2017

Updated aviation section below for 06Z TAF issuance.

UPDATE Issued at 938 PM CDT Thu Aug 10 2017

Upper level low continues to slowly pull eastward away from the
DLH CWA this evening, and the few lingering light showers that
remain are expected to completely dissipate in the next hour or
two. In the wake of the departing system, the combination of
slowly clearing skies, near-calm winds, and a very moist near-
surface airmass from recent rains, and longer hours of darkness
should result in the development of areas of fog. We already are
seeing some 2 to 4 mile visibility reductions in observations,
and we expect this to expand over the next 2-4 hours as skies
clear. It`s possible that fog in some locations could become quite
dense after midnight through a couple hours after sunrise. The
only other issue is the northeast winds on western Lake Superior
that will continue to slowly diminish overnight, but will remain
strong enough to still warrant a continuance of the small craft
advisory on the south shore.

These trends have been reflected in the updated forecast, and the
updated products have already been sent.

&&

.SHORT TERM...(This evening through Friday)
Issued at 251 PM CDT Thu Aug 10 2017

Chances of showers and isolated thunderstorms will continue to
slowly diminish this evening as an area of low pressure, currently
located over north-central Wisconsin and the U.P. of Michigan, will
continue to move off to the east. These chances of showers and
storms will linger at least through the rest of the afternoon as we
remain under the cyclonic flow of the low, but nothing severe is
expected at this time as instability values are expected to remain
very low, with MLCAPE values possibly reaching up to 700 J/kg
through the early evening, which will quickly drop off after
sunset, as well as very low deep layer shear.

An area of high pressure will then move into the region overnight,
bringing clearing skies, especially over north-central Minnesota.
With these clear skies and light winds, radiational cooling will
again lead to a cool night, with lows in the middle to upper 40s
along the International Border to the lower 50s over northwest
Wisconsin western to the Brainerd Lakes region. Due to the rain
showers from earlier today, areas of fog are once again expected,
mainly from the Brainerd Lakes area, eastward towards the South
Shore. Quiet and dry conditions will continue through the day
Friday as the high pressure remains in control. Diurnal cumulus
clouds could develop in the late morning and afternoon hours, per
the NAM/GFS model soundings. Winds should remain light despite
boundary layer mixing up to over the 800 mb level.

.LONG TERM...(Friday night through Thursday)
Issued at 251 PM CDT Thu Aug 10 2017

A few low chances for precipitation during an otherwise seasonable
period this weekend through Tuesday. Next chance for widespread
precipitation will be mid to late week when a warm front approaches
from the west. Highs in the 70s to near 80.

On the synoptic scale, an omega block pattern will develop this
weekend across North America transitioning to more of a zonal
pattern next week. A broad area of high pressure will encompass the
Upper Midwest over the weekend as a result of the omega block at
mid/upper levels resulting in mainly sunny skies and seasonable
temperatures. A chance for rain showers Sunday and Monday afternoon
as a mid-level shortwave embedded in the north-northwest flow tracks
across the Upper Mississippi River Valley. The best chance for
precipitation Sunday will be towards central Minnesota, with the
threat shifting towards the Minnesota Arrowhead on Monday afternoon.
A thunderstorm can`t be completely ruled out, given instability as
great as 1000 j/kg MUCAPE per the 12z ECMWF, though most model
guidance depicts poor profiles for and sustained convection due to
winds less than 20 knots through the vertical column both days - at
some time steps not a wind barb above 10 knots from the surface
through 250mb on some guidance! Otherwise fair-weather cu most days
with light winds and highs in the 70s to near 80, perhaps a bit
warmer on Tuesday and Wednesday.

&&

.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 1243 AM CDT Fri Aug 11 2017

Focus overnight will be on the development of IFR fog at most
terminals. Vsbys already dropping at KHIB/KBRD/KHYR and bouncing
around, but more persistent fog is expected to develop as the
night progresses. Some periods of VLIFR fog may be seen at KHIB.
Fog will quickly burn off after sunrise with conditions rapidly
improving to VFR. With high pressure in place, expecting
development of fair weather cumulus clouds by midday and
persisting through the afternoon. This will lead to broken VFR
ceilings. Skies will then clear out by the evening hours, setting
up the potential for another foggy night.

&&

.PRELIMINARY POINT TEMPS/POPS...
DLH  52  73  53  77 /  20   0   0  10
INL  47  76  49  78 /   0   0   0  10
BRD  52  75  52  76 /  20  10   0  10
HYR  52  73  48  76 /  30  10   0   0
ASX  52  72  51  78 /  30  10   0   0

&&

.DLH WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
LS...Small Craft Advisory until 5 AM CDT early this morning for
     LSZ121-148.

&&

$$

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



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