Area Forecast Discussion
Issued by NWS Duluth, MN

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FXUS63 KDLH 171743

Area Forecast Discussion
National Weather Service Duluth MN
1243 PM CDT Mon Jul 17 2017

Issued at 1227 PM CDT Mon Jul 17 2017

Updated for the new 18z Aviation Discussion below.

UPDATE Issued at 628 AM CDT Mon Jul 17 2017

Updated for the new 12Z Aviation Discussion below.


.SHORT TERM...(Today through Tuesday)
Issued at 331 AM CDT Mon Jul 17 2017

Hot today with scattered thunderstorms expected in the late afternoon
as a cold front moves in from the northwest. A second round of
storms along and ahead of the cold front on Tuesday in northwest
Wisconsin, with temperatures not as hot behind the front. Storms
could be strong to severe today into tonight, producing large hail
and damaging winds across north-central to northeast Minnesota.

On the synoptic scale a mid-level shortwave ridge over the Upper
Midwest and the associated area of surface high pressure over the
upper Great Lakes will move east today allowing south to
southwesterly flow to dominate at low levels. A fairly strong mid-
level shortwave trough/vort max will traverse east across southern
Saskatchewan and Manitoba tonight into Monday with the resulting
surface low developing in far northwest Ontario. The cold front
associated with this low will extend southwest into the northern
Plains by tonight, moving east into the Upper Midwest tonight into
Tuesday. A warm front ahead of this cold front will move east across
the Upper Midwest today with strong southerly flow within the warm
sector helping to advect a fairly moist airmass at low levels with
dew points approaching 70. While low levels will be very warm,
strong large-scale forcing for ascent combined with surface heating
is expected to be enough to break the cap by the late afternoon
hours, causing isolated to scattered thunderstorms to develop.
Fairly steep mid level lapse rates combined with the moist low
levels will lead to about 1500 to 3000 j/kg MUCAPE, sufficient for
strong updrafts to produce large hail and damaging winds. The deep
layer wind field is on the low end for sustaining supercells with
perhaps 30-40 knots of 0-6km shear, with a number of models
depicting wind directions veering at low levels then backing at mid
levels, which would suggest "messy" storms. Still, with decent
forcing and strong mid level lapse rates large hail and damaging
winds will be possible with any stronger storms. The strong low
level lapse rates and the related DCAPE parameter combined with
relatively high-based storms suggest a strong than usual risk for
downbursts leading to straight-line wind damage. Strong low level
lapse rates and sufficient low level shear may lead to a tornado
threat as well, though with the limited deep layer wind shear to
support long-lasting supercells the tornado threat may be limited to
weak spin-ups associated with bowing line segments.

Storms are expected to develop in north-central Minnesota around 21-
22z and move east across northeast Minnesota towards the evening
hours, with the threat for severe storms greatest in the first few

Otherwise today, highs in the 80s to near 90 with dew points in the
mid 60s to low 70s will lead to heat index values approaching 100
for parts of Cass and Crow Wing county. Heat Advisory criteria is
heat index values of 100+, and while the current forecast is still a
few degrees shy, a Heat Advisory may be considered by the day shift
if temps and dew points rise faster than currently anticipated.
South winds will be breezy today with gusts to 20-30 mph possible
during the afternoon hours.

Tonight storms will gradually weaken as they track east into the
night, with patchy fog possible as skies clear out behind the cold
front in north-central Minnesota late tonight. Lows mild in the 60s,
except where skies clear out in the Borderland where temps will fall
to the mid 50s.

Another warm one Tuesday with highs in the upper 70s in northeast
Minnesota to the mid 80s across much of northwest Wisconsin. Another
round of thunderstorms are expected to develop in the afternoon, but
ongoing showers from overnight convection may limit the severity of
storms. Still, strong storms possible given ample instability in
ahead of the cold front.

.LONG TERM...(Tuesday night through Sunday)
Issued at 331 AM CDT Mon Jul 17 2017

The Northland can expect seasonably warm weather through the
upcoming weekend. The chances of showers and storms look fairly low
for much of the period, but there is a good chance of rain Saturday
and Saturday night.

Surface high pressure will build out of Canada into the Northland
Tuesday night and Wednesday, providing a period of clear and drier
weather through Wednesday. There will be a warm/stationary front
south of the Northland Wednesday evening. Passing shortwaves within
the near-zonal flow aloft could help trigger showers and storms
north of the front Wednesday evening and night, possibly affecting
parts of the southern forecast area.

Another area of high pressure will build into the Northland
Thursday. Warm return flow will redevelop Friday. The GFS, European,
and Canadian models suggest a shortwave trough will likely pass
through the Northland around this time. It could bring enough
forcing to generate some showers and storms. A much better wave,
though, will likely pass through the region Saturday and/or Saturday
night. This will be more potent upper trough and accompanying
surface low (GFS), or even a vertically stacked low (European and
Canadian). There are differences on its track, but it could dig
across southern Canada, or from southern Canada through the
Northland. This potent wave will bring good large-scale forcing for
ascent. Provided its track is more through the Northland, as
depicted by the latest European run, then the Northland would be
most impacted by the forcing, and would likely get a period of
widespread stormy weather Saturday and Saturday night. The GFS and
Canadian, with its more northerly tracks of the wave, would mainly
affect the northern forecast area. High pressure will likely return
to the Northland Sunday.


.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1243 PM CDT Mon Jul 17 2017

Shower and thunderstorm activity is expected to ramp up later this
afternoon as a push of southerly winds and warm air ahead of a
cold front boundary moves eastward through the region later this
afternoon and evening. Some storms could be strong to severe,
with the main threats being damaging winds, large hail, and heavy
downpours of rain. The high resolution model guidance indicates
the best chances of seeing these storms will be over KHIB, KBRD,
and KDLH. TEMPO groups in for best timing of storms, along with
some MVFR visibility reductions.

Winds will be gusting between 15 to 25 knots across much of the
Northland, with potentially stronger gusts within any
thunderstorms that develop or move over the TAF terminals. Winds
will also turn more westerly as the cold front boundary moves
through later this evening and overnight. There could be some MVFR
ceilings developing over some TAF sites overnight after the cold
front boundary passes through as well.


DLH  80  63  77  57 /  50  80  30  10
INL  86  55  80  51 /  60  50   0   0
BRD  91  66  80  57 /  60  70  30  10
HYR  81  68  85  56 /   0  50  60  30
ASX  82  66  82  56 /   0  60  40  20




LONG TERM...Grochocinski
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