Area Forecast Discussion
Issued by NWS Duluth, MN

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561
FXUS63 KDLH 170831
AFDDLH

Area Forecast Discussion
National Weather Service Duluth MN
331 AM CDT Mon Jul 17 2017

.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
hours.

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 06Z TAFS through 06Z Monday night)
Issued at 1220 AM CDT Mon Jul 17 2017

High pressure has moved east of the forecast area early this
morning while low pressure was slowly advancing over the Dakotas.
Winds will be from the south and gradually increase by morning and
become a bit gusty to around 20 to 25 knots Tuesday morning.
Thunderstorms will move into northeast MN late today and gradually
spread east as a cold front slowly moves through. By 06z the
front will likely be nearing the MN Arrowhead to the KBRD area.


&&

.PRELIMINARY POINT TEMPS/POPS...
DLH  80  63  77  57 /  50  80  30  10
INL  85  56  80  51 /  60  50   0   0
BRD  89  66  80  57 /  60  70  30  10
HYR  82  67  85  56 /   0  50  60  30
ASX  82  63  82  56 /   0  60  40  20

&&

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

$$

SHORT TERM...JJM
LONG TERM...Grochocinski
AVIATION...CLC/Grochocinski



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