Area Forecast Discussion
Issued by NWS Duluth, MN

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FXUS63 KDLH 240942

Area Forecast Discussion
National Weather Service Duluth MN
442 AM CDT Mon Jul 24 2017

.SHORT TERM...(Today through Tuesday)
Issued at 442 AM CDT Mon Jul 24 2017

At 430 AM, widespread fog covered much of the CWA. Surface
observations, along with GOES 16 imagery, indicate fog and stratus
throughout the region. Visibilities were as low as a quarter mile
from the Head of the Lakes region into northwest Wisconsin.
Temperatures ranged from the 40s in the Minnesota Arrowhead, to
the 50s elsewhere. The cool spot so far this morning is the
Superior RAWS station number 1, at 40 degrees.

The weather today should be very quiet. Under high pressure, we
should see temperatures in the 70s. We should see fog and stratus
gradually give way to sunny skies.

Another area of low pressure will approach the Northland later
tonight and Tuesday. This will bring the next chance of showers
and thunderstorms into the Northland. Shortwave energy in a
westerly upper level flow should help to bring showers and
thunderstorms to the region on Tuesday, and perhaps as early as
later tonight in the western zones. SPC has the Brainerd Lakes
area in a Marginal Risk of Severe Thunderstorms tonight. Will
continue with chance POP`s for Tuesday at this point, as it is
unclear where potential MCS activity will develop. Our entire CWA
is in the Slight Risk of Severe from SPC. We should see the
development of thunderstorms during the day, as a strengthening
LLJ brings increasingly warm and humid air back into the region.
Despite thunderstorm development on Tuesday, think there is a
greater likelihood that we will see major MCS development by
Tuesday night. After lows in the 50s and 60s tonight, we will see
highs close to 80 Tuesday.

.LONG TERM...(Tuesday night through Sunday)
Issued at 442 AM CDT Mon Jul 24 2017

The main forecast concerns for the long term are the continued
chance of strong to severe thunderstorms Tuesday evening through
Wednesday morning and the potential for excessive rainfall.

A shortwave trough is forecast over eastern Manitoba and
northwest Ontario Tuesday evening. Surface low pressure over
northeast Manitoba and western Hudson Bay will trail a cool front
southeastward into the Upper Midwest. Showers and thunderstorms
may be ongoing at 00Z Wednesday along the front from northwest
Ontario through the Arrowhead and into the Brainerd Lakes area. A
warm and moist boundary layer will support MLCAPE of 1500-3000
J/kg mainly south of US Highway 2 in Minnesota by early evening.
Convergence and moisture pooling along the front will bring a
ribbon of 1000-2500 J/kg MLCAPE into northwest Ontario.
Convergence is forecast mainly along the frontal boundary as it
moves into north-central Minnesota during the evening and think
the best chance of storms will be over Koochiching and Itasca
Counties initially. The juiciest airmass may remain capped until
the arrival of the front. Think scattered to isolated storms will
be the threat early in the evening, especially in the north,
quickly evolving into one or more MCS as the front plows into the
more unstable airmass over the southern half of the forecast
area. With 0-6 km bulk shear forecast between 40 and 55 kts,
think supercells may be the initial storm mode before the rapid
upscale growth during the evening. A strengthening low-level jet
over east-central Minnesota, west-central, and northwest
Wisconsin will pump additional moisture into the frontal zone

The risk of flash flooding from the thunderstorms has increased
with this forecast package. The 00Z ECMWF ensembles bring 1.75 to
2 inch precipitable water into east-central Minnesota and
northwest Wisconsin Tuesday night on the low-level jet.
Deterministic PWATs off the NAM are even higher, in the 2 to 2.25
inch range, and the GFS features 1.75 to a little over 2 inches.
These values are greater than 97% of climatology. With the
ongoing thunderstorms by 06Z Wednesday and the enhanced low-level
convergence on the nose of the LLJ, think there is a possibility
for additional thunderstorm development along an east to west
axis over our southern forecast area Tuesday night through
Wednesday morning. WPC has highlighted much of the CWA in a
Marginal Risk of excessive rainfall, with the Slight Risk area
nosing north into the Brainerd, Hinckley, and Spooner areas.
Flash flooding is certainly a possibility, especially in the
variable terrain from east of Aitkin across much of northwest
Wisconsin. Have added heavy rainfall to the weather grids and
will mention a potential for flash flooding in the HWO. A Flash
Flood Watch may be warranted with the afternoon package or
possibly tomorrow morning.

The cool front will move through the remainder of east-central
Minnesota and northwest Wisconsin Wednesday morning. Think
showers and storms will continue through mid-morning and there`s
a chance of additional storm development during the afternoon.
Not much of a change in temperatures behind the cool front with
near normal to slightly above normal temperatures in the low 70s
to around 80 degrees expected for Wednesday. Mid-level ridging
will build across the Rockies and into the Canadian Prairies and
Northern Plains Wednesday. A northwest flow regime will develop
over the Northland and linger through Friday evening. Expect
surface high pressure to slowly push eastward at the surface
during the second half of the work week keeping conditions
generally drier with a slight warming trend Thursday and Friday.
Near to slightly above normal temperatures are expected to
continue through the upcoming weekend. A weak shortwave trough is
forecast to move through the region Friday, but a slight increase
in cloud cover is expected to be the only sensible weather
change. Another shortwave trough will ride over the crest of the
ridge across the northern Canadian Prairies Friday and Saturday.
The ridge will flatten as the trough advances eastward with quasi-
zonal flow developing over the Upper Midwest. A cool front is
forecast to move across the Prairies and Northern Plains and into
the Upper Midwest on Saturday which may trigger a few showers and
thunderstorms, especially Saturday evening and Sunday. Models
diverge during this period warranting only slight chances of
showers and storms with this forecast.


.AVIATION...(For the 06Z TAFS through 06Z Monday night)
Issued at 1254 AM CDT Mon Jul 24 2017

An area of high pressure will continue to move southeast through
the region tonight into Monday allowing surface winds to turn
southerly. The wind for most areas tonight will be light allowing
for fog to develop. Stratus and fog was already expanding across
portions of northern Wisconsin west toward KDLH. We expect this
trend to continue tonight with increasing IFR/LIFR conditions. The
fog will lift Monday morning with VFR conditions then prevailing
through the rest of the period.


DLH  74  57  78  63 /   0  20  40  50
INL  79  60  78  59 /   0  40  50  20
BRD  77  63  83  65 /   0  30  40  60
HYR  77  58  80  65 /   0  10  20  70
ASX  76  56  81  65 /   0  10  30  70




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