Area Forecast Discussion
Issued by NWS Duluth, MN

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FXUS63 KDLH 241155 AAA
AFDDLH

Area Forecast Discussion...UPDATED
National Weather Service Duluth MN
655 AM CDT Mon Jul 24 2017

.UPDATE...
Issued at 654 AM CDT Mon Jul 24 2017

Update for new 12Z Aviation Discussion below.

&&

.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 overnight.

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 12Z TAFS through 12Z Tuesday morning)
Issued at 654 AM CDT Mon Jul 24 2017

Dense fog this morning should burn off quickly. The fog is thin
enough for GOES-16 shortwave infrared imagery to show surface
features through the fog/stratus overnight, especially on the
periphery of the fog. Look for quickly improving visibility at all
sites, with DLH and HYR hanging onto the low fog and stratus the
longest. VFR conditions expected through today and into this
evening at all sites. Winds will increase out of the south as the
boundary layer deepens and mixes into higher momentum air flow
aloft. A few cumulus will pop this afternoon, but expect scattered
coverage. Surface wind speeds will decrease this evening as
temperatures cool after sunset. Think we`ll see some fog redevelop
at most terminals. A strengthening nocturnal low-level jet will
bring a potential for low-level wind shear to INL overnight. Think
winds aloft will not be as strong at other terminals.

&&

.PRELIMINARY POINT TEMPS/POPS...
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

&&

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

$$

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


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