Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 190657

Area Forecast Discussion
National Weather Service Marquette MI
257 AM EDT Sat Aug 19 2017

.SHORT TERM...(Today and tonight)
Issued at 256 AM EDT SAT AUG 19 2017

An area of scattered showers with some isolated thunder moved into
far northwest portions of Upper Michigan this morning as a
shortwave continued to move across western Lake Superior. Through
the morning hours, these scattered showers and thunderstorms will
continue to push southeast into central portions of Upper
Michigan, primarily the north central, before diminishing over the
next few hours. Elsewhere, lingering cloud cover was observed
early this morning.

Later today, as the main upper-level wave lifts out of the region,
cloud cover will gradually start to wane from west to east. With
increasing insolation and a somewhat dry air mass overhead, expect
temperatures to warm nicely into upper 70s and low 80s. Locations
that see temperatures climb into the low 80s will likely be confined
to areas of better downsloping. Given the increased insolation, lake
breeze boundaries are expected to develop and push inland through
the afternoon and evening hours. Increased convergence along the
lake breeze boundaries and area of more substantial terrain, and
along lake breeze interactions, will allow for afternoon showers and
thunderstorms to develop. While there will be a small chance that a
few of these storms may develop across the north central portions of
the area, the main focus should remain where the Lake Superior and
Michigan breeze converge across the central and east. A weak PV
anomaly/shortwave is progged to clip the area this afternoon and
should also provide some additional lift for afternoon convection.
It will also help increase the amount of deep-layer shear as well,
with 0-6km shear increasing to around 30 to 40 knots by the mid-
afternoon hours. Along these lake breeze boundaries, low-level
moisture is progged to pool with dew points climbing into the low
60s. Therefore, it looks like around 1000 to possibly upwards of
1500 J/kg of MUCAPE will develop. These ingredients should allow for
some storms to remain organized, and possibly strong at times,
especially considering the shear orientation will remain quasi-
perpendicular to where the lake breezes are progged to interact.

Tonight, any lingering showers and thunderstorms across the south
central and east will push out over Lake Michigan. Temperatures will
remain mild as winds become southwesterly ahead of an approaching
cold front.

.LONG TERM...(Saturday night through Friday)
Issued at 346 PM EDT FRI AUG 18 2017

Saturday night and Sunday: Weak upper level ridging and a surface
high pressure ridge are expected to build across the Upper Great
Lakes Region for Saturday night into Sunday morning. This will allow
winds to diminish across the area and allow skies to become clear to
partly cloudy through Sunday morning. Sunday afternoon a weak
surface trough is expected to slide in from the west in response to
a shortwave moving through NW Ontario, which will spread scattered
showers and thunderstorms into the west half of the U.P. mainly late
afternoon through the evening hours. Sunday afternoon will be very
warm ahead of the surface trough with mixing of around 18c temps
from h85 thermal ridge overhead to sfc resulting in many locations
warming into the mid 80s.

Monday into Tuesday: The next area of broader mid-level troughing
will shift eastward toward the Upper Great Lakes for this time
period. As this happens, a cold front is expected to shift into the
area Monday afternoon and then slowly shift eastward into Tuesday
afternoon. As moisture, forcing and instability (MLCAPEs approach
1000 j/kg) increase along and ahead of the front, expect showers,
thunderstorms and cloud cover to increase across the area Monday
afternoon into Tuesday. Also not out of the question there could be
some isolated severe storms Mon afternoon into evening given
instability and deep layer shear increasing to 30-35 knots.

Wednesday: With the broad mid-level trough still lingering over the
area and the models hinting at another shortwave moving down from
Ontario, scattered showers could persist into Wed. The 12z ECMWF and
CMC models also suggest the potential for some lake enhancement to
showers on Wednesday as h85 temps fall near 7C Wed afternoon. Given
mid-lake Superior temps 15-16C this would create a lake-h85 delta-t
of around 8C. With a possible shortwave moving through the area
could see a hybrid of lake enhanced and diurnal instability showers.

Thursday and Friday: Should see a drying trend toward the end of
next week as broad sfc ridging builds in fm northwest of the lake.
Temperatures will likely be below normal for the latter half of the
work week.

.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 120 AM EDT SAT AUG 19 2017

VFR conditions are expected through the TAF period. There is some
fog developing over the western U.P. but that is expected to stay
out of KIWD.

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 256 AM EDT SAT AUG 19 2017

Winds are expected to remain 10 to 20 knots through the weekend.
Early next week, winds will relax to around or less than 15 knots.
Tuesday and Wednesday as the surface pressure gradient is progged to
increase across the area, winds will pick up to around 20 knots.
Then towards the latter half of the week, high pressure will take
over and winds are expected to remain under 15 knots.

Upper Michigan...
Lake Superior...
Lake Michigan...


SHORT TERM...Ritzman
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