Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 190821

Area Forecast Discussion
National Weather Service Marquette MI
421 AM EDT FRI AUG 19 2016

.SHORT TERM...(This evening through Friday)
Issued at 414 PM EDT THU AUG 18 2016

WV imagery and RAP analysis indicated mainly zonal flow through most
of the nrn CONUS between a trough over nrn Manitoba and a ridge
through the southeast CONUS. At the surface, a cold front extended
from nw Ontario through the nw MN into nrn South Dakota with srly
flow ahead of the front over the upper MS valley and nrn Great Lakes.
Vis loop showed Cu over the cwa with a tsra near Whitefish point
where lake breezes converged. Although there were also some isold
shra over nrn WI, stronger capping today compared to the past few
days has reduced chances/coverage of shra over the cwa even with
MLCAPE values in the 500-1000 J/Kg range. An upstream shrtwv over
cntrl MN supported tsra into far wrn WI.

Tonight, radar/satellite trends, short range models, and position of
CAPE gradient, and 850 mb llj/theta-e advection, suggest the most
numerous/heavier shra/tsra will remain to the south of the cwa.
However, sct shra/tsra may still develop farther north as models
hint that a weak shrtwv will slide through the area.

Friday, The cold front is expected to sag into Upper Michigan and
provide the focus for additional shra/tsra development as daytime
heating increases. With considerable clouds and humid conditions
(dewpoints in theupper 60s) temps will climb into the upper 70 and
lower 80s. Resulting modest MLCAPE values to around 1k J/kg and 0-
6km shear of around 30 knots, should only support isold stronger
storms if any. There is less confidence whether additional
shortwaves could move through the area and enhance shra/tsra

.LONG TERM...(Saturday through Thursday)
Issued at 421 AM EDT FRI AUG 19 2016

Still looking like the weekend will be wet for the Upper Great Lakes
Region. There are some model inconsistencies that could cause
significant changes, mainly to the winds for Saturday night into
Sunday, so that will need to be watched for further adjustment as
models hopefully come into better agreement.

Saturday through Sunday: With continued uncertainty in mind, the
cold front is expected to stall out across the central U.P. and
eastern U.P. for most of the day Saturday as the main upper level
500 mb trough axis slides from MN/Western Ontario into the western
U.P. Out ahead of the upper level trough, a surface low is expected
to develop/intensify over central to eastern WI and ride along the
front as it lifts northeastward. This low is expected to cross the
central U.P. by Saturday evening and then slide into southwest
Quebec by Sunday afternoon. The GFS/EC/UKMET have a similar
trek/strength while the NAM/GEM are much farther west with the
surface low and have the low much stronger. This added support from
the GEM is really in the wind fields only as the mid level low only
closes off briefly with the GEM and then fills in. The NAM maintains
a stronger mid level low for a longer period of time. PWATs are
still progged to be around 1.5 to 2 inches Saturday afternoon and
evening as the low pass through the area so moderate to heavy rain
would likely be the main threat. It looks like a dry slot will slide
into the eastern U.P. Saturday evening through Sunday, which would
act to limit the rain shower potential during that time period;
however, this may lead to more instability over those areas,
allowing for isolated to scattered thunderstorms Saturday afternoon
and evening. Behind the front/surface low , broad 500mb troughing
will slide into the Upper Great Lakes Region as well as a tighter
pressure gradient on the back side of the departing low. This
tighter gradient will allow strong, gusty north to northeast winds
to develop, creating a moderate to high risk swim risk by late
Saturday afternoon. The main 500mb trough axis will slide across the
U.P and moisture will continue to wrap back into the area on the
back side of the departing surface low late Saturday night into
Sunday morning, which will keep scattered rain showers in the
forecast. Temperatures will be more Fall-like as the low/cold front
continues east of the area along with the decreased heights
overhead. Sunday will continue to see gusty north to northeast winds
with the continued tight pressure gradient across the area, which
would support a continued moderate to high swim risk along Marquette
and Alger counties. The tight pressure gradient looks as if it may
also be strong enough for Gales over central and eastern Lake
Superior later Saturday night into Sunday, but the exact location
for the strongest gusts will be highly dependent on the low

Sunday night through Tuesday: Overall moisture looks to be fairly
limited through this time period along with a surface ridge in place
across the area. There may be a couple shortwaves that try to round
the base of the overall troughing across the area, but the limited
moisture and anticyclonic flow should limit any shower chances
through this time period.

Tuesday night through Wednesday night: Models are depicting a low
pressure system and 500mb trough sliding across central Canada to
northern Ontario during this time period. This would also allow a
cold front to slide through the area. Ahead of the front, southerly
flow will kick in, allowing temperatures to again warm to above
normal for Wednesday. Showers and thunderstorms are expected to
develop along and ahead of the front, with the best chances expected
Wednesday afternoon into Wednesday night.

Thursday through the extended: Broad troughing is progged to be in
place across the area; however, there looks to be very little
moisture to work with for precipitation. As timing of subtle
features is tough, at best, to pin down this far out, have decided
to stick with a consensus of the models.

.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 122 AM EDT FRI AUG 19 2016

VFR conditions are expected into Fri aftn. There will be potential
for shra and possible tsra, especially late tonight through Fri at
IWD and SAW. A front sliding through the area will settle south of
all terminals by late Fri aftn and evening. As this occurs, expect
flight conditions to deteriorate to MVFR or lower through the rest
of Fri evening as cooler and moist northerly flow develops off Lk
Superior. Some showers may continue at times.

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 414 PM EDT THU AUG 18 2016

Despite a slow moving cold front pushing through the region, winds
will remain at or below 15 knots until the weekend. High pressure
building in behind the front will boost the pressure gradient enough
to produce stronger N winds to 25-30 knots Saturday night into
Sunday, mainly over the east half of Lake Superior.

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


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