Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 221946

Area Forecast Discussion
National Weather Service Marquette MI
346 PM EDT Fri Sep 22 2017

.SHORT TERM...(This evening through Saturday)
Issued at 343 PM EDT FRI SEP 22 2017

Short term forecast complicated by MCS moving through the Upper Mi
today. Latest radar imagery shows an intense line of strong to
severe storms moving into the east half of Upper Mi with generally a
weaker line of storms moving thru south central Upper Mi. Mixed
layer CAPE values up to 2000 j/kg combined with effective shear
values of 35-40 knots have supported isolated severe storms over the
west half of Upper Mi earlier today. Convection and more clouds than
expected have kept temps down cooler than forecast for many places
over the west half so made some necessary adjustments downward. It
will be tricky though if we see any partial clearing late afternoon
behind the MCS over the west as it would not take much mixing to tap
into much warmer air just off the sfc.

Tonight, better performing experimental HRRR model indicates any
remaining convection dissipating over eastern and south central
Upper Mi early this evening as air mass dries and becomes
increasingly capped by very warm 22-25c temps from 950-850 mb. With
models showing the mid-level ridge strengthening and the sfc-850 mb
warm front lifting north of Upper Mi, expect counties across Upper
Mi to be dry tonight. There may be some isolated convection along
the warm front over northern Lake Superior. Southerly gradient winds
between high pressure centered over the eastern CONUS and low
pressure and frontal system over MN will provide enough mixing to
preclude fog development over land areas.  Dewpoints in the lower to
mid 60s however could support locally dense fog over marine
areas, especially given the recent rainfall from today`s MCS. Min
temps will stay well above normal given warm airmass and southerly
winds. Expect many record high minimum temps to be set today into
Saturday. Readings tonight will generally be in the upper 60s to
lower 70s.

Saturday, even with a strong subsidence inversion under the 590 DM
ridge over the region, forecast mixing to near 800 mb with temps
around 20C will support record to near record high temps in the
upper 80s and possibly lower 90s over much of the area except
downwind of Lake Michigan. Adding to the discomfort will be
dewpoints into the mid and upper 60s. Capping should be strong to
minimize shower/t-storm chances, per NAM/ECMWF/GEM keeping any
convection to the north and west. However, the frontal zone over
ne MN into western Lake Superior by late Saturday may allow some
showers/t-storms to sneak into the far west from IWD to CMX
toward evening.

.LONG TERM...(Saturday night through Friday)
Issued at 259 PM EDT FRI SEP 22 2017

Nam shows a deep 500 mb trough over the Rockies and a strong 500 mb
ridge over the ern U.S. 00z Sun. Upper air pattern changes very
little through 00z Tue with the ridge slowly moving east to New
England by 00z Tue. What this will mean is warm and humid conditions
will continue with summer like weather. Pops will remain mostly to
the north and west of the cwa with area in the warm sector for this
forecast period and some record highs are possible for this forecast

In the extended, GFS and ECMWF show a 500 mb trough in the Rockies
and northern plains 12z Tue with a ridge over the ern U.S. 12z Tue.
This trough moves into the upper Great Lakes 12z Wed and this trough
remains into 12z Thu. Starting on Wed, a cold front moves through
and brings an end to the summer like temperatures with cooler air
moving into the area. Temperatures will go from above normal on Tue
to below normal for Wed through Fri.

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 132 PM EDT FRI SEP 22 2017

Challenging forecast in near term in regards to timing of
convection moving across TAF sites. Also gusty southerly wake low
winds to near 30 mph are developing behind the stronger convection
and may continue into late afternoon. T-storms have moved mostly east
of KIWD and KCMX but will affect KSAW through 20z with possible
MVFR conditions before shower activity begins to taper off at all
sites and VFR conditions finally prevail. Should be enough mixing
from southerly winds to preclude fog development tonight and keep
conditions VFR. A low-level wind max moving across the region will
result in LLWS at all TAF sites tonight into early Sat.

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 343 PM EDT FRI SEP 22 2017

Low to mid 60s dewpoints sliding across Lake Superior are expected
to linger into early next week bringing patchy to areas of fog for
several days across the lake. Some of the fog could be locally dense
at times, especially tonight considering today`s rainfall over the
lake. Expect winds to generally be below 20 knots through the early
part of next week under a weak pressure gradient.

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


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