Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 150917

Area Forecast Discussion
National Weather Service Marquette MI
517 AM EDT Tue Aug 15 2017

.SHORT TERM...(Today and tonight)
Issued at 517 AM EDT TUE AUG 15 2017

Water vapor imagery and RAP analysis still show a blocky/omega
pattern across Canada with sharp/strong ridging across central
Canada, flanked by trofs over the Rockies and over eastern Canada.
The eastern trof is anchored by a mid level low centered along the
se shore of Hudson Bay. Shortwave that was over s central MN 24hrs
ago is now in the vcnty of the Straits and is continuing to move
eastward. In its wake, skies have cleared over much of the area.
Some fog has formed, but it appears to be shallow as obs have been
showing widely fluctuating vis. Temps have fallen to as low as the
low/mid 40s at some of the traditional cold spots over interior
western Upper MI.

Sfc high pres currently over northern Ontario will build over the
Upper Great Lakes today, providing a dry day. Only concern is
potential of lower clouds to develop and persist for a good part of
the day over portions of the fcst area. Stratus has recently
developed over the Keweenaw and is tied back to the n and ne into
northern Ontario. Much of the model guidance, including hourly
RAP/HRRR runs, suggest an expansion of stratus into at least n
central Upper MI this morning, and these clouds may persist well
into the aftn. This moisture should also lead to some lower based cu
development elsewhere across the central and e. Will see how clouds
develop over the next several hrs to see if a change to a more
pessimistic cloud fcst is needed for today. Otherwise, since ongoing
patchy fog is shallow, it will burn off quickly this morning. As for
temps, expect highs ranging from the upper 60s lakeside along Lake
Superior to the upper 70s around 80F s central.

Dry weather will continue tonight with sfc high pres slowly shifting
eastward. Should be another cool night in the interior with mins in
the low/mid 40s though this will be dependent on how much high
cloudiness overspreads the area. May see some patchy ground fog
interior central and e.

.LONG TERM...(Wednesday through Monday)
Issued at 430 AM EDT TUE AUG 15 2017

Potential for hazardous weather in the long term is centered on Wed
night into Fri as low pressure system crosses Upper Great Lakes.
Heavy rain possible and there is a small potential for stronger
storms Thu aftn over the south central. Small craft conditions on
parts of Lk Superior and Bay of Green Bay/Lk Michigan looking likely
late Wed Night into Friday.

Higher heights still over Upper Michigan on Wed as lead shortwave
trough moves from central Plains to the Upper Mississippi River
Valley. Mid level moisture advection ahead of shortwave could lead
to some showers over western Upper Michigan through the day but
soundings are dry blo h7 so any rain would be light. Temps on Wed
mainly in 70s with upper 70s interior east with less cloud cover
there through the day. Best chance of rain with this system comes in
later Wed night as primary shortwave trough and associated deep
layer q-vector convergence spreads acrosss Upper Michigan from west
to east. PWATs nearing 2.0 inches into the system could lead to
heavy rain with greatest chance of that on cyclonic nw side of sfc-
h85 lows whch now looks to impact mainly western fringe of Upper
Michigan late Wed night into Thu morning. Could see rain totals over
1.5 inches during this time in those areas while elsewhere totals
could still reach 1 inch. Mid level dry slot working in on Thu will
diminish steady rain, but since sfc low tracks more over north
central U.P. by early aftn and warm sector will affect at least
parts of forecast area could see shra/tsra develop during peak
heating of aftn over scntrl Upper Michigan. If tsra can develop
effective shear 25 to 35 kts could support stronger storms. Still
seems best chance for severe storms will remain south of Upper
Michigan but will need to continue monitoring this potential.

Low pressure will move east of Upper Michigan by Friday morning.
Still will be a lot of low-level moisture lingering in cyclonic NW
flow in wake of the low. Continued to linger clouds/small pops
longer on Friday over the north and east forecast area. Went with
cooler CONSraw temps for highs on Fri which seemed more reasonable
with low to mid 60s near Lk Superior and maybe mid 70s far scntrl.

Dry weekend not as clear cut as it looked yesterday. ECMWF stronger
with secondary shortwave working through on Sat but the other models
are weaker/farther south with the wave that is producing the shra.
Overall all the guidance shows dry weather Sun and increasing
chances of shra/tsra on Monday as cold front approaches. Only main
change was to increase max temps Sun and Mon ahead of the front.
Should see temps each day be able to reach upper 70s or lower 80s.
Could even be warmer with h85 temps 16-18c, but the adjustment
over consensus is a start for now.

.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 136 AM EDT TUE AUG 15 2017

Radiational fog, dense at times blo mins, will continue to develop
and thicken at KIWD overnight but should be relatively shallow and
variable. Some fog will also develop at KSAW and KCMX but is not
expected to be as thick with only occasional IFR conditions. Expect
the fog to dissipate by mid morning with VFR conditions through
the rest of the day.

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 517 AM EDT TUE AUG 15 2017

High pres building over the Upper Lakes will result in winds mostly
under 15kt across Lake Superior today and tonight. Easterly winds
will then increase Wed into Thu as low pres moves from the Central
Plains to the Upper Great Lakes. Wind gusts on Thu will be as high
as 30kt as the low reaches the area. Could be higher if the low pres
is deeper. These stronger winds will linger into Fri over eastern
Lake Superior as the low departs. Lighter winds, mostly under 15kt,
are expected over the weekend with high pres over the region.

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


SHORT TERM...Rolfson
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