Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 161104

Area Forecast Discussion
National Weather Service Marquette MI
704 AM EDT Wed Aug 16 2017

.SHORT TERM...(Today and tonight)
Issued at 432 AM EDT WED AUG 16 2017

High pressure remains in place over the Great Lakes this morning.
Light onshore flow off Lk Superior and nighttime cooling has
resulted in fog central and east, most dense inland. Otherwise high
clouds are spilling in from the west out ahead of pair of shortwave
troughs over the mid Conus. Lead shortwave with moisture advection
is leading to rain over ND and northwest MN while stronger shortwave
trough and sfc low pressure system is resulting in widespread shra
and tsra over KS and Neb. After fog diminishes this morning, winds
turning SE ahead of approaching low pressure system could lead to
intervals of more low clouds across central at times. Initial push
of moisture advection aloft may lead to a few showers this aftn over
the west. Highs low to mid 70s, warmest east where there could be
more sunshine.

Decent agreeement that most forecast area stays dry in the evening
except far west, then widespread showers move in after midnight
from the west and southwest as main shortwave trough/deep layer
q-vector convergence and sfc low move toward western and northern
WI. Have pops ramping up quickly after midnight but far north
will stay with just chancy pops all night as main forcing does not
arrive there til Thu morning. Strong h925-h7 moisture tranport
with pwats 1.5-2.0 inches and warm cloud depth of at least 12kft
will lead to efficient warm rain processes with moderate to heavy
rain expected after midnight. Some areas over southwest and scntrl
could see rain amounts by daybreak Thu near an inch. Elevated
instability (1-6km MUCAPE over 500j/kg) moves in very late
tonight so there could be embedded thunder which will only further
enhance rainfall rates. E-SE winds will be strong enough late
tonight for small craft conditions to develop on both Lk Superior
and Bay of Green Bay/Lk Michigan and these conditions will carry
on into first part of the long term Thu into Fri.

.LONG TERM...(Thursday through Tuesday)
Issued at 455 AM EDT WED AUG 16 2017

Despite blocky flow across Canada early this morning, a fairly
progressive pattern will prevail over the next 7 to 10 days.
Currently, sharp/strong ridging is over central Canada with strong
positive 500mb height anomalies centered over the far n central part
of the country. Upstream, a trof over western N America has been
making eastward progress over the last 48hrs. Flow in the trof is
split with a more vigorous shortwave over Saskatchewan. To the s,
srn stream shortwave over CO will lift ne and generate a rather
vigorous low pres system for Aug that will track ne into the Upper
Great Lakes on Thu. This system should provide a widespread mdt/hvy
rainfall for the fcst area tonight thru Thu with some pcpn lingering
into Fri as it departs. As that trof continues eastward, the next
trof which arrives over western Canada late this week will reach
central Canada early next week and will then be in the Hudson Bay to
Great Lakes region by Tue/Wed. This progression should lead a mostly
dry weekend. The next potential of a more widespread pcpn event
should arrive on Mon in association with the cold front tied to the
trof progressing across central Canada. Drier weather will return
Tue/Wed, but if the trof is more amplifed than currently fcst when
it reaches the Great Lakes, there could be some diurnally driven
isold/sct convection Tue/Wed. As for temps, cool conditions will
accompany the low pres system across the area Thu/Fri. Could be
quite chilly near Lake Superior either day if pcpn/clouds dominate
the daylight hrs. Temps will rise back to above normal over the
weekend into Mon ahead approaching cold front and will then fall to
normal to a little blo normal for Tue/Wed. Looking farther ahead,
GFS/CMC/CFSv2 suggest positive 500mb height anomalies will set up
across much of Canada during late Aug, which would tend to favor
somewhat above normal temps overall across the Upper Lakes.

Beginning Thu/Thu night, shortwave lifting across the Upper
Mississippi Valley to the Upper Lakes will support a low pres system
tracking from se MN across WI into central Upper MI and se Lake
Superior. Healthy deep layer forcing per q-vectors combined with
precipitable water of 1.75-2 inches (around 200pct of normal) will
set the stage for mdt/hvy pcpn amounts. Expect an organized band of
mdt/hvy shra and some embedded thunder to lift ssw to nne across
Upper MI, mainly Thu morning thru mid aftn, in association with a
progressive zone of strong isentropic ascent/moisture transport. In
the wake of this band of stronger forcing, shra should diminish in
coverage. Then, if clouds manage to break some in the vcnty of the
approaching sfc low moving toward central Upper MI, there will be
some concern for stronger, organized convection to develop in the
late aftn/early evening under deep layer shear up around 30kt. Right
now, it appears unlikely that there will be enough heating to build
up instability sufficiently, but it will be something to watch for
Thu aftn. Shra will continue Thu night, but will diminish far w and
s central overnight. Wrap around/upslope enhanced shra affecting the
n and e will then end from w to e during Fri into Fri evening. Event
total qpf will probably be on the order of 1-2 inches across the
fcst area. Temps could struggle to get out of the lower 60s Thu
and/or Fri across the w and/or n where shra/cloud cover are most
persistent. Not out of the question that a few locations across the
n central won`t reach 60F on Fri if shra/clouds persist thru the
daylight hrs.

Sat is looking like a dry day in the wake of the system. Only
possible exception might be a few isold shra along lake breeze
convergence zone over the e half of the fcst area. Potential looks
very low. Temps will rebound back to normal or even slightly above
normal Sat aftn.

Trof moving across western Canada late this week will evolve into a
mid level low w of Hudson Bay by Sun aftn. Shortwave swinging around
the s side of the low will push associated cold front toward the
Upper Lakes late in the day, and it may spark a few shra over the w.
Ahead of the front, expect a warm day Sun with highs in the 80s,
except e along Lake Michigan.

As the mid level low w of Hudson Bay drifts e, a shortwave will
amplify the trof into the Great Lakes by Tue. This additional energy
should support an increase in shra/tsra coverage along frontal
boundary and across Upper MI for Mon, perhaps lingering into Tue.
Dry weather will follow on Wed, provided the trof doesn`t become
more amplified and allow a shortwave to drop s into the Upper Lakes.

.AVIATION...(For the 12Z TAFS through 12Z Thursday morning)
Issued at 703 AM EDT WED AUG 16 2017

Patchy low clouds early on at IWD and CMX while widespread VLIFR-
LIFR fog/stratus gradually dissipates at SAW. Expect sct-bkn mid
clouds rest of the day with cigs lowering to possibly as low as
MVFR late tonight as low pressure system/steady rain moves in.
Could be some low-level wind shear at IWD late tonight but not
enough confidence in strength of winds aloft to put that into the
TAFs attm.


.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 432 AM EDT WED AUG 16 2017

Easterly winds will increase 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 some gale
force gusts over eastern Lk Superior if the low pres is deeper.
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...


LONG TERM...Rolfson
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