Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 260901

Area Forecast Discussion
National Weather Service Marquette MI
501 AM EDT MON SEP 26 2016

.SHORT TERM...(Today and tonight)
Issued at 501 AM EDT MON SEP 26 2016

Nam shows a 500 mb ridge on the west coast, a closed 500 mb low in
Baja California and a deep trough across the north central U.S. this
morning. Nam shows this upper trough heading slowly east and
reforming a closed low this morning. GFS and ECMWF show about the
same thing as well. Wraparound part of storm will continue to affect
the area through tonight and there will also be some lake
enhancement pcpn thrown in as well as 850 mb temperatures fall to 2C
to 4C today and stay there through tonight. With Lake Superior water
temperatures ranging from 15C to 17C, this is enough lake-850 mb
delta-t for lake effect pcpn and have some higher pops along the
lake shore to account for this. Overall, did not make too many
changes to the going forecast for temperatures or pops.

.LONG TERM...(Tuesday through Sunday)
Issued at 333 AM EDT MON SEP 26 2016

Focus for this week is on deep upper low and wrapped up sfc low
meandering over the Upper Great Lakes on Tue/Tue night. Ample deep
moisture to h7 and cyclonic flow with lake-h85 delta t/s over 8c
support widespread showers across Upper Michigan. WNW low-level
winds favor higher terrain of western Upper Michigan for the most
rain but it will be windy and damp across the entire cwa.

As upper low center slides across eastern Lk Superior on Tue aftn
and Tue evening and forecasted instability increases /sfc based CAPE
values 400-800j/kg/ could be setting stage for some thunderstorms
and possible waterspout development over scntrl and southeast Lk
Superior. Sfc low in vcnty only boosts low-level convergence which
would provide focus for waterspouts. Delta t/s 6-7c only marginal
for waterspouts per Szilagyi nomagram but convective cloud depth
forecasted up to 23-25 kft could tip the scales. See no reason to
not introduce at least a slight chance of waterspouts Tue aftn into
Tue evening for southern portions of Lk Superior. Locations along
LkSuperior shoreline from Big Bay to Marquette to Grand Marais and
Whitefish Point would be most favored to see waterspouts.

Sfc low sliding by just south of Upper Michigan on Tue night brings
winds around to a more NE direction. Focus for lake enhanced rain
showers should set up mainly west and north central cwa. Rain over
the east may tend to diminishing with downsloping/subsident flow
developing. System should slowly move toward Ohio Valley Wed into
Wed night as strong upper jet plowing across western Canada helps to
push ridge across the northern Plains to northern Ontario and Upper
Great Lakes. Northerly cyclonic flow on northwest flank of exiting
sfc low and lingering moisture blo h7 along with h85 temps 4-5c
should keep some showers going Wed as a weak lake enhanced setup
persists. Coverage and intensity will diminish though as drying
works in from the north as inversion steadily lowers. Waterspout
risk shifts to northern Lk Michigan on Thu as the upper low slides
across. Potential for waterspouts on Wed on northern Lk Michigan may
be even greater than on Lk Superior the previous day as delta t/s
with warmer water temps are 15-16c instead of less than 10c on Lk
Superior. Since upper ridge does not arrive in full force until Thu
there could be a few showers or at least mostly cloudy skies even as
late as Wed night into Thu morning.

Eventually ridging aloft and at the sfc should move in later Thu
into Fri bringing dry weather and a warming trend. ECMWF and to a
certain degree the GEM try to bring the upper low far enough north
by the weekend to bring rain chances back to the Upper Great Lakes.
ECMWF trended this way with 00z run last night and 12z run continued
to show that as well. Latest 00z run from tonight still on board
with that idea and even has qpf across Upper Michigan late Fri. GFS
keeps the upper low too far east of Upper Lakes to bring any precip
to the area. WPC hand drawn progs favor the farther east solution as
well. Will keep riding with the consensus of all guidance which
keeps it dry for Fri into the weekend. Next chance of rain comes
back into the area early next week. Highs Fri into the weekend
should top out in the 60s. Late this week if the high becomes
centered overhead for a night could see mins dip into the upper
30s at typical inland cold spots.

.AVIATION...(For the 06Z TAFS through 06Z Monday night)
Issued at 103 AM EDT MON SEP 26 2016

With low-level moisture already back on the increase over western
Upper MI, lower end MVFR conditions will likely prevail thru the
fcst period at KIWD/KCMX as sfc low pres drifts se toward Lake
Superior. Expect an increase in -shra coverage as well with deep
cyclonic flow and cooling air mass introducing a lake enhanced
component to the shra. At KSAW, some drying following recent cold
fropa combined with a downslope component to the wind should allow
VFR conditions to prevail into the morning hrs. MVFR conditions
should redevelop by early aftn and then persist thru the evening.
Winds will also become increasingly gusty today with the strongest
winds at more exposed KCMX where gusts will reach up to around 35kt
in the aftn/evening.

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 501 AM EDT MON SEP 26 2016

Active pattern on the waters continues with a gale event across most
of Lake Superior today into Tue morning for most of the lake. Tight
pressure gradient/increasing instability behind a cold front will
cause gales into Tue morning. With the slow approach of high
pressure, these strong winds will diminish later Tue into Wed. This
high pressure will then bring light winds to end the week. Could be
some waterspouts on Eastern Lake Superior Tuesday through Tue night
and also across northern Lake Michigan and bay of Green Bay Tue

Upper Michigan...
Lake Superior...
  Gale Warning from 2 PM this afternoon to 5 AM EDT Tuesday for

  Gale Warning until 11 AM EDT /10 AM CDT/ Tuesday for LSZ162-263.

  Gale Warning from 11 AM EDT /10 AM CDT/ this morning to 8 AM EDT
     /7 AM CDT/ Tuesday for LSZ240>242.

Lake Michigan...


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