Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 121723
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
123 PM EDT Sat Aug 12 2017

.SHORT TERM...(Today and tonight)
Issued at 327 AM EDT SAT AUG 12 2017

High pressure will continue to build into the U.P. and Upper Great
Lakes from Minnesota through the day today. Clouds will diminish
over the east early this morning with a sunny day expected for all.
The return of sunshine will boost temperatures back to their
seasonal normals in the 70s. Clear and calm conditions will last
through tonight.

.LONG TERM...(Sunday through Friday)
Issued at 425 AM EDT SAT AUG 12 2017

Ridging/positive height anomalies which have been across western N
America, western Canada in particular, are now shifting e and ne in
response to a trof approaching western Canada. These positive height
anomalies will build while shifting to n central Canada this
weekend. Medium range guidance still indicates that this area of
positive height anomalies will then gradually settle into the Hudson
Bay vcnty and eastern Canada during next week. Initially, the
shifting of positive height anomalies to n central Canada will aid
in maintaining troffing over eastern Canada into the Great Lakes
thru Mon. Then, gradual progression of the positive height anomalies
will push the eastern trof out next week, leading to a more zonally
oriented flow across the northern CONUS. For Upper MI, these changes
will mean temps near normal initially will trend to modestly above
next week. Looking farther ahead, GFS/CMC/CFSv2 ensemble means
suggest that the shifting of positive height anomalies to eastern
Canada next week may be a new pattern that persists out thru the end
of the month. So, late Aug may end up on the warm side of normal. As
for pcpn over the next 7 days, drier conditions will be setting in
thru the first half of next week with any minimal pcpn chances tied
to lake breezes and/or shortwaves that may brush the Upper Lakes as
the eastern trof departs. One or more shortwaves tracking eastward
in the more zonally oriented flow developing mid week will then
bring the next potential of more organized pcpn in the Wed-Fri time
frame.

Beginning Sun, fcst area will be btwn a shortwave moving over the
Upper Mississippi Valley and another dropping thru northern Ontario.
While this favors a dry day, there is concern that isold convection
may develop along lake breeze boundaries, especially across the e
half where the lake breeze from Lake Superior and Lake MI converge.
Regional CMC is most aggressive with convection owing to its MLCAPES
as high as 1000j/kg. The NAM is more modest in the 300-500j/kg range
while the GFS only has 200j/kg or so. Given the warmer lake waters
at this time of year which become a source for greater boundary
layer moisture, in addition to the recent wet weather/greater soil
moisture which also contributes to boundary layer moisture, will add
a schc mention of shra to the interior central and e on Sun aftn. If
the CMC ends up being right, there will be some thunder as well.

As the eastern trof begins to exit out of the Upper Lakes on Mon,
shortwave that was over the Upper Mississippi Valley late Sun will
move over the western Great Lakes. This shortwave may aid isold
shra/tsra development Mon, especially along lake breezes.

Tue still looks dry with shortwave ridging pushing into the area
btwn departing eastern trof and trof moving across western Canada
and the western CONUS.

Medium range models still show shortwave energy progressing eastward
toward the Great Lakes in the mid to late week period under more
zonally oriented flow that will be developing. Since the 11 Aug 00z
model runs, there has been considerable run-to-run inconsistency in
the structure of the shortwave energy, including whether there will
be 1 or 2 waves. Given the inconsistencies, utilized a consensus of
current and recent model runs which results in chc pops for much of
the last half of the week, beginning as early as late Tue night.
&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 123 PM EDT SAT AUG 12 2017

VFR conditions expected at all TAF sites through the period.
&&

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 327 AM EDT SAT AUG 12 2017

Winds will remain at 20 knots or less through the remainder of the
weekend and through much of next week. The strongest winds of 20 to
30 knots will occur late Wednesday into Thursday as a cold front
approaches Lake Superior from the west.
&&

.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
None.
Lake Superior...
None.
Lake Michigan...
None.
&&

$$

SHORT TERM...MZ
LONG TERM...Rolfson
AVIATION...07
MARINE...MZ



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