Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 121142

Area Forecast Discussion
National Weather Service Marquette MI
742 AM EDT Thu Oct 12 2017

.SHORT TERM...(Today and tonight)
Issued at 444 AM EDT THU OCT 12 2017

...Becoming cloudy from west to east with some drizzle by tonight...

High pressure has moved into Quebec while sfc low and associated
trough runs from scntrl Canada to the high plains. E to SE return
flow rotating around the high is bringing widespread low-level
stratus across the Ohio Valley into the western Great Lakes with the
clouds extending now as far as northwest Ontario. The moisture along
with SE winds are helping to develop low clouds in the U.P. as far
east as Marquette to western Delta county. Eastern forecast area
remains clear closer the departing high. Where skies have stayed
clear temps have fallen into the 30s. Clouds over the west has
allowed temps to bump back up into the 40s after being in the 30s
earlier tonight. Moisture advecting into the area from the south and
east is pretty thick with 00z sounding from Detroit (DTX) showing
moisture depth extending from 925mb/1500 ft AGL up to 750mb/7500ft
AGL. Clouds should continue to fill in from west to east into this
afternoon. With more sunshine over the east temps there could reach
mid to upper 60s, especially in downslope areas near Lk Superior
such as Munising and Grand Marais. Clouds will keep temps down more
over the west half of Upper Michigan.

Suppose there could be some drizzle late today over the west with
the depth of the moisture advection but think better chances of
drizzle and maybe even some light rain with up to 0.10 inch of qpf
holds off til this evening into the overnight hours tonight as lift
increases ahead of approaching front from the Northern Plains and
due to at least weak shortwave energy working in with developing sw
flow aloft. Also will be increasing divergence aloft/convergence in
low-levels due to approaching upper level jet from the Northern
Plains. May stay too mixed/too dry in the sub cloud layer with
southerly flow near Lk Superior for much drizzle but inland
locations and areas downwind of further moistening off Lk Michigan
could see some drizzle/light rain. Increased winds tonight over
north central and east closer to Lk Superior as low-level jet
arrives ahead of the front. Favored locations from Big Bay and
Marquette to Grand Marais and Whitefish Point could see wind gusts
up to 30 mph in the evening and early overnight hours. With the
winds and clouds and possible rain, temps tonight should be mainly
around 50 into the low 50s expect for coldest interior areas in the
upper 40s.

.LONG TERM...(Friday through Wednesday)
Issued at 409 AM EDT THU OCT 12 2017

The main weather impacts in the extended will be rain potential
Friday into Friday night and again Saturday night into Sunday. The
weekend system will also produce some gusty n-nw winds and also
higher waves/beach erosion along the Lake Superior shorelines,
depending on the exact strength of the system.

Friday into Friday night: A low pressure system over southern
Saskatchewan early this morning will lift into Hudson Bay Fri
morning. As this happens, the associated cold front with the system
will slide across the U.P. on Friday. Limited moisture transport and
weak forcing along and ahead of the cold front may only result in a
narrow band of isolated to scattered light showers along the frontal
passage. Given limited instability, thunder is not expected.
Temperatures will remain at or above normal Friday into Friday night.

Saturday and Sunday: After being in fairly good agreement with last
night`s runs regarding system fcst to move across the Upper Great
Lakes, models are now exhibiting much greater uncertainty with
track/strength and timing of system.  Models, particularly the GFS
and ECMWF, trending faster and stronger with shortwave approaching
from the west Sat night, which is having a bigger impact on
evloution of associated sfc low moving through the Upper Great Lakes
Sat night and early Sun. The 00z GFS shows the biggest change and
continues to trend even farther west and stronger/faster than 12z
run by tracking deepening sfc low across central Upper Mi at 997 mb
by 06z Sun and 992 mb low across eastern Lake Superior by 09z Sun.
The 00z Canadian remains similar in strength to last night`s 00z run
with a 1007 mb low tracking across northern Lower Mi in vicinity of
Gaylord around 12z Sun. The 00Z ECMWF has trended slightly farther
west and stronger than its 12z run with a 1001 mb low tracking
across eastern Upper Mi just after 06z Sun. Meanwhile the 00Z NAM is
closer in strength to the 00Z GFS but follows a track similar to the
00Z ECMWF only much slower than both the GFS and ECMWF. Following a
WPC preferred 00Z ECMWF/GFS/Canadian compromise with most of these
models trending quicker/stronger and farther northwest with sfc low,
would expect rain to spread in quicker from the south on Sat with
the best chance of widespread rain Sat night and then rain tapering
off quicker from the west on Sunday, except for some lingering
isolated to scattered nw-w flow lake effect showers along the Lake
Superior shores Sun night into Mon morning. Using a blend of the
ECMWF and GFS solutions would expect gusty n-nw winds and
breezy/windy conditions in the wake of the low late Sat night into
Sun as colder air moving in provides decreased stability, and thus,
better mixing especially near Lake Superior. Looks like gales late
Sat night into Sun would be a good bet across Lake Superior and
expect waves building to 10 to 12 feet to cause some minor beach
erosion especially along the central and eastern Lake Superior
shorelines on Sunday.

Rest of the extended (Mon afternoon into Wed:  Model consensus shows
absence of any shortwave troughs moving through the Upper Lakes with
a trend toward a mean mid-upper level ridge building over the region
and a return of much above normal temps through much of next week.

.AVIATION...(For the 12Z TAFS through 12Z Friday morning)
Issued at 740 AM EDT THU OCT 12 2017

Advection of low-level moisture to the west of high pressure to
the east of Upper Michigan has resulted in expanding stratus this
morning at IWD and SAW. Stratus should also move over CMX through
the rest of the morning. Expect the MVFR to lower VFR cigs to
continue over the area through tonight. There may be some drizzle
tonight at IWD and SAW but vsby will not be enough to reduce vsby
so have not included any drizzle in the TAFs attm.


.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 444 AM EDT THU OCT 12 2017

...NE to N gales possible on Lake Superior Sat night into Sun

Tightening pres gradient btwn high pres to the e and low pres
tracking ne to s central Canada will lead to an increase in winds to
generally 15-25kt across much of Lk Superior through tonight.
Winds will diminish slightly for Fri/Fri night as weakening cold
front associated with low pres tracking to Hudson Bay moves across
the Upper Lakes. New low pres will then lift ene along the
frontal boundary this weekend, passing across the Great Lakes Sat
night/Sun morning. Depending on the strength of the low and cold
air moving in behind the low, there may be a period of NE to N
gales Sat night into Sun morning over the west half of Lk Superior
and then Sun morning into mid Sun afternoon for the east half of
Lk Superior. Winds should be down to less than 20 kts by Mon.

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


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