Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 151914

Area Forecast Discussion
National Weather Service Marquette MI
314 PM 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 night through Tuesday)
Issued at 312 PM EDT TUE AUG 15 2017

The arrival of the strengthening low pressure system that has been
advertised for days still looks to move across Upper Michigan late
Wednesday night through Friday. The models have remains consistent
with the track of this low across portions of Upper Michigan and
Lake Superior during the day on Thursday. As the warm front pushes
north and moisture transport ramps up, as the ridge of higher theta-
e noses into the region, expect a fairly widespread area of rain to
move across much of the area. With PWATs approaching 1.5-2.0 inches
and warm cloud layer depths approaching 11,000-13,000 feet, rain may
fall heavy at times. Right now the timing of this rainfall across
the west  looks to be early Thursday morning through early afternoon
hours. The highest amounts are expected to reach the 1.5-2.0 inch
range primarily over the western half of Upper Michigan, where not
only the leading edge of the better moisture will take aim, but also
where wrap around precipitation within the deformation zone will
linger into the evening hours on Thursday. Through the morning and
afternoon hours, as the low pressure system tracks across the area
and the warm front lifts north the area of fairly widespread rain
showers will lift into central and eastern portion of the area.
Through the afternoon hours, models try to bring in a dry slot
across central portions of Upper Michigan. This will allow for a
break in the rainfall in some locations; however, as the cold front
pushes through later in the afternoon and evening hours, depending
on how much instability can get into south central portions of Upper
Michigan, there may be a round of afternoon/evening thunderstorms
near the triple point and south along the cold front. While mid-
level lapse rates do not look terribly impressive, resulting in
skinny CAPE profiles, models are forecasting upwards of 1500-2000
J/kg with around 30-40 knots of bulk shear. Therefore, it isn`t out
of the question that if we can get additional development, a few
storms could be on the stronger side across the south central on
Thursday afternoon/evening. This remains conditional as it will all
depend on how cloud cover evolves during the afternoon hours and how
far north the better moisture can get.

Lingering wrap around showers are possible across the central and
east Thursday night into Friday morning as the area of low pressure
moves over eastern Lake Superior and eventually tracks eastward into
Canada. Low-level wind fields are fairly consistent with northwest
winds behind the exiting low across much of the area, albeit not as
conducive in some locations to upslope flow as northerly flow would
be, still expect low clouds and perhaps some drizzle across northern
and eastern portions of the area on Friday. Due to the lingering
cloud cover and cold air advection behind the system, temperatures
will be about 10 degrees below normal.

The first part of the weekend looks like we could see a few showers
and perhaps a few rumbles of thunder as another shortwave trough
swings through the region. As this shortwave digs into the eastern
Great Lakes region, high pressure will take over on Sunday and allow
for temperatures to climb a few degrees above normal with drier
weather. A few locations may even see temperatures climb into the
lower 80s by the end of the weekend.

Early next week upper-level flow looks to become more zonal with
broad longwave troughing spanning much of central Canada. This will
push a trailing cold front eastward across the Upper Great Lakes
region and return chances for showers and thunderstorms.
Unfortunately, right now it looks like cloud cover may hinder our
ability to see the partial solar eclipse on Monday. However, given
the transition from a quasi-amplified upper-level pattern to more
zonal, there certainly is time for things to change!

.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 153 PM EDT TUE AUG 15 2017

Conditions continue to improve this afternoon as high pressure moves
in. Low stratus and/or fog may move in at KSAW tonight, but
confidence is low in exact details.

.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
LONG TERM...Ritzman
MARINE...Rolfson is the U.S. government's official web portal to all federal, state and local government web resources and services.