Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 220847

Area Forecast Discussion
National Weather Service Marquette MI
447 AM EDT Sat Jul 22 2017

.SHORT TERM...(This evening through Saturday)
Issued at 400 PM EDT FRI JUL 21 2017

The main impact during the short-term portion of the forecast will
be severe weather potential Saturday afternoon into Saturday evening.

Tonight: A convectively induced shortwave is progged to slide across
southern WI this evening into the overnight hours. Models have been
steadily trending a bit farther to the south with this over the past
couple days, with the latest 12Z data continuing that trend. The
best moisture convergence is progged to remain across central to
south-central WI, which again lends more support to keeping the more
concentrated area of convection south of the U.P. It is still
possible that a few showers an maybe an isolated thunderstorm may
make it into the U.P., along the WI border, but the chances look to
be fairly limited. Southern Menominee county would have the best
chance of seeing some precipitation out of this, but it would be
fairly fast moving during the overnight hours, with very little
severe potential. Instability in the U.P. looks to be fairly limited
to the north of the Theta-e gradient across WI with only around 100 -
 200 J/kg expected along the southern portions of the U.P. this
evening. Outside of that, not really expecting much in the way of
widespread precipitation tonight. There could be a few rain showers
that slide across the rest of the area overnight tonight as another
area of decaying showers and thunderstorms/shortwave slides across
northern MN toward the U.P. Again, the lack of instability and
limited moisture convergence across the northern half of the U.P.
would help to steadily diminish the coverage and intensity of any
showers as shown by most of the hi-res model guidance.

Saturday: Cloud cover will steadily increase across the area through
the afternoon hours. This will be along and ahead of an approaching
cold front from the northwest. In addition, a stronger shortwave
will push into the western portion of Lake Superior by early evening
as the cold front progresses through the west half of the U.P.
Dewpoints will steadily increase ahead of the cold front, reaching
into at least the mid 60s by Saturday afternoon. The increasing
moisture advection along with heating of the day and increased
forcing along the front will help to touch off showers and
thunderstorms over the west half of the U.P. by late Saturday
afternoon into the evening hours. Some of the thunderstorms ahead of
the cold front could be strong to severe with the main threats being
gusty winds and large hail from the strongest storms. Instability is
progged to be around 1000-1500 J/kg along with shear values around
35 to 45 knots perpendicular to the front, which again lends support
to better organized storm structure during peak heating.

.LONG TERM...(Sunday through Friday)
Issued at 356 AM EDT SAT JUL 22 2017

Generally a pretty quiet stretch of weather in the long term. Strong
shortwave trough still will be over the Upper Great Lakes on Sunday.
This wave along with inverted sfc trough will support showers and
some thunderstorms mostly over the east half into early Sun aftn.
Sun will also be cooler (all but the far scntrl) with low clouds
and given the moist cyclonic upslope flow behind the departing low
there may also be drizzle in the higher terrain of the west and
north central. Low clouds and some drizzle likely will persist
well into Sun night before high pressure/drier air lead to improving
conditions through Mon morning.

The high pressure will result in quiet weather Mon into most of Tue.
Next shortwave in NW flow aloft will move through on Tue night.
Could be scattered showers and a few thunderstorms late Tue aftn
into Tue night. Appears forcing outruns greater instability which
pokes into southern U.P. Tue evening. Mismatch of these two factors
probably reduces the chances of seeing any severe storms. Once the
trough moves through, high pressure resumes dry weather for the rest
of the week.

Temperatures will generally be at or slightly above normal but we
should not be dealing with more persistent summertime humidity.
Coolest temps will be on Mon in wake of the low pressure system that
moves through this weekend. Warmest days of the week, with readings
possibly well into the 80s in parts of forecast area, will be Tue
and Wed. The humidity this weekend will be replaced by less humid
conditions on Mon with the high drifting overhead. Humidity will
increase again Tue/Wed as the sfc trough moves through. Less humid
conditions then return later this week.

.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 123 AM EDT SAT JUL 22 2017

With rainfall that has occurred around KIWD, expect VFR conditions
to fall to MVFR by daybreak. Not out of the question that conditions
could fall to IFR. MVFR conditions should then continue into early
aftn. At KCMX and KSAW, VFR conditions should prevail thru the
morning hrs, but will need to watch for stratus to develop northward
toward KSAW. There could be some shra and isold thunder overnight
thru the morning, but confidence in any of the terminals being
impacted is low. Better potential of shra/tstms will arrive this
aftn/evening as a vigorous disturbance approaches. MVFR or even
brief IFR conditions may occur with any of the shra or tstms.

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 440 AM EDT SAT JUL 22 2017

East to northeast winds gusting to 25 kts today, strongest over
western Lk Superior, as low pressure system and cold front slide
toward Great Lakes from the northern Plains. East to southeast winds
will remain gusty tonight mainly over eastern Lk Superior toward
Whitefish Bay. Sfc low slides over central Great Lakes on Sunday
while cold front drops south across Lk Superior. Expect east winds
to shift north to northeast 20 to 25 kts on Sun aftn behind the
front. Winds will gradually diminish Sun night into Mon as high
pressure builds across the region. Low pressure trough moving in
late Tue may lead to southwest winds increasing to 25 kts late Tue
into Tue night. Otherwise, winds this week should be 20 kts or less.

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


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