Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 151131

Area Forecast Discussion
National Weather Service Marquette MI
731 AM EDT Fri Sep 15 2017

.SHORT TERM...(Today and tonight)
Issued at 455 AM EDT FRI SEP 15 2017

An inverted surface trough/warm front is currently draped southwest
to northeast across Lake Superior, with much of the area under a
warm and humid airmass early this morning. Showers and
thunderstorms that developed last night across the Arrowhead of
Minnesota have tracked across western portions of Lake Superior.
The main forecast concern today and tonight will be the showers
and thunderstorms moving across western portions of Upper Michigan
through the morning hours, unseasonable warm temperatures, a
moderate swim risk for the beaches along northern Lake Michigan in
southern Schoolcraft County, and then the arrival of additional
showers and thunderstorm later this evening across the west.

Today: With the main axis of warm, moist air advection associated
with the ongoing early morning convection taking aim towards north
central portions of Lake Superior, expect these showers and storms
to continue to lift northeast across the west and north central
portions of Upper Michigan through the rest of the morning. With an
outflow boundary trailing into southwest portions of the area,
cannot rule out some additional development across the south as
moisture continues to stream overhead. However, the more
widespread convection is expected to stay across the west and
north central. By the mid/late morning hours, lingering showers
and storms should vacate the area and push out across the open
waters of Lake Superior. Cloudy skies will begin to break up a
bit, and possible even clear out in some locations through the
afternoon hours. We`re looking at another unseasonable warm
summer-like with temperatures around 10 to 15 degrees above normal
with breezy south winds. The breezy southwest winds will create a
moderate swim risk at Lake Michigan beaches in southern
Schoolcraft County.

This evening/tonight: Showers and thunderstorms will be possible
late in the day across the far west as the inverted surface
trough/warm front is progged to anchor across Upper Michigan. This
baroclinic zone should be further enhanced by the cooler air pushing
inland and increasing low-level moisture. Later tonight, the main
axis of better moisture is progged to lift north of the area as mid-
level flow transitions from westerly to southwesterly in response to
shortwave energy lifting north across the northern Plains. This will
keep the better instability west of the area for the most part, but
we should still see enough instability to warrant mentions of
thunder in the forecast. As the better, deeper moisture lifts north
into the Arrowhead of Minnesota over night, expect showers and
thunderstorms to come to an end across the west as we progress into
the overnight hours.

.LONG TERM...(Saturday through Thursday)
Issued at 441 AM EDT FRI SEP 15 2017

Recent medium range model runs have shown good overall agreement in
depicting a mean trof setting up over the western CONUS into
adjacent western Canada for the next 7 to 10 days. This will force
mean ridging over eastern N America. Pattern will be fairly
amplified with 500mb height anomalies in the trof and ridge reaching
200-250m in the middle and end part of next week. Under sw flow btwn
the trof and ridge, warm conditions will dominate the Upper Great
Lakes, resulting in above normal temps prevailing most days for at
least the next 10 days. Some days will be unseasonably warm. As for
pcpn, there will be some risk of pcpn for the next couple of days as
weak shortwaves lift ne, though much of the pcpn will end up n and w
of Upper MI, closer to and behind nearly stationary front extending
ne into the Upper Mississippi Valley and northern Ontario. Stronger
shortwave lifting from the Rockies to Hudson Bay will then push cold
front across the area Sun. A mostly dry pattern will follow fropa
early thru perhaps the middle of next week. Then, as western trof
deepens, where the associated sw to ne downstream sfc front sets up
will dictate pcpn pattern for the last half of next week. At some
point, the Upper Lakes should have the potential for decent rainfall
as the front shifts eastward, especially if the front is slow moving
as it passes across the area.

Beginning this weekend, stronger shortwave will lift out of the
Rockies and across the Dakotas Sat/Sat evening and into northern
Ontario on Sunday. This will support another sfc low pres wave
lifting along sfc front extending from the Plains to the Upper
Mississippi Valley. Although most of the height falls associated
with shortwave lift ne well to the nw and n of Upper MI, the
shortwave will finally give a push to the frontal boundary that has
been stalled out to the w and nw of here. Model agreement is quite
good showing cold front slowly shifting across the fcst area Sat
night thru early Sun aftn. With the main dynamics passing well nw of
here, shra/tsra coverage along cold front will probably tend to
diminish as it pushes across the area (greater coverage w, less e).
Nothing higher than chc pops appears warranted at this time along
and ahead of cold front. It will be an unseasonably warm/humid day
on Sat. Expect highs in the mid 70s to mid 80s with dwpts mostly in
the low/mid 60s. Fropa will bring cooler conditions on Sun, but
still above normal temps for most of the area with highs in the mid
60s to mid 70s. Should be breezy a day on the Keweenaw under post-
frontal westerly winds.

Sfc high pres will settle over the Upper Lakes on Mon. Despite this,
some current and recent model runs show some spotty pcpn. With the
anticyclonic flow in the lower levels, will maintain a dry fcst. Max
temps Mon will be in the mid 60s to around 70F.

Trof amplifying into the Rockies on Tue will lead to height rises
downstream over the western Great Lakes, and this should allow dry
weather to continue on Tue. However, there will be a weak shortwave
drifting within the rising heights over the western Great Lakes, and
it could end up generating some isold/sct shra.

Mid and late week, medium range model runs are suggesting that the
longitude of the western trof will be far enough w to allow
mid/upper ridging to be more dominant across the Upper Great Lakes
at least during the mid week period. As a result, the next
meaningful chc of pcpn will probably hold off until late week. Not
completely out of the question that remnants/moisture from tropical
storm Norma in the eastern Pacific could get caught up by the
western trof and transported ne toward the Great Lakes to enhance
rainfall potential late in the week.

.AVIATION...(For the 12Z TAFS through 12Z Saturday morning)
Issued at 731 AM EDT FRI SEP 15 2017

Showers and thunderstorms tracking east across the area this morning
will continue to impact KCMX, otherwise, expect dry conditions to
prevail today with increasingly gusty winds, especially at KSAW,
this afternoon. There is a slight chance KIWD could see storms later
this evening, but coverage doesn`t look like it will be terribly
high so opted to leave mentions out for now. Late tonight into early
Saturday morning, it does look like low-level wind shear will be on
the increase as enhanced flow just above the surface tracks
northeast across the area. As low-level moisture increases some
terminals may also see lower ceilings develop tonight.

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 455 AM EDT FRI SEP 15 2017

An inverted surface trough currently anchored across Lake Superior
will strengthen later today and tonight, expect winds between 20 to
30 knots in response. Saturday through Sunday, winds will be around
or less than 20 knots. Next week, winds look like they will remain
less than 15 knots through the first half of the week.

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


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