Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 260837
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
437 AM EDT FRI AUG 26 2016

.SHORT TERM...(Today and tonight)
Issued at 340 AM EDT FRI AUG 26 2016

A surface cold front trailing a shortwave trough crossing Northern
Ontario into Quebec has crossed the Keweenaw Peninsula early this
morning. Slowly seeing expansion of low clouds as cooler air works
across Lk Superior behind the front. 00z KINL sounding showed h85
temps down to +7c and with water temps on Lk Superior in mid to
upper 60s (18-20c) we are coming close to meeing threshold for lake
effect rain showers. Airmass along and ahead of the sfc front fairly
dry so thus far the increase of clouds has been slow. Expect clouds
to continue to expand as h9-h8 moist layer just behind front settles
over Lk Superior. Before daybreak expect lake effect showers to
begin to form in wnw low-level flow over the west cwa. Additional
lift for showers will also come in this morning as shortwave over
eastern ND crosses western and northern cwa and Lk Superior. Cverall
the sufficient over-water instability along with lift fm the
shortwave and additional convergence along the sfc front moving
through will combine to produce isolated to scattered showers from
western cwa into central cwa through the morning. Not expecting a
lot of rain as deeper moisture is limited with this system but could
see up to a tenth of an inch of rain in areas that see the more
persistent showers.

Cold front settles over eastern cwa this aftn and with 925mb winds
more westerly, the low-level convergence near the front along with
daytime heating should be enough to develop additional showers near
the front over the east, especially mid to late aftn. Recent runs of
the HRRR show good continuity here and even suggest a few showers
may linger near Lk Michigan into early this evening as the front
slowly moves through. Highs today will remain in the 60s behind the
front especially near Lk Superior. Temps could reach low 70s over
scntrl with later arrival of cold front. High pressure is overhead
most of the night so interior cool spots may see temps as low as mid
to upper 40s. Return flow warm air and moisture advection kicks in
late tonight as upper trough deepens over the Northern Plains. High
clouds should increase but attm it appears bulk of any rain will
hold off til after daybreak on Sat morning.

.LONG TERM...(Saturday through Thursday)
Issued at 435 AM EDT FRI AUG 26 2016

Current pattern features a ridge/strong positive height anomaly over
the Gulf of Alaska extending n and e across the Arctic to Greenland.
To the s, a broad mid level low is centered in the vcnty of northern
Hudson Bay with trof extending sw into the southern Rockies. Over
the next few days, the swath of positive height anomalies across the
Canadian arctic region will strengthen in response to a powerful
storm moving from Siberia across the North Pole. The strengthening
positive height anomalies will lead to an elongated trof setting up
to the s from the Gulf of Alaska eastward across Canada early next
week, and farther s, a lower amplitude/zonally oriented flow across
southern Canada and the northern CONUS. As this occurs, one last
shortwave ejecting the current trof over the w will move across the
Upper Great Lakes this weekend. During the middle and later part of
next week, the flow will amplify as troffing deepens along the W
Coast, forcing a building ridge over central N America and a trof
over eastern N America. Under these expected changes, the current
cool down will transition to warmer conditions/above normal temps
early next week as westerlies retreat northward. Mid and late next
week, temps will depend on the amplitude and placement of the
trof/ridge/trof pattern across N America. If the central ridge and
eastern trof is displaced westward (eastward), the Upper Lakes will
be under cooler nw flow associated with the trof (warmer/more humid
conditions associated with the ridge). There is plenty of uncertainty
in this regard, and while above normal temps remain favored for now,
the 00z model runs are mostly trending toward greater amplification
and a westward shift of the ridge/trof so that the cooler scenario
may play out for a time. As for pcpn, aforementioned shortwave
lifting into the Upper Lakes will provide an opportunity for pcpn
this weekend, mainly Sat. Next shortwave will be moving across
southern Canada Mon/Tue. Associated cold front swinging across the
area will bring the next chc of pcpn, probably later Mon. As with the
temp uncertainty, pcpn chances for the remainder of next week will
depend on amplitude/placement of the trof/ridge/trof pattern. If the
area is more firmly under nw flow, it will be a drier pattern. If
not, there will be the potential for active tstm clusters at times as
disturbances ride around the ridge/hot air over the central CONUS.

Beginning Sat/Sat night, shortwave over the Dakotas Sat morning will
shift ene, crossing the Upper Lakes late Sat Night and reaching
Quebec Sun evening. The high res NAM window is a nw outlier bringing
a more defined sfc low and heavier pcpn ne across western Upper MI.
Other guidance generally points toward an ill-defined sfc low on
track farther e, yielding 2 areas of greater concentrated pcpn, one
associated with the ill-defined sfc low affecting more of WI/lower
MI/eastern Upper MI and the other more closely tied to the
approaching shortwave across MN. This could lead to gap of
dimimished pcpn coverage across a good portion of the fcst area.
For now, fcst will show pops generally chc w half/likely e half,
mainly Sat aftn/evening. Cloud cover/limited instability will keep
thunder potential low.

There should be some lingering morning low clouds Sun, especially if
the NAM is correct, but arrival of larger scale drying in the wake
of shortwave will result in increasing sunshine thru the day. GFS
looks too aggressive/quick in pushing a stronger WAA pattern into
the western Great Lakes already in the aftn, resulting in pcpn
developing across the w half of Upper MI Sun aftn. This solution was
discarded in favor of the majority drier idea.

Next shortwave tracking from s central Canada Sun night to northern
Ontario by Tue morning will push a cold front across the area,
probably Mon night. While there could be some convection in the waa
pattern ahead of shortwave, better chc of shra/tsra should occur
vcnty of cold front as it moves across the area Mon night. Max temps
Mon will be back to aoa 80F for much of the area.

If the model trend toward greater pattern amplification and westward
shift of central ridge/eastern trof is correct, front will be pushed
far enough s with sfc high pres building more strongly into the
Upper Lakes to allow dry weather to prevail for Tue/Wed and perhaps
even into Thu. Previous runs of the ECMWF had a flatter ridge,
allowing a shortwave and convective complex to round the ridge and
reach the area Thu. The more amplified ridge in the 00z run, similar
to the GFS, greatly diminishes that potential. In contrast, pcpn
potential could be tied to shortwave energy dropping s into the
deeper trof over se Canada.
&&

.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 1224 AM EDT FRI AUG 26 2016

A trough will drop through the area later on tonight. Behind it,
MVFR cigs should develop at all TAF sites late tonight into Friday
morning. Conditions will begin to improve Friday afternoon.
&&

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 340 AM EDT FRI AUG 26 2016

Lingering high waves are gradually coming down along the west shore
of the Keweenaw Peninsula early this morning. Otherwise, despite the
passage of a cold front today, expect winds into this weekend and
early next week to remain at 20 kts or less as the overall pressure
gradient will remain weak.
&&

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

$$

SHORT TERM...JLA
LONG TERM...Rolfson
AVIATION...Voss
MARINE...JLA


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