Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 170905

Area Forecast Discussion
National Weather Service Marquette MI
505 AM EDT Thu Aug 17 2017

.SHORT TERM...(Today and tonight)
Issued at 501 AM EDT THU AUG 17 2017

WV imagery and RAP analysis indicated a vigorous mid/upper level low
over srn MN. At the surface, a 998mb low was located near MSP with a
warm front extending into se WI. A shortwave ahead of the low
supported a band of showers from wrn Lake Superior through west and
srn portions of the cwa.

Today, radar trends and short range high res models suggest that the
initial rain band will move into the ern cwa and nrn Keweenaw by 12z
with only isold/sct lighter showers over the rest of the area for
most of the morning. However, expect rain coverage to increase
during the afternoon with daytime heating and the approach of the
mid level low that should track into wrn Upper Michigan. Forecast
MLCAPE to around 1k J/Kg will also be enough to support
thunderstorms. The main threat will be for heavy rainfall,
especially central, of several inches with any stronger slow
moving shra/tsra clusters as PWAT values climb into the 1.50-2.00
inch range. Even though 0-6km shear will be weak, with the strong
vorticity center moving into the area there may be a slight
potential for a brief/weak funnel/tornado similar to what occurred
over srn MN Wednesday afternoon and evening.

Tonight, as the mid level low lifts to the northeast, the heavier
shra/tsra will diminish by late evening. Additional lighter wrap-
around rain/drizzlle will develop over the northwest half especially
where upslope nnw flow/lift is strongest.

The gusty southeast winds ahead of the low will result in high waves
and high swim risk for the beaches of Schoolcraft County today where
a Beach Hazards Statement is in effect.

.LONG TERM...(Friday through Wednesday)
Issued at 413 AM EDT THU AUG 17 2017

A fairly progressive pattern will prevail over the next 7 days. Very
well-defined shortwave currently lifting toward the Upper Great
Lakes will reach Quebec/New England on Sun. Meanwhile, the next trof
which arrives over western Canada Fri will reach central Canada
early next week and will then be in the Hudson Bay to Great Lakes
region on Tue. Longer range guidance is in quite good agreement that
the pattern should then slow down/become much more amplified across
Canada again as sharp ridging rebuilds over central Canada by late
next week. This will result in the trof over the Hudson Bay to Great
Lakes region on Tue amplifying over eastern N America during the
last half of the week. These large scale changes will lead to cool
conditions over the next couple of days as approaching trof crosses
the area. Temps will then swing above normal over the weekend ahead
of approaching cold front tied to the trof reaching central Canada.
As that trof then goes on to amplify over eastern N America, temps
will fall back, and there will probably be at least a couple of days
of blo normal temps during the last half of next week. As for pcpn,
wet period today into Fri associated with passing trof will give way
to a dry weekend for most of the fcst area. The next potential of a
more widespread pcpn event should arrive Mon into early Tue in
association with the cold front tied to the trof progressing from
central Canada to the Great Lakes region and Hudson Bay. Drier
weather will return late Tue thru Thu, but the amplifying trof over
eastern N America raises some concern for diurnally driven isold/sct
convection as summertime nw flow over the area is notorious for that
kind of activity.

Beginning Fri, sfc low pres will be exiting to the e of Lake
Superior/Upper MI during the morning. Wrap around/upslope enhanced
shra affecting much of the area early in the morning, except the s
central, will end from w to e during the day into the evening. It
will be a breezy day behind the rather vigorous low pres system for
Aug. NW winds will likely be gusting frequently into the 15-25mph
range from the Keweenaw to central and eastern Upper MI. Gusts up to
30 mph will be possible along the lakeshore over n central and ne
Upper MI. These blustery winds will lead to large waves and a high
swim risk for the Lake Superior beaches of Marquette and Alger
counties on Fri. However, it won`t be a day to go to the beach due
to clouds/shra and temps struggling to get out of the lower 60s over
the n central and ne fcst area where shra/cloud cover will be most
persistent. Not out of the question that a few locations will fail
to get above 60F if shra/clouds persist thru the daylight hrs. Over
the w and sw fcst area, temps may reach 70F, aided by some breaks in
the cloud cover during the aftn. Trailing shortwave dropping into
the departing trof late Fri night will probably prevent skies from
completely clearing out. Could even be a few sprinkles over the w
late Fri night.

Although potential is very low, passage of the trailing shortwave on
Sat may lead to isold -shra or a few sprinkles. Otherwise, expect a
partly cloudy, warmer day with temps rebounding back to normal or
even slightly above normal Sat aftn.

Trof moving across western Canada Fri will evolve into a broad mid-
level low over central Canada on Sun. Shortwave swinging around the
s and se side of the low will push associated cold front toward the
Upper Lakes late in the day, and it may spark a few shra/tsra over
the w. Ahead of the front, expect a warm day Sun with highs in the
80s, except e along Lake Michigan.

As the mid level low w of Hudson Bay drifts e, a shortwave will
amplify troffing into the Great Lakes by Tue. This additional energy
should support an increase in shra/tsra coverage along frontal
boundary and across Upper MI for Mon, perhaps lingering into Tue.
Dry weather should mostly follow for Wed/Thu. However, nw flow in
addition to the potential of shortwaves to drop se across area could
generate mainly diurnally driven isold/sct convection.

.AVIATION...(For the 06Z TAFS through 06Z Friday morning) Issued
at 122 AM EDT THU AUG 17 2017

VFR conditions are expected at all sites into early morning. A
shield of SHRA will spread northeastward across all sites overnight
through Thursday, resulting in deteriorating conditions at all
sites. Conditions will drop to LIFR/VLIFR at all sites on Thu and
this will last into Thu evening.

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 501 AM EDT THU AUG 17 2017

Easterly winds will increase today across central and eastern Lake
Superior as low pressure lifts from MN to the Upper Great Lakes.
Some gale gusts to 35 knots will be possible across eastern Lake
Superior from late morning into the afternoon. The winds will become
NW on Friday as the low departs to the east, with 20-30 knots
expected for the east half. Lighter winds, mostly under 20 knots,
are expected over the weekend into early next week with high
pressure over the region.

Upper Michigan...
  Beach Hazards Statement through this evening for MIZ014.

Lake Superior...
Lake Michigan...


LONG TERM...Rolfson
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