Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 191136
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
736 AM EDT Tue Sep 19 2017

.SHORT TERM...(Today and tonight)
Issued at 508 AM EDT TUE SEP 19 2017

Water vapor imagery and RAP analysis show long advertised trof
amplifying into the western CONUS. Mid-level low that was over
northern Ontario 24hrs ago is now over Hudson Bay. Result is wsw
flow over the Upper Lakes early this morning. Shortwave and right
entrance of an upper jet streak supported shra that moved into
western Upper MI yesterday aftn. Those shra have shifted e thru the
night while diminishing in coverage/intensity. Sct -shra currently
still linger from Menominee County to eastern Lake Superior. Plenty
of cloud cover remains over the fcst area, and this has helped to
hold temps up in the 50s during the night.

The ongoing lingering -shra will end over the next couple of hrs as
upper jet shifts e. Breaks in the cloud cover are beginning to show
up in northern WI, and this improving sky trend should expand across
the area today, leading to mostly skies for the aftn hrs. This
should allow temps to rise into the low/mid 70s for much of the fcst
area. Coolest conditions should be n of the Portage Canal under ese
winds off Lake Superior.

Vigorous shortwave will swing out of the western trof tonight. This
shortwave will reach the eastern Dakotas by 12z Wed with associated
sfc trof running n-s thru MN. Strong to svr thunderstorms should
develop along the sfc trof late this aftn/evening over the Dakotas,
then spread across MN overnight. This convection will then be
weakening as it approaches far western Upper MI toward daybreak.
Consensus of model guidance supports chc pops into Gogebic/Ontonagon
counties after 09z. Increasing southerly flow will lead to a warm
night in the downslope locations over the western fcst area. Temps
won`t drop blo the lower 60s in that area. 50s should be the rule
elsewhere.

.LONG TERM...(Wednesday through Monday)
Issued at 353 AM EDT TUE SEP 19 2017

Overall, there is not much of a change to the extended than what has
been advertised now for the last couple of days. We will see a
significant warming trend through the end of the work week, with
record heat looking likely on Friday as temperatures soar 15 to 25
degrees above normal for this time of year. This warm weather is
expected to persist through the weekend. Periodic chances for
showers and thunderstorms are expected into early next week,
especially out west.

Wednesday and Wednesday night: The main concern is the potential for
thunderstorms as a cold front arrives from the west during the
afternoon hours and into the overnight hours. Also, ahead of the
front, south-southwest winds are expected to increase and become
gusty and may impact mariners in the near-shore zones from Big Bay
down through Munising on Lake Superior. BUFKIT soundings show
momentum transport values approaching the 30 to 40 knots in these
downslope regions near Lake Superior during the afternoon hours.
Also ahead of the cold front, the medium range models are in fairly
good agreement with surface dew points climbing into the low to mid
60s; this combined with steepening mid-level lapse rates should
allow 1000-1500 J/kg of MUCAPE to develop through the afternoon
hours and sustain updrafts of any ongoing or newly developing
convection. With the deep-layer shear expected to be around 40 knots
and oriented quasi-perpendicular to the cold front, this will also
allow updrafts to remain organized. However, there are a few
concerns/caveat that will likely impact the coverage and/or
intensity of showers and thunderstorms. First, the main forcing is
expected to lift northeast into Canada as the main shortwave lifts
across the Arrowhead of Minnesota. Secondly, CAPE profiles do not
look terribly impressive and are very skinny given the amount of dry
mid-level air expected to be in place. That being said, do not
expect coverage to be widespread, rather thinking that convection
should remain more scattered along the front as it pushes east
through the day on Wednesday. A few storms may be strong to severe,
especially further south along the Wisconsin border where the nose
of better instability is progged to nudge northward. As the front
continues its eastward push, lingering showers and thunderstorms
will continue mainly across the central and east into the overnight
hours.

Thursday through Friday:  The above mentioned cold front will slow
its southward progress and retreat back northward as a warm front.
This should allow for small chances for showers and perhaps a few
rumbles of thunder late Thursday into Friday. Then the attention
turns towards the significant warm up expected as a highly amplified
upper-level pattern sets up across the central CONUS and ushers in
unseasonably warm air, with 925 to 850mb temperatures pushing
upwards of 19-22C on Friday. These warm temperatures within the
boundary layer will work in concert with downslope winds to allow
temperatures to climb into the 80s across much of the area.
Numerical guidance over the past couple of days has trended a bit
warmer each day; therefore, wouldn`t be surprised if a few locations
break the 90 degree mark. With the synoptic flow not expected to be
terribly strong, the lake breeze should develop and increase in
strengthen during the afternoon hours. A few models are showing the
potential for some convection along this lake breezy boundary across
the north central; however, capping looks stout given the warm air
aloft.

This weekend into early next week: The main baroclinic zone progged
to develop in response to the longwave troughing out west is
expected to remain west of the area across the Arrowhead of
Minnesota for the most part through the weekend and into early next
week. Therefore, we will remain on the warm side of this boundary
with temperatures expected to remain 10 to 15 degrees above normal
for this time of year. Confidence is not high in regards to how
precipitation chances will play out, but there definitely looks like
a chance for periodic showers and perhaps some thunder as the
baroclinic zone looks to wobble a bit west to east with subtle
shortwave energy lifting across the Upper Great Lakes region. The
main baroclinic zone is progged to finally push across Upper
Michigan early next week as the main trough axis finally begins to
eject out of the west and across the Upper Great Lakes region. This
will bring increased chances for showers and thunderstorms, along
with cooler more seasonable temperatures towards the middle/end of
next week.
&&

.AVIATION...(For the 12Z TAFS through 12Z Wednesday morning)
Issued at 736 AM EDT TUE SEP 19 2017

VFR conditions will prevail into the evening hrs at KIWD/KCMX/KSAW
under a relatively dry low-level air mass over the area. Approaching
sfc trof will result in a tightening pres gradient tonight.
Increasing winds above sfc based stable layer as low-level jet
approaches will lead to LLWS developing at KIWD/KCMX tonight.
Meanwhile, upslope flow off Lake MI should lead to fog (IFR vis) and
potentially an LIFR cig late tonight at KSAW. Could be a shra/tsra
at KIWD near the end of the fcst period, but confidence in arrival
before 12z is too low to include mention in this fcst issuance.
&&

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 508 AM EDT TUE SEP 19 2017

With high pres e of Lake Superior shifting to southern Quebec and a
low pres trof moving out over the Plains today, winds will begin to
increase some across Lake Superior today, most notably over western
Lake Superior where easterly winds will increase to 15-25kt in the
aftn. Winds will increase more so tonight into Wed as the trof moves
closer. SE to S winds will increase to 20-25kt across much of the
lake tonight and will increase up to 30kt over north central and
eastern Lake Superior on Wed. Not out of the question that there
could be some gale force gusts to 35 knots. With passage of the
trof, winds will drop off quickly to under 15kt from w to e
Wednesday night with these lighter winds lingering thru Thu. Wind
should be mostly under 20kt Fri and Sat as Lake Superior becomes
situated btwn a low pres trof the w and high pres to the e. Could be
some stronger winds at times, depending on whether any low pres
waves track ne along the trof.
&&

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

$$

SHORT TERM...Rolfson
LONG TERM...Ritzman
AVIATION...Rolfson
MARINE...Rolfson



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