Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 190755
AFDMQT

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

.SHORT TERM...(This evening through Tuesday)
Issued at 421 PM EDT MON SEP 18 2017

High pressure brought dry weather to start the day but am now seeing
rain move back into western Upper Michigan. Rain is tied to
shortwave and right entrance region of upper level jet lifting
through in persisting southwest flow aloft. Expect the rain over the
west to slowly slide into the central and eastern forecast area
through the evening. Since forcing is not strong and the rain is
running into a dry airmass as seen on 12z raob from Green Bay WI,
expect the rain to diminish steadily as it moves through the area
this evening. As upper jet continues to lift north of Upper Michigan
overnight, expect any rain to end by that time. Did increase pops
through the evening as rain is expected, but again not looking at
much rain with most areas seeing less than a tenth of an inch of
rain. Clouds will hang around most of the night but should see
partial clearing overnight. If clearing occurs earlier in the night
there would be risk of shallow ground fog.

Improvement continues on Tuesday and this will be the start of
warming trend as well. H85 temps rising up to 12C will support highs
well into the 70s, especially inland west. High pressure sliding
east and approaching low pressure trough and warm front will result
in increasing east to southeast wind with strongest gusts over the
more exposed Keweenaw Peninsula.

.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 06Z TAFS through 06Z Tuesday night)
Issued at 131 AM EDT TUE SEP 19 2017

A disturbance that brought light showers to west and central
Upper Michigan during the evening will move out of the area
overnight. Conditions are expected to remain VFR through the
forecast period with mainly mid clouds prevailing overnight that
will clear out on Tuesday.
&&

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 421 PM EDT MON SEP 18 2017

High pres over the Upper Lakes will lead to winds mostly under 15kt
across Lake Superior through tonight. As the high shifts e on Tue
and a low pres trof moves out over the Plains, winds will begin to
increase a bit on Tue, but much more so Tue night and Wed as the
trof moves closer. SE to S winds will increase to 20-25kt across
much of the lake Tue night and will increase up to 30kt over north
central and eastern Lake Superior on Wed. 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.
&&

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

$$

SHORT TERM...JLA
LONG TERM...Ritzman
AVIATION...JLB
MARINE...JLA



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