Area Forecast Discussion
Issued by NWS Marquette, MI

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155
FXUS63 KMQT 291030
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
630 AM EDT Mon May 29 2017

.SHORT TERM...(Today and tonight)
Issued at 321 AM EDT MON MAY 29 2017

Upper air pattern consists of a closed 500 mb low over the upper
Great Lakes this morning that will slow move to between Lake
Superior and James Bay by 12z Tue. Numerous shortwave will continue
to move through the associated trough and rotate around this upper
low and this will continue to cause waves of convection to move
across the area and coverage will be determined by how strong the
diurnal heating is. Nam keeps some weak 850-500 mb q-vector
convergence over the area through 12z Tue along with some moisture.
Persistence is the way to go with this forecast and will again have
likely pops in for the afternoon into early evening with diurnal
heating being the strongest and causing the highest instability and
then diminish pops to chance tonight with diurnal cooling taking
place. Overall, did not make too many changes to the going forecast.

.LONG TERM...(Tuesday through Sunday)
Issued at 357 AM EDT MON MAY 29 2017

The main forecast highlights will be the warming trend through the
end of the week a periodic chances for rain showers. Tuesday looks
to be the coolest day through the beginning of next week, as cloud
cover remains in place and lingering rain showers across much of the
area. Confidence in how the weather will unfold this weekend has
increased a bit for Saturday, but early next week confidence remains
low.

On Tuesday as the pesky cutoff low lingers across the Upper Great
Lakes, rain showers are expected to linger, especially across the
northern portions of the area. As cooler 850mb air continues to wrap
around this system, expect temperatures to remain on the cool side,
about 10 degree below normal for this time of year. Tuesday night
through early Wednesday, rain showers will begin to exit the region
as the main upper-level low slowly begins to lift north towards the
Hudson Bay. During this time period, given the increasing 850mb
flow, along with a persistent pressure gradient at the surface with
cold air advection aloft, winds during this time period are expected
to be gusty.

Wednesday through Thursday, temperatures will rebound back to near
normal for this time of year, 60s and even some lower 70s. During
the day on Wednesday, conditions will begin to dry out as skies
clear with the main upper-level forcing well north of the area.
However, Wednesday night through Thursday, shortwave energy will dig
south across Ontario, merging and reinforcing the remnant cutoff low.
Depending on how far south this upper-level energy can return, we
could see the rain showers return in the afternoon hours on
Thursday/Thursday night. Friday looks dry as the medium range models
are in good agreement with upper-level subsidence increasing as the
main axis of the upper-level trough/cutoff low digs just east of the
of the region.

For the first half of the weekend, the ECMWF and GFS are coming into
better agreement with how the upper-level flow will evolve and
eventually exit the region as a shortwave traverses the northern
Plains and breaks down upstream upper-level ridging, acting as a
kicker wave to get the cutoff low to finally move. These model
trends favor high pressure dominating the Upper Great Lakes,
reducing precipitation chances. The GEFS plumes tend to favor this
as well, especially along the northern portions of Upper Michigan as
QPF among many of the ensemble members show little to no
precipitation accumulations. However, the Canadian is the outlier
among the deterministic models, as it is much stronger with the
above shortwave digging across the northern Plains, favoring the
development of low pressure in the lee of the northern Rockies, and
quickly moving into the western Great Lakes, bringing precipitation
chances across portions of Upper Michigan. Given the uncertainty,
still maintained PoPs for Saturday; however, with the evolution of
the upper-air patten coming into better agreement with the ECMWF and
GFS, tending to lean more towards the drier solutions at this time
across the north.

The end of the weekend into the beginning of next week, the
differences among the medium range model previously discussed begin
to snowball. With the GFS being a bit weaker with the aforementioned
shortwave digging across the northern Plains, it develops low
pressure and tracks it across the western Great Lakes Saturday night
through Sunday. This would favor chances for precipitation across
the area. Interestingly, the deterministic run of the GFS during
this time period compared to the GEFS plumes, albeit still a
positive outlier for precipitation, is one of the lower end
outliers. The Canadian on the other hand has the surface low moving
over the Lower Great Lakes and up into the Northeast; while the
ECMWF being much weaker with said shortwave activity, has high
pressure dominating over much of the Great Lakes region. Given the
significant differences among the medium range models, liked the
mentions of at least slight chance PoPs Sunday through Monday.
&&

.AVIATION...(For the 12Z TAFS through 12Z Tuesday morning)
Issued at 629 AM EDT MON MAY 29 2017

As a mid-level low drops into the Upper Great Lakes, disturbances
wrapping around it will generate sct to nmrs shra at times, most
nmrs during the daylight hrs today. These shra occurring over Lake
Superior will continue the low clouds over the waters, and with an
upslope wind off the lake at KCMX, conditions at that terminal will
improve to MVFR late morning and remain there thru the end of the
forecast period. At KIWD, will remain MVFR thru the fcst period. At
KSAW, VFR conditions should generally prevail today and will drop to
MVFR tonight.
&&

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 321 AM EDT MON MAY 29 2017

Winds are expected to be between 15 to 25 knot through Wed as an
area of low pressure is progged to dig across portions of the Upper
Great Lakes. Toward the end of the work week, as the surface
pressure gradient relaxes behind the exiting low pressure system,
winds will decrease to around 10 to 15 knots.
&&

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

$$

SHORT TERM...07
LONG TERM...Ritzman
AVIATION...07
MARINE...07



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