Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 280657

Area Forecast Discussion
National Weather Service Marquette MI
257 AM EDT Sun May 28 2017

.SHORT TERM...(This evening through Sunday)
Issued at 355 PM EDT SAT MAY 27 2017

Tonight: As a broad surface low and upper level 500mb closed low
remains nearly stationary over northwestern Ontario, a cold front
will slide from the central U.P. into the eastern U.P. this evening
and stall during the overnight hours. At the same time, a quick
moving shortwave is progged to slide through the east half of the
U.P. This will help to focus scattered rain showers across mainly
the central to eastern portions of the area through the overnight
hours. There may be enough instability in the evening for a couple
rumbles of thunder; however, with the loss of daytime heating, the
thunder potential should quickly diminish. Otherwise, expect partly
to mostly cloudy skies across the CWA with the best chance of seeing
partly cloudy conditions over the west half.

Sunday: The cold front/trough is expected to be nearly stalled out
over the eastern U.P. At the same time, a surface low over the mid-
Mississippi Valley is expected to lift northeastward and ride along
the surface trough/front into Lower Michigan. The added
moisture/forcing from the approaching low along with the continued
weak forcing along the front/trough will allow for widespread
showers and thunderstorms, with the main focus being over the east
half of the U.P. The west half of the area will see heights fall
throughout the day as the broad trough begins to slide over the
area. This will allow for enough instability to cause the coverage
of showers and thunderstorm to increase for the west half as well,
during the afternoon hours. While there will be some instability
around, weak wind shear will greatly reduce any severe potential
from any thunderstorms that form with only isolated small hail
possible with lowering freezing levels. Any lightning that occurs
would be the biggest threat due to the holiday weekend.

.LONG TERM...(Monday through Saturday)
Issued at 256 AM EDT SUN MAY 28 2017

The main forecast highlights are a cloudy and cooler Memorial Day,
with chances for lingering showers across much of the area, and some
thunder possible across the south central and eastern portions of
Upper Michigan. The cooler temperatures will linger through Tuesday,
with lingering rain showers across the area. Towards the middle/end
of the week, temperature will rebound back to near normal, but
additional precipitation chances may be on the horizon. Next
weekend is a challenging forecast considering the models are
struggling to break up the dominant cutoff blocking flow across the
Great Lakes region.

As a pesky upper-level low is expected to linger across the region,
confidence is high that cooler temperatures will prevail with
lingering chances for rain showers, as multiple rounds of vort
maximums rotate in and out of the area, through Wednesday. It
doesn`t look like we will see a persistent rain through the whole
time period, rather periods of rain showers across the area. Monday
will be the best chance at seeing any additional thunderstorm
activity, as mid-level lapse rates will be steepest, with the cutoff
low pushing overhead during the day, and one last bout of
instability develops across central and eastern portions of Upper
Michigan. The shear on the other hand doesn`t look impressive, so
updrafts may struggle a bit to maintain their intensities. Scattered
area-wide showers will continue Tuesday and early Wednesday, then
the main upper-level low slowly try to lift out of the region.

Towards the middle/end of the week, the medium range models start to
diverge on the track and return of cutoff energy aloft. The GFS is
stronger, and thus slower; while the ECMWF is much faster with the
cutoff energy. Depending on how the upper-air pattern evolves the
better precipitation chances could come on either Thursday or
Friday. Therefore, confidence is a low in how precipitation chances
will pan out. All that being said, how far west the main trough axis
gets and where additional shortwaves track will be the key to where
any additional precipitation develops later this week.

Confidence continues to decrease as we get to next weekend with the
medium range models struggling to come to a consensus, which makes
sense as they struggle to break up the blocking pattern we will be
in for much of this week. Given the potential for lingering upper-
level energy with vort maximums still rotating and digging across
the area; cannot rule out additional chances for rain next weekend.

.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 1254 AM EDT SUN MAY 28 2017

VFR conditions should mostly prevail at KIWD/KCMX/KSAW thru this
fcst period. However, there are some concerns. First, with the
rainfall that has occurred at KSAW during the evening, expect some
fog at times overnight, reducing vis to MVFR. If clouds happen to
scatter out, vis will fall more substantially. A couple of
disturbances will then affect the Upper Lakes, mainly during the day
today, generating sct to nmrs shra across the area. Conditions could
certainly fall to MVFR if any of the shra affect the terminals. Not
out of the question that there could be a rumble of thunder as well.

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 355 PM EDT SAT MAY 27 2017

Through the weekend, winds of 10 to 20 knots are expected across
Lake Superior. Early next week, winds will increase to around 20 to
25 knots as an area of low pressure is progged to dig across
portions of the Upper Great Lakes. Towards the end of the week as
the surface pressure gradient relaxes behind the exiting low
pressure system, winds will decrease to around 10 to 15 knots.

Upper Michigan...
Lake Superior...
Lake Michigan...


LONG TERM...Ritzman
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