244
FXUS63 KMQT 060538
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
138 AM EDT Sat Jul 6 2024

.KEY MESSAGES...

-Mainly dry Saturday, but a rain shower cannot be entirely ruled out
(~20%) along the MI/WI state line in the afternoon.

-Sunday through Wednesday, daily chances of showers and
thunderstorms, highest chances in the afternoons.

-Dry period begins Thursday, could be dry into next weekend.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 232 PM EDT Fri Jul 5 2024

Water vapor imagery showing shortwave/mid-level low moving out
of WI into Lake Michigan. Dry slotting over the central U.P. has
kept the precipitation to mainly isolated shras there but with
some recent breaks in the clouds across baraga and Iron counties
additional shras are beginning to pop up. Better forcing has
been over the eastern U.P. where the rain has been more
persistent. As forcing continue to wane this afternoon,
precipitation coverage will become less and less from west to
east. Skies will then clear from west to east tonight as the low
moves across lower Michigan into Ontario by Saturday morning.
Still can`t rule out some patchy fog later tonight especially
where rain as been more persistent. Temperatures tonight will
fall into the 50s, perhaps a few upper 40s in the typically
interior west cooler locations.

&&

.LONG TERM /SATURDAY THROUGH FRIDAY/...
Issued at 327 PM EDT Fri Jul 5 2024

After a very progressive pattern kicked off this summer, a more
blocky pattern has now emerged as 500mb ridging over western North
America will only very slowly progress eastward with time throughout
this forecast period. The consequence of this for the UP will be
dealing with the low-amplitude shortwaves that spill southeast from
the ridge. While none of these shortwaves on their own are going to
be strong enough to force any surface low pressures deeper than
about 1010mb per the 12Z GEFS, with the help of diurnal heating,
chances of rain will increase each afternoon with 20-35% chances of
thunder with each round. As the the northern arm of the ridging
slowly moves off of the Canadian Rockies, signal is strong for high
pressure to usher in a period of dry weather Wednesday night into
the weekend for the longest dry stretch of the summer for the UP so
far.

By Saturday morning, with the previous low pressure over the Lower
Great Lakes, the final showers will end in the far eastern UP. Weak
surface ridging is expected to take the place of the departing low,
as the high pressure center is forecast to be near TN at 1015 mb.
Because the high is so weak and far away from the UP, not enough
subsidence will be present to completely preclude some low-impact
diurnal showers along the MI/WI state line, with the HREF showing
only scattered 20% PoPs by 00Z. A quiet night is expected Saturday
night, but cloud cover begins to increase ahead of the next
shortwave trough sliding southeast off the western ridge. Global
deterministic models do begin to diverge here as to how the series
of minor shortwaves progresses, but the general outcome seems to be
a mainly diurnal pattern of precipitation Sunday through Wednesday
with lower PoPs in the overnight periods in between. Given how weak
synoptic surface forcing is, the ability of diurnal forcing to help
initiate showers will be key in determining PoPs as well as
thunderstorm chances, though severe weather is unlikely because of
said lack of forcing and wind shear. Most deterministic guidance
does have the trough beyond the UP by Wednesday, so PoPs are lower
by a fair margin on Wednesday, but enough ensemble spread exists to
keep at least 20-40% PoPs in the forecast for now. As the northern
portions of the ridge shift off of the Canadian Rockies over the
Prairie and towards the Upper Great Lakes, high pressure looks to
settle over the UP for Thursday and beyond, with the 12Z GEFS
showing a ~1020mb high over the UP Thursday morning and building to
the mid 1020s mb over the rest of the Great Lakes basin by the
weekend. This will usher in a dry period to end next week, with the
potential of a multiple-day period of no rain across the UP,
something that has not been common this summer so far.

&&

.AVIATION /06Z TAFS THROUGH 06Z SUNDAY/...
Issued at 137 AM EDT Sat Jul 6 2024

Patch of LIFR/IFR cigs/vsby originating from Lake Superior continues
to blow into SAW. They are near the edge of this cloud patch, so
conditions may fluctuate between VFR/LIFR through around 12Z before
any remaining low cigs/vsby mixes out, with VFR expected for the
remainder of the day. Shallow MVFR/IFR fog patches will probably
plague IWD up until shortly after sunrise. VFR should prevail there
for the upcoming day, but a few showers and perhaps an isolated
thunderstorm will be possible during the 21-03Z timeframe. VFR
expected to continue through the TAF period at CMX, but will be
watching for fog/stratus patches over the lake to upslope to the
terminal under WNW winds. Included SCT clouds at 400ft for now, but
there is potential for a few hrs of LIFR conditions until shortly
after sunrise.

&&

.MARINE...
Issued at 327 PM EDT Fri Jul 5 2024

Light winds of 20 knots or less will continue across Lake Superior
this weekend through next week as a cycle of weak shortwave lows
followed by weak ridging continues across the Upper Great Lakes as
high pressure continues to build over the western CONUS. That being
said, a few of the disturbances will be strong enough to produce
some thunderstorms across the lake from time-to-time over the next
several days, mainly along the nearshores today into this evening
and again each day during the daylight hours Sunday through next
Wednesday.

&&

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

&&

$$

SHORT TERM...MZ
LONG TERM...GS
AVIATION...Thompson/Rolfson
MARINE...GS/TAP