106
FXUS63 KMQT 060722
AFDMQT

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

.KEY MESSAGES...

- Slight chance (~20%) for late afternoon showers and thunderstorms
across interior western Upper MI today.

-Sunday through Wednesday, daily chances of showers and
thunderstorms, highest chances in the afternoons. Could see a couple
of strong storms Sunday and maybe Monday (higher uncertainty).

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

&&

.SHORT TERM /THROUGH THIS AFTERNOON/...
Issued at 321 AM EDT Sat Jul 6 2024

Water vapor imagery and RAP analysis show that the shortwave that
brought shra to the area yesterday is exiting eastern Upper MI. A
few -shra associated with that feature are still lingering over the
eastern fcst area. The rainfall that occurred over Lake Superior has
generated fog/stratus, and the fog/stratus has been moving onshore
across the e half of the fcst area, roughly e of Marquette to
Menominee line. To the w, skies are clear, and with winds light to
calm, patchy fog is developing. Current temps generally range
through the 50s F, but some mid and upper 40s F are noted at
traditional interior cold spots over the w.

Patchy fog over the w will dissipate within an hr or so after
sunrise. To the e, fog/stratus will also dissipate this morning
after sunrise from s to n. However, GOES night fog imagery shows
quite a bit of fog/stratus over eastern Lake Superior. With meso
high developing over eastern Lake Superior today, resulting in
onshore winds, areas very close to the lake may see fog/stratus
linger well into the aftn. Attention then turns to possible aftn
convection over western Upper MI. Models show MLCAPE building to
anywhere from a few hundred j/kg to up to around 1000j/kg this aftn.
Although weak mid-level shortwave ridging moving over the area is a
negative for convection, nearly all of the 00z models show isolated
convection developing this aftn, similar to previous runs. Have thus
opted for slight chc pops (15-24%) over interior w half of Upper MI,
roughly s of a line from around Ironwood to Champion, Gwinn to
Menominee. High temps today will range thru the 70s to around 80,
except 60s F along Lake Superior, especially from around Marquette
eastward. If fog and stratus linger thru the day close to the lake,
lakeside locations in Alger/Luce counties will only top out at about
60F.

&&

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