Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 081120

Area Forecast Discussion
National Weather Service Marquette MI
720 AM EDT Sat May 8 2021

.SHORT TERM...(Today and tonight)
Issued at 441 AM EDT SAT MAY 8 2021

Water vapor imagery and RAP analysis show an amplified pattern over
N America. A mid-level trof extends from BC to CA/AZ, a ridge is
over the High Plains extending n to the NW Territories and a trof
extends from Hudson Bay into the eastern U.S. Within the trof, a mid-
level low is centered over far northern Ontario, vcnty of James Bay.
Result is nnw mid-level flow across Upper MI early this morning with
areas of high based stratocu and ac cloudiness noted. These clouds
have mainly been over central Upper MI during the night, but there
is another area of clouds moving across western Lake Superior into
portions of western Upper MI. This second area of clouds is tied to
weak waa, and KDLH radar has shown some weak returns from the
clouds. The radar returns are too weak to support any pcpn reaching
the ground. Where skies are clear, temps have tumbled into the
middle 20s at traditional interior cold spots.

Today, Upper MI will remain under the influence of the mid-level low
centered over far northern Ontario. There are some hints that a
subtle shortwave will swing over the area within otherwise slightly
rising 500mb heights. Gradient flow today will be sufficiently weak
(950mb winds under 15kt) to allow lake breeze development. With the
subtle wave moving across the area, the sharper convergence zones
where the Lake Superior and Lake MI lake breezes meet and where the
Lake MI lake breeze pushes nw into the gradient nw flow may trigger
a few -shra/sprinkles during the aftn. Although there is a fairly
deep well-mixed subcloud layer that will work to evaporate falling
pcpn, a mention of isold -shra/sprinkles appears warranted over a
small portion of central Upper MI, basically s of Gwinn. Could be a
few sprinkles eastward toward Manistique/Newberry as well within
weaker portion of the convergence zone extending eastward.
Otherwise, inland from the stabilizing lake breezes, expect quite a
bit of diurnal cloud development today. High temps will range from
the 40s F lakeside along Lake Superior to the mid 50s F interior w
half. Aftn RH will fall to as low as around 25pct interior w, but
wind gusts will only be around 15mph this aftn in that area to help
keep fire wx from becoming more of a concern.

Any sprinkles will end early this evening. Under generally partly
cloudy skies, temps will fall back to readings similar to those
being observed early this morning, mid 20s to mid 30s F.

.LONG TERM...(Sunday through Friday)
Issued at 327 AM EDT SAT MAY 8 2021

The dominant weather feature for the CONUS and much of North America
will continue to be the broad trough and closed upper low over
Hudson Bay, the Great Lakes, and eastern Canada for the start of the
long-term period. However, as time goes on, this trough will lift
off to the northeast and ridging will build from the Northern Plains
eastward to the Upper Great Lakes, finally leading to a warming
trend. More unsettled weather is possible by the middle or end of
next week.

Sunday and Monday look to be a continuation of what we`ve been
seeing the past several days while in this pattern. Both days could
feature scattered daytime instability showers, especially Monday
when models show the ULL making its closest pass to the area and a
strong short wave trough pivoting around it. Precip is likely to be
a rain/snow mix in the morning both days transitioning to mainly
rain by afternoon. Model soundings show a thin sliver of CAPE
extending above the -10 C level to about 15 to -18 C both days, but
more so on Monday. This little bit of instability along with wet bulb
zero heights generally in the lowest 500-1000 ft AGL could support
some graupel with the stronger showers. 850 mb temps are likely to
remain around -5 to -6 C which will translate into highs mainly
in the 40s each day.

Beginning on Tuesday, troughing pulling out to the east will lead to
height rises aloft and warming temps. Given it will still be chilly
aloft in the morning with some cloud cover around to start the day,
have nudged temps down a couple degrees from the NBM initialization.
Still, highs in the 50s are likely in most areas as 850 mb temps
climb to around 0 C by late Tuesday afternoon. Wednesday is looking
even warmer with 850 mb temps reaching +1 to +2 C. EPS plumes show a
strong consensus for 850 mb temps to then increase further to
around +3 to + 5 C on Thursday and then remain there for Friday.
GEFS plumes show a little bit more spread but have the same general
signal. However, there is also a signal for cloud cover and showers
Thursday or Friday. Depending on how that evolves, Wednesday could
end up the warmest day of the week. Given the model spread that
emerges around Thursday-Friday, have opted to leave the NBM temps in
for this period which is mostly highs in the 60s.

.AVIATION...(For the 12Z TAFS through 12Z Sunday morning)
Issued at 720 AM EDT SAT MAY 8 2021

With dry air at the lower levels, VFR conditions will prevail thru
this fcst period at KIWD/KCMX/KSAW. Higher based cu/stratocu field
will expand today due to daytime heating, but cloud bases are likely
to be aoa 5kft.

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 441 AM EDT SAT MAY 8 2021

Winds across Lake Superior are expected to remain mostly under 20kt
thru the middle of the upcoming week. However, there will be a
couple of periods of somewhat stronger winds. The first will be Sun
morning when NE winds may gust to a little over 20kt over far
western Lake Superior. The second will occur on Mon when tightening
pres gradient will lead to NW wind gusts to around 25kt across much
of the e half of Lake Superior.

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


SHORT TERM...Rolfson
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