Area Forecast Discussion
Issued by NWS Marquette, MI

Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
FXUS63 KMQT 222036

Area Forecast Discussion
National Weather Service Marquette MI
436 PM EDT Fri Sep 22 2023

.SHORT TERM...(This evening through Saturday)
Issued at 313 PM EDT FRI SEP 22 2023

GOES Day Cloud Phase imagery shows an expansive marine fog layer
over the west half of Lake Superior and the first signs of some cu
field development. This cu field is developing ahead of a shortwave
riding the ridge currently over the Great Lakes Basin. The diurnal
heating support has about a 20-30 percent chance of kicking off some
scattered to isolated thundershowers in the western half this
evening as shown in the NAM Nest, WRF Fv3 and WRF ARW, though many
other CAMs do not show convection, so PoPs are limited. A more
prominent backdoor shortwave will be arriving overnight, supporting
a more widespread round of showers and thunderstorms for the western
half of the UP. For the eastern half of the UP, skies remaining
mostly clear should allow for yet another round of patchy dense fog.
However, with the approaching disturbed weather, the compressed
pressure gradient may drive surface winds to be too high for
radiation fog in some spots. Therefore, widespread fog that
necessitates a product is unlikely, but patches of dense fog are
certainly possible, especially as ENS visibility meteograms show 50
percent or higher chances of dense fog for Marquette, Houghton,
Escanaba, Munising, and more locations. One area of particular
concern is the potential for any marine fog that develops east of
the Keweenaw Peninsula to advect westward onto land, in which case
the fog may be more uniform and more difficult to dissipate.

.LONG TERM...(Saturday night through Friday)
Issued at 436 PM EDT FRI SEP 22 2023

Key Messages:
-Patchy fog at times, mainly near and downwind from Lake Michigan.
-Low pressure system provides precip chances Saturday morning
and gusty winds Saturday afternoon over the far western U.P.
-Mostly dry forecast after the weekend, dominating high pressure
could lead to increasing fire weather concerns.

Starting with Saturday morning, the UP is wedged between a sprawling
1028 mb surface ridge centered near James Bay and a pair of closed
lows to our south. The closed low currently approaching Jackson
Hole, Wyoming brings our next batch of weather. Warm air advection
and isentropic ascent associated with a shortwave (currently over
Iowa) pivoting around this low results in an area of showers/rain.
Guidance appears to be trending toward rain making it farther into
our area so PoPs were boosted accordingly across the west, but east-
central portions of our area still appear to stay dry. Judging by
current radar over Iowa, steady rain seems to be more likely than
showers with embedded thunderstorms but wasn`t confident enough to
make those changes at this time. This area of rain should be ending
by early afternoon as the associated surface low deepening to around
1000 mb near Sioux Falls, SD. The resulting pressure gradient should
result in some gusty winds across our far western zones where
pressure falls may exceed 1 mb/hr. Looking at soundings this
gustiness depends on enough surface heating to mix stronger winds to
the surface from a 35-40 knot LLJ, which may not happen if it ends
up being more cloudy/rainy.

The surface low begins to occlude Saturday night, but doesn`t appear
to move much through Monday due to the impressive blocking ridge
centered near James Bay. This blocking ridge dominates local weather
with generally dry easterly flow persisting through most of the
extended time frame. EPS ensemble means show gradually decreasing
Pwats and a slight cooling trend through the middle of next week,
but temperatures still stay warmer than seasonal normals. The
combination of high pressure and southeast flow off Lake MI suggests
chances for fog just about each night, mainly across adjacent
portions of the UP. The blocking ridge shifts eastward late next
week allowing for more south/southwest flow that transports deeper
moisture into the area resulting in noticeably warmer temperatures
by next weekend. The prolonged stretch of dry and warm weather
raises fire wx concerns, especially as trees begin to lose their

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 150 PM EDT FRI SEP 22 2023

IWD: Scattered to isolated thundershowers are expected in interior
western Upper Michigan today, but confidence is low enough in the
placement of these showers that they are left entirely out of the
TAF. A more widespread round of showers is expected in the overnight
hours, which in addition to VCSH mentions, is expected to lead to a
lowering in ceilings to IFR territory. Additionally, a LLWS threat
may occur, but based on current model guidance, there is only a
couple hour window when LLWS criteria is met, and that is near the
end of the TAF period, so left that out of the TAF as well.

CMX: The showers only have a 10-20 percent chance of reaching the
terminal during this TAF period, so left shower mentions out of the
TAF. However, under increasingly easterly flow, a layer of marine
fog could drastically reduce visibility overnight, potentially to
airport minimums, but as those impacts are likely 12-18 hours out,
will keep the impacts to IFR as uncertainty still exists in the
timing and magnitude of the impacts of the marine fog. By the end of
the TAF period, any lingering low clouds should scatter out.

SAW: The main weather impact at this terminal will be the potential
for radiation fog as winds are forecast to be right at the threshold
of what is too much wind for fog formation. Only put MVFR visibility
in this TAF period given the wind uncertainty, but some model
data indicates as high as a 50 percent chance of some period of
time where visibilities fall to VLIFR conditions. As per usual,
once the sun rises, fog will clear out for the end of the TAF

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 436 PM EDT FRI SEP 22 2023
Tonight into Saturday, high pressure builds over Ontario while
deepening low pressure moves into the Dakotas. This will result in a
tightening pressure gradient especially across western Lake
Superior. Easterly winds increase to 20-25 knots across western Lake
Superior Saturday with gusts increasing to 25-30kt. There`s a very
low chance (less than 5%) for a few gale force gusts over far
western Lake Superior Saturday afternoon and evening. The pattern of
high pressure centered to the east and low pressure to the west will
hold into early next week, but as the low weakens, expect a
slackening pressure gradient. Winds may continue to gust up to 20-25
knots over western Lake Superior early Monday before falling back
below 20 knots for the rest of the forecast period.

Upper Michigan...
Lake Superior...
  Dense Fog Advisory until 8 AM EDT /7 AM CDT/ Saturday for LSZ162-

Lake Michigan...


MARINE...EK is the U.S. government's official web portal to all federal, state and local government web resources and services.