Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 212020

Area Forecast Discussion
National Weather Service Marquette MI
420 PM EDT Sat Oct 21 2017

.SHORT TERM...(This evening through Sunday)
Issued at 315 PM EDT SAT OCT 21 2017

No significantly impactful weather is expected in the short term.

A weak shortwave lifting across the western forecast area today will
bring some isolated to scattered showers and possibly some thunder
to mainly western Upper MI this afternoon. Instability is minimal
with only a couple of hundred j/kg of MUCAPE and with only weak
shear, so only isolated thunder is expected. South winds will gust
to 20-30 mph through the remainder of the afternoon, strongest near
northern Lake Michigan and in downslope areas along the eastern
shore of Lake Superior. Temps under partly sunny skies this
afternoon have climbed to nearly 20 degrees above normal with
highs in the mid 60s to mid 70s.

As a stronger shortwave trough shifts east through the Plains a
cold front will move into the western U.P. later tonight, which
will likely bring in showers and maybe a thunderstorm. Chances
should be confined to mainly the west half through 12Z Sun. Lows
tonight will be 20-25 degrees above normal with lows expected in
the 50s. Record high minimum temperatures will likely be set at
many locations including WFO MQT.

Sunday, the progression of the shortwave trough eastward into the
Upper Great Lakes will push the cold front through the rest of Upper
Mi on Sunday. Fairly vigorous deep layer forcing and abundant
moisture with pwat upwards of 1.3 inches/250pct of normal should
support a band of showers in the vicinity of the front. Very little
instability is forecast along/ahead of the front by 12z Sun and thru
the day Sun (MUCAPE is mostly less than 100j/kg), so no mention of
thunder is warranted. Showers should be out of the w half by late
afternoon but won`t exit the e until mid-late Sun evening. Since
front progresses through area fairly quickly not expecting a lot of
rain despite high pwats Look for the greatest amounts of .2 to
.5 inches over the east half. Skies should clear fairly quickly once
the pcpn ends. Sun will be cooler under clouds/showers and in wake
of passing cold front. Expect highs from around 60F west to
generally mid 60s east half.

.LONG TERM...(Sunday night through Saturday)
Issued at 420 PM EDT SAT OCT 21 2017

Significant changes in the weather pattern in favor of more
seasonable conditions for late October will occur across the Upper
Great Lakes next week.

Sunday Night: The back edge of ongoing rain across the eastern CWA
will gradually shift eastward through the night. Then, troughing
approaching from the east late Sunday night may be enough to induce
some rain showers for most of the area through the day Monday, but
drier conditions will likely limit covered to just a few showers.

Monday night through Wednesday: Phasing between a northward-moving
Lower Mississippi Valley trough and a southeastward-moving Upper
Mississippi Valley trough will occur over the Great Lakes region
Monday night into Tuesday. Deterministic and GEFS guidance continues
to show decent spread in how this phasing will evolve, but there is
high confidence of a strong fall low-pressure system across the
region. The GFS is the deterministic outlier, with a more
progressive southern trough resulting in less phasing, so this
forecast follows more of the CMC/ECMWF solution. Following that
idea, a period a strong winds and potentially heavy rain would occur
late Monday night through the day Tuesday. While most of the CWA
would experience north winds gusting over 30mph, shoreline locations
from the Keweenaw eastward would see gusts over 40mph. It is not out
of the question that if this solution occurs, wind advisory
headlines would be needed for the aforementioned locations. The
strong winds would also lead to waves over 15 feet and resultant
beach erosion given Lake Superior`s above normal water level. The
strongest winds would occur Tuesday afternoon before diminishing
through the night.

In terms of precipitation, the CMC/ECMWF solution produces storm
total precip of around 2" east and north central to less than 0.25"
across the far west, with the heaviest precip occuring late Monday
night through much of Tuesday. Sufficiently cold air will lag enough
to prevent snow through the day Tuesday, but a quick change over to
snow across the high terrain of the west half will be possible as
precip diminishes Tuesday night. Little accumulation would be
expected unless precip hold on longer than is currently forecast.

Wednesday through Saturday: A colder pattern will settle in behind
Tuesday`s storm. Indications are for another low pressure to develop
across the western Great Lakes Thursday into Friday as strong
troughing tracks SE from central Canada. Colder air with this system
will result in more favorable conditions for precip changing over to
snow Friday night, with some minor accumulations possible for the
high terrain of the west half.

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 152 PM EDT SAT OCT 21 2017

Showers and maybe some thunderstorms are possible near KIWD today,
but with limited confidence in coverage just used VCSH in the
forecast. A cold front will move through the area late tonight and
Sunday, bringing rain and reduced CIGs from west to east across
the TAF sites. LLWS is expected tonight at KSAW. Improvement to
VFR is expected at KIWD and KCMX by early Sunday afternoon with
drying behind the front.

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 315 PM EDT SAT OCT 21 2017

South-southeast winds will gust 20-30 kts through tonight, strongest
over the eastern half Lake Superior. Sun, south-southeast 20-30 kts
winds will shift west-southwest in the wake of a cold frontal
passage. Southwest winds will diminish to 15-25 knots Sun night into
Mon. Northerly winds will pick back up again Mon night into Tue as a
low pressure system is expected to rapidly deepen just east of Lake
Superior. North gales are possible late Mon night into Tue evening
with the deepening low but should diminish blo gales late Tue night
into Wed as sfc low weakens and lifts east of the region.

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


LONG TERM...Kluber
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