Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 221859

Area Forecast Discussion
National Weather Service Marquette MI
259 PM EDT Sun Oct 22 2017

.SHORT TERM...(This evening through Monday)
Issued at 256 PM EDT SUN OCT 22 2017

Water vapor imagery and RAP analysis show a shortwave trough moving
east across the central CONUS.  Associated cold front extending
south from sfc low over northern Manitoba has also moved east across
Upper Mi today providing a focus for numerous showers this afternoon
into central and eastern portions of the cwa. Showers will continue
to diminish or end over the west half later this afternoon and
should be out of the eastern fcst area by midnight tonight.
Considerable high cloudiness will linger after the pcpn ends, but
skies should generally begin to clear from the w toward evening.
The next shortwave trough will dig into the Northern Plains
tonight. Narrow zone of waa/isentropic ascent ahead of this
feature may generate some showers that could reach western Upper
MI by 12z Mon, but given the antecedent dry air mass pcpn chances
appear minimal. Will continue to carry dry fcst during the
overnight. Expect cooler min temps with lows ranging from the mid
30s over the typical interior cool spots west and central to the
lower to mid 40s far west due to increasing clouds later tonight
ahead of approaching Plains trough and for well-mixed locations
along Lake Superior in downsloping sw flow.

On Monday, the Northern Plains trough will begin to push east into
the Western Great Lakes region. Weak q-vector convergence and mid-
level moistening ahead of this feature combined with steepening
lapse rates from sfc to 700 mb should generate isolated to scattered
showers into Upper Mi especially into the afternoon hours with the
best chance of rain over the west half.  Expected highs Monday in
the mid to upper 50s will still be above normal but a bit more
typical of mid to late October readings.

.LONG TERM...(Monday through Saturday)
Issued at 339 AM EDT SUN OCT 22 2017

Main story in the long term is potential for a significant storm
system to bring strong winds and very large waves Mon night into Tue

Confidence in this event is still on the low side given model
variability and disagreement, but users of this forecast should
certainly keep aware of potential threats from the system. The CMC
and ECMWF are is decent agreement in showing a sub-980mb SFC low
moving to the SE of the CWA, while the GFS is considerably weaker at
just under 1,000mb. If the stronger consensus of CMC and ECMWF
verifies, Strong winds over and near S-central Lake Superior could
gust to around 60mph along the central and eastern Lake Superior
shorelines, but for now have kept with a more moderate consensus
solution featuring gusts to around 45mph. These winds would lead to
waves over 15ft across S-central Lake Superior, which would cause
lakeshore flooding and beach erosion, especially since the lake
levels are well above normal. Still plenty of chance for things to
change, stronger or weaker than the consensus mean in the forecast,
so stay tuned. Storm total QPF is forecast to be around an inch over
the N-central and eastern UP, with almost all of that being rain.
There is a chance that portions of the interior W could see some
traces of snow Tue night, but at this point not expecting enough for
any impacts.

Attention then turns toward Fri into Sat when another system may
move through the region. Lots of uncertainty with this system, so
will just be using consensus mean and monitoring for now. There is
potential for some more significant snowfall totals with the
strongest/coldest/optimally-placed solutions.

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 133 PM EDT SUN OCT 22 2017

A cold front has moved east across the TAF sites today. Showers
along the front have expanded into central Upper Mi this afternoon,
affecting KSAW mostly. However, there may be some lingering
showers at KIWD and KCMX as well into mid afternoon. Expect MVFR
cigs to linger at KSAW into mid-late afternoon before improving to
VFR as drier air arrives in the wake of the front. KCMX and KIWD should
be VFR through the fcst period. Winds will gust above 20kt at
times at KCMX this afternoon, and LLWS may develop at KIWD late
tonight as low-level winds increase above nocturnal inversion in
advance of next approaching low pres trof.

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 256 PM EDT SUN OCT 22 2017

West-southwest winds of 20-30kt strongest over the west and north
central portions of Lake Superior will continue to diminish into the
evening hours in the wake of the cold frontal passage, but should
pick up again slightly over the west and north central ahead of the
next approaching low pres trough. Southwest winds will then
generally be in the 15-25kt range on Mon strongest west half. A
deepening low pres lifting north from the Ohio Valley on Mon and
reaching a position near Drummond Island on Tue morning will result
in increasing winds on Lake Superior. Northerly gales of at least 35-
40kt will develop from w to e Mon night through Tue. If the sfc low
ends up deeper than currently expected, winds will be higher. With
the low quickly exiting to the nne, winds will fall back to under
20kt on Wed. Look for increasing se winds again on Thu ahead of the
next low pres trough moving across the Plains.

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


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