Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 221135

Area Forecast Discussion
National Weather Service Marquette MI
735 AM EDT Sun Oct 22 2017

.SHORT TERM...(Today and tonight)
Issued at 509 AM EDT SUN OCT 22 2017

Water vapor imagery and RAP analysis show a shortwave trof across
the central CONUS. At the sfc, associated cold front arcs from low
pressure over northern Manitoba across western Lake Superior to near
Ironwood and then to TX. Shra and tsra along frontal boundary were
much more consolidated earlier in the night though thunder never
made it out of WI into Upper MI. Over the last few hrs,
coverage/intensity has diminished significantly with only isold
-shra now over the western fcst area. Ahead of the front, it has
been an unseasonably warm night for this time of year. Current temps
across the fcst area as of 08z are in the upper 50s to mid 60s.

As shortwave trof continues eastward today, cold front will follow
suit, likely exiting the eastern fcst area by 21z. As mentioned
-shra along front have diminished significantly, but this should
change during the day as right entrance of upper jet along front
side of the shortwave trof becomes a little better positioned and
deep layer forcing per q-vectors increases some. This pcpn trend is
evident in much of the model guidance as most generally indicate the
ongoing diminishing trend to pcpn, followed by a resurgence to some
degree later this morning into the aftn. Shra will end over the w
this aftn and should be out of the eastern fcst area by midnight
tonight. Considerable high cloudiness will linger after the pcpn
end, but skies should generally clear from w, beginning later in the
aftn over the w. Next shortwave trof will dig into the Northern
Plains tonight. Narrow zone of waa/isentropic ascent ahead of the
this feature may generate some shra that could reach western Upper
MI by 12z Mon. Looks unlikely given antecedant dry air mass. So for
now, will carry dry fcst during the overnight.

.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 12Z TAFS through 12Z Monday morning)
Issued at 735 AM EDT SUN OCT 22 2017

A cold front over western Upper MI will continue eastward today.
Showers are expected to expand in the vcnty of the front this
morning into the aftn, affecting KSAW mostly. However, there may be
some -shra at KIWD and KCMX as well thru the morning. A period of
MVFR cigs, perhaps brief IFR, is expected around the time of fropa.
These lower cigs are currently shifting e of KIWD, so VFR conditions
should prevail at that terminal thru the fcst period as drier air
arrives in the wake of the front. KCMX should see improvement to VFR
by late morning with KSAW improving to VFR mid to late aftn. Winds
will gust to around 25kt at KCMX today, 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 AM Lake Superior forecast issuance)
Issued at 509 AM EDT SUN OCT 22 2017

Winds of 20-30kt will generally be the rule today on Lake Superior,
though winds over the e half of the lake will diminish this aftn
following passage of a weakening cold front. The stronger winds will
continue over the w half of Lake Superior tonight ahead of the next
approaching low pres trof. Winds will then generally be in the 15-
25kt range on Mon. A deepening low pres lifting n 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 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 winds again on Thu
ahead of the next low pres trof moving across the Plains.

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


SHORT TERM...Rolfson
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