Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 202326
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
726 PM EDT Wed Sep 20 2017

.SHORT TERM...(This evening through Thursday)
Issued at 342 PM EDT WED SEP 20 2017

A cold front over NW WI and western Lake Superior will push through
this evening into tonight, which should force convection as it moves
across Upper MI. Greatest uncertainty is with coverage and strength
of convection as cloud cover is widespread over the west half. Think
the best chance for stronger to possibly severe storms is over the
south-central where models depict the cap may weaken. In that area,
MLCAPE may increase up to around 1,500 J/kg with around 30kts of
effective shear, with potential for large hail and damaging winds at
worst.

Strong southerly winds have been noted across the area as mixing has
tapped into strong low level winds. The unofficial observation at
Brockway Mountain even gusted to 54kts for a time (winds have since
diminished). Winds will diminish across the area as SFC heating is
lost.

Expect fog across much of the area tonight, which will be somewhat
dependent on how much rain we receive.

Thursday looks to be pretty fair with highs from the upper 60s to
mid 70s.

.LONG TERM...(Thursday night through Wednesday)
Issued at 311 PM EDT WED SEP 20 2017

High amplitude trough/ridge pattern setting up over the CONUS by the
end of the week will position the western Great Lakes in a south-
southwest flow which will likely result in record warmth across the
area from Fri through Sun. Best potential of pcpn across Upper MI
will occur early next week (at some point between Mon and early Wed)
as a slow-moving frontal boundary drifts across the Upper Lakes in
response to the eastward progression of the western CONUS mid-level
trough. Given the days of deep moist sw flow ahead of the trof and
fcst precipitable water values exceeding 1.5 inches or more than 200
pct of normal for this time of year, the potential will be there for
moderate to heavy rainfall as the front moves across the area.

Beginning Thu night...The front moving through the fcst area today
and tonight will lift back north Thu night/Fri morning as mid-level
trough deepens over the western CONUS. Could be some showers/t-
storms on the elevated cape gradient as it lifts nne in conjunction
with low-level jet. Nose of low-level jet suggests the western and
northern fcst area has a better chance of seeing some convection
overnight.

Friday through Sunday look to be unseasonably warm to record warm
days across the fcst area. As the warm front lifts well north of the
area Fri afternoon, warm advection in a ssw flow will bring 925-
850mb temperatures up to 20C or greater across the area. Mixing this
warmer air to the sfc will result in max temps 20 to 25 degrees
above normal for this time of year across much of the area on Friday
and possibly Saturday into Sunday as well with expected readings
in the mid to upper 80s over much of the western two thirds of
Upper Mi. Would not be surprised to see a few downsloping areas
along Lake Superior reaching 90F where compressional warming will
occur under southwest winds of 15 to 25 mph. Cooler 70s to lower
80s readings can be expected downwind of Lake Michigan. Southerly
flow in warm sector ahead of frontal boundary over the Plains will
also tap into Gulf moisture and bring low to mid 60s dewpoints
northward through the central CONUS into the Great Lakes region.
As a result, expect the increase in humidity to make for rather
muggy and uncomfortable conditions over the weekend. However, the
cap of warm air aloft will likely inhibit formation of convection
for the most part, despite the increase in moisture and
instability. By Sunday, model uncertainty increases regarding
progression of Plains frontal boundary eastward into Upper Mi. The
GFS is still the most aggressive pushing boundary eastward toward
western Upper Mi, while the ECMWF and GEM keep the stronger mid-
upper ridge intact with the frontal boundary farther west into MN.
Still possible there could be a few storms popping up over the
western cwa Sat night into Sun as frontal boundary draws closer
from the Plains. While there may be some increase in clouds to
keep max temps down a bit over the nw portion of Upper Mi on
Sunday, much of the cwa should still see plenty of sun to allow
for low to mid 80s readings away from the moderating influence of
Lake Mi.

Given strength of the eastern ridge in place, the slower frontal
progression of the ECMWF and Canadian models will likely be favored
over the quicker GFS solution. Slower solutions would argue that it
might not be until late Tue or early Wed that the front finally
clears Upper MI. As a result, Monday may trend drier across much of
the cwa while the better chance for showers and thunderstorms and
potential for locally heavy rain may be delayed until Tue with a
drying trend still expected Wed afternoon. Temps by Wed are expected
to cool back down to more seasonable late Sept readings.
&&

.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 726 PM EDT WED SEP 20 2017

VFR conditions will prevail at KIWD, but the other two sites will be
dealing with restricted visibilities and ceilings for a time. KCMX
has low clouds and fog producing LIFR conditions at this time, but
this will quickly improve to VFR once the winds shift to the west.
KSAW will see shower and some thunderstorm activity through 4Z as
the front moves through, and once the precipitation ends fog will
develop. IFR conditions will persist at KSAW through much of the
night once the develop and will eventually dissipate once downslope
winds develop and daytime mixing occurs. VFR conditions will prevail
through the rest of the forecast period.
&&

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 342 PM EDT WED SEP 20 2017

Expect winds to diminish this evening and become westerly into
tonight as a cold front passes. Fog is possibly across mainly the
central and eastern lake tonight. East to northeast winds will then
increase Thursday afternoon and evening with gusts to 20-30kts over
the western lake. Winds are then expected to remain below 20kts
through the rest of the forecast period.
&&

.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
None.
Lake Superior...
None.
Lake Michigan...
None.
&&

$$

SHORT TERM...Titus
LONG TERM...Voss
AVIATION...RJT
MARINE...Titus


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