Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 191945
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
345 PM EDT MON SEP 19 2016

.SHORT TERM...(Today and tonight)
Issued at 507 AM EDT MON SEP 19 2016

WV imagery and RAP analysis indicated a strong zonal flow pattern
across the nrn CONUS upstream of the Upper Great Lakes with a 130-
140 knot 250-300 mb jet from the Pacific Northwest into the Northern
Plains. A vigorous shortwave trough at the nose of this jet max and
associated WAA has supported showers/t-storms over western Upper Mi
and Lake Superior early this morning. Elevated instability to near
1000 j/kg even supported a few stronger storms over western Lake
Superior which warranted the issuance of a special marine warning.
Elevated instability appears to be waning a bit in a past few hours
as airmass may be drying out and becoming more capped at mid-levels
per forecast soundings. This is reflected in weakening trend in
convection over north central Upper Mi in past hour. Convection
still going over eastern Lake Superior aided by lift 850 mb warm
front, but generally showing a weakening trend as well.

Today, the cold front will sweep through the cwa this morning into
early afternoon bringing gusty winds and drier air to the area with
gusts approaching 40 mph over the higher favored terrain of the
Keweenaw as noted on 00z forecast soundings. Although models show
best q-vector convergence and deeper moisture lifting generally
north and east of Lake Superior later this morning, there is another
pocket of q-vector convergence that moves into the south central and
eastern forecast area later this morning into the early afternoon
hours assoc with a secondary weaker shortwave now over the Dakotas.
Although models show drier air at mid-lvls there are a few hundred
j/kg of MLCAPE and low-lvl convergence along frontal boundary could
maybe touch off a few showers and possibly a thunderstorms over the
scntrl and ern fcst area by early-mid afternoon so wl include lower
chc pops for this possibility. Look for drier conditions later in
the afternoon as frontal boundary pushes se of Upper Mi. Sunshine
and mixing with 850 mb temps around 12C will support max readings in
the mid to upper 70s, possibly pushing 80F for west wind downsloping
locations over scntrl Upper Mi.

Drying and clearing skies along with diminishing winds will lead to
cooler conditions tonight especially over the interior, where min
temps will lower to 45 to 50.  Tighter pressure gradient and more
winds/mixing will allow min temps to stay up a bit more near Lake
Superior. Look for min temps generally in the mid to upper 50s along
the Lake Superior shore.

.LONG TERM...(Tuesday night through Monday)
Issued at 330 PM EDT MON SEP 19 2016

Zonal flow aloft the middle of this week becomes much more amplified
the upcoming weekend as sharp ridge develops mid North America btwn
upper trough over eastern Canada and trough across western Conus. At
the sfc, a low pressure system and warm front emerging onto the
Central Plains on Wed will track over the Upper Great Lakes Wed night
into Thu. This system will bring best chance of widespread rain to
the region this week. An west to east frontal boundary and pwats over
1.25 inches lifting into the boundary along with area being situated
in right entrance region of upper jet over northern Ontario suggest
could be moderate or heavy rain. Since tighter h85 temp gradient and
edge of higher instability stays south of Upper Michigan closer to
the sfc low pressure system, may also see the heavier rain remain
south. Will keep featuring highest pops over south half of cwa. Even
as sfc low and stronger instability stay to the south of cwa, there
is weak elevated CAPE and near 0c SI/s to support some rumbles of
thunder later Wed into Wed night. Best chance would be over scntrl.
Highs in the midweek period should be mainly in the 60s.

Questions remain in how strong upper trough is over eastern Canada
Thu into Fri as a stronger trough would push the sfc front far enough
south to keep conditions dry Thu night into Fri. Models are going
back and forth on this. Latest consensus suggests though there may be
some lingering showers on Thu night, most of Fri would end up dry.
Temps through this period will be at or slightly below normal. Normal
highs are in the mid-upper 60s.

Appears that high pressure will then attempt to build southward from
Manitoba and northern Ontario Fri night into Sat resulting in mostly
dry weather. However, the GFS solutions over the last couple days,
at least the ones that are reasonable in terms of the projected
upper level pattern, do indicate there still could be some rain Fri
night into Sat morning, at least for west and southwest portions of
cwa. Latest GFS has trended drier though with only far west cwa
getting clipped by additional showers. ECMWF has trended steadily to
drier weather over most of the cwa but does keep some qpf over west
cwa. Based on the trends, will keep small chances for rain Fri night
over far west and southwest cwa. Dry weather should then hold most
of Sat into Sat night as high pressure, both sfc and aloft, remains
over the Great Lakes. Highs remain in the 60s. Lows Fri night and
Sat night will dip into the low 40s inland. One of these nights may
see even lower temps perhaps as low as upper 30s, but right now not
looking for any frost.

Next chance of rain with some small chances of tsra returns Sun into
Mon. Ridging moving east and approach of at least a piece of
shortwave trough energy from the Plains will support the increasing
rain chances. Given the strength of the ridging departing and drier
air could take some time for the rain to arrive on Sun. Model
consensus works for now owing to the quicker GFS and slower
ECMWF/GEM. Latest ECMWF has edged trough aloft farther east and
would support arrival of rain earlier on Sun. Highs both days
should stay in the 60s though if the rain for later in the weekend
is delayed could see temps make run toward low 70s on Sun over parts
of the cwa.

&&

.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 150 PM EDT MON SEP 19 2016

Gusty west winds are expected this afternoon behind a cold frontal
passage, especially at CMX where gusts near 35 knots are likely.
Light showers at/near SAW at the start of the period should move out
by 20z. Expect VFR conditions at taf sites through the period.
&&

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 507 AM EDT MON SEP 19 2016

Gusty s-sw winds will shift wsw later this morning into the
afternoon hours as a cold front move across the area. The tightening
pres gradient between high pressure area over the Plains and the low
assoc with the front tracking through northern Manitoba toward
Hudson Bay will result in WSW winds to 30 knots today in the wake of
the cold front. In fact, there could be a period of gale gusts to 35
knots between Isle Royale and the Keweenaw Peninsula this afternoon
as west-southwest winds will become enhanced by channeling between
these features. West winds should generally diminish to 25 knots Mon
night into Tue as gradient slackens with the Canadian low lifting
farther ne across Hudson Bay. Winds will diminish to less than 20
kts Wednesday into Friday under weak pres gradient across the Upper
Lakes.
&&

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

$$

SHORT TERM...Voss
LONG TERM...JLA
AVIATION...JLB
MARINE...Voss



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