Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 232343

Area Forecast Discussion
National Weather Service Marquette MI
743 PM EDT SAT JUL 23 2016

.SHORT TERM...(This evening through Sunday)
Issued at 402 PM EDT SAT JUL 23 2016

12Z raobs/latest wv imagery and RAP analysis show an upr rdg over
the Upr MS River Valley extending into NW Ontario, supporting sfc hi
pres over NW Ontario into the Upr Lks. This hi pres and dry airmass
shown on the 12Z GRB raob are bringing a mosunny conditions to Upr
MI today. With h85 temps up to 18-20C near the WI border, sfc temps
away fm lk moderation have risen into the 80s and are even aprchg 90
at a few spots even though hi clds are rolling into the area.
There is a potent shrtwv over srn Saskatchewan moving to the E,
supporting a lo pres moving into Manitoba under 00Z-12Z h5 hgt falls
up to 100m. A complex of showers/TS in the nrn plains ahead of
occluded fnt stretching to triple pt lo pres moving toward wrn MN.
Another band of showers and storms are aligned fm central MN into SW
WI along the warm fnt to the E of this lo and SPC mesoanalysis axis
of hier muCape. Sfc dewpts just to the S of the warm fnt are as hi
as the mid/upr 70s close to area of pwat aprchg 2 inches shown on
the 12Z Omaha/Des Moines raobs.

Main fcst concerns in the short term focus on shower/TS chances as
shrtwv to the W continues along just to the N of the Cndn border and
the potential for some severe TS.

Tonight...Scattered showers/a few TS may dvlp as early as 22-23Z
near Ironwood with aprch of MCV generated by upstream convection in
MN and as the sly flow increases btwn the departing sfc hi pres rdg
and aprchg shrtwv/axis of lo pres and advects some moister air back
into that area even though thickening hi clds wl limit the sfc-based
destabilization. Then more widespread elevated showers/TS wl arrive
over the W by late evng as the strenghtening SW llj, with h85 winds
up to 45-50kts, results in vigorous h85 theta-e advctn/h85-5 qvector
cnvgc. Strong W winds aloft up to 40-45 kts suggest the elevated TS
may tend to bow out. Although bowing storms would favor damaging
winds, hier near sfc stability ahead of warm fnt and rapid
moistening aloft that would reduce negative buoyancy might tend to
offset that threat. Fcst marginal lapse rates/hi frzg lvl arnd
13kft/moist mid lvls wl reduce the threat of large hail. Best chc of
strong winds would be over the W in the evng when residual effects
of daytime warming would support more unstable llvl lapse rates. As
the showers/TS move E, model fcsts of weakening deep lyr shear and
weaker lapse rates/SSI sug the severe threat wl diminish. Some
drying late under the jet surge region of the shrtwv tracking to the
N wl tend to diminish the showers late over the W. With the influx
of deep mstr/clds and steady S winds, lo temps wl hold above 65 at
most places and drop not much blo 70 at a few spots.

Sun...Vigorous dry slotting under the jet surge region of the shrtwv
passing thru Ontario wl diminish pops W-E on Sun perhaps even ahead
of the occluded/cold fropa, but more sfc based showers/TS may dvlp
on Sun if there is sufficient clrg of lingering lo clds and the mid
lvl drying/capping are not overwhelming ahead of the fropa. Models
show some fairly sgnft differences on this impact, but very
aggressive mid lvl drying favors the 12Z WRF-ARW/Regional Cndn model
scenario. These models show dry wx over most of the cwa but
convection redeveloping arnd 18Z over the far ern cwa arnd Newberry,
where the daytime heating cycle/some lk breeze cnvgc under weaker
pres gradient close to slow moving fnt wl have an impact before the
arrival of the more sgnft capping. If storms do dvlp, they could
become severe under axis of strong mid lvl winds/drying with sfc-12k
ft agl delta theta-e exceeding 30C/sfc-6km shear up to 45kts/h7-5
lapse rates up to 7C/km. With more aggressive dry slotting and
faster return of sunshine especially over the W half, temps should
rebound into the 80s at most places.

.LONG TERM...(Sunday night through Saturday)
Issued at 404 PM EDT SAT JUL 23 2016

Decent agreement in overall look of upper level pattern through next
weekend, though differences develop late in the week. Broad ridge
over much of conus that brought the heat to parts of Upper Michigan
late this week becomes reoriented over southwest conus as troughing
increases across eastern Canada and the Great Lakes to northeast
conus. Troughing is strongest Wed/Thu but with ridging spreading
back across central plains by next weekend, lower heights should
persist across the Great Lakes. Strong sfc cold front moves through
early on Sunday night and another weaker front slides across from
Northern Ontario Tue night into Wed. Another low pressure system
will be over the western Great Lakes Fri/Sat but there are
differences in how far north this system tracks. Otherwise, weak
high pressure will be primary feature. In general, this type of
pattern should not produce much rain, but there are some chances
especially late Tue into Wed with the mid week fropa.

After a very warm period through this weekend, temps will head back
below normal Mon in wake of the front that moves through on Sun aftn,
especially near Lk Superior. Stronger northwest winds behind the
front and cooler temps flowing over an increasingly warming Lk
Superior likely will lead to building waves and a possible high swim
risk on Monday for the Lake Superior beaches of Alger counties. After
a quiet night beneath sfc ridge on Mon night, warm air advection and
moist advection aloft will bring increasing clouds and some showers
west to east across cwa on Tue. As far as thunder chances go, GFS
soundings show marginal elevated instability on leading edge of an
elevated mixed layer emerging fm the northern plains, but with sfc
dwpnts in the 50s, forecast mlcape across Upr Michigan struggles to
reach 500-1000j/kg. Slight chance of tsra but not expecting any
severe weather. Away fm the flow off Lk Michigant highs on Tue should
bounce back into the low 80s as long as thicker mid clouds don`t move
in too quickly.

As front crosses Upper Great Lakes Tue night into Wed will keep
small chances for showers going. Chances for thunder look small Tue
night with minimal mucape less than 500 j/kg in most areas. Shear is
weak so again no severe storms are expected. On Wed could see higher
dwpnts pool along departing front, especially eastern cwa. MLcape up
to 1000 j/kg could support a bit better coverage of storms. However,
effective shear remains weak so chances of organized severe storms
looks low. Wbzero heights less than 11kft could support risk for
some hail, especially if instability ends up greater. Consensus of
models keeps low end chances going Wed night into Thu. Seems that
most of the pops are influenced by the wetter GFS as it shows a
stronger wave dropping through in nw flow aloft. ECMWF and GEM are
farther south with this initial wave and show minimal chances for
precip with high pressure influencing the weather.

Near or even slightly blo normal temps should develop behind the
midweek fropa and temps will remain that way into next weekend.
Bigger differences between the GFS and ECMWF with extent of
troughing aloft will mainly impact extent of rain chances late this
week. GFS would indicate a wetter pattern will continue while the
ECMWF continues to split troughing aloft, focusing rain chances
farther north across Northern Ontario and closer to another
shortwave crossing the central and lower Great Lakes. WPC hand drawn
progs keep the sfc low too far to the south of Upper Michigan for
much rain here. Only have slight chances Thu night into Fri in case
the system jogs back northward some. Have small chances in for next
Sat as southerly flow/warm air advection kicks back in.

.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 743 PM EDT SAT JUL 23 2016

Showers and a few thunderstorms continue to move into the region
ahead of a warm front this evening with most of the thunderstorm
activity well to the south of the area where better instability and
moisture exists. With continuing southerly flow over the area
tonight and with an approaching cold front expect thunderstorm
activity to be on the increase tonight. Timing of the most likely
thunderstorm activity should be coincident with approach of the cold
front with showers ending shortly after fropa. This activity
will result in MVFR conditions at times. With development of LLJ
tonight kept mention of LLWS in all three TAFs. Once the cold front
pushes through the area conditions will quickly improve with VFR
conditions spreading from west to east through the day. Mixing of
the boundary layer will produce some gusty winds during the late
morning and afternoon hours.

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 404 PM EDT SAT JUL 23 2016

Winds will stay less than 20 kts tonight into Sun but west winds
increase to around 20 kts with gusts to 25 kts Sun aftn into Sun
night and on into Mon morning as winds shift northwest behind a cold
front that moves through late Sun night. Another front moves through
Tue night into Wed, but winds beyond Mon will remain 20 kts or less
as pressure gradient stays weak. Patchy fog is possible tonight and
Sun as a humid airmass briefly returns to the Upper Great Lakes.

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


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