Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 232003

Area Forecast Discussion
National Weather Service Marquette MI
403 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 through Friday)
Issued at 432 AM EDT SAT JUL 23 2016

A subtropical ridge still dominates much of the CONUS though it has
weakened some over the last 24hrs. To the n, an impressively deep
mid level low remains over nw Canada with 500mb heights 4 standard
deviations blo the long term late July avg centered over far nw
Nunavut. Medium range model runs over the last 24hrs remain
consistent on the overall pattern evolution during the next 7 days.
The subtropical ridge dominating much of the CONUS will continue to
weaken gradually, and then later next week, there will be some
building of heights near the w coast. Although heights are forecast
to remain above normal here, there will be a trend toward weak
troffing into the Great Lakes late next week in response to the
building heights to the w. The deep mid level low over nw Canada
will also weaken during the long term and will drift n with time.
In the shorter term, the subtropical ridge and mid level low in nw
Canada will continue to guide a significant shortwave currently over
the northern Rockies eastward, reaching northern Ontario and the
Great Lakes region late Sun. This system will bring the first
opportunity of shra/tsra tonight into Sun. More shortwave energy
tracking along in still zonally oriented flow into mid week may
provide some pcpn Tue/Wed. Later in the week, weak western ridging
and weak eastern troffing may allow sfc high pres to build s into
the area, pushing a frontal boundary and associated pcpn to the s of
Upper MI. As for temps, above normal heights thru the period suggest
above normal temps will mostly prevail, especially early on, but as
heights fall closer to normal as weak troffing develops, there will
be gradual cooling next week, dropping temps to around normal for
the last half of the week. Looking farther ahead, CPC/NAEFS outlooks
indicate troffing into the Great Lakes may persist to sustain this
near normal temp regime into the 8-14 day period.

Beginning Sun, the vigorous shortwave trof currently over the
northern Rockies will reach the Upper Great Lakes and northern
Ontario Sun night. Cluster or line of shra/tsra should be over the
eastern fcst area at 12z Sun, supported by 40kt low-level jet ahead
of the approaching shortwave. Models are in decent agreement showing
that main area of pcpn exiting the fcst area prior to 15z, but there
may be some isold shra/tsra hanging back to the w ahead of the
approaching occluded/cold front. Question then becomes whether any
new convection will develop along occluded/cold front pushing across
the area. With sharp midlevel drying and developing capping pushing
into the area, there`s considerable uncertainty in whether any new
convection will be able to develop. If the drying/capping push out
ahead of front, new convection won`t be able to develop. At this
point, only the eastern fcst area appears to have any potential for
new convection to develop prior to fropa. With mlcapes fcst to
increase to around 2000j/kg on the more conservative GFS as opposed
to 4000+j/kg off the NAM, 35-40kt of deep layer shear will support a
svr risk if any storms develop. Of note is the sfc-mid level delta
theta-e of 30-35c which will enhance the potential of damaging winds.

Sun ngt thru Mon ngt...Deep/vigorous drying in the wake of the
shortwave/fropa will lead to skies becoming mostly clear. Max temps
on Mon will still be above normal, but not as warm as recently. With
850mb temps falling back to 12-14C, expect highs on Mon around 80F
to the lower 80s with 70s closer to Lake Superior. Dwpts should fall
off during the day as mixing brings drier air down. While bias
corrected guidance drops dwpts down to the mid 50 to lower 60s,
readings could be 5-10F degrees lower based on mixing depth, making
the day more comfortable. Lows Sun night should slip blo 60F over
the interior west. Mid/upper 50s should be more common Mon night
under light winds with high pres nearby.

Shortwave arriving Tue will bring a return of shra/tsra chances.
Then, a stronger shortwave passing across northern Ontario will push
a cold front thru the area Tue night/Wed morning, maintaining pcpn
chances. Whether sufficent troffing develops into the area with this
latter shortwave to push frontal boundary and associated pcpn far
enough s to allow dry weather for Thu/Fri remains to be seen. 00z
medium range guidance has leaned toward the dry weather scenario.
With high pres building toward the area from the n, dwpts may
finally fall to more sustained lower values, leading to a more
comfortable period late next week.

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 144 PM EDT SAT JUL 23 2016

Expect VFR conditions/dry wx to predominate until about 24/00Z with
lingering llvl dry associated with slowly retreating Hudson Bay hi
pres. But as the S wind btwn the retreating hi pres and a lo pres
moving E near the Cndn border draws more mstr into the area, some
showers/TS will develop W-E tonight. Timing on TS occurrence is too
lo to go with more than a VCTS group attm. Added some LLWS to
account for strengthening LLJ during period of nocturnal cooling and
near sfc stabilization ahead of aprchg warm fnt. Arrival of drier
air aloft will end the showers late tngt at IWD and just after
sunrise at SAW. Once lingering lo clds/MVFR cigs mix out with
daytime heating on Sun, expect VFR wx to return. This mixing wl also
cause some gusty W winds, especially at the more exposed CMX

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 432 AM EDT SAT JUL 23 2016

Winds will remain at 20 knots or less into next week as pressure
gradient remains weak and overwater stability is increased. Only
exception may be Sun/Sun night as stronger westerly winds gusting
to 20-25kt may occur at times following the passage of an occluded
front. Patchy fog is possible tonight and Sunday as another humid
airmass moves over the Upper Great Lakes.

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


LONG TERM...Rolfson
MARINE...KEC/Rolfson is the U.S. government's official web portal to all federal, state and local government web resources and services.