Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 231139

Area Forecast Discussion
National Weather Service Marquette MI
739 AM EDT SAT JUL 23 2016

.SHORT TERM...(Today and tonight)
Issued at 432 AM EDT SAT JUL 23 2016

Another quiet day with well above normal temperatures in store today
before active weather slides across the Upper Peninsula tonight.

Today: A pretty nice day is in store for the beginning of the
weekend as high pressure remains in place over the Upper Great
Lakes. This, along with dry air in place, will keep skies mostly
clear to partly cloudy throughout the day. The high pressure system
will begin sliding to the east late in the afternoon, which will
allow warm-moist southerly flow to kick in across the west half of
the U.P. This will cause an increase in cloudiness late in the
afternoon over the far west. Otherwise, temperatures will continue
to be above normal with highs in the mid to upper 80s, except cooler
along the Great Lakes Shorelines.

Tonight: The aforementioned high pressure system will continue to
slide off to the east of the area as low pressure slides from the
Saskatchewan-Manitoba border to the Manitoba-Ontario border late
tonight. This will drag an associated warm front and then cold
front/upper level 500mb height falls into the U.P. Timing of the
cold front and shower and thunderstorm activity looks as if it would
slide into the western U.P. between 00Z/24 and 03Z/24 and then reach
the central U.P. by 06Z/24 and eastern U.P. by around 09Z as shown
by several of the Hi-Res model solutions. Again the best chances for
showers and thunderstorms will be right along and just ahead of the
cold front, which will be along the area of best forcing.
Additionally, a LLJ core around 50 knots between 925-850mb is
expected to set up over southern MN and western WI. The additional
influx of moisture along with convergence at the nose of the LLJ
would support enhanced lift over the aforementioned areas as well as
the western U.P. The main thunderstorm mode across the U.P. looks to
be more linear, which would be more supportive of a wind threat than
a hail threat at this time as the cold front approaches. Deep layer
shear values, orthogonal to the front, of around 30 to 40 knots
would be supportive of more organized strong to severe thunderstorms
over the west. MUCAPE values are progged to be around 1000-1500J/KG,
especially in the evening over the far west. With that said, the
best chance of seeing severe weather would be over the west half in
the evening with a general weakening trend expected across the
central and east half. For this reason, the SPC has the western half
of the U.P. under a marginal risk for severe weather.

.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 12Z TAFS through 12Z Sunday morning)
Issued at 738 AM EDT SAT JUL 23 2016

VFR expected to linger at all TAF sites through this afternoon. A
low pressure system and associated cold front will bring shower and
thunderstorm activity to the KIWD and KCMX TAF sites beginning
around 02Z at KIWD and 3Z at KCMX. Timing of arrival is a bit
uncertain at this time but confidence is high that both sites will
experience TSRA at times...especially late this evening. KSAW will
also likely see TSRA by late evening into the early overnight hours.
MVFR visibilities are possible with the heavier showers and
thunderstorms and have included this in the forecast at each TAF
site during more concentrated rain. Again, exact timing of the
showers and thunderstorms will continue to be fine-tuned.

.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.