457
FXUS63 KIWX 220748 CCA
AFDIWX

Area Forecast Discussion...CORRECTED
National Weather Service Northern Indiana
348 AM EDT Thu Jun 22 2017

.SYNOPSIS...
Issued at 345 AM EDT Thu Jun 22 2017

An isolated shower or thunderstorm is possible early this morning,
but otherwise mainly dry conditions are expected through this
afternoon. Hot and humid conditions can be expected today with
high temperatures from the mid 80s to around 90. Chances of
showers and thunderstorms will increase later tonight into Friday
as system tracks across the Great Lakes region bringing a cold
front southward. Cooler and drier conditions are then expected
behind this system for the upcoming weekend.

&&

.SHORT TERM...(Today and Tonight)
Issued at 345 AM EDT Thu Jun 22 2017

Convective potential and increasing heat/humidity will be the
primary forecast concerns for the short term period.

Low level warm front will continue to shift northward this morning
with additional showers and thunderstorms expected to develop in
this warm advection zone at leading edge of modest southwesterly low
level jet. The bulk of this scattered shower/storm activity is
expected to remain across the central Great Lakes this morning, but
will maintain slight chance PoPs through daybreak with
instability limited by lack of significant deep moisture.

Low level thermal ridging will continue to rapidly build in from the
west this morning. Warmest temps this afternoon may actually be
across the north with onset of weak low level CAA this afternoon
as south winds bring slightly cooler air from lower MS Valley
northward. Low clouds may also tend to increase this afternoon
from south to north as low level moisture advection becomes more
pronounced. Decent mixing/breezy conditions this afternoon should
prevent dew points from getting too out of hand, generally in the
mid 60s with upper 60s a possibility. The combination of highs
from upper 80s to around 90 and these dew points should limit peak
afternoon heat indices from the upper 80s to lower 90s.

Outside of aforementioned isolated shower/storm chances early this
morning, confidence remains quite low for any isolated redevelopment
this afternoon. Eastward advection of remnant EML this morning may
tend to cap surface based convection this afternoon. A discernible
mid/upper level trigger also hard to come by this afternoon, with a
possibility of only weak sheared vortices lifting northeast
across Ohio Valley from the lower MS Valley. Will keep PoPs below
mentionable levels this afternoon, although cannot completely rule
out a stray shower or thunderstorm.

For tonight, thunderstorm chances will increase, especially during
the overnight hours. A couple of areas of focus for thunderstorm
development will need to be watched, one closer to cold frontal
boundary from central Great Lakes to the Corn Belt, with secondary
area along broad pre-frontal low level confluence zone which will be
characterized by PWATS in excess of 1.75 inches. Convective cluster
to the west/northwest should begin to exhibit both upwind/downwind
propagation characteristics tonight as southwesterly low level jet
begins to ramp up across mid MS River Valley eastward to the Ohio
Valley. Thus, expecting storms to gradually propagate southeastward
across the southern Great Lakes late this evening/early overnight.
Additional thunderstorms should develop overnight along the low
level confluence zone well out ahead of the cold front. Best chance
of strong-severe storms still appears to be across the far northwest
where shear profiles should be slightly more supportive of
convective line maintaining itself. Confidence in severe potential
still higher more to the northwest of local forecast area given
unfavorable diurnal timing, with wind appearing to be the main
threat across northwest portions of the forecast area if storms
can maintain intensity. Given fairly dry conditions over past few
weeks, heavy rainfall not a huge concern at this time, but may
need to watch for some localized heavier rainfall amounts along
that pre-frontal confluence zone with LLJ development possibly
allowing some training of cells overnight across southeast
portions of the forecast area.

&&

.LONG TERM...(Friday through Wednesday)
Issued at 345 AM EDT Thu Jun 22 2017

Showers and thunderstorms should be ongoing Friday morning in
associated with two regions of favored forcing discussed in short
term. Eventually, frontal forcing will become primary forcing
mechanism late morning/afternoon Friday. Great Lakes short wave
should gradually dampen on Friday but frontal convergence should
still be strong enough to support scattered-numerous showers/storms
following frontal progression from northwest to southeast Friday
afternoon. Significant destabilization may be difficult to come by
Friday given ongoing showers/debris cloudiness. Severe potential
still looks to be on the low side with more notable shear profiles
post-frontal in nature. Some modest increase in undirectional
shear profiles for Friday could support some isolated wind threat
approximately southeast half of the forecast area, but confidence
in isolated severe threat remains very low given destabilization
questions. However, primarily unidirectional and wind profiles
Cooler and drier conditions to commence Friday night and persist
through the early portions of next week as broad low level thermal
trough settles across the region. Several central Canada vorts
are expected to drop across the western Great Lakes this weekend
which could bring periodic isolated shower chances, but meager
moisture availability should provide for mainly dry conditions for
the weekend. Will keep isolated shower mention into Monday as
cold pool aloft persists. Temps to moderate toward the middle of
next week due to eventual departure of upper level trough.
Transition to WAA regime and active northern stream short wave
pattern should result in increasing shower/storm potential again
for the Wed-Thu period.

&&

.AVIATION...(For the 06Z TAFS through 06Z Thursday Night)
Issued at 140 AM EDT Thu Jun 22 2017

Southwest winds will be increasing ahead of a cold front today.
Winds could gust to 25 knots today. Added thunder vicinity at SBN
after 00Z; however, it looks like the best chance for storms will
be after the end of the TAF period, after 06Z.

&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...NONE.
MI...NONE.
OH...NONE.
LM...NONE.
&&

$$

SYNOPSIS...Marsili
SHORT TERM...Marsili
LONG TERM...Marsili
AVIATION...Skipper


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