Area Forecast Discussion
Issued by NWS Northern Indiana

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415
FXUS63 KIWX 231927
AFDIWX

Area Forecast Discussion
National Weather Service Northern Indiana
327 PM EDT MON MAY 23 2016

.SYNOPSIS...
Issued at 305 PM EDT Mon May 23 2016

Seasonably warm conditions will continue through the remainder of
the week with highs expected to reach the lower 80s.  A series of
upper level disturbance will interact with this warm and
increasingly humid air mass to produce periodic chances of showers
and thunderstorms from Tuesday night through the weekend. The
greatest coverage of showers and storms is expected for Wednesday
night.

&&

.SHORT TERM...(This Evening through Tuesday)
Issued at 305 PM EDT Mon May 23 2016

A sharp mid/upper level ridge will be very slow to track across the
Ohio Valley and southern Great Lakes tonight into Tuesday providing
continued dry conditions. Low level winds will veer westerly this
evening promoting weak low level warm advection tonight. Weak low
level warm advection and eastward departure of low level ridge axis
should provide milder conditions tonight in comparison to the past
few nights. Coolest mins of around 50 are expected across eastern
portions of the forecast area, although upper 40s are possible given
closer proximity to departing pocket of slightly cooler air, and
persistence of a slightly weaker gradient.

Good deal of insolation expected once again for Tuesday, with some
increase in high clouds possible later in the afternoon. Slightly
warmer low levels and better low level mixing should support highs
a few degrees warmer than today, around 80 or in the lower 80s.

&&

.LONG TERM...(Tuesday Night through Monday)
Issued at 305 PM EDT Mon May 23 2016

For Tuesday night, an upper level short wave currently across the
Plains aiding in shower/thunderstorm coverage will lift northeast
and dampen across the Great Lakes. Forcing from this wave should
initially outrun higher quality moisture across the Mid Ms River
Valley Tuesday night lending to some low confidence on convective
coverage. A modest 25 knot southwesterly low level jet should advect
increased low level moisture into the area overnight with main
question by this time on extent of any lingering mid/upper level
forcing. Did maintain low chance thunder PoPs for Tuesday night
mainly due to advective forcing and development of some weak
elevated instability. Confidence is low for Tuesday night
regarding instability magnitude however, as a relatively warm
800-650 mb layer may tend to be a limiting factor.

The next mid/upper level perturbation should approach the western
Great lakes on Wednesday with persistent broad positive low/mid
level thetae advection. Strongest low level flow/moisture
transport during this forecast period should occur Wednesday
night in advance of this wave and have maintained inherited likely
PoPs. Several scenarios still possible for Wednesday night.
Prospects of elevated convection should be on the increase given
this setup. Could also see a more organized cluster of convection
develop across northeast Iowa/northern Illinois in closer
proximity to this forcing and eventually propagate southeast.
Expected orientation of instability/thickness gradient may tend to
favor areas just west and southwest of the local area to be inline
for any forward propagating convective system. Remnant
outflows/convectively enhanced vortices emanating from upstream
convection may also serve a focus for greater shower/storm chances
Wednesday night however. Confidence in any severe weather
Wednesday/Wednesday night remains on the low side given the above
uncertainties and how instability magnitude will play out.
However, given some increase in the low level jet, weakening
propagation vectors overnight, and warm cloud depths approaching
10k feet, some locally heavy rain is not out of the question.

Thursday looks to be a transition day between higher precip chances
as aforementioned upper disturbance shifts east, and potential
composite outflow settles south of the area, and will just maintain
low chance pops during the day.  A secondary time of greater
shower/storm chances may evolve Friday or Friday night as a more
amplified mid level wave ejects across the upper MS Valley. Primary
forecast challenge for the Thursday night-weekend period in terms of
additional precip chances is resolving the strength of mean
mid/upper level ridging across eastern CONUS. Given recent blocky
nature to the pattern and preference to maintenance of mean ridging,
it is difficult to go more than low to mid chance pops through
this period with better forcing and stronger shear displaced to
the west. Shear profiles should also diminish post-Friday, which
should limit extent of severe potential late week/weekend.

In terms of temperatures, not much day to day variability is
expected with highs around 80 and lows in the 60s as increasingly
moist air mass provides a much more limited diurnal range in temps.

&&

.AVIATION...(For the 18Z TAFS through 18Z Tuesday Afternoon)
Issued at 305 PM EDT Mon May 23 2016

Upper level ridging will provide quiet aviation weather through
this period. A very slow eastward migration of the surface high
will maintain light south sfc winds at terminals through the
period.

&&

.IWX Watches/Warnings/Advisories...
IN...NONE.
MI...NONE.
OH...NONE.
LM...NONE.
&&

$$

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


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