Area Forecast Discussion
Issued by NWS Northern Indiana

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000
FXUS63 KIWX 142327
AFDIWX

Area Forecast Discussion
National Weather Service Northern Indiana
727 PM EDT Mon Aug 14 2017

.SYNOPSIS...
Issued at 330 PM EDT Mon Aug 14 2017

An upper level disturbance across Minnesota will dive southeast
overnight into Tuesday morning. Scattered showers may develop in
advance of this disturbance late tonight into Tuesday as a weak
frontal boundary drops into the area. Dry weather is then expected
Tuesday night into early Wednesday, but chances of showers and
thunderstorms will increase again Wednesday night and Thursday as
a stronger system moves in from the west. Low temperatures
tonight will drop into the lower to mid 60s. High temperatures on
Tuesday will reach into the lower to mid 80s, except in the upper
70s closer to Lake Michigan.

&&

.SHORT TERM...(This Evening through Tuesday)
Issued at 330 PM EDT Mon Aug 14 2017

The potential of scattered showers and a few thunderstorms will
increase overnight into Tuesday, but the better chance of more
widespread showers and thunderstorms should hold off until the
long term period closer to very late Wednesday night or Thursday.

Weak lake breeze has formed and is confined fairly close to the
shoreline this afternoon. Visible satellite imagery starting to
indicate a bit more in the way of vertical growth along lake
enhanced convergence zone. Instability magnitude is being limited
this afternoon by marginal moisture profiles and lingering mid level
inversion. However, cannot completely rule out an isolated shower or
thunderstorm across extreme northern Indiana/southern Lower Michigan
where mid level lapse rates are a bit steeper (although still on
marginal side). An approaching upper level short wave may also
enhance isolated shower potential over next few hours, with perhaps
best prospects of isolated shower in vicinity of lake breeze.
Remnant cirrus shield entering NW Indiana this afternoon from
overnight Corn Belt convection may tend to limit more vigorous
updrafts however. Will continue with "silent" 10-14 PoPs with low
end prospect of an isolated shower developing through 22Z.

For remainder of night, attention will turn to a more vigorous upper
level trough digging southward across central Minnesota this
afternoon. This short wave will eventually drop southeast through
large scale cyclonic flow to the southern Great Lakes by daybreak. A
weak westerly low level jet ahead of this trough will advect a low
level theta-e ridge across the north late evening/overnight with a
weak MUCAPE axis likely to accompany this feature. While moisture
quality should continue to be a limiting factor, more dynamic nature
of this short wave should allow for isolated-scattered showers
(perhaps isolated storms) to develop late evening into the early
morning hours Tuesday. Will maintain 30-40 PoPs overnight and
focused mainly across northwest half of the area.

Frontal boundary should stall out across central Indiana on Tuesday
with overnight short wave dampening across the eastern Great Lakes.
Not a good deal of confidence in diurnal redevelopment in vicinity
of this front Tuesday afternoon due to lack of forcing, but best
chances would be across approximately southeast half of the area.

&&

.LONG TERM...(Tuesday Night through Monday)
Issued at 330 PM EDT Mon Aug 14 2017

Loss of diurnal instability Tuesday afternoon and next mid/upper
level wave well upstream across the Rockies suggest that a lull in
rain chances is likely from Tuesday evening through the first part
of Wednesday. Low level warm/moist advection will begin to increase
across southwest half of the area Wednesday afternoon, although
more substantial low level jet/low level moisture transport should
remain across mid MS Rvr Valley into Wednesday afternoon. Based on
latest model trends of holding mid level ridging in place a
bit longer Wednesday, have generally accepted blended low chance
PoPs following the southwest to northeast instability gradient.

The greatest chance of showers and thunderstorms is still expected
in the late Wednesday night through Thursday timeframe as large
scale support increases with approaching upper trough. Low level
warm front will lift northward through the area later Wednesday
night into early Thursday morning allowing for increasing moisture
transport and PWATS increasing above 1.75 inches. With Dprog/Dt
trends showing an increasing slower evolution, these higher PoPs may
end up being focused more in the Thursday morning period as opposed
to late Wednesday night.

If nudge to slower idea does verify, the window that may need to be
watched for conditional severe potential appears to be Thursday as
deep layer shear increases into the 30-40 knot category, and when
large scale forcing is maximized. Instability magnitudes due to
impacts from early morning convection remain in question however,
and confidence remains low in extent/placement of afternoon
destabilization as system begins to occlude across the western Great
Lakes. Cold front will sweep across the region late Thursday
afternoon/Thursday evening setting up dry conditions later Thursday
evening through Friday night.

Several northwest flow waves should reinforce broad low level
thermal troughing next weekend with below normal temps expected
along with periodic low chances of showers.

&&

.AVIATION...(For the 00Z TAFS through 00Z Tuesday Evening)
Issued at 723 PM EDT Mon Aug 14 2017

Short wave will drop southeast overnight with a weak surface front
moving through terminals Tuesday morning. Small chances for shra
and an isolated tsra overnight but not enough confidence in
coverage to include more than a vcsh at KSBN for now. Hires
guidance does point to window of 06-10z at KSBN but not much
activity at KFWA. Residual VFR to MVFR cloud deck possible at KSBN
toward daybreak so kept that trend in TAF. Otherwise becoming VFR
mid to late morning with front south of terminals and west to
northwest wind 5 to 10 knots.


&&

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

$$

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


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