Area Forecast Discussion
Issued by NWS Northern Indiana

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FXUS63 KIWX 190706

Area Forecast Discussion
National Weather Service Northern Indiana
306 AM EDT Wed Jul 19 2017

Issued at 1159 PM EDT Tue Jul 18 2017

High pressure will continue to provide mainly dry and clear
conditions tonight. A weak front will bring a low chance for
showers and thunderstorms on Wednesday. Lows tonight will drop
into the 60s, with highs on Wednesday well into the 80s. Thursday
through Sunday will feature humid conditions and periodic chances
for showers and thunderstorms.


.SHORT TERM...(Today and Tonight)
Issued at 302 AM EDT Wed Jul 19 2017

Convective complex moving across southern WI decaying as it moves
eastward out over lake Michigan and away from instability axis
and better flow/forcing. IR imagery showing warming and lowering
of cloud tops over the past couple hours with any new cells
regenerating/backbuilding to the west where better influx of low
level moisture and mid level flow exists...but even those are
fading fast. CAMs continue this downward trend toward daybreak and
current grids have good handle as just slight chance of lingering
shower/storm in far NW this morning. Potential of remnant
boundary from this convection may linger in vicinity and combine
with diurnal instability to generate a pulse storm or two but
lacking any type of organized flow these should be sparse and
short lived. Any lingering high clouds expected to erode quickly
this morning and lead to a hot and humid day as temperatures
expected in the upper 80s to around 90 with dewpoints rising to
around 70. 95kt upper jet streaming up over plains ridge will be
positioned this afternoon to favor MCS development similar to last
night. Difference tonight will be better flow and forcing should
have more well developed complex rolling toward our far NW by
early Thursday morning and will therefore maintain POPs here after
midnight. Otherwise warm and muggy with lows around 70.


.LONG TERM...(Thursday through Tuesday)
Issued at 302 AM EDT Wed Jul 19 2017

Remnants of nocturnal MCS mentioned in short term expected to be
in play across the northern CWA Thursday morning. Chances for
storms spreads south by Thursday afternoon as leftover outflow
boundary once again combines with diurnal instability. Large scale
pattern remains rather stagnant through Saturday bringing
multiple rounds of storms to the region as our area remains on NE
edge of plains ridge allowing short wave impulses riding along
the ridge to turn E/SE toward us. Timing and placement of each MCS
to be modulated by the previous one as quasi-stationary surface
boundary is continually convectively modified by these systems. So
while confidence in the occurrence of each MCS remains high...the
mesoscale dominant nature of this pattern yields low confidence
in the predictability in any one particular forecast
period...making it prudent to continue to avoid mention of likely
POPs in this time range. Hot and humid conditions will continue
through Saturday with highs upper 80s to around 90 and heat
indices reaching the mid to upper 90s in some areas. A break from
this pattern expected to come beginning of next week. Upper low in
eastern Pacific just off British Columbia coast will come onshore
and move along the US/Canadian border and dig into the great
lakes region by Monday and carve out longwave trough over the
region as surface frontal boundary pushes south into the Ohio
valley. Cooler and less humid air behind front as high pressure
builds into the region.


.AVIATION...(For the 06Z TAFS through 06Z Wednesday Night)
Issued at 1158 PM EDT Tue Jul 18 2017

A large upper ridge will build toward the mid Mississippi Valley
this period as weak disturbances track over the top of the ridge
and move into the Upper Great Lake region. Convection this evening
over IL associated with one of these weak systems was moving into
much more stable air and is expected to dissipate overnight and
not reach the terminals. There could be some regeneration over
northern Indiana with daytime heating later today, but given the
stable mid level lapse rates and some large scale subsidence on
the northeast fringe of the upper ridge, have kept thunder out of
TAFs. It appears activity will be too isolated to include in TAFs
at this time.





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