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Area forecast discussion 
National Weather Service northern Indiana
440 PM EDT Thursday Sep 3 2015

issued at 440 PM EDT Thursday Sep 2 2015

A series of upper level disturbances will track across the Great
Lakes and Ohio Valley regions tonight and Friday resulting in
isolated to scattered showers and thunderstorms...especially early
tonight. Otherwise...very warm and humid conditions will persist
through the rest of the week. Highs will be in the middle to upper
80s. Lows will be in the middle to upper 60s.


Short term...(this evening through friday)
issued at 438 PM EDT Thursday Sep 3 2015

An upper level system over lower Michigan will move southeast and
will help trigger storms over the forecast area late this afternoon
and early tonight. The best chance for storms will be in the
proximity of this system over far Southern Lower Michigan into
Northwest Ohio. A second upper level disturbance was over northern
wisconsic this afternoon. This system should reach the area Friday
morning....and may help trigger more storms. not feel
NCEP/wpc models have a good handle on convective initiation with the
first have adjusted timing of the storms which reflects
the best window for storms based on a blend of the latest model data
and radar trends. Concern for locally heavy rainfall given favorable
heavy rain parameters including a deep warm clouds layer with high
precipitable water values and low net storm movement. Otherwise...
heat index values continue to approach the threshold for an
advisory. For now...have handled through social media and will
update the hazardous weather outlook to highlight these heat issues.


Long term...(friday night through thursday)
issued at 438 PM EDT Thursday Sep 3 2015

Amplified upper air pattern to undergo transition this period with
cooler broad northwest flow expected toward end of period. Models in
agreement on general transition but numerous discrepancies in
details on how we get there.

Weak perturbation in middle level height field to still be over the
area early Friday evening. Afternoon heating and a lingering weak
surface boundary along with a Theta-E maximum over the area should allow any
ongoing isolated thunderstorms and rain to continue into early evening before
dissipating. Carried a slight chance pop into the 00-03z time frame
to account for any residual activity. Middle level ridge then re-
establishes itself Saturday into Monday with heat and humidity
continuing. Another chance for isolated convection Saturday
afternoon but ridge and warming looks strong enough by Sunday to
preclude any addition of probability of precipitation for now.

Questions begin to arise for Monday into Wednesday with approach of
height falls and cold front which will finally cool US back down to
near or below normal by middle to end of next week. Medium range models
continue to struggle with timing of front through our area as best
forcing remains well north of the area but several weak disturbances
appear to disrupt eastward push of boundary. Will maintain the low
to middle chance probability of precipitation from Monday afternoon through Wednesday with
drier and cooler air working in Wednesday into Thursday.


Aviation...(for the 18z tafs through 18z Friday afternoon)
issued at 151 PM EDT Thursday Sep 3 2015

An upper level system will move southeat and will help trigger
storms over northern Indiana. Have adjusted timing of the storms
which reflects the best window for storms based on the latest
model data and radar trends. However...other storms are possible
outside the thunderstorms in the vicinity as indicated in the a taf amendment
may eventualy be needed to take these timing issues into account.


Iwx watches/warnings/advisories...


short term...skipper
long term...Lashley

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