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

issued at 804 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. 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
Wisconsin 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 00z tafs through 00z Friday evening)
issued at 805 PM EDT Thursday Sep 3 2015

Uncertainty with respect to convective trends this evening.
Stabilization of boundary layer with surface cooling plus potential
split between southeastern Michigan and northestern Illinois thunderstorms and rain clusters suggests point
chances for ksbn/kfwa airfields are too low for inclusion.
Relative high xover in upper 60s raise potential for shallow br
formation near daybreak and cover for now with short period MVFR


Iwx watches/warnings/advisories...


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

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