Scientific Forecaster Discussion
Area forecast discussion
National Weather Service northern Indiana
751 PM EDT Wednesday Oct 1 2014
issued at 730 PM EDT Wednesday Oct 1 2014
A low pressure system will move toward the region tonight and
Thursday. Small chances for precipitation will begin across
western areas late tonight and increase through the day on
Thursday. Widespread showers and thunderstorms are expected
Thursday night across most of the region just ahead of a strong
cold front that will usher in much cooler air.
Low temperatures tonight will fall into the lower and middle 50s
as skies become mostly cloudy. Above normal temperatures are
expected on Thursday with highs ranging from the middle 70s north
to lower 80s south.
Short term...(this evening through thursday)
issued at 334 PM EDT Wednesday Oct 1 2014
Deep trough to the west that has brought lots of rainfall across the
plains and Midwest will begin to gain some momentum but also
strengthen significantly (mainly in the long term period) as a
series of stronger pieces of energy eject from closed low pressure
over northern Canada. For the short term period the main impacts of
the process will be a further carving of the trough and subsequent
height rises to usher in a quick shot of much warmer air but also
set the stage for increasing moisture. Convection over far western
Illinois will work east tonight. Models vary on timing and extent of
this area later tonight into early Thursday before main low level
jet sets up to the west again. While some signals suggest a dramatic
increase in probability of precipitation is warranted in this time frame enough uncertainty
exists to hold off on extreme increases and simply introduce slight
chance/chance probability of precipitation overnight in western areas and will defer to evening shift
to monitor trends. Better chances definitely begin to arrive
Thursday afternoon as main wave draws closer with likely probability of precipitation
warranted by middle afternoon in west areas. Highs should reach the middle
70s to around 80 with locations in the west and north coolest due to
increasing cloud cover. If rainfall does occur/linger in the west
highs could be in jeopardy of being reached.
Long term...(thursday night through wednesday)
issued at 334 PM EDT Wednesday Oct 1 2014
Potent southern stream wave across the central rockies will drive eastward short
term and then phase west/rapidly southeastward digging northern stream SW out of western
ab Friday. Resulting sigly deep trough development across the western Great
Lakes subsequently highlites the period early on.
As was the case yesterday and in conjunction west/prior shift will again bump
probability of precipitation higher lt Thursday night through Sat am in reflection of greater
trough dig/amplification seen throughout the 12z guidance spectrum.
In fact yesterday/S outlier European model (ecmwf) 700 mb-5 evolution aloft now seen in both
the GFS and Gem...taking 500 mb hfc in excess of 22 dm through southern in
Friday night. Thus will break even higher lt Friday night west/likely
mention across the north in light of both stronger ll thermal trough
wrapping southeastward through County Warning Area underneath what shld be a robust commahead in vicinity of
of bottoming northern stream SW. That said...enough detail/timing
uncertainty exists to hold west/high chance mention for the moment Sat am.
However regardless of solution yesterday/S 40 degree hold hunch holds per
lower trending guidance temperatures and will hedge lower further this cycle.
Slw moderation follows then into early next week although punctuated
by a pair of waves embedded within steep northwest follow aloft.
Timing/details vary considerably yet will follow super blend
approximation in spite of anything else making a more compelling
case to stray at this point.
Aviation...(for the 00z tafs through 00z Thursday evening)
issued at 728 PM EDT Wednesday Oct 1 2014
VFR to start the period but conditions will begin to deteriorate
late in this valid period. Expect a decaying area of showers in
vicinity of taf sites late tonight into Thursday morning. Not
currently expecting restrictions with dry lower levels initially.
More substantial rain and restrictions expected later Thursday and
especially Thursday night ahead of strong cold front. For now kept tafs
in the VFR category but this could change Thursday afternoon depending
on how convection develops.
Visit US at www.Weather.Gov/iwx (all lower case)
Follow US on facebook...twitter...and youtube at: