Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Indianapolis in
950 PM EDT Monday Sep 1 2014
the aviation section has been updated below.
issued at 321 PM EDT Monday Sep 1 2014
Widespread rain showers and thunderstorms will impact central
Indiana tonight through tomorrow morning as an upper trough and
associated cold front track across the area. After calm conditions
on Wednesday...a warm humid airmass will enter the forecast area
at the end of the week...also bringing the threat of additional
showers and thunderstorms. Further out...high temperatures will drop
drastically from the upper 80s/low 90s on Thursday and Friday to
70s for the weekend.
Near term /rest of tonight through tomorrow/...
issued at 950 PM EDT Monday Sep 1 2014
Update...thunderstorms over Missouri and western Illinois are
continuing to spread this way as precipitable water upstream has
increased to 2 to 2.25 inches. Rapid refresh model indicates
thunderstorms should reach Indiana Illinois border shortly after
midnight and indy by 06z. Numerous showers and thunderstorms will be
the rule rest of tonight as the developing thunderstorm complex to
our west spreads across our region.
Main threat will be heavy rain late tonight and early Tuesday.
Expect numerous rain amounts of 1 to 2 inches late tonight and early
Tuesday. Since 3 hour flash flood guidance is running about 3
inches...will not issue any flood headlines at this time. However
there is a concern that a few could have localized flooding issues
due to the high precipitable water.
A few strong storms are possible late tonight too. However it
looking less likely that there will be any outbreak of severe weather
over our area as the more unstable conditions remain to our west.
Did not make any significant changes to low temperatures tonight.
Portion of previous near term discussion follows...
the main focus of the near term is thunderstorm chances and severe
threat for tonight.
At this point...heavy rain/flooding will be the main threat
overnight...but will not issue watch at this time due to
inconsistencies in models in regard to location and amounts. The
GFS and Canadian are trending with higher amounts than the
NAM/Euro...in the 2 to 3 inch range. But the GFS takes the heavy
rain band over central portions of the forecast area...and the
Canadian takes it over the northern counties. Meanwhile...the NAM
and Euro are consistent in regard to location of rain /central
portions/...but are trending more toward 1 to 2 inches. Without
any significant rainfalls recently either...have trended toward
Activity will taper off rather quickly from northwest to southeast
around middle morning tomorrow as isentropic lift weakens. Drier air
will be over most of the area by tomorrow afternoon...except the
far southeast counties...will hold onto low end probability of precipitation over that
area into the early evening hours.
Temperatures...overnight lows will be in the upper 60s/low 70s with
plenty of cloud cover over the area...stuck close to guidance.
Short term /tomorrow night through Thursday/...
Issued at 321 PM EDT Monday Sep 1 2014
The main focus of the short term period will be the re-
introduction of probability of precipitation into the forecast on Wednesday night
Zonal flow aloft and high pressure at the surface will result in
dry conditions for tomorrow night through Wednesday. However...a
warm front will start pushing into the area from the southwest on
Wednesday night. Models are not agreeing on timing...with the GFS
a tad faster than the Euro in regard to start time of precipitation.
So...will just introduce slight chance probability of precipitation over the southwest
counties on Wednesday night...expanding further into central
Indiana on Thursday.
Temperatures...stuck close to guidance through Wednesday night and
trended on the warmer side for Thursday with approaching warm front.
Long term /Thursday night through Monday/...
Issued at 321 PM EDT Monday Sep 1 2014
Model guidance remains in very good agreement on the main weather
impacts through the extended. A very warm and humid airmass will be
present across the Ohio Valley for the end of the week as a strong
upper ridge is centered over the Tennessee Valley and southern
Appalachians. High temperatures will be around 90 degrees on Friday.
A sharp wave aloft moving across the northern plains will serve to
buckle the ridge and enable a cold front to drop into the Ohio
Valley with scattered thunderstorms from Friday afternoon through
The passage of the front will usher in a much cooler and drier
airmass beginning Sunday as large high pressure overspreads the
lower Great Lakes. The high will remain the dominant weather feature
for central Indiana into early next week as it drifts slowly east
into New England. High temperatures will fall back into the 70s Sunday and
Monday with overnight lows the coolest seen in the region since the
middle of August.
Aviation /discussion for 020000z taf issuance/...
Issued at 703 PM EDT Monday Sep 1 2014
VFR across the sites to start out but conditions should
deteriorate during the night with the arrival of organized
convection. Winds should remain around 5-10 kts out of the
southwest with the exception of gusts within thunderstorms.
Thunderstorms have begun to fire in central and eastern Missouri
and the forcing producing these will be moving this way. Expecting
storms to arrive at the sites starting with khuf around 3-4z and
kbmg/kind around 4-5z and klaf closer to 7z. Rain and
thunderstorms could remain over the sites for several hours so
continued with earlier forecast of storms through around 13-15z
with MVFR conditions. Dry air will arrive after that and within a
few hours should mix ceilings/visibilities back up to VFR for
Visit US at http://www.Weather.Gov/ind
Follow US on facebook...twitter and youtube at: