Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service northern Indiana
1256 PM EDT Wednesday may 27 2015

issued at 1256 PM EDT Wednesday may 27 2015

Weak cold front is expected to move across the area this
afternoon causing scattered showers and thunderstorms. High
pressure will build into the area tonight into Thursday providing
fair weather. Highs today will be in the upper 70s and lower
80s... with lows tonight in the middle and upper 50s.


issued at 1121 am EDT Wednesday may 27 2015

Little change needed to the forecast going into the afternoon
hours as chances for scattered showers/isolated storms increase
with remnant mesoscale convective vortex tracking east into central in...and primary middle
level trough axis and associated surface front propagation east into
the lower Great Lakes. This forcing combined with modest surface based
destabilization, steep low level lapse rates, and just enough
unidirectional flow (effective shear values 30-35 kts) may be
enough to support an isolated strong-severe storm (damaging winds)
mainly along/east of Interstate 69 by middle-late afternoon. Lacking
middle-level lapse rates and marginal shear should limit
organization/updrafts and keep this an isolated wind threat at


Short term...(today and tonight)
issued at 420 am EDT Wednesday may 27 2015

Shortwave and associated cold front over the upper MS valley this morning
expected to move east-NE across our County Warning Area this afternoon. Diurnal heating
should result in around 1000j/kg cape while still respectable
30-40kt unidirectional deep layer shear remains over the area ahead
of the upper level trough suggesting some potential for severe storms with
damaging winds across the southeast portion of County Warning Area where later frontal passage should
allow for better instability. High res convective allowing models in
decent agreement suggesting thunderstorms will impact southeast 1/2 of area this
afternoon so bumped up probability of precipitation in this area to likely range. Rather strong
gradient/mixing ahead of the front should result in breezy/warm
conditions once again with high temperatures ranging from the u70s northwest to
the l80s southeast.

Surface high expected to move east across the area tonight as the front
sinks S-southeast to southern in/OH. Light winds and clearing skies should
provide good radiational cooling allowing temperatures to fall into the
M-u50s. Some potential for fog development but held off adding to
forecast to see how significant the drying is behind the front this afternoon.


Long term...(thursday through tuesday)
issued at 420 am EDT Wednesday may 27 2015

The main challenges this period concern the evolution and phasing of
a northern stream system dropping south out of Canada and a southern
stream wave ejecting east across the Continental U.S. Friday and Saturday. For
this package...favored the European model (ecmwf). The European model (ecmwf) continues to have a
better overall handle with this system which is reflected in better
run to run consistency than the GFS. Also...the upstream airmass has
been very efficient in producing showers and storms. Thermal and
wind profiles support only a marginal severe storm threat...but
given the history of this airmass and the likely hydrologic
recycling upstream...have raised rain chances Friday night and
Saturday. Precipitable water values should rise close to 1.75. Cape
values should remain around or under 1000 j/ locally heavy
rainfall is likely. After Saturday night...removed all rain chances
except for a low chance for a lingering shower over southeast areas
Sunday. Temperatures should be very warm Thursday and Friday with
highs from 82f to 86f.


Aviation...(for the 18z tafs through 18z Thursday afternoon)
issued at 1256 PM EDT Wednesday may 27 2015

Middle level trough tracking into the Great Lakes in concert with a
separate remnant mesoscale convective vortex into southern/ctrl Indiana will provide enough lift
over a moderately unstable/moist environment to produce scattered
showers/storms through appromiately 20-22z at kfwa and through
19-20z at ksbn. Broken-overcast ceilings will likely oscillate between
high MVFR and low VFR through the afternoon at each site. Light
winds and dry/VFR conditions are expected behind the associated
cold front this evening into Thursday as high pressure builds in.


Iwx watches/warnings/advisories...


short term...jt
long term...skipper

Visit US at www.Weather.Gov/iwx (all lower case)

Follow US on facebook...twitter...and youtube at:

National Weather Service Glossary of Abbreviations