Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service northern Indiana
545 am EST sun Dec 21 2014

issued at 1217 am EST sun Dec 21 2014

High pressure will continue to provide the region with dry
conditions...light winds...and mostly cloudy skies today into
tonight. Highs are forecast to reach the middle to upper 30s today
and drop to near 30 degrees tonight. Rain chances and temperatures
will increase Monday into Tuesday as an upper level trough digs
into the plains and Gulf moisture streams north into the region.


Short term...(today and tonight)
issued at 330 am EST sun Dec 21 2014

Forecast area will remain under the influence of a Quebec to Tennessee-
Ohio Valley surface ridge today resulting in more of the same. Latest
satellite/observation data showing low clouds still in place under
subsidence inversion. Slight low level drying as winds back more
southeasterly may allow for some erosion across southern/eastern
zones...although kept most locations mostly cloudy given expected
increase in middle-high clouds.

Impressive east Pacific jet now translating into the Pacific
northwest will help carve out a decent 500 mb height minimum and
attendant surface reflection into the northern plains by later
tonight/Monday. Increasing isentropic ascent/warm air advection within
deepening/strengthening southerly flow downstream into the MS
valley/western lakes expected to help keep clouds locked in across
at least western County Warning Area tonight...with any precipitation focusing well
west of the forecast area through 12z Monday.


Long term...(monday through saturday)
issued at 330 am EST sun Dec 21 2014

As discussed several days ago...expected changes in model iterations
have been ongoing and a major adjustment has occurred with several
of the latest 00z model runs. The intense cyclogenesis and
associated surface low bomb has basically disappeared from many
models with a much weaker surface reflection. Overall picture
remains similar with mainly rain followed by some cold air on back
side and some snow still possible...but intensity of system is now
much weaker. Confidence remains low and by no means making any
significant changes to forecast as further adjustments likely over
next 24 to 36 hours.

Impressive water vapor shows jet energy coming onshore over Pacific
northwest. This energy will still carve out a deep trough over the
central Continental U.S. With a closed low over the plains Monday and into the
Midwest Tuesday. This will strengthen low level jet and moisture
transport into our region with warming thermal profiles supporting
rain chances Monday afternoon into Tuesday. The secondary
cyclogenesis now comes into question and this has plagued models
since the beginning. Operational GFS and Gem still show a decent surface
low developing in the deep south and moving north through eastern in
or western Ohio. GFS is much slower compared to Gem. Of concern is the
parallel GFS which is nothing like the operational model and
actually closer to 00z European model (ecmwf) showing little in way of development
with secondary low and basically bringing an open trough through the
region with less rainfall and little snow on the back side. All of
this still hinges on how jet energy dives into the central Continental U.S. And
still suspect model physics not handling this complicated factor
well at all so additional model changes likely. Thus staying close
to previous conservative forecast and latest superblend init for
consistency which overall still in line with basic large
scale/ensemble output. This still means rain moving in later Monday
afternoon and being around into Wednesday. Best chance for any snow
still looks to be Christmas evening night on back side of whatever
solution verifies and amounts still highly questionable for our area
given variable solutions.

Beyond this system another fast moving clipper looks to race across
the region Friday. Kept low chance probability of precipitation in for this but doubt models
will have any clue to its evolution until the initial system is
sorted out.


Aviation...(for the 12z tafs through 12z Monday morning)
issued at 545 am EST sun Dec 21 2014

Mainly VFR through the taf cycle. Surface ridge from Quebec southwest
into the lower lakes/Ohio Valley will gradually edge east this
period allowing winds to become southeasterly by the way 4-10 kfts. Dry
otherwise with moist boundary layer likely keeping low clouds
(mainly VFR by the way 3-7 kft) around through the period.


Iwx watches/warnings/advisories...


short term...steinwedel
long term...Lashley

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

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

National Weather Service Glossary of Abbreviations