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Area forecast discussion 
National Weather Service Indianapolis in
623 PM EST Monday Dec 22 2014

the aviation section has been updated below.


issued at 312 PM EST Monday Dec 22 2014

An upper trough over the central U.S. And low pressure over the
upper Midwest will bring rain across our region tonight and early
Tuesday. Rain may temporarily end by late Tuesday as this first low
pressure system moves on to the northeast. Models move another area
of low pressure into Tennessee and Kentucky early Wednesday and into
the eastern Great Lakes Tuesday evening. Colder air on the back
side of this low will cause precipitation to chance to snow late
Wednesday and Wednesday night. Light accumulations are possible
northwest sections. In the low term another area of low pressure
will bring a chance of mixed precipitation around Saturday and a
chance of light snow Sunday. The rest of the periods will be dry
with temperatures near or slightly below normal.


Near term.../tonight and Tuesday/
issued at 312 PM EST Monday Dec 22 2014

Radar shows an area of light rain across Illinois and extreme
western Indiana. Models move this area of rain eastward as low
pressure over the upper Midwest moves into the Great Lakes. Will go
with high rain chances all areas tonight. Models push a dry slot
east into our area by Tuesday afternoon. Even drier air will move in
Tuesday...models maintain a low pressure inversion which should keep
clouds across our region.

Concerning temperatures expect a slow rise continuing this evening
then near steady temperatures the rest of tonight. On Tuesday went
closer to the cooler mav temperatures as clouds should hold surface
temperatures down a few degrees.


Short term.../Tuesday night through Christmas day/
issued at 312 PM EST Monday Dec 22 2014

Forecast focus will be on rain chances tonight into Wednesday.
Models indicate precipitation may chance over to snow over northwest
sections late Wednesday and elsewhere Wednesday night. All models
indicate rain will spread north across our region Tuesday night and
then change over to snow over western sections late Wednesday and
elsewhere Wednesday night. Even though all models indicate this
change over...there are difference on the track of the surface low
and how much snow will occur to expect.

The NAM seems overly aggressive and produces too much snow as it
takes the surface low farther east and has develops more of a closed
upper low across our region Wednesday evening. BUFKIT gives as
much as 9 inches of snow in Lafayette which is way too much. The
NAM shows some convective feed back issues and will discard. Will
go more of GFS European blend which takes the surface low near or
slightly just east of indy and is somewhat more conservative with

Believe HPC numbers snow amounts seem reasonable. But I cut them
slightly. At the present time...expect around 2 inches of snow over
northwest sections and an inch of snow as far southeast as indy
mainly Wednesday night.

Finally the snow will end quickly Christmas day as the surface low
moves on to the northeast. In regards to temperatures went with a
slow fall over central and western sections Wednesday and all areas
Wednesday night. With a little snow cover possible Thursday...cut
high temperatures slightly over northern sections. Otherwise...a
MOS blend on temperatures seem reasonable.


Long term /Thursday night through Monday/...
issued at 312 PM EST Monday Dec 22 2014

The extended period is quite unsettled as the models appear to be
all over the place with systems. Superblend initialization seemed to
do the best job of blending the differing solutions and showing at
least two distinct systems moving through the region over the course
of the weekend. The first beginning Friday night and the next middle
weekend. Very difficult to nail down probability of precipitation at this early
time...especially with models in disagreement. Left in broad brush
chances for scattered rain and/or snow through most of Friday night
through Sunday. Light snow accumulations look possible Sat night.
High pressure appears to builds back over the region Sunday night
and dry conditions will then prevail across central Indiana for
early next week.


Aviation /discussion for 230000z taf issuance/...

Issued at 622 PM EST Monday Dec 22 2014

Taf period starts out with VFR/MVFR ceilings and light rain over the
sites. While some of the sites have VFR ceilings they could fill in
at any time and thus will go with prevailing MVFR to begin. Expect
conditions to deteriorate further based on IFR ceilings currently
over Illinois moving this way slowly. Brought IFR into the sites
after 2-3z west and 4z at kind. Around the same time should see some
marginal wind shear set up with southwesterly winds around 40-45 kts
atop a surface layer of 10-14 kts out of the southeast. After 4-6
hours the winds aloft will decrease a bit and the surface winds will
veer a little along with gusts mixing down so ended the shear then.
Looks like there could be a break in the rain and low ceilings from
middle morning until afternoon before another wave of rain and at least
MVFR ceilings move in after 0z Wednesday.


Ind watches/warnings/advisories...


near term...jh
short term...jh
long term....smf

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