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Area forecast discussion 
National Weather Service Indianapolis in
323 PM EST sun Dec 21 2014

Update...
the aviation section has been updated below.

&&

Synopsis...
issued at 240 PM EST sun Dec 21 2014

High pressure will push off to the east tonight. A complex low
pressure system will affect the area towards the middle of the week.
Another frontal system may affect the area by the end of the week.

&&

Near term /tonight/...
issued at 240 PM EST sun Dec 21 2014

No precipitation expected tonight as surface high pressure retreats
off to the east...however there should be a gradual increase in
cloud cover with time as next system begins to organize in the
plains.

Developing warm advection and increasing cloud cover should help to
limit the temperature fall tonight. Low level thicknesses suggest
the GFS MOS lows tonight look reasonable.

&&

Short term /Monday through Wednesday/...
issued at 240 PM EST sun Dec 21 2014

Model data continue to offer differing solutions as to the evolution
of the pattern during this period. There is considerable spread
among the operational and ensemble data as to the location and
intensity of a secondary wave along a trailing frontal system
towards the middle of the week...so forecast confidence is lower than
usual. The track of this wave varies anywhere from up through
western Illinois to along the west side of Appalachian
Mountains...with sea level pressures ranging from 982 mb to 1005 mb.
The ensembles at this time seem to favor a warmer more westerly
solution...so will nudge the forecast in that direction in the later
periods.

Lift is prognosticated by the models to brush through the west central and
northwest zones by the midday hours on Monday and on into the
afternoon hours. Will start to bring in some probability of precipitation by that
time...with the highest probability of precipitation over west central and northwest zones
closest to better lift.

Will go with high probability of precipitation for Monday night into Wednesday as the
primary frontal zone slows down and the secondary wave moves up from
the south. Model data in general suggest air mass won't be cold
enough for a changeover to snow until Wednesday...with the warmer
solutions suggesting not until Wednesday afternoon or even later.
For now...based on the overall trends...will push back the
changeover to snow from the previous forecast more into the
afternoon hours. Some accumulating snow still looks possible
Wednesday afternoon...especially over the northwest zones.

Given the warmer trend in the model data...will lean towards the
warmer side of the MOS guidance. Highs on Wednesday will probably be
reached early in the day...with temperatures falling off later.

&&

Long term /Wednesday night through Sunday/...
issued at 246 PM EST sun Dec 21 2014

Main focus for the extended will be on precipitation potential for
the tail end of a strong Christmas evening system along with a Friday
and Friday night system.

Models and ensembles agree frontal system will be moving to the East
Coast Christmas evening night which should bring an end to the midweek
precipitation event. Partial model thicknesses suggest it should be
all snow Wednesday night and ending overnight from east to west.
So...chance probability of precipitation look OK with likely only a minor accumulation.

Upper ridging will result in dry weather with warming temperatures
late week before another frontal system brings a small chance of
rain on Friday and snow Friday night. Again...any accumulation looks
to be minor at best. The rest of the extended looks dry as surface
high pressure builds in from the plains.

Should see some gusty winds mainly through Friday night as surface
pressure gradient is tight. Meanwhile...expected cloud cover and low
level thermal forecasts suggest regional blend looks good with above
normal highs mainly in the 40s on Thursday and Friday and colder
temperatures for the weekend with highs in the lower to middle 30s.
Overnight lows should mostly be in the 30s Christmas evening night and
Thursday night and the 20s after that.

&&

Aviation /discussion for 211800z taf issuance/...

Issued at 322 PM EST sun Dec 21 2014

2022z update...no changes needed at this time. Previous discussion
follows.

VFR conditions should continue through tonight with MVFR ceilings
increasing after 14z Monday as a warm front approaches from the
southwest.

Winds will be southeast to near 10 knots this afternoon...6 knots or
less after 00z tonight and 10 knots or more after 14z Monday.

&&

Ind watches/warnings/advisories...
none.
&&

$$

Synopsis...jas
near term...jas
short term...jas
long term....mk
aviation...smf/mk

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