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Area forecast discussion 
National Weather Service Indianapolis in
631 am EDT Friday Oct 31 2014

the aviation section has been updated below.


issued at 222 am EDT Friday Oct 31 2014

A strong cold front is expected to push across central Indiana
this afternoon...allowing much colder Canadian air across central
Indiana for tonight and into the first part of the weekend. Some
showers will be possible today ahead of the front...and even a few light
snow showers will be possible in the wake of the front this
evening. By Saturday morning...central Indiana will have had a
killing freeze.

Cool high pressure is expected over the region on Sunday and into
Monday with dry weather and below normal temperatures. By Monday
night and Tuesday...warmer temperatures are expected to arrive on
southerly winds on the backside of high pressure...however another
approaching cool front will result in more chances for rain.


Near term /today/...

Issued at 222 am EDT Friday Oct 31 2014

Surface analysis early this morning shows a strong area of low
pressure over the Great Lakes with a poorly defined yet strong cold
front stretching south across eastern Wisconsin...eastern
Illinois to the lower Mississippi River valley. Strong and cold
high pressure was found over the upper Midwest. Much colder air
was found in the wake of the front...with temperatures in the 30s and low
40s across Wisconsin...Iowa and Minnesota. Aloft...water vapor
showed a strong ridge in place over The Rockies and a deep broad
trough in place across the eastern half of the United States. A
strong upper level disturbance was embedded in the flow aloft over
Western Lake Superior and was diving southeast. Radar shows a few
scattered rain showers over southern central Indiana...along with
a few more very light rain showers over central Illinois.

GFS and NAM suggest very strong cold air advection to start
shortly after 12z today with 850mb temperatures falling toward -6c by 00z
Sat. Given this we will expect steady or slowly falling
temperatures through the day today. Will aim for high temperatures for
today occurring at or shortly after 12z...ahead of the front. Furthermore
the strong pressure gradient building across the will result in
gusty north winds with wind chills around 30 this afternoon and in
the middle 20s tonight.

As for moisture appears in place with today/S
system...however strong forcing and dynamics are in place as this
system passes. Best moisture appears to be passing near frontal
passage around 12z. Forecast soundings appear to dry out late this
morning and this afternoon as northerly flow resumes. However by
late this afternoon and near 00z a second batch of precipitation will be
possible as the models suggest the previously mentioned strong
upper level disturbance will dive across central Indiana. By
00z...forecast soundings show good saturation in the lower and middle
levels...all while an 850mb jet of 50+ knots screams aloft.
Furthermore by 00z forecast soundings show just about the entire
column below US a snow profile.

Still...moisture appears limited as these two forcing mechanisms
pass...thus will trend toward higher probability of precipitation than mavmos but
expecting light amounts of precipitation.


Short term /tonight through Monday night/...

Issued at 222 am EDT Friday Oct 31 2014

GFS and NAM continue to suggest active weather ongoing during the
evening hours as the strong upper disturbance will continue to be
passing through Indiana at 00z before exiting to the southeast
shortly after 06z. Again...favorable conditions will exist for
precipitation during the first few hours after 00z as forecast soundings
remain saturated for the first few hours after 00z...before drying
out rapidly as the upper low and strong winds aloft depart
quickly. Deep moisture remains limited with northerly flow...but
strong dynamics should be able to produce some light precipitation. Warm
ground should result in any snow melting upon reaching the
ground. Thus will trend at or slightly above mavmos probability of precipitation for a few
hours this evening before dropping probability of precipitation off quickly by 06z as the
forcing mechanism exits.

Evening hours will be blustery...with snow showers or ice pellets
possible amid wind gusts of 20 to 30 miles per hour producing wind chills to
near 25 degrees. Folks who will be outside this evening will get a
taste of early winter...and will issue an Special Weather Statement to address this.

As for lows...given the strong cold air advection...the freeze
warning remains a good bet...with a hard freeze expected by 12z Sat.

Dry weather will then be expected on Saturday through Monday as
the GFS and NAM suggests the strong ridge over The Rockies will
push east and build across the Central Plains and then the Ohio
Valley by Monday...with the ridge axis over Indiana by 18z Monday.
Forecast soundings through this period show a dry column with
unreachable convective temperatures with good subsidence in place. Thus
will trend toward mostly sunny days and mostly clear night during
this period. As for temperatures will trend both highs and lows cooler
than mavmos on Saturday and Saturday night. However by Sunday
southerly flow returns amid some warm air advection aloft. Will
stick close to mavmos lows and highs Sunday through Monday night.


Long term /Monday through next Thursday/...
issued at 222 am EDT Friday Oct 31 2014

Ensembles suggest a progressive upper pattern can be expected during
this period. An upper level ridge will be in the process of moving
over the forecast area on Monday...while the next trough will affect
the area around the middle of next week. There are timing
differences with respect to the individual ensemble members as to
how fast the next trough will move through...with some of the slower
members suggesting the trough will not pass until Wednesday night.
Will go with probability of precipitation for rain starting Monday night and lingering into
Wednesday night. At this appears the best precipitation
threat will be in the Tuesday to Wednesday time frame.


Aviation /discussion for the 311200z tafs/...
issued at 631 am EDT Friday Oct 31 2014

Cold front currently pushing through Northwest Indiana. Short term
models suggest this front will be near klaf by issuance
time...reaching kbmg around 311500z. Some light rain...along with
the arrival of MVFR ceilings around 025 expected near and in the
Post frontal zone. Should be a rather sharp increase in the surface
winds as well with frontal passage...with winds becoming 310-330
degrees with gusts around 25 kts in the wake of the front.

Additional rain and snow showers expected to develop by the middle to
late afternoon hours as the upper low moves overhead. At this
point...appears the best threat for IFR visibility restrictions this
afternoon will be off to the northeast of the taf sites where lift
will be better. As a result...will keep visibility restrictions
above IFR for now.

The core of a 50kt 850mb jet is prognosticated to move into the area later
this afternoon. Given the cold advection helping to mix these winds
down...expecting some surface gusts in the 30-35 knots range from
320-340 degrees by the middle to late afternoon hours.


Ind watches/warnings/advisories...
freeze warning from midnight tonight to 10 am EDT Saturday for



near term...puma
short term...puma
long term....jas

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