Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Indianapolis in
600 am EST Wednesday Dec 18 2013
the aviation section has been updated below.
issued at 317 am EST Wednesday Dec 18 2013
The forecast will start out dry with some weak ridging aloft. That
ridging will quickly break down though as a cut-off low moves into
California and makes its way across Mexico. This will put central
Indiana in an unseasonably warm weather pattern for most of the
forecast period due to the southwest flow. The next chance for
precipitation will come on Thursday afternoon and last through the
weekend. Since temperatures will be so warm...precipitation will fall in the
form of rain for the majority of this event. The exception will be
on Sunday when colder air filters in behind a cold front. Rain will
then slowly make a transition to a rain/snow mix. Beyond that...dry
conditions will return at the very end of the extended period.
Near term /today/...
Issued at 317 am EST Wednesday Dec 18 2013
Dry conditions will prevail today with high pressure/ridging over
the forecast area. The main focus will be the start of warming
trend expected to last through weekend. Surface winds will
initially start out westerly this morning...but will take on more
of a southwesterly component through the course of the day while
strengthening. Sustained speeds will be between 10 to 15 miles per hour with
gusts up to 25 miles per hour as pressure gradient tightens. This will allow
temperatures to climb into the upper 30s/low 40s this afternoon. Latest
GFS has been starting to pick up on the warming trend that NAM has
been focused on over the last several days....so was able to go
with a blend for today/S highs.
Short term /tonight through Friday night/...
Issued at 317 am EST Wednesday Dec 18 2013
Dry conditions will persist through tonight. However...flow
aloft will become more zonal as an upper low moves into the
Pacific northwest. This low will deepen over the next several
days...tracking along the California coast...and then through
Mexico. This will put central Indiana under southwest
flow...allowing temperatures to top off well above normal. Highs will be
close to the middle 50s by Friday with lows in the upper 30s/low 40s.
The NAM has been trending much warmer than the GFS over the last
several days...but the GFS has come into better line with it.
Plus...the NAM may be starting to trend a tad too high. So...opted
to go with a blend for the duration of short term period.
The next chance for precipitation will start on Thursday afternoon and
prevail for duration of short term period as a cold front enters
the region. Precipitation is still expected to be in the form of rain
though through Friday night as central Indiana remains under the
influence of warm air.
Long term /Saturday through Wednesday/...
Issued at 414 am EST Wednesday Dec 18 2013
An active first half of the extended forecast period is expected as
the timeframe starts with unsettled weather in progress over central
Indiana. GFS and European model (ecmwf) again appear in good agreement with regard to
the main features impacting the area. 12z Saturday has a frontal
boundary stalled near the Ohio River. This boundary is not expected
to move much. A strong area of low pressure will move northeast
along the front. This area of low pressure coupled with an upper
level trough approaching the area from the southwest...will provide
sufficient lift for heavy rain to become an issue Saturday night into
There remains some uncertainty as to where the heaviest rain will
fall due to differences in model placement of the frontal boundary
by Saturday night...with the European model (ecmwf) a bit further north with the
front...draping it over some of our southeastern counties while the
GFS has the front over the Ohio River. Localized flooding may be a
threat during this timeframe as previous snow melt would couple with
possible heavy rain. Snow may begin to mix in from the northwest on
Sunday as cold air advection finally begins to push across central
Indiana behind the departing system. Light snow may linger in the
area Sunday night. High pressure then filters into the Ohio River
valley behind the system bringing below normal temperatures for
Monday and Tuesday...before returning to more seasonal values for
Aviation /discussion for 181200z taf issuance/...
Issued at 554 am EST Wednesday Dec 18 2013
Mostly VFR conditions expected throughout this taf period. Has
mainly been a wind focused forecast...surface and low level wind shear. Winds will
back from westerly to southerly as high pressure currently to our
south presses off to the east late morning to early afternoon
Wednesday. Model forecast soundings are depicting an increase in
low level wind shear starting near 00z Thursday...as low level pressure gradient
tightens between a ridge of high pressure over the Gulf states and
a clipper system passing by to the north. Can expect winds out of
230-240 degrees at about 50 kts at 2kft...subsiding around 12z
Expect some scattered middle to upper level clouds to be around for
Wednesday. Thus left the scattered 10-20kft deck in. Introduced a
scattered 1kft deck around 05z Thursday at all taf sites...as
model solutions show lower level moisture and lift begin to
increase to the northwest Wednesday night. Currently expect this
to have the best chance of occurrence over laf and huf...as they
are located closer to the deeper moisture to the northwest.
Visit US at http://www.Weather.Gov/ind
Follow US on twitter and youtube at: