Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Indianapolis in
1157 PM EST Friday Dec 6 2013
the aviation section has been updated below.
issued at 1000 PM EST Friday Dec 6 2013
Arctic high pressure over the Central Plains states will build
across central Indiana overnight. This will result in dry but
very cold weather across Indiana overnight.
The high will push across central Indiana on Saturday and depart
on Saturday night as yet another storm system approaches from the
southwest for Sunday. A mix of precipitation will be possible on
Sunday and Sunday night as this quick moving pushes yet another
cold front across the region on Monday.
Dry and very cold weather is expected during the next work week as
Arctic high pressure builds across the region. Temperatures may
not rise above freezing until next Friday.
Near term /tonight/...
issued at 1005 PM EST Friday Dec 6 2013
Pulled the Winter Storm Warning as what snow remained was vastly
diminishing and will be all gone no later than midnight.
Then...Arctic high pressure will build in from the plains. 850
millibar to 700 millibar layered relative humidity forecasts suggest clearing line
should be near Muncie to Indianapolis to Terre Haute by 06z and
through the whole forecast area before 12z. With northwest winds
near 10 miles per hour...and temperatures bottoming out near 10 degrees...wind
chills will nose dive to zero to 4 degrees below zero towards
daybreak. So...hit that in the weather story...hazardous weather
outlook and a new Special Weather Statement. Also...mentioned slick
and or snow covered roads from the now deparing system in the
Special Weather Statement...especially across rural areas...where
many roads may not have been treated.
Short term /Saturday through Monday/...
issued at 153 PM EST Friday Dec 6 2013
Models show pretty good agreement and will use a blend. Main
forecast challenge will be precipitation type on Sunday.
Dry weather is expected across the area on Saturday. Surface ridge
of high pressure is expected to build across the area and models
show middle level subsidence. Forecast soundings remain quite dry as
do the time height sections. Thus will trend toward a mostly sunny
sky with very cold conditions. With cold air advection ongoing and
850mb temperatures expected to be only near 10c will trend highs at or
As the core of cold air departs on Saturday night...forecast
soundings show high cloud starting to increase across the region
as warm air advection begins aloft. However...cold and dry
easterly flow looks to remain in place at the surface. Forecast
soundings also fail to show deep saturation. Thus will trend
toward increasing clouds but also stick close to the cold mavmos
lows as high clouds and fresh snow may counter act radiational
GFS and NAM both suggest a quick moving short wave pushing across
the region on Sunday and Sunday night. Forecast sounding show good
lower level saturation by 18z Sunday...however the forecast
soundings remain below freezing. Thus this event should begin as
all snow. However warm air advection is expected through the late
afternoon and forecast soundings show a warm layer aloft...above
freezing...intruding ito the forecast column...particularly across
the southern parts of the forecast area. Enough warming appears to
result in a mix of precipitation to develop by 00z Monday. Meanwhile the
290k GFS isentropic surface shows good upglide...with mixing
ratios near 3.9 g/kg. The isentropic forcing is lost quickly after
00z Monday and the GFS and NAM show very good middle level drying
arriving after 06z Monday. Only caveat will be the cool...dry
lower level surface flow which often can eat away at moisture
arriving in this set up. Nonetheless...a light precipitation event seems
quite reasonable and will bump up probability of precipitation slightly...particularly
across the central and south parts of the forecast area where ethe
forcing seems best. As for temperatures will continue to stick close to
both Sunday highs and Sunday night lows with expected precipitation and
changing air mass uncertainty.
A strong Arctic cold front will pass across central Indiana on
Monday. Moisture looks to be very limited at that system passes as
forecast soundings only show a little bit of saturation in the
lower levels. Strong cold air advection is expected through day
and will look for steady or slowly falling temperatures as the day
progresses under mostly cloudy skies. This will mark the arrival
of the coldest air of the season. Temperatures through Thursday
will fail to rise above freezing.
Long term /Monday night through Friday/...
issued at 157 PM EST Friday Dec 6 2013
Arctic high pressure will be the dominant force across central
Indiana during the long term period. As such...a prolonged period of
dry weather is expected. The next opportunity for precipitation is
unlikely to arrive before the very end of the period.
This leaves temperatures as the only significant forecast issue in the
extended. With fresh snow/ice pack on the ground across much of the
area...allblend should represent a high end for temperatures. Trimmed a
degree or two across the board most periods.
Aviation /discussion for 070600z taf issuance/...
Issued at 1154 PM EST Friday Dec 6 2013
VFR through the period. Northwesterly winds could shift around to
northeasterly during the day Saturday but speeds should remain
around 5 to 10 kts. Middle level ceilings will clear from west to
east during the next 6-12 hours but then will start to lower
Saturday night back to around 5-10000 feet as the next weather
Visit US at http://www.Weather.Gov/ind
Follow US on twitter and youtube at: