Scientific Forecaster Discussion
fxus63 kind 111104
Area forecast discussion
National Weather Service Indianapolis in
604 am EST sun Dec 11 2016
the aviation section has been updated below.
issued at 209 am EST sun Dec 11 2016
Strong low pressure will push from the Central Plains to the Great
Lakes today...pushing a quick moving warm front across Indiana.
This will result in snow showers across central Indiana changing
over to rain across much of the area today.
A cold front will push across Indiana late tonight...bringing the
precipitation to an end. High pressure is then expected to linger
across the region Monday and Tuesday along with seasonable
More active weather is ahead later this week. Two weather systems
will bring Arctic air to central Indiana along with chances for
accumulating snow on Wednesday and Wednesday night as well as next
Near term /today/...
Issued at 209 am EST sun Dec 11 2016
Surface analysis early this morning shows low pressure over the
Central Plains and high pressure in place over the Carolinas.
Warm...southerly flow was in place across Indiana and the Ohio
Valley. Water vapor imagery shows mainly a quick zonal flow in
place over the Continental U.S....with a poorly defined short wave over the
plains with plenty of streaming aloft into our region. Radar shows
areas of scattered snow showers ... north of i70...with
temps in the middle 20. Warmer temps in the lower to middle 30s
were not too far away...over SW Indiana.
GFS and NAM suggest a few...subtle quick moving short wave moving
across the state within the quick flow aloft today. The first
this morning and a second this afternoon...all ahead of the main
weak pressure trough. Isentropics look quite favorable. GFS 290k
surface shows perpendicular flow with specific humidities over 4
g/kg. Forecast soundings show the warm layer aloft with gradually
warming continuing through the day. Forecast soundings and time
heights do show deep saturation through much of the column over
the course of the day...but a limited lower level of dry air looks
to persist through the morning hours. Although that did not
appear to effect precip across northern parts of the forecast
area tonight. Top down methodologies suggest snow for precip
type...but as gradually warming builds through the day...a mix of
sleet and freezing rain should push north across the area as warm
air advection continues. Eventually most area should see rain.
Thus with all of these favorable dynamics and forcing in place
will aim toward 100 pops today...with a slow change over toward
rain. Given the ongoing warm air advection and southerly flow will
trend highs warmer than mavmos.
Will probably issue Special Weather Statement for light icing this morning...and keep
the advisory in place across carrol and Howard counties.
Short term /tonight through Tuesday night/...
Issued at 209 am EST sun Dec 11 2016
Models continue to suggest as the surface low pushes through the
Great Lakes overnight...a cold front will get dragged across
Indiana. Isentropic surfaces show lift getting cut off by 06z-09z
as subsidence begins along with drying and best moisture shifts to
the Appalachians. Time heights go dry as do the forecast
soundings...as they show trapped stratocu lingering in the lowest
levels. Again, plenty of moisture and forcing still lingering after
00z for a few hours...thus will again trend pops toward 100...but
drop drastically as the night progresses. Any precip overnight
should be snow as forecast columns remain below freezing. However
with most moisture well gone...any additional accumulations will
High pressure will quickly move across the region on Monday
through Tuesday. Forecast soundings during this period remain
dry...but do continue to show saturated lower levels...suggesting
typical winter-time stratocu. Thus will trend toward a mostly
cloudy sky through Monday night...with a blend on temps.
Forecast soundings even dry out within the lower levels on
Tuesday...however a strong cold front is taking aim at Indiana
from the upper Midwest then...poised push across the state during
the day. Moisture with that system remains quite limited as Gulf
moisture remains blocked. Thus will trend toward a part cloudy sky
and again use a blend on temps.
Long term (wednesday through saturday)...
Issued at 230 am EST sun Dec 11 2016
The models agree broadly. Confidence is high about overall trends.
The first part of the period will be cold and dry, except for a
slight chance for snow Wednesday. The last part of the period will
wetter and warmer. By Saturday temperatures should be too high for
any type of precipitation except rain.
However there is not strong agreement between the European and
American models on details of how this works. This makes for
considerable uncertainty about what will happen on a given day.
Potential temperature forecast errors are 3-4 degrees into Friday,
then 4-6 degrees. Precipitation forecasts may have to be changed by
5- 10 percent through Thursday night and 20-30 percent Friday into
Saturday. Accumulating snow is possible, but the outlook is very
The blend from region will be used.
Aviation (discussion for 111200z tafs)...
Issued at 605 am EST sun Dec 11 2016
A warm front passing Indiana today and a cold front crossing the
state tonight will bring increasingly poor flying weather.
Widespread precipitation will develop by early afternoon. Snow,
sleet, freezing rain, and liquid rain may all occur. MVFR ceilings
and visibilities can be expected soon after precipitation starts.
Ceilings should drop to LIFR and possibly even vlifr during the
When precipitation ends after about 06z, visibilities will
recover to p6sm and ceilings should rise to around 8 hundred
Winds of about 10 knots are expected to veer from southeast to west
over the forecast period.
Winter Weather Advisory until 1 am EST Monday for inz021-031.