Area forecast discussion 
National Weather Service Indianapolis in 
617 PM EST sun Nov 23 2014 


The aviation section has been updated below. 


issued at 307 PM EST sun Nov 23 2014 

An area of low pressure and a cold front will bring rain to central 
Indiana tonight into Monday. Behind the front will come windy and 
much colder conditions. Another system could bring some light rain 
and snow to the area on Wednesday. Thanksgiving into Saturday will 
be cold and dry before another system brings low chances for 
precipitation Sunday. 


Near term.../rest of this afternoon and tonight/ 
issued at 307 PM EST sun Nov 23 2014 

Rain continues to develop and overspread central Indiana this 
afternoon ahead of an upper tough and potent vorticity maximum. 
Expect rain to continue through the afternoon. 

Rain will continue into this evening with the upper trough and vorticity 
maximum. 850mb winds around 50kt will bring in plentiful moisture...and 
perhaps some instability. Will go categorical probability of precipitation this evening all 
areas and mention isolated thunder. 

As the first upper wave passes off to the northeast by late evening 
rain will diminish to scattered showers. a cold front 
and other upper trough approach the area late tonight...rain will 
once again become more widespread. Went likely probability of precipitation once again 
across the west after 09z with high chances east. 

Temperatures will be tricky with rain across the area as well 
central Indiana moving more into the warm sector ahead of the cold 
front tonight. Readings may rise some overnight before starting to 
fall late west as the cold front moves in. 

For now went near or just above MOS for low temperatures...but these 
will likely have to be adjusted as the situation unfolds. 


Short term.../Monday through Wednesday/ 
issued at 307 PM EST sun Nov 23 2014 

Focus is on windy conditions Monday and on any chances for rain 
through the period. For the most part models are close enough that a 
blend can be used...but GFS looks too fast with Wednesday/S system. 
Relied less on GFS then. 

Looks like there will be some decent forcing with the cold 
front...and most models are putting out rainfall with the front as 
it passes through. Thus went likely probability of precipitation most areas Monday morning. 
As front passes by forcing will weaken so lowered probability of precipitation after it GOES 

Forcing with the upper trough will still be close enough to the area 
to go chance probability of precipitation across the northwest forecast area Monday 
afternoon and slight chance remainder of north half. As colder air 
moves in during the day precipitation will mix with and change to 
snow. Not expecting any accumulation at this time. 

Main story Monday will be the winds. Strong winds will be not too 
far off the surface...with 850mb winds over 50kt and 925mb winds 
over 40kt. Surface pressure gradient will be tight across the area. 
These plus cold advection helping mix the winds down will create 
windy conditions across the entire area. Sref forecasts show high 
chances of sustained winds over 25kt across parts of the area Monday 
as well. 

Strongest winds look to be across the northeast forecast area in the 
tighter pressure gradient where wind gusts around 45 miles per hour will be 
possible. Elsewhere winds could gust around 40 miles per hour and will be close 
to advisory criteria. /GFS shows even higher gusts possible...with 
gusts more widespread than the NAM/. After collaborating with 
surrounding offices decided to go Wind Advisory across all of the 

For most areas went 12z-00z...but in the northeast where pressure 
gradient will arrive later and remain a factor longer...went 14z-03z. 

Upper trough could still bring a few snow showers to northern areas 
Monday night. High pressure will bring dry conditions to the area 
Tuesday into Wednesday morning. 

Another front will bring chances for precipitation Wednesday 
afternoon. Uncertainties in timing and forcing leads to only low 
probability of precipitation for now. Based on expected temperatures went mixed rain and 
snow most areas. 

Looking at temperatures...on Monday readings will fall during the 
day. A model blend looks good for lows Monday night. Mav MOS looks 
too warm on Tuesday with expected cloud cover. Went closer to a 
model blend. 


Long term /Wednesday night through Sunday/... 
issued at 224 PM EST sun Nov 23 2014 

A broad upper trough may bring mix precipitation chances to the area at the 
beginning of the period and then zonal flow will commence through 
the first half of next weekend. An upper level disturbance is next 
due to impact the region Saturday night into Sunday with chances for 
rain/rain and snow mix/and snow. Accumulations appear very light at 
this time and this is not a lot of confidence this far out in the 
extended so stuck with 20 percent probability of precipitation. Superblend guidance 
initialized well. Only need to make a few minor tweaks. 


Aviation /discussion for the 24/00z tafs/... 
issued at 617 PM EST sun Nov 23 2014 

Widespread IFR through the first 12 to 14 hours of the taf 
period...followed by widespread MVFR and then some improvement to 
borderline VFR tomorrow afternoon. 

Rapidly strengthening low pressure will move through the region 
tonight into tomorrow. Widespread light to moderate rain and IFR 
restrictions noted ahead of the low...which should persist through 
the night. 

Could see some gustiness overnight as the low strengthens...but not 
convinced it will be persistent enough to go with more than a strong 
sustained wind. Low level wind shear is a more potent threat east of 
the sites where the low level jet will be far more pronounced...and 
area VAD wind profiles support winds below 2kft no more than 30-35kt 
at this time. 

As the cold front passes tomorrow morning and the surface pressure 
gradient tightens...low level winds will strengthen and cold 
advection will help mix some of this down to the surface. Wind gusts 
from the west/southwest may approach and even occasionally exceed 
40kt at the sites...especially tomorrow afternoon. 

Thunder will be at least a marginal threat with the rapid 
development of the low...strong dynamics...and at least a small 
amount of shallow instability...but with no confidence in timing or 
placement of the threat...cannot include a mention at this time. 


Ind watches/warnings/advisories... 

Wind Advisory from 7 am to 7 PM EST Monday for 

Wind Advisory from 9 am to 10 PM EST Monday for inz031-038- 



near term...50 
short term...50 
long term...smf 

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