Area forecast discussion 
National Weather Service Indianapolis in 
1150 PM EST Friday Nov 27 2015 


The aviation section has been updated below. 


issued at 320 PM EST Friday Nov 27 2015 

Chilly...wet and raw conditions are expected through late Saturday 
as a cold front slowly slips south through the region. After a brief 
period of dry weather Sunday...the front will return north into 
central Indiana early next week...ushering in more rain and 
unsettled conditions. Cooler and drier weather is then expected by 
midweek as high pressure builds across the Midwest. 


Near term /tonight/... 
issued at 920 PM EST Friday Nov 27 2015 

Cold front currently sagging south through the southern parts of the 
forecast area at this time...with short term model data suggesting the 
front will reach the southeast border zones just prior to daybreak. 
Widespread rain should begin to diminish some in coverage and intensity 
over the next few hours as main region of lift diminishes...but will 
probably see some rain continue for the balance of the night as 
overrunning lingers along front. 

All in all...previous forecast still looks good. Only adjustments made 
on the update will be for the winds due to frontal position. 

Previous discussion follows. 

Rain continues across the forecast area this afternoon with a cold 
front slowly sagging into northern counties. Have seen a 7 to 10 
degree drop within a short period of time immediately following the 
frontal passage. At 20z...the front was roughly aligned from just 
north of kmie west/SW through central Vermillion County. Temperatures were in 
the 40s north of the front...with middle 50s to lower 60s south of the 

The rain and temperature shift are the primary issues for the near 
term as the frontal boundary continues its slow southward trek 
through the night. Expect the front to pass the indy metropolitan over the 
next 3 hours or so...and should clear the metropolitan area to the south 
around or shortly after 00z. The development of a secondary surface 
wave along the front will slow the southward push of the boundary 
even further overnight...with the front likely to be located 
somewhere in the vicinity of the the far southern counties by 
daybreak Saturday. 

The low level jet will weaken through the evening as the front 
stretches out. While the jet weakens...deep isentropic lift will 
continue overnight and become focused over the southern half of the 
forecast area in close proximity to the surface boundary. 
Additionally...favorable upper level dynamics will persist for much 
of the night with the region remaining near the right rear quadrant of 
the departing upper jet over the eastern Great Lakes. All this 
points to continued rain overnight with most widespread and heavier 
rates setting up along and south of I-70. 100 probability of precipitation remains valid for 
the entire forecast area. Winds will remain around 10-15 miles per hour 
overnight...shifting to a raw and chilly north/NE flow with the frontal 

Temperatures...took current observation and utilized the 18z rap as a starting 
point for hourly temperature trends over the next 6 to 8 hours with the 
front sliding south. Lows will range from the upper 30s to middle 40s 
from north to south over much of the area which is much closer to 
the warmer mav guidance. Depending on where the front lies at 12z 
Saturday will ultimately determine how cool far southern counties 
get. Quite possible that locales from Bedford through Seymour and 
North Vernon hang up closer to 50. 


Short term /Saturday through Monday/... 
issued at 320 PM EST Friday Nov 27 2015 

Forecast challenges remain focused primarily on precipitation chances with 
a persistent unsettled weather pattern for much of the short term 
with a brief break wedged into the middle of the period on Sunday. 

Aforementioned secondary surface wave will drift slowly along the 
boundary through the Ohio Valley Saturday...with rain continuing 
across most of the forecast area. Isentropic lift and low level 
forcing will be strongest over the southern half of the forecast 
area with most widespread rain expected here through the day. The 
deeper lift and moisture will begin to shift southeast as the low 
moves into the central Appalachians Saturday evening...resulting in 
light showers ending from northwest to southeast over most of the 
area Saturday night. Model soundings and relative humidity forecasts Show Low level 
moisture lingering well behind the precipitation shield with most areas 
remaining cloudy into Sunday. Some clearing is possible over far 
northern counties towards daybreak Sunday. 

Persistent southwest flow aloft drawing Pacific moisture into the 
region will become zonal and even briefly ridge as strong surface 
high pressure expands east across the Great Lakes on Sunday. This 
will serve to shift deeper moisture and bulk of the rainfall south 
into the Tennessee and lower Ohio valleys late Saturday night 
through Sunday and give most of the forecast area a respite from the 
wet pattern. Expect some sunshine for northern counties Sunday with 
mostly cloudy skies persisting near and south of I-70. Cannot rule 
out a couple light showers over southern counties Sunday but most 
should stay dry. 

Elongated and strong upper low over the intermountain west will 
begin to eject out into the Central Plains Sunday night and 
Monday...leading to a resumption of the moist southwest flow into 
the Ohio Valley ahead of the system. Surface cyclogenesis will 
commence early Monday in response to the eastward movement of the 
upper low...deepening quickly as it pulls north into the upper 
Midwest Monday night. This will prompt the frontal boundary to lift 
back north into the region as a warm front. Timing differences in 
play at this point between models with the European model (ecmwf) and to a lesser 
extent the op GFS faster in bringing precipitation back north late Sunday 
night into Monday. Will reintroduce low probability of precipitation Sunday night over all 
but far northern counties...with higher probability of precipitation Monday as steadier 
rains encompass the forecast area as the warm front lifts north. 

Temperatures...a MOS blend overall worked well for highs through the 
period...with temperatures primarily in the 40s Saturday and Sunday...and 
upper 40s to lower 50s Monday. Leaned closer to raw model temperatures for 
lows as mav and met guidance looked too aggressive and far too cold 
with lows through the period. Lingering clouds should keep most 
areas above freezing both Saturday and Sunday nights. 


Long term /Monday night through Friday/... 
issued at 230 PM EST Friday Nov 27 2015 

A frontal system and associated upper level low will move through 
the Great Lakes region to start the long term...bringing rain 
chances to the area Monday night into Tuesday. By Tuesday night 
cooler temperatures will move in behind the front and could see 
chances for light rain and snow for Tuesday night into Wednesday 
with the upper low moving through to the north. After that high 
pressure will build over the area bringing dry weather with it. 
Highs should be in the low to middle 40s Wednesday and warm by a 
couple degrees by Friday. 


Aviation /discussion for the 28/06z tafs/... 
issued at 1150 PM EST Friday Nov 27 2015 

IFR or worse conditions likely much of the period at all sites with 
front slowly moving through the area. 

Winds will be northerly at most sites throughout as the front pushes 
south...with speeds as high as 14-15kt at times. A periodic gust 
cannot be ruled out but will be too infrequent to mention. 

Ceilings are likely to stay IFR or worse through at least 
Saturday afternoon with light to moderate rain and/or some drizzle. 


Ind watches/warnings/advisories...none. 



near term...Ryan/jas 
short term...Ryan 
long term...cp 

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