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Area forecast discussion 
National Weather Service Indianapolis in
329 PM EST Sat Nov 28 2015

the synopsis...near term and short term sections have been updated


issued at 329 PM EST Sat Nov 28 2015

A frontal boundary will shift south into the Tennessee Valley
tonight...with most of the region drying out for Sunday. The front
will return north Monday with rain for the area as low pressure
develops and strengthens over the Central Plains. Drier weather with
seasonable temperatures are then expected for the second half of
the upcoming week.


Near term /tonight/...
issued at 329 PM EST Sat Nov 28 2015

Low pressure just south of kcvg over northern Kentucky early this
afternoon with a cold front extending southwest from the low into
western Kentucky. Light rain and drizzle persist over the region to
the northwest of the low...but precipitation has become light and coverage
much more scattered since midday with widespread rains shifted
down into far southern Indiana. Raw chilly day with 20z temperatures ranging
from the upper 30s to middle 40s from north to south aided by a stiff
north/NE wind.

Focus for the near term is on ending precipitation as strong high pressure
over the Great Lakes begins to exert its influence over the
region...with progressively drier air expanding into the boundary
layer from the north overnight. Precipitation shield extending back north
to near kstl and as that shifts east over the next few hours...may
serve to keep coverage of light rain up over the southern counties
through the evening. Further north...lingering light showers and
drizzle will diminish through sunset with areas north of I-70
becoming dry this evening.

Drier boundary layer air will steadily expand south overnight as
surface pressures rise and deeper lift and moisture shift south
closer to the remnant frontal boundary over the Tennessee Valley.
Will maintain low probability of precipitation over the far southern counties all night to
capture any lingering light showers...but the overall trend will be
towards drier conditions overnight. Despite the noted drier air
within the boundary layer...model soundings and relative humidity forecasts continue to
maintain near saturated conditions in the 750-650mb layer for much
of the night...and this should result in skies remaining mostly
cloudy over the entire area as a predominant middle level deck
persists well north of the lower ceilings and lingering light showers
over southern Indiana. May start to see some partial clearing over
northern counties towards daybreak as subsidence increases.

Temperatures...MOS guidance continues to be far too cold for overnight
lows...especially considering the lingering cloud cover. Warmer raw
model surface temperatures are much more supported by model sounding
analysis of low level thermals and are preferred. Will run above MOS
overnight with lows ranging from the lower 30s far north to lower
40s far south.


Short term /Sunday through Tuesday/...
issued at 329 PM EST Sat Nov 28 2015

Forecast challenges focus on precipitation chances returning as the front
lifts north Monday into Tuesday.

The aforementioned high pressure moving east through the Great Lakes
will be the primary influence for most of the forecast area for the
first 18 hours or so of the period. Persistent northeast winds
through the boundary layer will advect drier air and subsidence into
central Indiana from the north Sunday...and should finally enable
skies to become partly cloudy for much of Sunday afternoon over the
northern half of the forecast area. Despite the deeper moisture
shifting largely south of the Ohio River...some model uncertainty
still exists with how far south the drier airmass can push into the
region. That uncertainty remains high enough to maintain a low
chance for a few light showers over far southern counties and the
lower Wabash valley for much of the day. Clouds will linger from I-
70 south for much of the day as well.

Strong upper low over the intermountain west will pinwheel out into
the Central Plains and eventually the upper Midwest by early
week...resulting in surface cyclogenesis over the Missouri Valley on
Monday. The northward track of the surface low into the northern
Mississippi Valley will prompt a return north into the forecast area
of the remnant frontal boundary by late Monday...followed by the
passage of a cold front on Tuesday as the low occludes over the
northern Great Lakes. Moisture will begin to return north Sunday
night...but overall isentropic lift and moisture remain weak with
the northeast winds in the low levels maintaining dry air below 8-
10kft. Presence of the weak lift supports reintroducing low chance
probability of precipitation over the southwest half of the forecast area late Sunday night.

The arrival of strong positive vorticity advection and diffluence in the middle and upper levels
ahead of the upper low will support increasing rain chances
Monday...peaking Monday night and early Tuesday as a low level jet
draws deeper moisture into the Ohio Valley. Model soundings show
elevated instability developing late Monday night ahead of the cold
front which will promote more showery convection and possibly a few
rumbles of thunder. Confidence not high enough just yet to introduce
isolated thunder mention...but trends will need to be monitored over
the coming day or two.

Timing difference still remain regarding the cold frontal
passage...with the op GFS about 6 hours slower than bulk of the
model consensus early Tuesday. Will maintain probability of precipitation through Tuesday
morning with much drier air advecting in behind the front for the

Temperatures...felt a MOS blend looked reasonable for highs Sunday and
Monday...then undercut MOS Tuesday with cold advection following the
morning frontal passage. Went above MOS Sunday night as temperatures should
remain up with clouds increasing again. Trended towards warmer
mavmos for Monday night.


Long term /Tuesday night through Saturday/...
issued at 224 PM EST Sat Nov 28 2015

An upper low moving through the Great Lakes will keep upper
troughing over central Indiana to start the long term. A weak wave
moving through the trough could bring a mix of rain and snow to
the northern counties Tuesday night into Wednesday. By Wednesday
night the trough axis will be off to the east and high pressure
will build in behind it. Wednesday will see highs in the low to
middle 40s but warm advection begins during the day and then should
see temperatures warm by a couple degrees Thursday and Friday. Lows will
be in the upper 20s to lower 30s with mostly clear skies from
Thursday on. Superblend captured the pattern well with no need for
major changes.


Aviation /discussion for 281800z taf issuance/...
issued at 1148 am EST Sat Nov 28 2015

Mainly IFR at all sites but possibly klaf for the afternoon and
into the evening with improvement to MVFR moving in from the
northwest. Winds will remain out of the northeast through the
period. Off and on light showers and drizzle could continue into
the evening at all sites but klaf as well. Improvement to VFR can
be expected at klaf around 3-6z but will not reach kbmg until
around 15z...with khuf and kind around 9-12z.


Ind watches/warnings/advisories...none.



near term...Ryan
short term...Ryan
long term....cp

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