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Area forecast discussion 
National Weather Service Indianapolis in
545 PM EST Friday Feb 5 2016

the aviation section has been updated below


issued at 306 PM EST Friday Feb 5 2016

Mainly dry and seasonably mild conditions are expected through the
weekend with high pressure predominantly in control. A deepening
upper low will dive into the region early next week and bring a
transition to a colder and snowier pattern for central Indiana
through the middle of next week.


Near term /tonight/...
issued at 306 PM EST Friday Feb 5 2016

Stratus associated with the weakening surface trough continues to
move across the northwest part of the forecast area. Recent visible
satellite pics showing that the stratus is beginning to erode on its
forward flank...with the extent of the coverage likely maxed out.
Mainly sunny skies were present elsewhere. Temperatures were generally just
in the lower 30s under the stratus...with upper 30s to middle 40s
across the rest of the area at 20z.

As the stratus continues to erode through the rest of the
afternoon...will see more extensive middle and high level clouds expand
into the region. This should translate to a period of mostly cloudy
skies for most of the forecast area into the evening...with some
clearing returning overnight...especially south of subtle
surface ridging attempts to reestablish. Clouds will then once again
increase in coverage in the predawn hours from the northwest with
the approach of the wave aloft.

Temperatures...took a MOS blend for lows overnight considering periodic
clouds. Should the bulk of the clouds associated with the wave aloft
hold off until closer to daybreak or after...may see lows
trend towards cooler mavmos.


Short term /Saturday through Monday/...
issued at 306 PM EST Friday Feb 5 2016

Forecast challenges focus on snow chances Monday as a colder and
more unsettled weather pattern develops to begin the new work week.

First though...a mainly dry and seasonably mild pattern will
continue for most of the weekend as the Ohio Valley resides in a
fast quasi-zonal flow aloft. The aforementioned upper wave will
transition across the region Saturday in an increasingly weakened
state. Energy aloft will split between a stronger upper wave
tracking through the lower Mississippi Valley and a surface low
moving through Ontario and Quebec. The lack of appreciable forcing
aloft combined with poor moisture advection will keep impacts
minimal with the passage of the wave through the area. Cannot
entirely rule out a few sprinkles Saturday afternoon...otherwise
just anticipating a period with increased clouds through early
afternoon with increasing sunshine later in the day. Dry weather
will continue Saturday night and Sunday as ridging at the surface
and aloft briefly establish over the Ohio Valley.

A strengthening upper low will dive out of the Canadian prairies
Saturday night and expand into the Great Lakes by Monday. The upper
low will progressively deepen and carve out a sharp trough poised to
encompass the eastern half of the country to start the new week.
This will bring an abrupt return back to winter weather for central
Indiana beginning Monday and likely continuing for much of next week.

Initially...moisture drawn north into the region late Sunday will
enable an increase in cloud coverage...but precipitation is likely
to hold off until after dark as isentropic lift becomes more
established. Low level thermals support precipitation in the form of rain
Sunday evening gradually transitioning to scattered snow showers in
the predawn hours Monday as colder air advects into the region
around the base of the approaching upper low. With the exception of
possibly far southeastern counties...low level thermal analysis
strongly suggestive that precipitation will be in the form of all snow by
12z Monday.

Model consensus favors the upper low settling over the region
Monday...with scattered snow showers expected to become widespread
through the course of the day as subtle instability and steepening
lapse rates contribute to the strong forcing present in the middle
levels. While would like to see a slightly more favorable look to
the soundings...certainly think we may be looking at a high impact/
low accumulation scenario Monday with snow showers and squalls
scattered all day. The presence of a few hours with the dendritic
growth zone at 50-100mb depth during the afternoon may enhance
snowfall rates with ratios closer to 15 ot 1 by late day.

Adding to the potential impacts will be steady to slowly falling
temperatures during the day as cold advection strengthens. Expect temperatures into
the upper 20s and lower 30s by sunset Monday. Will carry high chance
probability of precipitation and beef up wording for impacts in the severe weather potential statement. Potential for 1 to
2 inches in some areas by Monday evening...with the presence of a
trowal bending back into the area Monday night possibly maintaining
enhanced snow showers Monday night.

Temperatures...generally trended towards the warmer mavmos for highs over
the weekend as temperatures have overachieved the last few days when the
sun has been present. Indicated morning highs on Monday with slowly
falling temperatures the rest of the day with strong cold advection. Used a
MOS blend for lows through the period.


Long term /Monday night through Friday/...
issued at 306 PM EST Friday Feb 5 2016

Models are in excellent agreement in regard to track and timing of
the low pressure system still expected during the extended period.
The long term period starts out with the center of the upper low
situated over Northeast Indiana and the surface low entering the
northeast U.S. Colder air will already be in place by Monday precipitation will fall in the form of snow from Monday
night through Tuesday. After snow tapers off from west to east on snowfall amounts across central Indiana are
currently expected to range from 1 to 2 inches with localized higher
amounts. Strong subsidence with a strengthening ridge over the
western U.S. Will provide dry conditions from Wednesday night
through Thursday night...but there will be low chances for rain/snow
showers across the northern counties on Friday as another upper low
traverses Ontario and Quebec.


Aviation /discussion for 060000z taf issuance/...

Issued at 532 PM EST Friday Feb 5 2016

VFR through the period for most of the sites. Exception is at klaf
where MVFR ceilings are in place but should scatter out over the
next couple hours. Winds should be light and variable overnight
under high pressure and time heights show middle and upper level
clouds moving in to the area. This should help stave off any fog
formation and will forecast tafs this way...but should mention there
is a small chance fog could develop at the outlying sites sometime
after 6z. Saturday could see some 5000 feet ceilings develop late
morning into the afternoon as a weak upper wave moves through
the area but again no restrictions expected.


Ind watches/warnings/advisories...


near term...Ryan
short term...Ryan
long term....tdud

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