Area Forecast Discussion
Issued by NWS Indianapolis, IN

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FXUS63 KIND 222024

Area Forecast Discussion
National Weather Service Indianapolis IN
424 PM EDT Thu Mar 22 2018

The AVIATION Section has been updated below.


Issued at 325 PM EDT Thu Mar 22 2018

A low pressure system will bring wintry weather to parts of central
Indiana later Friday night into Saturday. Another frontal system
will bring frequent chances for rain next week. After a cold
weekend, temperatures will return to near average next week.


.NEAR TERM.../Rest of This Afternoon and Tonight/
Issued at 325 PM EDT Thu Mar 22 2018

Quiet weather will continue across central Indiana into the evening
hours with high pressure remaining in control. Clouds will slowly
increase across southwestern sections of the area as lift continues
east of a warm front across Missouri.

Some of the isentropic lift associated with the warm front will
brush the far southwest forecast area late tonight, so will include
some slight chance PoPs there late tonight.

Went a little cooler than the blend for lows tonight east where
clouds will be fewest. Elsewhere stayed close to the blend.


.SHORT TERM.../Friday through Sunday/
Issued at 325 PM EDT Thu Mar 22 2018

Models are close enough that the model blend initialization
was accepted for most items.

An upper level system will move southeast across the area Friday
night into Saturday as a weakening area of surface low pressure
moves into Kentucky. An upper level jet will move into the area on
Saturday as well.

There will be plenty of forcing with this system, and a low level
jet will bring in plentiful moisture. PoPs will increase from the
southwest Friday afternoon into Friday evening, with high PoPs
looking good later Friday night into Saturday as the best forcing
moves through.

There will be a tight temperature gradient aloft across the area,
with the southwest getting several degrees above zero at 850mb while
the northeast remains near to below zero. At the surface, an
easterly wind will work to bring in cooler and drier air.

Expect rain across the southwest forecast area thanks to the warm
air aloft. Across the remainder of the area, soundings show
isothermal conditions near freezing. Thus am expecting snow with
some rain mix for the most part, with big bust potential either way
if temperatures change even just a degree.

Additional complicating factors for precipitation type including
potentially heavy precipitation rates with some frontogenetical
forcing and some weak instability. This would trend the
precipitation to change into heavy snow at times. Drier air at the
surface may not only make evaporative cooling northeast Saturday but
also dry up some of the precipitation before it reaches the ground.
Finally, SREF means are warmer than the other models which could
produce more rain.

Thus am not confident enough to do anything more than continue the
watch at this time. Amounts still look to be in the 3 to 7 inch
range, with locally higher amounts possible if banding sets up.
Looks like the heaviest band shifted southwest just a bit, so will
add Johnson County to the watch. Timing still looks good.

Wouldn`t rule out a little freezing rain late Friday night & early
Saturday morning, but with temperatures rising to above freezing
don`t see many issues for roads.

Precipitation will move off Saturday evening, with dry conditions
expected Sunday.


.LONG TERM /Sunday Night through Thursday/...
Issued at 240 PM EDT Thu Mar 22 2018

Ensembles indicate a progressive nature to the long wave features
during this period. Upper ridging initially over the Midwest will
drift off to the east, while mean troughing moves into the Plains by
the middle of next week.

Ensembles suggest unsettled weather is on tap for the local area
during most of this period, as occasional embedded disturbances
eject out of approaching mean trough. At this point, will
broadbrush PoPs from Monday through Thursday, although timing of
individual disturbances may result in some dry periods.

Long range operational models suggest precipitable waters may get
close to climatological maximums by the early to middle parts of
next week, so heavy rain may become an issue.


.AVIATION /Discussion for 22/21Z TAF Update/...

Issued at 421 PM EDT Thu Mar 22 2018

Added a few hours of gusts up to 20 kts for IND through the rest
of the evening to account for recent observations. Previous
discussion follows...

High confidence in VFR conditions through the TAF period.

Mostly clear skies influenced by high pressures over the area will
continue through most of the period. Clouds could start to move in
at the end of the TAF period ahead of a frontal system.

Wind speeds near 12 kts with occasional gusts up to 20 kts to
start the period. These winds will diminish before 00Z and gusts
will die off within the next few hours which is why they were
left out of the TAFs.


Winter Storm Watch from late Friday night through Saturday
evening for INZ021-028>031-035>042-046>049-055>057-065.



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