Area Forecast Discussion
Issued by NWS Indianapolis, IN

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FXUS63 KIND 122308

Area Forecast Discussion
National Weather Service Indianapolis IN
608 PM EST Thu Jan 12 2017

The AVIATION Section has been updated below.


Issued at 300 PM EST Thu Jan 12 2017

This weekend will see a return to seasonable weather in the wake of
a strong cold front. Precipitation will return late Friday and
chances will continue through the middle of next week. The
precipitation type is expected to alternate between mainly rain and
freezing rain this weekend.

A cold front will push through central Indiana today and usher in a
shallow cold airmass, bringing a return to cooler temps and setting
the stage for light icing potential over the weekend, mainly Friday
Night into early Saturday, and late Saturday into early Sunday. The
active pattern will continue into next week with rain chances most
days through the end of the period. The best chances for freezing
rain will be Friday night into Saturday morning and Saturday night
and into Sunday morning. Light icing is possible. Well above normal
temperatures will return by Monday as the stalled cold front returns
north as a warm front.


.NEAR TERM /Rest of today and Tonight/...
Issued at 300 PM EST Thu Jan 12 2017

Large temperature gradient over the forecast area early this
afternoon as a strong cold front was moving southeast across our
southeastern counties. Radar trends suggest showers will move
southeast of the forecast area by 00z this evening as a dry slot
moves in. Satellite trends and model rh time sections suggest there
will be at least partial clearing tonight. Winds will diminish a bit
after dark as arctic high pressure drifts east over the Dakotas and
Minnesota. Blend looks good with overnight lows in the 20s. With
temperatures that cold wet surfaces, certainly could see some icy
conditions on untreated roadways tonight.


.SHORT TERM /Friday through Sunday/...
Issued at 300 PM EST Thu Jan 12 2017

Main concern this weekend will be freezing rain as warm air aloft
overruns a Tennessee Valley boundary and moves overtop a shallow
cold layer over the Ohio Valley. Model rh time sections and 295K
isentropic analysis suggest precipitation will spread north to south
Friday afternoon and night. Model soundings and critical thicknesses
favor rain changing to freezing rain or sleet late Friday afternoon
and night.

In addition to isentropic lift, models take the upper low, currently
over northern California, to Baja California on Friday night and
Saturday and northern Mexico Saturday night and Sunday. This feature
will eject weak impulses northeast and east across the Ohio valley
through the weekend. These will also interact with a moist
atmosphere and provide additional chances for precipitation through
the weekend. Model soundings and critical thicknesses suggests a
transition from freezing rain and sleet to rain from north to south
Saturday mid morning to early afternoon. Then, look for rain to
change back to freezing rain over all but the far southern tier or
two of counties Saturday night before it once again changes back to
rain Sunday morning.

Low level thermal progs favor seasonable temperatures per model


.LONG TERM /Sunday Night Through Thursday/...
Issued at 237 PM EST Thu Jan 12 2017

Ensembles in good agreement during this period. Mean upper ridging
expected to hold over the eastern parts of the country, while a
fairly deep mean trough will be located just off the West Coast.

There are differences in timing and intensity of individual
disturbances that are expected to eject out of the western trough
during the period. Ensembles suggest PoPs will be required
throughout the extended at this time. Other than the potential for
some freezing rain over the northern zones Sunday night,
temperatures at the surface and aloft support rain as the main
precipitation type. Long range model data suggest some threat for
thunderstorms around next Tuesday as well.

Temperatures through the period should average well above normal
given the strong positive height anomalies predicted over the
eastern parts of the country.


.AVIATION /Discussion for 130000Z TAF Issuance/...
Issued at 608 PM EST Thu Jan 12 2017

VFR conditions will return later this evening and continue through
most of Friday. Deteriorating conditions expected with precip
Friday night.

Frontal boundary continues to move away to the southeast with rain
showers tracking with it. Lower stratus lingering back across the
region but expect that to diminish through the evening as a strong
high pressure expands southeast into central Indiana. Winds will
remain northerly through the night.

The high will drift east across the Great Lakes on Friday as the
frontal boundary becomes stalled across the lower Ohio Valley.
Moisture advecting north into the region through the day will set
up an overrunning precipitation scenario. Expect clouds to thicken
with light rain expanding north during the late afternoon. As low
level thermals cool however...freezing rain will become the
primary precip type for Friday night. Winds will veer to E/NE by
the end of the period as the center of the high pressure moves
into the eastern Great Lakes.


Winter Weather Advisory from 7 PM Friday to 1 PM EST Saturday
for INZ043>049-051>057-060>065-067>072.



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