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FXUS63 KIND 202320

Area Forecast Discussion
National Weather Service Indianapolis IN
720 PM EDT Tue Mar 20 2018


The Aviation section has been updated below.


Issued at 254 PM EDT Tue Mar 20 2018

A rather active forecast period is expected across central Indiana 
over the next several days.  First, an upper low will generate 
accumulating snow across the eastern third of central Indiana 
tonight/tomorrow morning. Then a weak disturbance could produce a 
light wintry mix from Thursday night into Friday.  After that, a 
more potent system will bring higher chances of rain, snow, and a 
combo of the two early in the weekend.  Light snow accumulations 
will be possible with this system.  After a bit of a lull over most 
of the forecast area on Sunday, the effects of a very broad upper 
low over the central U.S. will start impacting the forecast area 
late in the extended period.


.NEAR TERM /Tonight/...
Issued at 658 PM EDT Tue Mar 20 2018

Temperatures have wetbulbed quickly where significant
precipitation has begun, especially south and southeast, and thus
expect less mixing with rain than prior grids were depicting.

Additionally, based on latest radar trends and a look at webcams 
around the forecast area, especially south and southeast, have 
tweaked snowfall totals, mainly slightly increasing in the south 
central forecast area/Bloomington and Bedford areas. Warning and 
advisory will be left as is. Previous discussion follows.

Issued at 254 PM EDT Tue Mar 20 2018

The main focus of the near term period will be snow total across
the eastern and southern counties with low pressure system.

Forecast models continue to have an upper low rotating through
Kentucky tonight and then continuing east/northeast toward New
England. The initial forecast issuance on this event targeted the
east/southeastern portions of central Indiana, and this continues
to be the trend with a few additional counties added westward. 
However, latest QPF and snow amounts have come in higher over the
southeasternmost counties. This matches well with a deformation 
band set up to track along the Indiana/Kentucky border tonight 
and a weak trowal. As a result, will go with a winter storm 
warning for the following counties: Jackson, Jennings, 
Bartholomew, Decatur, and Rush. Even though most areas will end up
on the low side of the warning criteria, this is an event where 
very localized areas could see up to 6 inches of snow accumulation
dependent on where that deformation band sets up.

Current radar mosaic shows precipitation filtering into the
southern and eastern portions of central Indiana, but it will be
in the form of a wintry mix through the evening hours. The main
time frame of impact will fall between 800 PM EDT through 4 AM EDT
tonight when temperatures really start to drop and the main band 
comes through the area. As a result, this will result in a poor 
morning commute on Wednesday morning. 

Generally relied on the blended initialization for temperatures
during the period. However, did trend toward the NAM for QPF and
snow amounts tonight since it correlated best with deformation
band track and trowal set up.


.SHORT TERM /Tomorrow through Friday/...

Issued at 254 PM EDT Tue Mar 20 2018

The main focus of the short term period will be lingering snow
chances tomorrow morning and additional winter precipitation from
Thursday night into Friday.  

Snow rates will rapidly diminish from west to east by mid-morning
tomorrow as aforementioned upper low tracks farther east. So, only
expect up to an additional inch at most during the Wed 12-18Z
hours over the far eastern counties. At that point, the upper low
will be well into Virginia, and high pressure will become the
predominant weather feature over central Indiana. Nonetheless,
there will be low chances for rain and a wintry mix as
temperatures fall Thursday night over the southwest corner of
central Indiana due to a strong upper level jet. This is a low to
moderate confidence forecast though, and no snow accumulations are

Meanwhile, temperatures through the period will generally be below
normal with highs generally in the 40s and lows in the 20s and
30s. No changes were made to blended initialization.


.LONG TERM /Friday Night through Tuesday/...

Issued at 148 PM EDT Tue Mar 20 2018

Active weather pattern will continue this weekend and early next 
week as several systems flow across the Ohio valley.

The ECMWF suggests a warm front and associated low pressure system
push across southern Indiana on Late Friday into the
broad troughy pattern aloft across the eastern parts of the 
Unites States continues. As the low pressure system departs on
Saturday night...Subsidence...ridging aloft and High pressure
looks to arrive across the area fro Sunday and Monday. Surface
flow looks to remain from the northeast...thus cool...continental
air will remain across Indiana...providing below normal

Another chance for precipitation will be expected on Monday Night
into Tuesday as a warm front arrives from the southwest.


.AVIATION /Discussion for the 21/00Z TAFs/...
Issued at 718 PM EDT Tue Mar 20 2018

Periods of IFR or worse conditions at IND/BMG this evening and
overnight in snow, LAF/HUF will likely remain VFR.

An upper level disturbance pivoting through the Ohio Valley
tonight is producing snowfall, with some periods of intense
snowfall impacting BMG this evening. Snow impacts will mainly be
at IND and BMG with HUF/LAF largely seeing only flurries or some
light snow showers.

There will be a fairly sharp gradient to the intense snowfall and
as such an intense visibility and ceiling gradient as well, which
contributes to a lower than desired confidence forecast.
Nevertheless, expect IFR conditions much of the overnight at BMG
with periods of IFR possible at IND.

Winds will generally be northerly early in the period around
10-12KT, becoming more northwesterly with time as the upper low
pulls away later tonight.



Winter Weather Advisory until 2 PM EDT Wednesday for INZ041-042-

Winter Storm Warning until 2 PM EDT Wednesday for INZ057-064-065-



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