Area Forecast Discussion
Issued by NWS Indianapolis, IN

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FXUS63 KIND 191921

Area Forecast Discussion
National Weather Service Indianapolis IN
321 PM EDT Mon Mar 19 2018

The LONG TERM Section has been updated below.


Issued at 310 PM EDT Mon Mar 19 2018

A low pressure system is expected to affect the area from tonight
through Wednesday morning. High pressure is expected to build
into the area for the later parts of the week. Another low
pressure system may affect the area over the weekend.


.NEAR TERM /Rest of This Afternoon and Tonight/...
Issued at 310 PM EDT Mon Mar 19 2018

Short term models suggest main lift from approaching system will
begin moving into the southwest zones over the next couple of
hours, with this area of lift pivoting across the southern half
of the forecast area later tonight. Will go with high PoPs over
the southern zones, tapering the chance PoPs farther north. Still
appears there will be sharp cutoff to the northern extent of the
precipitation shield, so will keep the far northern zones dry.

Appears most of the precipitation will be in the form of rain,
although there is a potential for some mixed precipitation late in
the night over the central zones along the northern end of the
precipitation shield. Could be some minor accumulations of snow
late tonight, but given current temperatures approaching 60, the
best chances for any accumulations will be on elevated and grassy

Low level thicknesses suggest the GFS MOS lows tonight may be a hair
on the warm side, but overall the guidance isn`t too bad.


.SHORT TERM /Tuesday through Thursday/...
Issued at 310 PM EDT Mon Mar 19 2018

Operational and ensemble data are coming into better agreement
during this period, so believe the gradual slowing down of the
system over the past couple of days is about over.

Model data suggest most of the organized lift that will be affecting
the area tonight will be in the process of moving out of the
southeast zones Wednesday morning. Otherwise, lift looks rather
disorganized throughout the morning hours, possibly getting better
organized during the afternoon hours. As a result, there may a
relative lull in the precipitation threat for a time on Tuesday.
Will keep the highest PoPs on Tuesday over the southeast zones for
mainly the morning hours, tapering them off to the northwest. Mixed
precipitation expected during the morning hours, but this should
trend towards rain by midday as the boundary layer warms.

Will keep PoPs high over the eastern zones Tuesday night, as models
suggest a well developed deformation zone may set up in those areas.
Rain is expected to transition back to snow during the night as the
boundary layer cools and thicknesses lower. A few inches of snow
accumulation is possible over the eastern zones Tuesday night,
depending on how fast the change over occurs.

Most of the organized lift appears to be east of the area by
Wednesday morning as the upper low pulls away. Will keep some chance
PoPs for light snow over the eastern zones Wednesday morning.
Dry weather expected for the rest of the short term as high pressure
builds in.

Progged low level thicknesses suggest the GFS MOS temperature
guidance in the later periods looks too warm. Will cut about a
category of the guidance from Tuesday through Wednesday night.


.LONG TERM (Thursday night through Monday)...

Issued at 322 PM EDT Mon Mar 19 2018

Mostly dry weather is likely early in the period. There should be a
wet spell during the weekend, then drying again. Exact timing is
quite uncertain and potential POP errors are 20 percent or higher.

It is also likely most precipitation will be rain, but
there is uncertainty about whether any snow will fall.

For temperatures, possible errors are 5 degrees.

The reason for all the uncertainty is the American and European
models disagree in many aspects about how a low pressure system will
affect our area. They do concur the best chance for precipitation
will be during the weekend and that most of the time temperatures
will be too warm for ice or snow.


.AVIATION /Discussion for 19/18Z TAF issuance/...

Issued at 126 PM EDT Mon Mar 19 2018

VFR conditions will start out the TAF period and then visibilities
are expected to reach MVFR conditions overnight for most sites as
rain/snow mix moves into the area. BMG could have visibilities
that reach IFR conditions overnight.

An upper level low pressure system will be moving over southern
Indiana Monday night. This system will bring with it snow, rain
and a rain/snow mix for our central and southern TAF sites
starting tonight and lasting through the TAF period. Models differ
on the northern extent of the precipitation coverage as the HRRR
has the precip setting up further south than other models. Thus
confidence is not high that IND and HUF will be impacted and left
VCSH at those sites.

Winds will start out easterly and transition to northeasterly and
northerly by the end of the TAF period. Winds could gust up to 20
to 25 kts at some sites.




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