Area Forecast Discussion
Issued by NWS Indianapolis, IN

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FXUS63 KIND 201045

Area Forecast Discussion
National Weather Service Indianapolis IN
645 AM EDT Tue Mar 20 2018

The AVIATION Section has been updated below.


Issued at 411 AM EDT Tue Mar 20 2018

A wintry mix across the southern half of central Indiana early this
morning will move off to the east before rain chances return this
afternoon. Tonight this will change over to a mix and then snow.
Eastern counties could see 4 inches of snow by Wednesday morning,
while western counties will probably remain mainly dry. Small
chances for precip will occur over parts of the area Thursday night
into Friday, with a stronger system bringing better chances for
precip for the weekend.


.NEAR TERM /This morning and today/...

Issued at 411 AM EDT Tue Mar 20 2018

Northern counties are dry this morning with a system moving through
the south. Radar continues to show strong bright band signature
south of Indy metro area, with less bright echoes surrounding.
Surface observations north of this area are mainly snow with some
sleet, with those to the south generally rain. It`s likely the band
itself is a wintry mix of rain, snow and sleet given the dual pol
signatures. Most of the sites reporting rain are still above
freezing, but a couple are hovering at the freezing mark. A recent
look at road temperatures continues to show mostly mid 30s to low
40s where precip is falling, but a couple of observations at
bridges/overpasses are approaching 32 so more likely to see slick
spots there. With much of the area seeing the precip mix don`t
expect to see much accumulation from the snow/sleet, and with the
aforementioned warm road temperatures, do not expect to see a lot in
the way of impacts this morning.

A look at satellite loop shows colder cloud tops moving
off to the east, and should see this trend reflected in radar echoes
as well over the next couple of hours and echoes already weakening
over the western counties. Think most of the precip will be east of
the area by 12z, but may still see some light echoes over the
southeastern counties at that time.

For today, a wave will move in from the east as the low pressure
system pivots, and precip will move back in from east to west and
still see a fairly sharp gradient somewhere in the central counties
with the northwest continuing to stay dry. High temperatures will
stall in the low 40s, but this will be warm enough that when precip
arrives in the afternoon it will be in the form of rain.


.SHORT TERM /Tonight through Thursday night/...

Issued at 411 AM EDT Tue Mar 20 2018

Main focus is on changeover to snow tonight and snowfall amounts.
Models in pretty good agreement and generally used a consensus.

Another upper low moves in tonight and keeps the surface low stalled
just southeast of the area. This could set up a strong deformation
zone over the eastern counties of the forecast area. Temperature
profiles indicate a changeover to snow from north to south from
around 8 pm to midnight. The best forcing will set up before
midnight but likely remain across the eastern counties through
much of the overnight. Given the cooler highs today and mostly
cloudy skies, road temperatures will start out cooler then last
night and cool to below freezing without much trouble. Snowfall
rates with the cooler but more saturated profiles and some
possible dendritic growth could approach an inch an hour at their
height, and thus think 4 inch amounts are possible across some of
the eastern counties. With the colder road temps and this bumping
up to the morning commute time, impacts and amounts necessitate a
winter weather advisory beginning at 8 pm and running through
midday Wednesday. Will likely be able to end the advisory a bit
earlier than that but including a buffer in case the system slows
even more as this has been a trend.

This system will finally kick out by Wednesday afternoon and dry
conditions will move in. Temperatures will rebound a bit Thursday
into the mid 40s to around 50, but more chances for precipitation
will arrive in the southwest counties Thursday night as a front
approaches. A wintry mix looks possible at onset.


.LONG TERM (Friday through Monday)...
Issued at 311 AM EDT Tue Mar 20 2018

Mostly wet weather and below normal temperatures are expected this
weekend as Winter refuses to give up without a fight.

Models agree that the long term will start off with an upper low
over the northeastern states, a high amplitude ridge over the
central states and troughing over the west coast. Models also agree,
the central ridge will flatten as it moves overhead on Saturday.
Meanwhile, energy from the western trough and accompanying frontal
system will approach. Models have timing differences with these
features along with timing of QPF. So, confidence is not good on
timing and thus do not have enough to overturn the blend output
which has PoPs starting off Friday afternoon and maximizing Friday
overnight through Saturday evening. After that, upper waves in
southwest flow aloft could bring more showers to the area.

With below normal temperatures, nighttime and morning snow and or
wintry mix looks reasonable. Should see just rain during the
afternoon hours.

Confidence is high on below normal temperatures to start off with.
Meanwhile, temperatures closer to normal look good by Monday.
However, with model differences, confidence is low.


.AVIATION /Discussion for 20/12Z TAF Issuance/...
Issued at 645 AM EDT Mon Mar 19 2018

High confidence that VFR conditions will dominate through 19z-21z.
Then, another wave of low pressure will bring chances for lowered
ceilings and visibility in rain or snow.

Winds will be northeast to 15 knots with gusts to over 20 knots


Winter Weather Advisory from 8 PM this evening to 2 PM EDT
Wednesday for INZ041-042-048-049-056-057-064-065-071-072.



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