Area Forecast Discussion
Issued by NWS Indianapolis, IN

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FXUS63 KIND 221728

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

The AVIATION Section has been updated below.


Issued at 400 AM EDT Thu Mar 22 2018

Below normal temperatures continue across central Indiana today, but
a brief respite from precipitation is in store until Friday
afternoon. At that point, a low pressure system will exit the plains
and bring in initially chances for rain in the southwest, and then a
wintry precipitation mix and some heavy snow potential across
central and northern parts of the area with rain remaining across
the south. This system will exit Saturday night. Another system will
approach Monday, but this will bring in temperatures near to
possibly above normal to get into next week.


.NEAR TERM /Today/...

Issued at 400 AM EDT Thu Mar 22 2018

Quiet weather is expected today with sunny skies under the influence
of high pressure. High temperatures will climb into the low 40s east
to the upper 40s to around 50 in the western counties, but still
remain below normal.


.SHORT TERM /Tonight through Saturday Night/...

Issued at 400 AM EDT Thu Mar 22 2018

Spring has sprung...or maybe not. Mother Nature continues to play
her cruel joke on central Indiana with another winter storm arriving
for the weekend. While tonight will be dry (only a slight chance for
any precip in the southwesternmost counties), lows will be in the
mid 20s to mid 30s. Friday will bring highs in the mid 40s to around
50 with chances for rain arriving in the southwest in the afternoon.
By Friday night, though, the rug is pulled out from us once again as
winter returns on a low pressure system moving out of the plains.

Strong frontogenesis along with upper forcing and some conditional
instability (showing up as negative EPV) are showing up in model
time heights in some spots at times from 6z through 18z Saturday.
This indicates the potential for some heavy snow. A low level jet
will be bring some moisture up into the area to continue to feed the
storm. There appears to be some potential in the forecast sounding
profiles for a zone of sleet/freezing rain somewhere in the area
dividing the rain area from the snow, and this will cut into total
amounts wherever it sets up. Doesn`t look like a lot in the way of
ice accumulation from this however, and right now looking at less
than a tenth of an inch in a narrow band. North of that band, with
the aforementioned strong forcing and some instability could see a
snow band with amounts approaching 6 to 8 inches. The cutoff between
snow and rain looks to be very sharp north to south with this
system, and could see counties with nothing on one end and several
inches on the other. With models coming into better agreement with
this system and the potential for heavy snow, have decided to issue
winter storm watch at this time for areas approximately along and
north of Interstate 74. Any change in the track of this potent
little system will change the location of heaviest amounts, and a
greater intrusion of warm air would cut total snowfall but possibly
bring more icing potential, so these will be things to watch in
upcoming forecasts.

Potential for snow and mixed precipitation will continue through the
day on Saturday and even into Saturday night. Think the worst should
be over by 0z Sunday if not before, so let the watch end then.
Across southwestern Indiana Saturday, enough instability is moving
in to add a slight chance for thunderstorms to the forecast to go
along with the rain there, and this is another indication of the
strength of this system.

The system should move out of the area late Saturday night and allow
dry conditions to return.


.LONG TERM /Sunday through Wednesday/...
Issued at 323 AM EDT Thu Mar 22 2018

Will focus on PoPs and temperature trends for the long term.

Models agree that upper waves will lift northeast across the Ohio
Valley in southwest flow ahead of a southwestern upper low and
trough. High confidence, these features combined with a northern
stream trough and a moist flow off of the Gulf of Mexico, ahead of a
surface system, will result in widespread showers by Tuesday. Prior
to that, highly confident high pressure will provide dry weather
Sunday and Sunday night.

High confidence the southerly low level flow will also result in
moderating temperatures back to normal and beyond. Blend highs in
the 50s and lower 60s by next Tuesday per the blend look reasonable.


.AVIATION /Discussion for the 22/18Z TAF Issuance/...

Issued at 121 PM EDT Thu Mar 22 2018

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>049-056-057-065.



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