Area Forecast Discussion
Issued by NWS Indianapolis, IN

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111
FXUS63 KIND 291814
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
214 PM EDT Sat Apr 29 2017

.UPDATE...
The LONG TERM section has been updated below.

&&

.SYNOPSIS...
Issued at 159 AM EDT Sat Apr 29 2017

Active and wet weather will continue again today and Sunday. A
warm front across southern Indiana is expected to lift northward
across the state today. This will allow numerous showers and
storms develop today. A severe storm cannot be ruled out...and
some storms may produce heavy rain and possible flooding.

Rain chances will diminish late tonight as the warm front surges
northward to northern Indiana. On Sunday and Sunday night a cold
front will surge toward Central Indiana from the Central Plains
states. This will result in more showers and storms.

More spring...showery rains and cooler temperatures are expected
next work week.

&&

.NEAR TERM /Tonight/...

Issued at 159 AM EDT Sat Apr 29 2017

Surface analysis early this morning shows a warm frontal boundary
across southern Indiana. Ongoing convection was occurring along
the front...just south of the Indianapolis Forecast area. Very
warm and humid air mass was in place south of the front with temps
in the 70s and and dew point temps in the upper 60s and lower
70s. Main forecast challenge today will be pops and heavy rains.

Models are in pretty good agreement...slowly progressing the warm
front northward...bisecting the Indianapolis CWA by mid day. 305K
GFS Isentropic surface shows excellent up-glide...with specific
humidities in excess of 9 g/kg. which continues into the tonight
period. Forecast soundings show a saturated column much of the
day...with some dry air arriving late this afternoon. Pwats remain
over 1.5 today though. Furthermore models suggest a short wave
ridging over the warm front aloft...aiding its northward
progression. Finally...Rapid refresh is suggesting yet another
slug of moisture arriving in Central Indiana this morning as the
front lifts north. Thus will trend pops toward 100 today...and
trend temps closer to the MAVMOS 3 hourlys as rain should provide
some cooling. Given the possibility of heavy rains...it seems
prudent to expand the Flash Flood Watch northward to include the
entire Forecast area.

Confidence is high in rain today. Confidence for some flooding due
to heavy rains is moderate.

&&

.SHORT TERM /Tonight through Monday Night/...

Issued at 159 AM EDT Sat Apr 29 2017

Active Weather looks to persist tonight and Sunday. Models
suggest the warm front will surge northward to northern Indiana
and southern Michigan. The 305K Isentropic surface continues to
show strong lift tonight...again with specific humidities in
excess of 8 g/kg. Thus will again trend pops higher than mavmos
along with low warmer than mavmos.

As the warm front pushes northward tonight...it will place
Indiana firmly in the warm sector where we will expect dew points
in the 60s for Sunday. Forecast soundings on Sunday show
convective temps near 80 with abundant CAPE available. GFS shows a
short wave ahead of the cold front poised to push in to Central
Indiana by late afternoon within the sw flow aloft. Thus will once
again keep pops in the forecast...trending higher than MAVMOS.
Will stick close to the MAVMOS values for highs.

As the low pressure system to our west begins to pull
northward...the associated cold front will begin to pull across
Indiana on Sunday Night. Now, precip chances along the front could
be less due to earlier afternoon convection ahead of the front
and dry slot intrusion...however there are still plenty of
dynamics going on here to warrant continued pops.

The GFS shows the cold front will be east of Central Indiana by
Monday morning...and broad cyclonic flow will be in place across
Central Indiana...along with a much cooler air mass. Forecast
soundings indicating trapped strato-cu within the lower
levels...with convective temperatures near 50. Thus a few
convective...wrap around light rain showers on Monday cannot be
ruled out. Will use a forecast builder blend to get to low chc
pops for light precip and trend temps cooler than Mavmos given the
expected clouds and cooler flow in place. Will taper pops off on
Monday night as daytime heating forcing element is lost.

&&


.LONG TERM /Tuesday Night Through Saturday/...
Issued at 214 PM EDT Sat Apr 29 2017

Highly variable model solutions lead to low confidence, so the model
blend initialization was accepted.

Models continue to have different solutions on how an upper level
system will develop during the long term, including individual model
variability from run to run.

Thus as noted above, confidence is low. Left the initialization
alone which leads to some PoPs for several periods during the long
term.

Temperatures will remain below average. (Some models have highs
nearly 20 degrees below average at times.)

&&

.AVIATION /Discussion for 29/1800Z TAF Issuance/...
Issued at 100 PM EDT Sat Apr 29 2017

Low confidence forecast regarding timing of flying conditions.
However, current thinking is IFR and worse conditions will improve
to MVFR or better 18z-20z. In addition, with instability and
moisture increasing, pop up thunderstorms are possible ahead of the
slow moving warm front over southern Indiana. Kept LAF and HUF with
at least VCTS through the night with a low level jet pumping in deep
moisture there, and the HRRR hinting at such.

Southeast winds to 11 knots will gradually become southerly 02z-11z
as a warm front moves in from the south.

&&

.IND WATCHES/WARNINGS/ADVISORIES...
Flash Flood Watch through Sunday morning for INZ021-028>031-
035>049-051>057-060>065-067>072.

&&

$$

SYNOPSIS...Puma
NEAR TERM...Puma
SHORT TERM...Puma
LONG TERM....50
AVIATION...MK



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