Area Forecast Discussion
Issued by NWS Indianapolis, IN

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FXUS63 KIND 291030

Area Forecast Discussion
National Weather Service Indianapolis IN
630 AM EDT Sat Apr 29 2017

The AVIATION Section has been updated below.


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 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 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 Through Friday/...
Issued at 223 AM EDT Sat Apr 29 2017

Main weather feature during this period will be an upper trough that
is expected to move through the Great Lakes and Ohio Valley towards
the middle and later parts of next week. There is still quite a bit
of variance among the individual members as to the timing and
strength of this trough, although there seems to be a slight trend
towards more of an open wave, with a weaker more southerly track to
the surface system.

Will go with PoPs from Tuesday night through Thursday to cover the
passage of this system. Some of the slower solutions would suggest a
PoP may be needed into Friday as well, but these solutions are in
the minority at this time.


.AVIATION /Discussion for the 291200Z TAFS/...
Issued at 630 AM EDT Sat Apr 29 2017

Considerable shower and thunderstorm activity currently across the
area as a 40-50 kt low level jet flows over a surface boundary
near the Ohio River. Activity should diminish towards the late
morning to midday hours as low level jet weakens. IFR visibility
restrictions expected in the heavier cells.

Additional organized convective threat may approach the western
terminals towards 300000Z as another upper disturbance, currently
in the Kansas area, moves into the area accompanied by steep mid
level lapse rates.

Low confidence in how far north surface boundary gets later today,
given current large precipitation area. This results in low
confidence on how fast and how far north IFR ceilings will scatter
out later today. Some of the short term model guidance keeps
surface boundary south of the KBMG terminal until the mid to late
afternoon hours. For now, will keep IFR ceilings in the southern
terminals through midday or early afternoon, and longer into the
afternoon at KLAF.

Surface winds 020-050 degrees at 5-8 kts this morning expected to
gradually veer around to 080-140 degrees at 8-14 kts by later this
afternoon, withe highest speeds in the KLAF area. Lower confidence
in wind forecast, particularly at KBMG/KHUF/KIND due to proximity
of surface boundary.


Flash Flood Watch through Sunday morning for INZ021-028>031-



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