Area Forecast Discussion
Issued by NWS Indianapolis, IN

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417
FXUS63 KIND 281426
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
1026 AM EDT Fri Apr 28 2017

.UPDATE...
The AVIATION Section has been updated below.

&&

.SYNOPSIS...
Issued at 218 AM EDT Fri Apr 28 2017

Active Spring weather will be ahead this weekend. Low pressure
developing over the Central Plains is expected to push a warm
front back across Indiana late tonight and tonight. Showers and
storms are expected to accompany the front.

Warm and moist southerly flow will be in place across Indiana for
Saturday and Sunday. This along with weak upper level weather
disturbances emerging from the low to the west may generate more
showers and storms on Saturday and Saturday night.

The best chances for showers and storms will be on Sunday Night as
the Low to the west finally pulls northeast toward the great
Lakes...dragging a strong cold front across Indiana. Heavy rains
could occur.

The spring like pattern of cool and wet weather is expected to
continue into the next work week.

&&

.NEAR TERM /Today/...
Issued at 928 AM EDT Fri Apr 28 2017

Added slight chance morning showers southwest to cover current
activity that was lifting northeast per radar loop.

Previous discussion follows...
Issued at 218 AM EDT Fri Apr 28 2017

Surface analysis early this morning shows broad high pressure in
place across the Ohio Valley. Low pressure was found across the
Texas panhandle. National Radar Mosaics showed showers streaming
across Oklahoma...ahead of the low. Water Vapor imagery shows a
broad trough in place across much of the CONUS...sweeping
southeast from the pacific northwest to Texas...then northeast
toward eastern Great lakes.

Models suggest the weak high pressure system across the area will
quick move east today. Return flow around the low will allow a the
old stalled front to the south to return to the Ohio Valley late
this afternoon and early this evening. THis will act as a trigger
for showers and storm development. Time height sections show
excellent lower and mid level moisture available as this feature
passes toward 00Z. Models also hinting at good pwats over 1.5
inches. The 300K GFS Isentropic surface shows excellent up-glide
late today with specific humidities over 9 g/kg. Thus will start
much of the day as dry...but will really ramp pops upward in the
20Z-24Z period as the warm front begins to pass across the area.
Given the expected heating...warm air advection and several rain
free hours today...will trend highs warmer than mavmos.

&&

.SHORT TERM /Tonight tHrough Sunday Night/...

Issued at 218 AM EDT Fri Apr 28 2017

A very active weekend ahead. GFS and NAm push the warm front north
to Northern Indiana and Michigan on Friday night...placing much of
Indiana within the warm sector. Best Isentropic lift is lost
after 06Z-09Z as the front and the associated dynamics push
northward. Time heights also trend toward subsidence after 06Z.
THus will start the tonight period with high pops as the front is
expected to be passing and then trend lower as the night
progresses as the front and associated dynamics weaken and push to
the north. Given the expected ongoing warm air advection tonight
and cloud cover will trend lows at or above mavmos.

More rounds of rain will be possible on Saturday and Saturday
Night. GFS and NAM suggest Indiana will be place within the warm
and moist flow within the warm sector. Models suggest that the deep
low pressure over the deep low pressure over the southern plains
will eject several weak embedded short wave toward
Missouri...Illinois and Indiana. However...the warm frontal
boundary which should be a focus for precip should be well to the
north by Saturday. Furthermore...as the day progresses on
Saturday...forecast soundings show some drying within the column.
As the models tend to have difficulties tracking these weak waves
being ejected and the placement of the expected warm front remains
to the north of Central Indiana...confidence is low in this
forecast. Higher confidence for heavy rains appear to be out of
the IND forecast area...farther to the west...within the expected
flow. Thus will keep pops in the forecast for now given the
uncertainty of the evolution of this system...with best pops on
Saturday and Saturday Night at the NW points of the forecast
area. Again...with Indiana within the warm sector...will trend
highs and lows at or above MAVMOS.

Best organization arrives in the area on Sunday afternoon and
Sunday night as the upper low is finally expected to begin to push
northeast. Strong dynamics ahead of the low will push across
Indiana late in the day and into Sunday evening. Forecast
soundings again suggest a saturated column from 21Z monday through
06Z Sunday. The 310K GFS Isentropic surface shows strong upglide
along with favorable specific humidities over 5 g/kg. Forecast
soundings show Pwats are over 1.5 inches as well. Thus confidence
for showers/storms a is High for Sunday afternoon and Sunday
night. Forecast Builder willing...will try to trend pops highest
during that time frame. Will work a blend on Temps.

Confidence in widespread heavy rain event for Central Indiana
remains low. As stated earlier...best forcing appears to be west
of central Indiana...across Illinois and Missouri...within the
flow. Furthermore the the warm frontal position on Saturday
remains uncertain. Don`t get us wrong...we have high confidence in
some rain for central Indiana this weekend...particularly on
this afternoon/tonight and again on Sunday afternoon and Sunday
night as it is at these time when the best forcing will be pushing
through the area. However...the extra forcing and rain to result
in a heavy rain event on Saturday an Saturday Night remains
uncertain for Central Indiana...due to a lack of organized
forcing...and models hinting at a dry column much of Saturday
Afternoon and Saturday Night.

&&

.LONG TERM /Monday through Thursday/...
Issued at 240 AM EDT Fri Apr 28 2017

Ensembles indicate that system that is expected to affect the area
over the weekend will be in the process of lifting off into the
Great Lakes by Monday. Will keep some PoPs in the forecast for
Monday and Monday night to cover potential shower activity in the
post frontal zone.

There is quite a bit of variance among the ensembles as to the
strength and location of the next trough that is expected to move
into the area around the middle of next week. Some of the members
indicate a strong low pressure system moving into the area, while
others are weaker and/or more suppressed. Differences are
probably due to phasing issues. Will go with PoPs for next
Wednesday and Thursday for now and monitor future trends.

&&

.AVIATION /Discussion for the 281500Z TAF Update/...
Issued at 1026 AM EDT Fri Apr 28 2017

A band of light rain might move through KIND within an hour, but no
impact to visibility or ceiling is expected. Better chances for rain
arrive in afternoon, so only made minor changes to the TAF.

Previous discussion follows...

Layered clouds above 050 expected at the terminals today, along
with the potential for some diurnal cloud development based near
035 by the early afternoon hours.

Although there may be some widely scattered light shower activity
around later this morning, it appears the better threat for
convective activity in the vicinity of the terminals will be
after about 282000Z. Upper disturbance currently located over
eastern Oklahoma/Kansas will begin moving into the area by that
time, accompanied by steepening mid level lapse rates. Brief IFR
visibility restrictions possible in heavier showers. CB bases
035-040.

Surface winds 110-150 degrees at 5-8 kts this morning will
increase to 9-12 kts by this afternoon.

&&

.IND WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

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



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