Area Forecast Discussion
Issued by NWS Indianapolis, IN

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FXUS63 KIND 270530

Area Forecast Discussion
National Weather Service Indianapolis IN
130 AM EDT Sat May 27 2017

The LONG TERM Section has been updated below.


Issued at 152 PM EDT Fri May 26 2017

An active weather pattern is taking shape for this weekend.

HIgh pressure over Indiana is expected to quickly move east...this
afternoon as a weak low pressure system over Illinois quickly
moves across Northern Indiana tonight. This will spread showers
and storms across the northern part of the state tonight.

A weak high pressure system will then settle across the area for
Saturday...bringing more dry weather for much of the day. Another
quick moving upper level weather disturbance will arrive in the
area on Saturday night. This will bring another round of showers
and storms to Indiana.

Dry weather is expected on Sunday morning before a cold front is
expected to pass on Sunday afternoon and evening. Once again, this
may bring a round of showers and storms.

Slim Storm chances will linger on Monday as broad cyclonic flow
will remain across the region...however many dry hours will be

With the exception of a secondary front bringing low chances for
storms Tuesday...expect primarily dry weather for much of next
week with seasonable temperatures.


.NEAR TERM /Rest of Tonight/...

Issued at 934 PM EDT Fri May 26 2017

Thunderstorm complex moved southeast across the area and has
produced severe weather. The storms are trending down at the moment
though. Have upped PoPs to reflect where these storms are and will
be in the next couple of hours.

Meanwhile, additional thunderstorms continue to develop to the
northwest of the forecast area. Unstable air continues to flow into
the area above the cold pool from the thunderstorms. Thus hail
remains a threat. After coordinating with the Storm Prediction
Center, have already expanded the Severe Thunderstorm Watch back
northwest across the forecast area. Will continue to monitor trends
to see if the watch needs to go all the way to 2 AM though.

Remainder of forecast looks ok with only minor changes to low

Previous discussion follows...

Surface Analysis early this afternoon shows a ridge of high
pressure over the Indiana/Ohio boarder. Compact Low pressure was
found over western Illinois...surging eastward. Southerly flow was
in place across Indiana with dew points in the 50s. Water vapor
imagery shows a short wave associated with the over
Iowa...drifting NE.

GFS and NAM suggests the short wave will progress northeast
across NRN Illinois toward Michiana. Rapid refresh depicts
convection development mainly across the northern parts of the
state from 22Z-03Z...progressing eastward. Southern parts of the
convection area may be overdone. Forecast soundings show
convective temperatures in the middle 80s and 700mb temps are near
8C...providing good cap. Thus the HRRR appears a bit over done
with the southern extent of the showers and storm development this
evening. Still Pop will be warranted given the dynamics...just
will limit the highest pops to the northern areas as those
locations will be in a better position to receive precipitation.
Furthermore will taper pops off by 05Z-07Z as the wave aloft
should be quickly departing by that time.

Models appear in good agreement on temps and will stick close to
the blend on expected lows.


.SHORT TERM /Saturday through Monday/...

Issued at 152 PM EDT Fri May 26 2017

Confidence in a dry Saturday is high. Forecast soundings and Time
heights reveal a dry column. Weak high pressure in the wake of the
departing low looks to be in place across the southern Great
lakes...providing northerly flow. However...this does result in a
warm front taking shape along the I-70 corridor...which will come
in to play later.

Thus will trend toward a partly cloudy sky on Saturday along with
a blend on highs which should result in an outstanding weather

Things change on Saturday night as the high quickly departs and
another more organized shortwave pushes toward Central Indiana
from the Central Mississippi valley. Positioning for this wave is
much more favorable for Central Indiana...along with the some
surface convergence available due to the lingering boundary that
was previously mentioned. Models have backed off on the amount of
instability as compared to yesterday...with CAPES now generally
less than 1000 g/kg on Saturday night. While this will diminish
the severe threat somewhat...showers and storms still cannot be
ruled out given the expected dynamics. Will raise pops from the
MAVMOS here...and trend lows toward wetbulbs.

Confidence continues to grow for Dry weather on Sunday morning and
early afternoon. GFS and NAM suggest that Indiana will once again
be caught between two short wave at that the Saturday
Night system will have departed and the the next wave appears to
be over Illinois...poised to arrive by late afternoon. Thus
forecaster builder willing...we will try to keep pops out of the
morning hours and begin a ramp up on Sunday mid-afternoon and
evening as the expected dynamics approach from the west. Again a
blend on highs will work fine.

GFS suggests the quick moving wave should depart the area by 03Z-
05Z. Forecast soundings suggest rapid drying and subsidence in its
wake. Thus will quickly taper pops toward dry on late Sunday
night...trending temps at or below the blend.

Models then depict broad cyclonic flow across the Great Lakes and
Indiana on Monday. Yet another short wave is suggested to push
through the circulation toward Central Indiana...but confidence for
precip will be low at this point given the generally expected
northwest flow of air to Central Indiana in the wake of the cold
front. Still at this time forecast soundings are suggesting steep
lapse rates and attainable convective temperatures...thus weak and
light instability showers in the afternoon do not appear out of the


.LONG TERM (Monday night through Friday)...

Issued at 207 PM EDT Fri May 26 2017

Ensembles in fairly good agreement during this period. An upper low
will gradually shift east across the upper Great Lakes during the
early parts of the extended, with the flow flattening out later next

Ensembles suggest an upper disturbance may rotate through the area
around the upper low in the Tuesday night or Wednesday time frame.
Will put some chance PoPs in the forecast during those periods to
cover this feature.

Some of the ensembles suggest an upper disturbance may eject out of
the southwest into the local area by late next week. Will put some
chance PoPs in for next Friday at this time, however they may be
needed for Thursday as well if the faster solutions come to pass.


.AVIATION (Discussion for the 270600Z TAF Issuance)...
Issued at 1138 PM EDT Fri May 26 2017

Conditions expected to deteriorate to IFR overnight, then gradually
improve to VFR by Saturday afternoon.

Convection has ended across the area. MVFR then IFR conditions will
develop overnight. There remains some uncertainty on the timing, but
may start out with MVFR from beginning of valid time. Will watch
trends and make final decision at issuance time.

Expect some fog to develop, especially at KLAF/KIND where it rained
Friday evening.

Fog will burn off first Saturday morning, followed by a slow
improvement of clouds, with all sites returning to VFR by afternoon.

Convection looks to hold off until late in the valid period, so left
mention out for now.




NEAR TERM...Puma/50
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