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Area forecast discussion 
National Weather Service Indianapolis in
426 am EDT Wednesday Aug 27 2014

the aviation section has updated below.


issued at 228 am EDT Wednesday Aug 27 2014

Poorly organized high pressure will remain across central Indiana
the next several days amid a very warm and moist air mass. This
will continue to result in more of the same in our day today and muggy days with chances for afternoon and
evening showers and thunderstorms...and warm and sultry nights.

Little change in the pattern is expected through the Holiday
weekend as the heat and rain chances are expected to continue.


Near term /today/...

Issued at 228 am EDT Wednesday Aug 27 2014

Surface analysis early this morning shows weak and poorly
organized high pressure over the Great Lakes and also over the
virginias. A weak surface trough was found stretching from Lake
Erie across Northwest Ohio and southern Indiana to Arkansas. Dew points
across central Indiana remained very moist...holding in the upper
60s. Satellite shows some high cloud across central
Indiana...essentially blow off from ongoing convection over west
central Illinois.

Main forecast challenge today will be probability of precipitation.

Models show little change in the overall pattern today as the
previously mentioned lower level boundary looks to remain in place
across the southern parts of the forecast area. Meanwhile the
water vapor imagery this morning shows a tropical plume of
moisture stretching from the Desert Southwest into the Central
Plains and then poised to spill into the Ohio Valley. This
plume surely has a few embedded short waves to aid forcing.
Forecast soundings today show the same conditionally unstable air
mass with attainable convective temperatures in the middle 80s and
plenty of convective available potential energy which is in excess of 2000 j/kg. Persistence has
shown we continue to easily pop off a thunderstorms and rain each afternoon. Thus
with little change in the air mass and several of the previously
mentioned available ingredients for showers and storms...will
continue to mention at least 30 probability of precipitation across the forecast area.

As for temperatures...there has been just some slight cooling in the
850mb temperatures today. Thus will use highs just slightly cooler than
persistence...which will still be warmer than mavmos.


Short term /tonight through Friday night/...

Issued at 228 am EDT Wednesday Aug 27 2014

GFS and NAM depict ridging developing aloft across Indiana and the
Great Lakes tonight and Thursday. Meanwhile at the surface a
frontal boundary looks to remain in place across Indiana...being a
focus for lower level convergence. Forecast sounding and time
height sections continue to show a few moist air mass in
place...with slightly higher convective temperatures.
Overall...there is not enough evidence or change to sway from the
persistence type forecast as too many ingredients for afternoon
and evening thunderstorms remain. Thus will taper probability of precipitation off tonight
after sunset once again...and start things back up on Thursday
afternoon as daytime heating peaks.

On Thursday evening the GFS shows an upper short wave over
northern Illinois and northern Indiana...riding the ridge. Will
again need to continue probability of precipitation into the evening...particularly across
the northern parts of the forecast area as this wave passes as the
very warm...moist and unstable air mass will still be in place. As
ridging builds aloft on late Thursday night and the short wave
departs...convection should once again taper off. Thus even after
all that explanation...we are still at the same result...probability of precipitation
during the evening on Thursday...tapering off overnight.

On Friday and Friday night ridging remains in place aloft over
Indiana...however southwest flow over the lower Mississippi Valley
looks to be pushing yet another short wave toward the Ohio Valley
on Friday afternoon and Friday night. Again the warm and moist air
mass looks to remain in place across the area and forecast
soundings again show plenty of cape. Thus will once again include
chances for afternoon and evening probability of precipitation.

As for temperatures through the period...given the warm and moist air
will trend lows at or above mavmos and will also trend highs at or
above mavmos.


Long term /Saturday through next Tuesday/...
issued at 228 am EDT Wednesday Aug 27 2014

Ensembles indicate an unsettled period as the local area remains
along the southern edge of the westerlies...with upper disturbances
moving along the Canadian border and the subtropical ridge holding
over the southern parts of the country.

Ensembles continue to indicate daily chances for precipitation as
upper disturbances rippling through the flow interact with a frontal
system. Will continue to carry probability of precipitation throughout the extended.


Aviation /discussion for the 270900z kind taf update/...
issued at 426 am EDT Wednesday Aug 27 2014

No significant changes made to the forecast at this time. Previous
discussion follows.

VFR conditions and winds under 10 knots expected through the
forecast period save for a brief period of MVFR fog near daybreak.
The other caveot is that if storms occur this morning they may
briefly produce MVFR visibility and wind gusts to 35 miles per hour.

Some taf saw rain Tuesday afternoon that may help develop the MVFR
visibility issues near daybreak today.

Will not carry any thunderstorms in the vicinity in forecasts since rain threat today appears
slightly less than recent days. Shortwave trough over North Dakota
at 270330z will be crossing the Great Lakes by 271800z brining
slightly better wind field for storms. It appears surface wind shift
to northerly direction in advance of building high pressure may push
the surface boundary too far south too early today for upper wind
field to act on. In addition models suggest increased humidity in
the lower layers perhaps translating to more clouds than recent days
and slower temperatures rises. Having said all that all models
produce at least a small amount of quantitative rainfall with front
so storm threat cannot be completely ruled out and will need to be
watched for.


Ind watches/warnings/advisories...


near term...puma
short term...puma
long term....jas

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