Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Indianapolis in
1019 PM EDT Wednesday Aug 20 2014
the aviation section has been updated below.
issued at 245 PM EDT Wednesday Aug 20 2014
A ridge of high pressure will strengthen over the eastern third of
the nation through the course of the forecast period...bringing
the hottest weather of the Summer. Highs will soar into the low
90s by the end of the week. However..weak waves will rotate
around that ridge...keeping chances for showers and thunderstorms
over central Indiana through the short term period. A surface warm
front will also provide additional lift for convective development
through Saturday as it stalls over northern Indiana.
Near term /rest of tonight/...
Issued at 1007 PM EDT Wednesday Aug 20 2014
Chances for storms will increase across the area after 06z as a warm
front slowly moves north into the area and a low level jet ramps up
to the west. Short range models continue to indicate some potential
for convective development along the front as well as potential for
some development in southern Minnesota/northern Iowa that could move
into the northern counties very late in the tonight period into
Thursday morning. Made only small adjustments to going probability of precipitation to keep
the forecast dry for another hour or two before having a slight
chance and then increasing chances after 6z. Still a relatively
large spread in potential solutions for the overnight and thus lower
than average confidence for the overnight.
Temperatures...cloud cover due to frontal boundary over the area will
keep temperatures in the upper 60s/low 70s tonight. The NAM seemed to be
over doing cloud cover for most of the near and short term
periods. So...leaned toward the slightly lower temperatures of the GFS.
Short term /tomorrow through Saturday/...
Issued at 245 PM EDT Wednesday Aug 20 2014
The main focus of the short term is hot temperatures and scattered
showers and thunderstorms.
Environment will destabilize tomorrow as warm advection spreads
over central Indiana behind front...triggering showers and
thunderstorms. The highest chances will be over the northern
counties where additional forcing from the front will aid in
convective development. As a result...carried likely probability of precipitation over
that area tomorrow.
High pressure will continue to strengthen over the area for the
remainder of short term period...but weak waves in the flow will
drift along the ridge...keeping chances for showers and
thunderstorms in the forecast through Saturday.
Temperatures...the highest temperatures of the season will commence during this
forecast period with highs reaching into the low to middle 90s on
Friday and Saturday. Trended on the warmer side of guidance due to
persistent southwest flow.
Long term /Saturday night through Wednesday/...
Issued at 245 PM EDT Wednesday Aug 20 2014
Models continue to indicate some of the warmest weather this season
as a strong upper ridge builds over the middle Mississippi Valley
by this weekend and then shifts to the Ohio Valley by Monday and then
weakening some by the middle of next week which will allow a cold
front to move south into our area. Models indicate 850 mb
temperates of +20 to +22 celsius and 700 mb temperatures near +10
mb which may leave US pretty well capped Sunday and Monday.
Guidance temperatures indicate highs in the lower to middle 90s. But
due to the wet ground conditions initially...will shave 1-2 degrees
off high temperatures. Temperatures will begin to moderate a little
Tuesday and even Wednesday as the upper ridge breaks down some.
There are some differences between models on how much of this occurs.
However will lean towards model consensus for now.
Aviation /discussion for 210300z taf update/...
issued at 1019 PM EDT Wednesday Aug 20 2014
Only minor changes for the update as conditions remain tranquil this
evening. Middle and high level clouds continue to drift across the
forecast area. As the low level jet strengthens overnight...still
anticipate scattered convective development sometime after
06z...with the potential for more widespread storms arriving from
the northwest towards daybreak.
00z discussion follows.
MVFR visibilities possible late tonight with fog. Restrictions
possible in any convection overnight and Thursday morning.
Very low confidence convective forecast into Thursday. Weak
surface ridging has developed over central Indiana in the wake of
the afternoon storms with just middle/high level clouds drifting
through. Most of the storms are now focused near the remnant
surface boundary...extending west/northwest from convective complex over the
Tennessee Valley back into western Kentucky. The boundary will
begin to lift back north overnight as the next upper level wave
over the Missouri Valley early this evening shifts east towards
The combination of these features along with a low level jet
nosing into central Indiana should support convective development
primarily after 06z. High uncertainty however exists in extent to
convective coverage and specific impacts to terminals. It appears
kind and klaf will stand the best chance at storms late with
slightly lower threats at kbmg and khuf. While instability is
likely to recover overnight...uncertainty in coverage and timing
makes it difficult to go any higher than thunderstorms in the vicinity at this point.
Upper ridging will attempt to expand across the forecast area
Thursday as the upper wave departs. Potential exists for isolated/
scattered storms to redevelop Thursday afternoon during peak
heating...but will keep conditions dry at this time. Southwest
winds to around 10kts possible Thursday.
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