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Area forecast discussion 
National Weather Service Indianapolis in
715 PM EDT Wednesday Jul 23 2014

Update...

The aviation section has been updated below.

&&

Synopsis...
issued at 159 PM EDT Wednesday Jul 23 2014

High pressure moving into Indiana from the northwest will give our
state dry weather starting tonight and lasting through tomorrow
night. A low pressure system is forecast to approach Indiana Friday.
It will be very slow moving and dominate our weather into early next
week resulting in a persistent chance of showers or thunderstorms.

Tuesday an area of high pressure is expected to arrive from the
west...bringing drier weather with it.

&&

Near term /tonight and Thursday/...
issued at 159 PM EDT Wednesday Jul 23 2014

The main issue is when rain will end this evening. The mav probability of precipitation look
reasonable based on how the situation is evolving now.

Dry weather can be expected overnight and Thursday as high pressure
builds in. Despite the high pressure...there are apt to be some
clouds tonight and Thursday because boundary layer moisture from
todays rain should favor stratus tonight and cumulus Thursday.

The damp boundary layer will reduce diurnal temperature change.
Given that and the projected thermal fields..the met temperature
forecast looks good both tonight and tomorrow.

&&

Short term /Thursday night through Saturday/...
issued at 159 PM EDT Wednesday Jul 23 2014

The most important problem is when rain will start.

The models agree Thursday night is going to be mostly clear. Friday
the NAM is much more aggressive starting rain than the GFS. Lately
the NAM has tended to start rain too fast...but this time the
European model quantitative precipitation forecast supports the NAM over the GFS.

Given the discrepancy between the GFS and the NAM...and each having
potential weaknesses...a consensus pop from their statistical
guidance will be used Friday. This is often an effective way to
cancel out errors.

All models build a boundary across the area and increase cape
Friday night into Saturday. That should favor precipitation.
However...not one model raises probability of precipitation above the chance category. Given
they all agree chance probability of precipitation will be used for now.
However...confidence is low for this part of the forecast.

For temperatures the main problem is on Friday with the model
guidance being close at other times. On Friday significant
differences between the guidance seem to reflect how the parent
models are handling precipitation. Given a consensus will be used
for probability of precipitation..a consensus will be used for temperatures also.

&&

Long term /Saturday through Wednesday/...
issued at 216 PM EDT Wednesday Jul 23 2014

Seems that the European model (ecmwf) and GFS are in fairly good agreement for this
period. Both models take a middle/upper level low/associated trough
from off the northwest U.S. Coast east/northeast across extreme
southern Saskatchewan and Manitoba before having it dive southeast
into the Great Lakes region where it reintensifies to where there
is ridging across the intermountain region and an upper low over
the Great Lakes and a trough southward through the Ohio Valley.

Thus...the area will start out with high pressure moving eastward
across Indiana into Ohio warming the area into the middle 80s /more
average for this time of year/. Changes begin overnight Friday
into Saturday as strong low pressure develops over the middle
Missouri Valley and moves eastward towards northern Illinois Saturday
then into Northwest Ohio Sunday. A cold front will then move south
across central Indiana late Saturday into middle Sunday. Both models
seem to hint at a thunderstorm complex moving just ahead of the
low Saturday...with redevelopment over central or southern Indiana
Sunday afternoon. Uncertainty lies in the timing of
rain/thunderstorms Saturday and Sunday at this time.

Looks like temperatures will fall back into the 70s for early next
week.

&&

Aviation /discussion for the 24/00z tafs/...
issued at 720 PM EDT Wednesday Jul 23 2014

Some lingering MVFR ceilings across the south this evening. Expect
with low level dry air slow to move in that some light fog and low
stratus will develop later tonight...and have included that at all
sites in one form or another. Sref probabilities agree with this and
forecast soundings are supportive...but lamp guidance does not. Will
have to see how things evolve this evening.

Winds will be generally northerly throughout the period.

&&

Ind watches/warnings/advisories...none.

&&

$$

Synopsis...jk
near term...jk
short term...jk
long term...dwm
aviation...nield

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