Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Indianapolis in
658 PM EDT Sat Aug 1 2015
the aviation section has been updated below
issued at 159 PM EDT Sat Aug 1 2015
High pressure in place over the Central Plains and Ohio Valley
will provide dry and quiet weather across central Indiana tonight
and Sunday. An upper level weather disturbance in combination
with a weak cool front will sweep through the southern Great
Lakes on Sunday night into Monday. This will bring a chance for
some rain showers to mainly northern central Indiana on late
Chances for showers and storms will persist through much of next
week as several weak upper level weather disturbances are expected
to pass across Indiana from time to time amid quick northwest flow
Near term /tonight/...
Issued at 159 PM EDT Sat Aug 1 2015
Surface analysis early this afternoon shows a ridge of high
pressure stretching across Illinois into the Ohio and Tennessee
River valleys. Water vapor imagery shows a quick northwest flow in
place aloft with an upper disturbance over Nebraska and South
Dakota. Visible pictures show a cloud free sky across the state.
Forecast soundings and time heights once again remain dry tonight
as the surface high remains in place. Good subsidence seen
through the forecast soundings tonight as there appears no support
aloft. Thus will trend toward a dry forecast with mostly clear
skies. As for temperatures...850mb temperatures are expected to be a bit warmer
tan last night with some warmer air pooling ahead of the
approaching surface trough. Thus will trend lows tonight at or
slightly above persistence.
Short term /Sunday through Tuesday/...
Issued at 159 PM EDT Sat Aug 1 2015
Models continue to suggest that quick northwest flow aloft will
remain in place through Tuesday. This flow is associated with a
strong ridge in place across the western United States and a deep
upper low over Ontario. Models suggest a weak short wave pushing
across the area on Sunday afternoon...however moisture is too
limited. Forecast soundings remain dry with convective temperatures in
the lower 90s...which will be hard to reach. Thus will trend for
mainly a dry forecast during the afternoon hours along with an
increase in cloud cover. With some warm air pooling ahead of the
next surface trough...will trend highs on Sunday at or slight
GFS and NAM push a weak surface trough along with a weak wave
aloft across the Great Lakes and northern parts of central Indiana
on late Sunday night. GFS 210k isentropic surface shows a thin
band of high specific humidities...over 7 g/kg surging into the
northern parts of the forecast area. Forecast soundings and time
height appear marginal...particularly across the southern parts
of the forecast area. Thus with some good moisture and lower
level convergence...will include some low chance probability of precipitation for light
precipitation across the northern parts of the forecast area...trending
toward a dry forecast across the south. With expected clouds and
possible precipitation will trend lows at or above mavmos on Sunday
As the weak short wave passes on Sunday night...northwest flow
aloft continues to dominate with best forcing feature remaining
well north of central Indiana across the Great Lakes. Meanwhile
at the surface a weak frontal boundary appears to remain in place
across central Indiana on Monday before washing out as a ridge a
of high pressure re-establishes itself over the deep
south...stretching north into the Ohio Valley to the northern
plains. Thus will trend toward a dry forecast for Monday and
Tuesday. Convective temperatures appear too high on Monday for diurnal
precipitation...and forecast soundings on Tuesday show 700 mb temperatures
reach nearly 10c...providing a good middle level inversion. As for
temperatures will broad but weak warm air advection in play will trend
high and slowly slightly above mavmos.
Long term /Tuesday night through Saturday/...
Issued at 234 PM EDT Sat Aug 1 2015
The upper level pattern consisting of a trough over the eastern
United States and a ridge over the western United States will
continue through the period...keeping central Indiana in a
northwesterly flow aloft. This will allow for multiple upper level
waves to flow into the region bringing chances for showers and
thunderstorms through much of the extended period.
Models are not in good agreement as to the track of these weather
systems...with the GFS keeping them across central Indiana or
skimming just south from Wednesday morning to Saturday afternoon and
then drying out for the remainder of Saturday. The Euro on the other
hand tracks the systems further south...giving the area a chance for
shower or thunderstorms at the beginning of the period and then
keeping US dry until another wave moves through Friday night through
Saturday night. However initialization favors the GFS solution.
Therefore...will be keeping chance probability of precipitation in the forecast at this time
for through the period.
Overnight temperatures will be normal for the season to start the
period in the middle 60s...then drop to below normal by Saturday.
Afternoon highs of upper 70s to low 80s however will be slightly
below normal for the entirety of the period.
Aviation /discussion for 020000z taf issuance/...
Issued at 653 PM EDT Sat Aug 1 2015
VFR through the period. Few to scattered high clouds over the
sites overnight. Winds will be light and variable overnight at the
outlying sites. Sref probabilities and time heights show no
potential for fog though likely due to the very dry column.
Tomorrow should see winds pick up to around 9-14 kts out of the
southwest and expect to see some cumulus with bases around 5 kft.