Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Indianapolis in
1021 PM EDT Sat may 23 2015
the aviation sections have been updated below.
issued at 910 PM EDT Sat may 23 2015
High pressure east of Indiana will keep it dry through at least
early afternoon Sunday.
There is a small chance of thunderstorms late Sunday with better
chances Sunday night and Monday as a trough of low pressure
pivots across central Indiana on Monday.
There will be additional thunderstorm chances at most times through
Temperatures will be slightly above normal with afternoon highs in
the 70s and 80s.
Near term /rest of the night/...
Issued at 910 PM EDT Sat may 23 2015
Increased cloud cover a bit tonight based on satellite trends.
Previous discussion follows...
Issued at 105 PM EDT Sat may 23 2015
Surface analysis early this afternoon shows high pressure in place
over the Middle Atlantic States and the northeast...providing a
warm and more moist southerly flow of air to central Indiana.
Water vapor shows a weak short wave over Kansas and Oklahoma
producing convection. Ridging was in place aloft over the Ohio
Valley. Satellite shows some of highs and middle cloud advecting
toward the Ohio Valley from the Central Plains.
Main forecast challenge at this time is temperatures.
Broad warm air advection pattern remains in place as the ridging
aloft is expected to drift to the east. Forecast soundings and
time height sections both indicate some saturation aloft as clouds
from the convection upstream drifts toward the Ohio Valley.
Furthermore...continuing warm air advection should also result in
more clouds. Thus will trend lows tonight warmer than mavmos at
most spots...along with increasing clouds overnight.
Short term /Sunday through Tuesday/...
Issued at 105 PM EDT Sat may 23 2015
Main forecast challenge during this period will be probability of precipitation.
GFS/NAM suggest broad warm air advection pattern continuing into
Sunday...along with ridging in place aloft through Sunday
afternoon. Forecast soundings show some saturation aloft...but
lower levels remain dry as convective temperatures look to be in the
lower 80s. 305 GFS isentropic surface shows broad lift with
specific humidities over 7 g/kg. Thus will the protective ridge
remains across central Indiana on Sunday...rain should hold
off...however the ridging is expected to depart by late
afternoon...and as convective temperatures may be reached at that
point...low chances for precipitation cannot be ruled out by late
afternoon. As for temperatures will trend highs at mavmos given te
expected clouds and broad warm air advection ongoing simultaneously.
GFS and NAM both suggest the weak upper trough southwest of
central Indiana pushing northeast into the Ohio Valley overnight.
Forecast soundings reveal deep saturation toward 12z Monday as
isentropic surfaces show quite a moist air mass in place as
specific humidities were over 7 g/kg. Thus will trend probability of precipitation higher
than the GFS. Given the ongoing warm air advection and expected
rain will trend Sunday night lows warmer than mavmos.
After the previously mentioned shortwave departs on Monday
morning...the GFS and NAM suggest subsidence aloft in the wake of
that short wave during Monday afternoon. This will result in some
dry air in the middle and upper levels that will give US a better
trend toward a dry afternoon. Will trend probability of precipitation lower on Monday
afternoon in the wake of the system as the forcing departs. Will
use a blend on temperatures.
Southwest flow looks to remain in place aloft on Monday night and
Tuesday as low pressure aloft digs in the Central Plains. The
GFS and NAM suggest yet another short wave approaching the area
late Monday night before once again departing by late Tuesday
afternoon. The warm...and humid air mass looks to remain in place
across the area as the lower level flow remains southerly. Further
support is seen in the forecast soundings which imply deep
saturation...some cape and attainable convective temperatures on
Tuesday. Thus will trend lows warmer than mavmos and highs cooler
along with probability of precipitation higher than mavmos.
Long term /Tuesday night through Saturday/...
issued at 145 PM EDT Sat may 23 2015
Ensembles indicate the local area will be located between a mean
upper ridge over the southeast parts of the country and a mean
upper trough over The Rockies.
Ensembles suggest daily chances for showers and thunderstorms
throughout the extended with the potential for periodic waves to
eject out of The Rockies trough. Will continue to broadbrush probability of precipitation
over the extended period.
Aviation /discussion for 240300z taf issuance/...
Issued at 1021 PM EDT Sat may 23 2015
Tweaked current conditions only. Previous discussion follows...
VFR expected through the period. Winds will drop to 5 kts or less
during the overnight hours out of the southeast. By middle morning they
will increase to 10-15 kts and range from 170-190 during the day.
Middle and high level clouds will increase during the overnight. Time
heights and forecast sounding indicate potential for scattered to
broken ceilings around 4 kft by middle morning as well...with broken
more likely in the west in the morning and the broken deck spreading
east during the afternoon. Could see some isolated to widely
scattered showers moving into the western sites during the late
afternoon and eastern sites during the evening...but probability at
any one point is low enough to leave out at this time.
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