Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Indianapolis in
630 am EDT Monday Jul 6 2015
the aviation section has been updated below.
issued at 256 am EDT Monday Jul 6 2015
There will still be plenty of sunshine today...but clouds and
precipitation chances will increase tonight as a cold front
approaches from the northwest. This front will stall out near the
Ohio Valley and shift back north by Wednesday. As a result...there
will be shower and thunderstorm chances throughout the short term
period. Further out...showers and thunderstorms will remain in the
forecast into the extended period...but high pressure over the
deep south will inhibit moisture a bit. A short wave will provide
some extra reinforcement on Friday.
Near term /today/...
Issued at 256 am EDT Monday Jul 6 2015
The main focus of the near term period will be the very brief heat
wave. Temperatures will soar into the upper 80s this afternoon as 850 mb
temperatures approach the 16-18 degree celsius mark.
Meanwhile...southwest flow at the surface will enhance
temperatures even further. So...trended slightly above guidance
for today/S highs with the plentiful sunshine.
The ridging aloft will hold for most of the day...but skies will
become partly cloudy late in the day as a cold front approaches
from the northwest.
Short term /tonight through Wednesday night/...
Issued at 256 am EDT Monday Jul 6 2015
The main focus of the short term period is shower and thunderstorm
chances with a cold front.
Good model consensus makes this a relatively high confidence forecast
in regard to timing of precipitation. Western counties could
start seeing some showers and isolated thunderstorms some time
after Tuesday 03z with precipitation into most of central Indiana by Tuesday 06z.
Isentropic lift will start strengthening around Tuesday 12z...with the
best forcing between Tuesday 18z-Wednesday 00z. Forcing will taper off
across the northwest third of central Indiana after Wednesday 00z though
as aforementioned cold front shifts farther south and high
pressure strengthens over the Great Lakes region. Nonetheless...the
southeastern two-thirds of the forecast area will remain under
likely probability of precipitation for Tuesday night.
Cold front will stall out near the Ohio River on
Wednesday...gradually shifting back north again by Wednesday
evening. As a result...the northern half of central Indiana will
then be under likely probability of precipitation for Wednesday evening/night...while
probability of precipitation decrease to chance over the southern counties.
Temperatures...there will be a weak temperature gradient over the
forecast area as front stalls out. The northern half of central
Indiana will see more of an impact in temperatures with highs only in
the middle to upper 70s for Tuesday and Wednesday. Meanwhile...the
southern half of central Indiana will hold steady in the low to
middle 80s. As front shifts north...some of this warmer air will
start spreading back into the northern counties early in the
extended period. Northern counties can even expect some overnight
lows dipping into the upper 50s for tomorrow night. These will
also recover back into the middle 60s by Wednesday night as that
front shifts. Did not deviate much from models in regard to temperatures
due to the fluctuation in frontal location.
Long term /Thursday through Sunday/...
Issued at 235 am EDT Monday Jul 6 2015
Zonal flow appears to be on place aloft on Thursday as an
elongated area of high pressure remains in place across the deep
south. GFS hints at a weak...poorly organized short wave passing
across Indiana on Friday as a weak surface low rides northeast
along the ridge of high pressure to the south. With the high to
the south...deep Gulf moisture should be cut off...but warm and
moist Summer dew points in the 60s look to remain. Thus will need
to keep some low chance probability of precipitation on Thursday and Friday as indicated by
all blend...but confidence is low.
Surface ridging looks to build across Indiana and the Ohio Valley
on Saturday into Sunday. GFS also hints at ridging aloft. Yet all
blend continues to insist on chance probability of precipitation. With no Gulf moisture or
forcing present...have removed chance probability of precipitation where possible. Temperatures
appear close to seasonal normals.
Aviation /discussion for the 061200z tafs/...
Issued at 630 am EDT Monday Jul 6 2015
VFR conditions expected for much of this taf period.
After any lingering diurnal fog Burns off this morning...high pressure over
the area will continue to provide VFR conditions through the day.
Forecast soundings remain dry and show ccls near 4500ft with
attainable convective temperatures in the middle 80s. Thus have included
some cumulus through the day.
Tonight the frontal boundary over the upper Midwest and Central
Plains will sag southeast toward Indiana. Clouds are expected to
increase ahead of this system overnight as forecast soundings
begin to become saturated. Expect main VFR ceilings with the system
approach...however once precipitation begin toward 09z-12z...MVFR ceilings
will be possible. Have covered this with just a vcsh mention for now.
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