Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Indianapolis in
215 PM EDT Friday Sep 4 2015
the long term section has been updated below.
issued at 127 PM EDT Friday Sep 4 2015
Weak but hot high pressure in place over the Ohio Valley will
provide warm and humid weather through the Holiday weekend.
Isolated showers and thunderstorms will be possible each afternoon
through the weekend...however most areas will remain dry...hot
A weak cool front is expected to pass across the area on Monday
night and this will bring some relief to the heat and humidity
during the next work week.
Near term /tonight/...
Issued at 127 PM EDT Friday Sep 4 2015
Surface analysis early this afternoon shows weak but broad and
poorly organized high pressure in place across Appalachia and the
Ohio Valley. Water vapor imagery shows a strong ridge in place
aloft across the eastern United States...however a weak upper low
was cut off from the flow aloft over Michigan. Dew point temperatures
remained rather humid across the region in the upper 60s and lower
Main forecast issue for tonight will be probability of precipitation. GFS and NAM continue
to suggest the cut off low aloft will retrograde and sag south
somewhat into northern Indiana overnight. Time heights only show
lower level moisture available...representing the very high
surface dew points. Forecast soundings continue to show a
relatively dry column with conditions only favorable for diurnal
convection during the early evening. Rapid refresh appears a bit
overdone with expected convection this afternoon...showing
widespread coverage. Given the recent trends and the lack of
ongoing precipitation will trend bearish on probability of precipitation. Will be unable to rule
out some low pop chances early this evening...particularly across
the north...but will attempt to trend toward a dry a dry forecast
As for temperatures...there continues to be little change in the overall
pattern. Will stick close to persistence. Again with light
winds...mostly clear skies and very low dew point depressions
expected...favorable conditions will exist for fog. Thus will
continue with patchy fog mention...particularly away the the urban
Short term /Saturday through Monday/...
Issued at 127 PM EDT Friday Sep 4 2015
Models remain in pretty good agreement during this period and will
use a blend. Upper flow remains highly amplified through Monday
with a strong ridge in place across the Great Lakes and the Ohio
Valley. Meanwhile at the surface the weak and poorly organized
high pressure system remains in place...providing weak southerly
flow and very moist dew points in the upper 60s and low 70s.
Little change in the overall pattern is expected during this
period and will continue with a persistence type forecast through
the period. Forecast soundings continue to suggest plentiful lower
level moisture with dry air aloft and no lift. Each day forecast
soundings show convective temperatures in the upper 80s to around
90...with cape diminishing each day...falling from around 2000
j/kg on Saturday to near 1200 j/kg on Monday. With little support
in the area...only chances for precipitation will be due to diurnal
heating. As the heat builds through the weekend...even that will
diminish some as cape lessens. Thus will probably need every low
probability of precipitation on at least Saturday to cover for the isolated pop up
shower...but may be able to trend toward a dry forecast on Sunday
and Monday depending upon collaboration.
As for temperatures...thicknesses and 850mb temperatures appear rather steady
state through the period. Thus will trend toward a persistence
type forecast fro highs and lows. Mavmos looks to have a pretty
good handle on that.
Long term /Monday night through Friday/...
issued at 215 PM EDT Friday Sep 4 2015
Models are close enough that the superblend initialization was
accepted for most items.
An upper ridge will flatten out and allow upper troughing to build
into the eastern USA. This will result in chances for rain and a
cooling trend during the long term.
A cold front will gradually work its way through the area during the
long term. The result will be chances for rain Monday night through
Thursday...with best chances Tuesday night into Wednesday.
High temperatures will start out in the upper 80s on Tuesday but end
up in the 70s Thursday and Friday.
Aviation /discussion for the 041800z taf issuance/...
issued at 1232 PM EDT Friday Sep 4 2015
MVFR /potentially IFR/ fog at all but kind overnight...otherwise
Scattered cumulus will dissipate after sunset. Isolated
thunderstorms possible this afternoon...especially near klaf...but
odds of them hitting a terminal are too low to mention in the taf.
Shallow ground fog likely to develop again tonight at all but kind.
Put MVFR fog with mention of dense shallow fog. This will burn off