Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Indianapolis in
1150 PM EDT Sat Oct 25 2014
the aviation section has been updated below.
issued at 157 PM EDT Sat Oct 25 2014
Quiet...dry and mild weather is expected to persist through the
weekend as high pressure over the Central Plains builds across the
Ohio Valley through Monday. Cooler temperatures are expected on
Sunday as northerly winds arrive with the high. However...as the high
departs to the east...warmer southerly flow will return...allowing
warmer temperatures for Monday.
A cold front will approach the area on late Monday night and early
Tuesday...bringing clouds and rain showers back to Indiana.
High pressure is expected to return for the middle of the work
week bringing a return of dry...cool Fall weather.
Near term /tonight/...
Issued at 157 PM EDT Sat Oct 25 2014
Surface analysis early this shows a weak surface trough over the
east central part of the state. Large high pressure was found the
Dakotas...building southeast. Southwest to west winds across
central Indiana were in place across central Indiana...however
that was expected to change as cooler northwest winds over
northern Illinois were expected to arrive in the area late this
afternoon. Dew points were in the mild middle 50s...however this too
is expected to change as winds turn northwesterly. Satellite
images show clear skies across the forecast area. Wsr88d was quiet.
Main forecast challenge tonight will be temperatures.
NAM and GFS agree that the surface high will build across the
region tonight as winds become northwesterly. Forecast soundings
and time height sections show a dry column. Thus will aim for
clear skies. NAM suggests weak cold air advection in place
overnight and by 12z both the NAM and GFS suggest the surface high
settling across central Indiana and relaxing the surface pressure
gradient. Thus with good radiational cooling conditions in
place...will trend lows at or below a blend of mavmos and metmos.
Short term /Sunday through Tuesday/...
Issued at 157 PM EDT Sat Oct 25 2014
Quiet weather is expected on Sunday through Monday evening. GFS
and the NAM and European model (ecmwf) all agree that ridging aloft in combination
with the passing surface high pressure will result in dry weather
through Monday night. Forecast soundings and time height sections
show a dry column through Monday night...and convective
temperatures look to be unreachable. Thus mostly sunny days and
mostly clear nights look in store through Monday night.
Weak cold air advection ends on Sunday...however 850mb temperatures
remain around 10-11c. Still with neutral advection and plenty of
sun will trend highs at or above a mavmos/metmos blend for Sunday
highs. 850mb surface shows warm air advection and SW flow
beginning on Monday night and continuing through Monday night.
Thus will trend lows and highs during that period both warmer than
the mavmos/metmos blend.
GFS and NAM differ a bit on the timing of the arrival of the next
cold front on Monday night. Many good features look to be in place
as this front arrives...including ample moisture...and good
isentropic lift ahead of the front. Timing remains a bit of
a concern as system looks to arrive near 12z...give or take 3hrs.
Thus will trend probability of precipitation highs on both late Monday night and early on
Tuesday before tapering things off on Tuesday afternoon as
forecast soundings show a rapid infiltration of dry air into the
column by Tuesday afternoon. Here will trend Tuesday high temperatures
cooler than mexmos given the expected clouds...rain and cold air
advection in the wake of the cold front.
Long term /Tuesday night through Saturday/...
issued at 223 PM EDT Sat Oct 25 2014
Still a decent amount of uncertainty in how pattern will evolve at
the end of the long term period. 00z European model (ecmwf) brings an upper low into
the southeast USA while 12z GFS and 00z GFS ensemble mean keep
lowest heights across the northeast USA.
With the uncertainty involved did not stray from the superblend
initialization at the end of the period...with only minor tweaks
made elsewhere as models are similar early on.
Rain will exit the area early Tuesday evening as a system exits. Dry
and cooler conditions will be rule on Wednesday...but another system
will move through the northwest upper flow and bring chances for
rain to the area mainly Thursday night into Friday. High pressure
will bring a return of dry conditions Saturday.
Temperatures will cool through the period...with highs on Halloween
and Saturday only in the upper 40s to lower 50s.
Aviation /discussion for the 260600z tafs/...
issued at 1150 PM EDT Sat Oct 25 2014
Dry advection and a light wind should prevent widespread or
prolonged visibility restrictions overnight.
No significant cloud cover...surface wind 7 kts or less through
Visit US at http://www.Weather.Gov/ind
Follow US on facebook...twitter and youtube at: