Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Indianapolis in
708 am EDT sun Apr 26 2015
the aviation section has been updated below.
issued at 153 am EDT sun Apr 26 2015
Quiet and cool weather is expected to start the new week as high
pressure over Canada remains over the western Great Lakes through
the middle of the week. This will result in dry and cool weather
along with cool northerly winds.
By late in the work week...the high will drift east of
Indiana...and warmer air expected to arrive on southerly winds for
next weekend...bringing temperatures closer to normal values.
Near term /today/...
Issued at 153 am EDT sun Apr 26 2015
Surface analysis early this morning shows low pressure over
eastern Kentucky and strong high pressure in place western
Ontario. Cool north winds were in in place over central Indiana
and dew point temperatures were in the 30s. Aloft...water vapor shows
a ridge of high pressure over the plains states...providing
blocking of an upper trough over the inter mountain west.
Main forecast challenge today will be temperatures.
Dry weather is expected today as the cool north flow ahead of the
high to the west continues across the area. Forecast soundings and
time heights show a dry column with some subsidence. Forecast
soundings show convective temperatures in the middle 50s...thus some
afternoon cumulus can be expected. Given the strong cold air advection
that will be ongoing today...850mb temperatures fall to around 1c by
00z...will trend highs closer to the 3 hourly mavmos values.
Short term /tonight through Tuesday night/...
Issued at 153 am EDT sun Apr 26 2015
GFS and NAM continue to suggest dry weather will be in store for
this period. A large upper ridge of high pressure from the Western
Plains to Ontario will continue to provide cool north flow aloft
along with subsidence through Tuesday. In the lower levels high
pressure remains in place west of Indiana over the Great
Plains...this will result in the continue flow of dry Continental
air to the Ohio Valley on north winds.
Thus a dry forecast will be in store for the period and the main
challenge will be temperatures.
Decent gradients looks to remain in place through Tuesday as
surface high pressure remains centered to the northwest...keeping
light north winds across the area. Temperature advection remains
rather neutral tonight and on Monday as 850mb temperatures linger near
0c-1c. Thus will trend lows tonight at or slightly below
mavmos...given the clear skies...and trend highs on Monday toward
By Monday night and Tuesday...the pressure gradient remains
similar...keeping winds near 5-10 knots and some slight warm air
advection begins as the coolest air departs to the east and 850mb
temperatures rise toward 3-4c. Thus will begin our gradual warm on
starting on Monday night and Tuesday...trending lows and highs
slightly warmer than the previous day. Ongoing mavmos handles this
well. Given the little change in the overall pattern on Tuesday
will will continue the slow warming trend on lows for Tuesday night.
Long term /Wednesday through Sunday/...
Issued at 211 am EDT sun Apr 26 2015
Issue this forecast period is whether rain may need to be added
midweek but for now will stay dry.
Couple of short wave troughs dropping south into the region
midweek on the east side of the western upper ridge pose potential
for some light rain Wednesday and Thursday. Main negating factor
is limited moisture given the Gulf being cut off by a system
moving across the Tennessee Valley. Will thus keep it dry for now.
As Tennessee Valley system moves east the western ridge will build
into our region which spells continued dry weather and late week
Aviation /discussion for the 261200z tafs/...
issued at 708 am EDT sun Apr 26 2015
VFR through the forecast period. Winds at or above 10 kts will ease
below 10 kts after 262300z.
Drying air column in the wake of the surface low pressure exiting
the region will result in frontal cloud band pushing south of the
Ohio River. Cyclonic turning aloft combined with somewhat cool 850
mb temperatures and residual ground moisture will help to develop
some cumulus clouds by midday but these will dissipate by Sundown.
Mixing of slightly stronger wind aloft will result in a few gusts to
near 20 kts this afternoon but stabilizing at Sundown will lead to
winds dropping below 10 kts by that time.
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