Scientific Forecaster Discussion
fxus63 kind 301031
Area forecast discussion
National Weather Service Indianapolis in
631 am EDT sun Apr 30 2017
the aviation section has been updated below.
issued at 231 am EDT sun Apr 30 2017
A warm front across central Indiana will lift north
today...allowing a warm and humid air mass to surge into the
state. As the front passes northward...an upper level weather
disturbance will generate showers and storms today. Some of the
showers and storms could produce heavy rain.
As the low over the Southern Plains begins to move toward the
western Great Lakes tonight...it will drag a cold front toward
Indiana. This will once again bring chances for more showers and
The cold front will cross Indiana early on Monday
morning...bringing an end to the heavy rain threat. However light
showers will still be possible as the new work week starts as low
pressure remains across the Great Lakes and Indiana.
A cool and somewhat wet work week lies ahead.
Near term /today/...
Issued at 231 am EDT sun Apr 30 2017
Surface analysis early this morning shows deep low pressure in
place over NE Oklahoma...with a warm front stretching northeast
across to central Illinois and central Indiana. Water vapor
imagery shows a plume of moisture riding streaming northward
across Missouri toward Illinois and Indiana.
Confidence again remains very high today to rain...some of which
could be heavy at times. Models are in good agreement lifting the
warm front northward today...aided by an upper level short wave
that was ejected from the deep upper low to the southwest. As
this wave passes across Indiana this morning...another round of
showers and storms are expected. Some producing heavy rains. Time
height sections show a deeply saturated column today with
excellent lift. Forecast soundings are also in
agreement...indicating deep saturation and pwats still over 1.7
inches. The 305k GFS isentropic surface shows excellent lift
again today...with specific humidities in excess of 9 g/kg.
Finally...radar upstream shows quite the massive area of showers
and storms over Missouri and Arkansas...poised to pushed northeast
within the flow. Thus will continue toward 100 pops today...with
best chances expected during the morning hours with the arrival of
showers and storms from the southwest. Given the expected rain
today will trend highs cooler than mavmos...closer to the 3
Given the expected rain...the ongoing Flash Flood Watch is in good
Short term /tonight through Tuesday night/...
Issued at 231 am EDT sun Apr 30 2017
More active weather is in store tonight. The GFS suggests the deep
upper low over Kansas will continue to pull northeast...and drag a
cold front across Indiana during the overnight showers. Plenty of
moisture should be in place across Indiana as the warm front
should be north of central Indiana and dew points will surge in to
the 60s amid southerly Gulf surface flow. Forecast soundings sing
a similar tune...showing deep saturation through the evening
hours along with the continued very high pwats over 1.6 inches.
Thus will again trend toward 100 pops...particularly during the
evening hours when best influence from the front appears.
GFS shows dry slot intruding across central Indiana on Monday...as
the deep low spins to the northwest. Broad cyclonic flow looks to
remain in place across the area on Monday and Monday night. The
dry slot should lead to a dry start to Monday...however the models
suggest the upper low sags a bit southeast by afternoon and wrap
around moisture should arrive across the state. Forecast soundings
by late afternoon Monday and Monday night suggest trapped strato-
cu. With convective temps in the lower 50s...an light rain showers
in the afternoon and evening cannot be ruled out. Thus will trend
toward some low pops at those times.
GFS suggests the upper low lifts completely north of Indiana by
Tuesday morning as a weak ridge of high pressure builds in its
wake. Thus with a lack of upper support and the models trending
toward a dry column...will trend toward a dry forecast on Tuesday
and Tuesday night...working a blend on temps.
Long term /Wednesday through Saturday/...
issued at 242 am EDT sun Apr 30 2017
Ensembles continue to key in on an upper trough that is expected to
move across the area during the middle and later portions of the
week. There are still some timing and intensity differences among
the individual members, but overall The Spreads are lessening. Most
of the ensembles take the associated surface low through the
Tennessee Valley, keeping the local area in the cool sector.
Will keep pops in the forecast for the Wednesday to Friday period
to cover the passage of the upper trough. A few of the slowest
members suggest there may be a lingering shower threat into
Saturday as well, but these solutions are outliers at this time.
Aviation /discussion for the 301200z tafs/...
issued at 630 am EDT sun Apr 30 2017
Vorticity center over eastern Missouri expected to lift northward
into northern Illinois by the early afternoon hours. Shower and
embedded convective activity should spread over the terminals by
the mid morning hours, with activity diminishing during the early
afternoon hours as vorticity center pulls off to the north. Lapse
rates steepen up again by the mid to late afternoon in the wake
of upper disturbance, so convection may redevelop later in the
afternoon along trailing vorticity tail, but this activity looks
to be more scattered in nature with the main upper support
pulling away. Brief IFR visibility restrictions in the heavier
Outside of convective areas, ceilings generally near or above 050
today. IFR ceilings in the klaf area may linger into the late
morning hours, before scattering out.
Surface winds 110-160 degrees at 7-10 kts this morning will
gradually veer around to 170-190 degrees this afternoon. Some
surface gusts 20-25 kts possible this afternoon.
Flash Flood Watch through Monday morning for inz021-028>031-