Scientific Forecaster Discussion
fxus63 kind 260344
Area forecast discussion
National Weather Service Indianapolis in
1144 PM EDT sun Aug 25 2019
the aviation section has been updated below.
issued at 323 PM EDT sun Aug 25 2019
An upper level system combined with a surface cold front will bring
rain to central Indiana at times tonight into Tuesday evening.
Another front will bring rain chances early next weekend. Otherwise
dry conditions are expected. Temperatures will be near normal to
below normal into next week.
Near term /tonight/...
issued at 855 PM EDT sun Aug 25 2019
Shower activity expected to gradually increase with the approach
of an upper low, currently over Missouri. Appears the more
widespread precipitation may hold off until the pre dawn hours of
Monday, as a 25-30 kt 850mb jet noses into southern Indiana.
Current forecast still has a good handle on things. No updates
planned at this time. Previous discussion follows.
This afternoon some showers were across southern Illinois and
southwest Kentucky. These were moving north or north-northeast. Dry
air is holding across much of central Indiana, with just far
southern and western areas seeing higher dewpoints.
Believe that far western and southern areas may see a light shower
for the remainder of today, so have some slight chance pops in those
areas. Elsewhere believe the drier air will win out, but will keep
an eye on it.
Warm advection and moisture advection will continue tonight across
the area. This will allow the atmosphere to slowly moisten up and
for forcing to gradually increase. With this in mind went chance or
lower category pops this evening.
By late tonight forcing and moisture will be enough to go with
likely category to categorical pops across much of the area. At the
moment, based on expected forcing, it looks like the southeast
forecast area will see the highest chances and highest quantitative precipitation forecast.
Given only slow increases in dewpoints expected, the blend's low
temperatures look reasonable.
Short term...(monday through wednesday)
issued at 323 PM EDT sun Aug 25 2019
Models are close enough that the National blend of models
initialization was accepted for most items.
Isentropic lift will continue across the area Monday, as will a good
flow of moisture from the south. Thus, likely category or higher
pops look good for the entire forecast area. Forcing shifts to the
north and east during the day, so pops will diminish south and west
during the afternoon.
The area will be in a relative lull Monday night as the first round
of forcing will have moved off to the east, and the cold front/next
upper support is to the west. Will have low pops during the evening,
with an increase in pops overnight, but most areas still staying in
the chance category.
The cold front will move in on Tuesday. Timing is faster then
previously thought, so the amount of instability will be lower.
Remnants of stronger thunderstorms to the west of the area will move
through early Tuesday, with perhaps some additional weaker
development Tuesday afternoon. Will go likely category pops for now.
Kept some low pops in the east Tuesday evening for any lingering
convection, then dry weather should rule for Wednesday as drier air
flows into the area.
Long term /Wednesday night through Sunday/...
issued at 244 PM EDT sun Aug 25 2019
The last few days of August will see an amplified flow aloft
across the country with a persistent ridge centered over the
southwest U S and a broad trough over the eastern U S courtesy of
a deep early autumn-type upper low near James Bay. This will keep
central Indiana and the Ohio Valley within a dry northwest flow
regime that will gradually relax into the Holiday weekend.
A weak frontal boundary will slide south into the region Friday
and Saturday but will have limited moisture as low level winds
suggest the Gulf of Mexico will be cut off. Hard to justify much
more than low chance pops both days before dry weather resumes
Sunday. Highs will be seasonable through the period...generally
running a few degrees below normal in the upper 70s and lower 80s.
Lows will focus in the upper 50s to the mid 60s.
Aviation /discussion for the 260600z tafs/...
issued at 1142 PM EDT sun Aug 25 2019
Rainfall expected to gradually increase in coverage and intensity
overnight as an upper low, currently over Missouri, approaches.
It appears the most widespread precipitation will occur by the pre
dawn hours on Monday, and on through the late morning hours, as a
25-30 kt 850mb jet noses into the area. Areas of IFR visibility
restrictions expected in the heavier precipitation areas.
Some embedded lightning strikes are possible, although generally
poor lapse rates should keep any lightning activity fairly
isolated in nature.
Otherwise, ceilings will continue to fall overnight, due to
sustained warm/moist advection. Areas of IFR ceilings may start
showing up by the pre dawn hours of Monday, become more widespread
Surface winds 100-130 degrees at 5-9 kts overnight are expected to
gradually veer to 150-170 degrees at 8-12 kts towards midday Monday.