Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Indianapolis in
414 PM EDT sun Jul 24 2016
the aviation section has been updated below.
issued at 300 PM EDT sun Jul 24 2016
One more relatively warm and humid day is expected
Monday before slightly cooler and less humid air filters
into our area Tuesday and Wednesday. The change in air mass will
be accompanied by scattered thunderstorms though not all
locations will receive this rain. The next weather system and
return of slightly warmer and humid air will bring a better
rain/storm coverage for the latter half of the week.
Temperatures for this period will start above normal then dip to
seasonal values for the balance of the week.
Near term /tonight/...
Issued at 300 PM EDT sun Jul 24 2016
Synoptic models have been fairly consistent with the
approaching frontal system and associated timing and coverage
with precipitation. The rapid refresh has been a bit aggressive
with precipitation development for this afternoon relative to
observations perhaps the result of the extreme cape values being
observed. Cap appears to be well in place still so will lean
towards slower storm development of synoptic models. Lafayette to
Kokomo area looks to have best shot at getting rain being closest
to approaching front and instability still being relatively high.
Remaining areas rain chances are not as great as stabilizing
cooling occurs and frontal boundary and its lift only slow to
approach northern counties before daybreak.
Guidance minimum temperatures a tad on the warm side the last
few days and will go just below those...but with winds to remain
up a little...minimums should be several degree warmer than this
Short term /Monday through Wednesday/...
Issued at 300 PM EDT sun Jul 24 2016
Models are in fairly good agreement on movement and position
of front over the next several days as high pressure takes over.
The front will move from just north of our area at daybreak
Monday to our southern counties by Sundown. With the strongest
wind fields and best upper support well to the north and northeast
convection should be relatively scattered. Where storms do
develop expect heavy rainfall given our fairly high precipitable
Do not plan to add heat advisory for Monday with heat indices
at highest just over 100 in our southern counties. Monday will
still feel relatively warm and humid though. Will keep Max temps
near guidance and previous forecast. Rain chances will likely
follow diurnal trend with better chances at peak heating and
along and ahead of southeast advancing cold front. Again given
best dynamics being well northeast would expect no more than
scattered convection and pops still in the chance category.
For Tuesday and Wednesday the frontal boundary will slip south
of the Ohio River. Current forecast of rain chances in
southern counties may be a bit pessimistic as high pressure may
more likely drive rain chances south of the Ohio River. Will keep
low chances for now but another model run may suggest their
Temperatures Tuesday and Wednesday still look fairly good with
mid and upper 80s appearing reasonable. Might be a tad high on
holding southern County dewpoints in the lower 70s. High pressure
scouring out the tropical air may reach south of our area by
Wednesday and may need future adjusting.
Long term /Wednesday night through Sunday/...
Issued at 218 PM EDT sun Jul 24 2016
Main challenge for the long term will be timing various upper waves
moving through and ahead of a mean Mississippi Valley trough.
Judging by the differences in the operational GFS and European model (ecmwf) and
individual ensemble spaghetti plot members, the confidence in
strength and timing of these waves is not good. For instance, the
00z and 12z GFS runs have a strong wave moving through Thursday
night, while the 00z European model (ecmwf) version is much weaker. Thus, will
accept regional blend, which has chance pops Wednesday night through
Low level thermal progs support normal to slightly below normal
blend highs in the lower to mid 80s. Meanwhile, look for overnight
lows mostly be in the mid to upper 60s.
Aviation /discussion for 242100z taf update/...
issued at 414 PM EDT sun Jul 24 2016
Little change necessary for late afternoon update. Convection
beginning to fire across northeast Illinois and current hi-res
guidance suggests further development south and west over the next
few hours. This convection then may work down into the northern
forecast area after sunset.
18z update follows.
Moderate to high confidence that VFR conditions and dry weather will
continue through 00z. Cu development progs and model soundings
suggest there will be only scattered diurnal cu with bases around 4k
feet and perhaps a higher deck at times.
Tonight, a cold front will drop southeast and bring an increased
chance of thunderstorms, especially at laf. Will start off with thunderstorms in the vicinity
at laf by 00z and then prevailing MVFR thunderstorms there from 05z-
12z. The hrrr reflectivity progs are in good agreement with this
thinking. Will start thunder mention a few hours later at the other
sites, but confidence is not high enough for prevailing thunder at
those airports. The cold front should reach laf around 09z, ind and
huf around 12z. After that a wave will move along the front will
slow it up. So, the front may not even reach bmg during the taf
South and southwest winds around 10 knots this afternoon will drop
to 5 knots or less after 01z and then shift to west and northwest
behind the cold front.
heat advisory until 8 PM EDT this evening for inz021-028>031-