Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Indianapolis in
440 PM EDT Tuesday Jul 7 2015
the aviation section has been updated below.
issued at 230 PM EDT Tuesday Jul 7 2015
Frontal boundary settling south across Indiana today has been a
heavy rain producer. Several more short waves will gradually lift
this boundary back to the Great Lakes this weekend but establish a
northwest flow scenario for thunderstorm complexes early next week.
Widespread 2 to 5 inches rainfall coming 7 days with locally
higher amounts likely to cause short term street flooding problems
at times and renew longer term river flooding issues again.
Cloudy and wet start to period keeps temperatures below normal the next
few days but gradual warming to normal by weeks end and above
normal early next week as upper ridge axis builds over plains.
Near term /tonight/...
Issued at 230 PM EDT Tuesday Jul 7 2015
Current mesolow evident in radar loop will clear last of
substantial rain out of the area early this evening while
secondary band across the Ohio Valley remains flood player.
Models surprisingly in slight disagreement on return rainfall
tonight as Texas wave begins to lift northeast. Feel GFS and Euro
a bit overdone on precipitation amounts while lighter NAM and sref given
nod. Showery weather is expected to redevelop for all areas and
have kept probability of precipitation high.
Given model discrepancies have blended min temperatures from mav and met
MOS with upper 50s north and middle 60s south.
Short term /Wednesday through Friday/...
Issued at 230 PM EDT Tuesday Jul 7 2015
As mentioned...models differ on speed of low pressure and upper
wave lifting northeast from Texas along with associated rain
amounts. Have used a blend and made slight adjustments to current forecast.
Looks like this next wave will lift across central Missouri
Wednesday and northern Indiana Wednesday night. This will help
lift frontal boundary a bit further north in our southern counties
but main forcing will remain northwest of our forecast area. This should
result in periods of showers lifting northeast Wednesday and
Wednesday night and exiting Thursday morning. Heaviest rain
amounts expected closest to surface low track and in our northwest
counties which fortunately did not see much rain today.
Yet one more wave finally lifts the surface boundary back to
northern Indiana Friday as upper ridge builds in plains states
ahead of unusually deep trough over western states. Boundary lift
across the area results in yet another round of showers and storms
Friday but best odds and rain amounts occur just northwest of our area.
Temperatures in this period have been blended again with mins near or
slightly below normal and maximums below normal until Friday when warm
front pushes through and returns highs to the 80s.
Long term /Friday night through Tuesday/...
Issued at 200 PM EDT Tuesday Jul 7 2015
Deterministic models continue to have issues in various small scale
features...at times complicated by convective feedback.
Thus...continue to favor blend of ensemble means and have a warm
front lift northeast across central Indiana on Friday and Friday
night before stalling. Then...a retrograding upper dome of high
pressure over the south will result in northwest flow aloft over the
upper Midwest and Ohio Valley by late in the weekend. This setup
will drive a backdoor cold front southeast over the area early next
Regional blend probability of precipitation look OK. With the front lifting northeast of the
area by Saturday morning...the blend has chance or slight chance
probability of precipitation close to the front or roughly the northeast half Friday night
through Sunday. Then...chances increase early next week with the
backdoor front. All this seems reasonable and also consistent with
regards to the previous forecast.
Slightly above normal temperatures at the beginning of the long term
will cool a bit with the increasing convection associated with the
front next week. Overall regional initialization highs in the middle
80s to around 90 look good for the weekend with highs early next
week in the lower to upper 80s.
Aviation /discussion for the 072100z kind taf update/...
issued at 440 PM EDT Tuesday Jul 7 2015
Back edge of the rain area expected to pass through the kind
terminal over the next couple of hours...so should see the rain
diminish by then. Lapse rates very poor...so doubtful there will be
much organized lightning activity.
Surface winds expected to shift to 330-350 degrees as the rain ends.
Previous discussion follows.
Pretty good confidence that MVFR or worse conditions will continue
the majority of the time through Wednesday per model relative humidity time
sections and 12z MOS.
Rapid refresh reflectivity forecasts have handled the current shower
swath well per radar trends. This suggests the widespread showers
will end after 20z at laf...22z at ind and 00z at bmg. Would not
rule out more showers later this afternoon...tonight and
Tuesday...but chances too low to mention. Will take a last minute
look to see if we have the confidence for a tempo thunderstorm group
to start out with at huf...bmg or ind.
Winds will switch from southwest to northwest and then north 10
knots or less...with the frontal passage. That should occur at or
shortly after 18z at ind and huf and around 20z at bmg.
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