Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Wilmington Ohio
800 PM EDT Tuesday Jul 7 2015
a cold front will cross southeast through the region tonight. It
will lay out a boundary along the Ohio River Wednesday which will
then lift northward. A strong low pressure system will track
towards this boundary early Thursday morning...followed by a cold
front that will set up a similar repeating process for the latter
part of the week.
Near term /until 6 am Wednesday morning/...
Flash Flood Watch for tonight into early Wednesday was issued with
an over-abundance of caution. Isolated thunderstorms in the warm
sector to the east look to be exiting central Ohio and County Warning Area in the
next few hours. Widespread showers with isolated thunderstorms are
found along and ahead of the front and will occur in an area of
very high precipitable water >2" which naturally result in a higher than average
potential for very heavy rainfall. The heavy rain threat will also
be a prolonged heavy rain threat and that was the kicker for
issuing a watch this afternoon.
Models are discongruent with quantitative precipitation forecast fields but all show a high
probability of heavy rain over northern Kentucky and south central Ohio. NAM
appears to be on track and resolves the surface low nicely with
where it is observed just by the pure spin in the reflectivity loop.
Given that the NAM may have an edge on the forecast...hedged a
couple of counties northwest of the larger threat and included
southeast Indiana and a tier of counties in Ohio to the watch. NAM
is also showing a minimal quantitative precipitation forecast field where other models show the
best threat for heavy rain...leading to a higher level of
uncertainty in the watch area.
Lows tonight will be in the low 60s to the northwest behind the
front...low 70s in Kentucky ahead of the front.
Short term /6 am Wednesday morning through Wednesday night/...
front will lay out in the vicinity of the Ohio River early
Wednesday and the threat for continued moderate to heavy rain
continues over Kentucky for the latter part of the watch that is still
in effect for the morning hours.
The front lifts northward during the day and a strong surface low
pressure circulation noses towards Northern Ohio overnight
Wednesday. Highs Wednesday in the Post-frontal atmosphere will
range from around 70 in the north to around 80 in the south.
Overnight lows Wednesday night will be in the middle 60s for most areas.
A lull in the rain is expected Wednesday evening and the better chances
for rain overnight will be to the northwest where the circulation
is expected to enter.
Long term /Thursday through Tuesday/...
unsettled weather conditions are expected through most of the
extended forecast period. Heights will begin rising over the
southeastern states on Thursday morning...and in the westerly flow
just to the north...a shortwave and surface low will likely
combine to produce a significant amount of rain and storms for the
Northern Ohio valley. Model trends have been a little further
north today with this convective complex...with enough confidence
to include likely probability of precipitation for the northern half of the iln forecast
To the south of this surface low...and trailing well to the west...a
frontal boundary will settle to the south of the iln County Warning Area on Thursday
evening. As ridging continues to build over the southeastern
states...this boundary will pivot and move north as a warm front on
Friday and into Saturday. With generally weak
forcing...precipitation chances will be largely diurnal...and
gradually decreasing from each day (thursday into Friday into
saturday). However...temperatures will increase...as warm advection
is expected to continue through the weekend. Highs near 90 degrees
are expected in the southern third of the County Warning Area on Saturday.
By Sunday...the large ridge / upper high over the southern states
will be retrograding westward...placing the Ohio Valley into a
pattern of falling heights and upper flow that shifts to the northwest.
With respect to the eventual evolution of upper troughing in the
Great Lakes region...model solutions become quite divergent with
regards to the details. However...it is clear that precipitation
chances will exist through at least Monday and Tuesday...with
temperatures decreasing slightly from the values experienced over
Aviation /00z Wednesday through Sunday/...
a frontal boundary is continuing to sag slowly southward early
this evening with widespread showers along and ahead of it. We
are still seeing a few embedded thunderstorms...especially across
central Ohio...but expect these to transition to generally just
showers as we continue to lose the diurnal enhancement. The
boundary will stall out along the Ohio River overnight before
beginning to lift back to the north through the day on Wednesday.
Instability is marginal at best tonight into Wednesday...generally
remaining to the south of the Ohio River. As a result will limit
precipitation to just rain showers and vchs through the remainder of the taf
period. With abundant low level moisture...expect ceilings to remain
MVFR through the period with some IFR ceilings lately later tonight
into Wednesday morning.
Outlook...thunderstorms possible through Friday.
Ohio...Flash Flood Watch through Wednesday afternoon for ohz063>065-
Kentucky...Flash Flood Watch through Wednesday afternoon for kyz089>100.
In...Flash Flood Watch through Wednesday afternoon for inz075-080.