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Area forecast discussion 
National Weather Service Wilmington Ohio
751 PM EDT Wednesday Jul 27 2016

Synopsis...
a stalled frontal boundary near the Ohio River will provide a
chance for scattered showers and thunderstorms through this
evening. A wave of low pressure traveling along the front will
bring an increased likelihood for showers and thunderstorms
Thursday into Friday. Unsettled weather will continue into the
weekend as several disturbances aloft interact with a persistently
moist and unstable airmass.

&&

Near term /until 6 am Thursday morning/...
afternoon satellite imagery reveals the stationary front
positioned just south of the Ohio River where dewpoints are in the
low to mid 70s. Isolated to scattered showers and storms are
forecast through this evening mainly in the vicinity of the front.
Mid level energy currently triggering a thunderstorm complex over
the lower Mississippi Valley will lift northeast and become caught
up in a digging trough over the upper Midwest. This will carry
the energy into the Ohio Valley late this evening into early
Thursday, with the better forcing triggering a better chance of
showers and storms across our southwest between 04-10z. This
scenario is supported by various cams, though they remain split on
timing. The good news is that any activity tonight, though it will
develop in a moist environment with pwats around 2 inches, should
be pretty progressive as it pushes east through the greater cincy
tri-state area. Aside from some recent heavy rain over Ripley
County and just south of Cincinnati, this area has not seen much
excessive rainfall lately. Cannot rule out some storms with heavy
rain, but am not expecting more than a very localized flash flood
threat from the activity late tonight. Went close to guidance for
lows tonight in the upper 60s to lower 70s.

&&

Short term /6 am Thursday morning through Thursday night/...
main concern on Thursday will be a higher potential for some flash
flooding across mainly south-central Ohio and northeast Kentucky
as a potent shortwave crosses the iln County Warning Area and interacts with a
very moist airmass. This shortwave energy will develop a couple
weak surface lows that will lift through eastern Kentucky into south-
central Ohio in a moisture rich environment with pwats of 2 to 2.2
inches (2-3 sigma above normal for this time of year). Warm cloud
depths will be >4km and a modest low level jet will lead to favorable
moisture transport across our southeast, though conditions will be
most favorable just outside of the iln County Warning Area. Given bulk shear
vectors from the southwest, do expect potential for training
cells over southern Ohio and northern Kentucky. Synoptic models are in
pretty good agreement with the axis of heaviest precip setting up
over our southeast, so have issued a Flash Flood Watch for this
area. At this time expect 1.5 to 2 inches of rainfall within the
watch area with locally higher amounts possible. Later shifts will
have to monitor whether the better forcing and axis of heaviest
precip may shift further west, though. While 0-6km wind shear
across our south will range from 25-35 knots, forecast soundings
show a nearly saturated column through the mid levels with tall
skinny cape <1000 j/kg. Thus, severe potential should be limited.
Precip chances will decrease Thursday night as the best forcing
pushes east.

Cloud cover and rain will keep temperatures down across our
southeast, where highs will likely struggle to reach 80. It will
be warmer northwest of I-71 where temperatures will climb into the
low to mid 80s. Lows Thursday night will be in the mid to upper
60s.

&&

Long term /Friday through Wednesday/...
the long term will start with a series of upper level disturbances
moving across the area along with a front stalled out. This will
help to keep the chance of rain in the forecast almost through the
entire extended until Tuesday when weak mid-level ridging moves into
the region.

Looking more into the details, Friday will open up with a shortwave
moving across the region and the leftover frontal boundary from
earlier in the week still across the area. Upper level lift is
sufficient with weak positive vorticity advection moving across and moisture values remain
above average for this time of year with pwats forecasted to be
around 1.70". Instability is also present with ml cape values around
500 j/kg. As the shortwave exits Friday pops will slowly taper off
due to weak subsidence behind the wave.

Saturday through Sunday another weak shortwave trough will remain in
close proximity to the area with a surface front located across the
County Warning Area. This will help to bring the chance of rain right back to the
area. Given the weak upper level trough quickly pulling east the
cold front stalling across the area seems likely. Given the chance
of showers and thunderstorms during the day have kept high
temperatures near climo. Monday into Tuesday as the shortwave trough
exits weak mid-level ridging will then build overhead as mid-level
high pressure builds over the central United States. There still
remains timing differences on when the high will build and how far
it will build east. For now have just trended pops down.

&&

Aviation /00z Thursday through Monday/...
convection has developed this afternoon/evening across parts of
the southern Ohio Valley but has remained south of the terminals.
Forcing will remain fairly weak through the evening hours, so
kept taf sites dry through evening period. VFR conditions are
expected for the first part of the taf period.

A h500 S/W will begin to approach the region late tonight,
allowing for a surge of moisture northward as a weak sfc boundary
begins to pivot back into the area. -Shra with potential for ts
across southern taf sites will work into area from southwest as
warm front begins to slowly lift northward. Activity will increase
in coverage after 09z, with most widespread coverage expected
along and south of the I-71 corridor. Br could result in MVFR
vsbys at kluk before pcpn moves in, but anticipate that increase
in cloud cover/pcpn should keep VFR vsbys at all other sites.

Went ahead and sped up onset of rain showers/ts activity per latest hi
resolution models. Before 18z, potential for ts should be limited
to southern taf sites as shield of rain showers moves east-northeast thru area. As
main pcpn shield migrates east of wstrn sites by early aft,
instby may begin to increase for western parts of area.
Therefore, kept thunderstorms in the vicinity in for remainder of period despite
uncertainty regarding mesoscale environment in wake of
morning/early afternoon activity.

Outlook...thunderstorms likely Thursday night through Saturday.

&&

Iln watches/warnings/advisories...
Ohio...Flash Flood Watch from 2 am EDT Thursday through Friday
morning for ohz079-081-082-088.
Kentucky...Flash Flood Watch from 2 am EDT Thursday through Friday
morning for kyz097>100.
In...none.

&&

$$
Synopsis...kurz
near term...kurz/sites
short term...kurz
long term...jdr
aviation...kc

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