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Area forecast discussion 
National Weather Service Louisville Kentucky
325 am EDT sun Aug 31 2014

Short term (now through monday)...
issued at 315 am EDT sun Aug 31 2014

..Flash Flood Watch remains in effect for east-central Kentucky...

Deep southwest flow will continue over the Ohio Valley today as we
remain positioned between troughing over the central Continental U.S. And a
strong southeast Continental U.S. Ridge. This flow will set the stage for another
impressive plume of moisture riding over the area, ahead of another
disturbance. The threat for heavy rain will continue along and east
of the I-65 corridor today, although all locations are likely to see
rainfall.

Current radar shows the County Warning Area in a relative precipitation lull as the
evening's initial surge of moisture moves off to the NE, and we
await another round set to arrive around dawn. There are scattered
to numerous light rain showers lingering across the area, especially
along and south of the Ohio River. Expect this to continue through
the pre-dawn hours.

Focus will then shift to the next plume of moisture (characterized
by pwats in the 2"-2.2" range) ahead of a wave currently near
Memphis. A 30-40 knot low level jet will accompany this feature,
aiding moisture transport through midday east of I-65. Additionally,
have seen some baroclinic leafing on infrared satellite over the Wabash
River valley associated with the right entrance region of an upper
level jet. This will slide east through the morning, overlapping the
best low level moisture surge from the low level jet over the
current Flash Flood Watch area. The end result will be potential for
bands of heavier rainfall setting up along and east of a bwg to Lex
line, where an additional 1 to 2 inches of rain (locally higher)
are possible. Embedded thunderstorms are expected with this surge.
Therefore, will extend the Flash Flood Watch to 18z in coordination
with surrounding offices. One thing to note is that models have been
too far west with heaviest rainfall axis to this point. It is
possible that the heaviest axis will end up being further east by 50
to 100 miles if that bias continues. Areas outside of the watch can
expect another quarter to three quarters of an inch of rain through
today.

Will also mention that a few storms could rotate with the low level jet surge
this morning. Storm Prediction Center highlighted where this low level jet core will track with a
2% tornado contour, however surface based instability should be hard
to come by so don't expect any problems at this point. Just some
food for thought if we do start seeing a few storms rotate. Most
probable area for an issue would be toward the Lake Cumberland
region.

Highs are not expected to budge a whole lot today as the Mercury
struggles under heavy cloud cover and precipitation. Will call for
upper 70s NE to low 80s SW.

Precipitation will taper from west to east later this afternoon and
into the evening as the wave pushes east along with the deeper
moisture. Enough low level moisture will linger to leave mention of
an isolated shower through tonight, however most places are likely
to stay dry. Not too concerned about fog at this point since low
stratus seems to be the more likely player overnight. Look for lows
in the upper 60s to around 70.

Labor Day is expected to be a mostly dry day with fairly steady SW
winds in a tighter pressure gradient between a Southern Plains low
and high pressure to our southeast. Can't rule out an isolated
thunderstorm, however the pattern seems benign of any real triggers
in the SW flow aloft. The combination of decent amounts of sun and
the warm advective component should bring temperatures back in the
85-90 range.

Long term (monday night through saturday)...
issued at 300 am EDT sun Aug 31 2014

Models continue to show showers and storms north of our region at
the start of the period, near a front that will make slow progress
toward the region. It is looking more likely that at some point
Tuesday we'll get another round of heavy rain, as precipitable
waters once again head up to around 2 inches. That rain will come
either as a low-level jet ramps up across southern in early Tuesday
or with peak heating during the day Tuesday. Thus will ramp up pops
to the 50-70 percent range. Will continue to undercut guidance
temperatures based on this thinking, but readings still should be
above normal.

Models had been portraying Wednesday as a transition day to hotter
and somewhat drier conditions for the rest of the period. However,
the latest GFS doesn't have as strong of a ridge across our region,
in fact placing a weak upper low over the Wabash Thursday and mid
Ohio River Friday, then another disturbance enhancing rain chances
Saturday. The 12z Euro hints at these features as well. NOGAPS
ensembles still show the ridge pattern in the mean fields, but the
spread fields are much more wavy, indicative more of these
disturbances being shows in the various ensemble members. Thus will
maintain chances for storms each day. Most likely the above normal
temperatures will continue through the end of this period.

&&

Aviation (06z taf update)...
issued at 111 am EDT sun Aug 31 2014

A tricky forecast over the next 24 hours as plumes of Gulf moisture
stream through the Ohio Valley ahead of individual disturbances
embedded in the deep southwest flow. Current conditions are ranging
from VFR at sdf on the north side of the precipitation shield, to
IFR at bwg/Lex more into the deep moisture. Biggest challenge will
be to forecast ceilings in the lull between this plume of moisture
and the next that is expected to arrive toward dawn. Guidance would
suggest VFR until that time, but the current obs are a different
story. Will monitor the situation and make a decision when tafs are
issued in a half an hour.

Expecting another wave of widespread showers and embedded thunder to
roll into the taf sites around dawn at sdf/bwg, and through the late
morning hours at Lex. This will be in response to another
disturbance currently over eastern Arkansas/western Tennessee and a low level jet
around 30-40 knots. Have tried to time this out at each site, with
low MVFR or possibly brief IFR visibilities in moderate or heavy
rain. Additionally, ceilings should drop solidly into the MVFR
range, and potentially IFR.

Expect solid MVFR ceilings to persist at bwg/sdf through mid
afternoon, before some improvement as deepest moisture exits. Lex
could stay MVFR through the end of this forecast cycle.

&&

Lmk watches/warnings/advisories...
Kentucky...Flash Flood Watch until noon EDT /11 am CDT/ today for
kyz033>043-045>049-053>057-062>067-071>078-081-082.

In...none.
&&

$$

Short term........bjs
long term.........Rjs
aviation..........bjs

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