Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 310255
AFDLMK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
1055 PM EDT Sat Aug 30 2014

...Forecast Update...
Issued at 1054 PM EDT Sat Aug 30 2014

A large amount of convection continues to move northeastward this
evening.  Mid-level wave rotating NE through NW Mississippi will
continue to move northeastward overnight.  This will push an area of
convection from middle Tennessee into central and eastern KY
tonight.  Additional convection is likely to develop later tonight
on the heels of the nocturnal low-level jet.  Some evidence of this
is already showing up SW of Memphis.  The 31/00Z NAM suggest that
the axis of heaviest rainfall would fall along and just south of the
Ohio River.  However, this model has tended to be a little to N/NW
with its heavy rain placements this summer.  Thus, feel that the
highest risk of heavy rains will be a little further south/east
where we have the Flash Flood Watch placed.  Widespread 1-1.5 inch
amounts will be possible across the watch area...though some places
that have training of cells could pick up as much as 3-4 inches.

A sharp gradient in PoP is likely further NW of the watch.  However,
some additional activity along the aforementioned low-level jet may
push rains a bit further north and northwest into NW KY and southern
Indiana tonight.  However, rainfall amounts in this area will be
generally less than 1 inch.

Update issued at 825 PM EDT Sat Aug 30 2014

Convection continues to intensify over the Tennessee Plateau area
this evening ahead of an approaching mid-level wave.  Large area of
torrential rainfall has been observed over middle Tennessee this
evening and this activity will spread northeastward into portions of
central Kentucky overnight.  After coordination with surrounding
offices have gone with a flash flood watch for the eastern half of
the forecast area.  Widespread 1-2 inch rainfall amounts are
expected.  However, areas that see repeated rainfall could see
upwards of 3-4 inches.  Will be updating the rest of the product
suite shortly to account for the watch.  Watch product has already
been issued.

Update issued at 735 PM EDT Sat Aug 30 2014

Tropical moisture plume is becoming more defined this evening.  This
feature will bring rounds of showers and embedded thunderstorms to
the region this evening and overnight.  With such ample moisture in
place, torrential rainfall will be the main weather hazard with this
activity.  Several mid-level perturbations were evident in radar
imagery and satellite imagery.  The first one is currently moving NE
out of the region while a second and stronger one is rotating NE
through Mississippi.  This second wave is inducing stronger
convection from north-central AL into middle Tennessee.  This
activity will move northward into southern KY shortly and affect
areas mainly east of I-65 and along and west of I-75.

Moist adiabatic profiles are likely to keep severe weather risks
relatively low this evening.  However, decent precipitation loading
will likely lead to low-centroid cells to develop capable of
producing torrential/tropical rainfall.  While basin averages will
likely range from a half to one and a half inches, areas that see
repeated rainfall could see upwards of 2-3 inches locally which
would result in local hydrologic issues.

.SHORT TERM (Now through Sunday Night)...
Issued at 255 PM EDT Sat Aug 30 2014

An impressive plume of moisture easily visible on regional satellite
and radar loops has been streaming northward up the lower
Mississippi Valley today. Small waves are embedded within this
moisture, with one moving into west Tennessee and the other crossing
northern Louisiana this afternoon. The moisture and its embedded
waves will continue to push to the north and northeast,
overspreading southern Indiana and especially central Kentucky
tonight and Sunday.  As a result, we can expect widespread showers
along with enough instability for some embedded thunder.  The
wettest time period will be from late tonight into Sunday morning.
Showers will become more scattered from southwest to northeast
Sunday afternoon.  Coverage will taper off even more Sunday night as
the deep moisture moves off to the northeast.

Precipitable water values will be in the 2 to 2.4 inch range through
Sunday, with K Index values solidly in the middle 30s.  We`ll have
some dynamic assistance from an increasing low level jet and from
being situated near the right entrance region of the upper jet.  It
looks like general rainfall amounts of one to two inches will be
possible in central Kentucky, especially along a corridor from
Bowling Green to Lexington.  Lesser amounts (one-half to one inch)
in southern Indiana.  The individual showers and thunderstorms will
have a progressive forward movement, but training will be a
concern.  Spots that get stuck under narrow bands of heavier
rainfall could see three inches of precipitation.  Any flooding is
expected to be minor given 6-hour flash flood guidance values of two
to four inches.  The best chance for flooding will be in urban areas
and along small streams.

Bowling Green will end up with its wettest August on record, and
Lexington has a shot at their wettest August as well.  Louisville
will end up somewhere in the top ten.

Low temperatures tonight and tomorrow night should be around 70.
Went on the low end of guidance for highs tomorrow with all the
clouds and rain.  Got burned on the high temp forecast on a
similarly rainy day a couple of weeks ago when highs were only in
the 70s.  For now will go for highs in the upper 70s to lower 80s,
though the final answer will depend on just how much we can manage
to dry out Sunday afternoon, allowing temperatures to rise further.

.LONG TERM (Monday through Saturday)...
Issued at 255 PM EDT Sat Aug 30 2014

Monday through Wednesday...

A potent jet is forecast early Monday to exit the central Rockies
and help carve out a strong, yet progressive trough over the
northern Plains. Low pressure will deepen early Tuesday as it moves
northeast well north of the Great Lakes towards James Bay. By the
middle of next week, zonal flow will develop as the jet will align
over the northern tier of states near Canada. For Wednesday through
the early portion of the weekend, strong ridging will develop over
the southern two thirds of the CONUS, including the Lower Ohio
Valley.

The Commonwealth on Labor Day will lie in between an exiting wave
over the Appalachians and an approaching cold front that may
approach southern Indiana Tuesday. Expect warm and continued humid
conditions with decent southwesterly low level flow and highs in the
upper 80s to around 90. Any afternoon convection will likely stay
isolated and unorganized with only 20 to 30% coverage.

For several days, extended guidance has forecast the development of
widespread convection late Monday and early Tuesday along a cold
front that is forecast to lie along a line from northern Illinois
through Missouri. This boundary is expected to sag southeast,
weaken, and briefly stall along or north of the Ohio River Tuesday
afternoon. Southwest flow ahead of this boundary and pre-frontal
convergence will bring very humid air overhead Tuesday with PWATs
approaching 2 inches. Scattered thunderstorms are a good bet Tuesday
afternoon and evening, with the best coverage expected along and
north of the Ohio River. Should morning skies remain clear and we
realize adequate surface instability, some storms may become strong
with a potential for localized heavy rainfall. Highs Tuesday may be
modified by cloud cover and precipitation, but should generally
reach the mid 80s to around 90.

Wednesday through Saturday...

500mb ridging, already in place across the southern states late
Tuesday will build northward across the Tennessee and Ohio Valleys,
peaking in strength late Friday. Humid air will remain in place,
with dewpoints probably remaining in the upper 60s at least. If not
for our recent widespread rains, this period could become quite hot
with highs in the middle 90s. With relatively lush vegetation and
moist soils, think that highs around 90 to the lower 90s are more
likely. Winds will stay light through the period. Afternoon and
evening convection are possible each day, but think coverage will
range from isolated to scattered at best Wednesday, and only
isolated Thursday through Saturday as ridging really becomes
established.

&&

.AVIATION (00Z TAF Update)...
Issued at 720 PM EDT Sat Aug 30 2014

Plume of tropical moisture streaming up from the Mississippi Valley
will set the stage for periods of showers with some embedded
thunderstorms for much of the TAF period.  Initial lead wave is
moving NE of the region this evening.  However, second wave is now
moving up from MS/AL and this will affect the terminals this evening
and into the overnight period.  A third wave down along the gulf
coast will impact the region later on Sunday morning.

For the evening/overnight period, expect low end VFR to high end
MVFR conditions at the terminals.  It appears best chances of
thunder will be at KBWG and KLEX this evening as stronger wave pulls
northward out of Tennessee.  While MVFR conditions are expected to
prevail...short term drops into IFR or even into LIFR will be
possible as showers/storms pass through the terminals.  Based on
current trajectories, feel that KSDF will likely see light/moderate
rain at times this evening and overnight, but conditions will likely
remain MVFR with a lesser risk of IFR/LIFR conditions.  Winds
overnight will remain out of the south with speeds less than 8kts.
Some occasional higher gusts may be possible within convection.

&&

.LMK WATCHES/WARNINGS/ADVISORIES...
KY...FLASH FLOOD WATCH through Sunday morning FOR KYZ033>043-045>049-
     053>057-062>067-071>078-081-082.

IN...NONE.
&&

$$

Update.........MJ
Short Term.....13
Long Term......JSD
Aviation.......MJ





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