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Area forecast discussion 
National Weather Service Louisville Kentucky
1245 PM EDT Thursday Jul 28 2016

..updated aviation discussion...

..Forecast update...
issued at 1135 am EDT Thu Jul 28 2016

..Flash Flood Watch remains in effect...

Have made several short term updates to grids to account for ongoing
precip over the past few hours. Tropical rainfall rates continue to
occur in association with vort Max near Lexington and another along
the Tennessee line despite the absence of thunder. Extensive cloud
cover is helping to keep surface temperatures down and may need to
tweak Max temps back a bit today over southern Indiana for this
reason. Mesoscale models all show a break in precip over the
forecast area this afternoon and evening, but am not yet confident
enough in this to end Flash Flood Watch any earlier than current
06z expiration.

Short term (now through friday)...
issued at 300 am EDT Thu Jul 28 2016

..heavy rainfall this morning...

The synoptic pattern early this morning features a ridge across the
western conus, with a low-amplitude trough across the northeast. A
shortwave trough emanating from the Gulf of Mexico was located
across western Tennessee/southwest KY, and will be the main focus of the
short term period.

Convection continues to affect much of the region this morning,
especially areas along and east of Interstate 65. With the
approaching vort Max, moisture transport aided by a seasonally
moderate low-level jet has commenced. This transport of a very high
precipitable water airmass (values in excess of 2.25") into an old frontal
boundary and lingering outflow boundaries from yesterday's
convection has resulted in widespread thunderstorm development.
Instability is not very impressive, but low centroid storms in this
high precipitable water airmass has resulted in heavy rain makers which will
continue to push off to the northeast through the morning hours.
Luckily, storm motions have been just to the north of the main
boundary orientation, which has kept flash flooding at a minimum
thus far. However, will continue to watch for localized flash
flooding through the morning hours in some areas where storms are
able to train. The Flash Flood Watch was expanded to the north
earlier this morning to account for the heavier rains pushing into
lower flash flood guidance areas, especially across the northern
Bluegrass region.

For this afternoon, deep moisture transport will push off to the
east of the region as the vort Max pivots through the area. Still
think there will be some scattered thunderstorm development behind
this morning's convection later this afternoon into early this
evening, but most activity will likely stay along/west of I-65 where
atmospheric recovery seems more plausible. In coordination with
surrounding offices, will keep the Flash Flood Watch up through this
afternoon/evening to account for this, but will trim the expiration
time up to 06z Friday. Day shift may be able to cancel the watch
completely this afternoon if current trends hold.

Convection should diurnally wane tonight with the loss of daytime
heating and no apparent synoptic trigger. Overnight lows will dip
into the upper 60s and low 70s.

The upper-level flow will turn a bit more zonal on Friday, with weak
perturbations in the flow traversing through it. Therefore, will
continue with scattered convection on Friday, mainly in the
afternoon and early evening.

Long term (friday night through wednesday)...
issued at 330 am EDT Thu Jul 28 2016

The synoptic pattern at the start of the long term period will
feature a low-amplitude trough persisting across the eastern conus,
with a ridge over the west. This will keep the Ohio Valley within
northwest flow through the upcoming weekend, before heights start to
rise by the middle of next week.

Will continue with an ensemble approach to the forecast through the
period given there is not a whole lot synoptically to focus on.
Precipitation chances will come down to where an effective boundary
is pushed (or not pushed) by convection each day. At this time, it
appears Saturday will be the best chance for showers/storms through
the period, with the boundary perhaps sagging south enough to lower
chances in the northern County Warning Area Sunday through early next week. Heights
will rise early next week which will allow for another warmup as
highs climb back into the upper 80s/90s. Will have to watch trends
through the middle of next week as we will still be on the edge of
the building ridge, which could put the region in a favored path for
mcss.

&&

Aviation (18z taf update)...
issued at 1244 PM EDT Thursday Jul 28 2016

One fairly large slug of rain is pushing NE of Lex, with another
lifting through bwg at this time. To the north and west, the
boundary layer is quite stable, with extensive stratus holding in a
borderline MVFR/IFR ceiling.

Bwg initialization will be tricky, as the precip shield may well be
just east of there by the valid time of the taf. Sdf is also
starting to go in and out of a fuel-alternate ceiling, but Lex will
begin with a drizzly/showery IFR.

Will be in fuel-alternate ceilings on at least a tempo basis through
the afternoon at all terminals. Lex will be the worst with plenty of
IFR, including tempo IFR vis in showers. Will have to watch
convection over the Wabash valley, as the hi-res models have storms
making a run at sdf/Lex around 00z, but initializations are overdone
with the current activity.

Plenty of recent rainfall will support fog development toward
morning, even though it will be mitigated by a broken stratus deck.
Really that just makes the difference between our current MVFR
forecast and a potential IFR restriction.

Look for ceiling/vis to improve to VFR late Fri morning on light SW
winds.

&&

Lmk watches/warnings/advisories...
Kentucky...Flash Flood Watch through late tonight for kyz026>043-045>049-
053>057-061>067-070>078-081-082.

In...none.
&&

$$

Update.........Jbs
short term.....Kjd
long term......kjd
aviation.......Ras

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