Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 021707
AFDLMK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
107 PM EDT Thu Jul 2 2015

...Updated Aviation Discussion...

...Forecast Update...
Updated at 1155 AM EDT Thu Jul 2 2015

Opted to extend the Flash Flood Watch northward into southern
Indiana and the remainder of central Kentucky. Stalled boundary
interacting with a very moist air mass and combined with subtle
northwest flow disturbances will result in scattered to numerous
showers/storms at times through Friday. PWATs are expected to remain
between 1.5 and 2.0 inches and storm motions have been relatively
slow. This, combined with low FFG values across the area, suggests
flash flooding is possible across the entire area.

Updated at 940 AM EDT Thu Jul 2 2015

Efficient rain producing showers and thunderstorms are mainly
confined east of I-65, closer to the I-75 corridor of the Bluegrass
region, as of mid-morning. In its wake, there is a relative lull
back to the west. Surface analysis shows an area of low pressure
across southwest Missouri with a stalled boundary stretching east
into southern Indiana and northern Kentucky. Visible satellite shows
a pocket of clearing as well across southwest Kentucky. Lots of
mesoscale features to be the focus for additional development later
this afternoon. With PWATs remaining in th 1.5 to 2.0 inch range,
this boundary, differential heating and any afternoon instability in
a generally uncapped environment will support scattered showers,
heavy downpours and thunderstorms. Some of the storms may train,
backbuild and overall be slow moving. Main hazard is heavy rain and
flash flooding.

Updated flash flood guidance incorporating rainfall through 8 am
shows much of south-central KY is around 1 inch in 1 hour (or less),
so current flash flood watch looks good. Further north, pockets of
low FFG (Dubois, Orange, and Crawford IN) exist but overall guidance
is 2-3 inches/hour.

.SHORT TERM (Now through Friday)...
Issued at 314 AM EDT Thu Jul 2 2015

...Heavy Rainfall Across Central and Southern Kentucky thru
Morning...

A nearly stationary frontal boundary is currently sitting WNW-ESE
across our CWA with deep moisture pooling south and west of it. It
is not expected to move a whole lot through the day, meanwhile a
higher precipitable water airmass (> 2") will continue to move in. A
complex of showers and storms has organized over MO and southern IL
over the past few hours ahdead of an upper disturbance embedded in
the NW flow. This complex will steadily push east toward our CWA,
arriving in our west around 5 AM EDT. Expect widespread rainfall,
with pockets of very heavy rainfall, to push east through the
morning across our southern CWA. Be careful through the morning
commute!

In collaboration with surrounding offices, decided to keep
the ongoing Flash Flood Watch as is across southern KY where
heaviest rainfall is expected to fall (1-2", locally higher).
Rainfall amounts should taper further north as you near the I-64
corridor. Had been concerned about our far NW given the amount of
rain that fell earlier this evening, however think this area will
only see scattered shower activity through today being north of the
boundary.

The main batch of showers and thunderstorms exits our east by 11
AM/Noon EDT, with a relative lull in coverage through early and mid
afternoon. Scattered showers will then have the potential to
redevelop mid to late afternoon, mainly across KY. Given the lack of
insolation, this may be overdone by current model solutions so will
rely more on hi-res output, which puts less coverage this evening
into tonight.

Another disturbance will dive through the NW flow aloft later
tonight and into tomorrow, which will drag an associated surface low
south of our CWA. The end result will help to pull the stalled
synoptic boundary still sitting over our CWA through as a cool front
through the day on Friday. As a result, only expect scattered
coverage of showers and a few storms mainly across our south from
later tonight through Friday.

High temperatures will struggle today under rainfall and cloudy
skies. Will go with max readings in the 74-79 range. Lows will
mostly range in the 65-70 range tonight. Highs Friday will be
similar to today, in the mid and upper 70s.

.LONG TERM (Friday Night through Wednesday)...
Issued at 305 AM EDT Thu Jul 2 2015

Pattern remains fairly unsettled for most of the next week. No
single day appears to be a washout, but there is also no
identifiable dry period either.

Best precip chances Fri night through Monday will be across south
central Kentucky, as shortwave upper ridging takes hold over the
Great Lakes, and a bubble of surface high pressure tries to nose
into the Ohio Valley from the north.

Better coverage and organization of storms is expected by Tuesday or
Wednesday with the cold front trailing off a fairly vigorous upper
trof passing through the Great Lakes. Better instability and better
dynamics could support some stronger storms, but that remains a
low-confidence forecast at this time.

Temps through the period will run near or slightly below climo by
day, and near or above climo by night, as abundant clouds and
moisture will limit diurnal ranges.

&&

.AVIATION (18Z TAF Update)...
Issued at 105 PM EDT Thu Jul 2 2015

Afternoon destabilization ahead of a surface low combined with a
stalled frontal boundary across the area will support an uptick in
showers/storms through the early evening hours. Highest chances are
centered around 21-00z timeframe...and BWG to LEX looks to have the
greatest chance of seeing aviation restrictions.

As precipitation wanes this evening, attention turns to fog
potential. Light/variable winds tonight combined with the moisture
and recent rainfall leads to higher confidence for periods of MVFR
to IFR fog potentially. Guidance hits LEX/BWG...so have trended TAFs
toward that possibility. By Friday morning, another weather system
could bring more showers/storms to the area.

&&

.LMK WATCHES/WARNINGS/ADVISORIES...
KY...FLASH FLOOD WATCH through Friday morning FOR KYZ023>043-045>049-
     053>057-061>067-070>078-081-082.

IN...FLASH FLOOD WATCH through Friday morning FOR INZ076>079-083-084-
     089>092.

&&

$$

Update.........ZT
Short Term.....BJS
Long Term......RAS
Aviation.......ZT




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