Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 121723
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
123 PM EDT Sat Jul 12 2014
...Updated Aviation Discussion...
.SHORT TERM (Now through Sunday)...
Issued at 310 AM EDT Sat July 12 2014
Weak high pressure - both at the surface and aloft - continue over
the area early this morning. Because this high pressure is so weak,
though, a weak disturbance aloft was able to generate a line of
light showers that has persisted through the night while moving
southeast over Illinois. As of 3 am EDT, this line was knocking on
the door of our CWA. While likely little more than sprinkles, none
of the models handled this area very well. The only matching
feature lining up with it was a vort lobe in the 12km NAM. With
nothing else even close, will use the NAM guidance for at least the
first part of the forecast. With that in mind, have inserted low
POPs for thunder this afternoon as vertical cross sections of the
NAM show a small area of instability continuing across the CWA
immediately behind this weak short wave. Again, it is not anything
big, but will likely be enough dynamics with it to generate a few
garden variety thundershowers.
Any convection that does develop today will quickly die with the
setting sun, leaving the overnight hours dry. On Sunday, though, a
better chance for thunderstorms returns to the northern half of the
CWA in advance of a cold front poised to make the first day of the
extended forecast period more interesting.
Weak southerly winds will work to return higher dew points north of
the Tennessee and into the Ohio Valley over the next 36 hours. This
will work against the increase in cloud cover to boost temperatures
by a couple of degrees today and Sunday. Look for highs around 90
today and in the lower to mid 90s Sunday. Overnight lows, thanks to
the influx of gulf moisture, will remain in the 70s, save for a few
upper 60s along the I-75 corridor.
.LONG TERM (Sunday night through Friday)...
Issued at 310 AM EDT Sat Jul 12 2014
The long term will start out with upper level ridging building
across the western CONUS as a deepening trough slides southeastward
towards the Great Lakes region. A cold front will lie to the north
of the region across central Indiana. There is still some
disagreement in the models as to how fast this cold front will push
through the forecast area with the GFS being the fastest and having
it clear out by Monday evening. Think this may a bit too fast, so
will lean more towards having the front move through by Tuesday
Given the model differences, there is naturally still some
uncertainty in the precipitation evolution with this system.
Sounding show quite a bit of instability will be present Sunday
night and Monday. In addition, precipitable water values will rise
to around two inches. Scattered to numerous thunderstorms look to
develop overnight Sunday night into Monday as the front nears and a
weak disturbance crosses the area. There is the possibility of MCS
development overnight. The most widespread storms overnight look to
be across southern IN and north central KY. With the high PWAT
values, these storms have the potential to produce torrential
The evolution of storms overnight and how much convective
debris remains on Monday will impact the development of storms
Monday afternoon. However, if we are able to clear out or storms
overnight are less than expected numerous storms may develop Monday
afternoon with strong to severe storms possible. Damaging winds would
be the main threat with the strongest storms.
Scattered storms will continue until the passage of the cold front
late Monday night to Tuesday. Behind this front much cooler and
drier air will push into the region. Dewpoints will fall back into
the mid 50s by Tuesday night. Highs Tuesday and Wednesday will be
much cooler than normal for this time of year, topping out in the
mid to upper 70s. Lows will drop down into the the mid to upper 50s.
We will see a gradual warming for the end of the work week. A few
showers or storms may move into south central KY Friday afternoon,
as a system passes by to the south, but given model differences and
uncertainty will keep the forecast dry for now.
.AVIATION (18Z TAF Update)...
Issued at 110 PM EDT Sat Jul 12 2014
Scattered decaying thunderstorms to our west will spread some high
and mid-level cloudiness across the region, but will very likely not
affect otherwise VFR flying conditions for this evening and
Southwest winds of 5 to 9kt this afternoon will continue through the
overnight before increasing to 10 to 15kt by late morning Sunday.
Some winds may gust up to 25 mph early Sunday afternoon.
A line of convection will likely develop during the late afternoon
or early evening on Sunday north of SDF and LEX. However, they will
likely not affect LEX by 18z. For SDF, will put VCTS in TAFs after
20z Sunday afternoon.