Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 240547
Area Forecast Discussion
National Weather Service Louisville KY
147 AM EDT SUN JUL 24 2016
...Updated Aviation Discussion...
.SHORT TERM (Now through Sunday Night)...
Issued at 300 PM EDT Sat Jul 23 2016
...Hot and Humid Conditions Continue For the Weekend...
Current visible satellite shows a ridge axis across Kentucky, with
slow flow of the cloud field pivoting around that axis roughly along
a line from Beaver Dam to Elizabethtown to Richmond. There is a
relative minima in clouds along this axis, with clouds puffing up a
little more north and south of it. Convective Initiation tool and
radar mosaic show the best activity over the Appalachians as well as
a few blips in southern Indiana. For the rest of this afternoon,
lowered pops over the Bluegrass and limited the widely scattered
values to our southern border with TN. Expect this activity to wane
with sunset and some pockets of fog to develop overnight, especially
where this rain falls.
As for the heat, as of this writing, SDF briefly poked up to a 102
heat index, with a 93 temperature and a 73 dewpoint. With limited
coverage of storms today, expect a little less coverage of storms
tomorrow, given a similar setup and fewer boundaries out there to
work with. Given the subsequent longer period of sunshine and a
little higher surface dewpoint to work with, will be extending the
heat advisory through Sunday, but tailoring back a few of the
Monday we should see dewpoints inch up another degree or two, but
lower thicknesses due to an approaching trough should limit us from
reaching the higher heat indices of this weekend. Models, are
trending a little slower with the front coming down, so that puts
more of a question mark on pops and heat, especially in our south.
For now, will keep high-end chance pops in the north and go a little
lower down south.
With the slower progression of the front Tuesday, we should end up
with chance-range pops, 30-50%, areawide, with the best focus down
south. The cloud cover should limit temperatures this day to the mid
to upper 80s for highs.
.LONG TERM (Monday through Saturday)...
Issued at 221 PM EDT Sat Jul 23 2016
The upper ridge we have been talking about for the past several days
will recenter itself over the western half of the United States
during this period as troffing digs into the east. This suggests a
break from significant heat and increased chances of thunderstorms.
The GEFS QPF plumes are noisy but do show a general trend of daily
convection. The operational run of the ECMWF, with regard to 12-hr
PoPs, is in fairly good agreement with the ensemble mean and are
within 90% confidence bounds for the most part. Precipitable water
values are consistently in the 1.5 to 2 inch range (mostly the high
side of that range) with surface dew points in the lower 70s. Given
all of the above, it makes sense to continue with scattered daily
shower and thunderstorm chances. Chances should increase towards the
weekend as the axis of the upper trof approaches.
Afternoon highs will be typical for this time of year in the 85 to
90 degree range but the expected dew points and our green summer
will keep humidity levels on the uncomfortable side.
.AVIATION (06Z TAF Update)...
Issued at 130 AM EDT Sun Jul 24 2016
A stagnant weather pattern has the TAF sites in the doldrums as a
flat upper level ridge covers the southern half of the U.S. The
upper pattern actually looks more typical of the tropical horse
latitudes, with variable winds at or below 10 kts through the lowest
30 thousand feet of the atmosphere.
With no appreciable pressure gradient at the surface and no defined
pockets of energy aloft in the weak flow, there is only diurnal
surface heating to drive the weather this forecast period. Surface
dewpoint depressions place cloud bases in the VFR range...perhaps
initiating around 040 before rising to 050 with an occasional broken
ceiling during the afternoon. Cannot rule out isolated
thunderstorms that manage to break through the warm cap that will
otherwise will keep flat cumulus limited to about 2000 feet of
growth, but with no surface focal point to key on - and little
movement of any that develop - confidence is too low to even include
VCTS until they form.
KY...Heat Advisory until 8 PM EDT /7 PM CDT/ this evening for
IN...Heat Advisory until 8 PM EDT /7 PM CDT/ this evening for