Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 221046
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
646 AM EDT Tue Jul 22 2014
...Updated Aviation Discussion...
.SHORT TERM (Now through Wednesday night)...
Issued at 305 AM EDT Tue Jul 22 2014
The synoptic pattern early this morning features an amplified ridge
across the western CONUS, with a trough across the northern Great
Lakes. There is also a weak cutoff upper low across the Southeast.
The Great Lakes trough will amplify into the Ohio Valley through the
short term period, driving a surface cold front southeast through
Temperatures and humidity will certainly be on the rise today as an
area of high pressure shifts east of the region. This will allow
for light southerly flow to commence this afternoon. Given a good
deal of sunshine (especially across north-central KY and southern
IN) and generally dry ground conditions, we should warm efficiently
this afternoon. Really the only deterrent will be generally weak
turbulent mixing (winds in the ML around 5 knots). Therefore, think
temperatures should warm into the 90s across most locations, with
some of the typically warmer areas possibly touching the mid 90s.
Heat indices will climb into the upper 90s to near 100 degrees at
times this afternoon.
The other story today will be convective chances across southern and
central KY. There will be a weak deformation zone around 850-700mb
that will develop across southern and central KY this afternoon,
emanating out of the Southeast cutoff low. In addition, low-level
moisture will be on the increase across south-central KY, which will
aid in afternoon instability. However, am struggling to find any
surface triggers to help focus convection. Therefore, think
coverage will remain quite sparse. There will likely be a thin
southwest to northeast line of convection that develops along this
def zone with little additional coverage elsewhere. Do not expect
any of these storms to be overly strong (most may actually be just
showers), with just some heavier rains, lightning and winds to
around 40mph being the main threats in any isolated storm.
Any lingering convection will dissipate by sunset. Additional
convection will develop today across IL/WI along the approaching
cold front and drop southeast tonight into IN. It appears that this
activity will likely weaken and dissipate before it gets to our
southern IN counties by daybreak Wednesday, thus will continue with
a dry forecast tonight. Overnight lows will be in the lower 70s.
Guidance has trended quicker with this cold front slated to move
through on Wednesday. Model consensus places the cold front near
the Ohio Valley by Wednesday afternoon. Therefore, have focused the
best pop chances along and south of the Ohio River Wednesday
afternoon into Wednesday night. Still am not impressed with any
organized severe potential with this system, as weak winds aloft
will yield deep-layer shear <25 knots and 0-3km shear will be <10
knots. Steep low-level lapse rates coupled with 1500-2000 J/kg of
MLCAPE may yield a few stronger storms capable of some gusty winds
(perhaps a marginally severe storm), but agree with SPC in keeping
the region out of a Slight Risk. Locally heavy rains will also be
possible given PWATs around 1.8-1.9 inches. Given the quicker
arrival of the front, have knocked highs down a degree or two which
puts them in the upper 80s to lower 90s.
The front will push through the region Wednesday night, allowing for
drier air to filter into southern IN and northern KY. Convection
will continue along the front across southern KY through the late
evening, but will likely decrease in coverage overnight. Overnight
lows will be in the 60s.
.LONG TERM (Thursday through Monday)...
Issued at 317 AM EDT Tue Jul 22 2014
Upper troffing looks to continue over the eastern United States
throughout the long term as the Rockies ridge remains to our west
and south. Looking beyond this long term period the upper trof in
the east appears to get reinforced even further. So, extreme heat
appears to not be in the cards for the rest of July.
At the surface, high pressure will build in behind the departing mid
week cold front. Some lingering showers may still be found in the
Lake Cumberland region before we dry out completely in the
afternoon. This high will be of Canadian origin and will bring
another spell of pleasant summer weather to the region. High
temperatures Thursday and Friday will be around the lower 80s with
lows Friday morning in the lower 60s and upper 50s.
Friday night weak low pressure will organize over the mid Missouri
Valley with a weak surface trof reaching east. Models are hinting
at a possible MCS developing along and north of the trof. Mid level
flow suggests any MCS that develops would move primarily to the east
and would mostly stay to our north over Illinois and Indiana. Will
include a small PoP in our southern Indiana and far north central
Kentucky counties that will be closest to the system late Friday
The picture becomes murkier as we get into the weekend. Overall,
we`ll have northwest flow aloft with the aforementioned upper
troffing along with possible weak surface systems. As a result,
we`ll continue with scattered PoPs in the forecast through the
weekend and into Monday. Highs will be in the 80s and lows mostly
in the 60s, though Sunday morning we may have some difficulty
dropping below 70.
.AVIATION (12Z TAF Update)...
Issued at 644 AM EDT Tue Jul 22 2014
After the potential for a very brief period of MVFR vsbys early this
morning in light fog, VFR condtions are expected through the period.
Winds will be rather light today out of the SSW with sct cu
developing this afternoon. There remains a very small chance of a
stray shower/storm affecting KBWG or KLEX, but the chance remains so
small that it does not warrant any mention at this time.
A decaying line of storms will approach KSDF from the northwest
tonight, which may spread a mid/upper cloud deck into northern KY
towards dawn Wednesday. Otherwise, winds tonight will continue to
be light out of the SSW.