Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 261709
AFDLMK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
109 PM EDT Sun Jul 26 2015

...Updated Aviation Discussion...

.SHORT TERM (Now through Monday)...
Issued at 313 AM EDT Sun Jul 26 2015

The upper pattern will continue to feature NW flow on the eastern
edge of a ridge centered over the southern Plains. At the surface, a
weak frontal boundary will sag across central IL/IN/OH through the
day with a moderately unstable airmass building in to the south and
west of this boundary. Will watch an ongoing complex currently over
northern MO slide SE along the instability axis through the morning,
possibly surviving into our CWA by mid to late afternoon. Best
chances for 1000-2000 J/KG of CAPE will lie along and west of I-65,
however this area will also be under the influence of some mid level
capping as it will be closer to the upper ridge center. Think the
most likely scenario will be for convection to fall apart just to
our north and west as most hi-res models and somewhat capped
environment would suggest. One other limiting factor will be
convective debris overspreading the area in the morning and limiting
destabilization potential. Will leave at least some small chances in
the forecast through the afternoon and evening hours. Overall, its a
low confidence forecast w/ respect to convective evolution over the
next 24 hours.

Best chances for showers and storms should be late evening into the
overnight hours ahead of another disturbance/remnant MCV (currently
over SD/IA/NE) embedded in the NW flow aloft. The feature should
provide enough of a low level response and convergence along the
aforementioned frontal boundary for scattered coverage over southern
IN and north central KY. Storms should die off in the overnight
hours.

Monday will bring another day of low confidence in convective
evolution, however will continue to lean toward a drier forecast as
upper ridge axis will be center just to our west and we will be more
under influence of mid level subsidence. Plus, NW flow aloft will be
more to our NE. The drier forecast does have support from the higher
res 26/00Z Nam and WRF NMM, along with most of the other 00z
operational models. Will leave small chances in to account for the
possibility of the lingering overnight MCS, but again leaning away
from this scenario.

Temperatures today will be similar to yesterday, perhaps a degree or
two warmer. Much will depend on upper level clouds and convective
evolution. Expect a mild overnight with lows in the 70-75 range.
Monday highs are again dependent on convective evolution, but
leaning toward the drier solution yields highs in the upper 80s and
low 90s.

.LONG TERM (Monday Night through Saturday)...
Issued at 300 AM EDT Sun Jul 26 2015

Expect very warm temps through the middle of the week with upper
ridging over the southern Plains. This ridging should keep any
disturbances that could help organize convection to our north and
east, but the air mass is still juicy enough to support diurnally
driven isolated T-storms Tuesday and Wednesday. Temp forecast will
lean on the cooler NAM guidance, given recent GFS warm bias.
However, those temps are still above climo and dewpoints will be
high enough that heat index values will be close to 100 each day,
especially west of I-65.

Wednesday night and Thursday the ridge will retrograde toward the
Rockies, and fairly broad trofiness will push ESE into the Great
Lakes. Cold front moving through the Ohio Valley is trending a bit
faster, which will put our best rain chances on Wednesday night.
Biggest threat with this system is heavy rain, as we`ll have
precipitable water approaching 2 inches, and slow storm motions.

Surface high pressure will move through the Ohio Valley Thursday
night through Saturday, along with a marked decrease in atmospheric
moisture, so dry conditions are expected along with seasonable
temperatures. Dewpoints dropping into the upper 50s/lower 60s will
actually make it a bit more comfortable than typical late July/early
August weather.

&&

.AVIATION (18Z TAF Update)...
Updated 109 PM EDT Sun Jul 26 2015

SDF stands the best chance at receiving TSRA this afternoon/evening
as a weak cool front drops down from the north and an outflow
boundary coming in from the west sparks scattered convection. A few
TSRA could affect BWG as well from that outflow boundary as it sinks
to the southeast. Will keep LEX dry for now.

Tonight should be quiet with scattered clouds and nearly calm winds
once again. Could see some BR around dawn, especially at BWG, but
more cloud cover tonight than the past couple of nights may help it
from becoming dense.

&&

.LMK WATCHES/WARNINGS/ADVISORIES...
KY...NONE.
IN...NONE.
&&

$$

Short Term........BJS
Long Term.........RAS
Aviation..........13





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