Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 211929
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
329 PM EDT Tue Oct 21 2014
.SHORT TERM (Now through Wednesday Night)...
Issued at 325 PM EDT Tue Oct 21 2014
...Frost potential increasing for Wednesday Night...
Latest water vapor imagery overlaid with 500 mb heights shows
cyclonic flow with deep upper level trough across the eastern CONUS.
Altostratus deck exists across much of IN and central into eastern
KY thanks to cooler air aloft steepening lower level lapse rates. As
surface heating wanes later this afternoon, the periphery of this
cloud deck, which is more cellular, is expected to dissipate as main
upper level cyclonic flow shifts to the east.
At the surface, high pressure centered across Wisconsin will begin
to slowly shift southeastward toward the area tonight, which is
expected to keep the western forecast area mostly clear. However,
clouds will be slow to erode across the eastern areas thanks to the
influence from the upper level trough. Plan on seasonably cool
temperatures tonight with lows ranging across the area from the
upper 30s to lower 40s.
For Wednesday, look for pleasant but seasonably cool October
conditions as high pressure centers itself across the Ohio River
valley. Sunny to mostly sunny skies are expected with highs ranging
from the upper 50s in the east to lower 60s across the southwest
forecast area. Winds will be light and out of the north.
Wednesday night into Thursday looks to be the coolest night of the
entire forecast period as the surface high will be positioned over
the forecast area. This will provide ideal radiational cooling
conditions and Thursday morning lows are expected to dip into the
lower to middle 30s. With light winds and the seasonably cool
airmass in place, patchy to areas of frost look likely. The favored
areas appear to be the eastern forecast area where temperatures may
approach the freezing mark. Otherwise, lows look to vary from the
lower to middle 30s. Frost advisories may be needed for Wednesday
night into Thursday morning across portions of the forecast area if
confidence continues to increase.
.LONG TERM (Thursday through Tuesday)...
Issued at 243 PM EDT Tue Oct 21 2014
After a chilly start to the day temperatures will remain on the cool
side Thursday, topping out in the lower 60s despite quite a bit of
sunshine. For Thursday night into Friday a shortwave will drop
southeast through the northwesterly flow aloft. Precipitation with
this system will be weakening as it approaches the area. However,
most of the models now show at least a slight chance for showers
across southern IN and north central KY Thursday night so will
increase pops to around 20% in this area. The strength of the
shortwave varies from model to model and if it does trend towards
the stronger side, a chance for light showers may eventually need to
be added for Friday as well.
Beyond Friday, upper level ridging will be building in across the
lower Ohio Valley with high pressure at the surface. This will bring
mostly clear to partly cloudy skies with warming temperatures
through Monday. Highs Friday will be in the lower to mid 60s while
Monday`s highs look to be in the mid to upper 70s. Lows will
increase from the lower to mid 40s Friday morning to the lower to
mid 50s Tuesday morning. The next chance for rain will come Tuesday
into Tuesday night as a front moves through.
.AVIATION (18Z TAF Update)...
Updated at 140 PM EDT Tue Oct 21 2014
Latest visible satellite shows large expanse of altostratus with
bases in the 4 to 5 kft range with cyclonic flow at the surface and
aloft. For SDF, plan on VFR conditions throughout the period with
cloud deck dissipating later this evening. LEX will remain closer to
stronger cyclonic flow and likely to remain within stratus deck
through the night. Forecast guidance suggests a possibility of
broken ceilings lowering to MVFR but confidence was not high enough
at this time to include. At BWG, trended previous forecast of IFR
fog to MVFR as guidance suggests winds may remain high enough to
preclude fog development. Cooler and drier air thanks to northerly
flow on Wednesday from late morning into the afternoon is expected
to keep skies clear.