Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 311040
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
640 AM EDT Thu Jul 31 2014
...Updated Aviation Discussion...
.SHORT TERM (Now through Friday)...
Issued at 300 AM EDT Thu Jul 31 2014
A broad immobile longwave 500mb trough continues over the Great
Lakes, seemingly locked in place be bracketing ridges over the
inland Pacific Northwest and the eastern Atlantic. This trough will
not move much during the next several days.
Currently, a shortwave trough and corresponding inverted surface
front is moving through northern Texas. This feature will continue
to dig southeast around the longwave trough over the Lakes. Rain and
cloud cover will miss to our south, with widespread showers expected
over Arkansas and southern Missouri late this afternoon, spreading
east across the northern Gulf States by Friday afternoon.
The Commonwealth and southern Indiana will remain in a benign
weather pattern for the next several days. A light pressure gradient
will lead to nearly calm winds at night and light winds each
afternoon. Expect westerly winds this afternoon at around 5 mph,
becoming light northeasterly by Friday afternoon. High cloudiness
associated with the Texas shortwave will erode by morning, with just
some afternoon fair weather cumulus developing both today and Friday
afternoons. Will continue just a slight chance of some isolated
thunder Friday afternoon.
Under the influence of a modifying trough, temperatures will rise a
couple of degrees today and Friday, but still remaining a few
degrees below normal. Highs will generally reach the mid 80s, with
lows in the lower to mid 60s.
.LONG TERM (Friday Night through Wednesday)...
Issued at 318 AM EDT Thu Jul 31 2014
Long Term Synoptic Overview
In the long term, a rather amplified upper flow pattern is expected
to persist across North America with a ridge out over the western US
and a trough over the eastern US. The Ohio Valley will remain under
the influence of the upper trough early in the period. Some weak
vorticity within the flow is expected to transverse through the base
of the trough in the early part of the extended. As the weekend
draws to a close, the upper trough is expected to lift out as the
western Atlantic ridge will attempt to retrograde eastward into the
eastern US. As this occurs, the upper ridge over the western US
looks to close off. The Ohio Valley will reside in a cull between
these two ridges early next week. However, these two ridge will
link up by midweek resulting in more of zonal pattern developing
across the eastern US. By the end of the period, the deterministic
and ensemble guidance are in agreement with another strong vorticity
lobe dropping into the northern US which will eventually render the
flow back to a trough west/ridge east pattern with the strong
possibility of an upper level low getting cut off across the Ohio
Model Preference & Confidence
As for model preference, a 33/33/33 blend of the previous forecast
and the 00Z OP GFS and 00Z OP Euro were used for the early part of
the extended period (weekend period). For early to middle of next
week, generally used a 50/50 blend of the OP GFS and Euro along with
their respective ensembles. A slightly higher weight was given to
the ensemble solutions. Forecast confidence through the period is
slightly above average with respect to temperatures and
precipitation. We heavily leaned on the SuperBlend guidance for
temperatures through the upcoming period.
Sensible Weather Impacts
At the beginning of the long term period, we expect mainly partly to
mostly cloudy conditions as we will be under the influence of the
upper trough. With this feature in the region, scattered showers
and thunderstorms will be possible Friday night through Saturday
night. A marked decrease in activity is expected by Sunday as the
upper trough lifts out. Overall coverage of convection is expected
to be scattered at best and will probably not put a big dent in any
of our rainfall deficits. Drier and warmer conditions are expected
as we move into early next week. Temperatures are expected to
rebound to near seasonal normals from Monday through Wednesday.
Daytime highs on Saturday will generally run from the upper 70s in
the east to the lower-middle 80s in the west. Slightly warmer
temperatures are expected on Sunday with mainly 80s. More
seasonable middle to upper 80s are expected on Monday and Tuesday
with upper 80s to near 90 expected by Wednesday. Overnight lows
will generally be in the middle to upper 60s.
A turn to more unsettled weather looks likely toward the end of the
forecast period and into next weekend as the aforementioned upper
level cut off low develops across the region. This would likely
result in cooler temperatures returning to the area late next week.
.AVIATION (00Z TAF Update)...
Issued at 640 AM EDT Thu Jul 31 2014
VFR conditions expected through the TAF period. Clear skies and calm
winds this morning will give way to some afternoon fair weather
cumulus. Winds will increase from the west at 5 mph or less this afternoon.
Skies will clear this evening and winds will become calm once again.