Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Louisville Kentucky
259 PM EDT Sat Aug 30 2014
Short term (now through Sunday night)...
issued at 255 PM EDT Sat Aug 30 2014
An impressive plume of moisture easily visible on regional satellite
and radar loops has been streaming northward up the lower
Mississippi Valley today. Small waves are embedded within this
moisture, with one moving into west Tennessee and the other crossing
northern Louisiana this afternoon. The moisture and its embedded
waves will continue to push to the north and northeast,
overspreading southern Indiana and especially central Kentucky
tonight and Sunday. As a result, we can expect widespread showers
along with enough instability for some embedded thunder. The
wettest time period will be from late tonight into Sunday morning.
Showers will become more scattered from southwest to northeast
Sunday afternoon. Coverage will taper off even more Sunday night as
the deep moisture moves off to the northeast.
Precipitable water values will be in the 2 to 2.4 inch range through
Sunday, with k index values solidly in the middle 30s. We'll have
some dynamic assistance from an increasing low level jet and from
being situated near the right entrance region of the upper jet. It
looks like general rainfall amounts of one to two inches will be
possible in central Kentucky, especially along a corridor from
Bowling Green to Lexington. Lesser amounts (one-half to one inch)
in southern Indiana. The individual showers and thunderstorms will
have a progressive forward movement, but training will be a
concern. Spots that get stuck under narrow bands of heavier
rainfall could see three inches of precipitation. Any flooding is
expected to be minor given 6-hour flash flood guidance values of two
to four inches. The best chance for flooding will be in urban areas
and along small streams.
Bowling Green will end up with its wettest August on record, and
Lexington has a shot at their wettest August as well. Louisville
will end up somewhere in the top ten.
Low temperatures tonight and tomorrow night should be around 70.
Went on the low end of guidance for highs tomorrow with all the
clouds and rain. Got burned on the high temp forecast on a
similarly rainy day a couple of weeks ago when highs were only in
the 70s. For now will go for highs in the upper 70s to lower 80s,
though the final answer will depend on just how much we can manage
to dry out Sunday afternoon, allowing temperatures to rise further.
Long term (monday through saturday)...
issued at 255 PM EDT Sat Aug 30 2014
Monday through Wednesday...
A potent jet is forecast early Monday to exit the central rockies
and help carve out a strong, yet progressive trough over the
northern plains. Low pressure will deepen early Tuesday as it moves
northeast well north of the Great Lakes towards James Bay. By the
middle of next week, zonal flow will develop as the jet will align
over the northern tier of states near Canada. For Wednesday through
the early portion of the weekend, strong ridging will develop over
the southern two thirds of the conus, including the lower Ohio
The commonwealth on Labor Day will lie in between an exiting wave
over the Appalachians and an approaching cold front that may
approach southern Indiana Tuesday. Expect warm and continued humid
conditions with decent southwesterly low level flow and highs in the
upper 80s to around 90. Any afternoon convection will likely stay
isolated and unorganized with only 20 to 30% coverage.
For several days, extended guidance has forecast the development of
widespread convection late Monday and early Tuesday along a cold
front that is forecast to lie along a line from northern Illinois
through Missouri. This boundary is expected to sag southeast,
weaken, and briefly stall along or north of the Ohio River Tuesday
afternoon. Southwest flow ahead of this boundary and pre-frontal
convergence will bring very humid air overhead Tuesday with pwats
approaching 2 inches. Scattered thunderstorms are a good bet Tuesday
afternoon and evening, with the best coverage expected along and
north of the Ohio River. Should morning skies remain clear and we
realize adequate surface instability, some storms may become strong
with a potential for localized heavy rainfall. Highs Tuesday may be
modified by cloud cover and precipitation, but should generally
reach the mid 80s to around 90.
Wednesday through Saturday...
500mb ridging, already in place across the southern states late
Tuesday will build northward across the Tennessee and Ohio valleys,
peaking in strength late Friday. Humid air will remain in place,
with dewpoints probably remaining in the upper 60s at least. If not
for our recent widespread rains, this period could become quite hot
with highs in the middle 90s. With relatively lush vegetation and
moist soils, think that highs around 90 to the lower 90s are more
likely. Winds will stay light through the period. Afternoon and
evening convection are possible each day, but think coverage will
range from isolated to scattered at best Wednesday, and only
isolated Thursday through Saturday as ridging really becomes
Aviation (18z taf update)...
issued at 138 PM EDT Sat Aug 30 2014
An impressive plume of moisture streaming up the Mississippi Valley
will advance into central Kentucky this afternoon and evening, then
take up residence over the region through the rest of the taf
period. Widespread showers with isolated embedded thunder can be
expected for much of the forecast period, with the wettest weather
taking place overnight tonight into Sunday morning. Flying
conditions will gradually deteriorate this afternoon, and may go
high-end MVFR tonight into Sunday morning with both lowering
ceilings and visibilities in rain. Winds will be consistently from
the south in the 6 to 11 knot range.