Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Louisville Kentucky
328 PM EDT Tuesday Aug 4 2015
Short term (tonight through Thursday night)...
issued at 315 PM EDT Tuesday Aug 4 2015
Scattered showers and storms have developed on a differential
heating and dew point boundary across central and south central Kentucky.
The slow moving nature of these storms may put down some heavy
rainfall in spots. A few stronger storms are possible given the
amount of instability, although overall organization is not expected
due to the lack of stronger deep layer shear. Showers/storms will
push off to the east through the early evening hours, before a
relative lull through the overnight. Can't rule out a few showers
dropping in from the NW, so will leave small chances in through the
overnight. Look for lows in the upper 60s NE to low 70s SW.
Do expect to see isolated to widely scattered shower/storm activity
mainly confinded to our western County Warning Area roughly along the stalled
boundary that will be in place. Expect most highs to be in the upper
..Flash Flood Watch late Wednesday evening through early Friday...
As we enter later Wednesday afternoon and evening a slow moving
upper wave and associated surface low will move into the Mississippi
River valley and then lower Ohio River valley. As this occurs deeper
moisture will be transported in through a deep layer, particularly
of note will be a 40 knot low level jet. Precipitable water amounts
will range in the 2 - 2.5 range from late Wednesday night through
Thursday as the slow moving system moves through. Some areas will
likely see repeated rounds of heavy rainfall. During this time, 1.5
to 2 inches of rain is expected with locally higher amounts possible
across southern in and north central Kentucky. Given the meteorological
setup, recent heavy rainfall in spots, and a wpc slight risk of
excessive rainfall elected to issue a Flash Flood Watch in
coordination with jkl from later Wednesday evening through early
Friday morning across the northern two-thirds of the County Warning Area. At this
point, expect the heaviest axis of rain to fall along and on either
side of the I-64 corridor.
The system slides east by Thursday night with precipitation ending
from west to east. Flash Flood Watch is set to expire at 2 am EDT/1
Long term (friday through tuesday)...
issued at 325 PM EDT Tuesday Aug 4 2015
Middle level vorticity maximum will push on off to the east on Friday
and in its wake, a bit of middle-level ridging will build in from the
west. This should give US a temporary break from the rains from
midweek. However, this dry trend will not last all that long. The
latest forecasts suggest that a middle-level ridge axis will set back
up across Texas by the late part of the weekend and into early next
week. The upper level ridge is expected to be more flat, thus, the
Ohio Valley will remain on the periphery of the ridge axis setting
the stage for more unsettled weather as middle-level vorticity maxes round
the top of the ridge.
While forecast confidence is low regarding the timing of the waves
in the late part of the period, it does appear that several will
impact the region from late Saturday night through Tuesday. The
first may affect our region late Saturday night, followed by another
one on Monday. The pattern is one that favors one or more mesoscale
convective complexes developing and then racing from the Central
Plains through the Ohio Valley. It is really not all that
surprising given this pattern has been seen in recent weeks. The
threat of additional heavy rainfall is certainly there, and we may
see additional Hydro issues in some parts of the area early next
week, depending on where the eventual mesoscale convective system track sets up.
Temperatures will start off below normal for the period with low-middle
80s across the region on Friday. A brief moderation in temperatures looks
likely for Saturday and Sunday with highs in the middle 80s north and
middle-upper 80s in the south. Low to middle 80s look likely for Monday
and Tuesday as well, given that we're expecting clouds and
precipitation to be in the area. If convective coverage is less,
then temperatures may need to be increased slightly in subsequent
forecasts. Overnight lows during the period will be in the upper
60s to the lower 70s.
Aviation (18z taf update)...
issued at 124 PM EDT Tuesday Aug 4 2015
Conditions are expected to be mostly VFR the remainder of this
afternoon and evening with the exception that scattered storms could
impact the bwg terminal. Have the most confidence that storms will
develop across central Kentucky along a weak boundary, in between all 3
sites so will not mention any ts at this time.
Variable middle and upper clouds will steam over the area tonight,
helping to keep the fog theat lower. However, do expect to see at
least temporary visible restrictions around the VFR/MVFR range at times.
There may also continue to be periods of showers/storms moving over
the area toward dawn.
Winds will become light and variable after sunset this evening.
Kentucky...Flash Flood Watch from Wednesday evening through late Thursday
night for kyz023>043-045>049-053>057-063>067.
In...Flash Flood Watch from Wednesday evening through late Thursday
night for inz076>079-083-084-089>092.