Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Louisville Kentucky
330 PM EDT Mon may 25 2015
Short term (now through Tuesday night)...
issued at 330 PM EDT Mon may 25 2015
Mostly cloudy conditions were noted across the forecast area this
afternoon. A mid-level wave was riding northeastward along the
western periphery of a mid-level ridge axis centered well to our
east. Area radars show a large area of rain extending from near
Bowling Green northeastward to near Frankfort. This area of rain
will continue to move off to the east/northeast during the remainder
of the afternoon. Areas west of I-65 in in and Kentucky are expected to
see drier conditions as we head into the evening hours.
Temperatures have remained on the cool side of the guidance envelope
in the west/central due to ongoing cloudiness. Afternoon readings
ranged from the upper 70s to near 80 in the I-75 corridor with upper
60s to the lower 70s in area out from I-65 and points west. There
may be a little bit of temp recovery in our central/west sections as
the rain shield shifts eastward.
For tonight, mid-level wave over US now will continue to trek off to
the northeast. This should result in a decrease in precipitation
this evening and into the overnight hours. A persistent southerly
flow will keep temperatures warm though, with overnight lows in the
mid-upper 60s. Mid-level wave currently over Texas will lift
northeastward late tonight and into the mid-Mississippi Valley
toward morning. This may result in some additional shower develop
late tonight over our far west/southwest sections. However, much of
the region looks to remain generally dry overnight.
For Tuesday, upper level wave will approach the region from the
southwest. This should allow precipitation to spread into western
Kentucky during the morning hours...especially in areas west of I-65. As
this system approaches, model forecast soundings for tomorrow
afternoon show a moderately unstable atmosphere with mixed layer
cape values in the 1700-2600 j/kg range. Wind profiles remain
rather strong (especially with strong speed shear in the mid-levels)
though not much low level speed/directional shear is forecast. With
the wave approaching, atmosphere looks to be a bit more favorable
for organized strong/severe convection tomorrow afternoon. Initial
thinking is that multi-cellular and multi-line convection will
likely develop in the afternoon in/around the I-65 corridor and then
push eastward. Overall profiles suggest a damaging wind threat with
these storms...especially in areas along/east of I-65. In addition
to the wind threat, heavy rainfall will be possible with any of the
Confidence in the development of severe convection is still a little
below average here due to the possibility of morning convection
disrupting the destabilization process for the afternoon. The
cloudiness also will make forecasting high temperatures a challenge
as well. Have leaned heavily on the multi-model consensus here with
highs in the low 80s in the east and upper 70s in the west.
Bulk of the convection is likely to push off to the east tomorrow
evening, but some additional scattered convection will be possible
overnight Tuesday/into Wednesday. Lows tomorrow night look to cool
into the mid-upper 60s.
Long term (wednesday through monday)...
issued at 315 PM EDT Mon may 25 2015
Wednesday - Wednesday night...
SW flow through a deep layer will be in place on Wednesday, with
scattered showers/storms ongoing across our eastern County Warning Area on Wednesday
morning. This precipitation will be ahead of a disturbance embedded
within the flow, and will leave a subsident airmass in their wake as
they diminish by late morning/midday. Expect a fairly quite early
and mid afternoon as the stable airmass then tries to destabilize
under increasingly less cloudy skies across the west. There is a
possibility of more scattered showers/storms then working into our
northwest County Warning Area late afternoon ahead of a weak cool front trailing from a
system moving into southeast Ontario. So in summary, expect scattered
convective coverage generally in our east in the morning, and
focused across our northwest in the late afternoon. The northwest should see more
sun through much of the day so will go with low 80s there, and upper
The weak cool front will wash out over our County Warning Area on Wednesday night
with scattered showers/storms slowly diminishing across the center
part of our County Warning Area. Expect lows in the mid 60s.
Thursday - Friday night...
Expecting less in the way of storm coverage Thursday through Friday
night as a southeast Continental U.S. Upper ridge becomes more established over the
Ohio River valley, and pushes the stronger westerlies north. This
will set the stage for an "early Summer-like" pattern where moderate
afternoon instability will give way to isolated to widely scattered
storms. Expect week flow through the atmospheric column, so nothing
organized during this time. Highs should be warmer given more peaks
at the sun, so calling for mid and upper 80s. Lows each night should
mostly range in the 65-70 range.
Saturday - Monday...
A stronger shortwave will move across the northern Great Lakes to
eastern Quebec on Saturday, helping to suppress the southeast Continental U.S. Ridge
over our region. This will allow the trailing cold front from the
aforementioned system to work into our County Warning Area and should provide
slightly better focus for convection. Main focus should be across
our northwest where sct-num coverage should exist. More widely scattered
coverage is expected east. Saturday won't be a washout as it will
take until the afternoon to kick off precipitation. So, expecting
temps to reach the mid 80s for highs.
The frontal boundary will still be in the region through the weekend
and into the first part of next week. Meanwhile, weak forcing for
ascent is anticipated ahead of a slowly ejecting Southern Plains
disturbance. So, will keep mainly diurnally driven chances going
during this period. This won't be a wash out, however several
chances for precip should present themselves mainly each
afternoon/evening and with any subtle disturbance causing local
mesoscale convergence sufficient to kick of showers/storms. Temps
will be dependent on position/orientation of the frontal boundary,
but should generally be in the upper 70s or lower 80s dependent on
which side you are on.
Overall, the threat for severe is expected to be pretty low through
the long term, although not zero. Early in the weak, instability
will be more plentiful so can't rule out a pulse storm or two. Later
in the weekend and into Monday, better (still marginal) deep layer
flow will be in place with less in the way of instability. Some
places may accumulate decent rainfall amounts if they see repeated
Aviation (18z taf update)...
updated 158 PM EDT Mon may 25 2015
Upper level vort maximum will continue to lift northeastward
along the western edge of an upper level ridge axis. This will
bring widespread showers and possibly a few thunderstorms to the
terminals this afternoon and evening. Ceilings will likely remain
generally VFR, but will likely drop to MVFR in passing
showers/storms. South to southwesterly winds of 10-15 knots are
expected with wind gusts of 20-25 knots being possible.
Convection looks to taper off from west to east this evening, so
feel that ksdf and kbwg should break out of the precipitation later
this evening with Lexington seeing precipitation ending by late
evening. More convective development is expected later tonight as
another wave currently over Texas heads northeastward to our area.