Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 261426
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
1026 AM EDT Tue May 26 2015
Updated 1026 AM EDT Tue May 26 2015
The forecast is on track this morning. Isolated severe threat
remains conditional for this afternoon. Thick cloud shield left over
from last night`s convection upstream is beginning to work into our
CWA. Still have another 1 to 3 hours of mostly sunny skies before
these clouds get along and east of I-65. This will allow for some
destabilization as we head into the afternoon hours.
Will have to watch for 2 separate areas of development. The first
would be in the MO Bootheel/western KY just ahead of a cold front
trailing from the Iowa surface low. The second could be development
in our clear area to the east as better forcing arrives around
midday. Its tough to imagine cold frontal storms getting too strong
as environment ahead will stay under heavy cloud cover.
Nevertheless, some of the hi-res models suggest they will. Can`t
rule this out as they will initiate in a stronger area of forcing
underneath the right entrance region of an upper impulse.
Have been keeping an eye on NAM forecast soundings as they continue
to hint at a fairly substantial subsidence inversion around 600 mb
this afternoon. This feature does not show up on GFS soundings,
which yield a more unstable atmospheric profile. Will monitor AMDAR
soundings through the late morning and afternoon, and if it develops
will back off on severe threat as updrafts would struggle above 15 K
.SHORT TERM (Now through Wednesday)...
Issued at 300 AM EDT Tue May 26 2015
...A Few Strong/Severe Storms Possible This Afternoon...
As of 3 am, water vapor imagery with 500 mb heights showed a ridge
centered off the GA/SC coast while a shortwave trough was lifting
northeast through the central Plains. At the surface, a weak area of
low pressure was noted near Kansas City while high pressure remained
off to the east. Moist southerly/southwesterly flow lied in between,
characterized by mild temperatures in the 70s and mid/upper 60
dewpoints. Winds were light and with some breaks in the clouds,
patchy fog was reported in a few locations across central Kentucky.
The surface low is expected to deepen as it lifts to central
Wisconsin this evening while the shortwave trough pivots into the
lower Great Lakes. Meanwhile, daytime heating of a moist boundary
layer across our area will likely result in modest instability this
afternoon. Forecast soundings and SREF probabilities indicate around
1500 J/kg this afternoon across south-central KY into southern
Indiana. The main dynamic forcing for ascent with this system is
expected to be focused to our north, however increasing southwest
flow in the mid-levels will result in about 30-35 kts of 0-6 km bulk
Expecting broken lines of thunderstorms in the western forecast area
to form late this morning or early this afternoon, gradually
intensifying as they lift northeastward. Main threat is strong to
damaging winds as a few bowing segments may develop. The bulk of the
activity looks to pass through between noon and 6/7pm. The higher
confidence for strong/severe storms is from central KY northward
into southern Indiana, tied closer to the more favorable dynamics.
Hi-res models such as the HRRR, NSSL and SPC WRF are in relative
agreement with storm mode/timing. Also, given the moist airmass in
place, heavy rainfall will be possible though storm motion is
expected to be fairly progressive.
Cloud cover and its affect on our destabilization is a concern as
there is significant debris clouds along the Gulf Coast region that
will likely push northward this morning. There are some signals in a
few forecast models that this could rob a lot of the instability, so
something to keep in mind.
Isolated/scattered showers/thunderstorms will remain possible later
this evening and tonight as another weak wave passes through. Patchy
light fog may develop as well in the favored areas, especially if
skies clear out and winds slacken off. Otherwise, plan on lows mid
60s to around 70.
For Wednesday, synoptic setup is less pronounced so overall storm
organization and coverage will be less than today. Nonetheless,
daytime heating and the moist airmass could generate some
thunderstorms, though warming at 850 mb may cap off convection. Kept
POPs in the 30-40 percent range, mainly in the afternoon hours.
.LONG TERM (Wednesday Night through Monday)...
Issued at 310 AM EDT Tue May 26 2015
Wednesday Night - Friday...
An upper level shortwave trough will pass through the region Wed
night bringing just enough forcing for showers/storms in our area.
Storms look to be mainly elevated Wed night with the better
convection mainly to our north.
Thu/Fri upper level ridging will build over the region resulting in
warmer temps and lower chances for convection but still not
completely dry. The better chances for showers/storms look to be
Friday with slightly better wind profiles. Convection both Thur/Fri
looks to be diurnally based with showers/storms mainly firing
during the afternoon/evening hours during or just beyond peak
heating. No organized severe wx threat looks likely for the Wed
Temperatures will ranging from the mid to upper 80s for highs to
mainly 60s for lows.
Saturday - Monday...
A more significant upper level shortwave trough looks to approach
the Midwest for the weekend and early next week. This trough and
associated sfc low pressure and fronts should provide a better focus
for convection for the weekend and early next week. Thus, felt
comfortable with POPs in the 40-60% range for Sat/Sun and 30-50% for
Mon. If a stronger upper level trough moves into the Midwest like
the GFS and GEM suggest, we may have better chances for organized
convection that could be on the strong side. If the sfc front
becomes elongated and stalled over the Ohio Valley like the ECMWF
suggests, we could receive multiple rounds of storms which could
lead to some minor flooding issues. Will wait and see which
solution the models converge on in the coming days before jumping on
any one soln.
With the upper trough in the area, temps should cool down some for
early next week. Highs Sat should still reach the low to mid 80s
with temps falling back into the mid 70s to low 80s for early next
.AVIATION (12Z TAF Update)...
Updated 630 AM EDT Tue May 26 2015
Focus is on thunderstorm chances and timing at SDF/LEX/BWG as a
weather system approaches the region today. South winds will be on
the increase later this morning with gradient winds gusting 20 to
near 25 kts. Showers/storms look to move in from the west by noon at
BWG, spreading east to SDF/LEX by early/mid afternoon. A few broken
lines of storms, some strong, look to pass through the terminals.
Convection likely to end west to east late afternoon to early
Winds will subside toward sunset and models are suggesting moist,
near saturated boundary layer sets up at SDF/LEX overnight. At this
time, there are favorable signals for MVFR ceilings, possibly lower.
Depending on how showers/storms evolve today, patchy fog could
develop as well tonight.