Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 270509
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
109 AM EDT Wed May 27 2015
...Updated Aviation Discussion...
Updated 910 PM EDT Tue May 26 2015
Convection has left the CWA, with only some stratiform rain left in
the northern Bluegrass. A few additional showers have recently
developed along the main wind shift across portions of southern IN.
Therefore, will leave in slight chance pops for the next few hours
to account for these. Don`t expect them to grow much further given
the weak convergence along the wind shift,growing mid-level
subsidence in the wake of the departing wave, and the loss of solar
Have decided to trend the forecast dry for the overnight period.
There does appear to be another PV anomaly approaching towards 12Z
Wednesday, but most of the hi-res guidance has trended drier with
this feature. While we can`t completely rule out a shower/storm,
think coverage will be less than 20% so will go with a dry
forecast. Given the clearing skies tonight, there could be some
patchy fog. However, winds should stay up just enough to there
should be some clouds streaming through from time to time which
should help limit the density and coverage of any fog.
Updated 618 PM EDT Tue May 26 2015
Storms continue to blossom along a weak surface trough out ahead of
a compact shortwave now sliding into eastern IL and western
IN. The highest concentration of storms will continue to be across
the Lake Cumberland region and the northern Bluegrass over the next
hour or so before all activity shifts east. The very low DCAPE
values (<500 J/kg) have likely resulted in these storms struggling
to put down severe wind given a lack of dry air through the low/mid
levels. However, still can`t rule out a stronger storm with winds
around 50mph over the next hour or so.
Otherwise, overnight will be mainly dry. There continues to be a
signal in the guidance members that some additional shower/storm
activity could reinvigorate tonight as yet another wave slides
through. Will revisit that potential in a later update this
evening, but will leave in 20-30% pops for now.
.SHORT TERM (Now through Wednesday Night)...
Issued at 311 PM EDT Tue May 26 2015
Widespread showers and scattered thunderstorms have developed this
afternoon ahead of a negatively tilted shortwave rotating up through
the mid Mississippi River Valley. Atmosphere is moderately unstable,
however mid level inversion evident on NAM soundings and verified by
AMDAR is limiting updrafts above 15-20 K feet. Mid level lapse rates
are expected to remain weak through the afternoon/evening.
Showers and storms will continue to lift NNE as the entire focus
shifts slowly east through the evening. Storms are already shutting
off from the west as a subtle front moves through the region and
subsidence behind the wave takes over. So, will hold onto
categorical pops east of I-65 through around sunset.
Expecting a pretty quiet overnight, although an isolated shower or
storm may scoot along and north of the I-64 corridor around and just
after Midnight. This would associated with another weaker PV anomaly
scooting through the flow. Expect lows in the mid and upper 60s as
SW winds stay up just a bit. There is some concern for fog potential
given the moist low level airmass and lighter winds. However,
stratocu deck has potential to develop which would be another
limitng factor. Overall, confidence is too low to include mention at
Wednesday morning should start out mostly dry with any isolated to
widely scattered showers (iso-storm) confinded to our far south and
east. Our NW half of the CWA should stay dry through the morning and
most of the afternoon, with partly cloudy skies and a steady SW
wind. With decent heating, expect temps to rise into the low and mid
By Wednesday afternoon, another disturbance passes through the SW
flow and should be able to initiate scattered to numerous storms
across our NW. Actually more impressed with isolated severe chances
across southern IN tomorrow afternoon as atmposphere should be more
unstable than today. Flow will still be weak, although just marginal
enough for perhaps some organization. This wouldn`t be a widespread
threat, but a few instances of gusty winds or hail seem possible.
Scattered showers and storms should hang around mainly across the
northern CWA through the Wednesday evening hours with lows in the
low and mid 60s.
.LONG TERM (Thursday through Tuesday)...
Issued at 310 PM EDT Tue May 26 2015
Wet. That`s all you need to know about the extended forecast. OK, if
not wet, then at least the chance of wet...for every 12-hour period
through day 7. I will concede that for Thursday night the precip
chances will only be down in the southeast part of our area (near
Lake Cumberland), but otherwise, the forecast is a broken record.
On the plus side, despite the persistent chance for rain, the chance
for excessive rain, and severe weather, for that matter, do not look
impressive. The overall upper air pattern through the period keeps
an elongated positively tilted trof to our west, but close enough
for the Ohio and Tennessee Valleys to receive showers or low-end
thunderstorms as short waves ride through to the north. There are
hints by the second half of the weekend into early next week of a
trof digging down into the southern Mississippi Valley. This could
give the area the best chance for significant convection, but this
far out, it is only worthy of mention.
Despite the persistent rain chances, the overall rainfall totals
expected for the entire week are only on the order of 1.5 to 2.5
inches, so no widespread river or flooding issues are anticipated.
Of course, the usual caveat of any individual storm being capable of
producing isolated heavy rains still applies. Probability-wise,
chances are only in the 30-50% range...not because it won`t occur,
but because when it rains, coverage will be spotty.
As far as temperature go, highs will be in the 80s through Saturday,
then in the upper 70s to lower 80s for the remainder of the period.
Lows will be in the 60s.
.AVIATION (06Z TAF Update)...
Updated 105 AM EDT Wed May 27 2015
Low clouds and light br may affect the TAF sites this morning in the
wake of showers/storms that moved through yesterday evening.
SDF/LEX are already showing hints at some low clouds developing.
Most of the model guidance keeps the thicker low clouds near LEX but
they can`t be ruled out at SDF either. BWG may see more of a break
in cloud cover early this morning resulting in better chances at
some light br. Overall think flight restrictions should stay in the
MVFR cat this morning, however, IFR can`t be ruled out.
Any restrictions should clear shortly after sunrise this morning
with another upper level disturbance bringing showers/storms this
Winds will be light SSW early this morning and more SW for the
daylight hours today. Winds may gust up to around 15-18 kts today.