Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 181528
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
1128 AM EDT Mon May 18 2015
Updated 1126 AM EDT Mon May 18 2015
A large area of light rain continues to slowly work its way east
across the region late this morning. This will slowly shift east of
the area this afternoon. Behind this scattered showers and storms
will move in. These storms will continue through the afternoon and
early evening hours. A few showers or possibly storms will be
possible along the cold front as it moves through tonight. However,
widespread precipitation is not expected. The forecast was updated
to reflect current radar trends and the latest thinking for pops
this afternoon and evening.
.SHORT TERM (Now through Tuesday)...
Issued at 314 AM EDT Mon May 18 2015
Conditions are fairly quiet across the CWA at this hour. A batch of
light showers is now moving into our western CWA, although
continuing to weaken as it does so. Otherwise, temperatures are
mostly running in the upper 60s to around 70.
The upper Midwest system will move across Lake Superior today, with
the trailing cold front slowly sagging toward the Ohio River Valley
by later this evening. The upper ridge axis that is currently
situated roughly along the Appalachian spine will shift east to the
Atlantic seaboard in response to the aforementioned trough to our
NW. As a result, our upper flow will transition to a more WSW
orientation. We`ll continue to see deep moisture transport over the
region under this setup, along with a couple of disturbances moving
across our region. This will allow for scattered to numerous
shower/storm chances in the forecast today.
The first disturbance is currently sitting over the lower
Mississippi River Valley with a nice batch of showers and storms
ahead of it beginning to move into SW Tennessee. This convection
should begin to impact our SW CWA around or just after daybreak,
then move NE across our CWA through early to mid afternoon. Expect
50-70% coverage with round 1.
While round 1 is exiting our CWA, round 2 will be getting organized
ahead of a SW to NE oriented disturbance ahead of the front. Given
the subsidence behind round 1 and a generally weaker round 2
disturbance, think coverage will be more widely scattered side
through early evening.
A final round of potential convection then looks to develop along
the actual cold front through the late evening hours. Most of this
activity should be upstream of our CWA, however isolated coverage
may survive into our NW and W CWA before the loss of heating
diminishes coverage. So, bottom line is that round 1 should be the
best coverage, with the last round yielding little to no coverage
and confined to our far W/NW.
Atmosphere does not look quite as unstable as it was yesterday
(~1000-1500 J/KG CAPE), and it looks like we will be dealing with
that subsidence inversion around 600mb once again like we saw
yesterday. A few strong storms can`t be ruled out, especially
through early afternoon before that inversion really takes hold and
strongest triggering will be in place. After all, it does appear we
have up to 30 knots of deep layer shear in place at times which
would be marginally sufficient for a few multicell clusters. For the
most part though, updrafts should struggle once they get above 15 K
feet. Main threat is still expected to be locally heavy rain as
PWATs remain north of 1.6 inches through the column.
After convection dies off along the front later tonight, expecting a
pretty quiet overnight. Although, will still at least carry 20%
chance until the front actually passes. Temps will drop off by dawn
on Tuesday with readings down to the upper 50s NW and low 60s SE.
Tuesday will be a dry day, minus 20% shower chance around Lake
Cumberland through midday. Skies will be mostly sunny with temps
only around 70 NW to the mid 70s SE.
.LONG TERM (Tuesday Night through Sunday)...
Issued at 245 AM EDT Mon May 18 2015
Mainly a quiet and cool pattern for the upcoming week. Zonal pattern
aloft with Canadian high pressure at the surface will keep temps
solidly below normal Tuesday night and Wednesday.
Just one precip chance for the rest of the work week, as an
upper-level disturbance crossing the Plains tries to draw moisture
northward into the Ohio Valley before weakening. NAM solution came
in substantially faster and wetter than previous runs, but that
combination doesn`t make much sense as available moisture will have
a hard time recovering. However, there is enough consensus among the
models to warrant a chance POP for Wednesday night, but QPF will be
quite low as the upper forcing gets sheared out and there just isn`t
that much moisture or instability in place.
Zonal flow aloft continues into the weekend, and we`ll see temps
recover to near climo by Saturday as low-level return flow starts to
develop. We`ll see a return of the early summer humidity and
unsettled weather on Sunday as the pattern starts to amplify and
moist SW flow over the Ohio Valley deepens. Will carry chance POP at
this time, and not jump on a particular solution too early.
.AVIATION (12Z TAF Update)...
Updated at 645 AM EDT Mon May 18 2015
An expansive cluster of showers and t-storms is beginning to work
its way into BWG, and will be ongoing at the start of the new
forecast cycle. Will forecast prevailing 5SM in -SHRA, with a TEMPO
for -TSRA and low MVFR visibilities. Ceilings should mostly stay
just above the MVFR/VFR threshold. Best timing for the morning
showers and storms will be between 7 AM CDT and 11 AM CDT.
The same complex is expected to affect SDF between 10 AM and 2 PM
EDT, and at LEX between 11 AM and 3 PM EDT. Will forecast the same
prevailing and TEMPO conditions as at BWG.
After the morning and early afternoon showers/storms, expect brief
lull before another round of more widely scattered showers/storms.
Will only mention VCTS for now and will update if confidence becomes
higher in a terminal being impacted. Best timing for round 2 will be
around 5 PM CDT at BWG, 5 PM EDT at SDF, and 7 PM EDT at LEX.
Isolated showers may develop along a cold front to the NW of the TAF
sites as we move into the late evening, however expect these to
diminish before arriving. So, will go with a wind shift to NW and
gradually clearing skies through the overnight.