NWS Louisville, KY wrote its last area forecast discussion before the first event at Apr 27, 1:19 PM CST, 1 hour 41 minutes earlier.
Area forecast discussion, Apr 27, 1:19 PM CST, 1 hour 41 minutes before
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
319 PM EDT Sun Apr 27 2014
.SHORT TERM (Now through Monday Night)...
Issued at 310 PM EDT Sun Apr 27 2014
...Severe Weather Possible Monday Afternoon into Monday Evening...
The synoptic pattern this afternoon features a potent cutoff
upper-level low across the central CONUS. Strong PV anomalies and
associated jet maxes continue to round this trough, ejecting out
towards the Ohio Valley through the short term period. These
disturbances will bring several rounds of showers and thunderstorms
to the region, some of which could turn severe mainly Monday
afternoon and evening.
Convection continues to develop across portions of western KY and TN
this afternoon. Much of this is developing along a weak pseduo warm
front, seemingly enhanced by a differential heating zone from the
cloud shield associated with the convection across AR/TN.
Thunderstorms will continue to erupt this afternoon along this
feature, slowly spreading northeast this evening. Despite rather
meager effective shear values (around 20 to 25 knots), some of these
storms could become strong late this afternoon, with small hail and
gusty winds being the primary threats. This threat will be confined
mainly to areas along and west of I-65, where MLCAPE values of 1000+
J/kg will be co-located with better kinematics.
The forecast becomes a bit murkier as we head into tonight and
Monday. Hi-res guidance has struggled today with the convection to
our west and southwest, and each solution depicts a slightly
different picture as to what will happen over the next 24-36 hours.
Therefore, will rely more on synoptic details with this forecast, as
the mesoscale details will be tough to ascertain at this timeframe.
The first PV anomaly and slug of isentropic ascent will lift
northeast through the region this evening. Subsidence in its wake
should help to limit coverage of convection from about 3-9Z
tonight. However, a low-level jet of 45-50 knots will ramp up
tonight in response to the strong PV anomaly ejecting out of the
parent trough. This should result in widespread convection
developing out to the west across MO/AR and western KY tonight which
will push into central KY in the late overnight hours. This
activity looks as if it will outrun the best instability axis, and
forecast soundings depict a low-level inversion setting in, which
should help keep the stronger winds elevated. Nonetheless, a few
cases of gusty winds will be possible, especially if this system can
develop and maintain a strong cold pool tonight as it pushes in from
the west.
The evolution of the Monday morning convection will ultimately play
into the severe potential Monday afternoon and evening. However,
the latest guidance depicts that the morning convection will move
through quickly enough to allow for some airmass recovery in the
afternoon hours. The GFS/EURO are the more robust with this
recovery, painting anywhere from 1000-1500 J/kg of MLCAPE by Monday
afternoon. The NAM is not so optimistic. Will side more with the
GFS/EURO with this forecast, which keeps the threat for severe
weather in play across the region. Convection looks as if it will
develop prefrontally, possibly along a pre-frontal trough or remnant
outflow boundary across portions of west-central KY northward
through southern IN. Initial convection could be semi-discrete, but
a veer-back-veer wind profile will tend to favor a messy storm
mode. Nonetheless, it appears as if convection will become more
linear by Monday evening, as the LLJ intensifies and 0-6km shear
vectors back and become more parallel to the forcing. The main
threats with this convection will be large hail and damaging winds,
along with isolated tornadoes, especially across southern KY where
the better low-level wind fields will be co-located with better
instability (and better potential for supercell storm mode).
The main threat will transition to heavy rainfall Monday evening
into Monday night, especially across east-central KY where the nose
of a LLJ will be located. Guidance is hinting at the potential for
storms to train across this area within this regime, which could
bring heavy rainfall to portions of the region. Given the continued
uncertainty on just how convection tomorrow into tomorrow night will
play out, will just continue with an ESF for now, and not go with
any flash flood headlines. However, do have storm total QPF values
(today through Tuesday night) in the 2-3 inch range, with local
amounts in excess of 4 inches possible. This will likely cause at
least some minor flooding issues across the region.
As a final note, the exact evolution of this system remains rather
uncertain, even within this short timeframe. Monday has a
conditional potential to bring some significant severe weather to
portions of the region, but uncertainties regarding the morning
convection and the exact evolution of convection to our south remain
in place. Therefore, continue to monitor the latest forecasts
closely as the event draws closer in time.
.LONG TERM (Tuesday through Sunday)...
Issued at 242 PM EDT Sun Apr 27 2014
...Severe Weather Possible Tuesday Late Afternoon/Evening...
As an upper low circulates above Iowa a vort max is expected to
eject out of the Red River Valley and into the Tennessee and Ohio
Valleys by Tuesday evening. Meanwhile, surface low pressure
advancing from Kansas City to Chicago will sweep a cold front into
the middle and lower Mississippi Valley. Thunderstorms are expected
to develop just west of the Mississippi River by late morning and
move through central Kentucky and southern Indiana during the
afternoon and evening hours...moving off to the east overnight.
While widespread convection to our south will steal some of our
thunder, strong to severe storms still appear possible here,
especially east of I-65 in Kentucky from late afternoon into the
evening. If the Monday night storms move off to the east as early
as currently expected, it appears Tuesday morning should be mostly
dry. RH cross-sections suggest that we could actually get a fair
amount of sunshine as well. By evening we'll be unstable as the
upper disturbance and surface front approach from the west, combined
with upper level divergence and increasing shear. Temperature
profiles support the idea of hail in the stronger storms. The best
chance of a weak short-lived tornado still appears to be in the Lake
Cumberland region during the evening hours.
Though locally heavy rains within thunderstorms are certainly
possible, widespread heavy rain appears unlikely on Tuesday at this
time. Precipitable water values only get up to around 1.2 inches,
which is just slightly above normal for this time of year. The K
Index only briefly peaks in the lower and middle 30s. The storms
will be moving rapidly to the northeast...though some training will
be possible. Moisture is much deeper to our south.
Will go with high temperatures on Tuesday in the middle and upper
70s, though that will be highly dependent on cloud cover and the
presence/absence of any storms.
Wednesday through Thursday the upper low will wander around the
Great Lakes, and then get absorbed into a larger trof digging down
out of eastern Canada Friday through Sunday. These features and
occasional embedded waves will necessitate keeping the possibility
of showers in the forecast into the weekend. However it's important
to note that any showers will be very light and widely scattered,
with low PoPs in the forecast. No wash-outs are expected. As a
matter of fact, it should be a fairly pleasant week with afternoon
temperatures in the 60s. Admittedly, mornings will be on the cool
side for early May with lows in the 40s.
&&
.AVIATION (18Z TAF Update)...
Issued at 119 PM EDT Sun Apr 27 2014
A rather complex TAF period is in store as multiple rounds of
convection look to affect TAF sites, along with a marginal LLWS
setup tonight. Current radar imagery shows scattered storms
developing across portions of TN and western KY. These storms will
continue to develop northeast through the afternoon hours.
Confidence in storm coverage is highest at KBWG, with decreasing
confidence at KSDF and KLEX. Any terminal that does get a storm
could see briefly reduced cigs/vsbys, perhaps to IFR in the heavier
precipitation.
Otherwise, storms should diminish a bit in coverage late this
evening as the first wave pushes northeast. A low-level jet will
ramp up to the west and slide into the Ohio Valley overnight,
helping to bring renewed showers and thunderstorms into the region.
This low-level jet will produce a marginal LLWS setup, but think
surface winds will likely stay up a bit (perhaps even more than
currently forecasted), which should limit impacts. Again,
cigs/vsbys will likely drop in the heavier convection.
Precipitation will again diminish by mid-morning Monday, setting the
stage for another round of convection to develop in the afternoon,
possibly affecting KSDF during the planning period. Winds on Monday
will be considerably stronger than today, with sustained southerly
winds at 13-18 knots, with gusts of 20-25 knots.
&&
.LMK WATCHES/WARNINGS/ADVISORIES...
KY...NONE.
IN...NONE.
&&
Short Term........KJD
Long Term.........13
Aviation..........KJD