Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 192327
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
726 PM EDT SUN MAY 19 2013
...Updated Aviation Discussion...
Issued at 640 PM EDT Sun May 19 2013
After a few storms that produced quarter to golf ball size hail this
evening over central KY, storm strength is beginning to wane with
loss of day time heating and arrival of an upper ridge. Expect
storms in the Bluegrass region to diminish over the next hour or two.
.Short Term (Now - Monday Night)...
Issued at 300 PM EDT Sun May 19 2013
The upper low is currently shifting east of eastern Kentucky while
an upper-level ridge axis builds over western and central portions
of the state. The subsidence inversion associated with the ridge
will act to shut down rain chances and shift the greatest potential
east. There are some isolated showers trying to form along the warm
front in western Kentucky, southeast Illinois, and southwest
Indiana, but these are capped by the ridge aloft, have limited
vertical extent, and should not last long. Otherwise, isolated to
scattered showers and thunderstorms will have the best potential
across south-central Kentucky and northeastward through the Kentucky
Blue Grass. These will dissipate this evening with loss of heating
and loss of forcing from outflow boundaries associated with previous
The upper ridge will hold over the area keeping things dry tonight.
Expect a light southerly flow, which should keep temps mild. Lows
should only drop into the mid and upper 60s. Light winds should also
keep down fog potential, particularly locally dense fog.
Upper ridge axis will continue to hold through the day Monday. We
will see no rain, but much warmer and humid conditions. As mentioned
in the previous discussion, H85 temps jump to around 18 C with only
partly cloudy skies and breezy south-southwest winds. Temperatures
should top out in the mid and upper 80s. Louisville, the heat
island, will make a run at 90 degrees, which will be close to the
record of 91 (1934). The ridge axis will begin to shift east Monday
night. Latest suite of guidance indicates convection that develops
across the Middle Mississippi Valley Monday afternoon and evening
will approach our northwestern CWA late Monday night. This should
approach in a weakening state with it arriving late at night, plus
the upper ridge will still have some influence on the area. Clouds
will increase through the night, which should hold lows in the mid
and upper 60s, with some locations around 70.
.Long Term (Tuesday - Sunday)...
Issued at 319 PM EDT Sun May 19 2013
Overall, not much change in the long term as the multi-model
consensus continue to show good run to run continuity. Stacked
upper low over the southern Midwest is forecast to slowly drift
eastward into the southern Great Lakes before merging with a larger
upper level wave over SE Canada. Associated surface cyclone is
forecast to move from the northern Plains and into the the Great
Lakes while dragging a surface cold front through the Ohio Valley.
The models have started to converge on a singular solution here with
the frontal boundary passing through Wednesday night...with a
secondary frontal boundary passing through on Thursday evening.
Before this system gets here, we`re going to see a generally
summertime pattern here in the Ohio Valley. Fairly healthy high
pressure system over the western Atlantic working in tandem with the
low off to our northwest will result in continued southwesterly flow
into the Ohio Valley. This will result in well above normal
temperatures at the beginning of the period along with increasingly
humid conditions. Convection chances for Tuesday continue to look
more or less scattered at this point. Still not seeing a well
defined lifting mechanism here other than differential heating and
convective overturning. With deeper moisture and less capping over
the west/northwest sections, feel that convective coverage would
generally be more west of I-65 on Tuesday afternoon/evening. Model
proximity soundings still suggest a high instability/low shear
profile suggestive of pulse type multi-cellular convection with a
threat of damaging winds and perhaps some hail. Further east out
toward the I-75 corridor, a bit more capping is expected and thus
convective coverage looks to be less at this point. High Tuesday
will warm into the mid-upper 80s with overnight lows in the upper
By Wednesday, surface cold front will be moving in closer from the
west. Despite having a little stronger wind field coming into the
region along with better upper divergence, instability looks less on
Wednesday. This is due to more mid-high level cloud cover expected
due to convective debris moving in from the west. This would reduce
effective insolation during the afternoon. Nonetheless, strong
storms will be possible given the overall profiles with damaging
winds and large hail being the primary severe weather threats.
Convection will likely continue into Wednesday night and Thursday as
we wait for the secondary front to push through along with the upper
trough. So plan on keeping chance PoPs running through Thursday
night. Highs Wednesday will be in the upper 70s to the mid 80s with
overnight lows in mid-upper 60s.
With the secondary front pushing through Thursday night, we`ll see
drier and cooler air push in late in the period. The model
consensus has sped up the pattern progression here and it appears
that Friday and Saturday will remain dry and mild. Highs Fri/Sat
look to top out in the 70-75 degree range with overnight lows in the
As usual for the later period, model differences start to emerge by
Sunday as some of the new data suggests that the cold front from
Thursday will stall out over the southern US and then retreat back
northward into the Ohio/Tennessee Valley. This may serve as focus
for convective development as we head toward Memorial day. For now,
will introduce some slight chc PoPs for Sunday, but if the latest
Euro trends continue, higher precipitation chances will be warranted
in future forecasts.
.Aviation (00Z TAF Issuance)...
Issued at 725 PM EDT Sun May 19 2013
VFR conditions expected for this TAF period as upper level ridging
moves through the area. The only TAF concern will be the
possibility for some light br at LEX/BWG toward sunrise. Not
totally confident that this will happen though given the mixy winds
aloft. For consistency, will go ahead and leave a brief window for
MVFR vsbys at LEX/BWG tomorrow morning. Once any light br clears,
SSW winds will pick up tomorrow afternoon as the sfc pressure
gradient tightens with winds gusting into the 17-20 kt range at
BWG/SDF. LEX looks to be a little too far east to experience gusty
winds tomorrow afternoon although gradient winds should solidly
reach the 10-12 kt range with a few isld gusts possible.