Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 241711
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
111 PM EDT Sun May 24 2015
...Updated Aviation Discussion...
.SHORT TERM (Now through Monday)...
Issued at 245 AM EDT Sun May 24 2015
Early morning surface analysis showed high pressure centered off the
mid-Atlantic coast with a broad area of low pressure over west
Texas. Aloft, water vapor imagery combined with 500 mb heights
revealed weak ridging over the lower Ohio Valley with a closed low
over the central Rockies. Moist southwesterly flow lied in between,
mainly over the southern and central Plains.
For today, plan on seasonably warm conditions as the upper ridge
holds for one more day across the region. It will be a noticeably
windier day as well as southerly return flow asserts itself during
the late morning and afternoon hours. Sustained south winds 10 to 15
mph with gusts 20-25 mph at times are expected for a few hours this
afternoon. Otherwise, look for a mix of sun and high clouds and high
temperatures to top out in the low to mid 80s.
Dry weather is expected for most, if not all, of the forecast area
through this evening. Dewpoints will be on the increase today, but
the greater pool of moisture and CAPE will be positioned well west
of I-65. HRRR/RAP soundings and NSSL and SPC WRF reveal at most 300
to 500 J/kg developing this afternoon along the far western areas.
With weak/little forcing for ascent, expecting mainly dry conditions
though couldn`t rule out a stray shower or a thunderstorm later this
afternoon. As such, maintained slight chances west of I-65 but
confined the chances to a few hours this afternoon.
As the western trough advances slowly eastward tonight, more
debris/high clouds will spill overhead and combined with a mixed
boundary layer through the night, this should keep lows in the 65-70
degree range. LLJ / 850 mb moisture transport axis noses into
southwest Kentucky and southern Indiana toward dawn Monday morning
as a subtle shortwave trough aloft pivots through the flow.
Shower/storm chances will be on the rise after midnight west of I-65.
For Memorial Day, morning showers/storms will decay as the LLJ and
moisture transport wane. Questions and model uncertainity remain if
afternoon redevelopment will take place along/east of I-65. Model
soundings reveal a cap holding in place for much of the day and with
weak subsidence in the wake of the morning shortwave, coverage may
be limited. Kept POPS in the 40 percent range for the afternoon,
mainly across the Bluegrass region. High temperatures will be in the
upper 70s to low 80s, though with dewpoints into the 60s, it`ll feel
more muggy for those with outdoor plans/activities.
.LONG TERM (Monday Night through Saturday)...
Issued at 259 AM EDT Sun May 24 2015
Through Wednesday we`ll be on the eastern edge of brisk upper flow
from the southern Plains to the Great Lakes. A significant
shortwave trof will eject from the Red River Valley Monday evening
to the mid-Mississippi Valley by Tuesday evening. With a slightly
unstable and very moist (precipitable water 1.5 to 1.75) atmosphere
in place, showers and thunderstorms are a good bet with this system.
Locally heavy rain and gusty winds will be the main threats with any
Southerly winds will increase on Tuesday as the surface gradient
tightens between low pressure west of Chicago and high pressure off
the East Coast. Gusts of 20 to 25 mph will be possible in the
afternoon. These winds suggest a warm day on Tuesday, but that may
be tempered by clouds and showers. For now will go with upper 70s
and lower 80s for highs.
There`s slightly less moisture available on Wednesday, allowing for
a bit more sunshine and instability than Tuesday. Forcing for
convection should be weaker than on Tuesday, but a shallow upper
trof coming in from the west may help to spark scattered convection.
For the second half of the week the flow over the United States
becomes weaker as the country sits between strong jets over the
north Pacific and north Atlantic. Some weak ridging may try to
build over the Ohio Valley on Thursday as a broad trof moves through
the Rockies. Will hold onto a chance of showers/storms Thursday
given the moist unstable summery atmosphere, but will keep PoPs low.
By Friday and especially Saturday shower/thunderstorm chances will
increase as that Rockies trof edges eastward and a surface cold
front reaching from the Great Lakes to the Big Bend on Friday enters
the Ohio and mid-Mississippi Valleys Saturday.
While there are many mentions of showers and thunderstorms in the
forecast, it won`t be raining all the time. Rather, expect periods
of showers and storms with dry spells in between. Wednesday through
Friday the best chances for storms will probably be in the afternoon
hours. As of right now, it looks like the days with the best chance
of the most widespread rains will be Tuesday and Saturday. Of
course, that may change so keep watching the forecasts.
.AVIATION (18Z TAF Update)...
Updated at 110 PM EDT Sun May 24 2015
VFR conditions will prevail through today and tonight with Few-Sct
lower clouds and Sct-Bkn upper clouds increasing. Main concern for
this afternoon is the steady S winds between 10 and 20 mph, gusting
up around 25 mph at times. Gusts will die off later this evening,
however sustained winds will remain around 8-13 mph. A 45-50 knot
LLJ will increase over SDF/BWG through the overnight hours and
despite the steady surface wind, enough speed shear exists to
mention LLWS. This is strictly a speed shear component with any
directional component less than 20 degrees difference. LEX will be
east of the main LLJ core so will not mention.
Cloud cover increases overnight with a few showers around by dawn on
Monday. Gusty S winds will again be observed with increasing chances
for T-storms at SDF/BWG in the afternoon.