Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 240719
Area Forecast Discussion
National Weather Service Louisville KY
319 AM EDT Fri Mar 24 2017
.Short Term (Through Saturday Night)...
Issued at 315 AM EDT Fri Mar 24 2017
Southerly gradient has set up over the Ohio Valley ahead of a deep
closed low currently nearing the OK/TX Panhandle. Steady south winds
overnight are holding temps solidly in the 50s in most locations,
and min temps have likely already been realized.
Unseasonably mild conditions will persist today and tonight, with
south winds a bit on the breezy side and thickening cloud cover.
With the warm start and continued warm air advection, most locations
should be able to get into the 70s.
Tonight the upper low will parallel the old Route 66 corridor out of
Oklahoma into southern Missouri, and the warm conveyor belt will
slowly edge eastward across Kentucky and Indiana. Could see a few
showers working into southern Indiana just before dawn on Saturday.
Look for precip to gradually overspread the area through the day on
Saturday, with categorical POPs on Saturday night with the strongest
low-level jetting overhead. Thunder chances will ramp up, but severe
potential is limited due to lack of instability in a nearly moist
adiabatic profile. SPC Marginal Risk does nose into south-central
Kentucky, mainly south and west of the Natcher Parkway where timing
is more favorable for a few strong storms. Saturday night will be
mainly a soaking rain, as decent winds just off the deck should
remain aloft in a fairly stable environment.
.Long Term (Sunday through Thursday)...
Issued at 300 AM EDT Fri Mar 24 2017
Upper pattern looks progressive through most of the week, with a
series of lows ejecting out of the Desert Southwest, and southeast
CONUS ridging to guide them ENE across the Ohio Valley. Therefore
expect mild but active weather to continue.
Pattern will be at its most amplified on Sunday, with a closed upper
low lifting NE from western Illinois into the Great Lakes. Main
southerly moisture surge will be to our east, but cyclonic curvature
in the flow and mid-level cold pool will support decent coverage of
showers. Best chances will be in the morning across the Bluegrass
region, where we are carrying likely POPs and tapering down to the
south and west.
Look for a brief break in the action Sunday night/Monday morning
before the next impulse swings through Monday afternoon and Monday
night. Decent instability with this system as CAPE cranks up to 1000-
1500 J/kg, and timing near the diurnal max will support a few strong
Beyond Monday forecast confidence is really limited by the
uncertainty of timing the parade of disturbances. And even where
shortwave ridging seems to be a good bet on Wednesday, models
disagree on where a decaying front will be. GFS hangs the boundary
up over the Ohio Valley while the ECMWF is more over the Tennessee
Valley. Will limit POPs for Wednesday and Thursday to the slight
chance range. Next bowling-ball upper low seems to be on track for
late in the week, but more likely will be beyond the 7-day forecast
at this time.
.Aviation (06Z TAF Update)...
Issued at 100 AM EDT Fri Mar 24 2017
AMDAR soundings within the past hour over SDF have revealed a 40-
45kt LLJ in the lowest few thousand feet of the atmosphere. Expect
the LLJ to strengthen to 50-55kts, and with winds at the surface
near 10-15kts, expect some LLWS for all TAF sites this morning. By
about 12z-13z, believe there will be enough mixing near the surface
to negate any LLWS mentioning in the TAF. Winds will be gusty out of
the south through the late morning and afternoon.
Model soundings (NAM/GFS/HRRR) show low level moisture increasing in
the 2500-3500ft region of the atmosphere by about 12z for all TAF
sites. If clouds/stratus do form, they will be borderline VFR/MVFR
criteria. For now, will keep forecast BKN/OVC ceilings just above
MVFR levels, but will be monitoring new model data and upstream obs
for signs that MVFR ceilings may develop.
Any low stratus that formed during the morning/afternoon should
begin to dissipate by late afternoon. Wind at the surface will also
begin to die down. Model soundings redevelop a 45kt LLJ tonight, and
with surface winds around 10kts, could potentially have some low-end
LLWS, though not enough to mention in the TAF at this time.