Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 020712
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
312 AM EDT Tue Sep 2 2014
.SHORT TERM (Now through Wednesday)...
Issued at 305 AM EDT Tue Sep 2 2014
A tricky forecast for the next 18 to 24 hours as the remains of a
convective complex roll into the area, and ultimately decide what
type of weather we see later this afternoon and evening.
Current radar imagery shows a convective complex that has developed
ahead of a shortwave over the eastern Plains. Clusters of strong
storms stretch from SE Kansas up through west central Indiana at
this hour, with a heavy rain threat also in play. The storms are
staying somewhat organized in an environment characterized by MU
CAPE values in the 2000-3000 J/kg range, and 0-6 km bulk shear
values in the 40-45 knot range. The environment over our CWA is less
conducive from an instability standpoint, however the corridor over
stronger deep shear layer values (35-40 knots) will slide across
southern Indiana and north central KY through the late morning. As a
result, expect scattered to numerous showers and a few rumbles of
thunder from the decaying complex to slide across our north around
dawn through mid morning. Some scattered showers may develop with
the nose of a LLJ lifting northeastward after 4 am across our north
Expect a relative lull in action from the late morning to the early
afternoon as morning activity dies and pushes east. However, by mid
afternoon concern for redevelopment along the remnant
outflow/differential heating boundary comes into play. This would most
likely occur east of the I-65 corridor where best instability on the
order of 1000-2000 J/kg of SB CAPE will line up with 0-6 km shear
values around 30-35 knots. Redevelopment of storms will be
conditional upon the morning convection. Given help from a mid level
wave passing through the mean H5 flow, do feel we`ll see the
redevelopment and a few multicell clusters capable of gusty winds
are possible. SPC has continued the low-end slight risk for eastern
portions of our CWA to account for this. Will mention potential for
a few strong storms and gusty winds in the HWO, but overall won`t
play today`s severe scenario up too much due to the conditional
nature and small time window for severe to occur. Look for highs
only topping out in the low and mid 80s.
Convective activity should quickly diminish around sunset as mid
level support exits to the east and we lose daytime heating. Will
keep some lingering small Pops across our south and east until the
early morning hours. Otherwise, expect surface high pressure
building in behind the system and skies becoming mostly clear across
the northern half of the CWA. This will allow lows in the upper 60s
north to around 70 south.
Wednesday should be mostly dry with surface high pressure in control
and only a small chance of diurnally driven convective development
across our south nearer the remnant boundary. Temperatures should be
slightly warmer with highs more solidly in the mid to upper 80s.
.LONG TERM (Wednesday Night through Monday)...
Issued at 305 AM EDT Tue Sep 2 2014
Overall model agreement is present in extended range models through
this coming weekend. Persistent mid-level ridge will remain anchored
over the southern third of the U.S. for the second half of this
week, with the ridge poking northward across the Tennessee and lower
Ohio Valleys. Then as stronger mid-level flow pushes east and
southeast over the Great Lakes this weekend, a decent cool front
will move southeast through central Kentucky and southern Indiana
bringing lower humidity and cooler air temperatures for late in the
weekend into early next week.
In the day to day weather, the extended period should start off dry
Wednesday night as surface high pressure overhead slides to the
east. Models hint that some dying scattered convection could
approach western parts of our area late Wednesday night associated
with weak warm advection on the back side of the high, but will keep
dry conditions in forecast. As better low-level moisture and higher
surface dewpoints return Thursday, isolated to scattered diurnal
convection is expected in the afternoon, with best chance north on
the periphery of the upper ridge. Highs Thursday will reach the
upper 80s and lower 90s.
Any cells Thursday should weaken Thursday night given limited or no
forcing and nocturnal cooling. Then on Friday, scattered diurnal
convection should again develop with the best chance north half
again, aided by the approaching cool front from the north. With
soundings suggesting rather steep low- and mid-level lapse rates and
lack of saturation, any storms that form in this environment would
be pulse cells capable of gusty downdrafts and a decent amount of
Scattered to perhaps numerous showers and thunderstorms will
accompany the front as it drops southeastward across Kentucky on
Saturday. The combination of clouds and showers will keep
temperatures lower on Saturday - around 80 in southern Indiana and
mid 80s in south-central Kentucky. The front will push though the
state Saturday night. Precipitation will sag southeast Saturday
night as well and be through much of our forecast area on Sunday,
although a few showers could linger over southern and eastern
counties of central Kentucky. Dry weather then takes hold Sunday
night and early next week.
The air behind the front will be cooler with max temperatures Sunday
into early next week a couple or few degrees below normal, mainly
from the upper 70s (southern Indiana on Sunday) to lower 80s over
much of the area into early next week, with some mid 80s over
south-central Kentucky by early next week. Lows will be in the 60s
Sunday morning through Tuesday morning, with some 50s expected
Monday morning. Dewpoints and humidity levels will drop as well
behind the front.
However, looks like the humidity and higher dewpoints will once
again rise by mid next week as another weather system approaches at
that time imports warmer, more moist air from the south into
.AVIATION (06Z TAF Update)...
Issued at 105 AM EDT Tue Sep 2 2014
VFR conditions will prevail at the TAF sites through the majority of
the remaining overnight hours, with a steady SSW wind between 5
and 10 mph. Upper level clouds will overspread the area ahead of an
approaching convective complex, along with a few lower level clouds.
A convective complex has developed across central IL southwestward
through southern Missouri ahead of several mid level disturbances.
Meanwhile, a weakly defined warm front was draped across central KY
between BWG and SDF. This feature will lift northward toward dawn
with isolated to scattered showers developing along it after 4 AM
EDT. Included VCSH mention at SDF/LEX through mid morning, with
potential to briefly go MVFR in a rain shower. There should be a
lull after the initial morning precipitation chances, then
convection is expected to fire in the early afternoon along the
remnant outflow/differential heating. This is expected to be between
SDF/LEX, although some thunderstorms could be around all terminals
through the afternoon and early evening. Expect convection to die
around sunset with some lingering clouds.
Winds will gradually veer to SW and then WSW through the day,
staying up around 10 mph. Once winds slacken late this evening, they
will return to SSW.