Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 171922
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
322 PM EDT FRI MAY 17 2013
.Short Term (Now - Saturday Night)...
Issued at 321 PM EDT Fri May 17 2013
Combination of satellite imagery and observations reveal an area of
surface low pressure over eastern AR/western TN with the upper low
spinning slowly into far western Kentucky. Out ahead of this
system, widespread cloud cover was noted over the region with a
large area of light to moderate rain across the southern half of
Kentucky. Given the widespread cloud cover and precipitation, lapse
rates are rather poor resulting in little, if any, instability.
Therefore, not expecting much in the way of thunderstorm development
across the region this afternoon...though can`t rule out a rumble of
thunder or two. We currently think the bulk of the thunderstorm
development will be just to our north along a line from near Cincy
to Indy and points northward. Temperatures were being modulated by
the cloud cover and precipitation. Readings ranged from the upper
60s to around 70 in the south with lower-middle 70s in the north.
For the remainder of the afternoon, expect widespread cloudiness to
continue. Band of widespread showers across southern Kentucky will
continue to slowly advect northward. Temperatures will not change
all that much over the next few hours with lower-middle 70s in
southern Indiana and northern Kentucky with upper 60s to around 70
in the south.
For tonight, the multi-model short term consensus is in pretty good
agreement with the upper low moving slowly across the middle Ohio
Valley. Associated surface low pressure will likely move across
southern TN overnight with the bulk of convection occurring just
ahead of this low. Shower activity across Kentucky and southern
Indiana will diminish after sunset due to the loss of daytime
heating. Isolated showers will probably continue overnight, but
widely isolated at best. With plenty of low-level moisture around
and winds becoming light as the upper low passes overhead, expect
another round of patchy dense fog to develop overnight. The fog
will be most dense in areas that received rainfall this afternoon.
In tonight`s case, the most widespread fog would probably be across
southern Kentucky. Lows tonight will remain mild with readings in
the 60-65 degree range.
On Saturday, the upper low will continue to slowly pull on to the
east. Combination of differential heating and a moist airmass will
likely result in scattered convection redeveloping during the late
morning and into the afternoon. At this juncture, it is difficult
to delineate an area at more risk for convective development. It
appears that convective coverage may be more favored over the east
which would be in closer proximity to the upper low feature. Severe
weather does not look likely at this point given the expected
widespread cloud cover and generally poor low-mid level lapse
rates. Any storm that does form will be capable of producing very
heavy rains...gusty winds and possibly some small hail. High
temperatures will warm into the mid-upper 70s.
By Saturday night, the upper level low should continue to move on
off to the east. We should see convection wane again with the loss
of heating. Thus, will keep higher PoPs in the forecast for the
evening and then let things diminish overnight. Patchy fog will be
a possibility again with lows in the 60-65 degree range.
.Long Term (Sunday - Friday)...
Issued at 300 PM EDT Fri May 17 2013
The upper low that moves over our forecast area Saturday should move
to the central Appalachians Sunday, with an upper level ridge axis
building in across western Kentucky. The upper low will still have
influence over eastern Kentucky, which includes portions of our
eastern CWA. Expect diurnally driven convection with afternoon
heating. High temperatures Sunday should range from the mid and
upper 70s in the eastern CWA to low and mid 80s in the west.
The upper ridge will strengthen over the Ohio Valley at the start of
the new work week. This will aid in capping the environment, which
will produce the best chance at mostly dry conditions Monday and
most of Tuesday. Tuesday will bring a return of scattered shower and
storm chances, but looks to be later in the day and mainly across
our northern forecast area, as a central CONUS trough approaches.
High temperatures Monday and Tuesday will be in the mid 80s, with
overnight lows ranging from the mid to upper 60s.
As the central CONUS trough slowly progresses eastward, a more
active weather period will take place midweek. A surface low will
track through the Great Lakes, and the trailing cold front will push
into our CWA. Numerous showers and storms will be possible ahead of
the front from late Tuesday night through Wednesday night. With
increasing speed shear expected with the stronger trough aloft, some
stronger storms are possible. High temperatures Wednesday and
Thursday will be a few degrees cooler, generally upper 70s to lower
80s with the additional cloud cover and rain.
Models are still having a difficult time deciding when that front
will push through the forecast area, but it appears to pass some
time during the day Thursday. This will keep scattered showers and
storms in the forecast for a little longer, but dry weather should
return Friday as the upper trough axis pushes east of the forecast
area. Temperatures should top out in the middle 70s Friday
.Aviation (18Z TAF Issuance)...
Issued at 110 PM EDT Fri May 17 2013
Upper level low pressure is forecast to slowly translate eastward
across the forecast area during the upcoming TAF period. This will
bring scattered showers and a chance of thunderstorms to the
terminals this afternoon and into the evening hours. This
afternoon, best chances of rain will be down at the KBWG terminal
where MVFR vsbys are expected as rain shield lifts out of
Tennessee. At KSDF and KLEX, more isolated-scattered showers will
be possible as the afternoon wears on. Several bans will translate
northward, so periods of rain showers will be possible at those
terminals. VFR conditions should prevail mostly at
KSDF/KLEX...though a very temporary drop to MVFR is possible as the
rain bands move through. Winds this afternoon will remain out of
the south at 5-10 knots.
Tonight, convection and shower activity will probably taper off due
to the loss of heating. With the upper level low moving over head,
expect winds to slacken off. With a rather moist profile in place
at the surface, probably will see clouds build down and fog
develop. There is an increasing likelihood of IFR vsbys and cigs
down at KBWG overnight after 18/05Z. Further north at KSDF and
KLEX, vsbys/cigs will probably drop down into the MVFR range after