Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 180108
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
907 PM EDT FRI MAY 17 2013
Issued at 905 PM EDT Fri May 17 2013
Tweaked grids toward current obs. Still have a fairly juicy airmass
in place with precipitable waters ranging from 1.4-1.6 inches, as
per latest SPC mesonanalysis. It will not take much for some light
rain/drizzle to come out of this airmass. Patchy fog will be an
issue as well, though no one location received lots of rain, as was
the case last night by this time. A look at the water vapor imagery
indicates some drier air working its way into the region by
daybreak. Have trimmed pops by daybreak over the west some in
response to this drier air. Updated products will be out shortly.
Issued at 535 PM EDT Fri May 17 2013
Pulled thunderstorm wording from the activity tonight. Not seeing
any lightning across our region this hour, and persistent cloud
cover has kept us from being able to generate anything more than
light rain showers. Areas to our north were able to warm up today,
and thus a nice band of storms developed across central IN/southwest
OH. Cannot rule out additional scattered activity through the night,
with the upper low moving right across us. Kept in patchy fog for
the night, given that more areas received rainfall today than
yesterday, albeit lighter totals.
.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 (00Z TAF Issuance)...
Issued at 715 PM EDT Fri May 17 2013
Upper low continues to bring extensive cloud cover and light rains
to our region. Those clouds this afternoon mainly have been VFR, but
with nightfall and a continued very moist airmass for mid May,
expect lower ceilings to develop. Cannot rule out continued showers,
but the threat for thunder still looks isolated enough to keep out
of the TAFs this go around. Latest high-res models show a push of
extra low-level moisture moving into KBWG late tonight, so have kept
in previous forecaster`s thinking of at least IFR cigs overnight. It
will take some time to lift those bases in the morning, and expect
additional showers to develop at the same time. Those chances should
fade with loss of heating Saturday afternoon.