Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 170137
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
937 PM EDT Thu Apr 16 2015
Issued at 935 PM EDT Thu Apr 16 2015
A weak boundary was stretched out just to our north and west from
southern IL to south central IN. This boundary and associated
isentropic lift just to the south were providing enough forcing for
some spotty shower activity over southern IN/central KY. According
to the latest model data, expect this showery activity to continue
through the overnight hours although don`t expect it to be as
intense as earlier showers which put down up to 0.75 to 1 inch of
rainfall in remote locations. Did take out thunder chances
overnight and through the morning hours tomorrow as none has been
observed in this weakly forced environment.
Added patchy fog to the forecast for tonight into tomorrow morning
also as low level moisture is plentiful with a light wind profile.
The boundary is expected to sag south overnight closer to the Ohio
River and there is a good dense fog signal north of the boundary.
Will need to watch portions of southern IN overnight for development
of more extensive fog coverage and intensity. With cloud cover
currently in place though and uncertainty of southward progress of
the boundary, didn`t feel confident enough to mention any dense fog
at this time.
.SHORT TERM (Now through Friday Night)...
Issued at 305 PM EDT Thu Apr 16 2015
MCV and associated precip exited the region early this afternoon,
giving way to partial clearing in the subsidence that followed.
The atmosphere remains fairly juicy, especially in the low levels,
with precipitable water pushing 1.5 inches in parts of the area.
Surface pressure pattern is weak with plenty of residual boundaries,
and we are seeing isolated to scattered convection over western
Based on hi-res models, expect isolated/scattered showers and
possibly T-storms to push eastward into central Kentucky this
evening, but it remains uncertain how far east it will go. For that
reason will keep the wording as chance/slight chance, rather than in
terms of coverage as much of the area could remain dry.
Other concern tonight is fog potential, as the ground is saturated
and we`ll be close to crossover temperatures. However, expect enough
cloud cover to keep visibilities from dropping below 2 miles, so
will not mention it in public forecasts.
Mid-level dry air filters in from the NNW on Friday, which will
suppress the precip chances farther south. Will just carry slight
chance, mainly south of the Bluegrass Parkway. Skies will finally
clear out Friday night. Temps through the period will run solidly
above normal, especially tonight.
.LONG TERM (Saturday through Thursday)...
Issued at 310 PM EDT Thu Apr 16 2015
...Unsettled Weather Continuing Into Early Next Week...
The upper pattern will feature a closed low centered over Colorado
on Saturday, with an amplified ridge in place over the Ohio Valley.
The forecast looks pretty good for Saturday as the bulk of
precipitation and higher clouds hold off until later Saturday night.
Will mention a slight chance of showers across our far SW CWA late
Saturday afternoon and dry elsewhere. Temperatures are expected to
reach into the upper 70s under mostly sunny to partly cloudy skies.
Mid and upper clouds will overspread the area into the evening
Saturday Night - Monday...
As we move past Midnight Saturday night, the ridge axis will be
pushed east as the closed low center moves into the high Plains and
opens up. As this occurs, energy ejecting out of the base of the
trough will slide near our region with a surface low passing just to
our NW. The resultant low level jetting and moisture transport will
lead to widespread precipitation through the overnight hours into
Sunday. Some rumbles of thunder will also be possible given some
elevated instability. Overall, expecting between a half and 1 inch
of rain through Sunday. Expect overnight lows in the 58 to 63 range
with highs on Sunday in the low and mid 70s. The CWA should see a
lull in precipitation activity Sunday afternoon and evening before a
final wave moves through the mean trough and sparks scattered to
numerous showers and a few storms Sunday night into Monday. Overall,
1 to 2 inches of rain is reasonable through this time period which
could be enough to agitate ongoing flooding concerns.
Monday Night - Wednesday...
We`ll keep the forecast dry Monday night through Wednesday as
surface high pressure controls our region. However, we`ll be cooler
during this time under the influence of broad upper troughing. Highs
Tuesday/Wednesday should be in the 60s with lows each night in the
40s. Tuesday night will be more in the low and mid 40s with a cool
spot or two possibly dipping into the upper 30s.
Wednesday Night - Thursday...
Low confidence beyond Wednesday as the upper pattern is quite
complex and models are struggling with placement of key features. In
general, it appears we`ll stay in a relatively dry zonal or NW flow
aloft that should keep precipitation chances pretty low. However, a
weak frontal passage with some available moisture can`t be ruled
.AVIATION (00Z TAF Update)...
Updated at 735 PM EDT Thu Apr 16 2015
Some spotty showers will remain in the vicinity of the TAF sites
this evening as we sit on the south/warm side of a weak frontal
boundary this evening. With a plentiful supply of low level
moisture, think that some fog and low cigs are likely tonight. Due
to a slightly mixy lower atmosphere, think that low cigs will be the
main issue overnight. Feel confident that IFR cigs will occur at
all TAF sites between roughly 8-16Z. The latest model runs have
delayed low cig development but also keep the low cigs around longer
through the morning hours tomorrow. Given a lighter wind profile,
the later scouring out is probably more correct. Thus, have
adjusted the IFR time frame with this TAF issuance. It should be
noted that there is a strong signal in MOS guidance for LIFR/VLIFR
at BWG during the pre-dawn hours as well. May need to add an
additional TAF grouping for that if confidence is there at the 6Z
Southerly winds will decline this evening and generally remain light
and variable or light S-SW-W through much of the TAF period.