Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 180129
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
929 PM EDT Fri Apr 17 2015
Issued at 925 PM EDT Fri Apr 18 2015
The forecast is largely on track this evening. Have updated mainly
to bring the forecast in line with current observations. Think the
only potential issue in the near term will be some fog development
tonight across southern KY. Guidance continues to suggest mainly
light fog development across southern KY towards Saturday morning.
Given skies look to clear out in the next few hours and dewpoints
still in the upper 50s/lower 60s there, have growing confidence
there will be some fog development. Some of this could be locally
dense, especially across the far southwestern CWA where dry air will
struggle to work in. Will highlight this potential in the HWO.
Otherwise, going forecast looks good.
.SHORT TERM (Now through Saturday Night)...
Issued at 310 PM EDT Fri Apr 17 2015
Pleasant weather more typical of late spring will prevail through
Saturday evening. The boundary layer is gradually drying from the
north as high pressure builds into the Great Lakes. This drying will
allow any remaining strato-cu to dissipate by early evening, and
dewpoints will continue to drop farther into the 50s. While
radiational cooling conditions are otherwise favorable, expect just
enough of a NE breeze across southern Indiana and north central
Kentucky to preclude fog formation, but we will include patchy fog
across south central Kentucky around daybreak Saturday.
The high to our north will be solidly in control Saturday into
Saturday evening, with plenty of sunshine and highs pushing 80.
Deepening SW flow ahead of an upper trof in the Plains and a surface
low developing over the Arklatex region will bring a quick increase
in moisture late Sat night. POPs will ramp up quickly after
midnight, with likely/categorical showers and storms by daybreak
.LONG TERM (Sunday through Friday)...
Issued at 300 PM EDT Fri Apr 17 2015
...Unsettled Weather Continuing into Early Next Week Before Drier
Conditions Finally Move in...
The synoptic pattern at the start of the long term period will
feature an amplified trough across the Central Plains, with
downstream ridging across the Ohio Valley. Two PV anomalies of note
will eject out of this trough Sunday into early Monday, each of
which will help induce surface lows and associated precipitation
across the Ohio Valley.
Sunday looks to start out rather wet. As mentioned above, a PV
anomaly will eject out of the parent trough to the west, helping to
induce a surface low across the mid-MS Valley by Sunday morning. In
response, isentropic ascent will increase and spread northeast along
with the deepening surface low Sunday morning into early Sunday
afternoon. This will lead to a widespread precip shield, likely
oriented northwest to southeast, that will spread across the Ohio
Valley. Within this precip shield, a few embedded thunderstorms
containing moderate to briefly heavy rainfall appear increasingly
likely. Given the overall forcing and good moisture transport, have
upped precip amounts a bit from the previous forecast. Think a
widespread half inch to an inch of rain looks possible with this
initial activity, which could lead to a few additional, minor
By late Sunday afternoon, the isentropic ascent will lift to the
north as a surface warm front slides north of the Ohio River. This
should place portions of KY within the warm sector, likely limiting
the coverage of showers/storms Sunday afternoon into Sunday evening,
especially across the southwestern CWA (near Bowling Green).
Therefore, will advertise highs approaching 80 on Sunday in these
locations, all depending on the amount of cloud cover that is able
to hang on.
By Sunday night, attention will turn to the west as yet another PV
anomaly ejects out of the main upper-level trough. This will induce
yet another surface cyclone across portions of Missouri, helping to
tighten an associated cold front over the MS Valley Sunday night.
This front will race into the Ohio Valley late Sunday night into
Monday morning, likely bringing renewed shower/thunderstorm
chances. There appears to be a pretty good threat of severe weather
further west with this activity, but it will be pushing through the
LMK CWA at an unfavorable time of day for a widespread severe threat
here. Nevertheless, can`t rule out a strong storm or two capable of
some strong, gusty winds especially west of I-65 with this activity
early Monday morning.
The precipitation chances will come to an end from west to east on
Monday as the front slides through. Will have to keep an eye on the
timing of the front Monday, as a slower solution may allow the
eastern CWA near the I-75 corridor to destabilize if it moves
through more into the afternoon hours.
Upper-level troughing will then remain in place through much of the
upcoming week, leading to cooler temperatures than we`ve seen as of
late. Highs each day will generally be in the 60s, with lows in the
40s. Some precipitation chances will arrive once again Wednesday
through Thursday of next week, but wide spread in guidance warrants
only slight chance mention at this time.
.AVIATION (00Z TAF Update)...
Updated at 650 PM EDT Fri Apr 17 2015
Generally VFR conditions are expected through the valid TAF period
except for a brief period of MVFR fog early Saturday morning at
KBWG. Any lingering low clouds will dissipate this evening, leaving
just some passing high clouds overnight. Drier air has worked into
KSDF and KLEX, but lingering moisture coupled with light winds may
lead to some fog development at KBWG early Saturday morning. Have
added a TEMPO group for low-end MVFR vsbys, but a brief period of
IFR vsbys is not out of the question.
Otherwise, Saturday will feature just some passing high clouds and
easterly winds at 6-10 knots. There may be a few diurnal cu around
FL040-FL050 in the afternoon, but otherwise a rather pleasant day
for those with aviation interests.