Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 190712
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
312 AM EDT Sat Jul 19 2014
.SHORT TERM (Now through Sunday)...
Issued at 250 AM EDT Sat Jul 19 2014
The synoptic pattern this morning is quite unusual for mid July, as
an amplified regime remains in place across the CONUS. This has
placed the Ohio Valley within a broad upper trough, which will begin
to weaken and slowly deamplify throughout the short term period.
The region remains in a general lull in shower activity early this
morning. However, a low-level jet continues to strengthen this
morning, with the nose of it edging into central TN as of this
writing. This region of isentropic ascent will continue to push
north/northeast through the early morning hours, helping to spread
the slug of precipitation across central TN into southern and
central KY this morning. The veering of this jet through the
morning hours will help keep the bulk of the precipitation along and
east of I-65, with the best coverage occurring near the I-75
corridor. Forecast soundings show very little potential for thunder
with this activity given weak mid-level lapse rates, thus have kept
it out of the forecast.
After these morning rains, conditions will begin to improve from
west to east through the afternoon. Think clouds will remain around
throughout much of the day (especially over toward the I-75
corridor), but forcing for precipitation looks quite nebulous by the
mid to late afternoon hours. Therefore, have reduced pops quite a
bit for this afternoon as drier mid-level air works in behind the
departing trough axis. With the clouds hanging around, have gone
quite cool across the Northern Bluegrass for high temperatures.
These areas may struggle to get out of the 60s in heavy cloud
cover. Further west across southern IN and north-central KY, some
peaks of sun appear more probable this afternoon, thus temperatures
in the upper 70s and lower 80s seem attainable.
A secondary trough axis will swing through the region late tonight
into Sunday. However, moisture will be less abundant with this
feature, thus think precipitation coverage will continue to remain
sparse (20-30 percent range) and mainly confined to areas east of
I-65. Forecast soundings show better potential for thunder on
Sunday, thus will continue with thunder mention in the forecast.
After lows in the low to mid 60s tonight, highs Sunday will rebound
into the low and mid 80s.
.LONG TERM (Sunday night through Friday)...
Issued at 310 AM EDT Sat Jul 19 2014
The main weather player for the first half of next week will be a
strong ridge over the western CONUS. Still questionable as to how
amplified this feature will get, and how strongly the ridge will be
able to nose eastward into the Ohio Valley. GFS is more bullish with
this hot and dusty pattern, while the 00Z run is the first time the
ECMWF has tried to pump up the heights east of the Mississippi. For
now will continue to carry diurnally driven 20-30 POPs mainly east
of I-65, and highs just getting into the lower 90s Tue-Wed. However,
if the latest model trends continue, that forecast may not be hot or
dry enough as extended GFS MOS pushes highs into the mid 90s.
By Wednesday night/Thursday, the longwave pattern will amplify with
a respectable trof being carved out over the eastern CONUS, and a
cold front diving SE through the Ohio Valley, providing our best
precip chances of the week. Mid-level flow picks up with this
system, so some organization to the convection is possible, but will
not play that up until the timing becomes more clear.
Confidence at the end of the week is a bit limited due to NW flow
aloft, but there is decent agreement on a surface high building down
through the western Great Lakes, and bringing in a modified Canadian
air mass with temps below normal and yet another break from
.AVIATION (06Z TAF Update)...
Issued at 100 AM EDT Sat Jul 19 2014
A rather complex TAF forecast in store as a rather unusual pattern
continues to remain in place across the Ohio Valley. An area of low
pressure continues to spin to the south of the region across
Mississippi, which has spread copious amounts of low-level moisture
into Kentucky. This moisture and incoming lift has resulted in MVFR
to IFR cigs along with associated MVFR/IFR vsbys in mist/light fog.
These restrictions will continue through the remainder of the
overnight hours into at least Saturday morning. Confidence in IFR
restrictions is highest at KLEX, as they will be in the better
low-level moisture axis. KSDF and KBWG will remain on the edge of
drier air to the west, but still think another slug of moisture
arriving towards dawn will keep conditions MVFR, possibly even IFR
at times in the heavier mist/light rain. Things will be slow to
improve through the day on Saturday, but KSDF and KBWG will be the
first to return to VFR as drier air finally works in from the west.
KLEX will likely remain at least MVFR throughout much of the day,
perhaps improving to VFR by the late afternoon hours. Winds through
the day will be generally light out of the east.