Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 020744
Area Forecast Discussion
National Weather Service Louisville KY
244 AM EST WED DEC 2 2015
.SHORT TERM (Now through Wednesday Night)...
Issued at 240 AM EST Wed Dec 2 2015
Main forecast challenges in the short term are fog this morning and
precipitation chances later this afternoon and evening.
As of 3 am, water vapor imagery with 500 mb heights showed a deep
anomalous closed upper low over La Crosse, WI while southwest flow
ahead of that feature continues to pull high level moisture into the
lower Ohio Valley. IR imagery showed high clouds over the forecast
area though the light/variable surface winds have allowed pockets of
fog, some locally dense, to develop. Readings were mainly in the 40s
with some 30s reported across portions of southern Indiana where
clouds have cleared some.
For this morning, fog/stratus pockets will continue in the favored
valley regions until a few hours after sunrise. Some locally dense
fog will be possible, though the high clouds should temper that
somewhat. Will have to watch for any expansion of fog, especially
where clouds clear but so far slight dry air advecting in from the
northwest is keep things in check.
The deep upper low will pivot 2 PV anomalies into the region today,
one this afternoon then a second by evening. Warm advection ahead of
the first wave should allow readings to rise into the 40s to low 50s
(southeast KY). The second wave will have better moisture and
forcing as it swings through southern Indiana and northern Kentucky
between 6p and midnight. Steep low-level lapse rates thanks to
falling temps aloft should briefly intersect the deeper moisture to
allow isolated to scattered showers to develop. Precipitation should
be mainly liquid but as evaporative cooling and surface temps cool
further, some pockets of rain/snow/graupel is possible. This would
be mainly for southern Indiana and far northern Kentucky (north of I-
64), including parts of the Bluegrass region. Hi-res models are in
reasonable agreement showing a few broken lines of precipitation
swinging through during the late afternoon to mid-evening hours. No
impacts are expected though a quick wet dusting on rooftops or
grassy surfaces could be possible, in the extreme northern
forecast area, where forcing/moisture will be the greatest.
It will also be blustery with wind gusts in the 20 to 30 mph range.
South of I-64, plan on a dry frontal passage but still some gusty
winds at times. Lows Wednesday night 28-32.
.LONG TERM (Thursday through Tuesday)...
Issued at 220 AM EST Wed Dec 2 2015
The weather pattern over the lower Ohio Valley will favor moderating
temperatures and dry weather Thursday through Sunday. Expect
Thursday to be the coolest of the period with highs in the mid 40s.
As the surface high advances eastward and southerly flow returns, a
slow warming trend will take place into this upcoming weekend,
pushing highs back into the 50s Saturday and Sunday. Overnight lows
will be coolest Friday morning as high pressure looks to be directly
overhead. Plan on readings in the mid/upper 20s to around 30
Forecast guidance still suggests another cut-off low coming out of
the southern/southwest US then lifting toward the region late Sunday
night into Monday. Timing details are below average but rain
chances look to return to the area, especially south of KY
parkways as early as Monday, potentially lingering into Tuesday.
.AVIATION (06Z TAF Update)...
Updated at 1225 AM EST Wed Dec 2 2015
A complex TAF forecast will keep periods of MVFR and even IFR at LEX
possible over the next 24-30 hrs. All TAF sites are currently at
VFR levels but should drop to MVFR during the pre-dawn hours due to
low clouds and light br. Around and after sunrise, some model
guidance and soundings indicate LEX could drop to IFR briefly but
not as confident with that forecast so put in an IFR tempo between
11-15Z for LEX. SW winds will turn gusty for late morning and
through the evening hrs with a cloud deck bordering VFR/MVFR at
SDF/LEX for much of the day. A vort max swing through the base of
an upper low will bring a chance for light rain or snow showers at
SDF/LEX this evening and conditions should drop back into MVFR. BWG
should stay too far south to experience any light precip or cigs