Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 201100
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
600 AM EST Thu Nov 20 2014
...Updated Aviation Discussion...
.SHORT TERM (Now through Friday)...
Issued at 300 AM EST Thu Nov 20 2014
Another cool down today followed by moderating temperatures Friday
is the main weather story for the short term period.
Latest water vapor imagery overlaid with 500 mb heights shows a deep
upper level trough across the eastern CONUS with an embedded
shortwave moving through northern Illinois. A surface analysis
depicts that the cold front has almost cleared through the forecast
area, and extends from central Ohio, eastern Kentucky and down into
central Tennessee. Outside of an increase in cloud cover, the front
came through dry locally with scattered flurries confined to central
IN and OH.
For today, cold advection will win out and bring a fresh, but brief,
surge of unseasonably cold air. Temperatures are expected to top out
in the lower 30s across southern IN to the upper 30s across
south-central KY, giving the region another day of readings 20+
degrees below normal. As the aforementioned shortwave passes to our
north and combined with the colder air aloft and steepening lapse
rates, the widely scattered strato-cu deck upstream currently is
expected to fill in somewhat, giving way to partly cloudy skies
later this morning into the afternoon. This is mainly for southern
IN and northern KY.
Surface high pressure builds in this evening through Friday, which
will provide a period of lighter winds, mostly clear skies but still
unseasonably cool air. A good radiational cooling night is on tap,
so lowered minimum temperatures a couple degrees in the colder, more
sheltered locations. Plan on lows ranging from the teens across
southern IN to lower 20s across southern KY. For Friday, the
beginnings of our weekend warm up takes place as 850 mb temperatures
climb a few degrees compared to today. This results in highs in the
middle 30s to lower 40s.
.LONG TERM (Friday Night through Wednesday)...
Issued at 320 AM EST Thu Nov 20 2014
The long term period will begin with a chance for some light
freezing rain Fri night over portions of southeast Indiana to the
Bluegrass region of KY. Return flow will bring a light moisture
feed into the region Sat night as sfc high pressure moves off to the
east. Although there will be a good dry layer in place initially,
feel that some light precip may still be possible overnight. Temps
will actually be on the increase overnight Fri night as warmer air
in return flow enters the region. However, southeast Indiana and
the northern Bluegrass will likely remain below freezing and thus
the chance for some light freezing rain is possible mainly after
midnight through the pre-dawn hours. Will need to keep an eye on
this light but possibly troublesome precip event.
Saturday light rain will be possible mainly over southern IN and
along and north of the parkways in KY. Expect only scattered light
rain showers on Sat as the main low pressure system gets organized
over the southern CONUS. A potent warm front will lift north
through the region Sun bringing plentiful rains and the chance for
t-storms. Precipitable water values will rise to 1.3-1.4 inches
which is well above climatological normals for this time of year so
we can expect some soaking rains Sun. Wind fields are quite
impressive as well although instability is lacking. Still could see
some strong storms or showers containing strong, gusty winds. The
chance for showers/storms will continue Sun night/Mon as we sit in
the warm sector of the low pressure system. Precip coverage will be
much less Sun night/Mon compared to Sun during the day. The cold
front will pass through early Mon.
After relatively mild temps Sat/Sun/Mon (Highs 50s/60s), temps will
fall back below climatological normals by mid week with highs in the
upper 30s and 40s again. Tues night/Wed night lows look to dip
back into the upper 20s. Will keep the mid week forecast dry
although it should be noted that precip chances are likely to
re-appear by the end of the week. Long range models are very
different in handling the weather pattern over the CONUS for late
next week so will hold off any POPs at the very end of the long term
.AVIATION (12Z TAF Update)...
Updated at 555 AM EST Thu Nov 20 2014
VFR conditions expected at SDF/LEX/BWG through the period. Westerly
flow prevails at the TAF sites and will remain in place through the
day as high pressure across the central Plains builds east. A very
dry air mass upstream is keeping clouds more scattered and skies
are to expected to remain that way throughout the day. Daytime
mixing will lead to some near 20 kt gusts at SDF/LEX this
afternoon. Otherwise, as the core of the high builds overhead this
evening through the overnight, plan on light winds. By Friday,
winds will start to become southerly as the high moves east.