Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 250959
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
459 AM EST Thu Dec 25 2014
Issued at 500 AM EST Thu Dec 25 2014
88D showing some light returns areawide, with reports of drizzle as
they go over various automated sites. Have expanded the drizzle in
the grids for the whole area for a few more hours.
.SHORT TERM (Now through Friday)...
Issued at 245 AM EST Thu Dec 25 2014
Relatively quiet weather period for the end of this Christmas work
week. We should see some sunshine this afternoon. Model time height
sections insist that the layer under a strong subsidence inversion
at 900 mb will dry out as a bubble of lower precipitable water air
moves over us. Temperatures will end up near normal for highs.
Despite the clearing skies, a steady southerly wind overnight should
keep us from bottoming out too much, with lows in the lower 30s, a
little above normal. Dewpoints will be up a little overnight, and
may lead to some patches of fog. The best chance, according to the
LVORI (low visibility risk occurrence index) is over the Lake
Cumberland region, where winds a little lighter overnight also will
let temperatures drop to around freezing. Thus also have some
patches of freezing fog. This probably will not be an issue on
roads, but may see some freezing on elevated surfaces.
Continued sunshine and stronger southerly winds Friday should make
for highs well above normal, in the 50s.
.LONG TERM (Friday Night through Wednesday)...
Issued at 309 AM EST Thu Dec 25 2014
The Ohio Valley will be positioned in deep SW flow between an upper
ridge axis over the Atlantic coast and upstream troughing to our
west. A surface low will move into the Great Lakes, with a trailing
cold front extending through the mid Mississippi River Valley. Will
keep our forecast area dry overnight, minus a slight chance of
measurable rain in our far NW by dawn on Saturday. Expect mid 30s
east to low 40s west for lows.
Saturday - Sunday...
The weak surface low will move out of the Great Lakes and into New
England, with the trailing cold front slowly moving through Saturday
night, and pushing east on Sunday. This trend in the data continues
to be more progressive than 24 hours ago. The result will be likely
rain chances along and west of I-65 by Saturday afternoon due to
isentropic ascent ahead of the front. Rain will continue to be
likely across our entire CWA Saturday night as energy ejects out of
the upstream trough, and a surface wave rides NE along the boundary
to our south. Once models can agree on the strength of the surface
reflection to our south, categorical rain chances may be needed,
especially across south central KY.
With the more progressive nature of the frontal boundary Sunday has
trended drier, especially across our NW CWA. Will likely still see
lingering light rain in our south and east Sunday morning, however
most of the area is expected to be dry by Sunday afternoon.
Expect mild highs on Saturday ahead of the cold front with mid and
upper 50s across Kentucky, and mostly lower 50s in southern IN. A
sizable gradient is expected from NW to SE on Saturday night behind
the cold front. Look for lows dropping into the mid upper 30s NW by
dawn on Sunday with our SE still holding onto upper 40s. Highs
should mostly be in the 40s on Sunday.
Sunday Night - Monday...
Confidence continues to be lower to start the new week. The forecast
continues to trend drier, however can`t completely rule out
precipitation chances until models come into better agreement on
what another southern stream impulse is going to do. Will keep
chance pops across south and east in the meantime. Look for lows in
the 30s Sunday night and highs in the 40s Monday.
Monday Night - Wednesday...
Actually have higher confidence in this portion of the forecast as
there is agreement on generally zonal flow and surface high pressure
building in. Expecting dry conditions through mid week with
seasonal, or just below, temperatures.
.AVIATION (06Z TAF Update)...
Issued at 1235 AM EST Thu Dec 25 2014
Still have some light rain showers out there, mainly over the SDF
and LEX terminals for the next few hours. MVFR cigs should rule at
all sites this period, though do see a few breaks in the clouds.
High pressure over the northwest Gulf of Mexico should travel up the
Appalachians this period, forcing winds to shift from westerly now
to more southerly by this evening. Expect the MVFR cigs to break up
during the afternoon hours, as drier air filters in.