Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 280248
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
948 PM EST Sat Dec 27 2014
Issued at 947 PM EST Sat Dec 27 2014
Current forecast remains in good shape this evening. Second wave of
rainfall today has pushed on off to the east. Third band of
precipitation out near the MS river will continue to push eastward
overnight, so another round of light to moderate rainfall is
expected overnight. Have backed off PoPs slightly in the forecast
for the early part of the forecast, but allow PoPs to ramp back up
from west to east after midnight.
.SHORT TERM (Now through Sunday Night)...
Issued at 250 PM EST Sat Dec 27 2014
A cold front associated with a low pressure system over the Great
Lakes region stretches from northern IN through east central IL into
southern IL this afternoon. This front will slowly push eastward and
into southern IN this evening. It will be along the Ohio River by
around midnight and will push through the Bluegrass and Lake
Cumberland regions by dawn tomorrow.
A second wave of rain ahead of this front currently stretches across
western portions of the forecast area. This wave will move through
and off to the northeast this evening. There may be another lull in
precip late this evening before a third round of showers accompanies
the front moving through overnight. Another upper level disturbance
will enhance the precipitation along and behind the front, with
showers continuing through the day tomorrow. The rain will diminish
from west to east through the day and into the evening. The last of
the showers should move out overnight tomorrow night.
Temperatures will gradually fall in the wake of the front overnight.
Temperatures around dawn will range from the upper 30s across
southern IN to the upper 40s across east central KY. Temps will move
little on Sunday. The east may fall a couple of degrees during the
day while the west warms a couple of degrees. Lows tomorrow night
will range from around 30 across southern IN to the upper 30s in the
Lake Cumberland region.
.LONG TERM (Monday through Saturday)...
Issued at 301 PM EST Sat Dec 27 2014
A large dome of Canadian high pressure will invade the Plains early
this week and slide southeast into Dixie mid-week. This should keep
us dry and chilly through Thursday. The coldest night looks to be
Wednesday night with lows in the lower 20s, so New Year`s Eve
revelers will need to bundle up.
The models sink into confusion from Thursday night through the end
of the forecast period, thanks to a storm system digging into the
Desert Southwest. The models have always had a hard time with these
systems, both in terms of how quickly to eject them northeastward,
and what path they should take.
Thursday night the GFS kicks the upper low out of the Four Corners,
but the ECMWF holds it back, so that by Saturday morning the GFS has
the upper low over Michigan and the EC has it over Texas.
Historically, the GFS has had a tendency to be too aggressive
ejecting Southwest U.S. lows, and the EC tends to be too
conservative, so taking a middle ground between these two models
makes some sense.
Looking at the recent past, from early October to mid December, most
of the lows coming in from the southwest have tended to pass by to
our west and north. Also, it`s been noticed that deepening lows
coming in from the southwest tend to trend farther and farther
northwestward with subsequent model runs. Indeed, the surface low
position at 12Z Saturday on the GFS has steadily moved to the
northwest, from being situated over North Carolina on the 12Z/25 run
to being over Michigan on this morning`s 12Z run.
The GFS has been pretty consistent over its past six runs with
surface low placement on Friday. The EC has been all over the map.
So, will slightly favor a slower and warmer version of the GFS.
Confidence is still low, however, that far out in the forecast.
Will keep PoPs in the chance category, albeit high chance. Could
see a light wintry mix Thursday night/early Friday morning, though
if this storm behaves like recent storms, we may end up with more
rain than currently projected. Regardless, rain should be the
primary precipitation type Friday through Saturday. If it is indeed
rain, it actually could be quite a bit...maybe an inch or two. Of
course, a lot can happen between now and then, so this system is
definitely something to keep an eye on.
.AVIATION (00Z TAF Update)...
Issued at 629 PM EST Sat Dec 27 2014
Surface cold front out to the west will move into the region
overnight. Ahead of this feature, widespread rain showers are
expected to continue through the evening and overnight hours.
Ceilings will start off the period in the low end of the MVFR range
and then dip to IFR levels for the overnight period. The cold front
will pass through the terminals late tonight resulting in a wind
shift to the northwest. IFR ceilings are likely to persist into
Sunday morning in the post frontal airmass. Some improvement is
expected by late afternoon and evening as the precipitation ends
from west to east.