Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 280541
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
1241 AM EST Sun Dec 28 2014
...Updated Forecast and Aviation Discussions...
Issued at 1240 AM EST Sun Dec 28 2014
Adjusted pop grids for current solid line of rains moving through
the Louisville metro this hour. Also tried to fine tune the timing
of the back end of the heavier precip, drying out our northern row
of counties by daybreak, though cannot rule out drizzle still
lingering given expected remaining low clouds. Will make adjustments
again with the 4 AM forecast package.
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 (06Z TAF Update)...
Issued at 1235 AM EST Sun Dec 28 2014
Surface cold front is getting closer to SDF this hour. Rain and/or
drizzle/mist will continue around this feature for the next several
hours. as it slowly crosses our region. Ceilings likely will hover
around IFR levels, and may briefly dip to LIFR in patches. Feel
statistical guidance is too quick in improving ceilings given how
far back the low-cloud shield is and how slowly it is advancing
eastward. Have gone more pessimistic through the day, keeping IFR
until some time in the afternoon, later at KLEX. Early in the TAF
period, have variable winds at all sites, but these will become
northwesterly by daybreak as the front moves through.