Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 291100
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
600 AM EST Thu Jan 29 2015
...Updated Aviation Discussion...
.SHORT TERM (Now through Friday)...
Issued at 315 AM EST Thu Jan 29 2015
Latest analysis shows surface low pressure centered over west
central Illinois while a cold front stretched through central
Missouri into northwest Arkansas. Ahead of this feature, a
tightening pressure gradient and strong 50-60 kt jet between 900 and
800 mb has brought warming temperatures to the Ohio Valley
overnight. After bottoming out in the 20s to to lower 30s, readings
have warmed into the mid 40s in the west while some eastern
locations are holding in the lower 30s.
The sheltered and valley locations across the far eastern and
northeast forecast area have been slower to respond. Temperatures
are expected to be right around 32 degrees as precipitation moves in
early this morning and combined with the drier low levels, concerned
that for a brief period, light freezing rain could fall and coat
road surfaces. Road temperature sensors across that area are in the
30 to 32 degree range. This could cause some travel issues,
especially for the morning commute. After coordinating with ILN/JKL,
have opted to issue a SPS to cover the potential slick and icy spots
across the Bluegrass region.
Hi-res models are capturing the band of showers associated with the
initial warming and PV anomaly fairly well, bringing it through
central KY and southern IN early this morning through the
mid-morning hours. Will time the highest POPs during its passage.
The true cold front and upper trough will arrive early to mid
afternoon which could bring additional rain showers. High
temperatures are expected to warm into the upper 40s to mid 50s
before beginning to fall mid afternoon post frontal.
Wrap around moisture then arrives later this evening and through the
overnight hours. Cross sections and soundings show the moisture
mainly resides in the low levels. As colder air filters in while
moisture exits, there`s still the window for wintry precipitation.
Soundings show loss of ice and saturation only reaches up to about
-5C, so there is a concern for a period of drizzle or freezing
drizzle across the Bluegrass region before enough cold air supports
a changeover to snow flurries or showers. Have added a slight chance
of freezing drizzle to the forecast for the late evening and
overnight hours. Plan on low temperatures in the mid to upper 20s.
Wrap around stratus is expected to hold in place Thursday night
through a good portion of Friday, especially east of I-65, as
moisture remains trapped beneath an inversion. Plan on a seasonably
cold day with highs only topping out in the 30s. If clouds hang on
longer into the afternoon, it`s possible forecast high temperatures
may be a few degrees too warm.
.LONG TERM (Friday Night through Wednesday)...
Issued at 325 AM EST Thu Jan 29 2015
...Accumulating Snow Possible Late This Weekend...
Sfc high pressure will briefly dominate the area Fri night/Sat.
With light winds and only partly cloudy skies Fri night, temps
should be able to drop into the mid teens to lower 20s for lows.
Clouds will be on the increase Sat ahead of an approaching weather
system with high temps topping out in the upper 30s and lower 40s.
The storm system to watch this weekend will get organized over the
central U.S. on Sat as energy ejects eastward out of an upper low
across the southwest U.S. and another wave dives southeast out of
Canada. Both waves are well removed from the continental U.S. right
now though and although 0Z GFS/ECMWF came in with surprisingly good
agreement with their solution for this system over the Ohio Valley,
beware that these upper level features still have a good way to
travel before they reach the North American coastline and thus
timing/intensity/phasing could change in coming model runs. Such
differences are apparent in 0Z GEM/NAM data which have
warmer/farther north solns. Still given decent agreement between
GFS/GFS ensembles/ECMWF/ECMWF ensembles, did trend the forecast
Thus, think that precip will overspread the area on Sat night as
perhaps a brief mix and transition over to light snow Sat night over
most locations. Sunday precipitation is likely over the entire
area. Models vary on QPF for Sun depending on strength and phasing
of the aforementioned waves and how much moisture they are able to
pull in. Think that all snow is mostly likely over southern
Indiana, the rain/snow line may hover somewhere over central KY, and
south central KY is likely to see a rain/snow mix perhaps transition
over to a period of all rain. Sun night precip will continue over
the area with most locations eventually changing over to all snow
before precip ends Sun night or early Mon. IF this scenario plays
out, portions of the area could see accumulating snow in the Sat
night-Sun night time frame. HOWEVER, if the warmer solns play out,
then our region would mostly see rain on Sun with perhaps some light
snow or a rain/snow mix possible on the front and back sides of the
system Sat night/Sun night.
Please stay tuned to upcoming forecasts on this weekend`s weather
Beyond this weekend, the pattern looks to remain fairly active with
a few clipper type systems attempting to bring us precip by mid
Temperatures will likely start out on Monday in the upper 20s/lower
30s (potentially colder in areas that receive snowfall) then
moderate toward mid week closer to seasonal normals. Temps look to
fall back below normal during the latter half of the week.
.AVIATION (12Z TAF Update)...
Issued at 555 AM EST Thu Jan 29 2015
Plan on the initial band of precipitation to pass through
BWG/SDF/LEX early this morning, exiting between 14-15z. This will
correspond to when winds begin to mix down to the surface, ending
LLWS threat. Southwest winds will then become gusty, between 20-25
kts. Plan on a dry slot / clear wedge to spread over the area ahead
of the cold front before quickly filling back in with wrap around
clouds as the surface low passes to the north. These clouds should
encompass the entire region by mid afternoon and last through the
TAF period. Current observations upstream are in the 1500 to 2500 ft
range, so below fuel alternate conditions are possible, especially
at SDF/LEX, by evening. Soundings show moisture remains trapped in
the low levels all night and there is the potential for snow
flurries or showers but isn`t likely to produce visibility