Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Louisville Kentucky
307 am EST Tue Dec 10 2013
Short term (now through wednesday)...
issued at 300 am EST Tue Dec 10 2013
Upper air pattern currently shows a weak 500mb trough extending from
Missouri through Wisconsin. Ahead of this feature, a powerful jet
extends northeasterly across the Northern Ohio valley into New
Light snow will continue through the pre-dawn hours in two separate
spots; southern Indiana and eastern Kentucky. In between these
spots, across central Kentucky and the Bluegrass region, only a few
flurries are forecast.
Our current light snow across southern Indiana is a result of lift
associated with the exiting jet. Despite very limited moisture, snow
will accumulate up to one inch across an axis extending from DuBois
through Jefferson County, Indiana, with lesser amount near the Ohio
River and Louisville.
Light snow will also affect the southern Bluegrass and the Lake
Cumberland regions. This area of precipitation has developed as
moist southwesterly low level flow is lifted over a low level
boundary extending from Nashville eastwards across extreme
southeastern Kentucky. Light accumulations have already developed
across northern Tennessee and still expect maybe an inch or more
over the Lake Cumberland regions as far northeast as Lincoln
Light snow will ending around dawn across both locations, with skies
actually clearing across the region from west to east by mid to late
afternoon. Light northerly winds early this morning will become
westerly by afternoon and increase to 10 to 15 mph, especially
across southern Indiana. Highs this afternoon will vary from the
lower to mid 30s.
In the wake of this exiting fast moving disturbance, surface high
pressure will settle south across Texas, with a ridge axis extending
eastwards along the Tennessee Valley. Westerly winds during the
evening will become nearly calm overnight before becoming light from
the south early Wednesday. Later in the day, southwest winds will
pick up to 10 to 15 mph ahead of an Arctic front that will bring
cooler temperatures by Wednesday night.
In general subsidence aloft will bring mostly clear skies Tuesday
night and for Wednesday. Highs Wednesday will warm a bit into the
upper 30s to near 40.
Long term (wednesday night through monday)...
issued at 300 am EST Tue Dec 10 2013
We'll begin the long term period with Arctic high pressure sliding
into the Ohio Valley causing very cold temps Wed night through thurs
night. With good subsidence, light winds, and mostly clear skies
both Wed and thurs nights, low temps will take a dive. The coldest
night will be Wed night when low temps bottom out in the single
digits (in areas with good snowpack) to around 20 degrees. The
airmass will moderate somewhat thurs. High temps are expected to
bounce back into the mid 20s to lower 30s under mostly sunny skies
thurs afternoon. For thurs night, temps will fall back into the mid
teens to around 20 degrees.
The next weather system will be spurred by the upper low currently
off the Southern California coast. This low will eject eastward as
an open wave over the southern Continental U.S. This weekend creating an
overrunning precip event. At this time, the model consensus is that
we will largely remain on the warm side of this weather maker.
Precipitation will likely overspread the area from sws to east-northeast Fri
evening in the form of rain or a light rain/snow mix and then to all
rain early Sat morning as thermal profiles largely remain above
freezing. Rain is expected on Sat with precip ending as a rain or
light rain/snow mix Sat evening. The warm moist air being pumped
into the region will cause high temps to range from the upper 30s to
lower 40s Fri/Sat with lows in the upper 20s and lower 30s.
There is some chance that thermal profiles could waiver a bit with
this weekend's weather maker causing more wintry weather to come
into play, but right now confidence is greater in the warm soln.
Sun/Mon look dry and cool with Arctic high pressure once again
taking control of the region.
Aviation (06z taf update)...
updated at 1220 am EST Tue Dec 10 2013
Low MVFR strato-cu has eroded away over bwg and sdf, but remain over
Lex with current ceilings around 1.5kft. For sdf and bwg, feel that
ceilings will stay VFR through around 10z.
Winds will stay out of the north at around 5 to 8kts overnight
before shifting to the west southwest by around 9am EST Tuesday
morning. West southwest winds will increase to 10 to 15kt by early
afternoon Tuesday, before diminishing by evening.
Light snow is possible north of sdf during the early morning hours
and also south and east of Lex and bwg during the same time period.
After 10z, light snow or flurries may develop for a few hours at
sdf. However, ceilings will likely stay above MVFR thresholds with
visibilities likely remaining above 3sm even if light snow develops.
Feel that precipitation will basically miss Lex and bwg, however
occasional MVFR ceilings are possible through 14z Tuesday.
Skies will become mostly clear after 15z at all taf sites with VFR
flying conditions expected after this.
Kentucky...Winter Weather Advisory until 10 am EST /9 am CST/ this morning