Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 102032
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
332 PM EST Tue Dec 10 2013
.SHORT TERM (Now through Wednesday Night)...
Issued at 240 PM EST Tue Dec 10 2013
A generally quiet short term period is in store as the synoptic
pattern this afternoon features confluent zonal flow aloft. The
main story through the short term period will be the cold
temperatures, especially over portions of the region that still have
a solid snowpack.
The first night of cold temperates will be tonight. Behind today`s
departing system, high pressure has begun to build into the region.
Despite a few passing high clouds, the night should generally be
clear. With the high pushing in, winds will also go calm. Have cut
guidance substantially in areas over the fresh snowpack from this
morning`s system across southern IN and portions of northern KY.
This puts lows in the upper 20s across southern Kentucky, with the
lower teens to perhaps a few isolated single digits over the best
snowpack in southern Indiana.
An Alberta clipper will quickly push into IL/IN/OH on Wednesday.
Some guidance tries to bring a few flurries to southern IN and the
northern Bluegrass with this system, but an analysis of soundings
shows the atmospheric layer being just too dry. Thus, will continue
with a dry forecast but introduce a bit more cloud cover in those
areas. High temperatures should top out in the low to mid 30s over
the snowpack, to the middle 40s across southern KY.
A weak cold front will push through Wednesday evening with the
aforementioned clipper, allowing an Arctic high to build into the
region by Wednesday night. This high will bring very cold
temperatures to the region. Some raw guidance is hinting at lows
perhaps falling below zero in isolated locations across southern
IN. Will not go quite that low as there is some signal in the
guidance that there could be a few clouds around. However, will
continue to advertise lows well into the single digits across
portions of southern Indiana, with low to middle teens elsewhere.
Children will certainly have to bundle up at area bus stops both
tomorrow morning and Thursday morning with temperatures at these
very chilly values.
.LONG TERM (Thursday through Tuesday)...
Issued at 332 PM EST Tue Dec 10 2013
Thursday through Friday...
Fairly quiet but cold pattern will dominate this portion of the
forecast period. Good model agreement and run to run continuity
result in above average confidence for precipitation coverage in
this period. Temperature forecasts continue to be below average for
a couple of reasons. First, there continues to be a bit of spread
in the overnight low temperatures for this period. Secondly, the
amount of snowpack on the ground through the period will modulate
overnight lows. For this forecast, have generally kept continuity
here with mostly sunny days and mostly clear nights. We should
start to see clouds increase late in the day on Friday as the next
weather system approaches from the west. Highs Thursday look to
range from the middle 20s across the snowpack in southern
Indiana...with readings around 30-32 across northern Kentucky.
Southern Kentucky looks to warm into the 33-35 degree range. Lows
Thursday night should drop back into the lower-middle teens across
southern Indiana with upper teens to the lower 20s across Kentucky.
With a stronger southwesterly flow developing on Friday, we will see
a moderation in temperatures with readings warming into the middle
30s across southern Indiana and into the upper 30s across the
northern half of Kentucky with the southern half of Kentucky warming
into the lower to middle 40s.
Friday Night through Tuesday...
Latest suite of guidance continues to strongly agree with an active
period of weather setting up from Friday Night through the day on
Sunday. A pair of upper level waves will dig across the US through
the period and then phase together to develop a rather impressive
New England storm over the weekend. The latest data continue to
indicate that there will be ample spacing between the waves so that
they will not phase to our west...but rather phase just to our
northeast. Thus, the overall model solutions continue to hold
pretty steady with a wave of low pressure developing over the
southern Plains and heading northeastward right through the Ohio
Valley. Large scale isentropic lift and synoptic scale lift will
lead to a decent batch of precipitation developing to our southwest
and spreading northeastward overnight Friday. A pre-existing
shallow cold airmass will be in place initially which will result in
the initial precipitation starting off as snow. However, as the low
heads toward the Ohio Valley, large surge of warmer air in the lower
atmosphere will move in transitioning the snow over to a wintery mix
of snow/sleet and eventually over to plain rain by Saturday
morning. Warm surge of air will continue through the day on
Saturday as the low passes through. As the low lifts off to the
northeast Saturday night, colder air will push in from the northwest
and will result in the rain changing back over to snow before ending
on Sunday. Lows Friday night will be in the upper 20s across
southern IN and northern KY....with lower 30s across southern KY.
Highs Saturday look to warm into the middle 30s across southern IN
with upper 30s to the lower 40s across KY.
It is far too early to speculate on accumulations, but signals in
the data suggest that a light accumulation of snow may be possible
late Friday night and early Saturday before the precipitation
changes over to rain across southern Indiana and the northern half
of Kentucky. We`ll need to watch this closely over the next few
days as this whole storm system has not been sampled well by the
observational data network. It is certainly possible that some
changes may be required to the forecasts during this time period.
Although, stronger model convergence should commence within the next
Sunday will be a challenging forecast as well. The model spread
here remains high as the GFS and Euro hold low-level moisture around
enough to produce snow showers...while the GEM dries things out. It
will be close as the GFS soundings do show moisture thinning in the
dendritic zone which could end up producing more drizzle or flurries
than actual snow showers. Temperatures will have a non-diurnal
curve here with readings falling throughout the day. Early day
highs will be in the mid-upper 20s in the north with highs around 30
in the south. Temps look likely to fall into the upper teens to
around 20 by Sunday evening...with overnight lows cooling into the
lower teens across the north and upper teens to around 20 across the
In the longer term, the latest data suggest that the northern stream
of the jet will become more active early next week. It appears that
we will need to watch for a clipper type system coming in for Monday
night and another one Tuesday night. The latter one looks more
impressive in today`s datasets...which could bring a swath of snows
to the northern forecast area late in the forecast period.
Temperatures will remain below normal with highs in the upper 20s to
the lower 30s and overnight lows in the 20s. These readings could
end up a little colder depending on how deep the eastern US trough
.AVIATION (18Z TAF Update)...
Updated at 1201 PM EST Tue Dec 10 2013
MVFR ceilings will persist through the early afternoon hours as cold
west/northwest flow will blow over the snow pack. Steep lapse rates
in the wake of this morning`s snow will result in a mix of low-level
stratocumulus to continue through about 10/19Z or so and then
ceilings should lift to VFR and begin to clear through the late
afternoon. Mostly clear skies are expected for this evening and
into the overnight period.
Surface winds this afternoon will remain out of the west to
west-southwest with speeds of 8-12kts. These winds will diminish
this afternoon and this evening to less than 5kts.