Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Louisville Kentucky
1201 PM EST Fri Nov 28 2014
..updated aviation discussion...
Short term (now through saturday)...
issued at 301 am EST Fri Nov 28 2014
In the short term, batch of low clouds mainly across our eastern
sections will continue to mix out and move east. In its wake, a
short period of clear skies will be seen...mainly across southern
Indiana and portions of north-central Kentucky. Within this clearing
slot, good radiational cooling will be seen with temperatures
dropping into the upper teens to the lower 20s. This clearing will
be short lived though as another round of mid-high level cloudiness
moves in from the west. This will shut off the radiational cooling
and allow temperatures to warm slightly as we head towards dawn.
For today, we'll see the mid-level cloudiness across our western
areas work its way eastward across the forecast area this morning.
By late morning and into the afternoon, we expect to see a mix of
sun and clouds with temperatures warming into the upper 30s in the
northeast with Lower-Middle 40s across the I-65 corridor and points
to the southwest. This is a little cooler than the previous forecast
and lines up well with the bias-corrected raw blend of guidance
which has verified quite well in the last 2-3 days.
For tonight and Saturday, we'll see clear to partly cloudy skies
during the overnight period. With high pressure drifting off to our
east, we'll see a south to south-southwesterly return flow develop.
This will keep our temperatures from dropping as much as we've seen
this morning. Lows will generally cool into the upper 20s to the
lower 30s across the region. A broad southwesterly flow will be in
full swing during the day on Saturday. Within this broad SW flow,
weak isentropic upglide will commence and lead to increasing
cloudiness throughout the day. The moisture and lift profiles look
sufficient enough to warrant some slight chance pops during the
afternoon hours in areas west of I-65. Current blend of
bias-corrected guidance suggests highs in the lower to middle 50s in
the northern half with middle to upper 50s in the south. However,
with the broad southwest flow in place, these readings may be a
little under done and may need to be adjusted upwards in subsequent
Long term (saturday night through thursday)...
issued at 258 am EST Fri Nov 28 2014
Southwesterly flow will be well established across the region by
Saturday night as the region remains in between high pressure to the
east and a low pressure system traversing southeastern Canada.
Warmer, moist air will continue to advect in ahead of a front that
will move through on Sunday night into Monday. Despite ample cloud
cover, this flow will bring with it above normal temperatures for
Saturday night and Sunday. Temperatures look to actually remain
steady or warm a bit Saturday night with lows in the lower 50s
expected early in the night. Highs Sunday will be in the lower 60s
across the region. Isolated to scattered light showers will be
possible through this time period as well.
A cold front will move through the area Sunday night into Monday
morning and looks to be through the forecast area by Monday
afternoon. Rain showers will be likely as the front moves through
across much of the area. Behind the front much colder air will build
in. Given the timing of the front, temperatures on Monday look to be
falling through the day in the wake of the front with temps in the
upper 30s to mid 40s by late afternoon.
Some precipitation will linger into Monday night, especially across
south and east central Kentucky. The models have trended colder with
temps behind the front. It is possible that there may be a light
rain/snow mix Monday night before the precip moves out of the area.
However, this will depend on how fast the cold air moves in with the
precip moving out.
Confidence in the forecast from Tuesday through Thursday remains low
as model disagreement continues. There will be a chance for showers
across east central Kentucky Tuesday night through Wednesday as a weak
disturbance moves to the northeast. Wednesday through Thursday looks
to be drier, though it will depend on if a surface high is able to
build in. The disparate model solutions will have a big impact on
temperatures as well. For now will go in between the warm and cold
solutions which works out to near normal temps for mid week.
Aviation (18z taf update)...
updated at 1155 am EST Fri Nov 28 2014
VFR conditions will persist at least through tonight as high
pressure over the Tennessee and Ohio valleys begins to retreat to
the east. Mid-level clouds are eroding and will leave only cirrus
for the balance of the afternoon, with gradually increasing
By mid-morning Saturday, low-level moisture will be on the increase
under deep warm advection. Confidence is limited regarding the
impact of this moisture, as strong mid-level warming could create
enough of an inversion to trap moisture. NAM MOS guidance wants to
bring in an MVFR ceiling, but this is often too pessimistic. For now
will introduce a low cloud deck around 4000 ft agl, and keep it
scattered. South-southwest winds will increase to 12-15 kt with gusts near 20.