Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 211710
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
1210 PM EST Fri Nov 21 2014
...Updated Aviation Discussion...
Issued at 1002 AM EST Fri Nov 21 2014
The forecast remains largely on track this morning. Just went ahead
and adjusted sky cover to delay clouds just a bit and also brought
the forecast up to speed with current observations. No other
changes are needed at this time.
.SHORT TERM (Now through Saturday)...
Issued at 300 AM EST Fri Nov 21 2014
Sfc high pressure will remain in control of the region today
providing mostly sunny skies for the first portion of the day.
Clouds will be on the increase this afternoon from the southwest as
sfc high pressure begins to move east and better moisture arrives on
arrival of return flow aloft. Although we won`t realize the full
effect of the warmer air arrival late in the day, we will still be a
few degrees warmer than yesterday with highs ranging from the mid
30s to mid 40s across the area.
Tonight moisture in low and mid levels will increase in return
flow. This moisture increase along with some isentropic lift will
result in light precip tonight mainly over southern Indiana and
north central KY after midnight. There will be a good dry layer in
place initially so expect a period of virga before precip begins to
hit the ground. Overall 0Z models trended a bit drier for our area
with a slightly faster warm air surge at the sfc. Thus, there is
still a brief window of some light freezing rain possible over
southeast Indiana and the northern Bluegrass but feel if it does
happen it should be inconsequential with temps rising above freezing
by around sunrise. Low temps tonight will be reached shortly after
midnight with forecast temps in the upper 20s to lower 40s at that
time. Temps will warm during the pre-dawn hours as return flow
For Saturday, expect a mostly cloudy day with 20-30% rain chances
over southern Indiana and northern Kentucky. Strong southerly winds
will usher in much warm air with high temps ranging through the
50s. Wouldn`t be surprised to see some locations near the KY/TN
border reach 60 degrees Sat. South winds of 10-15 mph will gust to
around 20-25 mph Sat afternoon.
.LONG TERM (Saturday Night through Thursday)...
Issued at 245 AM EST Fri Nov 21 2014
Focus in the long term forecast is on the storm system for Sunday,
including the threat for localized strong storms and heavy rain.
Saturday Night - Sunday Night
21.00z model guidance remains very consistent and shows little run
to run variability in the synoptic pattern with this storm system.
An anomalous upper level shortwave will dig out of the southwest US,
through the Texas gulf coast, before lifting northward toward the
mid-Mississippi River valley Sunday. Surface low pressure track
during the period is roughly along a Little Rock to St. Louis to
Chicago line, putting the forecast area well into the warm sector.
One impact from this system will be the gradient winds Sunday and
Sunday evening as the surface low deepens over Missouri. Sustained
20-25 mph winds are likely with gusts outside of showers/storms around
35 mph. The other story will be the threat for a few strong storms.
We`ll have support aloft in the form of very impressive 500-300 mb
PV advection, a 60+ kt jet between 900-800 mb, and strong omega from
the surface to 700 mb. Overall, dynamical setup is impressive. The
main limiting factor remains instability, with MUCAPE around 100
J/kg. Nonetheless the high shear, low cape environment remains
supportive of a few strong showers/storms. Main threat is gusty
damaging winds and the main timing is Sunday late morning and
As far as rainfall goes, some localized 1-1.5 inch totals are not out
of the question. Convection, possibly a MCS, Sunday morning along
the Gulf coast could limit the amount of moisture that makes it this
far north, and then more convection may be tied closer to the
surface wave across IL and western KY. It`s possible that a portion
of the forecast area could be split between the heavier, more
widespread showers. Still, models are suggesting that moisture
transport ramps up early Sunday, especially across southwest into
south central Kentucky. Plan on a sweeping band of showers to pivot
through Sunday morning through the afternoon, ending southwest to
northeast by evening. Depending on how fast conditions clear out,
temperatures across south central KY may be able to reach the middle
60s. Elsewhere, upper 50s to lower 60s look good. Increased highs a
couple degrees based on the latest guidance.
The surface low lifts into the Great Lakes region, and eventually
the influence of a secondary upper level shortwave trough will be
the kicker to push a cold front through Kentucky and Indiana.
Showers are possible across western and northern areas associated
with some 300-500 mb PV advection and isentropic lift on the
310-325K surfaces. Highs will be challenging, with the eastern areas
likely to warm into the lower 60s while the western areas will be
dictated by precipitation, clouds and a cooler air mass so highs may
only be in the lower 50s. A model consensus was used at this time.
Tuesday - Thanksgiving
21.00z guidance reasonably consistent early on showing that high
pressure builds into the region for Tuesday with cold air advection
taking place. Highs in the 40s. After Tuesday, the upper level
pattern becomes northwesterly with embedded shortwave troughs in the
flow though confidence beyond Wednesday, including Thanksgiving, is
very low as models are struggling with the strength of the western
ridge and its impact on the downstream trough. A model consensus of
20-30 POPs Thanksgiving is appropriate with highs in the 40s and
lows in the 20s. Beyond that, confidence is very low as the 21.00z
GFS/ECMWF are almost out of phase.
.AVIATION (18Z TAF Update)...
Updated at 1207 PM EST Fri Nov 21 2014
VFR conditions are expected to prevail through the valid TAF
period. Mainly clear skies will prevail through this afternoon,
although some VFR cigs (around FL040) will approach from the
southwest by late this afternoon into this evening as a storm system
organizes to the southwest.
This storm system will help to ramp up a SSW low-level jet of 35-40
knots over KSDF tonight. Given generally light ESE surface winds,
this may be just enough to include LLWS in the KSDF TAF overnight.
This is definitely a marginal setup but given the amount of turning
from the surface to 2000 ft AGL, went ahead and decided to include
it. Otherwise, a passing light shower may affect KSDF overnight but
think all sites will likely stay dry and within VFR conditions.
VFR conditions will persist into Saturday. Winds will increase out
of the south at 10-15 knots, with gusts approaching 20 knots at
times especially at KBWG.