Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 221708
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
1208 PM EST Sat Nov 22 2014
...Updated Aviation Discussion...
Issued at 857 AM EST Sat Nov 22 2014
Ran a quick update early this morning mainly to account for the
latest radar trends. A few light showers will continue this morning
for the next few hours. However, as the mid/upper-level flow begins
to back in response to a strong PV anomaly diving into the southern
CONUS, the warm conveyor belt should lift more to the north of the
region, leaving most dry from the mid afternoon hours through
tonight. Will have updated products out shortly once a new set of
fresh observations come in.
.SHORT TERM (Now through Sunday)...
Issued at 300 AM EST Sat Nov 22 2014
Milder air will flood the region as southerly winds pick up this
afternoon with high pressure moving well east of Kentucky. Indeed,
temperatures have been slowly rising all night, especially west of
Scattered very light rain showers will continue through the pre-dawn
hours across southern Indiana as a weak wave moves across the
Hoosier State. Only a few hundredths of an inch at most will
accumulate north of the Ohio with only some scattered light showers
or sprinkles expected southeast of the Ohio. By early to mid
morning, any lingering precipitation will end, although extensive
mid-level clouds will linger, giving us mostly cloudy skies today.
This afternoon, brisk southwesterly flow will already be established
along and northwest of the Ohio River as 925mb winds will increase
to around 30 to 35kt. 925mb temperatures are forecast to rise to
around 9C by this afternoon as well. These winds and temperatures
will not mix down completely, but south winds of 10 to 15 mph will
develop this afternoon, driving up our highs into the mid to upper
A complex upper air pattern will develop late Saturday as a northern
stream shortwave crossing the Rockies will begin to phase with a
southern stream 500mb trough across Texas. A coupled jet structure
will develop by late Sunday as these two systems join, leading to a
rapidly deepening cyclone over the lower Mississippi Valley. The GFS
and Canadian places a surface low near Arkansas late Sunday, while
the NAM places it closer to St Louis. In both cases however, low
pressure will deepen rapidly Sunday night as it moves toward the
western Great Lakes.
Saturday night will stay mild as brisk southerly winds aloft will
mix somewhat to the surface. Overnight lows will stay well up in the
mid to upper 40s.
Showers will increase in coverage Sunday through Sunday evening as
significant forcing develops ahead of a potent jet streak rounding
the base of the aforementioned developing cyclone. Dewpoints in the
lower to mid 50s will make it as far north as southern Kentucky by
mid to late afternoon. Maximum shower coverage will arrive by mid
afternoon and continue through Sunday evening. Instability will stay
quite marginal, with any thunder being quite isolated. However, with
strong wind fields aloft any surface-based showers may bring gusty
winds Sunday afternoon. Highs Sunday will stay quite modified by
clouds and rain, staying in the mid to upper 50s.
.LONG TERM (Sunday night through Friday)...
Issued at 300 AM EST Sat Nov 22 2014
...Looking cold for Thanksgiving...
We`ll begin the long term period with rain showers and some t-storms
Sun night as a strengthening low pressure system lifts north from
the ARKLATEX region Sun to Lake Michigan by Sun night. A strong low
level jet will accompany the warm front as it moves north through
our region early Sun night. Although instability will be a limiting
factor, we`ll enter the warm sector Sun night meaning convection may
have a chance to become more sfc based. Thus, the higher winds
aloft may mix down inside or outside of convection especially during
the first portion of Sun night. Strong wind gusts are possible Sun
The cold front associated with this system looks to swing through
the Ohio Valley during the first half of the day Mon. Scattered
showers will continue ahead of the front with models continuing to
vary on precip timing/coverage for Mon. Outside of any convection,
gusty winds are expected to continue for Mon as a we sit in a tight
sfc pressure gradient. Will need to monitor late Sun night and Mon
for wind gust strength that may warrant a wind advisory. Temps will
be quite mild Sun night/Mon with temps ranging from the mid 40s to
upper 50s to around 60.
Weather conditions will turn dry and cooler for Mon night/Tuesday as
sfc high pressure begins to work into the region. Expect low temps
to drop off Mon night into the upper 20s and lower 30s. High temps
will likely drop back below normal in the upper 30s and lower 40s
The next weather challenge will be a possible Clipper type system
coming in from the NW Wed night/Thurs. The 0Z ECMWF is the most
aggressive with this clipper bringing a light wintry mix and then
snow to the region on Thanksgiving. However, the 0Z GFS, GFS
ensembles and GEM all indicate a slightly less amplified pattern and
take any precip to our north. For now went ahead with a 20% POP for
most locations Wed night/Thur for a possible light wintry mix or
snow. If frozen precip does fall, it has a slight potential to
impact holiday travel. But for now too many model solns exist to
nail down any hazard threats for sure attm.
Beyond Thanksgiving expect a cold dry airmass. Models vary on the
pattern for the end of next week. However, it should be noted the
0Z ECMWF did trend toward the 0Z GFS/GEFS/GEM. Kept temps in the
mid 30s to lower 40s for highs with lows in the 20s for the second
half of the week.
.AVIATION (18Z TAF Update)...
Updated at 1207 PM EST Sat Nov 22 2014
VFR conditions will persist through most of the TAF period, but
deteriorating conditions will approach all sites near the end of the
forecast, especially into the planning period at KSDF.
Mid/high clouds will continue to stream by late this afternoon into
tonight. Winds this afternoon will continue to be out of the SSW,
gusting upwards of 20 knots at times.
Surface winds will slacken a bit tonight, but a LLJ just off the
surface will once again ramp up to around 40 knots. This will set
the stage for another marginal LLWS event at KSDF and KBWG. KLEX
looks to be on the eastern fringe of the stronger winds, thus will
leave LLWS out for now.
Lower ceilings and associated rainfall will approach the sites
from south to north through the day on Sunday. Expect at least MVFR
cigs/vsbys with this activity Sunday afternoon into Sunday evening.