Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 241707
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
1207 PM EST Mon Nov 24 2014
...Updated Aviation Discussion...
Issued at 935 AM EST Mon Nov 24 2014
Had some low-topped convection form right ahead of the front,
evident on first light visible satellite imagery. Have had some
sporadic reports over stronger wind gusts, but not quite mixing all
of the stronger gusts apparent on radar down to the surface,
fortunately! Also fortunate is that the cloud field has re-appeared
this morning, as sunshine would allow a lot more of the stronger
gradient winds to mix down to the surface even outside of
showers/storms. Still expecting 40+ mph gusts over most if not all
of the area. Precip should end quickly behind the front, with just
lower clouds. Temperatures will drop quickly from the low 60s now to
the 40s by late afternoon.
Issued at 640 AM EST Mon Nov 24 2014
Wind Advy still looks good. Downstream obs are gusting into the 35
to 45 mph range especially along the front and in and around
convection. Expect more occurrences of 40+ mph gusts to increase
over the next few hours over southern Indiana and central Kentucky.
Showers and scattered storms are still on track to move east through
our area this morning with the front as well.
.SHORT TERM (Now through Tuesday)...
Issued at 325 AM EST Mon Nov 24 2014
...Strong Winds Expected Today...
The low pressure system near Chicago early this morning is forecast
to continue to deepen as it moves NE through the Great Lakes and
into southern Canada today. Its cold front will push through our
area late this morning and early afternoon. An upper level jet nose
has entered the Ohio Valley this morning also and that jet will
continue to strengthen and spread NE throughout the day. VAD wind
profiles showed a 50 kt jet at 3 kft over the Ohio Valley early this
morning and expect that to strengthen to around 60 kts by around
sunrise. All of these dynamics continue to support the Wind
Advisory currently in effect this morning. As we get closer to
sunrise, lapse rates should steepen significantly over our region
allowing higher winds aloft to mix to the sfc. While southwest
winds during the pre-dawn hours should continue in the 15-20 mph
range with gusts between 25-35 mph, winds around and after sunrise
should strengthen to 20-25 mph with gusts in excess of 40 mph
likely. Some model soundings would suggest gusts could peak closer
to 50 mph in some areas between 12z-18z.
In addition to the dynamic forcing with this low pressure system,
convection progged to move through the area from roughly Paducah to
Louisville to Cincinnati may become another force to mix down
stronger winds as well. SPC mesoanalysis indicates an area of SB
CAPE will move along this trajectory as well as 50 kts of effective
bulk shear and 300-400 SRH. Thus, think that stronger convection in
the form of gusty showers and scattered t-storms will move NE along
the Ohio River and possibly cause higher winds aloft to mix down.
If this happens, a high wind warning or t-storm warnings may be
necessary. Will need to monitor convection and trends in wind gusts
closely this morning. Wind gusts should decrease to 25-35 mph by
mid to late afternoon with convection moving east of the area by
early to mid afternoon as the cold front pushes through.
Outside of the wind threat for today, temperatures will be on the
decline. We`ll start the morning in the upper 50s and lower 60s and
then fall into the 40s this afternoon as cold air rushes in behind
the cold front.
Tonight and Tues look dry with low clouds hanging around through a
good portion of tonight before scattering out. Low temps should
range from the upper 20s to lower 30s tonight depending on how
quickly clouds exit the area. Tuesday`s high temps should range
through the upper 30s to upper 40s.
.LONG TERM (Tuesday Night through Sunday)...
Issued at 300 AM EST Mon Nov 24 2014
Upper air pattern at 500mb early Wednesday will feature a broad
ridge centered along the west coast, a slightly positively tilted
trough along the Mississippi River, and ridging southeast of
Florida. This pattern will bring cold, but not unseasonably cold,
temperatures to the Great Lakes and Lower Ohio Valley through
Extended guidance has come into better agreement with a clipper
system moving across Kentucky late Wednesday into early Thanksgiving
Day. This is apparent in both the NAM and the GFS as the base of a
sharping 500mb trough is forecast to move right over northern
Kentucky late Wednesday. With the speed of this system and the lack
of moisture, only light precipitation is expected. However, forecast
soundings show relatively steep lapse rates above the boundary layer
and saturation above the -10C isotherm, indicating a potential for
snow. Surface temperatures are the main question however. Highs in
the lower 40s Wednesday means any afternoon or evening precipitation
will begin as rain. Forecast lows early Thanksgiving will only fall
to around freezing. Any light accumulations will certainly be wet.
As with many clipper-type systems, the exact path of the 500mb low
will prove important in exactly where a potential thin strip of
Thanksgiving day will likely have the coldest temperatures of the
week. High pressure over the upper midwest will move southeast
across the Commonwealth early Friday. After maybe some light snow
early, skies should clear Thanksgiving Day and become mostly clear
for Thursday night and Friday. Highs Thanksgiving Day will stay in
the upper 30s, with quite chilly temperatures early Friday. Highs
Friday will rebound into the lower to mid 40s.
Milder air of Pacific origin will move towards the Lower Ohio Valley
Saturday as brisk southwest flow develops on the back side of
departing high pressure. Both 925mb and 850mb temperatures are
forecast to rise quite a bit from Friday to Saturday afternoons.
Although warm air advection will bring increasing low clouds
Saturday, highs will rather easily reach the 50s.
Sunday is questionable, some guidance forecast a cold front to slide
south of Indiana, while some others keep us quite warm. Temperatures
Sunday will be a challenge, although the proximity of this boundary
will bring a chance of rain.
.AVIATION (18Z TAF Update)...
Updated at 1205 PM EST Mon Nov 24 2014
Pressure gradient should start relaxing some this afternoon as a
cold front is now east of all the terminals. Still should see some
gusts of 30-40 knots over the next hour or two before they drop off.
Cigs in the wake of the cold front are fluctuating between MVFR and
VFR, but likewise should start improving by late afternoon. West
winds will continue through the period as high pressure builds in
from the Southern Plains.
KY...WIND ADVISORY until 7 PM EST /6 PM CST/ this evening FOR
IN...WIND ADVISORY until 7 PM EST /6 PM CST/ this evening FOR