Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 251120
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
620 AM EST Tue Nov 25 2014
...Updated Aviation Discussion...
.SHORT TERM (Now through Wednesday)...
Issued at 300 AM EST TUE Nov 25 2014
At 500mb, a broad trough will continue across the central CONUS
through late Wednesday. Surface ridging will settle over Texas, with
an associated ridge axis extending northeast across southern
Illinois. Expect seasonably chilly temperatures today with generally
light winds out of the west. Highs will range from the upper 30s
across southern Indiana to the mid 40s near Tennessee. A broad
shield of low strato-cu now over Indiana and Illinois will settle
slightly southwards by mid-morning and may bring a period of
cloudiness along and north of the Ohio River through late morning.
Farther south, mostly clear skies are anticipated.
Tonight, surface ridging overhead will lead to mostly clear skies
and light winds. Mid-level clouds from a developing east coast storm
may spread back as far west as eastern Kentucky. Lows will fall into
the mid to upper 20s.
For Wednesday, a coastal storm will spread ice and snow inland of
the major urban areas along the east coast. An compact upper
disturbance will track southeast across Iowa and into Missouri by
noon Wednesday. This "clipper" will eventually track across the
Commonwealth Wednesday night. Expect increasing high and mid-level
clouds by mid-afternoon ahead of this feature. Some light rain may
move into Kentucky west of Interstate 65 by late afternoon
Wednesday. Highs Wednesday will rise into the lower 40s.
.LONG TERM (Wednesday Night through Monday)...
Issued at 302 AM EST Tue Nov 25 2014
...Light Wintry Mix To Snow Likely Wednesday Night and Early
Wednesday Night through Friday Night...
Early in the forecast period, the upper level pattern will be rather
amplified aloft with a fairly decent trough in the east with a
corresponding ridge out across the western US. The trough in the
east is expected to amplify a bit and result in a pre-Thanksgiving
day east coast storm across the eastern US. As this storm develops
and moves up the eastern seaboard on Wednesday, we`ll be watching a
fast moving upper level disturbance that will pass through the
region Wednesday night bringing light precipitation to the region.
Overall, the model guidance continues to show better convergence
with the track and timing of the system for Wednesday night. This
system will enter the region from the west Wednesday evening and
depart the region during the day on Thursday. As it approaches,
precipitation will streak eastward across southern Indiana and much
of central Kentucky. Thermal profiles at the beginning of the event
suggest a relatively warm boundary layer that will result in
precipitation falling in the form of light rain. As we head through
the night, the boundary layer will cool and we should see a change
from rain to snow from south to north as the night wears on. There
is some potential for this system to produce a little more snow than
current forecast by the models.
Model cross sections do continue to show a tightening of the
thermal gradient aloft due to the jet core passing by. This could
result in some heavier banded precipitation falling along and north
of the actual surface track. A second form of potential is that we
could get a little bit of dynamical cooling to get the column to
cool faster than the models currently prog. As previous forecast
noted, surface wetbulbs really stay at or above 0C through much of
the event, so snowfall accumulations still look generally light and
will likely be limited to elevated and grassy locations. Surface
temperatures are expected to drop to near or just below freezing
Thursday morning, thus some isolated-scattered slick spots may be
possible around the region. Given the busy travel period, this is a
system that will continue to be monitored closely.
For Thanksgiving day, we will probably see some lingering snow
flurries in the east during the morning, with clearing skies
developing from west to east during the afternoon. It will be a
cold Thanksgiving with highs topping out in the upper 30s. Clearing
skies and light winds will allow temperatures Thursday night to drop
into the lower-middle 20s. Dry conditions are expected for Friday
with highs topping out in the lower-mid 40s in the north and mid to
upper 40s across the south. Lows Friday night look to cool into the
lower-mid 30s in the north with mid-upper 30s in the south.
Saturday through Monday...
As we head into the weekend, the upper level flow pattern is
expected to flatten out as the western CONUS ridge begins to break
down. A slight increase in geopotential heights across the east
should allow a bit of a warm up to commence across the region on
Saturday and into Sunday with afternoon highs warming into the upper
50s in the north with lower 60s across the south.
The latest global guidance continues to be in general agreement with
a surface cold front pushing toward the region on Sunday. A wave of
low pressure looks to develop along this boundary and bring another
round of rain showers to the region Sunday and into Sunday night.
For now have kept decent PoP chances in for Sunday and Sunday night
with slightly drier conditions for Monday. Highs Monday will be a
little cooler than Sunday with lower 50s int he north with mid-upper
50s across the south.
.AVIATION (12Z TAF Update)...
Updated at 1110 AM EST Tue Nov 25 2014
The edge of a broad shield of MVFR strato-cu will sag south this
morning and may affect the SDF and LEX terminals in the 13 to 15z
time frame. However, for now, will keep all the terminal forecasts
VFR for today and tonight.
If low clouds do affect SDF and LEX, feel that clouds will scatter
out by mid-afternoon. Mostly clear skies are expected this evening
Light west winds of around 3 to 6kt will continue this
morning...increasing to 7 to 10kt later this afternoon. Winds will
become nearly calm by late this evening and into early Wednesday