Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 130523
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
1223 AM EST Fri Dec 13 2013
...Updated Aviation Discussion...
Issued at 730 PM EST Thu Dec 12 2013
Only made a slight tweak in the web forecast...to temperatures
across the south. That area will be closest to the center of high
pressure crossing the Tennessee Valley tonight, and consequently
winds already have gone calm at our southern locations. Thus under
clear skies, they should see temperatures drop quicker this evening.
Still think the north will keep up enough winds to prevent lows from
falling into the single digits again. Inherited temperatures across
the center of my forecast area have the best chance to bust, the
approximate dividing line between the decoupled boundary layer and
calm winds and more mixing to the north.
Will probably send out another update later this evening to match
obs in temperatures and see if we can fine tune the dividing line
.SHORT TERM (Now through Friday Night)...
Issued at 245 PM EST Thu Dec 12 2013
...ANOTHER ROUND OF SNOW LIKELY FRIDAY NIGHT FOR SOUTHERN INDIANA
AND PORTIONS OF NORTHERN KENTUCKY...
Afternoon satellite imagery reveals mostly sunny skies across the
forecast area. Despite full solar insolation, temperatures are
still cool due to good cold air advection. Readings generally were
in the upper teens to around 20 across southern Indiana with
mid-upper 20s across KY and upper 20s to the lower 30s across
southern KY. Temperatures are expected to cool back into the teens
this evening across southern Indiana and into the lower 20s across
Kentucky. Some mid-high level cloudiness will streak across
southern Indiana and portions of northeastern KY as a mid-level wave
swings to our north. Skies are expected to clear once again later
tonight. It doesn`t appear to look as cold tonight as we`ll see a
light southwesterly flow within the PBL developing. Lows will cool
into the upper single digits to the low teens across southern
Indiana. Upper teens to the lower 20s are expected across much of
Friday looks to be mainly a dry day, but we will see an increase in
clouds during the afternoon hours. A broad southwesterly flow will
allow an influx of warmer air to push further northward into the
region. Highs in the afternoon look to warm into the middle 30s
across southern Indiana with upper 30s to lower 40s across the
northern half of KY...with lower to middle 40s expected down towards
the Lake Cumberland area.
Latest model data continues to be in fairly good agreement with the
next weather feature moving into the region from the southwest
Friday night. Combo of an upper level wave and surface wave will
push into the region Friday night. As this occurs, influx of warm
air near the surface will work into KY overnight. Initially dry air
in the lower part of the atmosphere will impede precipitation
initially. However, precipitation falling aloft looks to saturate
the column from top to bottom (and fairly quickly) during the
evening. This will result in a mixed bag of wintry weather
developing across the region.
Latest model soundings show cold layer near the surface sticking
around across the northern half of our forecast area for a period of
light to moderate snow during the overnight hours. The area at most
risk for this to occur would generally be along and north of the
I-64 corridor. Much of our Indiana counties look to stay a little
cooler resulting in a higher probability of snow accumulation.
Forecast confidence south of the river is not as great as the warm
nose is forecast to push in during the overnight period which may
result in a quicker changeover to plain rain.
After a thorough analysis of soundings and coordination with
PAH/IND, will be going with a Winter Weather Advisory for our
southern Indiana counties from 00Z Saturday through 15Z Saturday.
Current thinking is that we`re likely to see 1 to 3 inches of snow
across our southern Indiana counties...with up to an inch of slushy
snow accumulation in areas just south of the river and down the I-64
corridor. We would like to emphasize that if future data suggests
slightly colder conditions for tomorrow night, a southward expansion
of the advisory would be required in subsequent forecasts.
.LONG TERM (Saturday through Thursday)...
Issued at 315 PM EST Thu Dec 12 2013
Saturday - Saturday Night...
Storm system will be ongoing across the Ohio Valley on Saturday with
the surface low underneath the weakly coupled upper level jet
pattern passing through or just south of the CWA. Data continues to
suggest that precipitation type will change to all rain very quickly
on Saturday as warm nose aloft nudges in on a stronger H85 jet.
Meanwhile, surface temperatures are expected to go from the 32-37
range in the morning up to the 39-44 range by afternoon.
The surface low will quickly push northeast late Saturday afternoon
and evening, with mid level trough axis swinging through Saturday
night. Cold air advection at the low and mid levels will quickly
commence Saturday evening behind the system, with a changeover back
to light snow from northwest to southeast through the overnight.
Data continues to suggest that this changeover will be a short lived
light snow event as we lose ice crystal formation with the exit of
deeper moisture. Would not expect more than a dusting of snow
Saturday evening. Will continue to be concerned about patches of
light freezing drizzle from west to east as the cold air at the
surface works in and temperatures drop into the 20s.
Sunday - Thursday...
There will be a brief period on Sunday where the low level
trajectories could favor some brief Lake Michigan enhanced (low
level moisture) upslope snow showers across our far northeast. The
degree of low level moisture will be in question, so prefer to keep
this time frame dry for now until more confidence in enough moisture
is present to warrant snow shower mention. Otherwise, expect a dry
day with temperatures not making it out of the 30-35 degree range.
As we move through the work week, fairly broad but low amplitude
troughing will encompass the eastern CONUS. This troughing will be
continually be reinforced by embedded shortwaves within the flow,
bringing a couple of recurring shots of cold air. These individual
disturbances continue to look moisture starved in the dry northwest
flow so will continue with a dry forecast. The main challenge will
be temperature forecasts through the week as the timing of
individual disturbances will play a big role in eventual
temperatures. In general, expect upper 30s to low 40s for highs
across southern Indiana, and generally in the 40s for highs across
Kentucky by midweek. Lows will generally be in the 20s through
.AVIATION (06Z TAF Update)...
Updated at 1220 AM EST Fri Dec 13 2013
Sfc high pressure will remain in the control of the region through
this evening providing VFR conditions. Upper level clouds will be
on the increase ahead of a low pressure system approaching from the
southwest. The cloud deck will begin to steadily drop this evening
as moisture associated with the low pressure system enters the
area. A thick dry layer in low levels will exist ahead of this low
pressure system so expect some precip to begin to reach the ground
in the form of very light rain or snow Fri evening, but the bulk of
precip will likely arrive after midnight when better saturation is
reached (just beyond this TAF period for BWG/LEX). According to
model soundings, late night precip would likely be in the form of
light rain or snow at SDF. When low levels finally do saturate, at
least low end MVFR conditions can be expected.
Winds will remain out of the SSW through this evening. Winds will
become predominantly SE as the low pressure approaches tonight.
KY...WINTER WEATHER ADVISORY from 7 PM this evening to 10 AM EST
Saturday FOR KYZ032.
IN...WINTER WEATHER ADVISORY from 7 PM EST /6 PM CST/ this evening to
10 AM EST /9 AM CST/ Saturday FOR INZ076>079-083-084-