Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 022031
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
331 PM EST Mon Dec 2 2013
.SHORT TERM (Now through Tuesday Night)...
Issued at 331 PM EST Mon Dec 2 2013
Variable cloudiness will continue the rest of this afternoon and
early this evening. Temperatures have risen solidly into the mid
50s, with a few upper 50 readings at this hour. Although they will
have little impact, big questions for tonight will center around
cloud cover, temperatures, fog potential, and patchy drizzle
Current water vapor imagery does show a shortwave over
the MO/IA/IL border with some patchy light radar returns out ahead
of it moving into the Wabash River Valley. The main energy from this
wave will pass to the north of the Ohio River, so expect most of the
drizzle to do the same. After midnight, some light isentropic ascent
will then set up and increase from south to north for the remainder
of the night. A few patches of light drizzle will be possible along
the TN border between 06-12Z. Most places will not see any, and low
temperatures should bottom out in the upper 30s and low 40s. There
is some question of whether fog will develop in the clear patches
overnight, but confidence is too low to add to the forecast due to
the variable cloudiness and some light winds picking up toward dawn.
By Tuesday, zonal flow aloft will dominate the upper air pattern,
with steady southerly flow taking shape through the lower third of
the atmosphere. The forecast will stay dry for this time period,
although with increasing low level moisture and a weak isentropic
lift component may have to watch for some sprinkles. As was
mentioned in the previous forecast, do expect to see some breaks in
the clouds, and with the steady warm air advective component
temperatures will rise into the upper 50s north to mid 60s south.
Tuesday night will bring an increase in southerly flow and low level
moisture transport as a 30-40 knot low level jet gets going over the
area in response to expansive cyclogenesis over the eastern Plains.
Tuesday night will be pretty mild with the steady southwest flow,
extensive clouds, and light precipitating. In fact, temperatures may
rise a bit toward dawn on Wednesday. Whatever the case, lows should
only bottom out in the 50-55 degree range.
.LONG TERM (Wednesday through Monday)...
Issued at 325 PM EST Mon Dec 2 2013
...Heavy Rainfall and Wintry Weather Possible for the Latter Half of
A moist southerly flow with several embedded shortwaves combined
with a semi-cold Arctic airmass near the region look to bring 2
threats to the Ohio Valley for the latter half of the week...Heavy
Rainfall and Wintry Precipitation. Confidence in waves of
precipitation traversing the area from Wed through Sunday is high.
Confidence in south central Kentucky receiving 2-3 inches of
rainfall with locally higher amounts is moderate. This could lead
to local flooding issues. Confidence in precipitation type over
southern Indiana and northern Kentucky (the transition zone) is low
which is the case in most overrunning precip events this far out.
Based on the latest model data which includes quite the range in
temp profiles, will continue to be very general in prediction of
precip types/areas. Overall, my resultant temp profile forecast may
be closest to the 12Z GEM which is between the 12Z GFS/ECMWF. One
thing to note...there are many model solns at this point in part
because they are trying to predict a phase of the northern and
southern stream jets over the Rockies Wed morning. Once this phase
actually occurs Wed morning, one would anticipate the model runs
later in the day Wed to converge on a common soln for Thurs-Sun.
Based on the above mentioned preferences/thoughts, here is a low
confidence forecast scenario for the latter half of the week...
Scattered rain showers and isld t-storms (low topped convection) are
expected to occur ahead of a cold front. Ahead of the front, expect
gusty southerly winds to around 30 mph with unseasonably warm temps
in the mid to upper 60s for highs Wed. Wed night the boundary looks
to settle over south central KY with a shortwave riding along it
causing a decent slug of rain to occur over south central KY.
Thursday temps will remain above freezing but a difficult temp
gradient will set up over the area with highs ranging from the mid
40s over southern IN to around 60 over south central KY. On and off
waves of rain will continue Thurs/Thurs evening.
Mixed precip may come into play late Thurs night into Fri morning as
the colder airmass tries to make an entrance from the NW. Wintry
precip may start out as freezing rain or sleet...it`s a tough call
this far out but a good warm nose aloft would indicate the
possibility of some icy precip before a transition to sleet/snow
Friday evening. Precip during the day on Friday is in
question...wintry precip is more likely over southern
Indiana/northern KY with south central KY probably remaining all
rain. Again...the confidence level with p-type is low at this
Late Friday night precip should exit the area leaving a dry Sat with
cold air spilling in over the entire region. This cold air may set
the stage for more wintry weather as another significant slug of
precip moves in for Sunday. Again another warm nose aloft would
suggest icy conditions possible but sfc temps will certainly be the
determining factor on impact. Next Monday looks cold and dry at
Stay tuned to coming forecast updates on the potential wintry
.AVIATION (18Z TAF Update)...
Updated at 1216 PM EST Mon Dec 2 2013
Conditions will stay VFR for the remainder of the afternoon and
evening with variable cloudiness between Sct and Bkn for much of the
day. Any of the lower ceilings should range between 4-5 K feet.
Winds will be light and variable with any noticeable gradient out of
the S or SE.
The forecast is low confidence as we head into the late evening and
overnight. The main problem has the been model guidance handling of
low level moisture. It does appear that we will see an increase in
low level moisture after Midnight as weak ascent commences from SW
to NE. This is expected to lead to at least high MVFR ceilings,
although potential exists for lower ceilings and some visibility
restrictions in BR. Additionally, some patches of drizzle cannot be
ruled out although impacts would be minimal to non-existent.
A more noticeable southerly gradient up to around 10 mph will set up
on Tuesday and sky cover will likely vary between Sct-Bkn between