Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 010508
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
1208 AM EST Sun Dec 1 2013
...Updated Aviation Discussion...
.SHORT TERM (Now through Sunday Night)...
Issued at 250 PM EST Sat Nov 30 2013
Upper level disturbance that brought us some high clouds this
morning has made its way east of the area, and mostly sunny skies
will persist for the remainder of the late afternoon and evening.
Temperatures have overachieved today under full sun and a steady
warm advective component. Most locations are solidly in the mid 50s.
Expect winds to slacken a bit and temperatures to quickly drop after
sunset with the large T/Td spread (currently 25-30 degrees). Some of
the cool eastern valley locations will probably drop into the upper
20s, with most other spots in the 30-35 degree range for lows. Many
lows will likely occur well before dawn as some low to mid level
clouds (4-7 k feet) begin to move into the area ahead of the next
weak system. Northern temps will likely rise a bit toward dawn as a
As we move into the day on Sunday, low and mid level clouds will
continue to be on the increase from NW to SE across the area. These
clouds are trending faster so will continue the downward trend for
the forecast high temperatures. Looking for mid to upper 40s across
southern Indiana, with low 50s across south central Kentucky as the
clouds get in pretty quick. Will continue to leave the forecast dry,
however there is some indication that enough low level moisture may
be present for some drizzle. Either way, measurable precipitation
does not look likely.
Will continue with slight chances for a light rain shower on Sunday
night, especially across south central Kentucky as deeper moisture
pools ahead of a southern stream system scooting across the Ozarks.
Overall, moisture will still be quite limited although slightly more
impressive. May end up with a high coverage drizzle/low coverage
measurable rain shower scenario. The extensive cloud cover will keep
temperatures milder with lows only bottoming out in the upper 30s
and low 40s.
.LONG TERM (Monday through Saturday)...
Issued at 230 PM EST Sat Nov 30 2013
Troughing will be over the region at the start of the period, and
forecast soundings show plenty of low-level moisture. Numerical
guidance has low ceilings/visibilities for Monday morning. The
moisture is shallow enough that it will be difficult to squeeze out
measurable precip, but drizzle will keep Monday raw. Those clouds
may stick around well into Monday night and would be a portent of a
dreary week to come.
That said, Tuesday may be the best day of the week. We will see a
brief zonal flow aloft, and highs look to get up to normal. Then
comes a front that will stall out as that flow aloft becomes
parallel to the surface flow. Models are in pretty good agreement on
this scenario, and these models paint a wet picture across our
region Wednesday through at least Friday. Multiple disturbances
riding northeast with that flow aloft will mean some heavier rain
periods than others, but the GFS and ECMWF differ on timing these
disturbances. The GEFS has precipitable waters going up to 2
standard deviations above normal Thursday, so this system will bear
watching for flood potential. Have put in a slight chance for
thunder across the south given the warm airmass in place ahead of
the presumed location of the front.
The temperature forecast will depend greatly on where the front
stalls as well as timing of rains, so confidence is lower here.
There is even a chance we could see some wintry precip later in the
day Friday, depending on how quickly the last surge of cold air gets
in here. For now Saturday looks like it should be dry but cold as
high pressure behind this slow-moving front finally moves into the
mid-Mississippi river valley.
.AVIATION (06Z TAF Update)...
Updated at 1208 AM EST Sun Dec 1 2013
Low level moisture will steadily increase ahead of an approaching
weak cold front. Clouds have already begun to develop, ahead of
schedule, from Michigan to western Kentucky. These clouds will
likely increase in coverage and remain in the region throughout the
The clouds have formed at the low end of VFR, and it appears they
should stay that way at least for several hours. Models have backed
off a bit on the MVFR ceilings they had been predicting for this
afternoon, so have reflected that in the TAFs. Still, ceilings
won`t be very far from the VFR/MVFR border, and prevailing MVFR
ceilings may still develop, especially this evening. There may also
be some restrictions to vsby late tonight. Future TAF packages can
address that in more detail, but for now will trend that way by
introducing 6SM BR.
Winds will be steady from the SSW at 5 to 9 knots through this
afternoon, becoming light and variable tonight.