Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 242014
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
314 PM EST Mon Nov 24 2014
.SHORT TERM (Now through Tuesday Night)...
Issued at 300 PM EST Mon Nov 24 2014
High pressure ridge axis over the Deep South will extend into the
Appalachians tonight, then across our region Tuesday and Tuesday
night. Aloft, broad troughing will continue to our west to Tuesday
night. By early Wednesday a vortmax crossing the Deep South looks
like it will spawn an east coast storm. This storm may be large
enough to allow for some mid/high clouds to reach into our Lake
Cumberland counties by daybreak Wednesday, but not expecting
precipitation at this point.
Temperatures have dropped into the 40s for all but our eastern and
southern sites, but they should be there soon. Winds already are
starting to relax over the region as the pressure gradient begins to
loosen. Will go ahead and drop the advisory across the region, as we
no longer are getting gusts to 40 mph.
Lows will get into the 30s tonight. Tuesday should be a nice day,
save for high temperatures below normal, generally in the 40s. With
lighter winds Tuesday night, readings should dip into the 20s,
though cloud cover may bring them back up across the southeast by
.LONG TERM (Wednesday through Monday)...
Issued at 255 PM EST Mon Nov 24 2014
...A light wintry mix possible for Wednesday/Wednesday night...
The synoptic pattern at the start of the long term period will
feature rather amplified flow aloft, with a western trough/eastern
ridge regime. This flow will transition to a more zonal look
towards the end of the long term period.
The main focus of the long term period continues to be on a Clipper
system progged to affect the Ohio Valley Wednesday into Wednesday
night. Guidance has come into better agreement regarding the
track/timing of this system, though some subtle differences do
remain. In these Clipper systems, the maximum in precipitation
tends to occur just to the north of the surface low, typically in a
narrow swath. A left-exit region of a strong upper-level jet will
help induce a tightening mid-level thermal gradient, which should
help to develop a band of more moderate precipitation within a
broader precip shield. Looking at model forecast soundings, it
looks like the precipitation will likely start as mostly rain across
the region. The timing of this system will be key, as a slower
arrival would put it more into the Wed. night timeframe and thus the
surface would be a bit cooler. As it looks now, this appears to
start as a rain event, with perhaps some snow mixing in on the
backside and/or in the more moderate precipitation band where
dynamical cooling may be just enough to get some snow to the
ground. Either way, with surface wet bulbs staying above 0C through
the bulk of the event, don`t expect too much in the way of impacts
except maybe some light grassy accumulations or perhaps an isolated
slick spot. Given the busy travel period, this is a system that
will continue to be monitored closely as a slower arrival/southward
shift could mean a bit more snow potential.
For the remainder of the extended, the flow flattens out toward the
end of the week as the western ridge breaks down. This will allow
for a moderating trend, with highs this weekend pushing into the
50s. A cold front will approach on Sunday, which will lead to some
rain developing across the region. There had been concern that this
front could undercut some warmer air aloft and this could turn into
an overrunning event, but that solution now appears unlikely as the
guidance has trended toward a warmer solution. Looks to be a liquid
event as we sit to the south of the arctic front.
.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.