Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 040246
Area Forecast Discussion
National Weather Service Louisville KY
946 PM EST Sat Dec 3 2016
Issued at 940 PM EST Sat Dec 3 2016
Mid-level cloud deck is solidly established over the Ohio Valley,
with the rain shield associated with an area of isentropic lift is
just trying to spread northward into south central Kentucky.
Precip looks well on track to overspread the area overnight, but
boundary layer is still dry enough that measurable rain will be
fairly spotty. Advertised timing looks fairly well on track, but we
have done some tweaks that will show up in the hi-res products.
Impacts to zone forecast are minimal.
With the surface wetbulb temps running above freezing over southern
Indiana and north central Kentucky, not to mention dewpoints above
freezing in south central Kentucky, confidence is fairly high
that precip type will remain all rain.
.Short Term...(This evening through Sunday night)
Issued at 230 PM EST Sat Dec 3 2016
Gentle, but deep-layered, isentropic lift will move into the region
overnight. Precipitable waters will increase slowly from the south,
to around an inch, roughly double the current value, by 12Z Sunday
down along the KY/TN border. The combination of this increasing
moisture and that lift will mean a chance for precipitation, albeit
relatively light. Forecast soundings indicate a steady saturation,
resulting in lowering high cloud bases tonight. Freezing levels will
drop a little tonight, but with the warming in the lower layers,
expect any initial mix of rain/snow on the northern edge to become
rain. Surface temperatures around daybreak will hover near freezing
in our Bluegrass and southern Indiana counties, but any precip
should be light enough not to cause any driving hazards, especially
with relatively warm road temperatures.
For the day Sunday, deeper moisture briefly departs, as we get
gapped between a vortmax crossing by to our north and the energy
heading through the Deep South. Despite this gap, the models keep
light QPF fields in through the day, perhaps indicating some
drizzle/light rain showers. Given the cloud cover, it will end up
being a another raw day, with temperatures likely rising only to the
mid to upper 40s, a little below normal for early December.
That precip will kick east of here Sunday night, with high pressure
building in behind it. Cannot rule out some linger light drizzle and
or patches of fog overnight. Expect temperatures to fall again into
the mid to upper 30s.
.Long Term...(Monday through Saturday)
Issued at 240 PM EST Sat Dec 3 2016
Models remain remarkably consistent in dealing with systems in the
first half of the work week, but then the ECMWF solution continues
to have a wetter system Wed. night and Thursday. Whatever the
outcome of that system, we`re still looking at a significant cool
down to close out the work week and head into the next weekend.
First off, we`ll start with high pressure shifting to the Mid
Atlantic states Monday, as our next system approaches from the
southern Plains. Stronger isentropic lift will accompany this
system, bringing a solid area of rains, likely up to an inch.
Surface low pressure will cross the state some time Tuesday, with
breezy conditions ahead of and behind it.
Large surface high pressure will ridge in from the southwest Canada
as a large upper low spins over south central Canada Wednesday. The
latter feature actually has a similar depiction in the various model
guidance, but 00Z Euro has continued its solution with another
surface low crossing our region. The 12Z Euro has backed off on
precip a little, as well as with the strength of that low. Still,
with the cold air, we`ll have a brief potential for snow on the
That cold air will mean highs Thursday struggling in the lower 30s
and Friday likely staying in the 20s. Lows Friday and Saturday
mornings will be the coldest of the season, in the teens.
.Aviation...(00Z TAF Issuance)
Issued at 600 PM EST Sat Dec 3 2016
Low clouds are all but gone, but high/mid-level ceilings remain in
place, with light E-NE winds. Expect that to continue through the
evening, with cloud bases lowering after midnight as isentropic lift
increases in response to the southern stream disturbance. Precip
late tonight into Sunday morning will be spotty enough to be handled
with VCSH and ceilings remaining just barely VFR.
However as the day progresses, the lower layers will continue to
saturate and a northern stream disturbance will swing into the Ohio
Valley. Expect more of a steady rain to develop, with ceilings and
visibilities dropping into fuel-alternate/MVFR by late morning, and
eventually into IFR in the afternoon.
Weakening upper trof axis pushes through in the evening, but that
will only dry out the planning period at SDF. Winds remain light as
they shift to the west, and ceilings stay in fuel alternate, perhaps
with some lingering drizzle.