Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 290817
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
317 AM EST Sat Nov 29 2014
.SHORT TERM (Now through Sunday)...
Issued at 250 AM EST Sat Nov 29 2014
A low pressure system will move out of the upper Midwest today into
southern Canada. It will continue to track to the north and east
through Sunday, dragging a cold front towards the region as it does
so. To the east an elongated area of high pressure along the eastern
seaboard will slowly shift eastward. This will leave southern IN and
central KY in southerly to southwesterly flow through the short term
Warmer and moister air will be advecting into the area today. As low
level moisture increases through the day so will the cloud cover. By
this afternoon saturation looks to be enough in the low levels to
squeeze out a few showers, though these should be rather light. The
best chance for any precipitation will be across the northwestern
half of the forecast area. The better chance for any showers will be
later this afternoon into the evening hours. Rain chances will
increase tomorrow as the front approaches from the northwest.
Warm air advection will continue through tomorrow ahead of the
front. Temperatures will rise into the lower to mid 50s by late
afternoon. For tonight we will see a non-diurnal temperature trend.
Temps may initially fall a degree or two, but are expected to then
stay steady or rise a few degrees overnight. Sunday`s highs will be
in the lower to mid 60s despite ample cloud cover.
It will be breezy today and tomorrow. Wind gusts this afternoon will
be in the 20-25 mph range. Tomorrow they will be a bit higher with
gusts up to 30 mph possible.
.LONG TERM (Sunday night through Friday)...
Issued at 315 AM EST Sat Nov 29 2014
Will have a front just north of the forecast area Sunday night. The
Parallel GFS and NAM are in agreement placing a very narrow ribbon
of precip right along or just behind this front. They also show very
light patches of precip right over the Ohio Valley, more indicative
of isolated to widely scattered light rain showers. This front looks
to get at least to the Bluegrass Parkway by daybreak Monday, pulling
that ribbon of moisture southward as well. High temperatures for the
day will be just ahead of this front.
Precip looks to linger on the back side of this front, deeper into
the cold air. Forecast soundings indicate a warm nose aloft that,
with a deeper cold near-surface layer may allow for some
re-freezing. Unfortunately, they also show a lack of ice crystals in
the layer above this warm nose, mainly in the area of the coldest
surface temperatures over the north. In addition, have some a gentle
slope of frontogenesis with stronger EPV above it across central
Kentucky. The shallower slope would indicate more widespread lighter
bands of precip, but the stronger EPV leans toward some stronger
embedded bands. All that said, we could see a light winter mix by
mid afternoon Monday over our northern row of counties in Indiana,
then spreading to the Ohio River by late afternoon Monday. That
winter mix will push southeast through the night. The good news here
is that ground temperatures should start off warm enough to preclude
any significant accumulations of snow or sleet. After the precip has
shut off overnight, we may have to deal with wet roads freezing as
the cold air pushes in.
The precip shield should be over the Appalachians by daybreak
Tuesday. High pressure will move quickly by to our north. In its
wake we will return to more rain chances as weak, and difficult to
time/place, disturbances cross the zonal flow over us. Thus have a
lower confidence in details from Wednesday through Friday. Despite
this difficulty, the model consensus brings a band of rain oriented
parallel to but south of the Ohio River Tuesday night and Wednesday.
Once again, totals are light with this feature. Temperatures should
be warm enough for this precip to fall as rain.
Another such disturbance looks to be strong enough, according to the
GFS, to push a surface low out of the Central Plains and pulling a
surface front up to our region Wednesday night and Thursday. Should
this occur, large area of rain ensues that persists in the vicinity
from Wednesday to Friday. The GFS then brings another system along
this boundary to keep our rain chances going to Saturday. The Euro
on the other hand, deals with these weak disturbances in the flow
differently, instead focusing our better rain chances Thursday night
and Friday. Given the lower confidence caused by the regime aloft,
will continue previous forecaster thinking of sticking with the
blended forecast and hoping for some continuity as we get closer.
That blended forecast does bring another slight chance for rain or
snow across the north Wednesday night.
.AVIATION (06Z TAF Update)...
Updated at 1201 AM EST Sat Nov 29 2014
VFR conditions are expected through the overnight period and most of
the morning. Winds will be out of the south overnight and will start
to increase towards dawn as the pressure gradient tightens across
the area. Winds are expected to become gusty by afternoon with
sustained winds of 10-15 knots and gusts as high as 20 knots. Low
level moisture will be on the increase today with these southerly
winds. Ceilings will lower through the morning with MVFR conditions
expected by the afternoon. A few showers may move through the
terminals this afternoon and tonight as well. Gusts will diminish
tonight after sunset, though sustained winds will remain in the
10-12 knot range. A low level jet will develop overnight. This may
require the addition of LLWS to the TAFs eventually.