Area Forecast Discussion
Issued by NWS Paducah, KY
FXUS63 KPAH 012140
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PADUCAH KY
340 PM CST Sun Dec 1 2013
.SHORT TERM...(This Evening through Tuesday night)
ISSUED AT 259 PM CST SUN DEC 1 2013
As referenced in the midday forecast update, insolation (sunshine)
working on the shallow stratus layer from above and weak warm
advection below around the weak cold frontal zone, helped to
dissipate a significant amount of cloud cover over the northern
three-quarters of the WFO PAH CWA. Air temperatures running close to
or a degree above forecast maxes for today.
Within 25 miles of the demarcation line between clear skies and
existing cloud cover this afternoon anticipate some differential
cooling this evening and overnight. This should set the stage for
fog development over Southeast Missouri, Southern Illinois (south of
I-64), and into parts of Northwest Kentucky and Southwest Indiana.
The SREF probability of visibilities less than a mile jumps to over
75 percent for parts of Carter, Ripley, Butler, and Wayne counties
in Southeast Missouri around 6 am CST Monday morning. In
coordination with WFO Springfield, a decision was made to delay any
consideration for a Dense Fog Advisory in this area. Given the
gridded data, it appears that the 3 am - 8 am CST time period will
be the most critical for Dense Fog production, Since fog potential
is not even expected until after midnight at most locations, will
defer to the evening shift for the need for any advisory.
Regardless, the potential will be addressed in the Hazardous Weather
Any small chance for drizzle and/or isolated light rain showers will
remain over West Kentucky tonight, as weak perturbations in surface
boundaries, seeder-feeder mechanisms aloft, and periodic vorticity
generation in a broad northwest trough aloft should support some
trace or barely measurable pockets of rain. Any chance for rain
should be gone before noon on Monday.
For Tuesday and Tuesday night, it was not possible to eliminate some
small probability of shower activity as the upper level flow shifts
from west-northwest to west-southwest and a warm advection
zone/conveyor belt begins to evolve in advance of the significant
weather system slated to move into the area during the later half of
By Wednesday, the warm advection scheme sharpens up over the WFO PAH
forecast area, lending to at least chance PoPs over most of the
forecast area. Most of the high resolution model suite, as well as
the medium range Canadian/European/GFS were used in the construction
of the sensible weather element grids and offered a good compromise.
With respect to the next system, the WPC frontal guidance did not
appear to be doing too bad with the timing of the Arctic/Canadian air
mass later this week. The cold air, showing up over northeast
British Columbia/northwest Alberta Canadian provinces appeared to be
moving southeast around 18 knots (via linear extrapolation) along
the eastern side of the Canadian Rockies. Timing places the leading
edge of the colder air along the MT/WY border by 20z Monday, fairly
close to the timing of the frontal passage by WPC. Timing will be
everything later this week.
.LONG TERM...(Wednesday through Sunday)
ISSUED AT 259 PM CST SUN DEC 1 2013
Discussion in this time frame will focus mainly on the upcoming
winter weather threat coming later this week. Models seem to be
converging on a signal that would bring at least some winter
weather to much of the forecast area Thursday night and Friday.
An arctic front is now expected to push through most of the region
later Wednesday night/early Thursday morning. There may be some
light rains associated with its passage, but most of the mid level
dynamics/forcing and moisture will actually lag the front and
build into the region Thursday night/Friday time frame. Numerical
models have consistently been bringing the arctic front and its
associated cold air into our area quicker and quicker, and this
will be a very cold dome of air from nw Canada.
Thinking (for now anyway) is that moist swly flow aloft will
continue to over run this dome of cold air for an extended time
Thursday night through Friday, with weak short waves ejecting ne
from the base of the H50 trof moving slowly east out of the
southern Rockies. This scenario should generate a least a couple
periods of generous qpf amounts.
The main precip event will begin as plain rain later Thu afternoon
or very early Thursday evening. However, very cold air from the nw
will continue to ooze se into OH Valley Thursday night. The cold
air will be shallow at first, so once the sfc temps reach freezing
early Thursday evening over se MO/srn IL, freezing rain will
become likely. The transition over to freezing rain is expected to
occur during night farther southeast into wrn KY. Our far
southeast counties may not get to near freezing until toward dawn
or so. The cold air should become deep enough during the night over
se MO/srn IL to change the freezing rain over to sleet/snow.
However, farther southeast along and south of the Ohio River,
there seems to be the potential for a more extended period of
Whatever precipitation falls on Friday morning should gradually
end or taper off as a second push of cold air comes in behind the
first short wave. At the same time, the main upper trof will head
toward the region, and possibly bring a swath of snow with it.
All should be pretty well said and done precip wise by midnight
Friday. However, the coldest air will still be yet to come over
the weekend, with teens most locations by Sat morning. It would be
colder if there happens to be any snow or ice cover.
It is way too early too early to speculate on specific amounts of
winter precip, as the system is still about 4 days off. The timing
of the cold air and the location(s) of the highest precip amounts
remain very much in question. However, confidence is increasing
that some type of winter weather event will occur in or close to
our forecast area later in the week.
ISSUED AT 1207 pm CST SUN DEC 1 2013
Given the effective mixing of the shallow moisture layer in the
vicinity of the cold front, moved all WFO PAH TAF`s back into VFR
ceiling category. Between 04z-06z Monday, MVFR to local IFR
visibilities and MVFR to VFR ceilings were returned to each of the
WFO PAH TAF sites, depending on their proximity to the decaying
cold frontal boundary. By 16z Monday, all of the TAF sites should
be back in VFR category.