Area Forecast Discussion
Issued by NWS Paducah, KY

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155
FXUS63 KPAH 130350
AFDPAH

Area Forecast Discussion
National Weather Service Paducah KY
950 PM CST Thu Dec 12 2019

.UPDATE...
Issued at 950 PM CST Thu Dec 12 2019

Aviation update (06z TAFs).

&&

.SHORT TERM...(Tonight through Saturday)
Issued at 200 PM CST Thu Dec 12 2019

In the immediate term, models were having difficulty handling the
dry air at the surface this pm. Dew points remain largely in the
20s and there`s even some upper teens around, which may be
suspect. The models appear better synchronized with clouds that are
largely mid and high variety and winds, with some gustiness, that
are higher closer to the tighter gradient in our northwest tier of
counties.

Beyond the immediate term, gridded time/height cross sections show we
should see a continuation of the very dry air in the lower trop
thru the day Friday. This should work to preclude (most) precipitation
chances from slinging much back into the FA, as moisture overruns
a boundary that is well to our south and east. But it looks like
we may carry a collaborative small pop in our far east, into
Friday evening. Pops there (east) should diminish late Friday
night, as upper trof energy swings thru. However, a 2ndary punch
of clipper wave energy will bring its own sling of moisture down
the nwly pike, and the blend has consistently picked up on
smallish pops with its track, across basically our northeast half
of the FA. We`ll stay with these ensembled assembly of smallish
pops for late Friday night thru Saturday, but overall QPF is
scarce, and boundary layer temps just warm enough, so they should
offer minimal impacts.

.LONG TERM...(Saturday night through Thursday)
Issued at 200 PM CST Thu Dec 12 2019

As a surface high builds into the Midwest and western Great Lakes
region Saturday night/Sunday, isentropic lift should get going by
Sunday afternoon east of a mid level trof out over the southern
Rockies. This may be able to generate some light precipitation
along and to the north of a west-east oriented sfc boundary
located from the western Gulf Coast states ne into the lower TN
River Valley. Precip chances will then increase Sunday night into
Monday as a surface low develops on the frontal boundary and
begins to strengthen and head northeast.

It seems as though enough cold air will be in place on Sunday into
Sunday night for any precipitation to fall in the form of snow or a
rain/snow mix, especially north of the OH River. Would not be
surprised to see some accumulations during the late afternoon and
night-time hours, but the qpf forecast is a bit problematic and
of lower confidence. For now, will compromise with a qpf close to
WPC numbers, but it should be noted that there are some models,
including the 12z ECMWF, that triple the WPC qpf. Of course, that
would translate into higher snow totals than we currently have in
the official forecast. In addition, there may well be a narrow
band of mixed wintry precip along or somewhere near the OH River.
Stay tuned.

On Monday, surface low pressure will rise northeast along the
frontal boundary. Though models have converged somewhat on the track
of the low, there is still uncertainty as to whether the track is
right up the OH River, or farther southeast toward the Nashville TN
area. For now, looking like consensus is to lean more toward the
farther south solution. This is important because if the low track
were to end up farther nw, then we could be dealing with a
convective risk too, as more instability would become available
along/east of the low track.

Thinking now is that just enough warming will take place during the
daylight hours Monday across our northern counties to allow any snow
to change over to a cold rain, which could dig into any snow totals.
In addition, it is now looking as though any deformation snows
wrapping around the back side of the system on Monday evening will
miss our forecast area to the nw and north, but not by much.
However, any lingering precip that does last into Monday night would
likely turn back over to a little light snow or flurries before
ending later in the evening.

Another shot of very cold, Canadian air will spill into the region
behind the system Tue/Wed, with high temps holding in the 30s to
near 40 and overnight lows down into the teens to lower 20s. Some
moderation should begin to take place by Thursday, but readings
should still be below seasonal norms.

&&

.AVIATION...
Issued at 950 PM CST Thu Dec 12 2019

Forecast looks more pessimistic than what we looked at earlier, at
least for west KY into southwest IN, and maybe the southern tip of
IL and part of SEMO. Clouds, MVFR cigs over TN will continue to
lift north and may expand a little northwest overnight. There may
even be some fog at the leading edge of the arrival of clouds
around daybreak, supported more strongly by guidance. The MVFR
cigs will persist through the day Friday especially west KY into
southwest IN. Cannot rule out some light rains as well in this
area, that may have to be added with time. Not a high chance
though. Winds will be light, mainly from the south. Overall, low
confidence call in terms of how far north and west the clouds will
spread.

&&

.PAH WATCHES/WARNINGS/ADVISORIES...
IL...None.
MO...None.
IN...None.
KY...None.
&&

$$

UPDATE...08
AVIATION...08



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