Area Forecast Discussion
Issued by NWS Paducah, KY

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FXUS63 KPAH 050259

Area Forecast Discussion
National Weather Service Paducah KY
859 PM CST Mon Dec 4 2017

Issued at 859 PM CST Mon Dec 4 2017

Updated the public forecast to delay the arrival of the convective
line by an hour or two. Radar trends through the evening have been
steadily downward and lightning activity has also been dwindling.
Given the strength of the wind field, especially in the low-
levels, a few gusts up to 40 mph will be possible, but severe
weather is unlikely. Of course gusts up to 35 mph will continue to
be possible ahead of the line.


.SHORT TERM...(Tonight through Wednesday night)
Issued at 1253 PM CST Mon Dec 4 2017

Early this afternoon, a deep surface cyclone was over southern MN
with a trailing cold front extending south into the southern
Plains, still well to our west. Sharp s/wv energy was moving
across the northern Plains, with a nice fetch of moisture seen on
wvapor moving NE along a 75-90 kt upper level jet. Radar showed an
increase in light showers over the past hour. Members of the HREF
and HRRR show an uptick in scattered convective activity this
afternoon. The activity should head NE 40-45 mph, with isolated
thunder possible. The models depict a lull after this initial area
of WAA convection driven by weak mid level support and low level
moist transport. Gusty south winds to continue.

Focus for convection tonight will be along the aforementioned
cold front, that will move across the area. Continued with
categorical 100 PoPs for showers and scattered thunderstorms.
PWAT`s will be unseasonably high as the front moves through. So
some decent and much needed rain is forecast. The chance of strong
and isolated severe will stay to our west. Even with a decent low
level jet, the low level lapse rates are not conducive to
downward momentum. Just gusty surface gradient winds ahead of and
behind the front.

The precipitation will move out quickly from west KY Tuesday
morning, with dry weather from Tuesday afternoon through Wednesday
night, as a surface ridge axis moves southeast across the area,
with dry NW flow aloft forecast. It will be colder behind the
front, but not too far from norms. Colder air arrives later in the
week. Stayed close to persistence and MOS for temps. Decent model
agreement overall in the short term. Precip/PoP trends will be
derived from the HRRR, and members that make up the HREF, and
some NAM incorporation.

.LONG TERM...(Thursday through Monday)
Issued at 1253 PM CST Mon Dec 4 2017

Confidence remains high that a high amplitude flow pattern will
prevail through the long term. The overall pattern will be a
strong mid level ridge over the west U.S., and deep trof over the
east 1/2 of the nation. The mean trof axis positions are similar
longitudinally to 24 hours ago, perhaps slightly slower per the
latest ensemble mean solutions. Significant negative anomalies
continue to be seen with this trof over our area. This will result
in below normal temperatures, as much as 5 to 15 degrees, and
unsettled weather, as impulses head SSE, bottom out in the base of
the trof and then head on east. Despite the very low heights
aloft, surface pressures are not terribly high, negative
anomalies minimal.

It continues to look dry Thursday. The models for two days now
show a lead wave that will move across the area late Thursday into
Thursday night then dampen. The uncertainty lies with forecast
moisture. The GFS is persistent suggesting some very light snow
showers or flurries may move across the area. However the EC and
CMC solutions remain dry. Sometimes the EC and CMC are too
conservative in this regard. So we prefer to keep a slight chance
20 PoP going.

The models depict a lull Friday. A consistent signal remains for
Friday night. Another s/wv will move SE across the area resulting
in additional h5 height falls, and greater moisture. There is
generally agreement across the board, that light snow will
accompany this system, with the best chances across the NW 3/4 of
the area. Bear in mind this is a late day 5 into early day 6
forecast, and the details may change. For now, conservative and
appropriate wording is we may see some snow, and possibly light
accumulations should the signal remain. Adjustments in timing and
such will continue to be made over the next few days. Will there
be any impacts? Way too early to tell. Other than maybe some
lingering light snow showers or flurries early Saturday SW Indiana
and KY Pennyrile, dry weather on through Sunday and most of
Monday. Temperatures will moderate Sunday into Monday as the mean
mid level trof axis moves on east.


Issued at 536 PM CST Mon Dec 4 2017

Little variation in timing and lowering of ceilings and
visibilities from VFR to MVFR (with locally brief IFR visibilities
possible) from 18z Monday WFO PAH TAF issuance. Current pre-
frontal and main cold front convection and cloud cover following
closely to the NAM-WRF model guidance. May have trended in the
wrong direction, but returned ceilings and visibilities back to
VFR category between 7z and 10z Tuesday as frontal boundary moves
east of the WFO PAH TAF sites.  Will monitor.




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