Area Forecast Discussion
Issued by NWS Paducah, KY

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FXUS63 KPAH 140535 AAC

Area Forecast Discussion...UPDATED
National Weather Service Paducah KY
1135 PM CST Mon Feb 13 2017

Issued at 1135 PM CST Mon Feb 13 2017

Updated the AVIATION discussion for the 06Z TAF issuance.


UPDATE Issued at 952 PM CST Mon Feb 13 2017

The second of two grid updates issued to reflect greater
saturation/condensation within the 850-600 mb layer after midnight
across Southeast Missouri, as well as some trace precipitation
accumulation along the I-64 corridor late this evening in Southern
Illinois and Southwest Indiana.

The warm nose aloft will be rather shallow (1 or less Celcius),
and some sub-cloud layer evaporative cooling will take place with
the early onset precipitation. Given the warm ground temperatures
and above freezing surface temperatures, anticipate either
sprinkles and/or light rain for now. Cannot rule out a few sleet
pellets at the beginning of the precipitation, but the probability
may be too low for occurrence. Will have to monitor overnight as
surface reports trickle across Missouri.


.SHORT TERM...(Tonight through Wednesday night)
Issued at 240 PM CST Mon Feb 13 2017

Dewpoints have mixed well into the teens over much of the area
this afternoon, and no guidance seems to have much of a clue.
Basically just extrapolated from the 18Z observations to bring the
forecast into line through 00Z.

The main story going forward is the potential for light
precipitation late tonight through Tuesday night. We will be in a
confluent flow situation with a trough developing over the Great
Lakes, and a compact system moving east out of the southern
Plains. This is not a high confidence situation, and with the dry
air obviously in place across the area, the 12Z models, which are
trending wetter overall, seem to be overblown with the QPF.

The latest development in the 12Z models is to bring a swath of
QPF farther north through the area late tonight into Tuesday
morning. This is in response apparently to a weak disturbance
rotating southeast through the area ahead of the southern stream
system. Not very confident at all in this development. Ended up
increasing PoPs overnight, but limited them mostly to southeast
Missouri. Otherwise kept 50-60% PoPs along the southern border
areas with a sharp gradient to the north Tuesday through Tuesday
night. This most closely resembles the 12Z ECMWF.

Model soundings suggest that the temperature profile should be
warm enough to support all rain, especially farther south where we
are most likely to actually get precipitation to ground. Cannot
completely rule out some partially melted snow which would result
in pellets of some form, but temperatures should be above
freezing, so there will be no impact.

A cold front will move through the area Tuesday night, and that
will lead to a cool down a few degrees below normal for Wednesday.
The surface ridge will settle over the area Wednesday night as we
continue to be in cyclonic northwest flow aloft.

As for temperatures, undercut consensus a bit for lows tonight,
figuring on some rapid radiational cooling this evening, before
the mid and high clouds thicken up. For Tuesday, temperatures in
the south are likely to be suppressed by clouds and any rainfall,
so tried to accentuate a trend from cooler south to warmer north.
Generally went with the cool side of guidance in the south and the
warm side in the north. North winds will stay up all night Tuesday
night, so the consensus of guidance should be good for lows. Left
the consensus alone Wednesday and Wednesday night. If winds really
drop out Wednesday night we may be well into the 20s for lows
over much of the region. We may not be cold enough then.

.LONG TERM...(Thursday through Monday)
Issued at 240 PM CST Mon Feb 13 2017

Models indicate high pressure will be moving across the Gulf Coast
states late in the work week.  South to southwest winds and plenty
of sunshine will lead to a significant warm up beginning Thursday
and continuing through the weekend.  Highs will be in the lower to
middle 50s Thursday, with the entire area well into the 60s by

Models show an upper level trof moving across our region Saturday
into Saturday night.  So far it looks like there will not be a lot
of moisture available, and models show just a few blips of 0.01
precipitation at times in the late Friday night through Sunday time
frame.  At this point prefer to keep the weekend forecast dry, and
we will see if the next few models runs show any more organized
precip chances.

As we get into Monday, the ECMWF and Canadian move a cold front into
the PAH forecast area. GFS is 18 to 24 hours slower with this
feature, but with the decent agreement in the ECMWF/Canadian
solutions, will go fairly close to their timing. This leads to
good chances of showers across our entire area by Monday
afternoon, and with the ECMWF showing some low CAPE values along
the front, included slight chances for thunderstorms.


Issued at 1135 PM CST Mon Feb 13 2017

Surface high pressure settling over the area will result in light
and variable winds overnight. Cigs will lower to around 10kft
across the TAF sites overnight, and there is a small chance of
light rain moving across KCGI/KPAH between 09-14Z as a storm
system approaches from the southern plains. VFR conditions should
prevail through the period.




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