Area Forecast Discussion
Issued by NWS Paducah, KY

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000
FXUS63 KPAH 200858
AFDPAH

Area Forecast Discussion
National Weather Service Paducah KY
358 AM CDT WED JUL 20 2016

.SHORT TERM...(Today through Friday night)
Issued at 335 AM CDT Wed Jul 20 2016

Main forecast issues with this package center around the heat
headlines, where to possibly upgrade to warnings and extend
current advisory in time.

Firstly, today looks like a wild card in the deck as far as the
overall picture that looks to be shaping up for the Thursday
through Saturday time frame. Mid level cloud deck left over from
last night`s convective complex could very well give us a
temporary break from the oppressive heat in many locations today,
esp along and east of the MS River. Much of the model data now
suggests this deck could hang on much of the day. However, even a
few hours of sun would pop temps into the 90s, so do not want to
back off too much at this point.

The bigger concern lies with the Thu-Sat time frame, when the
upper ridge is really expected to build excessive heat east into
the region. Surface temps could easily make it into the 96-98
degree range over the current advisory area, with heat index
values up close to 110. Decided to invoke two major changes at
this point. Firstly, even tho today may be iffy in many locations,
decided to go ahead and extend the current advisory out through
Saturday. Secondly, out in our far western four counties of se MO,
where clouds may end up being less of an issue this afternoon, per
collaboration with neighboring offices, decided to go ahead and
upgrade to an excessive heat warning through Sat. This may well
end up being the area that sees the highest heat indices the
quickest. That said, I would not be surprised if advisories and
warnings need to be expanded eastward across the rest of the
forecast area in later forecast packages. Most all of the region
could be flirting with 110 heat indices by the end of the week.

.LONG TERM...(Saturday through Tuesday)
Issued at 335 AM CDT Wed Jul 20 2016

The extended forecast period will start out with the expansive
mid/upper ridge dominating the weather picture for the PAH forecast
area, with oppressive heat and humidity in place and an unstable
atmosphere, at least in the low levels. Plenty of sun, and mainly
diurnal widely scattered shower and tstm development can be expected
over the weekend, with a possibility of an isolated strong downdraft
or two with better developed tstms. Highs should be in the middle
90s, lows in the upper half of the 70s. Dewpoints should stay in the
middle 70s, even considering afternoon mixing, what little there is.
This will yield heat indices between 105 and 110, especially on
Saturday, which should be a tad warmer than Sunday. The ridge will
begin to lose some of its influence next week.

The medium range models now appear to be in reasonable agreement
through the extended period with the overall mid level flow across
the CONUS. A persistent shortwave centered near the Canadian border
is progged to make its way eastward toward the Canadian maritimes.
The ECMWF has recently been bullish on digging the shortwave into
the upper Midwest and therefore slowing its forward speed, however
the 00Z run now moves it along, similar to the other models. This is
supported by the GFS/EC ensemble means solutions. This feature will
induce a trof of low surface pressure and a frontal boundary which
will trail across the Midwest. According to the initialization blend
of models, the front will make it into the PAH forecast area by
Sunday night/early Monday (the ECMWF depicts a tad slower fropa).
The frontal boundary will provide low level focus for scattered
showers and tstms across the region during the day Monday (the best
PoPs of the extended period), tapering off from the north Monday
evening. The leading edge of drier air may not make it all the way
to the AR/TN border by Tuesday, therefore shower/tstm activity may
still occur in that vicinity. by Tuesday, highs should cool at least
five degrees compared to Saturday.

&&

.AVIATION...
Issued at 1147 PM CDT Tue Jul 19 2016

A decaying thunderstorm complex over southern IL as of 0430z will
send an outflow boundary across the taf sites by 08z. Winds will
shift into the north for a couple hours in the wake of the boundary,
along with some showers and possible thunder.

Overall, no change in the weather pattern is expected this taf
cycle. MVFR vsbys in fog will be common around sunrise. The fog will
burn off shortly after sunrise, followed by scattered to broken
diurnal cumulus.

Winds be light and variable. Isolated thunderstorms will be possible
again Wednesday in this very humid and unstable air mass. However,
sparse coverage and lack of a specific time-frame precludes
mentioning them in the tafs.


&&

.PAH Watches/Warnings/Advisories...
IL...Heat Advisory until 7 PM CDT Saturday for ILZ075-080-081-084-085-
     088-089-092>094.

MO...Heat Advisory until 7 PM CDT Saturday for MOZ076-086-087-110>112-
     114.

     Excessive Heat Warning from 7 AM this morning to 7 PM CDT
     Saturday for MOZ100-107>109.

IN...None.
KY...Heat Advisory until 7 PM CDT Saturday for KYZ001>006.

&&

$$

SHORT TERM...GM
LONG TERM...DB
AVIATION...MY


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