Area Forecast Discussion
Issued by NWS Paducah, KY

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FXUS63 KPAH 220853
AFDPAH

Area Forecast Discussion
National Weather Service Paducah KY
353 AM CDT FRI JUL 22 2016

.SHORT TERM...(Today through Sunday night)
Issued at 313 AM CDT Fri Jul 22 2016

Main forecast head aches in the near term lie with MCS`s that
continue to form almost nightly up over the Midwest. The remnants
of which push outflow boundaries into very unstable conditions
that develop over our region during the heat of the day. This, of
course, could trigger sct strong thunderstorms. In other cases,
leftover cloud cover/sct precip could move into the region earlier
during the morning, and play havoc with our heat headlines.

Today`s decaying MCS moving south toward the region presents
another case of uncertainty regarding storm chances and also our
heat headlines. If storms can maintain another 3-5 hours, parts of
our north could be affected. Climatology is for the MCS to
continue to diminish during the morning hours, but even if this
occurs, there will likely be left over clouds and an outflow
boundary to contend with, especially east of the Ms River. Not
sure that even the meso models have a good handle on how the day
will pan out, especially over wrn KY. With all of this said, have
decided to up pops over sw IN/wrn KY today into the scattered
category to cover possible storm development along any outflows.
If we manage to heat up into the 90s ahead of any activity, would
need to monitor for isolated damaging wind gusts with stronger
cells. Due to uncertainties/low confidence in how all of this may
affect temps today, decided to leave all "as is" right now, and
continue with ongoing heat headlines. Sometimes, continuity pays
off.

Little changes will be made to the rest of the short term. Will
need to continue with 20-30 percent, mainly diurnal, POPs around
the eastern periphery of the massive heat dome in place over the
srn Plains. Even a couple hours of late morning or afternoon
sunshine will be enough to pop temps into the 90s and heat index
values up into 100-110 range. Muggy mid 70 sfc dew points are
going no where soon. That much is certain.

.LONG TERM...(Monday through Thursday)
Issued at 313 AM CDT Fri Jul 22 2016

Although minor intrusions of heat index values will push near 100
along the southern KY/MO border on Tuesday, and Southeast Missouri
on Wednesday, it appears that Monday (July 25th) will likely be the
last afternoon in which most of the WFO PAH forecast area will
approach Heat Advisory criteria, with the highest values centered
over West Kentucky. This is consistent with Thursday`s forecast
package.

During this model run sequence, the Canadian and GFS Ensemble, with
some influence of the ECMWF, tend to handle the northern stream
troughiness and mid-week 700 mb low transition through the middle
Mississippi Valley consistently, while weakening and bifurcating the
influence of the dominant coast to coast west to east ridge axis
across the southern half of the United States.

There may be a 50-75 mile variation from north to south where an
effective frontal boundary sets up on Tuesday (e.g. Confluence of
the Wabash/Ohio Rivers with the GFS & ECMWF or the Land between the
Lakes with the Canadian model) over the WFO PAH forecast area. The
variation will have a significant impact on how much enhanced QPF
(heavy rain) would impact the area. This WSW-ENE oriented frontal
boundary will occur along southeastward dip of the westerlies from
the Central Plains and Middle Mississippi Valley, flattening out
into a zonal flow across the WFO PAH forecast area.

Within the weakness between the western U.S. ridge dome and the
Southeast Coastal ridge dome axis, the ECMWF and GFS develop and
inverted trough/low across the Central Gulf Coast by Tuesday, this
would help to transport moisture towards Kentucky through mid-week.
These same models also develop a mid-level low lee of the Rockies
and move it east through the middle and latter part of the week. The
influence of this weak low and trough would be to maintain and
enhance convective activity over the WFO PAH forecast area on a
daily basis given a slight cooling at mid-levels.

The ECMWF, Canadian, and GFS Ensemble appear to focus on diurnal
(mainly afternoon/evening) development and propagation of showers
and thunderstorms on an impressed frontal boundary over the WFO PAH
forecast area starting on Tuesday. Depending on the duration of the
mid/upper level shortwaves, available pockets of deeper low level
moisture, could see sporadic to widespread convection along the
impressed frontal boundary. This boundary is maintained through next
weekend. The associated cloud cover and rain during the peak heating
to should limit temperatures to the upper 80s or lower 90s.

&&

.AVIATION...
Issued at 622 PM CDT Thu Jul 21 2016

With the exception of possible MVFR fog between 06-13Z, VFR
conditions should prevail at all sites through the period. Light
south southeast winds early will go calm overnight, then pick
back up again AOB 5 knots after 13Z.


&&

.PAH Watches/Warnings/Advisories...
IL...Excessive Heat Warning until 8 PM CDT Sunday for ILZ075>078-
     080>094.

MO...Excessive Heat Warning until 8 PM CDT Sunday for MOZ076-086-087-
     100-107>112-114.

IN...Heat Advisory until 8 PM CDT Sunday for INZ081-082-085>088.

KY...Excessive Heat Warning until 8 PM CDT Sunday for KYZ001>009.

     Heat Advisory until 8 PM CDT Sunday for KYZ010>022.

&&

$$

SHORT TERM...GM
LONG TERM...Smith
AVIATION...JP



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