Area Forecast Discussion
Issued by NWS Paducah, KY

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FXUS63 KPAH 110815
AFDPAH

Area Forecast Discussion
National Weather Service Paducah KY
315 AM CDT Fri Aug 11 2017

.SHORT TERM...(Today through Sunday night)
Issued at 315 AM CDT Fri Aug 11 2017

Confidence in the near term forecast has improved over what it has
been of late--particularly with respect to the now dry forecast
for Saturday. There is some question as to how quickly the chance
of precipitation will return late in the weekend, but the primary
focus remains the potential for showers and thunderstorms today.

The upper level pattern will continue to feature troughiness over
the northern and eastern quarter of the nation with an upper high
suppressed into the far southern states. At the surface, low
pressure over the western Great Lakes early this morning will
slowly shift east into southeastern Canada through Saturday. Mid
level energy over the Plains and Missouri Valley will stream
eastward into the Mid Mississippi Valley today as a cold front
attendant to the Great Lakes low drops southward across the
forecast area. This will provide the impetus for scattered to
numerous showers and thunderstorms today into at least the early
evening hours.

Exactly how all of this unfolds is still somewhat uncertain.
However, CAM models tend to bring the newly developed shower and
thunderstorm activity over Missouri and southwest Illinois east
into southeast Missouri and southern Illinois this morning. The
activity may tend to weaken towards the mid to late morning hours.
As the atmosphere destabilizes, the development of additional
shower and thunderstorm activity is expected during the afternoon
hours. Much of the model guidance seems too quick to shift winds
around to the northwest this afternoon. Generally favor the NAM
and HRRR for their slower wind shift with the frontal boundary
late this afternoon and evening.

While anticipated sky cover may limit destabilization, intervals
of sunshine will likely result in pockets of moderate instability
by afternoon. That may give rise to convective updrafts capable of
producing marginally severe wind and hail. In addition, deep layer
shear of 30 to 35 knots may be just enough to organize storms into
a couple of clusters or line segments, which could enhance the
potential for damaging winds. The storms should tend to weaken and
diminish from north to south this evening as instability decreases
and the front shifts south of the area.

By Saturday, the region will be under the influence of a cooler
and drier air mass north of the cold front. This should keep much
of Saturday, Saturday night, and even Sunday dry. Models are split
on how quickly the chance of precipitation returns to the area
early next week. Both the NAM and ECMWF bring a chance of showers
and storms back into the area as early as Sunday night, while the
GFS and Canadian are dry. I am not quite ready to bite into the
drier solution quite yet, so will keep a small chance for mainly
the southern half of the area Sunday night.

The model consensus blend appears to have a good handle on near
term temperatures. Today should be the warmest of the next 3 days
with highs in the mid 80s. There will be some variation influenced
by sky cover and convection. Highs are only forecast in the lower
80s both weekend days. Lows will generally range through the 60s,
though some upper 50s are possible in our northern counties
Saturday night.

.LONG TERM...(Monday through Thursday)
Issued at 315 AM CDT Fri Aug 11 2017

Forecast confidence has lowered from yesterday with respect to PoPs
weather across the WFO PAH forecast area next week. At this time,
have only a 30-40 percent confidence in the medium range model
guidance (namely the GFS/ECMWF) in depicting the precipitation
coverage and timing across the WFO PAH forecast area.

The problem area appears to be the impact of the cyclonic vortex
rotating around Alaska and the western provinces of Canada. This
feature seems to have an influence on periodically suppressing the
western U.S. broad flat ridge, generating a more zonal and slightly
wetter pattern downstream in our area. If anything, the western U.S.
flat ridge has been more consistent in generating a west-northwest
flow aloft over the region, pushing precipitation further to the
south and southeast with time.

In coordination and collaboration with surrounding NWS offices,
attempted to lower PoP`s across the most the WFO PAH forecast area
on Tuesday and into parts of Wednesday. This time period was
originally dry during previous model runs. For now, blended with
surrounding offices, keeping higher rain chances confined to
southeast Missouri and parts of the Pennyrile region of West
Kentucky. Unfortunately, this means that a small chance for
precipitation will likely be found with some persistence

When opportunities were presented, added the influence of the
Canadian model guidance, as well as MOS-based guidance for
temperature next week.

&&

.AVIATION...
Issued at 1146 PM CDT Thu Aug 10 2017

MVFR fog possible at KCGI between 09z-13z, otherwise VFR vsbys
expected. Increasing mid level clouds expected overnight ahead of
an approaching cold front. Scattered -TSRA/-SHRA possible at TAF
sites between 16z-19z, with increasing coverage after 19z. MVFR
vsbys/cigs possible with convection. Winds will be light and
variable to calm overnight, becoming southwest around 5 kts after
13z, shifting to the northwest around or after 00z.

&&

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

$$

SHORT TERM...RJP
LONG TERM...Smith
AVIATION...RST



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