Area Forecast Discussion
Issued by NWS Paducah, KY

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166
FXUS63 KPAH 190445
AFDPAH

Area Forecast Discussion
National Weather Service Paducah KY
1145 PM CDT Fri Aug 18 2017

.UPDATE...
Issued at 1145 PM CDT Fri Aug 18 2017

Updated for 06Z aviation forecast discussion.

&&

.SHORT TERM...(Tonight through Sunday night)
Issued at 303 PM CDT Fri Aug 18 2017

The main concern in the short term is the potential for an MCS to
develop to our north or northwest tonight. The HRRRs and WRFs are
have been all over the place, and not exactly consistent with
themselves in timing and strength. The 12Z NAM would represent the
strong end of the sprectrum and is likely overdone.

Really don`t have a great idea what is going to happen, so tried
to minimize it in the forecast. We will have chancy PoPs spreading
into southeast Missouri and southern Illinois after 06Z, and then
dampen them as they attempt to spread southeast across the rest
of the area into Saturday morning. The only real shot of
convection toward midday and into the afternoon would be right
near the southern border of the area, if the outflow boundary/cold
front hangs up there, which will be dependent on MCS tonight.

Weak surface high pressure will hold over the region through the
weekend. High pressure aloft will build overhead on Sunday, so
temperatures will be increasing, but the humidity will be slow to
increase, keeping the heat indices in the 90s. Accepted consensus
of guidance for lows through Sunday night, but they may be a bit
on the mild side. For high temperatures Saturday and Sunday, went
on the warm side of MOS guidance with plenty of sunshine and
somewhat dry air in place. Lower 90s will be common for highs on
Sunday.

.LONG TERM...(Monday through Friday)
Issued at 303 PM CDT Fri Aug 18 2017

Medium confidence persists in the extended.

The ECMWF, Canadian, and NAM all keep precip out of the area Monday
for the eclipse. The GFS has for sure made it into the blend since
its the one operational model that actually brings rainfall into
mainly SEMO Monday afternoon. The models are in agreement on upper
level ridging over the area Monday...the GFS drifts the axis farther
off the eastern coast than the other models. This allows for better
return flow of moisture from the south. hence the higher probability
of rain mainly west of the Mississippi River. Models are in good
agreement on an MCS to our northwest Sunday night into Monday.
Placement of this system varies model to model with some keeping up
in Iowa and others into MO. Debris cloud from this system may affect
the area during the day Monday. As previously mentioned any cloud
cover prior to eclipse would slow the heating which could prolong or
even eliminate scattered afternoon storms. The farther east will be
the least impacted over our area. One additional note will be that
where skies remain mostly clear we can expect heat index values to
easily soar into the middle 90s. Tuesday into Wednesday an upper
level trough will push through the area as it flattens out the pre
existing trough. There will also be a surface reflection of a cold
front that will move through in tandem. Tuesday afternoon and
overnight will be the best chance of the strongest storms. A severe
storm cant be ruled out at this time. After that high pressure will
take over the weather pattern for the end of the week

High pressure over the Atlantic coast will retrograde or build west
ward into the region. Also by Sunday a cold front will have moved
south of the Ohio and Mid Mississippi River Valleys...allowing high
pressure to build in at the surface early in the week. This has also
reduced expected cloud cover for early in the week as well as rain
chances. However we still have a very low chance mainly west of the
Mississippi River Monday afternoon. This will definitely have an
impact on sky cover for the rest of the area should any storms form
to our west. The models are also hinting at an Meso scale convective
system (MCS) forming overnight in northern MO and IA. However the
500 mb flow is nearly zonal with the 700 mb flow to the northeast.
This should keep most of the debris clouds from this system well to
our north. We will continue to monitor closely but for now we have a
fairly reasonable chance of observing the eclipse. This will
continue to change as we near the event. Dew points will take a dive
Sunday as the cold front pushes south of the area. However this will
be short lived as the southerly flow rapidly returns to around 70
Monday. Heat index values will be in the middle 90s Monday. By
Tuesday we will have a very weak warm front lift through the region
as high pressure builds even farther to south and west. This will
allow an upper or mid level trough with a surface reflection of a
cold front to move through the area creating rain chances for the
middle of the week. Thursday the cold front will move south of the
area bringing slightly cooler and drier air late next week.

&&

.AVIATION...
Issued at 1145 PM CDT Fri Aug 18 2017

Upstream convection has resulted in some sct-bkn mid and high
clouds streaming this way. All convection that has attempted to
move southeast has dissipated before reaching our area. However,
there are some indications that some isolated to widely scattered
showers and/or storms may impact mainly KCGI overnight. Confidence
not high enough at this point to include in the TAF. Otherwise we
will see a frontal boundary pass through Saturday afternoon so a
wind shift will occur. Otherwise some afternoon cu is likely.

&&

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

$$



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