Area Forecast Discussion
Issued by NWS Paducah, KY

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819
FXUS63 KPAH 212010
AFDPAH

Area Forecast Discussion
National Weather Service Paducah KY
310 PM CDT Fri Jul 21 2017

.SHORT TERM...(Tonight through Sunday night)
Issued at 310 PM CDT Fri Jul 21 2017

Although temperatures have panned out as predicted, dew points
have been running higher than expected in some areas. A corridor
of upper 70s to 80-degree dew points from kpof northeast across
kmdh to kmvn has resulted in widespread heat indices around 110.
The advisory was upgraded to a warning based on these readings, as
well as four consecutive days of 105-degree heat indices in the
warning area. Although the difference is small, dew points and
heat indices have been running a bit lower in much of the
advisory area. Sunday still is complicated by the potential of
clouds and storms, but it appears dew point pooling along a
boundary will bring heat indices over 100 then.

As of 3 PM, isolated showers and storms were ongoing across
southern Illinois, mainly east of I-57. This activity has been
very pulsy and disorganized. Given the lack of forcing due to the
proximity of the 500 mb ridge, these cells should dissipate with
loss of daytime heating. The conditions for development on
Saturday will be even less favorable. Model soundings indicate a
stronger cap in the form of warmer 800 mb temps Saturday. There
will also be somewhat drier air through the mid levels.

Given the drier air and potential for full sunshine Saturday, high
temps could reach the upper 90s in a few spots. This will not be
the case Sunday, when a weak boundary will move into our region
from the north. This boundary does not appear to be the true cold
front. See the long term discussion for details on that. The
boundary will likely cause dew points to pool well into the 70s.
Despite slightly lower temps in the lower 90s Sunday, heat
indices will still top 100.

Thunderstorms are possible as early as Saturday night north of a
Paducah to Madisonville line, then across the region on Sunday and
Sunday night. Development of storms may be handicapped by weak
low-level convergence. Winds are forecast to veer into the west
or northwest ahead of the front Saturday night. Any storms that
develop will form in a very moist and unstable environment. Heavy
rain and gusty winds will be the main concerns, even though shear
will be too limited for much in the way of organization.

.LONG TERM...(Monday through Friday)
Issued at 310 PM CDT Fri Jul 21 2017

Overall confidence is slightly below average through the period,
especially regarding timing and placement of precipitation chances.
Essentially tried to tone down the blended approach with slight or
low/mid chances PoPs in place for most time periods.

Upper level pattern will generally feature ridging/high pressure
aloft centered across the southern Plains/Rockies while troughing
persists over the northeast U.S. This essentially keeps us in more
of a west/northwest flow type pattern much of the week. Waves of
energy moving through this flow are difficult to pin down this far
in advance.

There has been an increasing signal the last several days to keep
temperatures slightly warmer (upper 80s/low 90s) with a more humid
airmass in place (particularly across the southern half).
Unfortunately it is becoming increasingly evident that we might not
see those 60s dewpoints penetrate all the way into the southern
counties, and if they do it`ll be brief for possibly 24 to 36 hours.

The 12z ECMWF has come into somewhat better agreement with the
Canadian and GFS deterministic/ensemble runs. It now shows a less
aggressive mid level trough coming through Tuesday into Wednesday.
With plenty of instability and moisture around, potential is there
for some isolated to scattered convective activity, especially
during the afternoon/evening hours almost every day. Guidance is in
fairly good agreement in bringing in a more pronounced wave of
energy later Thursday into Friday, thus siding with higher PoPs
during this time period, particularly across the northeast half of
the region.

As mentioned above, high temperatures are expected to be in the
upper 80s/low 90s most of this period. If the higher dewpoints in
the mid 70s come to fruition, as depicted by the ECMWF and Canadian
models, then we would be looking at heat index readings once again
near or over 100 for portions of the region almost every day. Will
have to fine tune this as models come into better agreement. For now
siding with the somewhat cooler/less humid blend incorporating the
lower dewpoints of the GFS. This keeps heat index values well below
100 on Tues/Wed before exceeding 100 on Thursday across the west
half.

&&

.AVIATION...
Issued at 1248 PM CDT Fri Jul 21 2017

A few cumulus clouds will continue through the afternoon,
otherwise clear skies are expected through Saturday morning.
A little fog is possible around sunrise, mainly at kcgi. Winds
will be southwest less than 10 knots, except variable this
afternoon near an outflow boundary in the kowb/kevv areas.


&&

.PAH WATCHES/WARNINGS/ADVISORIES...
IL...Excessive Heat Warning until 7 PM CDT Sunday for ILZ075>078-
     080>094.

MO...Excessive Heat Warning until 7 PM CDT Sunday for
     MOZ076-086-087- 100-107>112-114.

IN...Heat Advisory until 7 PM CDT Sunday for INZ081-082-085>088.

KY...Excessive Heat Warning until 7 PM CDT Sunday for KYZ001>005.

     Heat Advisory until 7 PM CDT Sunday for KYZ006>022.

&&

$$

SHORT TERM...MY
LONG TERM...SP
AVIATION...MY



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