Area Forecast Discussion
Issued by NWS Paducah, KY

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000
FXUS63 KPAH 251141
AFDPAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PADUCAH KY
641 AM CDT Mon Aug 25 2014

.UPDATE...
Issued at 641 AM CDT MON AUG 25 2014

The AVIATION section has been updated for the 12Z TAF issuance.

&&

.SHORT TERM...(Today through Wednesday)
Issued at 304 AM CDT MON AUG 25 2014

The upper high will remain over top of the region through
Wednesday, and is not forecast to weaken much, if at all. However,
it is forecast to flatten out and become more east/west oriented,
as a storm system moves eastward into Ontario Canada by this
evening. This allows the surface ridge to build back to the west
across the four state region through tonight. The resulting
easterly low-level flow will advect slightly cooler and drier air
eastward.

Although this has been a consistent signal in the models for a few
days now, the models have had a hard time keeping up with the
high dewpoints across much of the area over the weekend. So, the
bottom line is that confidence is low in the temperature and
dewpoint trends through Wednesday.

Heat indices today are forecast to be lower throughout the area,
with most areas in the 100 to 105 range. The Pennyrile region of
west Kentucky is in the upper 90s, similar to what happened
yesterday. Considered removing a few counties in the southeast
from the Heat Advisory, but given the uncertainty, and the last 4
or 5 days of 100+ heat indices, will keep the Advisory in force
for the entire area.

Temperatures, dewpoints, and heat indices drop another degree or
two throughout the forecast area on Tuesday, but most areas are
still at or slightly above 100, which will support the Heat
Advisory. Will take a wait and see approach to the Heat Advisory
in the southeast today, and possibly cancel it there for Tuesday,
if they don`t get there today.

A little more cooling/drying is forecast for Wednesday, which will
generally take the entire area out of the triple digit heat
indices. Much of the area will be close, so a small forecast error
could result in the potential extension of the Heat Advisory into
Wednesday at least for southeast Missouri and southern Illinois.

As for PoPs, the 00Z NAM, NMM and ARW WRF runs generate isolated
convection over the Pennyrile this afternoon, so will add the
smallest of PoPs in that region today. NAM soundings support some
diurnal convection near the confluence of the Ohio and Mississippi
Rivers on Tuesday, so likewise will have a small PoP in that
region.

The 00Z models seem to be in pretty good agreement in bringing a
backdoor cold front southward to near the I-64 corridor on
Wednesday, so will continue with the low chance PoPs up there in
the afternoon.

.LONG TERM...(Wednesday Night through Sunday)
Issued at 304 AM CDT MON AUG 25 2014

A transition to a more active progressive flow pattern is expected
during the long term. The blocking upper ridge over the Ohio Valley
will gradually retreat southward...allowing shortwave energy to
progress eastward across the Plains and eventually the Ohio Valley.
This will translate into a wetter pattern with less intense heat.

As far as the daily details...
For Wednesday night and Thursday...the 00z model suite is in good
agreement that a surface high over the Great Lakes region will push
a backdoor cold front southward into the Lower Ohio Valley on
Wednesday night. This boundary will stall in the vicinity of the
Ohio Valley on Thursday. Some convection is likely to accompany this
front...though coverage will be limited by the weakening upper level
ridge. Forecast will contain slight chance to low chance pops.

For Friday into Saturday...the models begin to diverge with
respect to the eastward progress of a 500 mb shortwave from the
Plains. The gfs and its ensemble mean are still somewhat faster than
the ecmwf...but the differences are smaller than 24 hours ago. The
forecast will be slanted toward the slower ecmwf...so forecast pops
will remain in the slight chance to low chance range for Friday into
Saturday.

For Sunday...most guidance indicates the shortwave will be crossing
the Lower Ohio Valley. Forecast pops will be highest on Sunday...but
still only in the chance category due to the weakening nature of the
shortwave. The associated cold front is forecast to weaken or
dissipate as it reaches our area...which will limit surface
convergence and associated convection.

High temps through the period will be heavily dependent on
cloudiness. With the expectation of gradually increasing moisture
and cloudiness...the slight downward trend in highs shown by gfs mos
looks reasonable. High dew points will keep overnight lows on the
warm side.

&&

.AVIATION...
Issued at 641 AM CDT MON AUG 25 2014

With surface high pressure in control through the entire 12Z TAF
period, winds will be light and variable. A few cu are possible
today, and some thin cirrus will continue to stream over much of
the region. Patchy ground fog developed over areas generally east
of the Mississippi River early this morning, and that should burn
off by 14Z. There is some chance of fog development again late
tonight, especially at KCGI.

&&

.PAH WATCHES/WARNINGS/ADVISORIES...
IL...HEAT ADVISORY until 7 PM CDT Tuesday FOR ILZ075>078-080>094.

MO...HEAT ADVISORY until 7 PM CDT Tuesday FOR MOZ076-086-087-100-
     107>112-114.

IN...HEAT ADVISORY until 7 PM CDT Tuesday FOR INZ081-082-085>088.

KY...HEAT ADVISORY until 7 PM CDT Tuesday FOR KYZ001>022.

&&

$$

UPDATE...DRS
SHORT TERM...DRS
LONG TERM...DRS
AVIATION...DRS





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