Area Forecast Discussion
Issued by NWS Paducah, KY

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000
FXUS63 KPAH 240833
AFDPAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PADUCAH KY
333 AM CDT Sun Aug 24 2014

.SHORT TERM...
Issued at 333 AM CDT Sun Aug 24 2014

There is very little change in the synoptic pattern or the
forecast this forecast cycle. The main issues continue to be the
timing and location of convection...as well as their impacts on
temps/dew points/heat indices.

In the near term...an outflow boundary from last evenings mcs
over the Lower Ohio Valley made it as far southwest as the
Missouri Bootheel by 08z. This mcs and its outflow has stabilized
the air mass for the time being...especially east of the
Mississippi River.

The latest model data /especially the rap/ still indicates the
surface wind flow will become easterly during the day today. The
rap indicates a surface convergence zone along the leading edge of
this easterly push. The rap model pools moisture along this
boundary...which results in high dew points and an axis of strong
instability by this afternoon. This axis extends from southern
Illinois into western Kentucky by early this afternoon. Based on
this data...will expand slight chance pops as far west as the
Mississippi River counties again today. The coverage of convection
should be rather isolated...given drier mid level air
overspreading the Mississippi Valley on water vapor imagery.

Heat indices will again reach 105 in most areas today. Even where
clouds were widespread on Saturday...heat indices still exceeded
105 due to extremely high dew points around 80. High temps should
be very similar to those on Saturday...except where localized
convection occurs.

The daily potential for isolated convection should be suppressed
further to the south and east Monday and Tuesday as the mid level
ridge axis establishes itself along the Ohio Valley. Will keep
slight chance pops mainly southeast of the Ohio River both days.

As for temps...will generally follow the hotter gfs mos for both
Monday and Tuesday. Some of the model guidance continues to lower
temps slightly. Given that the deep layer ridge will be positioned
nearly overhead through the period...this cooling looks suspect.
There may be a slight lowering of dew points as the low level flow
remains out of the east. This may lower heat indices a few
degrees...but they are still forecast to reach 100 to 105 Tuesday.

.LONG TERM...
Issued at 333 AM CDT Sun Aug 24 2014

Well there continues to be a rift between the GFS and ECMWF/GEM in
their 00Z runs. The trend with all of the models is slower with the
eastward movement of the western U.S. low/trough. The 00Z ECMWF is
leading the charge and tonight`s run basically builds an upper
ridge north of the trough, effectively removing it from the
westerlies. Am beginning to wonder if this system and its associated
surface boundary are ever going to reach our region.

The 00Z GFS brings the upper trough and cold front through the area
Thursday and Thursday night, and then brings drier, cooler air into
the region for Friday and next Saturday. The Canadian/GEM is a lot
closer to the ECMWF solution, but not quite as slow. Really think
the ECMWF is onto something, so will lean toward it for this
forecast.

The problem with the ECMWF and GEM solutions with respect to our
existing forecast is that they allow a significant upper trough to
dive southeast into New England by Thursday morning. That brings a
backdoor cold front southward into our northern counties late
Wednesday and Wednesday night. The front ends up draped across the
area from northwest to southeast Thursday and Friday. This leads to
a decent chance of convection both days.

The other effect of the ECMWF solution is the potential for the heat
and humidity to linger through much of the work week, if not all the
way through next Saturday. Bumped up temperatures just a bit
throughout the extended. Heat indices on Wednesday are generally at
or below 100, so there will be no need to extend the Heat Advisory
any further with this forecast package.

&&

.AVIATION...
Issued at 1130 PM CDT SAT AUG 23 2014

Convection induced by a westward moving outflow boundary at KPAH
should end by the time the 06Z TAFS begin so will have no mention
of any tsra. If we can get the clouds to clear out and the winds
to become calm for a while, we might actually get some fog to
develop. Opted to just leave the MVFR vsbys going for now since
confidence is still low whether or not it will form. Otherwise,
the rest of the overnight and into Sunday morning should be
tranquil. Plenty of instability will be present during the day on
Sunday for more isolated to scattered storms. But coverage of
storms is still unknown attm so will opt to leave any mention out
at this time. Winds will remain light and variable.

&&

.PAH WATCHES/WARNINGS/ADVISORIES...
KY...HEAT ADVISORY until 7 PM CDT Tuesday FOR KYZ001>022.

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

IL...HEAT ADVISORY until 7 PM CDT Tuesday FOR ILZ075>078-080>094.

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

&&

$$

SHORT TERM...MY
LONG TERM....DRS
AVIATION...CW




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