Area Forecast Discussion
Issued by NWS Paducah, KY

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FXUS63 KPAH 241708
AFDPAH

Area Forecast Discussion
National Weather Service Paducah KY
1208 PM CDT WED AUG 24 2016

.UPDATE...
Issued at 1208 PM CDT Wed Aug 24 2016

Aviation update.

&&

.SHORT TERM...(Today through Friday)
Issued at 222 AM CDT Wed Aug 24 2016

Satellite and Radar Mosaic shows some spotty convection extending
from Iowa down into far northern/northwest MO. The GFS is not
handling this well. It thinks this area of pcpn extends as far
south as our FA/doorstep. The NAM has a much better handle on it,
pinpointing its areal coverage/reach.

Both models show the pcpn in association with a weak perturbation
rounding a broad area of high pressure aloft that is anchored over
the heart of the South. Both models lift this weak wave to the
northeast/across the Great Lakes over the course of the day. And
more or less, continue this pattern of periodic ripples of weak
energy riding the peripheral of the broad High pressure aloft,
that builds ever stronger into/across the Tennessee valley.

Honing in on today, there are numerous negating factors that leads
us to minimize, if not altogether eliminate or make silent, the
going small pop. Namely is that H5 heights rise 20 DM as the
sinking air aloft ridges into/across the Tennessee valley, and various
models show 10-11C air working across the FA at H7, as this
occurs. While we cannot altogether rule out an isolated updraft
breaking thru, particularly on the periphery of the High aloft,
where it might overcome the Bernoullian sink, we believe it`s
enough to warrant a minimization of most pop mention.

An exception occurs late tonight, as most modeling shows a piece
of energy making enough southward progress on a dive toward the
middle Ohio valley such that a slight chance mentionable Pop is
warranted for the extreme north/northeast part of the FA. We
inherited that Pop and the 00Z models do not dictate or
necessitate a valid enough argument for us to change it.

Thursday-Thursday night, we see similar reasons to today, to
negate the Pop mention. H7 temps are even more broadly capping,
with the High now strongly centered over the Volunteer state and
extending its center near or even into the Commonwealth.

The wobbling High aloft shifts a little bit eastward by Friday.
While still a strong influence, it looks to be shifted just far
enough eastward to allow its buildup of warmth/humidity to result
in diurnally aided parcel lift, enough to mollify our sinking air
concerns to allow a chance category pop to prevail over the
course of the day.

Summer like synoptics mean summer like temps and humidity through
the course of the short term, or migrating toward/slightly above
seasonal norms.

.LONG TERM...(Thursday night through Tuesday)
Issued at 335 AM CDT Wed Aug 24 2016

The medium range models appeared to be in reasonable agreement with
their solutions at the surface and aloft through the extended
period, though the Canadian appeared to be more dynamic with the
surface features across the Midwest.

At the beginning of the period, low level winds over the PAH
forecast area (just above the surface) should begin to regain a
southerly component as shortwave energy aloft approaches, and a
surface high departs the Midwest. This will help to moisten up the
lower trop to provide fuel for scattered showers and tstms,
increasing in coverage from west to east Friday night/Saturday,
despite our region being on the periphery of a southeastern CONUS
mid level ridge. This time period represents generally the best
opportunity for rainfall occurring in the PAH forecast area. We will
carry 50% in the forecast for parts of the western half for now.
Some model data indicated higher.

As the primary energy for lift departs to the north Saturday
evening, shower and tstm activity should wane quickly with the loss
of insolation. This strong diurnal signal will be seen throughout
the rest of the extended forecast as subsidence from the
southeastern CONUS high will limit the strength and number of
updrafts. Best PoPs will be in the northwest, with the lowest PoPs
in the southern Pennyrile region, and no more than 30% for the
majority of the area from Sunday on.

Through Monday, afternoon heat indices may reach 100 in some parts
of the southern half of the PAH forecast area. Dewpoints will remain
in the lower 70s. Afternoon sunshine should be quite ample most
days, enabling highs to remain in the upper 80s to around 90. We may
start to see some cirrus from a developing tropical system to the
south by Day 7, depending on where it ends up.

&&

.AVIATION...
Issued at 1208 PM CDT Wed Aug 24 2016

Mixing up through 3-4k/ft resulting in 15-20 kt gusts from the
SSW. That trend should continue this afternoon. Some diurnal CU
and some high clouds expected. Hi resolution models bring some
convective activity into SE IL and SW IN. Not sure how this will
evolve coverage wise. But there is a chance the KEVV/KOWB
terminals could be affected. Otherwise overnight, light SSW winds
with possibly some high clouds. For now, no fog mention despite
climo based MOS forecasts. We are going to count on just enough
wind to prevent MVFR vsbys for now. Will monitor.

&&

.PAH Watches/Warnings/Advisories...
IL...None.
MO...None.
IN...None.
KY...None.
&&

$$


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