Area Forecast Discussion
Issued by NWS Paducah, KY

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000
FXUS63 KPAH 232315
AFDPAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PADUCAH KY
615 PM CDT Sat Aug 23 2014

.UPDATE...
Issued at 615 PM CDT SAT AUG 23 2014

Updated for 00Z aviation forecast discussion.

&&

.SHORT TERM...(Tonight through Monday night)
Issued at 333 PM CDT SAT AUG 23 2014

In a very moist and unstable atmosphere, shower and tstm activity,
primarily forecast to occur in the ern half of the region, has
been pretty sparse so far.

This forecast convection was in the general vicinity of a low
level area of convergence, supported by a subtle weakness in the
ridge aloft. All the moisture may convert to locally heavy rain
with any convection. It appears some isentropic lift was occurring
this afternoon over swrn IL/wrn KY/parts of sern MO in the mid
levels, providing cooling altostratus clouds over that region.
This may continue for a few more hours. Best guess at this point
is that the ern half of the region will continue to have a chance
of showers and tstms just about anywhere (PoPs for any one
location no more than 30 percent).

From tonight on, with the shrtwv energy aloft over the mid
Atlantic region diminishing, the mid/upper ridge over the PAH
forecast area should expand ewd again over the next couple of
days, limiting the chances of diurnally-driven deep moist
convection to primarily the ern third of the region.

Used a mix of existing, SuperBlend, and GFSMOS data for temps. The
hotter and somewhat drier area will continue to be west of the MS
River under the stronger subsidence of the mid/upper ridge. The
heat advisory will continue, with no immediate relief from the oppressive
conditions outside a widely scattered shower or tstm.

.LONG TERM...(Tuesday through Saturday)
Issued at 333 PM CDT SAT AUG 23 2014

First, model preference. Early on, not much difference in the
solutions. Large sprawling H5 ridge will persist from the Mid
Atlantic, across the Ohio Valley region and into west TX Tuesday.
Over the NW U.S. a trof is forecast by the models to move ESE into
the nrn/cntrl Rockies. Heading into Wednesday, the ridge is forecast to
be suppressed somewhat to the south with small height falls over the
region. Differences show up Thursday. The 12z GFS continues to be faster
moving the Rockies trof eastward in the Thursday through Saturday
time frame. This and its prior runs, are outliers to a consensus of
current and prior runs of the ECMWF/GFS Ensemble Mean, UKMET and
GEM. Was initially reluctant to completely discount the GFS, given
it actually has been verifying fairly well recently (such as the
strength of the current ridge vs. what the other models showed).
However, one of its biases is to merge energy too aggressively with
nearby stronger flow. The favored consensus keeps the energy over
the Rockies detached from the stronger flow over srn Canada, thus
moving the feature more slowly to the east. Following the consensus
solution has resulted in quite a few changes to the forecast
Thursday and beyond.

Tuesday, have limited convective chances mainly srn 1/2 of the area
into SEMO, where slightly deeper moisture exists. Wednesday, would
not be surprised if there`s little or no convection. But the NW
periphery of the CWFA is on the edge of a bit better moisture. Have
that covered. Have nothing in at night. Even Thursday, will be hard
pressed for convection. But by late in the day we may see some
activity creep into far north and west sections due to increased
moisture and little better WSW mid trop flow as heights continue to
fall. As the upper trof continues its slow east movement Friday into
Saturday, the accompanying surface front will sag into the area and
should stall as the low trop/sfc flow weakens. Will have our best
chance PoPs for convection when this happens, generally Friday
through Friday night. Still only chance PoPs for now.

Despite the fact we are slowing things down considerably, which
means we will be "warm sector" and without a front in the area til
the end of the week, the models and ensemble means lower H9/H8 temps
beyond Tuesday a couple of degrees. Also, we may see a little better
mixing of dry air, which could lower our dew points a few degrees.
Our computed Apparent Temperatures beyond Tuesday fall below
persistence Heat Advisory thresholds. Therefore no extension to the
Advisory. That said, it`ll be summer like and a tad on the hot side.
We used a blend of MOS and Raw Model output for temps, minus any GFS
influence.

&&

.AVIATION...
Issued at 615 PM CDT SAT AUG 23 2014

The main aviation concern for this evening continues to be the
potential for isolated to scattered thunderstorms. Given current
radar picture, will opt for at least a vcts at KEVV/KOWB for a
few hours. May have to update to make the TS predominant as the
storms get closer. Attention then shifts to fog potential late
tonight. There has been little in the way of fog the past few
nights...most likely due to clouds and wind. Fog potential looks
somewhat higher late tonight due to lighter winds and less
cloudiness. Winds will be light and quite variable through the
period.

&&

.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.

&&

$$




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