Area Forecast Discussion
Issued by NWS Paducah, KY

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FXUS63 KPAH 212007
AFDPAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PADUCAH KY
307 PM CDT Mon Jul 21 2014

.SHORT TERM...(Tonight through Wednesday night)
Issued at 257 PM CDT MON JUL 21 2014

The last vestiges of deep layer dry atmosphere from aloft to the
surface boundary layer continue to shrink from both the west and
east as the influence of the high pressure ridge continues to wane
with time. A minimum in precipitable water values (around an inch)
covers Southeast Missouri, Southern Illinois, and the Purchase area
of West Kentucky this afternoon. With the most stable air over the
WFO PAH forecast area, sharp thermal and moisture gradients are
building up over Southwest Indiana and the Pennyrile region of West
Kentucky.

The Short Range Ensemble Forecast (SREF), as well as the current
runs of the 3km HRRR, 13km RAP, and 12km NAM-WRF appear to depict
the transitional nature of the temperature and dewpoints across the
local area fairly well and were used as a template for any forecast
adjustments with this package.

The central U.S. middle to upper level tropospheric ridge weakens
only briefly tonight through early Tuesday before building back
across the area.  However, boundary layer southerly flow is becoming
established, increasing surface dewpoints over the area with time.

Added a mention of overnight to early morning fog to grids for
tonight, as wind, moisture, sky conditions will be conducive for
development.

The next shortwave riding down the northern limb of the ridge around
the eastern Canada closed low should alter lapse rates enough to
support at least scattered convection late Tuesday night into
Wednesday. At this time, prefer the slower timing of the SREF for
the onset of showers and thunderstorms ahead of the shortwave. The
highest PoP`s were left over western Kentucky where deeper low level
moisture and instability will be well established by Wednesday.

Given the increase in temperatures and dewpoints, will add a mention
of afternoon heat index values in the 95 to 100 degree range on
Tuesday and Wednesday, a marked difference from this past week and
weekend.

.LONG TERM...(Thursday through Monday)
Issued at 257 PM CDT MON JUL 21 2014

Much drier and cooler air will looks to filter into the region
from nw to se during the day Thursday, as a clod front conts
pushing south through the TN Valley. Another unusual cold frontal
passage for this time of year, but certainly will come welcomed.

Thursday night and Friday appear to be dry and unseasonably cool
as surface high pressure overspreads the area. However, precipitation
chances make their way back into the forecast by the start of the
weekend as low pressure forms over the Plains and lift a warm
front back north into the region. The presence of the boundary
and a series of ripples of energy in nw flow aloft will provide
the focus for occasional shower and thunderstorm development.
Timing of these impulses will be difficult at best this far out
in time tho...so will need to broad brush with chancy pops for
now.

&&

.AVIATION...
Issued at 1225 PM CDT MON JUL 21 2014

The moisture and wind gradient associated with the narrow ridge
axis oriented northeast to southwest across the area is allowing
the intrusion and development of diurnally-based 3-5kft
few/scattered/locally broken cloud bases/ceilings along the Ohio
and Wabash River valleys and Southeast Missouri.

Kept a mention of VFR/upper MVFR visibilities after midnight at
each TAF site. Introduced MIFG to account for denser patches of
LIFR visibilities due to microclimate influences.

Otherwise, VFR conditions will continue to dominate through the
forecast issuance period.


&&

.PAH WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
MO...NONE.
IN...NONE.
KY...NONE.
&&

$$

SHORT TERM...Smith
LONG TERM...GM
AVIATION...Smith





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