Area Forecast Discussion
Issued by NWS Paducah, KY

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FXUS63 KPAH 231643
AFDPAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PADUCAH KY
1143 AM CDT Wed Jul 23 2014

.MESOSCALE DISCUSSION...
Issued at 1137 AM CDT WED JUL 23 2014

Will attempt to define gridded forecast a little better during the
next hour to handle location and intensity of afternoon
convection. Main focus through most of this morning was to handle
near term, higher priority severe weather potential with storms
moving through Southern Illinois.

Somewhat convoluted mesoscale features this morning, owing to
disjointed moisture and wind fields, as well as existing
convection. The higher resolution model guidance having trouble
resolving movement and coverage of showers and thunderstorms in
this weak shear environment along and ahead of the cold front.

The last couple of days of the 12km NAM-WRF was advancing storms 3-4
hours too fast into the WFO PAH forecast this morning and too far
southwest (initially generating convection over Southeast
Missouri). There was also a suggestion that any nocturnal to mid-
morning convection would be more elevated in nature. This is just
now coming into fruition.

Lower base of mesoscale an organized mesoscale low showing up
around 750m (approx. 2500 ft agl, near the 925 mb level) per the
WSR-88d VAD Wind Profiles. The main 925 mb is elongated over east
central Illinois into Southeast Missouri. Northeasterly flow below
2500 ft AGL along the leading edge of the convection from the KPAH
VWP suggest enough a tentative balance to support upshear
convection with only limited outflow-dominated multicell clusters.
In the short term, this would allow for local wind gusts between
30 and 40 mph along the western (and leading edge of convection)
limb of thunderstorms moving into Southeast Missouri.

Above from 1500 meters to 3km AGF, WSR-88d VWP fields suggest a
narrow shortwave trough east of KLSX-KILX line concident with the
surface frontal boundary. It gets more complicatied further to the
east over the Pennyrile region of west Kentucky into Central
Kentucky and southern Indiana, as weak low level (below 5kft
AGL) ridging is in place over the Pennyrile, translating into a
low level trough over southern Indiana. This focused area,
combined with a narrow southwest-northeast Precipitable Water axis
of two plus inches, should limit the north-south edges of stronger storms.

The 16z MSAS surface low centers and intermediate convective
boundaries stretch from west of West Plains Misouri to French Lick
Indiana.

The main focus of higher surface-based theta-e air has now moved
along and east of the South Central Missouri surface low eastward
to the Land between the Lakes in West Kentucky.

Combining all of these little mesoscale tidbits together,
anticipate that a majority of the convective activity early this
afternoon will become eleveated over northern sections of
southeast Missouri and southwest Illinois, along and northeast of
the surface to 925 mb frontal boundary. This will likely be the
focus for enhanced heavy rainfall and lightning. Further to the
south over the aforementioned west to east oriented surface
theta-e convergence zone over Southeast Missouri and Purchase Area
of West Kentucky, some surface based instability will still be
possible, leading to the potential of a few wind gusts in excess
of 40 mph and small hail. Favorable conditions for strong/severe
storms will wane considerably through 21z (4 pm CDT) as cloud
shield limits surface based instability and main focus for lift
become associated with the low/mid level shortwave moving through
the region, leading to greater elevated versus surface based
instability.

&&

.SHORT TERM...(Today through Friday)
Issued at 250 AM CDT WED JUL 23 2014

An amplifying upper flow pattern will aid a cold front across the
region today. Accompanying frontal passage is a chance of showers
and thunderstorms. Mesoscale models have been greatly overdone
with respect to upstream convection over the past 24 hours, and
they suggest lesser coverage locally today. In addition, a decent
mid level capping inversion of warm air aloft (700 mb temperatures
around 10C) should limit the formation and maintenance of deep
convective updrafts. As a result, coverage of activity that
develops today should be rather hit and miss. By the end of the
day, I suspect many locations will be left without any rain. As a
result, we further reduced probabilities to 30 percent at best in
most areas.

After a lingering chance of thunderstorms over southern counties
this evening, much cooler and drier air will filter into the
region overnight and Thursday as high pressure builds south from
Canada. After morning lows in the upper 50s to lower 60s, Thursday
looks absolutely delightful with highs only in the lower 80s under
plenty of sunshine. Lows Thursday night should range in the upper
50s. Moisture return will begin in earnest on Friday as the upper
level trough and surface high begin to shift to the east. Any
precipitation should stay north of the area until Friday night.

.LONG TERM...(Friday night through Tuesday)
Issued at 250 AM CDT WED JUL 23 2014

Subtle changes to the long term. Overall, the same pattern
evolution is forecast. The models amplify the ridge out west and
trof over the east U.S. by early next week. Friday night into
Saturday, still looking for a warm front to move through, with best
moisture and subtle forcing possibly bringing convective chances to
the NE part of the region. It looks capped farther west toward the
MS river into SEMO. Cannot rule out additional convection Saturday
that may be diurnally enhanced, with better chances ENE part of the
region toward the KEVV tri-state. Same holds true for Saturday night.
Sunday a frontal boundary is forecast to move into the area, and
gradually reach NE AR into NW TN by 12z Monday. Have slightly higher
PoPs in the forecast with front. We raised high temps Saturday into
Sunday as well given latest numerical output. Isolated strong to
severe storms cannot be ruled out. Given the forecast convective
indices and shear, time of year, and what`s seasonally normal,
should not be a major threat. No PoPs in for Monday through Tuesday
in the wake of the front, and with high pressure building in from
the NW. The high will return temps to below seasonal norms.

&&

.AVIATION...
Issued at 653 AM CDT WED JUL 23 2014

A cold front will pass across the area today. Accompanying the front
is the chance for isolated to scattered showers and thunderstorms.
Of immediate concern, a complex of thunderstorms over the Wabash
Valley will impact KEVV and perhaps KOWB through mid morning. Early
morning activity should subside by mid to late morning, then storms
may refire along and south of the front this afternoon. In the wake
of the front, winds will swing around to the north/northwest as VFR
ceilings linger into the evening.


&&

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

$$

MESOSCALE...Smith
SHORT TERM...RJP
LONG TERM...CN
AVIATION...RJP





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