Area Forecast Discussion
Issued by NWS Paducah, KY
FXUS63 KPAH 252038
AREA FORECAST DISCUSSION
National Weather Service Paducah KY
238 PM CST WED NOV 25 2015
.SHORT TERM...(This evening through Friday Night)
Issued at 238 PM CST WED NOV 25 2015
We will be issuing a Flash Flood Watch for Friday and Friday night
generally along and west of a New Madrid to Pinckneyville line.
The overall forecast through Friday night has not changed much at
all. The most significant adjustment was to slow the onset of the
steady precipitation until late Thursday night over southeast
Missouri and southern Illinois. It should then push southeast
through the entire area during the day Friday and persist through
much of Friday night.
There continues to be no signal for thunder with this event, even
with mid 50s surface dewpoints in place along/ahead of the cold
front. This will be a slow developing flood situation typically
handled with a Flood Watch, but with the heaviest rains, around
3", expected over the western portions of southeast Missouri, we
figure that there could be some rapid rises along the Black,
Current and St Francis Rivers which could result in flash
The bottom line is that a Flash Flood Watch is likely to garner
more attention than a plain ole Flood Watch, and with lots of
folks traveling and generally out and about in places they may
not be so familiar with, we figured that the Flash Flood Watch
would provide the best message. Thanks to WFO MEG, LSX, and SGF
for collaboration on this event.
In the meantime, a few light showers are lifting northeast across
southern Illinois this afternoon, so continued with the scattered
sprinkles through sunset. This evening should be dry throughout
the area, but there is a decent signal in much of the 12Z guidance
that isentropic lift will touch off some showers late tonight and
Thursday morning, mainly over southeast Missouri and southern
Illinois. This activity should dry up before midday, and the
afternoon and evening should be dry for your Thanksgiving
As for temperatures, stayed close to consensus of guidance for
lows, and leaned toward the warm side of guidance for highs.
.LONG TERM...(Saturday through Wednesday Night)
Issued at 238 PM CST WED NOV 25 2015
Multiple factors influencing measurable precipitation chances
mainly on Saturday and Sunday.
In coordination and collaboration with the short term forecast
period and Flash Flood Watch for Southeast Missouri/small part of
Southwest Illinois through Friday night, do not anticipate any
extension of the watch further east at this time. Will elaborate
this thinking in the following text.
Looking at the larger (hemispherical scale) picture, satellite
trends suggest that the upper low moving across the northwest
pacific will just enhance and deepen the current low over the north
central Pacific (near 40 degrees north latitude/155 degrees
longitude), keeping the eastern Pacific ridge in place over the
southwest Canada/Northwest U.S. Looking much further to the
southeast, a closed circulation/low (currently near 10 degrees north
latitude/130 degrees west longitude) should move little in the face
of the west/northwest movement of Hurricane Sandra in the Pacific.
Of course, the closed low over Northwest Nevada will move little
through the weekend. It will serve as the focus for translating
energy from the Desert Southwest and into the Lower Mississippi
valley over the weekend.
The combination of all of the aforementioned factors above should
maintain a shortwave train of energy across the eastern Pacific
(namely between 28-30 degrees north latitude), then arc northeast
through the Desert Southwest and Lower Mississippi Valley.
There is much greater confidence that the mid-upper level vorticity
fields will be generated from Southeast Missouri to Southwest
Indiana Saturday afternoon into Sunday morning, enhancing
circulation (albeit mainly elevated and banded in nature) in the
vicinity of the leading edge of the cold front over the extreme
southeast Missouri Delta, the Purchase area of West Kentucky and the
southern half of the Pennyrile region of West Kentucky. Instability
below 700 mb will be hard to come by (as has been the case with
model forecast runs since late last week), so any thunder/strong
updraft potential will be minimal or non-existent. The NAEFS
climatologies and anomalies, suggest that the greater variation (up
to 4 standard deviations from normal) will be in the 700 to 500
millibar layer. This may be due to the anticipated input of upper
level moisture streaming northeast of an expected decay of Hurricane
Sandra over northern Mexico late Friday/early Saturday. However,
this moisture (which would increase precipitation efficiency would
be too little and too late for any further flood potential over
Southeast Missouri on Saturday.
At this time, with the deterministic GFS, ECMWF, and Canadian all
suggesting the cold front will be well into Kentucky by Saturday,
anticipate any measurable rain (aided by the banded vorticity at mid-
levels to the northwest) will occur over West Kentucky, southwest
toward the boot heel late Saturday afternoon through Sunday morning.
At this time, am only considering a mention of locally heavy rain in
the Hazardous Weather Outlook, considering the banded nature of any
focused rainfall along the front.
Made no changes to rainfall amounts in the extended period, with
only subtle spatial (mainly blending of gradient) changes in
temperatures,dewpoints, and winds behind the cold front.
Although it will be a rather wet, cloudy weekend for travel around
the Thanksgiving Holiday, do not anticipate any widespread flooding
concerns as the cold front slowly translates through West Kentucky.
Issued at 1149 AM CST WED NOV 25 2015
Mid-level ceilings will continue to spread eastward through all
sites by sunset. South winds will continue to gust to near 20kts,
especially at KEVV and KOWB where more sunshine is expected this
afternoon. Some guidance develops decent coverage of showers near
KCGI and KPAH late tonight into Thursday morning. Added in VFR
showers at KCGI, but confidence is not high enough to add it in at
KPAH. The forecast remains VFR despite lowering ceilings through
the period. KCGI will have the best chance to see an MVFR ceiling
from late tonight through the morning.
IL...Flash Flood Watch from Friday morning through late Friday night
MO...Flash Flood Watch from Friday morning through late Friday night