Area Forecast Discussion
Issued by NWS Paducah, KY

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FXUS63 KPAH 221649
AFDPAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PADUCAH KY
1049 AM CST Sat Nov 22 2014

.MESOSCALE DISCUSSION...
Issued at 1049 AM CST SAT NOV 22 2014

This morning into this afternoon will be a transition period in
advance of the approach of the major shortwave/low later tonight
into Sunday.

Differentials of moisture, wind, and temperature along the western
limb of the Southeast U.S. High pressure are focusing instability
into and along the western edge of the WFO PAH forecast area
(basically from Poplar Bluff MO (KPOF), Perryville, MO, and Mount
Vernon, IL (KMVN)).

For the first period (rest of today) update, added a differential
weather type for isolated thunderstorms over the foothill area of
Southeast Missouri, then northeast along the I-64 corrdior of
Southern Ilinois. The GOES Sounder derived Precipitable Water (PW) and
Lifted Index (LI) imagery, suggest a very narrow plume of near
one inch PW`s and a lowered axis of LI`s (albeit positive) arcing
from south to southwest through southeast missouri, then northeast
into Southern Illinois. The short range 12km NAM-WRF/13km RAP/3km
HRRR guidance indicate a narrow axis of 850 mb 0-3C LI`s in the
same region and is coincident with isolated thunderstorm activity
(per the lightning detection network). This activity should wane
as ridging and stable lapse rates build northwest later this
afternoon and limit updraft development. In addition, the
12zSaturday 12km NAM-WRF 0-1 km Bulk Shear shifts the southwest to
northeast of axis of 30-40kts/km shear to the northwest with time
this afternoon, reducing updraft potential with time.

May see some gusty winds feeding into to this gradient area during
the day, but any convective gust impact should be quite limited
for the rest of today.

&&

.SHORT TERM...(Today through Monday night)
Issued at 218 AM CST SAT NOV 22 2014

The main concern in the short term is the rather potent storm system
that will affect our region this weekend. This system will bring a
soaking rainfall and even a few thunderstorms, depending on the
exact track of the surface low. Right now, it appears that the
more unstable conditions will remain south of our region.

The primary 500 mb shortwave will take on a negative tilt as it
lifts northeast from the southern Plains into the Mid-Mississippi
Valley late Sat night/Sunday. Surface low pressure will deepen as it
tracks northeast across Missouri into the Great Lakes region. The
forecast area will be in the warm sector of the system, allowing
relatively warm and moist air to surge northward into the Lower Ohio
Valley. The ECMWF deepens the surface low over central Missouri on
Sunday, as the 850 mb jet axis of 50 to 60 knots passes over the
Lower Ohio Valley. Will leave pops at 100 percent for Sunday in all
locations. PWAT values near 2 standard deviations above normal
could lead to locally heavy rainfall amounts. In addition, a
period of strong gradient winds is likely Sunday afternoon and
into the evening as we get more into the warm sector,

Looking ahead to the next workweek, cooler air will gradually return
to our region in the wake of the cold front. Will need to keep
fairly high rain chances on Sunday night into early Monday until cold
front makes it through the region, but pops will decrease fairly
quickly behind the front.

.LONG TERM...(Tuesday through Friday)
Issued at 227 AM CST SAT NOV 22 2014

A weak surface high over the lower Ohio valley will keep the PAH
forecast area dry Tuesday into Tuesday night.  South winds on
Wednesday will lead to warming temperatures and increasing
moisture.  Models show a surface low moving across the Great Lakes
region late Wednesday into Wednesday night.  Latest GFS and GEM take
the associated cold front across our region dry, while ECMWF
generates some light QPF.  Going forecast had some small pops in our
area, and consensus is to keep some slight chance pops going for
now.  Went with slight chance pops for rain for our western two
thirds of counties on Wednesday, then slight chance pops for rain
and snow for our eastern third Wednesday night.  ECE numerical
guidance shows temperatures dropping off quite a bit behind the
front for Thursday, while MEX does not cool temperatures down until
Friday due to a slower passage of the front.  Ensemble guidance goes
middle ground with a more gradual cool down Thursday into Friday,
which seems a safe way to go for now.

&&

.AVIATION...
Issued at 1152 PM CST FRI NOV 21 2014

Cigs are expected to remain VFR through the 24 hr TAF period. Sfc
winds will continue to shift to the south overnight. Rain showers ne
overnight are expected to remain light and should not restrict
vsbys. Srly winds will strengthen on Sat, gusting to around 20 kts
by late morning, then should lose gusts by sunset. Some widely
scattered showers may affect parts of sern MO/swrn IL during the
day.


&&

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

$$

MESOSCALE...Smith
SHORT TERM...GM
LONG TERM...RST
AVIATION...DB






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