Area Forecast Discussion
Issued by NWS Paducah, KY

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FXUS63 KPAH 182001

Area Forecast Discussion
National Weather Service Paducah KY
301 PM CDT Sun Mar 18 2018

.SHORT TERM...(Tonight through Monday)
Issued at 301 PM CDT Sun Mar 18 2018

The 12Z guidance is in very good agreement with the limb of warm
advection rain/showers that will lift north into the region later
this evening. There is good consensus in holding the rain to the
south of the Evansville and Owensboro areas. It will slowly lift
north and stall out over southern Illinois and west Kentucky around
daybreak before quickly dissipating. There is no instability to work
with, so no thunder is expected tonight. QPF should be a quarter to
a third of an inch.

As the overnight rains are dissipating, convection will be pushing
eastward into southeast Missouri ahead of a compact mid/upper-level
storm system coming out of the Plains. The 12Z models are in good
agreement in pushing the upper low eastward across our region, but
there is some discrepancy in the character and path of the surface
system. At this point the farthest north the surface low and warm
front may go is across the southern border of the forecast area.

The presence of the enhanced shear near the warm front and surface
low as well as what should be a sharp baroclinic zone could result
in some enhanced tornado potential along the KY/TN border through
the afternoon even if the warm air remains just to the south of the
border. Supercells could develop in the warm sector to our south and
then lift northeast into the baroclinic zone along the border and
continue to produce tornadoes. Some large hail will also be possible
with the cold core of the system moving overhead.

.LONG TERM...(Wednesday through Sunday)
Issued at 301 PM CDT Sun Mar 18 2018

Somewhat challenging lower impact (PoP-wise) forecast with this
issuance. Although not poor by any means, the height and temperature
initialization of the 12z Sunday guidance was not ideal, especially
with the western U.S. trough and southwestern U.S. low. The 12z
Canadian and the 12z GFS initialized better than the 00z ECMWF (12z
not at the beginning of the gridded forecast process)and the 12z NAM-
WRF. This has some bearing, since the western trough dampens and
replaces the current ridge over the WFO PAH forecast area in less
than 48 hours. The degree of energy and moisture translated and
lifted along the western side of the trough, as it moves east of the
area, and the impact of the next approaching ridge will determine
whether there is a minor precipitation event mid-week.

The GFS and Canadian are split on a minor mid-week precipitation
event, with the Canadian much wetter, but in line with its previous
model runs. the latest run of the ECMWF appears to be wetter as
well. As a compromise with the regionally blended model guidance and
earlier forecast trends, kept a sharp gradient of PoPs/Weather
closer to the southern and eastern 1/3rd of the WFO PAH forecast
area.  Still believe that there will be a zone of subsidence along
the western edge of progressively slower moving eastern U.S. trough,
so attempted to keep southwest Illinois and most of southeast
Missouri dry later tuesday and Tuesday night.

The precipitation event with the next trough and surface low through
the area next weekend remains consistent. However, anticipate there
will longitudinal variations in the position of the surface low,
which will likely impact forecast coverage of rainfall. Kept
generally with the blended model guidance, but did add some wait
to the ECMWF. Have low confidence on the overall coverage and timing
of any thunderstorms through this period.

Little adjustment was made to winds or temperatures through the
extended period.


Issued at 1243 PM CDT Sun Mar 18 2018

MVFR ceilings are the rule across the region. The clearing line is
just northeast of KEVV, and with a bit better mixing there they
may climb into VFR territory whether they scatter out or not. KOWB
is not far away, but less likely to make it to VFR. Elsewhere,
guidance indicates that VFR ceilings will make it to KPAH this
evening, but that may be optimistic.

A band of showers/rain will bring MVFR visibilities to KCGI and
KPAH as it lifts slowly northward overnight. It is not expected to
reach KOWB or KEVV. There should be a break after sunrise there,
but a more significant area of showers and possibly thunderstorms
will approach KCGI and KPAH in the last hour or two of the
forecast period.




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