Area Forecast Discussion
Issued by NWS Paducah, KY

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FXUS63 KPAH 271941
AFDPAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PADUCAH KY
141 PM CST Sat Dec 27 2014

.SHORT TERM...(Tonight through Monday night)
Issued at 141 PM CST SAT DEC 27 2014

Rain and drizzle continues across the area, especially east of the
Mississippi early this afternoon. This will be the general trend
as a moist southwest flow continues, while the surface frontal
boundary slowly moves east through tonight. As the mid trop flow
turns more WSW Sunday, drier air will work in and push rain
chances off to the east by afternoon. Dry weather Sunday night
through Monday night with high pressure continuing to build in.
Temps will be a blend of previous numbers, and straight model
output.

.LONG TERM...(Tuesday through Saturday)
Issued at 141 PM CST SAT DEC 27 2014

The extended forecast period still begins with a flat west-east
oriented surface ridge axis bisecting the WFO PAH forecast area.
Aloft, a zonal flow over the area gradually arc into a low amplitude
ridge into the intermountain west region, leading to the closed
California/Southwest closed low.

Since this closed low has yet to develop from energy ridging over
the dominant eastern Pacific ridge, timing will be an issue with
respect to its formation and ejection into the Plains later next
week.

At this time, given the overall hemispheric pattern, am inclined to
lean toward a compromise of the deeper mean trough of the ECMWF with
a slightly lesser GFS. Believe the troughiness will remain more
persistent than the GFS hints at by next weekend.

Given the aforementioned uncertainty on the timing/placement of the
projected California low by the middle of next week, do not plan on
speeding up the onset of precipitation across the area. In fact,
precipitation onset could be delayed another 6-9 hours, not becoming
aggressive over the WFO PAH forecast area until 12-15z Friday time
frame (6-9 am Friday). Anticipate there will be some flip-flop until
the California low forms and translates eastward into the Plains.

Antecedent conditions will be cold enough for a wintry mix between
6-12z (midnight-6am) Friday, as moisture translates through the
dendritic growth zone. Initially, any precipitation should be very
light and it will take some time to saturate the lower layer of the
atmosphere below 700 mb. The GFS/ECMWF dynamically raise thickness
in the SFC-700 mb layer between 12z-18z Friday (6am-noon) with
decent warm advection in the layer. This combined with Top-Down
precipitation loading, should convert most of the precipitation back
to a cold rain Friday afternoon and night.

The question arises for Saturday and Saturday night, as the
California low is forecast to speed out into the Plains and over the
WFO PAH forecast area. The timing and placement of the cold front
associated with the passage of the low will determine the degree and
impact of the precipitation from rain, back to a wintry mix.

The overall trend with the model guidance has been for warmer
temperatures in the lower layers, compensating for the colder air
aloft...leading to a shorter period of wintry mix versus liquid
rain.

Period of greatest concern for wintry weather still remains late
Thursday night into Friday morning. Will continue to highlight in
the HWO regarding this potential.

&&

.AVIATION...
Issued at 1117 AM CST SAT DEC 27 2014

On and off rain and drizzle for the majority of the TAF forecast,
perhaps tapering off toward the end of the forecast period. IFR cigs
and MVFR vsbys will be predominant with some variation. Cold front
will push through this afternoon and switch winds from SSW to NNW.
Speeds will mainly be at or below 10 kts.

&&

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

$$







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