Area Forecast Discussion
Issued by NWS Paducah, KY

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FXUS63 KPAH 211915

Area Forecast Discussion
National Weather Service Paducah KY
215 PM CDT Wed Mar 21 2018

.SHORT TERM...(Tonight through Friday night)
Issued at 151 PM CDT Wed Mar 21 2018

Surface high pressure will continue working into/across the
Mississippi river valley during the next 24 hours, as the primary
winter storm bombs out over the Northeast. Another powerful storm
currently hitting the Pacific Northwest teleconnects upper ridging
that will move off the lee of the Rockies tmrw. This will
establish a strong nwly flow aloft overtop the PAH FA. With time,
beneath that, a surface warm front develops, and ultimately acts
as a focusing boundary for elevated moisture advection. Models are
picking up on this in the 850-700 mb and 700-500 mb qg forcing
fields. Pops show as early as Thursday pm/evening, spreading thru
the overnight hours. This could create an issue with critical
boundary layer temps realized late Thursday night-early Friday
morning, just north of the boundary, in our far northeast tier
counties. However, it does appear that we`ll be juuuuust warm
enough to keep it all liquid in our FA. It`ll be something to
watch closely though, with future runs on boundary placement.

By Friday-Friday night, the spill energy from the Pacific
Northwest has generated strong cylcolgenesis in the Plains
states, and this helps further ramp up the warming and moistening
of the tropospheric profile downstream/across the PAH FA. Ripples
of energy aloft will ride along this reinforced warm front`s
resurge across the FA, triggering showers and eventually, as
instability parameters suggest by late Friday night, a chance of
thunderstorms. At this point, rising PW`s make heavy rains an
increasing hazard, but the powerful shear/forcing may also hint at
stronger storm potential. A limiting factor will be the overall
instability fields.

Tonight`s lows will be 10 plus degrees below seasonal norms, in
the upper 20s/around 30. Tomorrow will begin recovery, but still
average 5 to 10F below norms, as most sites see the 50s. By
Thursday night-Friday-Friday night, temperatures will be closer
to seasonal expectations, even if remaining a shave on the cool

.LONG TERM...(Saturday through Tuesday)
Issued at 311 AM CDT Wed Mar 21 2018

Better than average confidence starts off the long term with good
model agreement through Sunday. However, confidence drops off early
next week with greater model variability--though improved over the
last 24 hours.

An unsettled pattern will prevail from late this week into the
middle of next week with multiple chances for showers. The period
will start with an upper level ridge centered over the Plains
flanked by troughs in the east and west. The ridge will translate
eastward through the end of the period, placing the forecast area in
southwest flow aloft during the first half of next week.

The first chance for showers arrives late Friday, Friday night, and
Saturday as energy tops the Plains ridge and streams eastward into
the Ohio Valley. At the surface, low pressure over western Kansas
late Friday is forecast to weaken as it moves east into the forecast
area by Saturday evening. The presence of elevated instability
supports a slight chance of thunder over southeast Missouri late
Friday night and into portions of southern Illinois and far western
Kentucky Saturday morning. Rainfall amounts during this period are
forecast to average around one half inch. Higher totals of up to an
inch are possible in closer proximity to I-64, with amounts less
than one quarter inch in much of southeast Missouri. This round of
activity should come to an end Saturday night as the cold front
slips south of the region.

Much of Sunday should be dry with the front stalled out south of the
region. Another low pressure system is forecast to develop over the
Central Plains and lift the front north across the area early in the
week. This will result in our next chance of showers during the
early to middle part of next week. The evolution of this system will
likely be gradual with the slow retreat of the upper level ridge
over the Southeast. As a result, better rain chances will exist over
western portions of the area, with lower rain chances in the east.
At this time, models suggest the heaviest rain should remain just
west of the immediate forecast area.

With developing southwest flow, temperatures should average near or
just above seasonal norms through much of the period. Saturday night
and Sunday are the main exceptions, with below normal temperatures
forecast both periods in the wake of the cold frontal passage.


Issued at 151 PM CDT Wed Mar 21 2018

Visible imagery shows scattered to at times broken low VFR bases
in the broader, mean cyclonic flow pattern left in the wake of the
departed storm system. We`ll keep this northwesterly flow aloft
thru the entirety of the aviation package, as teleconnected upper
ridging to our west firms our northwesterlies aloft. Today`s
clouds and gusts should subside with nightfall, and tmrw, with
surface high pressure more firmly impacting the Mississippi river
valley, fewer clouds and lighter winds will be the rule.




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