Area Forecast Discussion
Issued by NWS Paducah, KY

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FXUS63 KPAH 231124

Area Forecast Discussion
National Weather Service Paducah KY
624 AM CDT Thu Mar 23 2017

Updated aviation section for 12z taf issuance

Previous update
Issued at 510 AM CDT Thu Mar 23 2017

A narrow band of showers and even a few thunderstorms has developed
along an elevated warm front along the Mississippi River. Negative
showalter indices accompany the leading edge of the warmer air
aloft. The latest hrrr/ruc/nam all develop this area of showers
southeast to the Lower Ohio Valley this morning. The area should
dissipate by afternoon, as elevated mcs`s often do. The forecast has
been updated to reflect this area of showers and isold storms.


.SHORT TERM...(Today through Saturday night)
Issued at 320 AM CDT Thu Mar 23 2017

The main focus will be the storm system for late Friday night into
Saturday night. Overall, the models have shown good consistency
with the timing and intensity of this system and its associated
wind and instability fields.

A 500 mb closed low will move slowly east-northeastward from the
southern Plains on Friday, reaching central Illinois by Sunday
morning. An associated surface low will track northeast across
Missouri and Illinois. In advance of the system, a deep southerly
flow of moist and marginally unstable air will advect northward
through the Mississippi and Lower Ohio Valleys. Widespread
precipitation will occur within this corridor of deep moisture,
especially from late Friday night through Saturday evening.

The models continue to indicate widespread clouds and precip will
limit instability. Although shear profiles will be rather
favorable for convective organization, the relatively weak
instability suggests any severe activity would be very limited in
scope. Heavy rain is a possibility given the slow-moving corridor
of deep moisture. The latest forecast grids indicate storm-total
qpf would be around an inch on average, mostly occurring within a
12-hour window at any given point. Gusty gradient winds are
another forecast issue, given the presence of 35 to 40 knot winds
just off the surface late tonight through Saturday. Daytime mixing
will be limited by cloudiness, however a few gusts near advisory
levels cannot be ruled out at any time Friday into Saturday.

Otherwise, the main forecast issue is clouds and temps today
through Friday. The models do not appear to have a good handle on
the early morning cloudiness advancing slowly east-southeast
across our region. There is a great deal of model inconsistency
regarding the potential for warm-advection induced low and mid
clouds today through Friday. This in turn impacts the temperature
forecast. The forecast will generally follow a consensus blend.
This blend indicates considerable cloudiness for much of the
period, except for a period of relatively clear skies early
tonight. Highs are forecast mainly in the 60s today and lower 70s
on Friday.

.LONG TERM...(Sunday through Wednesday)
Issued at 320 AM CDT Thu Mar 23 2017

Average confidence through most of the long term, then models
begin to diverge significantly on Wednesday.

In the wake of a frontal passage Saturday night, wrap around
precipitation on Sunday will diminish from west to east. Sunday
evening looks to be dry at the moment, but by late Sunday night a
system moving out of the central plains will produce overrunning
precipitation that is forecast to spread eastward across our CWA.
Precipitation chances with this system max out Monday afternoon and
evening with the actual passage of the system. Precipitation chances
will diminish from west to east on Tuesday in the wake of the
system. Models showing minimal instability with this system so
included the mention of thunder over all or part of the CWA from
Sunday evening through Monday evening.

Models agree that Tuesday night should be dry due to high pressure
at the surface and the NW-SE axis of an H5 ridge somewhere over the
region. Model placement of the H5 ridge axis is what`s causing the
discrepancy between model solutions on Wednesday. The ECMWF is
showing the axis just to the north and east of our CWA thus allowing
overrunning precipitation from a developing system over the southern
plains to overspread our CWA. The GFS shows the axis just to the
south and west of our CWA which would keep precipitation at bay and
keeping the region dry Wednesday. Due to the uncertainty, will just
go with what Forecast Builder generated.

Temperatures will generally be 10 to 15 degrees above normal through
the period.


Issued at 624 AM CDT Thu Mar 23 2017

A narrow band of showers and isolated thunderstorms developed from
kcgi northward around 10z. This band is associated with a warm front
around 5k feet agl. This activity will continue to affect the
kcgi/kpah areas through mid-morning. Cloud bases are vfr, even in
the showers and storms.

Mid and high clouds will persist for much of the day at all taf
sites, then some clearing is likely by this evening. Winds will
increase from the south overnight, gusting to 20 kt by morning.

Some of the model guidance indicates mvfr cigs will arrive after 06z
at all sites. The forecast will include a scattered mvfr cloud deck,
and later forecasts can add mvfr cigs if this becomes likely.




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