Area Forecast Discussion
Issued by NWS Paducah, KY

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FXUS63 KPAH 140823

Area Forecast Discussion
National Weather Service Paducah KY
323 AM CDT Wed Mar 14 2018

.SHORT TERM...(Today through Friday night)
Issued at 323 AM CDT Wed Mar 14 2018

Today will be fully dominated by an approaching upper level ridge
from the west, with a broad surface ridge in the Lower
Mississippi Valley.

A minor wave in the northerly flow on the western edge of a
large northeast U.S. trough, will tighten the pressure gradient in
an north-south fashion to the lower Mississippi Valley ridge today.
This pressure gradient will increase west-southwest winds,
especially over parts of southern Illinois, southwest Indiana, and
northwest Kentucky during the afternoon hours.

As the aforementioned minor wave move to the mid-Atlantic, the an
impressed col will be centered in Missouri and Illinois, leading
back to a tightening area of surface low pressure in eastern CO and
western KS, associated with a strong (and eventually negative
tilted) shortwave being ejected from a northwest U.S. closed low on
the western side of a central U.S. upper ridge.

The main impact of this col will be to develop the northern limit of
convergence for warm air advection into and through at least 2/3rds
of the WFO PAH forecast area from the south. There will be sharp
gradient of temperatures on Thursday near the I-64 corridor, with a
more gradual change further south to the AR/TN borders. with the
west warm air advection (and warmest temperatures) over southeast
Missouri Thursday and Thursday night.  A distinct warm front will
set up by Thursday evening from Marble Hill and Cape Girardeau MO,
to Greenville Kentucky.

As the upper level level ridge dampens with the approaching
intermountain shortwave, the flow between the southeast U.S. surface
ridge and the Central Plains low will sharpen dramatically,
generating a rapid flow of moisture from the Gulf of Mexico Thursday
afternoon and evening. Showers should break out within the
isentropic/warm conveyor belt over the surface warm front, with the
best rain chances developing after midnight Thursday into early
Friday morning.

The persistence of the upper ridge, sandwiched between the
increasingly vertically stacked closed low in the foothills of the
Rockies and Central Plain, and the large northeast U.S. trough, will
prevent any further movement of the warm front north through the WFO
PAH forecast area Friday into Friday night. Subsequently, the
highest PoPs will be focused over southeast Missouri and eastward
along the Mississippi River and into the Purchase area of West
Kentucky. There will be enough instability along and south of the
warm front in this area to generate a few thunderstorms in the
aforementioned area. Given the helicity in this area, a few storms
may generate some stronger updrafts along the border counties of
southeast Missouri, with the potential of a few marginally severe
storms.  Most of the shear and instability will most likely be
elevated near and south of the warm front. This may promote some
hail production given the lowered freezing level and -20C level
growth zone for hail in the impressed updrafts.

The narrow blocking pattern in the northern U.S. and the
more zonal flow in the southern U.S. will likely shear this system
apart moving into the longer term forecast period.

The 18z Tue/00z Wed 12km NAM-WRF and the 12z Tue/00z Wed Canadian
(CMCNh) have been quite consistent with the previously discussed
weather features and have initialized well with observations. There
is better than average (50-60%) forecast confidence with this
weather scenario in the short term.

.LONG TERM...(Saturday through Tuesday)
Issued at 323 AM CDT Wed Mar 14 2018

An unsettled pattern is still expected this weekend into early next
week. Two low pressure systems in the progressive upper-level flow
pattern will move east-southeast across the mid section of the
nation. The first system will exit our region on Saturday. The
second system will cross our region early next week. The track of
both systems will be near or over the lower Ohio Valley.
Temperatures and convective chances will depend heavily on whether
the low pressure centers pass north or south of the Ohio River. The
model tracks continue to fluctuate, resulting in changes to the

The 00z runs of the gfs, ecmwf, and gefs mean have all trended north
with the track of both lows. For example, the 12z Tuesday gefs mean
placed a low pressure center near Nashville at 18z Saturday. The 00z
Wednesday run places it near EVV at that time. The Monday system has
also shifted north. The placement of the low pressure center on
Monday evening has shifted from middle Tennessee to southern Indiana
over the past 24 hours in the ecmwf model.

Rather than yank the forecast back and forth subject to model
variations, the forecast will be trended only slightly in the
direction of the latest 00z model runs. Forecast highs will be
nudged upward Saturday through Monday, mainly in the 50s north of
the Ohio River and 60s south of the river each day. Lows will be
mostly around 40. Thunder will be kept in the forecast for Monday.
Some thunder will be added for Saturday, mainly in western KY. A
mainly dry period is still expected between systems on Sunday.

A cool down is expected on Tuesday in the wake of the second low
pressure system. The models are still not consistent with respect to
the deepening of this system to our east, as well as the strength of
the cold advection in its wake. A model blend yields highs around 50
Tuesday, but this system is still far out in the model world.


Issued at 601 PM CDT Tue Mar 13 2018

Diurnally enhanced cu field in northeast (KEVV/KOWB) should
dissipate with loss of fuel, scattering mid (VFR) bases by mid
evening. Gusts may maintain until almost then, and then should
diminish as skies clear all sites. Nwlys will return tmrw, not as
gusty, then back during the day, with perhaps some scattered high
clouds at times.


Issued at 323 AM CDT Wed Mar 14 2018

Minimum daytime relative humidity values in southern Shannon and
most of Carter County Missouri will bottom out near 14 percent
this Wednesday afternoon. A west to east gradient of gradually
higher relative humidity values will work toward the Mississippi
River, increasing toward the Delta region of southeast Missouri.
Fuel moistures in this area will be close to 6-8 percent for the
short term fuels. Surface and twenty foot winds should remain
below critical levels, but transport winds are expected to sharply
increase from the southwest near the base of the southeast
Missouri foothills stretching from Poplar Bluff to Jackson
Missouri and Grand Tower Illinois toward dusk. At this point,
these weather conditions should keep things below elevated fire
danger, but it will be worth monitoring this afternoon.




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