Area Forecast Discussion
Issued by NWS Paducah, KY

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641
FXUS63 KPAH 181149
AFDPAH

Area Forecast Discussion
National Weather Service Paducah KY
649 AM CDT Wed Apr 18 2018

.UPDATE...
Issued at 649 AM CDT Wed Apr 18 2018

The AVIATION section has been updated for the 12Z TAF issuance.

&&

.SHORT TERM...(Today through Friday night)
Issued at 300 AM CDT Wed Apr 18 2018

A surface warm front has stalled out for a bit just to the south
of KPAH. It creates quite a temperature gradient from mid 60s to
its south to mid 40s over southwest Indiana. As a strong storm
system moves eastward across Iowa and toward the south end of Lake
Michigan by this evening, the warm front will push northward
through the entire region. As it makes it to I-64 around midday,
the cold front will start to sweep eastward across southeast
Missouri.

Surface high pressure will remain over the Gulf of Mexico and
prevent any substantial moisture return into this system, and thus
it will move through mostly dry. The lone exception will be a
brief period of slight chance PoPs for light showers over
southwest Indiana southward into the Pennyrile in the mid to late
afternoon. The capping inversion will lift just enough to carve
out a shallow layer of instability below it. Saw this in the NAM
yesterday and it seems to be more prevalent through the 00Z model
suite this morning.

Southwest winds will increase dramatically to the south of the warm
front today, and as the cold front passes winds will veer to due
west and will be even stronger. Gusts over 30 mph will be
common, with the strongest winds approaching 40 mph along I-64
behind the cold front late this afternoon. Will plan on issuing a
Special Weather Statement for these near advisory level winds.The
cold front could have an added impact this afternoon. Dust stirred
up over western Kansas yesterday is pushing eastward along with
the cold front, so there may be a brief period of slightly reduced
visibilities.

The 00Z models indicate that there will be plenty of low clouds
ahead of the cold front today, and that should hold temperatures
in check. There is quite a range of guidance for highs today, and
we will be in the middle ground, spanning the lower half of the
70s. If the clouds are more scattered than expected some 80 degree
readings will be possible, and winds may be even stronger with
the added mixing. If this occurs a Wind Advisory may be necessary
for a portion of the area.

North winds and mostly cloudy skies will be the rule tonight and
Thursday as surface high pressure builds over the region.
Temperatures will drop into the middle and upper 30s tonight, but
a stiff northwest breeze should prevent any frost formation.
Thursday will be blustery with highs only in the low to mid 50s.

Frost formation is likely over much of the region Thursday night
into early Friday morning. Surface high pressure will approach
from the west and winds will diminish to 5kts or less. Skies will
be mostly clear by sunset, setting the stage for some radiational
cooling and the frost formation. Sheltered areas along I-64 might
even have a brief light freeze.

Surface high pressure will keep a grip on the area Friday and
Friday night, as a skinny ridge of high pressure aloft builds
toward the area. There will be a slight warming trend for both
highs and lows. It will be sunny and dry with a modest northeast
wind during the day. A few patches of frost will be possible
Friday night mainly along the I-64 corridor.

.LONG TERM...(Saturday through Tuesday)
Issued at 300 AM CDT Wed Apr 18 2018

Average forecast confidence with minor precipitation event Saturday
night into Sunday, then again Tuesday into Wednesday of next week.

The last three model cycles of the ECMWF, including the 00z Tuesday
model run, have been taking the closed low that moves through
California Thursday further south into Texas and the Lower
Mississippi Valley by Sunday. The ECMWF, and most of the
deterministic guidance, have been following this southward trend, as
well as deepening and maintaining a vertically stacked low into
Sunday night. In this scenario, the majority of the precipitation
shield would be tied closer to the center of the low with the
greater baroclinic instability.

Given these trends, collaborated for lower PoPs along the southern
quarter of the WFO PAH forecast area, impacting mainly southern
counties in Southeast Missouri and West Kentucky late Saturday
through Sunday.

There is some uncertainty as to the evolution of the low late Monday
into Tuesday, as the low weakens and in sheared in the split flow.
Each of the models have different solutions and mechanisms
suggesting the shearing of the low, but in the shear zone (eastern
edge of the WFO PAH forecast area), we could see some minor
precipitation chances, mainly in the Pennyrile region of west
Kentucky late Tuesday.

There is a much lower forecast confidence in the approach of a
northern stream low/trough through the upper midwest late Tuesday,
with the southern end of the trough impinging on the WFO PAH
forecast area. At this time, left a general mention of lower PoPs
near the end of the forecast period for collaborative purposes just
in case.  We probably will not have a good idea on the evolution of
the Lower Mississippi Valley closed low into an open wave until at
least Sunday.

&&

.AVIATION...
Issued at 649 AM CDT Wed Apr 18 2018

The main concern to aviation this cycle will be very gusty winds.
Southwest winds will quickly become gusty this morning as a warm
front lifts north through the region. The winds will gradually
veer and end up west or west northwest behind a cold front that
will move through the region this afternoon. Gusts up to 30 mph
will be common and some gusts up to near 40 mph will be possible,
especially at KEVV and KOWB behind the cold front. Winds will
slowly diminish this evening, but may still gust up to 20kts
overnight.

There is some potential for a brief MVFR ceilings east of the
Mississippi River this morning, and also late in the period at
KEVV and KOWB. Confidence is too low to mention at this time. A
stray light shower will be possible at KOWB this afternoon near
the front, but little impact is expected.

&&

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

$$

UPDATE...DRS
SHORT TERM...DRS
LONG TERM...Smith
AVIATION...DRS



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