Area Forecast Discussion
Issued by NWS Paducah, KY

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000
FXUS63 KPAH 190652
AFDPAH

Area Forecast Discussion
National Weather Service Paducah KY
152 AM CDT Thu Apr 19 2018

.SHORT TERM...(Today through Saturday night)
Issued at 136 AM CDT Thu Apr 19 2018

Clouds still linger across the lower Ohio river valley, and will
apparently continue to linger until the energy within the mean
upper trof finally makes ultimate passage later today (pm). After
that, confidence grows in the drier air working down the column,
as surface high pressure anchors and strengthens across the
Mississippi river valley tonight from its centering over IA/nrn
IL. This will enable clearing skies and diminishing winds to
provide a good raditional cool thru the 30s, but some gradient
looks like it could maintain a light overnight breeze. Even so,
collab efforts yield substantial freezing temps reach along/just
north of our area, and frost advisories being posted in all
directions beyond that. As a result, tweaked winds down 1-2 kts
from guidance, and posted Freeze warning in/around the I-64
corridor of SEIL and extended across northern most SWIN. Frost
Advisory will cover the remainder of the area.

Temps look to continue their below normal trends Today thru
Friday, even as the surface High shifts eastward across the Great
Lakes by 12z Saturday. As lower trop winds veer easterly and upper
ridging follows by 6-12 hours lag, we`ll see temps begin to
moderate back closer to/but still just a tad shy of seasonal
norms to start the weekend.

The final 12 hours of the short term, Sat night, sees the varying
models approach to the energy off the California coast right now
and how it eventually evolves. We`ll follow the lead of our
veteran long term forecaster, who likes the Canadian deterministic
influence on the blend (see long term discussion for details).
That`ll result in some warm advection/overrunning shower chances
entering the SEMO forecast Sat night, as it appears the models
will be tracking the Low pressure storm system and its primary
impacts mainly to our south.

.LONG TERM...(Sunday through Wednesday)
Issued at 136 AM CDT Thu Apr 19 2018

The 00z Wednesday deterministic and ensemble guidance were almost 24
hours too fast in bringing the parent Low (that would bring
precipitation to parts of the WFO PAH forecast area Sunday into
Monday) onshore and through southern California. Until we get
better sampling of this Low, there is some concern that the
timing and location of the precipitation expected late in the
weekend will be in jeopardy.

At this point in time, the 00z Thursday Canadian (CMCnh) guidance
appears to be the best initialized in height/mass/sensible weather
fields and will be used to adjust/influence the regionally blended
model guidance initialization with this package.

Within the Canadian guidance, the vertically stacked upper low in
eastern OK at 1 am CDT Sunday begins to exhibit some
shearing/stretching, focusing the greatest lift into the Mid-
South/Lower Mississippi Valley area. With differential vorticity and
moisture advection, some of the lift along and south of the
deformation zone will bring the initial rain to southeast Missouri on
Sunday, gradually rotating the chances of rain to the southern 1/4
of the WFO PAH forecast area (southern sections of southeast
Missouri and west Kentucky) Sunday night into Monday, as the upper
Low slowly translates across the southeast U.S. and into the
Appalachians by early Tuesday. Lesser chances of rain will occur
during this time period over western Kentucky.

The bigger question for the middle of next week will be the
evolution and strength of a strong shortwave diving down from the
broad cyclonic circulation in central Canada. Forecast confidence is
low to medium with the timing of this feature. Anticipate some
additional changes for the approach of this shortwave and front next
Wednesday, otherwise next Thursday should remain relatively dry and
cooler across the WFO PAH forecast area.

&&

.AVIATION...
Issued at 136 AM CDT Thu Apr 19 2018

Satellite shows low VFR cigs swinging across the terminals as
another slug of energy within the mean upper trof makes its way
across the lower Ohio river valley. Mean rh panels show this
associated with 80 percent plus RH in the 1000-850 mb layer, with
some drier air beginning to wedge in from the southwest later this
am into the pm hours. It may be a good portion of the day before
all sites scatter, until then, low VFR to perhaps at times MVFR
cigs are expected. After the trof`s passage, High pressure
strengthens its grip across the Mississippi river valley and
effectively clears skies/returns VFR for all sites by tonight.


&&

.PAH WATCHES/WARNINGS/ADVISORIES...
IL...Frost Advisory from 1 AM to 9 AM CDT Friday for ILZ080-081-
     084>094.

     Freeze Warning from 1 AM to 9 AM CDT Friday for ILZ075>078-082-
     083.

MO...Frost Advisory from 1 AM to 9 AM CDT Friday for MOZ076-086-087-
     100-107>112-114.

IN...Frost Advisory from 1 AM to 9 AM CDT Friday for INZ085>088.

     Freeze Warning from 1 AM to 9 AM CDT Friday for INZ081-082.

KY...Frost Advisory from 1 AM to 9 AM CDT Friday for KYZ001>022.

&&

$$


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