Area Forecast Discussion
Issued by NWS Paducah, KY

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FXUS63 KPAH 171624
AFDPAH

Area Forecast Discussion
National Weather Service Paducah KY
1124 AM CDT Thu May 17 2018

.UPDATE...
Issued at 1124 AM CDT Thu May 17 2018

Some moderate changes to the gridded, text, and tabular forecast
for this afternoon and tonight.

Current convective activity is associated with an upper low
migrating to the southeast toward the Quad State region. As the
thin cirrus (high cloud) canopy thins this morning, abundant
moisture left behind from the old frontal zone will be lifted by a
combination of surface heating (insolation) and favorable moist
adiabatic lapse rates and increasing vorticity, updraft helicity
within counter-clockwise bands this afternoon.

Anticipate convection will have a sharp uptick in coverage between
noon and 1 pm across the area. During the following 1-3 hours,
there will be the potential for gusty winds, small hail, and
locally heavy rainfall (at least 0.75" an hour) with the initial
storms. As the coverage of thunderstorm canopies and outflow
boundaries increase during the afternoon, the main activity will
likely turn to widespread light to moderate rain with embedded
multi-cell convection. The sub-severe and isolated severe
potential will go likely go down as we move past the peak heating
this afternoon, but left a mention in for the remainder of the
afternoon for those locations not previously impacted by
convection.

Given the environment and climatology, will be issuing a general
public information statement for landspouts for this afternoon.
The environment is supportive these non-supercell marginal tornado
development. There was one reported in Butler County Missouri last
evening.

May still have some pockets of heavy rain overnight with any
storms that are maintained in the weak shear environment.

&&

.SHORT TERM...(Today through Saturday night)
Issued at 245 AM CDT Thu May 17 2018

Latest radar trends indicate southeast MO and far southwest IL are
the current hot spots for convection. The latest HRRR and RAP13
seem to have a pretty good handle on this and indicate pockets of
deeper moisture across these areas. Any future convection for the
rest of the overnight hours will be confined to mainly parts of
southeast MO.

An upper level area of low pressure was centered just northwest of
Kansas City at 06Z according to satellite, will slowly move
southeast throughout the day today. Not sure how much activity we
will see during the morning hours today (12Z-15Z) as latest CAMs
not indicating much. Will continue to indicate low chances that
increase over time given unstable airmass in place and approaching
upper low. Corridor of deepest moisture appears to be across
parts of southeast MO, far southern IL and over into the Pennyrile
region of west KY. Again highest chances will continue to be
across southeast MO this morning.

By late this morning and into the early afternoon, additional
convection should develop mainly over southeast MO, especially over
the Ozarks. As we head further into the afternoon hours, convection
chances will spread eastward into far southern IL and western KY.
Drier air will likely prevent much from developing in the far
northern tier counties. However, the chances are not zero up that
way by any means and that will change as we head into tonight/Friday.

By 00Z Friday (this evening), the center of our upper level low will
be situated over south central MO. Model consensus indicates
scattered convection will be likely across a good chunk of the CWA,
especially the southern half. As the low slides further southeast it
will be moving across far western portions of the CWA. Plenty of
lift and moisture will be available for continued shower and thunderstorm
activity across much of the area through the evening and
overnight.

While the center of the upper level low will skirt southeast toward
Memphis on Friday, the entire system will continue to impact our
area for Friday, resulting in cloudy and cooler conditions with
scattered showers and storms continuing. This system has been
advertised to slowly move out of the region from west to east
Friday night and the latest model solutions agree. An upper level
ridge will build into the area during the day on Saturday.
However, there are some indications that we might not get through
the day without some convection. However, signals do not appear
strong enough right now to get carried away with any higher than
slight chance POPs for Saturday into Saturday night.

Heavy rainfall does appear to be a concern from today into Friday
looking at precipitable water values. PWs will be running about 1.50-
1.65 which is about the 99th percentile for this time of the year.
Any severe weather should be rather isolated with high wind gusts
and hail possible with the strongest storms.

After a cooler day on Friday with the clouds/rain, southerly winds
will pick up on Saturday, resulting in temperatures rising well into
the 80s once again.

.LONG TERM...(Sunday through Wednesday)
Issued at 245 AM CDT Thu May 17 2018

There is fairly good agreement among the models concerning the
synoptic pattern next week. An area of deep southwesterly flow will
cover the Ohio and lower Mississippi Valleys for much of the period.
Our region will be prone to isolated to scattered convection in the
warm, moist and unstable warm sector. Daily highs will be in the
80s, with overnight lows in the 60s.

The primary feature of interest at 500 mb will be a trough which
will migrate east from the Pacific into the far western states. A
broad area of southwest flow aloft will encompass much of the
central states.

Around the middle of the week, there are hints of some weak 500 mb
troughing over the eastern US. This troughing is evident in the
ensemble means of both the gfs and ecmwf. This troughing could be
sufficient to push a weak surface boundary south into the lower
Ohio Valley on Wednesday, bringing an uptick in convective
coverage.

&&

.AVIATION...
Issued at 620 AM CDT Thu May 17 2018

The TAFs are mainly VFR with northeast winds outside of
convection. Dealing with a bit of MVFR fog this morning but that
should burn off quickly. As for convection, short range guidance
suggests scattered to numerous showers and thunderstorms possibly
developing at KCGI/KPAH by around midday, a bit later at
KEVV/KOWB. Opted for a VCTS btwn 17Z- 19Z with a prob30 to cover
the rest of the afternoon and early evening. Not sure how much
convection will be left by late evening and into the overnight
hours, so left a VCSH going as convection could linger late. There
are some signals that cigs and/or vsbys could go down close to
the end of the planning period. Something to watch.


&&

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

$$

UPDATE...Smith



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