Area Forecast Discussion
Issued by NWS Paducah, KY

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899
FXUS63 KPAH 250832
AFDPAH

Area Forecast Discussion
National Weather Service Paducah KY
332 AM CDT Thu May 25 2017

.SHORT TERM...(Today through Saturday night)
Issued at 332 AM CDT Thu May 25 2017

The upper-level storm system that brought rain to the region
yesterday, will steadily wobble eastward today. Any light showers
will come to an end by midday. Low clouds will linger over the
eastern half of the region well into the afternoon, but the entire
area should be clear by sunset. West northwest winds will push
Lake Wind Advisory criteria over the eastern half of the area
through the day. Given that the forecast only gets up to the
criteria, but not through it, will not issue an Advisory at this
time.

Winds will become southerly quickly tonight, as the flow aloft
becomes zonal. This will result in strong warm, moist advection in
the low-levels. Surface dewpoints Friday will climb well into the
60s throughout the area. A few areas of drizzle or light showers
may accompany this increase in moisture primarily near the Boot
Heel early Friday. An elevated mixed layer will overspread the
area early Friday, and this should effectively cap deep convection
through the day.

There is a fairly strong signal for a subtle disturbance in the
zonal flow to touch off convection near a cold front over
western/central Missouri Friday afternoon. This activity may shift
eastward, potentially impacting our I-64 corridor Friday night.
Given the amount of instability available, severe weather cannot
be ruled out. Our forecast keeps the larger-scale surface
boundary just to our north through the night, and then lifts it
back north a bit during the day Saturday. With the potential for
an outflow boundary to help overcome the cap, will have slight
chances of convection overnight throughout the area.

Not sure where the active boundary will be Saturday, but to its
south dewpoints will climb into the lower 70s, and the models
generate SBCAPEs over 5000J/kg and negative double digit LIs. Of
course these extreme values only develop with a major cap in
place. If the boundary indeed lifts back to our north, it will be
a very warm and sticky day with heat indices into the lower 90s
possible. If it doesn`t, we can expect to see convection focused
on the active boundary (front or outflow) slowly developing
southward into the unstable airmass. Wind fields will be plenty
strong enough to support severe storms Saturday into Saturday
night, with the potential for very large hail and significant
damaging winds. A few tornadoes will also be possible, primarily
near boundaries, or boundary intersections. With precipitable
water values pushing 2 inches and potential for the outflow
boundary to become parallel to the zonal flow aloft, training
storms could result in heavy rainfall and flash flooding.

The larger-scale front is still expected to move into the area
late Saturday night, but it is not likely to clear the area by 12Z
Sunday. If the above severe scenario develops, the severe
potential should be done by Saturday evening, but if the cap holds
through the day, the severe weather threat would be focused near
the cold front Saturday night. The stage is set for some
significant severe weather somewhere in our region Saturday or
Saturday night, we`ll just have to wait for the details to come
into better focus.

.LONG TERM...(Sunday through Wednesday)
Issued at 332 AM CDT Thu May 25 2017

Our weather will be dominated by a large upper-level low pressure
system that will slowly move east southeastward from central Canada
early in the weekend, to the upper Great Lakes region by early next
week.

A weak frontal boundary will be moving through the area early in the
day on Sunday, but an upper level disturbance, which will be in the
central Plains states early in the day, will move eastward through
the area as well. This combined with decent moisture should warrant
more scattered showers and storms. The ECMWF is the one model which
shows drier conditions due to the faster frontal movement as well as
a weaker upper level impulse. GFS ensembles mimic the GFS/Canadian
solutions and WPC also contends that the 12Z ECMWF is an outlier. In
addition, looking back on several previous runs of the GFS, we
indeed need to keep scattered convection chances going Sunday...with
the gradient from NW to SE, northwestern sections with the lower
POPS.

The general trend of drying things out Sunday evening still looks on
track. While a few lingering showers or storms could threaten some
areas (west KY/southwest IN) Sunday evening, we should see chances
gradually coming to an end. These dry conditions will continue into
Memorial Day as temperatures stay similar to what they will be on
Sunday, which is in upper 70s to lower 80s.

The GFS and its ensembles are steadfast in bringing yet another
upper level impulse down into the area on Tuesday afternoon/evening.
The other models continue to indicate dry conditions. However, the
previous runs of the GFS have increased confidence that at least a
low POP is warranted for this time frame.

Dry weather then returns briefly before models (ECMWF/Canadian) try
and ramp things up again as early as Wednesday afternoon/evening.
Will not get too carried away with POPs just yet as models are not
handling the timing well with this next chance for precip.

Temperatures will remain right around normal to slightly below
normal for the first half of the week.

&&

.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 1117 PM CDT Wed May 24 2017

Area of MVFR to IFR cigs about to drift into SW IN, SE IL, NW KY
overnight. Forecast will reflect this along with a light rain,
drizzle chance with MVFR vsbys possible. West of a KMVN to KPAH
line, much better conditions expected with mainly mid clouds
6-10k/ft expected, and little cloud cover farther west into SEMO.
Through Thursday morning, lower clouds will persist over the
KEVV/KOWB areas. Conditions will gradually improve with time,
though some diurnal CU development expected, even west toward the
MS River. Winds may gust WNW 15-20 kts by Thursday afternoon,
otherwise WNW mainly less than 10 kts.

&&

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

&&

$$

SHORT TERM...DRS
LONG TERM...CW
AVIATION...CN



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