Area Forecast Discussion
Issued by NWS Paducah, KY

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000
FXUS63 KPAH 270834
AFDPAH

Area Forecast Discussion
National Weather Service Paducah KY
334 AM CDT Thu Apr 27 2017

.SHORT TERM...(Today through Saturday night)
Issued at 320 AM CDT Thu Apr 27 2017

Will issue Flash Flood Watch with this package for the period of
00Z Sat (7 PM Friday night) through 06z Mon (1 AM Mon) for areas
along and west of a Fulton KY to Mt Carmel IL line.

An upper level ridge of high pressure will build over the southeast
U.S. today into early this weekend, while an upper level trough
digs into the southern Rockies. This trough will eject east into
the Southern Plains on Saturday night/Sunday. The Quad State will
be within deep southwesterly flow Friday night through Saturday
night. Right now, Friday night and Saturday night look to have
the highest heavy rainfall and severe storm risks.

After a dry and cooler day today, a warm front will develop
northward by Friday evening back over the southern OH Valley
region. Expect fairly widespread thunderstorm initiation during
the evening, which should last into the overnight hours along and
north of the warm front. A stenghening, broad low-level jet will
enhance convergence and lift along and north of this boundary.
In addition, strong vertical shear profiles and steep mid lvl
lapse rates will support organized storms including supercells
with large hail and damaging wind the main threats, though a few
tornadoes may also occur with surface-based storms developing
closer to the warm front.

It looks like the warm front will lift to the north of the region
Saturday as the upper level high pressure system off the Southeast
Coast tries flex it`s mustle and build back to the west toward
our region. This may bring a general break in the
shower/thunderstorm activity over much of the forecast area much
of the day, especially over western KY/far srn IL and sw IN. The
break in higher pops looks more iffy the farther north and west
you get in our forecast area. Some areas of western kY may even
see afternoon temps soar toward the mid/upper 80s.

However, shower/storm chances will ramp back up Saturday night into
early Sunday as the main upper trough and associated cold front
approach from the west. Model guidance has been consistent in
placing the heaviest QPF over southeast Missouri into southwest
Illinois Saturday night. Overall rainfall amounts Friday through
Sunday in the 3 to 5+ inch range will be possible from southeast
MO into IL and far western KY. With much of this area aleady
receiving 1.5 to 3 inches of rain in the past 12-18 hours, opted
to go ahead with flash flood headlines at this time for those
locations. Somewhat lighter amounts are expected as one heads
farther east into KY/sw IN where less rainfall occured overnight.

.LONG TERM...(Sunday through Wednesday)
Issued at 320 AM CDT Thu Apr 27 2017

This extended forecast period will also include the latter
portion of the Flash Flood Watch which persist through midnight on
Sunday night. Following collaboration with WPC (National Center)
and surrounding NWS offices, utilized WPC rainfall amounts (QPF)
through 7 am CDT Monday.

The challenge from now through Sunday night will be the cumulative
effect of antecedent precipitation and the minimum of rainfall
during the day on Saturday, which may allow drainage away from
overland areas versus rivers, which will see a rise regardless.

The GFS and ECMWF suite of guidance are grouped fairly well on the
temporal and spatial levels, with the Canadian (CMCnh) a little
further north with the warm sector.  At this point in time, kept
with the regionally blended model initialization, with some emphasis
toward the GFS/ECMWF in the outer time periods of the extended
forecast.

With the cold front still expected to remain just west of the WFO
PAH forecast area by Sunday morning and the upper low over KS/MO
expected to develop a negative tilt as it move north-northeast,
there will be a continued potential for severe weather across the
WFO PAH forecast area Sunday afternoon and evening.

The upper low and trough will move into the Great Lakes on Tuesday,
but leave a broad northwest trough across the eastern 3/4 of the
nation. This will place the WFO PAH forecast area into a pattern of
intermittent shower and thunderstorm activity late Tuesday through
Thursday.

There are some timing differences in both the GFS and ECMWF with
respect to upstream shortwaves sharpening the trough during the
middle of next week. However, both the aforementioned numerical models
suggest increase in baroclinicity over the WFO PAH forecast area
early Wednesday. As another low is expected to deepen across the
Great Lakes late in the week.

At this point in time, forecast confidence is 50 percent or less
after Tuesday, owing to timing differences. However, given the
trajectory of the flow, temperatures in the 60s and 70s appear
reasonable at this time for most of next week.

&&

.AVIATION...
Issued at 1129 PM CDT Wed Apr 26 2017

With the approach and passage of a cold front, all sites will have
periods of showers and thunderstorms along with VFR/MVFR
cigs/vsbys early, light drizzle and MVFR cigs/vsbys for 4-6
hours, then inproving to VFR during the last few hours of the
period. Winds generally out of the southwest to west AOB 10 knots
through the period.


&&

.PAH WATCHES/WARNINGS/ADVISORIES...
IL...Flash Flood Watch from Friday evening through late Sunday night
     for ILZ075>078-080>094.

MO...Flash Flood Watch from Friday evening through late Sunday night
     for MOZ076-086-087-100-107>112-114.

IN...None.
KY...Flash Flood Watch from Friday evening through late Sunday night
     for KYZ001>005.

&&

$$

SHORT TERM...GM
LONG TERM...Smith
AVIATION...JP


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