Area Forecast Discussion
Issued by NWS Paducah, KY

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FXUS63 KPAH 291853
AFDPAH

Area Forecast Discussion
National Weather Service Paducah KY
153 PM CDT Sat Apr 29 2017

.UPDATE...
Issued at 153 PM CDT Sat Apr 29 2017

Lots of shower and tstm activity noted to our west across central
MO. In the warm sector, still believe that the current void in the
pcpn will continue for most of the region during the afternoon
hours. Updated aviation discussion also.

UPDATE...Issued at 522 AM CDT Sat Apr 29 2017

Updated forecast products and gridded forecast to reflect
expiration of Severe Thunderstorm Watch 172 at 5 am CDT.

KPAH radar wind profiles showing more unidirectional flow now from
surface and aloft. The 50kt 3-5kft MSL southwesterly winds air
also shrinking, suggesting a gradual weakening of the low level
jet nearing its climatological diurnal minimum. Winds aloft are
also weakening slightly, holding near the 50-60 knots in the
9-25kft MSL layer. Suspect this is an baroclinic and ageostrophic
response to the upper low in the Southwest U.S. digging and
building in the mid-upper level ridge from southeast to northwest
across the WFO PAH forecast area.

KPAH radar reflectivity also suggests that stronger updrafts are
moving into a more elevated area of the frontal zone, away from
the adjacent upshear zone of the surface-near surface frontal
boundary. This transitional change will limit severe potential,
but with a persistent moisture influx, this will still maintain a
flood potential through the morning, gradually diminishing from
east to west toward southeast Missouri and southwest Illinois.

Still have to work on timing of severe thunderstorm potential, but
anticipate it will be delayed until later Saturday night.

&&

.SHORT TERM...(Today through Monday night)
Issued at 358 AM CDT Sat Apr 29 2017

Flash Flood Watch, including the extension from the Friday
afternoon package into Southwest Indiana and the border counties
into Northwest Kentucky will remain in effect until Sunday
evening.

Unidirectional wind fields above 5kft MSL on the KPAH WSR-88D is
helping to main sufficient shear for updrafts above the elevated
warm front (now stalled frontal boundary). Below 5kft MSL, there
is sufficient directional shear, with W-SWly 50kt 850 mb winds
riding over the frontal zone. The combination is supporting linear
bands with updrafts sufficient to support hail as well as
excessive amounts of rain given the rich low level moisture
transport and training taking place along and just north of the
frontal boundary. With pristine (not polluted by convection)
moisture inflow under the EML south of the frontal boundary,
excessive rainfall amounts will continue through daybreak.

Should see some relaxation of inflow along the boundary as the low
level jet diminishes by mid-morning.

Utilized Weather Prediction Center (WPC) QPF (rainfall amount)
estimates for remainder of Flash Flood Watch period.

The vast majority of the highest QPF will be retracted back to
the Southeast Missouri Foothills this morning as upper low deepens
over the Four Corners area and sharpens the frontal zone in
Arkansas and Southern Missouri. As the upper low ejects out this
evening and overnight into Sunday morning, the boundary will lift,
but convective line segments will move likely regenerate into
Southeast Missouri, supporting additional strong to severe
thunderstorm activity. Given the slow eastward progression of this
system, excessive rainfall will still be a major concern and
threat.

By Sunday, the WFO PAH forecast area will be well into the warm
sector. There will be the potential of some pre-frontal convective
activity in the 15-21z (10 am - 4 pm) time frame on Sunday, which
may muddle severe potential across parts of West Kentucky.
However, given the wind fields expected across the cold front as
it moves slowly east through the daytime hours on Sunday, there
will still be the potential for damaging winds along the front and
possibly some embedded tornadoes along the frontal boundary.

Once the cold front moves through Sunday night, cooler and drier
air should dominate Monday through Monday night.

.LONG TERM...(Tuesday through Friday)
Issued at 358 AM CDT Sat Apr 29 2017

The signal still remains consistent for a midweek system to
follow in behind the exiting closed low as it moves into the Great
Lakes and eastern Canada. The medium range guidance has been
suggesting a stronger shortwave will deepen in the northwest flow
and impacting the WFO PAH forecast area beginning late Tuesday and
persisting into Wednesday, before the trough axis moves through on
Thursday. Dry weather is then expected for the remainder of
extended forecast period as ridging builds into the area.

There still appears to be the potential for a band of southwest to
northeast oriented of heavy rainfall. The placement of this band
is still variable given the variability of medium range model
solutions, so will just highlight in the hazardous weather outlook
for now.

&&

.AVIATION...
Issued at 153 PM CDT Sat Apr 29 2017

It appears now that, through the daylight hours today, in the warm
sector, we will have VFR, if any cigs. Scattered cumulus development
should be between 3-4 kft, and little if any pcpn is expected.
Sustained winds 10-15 kts with higher gusts initially have been out
of the east southeast in the northern third of the region. They are
expected to gradually gain a more southerly component with time this
afternoon, to eventually join the rest of the region, which have
gone southerly. Overnight, in southeastern MO/southern IL, shower
and tstm chances are higher than in southwestern IN/western KY, but
there continues to be some uncertainty as to exactly when widespread
deep moist convection will occur. A tstm may not occur over eastern
parts of the region until after sunrise.

&&

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

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

IN...Flash Flood Watch through late Sunday night for INZ081-082-
     085>088.

KY...Flash Flood Watch through late Sunday night for KYZ001>005-014-
     018-019.

&&

$$

UPDATE...DB
SHORT TERM...Smith
LONG TERM...Smith
AVIATION...DB



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