Area Forecast Discussion
Issued by NWS Paducah, KY

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000
FXUS63 KPAH 131433
AFDPAH

Area Forecast Discussion
National Weather Service Paducah KY
933 AM CDT Thu Jul 13 2017

.UPDATE...
Issued at 933 AM CDT Thu Jul 13 2017

Mid-morning update to reflect slightly faster (about 2 hours)
onset of convection in Southern Illinois and Southeast Missouri.
NAM-WRF and HRRR numerical model families have picked up on this
convective activity and were used as a rough template for coverage
and timing for today and tonight. Although this convection is
likely getting some thermal profile (sharpening lapse rate) /localized
shear enhancement from a passing shortwave, our forecaster
monitoring radar trends indicated that the shear is weak enough to
allow an outflow-dominated environment with the storms. At this
point, locally heavy, but short duration rainfall and lightning
will be the main concerns this morning. MRMS FLASH rainfall
comparisons suggest ratio of 50 to 60 % of Flash Flood guidance
appears to be the norm for heavy rainfall episodes in the
thunderstorms at this time.

Given the earlier start time and orientation of thunderstorms and
cloud cover, adjusted temperatures in the short term. This will
keep Heat Index values in check today. Current special weather
statement on heat index values across the area handles the
situation fairly well.

&&

.SHORT TERM...(TODAY THROUGH Saturday)
ISSUED AT 254 AM CDT THU JUL 13 2017

Several interesting challenges over the next 24-48 hours.

Currently weak and rather flat flow across the northern tier of
states in the upper levels with a weak low just north of
Minnesota. By 00Z Friday the upper low deepens and moves over Lake
Superior which pushes a short wave into Iowa. By 00Z Saturday the
short wave is over our region.

A series of weak boundaries were to our north due to convection
and an actual cold front across northern Iowa into Wisconsin. A
combination of convection and the short wave will push the front
into our area on Friday and should be south of the area by early
Saturday. High pressure will bring mid 60 dew points into the area
by late Saturday.

For today, with more clouds expected than yesterday, the heat
indices across the area should generally remain below 105. We
touched 105 at a couple of locations yesterday and expect the same
today. SPC has a slight risk touching our northern tier counties
with a marginal risk north of a Cape Girardeau to Owensboro line.
Shear is weak, but instability will be quite high by mid
afternoon. Will also highlight locally heavy rain as storms will
moves slowly.

Friday looks to have more convection across much of the area. SPC
has a marginal risk over most of the area. Again, weak shear but
decent instability. Slow moving storms may produce locally heavy
rain.

.LONG TERM...(Sunday THROUGH Wednesday)
ISSUED AT 254 AM CDT THU JUL 13 2017

Beginning the long term, we still see a general ridge West/trof East
pattern. We`re in between, east of the main ridge and west of the
primary trof...and as such will have northwesterlies aloft for
Sunday. That`ll set the stage for our only Pop, as short wave energy
drops out of the Great Lakes and dives a cold front southward
into/across the Ohio river valley. Model blending shows Sunday
afternoon/evening look to be the best chance time period for the
front to hit our area, with peak heating Pops amplified as 0-1KM MU
Capes range from 1500-3000 J/KG, with best moisture convergence/low
to mid chance cat Pops mainly across our north/east in the vicinity
of the actual front. GFS deterministic modeling is hinting at a
slightly slower passage, however, and if that turns out to be the
case, Pops could struggle to even reach the I-64 corridor as even a
6 hour lag drops 0-1KM MU Capes to less than 1000 J/KG. It`s
something to keep in mind for potential future timing/tweaking if
that trending continues. But either way, the front`s
entrance/passage should give a little nudge of reinforcement for
another day of 80s/60s, as surface high pressure settles southward
across the Wabash river valley in its departure/wake. But then as
we head on into the mid week, we`ll get more and more ridge aloft
influence taking over, returning us to 90s/70s to finish out the
forecast. And while the blend modeling paints isolated pops each
day on through the extended , we chose to make their mention
silent with a mainly dry collaborative picture in place.

&&

.AVIATION...
Issued at 254 AM CDT Thu Jul 13 2017

VFR conditions should continue over the next 24 hours. Scattered
thunderstorms are expected around EVV possibly as early as this
morning. Additional thunderstorms will likely be across much of
the area by mid to late afternoon. Low coverage and not a lot of
confidence on exact location of thunderstorms so held off on
putting them in TAFs.


&&

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

$$

UPDATE...Smith
SHORT TERM...PS
LONG TERM...DH
AVIATION...RJP/PS



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