Area Forecast Discussion
Issued by NWS Paducah, KY

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000
FXUS63 KPAH 202034
AFDPAH

Area Forecast Discussion
National Weather Service Paducah KY
334 PM CDT Tue Jun 20 2017

.SHORT TERM...(Tonight through Thursday night)
Issued at 335 PM CDT Tue Jun 20 2017

The storm term will encompass the transition period with the
approach of the remnants of Tropical Storm Cindy from the northern
Gulf of Mexico and the transition from northwest flow toward a
more zonal flow in advance of a sheared trough axis and frontal
zone from the upper Midwest.

For early this evening, there will be shear and lift for a very
small chance of convection near the I-57/I-64 corridor in southern
Illinois, as minor wave moves by. Any precipitation chances will
become nil for the rest of the WFO PAH forecast area during the
overnight hours.

For Wednesday, as the cyclonic circulation associated with
Tropical Storm Cindy begins to move inland, the influence of the
southwest U.S. high pressure dome will retrograde slightly,
allowing for a more zonal flow to move toward the WFO PAH
forecast area Wednesday and Wednesday night, gradually replacing
ridging impressed by T.S. Cindy.

At this time, have very low confidence on the northward limit of
rain chances during the day on Thursday, especially in the morning
and early afternoon hours. The only factor that would support rain
chances would be the introduction of deep layer moisture ahead of
T.S. Cindy and a sharpened deformation zone. Any precipitation
potential would be along and south of the deformation zone. The
ECMWF/Canadian/NAM- WRF guidance do hint at this possibility and
is consistent with a precipitation signal, especially late
Thursday night, where the higher rain amounts are expected.

Some of the national discussions lend support to the 12z GFS
solution, but only a couple of members of the GFS ensemble
extract QPF (rain amounts) near one half of what the
deterministic guidance generated with todays numerical model run.
There is also too much forcing and lift generated ahead of the
baroclinic zone approaching from the north at this time. This run
is not consistent with previous model runs and appears to be an
outlier.

Even with timing and locations variability from the track of T.S.
Cindy, prefer the initialization of ECMWF, Canadian, SREF, and
some of the NAM- WRF suite. The initialized thermal profile and
satellite initialization of the aforementioned guidance was better
than the 12z GFS. Hopefully, there will be some convergence of
solutions.

The signal for moderate to locally heavy rainfall has consistently
been into the long term (Friday), especially over the southern
Pennyrile region of West Kentucky. To heighten the awareness of
heavier rainfall into parts of West Kentucky, the long term
forecaster has issued a hydrological outlook providing the general
scenario for rainfall associated with the remnants of T.S. Cindy
as it spreads across the Southeast U.S., including the Tennessee
Valley.


.LONG TERM...(Friday through Tuesday)
Issued at 335 PM CDT Tue Jun 20 2017

Main concern is heavy rainfall Friday into Friday night from the
remnants of Tropical Storm Cindy. The exact track of the low center
does not appear critical, since the models seem to be focusing more
on the interaction of Cindy with a northern stream shortwave. The
timing of the 500 mb shortwave and its associated cold front will
have a big impact on whether the moisture from Cindy is squeezed out
over our region.

Earlier model runs pegged much of the Tennessee Valley for the
heaviest rain. The 12z runs of the ecmwf and gfs have shifted
slightly northward. The 12z gfs qpf appears to be a worst case
outlier, since almost every gfs ensemble member shows lower amounts.
There is fairly good agreement between the ecmwf and gfs ensemble
mean qpf. It is still too early to be specific about rainfall
amounts or even the placement of the axis of heaviest rainfall. Much
will depend on where the front intercepts the plume of tropical
moisture. As indicated by the models, there is a potential for very
heavy rainfall amounts wherever this takes place. The official
forecast will nudge amounts upward across the area, but it will be
at least another 24 hours before the timing of the systems and their
qpf are pinned down.

Once the system moves past, mainly dry conditions are expected for
the weekend. The ecmwf has been more emphatic on the passage of a
secondary shortwave and cold front Sat night or early Sunday. This
front would encounter only limited moisture and instability.
Therefore, pops will be only in the slight chance range Sat night
and early Sunday. Humidity will gradually decrease this weekend.

A strong punch of cool dry air will arrive Sunday night and last
through early next week. A rather large 500 mb trough will be carved
out across the Ohio Valley and Great Lakes. 850 mb temps will fall
to around plus 10 for Monday, and possibly lower based on recent
ecmwf runs. This should translate to surface highs of around 80
Monday. Overnight lows will be in the upper 50s in many locations.
Precip chances appear too low to mention Monday through Tuesday, but
there may be periods of cloudiness associated with impulses in the
northwest flow.

&&

.AVIATION...
Issued at 1229 PM CDT Tue Jun 20 2017

VFR conditions to remain in place for the 18z WFO PAH routine TAF
issuance. A weak surface trough axis is currently moving through
the forecast area at this time, with west-southwesterly winds in
place. The flow will move back southerly with time. Some influence
of upper level moisture from the southeast U.S. is apparent with
some mid-deck clouds moving over the TAF locations at this time.


&&

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

$$

SHORT TERM...Smith
LONG TERM...MY
AVIATION...Smith



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