Area Forecast Discussion
Issued by NWS Paducah, KY
FXUS63 KPAH 291817
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PADUCAH KY
117 PM CDT Tue Jul 29 2014
.SHORT TERM...(Tonight through Thursday night)
Issued at 104 PM CDT TUE JUL 29 2014
The short term forecast remains largely unchanged, with the same
basic synoptics and only minor/subtle massaging/tweeking
necessary. Cu field today is less expansive/dense than yesterday,
given the lower rh in the lower trop.
Mos suggests patchy fog developing tonight, which is possible. But
it looks like some upstream mid-high cloud could advect in around
the same time frame, thus limiting its expanse.
Tmrw we see 700-500 mb lapse rates approaching 6C, but with low
layer flow having a tough time returning (surface high anchors
across FA and to the east), the lower trop will remain moisture
deficient and while we could not totally rule out an isolated
diurnally aided shower or storm, the PoPs remain
low enough to preclude from mention. This represents no
significant change from past few model runs/forecasts.
By Thursday, some more vigorous energy/moisture advection in the
southern stream promotes a slight uptick in the overall PoP, to at
least warrant a slgt chance mention during the diurnally aided
daytime hours. This will apply for all but the far eastern 1/3 of
the FA, where lingering surface high pressure should suppress the
parcel uvm field.
Daytime Highs should return to the lower 80s FA-wide beginning
tmrw. Lows will make a gradual move toward, and will eventually
achieve, the lower 60s by the end of the period.
.LONG TERM...(Friday through Tuesday)
Issued at 116 PM CDT TUE JUL 29 2014
Medium confidence in the extended.
The model runs constantly show a persistent trough over the eastern
half of the US. They are also in agreement on tapping into the
monsoonal flow overtopping the high over the southwest. It pulls
this moisture across the plains and reaches the area in concert with
the axis of the upper level trough. It also depicts a pool of
moisture advancing from the north caught up in the northwest flow
from the upper level trough. Forecast sounding are moistening up as
result of this combination...not as dry aloft as previous runs. The
question remains will the western moisture stay far enough north and
northern moisture make it far enough south to produce precip over
the area. Northerly winds indicate a surface reflection from the
upper level system may materialize as a weak cold front late in the
week. Will make final call when the 12z Tue ECMWF arrives. The ECMWF
is and has been advertising a dry weekend with the less consistent
gfs starting to lean that way a bit. Will likely have to maintain a
late week pop but may be able to dry things out for the weekend.
Otherwise the next system appears to be a cold front approaching mid
to late next week.
Not much change in temperatures with a slow warming trend through
the extended and near steady dew points.
Although there is still some run to run discontinuity especially
with the GFS. The models are consistently decreasing pops late
week and into the weekend. However the operational GFS come into
much better agreement with the upper level trough late in the
week. Its previous run indicated a slower cut off upper low over
the lower Ohio Valley. Now the 12z Sunday run shows a progressive
open low lifting out of the area quickly. This would be a
reflection of the lower pops from the extended init. Also with a
north wind predominant through the week with some easterly flow at
times...would not expect to advect adequate moisture for a
widespread rain event. However with a major upper level trough
swinging through and dew points in the 60s combined with daytime
heating could yield at least chance or slight chance for
Tweaked temps down a degree or two from what the extended init
yielded mostly for collaboration purposes.
Issued at 104 PM CDT TUE JUL 29 2014
Lower trop Temp/Td spread supports diurnally driven Cu field in
the 5-6K FT AGL range. Sky should clear of Cu with setting
sun/loss of fuel, though mid or high cloud blow off from upstream
makes an appearance by the planning period. Said appearance should
preclude MOS hints at vsby restrictions due to fog, although we
cannot rule it out.