JKL issues Area Forecast Discussion (AFD) at Jul 24, 1:36 AM EDT257
FXUS63 KJKL 240536
AFDJKL
AREA FORECAST DISCUSSION
National Weather Service Jackson KY
136 AM EDT Wed Jul 24 2024
.KEY MESSAGES...
- Showers and storms are possible through the weekend, especially
during the afternoon and evening.
- Through Friday, any areas that receive successive rounds of
heavy rainfall could experience instances of localized flooding.
- Highs will be about 5 degrees below normal to near normal (mid
80s) through Friday, before trending above normal this weekend.
&&
.UPDATE...
Issued at 635 PM EDT TUE JUL 23 2024
Shower coverage appears to be nearing a peak across the JKL
forecast area early this evening. An isolated lightning strike has
also been noted at times. Expect activity to generally continue
tracking northeast and diminish mid-to-late evening. However, at
least some convection is expected to continue through the
overnight and perhaps even uptick after midnight, especially for
those counties south and east of the Hal Rogers/KY-80 corridor.
&&
.SHORT TERM...(This evening through Wednesday night)
Issued at 400 PM EDT TUE JUL 23 2024
At 1950z, regional radar shows showers generally tracking
southwest-to-northeast along southeast of a line from
approximately Inez-to-Jackson-to-Mount Vernon. A diffuse boundary
remains stalled from roughly southern Ohio to along the Lower
Ohio River and back into the vicinity of the Jackson Purchase.
The ongoing shower activity appears to be largely due to the
combination of differential surface heating and an area of weak
divergence aloft due to our location under the right entrance
region of a 300mb 70-knot jet streak over southeast Ohio and
southwest Pennsylvania. The larger scale pattern continues to
feature upper level ridging stationed over the Atlantic and
extending in the far southeastern US while a positively-tilted
upper level trough extends southward from eastern Canada down
across the Great Lakes through the Mid-Mississippi Valley and
over the Southern Plains. Deep, moist southwesterly flow
continues to feed northeastward between the ridge and trough and
into the eastern Kentucky, though the highest PWATs remain
further southeast, feeding into Tennessee, Virginia and the
Carolinas. Multiple southern stream disturbances are also passing
through the flow and will be the trigger for multiple rounds of
convection through the short-term period. Finally, there is a
more pronounced northern stream shortwave over Upper Great
Lakes/Upper Midwest riding through the parent trough. This low is
supporting a weak surface low passing through southeast Wisconsin
while an associated cold front trails behind across the Northern
Plains.
That cold front will put an end, at least temporarily at the start
of the upcoming weekend, to the persistently showery pattern that
portions of southeastern Kentucky have been plagued with in recent
days. In the meantime though, multiple rounds of showers and a few
thunderstorms, generally more numerous during the afternoon and
early evening, will remain the theme as the weather pattern over the
Commonwealth remains largely unchanged through the end of the short-
term. A persistent upper level jet will provide at least weak
divergence aloft while passing subtle vort maxes, a lingering
diffuse surface boundary, and/or diurnal surface heating aid the
lifting process.
The presently ongoing convection is expected to peak in coverage
through 23z before diminishing. The highest rain chances, 60-80%,
are roughly south of the Mountain Parkway. Those rain chances
diminish to less than 30% in northern Fleming County. Some breaks
in the cloud cover may allow for fog formation overnight,
especially in the valleys, but thickening cloud cover from the
next disturbance should preclude the fog from becoming widespread
and dense. Rather, look for showers and possible thunderstorms to
increase in coverage again overnight though this next round
likely remains more confined between the Hal Rogers/KY-80
corridor and the Virginia border. More widespread shower and
thunderstorm activity can be expected again on Wednesday,
primarily near and south of the Mountain Parkway. Late in the day
or evening, a remnant convective outflow (generated by storms
ahead of the aforementioned cold front) coming in from the
north/northwest could spark a few scattered showers or storms
(40-50% chance) near and north of I-64 corridor before instability
wanes. Meanwhile, continued upper level divergence and yet
another disturbance will likely bring fourth round of shower and
thunderstorm activity to counties adjacent to the
Virginia/Kentucky border late Wednesday night.
Overall rainfall amounts through 12z Thursday are expected to
average from one or two tenths north of I-64 to between one half
and 1 inch in counties adjacent to the Virginia border. With that
being said, 48-hour 12z HREF QPF ensemble max (as a worst-case
scenario proxy) suggests that small pockets of 3-4+ inch rainfall
amounts could occur from today through 12z Thursday in the hardest
hit counties near the Virginia border. Given the isolated
footprint of these amounts as well as the fact that they will
likely be received in two or more distinct rounds, the threat for
substantial flooding remains low. Any possibility for flash
flooding would likely be limited to situations where these
amounts happened to fall in an area that had already seen multiple
inches of rainfall in the last few days. Accordingly, WPC has
maintained the Marginal risk for excessive rainfall across
southeastern Kentucky throughout the short-term period.
Temperature-wise, continue to look for a muted diurnal temperature
range due to cloud cover and precipitation. Highs on Wednesday
are only expected to reach the upper 70s in the upper reaches of
the Cumberland Valley where rainfall will be most prevalent up to
the mid 80s north of I-64 where it will be driest. Meanwhile,
nighttime lows are forecast to range in the mid to upper 60s with
plenty of cloudiness as well as some fog, especially in the
valleys.
.LONG TERM...(Thursday through Tuesday)
Issued at 510 PM EDT TUE JUL 23 2024
A positively tilted trough aligned from southeastern Canada down
through the middle Mississippi Valley will drift east into this
weekend, with upper level ridging temporarily working back in
across the Ohio and Tennessee valleys. This will result in
lessening PoPs with a bit less humidity across eastern Kentucky.
Unfortunately, this will not last, as another trough will move in
from the west, allowing for rising dew points and an increasing
threat of mainly diurnally-driven convection once again into early
next week. The models have maintained decent agreement on the
overall long wave pattern, although detail differences become more
apparent after Saturday.
We start out with one more day of more widespread convection with
the influence of the upper level trough and a surface front
nearby. 500 mb heights will then be on the rise Friday into
Saturday, with high pressure building in from the eastern Great
Lakes to New England. This will allow for the dew points to dip
into the mid and upper 60s, providing some relief from the
humidity. Low level winds will then veer around to the south
southwest from Sunday onward, with dew points gradually increasing
each day. Highs will average in the mid to upper 80s, with lows
modifying from the low to mid 60s early in the weekend, to the
65 to 70 degree range by early next week.
&&
.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
ISSUED AT 136 AM EDT WED JUL 24 2024
Currently all TAF sites are VFR and that will continue over the
next couple of hours before MVFR/IFR fog builds into all
terminals. Also, passing showers will bring VSBY and CIGS down to
MVFR/IFR through the overnight. Fog is forecast to burn off after
13Z but CIGS are expected to remain largely MVFR through the
remainder of the TAF period but mainly at all terminals minus
KSYM. Also, increased shower and thunderstorm activity is expected
during the day Wednesday that will persist through the remainder
of the TAF period. Aside from showers and storms bring gusty and
erratic winds, light and variable winds are forecast through the
period.
&&
.JKL WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
UPDATE...GEERTSON
SHORT TERM...GEERTSON
LONG TERM...GEOGERIAN
AVIATION...VORST
Source:
JKL issues Area Forecast Discussion (AFD) at Jul 24, 1:36 AM EDT---------------
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