JKL issues Area Forecast Discussion (AFD) at Aug 21, 7:36 AM EDT760
FXUS63 KJKL 211136 AAA
AFDJKL
AREA FORECAST DISCUSSION...UPDATED
National Weather Service Jackson KY
736 AM EDT Wed Aug 21 2024
.KEY MESSAGES...
- Below normal temperatures are expected through Thursday. Above
normal temperatures then return by the weekend.
- Dry weather will persist into the first part of next week.
&&
.UPDATE...
Issued at 736 AM EDT WED AUG 21 2024
Hourly grids were updated based on recent observations and trends.
This led to no substantial changes at this point. Initially
chilly temperatures, JKL set a record low for the date at 53
breaking the record of 55 form 2001, will moderate to a couple of
degrees warmer on average as compared to Tuesday. Initial fog,
mainly in the valleys should lift and dissipate over the next one
to two hours. Some of the guidance suggests a few cumulus may
occur late in the morning to the afternoon, but if it occur,
coverage should be less than what occurred on Tuesday.
&&
.SHORT TERM...(Today through Thursday)
Issued at 439 AM EDT WED AUG 21 2024
Early this morning, an upper level low was centered over the Lake
Ontario to upstate NY vicinity with an associated upper level trough
extending to the Carolinas to FL. Meanwhile, to the east and
southeast of this upper low, an upper level ridge was centered over
portions of the western Atlantic. Further west an upper level ridge
was centered over the NM to western TX vicinity with the axis of
this ridge extending north and northeast to the Dakotas and then
into Canada. KY and the Lower OH Valley region is located in between
these two systems with north to northwest flow aloft. At the
surface, a ridge of high pressure extended from northwest Ontario
to the western Great Lakes to OH and TN Valley regions. With high
pressure in place, valley fog has developed especially in deeper
sheltered valley locations, especially those near and to the south
of the Mountain Parkway and is evident per satellite imagery and
some area webcams. Temperatures ranged from the upper 40s in valleys
and some other locations devoid of fog such as the Bath County
Mesonet station and the KCPF airport area to the low to mid 50s
elsewhere. Overall a dry airmass is in place for this time of year
with PW analyzed per SPC Mesoanalysis at generally 0.4 to 0.5 inches
or generally below the 10th percentile for this time of year per
climatology.
Today and tonight, the upper level low initially over the Lake
Ontario to upstate NY area should meander gradually to the
Quebec/NH/ME border area, but also leave an upper trough axis in
place that should extend from the Northeast and mid Atlantic coast
to the western Gulf of Mexico. This trough axis should be in place
between ridging centered east of Bermuda and the upper level ridge
that builds east into the Plains/Central Conus. North to northwest
flow aloft will continue while the sfc ridge is expected to settle
south and become centered north of the Commonwealth and extend east
to the mid Atlantic coast. The airmass will remain dry with PW per
the 00Z HREF mean in the 0.45 to 0.6 inch range today and climb to
around the 0.5 to 0.6 range tonight. Mixing this afternoon should
support dewpoints during peak heating and mixing today dropping back
to the mid to upper 40s north to around 50 south. NBM deterministic
dewpoints during peak heating were trended down a couple of degrees
toward the NBM 10th percentile and some of the MOS guidance once
again.
Thursday, the position/axis of the trough to the east should not
change much through the northern portion of the trough should shift
east a bit more quickly than the southern portion while the ridging
over the Plains should strengthen and build into the OH
Valley/Commonwealth. Meanwhile the sfc ridge will remain in place to
the north and east of eastern KY but is forecast to weaken a bit. A
bit of a north to south difference in dewpoints/moisture is expected
on Thursday afternoon. Dewpoints during peak heating/ mixing should
drop back to the upper 40s north to mid 50s south. PW per 00Z HREF
mean should rise to near 0.7 late in the south with values roughly
in the 0.5 to 0.6 range elsewhere or generally in the 10th to 25th
percentile range for this time of year per climatology. NBM
deterministic dewpoints during peak heating were trended down a
couple of degrees toward the NBM 10th percentile and some of the MOS
guidance once again.
With the north to northwest flow aloft and northeast to easterly
flow today, highs will again be on the order of 10 degrees or so
below normal for this time of year. Following another day of drying
following recent rainfall and considering the position of the sfc
high tonight should be the coldest night on average of the week. Min
T will be more typical of Fall with valley locations that do not
experience fog development dropping into the mid 40s in valleys
without fog with upper 40s to low 50s elsewhere. Coalfield ridgetop
locations should generally be the warmest. Patchy fog should
again form in the deeper/sheltered valleys, especially along the
larger creeks, area rivers, and lakes. Temperatures will moderate
further on Thursday as the upper level ridge begins to build east.
.LONG TERM...(Thursday night through Tuesday)
Issued at 431 AM EDT WED AUG 21 2024
The models are in good agreement with an amplified long wave
pattern to be the rule over the CONUS through the extended portion
of the forecast. Ridging will start out centered over the southern
Plains, while two cutoff lows spiral over northern New England in
the East, and just off the coast of the Pacific Northwest. The
southern Plains ridge will expand northeast with time, allowing
for rebounding 500 mb heights across the Tennessee and Ohio
valleys through the weekend. The Pacific Northwest system will
swing east, generally dampening and getting shunted north
initially. Concurrently, short wave energy traversing Hudson Bay
and then Quebec will likely cutoff as it moves over northern New
England. Additional short wave energy inbound from the
northeastern Pacific will then reinforce a broader and deeper
trough that will affect locations mainly from the Pacific
Northwest to the northern Plains into next week, while the ridge
axis shifts east, aligning from Quebec through the eastern Great
Lakes and into the Ohio Valley by next Tuesday. While model
agreement breaks down regarding the evolution of the smaller scale
features by early next week, there is very little spread noted in
500 mb heights across the Ohio and Tennessee valleys, with
geopotential heights in the 590 to 595 decameter range being
maintained.
Sensible weather will features building temperatures throughout
the period. Lows initially will still be in the upper 40s in the
cooler valleys early Friday morning, but then moderate a few to
several degrees each morning thereafter, as high pressure at the
surface gradually weakens and shifts east with time. Highs will
start out near normal in the mid 80s for Friday, but then warm to
the lower 90s by early next week. PoPs continue to come in below
15 percent, given the persistent stronger ridging.
&&
.AVIATION...(For the 12Z TAFS through 12Z Thursday morning)
ISSUED AT 74035 AM EDT WED AUG 21 2024
High pressure at the sfc and aloft should lead to VFR prevailing
through the period, with a couple of caveats. Initial valley fog
down to IFR or worse in some locations should dissipate through
about 14Z. The TAF sites should not be affected. Some of the
guidance, especially the NAM suggests a few cumulus could develop
around or a bit after 15Z and dissipate by no late than about
22Z. if this occurs conditions should still remain VFR. Winds will
be light and variable on average through around 14Z and then
average from the northeast at less than 10KT through about 23Z,
before returning to light and variable to end the period.
&&
.JKL WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
UPDATE...JP
SHORT TERM...JP
LONG TERM...GEOGERIAN
AVIATION...JP
Source:
JKL issues Area Forecast Discussion (AFD) at Aug 21, 7:36 AM EDT---------------
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