-- Discussion containing changed information from previous version are highlighted. --
000
FXUS63 KJKL 251201 AAA
AFDJKL

AREA FORECAST DISCUSSION...UPDATED
National Weather Service Jackson KY
801 AM EDT Tue Jun 25 2024

.KEY MESSAGES...

- Heat and humidity returns for today and Wednesday.

- Next best chance of rain will be Wednesday into Wednesday
  evening.

- Hotter weather is expected to make a comeback by Friday and
  especially Saturday, with afternoon highs in the low to mid 90s
  and heat index values peaking around or in excess of 100
  degrees.

&&

.UPDATE...
-- Changed Discussion --
Issued at 755 AM EDT TUE JUN 25 2024

Hourly grids were updated based on recent observation and trends.
Fog in the river valleys continues to lift and should gradually
dissipate over the next hour. With high pressure in place to the
southeast of the area, warmer and more moist air will advect into
the region today with temperatures expected to peak again near the
90 degree mark.
-- End Changed Discussion --

&&

.SHORT TERM...(Today through Wednesday)
Issued at 455 AM EDT TUE JUN 25 2024

Early this morning, an upper level ridge was centered across the
Southern Rockies to Southwestern Conus with the ridge also extending
into the TN and OH Valley regions. At the surface, high pressure
was centered over the Appalachians. Upstream of the region, a
couple of shortwave troughs were moving from the Northern Plains
into the Great Lakes region while further north an upper level
low was located northeast of Hudson Bay while an associated trough
axis southwest across Hudson bay to northwest Ontario and then
west across Manitoba, Saskatchewan,and Alberta. Locally, some
valley fog has developed primarily in the KY and Cumberland River
basins and was generally more patchy in the Big Sandy basin.
Temperatures in the deeper valley locations have dropped off into
the mid to upper 50s while ridgetop locations remain generally in
the mid 60s.

Today, height rises are expected across the Commonwealth into the
afternoon before little change from late in the afternoon into the
evening as a couple of shortwaves pass generally north of the
area and through the Great Lakes. Meanwhile, a more substantial
shortwave/500 mb trough is expected to work into the Northern
Plains/Upper MS Valley late today and this evening and then into
the western Great Lakes to mid MS Valley tonight. At the surface,
low pressure should track from Ontario into Quebec with a trailing
frontal zone working across Ontario and the western and central
Great Lakes. The triple point is expected to move east of Lake
Huron this evening while the warm front to the south moves across
the Lower OH Valley today and the cold front settles southwest
across portions of MI to the Central Plains by this evening.
However, this boundary should continue sagging southeast tonight.

Height rises should keep eastern KY free of convection or
largely free of convection today and into this evening. However,
some of the CAMS have convection that develops over IN and OH or a
resultant outflow dropping to near if not south of the OH River
by this evening. This could result in some weakening convection or
an outflow reaching areas generally near or north of Interstate
64 this evening and some isolated convection in that area. By late
evening into the overnight hours, a period of relative lull is
the general consensus of guidance, although as the boundary
continues to sag south of the Central Great Lakes and nears the OH
Valley, additional convection could affect northern locations
generally north of the Mountain Parkway late tonight. A more
substantial shortwave trough should near the western Great Lakes
to Lower OH Valley late tonight as well.

Chances for convection will be more substantial on Wednesday as a
shortwave trough works further east across the Great Lakes and the
Lower OH Valley region and the cold front gradually sags south
into eastern KY. There is some uncertainty as to the degree of
instability, but dewpoints in the 60s to near 70 combined with
temperatures generally in the upper 80s to low 90s should result
in at least marginal to moderate instability. Confidences is
higher that shear will be more marginal, but possibly enough for
some storm organization. Ahead of the boundary on Wednesday,
rather marginal MUCAPE values of 1000 to 1500 J/kg are anticipated
per 0Z HREF mean with bulk shear on the order of 20 to 25KT.
Values of CAPE in the 03Z RAP are more substantial, with MLCAPE of
2000 to 3000 J/kg and MUCAPE of 3000 to 2500 J/kg while bulk
shear is similar with 20KT south and 30KT north. Low level lapse
rates should be quite steep ahead of the front in the 7 to 9C/km
range with mid level lapse rates less substantial in the 6 to
7C/km range. 0Z HREF mean PW is generally is in the 1.6 to 1.85
inch range with some models a little bit higher. DCAPE of 1000 to
1300 J/kg is forecast per the 03Z RAP. The 0Z HREF also has some
modest 2-5km UH probabilities for portions of the area. Given the
rather steep low level lapse rate forecast and the DCAPE forecast
combined with marginal shear and mid level lapse rates, strong to
damaging wind gusts would be the primary threat for storms on
Wednesday afternoon and evening with some generally small hail not
out of the question. Some locally heavy rain could also occur
with the stronger storms given the PW values around or in excess
of the 90th percentile range, but rather dry weather over the past
1 to 2 weeks would be a limiting factor to any flood threat and
for most locations what rain that falls would be beneficial.

.LONG TERM...(Wednesday night through Monday)
Issued at 500 PM EDT TUE JUN 25 2024

The 25/00z model suite 500H analysis beginning Wednesday evening
shows troughing over eastern North America associated with a parent
~534 dam low spinning over southern Baffin Island. At the surface, a
cold front extends from a low over the Labrador Sea southward to
along the New England Coast and then southwestward across the
Appalachians to near the mid and lower main stem Ohio River. To
the west, an ~595 dam high is found over the New Mexico/Mexico
border and an associated ridge axis extends northward along the
eastern slopes of the Rockies to an ~571 dam high over the upper
Yukon River basin. Surface high pressure is centered over the
Upper Midwest but extends from the Central Plains all the way into
the Mackenzie River basin of Northern Canada. Another ~560 dam
low is coming ashore the Pacific Northwest.

The axis of the upper level trough will pass through eastern
Kentucky on Wednesday evening, nudging the cold front through before
it hangs up just off to our south and east on Thursday. PoPs wane
from northwest to southeast behind the front as drier and somewhat
cooler air arrives on northerly winds. By Thursday, the ridging
aloft moves in from the west while subsiding ahead of the Pacific
Northwest low/trough. At the surface, high pressure passes through
the Great Lakes on Thursday and Thursday night. As that high departs
through the Northeast on Friday, mild and moist southerly flow
redevelops over the Ohio Valley. There is a small chance for deep
convection on both Thursday and Friday, primarily over and near the
high terrain adjacent to Virginia border. PWATs continue rising
heading into Saturday and Saturday night, potentially peaking around
2.0 inches (near climatological maximums for this time of year).
With 850 mb temperatures climbing to between 20-22C on Saturday and
those anomalously high PWATs, expect dew points to rise in the 70s
coincident with air temperatures well into the 90s. This will set
the stage for heat indices approaching 105F -- advisory criteria --
at some locations. There is a better chance (30-40%) for deep
convection on Saturday, particularly over the southeastern high
terrain, though neutral to weak height rises should temper overall
storm coverage and updraft intensity. In the meantime, a low
pressure system develops over eastern Wyoming/Montana (ahead of the
Pacific upper low) before trekking across the Upper Great Lakes on
Friday night and over eastern Canada this weekend. This low will
drag another cool front through eastern Kentucky on Sunday and
Sunday night. This will bring more widespread rain chances for the
second half of the weekend. Another high pressure builds across the
Great Lakes on Monday behind the cool front, bringing a briefly
cooler and drier air mass before the heat returns again as
Independence Day approaches.

This weather pattern may bring on deja vu for some as multiple weak
cool fronts will bring the opportunity for some rainfall, followed
by a day a cooler and drier weather before heat and humidity quickly
return on subsequent days and persist until the next weak cool front
arrives. While there is at least a slight chance of rain on every
day, at least over the higher terrain of southeast Kentucky, the
best rain chances will come ahead of and along the frontal
boundaries. In sensible terms, look for showers and thunderstorms to
diminish from northwest to southeast Wednesday evening and night
such that only a stray shower or storm is possible by Thursday.
Similar to earlier in the week, temperatures will cool off to the
mid 80s for highs on Thursday and will likely be followed by a
sharper ridge-valley split on Thursday night as high pressure
returns with clear skies and light winds. Look for lows in the upper
50s in northern sheltered valleys to the upper 60s on thermal
belt ridges/slopes. Daily high temperatures rebound to the lower
90s on Friday and lower to middle 90s on Saturday. A stray shower
or storm (10-20% chance) cannot be ruled again on Friday afternoon
and evening, mainly in those counties adjacent to the Virginia
border. Unlike the recent heat that was accompanied by moderate
humidity levels, dew points by Saturday are forecast to rise into
the 70s, which will support oppressive heat indices in the 100 to
105 range for most lower elevation locations. Better rain chances
(30-40%) are also forecast for Saturday afternoon, though again
the higher elevations closer to the Virginia border will be most
favored. The next cold front will brings the best rain chances
(50-70%) of the period on Sunday. Any leftover rain chances become
confined to southeast Kentucky on Monday as cooler and drier air
filters back across eastern Kentucky, holding highs in the mid 80s
for most. Nighttime lows, which rise in the upper 60s to mid 70s
over the weekend, retreat to the upper 50s to mid 60s early next
week behind that front.

&&

.AVIATION...
-- Changed Discussion --
(For the 12Z TAFS through 12Z Wednesday morning)
ISSUED AT 759 AM EDT TUE JUN 25 2024

High pressure at the surface will keep mainly VFR through the
period with one exception. Patchy valley fog initially in place
that is not affecting the TAF sites should dissipate by 13Z. Winds
will be light and variable or calm initially and after 23Z,
and generally south to west at less than 10KT otherwise.
-- End Changed Discussion --

&&

.JKL WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

UPDATE...JP
SHORT TERM...JP
LONG TERM...GEERTSON
AVIATION...JP