132
FXUS63 KJKL 260851
AFDJKL

AREA FORECAST DISCUSSION
National Weather Service Jackson KY
451 AM EDT Wed Jun 26 2024

.KEY MESSAGES...

- Heat and humidity lingers today.

- The next good chance of rain comes today into this 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.

&&

.SHORT TERM...(Today through Thursday)
Issued at 443 AM EDT WED JUN 26 2024

Early this morning, an upper level ridge was centered over New
Mexico and extended north through the Rockies while an upper level
low was centered northeast of Hudson Bay with a trough south
across the Great Lakes and into the eastern Conus. A shortwave
trough was nearing the mid MS Valley and Lower OH Valley while
another shortwave trough was further north and nearing Lake
Superior/western Great Lakes. At the surface, an area of low
pressure was centered over Quebec with a frontal zone extending
into the Great Lakes to Central Plains and then into the western
Conus. Locally, sprinkles or light showers falling mostly from mid
level clouds were moving across south central KY and eastern KY
while further west nearer to the approaching shortwave trough,
deeper convection including some thunderstorms extended from IN
into western portions of KY and TN. Cloud cover and a more moist
airmass in general was leading to milder temperatures compared to
24 hours ago. At present, PW is analyzed in the 1.2 inch to 1.5
inch range from southeast to central KY while PW increases further
toward the 2 inch mark in portions of the Lower to Mid MS
Valleys.

Today, the initial shortwave trough is expected to progress east
and more or less merge with the more potent shortwave to its
north that rotates across the Great Lakes and then works into the
Northeast, Mid Atlantic states, and Appalachians this evening and
tonight. The axis of the trough at 500 mb should shift east and
southeast of the Lower OH Valley late tonight and on Thursday with
a trend of increasing 500 mb heights during that timeframe.
Meanwhile, sfc low pressure will track into the Maritimes with the
trailing cold front sags southeast into the OH Valley today,
dropping south of the OH River this afternoon and evening and
southeast of eastern KY tonight. Sfc high pressure builds from the
Northern Plains into the Upper MS Valley and Great Lakes as well
as the OH Valley on Thursday behind the boundary.

Ahead of the boundary today, PW is forecast to climb to about the
1.5 to 1.9 inch range while dewpoints climb further through the
60s to near the 70 degree mark. Debris clouds from upstream
convection could limit instability during peak heating, and 0Z
HREF mean MUCAPE is forecast to climb to about the 1000 to 1750
J/kg range and bulk shear of about 20 to 25KT while 03Z RAP has
MUCAPE values peaking about 500 J/kg higher and bulk shear of
about 15 to 20KT in the south to nearly 30KT in the north.
Meanwhile, the 03Z RAP has MLCAPE peaking at about 1000 to 2000
J/kg. The 0Z HREF has the highest 2-5km UH probabilties in the
north where guidance generally has the higher MLCAPE and slightly
better shear. If debris clouds are more on the minimal side, the
higher end of the instability range would be realized while more
in the way of clouds would lead to cooler temperatures and less
instability. Low level lapse rates are forecast to peak in the 7
to 9C/km range with rather meager mid level lapse rates in the 5.5
to 6.5C/km range. Overall, these parameters as well as CAMS point
toward marginally severe wind gusts being the primary threat this
afternoon and evening with locally heavy rain possible with any
training cells and small hail not out of the question with the
strongest cells. The highest chances for convection are expected
this afternoon and evening near peaking heating which should
coincide with the front working into eastern KY and the approach
of the 500 mb trough.

Moisture will linger a bit longer over the southeastern portions
of the area later tonight and into Thursday as compared to
locations further north. Showers or an isolated thunderstorm will
be possible into Thursday south of the Mountain Parkway and
especially for areas south of the Hal Rogers Pkwy and KY 80
corridor with drier air moving into the area and height rises
combining for diminishing chances even in the south on Thursday
afternoon.

Highs today should be similar to Tuesday if not a degree higher
on average for most areas assuming debris clouds do not limit
temperatures. Highs mainly in the upper 80s to low 90s combined
with dewpoints well into the 60s if not around 70 should result in
peak heat indices in the mid 90s to near 100 for many locations.
Highs for Thursday are expected to be similar to what was
experienced with the post frontal airmass back on Monday, in the
low to mid 80s and in the 70s above 2500 feet.

.LONG TERM...(Thursday night through Tuesday)
Issued at 451 AM EDT WED JUN 26 2024

The 26/00z model suite is in fairly good synoptic agreement through
the long-term period. A forecaster analysis initially shows a
longwave 500H trough extending from a parent ~534 dam low over
Davis Strait down through eastern Canada and into the
Northeast/Mid-Atlantic US. Further west, an elongated ~590 dam
high is found along the US/Mexico border with a ridge axis extending
northward across the Plains and into the prairies of southern
Manitoba/Saskatchewan. At the surface, a large but relatively
weak surface high, centered over the Great Lakes, dominates the
from southeast Ontario down through the Tennessee Valley.
Upstream, an ~558 dam Pacific low is found over the Alberta/
British Columbia/Montana triple-point with a corresponding
surface low over near/over the Black Hills. A upper-level
shortwave disturbance extends from the low southward across the
High Plains. A second disturbance over the Pacific Northwest is
rotating around the parent slow. Additionally, an ~558 dam
low/trough is found further upstream over the North Pacific.

The upper level high over the southwestern CONUS will slosh from
west-to-east through the long-term period while each of the
aforementioned lows/troughs translate across the northern half of
the CONUS. Across eastern Kentucky, the first upper level trough
will depart as heights rise on Thursday night and Friday while the
surface high passes into southern New England. Southerly flow
returns to the Ohio Valley on the back side of the high, causing 850
mb temperatures to rebound to near 20C on Friday. With those
rising temperatures, PWATs will also rise quickly to around 1.75
inches after starting the day near 1.00 inch. Spotty convection
may ignite off of the high terrain of the Central/Southern
Appalachians near peak heating, but rising heights will tend to
minimize coverage and intensity. The first upper-level shortwave
trough then approaches Friday evening with weak height falls; but
by that time, any associated convection will tend to wane due to
the loss of daytime heating. Heading into Saturday/Sunday, the
next upper level low/trough continues to ride the US/Canadian
border eastward while its surface reflection treks into the Upper
Great Lakes by Saturday morning and eventually down the St.
Lawrence Valley on Sunday. PWATs continue climbing to around 2.00
inches (near climatological maximums) on Saturday as the second
upper level shortwave passes, likely firing off more widespread
convection. A cold front, trailing the surface low, eventually
sinks through the Ohio Valley on Sunday with the highest rain
threat of the period. Behind this system, upper level ridging
briefly returns to the Ohio Valley region early next week. Brief
cooling and drying on Monday will give way to renewed heat and
humidity by Tuesday ahead of the next trough and cold front`s
arrival just beyond the end of the forecast period.

Sensible weather will feature a refreshingly cooler and less humid
Thursday night and Friday morning. Low temperatures are forecast to
range from the upper 50s in the northern valleys to the middle 60s
over the thermal belt ridges/slopes. As southerly flow returns,
building heat and humidity will boost temperatures back into the
upper 80s to lower 90s by Friday afternoon while heat indices
reach 90 to 100F. A stray shower or thunderstorm (10-30%) is
possible near the Virginia border during the afternoon and then
north of the Mountain Parkway during the evening or overnight.
Similarly, hot temperatures are expected for Saturday but will
feel more oppressive due to dew points rising into the lower and
middle 70s leading to heat indices of 100 to 105F. There is a
better chance (40-50%) for scattered showers and thunderstorms
on Saturday afternoon which may give some relief. The highest
chance (60-80%) of rain comes on Sunday with the passage of a cold
front. Nights are forecast to be muggy with lows ranging in the
upper 60s to mid 70s for most locations. Behind the front, it will
be less muggy and cooler with Sunday night`s low temperatures
returning to the upper 50s to mid 60s. Mostly sunny, dry and
comfortable weather is expected for Monday with highs in the lower
to middle 80s before heat and humidity return on Tuesday as highs
return to the upper 80s and lower 90s.

&&

.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
ISSUED AT 220 AM EDT WED JUN 26 2024

VFR conditions were prevailing across the area at issuance time
and VFR and will generally persist through 00Z, before more
widespread convection will lead to areas of MVFR generally in the
north. Sprinkles and or mainly light showers are expected over
the first 6 to 12 hours of the period, before renewed chances of
showers and thunderstorms to all TAF sites after 18Z/Wednesday
through the remainder of the period as a cold front and shortwave
trough work across the Lower OH Valley. Lastly, light and
variable winds are largely expected except where convection
exists.

&&

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

$$

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