JKL issues Area Forecast Discussion (AFD) at Jul 20, 8:06 AM EDT935
FXUS63 KJKL 201206 AAA
AFDJKL
AREA FORECAST DISCUSSION...UPDATED
National Weather Service Jackson KY
806 AM EDT Sat Jul 20 2024
.KEY MESSAGES...
- Showers and thunderstorms will impact the region at times over
the next week. Probabilities will generally peak each afternoon
and evening.
- Highs will be near normal to about 5 degrees below normal
throughout the period, with humidity returning.
&&
.UPDATE...
Issued at 758 AM EDT SAT JUL 20 2024
Showers were occurring over portions of east central KY and over
the western portions of the CWA with precipitation more of the
stratiform nature along the VA border. Short term guidance to a
large degree was not handling the showers all that well, and per
extrapolations this should continue northeast over the next couple
of hours as a shortwave passes. Adjustments were made to pops for
the next 3 hours or so as well as thunder probabilities
accordingly.
&&
.SHORT TERM...(Today through Sunday)
Issued at 455 AM EDT SAT JUL 20 2024
The large scale flow pattern will feature troughiness in place over
the southeastern CONUS, with troughs of low pressure also in place
over the Pacific Northwest and on down the west coast into the
desert southwest. The prominent feature in our part of the country
is an extensive frontal boundary that is currently stretching from
the southeastern coast, through the Tennessee Valley and southern
Mississippi Valley and on into southern Texas. Extensive ridging is
in place from New England, through Great Lakes and Ohio Valley
regions, and out across the Great Plains. The ridging also extends
across and just to the west of the Rocky Mountains.
We're looking a pretty much the same story in the short term as
we've seen over the past few days. The models are still showing
differences in overall timing and coverage of showers and storms
across the area this weekend, so there is still some uncertainty
with the finer details of the forecast. However, the trend does
still seem to be for showers and storms to move in from the south
and southwest the next couple of days, as disturbances move from
west to east along the front that is still parked just to the south
of our area. Shower and storm activity should peak during the
afternoon and early evening hours both today and Sunday and when
southern stream waves of low pressure move close by, thereby pushing
the front north into our area from time to time. We should see
activity slack off quickly after sunset tonight, with dry weather
expected until very early Sunday morning, when frontal waves begin
moving northward toward the area again, bringing showers and storms
back in that will peak in coverage Sunday afternoon.
We are expecting warm and muggy conditions around the area over the
weekend, but with highs only expected to rise into the low to mid
80s for most locations today and Sunday, the heat should be
bearable. There are no significant weather concerns to speak of at
this time. We will, however, advise everyone to take the necessary
precautions if outdoors while a thunderstorm is approaching, as
cloud to ground lightning will still pose a hazard that folks need
to be aware of today and tomorrow.
.LONG TERM...(Sunday night through Friday)
Issued at 500 AM EDT SAT JUL 20 2024
The period is expected to begin with an upper level ridge extending
from portions of the western Atlantic into the Gulf of Mexico with
another ridge centered over the western Conus. In between, an upper
level trough is expected to expected to extend from Canada across
the Great Lakes region into portions of the Central Conus toward the
Arklatex region to southern Plains. Through the middle of next week,
upper level ridging is expected to remain in place from the western
Atlantic into the Gulf of Mexico. Another upper level ridge will
remain centered over the western/southwestern Conus, but this one
builds gradually into the Plains. The 500 mb trough axis should
continue working further east and southeast across the Great Lakes
and into the Northeast to mid Atlantic to the Lower OH Valley.
The axis of this trough should near the region toward end the
period, though model guidance varies from model to model and run
to run with this timing. At the surface, as the trough evolves to
the west, a quasi stationary front located east and southeast of
the upper trough and more or less the leading edge of deeper
moisture across the Southeastern Conus is expected to gradually
lift north to near or just north of the OH River as a warm front.
This boundary will become diffuse by midweek and serve as a
focal point for convection. A separate frontal zone should
gradually drop into the Great Lakes in the early part of the long
term forecast period, before settling near the OH River to end
the period. This will occur in tandem with a shift in the 500 mb
trough across the Great Lakes into the Northeast and mid Atlantic
states.
In the southwest flow ahead of the trough axis, multiple shortwave
troughs should impact the region. However, the low predictability
of timing of any individual shortwaves into the OH Valley and
Appalachians leads to low confidence in details. In general, pops
generally had a bit of a diurnal flavor through the period, with
the most likely time for the greatest coverage of convection
occurring from mid afternoon to early evening each day. Although
chances for convection will generally be a bit lower each time,
pops of at least isolated to scattered ranges were carried each
night.
Moisture will increase to begin the period across the region. South
to southwest flow between the upper ridging generally extending from
near Bermuda to the eastern Gulf of Mexico and upper level troughing
extending from eastern Canada into the upper MS Valley/Central Conus
to Southern Plains will transport moisture into the Appalachians and
OH Valley regions. Per 00Z LREF mean, PW is forecast to initially be
in the 1.5 north to 1.6 inch south range Sun evening, before
increasing to 1.3 north to 1.5 south around 0Z Monday, the 1.6 to
1.7 inch range on Monday, 1.7 to 1.8 inches Tuesday, and peaks in
the 1.7 to 1.9 range at mid week, before decreasing to the 1.5 to
1.7 inch range to end the period. Values in the 1.7 to 1.9 inch
range would be close to the 90th percentile for the timeframe for
the region. Any repeated rounds of convection or training across
over multiple days could eventually lead to hydro concerns. WPC EROs
for the Day 3 to Day 5 periods from Monday to Wednesday night
include some or all of eastern KY in a marginal risk. Day 4 from
Tuesday to Tuesday night appears to be the peak of the threat when
all of the the region is in a marginal risk of excessive
rainfall. Some concern of possible localized issues could linger
beyond that point particularly in the south where moisture is
forecast to remain deepest ahead of the approaching trough axis
and frontal zone settling into the OH Valley region.
With the trough in place, clouds should be quite prevalent
throughout the period, especially during each afternoon and evening.
This and anticipated convection from time to time will lead to highs
near if not as much as 5 degrees below normal for this time of year.
Normal highs outside of the highest terrain are generally in the mid
80s. With increasing moisture at the surface and through the column,
diurnal ranges will be a bit limited as well with lows anticipated
mainly in the mid to upper 60s.
&&
.AVIATION...(For the 12Z TAFS through 12Z Sunday morning)
ISSUED AT 805 AM EDT SAT JUL 20 2024
Any lingering valley fog will dissipate by no later than 13Z and
the TAF sites are not affected. Showers will affect some locations
with generally no reductions below the VFR range this morning,
with additional convection anticipated during the afternoon and
evening, with coverage peaking between roughly 17 and 23Z. All of
the TAF sites could be affected with KSYM having the lowest
chances. Low and mid level clouds may scatter out after 0Z and
this could give way to some fog formation or low clouds late in
the period, especially where heavier rain falls later today.
Confidence in timing and what areas may be affected is low. Winds
should generally be light and variable through out the period.
Any TAF site that experiences a thunderstorm could experience
breif periods of MVFR or even IFR conditions and a stronger wind
gusts.
&&
.JKL WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
UPDATE...JP
SHORT TERM...AR
LONG TERM...JP/Marcus
AVIATION...JP
Source:
JKL issues Area Forecast Discussion (AFD) at Jul 20, 8:06 AM EDT---------------
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