JKL issues Area Forecast Discussion (AFD) at Jul 22, 10:40 AM EDT339
FXUS63 KJKL 221440
AFDJKL
AREA FORECAST DISCUSSION
National Weather Service Jackson KY
1040 AM EDT Mon Jul 22 2024
.KEY MESSAGES...
- Showers and thunderstorms will impact the region at times this
week. Probabilities will generally peak each afternoon and
evening.
- Any areas that receive successive rounds of heavy rainfall
could experience instances of localized flooding.
- Highs will be near normal (mid 80s) to about 5 degrees below
normal throughout the period, with humidity running high.
&&
.UPDATE...
Issued at 1040 AM EDT MON JUL 22 2024
Convection from earlier this morning has largely lifted north of
the Commonwealth at this time. Additional spotty light shower
activity is noted on radar across Central Kentucky and may impact
locations adjacent to the Bluegrass later this morning and early
afternoon. Some additional spotty light shower has been bubbling
up near and east of US-23. Satellite imagery shows the best
clearing and heating now underway along and southwest of KY-421.
Expect renewed convection initiation to occur in this area of
partial clearing, especially near the Tennessee border, as we
achieve convective temperatures, which are around 80 degrees. Once
this activity develops and spreads, anticipate cell motions will
generally track northeast at 20 to 25 knots. Forecast was updated
to remove mention of fog and fine-tune PoPs using the latest CAM
output.
UPDATE Issued at 755 AM EDT MON JUL 22 2024
Convection continues to work across the OH Valley region
associated with a shortwave trough/MCV. As this feature passes
this morning, a bit of a lull in convection may occur from mid to
late morning, before daytime heating leads to another potential
peak in coverage this afternoon to early this evening. Any areas
that experience successive rounds of heavy rainfall could
experience instances of localized flooding and this remains the
primary concern. This potential would be greatest in the areas
generally experienced the heaviest rainfall Sunday and Sunday
night.
&&
.SHORT TERM...(Today through Tuesday)
Issued at 550 AM EDT MON JUL 22 2024
Early this morning, an upper level ridge was centered over the
western Atlantic near Bermuda and extended into the Gulf of
Mexico. Meanwhile another upper level ridge was centered over the
southeast Conus and extended to the Northern Rockies to western
Canada. In between, the axis of troughing extended from eastern
Canada across the Great Lakes region to the Southern Rockies
vicinity. At the surface, a quasi stationary frontal zone extended
from the mid Atlantic states into the OH valley and across the JKL
CWA before turning southwest to the middle TN vicinity and then
to the Southern Plains. Multiple disturbances were working through
the trough with one currently traversing the Lower OH Valley.
This shortwave was interacting with the boundary and a moist
airmass in place with PW in the 1.6 to 1.85 inch range across the
region to produce overnight convection across the Commonwealth.
Some of the activity had been less progressive with some mergers
of cells and led to locally heavy rainfall southwest and west of
JKL in particular.
Monday to Monday night, the upper level pattern is expected to
change little with southwest flow keeping PW generally in the 1.6
to 1.8 inch range. The initial shortwave trough is expected to
cross eastern KY this morning, while another impulse possibly
affecting the area during the afternoon to early this evening.
The surface front is expected to meander only slightly north
toward the OH River from today into tonight. After a peak in
coverage of convection through a couple of hours after sunrise,
the next possible impulse and daytime heating should lead to
another peak in shower and thunderstorm chances during the
afternoon to early this evening. Mid level height rises in between
shortwaves and the loss of daytime heating are expected to lead to
a lull in chances tonight.
Tuesday, the next shortwave working through the upper level
trough, should work across eastern KY. This shortwave, a moist
airmass lingering with PW averaging at least near the 1.75 inch
mark and daytime heating should result in chances for convection
peaking through the afternoon and evening.
Over the past couple of days, locally heavy rain amounts have
generally fallen near and generally to the south of the Mountain
Parkway. The main concern with convection in the near term will be
locally heavy rain. As repetitive rounds of convection cross the
area, some locations will become primed for any potential later
rounds of showers to possibly produce excessive rainfall leading
to instances of flooding. WPC has placed portions of the region,
generally along and in particular south of the Mountain Parkway in
a marginal risk for excessive rainfall today and Tuesday. This
potential continues to be highlighted in the HWO and the key
messages of the HWO.
As for temperatures, they will remain near if not a couple of
degrees below normal in the mid 80s with lows not far from normal
as well in the mid to upper 60s on average.
.LONG TERM...(Tuesday night through Sunday)
Issued at 516 AM EDT MON JUL 22 2024
At the start of the long term forecast period, model guidance
generally agrees that Eastern Kentucky will be situated in between a
fairly strong 500mb ridge over the SE CONUS and a positively-tilted
upper level trough stretching from the Ozarks up into the Great
Lakes. A series of shortwave disturbances will eject up the
downstream side of the aforementioned trough axis and into the
forecast area while the longwave pattern remains stagnant for a few
days. While confidence in the exact timing of these impulses is not
particularly high at this temporal range, their presence in the area
will enhance daily shower/storm chances, as will the convective
effects of diurnal heating. The greatest PoPs thus exist in the
afternoon and evening hours, although the potential for showers and
storms to continue into the overnight hours is noted amidst
uncertainty in the timing of these shortwaves. In addition to this,
the perpetual southwesterly flow around these upper level features
will advect plenty of moisture into the atmospheric column for
widespread cloud coverage. As such, the first half of the long term
forecast is similar to the short term forecast, with daily rain
chances and extensive cloud coverage across much of the JKL CWA.
The primary impacts of this disturbed weather will fall on the
hydrological side. Forecast soundings continue to demonstrate the
potential for efficient rainfall processes, and ensemble guidance
suggests mean PWAT values around 1.75 inches. While these are not
necessarily alarmingly high values, the repetitive nature of this
week's rain chances and the presence of antecedent heavy rainfall in
our southern counties suggests that a conditional flash flooding
risk might materialize. This notion is reflected in the most recent
WPC Excessive Rainfall Outlooks, where our SE counties continue to
be highlighted in a Marginal Risk through Friday. The risk of flash
flooding appears to be lesser in the northern portions of the
forecast area, although trends in the rainfall that falls in the
earlier periods of the forecast will be monitored closely. On a more
positive note, the thick cloud coverage during this portion of the
forecast will work to relegate temperatures to below to normal seasonal
averages, with highs in the low/mid 80s and lows in the mid/upper
60s.
By Friday, a pattern shift begins to emerge in the guidance package,
and dry air slowly begins to seep into the area from north to
south amidst the passage of a surface front. As a high pressure
system begins to build into the Ohio River Valley this weekend,
northern portions of the CWA will see a clearing trend in the sky.
Clouds and precipitation chances will linger around the south for
a little bit longer as daytime heating and the presence of a now-
diffuse frontal boundary enhance both. The signal for widespread
disturbed weather, however, is not nearly as strong this weekend
as it was earlier this week. While some forecast guidance develops
an upper level low pressure system and tracks it into the Ohio
River Valley by Sunday, others present an alternative solution in
which ridging builds in and reinforces drier conditions.
Confidence in the end of the long term forecast is low at this
time, but trended towards the drier solution at this moment in
time. Regardless, the forecast drying trend on Friday should
correspond with a widening diurnal range of temperatures this
weekend, with afternoon highs in the upper 80s and overnight lows
in the low 60s forecast at this time.
&&
.AVIATION...(For the 12Z TAFS through 12Z Tuesday morning)
ISSUED AT 810 AM EDT MON JUL 22 2024
At the start of the TAF period, KLOZ and KSME were reporting VFR
while reductions due to convection further east and northeast were
into the MVFR and IFR range for most. However, locally lower
reductions were reported as well at locations such as KJKL.
As a disturbance crosses the area this morning, an improvement in
conditions should spread from southwest to east and northeast in
its wake, with an anticipated lull in chances for convection. A
secondary peak in coverage should occur in the 17Z to 23Z
timeframe, with reductions into the MVFR if not briefly IFR
possible with this along with brief wind gusts to around 20KT or
so. Outside of convection, winds are forecast to be light and
variable. Although convection cannot be ruled out during the last
12 hours of the period, a lull is expected and some clearing or
partial clearing of low and mid clouds. Following recent and
expected rainfall later today, fog formation at least in valleys
and perhaps also affecting much of the region with reductions into
the MVFR and or IFR category could develop as early as 04Z and
06Z.
&&
.JKL WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
UPDATE...GEERTSON
SHORT TERM...JP
LONG TERM...MARCUS/JP
AVIATION...JP
Source:
JKL issues Area Forecast Discussion (AFD) at Jul 22, 10:40 AM EDT---------------
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