JKL issues Area Forecast Discussion (AFD) at Jan 30, 1:03 PM EST540
FXUS63 KJKL 301803
AFDJKL
AREA FORECAST DISCUSSION
National Weather Service Jackson KY
103 PM EST Thu Jan 30 2025
.KEY MESSAGES...
- Temperatures will average well above normal through early next
week.
- A cold front and an upper level low approaching the area will
bring a soaking rain for most places from late today into
Friday, with a few thunderstorms also possible.
&&
.UPDATE...
Issued at 1055 AM EST THU JAN 30 2025
Cloud shield is advancing northeast from the Cumberland/Tennessee
Valleys into the Kentucky River basin late this morning as the
well-advertised storm system approaches. The leading band of rain,
mainly light, is now approaching an imaginary line from
Knoxville, TN to Rockwood, TN to Bowling Green, KY. Latest hi-
res guidance suggests that this band of rain will move into the
Lake Cumberland area ~1230-130 PM EST and then intensify/expand
as it spreads northeast through the afternoon/evening hours.
Hourly forecast has been massaged to account for the latest
PoP/T/Td/Sky trends through this evening but was overall still in
good shape.
UPDATE Issued at 758 AM EST THU JAN 30 2025
Early morning temps and sky cover have been blended into the
forecast without substantive changes.
&&
.SHORT TERM...(Today through Friday)
Issued at 515 AM EST THU JAN 30 2025
A large closed upper low slowly moving out of the southwest CONUS
will be our main feature during the short term period. The low
will gradually open as it tracks from near the southeast corner of
Colorado early today to the vicinity of IN/OH by late Friday. It
will support a series of surface lows which will develop ahead of
the upper low along a frontal triple point and then recess
beneath the upper low. Large scale flow ahead of the low and its
cold front will draw large amounts of gulf moisture northward.
This will support soaking rain as it lifts over a warm front
which will approach us from the southwest today and tonight.
Exactly where the southern edge of this rain shield sets up is
still in question, with the NAM suggesting it will be slightly
further north than the GFS or ECMWF. In consideration of this,
have held back on the POP for the southern edge of the forecast
area today into tonight with only chance POP. Further north,
confidence is higher that rain will develop eastward into the
forecast area late today and this evening. The NAM shows elevated
instability developing as the system's cold or occluded front
approaches from the west late tonight and Friday morning, with a
low level jet bringing a surge of warm and moist air around 850mb.
In light of this, have included a slight chance of thunder. Won't
rule out a few hydro issues as the rain falls on ground still
fairly wet from snow melt and thawing, especially in the northern
portion of the forecast area.
The cold or occluded front (depending on whether the system's warm
front can make passage) will move east through the forecast area
on Friday, but initial temperature change will be minimal.
However, a dry slot will wrap around the low pressure system
simultaneously and bring us significant mid level drying from west
to east during the day, cutting off precip.
.LONG TERM...(Friday night through Wednesday)
Issued at 547 AM EST Thu Jan 30 2025
When the long term forecast period opens on Friday evening, the
upper atmospheric ingredients responsible for the early-day activity
will be positioned just to the west of the forecast area. The
formerly-closed upper low will have evolved into a positively-tilted
trough stretching from the southern Great Lakes down into the
Tennessee Valley. Forecast guidance has trended this trough's
eastward ejection a bit slower compared to this time yesterday,
which leads to a prolonged period of cyclonic vorticity advection
into the region. This will provide just enough atmospheric lift for
a second round of showers to develop late on Friday afternoon. The
increasingly-positive tilt of the parent trough will reduce the
amount of directional divergence aloft as the day progresses, and
the potent 850mb LLJ will be displaced on the other side of the
Appalachians by Friday evening. The loss of these two ingredients,
alongside diurnally-decreasing temperatures and instability, will
limit the intensity/coverage of this activity. Any showers that
occur on Friday night would add an additional few hundredths to the
early day event's precipitation totals. Since the time-lagged NBM
has struggled to resolve this second round of showers, slight chance
PoPs were manually added to Friday night's forecast grids. These
precipitation chances spread across the area from west to east
overnight, and then taper off by dawn on Saturday morning. A cooler
and drier airmass will have moved into Eastern Kentucky by then, and
forecast AM lows are accordingly in the upper 30s/lower 40s.
The rest of the long term forecast features zonal flow aloft,
meaning that the sensible weather specifics will largely be
determined by the placement of smaller-scale surface features. For
example, surface winds are expected to veer back towards the south
on Sunday and then the southwest on Monday. This will foster warm
air advection and some degree of moisture return into Eastern
Kentucky, and temperatures accordingly moderate. Saturday's highs in
the upper 40s/lower 50s will rise towards the 60s on Sunday and
Monday, with overnight ridge-valley temperature splits. A weak,
northern stream disturbance will pass through the flow aloft on
Monday night, but the lack of meaningful moisture return throughout
the column will likely limit its ability to produce significant
precipitation chances. A few showers cannot be entirely ruled out
before dawn on Tuesday morning across southeastern KY, but the
greatest effect from this system looks to be the slightly cooler
temperatures forecast on Tuesday afternoon (highs back in the 50s).
Model spread increases drastically beyond then. There are 15 to 20
degree differences between the 25th and 75th percentiles of the NBM
temperature guidance for each mid-week forecast period. The LREF
mirrors this heightened level of spread, and it appears that this
uncertainty is related to disagreements on the timing and track of a
late week storm system. The lack of well-defined upper level support
could yield a prolonged period of precipitation as said system
approaches, but it remains far too early to provide insight into any
potential hydrological impacts. For now, this system is reflected in
the grids as increasing rain chances throughout the day on
Wednesday, with the greatest chances just beyond the end of the
forecast period on Thursday.
&&
.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
ISSUED AT 103 PM EST THU JAN 30 2025
VFR conditions present at the start of the period will deteriorate
from the southwest this afternoon/evening as low clouds/rainfall
spread northeast. The rainfall is expected to be most persistent
north of the Hal Roger/KY-80 corridor through the night with
IFR to low VFR ceilings developing. Closer to the Tennessee/Kentucky
border, the outcome is more uncertain. However, even the most
southern locales should expect rain and MVFR conditions by dawn.
In addition to the rainfall, an incoming strong low-level jet will
cause LLWS to spread across all of eastern Kentucky tonight.
&&
.JKL WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
UPDATE...GEERTSON
SHORT TERM...HAL
LONG TERM...MARCUS
AVIATION...GEERTSON/HAL
Source:
JKL issues Area Forecast Discussion (AFD) at Jan 30, 1:03 PM EST---------------
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