JKL issues Area Forecast Discussion (AFD) at Nov 29, 12:43 PM EST233
FXUS63 KJKL 291743
AFDJKL
AREA FORECAST DISCUSSION
National Weather Service Jackson KY
1243 PM EST Fri Nov 29 2024
.KEY MESSAGES...
- Isolated snow showers or flurries and or sprinkles will linger
today with high temperatures 15 to 20 degrees below normal.
- Temperatures will remain 15 to 20 degrees below normal this
weekend and into Tuesday, before temperatures moderate to 5 to
10 degrees below normal to end next week.
- A quick moving system will bring the chance for light snow
accumulations Saturday evening into Sunday.
&&
.UPDATE...
Issued at 1242 PM EST FRI NOV 29 2024
No major changes made to grids aside from updating grids based on
recent observations and trends. Also, updated morning text and
radio products to reflect the changes. Grids have been saved and
sent.
UPDATE Issued at 745 AM EST FRI NOV 29 2024
Hourly grids were freshened up based on recent observations and
trends. This led to no substantial changes at this point.
&&
.SHORT TERM...(Today through Saturday)
Issued at 520 AM EST FRI NOV 29 2024
Early this morning, an upper level low was centered near the
southern end of James Bay with a broad trough extending across the
Great Lakes into the eastern and portions of the central Conus
downstream of an upper level ridge in eastern portions of the
Pacific. This is leading to northwest flow aloft from BC and the
northwest Conus to the MS River Valley at this time with eastern
KY east of the axis of the mid level trough axis that extended
across Lake MI to the MS River Valley. Cold advection was
occurring on west to west southwest flow over the Lower OH Valley
while moisture lingered below the 800 mb level. Max lapse rates
in the 2 to 6km layer were between 6.5 and 7.5C across the
southeastern portion of the CWA a line of snow showers was working
southeast. Outside of this line of snow showers, some spotty
drizzle or flurries were occurring with saturation to about -10C
to
-12C or marginal for the presence of ice in the clouds outside of
the convection. Temperatures across the area ranged through the
30s with mid and upper 20s above 2500 feet near the VA border.
Today and tonight, the upper level low in Canada is expected to
meander south and southwest and also become enlongated from west
to east as shortwave trough working north into the Maritimes and
largely responsible for a sfc low moving near Atlantic Canada
merges with the upper low center to the west. At the same time,
the axis of the mid and upper level trough will work east across
the Commonwealth today and through this evening, passing east of
eastern KY overnight tonight. Northwest flow aloft will persist
from west of BC across BC and into the Northern and Central
Rockies and spread into OH Valley. Cold air advection will
continue across the Commonwealth with 850 mb temperatures
bottoming out in the -7C to -11C range this afternoon to early
evening, before 850 mb temperatures begin to moderate tonight.
The cold advection will lead to temperatures rising little today,
only into the mid to upper 30s for most or roughly 15 to 20
degrees below normal. Increasingly shallower moisture is progged
to linger near 850 mb while the low level flow will remain
upslope. Solar insolation and the cold advection should combine
for low clouds to linger for much of if not the entire day in the
north and east along with some flurries as temperatures cool aloft
if not some isolated snow showers. Moisture diminishes this
evening with sfc high pressure building in from the MS Valley
leading to increasingly anticyclonic low level flow. Clearing
skies and slackening winds will likely set the stage for stage for
the coldest night so far this fall for most locations.
Saturday, the next shortwave trough that will have moved around
the eastern Pacific ridging and rode the northwest flow from
western Canada across the northern Rockies to the Central Conus
will reach the mid MS Valley and approach the Lower OH Valley.
This will result in an increase in clouds along with clouds
thickening and lower as deeper moisture begins to return to the
Commonwealth. Enough saturation may occur in northern locations
near sunset for spotty light snow or flurries to being reaching
the ground, but Although the airmass will have moderate a bit, the
increase in cloud cover will result in highs just a couple of
degrees warmer than average compared to today. In the mid 30s to
around 40 degree range for most or in the 15 to 20 degree range
below normal once again.
.LONG TERM...(After midnight Saturday night through Thursday)
Issued at 605 AM EST Fri Nov 29 2024
The long term forecast period is defined by a rather amplified
pattern aloft, with mean troughing over much of the eastern CONUS.
Out west, a blocking pattern appears likely to emerge, which will
direct a series of shortwave disturbances out of Canada and into the
Ohio River Valley. With the antecedent troughing in place and
persistent westerly to northwesterly flow throughout the column,
temperature profiles could be cold enough to support winter
precipitation types at times. However, questions regarding the
amount of moisture in place linger, and any accumulations, whether
they be for rain or for snow, are likely to be light. Furthermore,
the available model guidance disagrees on the exact timing and
placement of these smaller scale features as time progresses
further, which limits confidence in the precipitation forecasts.
The first of these disturbances, however, is now within the range of
some of the higher-resolution forecast guidance. On Saturday night,
models agree that a quick-moving Alberta Clipper-type system will
approach the region from the northwest. Out ahead of it, modified
Pacific moisture will be advected into the Ohio River Valley, and
there is a growing model consensus towards a localized moisture
maxima along the I-64 corridor in Kentucky. With this moisture in
place, the best dynamic lift should arrive after dark, when
temperatures are expected to quickly drop below freezing. Together,
these overlapping ingredients are expected to be sufficient enough
for measurable snowfall, especially in the northern half of the
forecast area. The first snowflakes on Saturday night should fall in
the Bluegrass, and then snow chances will spread southeast across
the forecast area as the fast-moving parent clipper system
propagates east. By daybreak, the area most favorable for snow will
shift to our northeastern areas, and some flurries may linger across
the higher southeastern terrain given a shift to upslope winds on
Sunday afternoon.
Despite the favorable set-up, the progressive nature of the clipper
system should relegate accumulation to between half an inch to one
inch. The latest (00z) LREF probabilistic guidance for at least half
an inch of snow continues to trend upwards for locations north of
the Mountain Parkway and east of KY-15. The currently available high-
resolution model guidance for this system agrees with this thinking,
and thus confidence in accumulations is highest in these corridors.
Mesoscale trends related to frontogenesis, banding, and atmospheric
moisture content will need to be monitored closely as the time
approaches, as these could all locally enhance accumulations. The
most realistic high-end scenario at the moment would be up to 2
inches of snow along the I-64 corridor, with upwards of an inch
along and east of the KY-15 corridor. Given the marginal moisture
levels and clipper-origins, this scenario appears less likely for
now.
Regardless of snow totals, it is going to get cold in the wake of
this system. After lows in the upper 20s on Sunday morning and highs
in the mid to upper 30s on Sunday afternoon, these values drop to
lows in the teens and highs near freezing on Monday and again on
Tuesday. Interests are encouraged to dress warm for their morning
commutes on Monday and Tuesday, as the apparent temperature at 8am
on these days is likely to be below 20 degrees. In far northwestern
portions of the forecast area, such as Fleming County, it is
possible that these wind chills briefly dip into the single digits.
Thankfully, temperatures are expected to gradually warm back up by
mid-week. This will be most apparent in the afternoon high
temperatures, which may reach 50 degrees by Thursday. Low
temperatures will also increase, but will remain at or below
freezing most nights. This leads to diurnally changing precipitation
types in the forecast grids, but it is important to note that this
is an artifact of the aforementioned uncertainty in the timing of
the late week shortwave features.
&&
.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
ISSUED AT 1242 PM EST FRI NOV 29 2024
Terminals are slowly improving to VFR as KLOZ and KSME are
currently in VFR but the remaining terminals are just below the
MVFR/VFR threshold. Over the next couple of hours, the remaining
terminals will move into VFR and remain VFR through the remainder
of the TAF period. Increased westerly sustained winds around 8-10
knots and gusts to 15 knots have been noticed across a few of the
TAF sites and those will persist through much of the afternoon
before dissipating to light and variable overnight. Lingering
flurries will be possible through 20Z before dissipating but
flurries aren't expected to cause a reduction in visibility.
&&
.JKL WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
UPDATE...VORST
SHORT TERM...JP
LONG TERM...MARCUS
AVIATION...VORST
Source:
JKL issues Area Forecast Discussion (AFD) at Nov 29, 12:43 PM EST---------------
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