JKL issues Area Forecast Discussion (AFD) at Nov 19, 3:33 PM EST144
FXUS63 KJKL 192033
AFDJKL
AREA FORECAST DISCUSSION
National Weather Service Jackson KY
333 PM EST Tue Nov 19 2024
.KEY MESSAGES...
- Colder temperatures arrive Wednesday night, and much of the area
will likely see precipitation change over to snow at times
Thursday through Friday.
- At this time, elevations above 2,000 feet are favored to receive
impactful snow accumulations, primarily Thursday night into
Friday morning.
&&
.SHORT TERM...(This evening through Wednesday night)
Issued at 332 PM EST TUE NOV 19 2024
Active weather pattern setting up across the country over the next
several days, as series of low pressure systems move through. The
overall large scale pattern will start off with a ridge of high
pressure situated just offshore of the southeastern part of the
country, with a large trough moving through the northern Atlantic
off the coast of southeast Canada. Meanwhile, another large trough
of low pressure will be in place over southern Canada, and will be
moving through the Great Lakes and into southern New England from
Wednesday onward. This system will bring repeated rounds of rain to
our area the next couple of days, as weak impulses rotate around it
aloft. High pressure will fill the void behind the aforementioned
low, and will bring a blast of much colder air into the region.
Further west, a powerful and explosively intensifying storm system
will be approaching the west coast, and will be moving onshore in
the Pacific Northwest Friday and Friday. That system will pack lots
of wind, rain, and mountains snows and is roars ashore.
The latest runs of the HRRR and NAMNEST models both have numerous
rain showers moving through eastern Kentucky through early this
evening, as a weak cold front, and an area of low pressure situated
on the south end of the front, move slowly through the Ohio and
Tennessee Valleys over the next several hours. Ongoing rain showers
should slowly taper off late this afternoon into early this evening,
before pausing briefly late tonight. By around dawn on Wednesday, a
secondary, and much stronger, cold front is forecast to move through
the region on Wednesday. This boundary will bring another round of
rain to the area on Wednesday. The highest rain chances tomorrow
should occur between roughly 16 and 22Z, as the cold front moves
quickly through the region. Temperatures will warm up quickly during
the first half of the day on Wednesday, ahead of the approaching
front, but will most likely begin to fall again late in the
afternoon/early evening time frame, as winds behind the front shift
to the west or west northwest, and begin bringing much cooler air
into the Ohio and Tennessee Valleys. Any rain ahead of the front
will steadily taper off late in the day on Wednesday, and should be
out of the area by around 0Z Thursday.
After seeing lows in the 50s on Wednesday morning, a large
temperature swing is on tap for Wednesday night, as a much colder
air mass filters behind a departing cold front. In fact, Wednesday
nights lows could fall into the mid 30s for most locations, or even
a bit colder than that depending on how quickly skies clear off late
Wednesday and Wednesday night. No weather hazards of note expected
in the short term.
.LONG TERM...(Wednesday night through Monday)
Issued at 548 AM EST TUE NOV 19 2024
The 19/00z model suite is in good agreement at the beginning of the
period. Multiple spokes of vorticity energy will be rotating
around a deep ~532 dam closed low over Wisconsin on Wednesday
evening. This system will be the dominant feature in our weather
into Saturday. Meanwhile, a 500H ridge axis is found upstream of
the low, initially extending from northwest Mexico to the along
the Alberta-Saskatchewan border. Another sub-520 dam low is
rotating over Pacific waters west of Vancouver Island/Olympic
Peninsula. At the surface, an occluding cold front sweeps out an
arc from a sub-1000 mb low over Lake Huron and/or Erie down along
the eastern slopes of the Central/Southern Appalachians to off the
Florida Gulf Coast.
00z Thursday -- 00z Sunday...
As the front occludes, a new triple point low develops near/over the
Delmarva Peninsula Wednesday night and rapidly deepens into a
sub-990 mb low as it lifts toward southern New England/southeast
New York. Once this more powerful low takes shape early Thursday
morning, the occluded low over the Great Lakes pinwheels to over
Lake Superior and then undergoes cyclolosis as it drifts to the
west side of its parent 500H low and into the Mid-Ohio Valley on
Thursday night. Prior to the surface low's arrival, a particularly
potent vorticity lobe will sweep across the Ohio Valley during the
day on Thursday bringing a surge of cold air advection across
eastern Kentucky during the day on Thursday. With 850mb temperatures
falling to near or below -6C, lapse rates will steepen while the
low and mid-levels become more saturated, though more due to the
cooling than moisture advection. Convective showers are likely to
develop in this environment. While temperatures at lower
elevations remain several degrees above freezing, dew points
falling into the 20s will support surface wet bulb temperatures
near freezing. Thus anticipate any stronger showers late Thursday
morning and afternoon, though initially mixed with rain in
valleys, will quickly switch to all snow/graupel due to wet-bulb
cooling processes. Any daytime accumulations should be primarily
confined to grassy/ elevated surfaces.
The more impactful period of precipitation comes Thursday night and
early Friday with deeper moisture from the remnant surface low
and a more northerly-oriented low-level fetch coming off of Lake
Michigan. The combination of weak isentropic upglide from the
remnant low into a moist dendritic growth zone as well as modest
orographic uplift on a west to west-northwest flow should set the
stage for snowflakes to fall area-wide. Locations east of I-75
are favored to be under the deeper moisture and thus have better
chances for seeing measurable snowfall. Very warm ground
temperatures and only marginally cold air temperatures at lower
elevations (below ~2,000 feet) should keep minor accumulations
largely confined to grassy/ elevated surface overnight. Conversely,
solidly sub-freezing air temperatures and orographically-enhanced
snowfall rates at those elevations around and above 2,000 feet
could overcome warm pavement temperatures, allowing for a sloppy,
slushy accumulation on untreated roadways. Due to uncertainty on
the persistence of the deeper moisture, there is still a
substantial range in the reasonable high/low end snow accumulation
totals over the higher elevations, ranging from less than an inch
in drier scenarios to as much as 4 or 5 inches in moister
scenarios. If the current forecast hold, headlines will likely be
needed for the higher elevations. Warmer air wrapping in from the
north around the upper low (situated to our east by that time)
will cause a gradually changeover back to all rain on Friday at
lower elevations. Precipitation then slowly tapers off from west
to east on Friday night and Saturday as the the upper level low
pulls away in the Canadian Maritimes. Any additional snow
accumulation from midday Friday onward will be minimal and
confined to the highest elevations of Pine and Black Mountains.
In sensible terms, blustery and wintry conditions are in store
to start the long-term. After the cold frontal passage on
Wednesday, a gusty westerly breeze will continue Wednesday night
while temperatures fall into the middle 30s in the lowlands and
lower 30s over the higher elevations. On Thursday, any morning
sunshine will fade to clouds. Blustery showers are expected to
increase through late morning and persist into the afternoon.
Snow will be favored precipitation form though some rain or
graupel cannot be ruled out in the valleys. Highs below 2,000 feet
will mainly be in the upper 30s to lower 40s but could drop
quickly to near freezing in any heavier precipitation. Winds could
gusts to 30 mph or better at times. After a lull early Thursday
evening, steadier snowfall is expected Thursday night into Friday
morning, especially east of I-75, though a few periods of light
snow are possible further west as well. At this point,
accumulations are forecast to range from a trace to around an
inch, primarily on grassy/elevated surfaces. At elevations above
2,000 feet, accumulations could reasonably range from 1 to 5
inches and lead to slippery travel on high-elevation roadways
such as US-119 and KY-160. Temperatures on Thursday night dip to
between 30 to 35F below 2,000 feet and into the mid to upper 20s
above. Snow changes back over to rain at lower elevations on
Friday before the precipitation slowly tapers off from west to
east through early Saturday morning. Forecast highs range in the
30s above 2,000 feet to the lower/middle 40s at lower elevations.
Skies begin to clear from the southwest on Friday night yielding
lows in the upper 20s to lower 30s over the Cumberland basin where
clouds thin up to the middle/upper 30s over the Big Sandy basin
where clouds and precipitation linger. Partly to mostly sunny
skies should gradually return on Saturday with highs in the
mid/upper 40s.
00z Sunday-Monday...
Surface high pressure becomes re-established over the Lower Ohio
Valley on Saturday night as pieces of energy from the aforementioned
Pacific low bombard and flatten upper level ridging aloft. By
Sunday night, a cold front will be settling toward the Ohio Valley
from the northwest while deep southwesterly flow advects in Gulf
moisture into the Commonwealth. Though timing is uncertain at this
juncture, this pattern will likely set the stage for one or more
rounds of soaking rain next week.
In sensible terms, partly cloudy skies and light winds on Saturday
night should set the stage for a hard freeze in the mid to upper
20s outside of thermal belts and away from lakes. Warmer temperatures
and increasing clouds return Sunday and Monday with highs in the
lower to mid 50s and mid 50s to lower 60s, respectively. Warm air
advection could lead to a relatively large ridge-valley split on
Sunday night, ranging in the 30s and 40s. Rain chances rise from
northwest to southeast on Monday.
&&
.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
ISSUED AT 107 PM EST TUE NOV 19 2024
VFR conditions prevailing across the forecast area at TAF
issuance, as we experience somewhat of a lull in what was
widespread rainfall earlier today. Based on the latest forecast
models, and upstream radar trends, it appears that rain showers
will begin filling in across eastern Kentucky between now and 20
21Z this afternoon. Once the rain begins again, we should see CIGs
lowering to MVFR or IFR levels at our airports. The next round of
rain, if the models are accurate, will last through around 1 or 2Z
this evening, before tapering off quickly overnight. The rain
should end by 8 or 9Z Wednesday. During the day on Thursday,
another incoming weather system is expected to bring rain and
continued low IFR CIGs to the area. These conditions should
steadily improve throughout the morning on Thursday, as a strong
cold front sweeps through the region. Cloud bases should raise to
1 to 2k by 15 or 16Z on Thursday. We will still see BKN to OVC
sky conditions as on Thursday as the front is moving through. As
for fog formation tonight, fairly widespread fog is expected
across the area, and could lead to IFR conditions for most
locations, with isolated instances of LIFR possible where more
rain fell today and temperatures stayed cooler than expected.
&&
.JKL WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SHORT TERM...AR
LONG TERM...GEERTSON
AVIATION...AR
Source:
JKL issues Area Forecast Discussion (AFD) at Nov 19, 3:33 PM EST---------------
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