JKL issues Area Forecast Discussion (AFD) at Oct 8, 4:54 PM EDT ...Much Below Normal Temperatures October 14 to October 18th...241
FXUS63 KJKL 082054
AFDJKL
AREA FORECAST DISCUSSION
National Weather Service Jackson KY
454 PM EDT Tue Oct 8 2024
.KEY MESSAGES...
- Cool and dry air is now in place across eastern Kentucky,
making for rain free and comfortable early autumn conditions for
much of this week.
- Patchy frost still looks possible Thursday night and early
Friday morning, primarily in the sheltered hollows away from
larger bodies of water.
- Patchy to widespread frost is likely Monday night and early
Tuesday morning; a freeze is possible in sheltered hollows away
from larger bodies of water
&&
.SHORT TERM...(This evening through Wednesday night)
Issued at 435 PM EDT TUE OCT 8 2024
Delightful early October weather continues across eastern Kentucky
this afternoon. Thermometers range from 68 to 74F at 4 PM EDT at
lower elevations and in the 60 to 68F range above 1,500 feet. The
surface analysis shows an ~1018 mb high pressure centered near
St. Louis though its influence extends wells to the south and east
across the Ohio and Tennessee valleys. Looking aloft, a broad
~535 dam low is slowly spinning over southwestern Quebec. Eastern
Kentucky remains under the southern periphery of this chilly upper
low's cyclonic flow. Meanwhile, a high-amplitude 500H ridge axis
extends from Arizona north northeastward to along the
northwestern shore of Hudson Bay. A raging Hurricane Milton spins
ferociously along the northern shore of the Yucatan Peninsula.
Models are in excellent agreement through the period, leading to
high forecaster confidence. Hurricane Milton and its fury stay
well to our south, pressing east northeast tonight/Wednesday and
making landfall on the Florida Peninsula most likely sometime
Wednesday evening/night. Meanwhile, the 500H ridge to our west
will trend more positively-tilted with time. At the same time, a
subtle vorticity lobe will develop in the cyclonic flow over the
western Great Lakes on Wednesday night and drop toward the Ohio
Valley. At the surface, high pressure will shift eastward into
the Ohio Valley and dominate our weather through Wednesday.
By late Wednesday, frontogenesis will commence over the Upper
Ohio Valley as a dry and chilly air mass seeps from Ontario/Quebec
into the Mid-Atlantic amidst weak northeasterly flow north of
Hurricane Milton. This new moisture-starved cold front will sink
southwestward down the Ohio Valley and across Kentucky late
Wednesday night.
In sensible terms, fair skies prevail through the period (except for
late night/early morning fog in the typically fog-prone river
valleys). Temperatures will drop off quickly this evening as winds
become light and variable with a 5 to 10 degree ridge-valley
temperature split is expected. Lows are forecast to range from the
mid 30s in the Bluegrass and northern sheltered hollows to the
upper 40s on thermal belt ridges. Wednesday's highs should be a
few degrees warmer than today, generally lower to middle 70s for
most places. Wednesday night will see a shift in winds to the
northeast overnight as the cold front pushes through. Weak mixing
should keep temperatures a tad wormer, generally in the 40s for
most locations.
.LONG TERM...(Thursday through Tuesday)
Issued at 435 PM EDT TUE OCT 8 2024
The 08/12z model suite analysis beginning Thursday morning shows
an ~540 dam low centered near/over the Gaspe Peninsula. Along the
southern periphery of this low, a subtle vorticity lobe, associated
with a surface cold front over the Ohio Valley, extends from the
Upper Midwest to Mid-Atlantic. Well to our south, the historic
Hurricane Milton is expected to be crossing the Florida Peninsula.
Meanwhile, positively-tilted ridging is found to our west from
the Desert Southwest northeastward to over the Hudson Bay. Broad
troughing is found further upstream from Western Canada to over
Alaska and the North Pacific.
Forecaster confidence has increased for the entire long-term period
as models have come into much better agreement, especially from
Sunday night onward. At the beginning of the period, Hurricane
Milton departs off the Florida Peninsula and into the Western
Atlantic on Thursday. Meanwhile, the cold front sinks into the
Tennessee Valley and allows Canadian surface high pressure to
build southward into the Central Appalachians. While the incoming
air mass won't be all that different temperature-wise at 850 mb
(~10C) than our current air mass, it will be drier and thus
favorable for more effective radiation and cooler nighttime
temperatures on Thursday night. Ridging aloft and at the surface
then breaks down this weekend as broad troughing amplifies and
dives toward the Ohio Valley. West to southwest low-level return
flow develops Friday night and Saturday ahead of the trough,
boosting 850 mb temperatures across eastern Kentucky back to
around 15C by Sunday. This milder air mass will be fleeting
however, as the incoming trough drops a sharp moisture-starved
surface cold front through the Commonwealth Sunday evening and/or
Sunday night. Some of the guidance suggests a dry secondary front
dropping trough eastern Kentucky on Monday. In either case, high
pressure then sinks south from northern Canada in the wake of the
cold front(s) and ushers in a much cooler air mass. By 6z
Tuesday, the GEPS/EPS/GEFS ensemble mean 850 temperature is 0 to
2C from north-to-south over our area and there is only 5 to 6C of
spread between the 10th and 90th percentile of the ensemble
members, indicating high confidence for a colder than normal air
mass. The multi-faceted combination of this chilly and dry air
mass of polar origin, post-frontal dew points falling to near or
below 32F, waning soil moisture and streamflows due to little
recent rainfall, and light winds will likely set the stage for
frost and/or freeze conditions on Monday night. Model spread in
the 850 mb temperatures begins to increase on Tuesday as the air
mass begins to moderate, yet mean 850 mb temperatures remain close
to 1C, which, if realized, would still favor another frosty to
freezing Tuesday night for many.
In sensible terms, look for fair skies and cool dry weather to
persist through Friday night. Temperatures peak mainly in the upper
60s to lower 70s on Thursday and lower to mid 70s on Friday.
Meanwhile temperatures are forecast to bottom out in the mid 30s
to lower 40s on Thursday night. The coldest temperatures are
expected in the sheltered northern hollows where there could be a
touch of frost. A quick warming trend then takes hold for the
upcoming weekend as high temperatures rebound into the mid 70s on
Saturday and upper 70s to around 80 for Sunday under abundant
sunshine. Overnight lows moderate from the upper 30s to near 50
on Friday night into the upper 40s to mid 50s for Saturday night.
There is a low end rain chance (less than 20%) on Sunday night
with the passage of a cold front, though there is a good chance
that this boundary could pass with no rain at all. Temperatures
tumble behind that front, struggling to reach 60F on Monday and
remaining in the 50s for most locations on Tuesday. Monday night's
lows are forecast to range in the 30s with patchy to widespread
frost likely.
&&
.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
ISSUED AT 135 PM EDT TUE OCT 8 2024
VFR conditions will hold through the period. There will be some
development of valley fog tonight, but it should not have any
impact on our TAF sites. Winds will be generally light and
variable, around 5 kts or less, except with a north-northwest
tendency during peak daytime heating.
&&
.CLIMATE...
Issued at 454 PM EDT TUE OCT 8 2024
...Much Below Normal Temperatures October 14 to October 18th...
Confidence is increasing for the coldest air mass of the autumn
season thus far to envelop eastern Kentucky next week. Normal
highs for October 15th range from 67F on northern foothills
(Gimlet) to 71F near Lake Cumberland (Somerset). Normal lows for
the same day range from 40F in the sheltered northern hollows
(West Liberty) to 49F on thermal belt ridgetops (NWS Jackson).
Forecast temperatures by next Tuesday are expected to be running
8 to 14 degrees below normal and could remain at similar levels
for several days. The average first 32F or colder autumn
temperature reading is around October 15th in the coolest hollows
and November 1st on thermal belt ridgetops.
&&
.JKL WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SHORT TERM...GEERTSON
LONG TERM...GEERTSON
AVIATION...GEERTSON/GREIF
CLIMATE...GEERTSON
Source:
JKL issues Area Forecast Discussion (AFD) at Oct 8, 4:54 PM EDT ...Much Below Normal Temperatures October 14 to October 18th...---------------
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