906
FXUS63 KJKL 282359 CCA
AFDJKL

AREA FORECAST DISCUSSION...CORRECTED
National Weather Service Jackson KY
759 PM EDT Sun Apr 28 2024

.KEY MESSAGES...

- Unseasonable warmth and dry weather prevails through Monday
  afternoon.

- Showers arrive Monday night through Tuesday, with a chance for
  thunder.

- More showers and storms are expected late this week.

&&

.UPDATE...
Issued at 647 PM EDT SUN APR 28 2024

Weak radar returns that were present earlier near Lake Cumberland
have diminished over the past hour or two. Some high base cumulus
and mid level clouds were present across the region with the
greater concentration over the western third of the area and west
into central KY. Accordingly, minor adjustments have been made to
the forecast with mainly just the inclusion of the latest obs and
trends for the T/Td/Sky grids with this update. These minor
adjustments have been sent to the NDFD and web servers.

&&

.SHORT TERM...(This evening through Monday night)
Issued at 400 PM EDT SUN APR 28 2024

19Z sfc analysis shows eastern Kentucky still between two strong
weather systems - a deep low over the Plains and somewhat weaker
high pressure area off to the southeast. This is maintaining a
flow of southerly air into the region - generally at 10 mph with
some gusts pushing 20 mph. Under mostly sunny skies, temperatures
soared from somewhat cool morning lows. Currently, readings are
fairly uniform in the lower 80s while dewpoints are generally in
the mid and upper 50s, for most places. There are a few sprinkles
in the far southwest parts of the CWA but those will be drying up
towards evening.

The models, and their individual ensemble suites, remain in fairly
good agreement aloft through the short term portion of the
forecast. They all depict Kentucky on the northwest fringe of a
large Southeast ridge through Monday afternoon while troughing
approaches from the west. This brings more impulses and
perturbations to the southwest mid-level flow over this part of
the state Monday night into Tuesday morning. At this point,
though, the models start to separate with the GFS cluster quicker
in moving a shortwave through eastern Tennessee compared to the
NAM and ECMWF ensembles. Even so, the model spread is small enough
to use the NBM as the starting point for the short term grids
along with the incorporation of the CAMs details for PoPs and
timing later Monday into Tuesday morning.

Sensible weather features warm and mostly dry daylight hours into
Monday evening as southerly winds continue to pump warm and
increasingly moist air into this part of the state ahead of an
approaching cold front. Skies will stay mostly clear tonight
allowing for one last night of good radiational cooling. As a
result, a decent ridge to valley temperature split has been added
to the temperature grids along with a touch of valley fog. The
front pushes its band of showers and thunderstorms into eastern
Kentucky towards evening. The best rain chances with this move
through the bulk of the area after midnight with a solid quarter
to an inch or so of rain expected as it passes - heaviest west and
driest in the far east. Temperatures with the rain chances Monday
night will be fairly uniform and mild.

The main adjustments to the NBM starting point were centered
around adding in terrain details to the hourly temperatures and
lows tonight. As for PoPs: the NBM values were adjusted to
include some CAMs details Monday evening through Tuesday morning.

.LONG TERM...(Tuesday through Sunday)
Issued at 410 PM EDT SUN APR 28 2024

The period is expected to begin with a shortwave trough moving across
the Lower Valley into the Southeast Conus, upper ridging north from
the Gulf of Mexico to MO, and a broad trough near the US/Canadian
border from the Northern Rockies west to the Pacific Northwest and
within it an upper level low centered over northern MT and another
upper low nearing the Pacific Northwest. At the surface, as the
period begins, an area of low pressure is expected to be centered
over Ontario near the northern end of Lake Superior with a cold
front extending south of the western to Central Great Lakes to near
the Lower OH Valley that is expected to be slowing down and stalling
with the western end becoming a warm front from the mid MS Valley
area northwest to a sfc low pressure system over the Dakotas. Sfc
high pressure should also be anchored off the southeast U.S. coast
at at that time. Locally, moisture is expected to be transported
into the OH Valley on return flow ahead of the passing shortwave
with 0Z LREF mean PW forecast in the 1 to 1.3 inch range across the
CWA.

Tuesday to Wednesday, the shortwave trough is expected to cross over
eastern KY during the Tuesday to Tuesday evening timeframe with
height rises/shortwave ridging building east into the MS Valley and
then into the eastern U.S. including the OH Valley behind it.
Further to the west, the first upper level low near the U.S./
Canadian border initially centered over MT should meander east and
northeast while the one nearing the Pacific Northwest as the period
begins becomes an open wave and works across portions of the western
Conus with the axis of the trough extending from MT to the Southwest
Conus by Wednesday evening. Meanwhile, at the surface, the boundary
that should be slowing down or stalling near or north of the OH
River should lift back north as a warm front downstream of low
pressure tracking from the Plains into Ontario. The trailing front
from that low should also tend to slow down or stall north of the OH
River late Tue night into Wed. Moisture and lift from the passing
shortwave should lead to showers across eastern KY form Tuesday into
Tuesday evening. Instability will be limited, but isolated to
scattered storm are possible, especially during peak heating on
Tuesday.

Wednesday night to Friday night, the upper low near the US/Canadian
border should meander further north or east through the period with
a rather large spread in the position and strength of the upper low
by late Friday night somewhere from Manitoba to Ontario. There is
also uncertainty in timing of individual waves moving from the
western Conus across the Plains and  into the eastern Conus during
this time. Despite the differences there is a general consensus of
a shortwave trough moving from the MS Valley and across the OH
Valley late Thu night through Friday night with an associated cold
front moving into and perhaps across eastern KY by late Friday night
or early on Saturday.

Saturday to Sunday, timing differences between individual shortwaves
lead to differences in tining of the passage of a cold front and
departure of deeper moisture. A lull in shower chances would occur
between this system and the next system approaching late in the
period if not beyond the end of the period. At this point stuck with
the NBM pops, though some recent guidance, including the 12Z
operational GFS and 12Z operational ECMWF suggests less shower
activity by late Saturday and into Sunday than currently forecast.

Clouds and convection will lead to high temperatures on Tuesday
returning to near normal, briefly, before warming to above normal
Wednesday to Saturday. At this time, the warmest day should be
Thursday when some of the deeper valleys, especially in the Big Sandy
region could reach 90 or near 90, with overall departures that
day near 15 degrees above normal.

&&

.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
ISSUED AT 705 PM EDT SUN APR 28 2024

Surface and upper level ridging will shift east through the
period and allow a disturbance to approach from the west. Overall,
no significant changes will be needed for the 0Z TAFs. High based
cumulus and some mid clouds lingered at issuance time in the west
though these should diminish overnight. Additional high based
cumulus and or mid level clouds should return during the last 12
hours of the period. Dry weather should prevail through at least
21Z before convection possibly encroaches on western and
northwestern locations late in the period, which could affect
KSME and KSYM. LLWS from the south at up to 40 KT was more
prevalent in the NBM guidance versus CONSSHORT was maintained for
continuity and could affect the western half to two thirds of the
area was maintained for a few hours between 03Z and 13Z including
all the TAF sites with the exception of KSJS. South winds at 10KT
or less, with some light and variable winds in valleys will
prevail through around 12Z, before winds become south to southwest
at 7 to 12KT areawide once daytime mixing commences.


&&

.JKL WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

UPDATE...JP
SHORT TERM...GREIF
LONG TERM...JP
AVIATION...JP