Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 270901
AFDJKL

AREA FORECAST DISCUSSION
National Weather Service Jackson KY
501 AM EDT Wed Mar 27 2024

.KEY MESSAGES...

- Temperatures cool to within a few degrees of normal through
  Thursday, with the threat for sub-freezing temperatures
  returning for many western valley locations Thursday morning and
  most valley areas Friday morning.

- PoPs start to creep back in from the northwest this weekend,
  with temperatures returning to well above normal.

&&

.SHORT TERM...(Today through Thursday)
Issued at 357 AM EDT WED MAR 27 2024

The latest upper level map features seasonably deep low pressure
spiraling over the northern Plains/Upper Midwest region within a
long wave trough aligned from south central Canada through
northern Mexico. At the surface, low pressure is seen near central
Ontario. A cold front arcs south through eastern Ohio and
Kentucky, with a secondary cold front/surface trough aligned from
eastern Indiana back through southern Illinois. Elongated high
pressure occupies the Plains states and into the middle and lower
Mississippi Valley. The cold front is making steady progress to
the east across our area, mainly initiating just some cloud cover
at this point. Enough clearing has occurred in the east overnight
to allow for valley decoupling, with colder sites still reporting
in the lower 40s, with upper 40s to lower 50s mainly occurring
elsewhere.

The models are in very good agreement aloft through the short term
period. The Upper Midwest low will swing into the western Great
Lakes and eventually across Ontario, reaching the southern
portion of Hudson Bay by late Thursday. The long wave trough will
gradually shift east with time, aligning from the eastern Great
Lakes through the central Appalachians, and then just off of the
coasts of South Carolina and Georgia by the end of the period. At
the surface, high pressure will gradually build across the Ohio
and Tennessee valleys. This will result in cooler and drier
weather across eastern Kentucky.

The cold front will exit early this morning, with cold air
advection and heating allowing for some reinforcing cloud cover
through the day. Temperatures will rebound to the mid 50s near the
Bluegrass, to the low to mid 60s in far eastern and southeastern
Kentucky. The surface high builds in more decisively tonight,
although some high clouds will be streaming overhead, mainly
affecting far southeastern Kentucky. Model guidance has trended a
bit cooler with the lows, with upper 20s looking like a good bet
for the colder valley sites west of I-75, with low to mid 30s at
most other locations. The cooler air mass that will be in place on
Thursday will temper the highs to the mid and upper 50s. Drier
air also looks to mix down during the late morning/afternoon
hours, with dew points likely dipping into the lower 20s, near or
below the 10th percentile of the blended guidance. The high clouds
will also gradually exit off to the east, as the trough moves
away aloft, allowing for a mostly sunny day.

.LONG TERM...(Thursday night through Tuesday)
Issued at 501 AM EDT WED MAR 27 2024

Pattern aloft transitions from northwest flow to zonal for the
bulk of the extended, then to southwest flow by the end of the
forecast window. Pretty good agreement with main synoptic
features, but solutions do become muddled during the last 36 to 48
hours of the period. Main features of interest center on a subtle
short wave tracking through zonal flow over the weekend and then
additional impulses that originate out of deep western CONUS
trough and west coast...California Baja low that suddenly sweeps
eastward across the CONUS at the end of the period. At the
surface, pattern become conducive to a baroclinic, or frontal zone
of sorts that develops across the Midwest before dropping
southeast to the Ohio River Valley. Strengthening winds fields
eventually become parallel with this frontal zone over time.
Trends develop this baroclinic zone further north, closer to the
Ohio River and this feature has a more stationary flavor to it
than previous runs. In addition, the overall evolution of the
storm system has become more progressive.

Sensible weather features a dry start to the extended. Fire
weather interests will note that deep mixing takes place within
the boundary layer Friday afternoon, forcing surface dew points
into the mid 20s and minimum afternoon relative humidities between
20-30% for portions of the area. Strong mixing will also support
an increase in boundary layer wind gusts to near 20 mph Friday
afternoon. Temperatures moderate through the weekend, with highs
climbing into the lower to mid 70s for the weekend, and upper 70s
by Monday. Rain cooled conditions and cloud cover in combination
with lower heights aloft will drop afternoon temperatures back
down into the 60s for Tuesday. A cold front appears to pass
through eastern Kentucky at or just beyond the end of the forecast
window. Trends have also slowed the onset of rain across the
forecast area, with better PoPs holding off until Saturday night
and/or Sunday, and greatest PoPs until Monday night into Tuesday.

Main hazards for the extended begin with the potential of sub
freezing temperatures for many of our valley locations, but
especially eastern valleys Thursday night into Friday morning.
Time height analysis and sounding profiles show some moisture
(6-10 kft) across the area during this time frame, which if
substantial enough would tend to help keep overnight lows up
despite high pressure being a bit more centered over the region.
Moisture at the top of the boundary layer does not provide ideal
radiative cooling conditions. However, ensemble probabilistic data
shows only a 10-20% chance of cloud cover being GTE to 50%, and
only slightly higher probabilities for GTE 25%. This suggests that
while moisture may be present, it probably is not substantial
enough to equate to cloud cover. Thus feel fairly confident in at
least going with the COOP MOS values, or upper 20s for some of the
coldest spots. Otherwise, instability in combination with
effective shear will increase with time, to between 750 and 1000
J/kg MUCAPES and 35-45 kts effective shear from Sunday through
Tuesday. Thunderstorm potential appears to be a good bet for that
time frame. Finally, our forecast area is within a favorable area
of moisture transport and convergence along and south of the axis
of the frontal zone Monday night into Tuesday. But convective
steering winds back more from the southwest during that same time
frame (less parallel with the baroclinic zone). This combined with
a more progressive speed to the system as it pushes through the
region decreases the overall threat of hydro issues.

&&

.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
ISSUED AT 202 AM EDT WED MAR 27 2024

Mainly VFR conditions are expected through the period. A passing
cold front will bring some ceilings ranging from 3-5k feet agl,
with model guidance generally showing a little less potential for
MVFR ceilings in recent runs. Clouds will scatter out behind the
front by dawn, but then reform during the day as we heat up. Some
scattered clouds ranging from 2-3k feet agl will be seen, but any
broken deck looks to stay in the low end of VFR category. Will
reevaluate this for the 12z TAF issuance. Once we lose heating
this evening, clouds will diminish. South to southwest winds of 5
to 8 kts will shift to the west northwest behind the cold front
which looks to clear the area through 09z or so. Winds will then
back more to the west during the day, increasing to 5 to 10 kts,
before lessening and veering to the northwest after dusk.

&&

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

$$

SHORT TERM...GEOGERIAN
LONG TERM...RAY
AVIATION...GEOGERIAN


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