Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 220329
AFDJKL

AREA FORECAST DISCUSSION
National Weather Service Jackson KY
1029 PM EST Fri Feb 21 2020

.UPDATE...
Issued at 1029 PM EST FRI FEB 21 2020

The grids are in good shape this evening and only had to make
some minor tweaks to blend in the latest obs and trends.

UPDATE Issued at 805 PM EST FRI FEB 21 2020

We see an area of surface high pressure cresting across the Lower
Ohio Valley and Tennessee Valley this evening. This will lead to
a cold night after such a dry day across eastern Kentucky. Still
prefer the COOPMOS for the deeper valley temperatures tonight and
perhaps a touch cooler in the Lake Cumberland region based on the
placement of the surface high. Overall thought the grids have this
handled well at this time and only made some minor tweaks for
this update.

&&

.SHORT TERM...(This evening through Saturday night)
Issued at 340 PM EST FRI FEB 21 2020

19z sfc analysis shows a large and strong area of high pressure
dominating the weather through Kentucky today. This has kept the
skies crystal clear along with the winds light. Thanks to plenty
of sunshine temperatures responded nicely into the mid to upper
30s most places. Very dry air also provided little hindrance to
the temperature climb with dewpoints down in the single digits to
around 10 above most places through mid afternoon. As a result,
relative humidities have fallen into the 20-30 percent range for
much of the area.

The models are in good agreement aloft through the short term
portion of the forecast. They all depict heights briefly
rebounding tonight in a wake of a trough dropping through the
southeast and moving away from Kentucky. This results in northwest
mid level flow across the area through Saturday night. While a
few shortwaves will pass overhead into Sunday morning - the lower
levels will be far too dry for anything more than some high clouds
to be activated by these waves. Given the small model spread and
limited wx effects through Sunday morning have favored the
blended models from the NBM - though significant attention was
paid to the lowest guidance for temps tonight and dewpoints each
afternoon.

Sensible weather will be quite quiet and calm through the period.
Good radiational cooling conditions in this dry air, light winds,
and clear skies will mean a large ridge to valley split both
nights. Fairly deep mixing into even drier air off the sfc will
mean dewpoints and RH values likely below the lowest of the model
guidance - similar to valley lows tonight and Saturday night with
the COOPMOS most favored. Only late in the period did any clouds
to start to arrive. Overall look for cold nights and pleasant low
RH days (and light winds) through the weekend.

Adjusted the NBM numbers most significantly for lows tonight and
Saturday night - opening up a large ridge to valley temperature
difference. Also, lowered the late morning and afternoon
dewpoints due to drier air mixing down from off the sfc.

.LONG TERM...(Sunday through Friday)
Issued at 231 PM EST FRI FEB 21 2020

The extended portion of the forecast begins on Sunday with an active
and progressive upper level pattern in place. The period begins on
Sunday with an a passing mid level ridge, retreating to the east, as
is the case with surface high pressure as it crosses the Appalachian
Range. Dry remaining in place will delay the onset of rainfall from
the next system. The NBM has not picked up on this as the Euro and
somewhat the GFS have. Thus will adjust a later arrival of precip to
more after 00Z Sunday night. Thus will expect stratiform precip
passing through the region late Sunday night into Monday. The
pattern does not support a large moisture surge into the OH Valley
from the Gulf of Mexico like the previous systems in the past few
weeks. This approaching system will weaken as it crosses the Mid MS
Valley and into the OH Valley Sunday night through Tuesday morning
giving a 36 hour rainfall total of 0.50 to 0.75 inches. At this
point, this is a very low impact rainfall amount. This is the case,
especially after a 3 to 4 day dry period from Thursday through
Sunday. Model soundings suggest low instability through the event
with the exception of more showery precipitation with and behind the
front as it passes Monday night into Tuesday morning. At this time,
moisture is expected to dry out and exit in the lower atmosphere
before the colder air moves in. This system lacks significant
baroclinicity anyway.

Expect a very breif break in precip from midday Tuesday into Tuesday
evening before the next wave moves into the region. The next trough
will drop southeast through the Plains and into the Midwest Tuesday
into Tuesday night. This push will bring some amplitude to the
pattern with a decent cold air push. This will bring another round
of light rainfall into Wednesday before the front passes through
Wednesday night. Northwest flow setting up behind this system with
slightly more moisture, an upslope component, and some instability
will make for a change over to a rain and snow mix and finally
changing over to all snow. Some light accumulation is not out of the
question Thursday morning at this time.

&&

.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
ISSUED AT 623 PM EST FRI FEB 21 2020

An area of strong surface high pressure will lead to a dry
weather and VFR TAFs for the period. This high pressure will also
keep the winds light and variable.

&&

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

$$

UPDATE...DJ
SHORT TERM...GREIF
LONG TERM...SHALLENBERGER
AVIATION...DJ


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