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afdjkl

Area forecast discussion...updated
National Weather Service Jackson Kentucky
705 am EST Mon Dec 16 2019

Update...
issued at 645 am EST Monday Dec 16 2019

Heavy rain and some thunderstorms ran up the Cumberland Valley
pre-dawn and necessitated an early update to the grids and a
couple of urban and small stream flood advisories, but now that
convection is settling down. Did also update the near term temps
and dewpoints with the latest obs/trends. These updates have been
sent to the ndfd and web servers.

&&

Short term...(today through tuesday)
issued at 440 am EST Monday Dec 16 2019

09z sfc analysis shows an elongated area of low pressure running
east along a frontal boundary that is lying over eastern Kentucky.
This boundary is an effective lifting and focusing mechanism for
heavy rains. Heavier showers are developing and moving along this
boundary currently - progressing through the Cumberland Valley
with occasional lightning. The Flood Watch kicks in at 7 am, but
we may need an urban and small stream flood advisory for portions
of this area before then - will continue to monitor. Currently
readings vary from around 34 degree in northwest parts of the area
north of the boundary while mid 50s are notes to the south of it
near the Tennessee border. Winds, likewise, vary on either side of
the boundary - north to northeast at 5 to 10 mph north of it and
from the southwest at 10 to 15 mph with higher gusts to the south.
Dewpoints, meanwhile, range from the mid 30s north to the low 50s
south across the area - all under cloudy skies along with some
fog patches around.

The models this morning are in better agreement aloft through the
short term portion of the forecast than 24 hours ago. They all
depict deep layer west southwest mid level flow through the
Southern Plains and into the central Appalachians. This fast flow
tilts more southwesterly in time as a broad trough sharpens up
during its travels from the southern rockies this morning and
into the mid Mississippi Valley. By the end of the period, a
northern stream trough will drop toward the eastern Great Lakes
and helping to refuel the energy of this trough and further lower
heights across the region through the day, Tuesday. Given the
smaller model spread this morning have more confidence in the nbm
as a starting point for the grids, though still favor the nam12
timing and placement of the key features for the forecast details
through Tuesday.

Sensible weather will feature very wet conditions through today
and tonight with times of thunder a good bet. The baroclinic zone
across the jkl County Warning Area will be a challenge for temperature forecasting
and the placement of the heavier rain bands. Nevertheless those
rain bands will waggle through the area into tonight with that
movement giving a larger portion of the area some of the better
rain totals, but this is preferable than the bands staying put
and really hammering one smaller area with hours upon hours of
heavy rains. The current Flood Watch has this covered and was re-
issued basically unchanged. The broad area of 2 to 3 inches will
affect all river basins and likely lead to flooding of the Stem
river points downstream of the headwaters later in the week -
primarily on the Kentucky and red, but the Cumberland is not out
of the Woods yet. Before that happens, though, the last surge of
moisture associated with a wave running along the boundary will
move past tonight allowing the winds to switch around through the
entirety of eastern Kentucky bringing drier and colder air into
the area. As a result, the significant pcpn will come to an end
early Tuesday with a mix and changeover to snow from west to east
for the lingering last bits of moisture on Tuesday.

Again did not deviate much from the temperatures, dewpoints, and
winds provided by the nbm - aside from deriving the maxt values
for Tuesday from the hourly T to better capture the nature of the
non-diurnal temperature trace. As for pops, mainly filled in the
higher pop gaps during the day and night given this stalled
boundary - lingering them a tad longer in the higher terrain
Tuesday afternoon for upslope influences. Did also go with mainly
wpc quantitative precipitation forecast for this event as it lined up best with the boundary.

Long term...(tuesday night through sunday)
issued at 315 am EST Monday Dec 16 2019

The majority of the extended should be dry, as a ridge of high
pressure settles over the region. The dry weather is expected to
last from Wednesday through Friday based on the latest model data.
We may see a few rain or snow showers across the southeastern
portion of the forecast area Saturday and Saturday night, as an area
of low pressure moves across the southeastern Continental U.S.. not all of the
models are in agreement on this, but with the latest blended data
and European model (ecmwf) model both bringing a bit of precip into our area, decided
to go ahead and keep some precip in for the weekend, albeit only low
chances. Temperatures should be below normal to start things off,
but will likely achieve above normal values Friday, Saturday, and
Sunday. Nightly lows will be in the 20s and 30s on average. The
coldest night should be Wednesday night, when lows may fall into the
upper teens to lower 20s across the area.

&&

Aviation...(for the 12z tafs through 12z Tuesday morning)
issued at 705 am EST Monday Dec 16 2019

A low level jet remains over the area making for some low level wind shear at
most sites (minus sym) for another hour or so before relaxing.
Periods of light to moderate rains have already commenced for most
of the area this morning and will continue through the remainder
of the taf period. These periods of rain, occasionally heavy, will
also lead to MVFR and IFR, perhaps lower, visible restrictions. The
winds will be mainly out of the south at 5 to 10 knots through
the period with occasional higher gusts now that the front has
started to lift back north.

&&

Jkl watches/warnings/advisories...
Flood Watch through Tuesday morning for kyz044-050>052-058>060-
068-069-079-080-083>088-104-106>120.

&&

$$

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