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Area forecast discussion
National Weather Service Jackson Kentucky
1241 am EST Fri Dec 6 2019

Update...
issued at 1241 am EST Friday Dec 6 2019

Clouds will increase quickly over the next 4 to 6 hours as evident
on satellite imagery of an expansive area of mid level clouds over
central and western Kentucky. Ceiling heights are generally around
120kft initially, but will gradually fall through dawn, before
some light rain becomes a possibility by 9 or 10 am. All in all,
forecast is in pretty good shape, so no update planned right now.

Update issued at 950 PM EST Thursday Dec 5 2019

The mostly clear skies and light winds are really allowing the
valleys to drop of this evening with many at or below forecast low
temperatures. These should be bottoming out as high clouds are
starting to move in - prompting rising temperatures toward dawn.
These rising temperatures are key to the early Friday morning
forecast keeping any light rain liquid and problem free. Should
the clouds stay thin until the rain showers arrive we could have a
potential for some icy patches on elevated surfaces, though. For
now will stick with a straight forward forecast of some sprinkles
and light rain starting around dawn. With this update have
adjusted the sky cover and added in those colder valley temps and
lower dewpoints. The freshened grids have been sent to the ndfd
and web servers along with the issuance of an updated set of
zones.

Update issued at 630 PM EST Thursday Dec 5 2019

23z sfc analysis shows high pressure briefly moving through the
area. This is keeping the skies clear and winds light, though
some high clouds are inbound from the northwest as low pressure
develops over the Central Plains. Currently, readings are showing
a solid 5 to 10 degree ridge to valley temperature split - varying
from the mid 40s on the ridgetops to the upper 30s in the
sheltered valleys. Dewpoints are more uniform across the area and
generally between the upper 20s and lower 30s. For this update,
have adjusted low temperatures for ridge to valley differences
for much of the night, but expect this to mix out toward dawn
under the increasing and lowering clouds and return of some light
pcpn. Did also add in the current obs and trends for the sky/T/TD
grids. These updated grids have been sent to the ndfd and web
servers.

&&

Short term...(this evening through Friday night)
issued at 344 PM EST Thursday Dec 5 2019

High pressure has led to a sunny day with temperatures peaking in
the low-mid 50s. Clouds will begin to roll into eastern Kentucky
this evening and overnight as the flow aloft backs more westerly
downstream of a shortwave trough, currently traversing onto the High
Plains. South to southwest surface winds on the backside of the
departing ridge will place eastern Kentucky in a warm air advection
regime. This combined with the increasing cloud cover looks to keep
temperatures above freezing overnight into Friday morning.

As this feature approaches and clouds lower overnight, rain chances
will increase near dawn and ramp up through Friday morning into the
afternoon. Given the quick-passing nature of this system and
associated deep layer moisture along with lack of instability,
rainfall amounts should top out below about two tenths of an inch.
Cooler air will then filter in Friday night into Saturday as the
rain comes to an end, with temperatures by Saturday morning
bottoming out in the upper 20s across northeastern Kentucky to mid-
upper 30s in southeast Kentucky.

Long term...(saturday through thursday)
issued at 349 PM EST Thursday Dec 5 2019

The long term period starts off Saturday with high pressure
shifting eastward across the Northern Ohio valley, encompassing the
state of Kentucky. With weak west-northwest flow still in place aloft also
keeping dry air across the region, and surface flow from the east-northeast
given our location on the south side of the high pressure system.
Highs will be similar to, if not a degree or so cooler than, the day
before...with highs in the upper 40s to low 50s. Flow aloft will
become more zonal by Saturday night, as surface winds become more
southerly on the back side of the high pressure system as it
continues eastward into New England. Southerly flow will intensify
on Sunday as a low pressure system develops across the Central
Plains during the day, and begins to shift eastward. Highs Sunday
will generally be in the mid 50s.

Precip will increase by late Sunday and through Sunday night ahead
of this approaching system. Widespread precip will make it into the
County Warning Area by Monday morning, continuing throughout the day as the area of
low pressure moves NE into the upper Ohio Valley and upper Great
Lakes regions, dragging a cold front eastward and towards the state.
Southerly flow will continue to intensify throughout the day at jkl
ahead of the front, boosting temps to around 60 degrees in some
locations despite the clouds and rain. The cold front is then
expected to pass over the jkl County Warning Area late Monday night and into Tuesday
morning, bringing the highest quantitative precipitation forecast during this time.

Models are in fairly good agreement with this system overall. The
main differences come in timing of the exit and the amount of quantitative precipitation forecast.
The GFS has higher quantitative precipitation forecast across the region Monday night, and a slower
progression of the cold front, with precip exiting from west to east
Tuesday evening. The European model (ecmwf) weakens the system as it moves over and
pulls it out much faster, with less quantitative precipitation forecast and all precip gone by early
afternoon Tuesday. Given the uncertainty and the fact that it is so
late in the period, generally kept with the nbm pops and quantitative precipitation forecast at this
time. There will also be a northwest flow component behind the system, so
would tend to think that precip may hold on a bit longer in the far
eastern portion of the County Warning Area.

Regardless of which model is correct, both show a much colder blast
of air moving into the region on steep northwest flow aloft behind the
departing system. While highs Tuesday will be in the upper 40s and
low 50s, highs Wednesday may not even make it out of the 30s. Monday
night lows will be in the low to mid 40s, but Tuesday night lows
will be about 20 degrees colder in most locations, in the low to mid
20s. Conditions will continue to cool to round out the extended
portion of the period as both the GFS and European model (ecmwf) have the center axis
of a deep longwave trough moving over during the day Wednesday,
continuing to strengthen as it does. With such a tight gradient aloft
for this system, and such a sharp temperature shift, also expecting
some decent winds to mix down to the surface throughout the duration
and even after this system departs.

&&

Aviation...(for the 06z tafs through 06z Friday night)
issued at 1241 am EST Friday Dec 6 2019

Clouds will be on the increase through the rest of the night, as
120kft ceilings overspread the region. The ceilings will very
slowly decrease through dawn, before some light rain becomes a
possibility by 14 or 15z. Conditions will likely stay VFR through
the day as the rain should not get too heavy to bring down
ceilings or visibilities. A front will drop south Friday night,
and that could lead to the development of some MVFR cigs as the
front presses southward. Winds will generally remain light out of
the south tonight, before going southwest during the day.

&&

Jkl watches/warnings/advisories...
none.
&&

$$

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