Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 171219

National Weather Service Jackson KY
819 AM EDT Sat Mar 17 2018

Issued at 800 AM EDT SAT MAR 17 2018

Forecast in pretty good shape this morning. Continuing to monitor
precip associated with a warm front across the region, which is
quickly dissipating as we head into the 8am hour. Adjusted pops to
better reflect the ongoing trends of less coverage, but forecast might
still be a bit high. Will continue to monitor and adjust as
needed. Regardless, any precip that does occur this morning will
be light and all thunder potential should be gone through this
afternoon. Also loaded in the latest observations to make sure the
near term forecast for temps, dew points, and winds was on track
with the current conditions. All grids have been published and
sent to NDFD/web.


.SHORT TERM...(Today through Sunday)
Issued at 530 AM EDT SAT MAR 17 2018

A warm front is currently pushing into the state, and will
continue to drift northward through around 12 to 15Z, making it as
far north as the Mountain Parkway. From 15Z, the warm front will
start to shift eastward, as a surface low pressure system begins
to traverse the state from the NW, riding along the southern
extent of the CWA through the afternoon, and exiting SE of the
state after 0Z tonight. Behind this system, winds will become
northerly as broad high pressure to our NW begins to take control.
This area of high pressure will continue to make its way into the
region through the day Sunday to round out the forecast period.

As for sensible weather... The warm front nosing into the region
will lead to an influx of warm and moist air, resulting in rain
chances (and possibly an isolated rumble of thunder) across
eastern Kentucky through this morning, with best chances exiting
east of the CWA between 13 and 15Z. Lingering chances will remain
across the northern half of the CWA through the first part of the
afternoon, however some drying may occur in the southern CWA due
to the dry slotting on the SW side of the approaching low pressure
system. This dry slotting will be key in the possibility of
afternoon convection, as any clearing in the skies could send
temps well into the 70s and effectively increase instability.
Forecasted temperatures were raised from the given model blends
for us and neighboring CWAs given the potential for localized
heating during any clearing that takes place. As the low pressure
system continues to progress southeast, and moisture starts to mix
back in with this warm air in the late afternoon, scattered
storms will begin to develop.

Based on the latest soundings, still looking at decent speed shear
throughout the day. However, the jet is actually well into the
mid levels, so expect any storms that develop to be fast movers,
tapping into these higher wind speeds. While higher wind gusts
could still translate to the surface, the best wind gusts will be
in the tallest storms able to tap into these higher winds.
Freezing levels, steep lapse rates, and dry air aloft also look
conducive to a hail threat. Forecasted storm total rainfall is
only between a quarter and a half of an inch, so not expecting
much of a flash flood threat. This is further deterred by the
fact that the storms will be so progressive, not allowing for any
long duration heavy rainfall in any one location.

The storm threat will quickly diminish between 0 and 3Z as the
low pressure system shifts SE of the area and northerly flow at
the surface creates a llvl inversion, preventing lift.

Meanwhile...for the northern portion of the CWA...the warm front
will never make it far enough northward during the day to allow
for the southerly flow and WAA to take hold and influence the
weather. As such, temperatures generally north of the Mountain
Parkway will only reach the low 40s to low 50s, which is not warm
enough to produce enough instability to instigate any storm
potential. Furthermore, the northern CWA will find itself on the
NE side of the passing low pressure system, which is more
conducive to colder NE flow and less storm threat. Left thunder
wording out of the northern CWA throughout the afternoon and
evening as a result, however rain will still occur.

Once the low pressure system exits to our SE this evening, wrap
around moisture will keep precip chances in place across the CWA
through much of the night, slowly tapering off from W to E by
Sunday morning. Llvl clouds will also remain in place through the
first part of the day on Sunday, clearing out by Sunday afternoon
as a drier airmass moves in overhead under the influence of high
pressure. Temperatures will be able to rebound back into the mid
and upper 50s for highs.

.LONG TERM...(Sunday night through Friday)
Issued at 426 AM EDT SAT MAR 17 2018

The long wave pattern looks to be fairly amplified as well as
progressive next week. The model agreement with regards to the
smaller scale features is pretty good early next week, but then
lowers through the rest of the period.

A southern stream system will be moving quickly east out of the
Four Corners region, reaching the mid-Atlantic by early Tuesday
morning. A developing warm front will bring a return of showers to
the area late Sunday night. Surface low pressure will be
developing and moving east into the Tennessee Valley Monday into
Monday night, bringing widespread showers to the area, with at
least a small threat of thunder.

Northwest flow will linger behind the departed low pressure on
Tuesday, with the northern stream lending energy, and carving out
a deeper trough across the eastern CONUS through mid-week.
Precipitation will linger across eastern Kentucky, with colder air
allowing for a snow threat, particularly across the higher
terrain by Tuesday night. There remains a bit too much
uncertainty at this point to play up any more specific impacts.

Drier conditions will work in by Wednesday evening, as ridging
moves in from the west. Dry weather will continue through early
Friday, before the next potential system moves in by late in the
day. Favored a slower arrival of the precipitation, given the
disagreement this far out. Near normal temperatures initially will
cool to well below normal by Wednesday, before gradually warming
once again towards the end of the work week.


.AVIATION...(For the 12Z TAFS through 12Z Sunday morning)

A warm front is currently impacting the southern 2/3 of eastern
Kentucky and will start to shift eastward over the next few hours
as a low pressure system enters the state from the NW. This low
pressure system will traverse the southern portion of the state
generally after 15Z today, exiting SE of the state by this
evening. In response to this system, abundant moisture flow into
the region will continue the llvl clouds across the TAF sites as
well as precip impacts (mainly this afternoon and into the
overnight). Locations south of the warm front (all TAF sites
except KSYM) can expect thunderstorm chances as well during the
afternoon and evening hours.

CIGS will remain in the MVFR range through the first half of the
day, though some temporary lowering to IFR will be possible,
especially for the northern most TAF sites. -SHRA and VCTS will
then return for the late afternoon and evening with CIGS lowering
to IFR generally after 0Z. Some thunderstorms could be strong to
severe, producing gusty winds and hail (mainly at KJKL and south).
Thunderstorm potential will be cut off after 0Z due to lowering
surface temperatures behind the departing low pressure system and
the resulting formation of a llvl inversion. Rain chances will
persist a while longer, but should start to diminish from west to
east throughout the overnight as the low pressure system exits to
the SE. Low IFR CIGS are expected to persist through the rest of
the TAF period. Winds will generally be light and variable under
10 knots sustained throughout the period, with the exception of
any storms that occur.




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