Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 221857
AFDJKL

Area Forecast Discussion
National Weather Service Jackson KY
257 PM EDT MON AUG 22 2016

.UPDATE...
Issued at 200 PM EDT MON AUG 22 2016

Fantastic day out there for sure. Light northerly winds bringing
in some drier air combined with good mixing within the boundary
layer are producing dew points well into the 50s this afternoon,
leading to pleasantly low humidities. Afternoon highs still look
on track but would not be surprised to see a few locations wind
up a degree or so higher than advertised. No major updates to the
forecast package and only minor tweaks to the grids.

UPDATE Issued at 1112 AM EDT MON AUG 22 2016

Quick update is out for this morning to remove fog wording from
the zones and to bump grids towards the hourly trends. Otherwise
forecast is on track. No other updates ATTM.

UPDATE Issued at 744 AM EDT MON AUG 22 2016

Fog is starting to lift and dissipate in some locations,
although it remains the most widespread and dense in some of the
valleys generally south of the Mountain Parkway and along and east
of Interstate 75. The HWO highlighted this and an SPS was issued
to handle the dense fog in the valleys through 9 AM earlier this
morning and with the fog starting to lift and mix out this timing
still remains on target. Only minor adjustments have been made to
the hourly grids based on recent observations.

&&

.SHORT TERM...(Today through Tuesday)
Issued at 339 AM EDT MON AUG 22 2016

Early this morning, a mid level trough continues to depart to the
east of the area with mid level height rises as a mid level ridge
is building into the area. At the surface, high pressure is
building into the Great Lakes and Lower OH Valley Region from the
mid MS Valley. The height rises are expected to continue on
average into the day on Tuesday, before the axis of the ridge
approaches and begins to shift east of the area late in the
period. The surface high will continue building across the OH
Valley today with the center of the high settling across the Mid
Atlantic States by late tonight. The axis of this high should move
to the Eastern Seaboard by the end of the period.

Fog should persist through sunrise, dense in some of the valley
locations, particularly the deeper valleys, before lifting and
dissipating by 2 to 3 hours after sunrise today. The dense valley
fog this morning will remain the primary weather concern in the
short term as high pressure will remain dominant. The fog is
already highlighted in the HWO and a Graphical Nowcast and plan to
highlight in an SPS for the morning commute.

Otherwise, the relatively cooler and drier airmass will bring a
reprieve from the warm and humid weather that has prevailed for
much of this month. Highs today will average around 5 degrees
below normal and this combined with dewpoints in the mid to upper
50s will make it feel more like early September. Lows tonight
should fall into the mid to upper 50s, especially in the valleys
while some ridgetops may not fall below 60 as the surface high
remains dominant, but begins to shift east leading to the small to
moderate ridge/valley temperature split. This pattern will favor
fog formation again, but this should be confined to the
climatologically favored spots for fog such as the deeper and more
sheltered valleys near the larger creeks, streams and area rivers.

The airmass will begin to moderate on Tuesday as the surface high
moves east. 850 mb temps are expected to be about 3 degrees C
warmer than today so highs should return to closer to normal with
mid 80s for highs common outside of the high terrain. However, the
break from the heat and humidity that has been prevalent this
month will continue as afternoon dewpoints should be in the upper
50s to around 60.

.LONG TERM...(Wednesday through Monday)
Issued at 257 PM EDT MON AUG 22 2016

High pressure which has encompassed the Ohio River Valley during the
short term will finally start pushing east of the region by
Wednesday morning at 12Z. While still in control, this will allow
return southerly flow and warming moistening conditions across the
region. High temperatures will find themselves back into the mid 80s
with higher humidity values Wednesday afternoon. Meanwhile, a closed
low will be rotating through along the central Canadian/US border.
This will slowly lose strength and dissipate as strong upper level
ridging holds tight across the southeast conus through Thursday,
blocking further forward propagation. At the surface a low pressure
system will traverse along the path of this upper low, along the
central US/Canada border, pulling a cold front southeast across the
plain states. As the upper level low becomes blocked from eastward
movement and loses strength, the surface low will also lose forward
propagation and the cold front will start to shear out.

So what does this mean for eastern KY? With our location between the
incoming cold front, and the return flow of the exiting high
pressure system, the stage will be set for possible convection.
However, with upper level ridging still in predominate control, all
forcing will be limited to the low levels with little upper level
dynamics. Both the GFS and ECMWF bring some isolated pops into the
region Wednesday afternoon, and continued the isolated to scattered
convection through Thursday. However, the location and timing of
this is still somewhat very uncertain. The frontal zone finally
progresses southeast through the state late Thursday night and into
the day Friday. But even then, the lack of forcing, in addition to
two strong high pressure centers on either side of the frontal
boundary, will keep pops at a isl/sct minimal, with only light QPF
expected.

Temperatures will modify little during this period, with no strong
wind shifts in place. Expect mid and upper 80s with decent humidity
each day into the weekend. High pressure should take hold post
frontal Saturday and Sunday, however the GFS and ECMWF are showing
varying solutions, with the GFS still trying to allow for convection
across the region. Given the uncertainty this far out in the
forecast, will continue with the model blend for pops and QPF
during this time, which keeps the CWA relatively dry.

&&

.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
ISSUED AT 200 PM EDT MON AUG 22 2016

VFR conditions expected through the period. Exception will be
our deeper valley locations where late night, early morning fog
will develop again late tonight. With drier air settling down
across the region do not expect the fog to be as prevalent
tonight as it was this morning except possibly in the river
valleys. Consequently KSME VSBYS will likely be influenced for a
few hours through the pre-dawn hours Tuesday and as such went
with a short period of MVFR/IFR VSBYS, 09-12Z. Otherwise winds
will generally be light and variable.

&&

.JKL Watches/Warnings/Advisories...
None.
&&

$$

UPDATE...RAY
SHORT TERM...JP
LONG TERM...JMW
AVIATION...RAY



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