Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 261143 AAA
AFDJKL

AREA FORECAST DISCUSSION...UPDATED
National Weather Service Jackson KY
643 AM EST Sun Feb 26 2017

.UPDATE...
Issued at 635 AM EST SUN FEB 26 2017

Hourly grids have been freshened up based on recent observations
mainly for temperature and dewpoint trends. Areas in the Big
Sandy region that experienced persistent stratocu have finally
cleared out over the past couple of hours and temperatures there
have fallen into the middle 20s in valleys. Temperatures will
moderate today back toward normal levels as warm air advection
commences though dewpoints will remain on the low side and low
min rh is anticipated this afternoon.

&&

.SHORT TERM...(Today through Monday)
Issued at 410 AM EST SUN FEB 26 2017

As of early this morning, the region was under westerly flow
aloft within a broad trough extended from the Rockies east into
the eastern Conus. 500 mid level heights are not all that high,
but surface high pressure has built into the Lower OH and TN
Valley region south into the southeastern Conus. A mid and upper
level low was centered in the vicinity of the Hudson Bay Region
with a shortwave trough rotating around it that is currently
approaching the upper MS Valley and western Great Lakes regions.
Another shortwave is moving across the Central Plains while a
series of shortwaves are moving across the southern and central
Rockies with the main mid and upper level shortwave trough nearing
the southwestern Conus. The airmass in place across the region is
dry with dewpoints on the ridges generally in the teens though
some decoupled valleys have dewpoints in the 20s.

The surface high will begin to depart to the east today before
settling off the Mid Atlantic coast late tonight. Mid level
heights are also expected to increase today across the
southeastern Conus as ridging builds across the Caribbean. The
northernmost shortwave will rotate through the Great Lakes today
and then into Ontario and Quebec and St Lawrence Valley while the
one now over the Central Plains region merges with it. These
should bring an increase in cirrus to the area late today. Warm
advection will begin today and high temperatures should fall only
a couple of degrees below normals for late February.

Tonight, a couple of lead shortwaves eject toward the Oh Valley
while the main mid and upper level trough moves into the southern
Plains. Another shortwave trough will move across the Plains and
approach from the west. An area of low pressure should develop
over the Plains while return flow and isentropic lift should bring
increasing initially mainly mid and high level moisture to the
region tonight and into the day on Monday with the atmosphere
moistening up from the top down as a lingering result from the
ridging that will be departing. Valley locations should decouple
Winchell and with the dry air in place some locations in the far
east may fall to near 30 degrees before mid level clouds increase
and temperatures warm by the overnight hours. In addition, there
will be downslope flow in the southeast.

At this time, it appears the best chance precipitation late
tonight and early on Monday will be across the western and
northern fringes of the area as a shortwave moves passes through
the OH Valley. After this shortwave passes there may be a relative
lull in the precipitation chances with warm air advection and
isentropic precipitation beginning to increase mainly south of
the area late on Monday as warm front starts to lift toward the
area. Higher chances for more substantial precipitation will come
during the long term period.

.LONG TERM...(Monday night through Saturday)
Issued at 330 AM EST SUN FEB 26 2017

The period will be met with broad southwesterly flow with surface
high pressure parked off to the east. Meanwhile quasi-zonal flow
aloft with perturbations riding through the flow will keep the
period active Monday night into Tuesday night. There is some
instability Tuesday into Tuesday night that will lead to slight
chances of thunder. That said there will be a period of transition
Tuesday night that will lead to little to no POPs particularly in
the southeast. This period of transition will occur, as an upper
level wave moves into the central plains and low pressure deepens
across the Great Lakes.

A trailing cold front and height falls, as upper wave progresses
east will lead to best chances of POPs late Tuesday into
Wednesday. There are some timing differences, with GFS being the
faster solution and digs the trough a bit more than other
solutions. The ensemble mean seems to better align with slower
solutions seen in the long term guidance, and therefore think the
overall model blend POPs look good at this point. Given the
reasonable consistency did go ahead and keep the model blends CAT
POPs. We stand to get a good soaking rain, but still a bit
uncertain on exact axis of heavier precipitation. Right now total
amounts of 1 to 1.5 inches would be quite possible throughout the
region Tuesday night into Wednesday evening. The severe chances
look relatively low with SPC MARS and CIPS analog keeping better
chances to the west and southwest. This lines up better with the
SPC climatology as well. However given deep layer shear and at
least some meager instability some of these storms could be
strong.

Cold air mass will arrive Wednesday night into Thursday,
but this will primarily bring us back closer to normal values for
this time of year. These near to a little below normal
temperatures will remain through Friday. A clipper does drop into
the Ohio Valley Thursday night into Friday and perhaps a few
sprinkles/flurries or rain/snow showers pass across NE portions of
the CWA. Right now feel the better forcing will reside NE of the
CWA and therefore low confidence on any measurable precip in KY.
Canadian high pressure quickly pushes southeast late Friday into
Friday night leading to a decent night for ridge/valley splits.
Right now with some uncertainty will go 5 degrees, but the COOP
MOSGUIDE suggests possibility of a larger split. Temperatures are
set to warm some as high shifts east Saturday, but air mass will
still keep low to mid 50s in place. Given upper level ridging we
should also remain dry to round out the long term period.

&&

.AVIATION...(For the 12Z TAFS through 12Z Monday morning)
ISSUED AT 642 AM EST SUN FEB 26 2017

The center of sfc high pressure is nearing the region. All the
stratocu has cleared and light winds are occurring. Just some
high clouds are expected to pass by from time to time today
increasing during the 20Z to 0Z period as an upper level
disturbance passes. Overall, VFR is expected through the period,
though mid level clouds are expected to arrive and spread south
and east between 0Z and 6Z should move into the area by the end of
the period with moistening from the top down ahead of another
disturbance leading to a few low clouds and possibly a few stray
showers across the far west and northwest late. Winds will remain
light through the period.

&&

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

$$

UPDATE...JP
SHORT TERM...JP
LONG TERM...DJ
AVIATION...JP


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