Area Forecast Discussion
Issued by NWS Jackson, KY

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594
FXUS63 KJKL 210839
AFDJKL

AREA FORECAST DISCUSSION
National Weather Service Jackson KY
439 AM EDT Tue Mar 21 2017

.SHORT TERM...(Today through Wednesday)
Issued at 435 AM EDT TUE MAR 21 2017

Convection near the cold front continues to move east southeast to
southeast from near Manchester southeast into southwest Virginia.
After a lull in lighting activity cloud top temps from GOES 16
test not yet operational imagery were near -51C with multiple
cloud to ground lighting strikes in the southeast Leslie, southern
Perry extreme western Letcher County and on into Harlan County
near Cumberland and Black Mountain. These will probably exit into
VA a bit earlier than the initial forecast grids per cloud top
temp and radar trends.

The cold front will continue to sag southeast before slowing down
or stalling out over the TN Valley. The boundary should reside
approximately near the I 40 corridor by midday. North of the
boundary, a considerable amount clouds are expected, but very
little if any convection is expected today. Convective allowing
models which did not handle overnight convection well, develop
convection near the vicinity of the confluence of the OH and TN
Rivers and then track it along the boundary generally south of the
area as a couple of surface waves of low pressure move along the
boundary. There is some uncertainty as to how far the boundary
will get before height falls associated with a shortwave trough to
move across the OH Valley region this evening. Also, recent GFS
and ECMWF have some weaker convection near the TN border during
the evening. Locations further to the north should only experience
an increase in clouds especially at mid and high levels as the
shortwave moves through. Showers and possibly a couple of
thunderstorms could affect parts of the Lake Cumberland region and
the TN border during the evening and some slight chance to chance
pops have been used during that time period in that area.

Otherwise as one of the surface waves of low pressure reach the
Carolinas and high pressure builds south from Ontario, the
boundary will sag further south of the area with cold air
advection in its wake anticipated along with a gradual decrease
in clouds from north to south. Temperatures generally along and
north of the I 64 corridor could fall to the freezing mark or just
below tonight with lows mainly ranging through the 30s elsewhere.
Locations along the TN border may not fall below 40 however. The
high will bring colder and drier air into the region overnight and
on Wednesday and below normal high temperatures are expected with
the far north probably not reaching 45 and the far south climbing
to about 55. This high and airmass will set the stage for a
rather cold late March night to start the long term period.

.LONG TERM...(Wednesday night through Monday)
Issued at 401 AM EDT TUE MAR 21 2017

Fairly meridional pattern setting up through the long term period
that will lead to multiple chances of precip. The period does
begin with high pressure east of the region along the Mid Atlantic
coast Wednesday night. There will be a period where decoupling and
radiational cooling can occur early on before some mid to high
clouds stream into the region. After this high pushes east as an
upper level ridge will build across the region. This ridging the
return flow around the surface high will put us securely in the
warm sector by Thursday. This will lead spring like temperatures
through most of the period.

Then we focus attention on vertically stacked system ejecting out
of the Front Range Friday and moving into the Ohio and Tennessee
Valleys Saturday into Sunday. There remains some timing
differences and therefore kept close to the blended guidance.
However did opt to cap POPs at likely given the timing uncertainty
at this point. Also in terms of storms it does look like we get
cutoff from better instability by convection along and near the
Gulf coast. This seems reasonable given this lines up well with
SPC severe probability climatology for this time of year. Overall
looks like QPE of around 0.75 inches is possible Saturday into
Sunday night. There could be a few showers Monday wrapping around
surface low, but ridging will build east ahead of next upper level
trough.

&&

.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
ISSUED AT 215 AM EDT TUE MAR 21 2017

A cold front continues to sag south tonight and ceilings are
expected to lower into the MVFR range behind it form north to
south, at least briefly, during the first 6 hours of the period.
Convection is also possible along or south of a JKL to SJS line
with thunder also possible. The MVFR may linger in the north
through around 18Z though surface heating and mixing should lead
to an improvement to VFR in the south during the 12Z to 18Z
period. As high pressure builds into the area after 18Z
improvement to VFR in all locations should occur by 22Z. VFR
should then prevail through the remainder of the period. Winds
will average 10KT or less through the period.

&&

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

$$

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



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