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Area forecast discussion 
National Weather Service Jackson Kentucky
722 PM EDT Wednesday Aug 20 2014

Update...
issued at 722 PM EDT Wednesday Aug 20 2014

Quick update to bring grids into line with hourly trends. Thunderstorms
have produced severe weather across the area this evening and there
have been reports of some flash flooding as well. Activity should
begin to wind down over the next couple of hours as the atmosphere
begins to stabilize. The severe line is pushing south of our area
now...thus discussions are under way to cancel the Severe
Thunderstorm Watch across our area by top of the hour.

&&

Short term...(this evening through Thursday night)
issued at 452 PM EDT Wednesday Aug 20 2014

A challenging forecast. Tail end of frontal zone...boundary evident
across the middle west is shifting eastward late this afternoon. This
feature will play a major role in our weather over the next several
days. Building ridge of high pressure aloft and to our west will
continue to force this boundary to the east over the next 18 to 24
hours. This boundary will become increasingly aligned with middle and
upper level flow patterns and become stationary across the middle Ohio
Valley region. Thereafter it serves as a focus for convection and the
occasional convective complex of storms. At this time it appears at least
part of our area will feel the effects of weak impulses of energy
riding over and dropping down along the east side of the ridge axis.

Short term high resolution models have not been much help and have
been slow to catch up with reality. GFS has performed decently
through the first 6 to 8 hours though and leaned towards its solution
for the short term portion of the forecast. Activity associated with
upstream storm complex weakened as expected. But convection has
refired along and ahead of the cold pool in very unstable air mass.
Ramped probability of precipitation up for the late afternoon and early evening time frame
for convection entering from the west and activity that has developed
across the south out ahead of the main line. Several of these storms
have been producing severe weather. Consequently a Severe
Thunderstorm Watch has been issued for areas generally along and west
of the Daniel Boone National Forest until 11 PM. With the surface
boundary shifting to the east across our area...left at least a
chance pop in place for the overnight period. Boundary should be just
to our east by tomorrow...so left highest probability of precipitation in our east...lower to
our west. Also thursdays temperature gradient should be significant from
west to east across the area due to precipitation cooled air and increased
cloudiness in the east.

Long term...(friday through wednesday)
issued at 452 PM EDT Wednesday Aug 20 2014

Stout upper level ridge will build over the region during the
period. A bit of uncertainty has been introduced...especially with
temperatures... as models indicate the core of the upper ridge will be just
to our west now with the thermal ridge remaining to our west as
well. So... temperatures were reduced a bit...but it is still going
to be warm and very muggy with dew points in the 70s through most of
the period. This juicy air mass along with a weak front in the area
through the period will result in thunderstorm chances each period.
The best chances (40 to 50 percent range) will be on Friday and
Saturday as northwest flow will be in place aloft putting US in the
prime location for mesoscale convective system activity in addition to the normal diurnal
based activity. The upper ridge will then build north so probability of precipitation will
decrease a bit into early next week.

&&

Aviation...(for the 18z tafs through 18z Thursday afternoon)
issued at 215 PM EDT Wednesday Aug 20 2014

Very juicy air in the boundary layer is responsible for low SC field
in place across the area. Ceilings have generally been within the MVFR
thresholds. With mixing and increased heating...cloud base of cumulus/SC
field should rise just a bit through the afternoon. Otherwise
confidence is low on exactly how upstream storm complex over Illinois/in
will affect our area. Model guidance suggest the system will fall
apart before activity redevelops later tonight along a surface
frontal boundary that will transit our area. Followed this train of
thought pretty closely for the forecast. In addition...guidance is
hitting fog across the area pretty hard tonight. But with extensive
cloud cover moving back into the area tendency was to go more
optimistic. Very weak upper level disturbance will approach between
06 and 12z...and be the catalyst for the aforementioned renewed
convective threat. Thereafter...the surface frontal boundary will
become stationary to our east and become the focus of additional
showers and thunderstorms over the next several days. Winds will be
light and generally from the west southwest through the forecast
period.



&&

Jkl watches/warnings/advisories...none.

&&

$$

Update...ray
short term...ray
long term...Abe
aviation...geogerian/ray

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