Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion...updated 
National Weather Service Jackson Kentucky
1100 am EDT Sat may 30 2015

Update...
issued at 1100 am EDT Sat may 30 2015

14z surface analysis shows high pressure to the east still holding
some influence over far eastern Kentucky while an area of low
pressure is moving into the middle Mississippi Valley. The pressure
gradient between these features is resulting in a continued flow
of warm and moist air into eastern Kentucky. Specifically...
readings are now in the middle to upper 70s through the area while
dewpoints hold in the middle 60s for most places along with south
winds at 5 to 10 kts. A bit more in the way of low and middle level
clouds overnight helped to limit the fog development this morning
and now all that is gone...while partly cloudy conditions remain.
A rogue area of showers moved north through the Cumberland Valley
earlier in the morning...though these have now dissipated. Based
on the latest hrrr and incoming nam12...along with diurnal
climatology... expect scattered convection to redevelop over the
area shortly afternoon. The better coverage should be concentrated
over our western counties late in the day closer to the surface low
and is slowly approaching front. However...the hrrr is more
insistent that convection is equally possible further east and
given this environment...of increasing instability and no
capping...will not rule it out. Accordingly...have brought high
chance probability of precipitation a bit further east with this update. Any storms that
develop could become strong with enough wind shear aloft to
suggest a potential for stronger wind gusts than we saw yesterday.
The entire area remains in a marginal risk for just that from Storm Prediction Center
while a slight risk outlook is found just to our northwest. Any
late day storm will need to be monitored closely for severe
potential. The updated grids...including adjustments to the T/dew point
grids per the latest shortblend guidance...obs...and trends...
have been sent to the ndfd and web servers. In addition...a
touched up set of zones...mainly removing the morning fog
wording...has been sent.

Update issued at 739 am EDT Sat may 30 2015

Fog is lifting across the region as the sun begins to rise. A few
locations in the east are still reporting visible below 2 miles. As a
result...updated the weather grids to take out fog in the western
County Warning Area...and the dense fog in the east. Fog will continue to lift
and dissipate across the east over the next hour or two...so left
in forecast through 12z. Also...rain showers are already starting
to develop across portions of eastern Kentucky...moving north-northeast. Also
updated probability of precipitation and weather grids to reflect the earlier onset of
convection. Once the latest observations were ingested into the
database...loaded these into the forecast to make sure current
conditions were well reflected in the near term forecast.

&&

Short term...(today through sunday)
issued at 418 am EDT Sat may 30 2015

After rains impacted sections of the County Warning Area yesterday...lingering
moisture has led to decent areas of fog development during the
overnight hours. Patchy dense fog has also been observed...and
will likely continue through the early morning hours. As the sun
begins to rise this morning...expect fog to lift and give way to
mostly to partly sunny skies across the region this morning.

Upper level ridging off the southeast Atlantic Continental U.S. Will slowly
break down over the next day as troughing over the Mississippi River
valley shifts eastward and across the Ohio River valley. This shift
will be our primary weather driver over the next 2 days. At the
surface...a low pressure system...currently moving across
Missouri...will reach western Indiana by this evening...then
continue to shift northeast...just north of the Ohio
River...through Saturday night and into Sunday morning. As this
occurs...a cold front is expected to push through Kentucky. Still
favoring the GFS solution of the frontal passage...which should
traverse western Kentucky late tonight...central Kentucky through 12z
Sunday...and stall out across the high terrain of Kentucky between 18z
Sunday and 0z Monday.

For today...continued strong warm moist southerly flow ahead of the
boundary will bring yet another high humidity/warm weather day to
the region...as well as the potential for convective development. As
has been the case in the previous days...best chances for convection
will be in the afternoon with peak heating and instability. Latest
forecast soundings for today Don/T look overly impressive for severe
potential...but could still see some good rainers and decent
lightning from any thunderstorm that develops. As we lose daytime
heating...expect coverage to decrease into the overnight
hours...especially in the southeast portion of the County Warning Area away from the best
forcing of the incoming front. Began increasing probability of precipitation again by 12z
Sunday as sun begins to influence unstable airmass once
more...peaking as the front begins passing over during the afternoon
hours. Forecast soundings are showing better hail potential during
the day Sunday...with much more drying aloft and decent cape values
in the 2 to 3k j/kg range. Lapse rates are not super
impressive...but Li/S will drop into the -5 to -6c range in some
locations...indicating good potential for thunderstorm initiation.
All in all...expect some decent scattered storm development to
potentially take place over southeast Kentucky...which corresponds well to
Storm Prediction Center/S marginal risk over this same area for Sunday. Something to
watch out for. However...did note the level of moisture in the
soundings are quite shallow...with unimpressive precipitable waters ...so not
expecting much Hydro concerns...unless storms continue to impact the
same locations multiple times.

With such a strong southerly flow expected today...temperatures
could warm well into the middle 80s across much of the region...with
continued high humidity values. However...with increased cloud cover
overnight and into tomorrow...as well as winds shifting to a more northwest
direction behind the front...expect temperatures to only reach the
upper 70 to low 80 range for during the day Sunday /coolest in the
west/. Overall...superblend and GFS were the models of choice during
the short term...though most short term models seemed to be in
decent agreement with one another.

Long term...(sunday night through friday)
issued at 418 am EDT Sat may 30 2015

The extended forecast period begins on Sunday night with a pretty
active and progressive pattern in place. As an upper low begins to
exit the Ohio Valley area and a cold front pushes through the area.
The front does wash out a bit and instability will begin to become
tied to diurnal trends but will keep probability of precipitation through the Sunday night
period and transition to slight chance probability of precipitation into Monday afternoon.
Temperatures really cool off with lower 70s expected with the
approaching cooler air mass. The front then becomes a stalled
boundary along the Kentucky/Tennessee border and along the Virginia/Kentucky border and so
will keep slight chance probability of precipitation each day along the high terrain areas
there. This will be the case each day from Monday through
Wednesday with the maximum chance occurring each day during the
afternoon but did go below the super blend solution with the lack
of upper level support and collaboration with the neighboring
offices.

By Thursday...with an increased southerly flow...a weak wave
overhead...and the mentioned stationary boundary...a better chance
for precipitation will be on tap fro Thursday afternoon and Friday
afternoon. This period will still maintain a diurnal trend to any
convection. Still kept close to the super blend solution but did
nudge probability of precipitation below a bit during the few days with lack of upper
level support. Overall...besides the exiting cold front on Sunday
night...no dominant weather feature will provide a definite chance
of precipitation or at least the lack of consistency in the models is
such that nothing above slight chance probability of precipitation is discernible. For
this fact...did stay rather close to the super blend.

&&

Aviation...(for the 12z tafs through 12z Sunday morning)
issued at 746 am EDT Sat may 30 2015

Fog will quickly burn off across eastern Kentucky over the next hour and
VFR conditions will take hold through much of the day. Strong
southerly flow will continue the trend of warm moist conditions
across the region. This will result in cumulus development and
scattered showers and thunderstorms throughout the day. Light
showers are already starting to develop this morning but have so
far had little impact. Given that the exact location and timing of
these developing storms is unknown...continued with mention of
thunderstorms in the vicinity for the hours when storms are most likely expected. Daytime
mixing will also lead to some decent wind gusts in the 10 to 20kt
range during the afternoon hours. By this evening...convection
will begin a downward trend as we lose best instability and
heating. Winds will also diminish...with patchy/areas of fog
taking hold across portions of the region once more. Unless rain
directly affects a taf site this evening...expect most of the fog
to remain in the valleys and not affect taf sites.

&&

Jkl watches/warnings/advisories...
none.
&&

$$

Update...greif
short term...jmw
long term...shallenberger
aviation...jmw

National Weather Service Glossary of Abbreviations