Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Jackson Kentucky
943 PM EDT sun may 24 2015

issued at 942 PM EDT sun may 24 2015

Current conditions across the area feature high pressure
retreating to the east with middle and upper level cloud cover
beginning to stream into central Kentucky. Given the dry air in
place and a slow response to the moist southerly flow...have
pushed the onset of precipitation a little later in the morning. Cloud
cover though has begun to move into the area in earnest. Some middle
level cloud cover will begin to move over the area through the
night and will limit the Ridge Valley split as well as any fog in
most areas with the exception of the far east. Especially with the
dry air in place right not...fog will be few and far in between
with the exception of some of the deeper river valleys. Have
updated the forecast and sent out a new zone forecast product.

Update issued at 707 PM EDT sun may 24 2015

Updated the grids to input the latest observation across the area. The
forecast remains on track and precipitation will not enter the area till
after day break. The grids have been send to ndfd and web servers.


Short term...(this evening through Monday night)
issued at 347 PM EDT sun may 24 2015

Upper level ridging has been shifting eastward across the Ohio River
valley throughout the day as broad troughing and an upper level
closed low continue to expand across the western half of the Continental U.S..
much of western Kentucky and the Mississippi River valley is finding
itself wedged in between the two patterns with increasing pressure
gradients...resulting in some breezy conditions across much of the
western and central portion of the state. Here in eastern
Kentucky...ridging is still trying to hold on for the next few hours...but
expect heights to be on a slow decline throughout the night and into
the day tomorrow as the upper level troughing begins to cross over
the Mississippi River valley. A river of moisture is currently
streaming from the Gulf of Mexico upwards through the Mississippi
River valley and then wrapping itself into the strong low currently
cover the northern plains...or eastward up and along the northward
extent of the upper level ridge. This is resulting in a large amount
of cloud cover across these above mentioned areas. While a few
clouds have found their way into eastern Kentucky...we are generally
mostly sunny with strong but dry southerly flow as of 1930z. As the
ridge continues to break down overnight...and the upper level trough
nears closer...expect these clouds to expand across Kentucky...generally
of the high variety...though some middle and lower clouds may begin
moving in as early as tomorrow morning.

Along with these clouds...there will continue to be an uptick in
moisture and temperatures for the day tomorrow. A shortwave moving
up and along the exiting ridge will provide a strong enough trigger
to allow scattered showers and thunderstorms to begin developing
tomorrow during the day...increasing in coverage and intensity as we
head into the afternoon hours with peak heating and instability. As
the ridge continues to break down over the east...expect this
convection to spread across the entire County Warning Area during the day. Loss of
daytime heating and fuel will allow diminished coverage overnight
Monday night...but continued lowering heights and more shortwave
influence will allow for showers and thunderstorms to quickly
begin ramping up again by Tuesday morning.

For temperatures...strong southerly flow across the region allowed
temperatures to make it into the low and middle 80s this afternoon. With
increasing moisture...continued strong southerly flow...and the
potential for an uptick in cloud cover overnight...expect overnight
temperatures to be much warmer than nights previous. Generally upper
50s to middle 60s are expected. We could still see some decent ridge to
valley temperature differences...but expect that given the above
mentioned factors...the best potential for this to occur will be in
the terrain across the far eastern portion of the County Warning Area...away from
the best cloud cover and wind influences. Temperatures could fall as
low as the low to middle 50s in some of these valleys overnight. By
tomorrow...two things will come into play. First...stronger
southerly flow across the region which would promote a continued
warm up across the region. However...this may be offset by
encroaching cloud cover and the possibility for rain. As
such...expect similar temperatures overall to that of today...generally in
the low to middle 80s. Temperatures will obviously likely fluctuate as
rain showers/thunderstorms pass over. tomorrow
night...the increasing clouds and moisture will work to alleviate
the large Ridge Valley differences...and will keep temperatures generally
mild across the the low to middle 60s for overnight lows.

Long term...(tuesday through sunday)
issued at 453 PM EDT sun may 24 2015

A warm and relatively humid air mass will be in place as the
period high pressure at the surface and aloft off the
East Coast transports deep moisture north and northeast over the
forecast area. A large chunk of the current southwest Continental U.S. Large
scale trough will lift out to the northeast as a shortwave
trough... crossing the Midwest on Tuesday. This should lend upper
support for precipitation locally. Sufficient shear will be present for
organized convection on Tuesday. The degree of instability which
will develop remains in question. If there is too much ongoing
cloud cover and precipitation during the day will limit our
destabilization and the threat of strong convection. But...if
enough heating occurs...there is a concern for severe weather.

After the Tuesday system passes...broad flow out of the west
southwest will persist from here northwestward. Models show
another shortwave trough approaching in the flow aloft late
Wednesday and Wednesday evening...justifying another period of
elevated pop. Once this passes...flow aloft relaxes and
geopotential heights rise...supporting a lower pop late in the
week. However...there will be no substantial change in surface air
mass...and with warm and moist air lingering...the pop will not
go away entirely.

Finally...another system could affect the region over the
weekend. The GFS and European model (ecmwf) do start to show more pattern
differences by then...but both show some semblance of the system
affecting US. The GFS has a cold front dropping in from the north
faster than the European model (ecmwf)...but both eventually show the front in our
vicinity by Sunday...with our area positioned on the eastern side
of an upper level trough. With disagreement for Saturday...have
stayed with fairly low probability of precipitation...but went up to high chance for
Sunday when both models show a more favorable environment.

Throughout the long term period...diurnal heating will likely
play a role in timing of precipitation coverage on the large scale...and
have timed peak pop locally during the late afternoon and evening
hours each day. This may be able to be further refined as time
passes and confidence grows in handling of smaller scale


Aviation...(for the 00z tafs through 00z Monday evening)
issued at 707| PM EDT sun may 24 2015

Expect VFR conditions to be in place through tonight. After
daybreak...ceilings will begin to lower as showers and
thunderstorms develop and move in from the southwest. This will
bring some MVFR and even some IFR ceilings into the area by middle
morning as well as low visibility where storms move over the taf
sites. This will continue through the afternoon with some
locations over the east...including sjs may not see any storms
during the day. Winds will be light through tonight but increasing
southwest winds as the showers and storms move into the area.


Jkl watches/warnings/advisories...


short term...jmw
long term...hal

National Weather Service Glossary of Abbreviations