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Area forecast discussion...updated 
National Weather Service Jackson Kentucky
1108 am EDT Tuesday Jul 22 2014

issued at 1107 am EDT Tuesday Jul 22 2014

The grids...zfp...and severe weather potential statement were updated mainly to remove morning fog
from the forecast. The region will remain in between an upper low
meandering across the southeast and a shortwave and developing trough
over southern Canada and the Great Lakes region. This put the area
just to the south and east of a ridge axis extending from The Rockies
east into the Ohio Valley region. This leaves the area under weak
steering flow and shear and little or no upper level support for
forcing through this evening. The latest GFS and NAM forecast
soundings have middle level warm air and keeps the atmosphere capped at
jkl through this evening. Near loz...there is a bit weaker capping in
both models...but at both locations the 6z and 12z NAM have the
stronger cap. Some shallow showers or sprinkles may still occur
across the northwest two thirds of the area...but thunder chances
appear very low.

The 12z NAM forecast soundings indicate a weaker cap in
the tier or two of counties along the Tennessee and Virginia border from McCreary
north and east to Pike County. Convection appears more probable in
this area...but coverage in all areas may again be limited in
coverage similar to yesterday. We will continue to evaluate trends and
cumulus for possible lowering of probability of precipitation into this evening.

Update issued at 745 am EDT Tuesday Jul 22 2014

Some of the deeper valleys have some dense fog that has developed
overnight and is now starting to lift a bit. Low temperatures have
dropped into the upper 60s to around 70 in most places. Have updated
to input the latest observation into the grids. The rest of the forecast is
good to go. Have sent the grids to ndfd and the web servers.


Short term...(today through wednesday)
issued at 348 am EDT Tuesday Jul 22 2014

Current conditions across eastern Kentucky features some dissipating
cloud cover as some upper level ridging is nudging into the area from
the height center over the south Central Plains. With this
dissipation...some fog will develop in the valleys towards dawn. Will
adjust temperatures a bit as well to address the low temperatures in the
more sheltered valleys. Heading into the day...the mentioned ridge
and warmer middle level temperatures into the middle levels will impact the air
mass over eastern Kentucky. This will impede convection again today
but mainly in the northwestern counties. Models have underestimated
the strength of the ridge axis nudging into the area on Monday but
recent runs look to have handled this scenario better. Will go with
aerial coverage again but with mainly isolated coverage northwest to
scattered in the southeast along the mountainous counties.

Heading into Wednesday...the strong shortwave moving into the Great
Lakes region and lower Ohio Valley will push through. This may be
scenario may be another example of the energy going through the base
of the trough and becomes cut off from the middle level ridges over the
southern Continental U.S.. nonetheless...will go with numerous coverage into
Wednesday as the front approaches and southwest flow increases.
Plenty of instability looks to be present with this set up with cape
values getting into the 2500 j/kg range and while the cap still looks
to be present...the forcing available should be enough to overcome
it. This and Storm Prediction Center has assigned a 5% severe threat for the northwestern
counties. Though with the slight increase steering flow...may need to
take the duration over an area concern. Shear looks to be weak as
well for this set up so any severe concern would be isolated for
collapsing cells with no organization. Will go with high probability of precipitation through
Wednesday with no severe mention but with some locally heavy rainfall
possible. Slightly above normal temperatures and dew points climbing into
the low 70s look top be the case through the short term.

Long term...(wednesday night through monday)
issued at 348 am EDT Tuesday Jul 22 2014

The models are in only fair agreement aloft through the extended
portion of the forecast. While they all depict the abnormal pattern
of a strong Four Corners Region Ridge and deep troughing in the east
continuing through the end of the week and into the start of the
next week...they differ on the magnitude and timing of the evolving
eastern trough...particularly over the weekend and into Monday.
Specifically...falling heights over Kentucky will be the rule into
Thursday night as the retrograding low to the south pulls away and
the northern stream sends a series of shortwaves through the area in
northwest flow. This eastern trough pulls away to start the weekend
with heights climbing temporarily before they fall again in the face
of a Node of the large northeast trough gearing up for a dive into
the upper Midwest and Ohio Valley. The 00z GFS is most aggressive
with this evolution while the 12 European model (ecmwf) keeps its core wave further
to the northwest and lags the GFS development. However...the latest
CMC and European model (ecmwf) are trending more toward the GFS. Regardless...
northwest flow will dominate the local pattern as heights fall into
Monday morning. Eventually...the European model (ecmwf) catches up...with the deeper
and more western trough idea of the GFS but some significant
differences remain with the pattern over the Ohio Valley to close
out the week. The better agreement earlier in the extended supports
a blended solution while the larger spread later on lowers
confidence so that the ensembles and a slight lean toward the GFS
are preferred solutions.

Sensible weather will feature an approaching cold front serving as a
focusing mechanism for showers and thunderstorms Wednesday night
into Thursday. Cooler and drier air will filter into this part of
the state later in the day Thursday putting an end to the convective
chances from northwest to southeast. Dry and relatively cool weather
follows into the start of the weekend thanks to a brief visit of
high pressure. However...the cold front that brought the drier
weather will start to surge north over the western parts of the
region and bring warmth...moisture...and better convective chances
back into the area on Saturday. A series of short waves at middle
levels...the developing trough...and the surface frontal structure over
the Ohio Valley keep shower and thunderstorm chances going into
Sunday and Monday.

The CR grid Load provided a decent start to the forecast for the
extended...though did adjust the probability of precipitation to add a tinge of diurnal to
the timing of the convection. Also...tweaked the low temperature
grids a tad to reflect ridge and valley differences Wednesday and
Thursday night.


Aviation...(for the 12z tafs through 12z Wednesday morning)
issued at 745 am EDT Tuesday Jul 22 2014

Patchy fog will dissipate within the next few hours across the area.
Cumulus will begin to develop early today with some isolated to scattered
showers and storms developing. The main bulk of the activity will be
to the east with isolated activity elsewhere so will go with out
thunder at the taf sites. Tonight will see more fog development as
southwest flow finally sets up ahead of an approaching cold front.
All thunderstorm activity associated with the front should hold off
till after 12z. Winds will be light through the period.


Jkl watches/warnings/advisories...

short term...shallenberger
long term...greif

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