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Area forecast discussion...updated 
National Weather Service Jackson Kentucky
115 PM EDT Friday Aug 29 2014

Update...
issued at 114 PM EDT Friday Aug 29 2014

The forecast remains on track. A few small showers are starting to
initiate along and south of the hal Rogers Parkway and Highway 80
corridors...aligning near the warm front. The latest short term model
guidance continues to support at least the threat of isolated
convection across most of eastern Kentucky through the rest of this
afternoon as the boundary slowly eases to the north. Will freshen up
some of the near term sky cover and probability of precipitation...as well as hourly
temperatures and dew points...according to the latest trends in
observations.

Update issued at 1005 am EDT Friday Aug 29 2014

Valley fog has burned off across most locations this morning...with
just a touch of stratus lingering along portions of the Big Sandy and
Cumberland River basins. The forecast is on track...with highs
topping out in and around the 90 degree mark for most locations. A
faint cumulus line shown on the visible satellite imagery near the Tennessee/Kentucky
border reveals the presence of a quasi-stationary frontal
boundary...which will be lifting north across eastern Kentucky today
as a warm front. Will maintain the isolated to possibly scattered
convection already advertised. Updates have been sent.

Update issued at 750 am EDT Friday Aug 29 2014

Hourly grids have been freshened up a bit based on recent observations.
No significant changes were made at this time. Lingering valley fog
should lift and dissipate through around 9 am EDT. An isolated shower
or thunderstorm remains possible later this afternoon and evening.
Some of the recent model guidance suggests that the start of slight
chance probability of precipitation may need to be pushed back a couple of hours.

&&

Short term...(today through saturday)
issued at 338 am EDT Friday Aug 29 2014

An upper level ridge of high pressure was centered over the
southeastern Continental U.S. Early this morning and extended north and
northwest into the Appalachians and the Ohio Valley region. Over the
middle of the country...an upper level trough extended south through
the plains states in between the ridge centered across the
southeastern Continental U.S. And another ridge centered to the southwest of
California. At the surface high pressure was centered over the Great
Lakes region. Meanwhile...a boundary is stalled out from southeast Virginia
south into the Appalachians and east Tennessee and then northwest to low
pressure over the plains states. Some passing cirrus and middle level
clouds are moving across the region at this point around the
ridge...especially the far west and the north. This has left the
Cumberland Valley with the least cloud cover.

During the period...the ridge is expected to remain in place across
the southeastern Continental U.S....though the axis of the ridge will depart to
the east today. The surface high will move east as well. Also during this
time...the trough over the middle of the country is expected to lift
toward the Great Lakes with deep moisture from the Gulf of Mexico
increasing late in the period on southwest flow aloft. The flow
between the departed surface high and the system moving into the Great
Lakes will have a bit of a downslope component early on Saturday.

Through sunrise and today...some areas of valley fog have formed or
are expected to form before sunrise...and might become dense in a
couple of spots. The Harlan Airport ki35 has the lowest visible at
present. However...any dense fog should not become widespread with
the passing debris clouds and some mixiness with east to southeast
flow around the western edge of the surface high. Otherwise...the stalled
boundary will lift north into the region today as a warm front and
combine with a weak approaching disturbance in southwest flow and
daytime heating to yield generally isolated to possibly scattered
rain showers and thunderstorms and rain during the afternoon and evening hours.

This boundary will exit to the north and east tonight and into early
on Saturday...leaving the region in the warm sector. A warm air mass
will remain in place and moisture will increase in all levels late in
the period as precipitable water is anticipated to rise to around 1.75 inches or
more in most places late. However...forcing for Sat remains very
limited and the 0z European model (ecmwf) and 0z GFS actually have surface dewpoints
decreasing for a while on Saturday possibly from the downslope low
level component to the winds. In addition...there is also a middle level
cap for much of the day as well. Any convection on Sat should be late
in the day or early in the evening...and the best chances appear to
be across the southwest and west. Temperatures on Sat should approach
or reach 90 in many locations.

Long term...(saturday night through thursday)
issued at 238 am EDT Friday Aug 29 2014

Models have been fairly consistent on advertising a fairly sharp
trough pushing across the Ohio River valley late Saturday night into
Sunday morning. Thus...confidence is fairly high we will see better
precipitation coverage around this period. We may see a lull from
diurnally driven convection on Saturday through the first part of
Saturday night. However...showers and storms will develop and push
across the area by daybreak. Precipitable waters will climb to 1.8 to 2 inches
during this period..yielding the threat for locally heavy rainfall
as these values are near the 99th percentile for late August.
Fortunately...storm motion should be sufficient to prevent slow
moving storms. Main concern will revolve around any training storms
which may occur. Regardless...storm will be heavy rainers with good
potential for ponding on roadways.

Shortwave trough will be on the way out by late Sunday with
precipitation chances decreasing. However...strong ridging will
develop over the deep south...with eastern Kentucky residing on the
north edge of this high pressure dome. This will keep the area
susceptible to weak shortwaves as they progress eastward along the
northern peripherals of this high pressure area through the week.
Thus...it looks like the weather may stay unsettled well into next
week and perhaps beyond. This warrants at least chance probability of precipitation all the
way through the end of the period. Does not appear we will see any
forcing quite as strong as this weekend...but any weak shortwave
this time of year...combined with daytime instability would be
enough to generate isolated to scattered storms. Given the tendency
for better coverage during the afternoons/evenings this time of
year...plan to go with a diurnal trend with probability of precipitation. Temperatures will
likely stay near or just above normal through the period as heat and
humidity continue through the next week.

&&

Aviation...(for the 18z tafs through 18z Saturday afternoon)
issued at 114 PM EDT Friday Aug 29 2014

A passing warm front will bring a threat of isolated convection
across eastern Kentucky this afternoon...diminishing from southwest
to northeast through this evening. Any direct hit from a thunderstorm
will bring temporary IFR or worse visibilities...however due to the
limited areal coverage...will continue to just maintain thunderstorms in the vicinity at the
taf sites with prevailing VFR conditions. Once the convection dies
off this evening...expect some IFR or worse fog development
overnight within the deeper river valleys...but likely steering clear
of the taf sites. Clouds will also be on the increase late tonight
and into the day on Saturday out ahead of an approaching upper level
system. The convective threat associated with this system looks to
hold off until later Saturday afternoon. Winds will average out of
the south and southwest at around 5 kts or less through the period.

&&

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

$$

Update...geogerian
short term...jp
long term...kas
aviation...geogerian

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