Scientific Forecaster Discussion
Area forecast discussion...updated
National Weather Service Jackson Kentucky
830 PM EDT Friday Jul 3 2015
issued at 810 PM EDT Friday Jul 3 2015
23z surface analysis shows low pressure riding through east Kentucky
along a stalled frontal boundary. This boundary has brought
showers...thunderstorms...and flooding to the area for the past
couple of days. That continues tonight with low centroid
convection training as it slowly marches west to east into the
area. Much of the heavy rains continue to fall in areas with very
low ffg and places that have already received excessive rains
like Pulaski and Laurel counties. As a result...flash flood and
areal warnings are out for much of the Cumberland Valley along and
west of I-75. The rains continue to the east but are weakening or
raining themselves out as they move into areas that have not been
hit quite so hard recently. Even so...it will not take much
training for flood issues to develop further east in the southern
half of the County Warning Area. Have updated the forecast to refine the probability of precipitation for
the rest of the evening as the bands of convection slowly settles
south. Also upped the quantitative precipitation forecast across the south and added some fog to
the grids through the night...becoming locally dense late.
Finally...tweaked the near term temperatures and dewpoints based on the
latest observation and trends. These updates have been sent to the ndfd
and web servers along with a freshened zone forecast product.
Short term...(this evening through Saturday night)
issued at 317 PM EDT Friday Jul 3 2015
Based on wind readings across the region...frontal boundary looks
to reside from between Morehead and Flemingsburg...back to the
east to Frankfort and Louisville. Breaks in the clouds in western
and central Kentucky has allowed for 2500j/kg of SBCAPE to
develop. In addition...we actually have some 30-35 knots of
effective bulk shear residing across eastern Kentucky. Showers and
storms continue to light up along and south of the frontal
boundary with the highest concentration closer to the boundary.
Unfortunately...activity is once again aligned east to west and
will track across the Red River basin again into this evening.
This will continue to lead to the threat of flash flooding. Given
the favorable conditions of instability and shear...this activity
should continue to push east through the evening hours. While
activity may decrease as we head overnight...front will still
reside across the area...leading to a continuation in the flash
flood threat through tonight. By tomorrow...front finally slips
south taking the bulk of the activity to our south...however...the
boundary may still trigger a few showers and storms during the
afternoon. They should be more hit or miss on Saturday and mainly
confined to the times of peak instability in the
Saturday night will feature quieter weather as diurnally driven
showers/storms die off around sunset. Still have to watch for some
locally dense fog in places.
Temperatures will remain below normal through Saturday night as we
remain under the influence of the upper level trough.
Long term...(sunday through friday)
issued at 515 PM EDT Friday Jul 3 2015
The models are in fairly good general agreement concerning the
upper pattern into about middle week. They all agree that a weak
trough will start to pivot slowly northeast and out of the
Tennessee and Ohio valleys Sunday into Monday. However...the bulk
of its considerable energy will swirl over eastern Kentucky during
this process only clearing out towards Tuesday morning. This
movement in the pattern will be thanks to a robust trough crossing
through central Canada and sweeping over the Great Lakes Monday
night into Tuesday. The GFS and European model (ecmwf) are similar with the timing
and placement of this...though the European model (ecmwf) is stronger and actually
closed off with its low. Meanwhile...the Canadian is weaker still
than the GFS along with being slower. As this feature passes...
heights will rise locally...though some weak energy will remain
over Kentucky through the day Wednesday. Following this...the GFS
continues with higher heights over the region...while the European model (ecmwf)
takes another trough into the Great Lakes and northeast Ohio
Valley with a wave of energy passing over Kentucky later Thursday.
The models then are in better agreement in showing more ridging to
end the week. A general model blend looks reasonable at least
through Tuesday before a slight lean toward the less progressive
European model (ecmwf) seems in order given recent trends.
Sensible weather will likely see an end to any break from the wet
weather we may enjoy from Saturday into Sunday morning as a low
pressure wave passing just south of the area will shift the front
back north into our area during the day Sunday with attendant
showers and thunderstorms. The convection should be more diurnally
driven into the start of the week with activity becoming more
scattered after sunset lasting through middle morning. The Great
Lakes trough at middle levels will send a slow moving cold front into
the area on Tuesday with renewed higher chances of showers and
thunderstorms. The probability of precipitation will remain elevated through Thursday as
the front lays out and lingers over the state while another surface
wave runs east along it...moving from the Southern Plains to the
central Appalachians Tuesday night through Thursday afternoon.
Again heavy rains will be a concern with this boundary as a wide
open Gulf of Mexico will help to support high precipitable waters across the
state. Should the European model (ecmwf) turn out more correct and the front sags
south we may actually see some drying for the end of the week.
However...the GFS lingers the front overhead so will maintain a
small chance for convection to close out the upcoming work week.
Given the convection and cloud cover expected throughout the
forecast...temperatures will be just on the cool side of normal
for highs and above normal at night for lows...with humid days
and muggy nights.
The CR grid blend came in reasonably well with the bulk of any
adjustments made to the probability of precipitation and sky to account for the diurnal
cycle early on followed by a lean toward the European model (ecmwf) late in the
period. As for temperatures...did tweak the lows a bit each night
to reflect only minor terrain effects given the high moisture
environment in place for the extended.
Aviation...(for the 00z tafs through 00z Saturday evening)
issued at 830 PM EDT Friday Jul 3 2015
Widespread showers and thunderstorms will impact most sited
through the rest of the evening with variable ceilings and visible the
result. Amid this a distinct trend toward lower aviation
categories will be noted. After midnight...expect less in the way
of storms around but also lower...IFR/LIFR...cigs and visible due to
the saturated air mass in place along with scattered showers.
These conditions will likely improve later Saturday morning...but
that will most probably just help fuel another round of showers
and storms for the afternoon...mainly in the southern parts of the
forecast area. Winds through the period will be light and
variable...outside of any storms.
Flash Flood Watch through Saturday morning for kyz044-050>052-