Scientific Forecaster Discussion
Area forecast discussion...updated
National Weather Service Jackson Kentucky
1021 PM EDT Wednesday Jul 29 2015
issued at 1020 PM EDT Wednesday Jul 29 2015
The cold pool associated with the line of storms has continued to
consolidate to the west and south of our area. Only a few of our
southwest counties will see likely rains over the next hour or so.
The remnant stratiform rainfall across central Kentucky is not
moving much...and will gradually weaken...mainly in place. The
last few runs of the hrrr has generally caught on to the ongoing
convective trends. As such...it appears that there may not be much
in the way of activity until the actual frontal boundary moves
southeast across the area deeper into the overnight hours...when a
slight uptick in activity may occur. Will therefore hang onto
slight to chance probability of precipitation. Also adjusted the lows up a touch...as the
push behind the front is not very strong. The best chance of
seeing some upper 60 degree readings looks to be along and north
of I-64. Updates have been sent.
Update issued at 813 PM EDT Wednesday Jul 29 2015
The latest radar mosaic shows a convective line across central
and western Kentucky. New cells had been more Lively a bit further
northeast earlier...but some precursory storms tapped into the
better available air mass...and now there is generally a weakening
trend on the eastern flank of the line...with better cold pool and
associated new development aligning more towards the south...where
better instability remains. Still...think that some debris cells
will make it into the west in the next 1 to 2 hours...and have
upped the probability of precipitation to high chance to likely for those locations. As we
lose heating...expect an overall gradual diminishment...however
will still have to keep an eye on heavy rainers...given the high
precipitable waters and the potential for training.
Short term...(this evening through Thursday night)
issued at 343 PM EDT Wednesday Jul 29 2015
As of middle afternoon a middle level ridge was centered over the
Southern Plains region...with a closed middle level low over
northwestern Ontario and the associated trough south into the MS
valley region. At the surface...an area of low pressure was centered
over Ontario with a cold front south into the central Great Lakes
and then southwest into the middle MS valley and Central Plains.
Convection has developed along or in advance of this front over Ohio
and in southwest into western Kentucky. Additional convection has
developed near a moisture gradient evident in precipitable water from northern Kentucky
south into central Kentucky. This convection has been generally slow
moving with heavy rainfall rates. Areawide...a warm and moist
airmass is in place with temperatures in the middle to upper 80s to
near 90 and dewpoints in the upper 60s to middle 70s.
The closed middle level low will track to Hudson Bay with the
trailing shortwave trough moving through the Great Lakes and middle
and upper Ohio Valley region tonight. This shortwave trough will
move into the northeastern Continental U.S. Through Thursday. At the same
time...the middle level ridge will retrograde and amplify and become
centered over the southern rockies or Four Corners region. This
will put the region in northwest flow aloft late in the period. At the
surface...the cold front will cross the region by late tonight or
early on Thursday. Then...high pressure will build in behind the
departing cold front and usher in slightly colder...but more
noticeably drier air into the region.
Rather meager middle level forcing and non optimal timing of the
frontal passage during the late evening into overnight hours should limit
convection this evening and tonight to isolated to scattered
coverage. It still appears that there should be a peak in coverage
over the next 3 hours or so...and then more organized convection
with a possible broken line or line segments of showers and
thunderstorms as the cold front moves through. With relatively
slow storm motions expected due to weak flow aloft and a moist
airmass in place...any stronger thunderstorms could produce very
heavy rainfall rates and outflow wind gusts in excess of 30 miles per hour
will be possible this evening similar to a gust observed over
central Kentucky earlier this afternoon.
A shower or possibly a thunderstorm could linger early on
Thursday...over the southeastern County Warning Area...particularly near the Virginia border.
Otherwise... as drier air moves in throughout the column skies
should become mostly sunny in most locations on Thursday afternoon.
With the high building in...clear skies and light winds should set
the stage for valley fog formation late in the period. Enough
drier air should work in for some of the normally colder locations
along...or north of the mountain Parkway could touch the upper 50s.
Long term...(friday through wednesday)
issued at 256 PM EDT Wednesday Jul 29 2015
The extended period looks fairly benign as surface high pressure
takes control of the region through early next week. This will
allow for slightly cooler and drier air to filter into the region
for the weekend. Highs Friday through Sunday will be in the low to
middle 80s...but dewpoints in the upper 50s and low 60s will make
those readings feel much more pleasant than they have recently.
A weak and moisture starved front approaches the region Saturday
morning...with both the GFS and European model (ecmwf) showing the precipitation falling
apart before it reaches the forecast area. This is likely due to
the dry air/ridging at the surface. There is some middle level
moisture and weak energy with the front as it passes to our north
so have kept a slight chance of an isolated shower in the far
northern counties. But do not expect much more than an increase in
some middle level clouds on Saturday for most areas.
Shower chances return to the region by Tuesday as the upper level
pattern becomes more active. Models indicate that several upper
level impulses embedded in the northwest flow will move across eastern
Kentucky through the end of the forecast period bringing increased
shower and thunderstorm chances through the end of the work week.
Temperatures (and humidity) will increase back into the upper 80s
by the end of the period...with heat indices likely surpassing the
90 degree mark.
Aviation...(for the 00z tafs through 00z Thursday evening)
issued at 813 PM EDT Wednesday Jul 29 2015
Convective line will gradually make it in from the west. Have
sym...loz and sme seeing the best chance of sustained convection
and MVFR conditions between 01 and 02z...with some temporary IFR
conditions possible at sme and loz between 02 and 03z. Have
allowed more temporary ts and MVFR conditions at jkl...with a
general thunderstorms in the vicinity at sjs...where there is more uncertainty whether more
organized storms can make it that far east. A cold front will
eventually push through the area overnight...with winds shifting
to the northwest. MVFR stratocu and a few showers will linger
through Thursday morning...before dissipating thereafter with a
return to VFR.