Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Jackson Kentucky
145 am EST Sat Dec 27 2014
issued at 145 am EST Sat Dec 27 2014
Radar is picking up on a rather large area of light echos early this
morning. While most of this activity is just virga...have seen some
-ip/-ra here at jkl as one cell intensified suddenly. There is an
additional shower or two showing similar intensification as well.
But the very isolated nature of the two or three renegade showers we
are seeing did not seem to warrant a slight pop. Also seeing rising
temperatures to our west and where more extensive cloud cover is
passing over the area. Updated the forecast package for the rising
trend in temperatures and to include mention of some sprinkles in the zone
Update issued at 919 PM EST Friday Dec 26 2014
Forecast seems to be well on track at this point. High clouds are
continuing to move into eastern Kentucky and will thicken throughout the
night. Meanwhile...light returns are starting to show up on the
radar. Given the abundant amount of low and middle level dry air...these
returns are dropping from high altitudes and then evaporating before
hitting the ground. As such...have not included any mention of rain
in the forecast until the system begins impacting the region. Loaded
in the latest observational data for temperatures...dew points...and
winds...to make sure the near term grids were on track with ongoing
conditions. This resulted in little change from the current forecast.
Short term...(this evening through Saturday night)
issued at 328 PM EST Friday Dec 26 2014
Models are in good agreement through the short term will only some
timing differences to deal with from the higher resolution 12z NAM.
But 18z run of the NAM has slowed onset of precipitation into the
area late Saturday...now more in line with the GFS and European model (ecmwf).
Middle/upper level ridge...centered over Cuba has amplified slightly
over the central and southern Appalachians due to the eastward
movement of a trough lifting out of the western Great Basin...
southwest Continental U.S.. at the surface...fairly stationary high pressure was
centered over the central Atlantic coastal region keeping our area
under the influences of southerly flow. Strong subsidence was
responsible for very dry air mixing into the top of the boundary
layer earlier today but dew points have recovered some this
afternoon. Position of this high and dry air at the surface will be
favorable for a strong Ridge Valley split across the area tonight.
Continued movement of middle/upper level trough out of the western Continental U.S.
Will induce a series of surface lows...the first developing over the
eastern plains and moving into the Great Lakes by Saturday. This
first low will drag a surface cold frontal boundary into the Ohio Valley
Saturday night into Sunday morning. A second low will develop much
further south over the southern Mississippi Valley region and track
northeast along the front as it pushes across the Appalachians early
Sunday morning. This will tend to keep our weather wet through to the
end of the short term.
For sensible weather...middle and high level clouds will enter our area
late this afternoon into this evening...then thicken and lower with
time. Timing the onset of shower activity into the area late Saturday
is main forecast challenge. But a blend of solutions suggests
scattered showers entering our western most counties late Saturday
afternoon and overspreading the rest of our forecast area Saturday
night. Increased probability of precipitation to categorical levels Saturday night. For
temperatures...went cold in our valleys area tonight....especially in our
east where southerly winds will not be strong to mix the nocturnal
inversion out. Highs Saturday will run 3 to 5 degrees warmer than
today...with a relatively broken sky cover tending to keep highs down
a bit. Cloud cover and rainfall will moderate lows Saturday night
into Sunday morning...with most locations only dropping into the middle
Long term...(sunday through friday)
issued at 407 PM EST Friday Dec 26 2014
The extended forecast period begins with an elongated trough moving
through the Midwest and into the appalachian chain. The southern
portion of the trough develops a stronger shortwave along the Gulf
Coast as it begins to ride to the northeast over the ridge located
in the Bahamas. As this feature and associated long wave trough exits
the eastern Continental U.S....the upper level pattern transitions to a broad
trough extended entirely across the lower Continental U.S. With a closed low
diving south along the West Coast and into the Baja California region. Models
still have this feature ejecting eastward into the Gulf Coast region.
At the surface...concerning the Sunday through Monday time frame the
front will be moving through eastern Kentucky on Sunday while
slowing along the appalachian chain. This will result in a longer
duration of rainfall across the area before exiting Monday night.
While some colder air will be filtering in behind this front...there
may be a few locations that will see a mix or change over to some
snow but no accumulation is expected since the duration will be so
short if at all. Quite a colder air mass will filter into the Ohio
Valley toward middle next week. This colder air will be in place for
the arrival on the next system moving up from the south on Thursday
and will result in some snowfall in southeast Kentucky. Any
accumulation is quite uncertain at this point.
Aviation...(for the 06z tafs through 06z Saturday night)
issued at 108 am EST Sat Dec 27 2014
Look for VFR conditions through the entire forecast period. Radar is
picking up on a rather large area of light echos tonight. Have even
seen some -ip/-ra here at jkl as one cell intensified suddenly. But
the bulk of this activity is virga and as such did not mention any
weather at any of our terminals. Also expect this activity to wane
as we progress through the early morning hours. Additional showers
associated with an approaching cold frontal system will develop
during the last few hours of the forecast. Ceilings and visibilities will drop
thereafter...just beyond the forecast window. Winds will run less
than 10 kts through the period...and generally from the S/SW.