Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Jackson Kentucky
924 PM EST Monday Dec 22 2014
issued at 815 PM EST Monday Dec 22 2014
The most significant updates involve pop on Tuesday and a potential
for thunder Tuesday night and Wednesday. Both the GFS and NAM suggest
the influence of downslope flow will outweigh synoptic scale forcing
for precipitation in our eastern counties tonight and Tuesday...and have
lowered the pop there. Eventually...forcing with the deep storm
system passing by should be enough for rain everywhere Tuesday night
and Wednesday. Models also show elevated instability ahead of the
system/S cold front. GFS MOS shows probability of thunder as high as
50-60 percent for portions of the jkl forecast area. Thunder has
already occurred tonight over west Tennessee and western Kentucky. Have added a
slight chance of thunder moving through from west to east Tuesday
night and Wednesday.
Update issued at 505 PM EST Monday Dec 22 2014
With showers having arrived from Tennessee...updated to bring a pop into
the forecast earlier than was previously forecast for tonight for
Short term...(this evening through Tuesday night)
issued at 325 PM EST Monday Dec 22 2014
Today has brought partly to mostly cloudy skies across eastern Kentucky
today. This will continue to be the trend before more substantial
cloud cover progresses northeast across the region tonight. Currently
we are tracking showers across middle Tennessee this afternoon...however
mesoscale models do weaken this and keeps much of the showers west.
This will need to continue to be monitored. However did opt to at
least introduce slight probability of precipitation across the region this evening into
tonight. The models do eventually introduce more precipitation overnight
along more of a warm frontal boundary that surges north. A trough
across the central US will continue to dig southeast and aid in developing a
surface low across the lower MS River Valley. There is expected to be
a transition in lifting mechanisms Tuesday as low across the upper
Midwest becomes vertically stacked and energy/lift moves NE with the
developing low. Also there could be some reasonable help from
downsloping during this period. Therefore will keep better chances of
precipitation across western portions of the County Warning Area Tuesday. Another tricky
part of this will be how much cloud cover will be across the east and
how that will affect temperatures. Right now going with temperatures generally in
the upper 50s to lower 60s across the County Warning Area...however if some clearing
is seen you could see higher temperatures. The low pressure across the MS
River Valley is expected to track north and east across the Tennessee/Ohio
valleys overnight Tuesday. This will lead to widespread showers
across the County Warning Area later Tuesday into Tuesday night.
Long term...(wednesday through monday)
issued at 400 PM EST Monday Dec 22 2014
The models are in good agreement with an amplified long wave pattern
to start out across the Continental U.S.. deep troughing will be ongoing across
the central Continental U.S....with an area of intensifying surface low
pressure taking shape across western Kentucky. The low will continue
to deepen and lift north into the Great Lakes by Wednesday
evening...swinging a strong cold front across eastern Kentucky.
Strong wind gusts up to 40 miles per hour still look like a good bet...although
these look to be mainly confined to a few hour window ahead
of...along...and behind the front.
Showers will be scattering out quickly behind the boundary into
Christmas evening night. Cold air/ice continues to look feeble...but will
continue to carry a small chance of snow by early Christmas morning.
Thursday afternoon through Friday night looks dry as heights
moderate and the long wave pattern turns more progressive.
The models are continuing the disagreement into the weekend and early
next week. The European model (ecmwf) remains more amplified and slower with the next
system to affect our area from early Saturday morning through
Sunday...while the GFS advertises a more transient system. Will side
closer to the European model (ecmwf)...since it tends to have better continuity this
far out. This will allow for chance probability of precipitation this weekend...with a little
snow possible as the system exits late Saturday night into Sunday
morning. Sunday night into Monday will see a return of dry weather...
with ridging taking place aloft once again.
Temperatures through the period will start out well above normal
through the end of the work week...before becoming closer to seasonal
normals for the weekend and into early next week.
Aviation...(for the 00z tafs through 00z Tuesday evening)
issued at 924 PM EST Monday Dec 22 2014
VFR conditions were present at the start of the period...but varying
VFR ceilings were prevalent. There were also a few light showers and
sprinkles. Ceilings will deteriorate to MVFR and IFR for most of the
region tonight. An exception will be extreme eastern Kentucky...where
downslope wind from the south will tend to keep largely VFR ceilings
in place. These trends will last into Tuesday. Showers will likely
occur late tonight into Tuesday in western locations such as
Monticello...Somerset...and Mount Sterling. The probability of rain
will be much less for locations further east due to downslope flow.