Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Jackson Kentucky
450 am EST Thursday Jan 29 2015
Short term...(today through friday)
issued at 400 am EST Thursday Jan 29 2015
Latest surface map features high pressure along the eastern
Continental U.S....with low pressure moving into the Great Lakes and Ohio Valley
regions. Aloft...a short wave trough is rotating towards the Ohio
Valley...with another trough dropping southeast into the northern
plains...and yet one more moving in across south central Canada.
Mainly middle and high level clouds have been streaming in across
eastern Kentucky. The southerly wind flow out ahead of the
approaching surface low has allowed for a nice Ridge/Valley split
across the area...with more sheltered valleys holding in the low and
middle 20s...while ridgetops are in the low to middle 30s.
The models are in good agreement through the short term...taking the
low pressure system east across the Ohio Valley during the day...and
allowing the associated surface cold front to move through the area
this afternoon into early this evening. Meanwhile...the more northern
short waves will continue to drop southeast in succession...helping
to establish a deep trough across the east by Friday.
The current radar shows a band of light rain from south central
Indiana down through western Kentucky. The latest hrrr shows this
activity making it to our doorstep by dawn or shortly thereafter...
although there is good agreement that the majority of the measurable
precipitation will stay just north...with more spottier activity to
contend with across our area through 14z. After 14z...precipitation
looks to Blossom as the better forcing arrives. Have been concerned
with the Cold Valley readings across our area...however it looks as
though that by the time the better precipitation does move in...that
most locations will be above freezing. As such...will issue a Special
Weather Statement covering the spottier precipitation at onset...as
mainly interior locations will still likely be below freezing. Will
continue to monitor trends very closely over the next few hours since
any ramp up in the precipitation will mean an icy commute potentially.
Once the first batch of precipitation moves through later this morning into
early this afternoon...there will likely be a lull in the
activity...before the colder air arrives on northwest winds and the
trough axis moves through tonight. This will allow for some light
snow across the area. Snow showers will likely linger in the east
through Friday morning...before tapering off. Any light accumulations
will favor the higher terrain in the far southeast.
Long term...(friday night through wednesday)
issued at 446 am EST Thursday Jan 29 2015
High pressure will take hold of sensible weather to begin this
period. While low pressure that is affecting the region today
develops into another strong coastal low across the northeast US.
This high pressure coupled with decreasing clouds will allow for
decoupling and lows dropping down into the middle to upper teens
area wide. This high pressure will allow mostly sunny skies early in
the day for your Saturday with increasing clouds in the afternoon.
Winds will also become more southwest bringing highs on Saturday into
the upper 30s to lower 40s.
Now the bigger concern continues to be late weekend storm and
confidence remains low in regards to this system. The setup is we
have a developing upper level closed low across the northern Baja California
peninsula and associated developing surface low Saturday morning.
Meanwhile a upper level wave rides over ridging across the northwest
US. Then this is where the models continue to struggle is in the
phasing process that occurs Saturday night in the upper levels.
Earlier the 18z/28 GFS and 12z/28 European model (ecmwf) had a more open wave which
translated to a weaker surface low. This was new based on the
previous runs seen over the past couple of days. The latest 00z/29
run of the GFS develops a stronger low with a bit of a deeper trough
setting up. The 00z/29 European model (ecmwf) does have similarities...however the
surface low pressure is not as deep. One thing that remains with both
models 00z runs is both have a good amount of quantitative precipitation forecast respectively. Another
question that remains is how much cold air stays in place with this
system on Sunday and this will depend heavily on the eventual track
of this surface low. That said have leaned toward a bit colder
through the day on Sunday. Thinking still much of Sunday would lead
to mixing across much of the County Warning Area with more in the way of snow across
the Bluegrass where temperatures remain cooler...however confidence in this
system remains low given the drastic run to run changes seen in the
deterministic models. Also keeping in mind that the ensemble mean has
been quite erratic and given that the 12 perturbations in our system
are erratic explains the lack of continuity. All this said still
think there is a reasonable shot of measurable snow Sunday into
Monday. Another piece to the puzzle to keep in mind is that a more
northerly track shown in earlier runs could allow for more southerly
flow and warmer air and lead to lessening snowfall totals. Although
behind this system expect cold air to filter into all of the County Warning Area
Sunday night into Monday. Also would expect generally falling
temperatures during the day on Monday.
After this the aforementioned low pressure is then forecast to track NE
and continue to deepen along NE Atlantic coast. High pressure will
build east Monday night and expect another cold night with generally
low to middle teens across the region. These temperatures may have to be
adjusted further depending upon if we receive measurable snow. This
high pressure will advance east of the region moving into the day on
Tuesday bringing return flow and welcoming rebound in
temperature...with highs in the middle to upper 30s. That said Wednesday
remains uncertain with yet another system developing and at this point
stuck close to the blend. Did introduce mainly slight probability of precipitation during
that portion of the period.
Aviation...(for the 06z tafs through 06z Thursday night)
issued at 219 am EST Thursday Jan 29 2015
A passing cold front will bring lowering ceilings...precipitation...
and gusty south to southwest winds to the area through Thursday
evening. A strong low level jet developing during the overnight hours
will also allow for low level wind shear between 08 and 14z across
the area. VFR conditions will likely hold on through the early
afternoon...before celings likely come down quickly to MVFR/IFR once
the front moves through the area later this afternoon into early this