Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Jackson Kentucky
1047 PM EST Friday Dec 19 2014

Update...
issued at 1047 PM EST Friday Dec 19 2014

Current conditions across the area feature cloud cover finally
starting to overspread the area along with some weak radar returns
finally making it into southeastern Kentucky. Adjusted the forecast
to increase the cloud cover for the system moving into the area. The
only other factor that needed adjusted was the temperatures. Still a
few breaks in the cloud cover hanging around till a bit later in the
night has resulted in some of the valleys dropping off a bit lower
and have adjusted low temperatures for tonight. With this...snow from the
incoming system from the southwest will last a little longer into the
after dawn hours. This precipitation is still expected to be light so
accumulations will still be a dusting at most. As of 0330z...in
western Kentucky...precipitation is developing a bit further north and moving
northeast...at this point...not alot of that is reaching the surface
and models still have this activity fizzling out before it makes it
into northeastern Kentucky so will continue to leave precipitation out in
the north but this area of precipitation needs to be monitored. A new zone forecast product
has been issued for these updates.

Update issued at 639 PM EST Friday Dec 19 2014

So far this evening the main forecast challenge looks like it will be
how far temperatures will fall in the first part of tonight before the middle
and upper level cloud cover associated with a system tracking to the
south and east of eastern Kentucky move over the area. This occurrence will
likely cause temperatures to become steady and hold near the freezing mark
for lows overnight. For now...these low temperatures seem to be on track but
will need to monitor for drastic changes in temperatures along with the
possibility of precipitation towards dawn. This evenings update will not
require a new zone forecast product.

&&

Short term...(this evening through Saturday night)
issued at 350 PM EST Friday Dec 19 2014

19z surface analysis shows high pressure still in control of the weather over
the Ohio Valley. The lower clouds over the northeast are finally
responding to the drier air from this high by eroding off beneath a
layer of high clouds spreading in and thickening from the southwest.
Temperatures across the area vary from the chilly low 30s in the
north to the lower 40s in the far southeast. Meanwhile...with light
winds in place over the area...dewpoints vary from the low 20s north
to the middle 20s south.

The models continue to be in good agreement with a couple of
dampening waves moving through the region over the next 36 to 48
hours. The first of these will pass to the south late tonight and
into Saturday morning...while a bit better defined one will move
just north of east through the central Ohio Valley during the day
Saturday. The models also continued their trend of these waves being
weaker and of less substance. Later Saturday night...heights will
rise ahead of the next more significant trough. Accordingly...have
followed a blended solution and leaned more closely to the nam12 and
hrrr.

Sensible weather will feature clouds thickening and lowering through
the night with a chance of light snow or rain moving into our
southernmost areas after midnight. Do not expect much in the way quantitative precipitation forecast
out of this with most of the precipitation falling as just virga or
flurries/sprinkles. Given the dry dewpoints the precipitation rate will likely
not fall fast enough to contribute to wetbulbing...keeping it as
liquid longer than normal in these type of situations. The weak
southern wave will move away from Kentucky by noon Saturday with even
some clearing possible before evening. This will make for a tricky
temperature forecast into Saturday with a wide variance between the
cooler met numbers and the much milder mav ones. As we are leaning
more toward the still rather dry nam12 solution will also favor the
cooler met maximum T numbers. Another cool night follows into Sunday
morning as some clearing will be possible from the west.

Again used the bcconsshort as a starting point for the T/TD/wind
grids for the first 20 hours or so before populating with the
superblend thereafter. Only minor adjustments were made for terrain
effects both tonight and Saturday night given the clouds...but did
drop the maxt down a couple of degrees from the too warm blend. As
for probability of precipitation...ended up close to a blend of the wetter met and dry mav
tonight into Saturday...and then dry on Saturday night.

Long term...(sunday through friday)
issued at 351 PM EST Friday Dec 19 2014

Active pattern continues to be the story for much of the long term
period. Sunday does look quiet for the beginning of the period with
mostly clear conditions...however clouds will increase from south to
north through the day into Sunday night. This is system one which
will come from the southern branch and will bring best chances of all
rain Sunday night into Monday. This system is expected to progress NE
but there is questions as to the phasing of this southern and
impending northern branch system. Given some uncertainty will keep
slight chance of precipitation Monday into Tuesday.

Then focus shifts to the northern system as upper level low and
surface low approaches the Great Lakes Monday night. The models are
still not in agreement on what happens with this system in terms of
timing and evolution. The GFS develops a secondary low later that
moves NE across the middle Atlantic Wednesday...while the European model (ecmwf)
develops a low across Tennessee and Ohio Valley then moves it straight NE
Tuesday night. These timing and evolution issues will play a role in
how much precipitation and precipitation types. Either way thinking Wednesday we
will see rain/snow to snow as we move through the day into the night
across portions of the region...however it does look like it will be
more wrap around later Wednesday. The wrap around snow showers
should die down as we move through the day Thursday with system
tracking into the far NE US by Thursday night. Surface high pressure
off to the south and upper level ridging will build east across the
southeast US Thursday night into Friday. This will lead to return flow and
high temperatures warming into the lower 50s by Friday.

&&

Aviation...(for the 00z tafs through 00z Saturday evening)
issued at 639 PM EST Friday Dec 19 2014

Tafs...for tonight and into tomorrow will not contain forecasts below
MVFR but will still be quite challenging. MVFR cloud cover to the
north in Ohio is ever so slowly creeping to the east. This should stay
north of sym and sjs but could creep south a bit if the middle and upper
level cloud cover streaming up from the south is any slower to move
over the area. For now most places will be VFR overnight with light
and variable winds. Towards dawn...mainly jkl...loz...and sme will
see MVFR cloud cover due to precipitation skirting along the Kentucky and Tennessee
border and east into extreme eastern Kentucky. Most precipitation should stay out
of the area but have put vcsh in most taf sites for the chance of
snow showers and rain showers. Unless this activity moves further
north...most places will be MVFR in the south and VFR in the north.
Any low cloud cover will exit the area by tomorrow afternoon.



&&

Jkl watches/warnings/advisories...
none.
&&

$$

Update...shallenberger
short term...greif
long term...dj
aviation...shallenberger

National Weather Service Glossary of Abbreviations