Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Jackson Kentucky
423 am EDT Tuesday Sep 23 2014

Short term...(today through wednesday)
issued at 346 am EDT Tuesday Sep 23 2014

Forecast has changed little from previous forecast package. Strong
upper level ridging...coinciding with strong surface high
pressure...will continue to be the main weather driver over the
short term period /today through tomorrow/. Upper level pressure
gradients will lesson today compared to yesterday...and we will also
lose the influence of the northern jet across the region. As
such...temperatures will modify slightly warmer...while still
remaining quite below seasonable normals. Highs today should reach
the low 70s across much of the region under sunny skies and light NE
winds. Dew points will be very low across the region...with some of
the highest elevations dipping into the 20 degree range through this

Kept mention of valley fog in for weather pattern will
be similar to that of last night. Strong subsidence will trap
moisture in the valleys and near bodies of water...while
temperatures quickly drop off under the influence of strong
radiational cooling. Overnight lows should be a couple degrees
warmer than this morning...but once again...still well below normal.
Ridges could see middle to upper 40s...while the valleys could dip back
into the low 40s once more.

Similar story for high pressure remains overhead. Very
little moisture across the area will cut down on dew points as well
as cloud potential. Temperatures will continue to modify upwards
with abundant sunshine and a slight wind shift to the east. Highs
Wednesday afternoon will be much closer to seasonable
norms...reaching the middle and upper 70s.

Long term...(wednesday night through monday)
issued at 405 am EDT Tuesday Sep 23 2014

The period is expected to begin with a deep upper trough nearing the
Pacific upper level ridge centered over The Four Corners
region with another centered over the Southern Plains/lower MS valley and
extending northeast into the middle MS valley region and another upper
level ridge centered in the vicinity of Bermuda. The main jet will be
displaced well north of the US/Canadian border from the central to
eastern Continental U.S.. however...there will also be weaknesses/weak upper
level troughs in between these upper level ridge centers. The region
should begin the period with one of these centered to our east and

This upper level trough initially centered to our east and southeast
should move into the northeast and Middle Atlantic States by Thursday night
and Friday per the 0z guidance with another weakness initially to our
northwest moving to the middle MS valley/plains states at that point
with ridging building across the southeastern Continental U.S. And from the
northern plains into the Great Lakes region. This will put the region
under the influence of upper ridging to begin the weekend. Model
agreement then decreases later in the period with the upper level low
that is expected to move southwest across the plains states from
Friday into Saturday and merges with another weakness over the
Southern Plains/Rio Grande Valley...and when or if it gets kicked
north and east by the trough working into and across parts of the
western US from the end of the week and early next week. The 0z
European model (ecmwf) is about 12 hours quicker than the 0z GFS in shearing this
system on into the northern rockies region and is slower to bring the
plains upper level system and deeper moisture into the Ohio Valley and
MS valley region and is slower working this upper system across the
area as compared to the 12z run from the 22nd. There have also been
some recent GFS runs that are slower to bring the plains upper level
system into the area and the deeper moisture compared to the 0z run.

Overall...the pattern should be rather benign into at least the first
part of the weekend...with temperatures and dewpoints gradually
moderating. With surface high pressure initially centered to our north and
northeast and then surface pressures rise over the Great Lakes with the
ridge building to our north Thursday into Friday and the surface ridge remaining
in place there into the weekend...some moderate Ridge/Valley
temperature splits will remain possible along with patchy River
Valley fog from at least Wednesday night into Friday night and possibly
Saturday night as well. Clouds will increase late in the period as
well as chances for precipitation. At this time...we opted to go more with
persistence and held of on any probability of precipitation until Sunday and Monday...though
the model consensus blend would bring some slight probability of precipitation into the west
and southwest on Sunday. Confidence in the timing of this system late
in the period remains below average.Instability might become great
enough for an isolated thunderstorm on Monday...depending on timing
of the moisture increase and upper level system.


Aviation...(for the 06z tafs through 06z Tuesday night)
issued at 126 am EDT Tuesday Sep 23 2014

Latest visible imagery is showing fog development across the valleys
of the eastern Kentucky coalfields...with rapid expansion over the last
hour. The fog is currently affecting ksjs...and should continue to
thicken to below Airport mins through early morning.
Unfortunately...given the location of this site...visible and ceilings may
bounce around a bit through the night from lower to higher
categories. Northeast flow should keep it out of kjkl...ksme...and
kloz...other than maybe an hour or two of MVFR as the fog rises from
the valleys near dawn. Once fog dissipates in the morning with
daytime heating...high pressure and strong subsidence will be the
driving force for weather during the day. Light winds /generally out
of the NE/ and clear skies can be expected at all taf sites.


Jkl watches/warnings/advisories...


Short term...jmw

National Weather Service Glossary of Abbreviations