Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Jackson Kentucky
1055 PM EDT Thursday Jul 31 2014
issued at 1055 PM EDT Thursday Jul 31 2014
Seeing a little convection in our far southeast...being the result of
some surface/boundary layer of convergence. Appears to be some upslope
component on the south side of Black Mountain as well which has been
strong enough to produce a couple of thunderstorm cells right along
or just south of the Kentucky/Virginia state line. The vast majority of the
activity has been outside of our County Warning Area...and the occasional cell that
manages to move into Kentucky weakens quickly. Being of such an isolated
nature...decided to leave any mention of thunder out of the grids and
zones and to address the potential with a graphical Nowcast product.
Also made a few minor adjustments to overnight lows as thin cirrus canopy
has done little to prevent a rapid drop off of temperatures through the
evening...which has been more dramatic in the north and east.
However...middle level clouds will be on the increase and are being
picked up now at a few of our southern stations. Increase in clouds
should help keep overnight lows from bottoming out too much and may
even tend to cause a bit of rebounding where ceilings materialize.
Otherwise updated the zone package to freshen up wording.
Update issued at 836 PM EDT Thursday Jul 31 2014
Forecast is in very good shape this evening. Made some minor tweaks
to the grids for latest hourly observation. Will hold off on any changes to
the zones until next update...when at a minimum wording will be
freshened up to remove evening references.
Short term...(this evening through Friday night)
issued at 355 PM EDT Thursday Jul 31 2014
19z surface analysis shows a weak area of high pressure through Kentucky
to the Middle Atlantic States. To the south...a couple of waves of low
pressure are taking shape...one over the southern Appalachians and
another near bayou country in Louisiana. On radar...a few showers
have developed over the southern Appalachians...but so far east
Kentucky has been clear. On satellite...the earlier low clouds broke
up in the south and a decent cumulus field has formed over the entire County Warning Area.
These clouds have not hampered temperatures much...though...as they
have made it to the upper 70s and low 80s...so far. With the return
of warmer afternoon weather...the dew points have also crept up so
that they are in the middle to upper 50s...and all the while the winds
remain light and variable.
The models are in good agreement aloft as the upper low that has
dominated the weather over the Ohio Valley will retreat to the north
through the short term allowing for more energy to move across the
Tennessee Valley into the day Friday. More significantly...though...a
middle level wave will drop southeast through the plains and into the
middle Mississippi Valley Friday night...starting to carve out another
Node of the eastern trough through the western Ohio Valley by
Saturday morning. The European model (ecmwf) and Gem are a bit quicker and further
east with this development than the NAM and GFS. For now...will
follow a general model blend with some leaning on the specifics from
the hrrr and nam12.
Sensible weather will feature a milder night through east Kentucky
due to an increase in cloud cover and higher dew points. This will
also likely limit the fog development to just the deepest valleys. In
addition to the clouds...a few showers will be possible later
tonight across the eastern parts of the area with more substantial
rains expected later Friday...primarily in the far east. Thunder will
be a possibility later Friday and into the night as a couple of surface
waves pass through the area. Have gone with just isolated thunder
chances...though...as the instability will be less then optimal for
widespread storms into Saturday morning. The clouds tonight and again
Friday night will also limit the ridge and valley temperature
differences so have minimized these. Likewise...temperatures will be
tempered by the clouds and precipitation during the day Friday.
Started with the British Columbia/consshort for the T...TD...and wind grids
through the first 24 hours and then plugged in the consall suite for
the remainder of the short term forecast. Made some small adjustments
to low temperatures tonight and Friday night for some minor ridge
to valley splits. As for probability of precipitation...ended up closer to the mav numbers
from later tonight through Saturday morning rather than the high met
ones tonight and low values for Friday.
Long term...(saturday through thursday)
issued at 300 PM EDT Thursday Jul 31 2014
Generally speaking our weather will be under the influence of a mean
eastern Continental U.S. Trough through the period. Exception will be a short
window of time...dys 6/7...Wed/thur of next week where flow aloft
will be anticyclonic to zonal in nature. This period of short wave
ridging will provide our warmest weather of the extended...allowing
temperatures to rise to more normal summertime levels and higher during the
latter half of the forecast. Models are showing a decent enough
consensus in solutions where deep trough over the eastern Continental U.S.
Gradually lifts out of the area by late dy5...Tue. Additional energy
drops out of Canada by late week...just beyond the extended forecast
window...effectively carving out a new eastern Continental U.S. Trough.
However...considerable disagreement exists between the GFS and a
more consistent European model (ecmwf) with respect to amplitude/structure of the
latter trough. European model (ecmwf) actually develops a stacked upper level low
over the southern Ohio Valley region while the GFS advertises a
lower amplitude trough with its parent low north of the Great Lakes.
For sensible weather...energy rounding the base of deep eastern
Continental U.S. Trough will keep a threat of mainly afternoon and evening
showers and thunderstorms in the forecast through roughly the first
30 hours of the extended. Then we will see warmer and dryer weather
through the middle term. Potential for rain returns at the end of the
forecast period with approach of another system from the west by
dy7...Thu. We can expect a moderation of temperatures through the
extended...peaking out close to 90 for afternoon highs by next
Wednesday...and possibly Thursday.
Aviation...(for the 00z tafs through 00z Friday evening)
issued at 836 PM EDT Thursday Jul 31 2014
In general expecting VFR conditions through the forecast period. Did
include some MVFR fog at loz and sme through the predawn time frame.
But middle level deck will be rolling in during the overnight as well
which may help keep much of any fog from forming. However...exact
timing of most significant cloud cover is in question and guidance is
quite a bit more pessimistic with visibilities. Therefore stayed with a
compromise since model guidance has been doing decently well over
the last two nights. Otherwise...disturbance moving through the south
and into the southern Appalachian Mountains will support some
scattered shower and thunderstorm activity across much of the area
Friday. Included some thunderstorms in the vicinity for now...leaving room/time for fine
tuning of activity at terminals with future taf issuance/S. Winds
will generally be light...backing out of the east/northeast by