Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Charleston WV
227 PM EDT Thursday Sep 18 2014
high pressure...centered to our north...moves off northeast coast
Friday. Cold front around late Sunday into Sunday night..
Near term /through Friday/...
area remains under control of high pressure that will move into
eastern Ontario/southern Quebec tonight. Weather maker tonight
will be the surface flow turning southeasterly giving upslope
clouds for the eastern slopes and a filling middle level trough
axis. The middle level trough should sling some moisture back into
the mountains as well in the form of middle level cloud cover.
Examination of the NAM bufr soundings shows enough of a saturated
layer Friday to warrant slight chance probability of precipitation over the southern
zones. No thunder expected with a middle level cap in place limiting
the vertical extent. And while coverage will be sparse...not
everyone will remain dry...especially in the southwest Virginia
Met guidance reigns supreme for the overnight lows...and used this
as the baseline for the temperature forecast tonight. Temperatures
tomorrow will be nudged upwards with the flow starting to shift to
a southerly direction.
Short term /Friday night through Sunday/...
quiet pattern will continue in the short term. Broad upper troughing
over the northeast Continental U.S. Friday will gradually break down with zonal
flow Saturday as another upper trough moves eastward across the
upper Midwest into the Great Lakes. No major changes from previous forecast
with latest data. Surface high pressure centered to the north at the
outset of the period continues to shift eastward off the New England
coast by 00z Sat with resultant bl winds setting up out of the
southeast. Low level moisture will bank up against the eastern mountains
and have continued a slight chance of showers in that general area
as such...again which previous forecast had a good handle on. Latest nam12
moisture profiles hint at some potential for convective showers
further west over the central WV lowlands but at this
point...moisture availability at around the 850mb-800mb level may be
somewhat overdone as well as the Colorado-located instability. Thus for
now...left the forecast dry for all of The Lowlands. Maximum temperatures
generally upper 70s lowlands still look good.
Dry weather under mostly sunny/clear to partly cloudy skies will
continue Friday night and Saturday with less low level moisture
available. Only change of any real significance was to ramp up
temperatures on Saturday by a good 3-5 degrees for much of The Lowlands.
Temperatures at 925mb prognosticated around 20c-22c should result in low 80s for
many locations...a trend which is also bearing out in latest MOS
guidance. Temperatures will be slightly warmer Sat night versus Friday night
with south/southwest winds and increasing clouds with an approaching
cold front moving into the lower Great Lakes region by 12z sun.
Long term /Sunday night through Thursday/...
used wpc thinking with some minor tweaks. Cold front will push
southeast of the mountains Sunday night with high pressure taking
control by Monday afternoon. The high should be in control through
the remainder of the period...resulting in dry and seasonably cool
Wpc temperatures looked good and were generally used.
Aviation /18z Thursday through Tuesday/...
expect overall clearing through the evening as diurnal heating
After 00z tonight...the mountains will be under the influence middle
level clouds and southeast flow at the surface. This should bring
clouds into the ekn area and halt the formation of the Tygart
Valley fog for that terminal. Further south at bkw...southeast
flow brings IFR ceilings late tonight...lingering into Friday with
drizzle possible. NAM bufr soundings were the most useful tool for
the bkw taf...showing the timing of boundary layer saturation and
thickness of the saturated layer resulting in drizzle potential
Elsewhere in The Lowlands...expecting a largely typical late
Summer nocturnal fog pattern. Relied on the lamp guidance for
timing of IFR/LIFR visibilities.
Forecast confidence and alternate scenarios through 18z Friday...
Forecast confidence: medium.
Alternate scenarios: NAM may be too aggressive with the eastward
extent of the upsloping IFR ceilings at bkw. Ekn fog may not begin
or erode at forecast time.
Experimental table of flight category objectively shows consistency
of weather forecast office forecast to available model information:
h = high: taf consistent with all models or all but one model.
M = medium: taf has varying level of consistency with models.
L = low: taf inconsistent with all models or all but one model.
UTC 1hrly 18 19 20 21 22 23 00 01 02 03 04 05
EDT 1hrly 14 15 16 17 18 19 20 21 22 23 00 01
crw consistency h h h h h h h h h h M M
heights consistency h h h h h h h h h h h h
bkw consistency h h h h h h h h h h h h
ekn consistency h h h h h h h h h M l l
pkb consistency h h h h h h h h h h h M
ckb consistency h h h h h h h h h h h h
After 18z Friday...
IFR conditions possible Sunday in showers/storms.