Scientific Forecaster Discussion
fxus61 krnk 221150
Area forecast discussion
National Weather Service Blacksburg Virginia
750 am EDT sun Sep 22 2019
high pressure will remain across the area through the remainder of
the weekend. A weak cold front will bring some isolated to scattered
showers to areas west of the crest of the Blue Ridge on Monday
afternoon and evening. High pressure quickly returns to the region
with the next chance of precipitation being a very small chance on
Thursday as another weak front enters the area.
Near term /through tonight/...
as of 240 am EDT Sunday...
Patchy fog across the area this morning will dissipate fairly
quickly after sunrise. An upper level ridge will be parked across
the region today and provide for mostly sunny to sunny skies and
high temperatures some ten to fifteen degrees above normal and light
and variable winds. Overnight, the ridge will begin to deamplify a
bit in response to the approach of a cold front to the west.
Temperatures will continue on the mild side with overnight low
temperatures around ten to fifteen degrees above normal for this
time of year.
Confidence in the above portion of the forecast is high.
Short term /Monday through Wednesday night/...
as of 415 am EDT Sunday...
An upper trough early in the week will move rapidly across the
Great Lakes atop the unseasonably massive 594-596dm upper ridge
dominating the central and eastern part of the U.S. This will
allow a weak cold front to move through the forecast area late
Monday into early Tuesday. The front is expected to be moisture
starved with the large upper high in place blocking any substantial
connection to deeper moisture. As such, the cold front will
pass through the forecast area within a westerly flow regime,
causing most, if not all, of the shower activity to dry up as
the front crosses the mountains Monday afternoon. Bottom line,
little or no quantitative precipitation forecast is expected with this frontal passage, most of
which will be confined to areas west of the Blue Ridge, and even
then generally netting less than a tenth of an inch.
The front is not expected to reach the area until late afternoon
into the evening. Thus, temperatures Monday will be well above
normal once again, especially east of the Blue Ridge. It will
essentially be another "hot" day as we close in on October.
Highs will range from lower 80s in the west to lower 90s in the
Piedmont, with any 70s confined to the higher terrain in the
west. Clouds will help hold down the heat some in the west.
A secondary trough moving through the Great Lakes Tuesday into
Wednesday along with the Post frontal conditions in place will
allow for closer to normal temperatures Tuesday under dry air
advection with surface high pressure becoming reestablished.
High temperatures will range from the 70s west to the lower and
mid 80s east. Minimum temperatures will cool into the 50s across
much of the area.
For the remainder of the period, the upper ridge will return
with a vengeance as the flow across the Continental U.S.
Becomes highly amplified with a deep trough in the western U.S.
Teleconnecting to the aforementioned massive 596dm ridge in the
eastern U.S. The ridge center will start midweek across the Gulf
and then amplify into the Appalachians and mid-Atlantic region
by Fri/Sat. Following the European model (ecmwf) vs. The GFS, which has had a
much better handle on temperatures this Summer and especially
this month, 850mb temperatures will close in on the +20c to
perhaps even +22c by the end of the week. MOS guidance strongly
leans toward climatology in the extended periods, thus
advertising highs only upper 70s via GFS MOS and lower 80s European model (ecmwf)
MOS. Even these readings are nearly 10 degrees above normal.
Given the number of days in the 90s we have recorded this month
and looking at the upcoming patter, unless clouds or easterly
flow become well established, which appears unlikely at this
point, it appears feasible to expect temperatures well into the
80s and some readings near 90 will be feasible before the week
comes to a close, especially east of the Blue Ridge. In essence,
high temperatures should average 15-20 degrees above normal
with minimum temperatures around 10-15 degrees above normal.
Rainfall chances through the period remain little to none under
the ridge. There are some indications that a tropical system may
sneak under the ridge across South Florida toward the weekend,
but it should remain well south of our area blocked by the
/Confidence in forecast parameters/...
temperatures - moderate to high confidence in above to well
above normal temperatures.
Precipitation probabilities - moderate to high confidence in
precipitation probabilities remaining low and confined mainly
to the western mountains.
Winds - moderate to high confidence in mostly light and variable
winds through the period.
Thunderstorm threat - moderate confidence in only limited 10-20%
chance of thunderstorms through the period, mainly west of the
Long term /Thursday through Saturday/...
as of 415 am EDT Sunday...
By Thursday expect a rapid transition to high amplitude flow as
noted above with a full latitude long wave trough on the West
Coast and an eastern U.S. Ridge of high pressure. Most models
indicate the eastern ridge may gain an amplitude to something
more typical of July or August with a 594-596 dm 500h anticyclone
centered somewhere vcnty of the mid-MS valley drifting squarely
over our forecast area by the weekend. As such this should
effectively block moisture over a big piece of real estate to
include our forecast area through next weekend, and most likely
prolonging/exacerbating the very dry d0-d1 drought conditions
developing throughout the region and insuring that we will
finish September with below normal rainfall in most areas.
CPC 6 to 10 day outlook advertising temperatures well above
normal and precipitation below normal. With 850mb temperatures
returning to the +16 to +20 degree range, the possibility for a
few more 90-degree days are still within reach in spite of the
shortening diurnal cycle and fall equinox.
Aviation /12z Sunday through Thursday/...
as of 745 am EDT Sunday...
Patchy early morning fog will dissipate by 13 or 14z. Otherwise,
strong high pressure aloft and surface high pressure just to our
southeast will result in another partly sunny/partly cloudy day
with warm temperatures and light southwest winds. Model
soundings continue to show a notable layer in the 040-060 range
where moisture is trapped under an existing strong marine layer
inversion. This will once again yield fairly widespread broken
ceilings in this range of 040-060 throughout the late morning
into the late afternoon, becoming scattered after sunset. Late night
fog and indefinite ceilings in the fog will develop at the usual
sites (e.G., Klwb, kbcb, etc.) After 08z Monday morning.
Otherwise, the taf valid period will be mostly VFR with light
/Confidence in forecast parameters/
ceilings - moderate to high,
visibilities - moderate to high,
winds - moderate to high,
thunderstorm threat - none.
Extended aviation discussion...
A weak cold front may bring scattered MVFR showers late Monday.
Strong high pressure aloft hen builds in behind the front with
a return to VFR conditions during the days and some IFR valley
fog during the nights through the later half of the week.