Scientific Forecaster Discussion
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Area forecast discussion
National Weather Service Blacksburg Virginia
352 am EDT Sat Aug 24 2019
high pressure over the Great Lakes will extend down the east
slopes of the Appalachians today through Monday. A cold front
will cross through the eastern United States during the middle
of next week.
Near term /through tonight/...
as of 320 am EDT Saturday...
Surface front was across Tennessee and North Carolina with high
pressure over the Great Lakes. High pressure will build down
the east slopes of the Appalachians with The Wedge of cooler air
deepening throughout the day. Above the cooler near surface air
west to southwest winds were lifting warm, moist air over the
front. Radar showed both the lighter rain over the Roanoke and
New River valleys and the showers and isolated thunderstorms
over the mountains and foothills of North Carolina where there
was still a small amount of instability. The more stable air
will advance south with The Wedge this morning, ending the
potential for thunderstorms before noon.
Enough of the stable low cloud layer with higher overrunning clouds
above to limit the amount of heating today. Will be using an
atypical diurnal temperature curve across southern Virginia and
northern North Carolina today. The northern edge of the clouds and
leading edge of the drier airmass had progressed into norther
Virginia. Models were bringing the clearing down to Route 460 today
and to the Virginia/North Carolina border overnight. Any sun at this
time of year will allow temperature to warm quickly. Maximum
temperatures will be highly dependent on when clearing takes place.
Will be trending cloud cover forecast more toward the slower NAM
Short term /Sunday through Tuesday/...
as of 330 am EDT Saturday...
Wedge boundary should reside well into the Carolinas by Sunday, with
related ridging trailing to a large anticyclone centered over
northern New England. East to northeast flow will transport shallow
moisture upslope against the Blue Ridge, contributing to a
considerable extent of cloud cover areawide, along with periods of
light rain to the east slopes of the Ridgeline through Sunday. Rain
showers may be intermittent or resemble drizzle, so we're not
talking about a substantial amount of rain from this - around a few
hundreths to a tenth of an inch. Best potential for breaks in the
overcast during the daytime hours looks closer to the I-64 corridor;
but even in these areas, should still be a fair amount of clouds
around. 850 mb temps will be cooler than normal, ranging in the low
teens celsius. Given spatial variation in cloud cover, uncertainty
regarding the high temp forecast Sunday is higher than it normally
would be. Kept highs in the 60s to mid 70s, coolest across the
mountains; but if any sustained breaks occur, late-August sun angle
could force highs to be several degrees warmer. Lows in the 50s to
lower 60s with mostly cloudy skies.
Though wedging is maintained Monday, it should begin to weaken
somewhat as the large-scale pattern undergoes nuanced changes. An
area of disturbed weather as of this morning was off the East Coast
of FL, which the National Hurricane Center is monitoring for
possible tropical or subtropical development as it stays close to
the southeast coastal waters into early next week. For the latest on
this system, please refer to the latest statements from the National
Hurricane Center. This circulation, combined with the strong
anticyclone over New England, will enhance the easterly pressure
gradient over the mid-Atlantic. Moisture is drawn back landward for
light showers across at least our eastern counties on Monday. Likely
light enough rain to not be a washout; though some level of
uncertainty on how far westward this moisture may extend, which
necessitates keeping at least slight chance pops for most areas from
the Blue Ridge east. Across our western/southwestern counties (esp.
West of I-77), a shortwave trough aloft over the Tennessee Valley should
induce increasing isentropic lift to support slightly better chances
for rain showers. Instability progged is too limited to warrant
thunder mention attm. Overnight, higher pops in the chance range are
confined to the west tied to this trough aloft. 850 mb temperatures
also begin to modify into the +12-14c range, which in spite of
mostly cloudy skies results in highs/lows a couple degrees milder
than Sunday...upper 60s to mid/upper 70s for highs, and lows in the
Wedge looks to substantially weaken Tuesday with moderating temps
and lightening winds shifting to southeast/south. Upper trough from
Monday should induce enough, though weak, instability to pop garden
variety showers and thunderstorms. Best chances are across the
western and northern two-thirds of our forecast area. Degree of
instability is limited by lack of higher dewpoints and cooler temps.
Expect variably cloudy skies - less further south/east, with
temperatures back closer to late-August normals in the 70s to
Long term /Tuesday night through Friday/...
as of 230 PM EDT Thursday...
A much cooler and drier period appears to be in store for the
into early next week. Highs will be 10 to 15 below what has
recently been experienced with daily highs in the 70s or even
upper 60s and overnight lows will be 50s west to low 60s east.
Will certainly feel different. The surface high will shift north
and east toward mid-week with increasing southerly flow and
warmer temperatures along with renewed chances for mainly
An approaching front toward mid- to late late week will
possibly trigger a few stronger thunderstorms in an increasingly
warm and unstable air mass. A trough of low pressure currently
along the Florida coast has been given a 30 percent chance of
tropical storm formation near the SC/NC coast in the latest NHC
5- day outlook but impacts on the local weather look to be
negligible or minimal at this writing.
Aviation /08z Saturday through Wednesday/...
as of 215 am EDT Saturday...
A surface cold front had moved into central North Carolina.
Behind the front, warm moist air will continue to move over
incoming cool surface wedge. A low stratus deck and/or fog will
move across the area IFR or lower ceilings along the central
Appalachians and foothills this morning with MVFR ceilings for
the rest of Virginia and North Carolina. There will be some
gradual improvement in ceilings in the late morning through the
afternoon. The northern edge of the clouds may get close to klwb
and klyh during the afternoon.
Confidence was below average on ceilings and average on
visibility and wind.
Extended aviation discussion...
Improving conditions with more VFR will be possible for Sunday,
pending just how far south of the mid Atlantic area the front
progresses. Some MVFR showers are possible in the southwest
Virginia and northwest North Carolina on Monday. Scattered
showers and thunderstorms with MVFR conditions are expected
Tuesday. On Wednesday, scattered showers and thunderstorms will
be mainly east of the Blue Ridge. Conditions will be VFR in the