649
FXUS61 KRNK 301546
AFDRNK

Area Forecast Discussion
National Weather Service Blacksburg VA
1146 AM EDT Sun Jun 30 2024

.SYNOPSIS...
A cold front pushes through the area today with a better chance
of storms. Less humid air arrives Monday, and sticks around into
Tuesday. Temperatures start to heat up again by the 4th.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 1100 AM EDT Sunday...

Key Message:

1) Unstable Airmass With Front To Lead To A Few Strong/Severe Storms
This Afternoon

2) Continued Muggy But Clouds/Storms Should Keep Heat Somewhat
Limited.

Steamy airmass covers entire forecast area with dewpoints in the
70s. Its uncomfortable to say the least... HVAC units having to
work a little harder to remove the moisture from the air. This
entire airmass is getting compressed ahead of an approaching
cold front...regional PWAT values AOA 2 inches.

Weather focus this afternoon will be on the potential for
showers and thunderstorms. The airmass certainly supports them,
but underlying question is where is the best opportunity. The
morning RNK and GSO soundings indicated westerly winds both
surface and aloft. Westerlies over the mountains tend to
suppress deep convection due to downward motion lee off the
ridges, but since there is no capping inversion, think we will
see at least some scattered activity over the mountains. Better
convergence is expected over the piedmont where the westerlies
over the mountains meet the southwesterly winds over the
piedmont. This lee trof or convergent area should provide the
better focus for deep convection this afternoon and evening.

Another area to watch is a mesoscale convective vortex (MCV)
that is moving east across north central TN. The models do not
seem to be picking up on this feature very well, but experience
would support clustering of deep convection inof this feature
as it moves east and into the NC High Country and Carolinas
later in the day.

That said, will maintain at least chance pops for scattered
showers across the entire CWA but likely pops or numerous
showers and thunderstorms for the VA/NC piedmont, and across the
southwest mountains (Mount Rogers) of VA and into the NC High
Country. Whether any of this becomes severe will be highly
dependent on buoyancy and organization at the time. Wind
profiles are unidirectional with little or no directional shear.
This would imply a predominantly multicellular storm mode. The high
PWATs suggest thunderstorm cores will be very rain efficient
with water loading resulting in some healthier downdraft winds.
Forecast SBCAPE of 2000 g/kg is respectable...so would think
damaging isolated severe gusts would be the modus operandi for
the stronger storm cells this afternoon and evening.

By in large today will be the best chance for getting any rain.
Once the front comes through tonight, pops go way down until
later in the week.

Until the front clears the area, humidity levels will remain
elevated. Temperatures will also remain quite warm with highs
this afternoon about 5-8 degrees above normal. Temperatures in
the Piedmont are expected to reach the lower to mid 90s. Heat
indices may reach 100 degrees from Reidsville, NC- Danville to
Farmville, VA. But still lower than advisory level of 105.

Storms should push southeast out of the area this evening with
subsidence starting clear skies out behind the convection. Could see
a few shower/storms linger as well in the far southwest with the
front stretching west-southwest across NC/TN. Drier air begins to
reach the mountains/foothills overnight allowing temperatures to
drop into the 50s. Could take longer to get the cooler/drier air to
the piedmont but still less humid than this morning with lows in the
lower to mid 60s.

Forecast confidence is moderate/average on storm coverage today and
severe threat as well as temps/sky cover. High confidence on
clearing skies and lower humidity later tonight.

&&

.SHORT TERM /MONDAY THROUGH WEDNESDAY NIGHT/...
As of 100 AM EDT Sunday...

Key Points:

1. Cooler and drier for Monday and Tuesday.
2. Still, mainly dry, but slightly warmer for Wednesday.

A look at the 29 June 00Z NCEP Ensemble Mean 500 mb Geopotential
heights shows a trough axis extending from eastern Canada south into
New England on Monday. Additionally, a broad latitudinal
oriented ridge across the southern half of CONUS with an
associated high center over the Arklatex region. Tuesday into
Wednesday, the trough flattens and lifts northeast, allowing for
building heights across our region. A shortwave trough is
expected to be moving through the Great Lakes region on
Wednesday. At the surface, on Monday, high pressure will be
centered over the Upper Ohio Valley while low pressure and a
cold front will be over the Dakotas. On Tuesday, the center of
high pressure shifts east into the western Atlantic. Low
pressure and a cold front advance into the Upper Mississippi
River Valley. By Wednesday, the high is still centered over the
western Atlantic while the cold front is positioned over the
Great Lakes and Lower Ohio Valley region.

Output from the 29 June 12Z Ensemble Situational Awareness Table
shows 850mb temperatures around +12C to +14C over the region on
Monday. These values correspond to the 2.5 to 10 percentile of the
30-year climatology. By Tuesday, values are only slightly higher,
around +14C to +16C. For Wednesday, values are expected to range
from around +18C to +20C. The top end of this range, over western
parts of the region, correspond to the 90 to 97.5 percentile of the
30-year climatology. Precipitable Water values on Monday will range
from 0.50 to 0.75 inch, or within the 1 to 10 percentile of the 30-
year climatology. Values increase only slightly on Tuesday to around
0.75 inch. By values are back to a more normal 1.00 to 1.25 inch for
this time of year.

The above weather scenario offers a forecast where cooler and drier
high pressure will impact our weather for Monday and Tuesday. By
Wednesday, the center of the high will be far enough east that we
will start getting a south or southeast return flow. This will begin
the process of advecting milder temperatures a more moisture into
the region. Some of this moisture may be realized in isolated
showers/storms over the southwest portion of the region thanks to
weak upslope slow, daytime heating within a slightly more moist,
thus unstable, lower troposphere, and a weaker cap than eastern
sections. The vast majority of the region however will be
precipitation free.

Confidence in this weather forecast is moderate to high.

&&

.LONG TERM /THURSDAY THROUGH SATURDAY/...
As of 100 AM EDT Sunday...

Key Points:

1. A return to hot and humid conditions.
2. Locally heavy rain producing showers and storms expected each day.
3. Confidence is low on timing/location of the showers/storms this
far out in time.

A look at the 29 June 00Z NCEP Ensemble Mean 500 mb Geopotential
heights shows a shortwave trough over the Canadian Maritimes and one
over the Upper Mississippi River Valley on Thursday. A broad trough
continues to be position over the southern half of CONUS, with its
high center over the Southwest US. Heading into Friday and Saturday,
the high centered over the Southwest US builds a bit farther north,
while the troughiness over Southeast Canada/Northeast US becomes a
bit more amplified. At the surface, on Thursday, Independence Day, a
cold front or lee side trough is expected to be over the region. By
Friday into Saturday, little movement of this feature is expected.

Output from the 29 June 12Z Ensemble Situational Awareness Table
shows 850mb temperatures  are expected to reach the +20C to +22C
range. This places the entire region within at least the 90 to 97.5
percentile of the 30-year climatology with the area near the crest
of the Blue Ridge from roughly Roanoke, VA southwest into the
mountains of North Carolina over the 99 percentile. For Friday, the
values are expected to be similar, but with the 99 percentile
shifted east into the Piedmont of NC. On Saturday, values are
expected be slightly less, +19C to +21C, but still within the 90 to
97.5 percentile for most of the region. Precipitable Water values on
Thursday are expected to be around 1.75 to 2.00 inches, with western
and northern parts of the area within the 90 to 97.5 percentile of
the 30-year climatology. For Friday, expect another juicy day with
values ranging from 1.75 to 2.00 inches. On Saturday, numbers fall
just a little to 1.50 to a little over 1.75 inches.

A frontal boundary/trough is expected to arrive and remaining over
the region for Independence Day and linger into the start of the
weekend. Additionally, with the position of the high remaining to
our east, we will see a continuation of a warmth and moisture feed
into the region. Add to these factors expected well above normal
Precipitable Water values, and we may be looking at multiple days of
showers and storms, with most capable of producing locally heavy
rain. The biggest question remains where will the focus for the most
activity be located? This may change from day to day as outflow from
storms help to reorient the location of the front/trough across the
region.

Confidence in the above weather forecast is moderate to high in
terms of the broader scale features including well above normal
temperatures and the potential for locally heavy rain. However,
confidence is low at this point in pinpointing just where and for
how long of time showers and storms will exist.

&&

.AVIATION /15Z SUNDAY THROUGH THURSDAY/...
As of 640 AM EDT Sunday...

Showers/few storms possible this morning across ROA/BCB/BLF/LWB
corridor so have some VCSH/VCTS with tempo thunder/showers
here. Mainly VFR outside of any storms. Appears better chance
for storms will be across the VA Piedmont into NC this
afternoon, so have more chance for thunder at DAN, with VCTS
elsewhere. Still aside from MVFR cigs at times in the mountains
this morning, should be VFR unless storms hit the airports
overhead which could bring vsby/cigs to MVFR/IFR. Heavy rain
could possibly occur along with some stronger gusts with storms
especially along/east of a UKF-CHO line.

Should see shower/storms shift east/southeast after 00z and
clearing skies for most outside of the mountains of WV and
southside VA/DAN but still VFR. Fog appears likely toward 12z
Monday as clear skies and light winds along with cooler air over
wet ground sets up fog formation mainly BLF/LWB where IFR or
lower possible.

Confidence in the above scenario is moderate to high.


EXTENDED AVIATION OUTLOOK...

Monday-Wednesday appear to be VFR as high pressure works in
from the north. Could be some fog Monday night in the river
valleys and for areas that received significant rainfall.
Storm chances increase by Thursday ahead of a front so sub-VFR
possible.

&&

.RNK WATCHES/WARNINGS/ADVISORIES...
VA...None.
NC...None.
WV...None.

&&

$$

SYNOPSIS...WP
NEAR TERM...PM/WP
SHORT TERM...DS
LONG TERM...DS/WP
AVIATION...WP