-- Discussion containing changed information from previous version are highlighted. --
083
FXUS61 KRNK 291828
AFDRNK

Area Forecast Discussion
National Weather Service Blacksburg VA
228 PM EDT Sat Jun 29 2024

.SYNOPSIS...
High pressure off the Atlantic coast will keep us in a southerly
flow of moisture today, with increased humidity and a chance of
showers and storms. A cold front pushes through late Sunday with
a better chance of storms. Less humid air arrives Monday.

&&

.NEAR TERM /THROUGH SUNDAY/...
As of 1130 AM EDT Saturday...

Key Messages:

1) Humid today with spotty storms this afternoon, with best
coverage across the mountains.

2) Increased confidence in organized line of the showers and
thunderstorms developing Sunday afternoon east of the Blue
Ridge.

Latest radar imagery is clear, with satellite imagery
indicating that clouds are gradually transitioning from the
blanket of low clouds to a mix of clouds and sunshine. Humid as
well as dewpoint temperatures per latest surface observations
range from the upper 60s to low 70s. Between the widespread
clouds and the high dewpoints, we are looking at the potential
for record high minimum temperatures for this date in the
Blacksburg and Bluefield areas.

Our warm & muggy conditions are thanks to deepening southerly
windflow around high pressure that is pushing east off the
Atlantic coast, while a low pressure system moves across the
upper Great Lakes, dragging a cold front eastward in its wake.
As daytime heating continues to increase, surface-based CAPES
will push into the 1,200-1,500 J/Kg range, supporting
development of spotty & disorganized showers and thunderstorms
that will develop after 2pm. Steering winds of 10 to 15 mph
will keep these cells moving, however still a potential for
locally heavy downpours as precipitable water values continue to
climb, reaching 1.5 to 1.7 inches this afternoon. Given
increasing humidity and scattered clouds, highs today will range
from the mid to upper 80s along and west of the Blue Ridge, and
reach into the low 90s further east.

Expect muggy conditions to remain tonight as moisture pools
ahead of the approaching cold front. A pre-frontal wave of
energy passing along the Ohio Valley tonight will trigger
showers and thunderstorms, with highest chances across southeast
West Virginia into southwest Virginia, potentially reaching as
far east as the Blue Ridge before fading away. Overnight lows
will hold in the upper 60s to the mid 70s.

As an upper level trough approaches during Sunday afternoon,
will then be keeping a eye out for redevelopment of
thunderstorms across the Piedmont, with scattered cells
developing in the foothills, then gradually increasing in
coverage as they approach a line stretching from Lynchburg to
Martinsville. Given these storms will develop around maximum
daytime heating, potential exists for wet microbursts to produce
damaging wind gusts. Heavy downpours are also likely as
precipitable water values increase to around 2 inches, or 2
standard deviations above normal for late June, though storms
are expected to remain progressive across the Piedmont.

&&

.SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY NIGHT/...
As of 1245 AM EDT Saturday...

Key Points:

1. Sunday...Above normal temperatures with a threat of showers and
storms containing damaging winds and locally heavy rain.
2. Monday and Tuesday...Drier and notably cooler.

A look at the 28 June 00Z NCEP Ensemble Mean 500 mb Geopotential
heights shows for Sunday a shortwave trough move towards and then
across our region. By Monday, this feature will be centered over the
Canadian Maritimes while high pressure builds into our region. On
Tuesday, the center of an upper high strengthens over the Southeast
US. A shortwave trough is centered over the Dakotas in an otherwise
nearly zonal flow pattern along the US/Canadian border.  At the
surface, a cold front will cross our region on Sunday with high
pressure behind it building over the Upper Mississippi Valley. On
Monday, high pressure progresses east and becomes centered over our
area. On tuesday, the center of the high shifts into the western
Atlantic with a southeast to south flow developing over our region.

Output from the 28 June 12Z Ensemble Situational Awareness Table
shows 850mb temperatures on Sunday with in the +18C to +21C range,
with the high end of this range across the Piedmont. Additionally,
the +20C to +21C values fall within the 90 to 99 percentile of the
30-year climatology. On Monday, drier and cooler air arrives with
values falling into the +14C to +16C range with the low end of this
range in the east, and also within the 2.5 to 10 percentile of the
30-year climatology. On Tuesday, values increase only slightly,
averaging around +16C. Precipitable water values on Sunday through
mid-day are expected to range from 1.50 to 2.00 inches with the high
end of the range across eastern parts of the area. Much of the area,
especially eastern sections, will have values above the 97.5
percentile of the 30-year climatology. Sunday night into Monday,
much drier air arrives with values falling into the 0.60 to 0.75
range by Monday afternoon. This range corresponds to the 1 to 10
percentile of the 30-year climatology. For Tuesday, values increase a
little bit to the 0.75 to 1.00 range.

The above weather scenario has a cold front crossing the region on
Sunday. Very high precipitable water values offers the potential for
locally heavy rain from any given shower or storm. Coverage of
showers and storms will be greatest during the morning and mid-day
time period, especially across eastern parts of the area. The latest
SPC Convective Outlook for Sunday after 8am offers a Marginal Risk
of severe weather for most of the region. Areas near, north, and
east of Lynchburg, VA will have a Slight Risk. For the entire
region, damaging winds will be the greatest risk. Sunday night, the
showers and storms will end from northwest to southeast as the front
exits the region. Much drier air will move into the region for
Sunday night and especially on Monday. Temperatures will be notably
lower Sunday night into Monday as compared to 24-hour prior. The
trend for cooler weather will continue Monday night into Tuesday.

Confidence in the above weather pattern is moderate to high.

&&

.LONG TERM /WEDNESDAY THROUGH FRIDAY/...
As of 1245 AM EDT Saturday...

Key Points:

1. Trending hotter and more humid over the Independence Day holiday.
2. Potential for an increase in showers and storms July 4 and 5, but
confidence in amount, timing and location is low at this time.

A look at the 28 June 00Z NCEP Ensemble Mean 500 mb Geopotential
heights shows an upper high maintain its location over the Southeast
US for Wednesday. A weak shortwave trough is expected to be over the
Great Lakes region within an otherwise nearly zonal flow along the
US/Canadian border. Thursday into Friday, the Southeast US high may
weaken slightly but hold fast over that region. The weak shortwave
trough along the US/Canadian border continues is slow progression
eastward. At the surface on Wednesday, a ridge of high pressure
remains over the Southeast US. A cold front will be moving through
the Ohio Valley with its tail potentially reaching the Tennessee
Valley. For Thursday, the Southeast US ridge will continue to
dominate that portion of the nation with a weak cold front
potentially across our area. By Friday, there is question as to
whether the front stalls over the area or makes progress eastward.

Output from the 28 June 12Z Ensemble Situational Awareness Table
shows 850mb temperatures in the +18C to +21C range with the high end
of these value across Southeast West Virginia. Additionally, these
values fall within the 90 to 99 percentile of climatology. For both
Thursday and Friday, values will range from +20C to +22C. This
places the entire forecast at least at the 90 percentile of the 30-
year climatology with the foothill region of Southwest Virginia and
Northwest North Carolina at or over the 99 percentile. Precipitable
water values on Wednesday are expected to be around 1.50 inches. For
Thursday values increase to 1.75 to 2.00 inches, or into the 90 to
99 percentile of the 30-year climatology. On Thursday, values are
expected to average 1.75 inches.

The above weather scenario keeps a persistent area of high pressure
across the Southeast US. A cold front may be able to move through
the northern end of this ridge Thursday into Friday. A big question
will be to what extent will convection along this feature be
potentially squelched by the broad are of high pressure. Warmth and
moisture will return to the area thanks to anti-cyclonic flow around
the center of the high.

Confidence in a warming trend for the region is moderate to high.
Confidence in the degree in which the cold front will or will not be
able to be effective in prompting convection is low to moderate.

&&

.AVIATION /18Z SATURDAY THROUGH THURSDAY/...
-- Changed Discussion --
As of 200 PM EDT Saturday...

Spotty showers developing across the mountains this afternoon
per latest radar imagery. Otherwise, a SCT to BKN CU field is
present across the Mid-Atlantic, with bases mainly in the 4kft
to 6kft range.

Showers, a few of which will develop into thunderstorms as the
afternoon progresses, will remain confined mainly west of the
Blue Ridge this afternoon. Convection is expected to remain
progressive to the northeast at around 10kt for those location
that do receive it. Expect downpours that will reduce visibility
to 1/2SM for brief periods of time, as well as localized storm-
produced wind gusts to 40kt. Convection will decrease at sunset
as daytime heating ends, though showers will linger into the
early morning hours as an upper level disturbance approaches
from the northwest.

This disturbance will bring a round of showers and thunderstorms
across southeast West Virginia into southwest Virginia, most
likely during the 30/08Z to 30/12Z timeframe. The best chances
for this activity occurring will be for BLF/LWB/BCB. Lower
chances for ROA and LYH as the activity diminishes in the
downslope flow. Westerly wind shift behind this activity will
also make for MVFR ceilings at BLF/LWB and possibly BCB that may
linger into late Sunday morning.

Confidence in the above scenario is moderate to high.


EXTENDED AVIATION OUTLOOK...

Coverage of showers/thunderstorms and associated MVFR flight
conditions are expected Sunday afternoon east of the Blue Ridge
as a cold front moves across the central Appalachains. Most
likely timing of this activity is between 30/18Z and 30/23Z,
before activity exits to the east.

Monday and Tuesday 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. On
Wednesday, isolated TSRA is possible in the mountains as a warm
front and pre-frontal trough nears, but still mainly VFR.
-- End Changed Discussion --

&&

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

&&

$$

SYNOPSIS...NF/VFJ/WP
NEAR TERM...NF/WP
SHORT TERM...DS
LONG TERM...DS
AVIATION...NF