-- Discussion containing changed information from previous version are highlighted. --
052
FXUS61 KRNK 291046
AFDRNK

Area Forecast Discussion
National Weather Service Blacksburg VA
646 AM 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 TONIGHT/...
As of 130 AM EDT Saturday...

Key Messages:

1) Humid today with scattered storms mainly in the afternoon,
wit best coverage across the mountains.

Stratocu/stratus across the Blue Ridge and Alleghanys this
morning with a shield of high clouds sliding through the
mountains from the west, will lead to a mostly cloudy sky this
morning. A few showers could pop along the the Blue Ridge into
the NC foothills with low level convergence set up here.

Leaned toward the RAP/FV3 in the near term for pops as these
models are handling the setup better than others, with the 3km
NAM as usual overdoing coverage this morning.

Should see skies gradually scatter out by late morning, which
will help wit heating. SBCAPEs increase to 1000-2000 J/kg in the
mountains this afternoon, less in the east, but expect enough
heating to destablize the airmass. However, limiting factor will
be the cap around 600mb. Will lean toward having widely
scattered convection in the piedmont to better coverage over the
NC mountains into southeast WV, as shortwave approaches by
evening. As far as severe, setup would favor isolated damaging
winds from microbursts given increasing moisture in the
airmass, but still looks marginal and mainly northwest of a
Roanoke to Bluefield line.

Storm coverage may slightly increase this evening in the east if
cap breaks but again low confidence so keeping pops on the low
end til later tonight as front and upper shortwave approach, and
even then higher pops will be relegated to the Alleghanys into
southeast WV, with low chance pops east.

As for temps, with humid airmass, it is harder to heat it up and
with clouds around, leaned toward the ADJMET for highs with
around 90 east to upper 70s to mid 80s west. Heat indices may
max out around 95 in the piedmont, as favoring slightly lower
dewpoints than MAV/MET.

Tonights lows stay elevated with front approaching and
raised RH, with upper 60s to around 70 in the mountains to lower
to mid 70s in the piedmont.

&&

.SHORT TERM /SUNDAY 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 /12Z SATURDAY THROUGH WEDNESDAY/...
-- Changed Discussion --
As of 640 AM EDT Saturday...

Ceilings in the 1-3kft range will improve after 14-16Z, to VFR,
scattering out and/or lifting for a few hours before afternoon
convection begins. Expect sct/bkn 4-8kft clouds in the
afternoon/evening.

TSRA to be widely scattered in the afternoon with less coverage
in the piedmont, and slightly more coverage over the WV/far SW
VA into NC mountains, but timing/model solutions are not
painting enough of a solid picture of when/if storms impact taf
sites, so removed the TSRA from the tafs and put in VCTS, which
could happening from 18z til the end of the taf valid period of
06z/30.

After midnight, sub-VFR returns to the mountains with fog
possible at LWB. Showers/few storms possible overnight but too
low coverage/confidence to have in tafs.

Confidence in the above scenario is moderate.


EXTENDED AVIATION OUTLOOK...

A greater coverage of showers/thunderstorms and associated MVFR
flight conditions are possible Sunday morning as a cold front
nears, then the highest chances moves to the Piedmont in the
afternoon, possibly affecting LYH and DAN.

Could be some fog Sunday and Monday night in the typical LWB/BCB
spots if it rains this weekend.

Monday and Tuesday appear to be VFR as high pressure works in
from the north. On Wednesday isolated TSRA 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...VFJ/WP
NEAR TERM...WP
SHORT TERM...DS
LONG TERM...DS
AVIATION...WP