-- Discussion containing changed information from previous version are highlighted. --
918
FXUS61 KRNK 041503
AFDRNK

Area Forecast Discussion
National Weather Service Blacksburg VA
1103 AM EDT Sat May 4 2024

.SYNOPSIS...
An upper level trough of low pressure will move across the Mid-
Atlantic Region this weekend resulting in mostly cloudy skies,
widespread showers, and a few thunderstorms. Rainfall amounts
will be highly variable, ranging from a quarter of an inch, to
as much as one inch. Temperatures will be lower today compared
to Friday, winds from an easterly direction.

&&

.NEAR TERM /THROUGH TONIGHT/...
-- Changed Discussion --
As of 1100 AM EDT Saturday...

Key Messages:

1. Rainy and foggy conditions continue.

2. Isolated thunder possible mainly for western and southern
sections of the forecast area.

Scattered rain showers continue this morning, although there are
large area where we are seeing only fog and drizzle instead of
bona fide showers. The eastern portion of our VA counties, and
to a lesser extent NC and WV, were embedded in a wedge of high
pressure strengthened by easterly flow. This was keeping
temperatures cool and thunderstorms out of the area. The
western side of the wedge was bounded by a warm front, and to
the west of this we were seeing heavier showers and an
occasional rumble of thunder.

Scattered showers and isolated thunderstorms continue through
today and into this evening. The wedge stays in place and will
keep the weather damp and foggy.

For this update, adjusted temperatures and dew points, as well
as PoPs, to account for cooler temperatures and breaks in
precipitation.



As of 230 AM EDT Saturday...

Key Messages:

1. Cool easterly wind today. Below normal high temperatures.

2. Widespread light to moderate showers through tonight with
potential for 0.25 to 1.00 of rain. Slight chance thunderstorms.


Cloudy skies observed across the entire forecast area this
morning along with patchy light rain and rain showers. This will
generally be the theme through tonight as lift associated with
an upper level trough persists across the region. Daytime
heating may provide enough CAPE to produce a few thunderstorms,
but not expecting anything severe per cool easterly wind flow
within the boundary layer. Models are hit and miss on the
heavier QPF, advertising a large deviation in rainfall amounts,
the SREF Plumes for many of our climate stations ranging from a
quarter of an inch to as much as 1.5 inches through 8AM Sunday.
The spread in the model data reflects the showery nature of the
precip, but do think we partake in at least a quarter inch of
much needed rain over the next 24 hours. Anything above that is
a bonus.

Wind flow today and tonight will be out of the east. This
combined with mostly cloudy skies will keep temperatures muted
today, down 15 degrees compared to Friday.
-- End Changed Discussion --

&&

.SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
As of 430 AM EDT Saturday...

Key Messages:

1) Wedge of cool/damp air begins to erode slowly on Sunday as a
strong short wave approaches from the southwest.

2) Warmer Monday with increasing chances for thunderstorms,

The wedge of much cooler air that spreads into the region early
Saturday will begin to erode slowly by Sunday afternoon.
Temperatures will moderate back into the 70s for most areas
except perhaps the far northeastern/northern portions of the
CWA. Short wave ridging ahead of a vigorous short wave lifting
northeast from the MidSouth will also help to warm conditions
across the region by Sunday afternoon.

Spotty, mostly light precipitation can be expected again Sunday,
especially during the morning. By afternoon, enough instability
should be present across most of the CWA for isolated to
scattered thunderstorms, especially along/west of I-77. This
disturbance and increasing amplitude of the upper flow/namely
ridging in the eastern U.S. will help to lift the backdoor
front/baroclinic zone back north toward the PA/MD/WV line for
the first part of next week. Consequently, precipitation should
become a bit more spotty and less organized going into Tuesday.

Cool temperatures Sunday mostly in the 60s to lower 70s will
moderate back into the 70s and 80s by Tuesday as heights rise
aloft and the baroclinic zone lifts back north. This will in
turn allow for more sunshine with breaks in the clouds more
prevalent than during the Sun-Mon time frame.

During the period of this forecast, severe weather is not
expected with weak dynamics and increased ridging aloft.
Rainfall amounts in the Sun-Tue time frame should average around
1/2 inch, which given the antecedent dry conditions is not going
to cause any real flooding issues at this time.

/Confidence Levels in Forecast Parameters/
- Moderate to High Confidence in Temperatures,
- Moderate to High Confidence in Precipitation Probabilities,
- Moderate to High Confidence in Wind Direction and Speed,
- Low to Moderate Confidence in Thunderstorm Potential.

&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
As of 500 AM EDT Saturday...

A rather active weather period is expected during this time
frame. To begin the period, look for quite warm conditions as
the upper flow amplifies in response to deep troughing in the
western/central U.S. An initial short wave will lift north of
the area by Tuesday, leaving behind a summerlike air mass over
the Mid-Atlantic/Southeast U.S. 850mb temperatures will reach
their warmest levels of the year so far with a pocket of +20C
air developing across the Shenandoah and Roanoke Valleys for
Wednesday into Thursday. The baroclinic/frontal zone will lift
north of the area Tuesday as this ridging pattern evolves. This
will shunt the main storm track to our northwest with any
significant convection remaining mainly to our west and north
through Wednesday

By Thursday, steady progressing of the central U.S. trough in
combination with it phasing with a northern stream short wave
will bring a good chance of showers and thunderstorms to the
area. Convective parameters suggest that adequate dynamics and
moisture will be present for strong thunderstorms and a few
severe thunderstorms cannot be ruled out Thursday. A strong cold
front advancing into the region from the northwest will also
bring good forcing. The limiting factor for a more significant
threat of severe thunderstorms is very warm air aloft yielding
weak lapse rates. The general pattern Thursday was also
discussed with SPC. Please reference their Day4-8 discussion for
further details on the potential severe weather threat for
Thursday, which at this point is uncertain but certainly non-
zero.

Substantially cooler air spreads into the region behind the
cold front for Friday into the weekend. Temperatures will be
well into the 80s ahead of the front Wednesday and Thursday,
cooling to just the 60s for Friday into the weekend. Minimum
temperatures will dip back into the 30s and 40s by the weekend
as well. Breezy conditions will add a definite chill to the
weekend weather.

Finally, it won`t necessarily be dry going into the weekend as
several models suggest that additional short waves could ride
along the baroclinic zone, located just to our south at this
point, and keep some threat of rain in our forecast going into
the weekend.

/Confidence Levels in Forecast Parameters/
- Moderate to High Confidence in Temperatures,
- High Confidence in Precipitation Probabilities,
- Moderate Confidence in Wind Direction and Speed,
- Moderate to High Confidence in Thunderstorm Potential.

&&

.AVIATION /15Z SATURDAY THROUGH WEDNESDAY/...
As of 230 AM EDT Saturday...

Cloud bases are lowering from the east. A cool easterly wind off
the Atlantic Ocean will bring marine air as far west as the Blue
Ridge resulting in a low IFR Cig today along with some partial
ridge obscurations. Patchy light rain this morning will become
more showery in nature during the day with light to moderate
showers becoming widespread for the afternoon and evening.
Thunderstorm threat appears too low to include in the TAFs
attm but do think some of the more robust convective cells will
contain lightning.

The easterly wind over the area is shallow, observed from the
surface up to about 3000 feet AGL. Above 3000 feet winds are out
of the southwest...the winds above 3Kft providing the steering
current for any deep convection...storm cell movement from SW-
NE.


Extended Aviation Outlook...

SHRA/TSRA with periods of DZ, BR, and MVFR/IFR/LIFR conditions
continue after 18Z Sunday. More diurnally driven -SHRA/TSRA are
expected Monday through Wednesday. This will bring periods of
MVFR ceilings and visibilities at times. Winds Monday through
Wednesday will be SSW and gusty at times.

&&

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

&&

$$

SYNOPSIS...PM
NEAR TERM...PM/SH
SHORT TERM...RAB
LONG TERM...RAB
AVIATION...PM