706
FXUS61 KRNK 201553
AFDRNK

Area Forecast Discussion
National Weather Service Blacksburg VA
1153 AM EDT Sat Jul 20 2024

.SYNOPSIS...
A stationary front extends west to east along the Virginia,
North Carolina border. This front will be the focus for clouds,
scattered to numerous showers and thunderstorms for the next
several days. The weather pattern stays active through the
beginning of next week with periods of showers and thunderstorms
and gradually warming temperatures.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 1115 AM EDT Saturday...

Key Messages:

1) Flood Watch for VA/NC border counties...Highway 58
Corridor...for potential for flash flooding until 8PM.

2) Stalled front remains along VA/NC border and will be focus
for clouds and periods of rain.

3) Heavy rain from slow moving showers and thunderstorms
expected through this evening...heaviest along frontal boundary.

A stationary front near the Virginia, North Carolina, border
will be the focus for slow moving showers and thunderstorms
through this evening...with primary focus for heavy rain along
the Highway 58 corridor across extreme southern VA. Much of this
area needs the rain (due to drought), but rain rates of 2+
inches an hour will result in rapid response within small
drainages and produce flooding of poor drainage areas. As such
will maintain Flood Watch for flash flooding in this area until
threat ends this evening. PWAT near 2" observed in GSO sounding
this morning and anticipate high rain efficiency with the shower
activity. Any training of showers/storms may result in observed
localized rainfall of up to 4 inches.

Convective Allowing Models (CAMS) show crux of current deep
layer moisture convergence moving east along the Hwy 58 corridor
from MTV-DAN then exiting the CWA mid-afternoon. Depending on
how much clearing and heating takes place behind this wave of
shower activity, a second round of deep convection may form
along this same corridor this evening...the surface front really
not moving that much through the remainder of the day and
remaining a source of moisture convergence.

Outside of this axis of heavy rain, the remainder of the CWA
will still experience considerable cloud cover with scattered
showers and a few rumbles of thunder. Cloud cover is muting the
temperatures, so lowered the Tmax a few degrees from previous
forecast for this afternoon.

Tonight, loss of daytime heating should allow weakening of deep
convection. Clouds are still expected to persist.

&&

.SHORT TERM /SUNDAY THROUGH TUESDAY NIGHT/...
As of 100 AM EDT Saturday...

Key Points:

1. Increasing chances of precipitation through the period.
2. Locally heavy rain possible, especially Tuesday into Tuesday
night.
3. Temperatures slightly above normal for this time of year.

A look at the 19 July 12Z NCEP Ensemble Mean 500 mb Geopotential
heights shows a persistent ridge, trough, ridge pattern across CONUS
during this portion of the forecast. The location of the trough and
the Southeast US ridge will place our region within a pattern of
southwest flow aloft. At the surface, ensemble averaging washes out
a lot of the specific detail, but the general trend is for a frontal
boundary initially south of the region to gradually move to a
location north of our region.

Output from the 19 July 12Z Ensemble Situational Awareness Table
shows 850mb temperatures will average around +17C to +18C through
the period. Precipitable Water (PW) values across the region are
expected to be progressively higher heading from northwest to
southeast across the region. For Sunday through Monday night, values
will range from roughly 1.50 to 2.00 inches. For Tuesday into
Tuesday night, values increase to the 1.75 to slightly over 2.00
inch range. The high end of this range touches the 90 to 97.5
percentile of the 30 year climatology.

The above weather pattern points toward increasing chances of
precipitation as we progress into mid-week with a front lifting
north across the area. Once north of the region, the area will
remain within warm and moisture rich lower troposphere, conducive
for additional rain. Locally heavy rain will be possible for parts
of the region, especially Tuesday into Tuesday night as PW values
top 2.00 inches over parts of the area. Temperatures are expected to
be slightly above normal for this time of year.

Confidence in the above weather scenario is moderate to high.

&&

.LONG TERM /WEDNESDAY THROUGH FRIDAY/...
As of 100 AM EDT Saturday...

Key Points:

1. Continued good chances of rain through the period.
2. Locally heavy rain possible, especially Wednesday and Thursday.
3. Temperatures slightly above normal for this time of year.

A look at the 19 July 12Z NCEP Ensemble Mean 500 mb Geopotential
heights shows limited changes to the ridge, trough, ridge pattern
over CONUS the first half of the week. The only notable change is a
bit of flattening of the amplitude of the trough while and Southeast
US ridge builds a bit more. Additionally, ridge in the west weakens
in response to a trough moving into the Pacific Northwest. At the
surface, a frontal boundary remains positioned north of the region
as high pressure strengthens over the Southeast US.

Output from the 19 July 12z Ensemble Situational Awareness Table
shows 850mb temperatures will trend gradually milder through the
period. For Wednesday expected a range around +17C to +18C during
the afternoon hours. By Friday, numbers closer to +18C to +19C are
expected. PW values Wednesday and Thursday will range from roughly
1.75 inches across the northwest portions of the area to slightly
over 2.00 inches across the southeast. The high end of this range
touches the 90 to 97.5 percentile of the 30 year climatology. On
Friday, values decrease slightly to the 1.50 to 2.00 inch range.

The above weather pattern continues to offer good chances of
precipitation across the region with locally heavy rain possible,
especially Wednesday into Thursday. Temperatures will average
readings slightly above normal for this time of year.

Confidence in the above weather scenario is moderate.

&&

.AVIATION /16Z SATURDAY THROUGH WEDNESDAY/...
As of 1145 AM EDT Saturday...

A stationary front near the VA/NC border will be the focus for
persistent cloud cover and clusters of showers and
thunderstorms. CIGS/VSBYS will be highly variable across this
area this afternoon and evening.

Through the TAF period expect widely varying flight categories
due to areas of showers and low clouds favoring sub-vfr.

AVIATION OUTLOOK...

An upper level trough over the Mississippi Valley and an upper
level ridge in the western Atlantic will keep an active weather
pattern through the beginning of next week with periods of MVFR
showers and thunderstorms.

Late night fog and stratus with result in IFR to MVFR
visibility, otherwise VFR.

&&

.RNK WATCHES/WARNINGS/ADVISORIES...
VA...Flood Watch until 8 PM EDT this evening for VAZ032-033-043-044-
     058-059.
NC...Flood Watch until 8 PM EDT this evening for NCZ003>006.
WV...None.

&&

$$

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