268
FXUS61 KRNK 201034
AFDRNK

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

.SYNOPSIS...
A stalled front over North Carolina moves north into Virginia
today. This front will continue to bring a chance for heavy
rain and isolated thunderstorms through this evening. 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 215 AM EDT Saturday...

Key Messages:

1) Stalled front remains draped across the VA/NC border.

2) Heavy rain from thunderstorms expected through tonight.

Frontal boundary remains stalled across the VA/NC border this
morning. Heavy associated with the front has dwindled somewhat
with loss of instability, but a few heavier downpours remains.
Hardest hit areas were across southern Patrick and Carroll
Counties where locally as much as 4 inches of rainfall have
fallen.

Front lift north slowly by this afternoon and hi-res guidance
advertising another round of heavy rainfall, possibly developing
by late morning across the VA/NC border region. This will be
within a zone of precipitable water values now creeping into the
2" range, which will lead to very efficient rainfall rates.
Nearly stationary storms with very heavy rainfall rates will be
closely monitored, especially across North Carolina and
southern Virginia where there has already been localized heavy
amounts of rainfall.

Coverage of rain/storms continues to expand into early
afternoon/evening and then subsiding again tonight as the front
drifts back south into the Carolinas.

Widespread cloud cover today, along with expected rain should
limit heating. 70s in the mountains and low to mid 80s in the
lower elevations.

&&

.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 /12Z SATURDAY THROUGH WEDNESDAY/...
As of 630 AM EDT Friday...

A mid-level disturbance will track across the area today. This
disturbance will push a boundary northward, increasing the
chance for showers and a few thunderstorms through this
afternoon/evening.

Widely varying flight categories can be expected due to areas of
fog/low clouds for another hour or two when fog dissipates and
then sub-vfr due to clouds and rain/storms through the evening
hours.

Off and on sub-vfr should continue tonight as rain tapers off,
but fog development seems probable once again.

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...None.
NC...None.
WV...None.

&&

$$

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