378
FXUS61 KRNK 040041
AFDRNK

Area Forecast Discussion
National Weather Service Blacksburg VA
841 PM EDT Wed Jul 3 2024

.SYNOPSIS...
Heat and humidity will increase Thursday through Saturday. Shower
and thunderstorm chances rise by Thursday afternoon and
continue through the weekend as a front stalls in the area.

&&

.NEAR TERM /THROUGH THURSDAY/...
As of 830 PM EDT Wednesday...

Key Messages:

1) More humid tonight.

2) Showers and storms return Thursday on Independence Day.

Little to no change needed to the forecast for tonight. Surface
dew points have returned to the 60s. The latest Convective
Allowing Models showed a majority of the thunderstorms will be
from 19Z/3PM through 00Z/8PM on Thursday.

Previous discussion
As of 150 PM EDT Wednesday...

A subtropical ridge continues to dominate our weather pattern
here in the Mid-Atlantic, but a surface high that has been
just to our north slides off the east coast by Thursday and
turns our surface level flow from southerly to southwesterly.
At the same time, a mid-level disturbance will move around the
north side of the sub-tropical ridge and into our area sometime
Thursday afternoon. This will herald the return of scattered
showers and storms to the area Thursday afternoon and evening.

This won`t be the only thing that could put a damper on holiday
activities though. As a result of the ridge and increased
southerly flow from the high off the Atlantic coast, heat and
humidity will continue to rise. Heat indices east of the Blue
Ridge will be in the upper 90s, and a few locations nearer
central VA could see a heat index over 100. With the sun out
before showers fill in, this will feel quite sweltering, and
folks should remain hydrated and try to stick to shade.

&&

.SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY NIGHT/...
As of 1215 PM EDT Wednesday...

Key Points:

1. Well above normal temperatures but with temperatures trending
slightly cooler each day.
2. Heat Index values over 100 deg possible Friday afternoon east
across portions of the Piedmont.
3. Daily chances of late afternoon/evening showers and storms
Thursday night through Friday night.
4. Showers/Storms chances throughout the day on Saturday, ending
Saturday night.

A look at the 3 July 00Z NCEP Ensemble Mean 500 mb Geopotential
heights shows a building upper ridge across the west coast of the US
through the period. A shortwave trough axis is expected to be over
the Upper Mississippi River Valley Thursday night into Friday. This
feature is expected to amplify moves slowly shift eastward eastward
into the Ohio Valley through Saturday night. A ridge of high
pressure remains over the Southeast US through the period. A the
surface, low pressure Thursday night into Friday is expected to move
through the Great Lakes region with a cold front trailing southwest
into the Mid-Mississippi River Valley. By Saturday into Saturday
night, this same front is expected to approach, cross and then head
southeast of our region with high pressure build in behind it.

Output from the 3 July 00Z Ensemble Situational Awareness Table
shows 850mb temperatures steadily increasing Thursday night through
Friday. By Friday afternoon, values of +20C to +22C are expected
across the area with high end of this range over the Foothills and
Piedmont region of VA/NC. Here values are expected to be higher than
the 99 percentile of the 30-year climatology with values over the
97.5 percentile for the remainder of the region. For Saturday,
values are only slightly cooler, by perhaps 1C. This decrease places
the eastern half of the region with the 90 to 97.5 percentile of the
30-year climatology.

The above scenario points towards a Friday that is expected to be a
bit hotter what we are expecting on Thursday. Given values are
expected to be well into the top end of the 30-year climatology,
guidance is likely to be too cool, gravitating towards values closer
to climatology. Our forecast will continue to offer temperatures a
few degrees above the deterministic model output. Temperatures are
expected to remain well above normal for Saturday, and still a bit
above normal for Sunday. A concern for Friday will be the heat index
value. Many locations with the Lower James, Lower Roanoke and Dan
River Valleys on Friday are expected to see the heat index value
reach, or top 100 degrees. Far eastern sections of the forecast
region (approximately those areas along and east of a Yanceyville,
NC to Buckingham, VA line) could see values top the 105 degree mark.
If these values persist within the forecast, a Heat Advisory would
be warranted for parts of most of this far eastern region as we get
closer to Friday.

Precipitation chances will come in the form of showers and storms
within a hot and humid airmass both in advance of an approaching
cold front on Thursday night through Friday night, and then
coincident to the passage of the front on Saturday. Saturday night
should see rapidly decreasing chance of showers and storms from
northwest to southeast as the front exits the region. Given the
uncertainty in timing and location, I`ll keep the POP values under
the likely category at this time from Monday onward.

Confidence in the above weather conditions is moderate to high.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
As of 1215 PM EDT Wednesday...

Key Points:

1. Above normal temperatures but with values trending cooler through
the period.
2. After a bit of a break in showers/storm on Monday, look for a
return of afternoon/evening showers/storms for the region,
especially the mountains Monday through Wednesday.

A look at the 3 July 00Z NCEP Ensemble Mean 500 mb Geopotential
heights shows the trough to our east is expected to remain nearly
stationary, but gradually become more amplified, with high pressure
remaining over the Southwest US and also over the far Southeast US. At
the surface, high pressure will briefly be over the region on
Sunday. A cold front is expected to move into and across our area
Tuesday into Wednesday. This feature is depicted on the mean
ensemble very poorly which suggested a lot of variation within the
timing and strength of the system among the various model members.

Output from the 3 July 00z Ensemble Situational Awareness Table
shows 850mb temperatures on Sunday are expected to range from +18C
to +20C, with the high end of this range over the NC mountains. The
+20C numbers touch the 90 to 97.5 percentile of the 30-year
climatology. For Monday, numbers inch up a bit to the +20C to +21C
range for the area, with most of the area with in the 90 to 97.5
percentile of climatology. For Monday, values are expected to be
almost the same, but perhaps +19C to +21C, with the warmest sections
in the east. On Wednesday, temperatures slide a bit more, with
numbers in the +17C to +19C range.

Temperatures through this portion of the forecast will still be
above normal, but just not as high as the end of the current week.
High pressure entering the region will bring a bit of a break to the
shower and storms activity for Sunday. However, southern sections
may still be close enough to the departing front for some isolated
to scattered afternoon coverage.

On Monday, a cold front will approach our region, arrive on Tuesday,
and perhaps linger overhead through Wednesday. The result will be a
return of primarily afternoon/evening showers/storms for the region,
with the best coverage over the mountains. Additionally, the greater
expanse of clouds and the precipitation chances will also partially
responsible for the expected slightly cooler temperatures.

Confidence in the above weather scenario is moderate.

&&

.AVIATION /01Z THURSDAY THROUGH MONDAY/...
As of 830 PM EDT Wednesday...

High pressure off the Carolina coast will continue to bring
warm and humid air to the region. VFR conditions are expected
tonight. There may be MVFR along the Greenbrier and New Rivers
but that will depend on clearing of the scattered to broken high
clouds over the region.

Some mid-level clouds will begin to fill in from the northwest
in the early morning hours Thursday. There is a slight chance of
showers and storms beginning in WV, potentially impacting BLF
and LWB before 18Z/2PM, but confidence is low that it will
begin that early.

The latest Convective Allowing Models showed a majority of the
thunderstorms will be from 19Z/3PM through 00Z/8PM on Thursday.
The storms are expected in the earlier part of that time range
at KLWB and KBLF and not until after 21Z/5PM at KLYH and KDAN.
Confidence was not high not high enough to include in the body
of the TA due to the random nature of convective initiation, but
added VCTS to all local TAFs sites after 18Z/2PM.

Average confidence for ceiling, visibility, and wind.

OUTLOOK WEDNESDAY NIGHT THROUGH SUNDAY...

Wednesday night-Saturday night: SCTD SHRA/TSRA remain possible
as a storm system continues impacting the region. Flight
category reductions are likely, especially Friday and Saturday afternoon
and evening.

Sunday and Monday: the probability of showers and thunderstorms
decreases behind a cold front. Prevailing conditions will be
VFR.

&&

.CLIMATE...
As of 200 AM EDT Wednesday...

Record highs and warmest lows temperatures for July 4th and 5th.

Thursday 07/04/2024
Site  MaxT Year  HiMin Year
KBLF    92 1957    68 2018
KDAN    99 1925    74 1999
KLYH    98 1966    76 1902
KROA    99 1999    74 2018
KRNK    94 1966    71 1941


Friday 07/05/2024
Site  MaxT Year  HiMin Year
KBLF    93 1948    71 1969
KDAN   103 1919    76 1926
KLYH    98 2012    75 1900
KROA   100 1999    76 2012
KRNK    94 1930    78 1949

&&

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

&&

$$

SYNOPSIS...AMS
NEAR TERM...AMS/VFJ
SHORT TERM...DS
LONG TERM...DS
AVIATION...AMS/VFJ
CLIMATE...RCS