015
FXUS61 KRNK 050247
AFDRNK

Area Forecast Discussion
National Weather Service Blacksburg VA
1047 PM EDT Thu Jul 4 2024

.SYNOPSIS...
Exceptionally warm and muggy air continues to pool to the south
of a stationary front situated near the Ohio River, while a
series of upper level disturbances passing across the region
will trigger rounds of spotty showers and thunderstorms through
Saturday. A weak cold front will pass across the Mid-Atlantic on
Saturday night into early Sunday. Spotty showers and
thunderstorms will remain in the forecast for early next week as
an upper level trough develops over the central United States.

&&

.NEAR TERM /THROUGH FRIDAY/...
As of 1045 PM EDT Thursday...

Key Messages:

  - Probability of rain lowered for the rest of the night.

  - Added fog for tonight

Showers have ended across the region. No change to the chance of
rain in southeast West Virginia Friday morning.

IR satellite images showers high clouds rapidly eroding over the
mountains and foothills. Fog was starting to develop as the
clouds cleared out.

Made minor adjustments to temperatures for the rest of the night
based on current observations and trends shown in the NBM and
gridded LAV guidance.


Previous discussions:

As of 810 PM EDT Thursday...

Leading edge of band of thunderstorms was advancing into central
North Carolina and eastern Virginia. Showers behind the more
intense part of this band extended back into the Virginia and
North Carolina piedmont. Based on the current speed and
direction, the west edge of the rainfall will be east of
Charlotte and Buckingham Counties by 11PM.

As clouds clear out late this evening, expecting fog to develop.

No changes to overnight temperatures at this time. Surface dew
points in the 70s will result in muggy conditions for the rest
of the evening.

As of 215 PM EDT Thursday...

Keeping an eye on scattered showers and a few thunderstorms
which have developed across the mountains this afternoon in an
exceptionally warm and humid airmass. Precipitable water
measured from this morning`s sounding was 1.72 inches, and it`s
likely that value has now risen above 1.8 inches as deep
moisture continues to pool ahead of a stationary front draped
near the Ohio River. Surface observations in spots where these
cells have passed overhead indicate they are efficient rainfall
producers, with rates in a few of them reaching 1" to 2" per
hour. However, the activity is expected to remain disorganized
and progressive, so believe the flooding threat will remain
localized. The severe threat will remain localized as well given
downsloping with the westerly motion of this activity, in
addition to limited shear aloft, both of which help to limit
storm intensification.

The other concern is heat index values reaching above 100 in
spots across the Piedmont through around 5 pm this evening north
of Highway 460, when showers and storms will bring rain-cooled
relief to the area. Locations further south, especially the
Southside area, may miss out on the scattered activity until
early evening when storms arrive in that area.

Rapid update weather forecast models seem to be in good
agreement that showers and storms will have diminished by 8 pm
for areas west of Highway 29, with activity fading quickly
further east. Expect warm and muggy conditions overnight, with
overnight lows ranging from the mid and upper 60s across the
mountains, to the low 70s across the Piedmont.

For Friday, upper level ridging over the Mid-Atlantic will
remain in place, with winds shifting more southwesterly. With no
change in airmass across our area, will again experience
unusually warm conditions across the region. Afternoon heat
index values are expected to reach above 105 degrees for large
portions of the Piedmont, most likely during the 1 pm to 5 pm
timeframe, but will issue a Heat Advisory from 11 am through 8
pm for those few areas that heat up sooner and/or remain hot
longer. Subtle upper level disturbances will again pass across
the region as well, and will trigger another round of spotty
showers and thunderstorms. This activity will again be capable
of producing locally heavy downpours and gusty winds.

Confidence in the above scenario is moderate to high.

&&

.SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY NIGHT/...
As of 1215 PM EDT Thursday...

Key Points:

1. Cooler weather than what is expected today and Friday but
still slightly above normal.

2. Good chances of heavy rain producing showers and storms
along and advance of a cold front passage Friday night through
Saturday.

A look at the 4 July 00Z NCEP Ensemble Mean 500 mb Geopotential
heights shows a shortwave trough moving from the Upper
Mississippi River Valley into the Great Lakes Friday night into
Saturday. Saturday night through Sunday night a longer wave
trough develops over the Upper and Middle Mississippi River
Valleys, and remains nearly stationary through this period. At
the surface, Friday night into and through Saturday, an area of
low pressure will progress from Michigan to southern Quebec. Its
associated cold front will first approach, and then cross our
region. Saturday night into Sunday, high pressure moves over our
area, but the cold front will still need to exit our area on
Saturday. By Sunday night, the surface high weakens in response
to an approaching front over the Upper Mississippi Valley and
winds across our region trend south.

Output from the 4 July 00Z Ensemble Situational Awareness Table
shows 850mb temperatures Friday night into Saturday within the
+18C to +21C range across the area with the high end of this
range across eastern sections of the region. Additionally, areas
with values of +20C to +21C fall within the 90 to 97.5
percentile of the 30-year climatology. For Saturday night
through Sunday night, values drop slightly and are expected to
be more within the +18C to +20C range. A look at Precipitable
Water (PW) values shows a distinct maximum around 2.00 inches
immediately in advance of an west to east moving cold front
Friday night. The farther away from this front, especially to
its west, the lower the PW. Values over roughly 1.75 inches fall
within the 99+ percentile of the 30-year climatology. On
Saturday, with the cold front still not quite out of the the
region, still expected PW value around 1.75 to 2.00 inches
across the far southeast portion of the region. Far western
parts of the region will be closer to 1.25 inches. Saturday
night through Sunday night, PW values of 1.25 to 1.75 will be
common across the area, with the highest amounts across
southeast sections.

The above weather scenario offers a Friday night with organized
convection in the form of showers and storms moving west to
east across the region. The greatest concentration should be
immediately along and advance of cold front. This front does not
clear the southeast portion of the area until either the late
afternoon or early evening on Saturday. Given the very high PW
values for this time of year, locally heavy rain could be
possible from any of the stronger showers or storms. Effective
bulk shear is expected to be weak, or around 20 to 25 kts nearly
parallel to the orientation of the cold front. This pattern
could more easily allow for training of showers/storms, adding
to the potential for locally heavy rain accumulations. Given our
current drought conditions, any flooding from this activity
would be likely confined to locations of poor drainage or urban
effects. On Sunday, high pressure is expected to take a firmer
hold on our weather pattern allowing for drier and less humid
conditions. The one question mark will be the southeast portion
of the region. This area may still be close enough to the
departing front to have some isolated to scattered
showers/storms during the afternoon hours. Sunday night, if any
area was not already rain-free during the daytime, it will
become rain-free during the night.

Confidence during this portion of the forecast is moderate to
high with the biggest question mark being the position of the
cold front Saturday night into Sunday and its influence on our
weather.

&&

.LONG TERM /MONDAY THROUGH THURSDAY/...
As of 1215 PM EDT Thursday...

Key Points:

1. Above normal temperatures.

2. Active period with daily chance of showers and storms.

A look at the 4 July 00Z NCEP Ensemble Mean 500 mb Geopotential
heights shows a long wave upper level trough over the Middle
and Upper Mississippi River Valleys that slowly flattens and
shifts northeast into and across the Great Lakes region by
Thursday. Concurrent to this slow progress of the upper trough,
high pressure builds over the Southwest US with the western
extent of another upper ridge over the Southeast US. At the
surface, high pressure will remain across the western Atlantic.
A slow moving trough will inch through the Great Lakes and Ohio
Valley region, keeping our area with a good warmth and moisture
feed. While this trough is the result of the ensemble averaging,
a look at some deterministic guidance suggests perhaps a cold
front passage that either stalls over the region, or returns
north as a warm front.

Output from the 4 July 00z Ensemble Situational Awareness Table
shows 850mb temperatures are expected to range from +18C to
+20C on Monday and Tuesday, and be slightly cooler in the +17C
to +19C range Wednesday and Thursday. The values on Monday and
Tuesday at the top end of the range touch the 90 to 97.5
percentile of the 30-year climatology. Regard the PW, values
creep back higher Monday through Thursday with values within a
couple tenths of an inch of 1.75 inches across the region.

The above weather scenario will place our region within a
continuous pattern of good feed of warmth and moisture into the
region. This will promote the lower portions of the troposphere
to be generally more unstable with afternoon heating and/or with
the passage of some form of lifting mechanism. While the broad
ensemble offers the region will remain on the southeast side of
persistent central CONUS trough, individual ensemble members and
other deterministic guidance offers the potential of a cold
front passage sometime either Tuesday or Tuesday night. This
front then either stalls over the region, or after shifting
south, returns north again over the region as a warm front.
Regardless, our overall pattern will be one with daily chances
of showers/storms with above normal temperatures. Given the
uncertainties in the position/timing of any fronts impact our
region, confidence is not high in trying to pinpoint when any
particular region or timeframe will be likely to see measurable
precipitation. Am still inclined to keep POPs sub-60 percent.
However, if I had to pick one day of the four to place likely
POPs, Tuesday/Tuesday night across western sections, would be my
choice. Will need to explore the thoughts of neighboring
offices and collaborate accordingly.

Confidence in this portion of the forecast is moderate to high
regarding temperatures and the fact that it will be active with
showers and storms. However, confidence is not very high in
terms of timing and location of time periods with the highest
probability save what what discussed regarding Tuesday/Tuesday
night.

&&

.AVIATION /03Z FRIDAY THROUGH TUESDAY/...
As of 820 PM EDT Thursday...

Leading edge of band of thunderstorms was advancing into central
North Carolina and eastern Virginia. Showers behind the more
intense part of this band extended back into the Virginia and
North Carolina piedmont. Based on the current speed and
direction, the west edge of the rainfall will be east of
KDAN by 02Z/10PM.

As clouds clear out late this evening, expecting MVFR to IFR fog
to develop. KBCB and KLWB may have a few hours of LIFR fog after
midnight.

Little change in the airmass is expected for Friday. Fog will
burn off quickly by late morning. Scattered thunderstorms will
redevelop between 16Z-19Z with daytime heating, forming mainly
along the Blue Ridge before spreading in coverage as the
afternoon progresses. MVFR visibility due to very heavy rain
should be expected with these storms.

Average confidence for ceiling, precipitation, wind.
Below average confidence for visibility.

OUTLOOK Friday night through Tuesday...

Friday night through Tuesday: SCTD SHRA/TSRA remain possible as
each afternoon and evening. Flight category reductions are
likely, especially Saturday and Tuesday afternoon and evening.

Sunday and Monday the probability of showers and thunderstorms
decreases, but remains possible in the afternoons and evenings.
Prevailing conditions will be VFR.

&&

.CLIMATE...
As of 300 PM EDT Thursday...

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...Heat Advisory from 11 AM to 8 PM EDT Friday for VAZ032>034-
     043>047-058-059.
NC...Heat Advisory from 11 AM to 8 PM EDT Friday for NCZ003>006-020.
WV...None.

&&

$$

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