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541
FXUS61 KRNK 071807
AFDRNK

Area Forecast Discussion
National Weather Service Blacksburg VA
207 PM EDT Fri Jun 7 2024

.SYNOPSIS...
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High pressure will promote dry conditions through Saturday.
A cold front tracks into the area Sunday with scattered showers
and thunderstorms. Dry weather returns Monday, followed by
additional opportunity for showers mid-week.
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&&

.NEAR TERM /THROUGH SATURDAY/...
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As of 200 PM EDT Friday...

Key Message: Less Humid.

Airmass change has resulted in lower humidity. This will make
if feel more pleasant. Once the sun starts to set this evening
it will set the stage for a cool night as temperatures slip
into the 50s. Mid-upper 40s are possible in the colder mountain
valleys.

In general, expecting mainly clear skies through tonight,
followed by increasing upper level cirrus Saturday as high
pressure dominates. A weak shortwave trough (upper level
disturbance) is progged to pass across the forecast area
Saturday afternoon. Model soundings suggest potential for some
virga per elevated CAPE above 15kft, but nothing reaching the
surface.

Winds subside this evening with loss of daytime mixing...remaining
light through the overnight before picking back up again Saturday,
from the west-northwest. High temperature Saturday...close to the
seasonal norm with highs in the 70s mountains, lower 80s in the
lower elevations.
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&&

.SHORT TERM /SATURDAY NIGHT THROUGH MONDAY NIGHT/...
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As of 130 PM EDT Friday...

Key Points:

1. Near or slightly above normal temperatures.
2. Showers, and a few thunderstorms, are possible Sunday into Sunday
evening.

A look at the 7 June 12Z NCEP Ensemble Mean 500 mb Geopotential
heights shows the region in nearly zonal flow on Saturday night into
Sunday, all while low pressure is centered near the Ontario/Quebec
border. An associated trough is expected to extend west along the
US/Canadian border. By Monday morning, the axis of this trough is
expected to be shifting southeast into the mid-Mississippi River
Valley. By late Monday night, this same trough axis will be nearly
parallel the spine of the Appalachians, centered over the Ohio and
Tennessee River valleys. At the surface, a cold front will be
approaching the region on Saturday night. This front will cross our
area on Sunday, and be located along the Atlantic coast by Monday
morning. In its wake, high pressure will be approaching the area and
be centered over the Mississippi Valley by late Monday night.
Between the departing front and the approaching high, the region
will be within a northwest flow pattern.

Output from the 7 June 00Z Ensemble Situational Awareness Table
shows 850mb temperatures around +15C to +17C on Sunday and +14C to
+16C for Monday.  Precipitable Water values will be around 1.25
inches Saturday night, 1.25 to 1.50 inches for Sunday, 1.00 to 1.25
for Monday and Monday night.

The above weather scenario will yield a forecast reasonably in line
with our ongoing forecast thinking. Specifically, Saturday night we
should see an increase in clouds from west to east in advance of the
approaching cold front. On Sunday, shower chances will increase from
west to east as the day progress with the approach and arrival of a
cold front. While not zero, thunderstorm chances should be minimal
as most deterministic guidance keeps expected afternoon CAPE values
under 500 J/kg and Lifted Index as low as only -1 or -2. Sunday
night precipitation chances in the evening should be limited to
mainly southern and eastern parts of the region as the cold front
exits the region. By late Sunday night, showers related to the
exiting of the front should be dissipated or have exited the region.
Additionally, at this time, an increasing northwest flow between the
departing front and high pressure across the center of the country,
look to help maintain clouds over western sections. Any associated
showers within this flow are currently expected to remain north of
the region during the overnight hours.

Confidence in the above weather pattern is moderate to high.
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&&

.LONG TERM /TUESDAY THROUGH THURSDAY/...
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As of 130 PM EDT Friday...

Key Points:

1. Initially cooler than normal temperature trending warmer each day.
2. Daily chances of mainly afternoon isolated showers, and perhaps a
stray thunderstorm or two. Coverage while still on the low side, will
be greatest across the mountains.

A look at the 7 June 12Z NCEP Ensemble Mean 500 mb Geopotential
heights shows an upper trough over, or nearly over, our region
during the extent of this part of the forecast. However, the
amplitude of the trough is expected to flatten as time progresses.
This could be an artifact of the ensemble averaging of the various
members. As such, not a lot of weight will be placed on the specific
axis of this trough as both northern and southern stream waves may
be averaging into this one depicted feature. At the surface, a weak
ridge of high pressure will be positioned over the region Tuesday
through Friday.

Output from the 7 June 00Z Ensemble Situational Awareness Table
shows 850mb temperatures around +12C to +14C for Tuesday, +14C to
+15C for Wednesday, around +16C on Thursday and around +17C to +18C
for Friday. Precipitable Water values will be around 1.00 inch
Tuesday and Wednesday and 1.00 to 1.25 inches for Thursday and
Friday. Precipitable Water values

The above scenarios leaves us with a forecast period with a number
of question marks. Aloft, we are expected to have a general period
of troughiness. However, at the surface, we are expected to have a
general period of weak ridging. Outside of moments when some
distinct forcing mechanism moves through the region, any
precipitation that develops will have to be robust enough to
penetrate trough the surface ridge, to then encounter the more
convective-friendly trough aloft with it associated jet dynamics and
potential steeper lapse rates aloft. Given the wide variety of
solutions offered by the deterministic guidance, our best option
would probably be to continue advertise what our previous forecast
offers. Specifically, we will have minimal shower chances, and
confine the highest probabilities to the peak heating of the day.
Additionally, we will have slightly higher probabilities over the
mountains where influence of differential heating and orographical
effects would added an element of focusing convection on weak
boundaries. While not zero, thunderstorm chances naturally will be
on the low side given the above convective challenges. Potentially,
as each day progresses, and if the ensemble trend of a weakening
trough unfolds, it may get harder each day for convection to fire.
Temperatures may start the period below normal, but trend to values
slightly above normal by Friday.

Confidence in the broad synoptic pattern during this time period is
moderate, but we have low confidence in the meso-scale aspects each
day.
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&&

.AVIATION /18Z FRIDAY THROUGH WEDNESDAY/...
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As of 130 PM EDT Friday...

VFR expected through the 24 hour valid TAF.

It will remain breezy through the remainder of this afternoon...
west/northwest winds 6-12kts with gusts 16-24kts. Winds subside
this evening by 00z/Sat...remaining light through the overnight
before picking back up again Saturday, from same general
direction.  There will be some increase in upper level cirrus
Saturday, thickening late Saturday afternoon, bases ABV 10kft.


EXTENDED AVIATION OUTLOOK...

VFR for most of the period. Exceptions being a few shower/storms
Sunday could bring sub-VFR mainly to the mountains. Isolated
chances of showers/storms Monday through Wednesday so low
confidence on sub-VFR.
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&&

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

&&

$$

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