Saturday, October 31, 2020

Late Autumn 2020_High Knob Massif

Head of Powell Valley (26 October 2020) 

   Wayne Browning Photograph © All Rights Reserved

The first snowflakes of the season fell at the summit level of the High Knob Massif during evening hours of 30 October 2020, as cold air was transported into the mountains in wake of heavy rains associated with former hurricane Zeta.

Air temperatures fell into the low-mid 20s within colder, high valleys of the massif by morning hours of Halloween as low clouds dissipated.  The first traces of rime formed in highest gaps and on peaks prior to cloud evaporation.

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Cloud Capped High Knob Massif

   Wayne Browning Photograph © All Rights Reserved

Mountain forests, standing mainly bare of leaves along and beyond the visible cloud line (above), received more than 4.00" of rain with remnants of Zeta during 28-29 October to elevate streams to ROARing levels!

The calcareous cliff line that rings the massif is a notable climatic marker.  Observe that the best lingering color occurs beneath these great cliffs, within a thermal belt zone located between them and the valley floor.  During winter this cliff line becomes a snow and rime marker, above which are 50+ square miles that spread outward above 3000 feet elevation.

High Knob Massif
Precipitation Update

(Totals Listed By AM Measurement Format)
Monthly Total Precipitation
Big Cherry Lake Dam
(Elevation 3139 feet)

2019

January
6.14"

February
12.50"

Winter 2018-19
(1 Dec-29 Feb)
26.56"

March
5.93"

April
6.64"

May
6.75"

Spring 2019
(1 Mar-31 May)
19.32"

June
10.68"

July
10.77"

August
4.15"

Summer 2019
(1 Jun-31 Aug)
25.60"

September
0.63"

October
5.01"
( 5.89" to Midnight 31st )

November
5.20"
( 7.04" to Midnight 30th )

Autumn 2019
(1 Sep-31 Oct)
10.84"

December
8.52"

2019 Total: 82.92" (M)
 (January 1 to December 31 Period)

2020

*January
7.15"

**February
13.01"

Winter 2019-20
(1 Dec-29 Feb)
28.68"

March
9.55"
( 10.77" to Midnight 31st )

April
11.59"

May
8.73"
(6.90" on Eagle Knob of High Knob Massif)

Spring 2020
(1 Mar-31 May)
29.87"

June
7.48"

July
9.72"
(10.48" to Midnight 31st)

August
8.12"

Summer 2020
(1 Jun-31 Aug)
25.32"

September
6.21"

October 
7.06"

Total Since January 1: 88.62"
[82.15"(M) on Eagle Knob of High Knob Massif]

Total During Past 12-Months: 102.34"

Autumn 2018 to Summer 2019: 91.21"

Autumn 2019 to Summer 2020: 94.44"

1 June 2019 to 31 Oct 2020: 133.58" (M)

(M): Some missing moisture in undercatch and frozen precipitation, with partial corrections applied for the 24.4 meter (80 feet) tall dam structure where rain gauges are located.  Corrections are based upon 86-months of direct comparisons between NWS and IFLOWS at Big Cherry Dam (including occasional snow core-water content data).

*General 7.00" to 8.00" at upper elevations (above 3000 feet) with 5.96" at the City of Norton Water Plant (official NWS rain gauge located at approximately 2342 feet elevation).

**Third consecutive February to reach double-digit precipitation totals within upper elevations of the 
High Knob Massif.

(26 October 2020)
Head of Powell Valley 
   Wayne Browning Photograph © All Rights Reserved

As many residents know, an amazing climatic gradient exists between the floor of Powell Valley, and the Clinch River Valley on the Scott County side of the massif, and upper elevations along and above the great cliffs.

While this general gradient exists throughout the year, 
it becomes most "visible" during spring, autumn, and winter (of course).

A drive, bike ride, or run along State Route 619 between Norton and Fort Blackmore is always educational and has been highlighting this climatic gradient during the past few weeks as the massif has been "undressing" from the top down as my late friend (and 99-year resident of Powell Valley) Addison Stallard wrote about decades ago.

(26 October 2020)
Head of Powell Valley
Wayne Browning Photograph © All Rights Reserved

Embedded within upper elevations are additional microclimates between ridges, high valleys, drainages, and varying slope exposures (lakes, wetlands, springs, and seeps adding even more variety at elevations 
above 2700-3000 feet).

(26 October 2020)
Head of Powell Valley
Wayne Browning Photograph © All Rights Reserved

Halloween morning (as highlighted below on GOES-16 imagery) featured fog in Powell Valley, along the Clinch River Valley leeward of the massif, and within the entire Russell Fork Basin (north of the massif).  Meanwhile, a hard freeze gripped high valleys in the massif where low clouds had dissipated prior to sunrise.

Halloween Morning

Lower slopes of the massif, along the Clinch River Valley, are covered by fog across Scott County, with higher portions of Little Stone Mountain, Stone Mountain, Wallen Ridge and Stocker Knob visible above the fog along the Wise County 
and Lee County side of the great mass.

To the north, only Pine Mountain and higher ridges along the Tennessee Valley Divide are above the fog bank covering the 680 square mile Russell Fork Basin.

November Sunrises & Sunset

05 November 2020
Tennessee Valley Divide
Sunrise Over Long Ridge
Wayne Riner Photograph © All Rights Reserved

Following more snowflakes at the summit level of the High Knob Massif, a widespread freeze finally gripped the entire mountain region to include thermal belt sites such as Long Ridge where my friend Wayne Riner captured a gorgeous morning sunrise.

Snowflakes flew during the evening of 01 November at highest elevations as air temperatures plunged into the 10s on peaks (with below zero wind chills).

The Year of 2020
Nora 4 SSE - Long Ridge of Sandy Ridge

The 2020 frost-free period in the Long Ridge thermal belt extended from 13 May to 16 October, with a below freezing temperature not being observed until the morning of 02 November 2020.

13 November 2020
Tennessee Valley Divide
Sunrise Over Long Ridge
Wayne Riner Photograph © All Rights Reserved

By contrast, high valleys upstream of Big Cherry Lake within the High Knob Massif had a frost-free period that extended only from 02 June to 19 September, with the first below freezing temperature of Autumn 2020 observed 40-days earlier than Long Ridge 
during the morning of 22 September.

01 September to 09 November 2020
Big Cherry Basin of High Knob Massif

This capped off a summer season featuring early 
June frost followed by above average night-time temperatures in Big Cherry Basin and across the mountain area.

01 June to 31 August 2020
Big Cherry Basin of High Knob Massif

Seasonal to excessive wetness gripped the High Knob Massif and other portions of the mountain area during Summer 2020, pushing the 12-month precipitation tally above 100.00" in Big Cherry Basin during the water year of October 2019-September 2020.

Past 12-Months
Big Stony Creek Stream Levels

The first major miss of 2020, it seems, finally spared 
the western front of the mountains in far southwestern Virginia as tropical moisture in advance of Eta remained to the south and east.

09 November 2020
Looking Across Wallen Ridge
Sunset From High Knob Lookout
Wayne Browning Photograph © All Rights Reserved

A beautiful sunset was captured, looking over Big Stone Gap and the Wallen Ridge State Prison, as clouds began increasing in advance of a tropical surge that finally missed the great Cumberland Overthrust Block 
to the south and east.

09 November 2020
Sunset From High Knob Lookout
Wayne Browning Photograph © All Rights Reserved

09 November 2020
Sunset From High Knob Lookout
Wayne Browning Photograph © All Rights Reserved

An illustration of how air temperatures can become much colder in high valleys of Big Cherry Basin, versus adjacent valleys like Powell Valley-Powell River Valley, the Clinch River Valley, and thermal belt sites such as Long Ridge, was captured by GOES-16 imagery 
around sunrise on 13 November 2020.

GOES-16 Image At 1416 UTC

Air temperatures, and minimums, are often 10-20+ degrees colder under such conditions as enhanced outgoing longwave radiation occurs in mostly clear air above the high basin floor, especially when decoupling with nocturnal inversion formation is observed.  In such cases, air temperatures are warmer at the summit level than within high valleys [temp differences of 
20-30+ degrees (F) can occur under extreme conditions 
(the summit level being warmer than the basin floor)]. 

This section is under construction.  Please check back.

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