Wednesday, March 17, 2021

Early Spring 2021_High Knob Massif


4 March 2021
High Knob Massif
Looking Across High Knob Lake Basin
Wayne Browning Photograph © All Rights Reserved

A pattern shift in late February essentially extirpated snow 
from the southern Appalachians (reference later photograph), restricting it to locations from central-northern West Virginia northeast along the mountain chain.  Observe Mount Mitchell and the Black Mountains in western North Carolina along the horizon in the above view from Eagle Knob and the northwest rim of High Knob Lake Basin.

4 March 2021
High Knob Lake Recreation Area
Majestic Cove At High Knob Lake
Wayne Browning Photograph © All Rights Reserved

Flooding rains at the beginning of March gave way to 
a stretch of dry conditions not observed since Autumn 2020, with seasonal days and frosty cold nights.

4 March 2021
High Knob Lake Recreation Area
Gorgeous Spillover At High Knob Lake Dam
Wayne Browning Photograph © All Rights Reserved

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"

November 
1.96"
(Eagle Knob Snowfall: 0.5")

Autumn 2020
(1 Sep-31 Oct)
15.23"

December 
6.22"
(Eagle Knob Snowfall: 34.0")

2020 Total: 96.80" (M)
 (January 1 to December 31 Period)

2021

January
6.35"
***(Eagle Knob Snowfall: 34.0")

February
7.42"
(Eagle Knob Snowfall: 19.5")

Winter 2020-21
(1 Dec to 28 Feb)
19.99"
(21.70" on Eagle Knob)

March
10.82"
(11.14" to Midnight 31st)

1-2 April
0.41"

2021 Total: 25.00"
 (January 1 to April 2 Period)

Total Past 12-Months: 92.09"

16-Month Total: 130.32"
(Mean 8.14" per month)

November 2019-October 2020: 102.34"

Autumn 2018 to Summer 2019: 91.21"

Autumn 2019 to Summer 2020: 94.44"

(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.

***Not a mistake, with a second consecutive month having 34.0" of snowfall (rare to have back-to-back months with the same total).

4 March 2021
Water Elevation 3500 feet
High Knob Lake Recreation Area
Reflections Upon High Knob Lake
Wayne Browning Photograph © All Rights Reserved

Although widespread snow cover melted away by 
23 February, with excessive late February rain, a little snow managed to some how linger along State Route 619 between the high peaks (within a shaded area receiving limited insolation).

4 March 2021
Lingering Snow Along State Route 619
Wayne Browning Photograph © All Rights Reserved

This snow lingered to beyond 11 March, with maximum depth on 4 March being 12" within the deepest section (only a portion is visible above).

March has featured an array of cold nights, especially within mountain valleys as exemplified by a recent array of nights in Big Cherry Basin.

6-11 March 2021
Big Cherry Basin of High Knob Massif

Observe the huge increase in air temperature a few hundred feet above the basin floor, with strong nocturnal temperature inversion formation being a consistent and repetitive feature of the cold air pooling climatology of these high mountain basins. 

17 March 2021
Long Ridge of Sandy Ridge
Coltsfoot (Tussilago farfara)
Wayne Riner Photograph © All Rights Reserved

Coltsfoot, typically the first wildflower to bloom, was recently captured by photographer Wayne Riner along the Tennessee Valley Divide on Long Ridge.


Winter 2020-21 Notes

While this winter was a little more like "average," it still fell to achieve extreme minima with the lowest observed temperature in Clintwood reaching 7 degrees above zero on 26 December 2020.  Over the past 33 winter seasons, this tied 1998-99 for the fifth highest winter season (December-February) minimum on record.

Clintwood 1 W
Elevation 1566 Feet

Abundant clouds and turbulent mixing were hinderances to winter minimums during 2020-21, even when snow cover was present on most nights.

This was true even within high basins, where lowest winter temperatures reached only 0 to -3 below zero within the classic cold air collection 
basins of Big Cherry and Burkes Garden.


This is part of a longer-term trend.

Wise Plateau
Elevation 2560 Feet

Going back even farther in time, this has been a trend with the 2020-21 season minimum of 5 degrees above zero in Wise also being tied for the fifth highest winter season (December-February) minimum on record for the past 66 winter seasons.  Clearly, the linear regression trend is upward on lowest winter temperature.

Burkes Garden Basin
Elevation 3068-3300 Feet

The same positive trend is observed within high mountain basins, with the past 66 winter seasons also showing the same increasing skew in lowest minimum temperature in Burkes Garden Basin.

Night-time minimums have been impacted most by current global warming, even within these classic frost pockets.

2020 Temperature Means

Big Cherry Basin
Average Daily Max: 60.0
Average Daily Min: 37.6
Mean: 48.8 degrees

Burkes Garden Basin
Average Daily Max: 60.6
Average Daily Min: 40.5
Mean: 50.5 degrees (+1.9)

Tri-Cities, Tennessee
Average Daily Max: 69.0
Average Daily Min: 46.8
Mean: 57.9 degrees (+2.2)

The average minimum for 2020 in Burkes Garden was +2.9 degrees above the long-term average (the mean annual about 2 degrees F above), suggesting that was likely also true for Big Cherry Basin.

Using Tri-Cities, Tn., as a control site, the average night-time minimum temperature during 2020 had nearly the same departure as observed in the high basin of Burkes Garden, being +2.7 degrees above the long-term mean to further suggest the average min was also in this range at the Big Cherry Basin research site (implying a long-term average minimum of 34.5 to 35.0 degrees F).

2020-21 Winter Means
(December-February)

Big Cherry Basin
Average Daily Max: 38.9
Average Daily Min: 20.0
Mean: 29.4 degrees

Burkes Garden Basin
Average Daily Max: 39.2
Average Daily Min: 22.5
Mean: 30.8 degrees

Tri-Cities, Tennessee
Average Daily Max: 48.3
Average Daily Min: 29.1
Mean: 38.7 degrees (+1.4)

The average night-time low during the 2020-21 winter season was +1.7 degrees above average in Burkes Garden Basin.

*Minimum temperature records in Burkes Garden Basin date back to 11 March 1896 (125 years).

4 March 2021
Water Elevation 3500 feet
High Knob Lake Recreation Area
Reflections Upon High Knob Lake
Wayne Browning Photograph © All Rights Reserved


Snowstreaks Open April


An array of training snow showers and snow squalls during 1 Apirl left behind streaks of accumulation as skies cleared on 2 April.

Local accumulations varied from a trace up to around 2" at the summit level of the High Knob Massif.  Ironic, given March was the first in the past 30-years to have produced only a trace of snow (much below the 29-year average of 18.8").

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