Monday, August 23, 2021

Late Summer 2021_High Mountain Basins


22 August 2021
Elevation 3040 feet
Burkes Garden Mill Dam
Single Outlet of Burkes Garden Basin 
Wayne Browning Photograph © All Rights Reserved

Burkes Garden is a classic, idyllic, elliptically-shaped mountain basin possessing a single outlet for water and 
air flow drainage.  It is known for generating some of the coldest night-time temperatures in Virginia.  Surprisingly low temperatures are possible during every month of the year under specific conditions.

Courtesy of Google Earth

Majestic Burkes Garden, located along the Tennessee Valley Divide in Tazewell County, Va.,
is one of several high mountain basins that I have been using for graduate field research through Mississippi State University.

                        Black Lives Matter Statement

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Burkes Garden is famous, of course, for being the first choice of the Vanderbilt family, but no one in this high mountain basin would sell.  The Biltmore House was built in Asheville, North Carolina.

22 August 2021
Basin Floor of Majestic Burkes Garden
Wayne Browning Photograph © All Rights Reserved

While the interior of Burkes Garden Basin drains into the New River, its highest southwestern rim (formed 
by the Tazewell-Beartown Mass of Clinch Mountain) drains into the Upper Tennessee River Basin. 

22 August 2021
Looking Toward Tazewell-Beartown
Towering Cumulus Build Above The Garden
Wayne Browning Photograph © All Rights Reserved

The basin of Burkes Garden, which geologically is an anticlinal dome that has been breached, is ruled by an interesting micro-climate.  Like the High Knob Massif toward the west-southwest, this is key to the Garden's interesting and diverse biological diversity. 

by Richard L. Hoffman

22 August 2021
New River Watershed
Majestic Burkes Garden Basin
Wayne Browning Photograph © All Rights Reserved

Burkes Garden Basin generates a great contrast with 
Big Cherry Lake Basin of the High Knob Massif which is much smaller, more sheltered and vegetated on its floor, and much, much wetter than Burkes Garden.

8 May 2017
High Knob Massif
Spring In Big Cherry Basin
Wayne Browning Photograph © All Rights Reserved

29 July 2017
High Knob Massif
Summer In Big Cherry Basin
Wayne Browning Photograph © All Rights Reserved

16 September 2017
High Knob Massif
Early Autumn In Big Cherry Basin
Wayne Browning Photograph © All Rights Reserved

I have many photographs on this site of Big Cherry Lake basin, with the above being representative of the cold air pooling area along the basin floor.

Rainfall Total of 0.93" during August 1-15, 2021

Prior to remnant rain from tropical storm Fred, only 0.93" of rainfall had been officially measured during August within Burkes Garden.  The drying effects of 
this could still be seen in some photographs above.

(2008-2020)
Mean Annual Precipitation
Big Cherry Basin vs Burkes Garden Basin
(To convert millimeters into inches divide by 25.4)

The Metric System is used in official field research given this 
is the world standard, used by every nation except the United States, Myanmar, and Liberia.

The annual precipitation difference between Burkes Garden and Big Cherry is so significant that they would not be recognized as being within the same climate zone (Southwestern Mountains) if looking at only this annual graph.  Outside of synchronous, annual fluctuations they possess dramatically different water budgets.
 
Relative to the western USA, and other locations where much of the nocturnal cold air formation, breakup, and applied research has been done, Burkes Garden has a wet climate even though it is relatively dry in direct comparison to Big Cherry Basin.

Precipitation Update

High Knob Massif
(Upper Elevations)

(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)

April
2.53"
(Eagle Knob Snowfall: 2.5")

May
4.54"
(Eagle Knob Snowfall: Trace)

Spring 2021
(1 Mar-31 May)
17.89"

June
4.79"

July
5.55"

August
10.39"

Summer 2021
(1 June-31 August)
20.73"

1-2 September
3.63"

2021 Total: 56.02"
 (January 1 to September 2 Period)

November 2019-October 2020: 102.34"

Autumn 2018 to Summer 2019: 91.21"

Autumn 2019 to Summer 2020: 94.44"

Autumn 2020 to Summer 2021: 73.84"

(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)

Precipitation Update

Elevation 1966 Feet
Big Stone Gap Water Plant
(Mouth of South Fork Gorge)
Gary Hampton & Staff
0900 Hours Daily

2021

January
4.03"

February
5.37"

March
9.97"

April
2.72"

May
4.58"

June
4.43"

July
3.56"

August
7.85"

1-2 September
2.83"

2021 Total: 45.34"
 (January 1 to September 2 Period)

A research focus is to better understand nocturnal cold air formation within upper elevation basins, specifically with respect to wet environments.


Total rainfall in Burkes Garden reached 6.72" from the beginning of August to the beginning of September.  During this same period, rainfall in Big Cherry Basin was 13.93" with a rise on Big Cherry Lake of 1.9 vertical feet in remnants of Fred causing overflow that increased with remnants of Ida.

2021 Total Precipitation
(January 1 thru September 2)

Burkes Garden Basin: 34.85"

Big Cherry Lake Basin: 56.02"

A primary research question is: 
how can mean minimum temperatures average colder within wet Big Cherry Basin than in the much drier setting of Burkes Garden?

Recall physics of drier air, it naturally tends to cool more at night (think of a desert and how night-time temps drop much more than in a humid setting).

32-Month Comparison
Mean Monthly Minimum Temperature

While the answer to this question (as well as numerous other questions) will not be given now, not until my research is reviewed and graded (and possibly published in a more official manner), the nature of these special places will be highlighted.

This is being done so that a greater appreciation and respect can be developed for the rich diversity (climatic, geologic, and ecological) of these unique landform settings.

22 August 2021
Burkes Garden Mill Pond Dam
Wayne Browning Photograph © All Rights Reserved

Water at the Mill Pond represents all that drains out from Burkes Garden along the surface.  This water contributes to the formation of Wolf Creek of New River.  Some water also likely sinks into the subterranean given its carbonate floor (Ordovician Carbonates). 

A dive into the climate history of Burkes Garden is not only to gain a better understanding for high mountain basins, like Big Cherry and Canaan Valley, but also to use a site not influenced by urbanization to look at climate change trends in these special places.


Climate of Burkes Garden

Recording weather conditions in Burkes Garden began in 1896.  This basin has one of the longest data records in southwestern Virginia. 

Data Courtesy of Colleen Cox and Pam Rose

I must make this crystal clear.  All data during my life-time is courtesy of two individuals, Colleen Cox and Pam Rose, who have officially documented all these weather conditions for the National Weather Service.  I had the honor and privilege to speak with Colleen a few times over the years.

Pam began recording in 2009, according to NOAA records, and Colleen it appears recorded for more than 
50 years prior to that time.  It would be interesting to learn more about the early history of this historic site.


The current 30-year climate period will be highlighted first, with monthly mean precipitation (above) and snowfall (below) for the 1991-2020 period.


The 6-decade precipitation trend in Burkes Garden has been strongly increasing since the late 1950s.


Annual precipitation impacts the temperature regime of any location, and is an important part 
of my research.

Although day-time temperatures are not directly part of my field research, I am going to show trends below that might be rather surprising.  Decreases in mean annual maximum temperature have been observed in both Burkes Garden and Wise for different time periods.

Various factors could cause this, including changes in instruments and station location that would require more intensive study.  Changes due to increasing mean annual precipitation are also possible, with increased moisture acting to reduce day-time max temperature due to both increased cloudiness and more partitioning of incoming solar radiation into latent heat for evapotranspiration. 


Climate forms the background conditions in which daily weather operates.  It is critical to capture the big picture and trends that develop and change through time.


Looking at the top 30 all-time highest day-time temperatures, 27 out of 30 occurred prior to 1989 (especially during the infamous 1930s).  This is not something you will see highlighted every day, but must be shown in the complete picture.

It should be stressed, that a different temperature recording system was also being used during the 1930s, manually read mercury-in-glass spin and reset thermometers versus the modern day thermistor or digital Maximum-Minimum Temperature System (MMTS).


Filtering data by removing any year with 30 or more missing days would remove 1958 and 2018, but would not change the decreasing trend in mean annual maximum observed since 1896.


Looking at the most recent 30-year climate period, the trend has been for increasing mean annual maximum temperature in Burkes Garden.

I show below a decrease in mean annual maximum temperature in Wise.  As discussed below, this may not all be due to natural causes.  It is very possible, however, that the longer-term temperature trend observed in Burkes Garden, of decreasing day-time temp, is real for much of far southwest Virginia (especially the wet High Knob Massif area) given documented increases in annual precipitation.


Decreases in mean annual maximum temperature show up during the 1991-2020 period in Wise.

A more detailed review of this is necessary, given there were station moves and a change in the daily recording time (from PM to AM format) that could have caused this trend (or that could account for part of the observed trend).  This would represent human caused changes not related to climate.

An increase in the mean annual precipitation and cloudiness could have also acted to lower day-time temperature.  These would be natural causes with possible indirect human influence.

Looking at my NWS data, I suspect this decrease in mean annual Wise maximum since 1991 is not all due to natural causes but instead was influenced by station moves and changes in the temperature recording time (as noted), however, I have not yet attempted to tease out the "truth" of what was observed.  Anyone using Wise data, however, must consider the above factors for any climate studies.


Nocturnal Cold Air Pooling

Development of cold air at night is to be expected during winter, so to illustrate the unique nature of these special places the summer season will be highlighted first.

Meteorological Summer
(June-August)

Formation of nocturnal cold air is at the heart of this research, and I illustrate this by highlighting the top 43 coldest nights for each month of Meteorological Summer (June-August).

Coldest June Nights
Burkes Garden Basin

The chance of a sub-freezing summer night is greatest during June and least during July, with increasing chances again during mid-late August.  This also follows the observed trend in Big Cherry Basin since recording started.

It should be noted that this is the same trend seen for nearly all cold places along the entire mountain chain, with the mid-summer period of July being statistically least likely to generate frost and/or sub-freezing air temperatures (although, as seen, it can happen).

Coldest July Nights
Burkes Garden Basin

Burkes Garden is a good guide for Big Cherry temperatures, even though any given night can be colder in either basin and the mean minimum is colder within the main cold air pooling area of 
Big Cherry than at the NWS site in the Garden 
(by direct comparison in the 2017-2021 period). 

Coldest August Nights
Burkes Garden Basin

Many more nights not listed here have been cold enough to generate summer frost.  At the level of an official temperature sensor, frost typically forms at ground level when the air temperature reaches around 36 degrees at sensor level.

Coldest Summer Nights
Burkes Garden Basin

Locations capable of generating summer temperatures like these are rare in the southern Appalachians, but become more common at middle to upper elevations within the central and northern Appalachians from central West Virginia northeast along the mountain chain.

Coldest Summer Nights
Tri-Cities, Tennessee

This can be illustrated by looking at the top 43 coldest summer nights observed within the Great Valley of northeastern Tennessee, where it would be rare even to have a summer air temperature 
cold enough to generate light frost.

Coldest Summer Nights
Kingsport, Tennessee

Travel far north, however, into upper elevations 
of extreme northern West Virginia and it becomes rather common to have summer-time frost within coldest locations.  This is exemplified by what is perhaps the most classic cold air forming basin 
in the central Appalachians.  Canaan Valley.

During Summer 2021, for example, temperatures dropped low enough for patchy, light frost in Burkes Garden and Big Cherry basins but were cold enough 
for a freeze and several frosts within coldest parts of 
Canaan Valley Basin.

June 2021
Canaan Valley National Wildlife Refuge
Air Temps Northern Canaan Valley Basin

July 2021
Canaan Valley National Wildlife Refuge
Air Temps Northern Canaan Valley Basin

August 2021
Canaan Valley National Wildlife Refuge
Air Temps Northern Canaan Valley Basin

As cited above, note June was (and typically is) 
the month featuring coldest nocturnal conditions.

In northern Canaan Valley Basin, which was significantly colder than the southern basin floor 
at the official NWS site (below), this was especially the case with a significant June freeze. 

June 2021
Canaan Valley 2 NWS Cooperative Station

July 2021
Canaan Valley 2 NWS Cooperative Station

August 2021
Canaan Valley 2 NWS Cooperative Station


Meteorological Autumn
(September-November)

While frost can occur earlier in these basins, as highlighted, it becomes much more common during mid-late September when the first 
freezes are also often experienced.

Significant color changes are common within Big Cherry Basin, especially along the basin floor cold air pooling zone, in the second half of September (but sometimes develop earlier).

I have seen first color changes by late August-early September if late summer-early autumn cold develops 
on the basin floor.

Coldest September Nights
Burkes Garden Basin

Coldest October Nights
Burkes Garden Basin

Coldest November Nights
Burkes Garden Basin


Meteorological Winter
(December-February)

Coldest nights during winter are most favored when clear skies and light winds develop following deep, fresh snow (especially when it covers an older snowpack).  This is applicable to generally all sites, not just these favored high mountain basins.

Coldest December Nights
Burkes Garden Basin

Coldest January Nights
Burkes Garden Basin

Coldest February Nights
Burkes Garden Basin

All-Time Minimums

An intriguing fact of these classic, high basins is that no temperature colder than -27 degrees (F) below zero has been observed in either Burkes Garden Basin or Canaan Valley Basin.

Coldest All-Time Mins
Burkes Garden Basin

Despite a global warming trend of increasing night-time temperature, I predict this is going to change.

The new observation site in northern Canaan Valley Basin (within the National Wildlife Refuge) and the cold air pooling area of Big Cherry Basin are both likely to get colder than this threshold.

Both of these basin sites have the potential to establish new all-time record minimums for 
West Virginia and Virginia, respectively.

To accomplish this notable feat, clear skies, light winds and fresh, deep snow during a long night is likely to be required.  While new all-time record minimums could occur in brutal cold air advection at highest elevations, it is more likely that these cold benchmarks will be broken within these high mountain basins.

Coldest All-Time Mins
Canaan Valley Basin

Coldest All-Time Mins
Canaan Valley Basin


Meteorological Spring
(March-May)

Coldest March Nights
Burkes Garden Basin

The first spring of high-resolution recording in 
Big Cherry Basin had the air temperature drop to 
0 degrees (F) on 16 March 2017.  It was clear a special place had been discovered, as this would have ranked in the top 10 coldest on record for Burkes Garden (above, where 2017 featured a minimum of 6 degrees that did not rank).

Coldest April Nights
Burkes Garden Basin

Coldest May Nights
Burkes Garden Basin


Climate Trends
(Nocturnal Cold Air Formation)

A small increase in the mean annual minimum temperature has been observed in Burkes Garden Basin when looking at the complete 124-year record during 1897-2020.

1897-2020 Climate Period
Mean Annual Minimum Temperature

A closer inspection finds that the majority of this night-time increase has been driven by warming observed since 1997, which also shows up during the 1991-2020 climate period.

1991-2020 Climate Period
Mean Annual Minimum Temperature

Last year (2020) ranked as the 4th warmest in the 124-year record for night-time warmth in Burkes Garden Basin, only behind the 1930s.

Mean Annual Minimum Temperature
By Rank (Top 43 Warmest On Record)

The 37.6 degree night-time average observed within 
the cold air pooling area of Big Cherry Basin during 
2020 would have ranked number 78 in the 124-year 
Burkes Garden record.

A breakdown of night-time temperature changes 
in Burkes Garden during this most recent climate period of 1991-2020 finds:

The temperature breakdown by season:

Summer: -0.2 degrees
Autumn: +2.9 degrees
Winter: +1.5 degrees
Spring: +1.1 degrees

So, what is the big deal with 
some night-time warming?

A perfect example can be found by looking at 
the current threat to Canadian Hemlock (Tsuga canadensis) trees, with massive dying along the Appalachian range.


Spread of adelgids across the Appalachian barrier from east to west has been facilitated by a lack of severely cold conditions since 1997, with air temps of -20 degrees (F) below zero or lower required to extirpate them.

 Lowest Annual Minimum Temperature
And Trend During The 1897-2020 Period

While the trend in observed lowest annual temperature has been flat when looking at the entire 124-year record (above), and decreasing when observing just the 1944-1996 period (below), that is not indicative of the most recent trend.

 Lowest Annual Minimum Temperature
And Trend During The 1944-1996 Period

The most recent trend, since 1996, has featured 
a notable lack of -20 degree (F) or colder temps 
in Burkes Garden Basin.

 Lowest Annual Minimum Temperature
And Trend During The 1991-2020 Period

Air Temps dropped well under -20 degrees (F) below zero in Big Cherry Basin during 2015, with a dying of Hemlock Wooly Adelgids.  Unfortunately, milder temperatures at the lower elevations and across adjacent regions allowed adelgids to survive with subsequent migration and/or transportation back into Big Cherry Basin.

Trend In Altantic Multi-decadal Oscillation

Like the Pacific Decadal Oscillation of the Pacific Ocean, the Atlantic also goes through cold and warm phases.  The current warm phase started during 1997.

There appears to be a strong correlation between widespread lack of -20 degree cold in the southern Appalachians and a shift into the positive phase of the Altantic Multi-decadal Oscillation (AMO).



While being counter-intuitive, with past studies suggesting that positive AMO phases favor -NAO phases (inverse correlation), it is not that simple.

With significant warming of sea surface temperatures in recent decades the response and linkage between the AMO and NAO appears to be changing even as the AMO may be trending back into a negative phase (time will tell).

Extreme cold in high mountain basins, above fresh snow, is driven by decoupling of the overlying atmosphere from basin floors.  This process is enhanced by a reduction in turbulent mixing.  A warmer Atlantic Ocean may enhance the pressure gradient as suggested by above studies.  This could increase storminess and reduce nights that are most favorable for extreme cold in mountain basins (my idea).


Nocturnal Summer Minimum Temperatures

There has been a small rise in long-term night-time summer temperature in Burkes Garden Basin.

1896-2021 Climate Period in Burkes Garden, Virginia
Mean Annual Summer Min Temperature

Most recently, and perhaps surprisingly, there has been a slight decrease in mean nocturnal minimum temperature (a station move occurred which must be considered as a possible influence on part of this observation period).

The temperature breakdown by month:

1991-2020 Climate Period in Burkes Garden
June: -0.7 degrees
July: -0.7 degrees
August: +0.9 degrees

1991-2021 Climate Period in Burkes Garden, Virginia
Mean Annual Summer Min Temperature

The year 2020 ranked as the 5th warmest and 2021 as 
the 16th warmest during the past 31-years for night-time temperatures during summer in Burkes Garden.

The 2020 mean in Big Cherry Basin would have ranked as the 26th warmest in Burkes Garden (all 2021 data has not yet been analyzed for Big Cherry).

1991-2021 Climate Period in Burkes Garden, Va
Mean Summer Minimum Temperature
By Rank (Warmest to Coolest)

That high mountain basin summer minimums are holding nearly steady (perhaps decreasing slightly during this present 30-year climate period) within Burkes Garden, and by implication within the basin of Big Cherry, has vast biological significance.

The reason, in part, is that summer minimums 
are increasing at middle to lower elevations across southwestern Virginia.  For example, consider the trend observed in Wise.

Wise, Virginia
1955-2021 Climate Period
Mean Annual Summer Min Temperature

Although station moves and a change in recording format during recent years have to be considered, in this case the change to an AM reporting format would act to lower (not increase) mean minimum.

Big Stone Gap, Virginia
1990-2021 Climate Period
Mean Annual Summer Min Temperature

The above trend is felt to be mostly real, given similar (although less steep) trends in Clintwood and at other surrounding stations like Big Stone Gap (above).

High mountain basins like those holding majestic Big Cherry Lake and High Knob Lake are strong-holds for species possessing northern affinities, making temperatures during the summer 
breeding-growing season critical.

1955-2021 Climate Period in Wise, Virginia
Mean Summer Minimum Temperature
By Rank (Warmest to Coolest)

The Wise record period implies that coolest summer minimums in Big Cherry Basin are in the 40s (that is, 
average night-time lows for the June-August period).

Observed that the 54.0 degree mean summer minimum in Big Cherry Basin during 2020 was significantly lower than ever recorded during the past 67-years in Wise and the past 32-years in 
Big Stone Gap.

1990-2021 Climate Period in Big Stone Gap, Virginia
Mean Summer Minimum Temperature
By Rank (Warmest to Coolest)

The coolest mean summer-time minimum in the 
125-year Burkes Garden record was 50.5 degrees during 1927.

1896-2021 Climate Period in Burkes Garden, Virginia
Mean Summer Minimum Temperature
By Rank (Top 46 Coolest)

Using two recent summers with no missing data for comparison, the 2017 mean minimum of 51.9 degrees 
in Big Cherry Basin would have ranked as the 7th-8th coolest in Burkes Garden (where it ranked as the 21st coolest).  The 2020 mean of 54.0 degrees in Big Cherry would have ranked as the 44th coolest in Burkes Garden (where it ranked as the 105th coolest, not shown above).

It is nearly certain, if records were long enough 
(or in coming years) that night-time temperatures average in the 40s in Big Cherry Basin during the coolest summers.

High Knob Massif
Summer At Big Cherry Lake
Wayne Browning Photograph © All Rights Reserved

This would be analogous to the coolest on record 
in Marquette, Michigan, more than 700 air miles 
to the northwest of southwestern Virginia.

That is why, in part, that birds which breed in Canada, the Great Lakes, and New England can also be heard singing during summer in Big Cherry Basin.

Why have nocturnal temperatures not increased in Big Cherry Basin and Burkes Garden Basin during this current cycle of global warming?

As graphically illustrated above, there has been a night-time warming in the 1896-2021 record of Burkes Garden but not during the 1991-2021 period.

This lack of increase in summer night temps is in contrast to a strong increase in night-time temperature for the entire period during 1991-2021.

That has partly been motivation for my current graduate research, given significant increases in night-time temperature at low-middle elevations.

 
Nocturnal Autumn Minimum Temperatures

Night-time warming during the year has been found to be greatest during Autumn in Burkes Garden Basin, with October (by far) featuring the greatest nocturnal warming during this current climate period (1991-2020).

1896-2020 Climate Period in Burkes Garden, Virginia
Mean Annual Autumn Min Temperature

Only a +0.3 degree (F) temperature increase has been observed in Burkes Garden at night during the entire 1896-2020 record period.  That is not the recent trend.

1991-2020 Climate Period in Burkes Garden, Virginia
Mean Annual Autumn Min Temperature

A +2.9 degree (F) temperature increase has been observed at night in Burkes Garden during the 
1991-2020 period.

A closer inspection finds huge departures from average during September and October.  Here is the breakdown by month for this most recent climate period:

The temperature breakdown by month:

1991-2020 Climate Period in Burkes Garden
September: +3.8 degrees
October: +6.4 degrees
November: -1.7 degrees

This correlates with later Autumn color changes documented during recent decades in the region.

Burkes Garden, Virginia
1991-2020 Climate Period
Mean September Minimum Temp & Trend

Burkes Garden, Virginia
1991-2020 Climate Period
Mean October Minimum Temp & Trend

Burkes Garden, Virginia
1991-2020 Climate Period
Mean November Minimum Temp & Trend

September 2018 featured not only the warmest nights of the past 3 decades, but the warmest 
since recording started in 1896.

1990-2021 Climate Period in Burkes Garden, Virginia
Mean September Minimum Temperature
By Rank (Warmest to Coolest)

1990-2021 Climate Period in Burkes Garden, Virginia
Mean October Minimum Temperature
By Rank (Warmest to Coolest)

1990-2021 Climate Period in Burkes Garden, Virginia
Mean November Minimum Temperature
By Rank (Warmest to Coolest)


Nocturnal Winter Minimum Temperatures

A decrease (-0.6 °F) in long-term mean annual night-time temperature is obtained by using the raw, unfiltered climate data for Burkes Garden.

1897-2020 Climate Period in Burkes Garden, Virginia
Mean Annual Winter Min Temperature

The above is in contrast to a +1.5 °F increase in mean annual night-time temperature during this most recent climate period.

1991-2020 Climate Period in Burkes Garden, Virginia
Mean Annual Winter Min Temperature

The temperature breakdown by month:

1991-2020 Climate Period in Burkes Garden
December: +4.7 degrees
January: -0.8 degrees
February: +1.1 degrees

The top three warmest mean winters for night temperature during the past 3 decades occurred since this cold air pooling study started.

1991-2020 Climate Period in Burkes Garden, Virginia
Mean Winter Minimum Temperature
By Rank (Warmest to Coolest)


Nocturnal Spring Minimum Temperatures

An essentially flat trend is observed within the 
long-term data set (since 1896) for mean spring minimum temperature in Burkes Garden.

1896-2021 Climate Period in Burkes Garden, Virginia
Mean Annual Spring Min Temperature

A 1.1 degree (F) increase in mean night-time temperature has been documented in Burkes Garden during this most recent climate period.

1991-2020 Climate Period in Burkes Garden, Virginia
Mean Annual Spring Min Temperature

The temperature breakdown by month:

1991-2020 Climate Period in Burkes Garden
March: +1.2 degrees
April: -0.5 degrees
May: +2.5 degrees


Summary of Temperature Trends

Different temperature trends are observed between the complete, long-term data set extending back to the late 1800s and the current 30-year climate period (1991-2020).

Burkes Garden Basin, Virginia
121-Year Mean Annual Maximum
Data filtered to remove any year with 30 or more missing days

A cooling of -0.7 degrees (F) since 1898 (above) on day-time maximum temperature combines with a slight warming of +0.3 degrees (F) on night-time minimum temperature (below) to generate a 
nearly flat long-term trend in Burkes Garden.

Burkes Garden Basin, Virginia
119-Year Mean Annual Minimum
Data filtered to remove any year with 30 or more missing days

The long-term mean annual temperature trend 
is nearly flat (below), as noted, with a slight -0.2 °F cooling over 117 years.

Burkes Garden Basin, Virginia
117-Year Mean Annual Temperature
Data filtered to remove any year with 30 or more missing days

The current 30-year climate period (1991-2020) displays a straight +1.3 degree warming on both day and night-time temperature.

1991-2020 Climate Period
Burkes Garden Basin, Virginia
30-Year Mean Annual Maximum

Although the current 30-year mean maximum is increasing, it must be noted that it is 0.8 degrees (F) cooler than the 1898-2020 mean maximum.

1991-2020 Climate Period
Burkes Garden Basin, Virginia
30-Year Mean Annual Minimum

Although the current 30-year mean minimum is also increasing, it must be noted that it is only 0.1 degree (F) above the 1898-2020 mean.

There has essentially been no change in nocturnal temperature over the entire data period (using 119 years) in Burkes Garden if just comparing the 38.0 degree mean during 1898-2020 with the current mean of 38.1 degrees during 1991-2020.

There have been consequences, however, as highlighted by a lack of extreme minimums 
(-20 F below or colder since 1996) that have enhanced invasive species as well as a increase 
in mean growing season driven largely by later onsets to autumn (reference discussion below).

1991-2020 Climate Period
Burkes Garden Basin, Virginia
30-Year Mean Annual Temperature

It is well known that there has been a so-called "warming hole" across the southeastern USA with respect to the globe.  There are numerous holes in global-scale warming where local air temperatures have not warmed as much as the global average.



This is also applicable to micro-climatic settings like Big Cherry Basin, Burkes Garden Basin, and Canaan Valley Basin where specific factors combine to buffer climate change.

Burkes Garden Basin, Virginia
Freeze-free Period Length And Trend

While long-term (mean) night-time temperature has not changed very much in Burkes Garden, this rise in short-term (since 1991) night temperatures is partially driven by significant warming at night during early-mid autumn (versus nocturnal cooling during early-mid summer).

The greatest driver of increasing growing season length from this perspective being the dramatically warmer conditions observed during early-middle autumn (in September and October).


Bottom Line
Magnitude of warming at night depends on the time period and season reviewed, with very little long-term change found across the entire history (1898-2020) versus significant change during this 
current climate period (1991-2020).

During this current climate period, there has been nocturnal cooling during early-mid summer and significant warming during early-mid autumn.

Night-time warming in Burkes Garden, and certainly in Big Cherry Basin, however, has not been as significant as observed across the lower and middle elevations.

With respect to species possessing northern affinities, these upper elevation basins function 
as climate change buffers.

My field research discovered and documents reasons for these observed differences across 
space and time.  It will officially be presented 
this autumn in graduate school.

Finally, I hope all this information will give you 
a greater appreciation for these special mountain basins (Big Cherry, Burkes Garden, Canaan Valley) that add wondrous diversity to the Appalachians.