The Observatory at Tangleroot Farm
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the The Observatory at Tangleroot Farm clear sky chart from 2005-11-06 to 2026-05-02.

This page is a summary of past forecasts. Even though it's based only on forecasts, some people use these pages as clue to a site's climate. But climate data based on actual observation should be preferred (if you can find it!).

Cloud, Transparency and Seeing forecasts are summarized individually. But because good observing conditions require a combination of minimum cloud cover, transparency and seeing, the individual forecast summaries can be difficult to interpret. The observing conditions section counts the combinations of conditions needed for common types of astronomical observation.

Observing Conditions

The following tables count the occurrence of the combinations of forecast and darkness conditions needed for different observations. Conditions are rated by by what percentage of the hours the observation would likely be attempted are usable.

Observation Type	Minimum conditions for hour to be usable				Out of hours
	Clear of Clouds	Transparency	Seeing	Sky Brightness
Planetary:	50%	(no limit)	Average	(no limit)	Nighttime Hours
Deep Sky:	70%	Average	(no limit)	5.9	Nighttime Hours
CCD Imaging:	70%	Below Average	Poor	(no limit)	Nighttime Hours

Percentages are of nighttime hours per month, or per year, when a particular observing conditions was met. Deep Sky percentages never exceed 50% because the moon is up half the time. Deep sky percentages are much lower for charts at high latitudes because of fewer dark hours in the summer.

Overall

By Month

Individual Forecasts

The length of each colored bar in the "occurrence of each Forecast" column is proportional to the number of times the chart forecast that color. The percentages are of the total number of hours per month, or per year, with a particular forecast. The colors as the same as those used in clear sky charts.

Note: Transparency probabilities are only counted for those hours that have 30% or less cloud cover. Seeing probabilities are only counted for those hours that have 80% or less cloud cover. If that's too tricky, try Observing Conditions instead.

Overall

		Occurrence of each Forecast	Data Points
Cloud Cover	Day	13% 9% 3 9% 6% 5% 5% 4 6% 7% 31%	131655
	Night	14% 11% 4 10% 6% 5% 5% 4 5% 6% 30%	130856
Transparency	Day	49% 8% 13% 20% 9% 1	135124
	Night	52% 7% 12% 18% 9% 1	135461
Seeing	Day	22% 20% 30% 19% 7% 2	16513
	Night	20% 16% 29% 25% 8% 1	25621

By Month

Percentage Cloud Cover NE (2006-)
Color Meanings: Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	9% 13% 6% 18% 8% 6% 5% 4 5% 5% 20%	4661
	11th to 20th	Day	9% 16% 7% 16% 7% 6% 5% 4 4 6% 19%	4650
	21st to end	Day	8% 10% 4 12% 10% 7% 7% 4 6% 7% 25%	5124
February	1st to 10th	Day	10% 13% 4 13% 7% 7% 6% 3 6% 7% 24%	1869
	11th to 20th	Day	8% 12% 5% 12% 8% 5% 5% 4 5% 6% 29%	2000
	21st to end	Day	13% 13% 5% 11% 7% 5% 4 3 5% 7% 29%	1730
March	1st to 10th	Day	16% 12% 4 12% 7% 6% 5% 4 5% 4 26%	4576
	11th to 20th	Day	10% 12% 4 9% 6% 6% 5% 5% 5% 6% 32%	4791
	21st to end	Day	16% 12% 3 9% 6% 4 5% 3 4 5% 32%	6102
April	1st to 10th	Day	17% 12% 3 9% 6% 4 4 3 5% 5% 32%	2520
	11th to 20th	Day	17% 9% 4 9% 5% 4 4 3 4 6% 35%	2494
	21st to end	Day	19% 9% 3 7% 5% 5% 5% 4 4 6% 34%	2677
May	1st to 10th	Day	25% 10% 4 9% 5% 5% 5% 4 5% 6% 23%	6116
	11th to 20th	Day	14% 9% 3 9% 6% 6% 5% 4 6% 8% 30%	6318
	21st to end	Day	18% 7% 3 7% 5% 5% 5% 4 6% 8% 32%	6949
June	1st to 10th	Day	18% 8% 3 8% 5% 5% 5% 4 6% 9% 30%	2800
	11th to 20th	Day	12% 6% 2 7% 5% 6% 5% 5% 7% 9% 36%	2800
	21st to end	Day	16% 8% 3 8% 5% 5% 6% 4 7% 8% 30%	2800
July	1st to 10th	Day	9% 6% 2 6% 6% 6% 7% 6% 8% 10% 35%	6360
	11th to 20th	Day	9% 5% 3 7% 5% 5% 6% 5% 8% 11% 36%	6360
	21st to end	Day	11% 5% 2 6% 4 5% 5% 4 6% 9% 42%	6926
August	1st to 10th	Day	12% 7% 2 6% 5% 5% 6% 5% 7% 9% 36%	4563
	11th to 20th	Day	11% 6% 3 8% 5% 6% 5% 5% 8% 10% 35%	4012
	21st to end	Day	9% 5% 2 7% 5% 5% 5% 4 7% 9% 41%	4312
September	1st to 10th	Day	11% 6% 2 5% 3 4 5% 4 6% 7% 48%	2400
	11th to 20th	Day	10% 6% 1 5% 4 4 3 4 5% 7% 50%	2296
	21st to end	Day	12% 6% 2 7% 5% 5% 5% 4 7% 8% 40%	2200
October	1st to 10th	Day	17% 9% 3 7% 5% 4 4 4 6% 6% 35%	2098
	11th to 20th	Day	14% 9% 3 8% 5% 5% 4 5% 6% 7% 35%	1961
	21st to end	Day	19% 9% 3 10% 5% 5% 4 4 5% 6% 30%	1980
November	1st to 10th	Day	13% 11% 3 8% 5% 6% 5% 4 5% 7% 34%	1851
	11th to 20th	Day	14% 10% 4 9% 5% 6% 5% 4 5% 6% 32%	1885
	21st to end	Day	15% 14% 5% 8% 6% 4 5% 4 6% 5% 29%	1680
December	1st to 10th	Day	12% 20% 7% 14% 6% 7% 5% 3 5% 5% 17%	2680
	11th to 20th	Day	17% 13% 4 8% 5% 4 5% 5% 6% 7% 25%	3066
	21st to end	Day	18% 12% 4 11% 6% 5% 5% 4 5% 6% 23%	4048
January	1st to 10th	Night	11% 15% 8% 18% 6% 6% 4 3 4 5% 20%	8234
	11th to 20th	Night	9% 17% 7% 18% 8% 6% 5% 4 4 4 17%	8235
	21st to end	Night	10% 11% 5% 12% 9% 7% 7% 5% 6% 7% 22%	9057
February	1st to 10th	Night	10% 12% 5% 14% 7% 6% 6% 4 6% 6% 24%	2746
	11th to 20th	Night	8% 12% 5% 14% 8% 6% 5% 3 5% 6% 29%	2505
	21st to end	Night	12% 11% 5% 11% 6% 6% 4 4 5% 5% 31%	2076
March	1st to 10th	Night	18% 12% 4 10% 7% 5% 5% 3 5% 4 28%	5484
	11th to 20th	Night	12% 13% 4 9% 5% 5% 5% 3 5% 7% 32%	5385
	21st to end	Night	14% 13% 4 10% 6% 5% 4 3 4 5% 31%	5072
April	1st to 10th	Night	16% 10% 3 9% 6% 5% 4 3 6% 6% 31%	2100
	11th to 20th	Night	19% 10% 3 9% 6% 5% 4 4 4 5% 33%	2075
	21st to end	Night	18% 8% 3 8% 4 4 5% 3 4 6% 37%	1943
May	1st to 10th	Night	25% 11% 3 9% 6% 5% 4 3 5% 7% 21%	3890
	11th to 20th	Night	15% 10% 4 10% 5% 5% 5% 3 4 6% 32%	3575
	21st to end	Night	15% 8% 3 9% 5% 5% 6% 4 6% 8% 31%	3926
June	1st to 10th	Night	18% 7% 3 6% 6% 4 5% 4 5% 7% 34%	1600
	11th to 20th	Night	15% 6% 2 6% 4 6% 4 4 6% 9% 39%	1600
	21st to end	Night	14% 6% 2 7% 5% 5% 5% 4 6% 8% 37%	1600
July	1st to 10th	Night	9% 5% 2 6% 5% 5% 5% 5% 8% 9% 40%	3600
	11th to 20th	Night	11% 6% 3 7% 5% 5% 5% 5% 6% 8% 41%	3600
	21st to end	Night	7% 6% 3 6% 4 5% 5% 4 6% 8% 46%	3926
August	1st to 10th	Night	12% 7% 3 7% 6% 5% 6% 3 6% 8% 38%	2586
	11th to 20th	Night	10% 7% 3 9% 6% 6% 5% 4 5% 7% 39%	2999
	21st to end	Night	9% 5% 2 5% 4 4 5% 4 6% 9% 46%	3586
September	1st to 10th	Night	10% 5% 2 5% 5% 4 4 4 6% 7% 49%	2000
	11th to 20th	Night	11% 6% 1 5% 4 4 3 3 5% 7% 51%	2102
	21st to end	Night	14% 5% 2 5% 5% 5% 4 4 6% 7% 44%	2200
October	1st to 10th	Night	17% 7% 2 7% 5% 5% 5% 4 5% 6% 37%	2299
	11th to 20th	Night	16% 8% 3 8% 4 5% 5% 4 6% 7% 36%	2438
	21st to end	Night	20% 10% 3 8% 5% 4 4 4 5% 6% 30%	2860
November	1st to 10th	Night	16% 10% 4 8% 5% 4 4 4 5% 6% 35%	2667
	11th to 20th	Night	16% 10% 2 8% 5% 5% 5% 4 5% 7% 34%	2732
	21st to end	Night	15% 13% 4 9% 5% 6% 5% 4 5% 6% 27%	2940
December	1st to 10th	Night	14% 18% 7% 13% 6% 6% 5% 4 6% 5% 17%	4720
	11th to 20th	Night	19% 13% 5% 10% 6% 5% 5% 4 4 4 25%	5348
	21st to end	Night	19% 13% 5% 11% 6% 6% 6% 4 5% 6% 19%	7150

Transparency (when cloud cover <= 30%)
Color Meanings: Too cloudy to forecast Poor Below Average Average Above average Transparent
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	62% 8% 11% 15% 3	4662
	11th to 20th	Day	65% 7% 8% 12% 7% 2	4680
	21st to end	Day	57% 7% 11% 14% 10% 1	5124
February	1st to 10th	Day	59% 8% 9% 16% 6% 2	1869
	11th to 20th	Day	55% 8% 11% 17% 8% 1	2009
	21st to end	Day	56% 7% 11% 14% 10% 2	1730
March	1st to 10th	Day	59% 7% 11% 11% 8% 5%	4579
	11th to 20th	Day	53% 6% 15% 15% 8% 3	4791
	21st to end	Day	53% 7% 7% 15% 16% 2	6102
April	1st to 10th	Day	53% 6% 9% 19% 10% 3	2520
	11th to 20th	Day	50% 6% 9% 18% 15% 2	2494
	21st to end	Day	52% 5% 10% 18% 12% 3	2677
May	1st to 10th	Day	62% 7% 9% 15% 6% 1	6127
	11th to 20th	Day	50% 9% 15% 15% 9% 1	6322
	21st to end	Day	48% 9% 12% 22% 8% 1	6949
June	1st to 10th	Day	50% 8% 13% 18% 10% 1	2800
	11th to 20th	Day	43% 9% 13% 21% 13% 2	2800
	21st to end	Day	49% 8% 13% 20% 9% 1	2800
July	1st to 10th	Day	40% 10% 16% 21% 12%	6290
	11th to 20th	Day	37% 11% 15% 26% 10% 1	6285
	21st to end	Day	38% 7% 13% 33% 8%	6728
August	1st to 10th	Day	43% 10% 15% 22% 9% 1	4549
	11th to 20th	Day	41% 10% 18% 25% 6%	4052
	21st to end	Day	37% 9% 17% 23% 13% 1	4312
September	1st to 10th	Day	34% 8% 13% 31% 13% 1	2400
	11th to 20th	Day	33% 6% 13% 31% 15% 1	2296
	21st to end	Day	40% 10% 16% 23% 11% 2	2200
October	1st to 10th	Day	37% 7% 15% 29% 12%	3410
	11th to 20th	Day	42% 6% 16% 23% 13%	3177
	21st to end	Day	42% 6% 16% 28% 7% 1	3180
November	1st to 10th	Day	50% 7% 14% 18% 10% 1	1851
	11th to 20th	Day	52% 7% 12% 16% 11% 2	1885
	21st to end	Day	55% 8% 14% 17% 5% 1	1680
December	1st to 10th	Day	69% 7% 9% 12% 3	2680
	11th to 20th	Day	54% 7% 13% 17% 8%	3066
	21st to end	Day	58% 8% 12% 15% 8%	4048
January	1st to 10th	Night	65% 7% 12% 10% 5% 1	8234
	11th to 20th	Night	68% 6% 9% 10% 6% 1	8280
	21st to end	Night	59% 6% 11% 12% 10% 1	9057
February	1st to 10th	Night	58% 6% 14% 13% 8% 1	2746
	11th to 20th	Night	55% 7% 11% 17% 9% 1	2507
	21st to end	Night	54% 6% 12% 17% 9% 2	2076
March	1st to 10th	Night	58% 6% 9% 13% 12% 2	5494
	11th to 20th	Night	51% 6% 17% 16% 9% 1	5386
	21st to end	Night	54% 6% 8% 18% 12% 2	5072
April	1st to 10th	Night	52% 5% 10% 18% 13% 2	2100
	11th to 20th	Night	53% 6% 10% 18% 12% 1	2075
	21st to end	Night	48% 5% 11% 19% 13% 3	1943
May	1st to 10th	Night	63% 6% 8% 14% 7% 1	3896
	11th to 20th	Night	52% 7% 10% 19% 10% 1	3576
	21st to end	Night	49% 8% 11% 18% 12% 1	3927
June	1st to 10th	Night	47% 8% 13% 19% 12% 2	1600
	11th to 20th	Night	42% 7% 14% 22% 13% 2	1600
	21st to end	Night	43% 9% 15% 22% 10% 1	1600
July	1st to 10th	Night	37% 8% 17% 26% 11%	3560
	11th to 20th	Night	38% 9% 13% 26% 13%	3552
	21st to end	Night	34% 9% 15% 32% 10%	3809
August	1st to 10th	Night	44% 8% 15% 24% 9%	2576
	11th to 20th	Night	42% 9% 15% 24% 10% 1	3025
	21st to end	Night	33% 9% 17% 27% 13%	3586
September	1st to 10th	Night	33% 8% 16% 29% 13% 1	2000
	11th to 20th	Night	33% 6% 15% 31% 14%	2102
	21st to end	Night	39% 7% 13% 25% 14% 1	2200
October	1st to 10th	Night	43% 9% 11% 27% 10%	3754
	11th to 20th	Night	39% 6% 13% 28% 14%	3961
	21st to end	Night	45% 6% 13% 26% 9% 1	4610
November	1st to 10th	Night	49% 8% 13% 19% 10% 2	2667
	11th to 20th	Night	50% 6% 13% 19% 9% 2	2732
	21st to end	Night	55% 8% 15% 17% 5%	2940
December	1st to 10th	Night	68% 7% 10% 12% 3	4720
	11th to 20th	Night	61% 6% 8% 13% 11% 1	5348
	21st to end	Night	63% 7% 12% 13% 5%	7150

Seeing (when cloud cover <= 80%)
Color Meanings: Too cloudy to forecast Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	21% 25% 31% 17% 5%	220
	11th to 20th	Day	24% 32% 32% 10% 1	220
	21st to end	Day	23% 26% 35% 13% 3 1	242
February	1st to 10th	Day	30% 31% 30% 8% 1	319
	11th to 20th	Day	25% 31% 31% 11% 2	488
	21st to end	Day	27% 25% 34% 12% 2	446
March	1st to 10th	Day	28% 24% 31% 15% 2	540
	11th to 20th	Day	29% 29% 25% 14% 3 1	540
	21st to end	Day	29% 29% 25% 12% 5% 1	594
April	1st to 10th	Day	32% 24% 26% 14% 4 1	540
	11th to 20th	Day	30% 27% 25% 12% 4 2	532
	21st to end	Day	29% 29% 23% 12% 5% 2	540
May	1st to 10th	Day	28% 23% 31% 11% 7% 1	507
	11th to 20th	Day	21% 19% 32% 20% 5% 2	527
	21st to end	Day	18% 20% 30% 23% 8% 1	573
June	1st to 10th	Day	25% 16% 35% 18% 6% 1	530
	11th to 20th	Day	16% 18% 35% 22% 8% 1	530
	21st to end	Day	20% 19% 33% 20% 8% 1	530
July	1st to 10th	Day	14% 14% 31% 29% 11% 2	525
	11th to 20th	Day	10% 10% 38% 29% 11% 1	524
	21st to end	Day	13% 11% 35% 29% 10% 2	576
August	1st to 10th	Day	10% 9% 33% 29% 16% 3	526
	11th to 20th	Day	13% 9% 32% 27% 14% 5%	519
	21st to end	Day	12% 16% 29% 27% 11% 4	583
September	1st to 10th	Day	15% 13% 29% 25% 14% 6%	530
	11th to 20th	Day	14% 11% 25% 22% 19% 9%	530
	21st to end	Day	15% 13% 33% 24% 11% 5%	530
October	1st to 10th	Day	20% 18% 25% 20% 14% 3	530
	11th to 20th	Day	22% 20% 29% 20% 7% 1	508
	21st to end	Day	27% 21% 27% 20% 4	462
November	1st to 10th	Day	28% 20% 28% 18% 6%	425
	11th to 20th	Day	29% 21% 29% 15% 5% 1	425
	21st to end	Day	31% 25% 28% 13% 2	220
December	1st to 10th	Day	25% 29% 28% 12% 5%	220
	11th to 20th	Day	27% 30% 33% 9%	220
	21st to end	Day	28% 24% 32% 12% 4	242
January	1st to 10th	Night	20% 22% 37% 18% 3	840
	11th to 20th	Night	24% 23% 31% 18% 4	840
	21st to end	Night	14% 20% 38% 22% 5%	924
February	1st to 10th	Night	17% 20% 38% 23% 3	840
	11th to 20th	Night	19% 23% 36% 19% 2	823
	21st to end	Night	20% 21% 34% 21% 3	692
March	1st to 10th	Night	25% 19% 31% 22% 2	840
	11th to 20th	Night	25% 24% 28% 19% 4	840
	21st to end	Night	25% 21% 28% 20% 5% 1	924
April	1st to 10th	Night	23% 23% 29% 21% 3	840
	11th to 20th	Night	26% 22% 27% 18% 7%	831
	21st to end	Night	23% 19% 30% 21% 6%	683
May	1st to 10th	Night	26% 15% 29% 24% 6%	534
	11th to 20th	Night	15% 17% 34% 27% 6% 1	394
	21st to end	Night	14% 14% 31% 29% 11% 1	433
June	1st to 10th	Night	22% 9% 29% 30% 11% 1	400
	11th to 20th	Night	17% 9% 27% 37% 11% 1	400
	21st to end	Night	16% 8% 31% 34% 11% 1	400
July	1st to 10th	Night	13% 6% 26% 39% 15% 1	390
	11th to 20th	Night	12% 4 25% 41% 16% 2	388
	21st to end	Night	11% 5% 23% 45% 14%	438
August	1st to 10th	Night	11% 4 21% 44% 18% 1	398
	11th to 20th	Night	11% 6% 20% 39% 22% 2	665
	21st to end	Night	12% 8% 23% 36% 20% 2	880
September	1st to 10th	Night	12% 7% 28% 35% 16% 2	800
	11th to 20th	Night	15% 8% 22% 30% 22% 3	800
	21st to end	Night	15% 10% 30% 27% 16% 2	800
October	1st to 10th	Night	22% 14% 23% 26% 15% 1	800
	11th to 20th	Night	20% 15% 26% 29% 9% 1	800
	21st to end	Night	27% 14% 29% 25% 5%	880
November	1st to 10th	Night	24% 16% 31% 20% 7%	820
	11th to 20th	Night	22% 20% 32% 17% 8% 1	840
	21st to end	Night	23% 22% 29% 20% 5%	840
December	1st to 10th	Night	26% 23% 29% 18% 4	840
	11th to 20th	Night	25% 20% 31% 19% 4	840
	21st to end	Night	28% 20% 31% 17% 3	924

Page generated at 2026-04-29 02:21:46. Version ac07

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