Beagle's Nest Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Beagle's Nest Observatory clear sky chart from 2005-11-06 to 2026-01-02.

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	12% 7% 3 7% 4 4 5% 4 6% 8% 40%	127170
	Night	13% 8% 3 7% 4 4 4 3 5% 7% 42%	124278
Transparency	Day	40% 6% 11% 22% 17% 3	130860
	Night	40% 5% 10% 22% 18% 4	128659
Seeing	Day	16% 11% 24% 23% 17% 7%	16732
	Night	17% 9% 25% 28% 18% 3	26471

By Month

Percentage Cloud Cover SE (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	14% 12% 7% 11% 4 4 4 2 3 6% 33%	3625
	11th to 20th	Day	15% 8% 3 12% 3 3 3 2 3 4 44%	3662
	21st to end	Day	19% 8% 4 5% 4 3 3 3 5% 7% 40%	4972
February	1st to 10th	Day	18% 11% 4 8% 4 5% 3 3 4 6% 35%	2000
	11th to 20th	Day	20% 10% 5% 8% 4 4 3 3 4 5% 34%	1948
	21st to end	Day	19% 10% 3 7% 4 4 4 4 4 5% 38%	1650
March	1st to 10th	Day	16% 14% 3 8% 4 4 4 3 3 5% 36%	4480
	11th to 20th	Day	12% 8% 3 6% 5% 4 4 3 4 5% 47%	4702
	21st to end	Day	11% 8% 3 7% 5% 4 4 4 5% 6% 43%	5868
April	1st to 10th	Day	13% 6% 2 6% 4 4 4 3 5% 7% 45%	2400
	11th to 20th	Day	13% 8% 3 6% 4 4 5% 3 6% 6% 43%	2374
	21st to end	Day	13% 7% 2 8% 4 5% 4 4 6% 7% 39%	2405
May	1st to 10th	Day	19% 8% 3 7% 5% 5% 5% 5% 7% 9% 27%	5862
	11th to 20th	Day	14% 9% 4 10% 5% 5% 5% 4 6% 7% 30%	5861
	21st to end	Day	16% 9% 3 6% 4 4 4 4 5% 7% 37%	6433
June	1st to 10th	Day	9% 6% 3 6% 5% 5% 6% 5% 6% 10% 40%	2655
	11th to 20th	Day	5% 5% 2 7% 5% 5% 5% 5% 8% 10% 44%	2800
	21st to end	Day	5% 4 2 5% 5% 5% 6% 5% 8% 12% 42%	2800
July	1st to 10th	Day	6% 5% 2 7% 5% 6% 6% 5% 8% 11% 39%	6360
	11th to 20th	Day	6% 5% 2 7% 6% 6% 7% 6% 9% 12% 34%	6324
	21st to end	Day	11% 8% 3 8% 5% 6% 6% 5% 8% 10% 30%	6424
August	1st to 10th	Day	4 3 1 4 4 4 5% 4 7% 10% 52%	3944
	11th to 20th	Day	6% 5% 2 7% 5% 5% 6% 5% 7% 10% 41%	3849
	21st to end	Day	5% 4 2 4 4 4 5% 4 6% 9% 53%	4312
September	1st to 10th	Day	10% 6% 2 6% 5% 5% 6% 4 7% 9% 41%	2392
	11th to 20th	Day	14% 5% 2 5% 4 5% 5% 4 5% 7% 44%	2200
	21st to end	Day	11% 6% 2 6% 4 4 4 3 6% 6% 49%	2200
October	1st to 10th	Day	11% 4 1 5% 4 4 3 3 4 6% 56%	2200
	11th to 20th	Day	10% 6% 2 5% 3 3 4 3 4 6% 54%	2123
	21st to end	Day	17% 7% 2 5% 4 3 4 2 4 5% 47%	2025
November	1st to 10th	Day	12% 7% 2 4 3 3 3 2 4 6% 54%	1852
	11th to 20th	Day	14% 7% 2 4 4 2 4 3 4 8% 47%	1890
	21st to end	Day	14% 8% 3 5% 4 4 4 3 5% 6% 45%	1890
December	1st to 10th	Day	15% 8% 3 7% 3 4 4 3 5% 5% 45%	3020
	11th to 20th	Day	19% 11% 4 8% 5% 4 3 3 4 5% 34%	3463
	21st to end	Day	16% 11% 4 8% 5% 5% 4 4 6% 7% 30%	4205
January	1st to 10th	Night	15% 14% 4 9% 3 4 3 3 4 6% 36%	6363
	11th to 20th	Night	17% 10% 4 9% 5% 3 3 2 3 4 42%	6293
	21st to end	Night	19% 11% 4 6% 4 3 3 3 4 4 39%	5984
February	1st to 10th	Night	19% 11% 3 8% 5% 5% 3 4 5% 5% 33%	2400
	11th to 20th	Night	22% 10% 4 8% 5% 3 3 3 4 4 36%	2338
	21st to end	Night	21% 10% 4 6% 3 3 4 2 5% 6% 35%	1980
March	1st to 10th	Night	18% 12% 3 7% 4 3 4 3 5% 7% 34%	5373
	11th to 20th	Night	11% 7% 2 6% 4 4 4 3 4 6% 49%	5256
	21st to end	Night	14% 8% 3 7% 4 4 4 3 5% 7% 40%	5103
April	1st to 10th	Night	12% 6% 3 6% 4 4 4 3 5% 8% 46%	2000
	11th to 20th	Night	15% 6% 2 4 4 4 4 3 4 7% 47%	1975
	21st to end	Night	12% 8% 2 6% 4 4 4 4 6% 8% 43%	1994
May	1st to 10th	Night	14% 10% 4 9% 6% 5% 5% 4 5% 6% 33%	4033
	11th to 20th	Night	13% 10% 3 9% 6% 5% 5% 3 5% 7% 33%	4032
	21st to end	Night	13% 7% 3 7% 5% 5% 5% 4 6% 9% 36%	4421
June	1st to 10th	Night	8% 7% 2 5% 4 4 4 4 7% 9% 45%	1739
	11th to 20th	Night	3 4 1 5% 3 4 5% 4 7% 10% 54%	1600
	21st to end	Night	3 3 1 4 3 4 5% 5% 7% 13% 50%	1600
July	1st to 10th	Night	6% 5% 2 6% 5% 5% 6% 5% 9% 12% 40%	3618
	11th to 20th	Night	4 5% 2 5% 4 5% 6% 5% 8% 15% 41%	3647
	21st to end	Night	7% 7% 3 8% 6% 6% 6% 6% 8% 13% 31%	4427
August	1st to 10th	Night	3 3 1 4 3 3 4 3 6% 8% 61%	3201
	11th to 20th	Night	4 3 1 5% 4 3 5% 5% 9% 13% 49%	3200
	21st to end	Night	5% 3 2 4 4 3 4 4 6% 9% 57%	3586
September	1st to 10th	Night	10% 6% 2 5% 4 4 5% 4 6% 6% 50%	2000
	11th to 20th	Night	11% 5% 2 5% 4 4 4 4 5% 7% 50%	2186
	21st to end	Night	10% 6% 2 4 4 3 4 3 5% 6% 54%	2200
October	1st to 10th	Night	9% 4 1 4 3 3 3 3 4 5% 63%	2200
	11th to 20th	Night	14% 5% 2 4 3 3 3 2 4 5% 53%	2273
	21st to end	Night	15% 7% 2 5% 3 3 4 3 5% 5% 49%	2812
November	1st to 10th	Night	12% 6% 2 5% 4 3 3 3 4 5% 52%	2666
	11th to 20th	Night	12% 7% 2 5% 3 3 3 3 6% 7% 49%	2730
	21st to end	Night	16% 9% 3 6% 3 3 3 3 4 5% 45%	2730
December	1st to 10th	Night	16% 11% 3 8% 4 3 3 3 4 5% 41%	4380
	11th to 20th	Night	20% 11% 3 6% 4 3 3 2 3 5% 41%	4952
	21st to end	Night	17% 12% 6% 10% 5% 5% 5% 4 4 5% 27%	6986

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	53% 4 9% 19% 12% 2	3626
	11th to 20th	Day	45% 4 4 21% 25% 1	3662
	21st to end	Day	44% 4 7% 22% 17% 6%	4972
February	1st to 10th	Day	51% 4 8% 20% 15% 3	2000
	11th to 20th	Day	53% 4 7% 19% 14% 4	1958
	21st to end	Day	49% 4 7% 17% 17% 6%	1650
March	1st to 10th	Day	51% 4 5% 14% 17% 9%	4480
	11th to 20th	Day	39% 5% 7% 21% 19% 9%	4702
	21st to end	Day	41% 5% 9% 27% 17% 1	5870
April	1st to 10th	Day	38% 6% 10% 22% 20% 3	2400
	11th to 20th	Day	40% 5% 8% 21% 20% 6%	2374
	21st to end	Day	42% 6% 11% 23% 15% 2	2405
May	1st to 10th	Day	49% 9% 13% 19% 9% 1	5897
	11th to 20th	Day	51% 8% 13% 19% 10%	5865
	21st to end	Day	44% 7% 9% 22% 16% 2	6447
June	1st to 10th	Day	37% 8% 13% 23% 17% 2	2655
	11th to 20th	Day	32% 9% 16% 23% 18% 3	2800
	21st to end	Day	31% 10% 17% 22% 15% 4	2800
July	1st to 10th	Day	34% 9% 19% 26% 10% 1	6291
	11th to 20th	Day	37% 10% 21% 25% 6% 1	6249
	21st to end	Day	44% 9% 21% 21% 5% 1	6240
August	1st to 10th	Day	23% 8% 15% 32% 20% 1	3931
	11th to 20th	Day	33% 8% 15% 26% 16% 2	3885
	21st to end	Day	27% 6% 11% 29% 24% 2	4311
September	1st to 10th	Day	37% 9% 11% 21% 17% 4	2392
	11th to 20th	Day	37% 7% 10% 23% 21% 2	2200
	21st to end	Day	34% 6% 11% 23% 22% 5%	2200
October	1st to 10th	Day	20% 4 6% 17% 43% 10%	3590
	11th to 20th	Day	23% 3 6% 23% 29% 15%	3441
	21st to end	Day	32% 3 5% 23% 31% 7%	3250
November	1st to 10th	Day	33% 4 8% 23% 27% 5%	1852
	11th to 20th	Day	37% 3 8% 23% 24% 6%	1890
	21st to end	Day	40% 3 7% 24% 20% 5%	1890
December	1st to 10th	Day	42% 4 5% 27% 20% 2	3020
	11th to 20th	Day	53% 3 8% 19% 13% 3	3460
	21st to end	Day	51% 6% 10% 24% 8% 1	4205
January	1st to 10th	Night	50% 4 9% 20% 16% 1	6363
	11th to 20th	Night	48% 3 6% 17% 22% 4	6293
	21st to end	Night	49% 3 5% 20% 17% 5%	5984
February	1st to 10th	Night	53% 4 9% 17% 16% 1	2400
	11th to 20th	Night	53% 4 6% 17% 16% 4	2339
	21st to end	Night	51% 4 8% 16% 17% 5%	1980
March	1st to 10th	Night	49% 5% 6% 15% 18% 7%	5373
	11th to 20th	Night	36% 5% 8% 19% 18% 14%	5256
	21st to end	Night	44% 4 8% 25% 17% 3	5103
April	1st to 10th	Night	37% 5% 11% 23% 20% 3	2000
	11th to 20th	Night	37% 5% 8% 21% 22% 8%	1975
	21st to end	Night	38% 6% 11% 25% 18% 2	1994
May	1st to 10th	Night	49% 7% 13% 19% 10% 1	4060
	11th to 20th	Night	49% 8% 15% 16% 12% 1	4033
	21st to end	Night	42% 9% 12% 22% 13% 1	4429
June	1st to 10th	Night	34% 7% 14% 23% 18% 3	1739
	11th to 20th	Night	23% 7% 17% 31% 19% 3	1600
	21st to end	Night	23% 10% 19% 29% 15% 4	1600
July	1st to 10th	Night	32% 9% 19% 27% 11% 1	3580
	11th to 20th	Night	28% 9% 26% 29% 5% 2	3602
	21st to end	Night	42% 10% 22% 20% 6% 1	4297
August	1st to 10th	Night	19% 7% 13% 38% 22% 1	3190
	11th to 20th	Night	23% 9% 23% 29% 15% 1	3230
	21st to end	Night	23% 6% 13% 31% 24% 3	3586
September	1st to 10th	Night	33% 8% 12% 24% 19% 5%	2000
	11th to 20th	Night	33% 6% 11% 22% 26% 2	2186
	21st to end	Night	31% 6% 10% 23% 25% 6%	2200
October	1st to 10th	Night	18% 4 7% 18% 41% 12%	3590
	11th to 20th	Night	21% 3 4 22% 31% 19%	3694
	21st to end	Night	26% 4 7% 25% 28% 11%	4537
November	1st to 10th	Night	35% 4 7% 23% 24% 7%	2666
	11th to 20th	Night	34% 4 7% 22% 26% 7%	2730
	21st to end	Night	42% 3 7% 22% 20% 5%	2730
December	1st to 10th	Night	46% 4 8% 16% 24% 2	4380
	11th to 20th	Night	48% 2 6% 22% 20% 3	4954
	21st to end	Night	57% 5% 7% 20% 8% 2	6986

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	25% 22% 36% 11% 6%	303
	11th to 20th	Day	30% 26% 28% 12% 2 1	300
	21st to end	Day	23% 24% 40% 11% 2	330
February	1st to 10th	Day	29% 25% 31% 13% 2 1	300
	11th to 20th	Day	36% 24% 31% 7% 2	300
	21st to end	Day	33% 27% 29% 9% 2	249
March	1st to 10th	Day	31% 20% 32% 13% 4	300
	11th to 20th	Day	25% 22% 33% 14% 5% 1	378
	21st to end	Day	25% 18% 35% 17% 5%	550
April	1st to 10th	Day	24% 17% 30% 21% 8% 2	500
	11th to 20th	Day	22% 17% 28% 23% 8% 1	492
	21st to end	Day	17% 19% 29% 22% 10% 2	500
May	1st to 10th	Day	21% 17% 28% 22% 10% 3	503
	11th to 20th	Day	15% 11% 27% 24% 18% 5%	527
	21st to end	Day	13% 8% 22% 27% 18% 12%	573
June	1st to 10th	Day	11% 4 23% 26% 20% 15%	585
	11th to 20th	Day	6% 4 18% 30% 30% 13%	730
	21st to end	Day	5% 3 21% 32% 24% 14%	730
July	1st to 10th	Day	7% 3 12% 33% 30% 15%	721
	11th to 20th	Day	6% 5% 14% 26% 32% 16%	708
	21st to end	Day	9% 3 13% 27% 30% 18%	576
August	1st to 10th	Day	7% 4 14% 27% 32% 16%	526
	11th to 20th	Day	10% 4 13% 33% 32% 8%	519
	21st to end	Day	10% 3 10% 24% 34% 17%	583
September	1st to 10th	Day	9% 4 15% 30% 29% 13%	530
	11th to 20th	Day	13% 2 12% 26% 31% 15%	530
	21st to end	Day	16% 5% 17% 29% 24% 8%	530
October	1st to 10th	Day	12% 4 22% 30% 24% 8%	530
	11th to 20th	Day	13% 12% 32% 26% 14% 2	453
	21st to end	Day	23% 15% 32% 21% 7% 1	363
November	1st to 10th	Day	20% 14% 29% 26% 9% 1	330
	11th to 20th	Day	18% 17% 38% 23% 4 1	330
	21st to end	Day	21% 19% 32% 17% 10% 2	330
December	1st to 10th	Day	29% 17% 34% 16% 4 1	330
	11th to 20th	Day	24% 21% 34% 15% 5% 1	330
	21st to end	Day	25% 22% 35% 17% 1	363
January	1st to 10th	Night	24% 16% 32% 24% 4	1006
	11th to 20th	Night	26% 19% 31% 19% 4	982
	21st to end	Night	22% 13% 41% 22% 2	880
February	1st to 10th	Night	25% 16% 33% 23% 3	800
	11th to 20th	Night	30% 16% 32% 20% 2	783
	21st to end	Night	30% 17% 33% 18% 1	660
March	1st to 10th	Night	22% 15% 33% 25% 4	800
	11th to 20th	Night	20% 14% 37% 22% 6% 1	800
	21st to end	Night	20% 14% 33% 26% 7%	723
April	1st to 10th	Night	15% 15% 32% 30% 8% 1	600
	11th to 20th	Night	18% 11% 34% 27% 8% 1	593
	21st to end	Night	15% 11% 33% 27% 13% 1	600
May	1st to 10th	Night	13% 10% 32% 29% 15% 2	600
	11th to 20th	Night	13% 5% 26% 33% 19% 4	591
	21st to end	Night	10% 3 21% 37% 25% 5%	650
June	1st to 10th	Night	11% 4 16% 35% 30% 4	600
	11th to 20th	Night	6% 2 12% 39% 36% 6%	600
	21st to end	Night	4 2 15% 36% 37% 7%	600
July	1st to 10th	Night	8% 2 10% 32% 36% 12%	585
	11th to 20th	Night	7% 2 10% 29% 42% 9%	582
	21st to end	Night	7% 1 8% 32% 42% 9%	657
August	1st to 10th	Night	8% 2 6% 32% 44% 8%	597
	11th to 20th	Night	6% 3 10% 40% 36% 6%	594
	21st to end	Night	9% 2 8% 33% 39% 9%	660
September	1st to 10th	Night	10% 3 12% 31% 39% 5%	600
	11th to 20th	Night	13% 2 12% 29% 38% 6%	786
	21st to end	Night	11% 4 18% 31% 32% 4	800
October	1st to 10th	Night	12% 4 18% 32% 29% 6%	800
	11th to 20th	Night	17% 8% 23% 33% 18% 1	800
	21st to end	Night	18% 9% 27% 31% 14% 1	880
November	1st to 10th	Night	16% 8% 23% 35% 16% 2	820
	11th to 20th	Night	14% 13% 33% 28% 12% 1	840
	21st to end	Night	22% 12% 27% 28% 10%	840
December	1st to 10th	Night	25% 14% 30% 25% 6%	840
	11th to 20th	Night	21% 12% 34% 26% 7% 1	840
	21st to end	Night	28% 14% 31% 23% 4	1082

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