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 2024-11-12.

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% 7% 3 6% 4 4 5% 4 6% 8% 41%	101136
	Night	13% 8% 3 6% 4 4 4 3 5% 7% 43%	98022
Transparency	Day	39% 6% 11% 23% 18% 3	104868
	Night	38% 6% 10% 22% 19% 5%	102429
Seeing	Day	16% 11% 24% 24% 18% 8%	15228
	Night	17% 9% 25% 29% 18% 3	24942

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	12% 13% 6% 10% 5% 5% 5% 3 4 6% 31%	2527
	11th to 20th	Day	20% 9% 3 10% 4 3 3 3 4 5% 36%	2545
	21st to end	Day	23% 10% 5% 5% 4 3 3 3 3 6% 35%	3476
February	1st to 10th	Day	18% 11% 3 8% 3 5% 3 3 4 6% 36%	1900
	11th to 20th	Day	19% 10% 4 7% 4 4 3 3 4 5% 35%	1848
	21st to end	Day	20% 10% 3 7% 4 4 4 3 4 5% 36%	1570
March	1st to 10th	Day	20% 14% 3 7% 5% 4 4 4 4 5% 31%	3120
	11th to 20th	Day	13% 7% 3 6% 4 3 4 3 5% 6% 47%	3286
	21st to end	Day	12% 8% 2 7% 5% 5% 5% 4 6% 6% 41%	4094
April	1st to 10th	Day	12% 6% 2 6% 4 4 4 3 5% 7% 45%	2280
	11th to 20th	Day	14% 8% 3 6% 4 4 5% 3 6% 6% 43%	2254
	21st to end	Day	13% 7% 3 8% 4 5% 4 4 6% 7% 40%	2285
May	1st to 10th	Day	17% 7% 2 6% 5% 4 4 5% 6% 9% 35%	4082
	11th to 20th	Day	16% 8% 3 7% 4 5% 4 3 5% 8% 37%	4081
	21st to end	Day	11% 7% 3 6% 5% 4 5% 5% 5% 9% 39%	4476
June	1st to 10th	Day	9% 6% 3 6% 5% 5% 6% 5% 6% 10% 40%	2522
	11th to 20th	Day	5% 5% 1 6% 5% 5% 5% 5% 8% 10% 45%	2660
	21st to end	Day	5% 4 2 5% 5% 5% 6% 5% 8% 11% 42%	2660
July	1st to 10th	Day	6% 5% 2 7% 6% 6% 7% 5% 8% 11% 37%	4440
	11th to 20th	Day	8% 5% 3 7% 6% 5% 6% 5% 8% 10% 38%	4418
	21st to end	Day	15% 10% 4 10% 5% 6% 6% 4 7% 8% 25%	4466
August	1st to 10th	Day	3 3 1 4 4 4 4 4 7% 10% 53%	3823
	11th to 20th	Day	6% 5% 2 7% 5% 5% 6% 5% 7% 11% 41%	3729
	21st to end	Day	5% 4 1 4 4 4 5% 4 6% 9% 53%	4180
September	1st to 10th	Day	11% 6% 2 6% 5% 5% 6% 5% 7% 8% 41%	2273
	11th to 20th	Day	14% 5% 2 5% 4 4 5% 4 5% 7% 44%	2090
	21st to end	Day	11% 6% 2 5% 4 4 4 3 6% 6% 48%	2090
October	1st to 10th	Day	11% 4 1 5% 4 4 3 3 4 6% 56%	2090
	11th to 20th	Day	11% 6% 2 5% 3 3 4 3 4 6% 53%	2017
	21st to end	Day	17% 7% 2 5% 4 3 4 2 3 5% 48%	1924
November	1st to 10th	Day	13% 6% 2 4 2 3 3 2 4 6% 54%	1762
	11th to 20th	Day	14% 7% 2 4 4 2 4 3 4 7% 48%	1719
	21st to end	Day	15% 8% 3 4 4 4 4 3 5% 6% 45%	1710
December	1st to 10th	Day	22% 9% 3 6% 4 4 3 3 5% 5% 36%	1710
	11th to 20th	Day	16% 10% 3 7% 5% 4 4 4 5% 6% 38%	2153
	21st to end	Day	14% 11% 4 8% 5% 5% 5% 4 5% 7% 31%	2876
January	1st to 10th	Night	18% 13% 3 6% 3 3 3 3 4 6% 37%	4428
	11th to 20th	Night	17% 12% 4 9% 5% 3 3 3 3 4 35%	4401
	21st to end	Night	23% 13% 4 5% 3 3 3 2 4 4 35%	4180
February	1st to 10th	Night	19% 11% 3 8% 5% 5% 3 3 5% 5% 33%	2280
	11th to 20th	Night	21% 10% 4 7% 5% 3 3 3 4 4 37%	2218
	21st to end	Night	22% 10% 4 7% 3 3 4 3 5% 5% 33%	1884
March	1st to 10th	Night	23% 11% 3 7% 4 3 4 3 4 6% 33%	3733
	11th to 20th	Night	13% 8% 3 5% 4 4 4 3 4 5% 47%	3672
	21st to end	Night	15% 9% 3 7% 5% 4 4 3 5% 6% 39%	3565
April	1st to 10th	Night	11% 6% 2 6% 4 3 4 3 5% 8% 47%	1900
	11th to 20th	Night	15% 6% 2 4 4 4 4 3 4 7% 47%	1875
	21st to end	Night	12% 8% 2 5% 4 4 4 3 6% 8% 44%	1895
May	1st to 10th	Night	14% 8% 3 7% 5% 4 5% 3 5% 6% 40%	2813
	11th to 20th	Night	12% 9% 3 6% 4 4 4 3 5% 7% 44%	2812
	21st to end	Night	7% 5% 2 6% 5% 5% 5% 4 7% 10% 42%	3079
June	1st to 10th	Night	9% 7% 2 5% 4 4 4 4 7% 9% 45%	1652
	11th to 20th	Night	3 4 1 4 3 4 4 4 7% 10% 56%	1520
	21st to end	Night	3 3 1 4 3 4 5% 6% 7% 13% 49%	1520
July	1st to 10th	Night	6% 4 2 6% 5% 5% 6% 5% 10% 13% 39%	2530
	11th to 20th	Night	5% 5% 2 5% 4 4 5% 4 7% 13% 47%	2547
	21st to end	Night	10% 9% 4 10% 6% 7% 5% 5% 7% 9% 29%	3087
August	1st to 10th	Night	3 3 1 4 3 3 4 3 6% 8% 61%	3102
	11th to 20th	Night	4 3 1 5% 4 3 5% 5% 9% 13% 48%	3100
	21st to end	Night	5% 3 2 4 4 3 4 4 6% 9% 57%	3476
September	1st to 10th	Night	10% 6% 2 5% 4 4 5% 4 6% 6% 49%	1900
	11th to 20th	Night	11% 5% 1 5% 4 4 5% 4 5% 6% 50%	2076
	21st to end	Night	9% 6% 2 4 4 3 4 3 5% 6% 54%	2090
October	1st to 10th	Night	9% 4 1 4 3 3 3 3 4 5% 62%	2090
	11th to 20th	Night	14% 5% 2 5% 3 3 3 2 4 6% 52%	2159
	21st to end	Night	15% 7% 2 5% 3 3 4 3 5% 5% 49%	2671
November	1st to 10th	Night	12% 6% 2 5% 4 3 3 3 4 5% 52%	2536
	11th to 20th	Night	12% 6% 2 5% 3 3 3 3 6% 7% 49%	2484
	21st to end	Night	16% 8% 2 6% 3 3 3 3 4 5% 46%	2470
December	1st to 10th	Night	19% 12% 3 7% 4 3 3 3 4 6% 36%	2470
	11th to 20th	Night	16% 10% 2 5% 4 3 3 3 4 5% 45%	3042
	21st to end	Night	16% 13% 5% 9% 5% 5% 4 4 4 5% 28%	4765

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	54% 4 7% 21% 12% 2	2528
	11th to 20th	Day	51% 5% 6% 19% 19% 1	2545
	21st to end	Day	51% 4 8% 23% 13% 1	3476
February	1st to 10th	Day	51% 4 8% 20% 15% 3	1900
	11th to 20th	Day	52% 4 6% 20% 14% 4	1858
	21st to end	Day	51% 4 7% 16% 16% 6%	1570
March	1st to 10th	Day	55% 5% 6% 13% 13% 8%	3120
	11th to 20th	Day	38% 6% 9% 24% 18% 6%	3286
	21st to end	Day	41% 6% 9% 26% 16% 1	4094
April	1st to 10th	Day	38% 6% 10% 22% 21% 3	2280
	11th to 20th	Day	41% 5% 8% 21% 20% 6%	2254
	21st to end	Day	41% 6% 11% 24% 16% 2	2285
May	1st to 10th	Day	44% 9% 12% 22% 13% 1	4120
	11th to 20th	Day	44% 7% 12% 23% 12% 1	4085
	21st to end	Day	39% 9% 11% 21% 19% 1	4489
June	1st to 10th	Day	37% 8% 13% 23% 17% 2	2522
	11th to 20th	Day	30% 9% 16% 24% 18% 3	2660
	21st to end	Day	32% 10% 17% 22% 15% 4	2660
July	1st to 10th	Day	35% 10% 20% 26% 7% 2	4371
	11th to 20th	Day	37% 8% 17% 27% 8% 2	4343
	21st to end	Day	54% 8% 12% 18% 7% 1	4324
August	1st to 10th	Day	23% 8% 15% 32% 21% 1	3810
	11th to 20th	Day	33% 8% 15% 26% 16% 2	3765
	21st to end	Day	28% 7% 11% 30% 24% 2	4179
September	1st to 10th	Day	37% 9% 11% 21% 17% 5%	2273
	11th to 20th	Day	38% 7% 10% 22% 20% 2	2090
	21st to end	Day	33% 6% 11% 23% 21% 5%	2090
October	1st to 10th	Day	20% 4 6% 16% 44% 10%	3480
	11th to 20th	Day	23% 3 6% 23% 29% 15%	3335
	21st to end	Day	31% 3 5% 23% 31% 7%	3149
November	1st to 10th	Day	32% 4 8% 23% 27% 6%	1762
	11th to 20th	Day	36% 3 7% 22% 25% 7%	1719
	21st to end	Day	40% 4 8% 24% 20% 5%	1710
December	1st to 10th	Day	50% 3 7% 21% 15% 3	1710
	11th to 20th	Day	46% 4 10% 21% 17% 2	2150
	21st to end	Day	50% 6% 11% 21% 10% 2	2876
January	1st to 10th	Night	48% 4 7% 24% 16% 1	4428
	11th to 20th	Night	52% 4 7% 16% 16% 5%	4401
	21st to end	Night	53% 3 7% 21% 14% 2	4180
February	1st to 10th	Night	53% 4 9% 17% 16% 1	2280
	11th to 20th	Night	51% 4 6% 18% 16% 4	2219
	21st to end	Night	53% 4 8% 15% 16% 5%	1884
March	1st to 10th	Night	52% 5% 8% 12% 16% 7%	3733
	11th to 20th	Night	38% 5% 9% 21% 16% 10%	3672
	21st to end	Night	44% 5% 8% 23% 18% 1	3565
April	1st to 10th	Night	36% 5% 11% 24% 21% 3	1900
	11th to 20th	Night	37% 4 8% 20% 22% 8%	1875
	21st to end	Night	38% 6% 10% 25% 18% 2	1895
May	1st to 10th	Night	43% 7% 13% 22% 14% 2	2840
	11th to 20th	Night	39% 8% 15% 20% 17% 1	2813
	21st to end	Night	33% 10% 14% 24% 17% 2	3087
June	1st to 10th	Night	35% 7% 14% 23% 17% 3	1652
	11th to 20th	Night	21% 7% 17% 32% 19% 3	1520
	21st to end	Night	24% 9% 19% 28% 16% 4	1520
July	1st to 10th	Night	31% 9% 21% 28% 9% 2	2490
	11th to 20th	Night	27% 7% 19% 36% 8% 3	2499
	21st to end	Night	50% 9% 12% 19% 8% 1	2988
August	1st to 10th	Night	19% 6% 12% 38% 23% 1	3091
	11th to 20th	Night	23% 9% 22% 29% 15% 1	3130
	21st to end	Night	23% 6% 13% 31% 24% 3	3476
September	1st to 10th	Night	33% 8% 11% 24% 18% 6%	1900
	11th to 20th	Night	34% 6% 11% 21% 26% 3	2076
	21st to end	Night	30% 6% 10% 24% 24% 6%	2090
October	1st to 10th	Night	18% 4 7% 18% 42% 11%	3480
	11th to 20th	Night	21% 3 4 22% 30% 19%	3580
	21st to end	Night	25% 4 7% 25% 28% 11%	4396
November	1st to 10th	Night	35% 4 7% 22% 25% 8%	2536
	11th to 20th	Night	34% 4 7% 21% 27% 7%	2484
	21st to end	Night	41% 3 7% 22% 21% 5%	2470
December	1st to 10th	Night	50% 5% 10% 17% 16% 3	2470
	11th to 20th	Night	42% 3 7% 21% 23% 4	3044
	21st to end	Night	55% 6% 9% 17% 11% 2	4765

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	24% 23% 36% 11% 6%	270
	11th to 20th	Day	31% 25% 26% 13% 3 1	270
	21st to end	Day	24% 23% 39% 12% 3	297
February	1st to 10th	Day	31% 22% 31% 13% 2 1	270
	11th to 20th	Day	35% 23% 31% 8% 2	270
	21st to end	Day	36% 27% 27% 8% 2	225
March	1st to 10th	Day	30% 19% 34% 13% 4	270
	11th to 20th	Day	25% 22% 33% 15% 5% 1	344
	21st to end	Day	24% 17% 34% 19% 6%	506
April	1st to 10th	Day	23% 15% 31% 21% 8% 2	460
	11th to 20th	Day	23% 15% 28% 24% 9% 2	452
	21st to end	Day	18% 18% 29% 22% 11% 2	460
May	1st to 10th	Day	19% 17% 27% 23% 11% 4	463
	11th to 20th	Day	14% 10% 26% 25% 19% 6%	487
	21st to end	Day	12% 7% 21% 28% 20% 13%	529
June	1st to 10th	Day	11% 5% 23% 24% 21% 16%	542
	11th to 20th	Day	5% 4 16% 31% 30% 13%	680
	21st to end	Day	6% 3 22% 34% 22% 13%	680
July	1st to 10th	Day	8% 3 12% 32% 30% 16%	671
	11th to 20th	Day	7% 5% 14% 26% 31% 17%	659
	21st to end	Day	10% 2 14% 28% 28% 19%	532
August	1st to 10th	Day	7% 4 14% 27% 32% 17%	486
	11th to 20th	Day	10% 4 14% 33% 32% 7%	479
	21st to end	Day	11% 3 9% 23% 36% 18%	539
September	1st to 10th	Day	9% 4 15% 30% 29% 14%	490
	11th to 20th	Day	14% 2 13% 26% 29% 16%	490
	21st to end	Day	17% 5% 17% 29% 24% 9%	490
October	1st to 10th	Day	13% 3 22% 29% 24% 8%	490
	11th to 20th	Day	14% 13% 33% 24% 14% 3	417
	21st to end	Day	23% 15% 31% 22% 8% 1	330
November	1st to 10th	Day	19% 14% 28% 27% 10% 1	300
	11th to 20th	Day	17% 16% 38% 23% 5% 1	273
	21st to end	Day	21% 17% 30% 17% 12% 2	270
December	1st to 10th	Day	31% 18% 28% 18% 4 1	270
	11th to 20th	Day	22% 21% 33% 17% 6% 1	270
	21st to end	Day	24% 23% 35% 17% 1	297
January	1st to 10th	Night	24% 17% 31% 24% 4	950
	11th to 20th	Night	27% 19% 30% 20% 5%	933
	21st to end	Night	22% 13% 41% 22% 2	836
February	1st to 10th	Night	25% 15% 33% 24% 3	760
	11th to 20th	Night	29% 16% 32% 21% 2	743
	21st to end	Night	32% 17% 33% 17% 1	628
March	1st to 10th	Night	22% 14% 33% 26% 5%	760
	11th to 20th	Night	20% 14% 37% 23% 6% 1	760
	21st to end	Night	20% 14% 33% 26% 7%	687
April	1st to 10th	Night	14% 15% 32% 30% 8% 1	570
	11th to 20th	Night	19% 12% 33% 27% 8% 1	563
	21st to end	Night	16% 11% 32% 28% 12% 1	570
May	1st to 10th	Night	12% 9% 31% 29% 16% 2	570
	11th to 20th	Night	12% 5% 25% 34% 20% 4	561
	21st to end	Night	8% 2 20% 38% 27% 5%	617
June	1st to 10th	Night	11% 4 15% 35% 31% 4	570
	11th to 20th	Night	5% 1 12% 39% 36% 6%	570
	21st to end	Night	4 2 15% 36% 36% 7%	570
July	1st to 10th	Night	8% 2 11% 32% 35% 13%	555
	11th to 20th	Night	7% 2 11% 29% 42% 9%	552
	21st to end	Night	7% 1 9% 33% 41% 9%	624
August	1st to 10th	Night	8% 2 6% 32% 44% 8%	567
	11th to 20th	Night	6% 3 10% 41% 35% 5%	564
	21st to end	Night	9% 2 8% 31% 40% 10%	627
September	1st to 10th	Night	10% 3 12% 30% 39% 5%	570
	11th to 20th	Night	14% 2 12% 29% 37% 6%	746
	21st to end	Night	11% 4 18% 31% 32% 4	760
October	1st to 10th	Night	12% 4 17% 32% 30% 6%	760
	11th to 20th	Night	17% 8% 23% 32% 18% 1	760
	21st to end	Night	18% 9% 26% 31% 15% 1	836
November	1st to 10th	Night	16% 8% 23% 35% 16% 2	780
	11th to 20th	Night	14% 13% 33% 28% 12% 1	765
	21st to end	Night	21% 12% 27% 29% 10% 1	760
December	1st to 10th	Night	25% 13% 29% 25% 7%	760
	11th to 20th	Night	20% 12% 33% 27% 8% 1	760
	21st to end	Night	28% 14% 31% 24% 4	978

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