Beaglehaven Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Beaglehaven Observatory clear sky chart from 2005-11-06 to 2024-11-02.

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	14% 6% 2 6% 4 4 4 4 6% 8% 41%	101216
	Night	15% 6% 2 6% 4 4 4 4 5% 7% 43%	97712
Transparency	Day	21% 50% 7% 13% 8% 1	101018
	Night	21% 50% 6% 13% 8% 1	97580
Seeing	Day	19% 13% 27% 23% 14% 5%	14962
	Night	17% 12% 29% 29% 12% 1	24479

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	17% 5% 2 5% 3 4 4 4 4 6% 46%	2621
	11th to 20th	Day	15% 11% 3 6% 5% 4 4 4 4 5% 39%	2840
	21st to end	Day	17% 10% 3 7% 5% 4 3 3 4 6% 37%	3124
February	1st to 10th	Day	13% 8% 2 7% 6% 4 5% 4 6% 7% 38%	1710
	11th to 20th	Day	18% 8% 2 5% 5% 4 4 4 5% 6% 41%	1696
	21st to end	Day	17% 8% 3 6% 4 4 5% 3 5% 5% 39%	1570
March	1st to 10th	Day	21% 7% 2 6% 4 5% 5% 3 5% 7% 34%	3417
	11th to 20th	Day	10% 5% 2 5% 4 5% 5% 4 6% 7% 49%	3480
	21st to end	Day	19% 6% 3 6% 4 4 4 3 5% 7% 40%	3861
April	1st to 10th	Day	12% 7% 2 6% 5% 4 4 4 6% 7% 42%	2280
	11th to 20th	Day	13% 6% 2 6% 4 4 3 4 5% 6% 46%	2254
	21st to end	Day	18% 6% 2 6% 4 4 4 4 5% 5% 41%	2280
May	1st to 10th	Day	22% 8% 2 7% 4 4 4 4 6% 8% 30%	4065
	11th to 20th	Day	23% 6% 2 7% 4 4 4 4 6% 9% 30%	4252
	21st to end	Day	11% 5% 1 5% 4 4 4 4 7% 9% 45%	4823
June	1st to 10th	Day	10% 4 2 5% 5% 5% 5% 4 7% 9% 43%	2660
	11th to 20th	Day	9% 6% 2 6% 4 4 5% 4 8% 10% 41%	2660
	21st to end	Day	9% 4 2 5% 5% 5% 5% 4 7% 10% 45%	2660
July	1st to 10th	Day	5% 4 2 6% 5% 5% 6% 6% 8% 11% 42%	4440
	11th to 20th	Day	8% 5% 2 6% 4 5% 5% 5% 8% 10% 40%	4258
	21st to end	Day	10% 7% 3 7% 6% 5% 6% 6% 7% 8% 37%	4466
August	1st to 10th	Day	14% 5% 2 7% 6% 6% 5% 5% 8% 9% 34%	4104
	11th to 20th	Day	9% 5% 2 6% 5% 5% 5% 5% 7% 9% 42%	3898
	21st to end	Day	10% 5% 2 5% 4 3 5% 4 5% 8% 48%	4180
September	1st to 10th	Day	14% 5% 2 4 4 4 4 4 5% 7% 46%	2280
	11th to 20th	Day	12% 6% 2 6% 3 3 4 3 5% 8% 48%	2280
	21st to end	Day	20% 6% 2 6% 4 3 4 4 5% 7% 38%	1987
October	1st to 10th	Day	16% 6% 1 4 4 4 3 3 5% 6% 46%	1900
	11th to 20th	Day	16% 4 2 6% 3 3 3 3 5% 6% 49%	1900
	21st to end	Day	13% 5% 3 5% 3 4 4 3 4 6% 50%	2090
November	1st to 10th	Day	12% 5% 1 5% 4 4 3 3 5% 7% 50%	1790
	11th to 20th	Day	15% 5% 2 4 3 2 4 3 6% 5% 50%	1668
	21st to end	Day	15% 6% 2 4 3 4 5% 4 5% 7% 46%	1520
December	1st to 10th	Day	15% 7% 3 6% 5% 4 4 4 6% 7% 39%	1520
	11th to 20th	Day	16% 5% 2 5% 4 3 4 4 5% 7% 44%	1910
	21st to end	Day	18% 6% 2 6% 5% 4 4 5% 6% 8% 34%	2772
January	1st to 10th	Night	14% 7% 2 6% 4 4 3 3 5% 6% 45%	4322
	11th to 20th	Night	19% 7% 2 5% 3 3 3 2 5% 5% 46%	4120
	21st to end	Night	20% 9% 3 6% 3 3 3 3 4 6% 40%	4532
February	1st to 10th	Night	14% 8% 3 5% 4 4 4 4 6% 5% 42%	2470
	11th to 20th	Night	18% 7% 3 6% 4 4 4 3 5% 6% 41%	2369
	21st to end	Night	17% 9% 2 5% 4 4 4 3 5% 5% 42%	1884
March	1st to 10th	Night	21% 7% 2 6% 4 4 4 3 5% 6% 38%	3432
	11th to 20th	Night	12% 5% 2 4 3 4 4 4 6% 8% 49%	3480
	21st to end	Night	15% 8% 3 6% 4 3 3 3 4 5% 47%	3769
April	1st to 10th	Night	14% 8% 2 5% 5% 4 5% 4 6% 7% 40%	1900
	11th to 20th	Night	13% 6% 2 6% 3 4 4 3 6% 7% 45%	1875
	21st to end	Night	16% 5% 2 5% 4 4 5% 4 6% 7% 44%	1900
May	1st to 10th	Night	23% 9% 2 6% 4 5% 5% 4 5% 7% 30%	2859
	11th to 20th	Night	23% 9% 3 7% 5% 4 4 3 4 6% 33%	2637
	21st to end	Night	10% 5% 2 5% 4 5% 5% 5% 8% 9% 43%	2732
June	1st to 10th	Night	10% 5% 2 4 4 5% 5% 4 6% 9% 45%	1520
	11th to 20th	Night	12% 5% 2 5% 5% 4 6% 4 7% 8% 42%	1520
	21st to end	Night	8% 4 2 5% 5% 5% 5% 4 7% 10% 44%	1520
July	1st to 10th	Night	6% 5% 3 7% 6% 6% 6% 4 8% 10% 40%	2520
	11th to 20th	Night	7% 6% 2 7% 6% 6% 6% 5% 7% 11% 38%	2698
	21st to end	Night	10% 7% 3 7% 5% 6% 5% 4 7% 9% 37%	3087
August	1st to 10th	Night	16% 6% 2 8% 5% 5% 6% 5% 7% 10% 31%	2825
	11th to 20th	Night	9% 6% 3 8% 5% 6% 5% 4 6% 9% 38%	2899
	21st to end	Night	11% 4 2 5% 3 4 4 3 5% 9% 48%	3476
September	1st to 10th	Night	14% 5% 2 6% 4 4 4 3 5% 7% 44%	1900
	11th to 20th	Night	10% 6% 2 5% 3 4 3 2 5% 7% 51%	1900
	21st to end	Night	21% 7% 3 6% 4 4 4 3 4 6% 40%	2188
October	1st to 10th	Night	20% 5% 2 6% 3 3 3 3 4 6% 45%	2280
	11th to 20th	Night	15% 5% 2 4 3 3 3 2 4 5% 53%	2280
	21st to end	Night	15% 5% 2 5% 3 3 3 2 4 6% 51%	2508
November	1st to 10th	Night	12% 6% 2 6% 3 3 3 3 4 6% 54%	2310
	11th to 20th	Night	14% 6% 2 4 3 4 3 3 4 6% 50%	2511
	21st to end	Night	13% 4 2 5% 4 4 4 4 6% 7% 48%	2660
December	1st to 10th	Night	17% 7% 2 6% 4 4 4 3 5% 7% 41%	2660
	11th to 20th	Night	17% 6% 2 5% 4 4 4 3 5% 7% 42%	3285
	21st to end	Night	17% 6% 2 6% 4 4 5% 4 7% 8% 35%	4884

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	23% 38% 5% 20% 9% 3	2622
	11th to 20th	Day	30% 38% 5% 13% 9% 5%	2840
	21st to end	Day	30% 42% 6% 14% 6% 1	3124
February	1st to 10th	Day	17% 66% 6% 6% 4 1	1710
	11th to 20th	Day	16% 64% 3 9% 6% 1	1705
	21st to end	Day	18% 65% 4 7% 6% 1	1570
March	1st to 10th	Day	34% 44% 5% 10% 5% 2	3417
	11th to 20th	Day	17% 41% 6% 20% 14% 1	3480
	21st to end	Day	26% 42% 6% 13% 10% 2	3861
April	1st to 10th	Day	16% 66% 4 6% 7% 1	2280
	11th to 20th	Day	13% 66% 4 9% 6% 1	2254
	21st to end	Day	16% 65% 4 8% 6%	2280
May	1st to 10th	Day	34% 43% 6% 13% 4	4103
	11th to 20th	Day	30% 44% 9% 14% 2	4256
	21st to end	Day	18% 44% 10% 15% 11% 2	4837
June	1st to 10th	Day	14% 66% 4 10% 5%	2660
	11th to 20th	Day	12% 67% 5% 10% 6%	2660
	21st to end	Day	11% 65% 6% 10% 7%	2660
July	1st to 10th	Day	21% 41% 15% 14% 6% 4	4370
	11th to 20th	Day	25% 38% 11% 20% 6%	4184
	21st to end	Day	29% 38% 6% 15% 11% 1	4324
August	1st to 10th	Day	30% 40% 10% 16% 3	4091
	11th to 20th	Day	20% 40% 8% 21% 10%	3937
	21st to end	Day	19% 39% 8% 19% 14% 1	4180
September	1st to 10th	Day	15% 61% 7% 9% 7% 1	2280
	11th to 20th	Day	14% 60% 4 11% 9% 2	2280
	21st to end	Day	22% 60% 3 9% 5% 1	1987
October	1st to 10th	Day	16% 61% 4 9% 8% 1	1900
	11th to 20th	Day	13% 59% 5% 11% 10% 2	1900
	21st to end	Day	12% 59% 5% 12% 10% 2	2090
November	1st to 10th	Day	16% 59% 5% 9% 7% 3	1790
	11th to 20th	Day	12% 60% 4 11% 12% 1	1668
	21st to end	Day	15% 60% 5% 13% 6% 1	1520
December	1st to 10th	Day	19% 61% 6% 8% 5% 1	1520
	11th to 20th	Day	18% 49% 6% 19% 7% 2	1906
	21st to end	Day	28% 42% 10% 15% 5%	2772
January	1st to 10th	Night	24% 38% 6% 18% 11% 3	4322
	11th to 20th	Night	26% 37% 5% 17% 12% 3	4120
	21st to end	Night	30% 40% 6% 15% 8% 1	4532
February	1st to 10th	Night	15% 66% 6% 9% 3 1	2470
	11th to 20th	Night	16% 64% 2 8% 8% 2	2371
	21st to end	Night	16% 65% 4 8% 5% 2	1884
March	1st to 10th	Night	32% 44% 6% 13% 5%	3432
	11th to 20th	Night	15% 43% 6% 21% 13% 2	3480
	21st to end	Night	23% 41% 5% 14% 14% 3	3769
April	1st to 10th	Night	15% 66% 4 8% 7% 1	1900
	11th to 20th	Night	13% 66% 5% 9% 5% 1	1875
	21st to end	Night	15% 66% 4 10% 5% 1	1900
May	1st to 10th	Night	36% 42% 6% 10% 4 1	2886
	11th to 20th	Night	33% 44% 7% 12% 3	2638
	21st to end	Night	19% 44% 11% 17% 7% 2	2739
June	1st to 10th	Night	14% 66% 4 9% 7%	1520
	11th to 20th	Night	12% 67% 5% 10% 5%	1520
	21st to end	Night	12% 64% 6% 10% 7% 1	1520
July	1st to 10th	Night	24% 40% 14% 10% 9% 3	2480
	11th to 20th	Night	26% 39% 13% 15% 6%	2649
	21st to end	Night	31% 39% 8% 11% 10% 1	2988
August	1st to 10th	Night	32% 40% 12% 12% 3 1	2814
	11th to 20th	Night	25% 40% 8% 19% 8%	2926
	21st to end	Night	18% 38% 8% 23% 12%	3476
September	1st to 10th	Night	15% 61% 7% 10% 6% 2	1900
	11th to 20th	Night	14% 60% 5% 11% 9% 2	1900
	21st to end	Night	21% 61% 4 9% 5%	2188
October	1st to 10th	Night	17% 60% 5% 9% 8% 2	2280
	11th to 20th	Night	13% 60% 3 11% 11% 2	2280
	21st to end	Night	13% 59% 4 12% 10% 2	2508
November	1st to 10th	Night	15% 59% 6% 11% 7% 3	2310
	11th to 20th	Night	13% 60% 3 9% 13% 3	2511
	21st to end	Night	13% 60% 6% 13% 7% 2	2660
December	1st to 10th	Night	20% 60% 6% 9% 5% 1	2660
	11th to 20th	Night	21% 49% 4 13% 10% 3	3288
	21st to end	Night	28% 42% 11% 12% 7%	4884

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	29% 25% 29% 14% 1 1	211
	11th to 20th	Day	34% 23% 28% 12% 2	270
	21st to end	Day	24% 29% 33% 10% 4 1	297
February	1st to 10th	Day	24% 24% 36% 11% 4	270
	11th to 20th	Day	33% 25% 35% 5% 2	303
	21st to end	Day	28% 20% 32% 18% 2	382
March	1st to 10th	Day	23% 23% 31% 18% 4	460
	11th to 20th	Day	27% 22% 29% 16% 4 2	460
	21st to end	Day	23% 20% 32% 19% 5% 1	506
April	1st to 10th	Day	23% 22% 30% 17% 6% 2	460
	11th to 20th	Day	17% 20% 28% 18% 13% 3	452
	21st to end	Day	27% 14% 32% 18% 8% 2	460
May	1st to 10th	Day	22% 17% 29% 19% 10% 3	463
	11th to 20th	Day	20% 12% 29% 23% 13% 3	487
	21st to end	Day	16% 6% 26% 27% 20% 5%	529
June	1st to 10th	Day	14% 8% 28% 24% 20% 5%	490
	11th to 20th	Day	13% 8% 26% 32% 17% 5%	490
	21st to end	Day	10% 6% 29% 32% 18% 5%	490
July	1st to 10th	Day	11% 4 17% 32% 26% 10%	485
	11th to 20th	Day	6% 3 20% 32% 31% 7%	484
	21st to end	Day	12% 3 22% 32% 24% 7%	532
August	1st to 10th	Day	12% 6% 20% 27% 25% 12%	486
	11th to 20th	Day	10% 5% 19% 33% 22% 10%	479
	21st to end	Day	9% 5% 20% 31% 22% 13%	539
September	1st to 10th	Day	17% 7% 21% 22% 22% 11%	490
	11th to 20th	Day	13% 4 20% 30% 20% 11%	490
	21st to end	Day	27% 9% 24% 24% 11% 4	490
October	1st to 10th	Day	22% 8% 20% 26% 18% 7%	490
	11th to 20th	Day	16% 15% 27% 25% 14% 3	490
	21st to end	Day	17% 12% 33% 22% 12% 3	539
November	1st to 10th	Day	17% 11% 33% 24% 12% 3	422
	11th to 20th	Day	20% 16% 34% 20% 10% 1	328
	21st to end	Day	22% 21% 32% 16% 9% 1	180
December	1st to 10th	Day	22% 22% 36% 15% 4 1	180
	11th to 20th	Day	27% 21% 26% 21% 6%	180
	21st to end	Day	26% 19% 30% 18% 7% 1	198
January	1st to 10th	Night	21% 18% 40% 17% 3	760
	11th to 20th	Night	23% 16% 33% 24% 3	760
	21st to end	Night	20% 19% 39% 21% 1	836
February	1st to 10th	Night	19% 17% 36% 26% 2	760
	11th to 20th	Night	25% 22% 36% 16% 1	743
	21st to end	Night	25% 19% 36% 18% 3	628
March	1st to 10th	Night	21% 17% 38% 21% 3	760
	11th to 20th	Night	23% 20% 33% 19% 5%	760
	21st to end	Night	19% 18% 38% 20% 4 1	836
April	1st to 10th	Night	19% 22% 34% 21% 4	760
	11th to 20th	Night	15% 15% 36% 26% 7% 1	751
	21st to end	Night	18% 13% 33% 27% 8%	760
May	1st to 10th	Night	20% 9% 28% 32% 10%	603
	11th to 20th	Night	20% 7% 28% 34% 11%	464
	21st to end	Night	13% 6% 24% 39% 17% 1	411
June	1st to 10th	Night	10% 4 26% 37% 22%	380
	11th to 20th	Night	11% 6% 23% 42% 17% 1	380
	21st to end	Night	9% 3 26% 45% 17% 1	380
July	1st to 10th	Night	11% 2 18% 41% 24% 3	370
	11th to 20th	Night	6% 1 14% 39% 37% 2	467
	21st to end	Night	10% 2 17% 42% 26% 3	624
August	1st to 10th	Night	13% 1 12% 43% 28% 3	567
	11th to 20th	Night	12% 4 14% 42% 26% 3	626
	21st to end	Night	12% 3 16% 39% 26% 4	836
September	1st to 10th	Night	15% 3 21% 31% 26% 3	760
	11th to 20th	Night	10% 4 18% 36% 29% 3	760
	21st to end	Night	24% 4 22% 30% 20% 1	760
October	1st to 10th	Night	22% 6% 21% 29% 19% 3	760
	11th to 20th	Night	16% 12% 28% 29% 14% 1	760
	21st to end	Night	18% 11% 32% 27% 12%	836
November	1st to 10th	Night	14% 10% 33% 32% 10% 1	745
	11th to 20th	Night	18% 16% 32% 27% 6% 1	760
	21st to end	Night	16% 16% 33% 28% 7%	760
December	1st to 10th	Night	22% 17% 33% 21% 7%	760
	11th to 20th	Night	18% 14% 39% 24% 4	760
	21st to end	Night	19% 15% 36% 27% 2	836

Page generated at 2024-10-30 01:22:54. Version ac07

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