Camp Sherman Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Camp Sherman Observatory clear sky chart from 2005-11-06 to 2024-11-05.

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	4 6% 2 6% 5% 5% 5% 5% 6% 7% 49%	105406
	Night	4 6% 2 6% 5% 5% 6% 5% 7% 8% 46%	102301
Transparency	Day	30% 7% 14% 24% 17% 9%	105149
	Night	31% 8% 17% 23% 14% 6%	102147
Seeing	Day	13% 18% 27% 23% 14% 5%	14666
	Night	10% 13% 22% 34% 18% 3	23669

By Month

Percentage Cloud Cover SW (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	4 7% 3 10% 9% 10% 10% 8% 9% 9% 20%	2539
	11th to 20th	Day	9% 12% 4 9% 8% 8% 8% 5% 9% 8% 21%	2540
	21st to end	Day	8% 12% 4 10% 7% 6% 7% 5% 8% 8% 24%	3022
February	1st to 10th	Day	5% 9% 5% 10% 8% 6% 7% 6% 8% 9% 28%	1710
	11th to 20th	Day	4 11% 3 7% 6% 6% 6% 6% 9% 9% 33%	1665
	21st to end	Day	3 7% 4 9% 7% 6% 7% 8% 9% 10% 29%	1553
March	1st to 10th	Day	2 7% 3 7% 7% 7% 7% 7% 10% 11% 32%	3200
	11th to 20th	Day	2 7% 2 7% 6% 5% 6% 6% 6% 6% 48%	3490
	21st to end	Day	4 10% 4 12% 9% 7% 7% 6% 8% 8% 25%	3971
April	1st to 10th	Day	5% 11% 4 11% 7% 8% 6% 5% 7% 8% 28%	2280
	11th to 20th	Day	4 10% 4 10% 7% 5% 5% 5% 7% 8% 35%	2249
	21st to end	Day	2 7% 3 9% 6% 6% 6% 6% 7% 9% 39%	2368
May	1st to 10th	Day	8% 7% 3 7% 5% 5% 5% 5% 6% 7% 43%	4404
	11th to 20th	Day	4 4 1 4 4 3 4 3 5% 6% 61%	4377
	21st to end	Day	6% 6% 3 7% 5% 5% 6% 5% 7% 9% 41%	4813
June	1st to 10th	Day	7% 8% 3 7% 5% 5% 5% 5% 7% 7% 42%	2660
	11th to 20th	Day	4 5% 2 6% 5% 4 6% 5% 7% 8% 48%	2660
	21st to end	Day	3 3 1 3 3 3 3 4 5% 6% 65%	2660
July	1st to 10th	Day	1 1 1 1 1 2 1 2 3 85%	4420
	11th to 20th	Day	1 2 2 1 2 2 2 3 4 82%	4420
	21st to end	Day	1 1 2 1 1 2 2 3 4 82%	4790
August	1st to 10th	Day	2 3 1 2 2 2 2 3 4 5% 74%	4168
	11th to 20th	Day	1 2 1 3 2 3 3 3 4 7% 71%	4026
	21st to end	Day	4 2 1 3 2 2 2 3 4 6% 72%	4190
September	1st to 10th	Day	2 1 1 2 2 2 3 2 4 5% 76%	2280
	11th to 20th	Day	3 4 1 5% 5% 4 5% 4 6% 7% 57%	2280
	21st to end	Day	5% 5% 2 4 4 3 4 4 5% 7% 57%	2024
October	1st to 10th	Day	3 4 2 4 4 3 4 4 4 6% 63%	3180
	11th to 20th	Day	3 4 2 5% 4 4 6% 6% 8% 10% 46%	3161
	21st to end	Day	4 7% 2 7% 6% 6% 7% 6% 8% 9% 38%	3323
November	1st to 10th	Day	4 8% 3 9% 7% 7% 7% 6% 8% 10% 32%	1701
	11th to 20th	Day	3 7% 3 10% 8% 9% 7% 7% 10% 10% 25%	1520
	21st to end	Day	4 7% 3 8% 6% 6% 8% 9% 9% 8% 32%	1520
December	1st to 10th	Day	4 8% 4 8% 6% 6% 6% 6% 8% 9% 36%	1520
	11th to 20th	Day	5% 9% 4 11% 6% 7% 7% 7% 10% 13% 22%	1928
	21st to end	Day	4 11% 5% 10% 9% 7% 7% 6% 8% 8% 24%	2794
January	1st to 10th	Night	4 9% 4 10% 7% 7% 9% 8% 9% 11% 21%	4406
	11th to 20th	Night	7% 10% 5% 10% 6% 7% 9% 7% 8% 8% 21%	4420
	21st to end	Night	9% 13% 4 10% 7% 7% 6% 5% 7% 9% 23%	4638
February	1st to 10th	Night	4 10% 4 10% 6% 6% 6% 6% 8% 9% 32%	2470
	11th to 20th	Night	4 11% 3 8% 6% 5% 5% 5% 8% 10% 36%	2402
	21st to end	Night	3 8% 4 10% 6% 6% 6% 6% 9% 10% 32%	1900
March	1st to 10th	Night	2 7% 2 7% 6% 5% 7% 7% 10% 12% 34%	3658
	11th to 20th	Night	2 4 2 5% 5% 5% 6% 5% 7% 8% 51%	3490
	21st to end	Night	5% 9% 3 10% 8% 7% 8% 7% 9% 10% 24%	3681
April	1st to 10th	Night	5% 8% 3 8% 7% 6% 5% 7% 8% 9% 34%	1900
	11th to 20th	Night	3 7% 3 6% 5% 5% 7% 6% 8% 11% 38%	1879
	21st to end	Night	4 6% 2 7% 6% 5% 7% 6% 9% 9% 39%	1809
May	1st to 10th	Night	9% 8% 2 6% 4 5% 4 5% 6% 8% 44%	2554
	11th to 20th	Night	3 3 1 5% 4 4 4 4 6% 8% 59%	2516
	21st to end	Night	3 4 2 6% 5% 5% 6% 6% 7% 9% 48%	2762
June	1st to 10th	Night	9% 7% 2 8% 5% 4 5% 5% 6% 8% 42%	1520
	11th to 20th	Night	5% 4 2 4 5% 4 6% 4 5% 8% 54%	1520
	21st to end	Night	4 3 1 3 3 3 3 3 5% 6% 68%	1520
July	1st to 10th	Night	1 1 1 1 1 2 1 2 3 87%	2540
	11th to 20th	Night	2 1 1 2 1 2 1 3 4 82%	2540
	21st to end	Night	2 1 1 2 1 1 2 1 3 2 84%	2761
August	1st to 10th	Night	2 2 1 2 2 2 3 2 5% 5% 75%	2752
	11th to 20th	Night	1 1 1 2 2 3 3 3 4 6% 75%	2812
	21st to end	Night	4 2 1 2 1 2 3 2 4 4 75%	3488
September	1st to 10th	Night	2 1 2 1 1 2 2 4 5% 80%	1900
	11th to 20th	Night	3 3 1 3 3 4 5% 4 5% 8% 61%	1900
	21st to end	Night	5% 5% 1 4 2 3 4 3 5% 8% 60%	2152
October	1st to 10th	Night	2 4 2 4 3 3 3 3 5% 6% 66%	3800
	11th to 20th	Night	3 3 2 5% 4 5% 5% 5% 7% 10% 51%	3777
	21st to end	Night	4 5% 2 7% 6% 6% 7% 6% 9% 10% 39%	4241
November	1st to 10th	Night	4 7% 3 8% 7% 6% 8% 6% 8% 9% 34%	2475
	11th to 20th	Night	3 7% 3 8% 8% 8% 7% 6% 9% 10% 31%	2660
	21st to end	Night	2 6% 3 7% 6% 6% 6% 7% 9% 11% 37%	2660
December	1st to 10th	Night	5% 7% 3 9% 6% 6% 6% 6% 8% 11% 33%	2660
	11th to 20th	Night	5% 11% 4 10% 7% 7% 7% 6% 8% 10% 24%	3276
	21st to end	Night	4 8% 3 10% 7% 6% 7% 6% 9% 8% 30%	4862

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	48% 12% 19% 18% 3	2539
	11th to 20th	Day	49% 13% 20% 10% 3 4	2540
	21st to end	Day	52% 8% 17% 16% 5% 1	3022
February	1st to 10th	Day	46% 11% 17% 18% 7%	1710
	11th to 20th	Day	39% 11% 17% 23% 9% 1	1674
	21st to end	Day	41% 12% 21% 19% 7% 1	1553
March	1st to 10th	Day	34% 9% 16% 31% 9% 1	3200
	11th to 20th	Day	31% 8% 14% 33% 14%	3490
	21st to end	Day	49% 8% 21% 17% 5%	3971
April	1st to 10th	Day	49% 8% 16% 19% 7% 1	2280
	11th to 20th	Day	42% 8% 16% 21% 10% 3	2252
	21st to end	Day	37% 7% 20% 25% 10% 2	2368
May	1st to 10th	Day	34% 6% 14% 31% 15%	4404
	11th to 20th	Day	23% 4 10% 35% 26% 2	4380
	21st to end	Day	33% 7% 25% 29% 5% 1	4814
June	1st to 10th	Day	37% 6% 15% 29% 11% 2	2660
	11th to 20th	Day	29% 5% 16% 34% 13% 3	2660
	21st to end	Day	19% 4 13% 33% 23% 8%	2660
July	1st to 10th	Day	7% 2 6% 14% 20% 51%	4351
	11th to 20th	Day	8% 2 5% 10% 23% 53%	4345
	21st to end	Day	7% 2 5% 18% 39% 29%	4639
August	1st to 10th	Day	13% 3 5% 19% 37% 22%	4152
	11th to 20th	Day	13% 3 7% 35% 31% 10%	4065
	21st to end	Day	15% 3 7% 29% 31% 14%	4189
September	1st to 10th	Day	11% 2 7% 27% 34% 18%	2280
	11th to 20th	Day	24% 5% 11% 27% 23% 9%	2280
	21st to end	Day	25% 5% 12% 26% 22% 9%	2024
October	1st to 10th	Day	21% 6% 9% 24% 28% 12%	3180
	11th to 20th	Day	26% 10% 17% 29% 16% 2	3161
	21st to end	Day	36% 8% 13% 27% 15% 1	3323
November	1st to 10th	Day	42% 8% 17% 22% 10% 1	1701
	11th to 20th	Day	43% 15% 20% 15% 8%	1520
	21st to end	Day	39% 12% 18% 17% 13% 1	1520
December	1st to 10th	Day	40% 12% 17% 21% 9% 1	1520
	11th to 20th	Day	46% 14% 19% 17% 4	1928
	21st to end	Day	48% 11% 16% 21% 3 1	2794
January	1st to 10th	Night	46% 14% 22% 15% 3	4406
	11th to 20th	Night	48% 14% 19% 12% 4 3	4420
	21st to end	Night	55% 8% 18% 12% 6% 1	4638
February	1st to 10th	Night	42% 13% 21% 16% 8%	2470
	11th to 20th	Night	40% 11% 20% 21% 7% 2	2404
	21st to end	Night	40% 11% 21% 20% 7% 1	1900
March	1st to 10th	Night	34% 11% 18% 31% 6% 1	3658
	11th to 20th	Night	25% 8% 21% 39% 7%	3490
	21st to end	Night	47% 10% 24% 17% 3	3681
April	1st to 10th	Night	40% 9% 25% 19% 7% 1	1900
	11th to 20th	Night	35% 11% 21% 23% 8% 2	1879
	21st to end	Night	36% 10% 21% 22% 9% 2	1809
May	1st to 10th	Night	33% 7% 15% 34% 10%	2554
	11th to 20th	Night	20% 7% 14% 41% 18% 1	2516
	21st to end	Night	27% 7% 39% 21% 5%	2762
June	1st to 10th	Night	38% 7% 16% 29% 10% 1	1520
	11th to 20th	Night	26% 7% 17% 37% 12% 2	1520
	21st to end	Night	18% 3 14% 35% 24% 6%	1520
July	1st to 10th	Night	7% 2 6% 15% 25% 46%	2500
	11th to 20th	Night	9% 2 5% 14% 21% 50%	2492
	21st to end	Night	8% 2 4 20% 40% 26%	2674
August	1st to 10th	Night	12% 3 6% 20% 42% 18%	2744
	11th to 20th	Night	12% 3 9% 40% 28% 8%	2839
	21st to end	Night	13% 3 10% 30% 33% 11%	3488
September	1st to 10th	Night	8% 2 8% 31% 36% 15%	1900
	11th to 20th	Night	19% 6% 14% 27% 24% 10%	1900
	21st to end	Night	21% 4 13% 30% 22% 9%	2152
October	1st to 10th	Night	18% 5% 11% 26% 31% 8%	3800
	11th to 20th	Night	24% 8% 22% 29% 14% 2	3777
	21st to end	Night	33% 10% 15% 29% 12% 1	4241
November	1st to 10th	Night	41% 10% 16% 20% 11% 2	2475
	11th to 20th	Night	40% 15% 18% 20% 7%	2660
	21st to end	Night	33% 11% 21% 18% 15% 1	2660
December	1st to 10th	Night	41% 11% 20% 20% 9%	2660
	11th to 20th	Night	46% 13% 17% 17% 6%	3276
	21st to end	Night	42% 14% 19% 22% 3 1	4862

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% 15% 27% 20% 12% 2	180
	11th to 20th	Day	21% 11% 26% 25% 13% 5%	180
	21st to end	Day	17% 20% 23% 23% 13% 4	335
February	1st to 10th	Day	20% 25% 24% 21% 9% 2	370
	11th to 20th	Day	19% 27% 30% 15% 8% 1	365
	21st to end	Day	21% 21% 29% 19% 8% 1	375
March	1st to 10th	Day	17% 25% 29% 20% 7% 1	460
	11th to 20th	Day	18% 20% 29% 22% 10% 2	460
	21st to end	Day	27% 22% 26% 18% 6% 1	506
April	1st to 10th	Day	22% 20% 28% 16% 11% 2	460
	11th to 20th	Day	19% 26% 28% 17% 6% 4	452
	21st to end	Day	17% 26% 27% 18% 9% 3	460
May	1st to 10th	Day	16% 19% 29% 22% 10% 4	463
	11th to 20th	Day	18% 17% 27% 22% 10% 6%	488
	21st to end	Day	15% 14% 26% 26% 14% 5%	529
June	1st to 10th	Day	12% 20% 24% 22% 14% 7%	490
	11th to 20th	Day	14% 23% 28% 21% 11% 3	490
	21st to end	Day	6% 16% 26% 29% 17% 7%	490
July	1st to 10th	Day	3 12% 35% 28% 15% 7%	486
	11th to 20th	Day	2 13% 31% 26% 20% 7%	484
	21st to end	Day	2 10% 31% 28% 20% 9%	531
August	1st to 10th	Day	3 10% 30% 29% 18% 10%	487
	11th to 20th	Day	5% 7% 25% 31% 19% 12%	477
	21st to end	Day	5% 14% 28% 27% 18% 8%	539
September	1st to 10th	Day	5% 12% 22% 31% 22% 8%	490
	11th to 20th	Day	8% 13% 24% 30% 20% 5%	490
	21st to end	Day	12% 15% 23% 29% 19% 3	490
October	1st to 10th	Day	12% 17% 23% 26% 19% 3	490
	11th to 20th	Day	12% 19% 22% 24% 19% 4	490
	21st to end	Day	18% 20% 24% 18% 15% 5%	463
November	1st to 10th	Day	17% 17% 25% 25% 13% 4	278
	11th to 20th	Day	15% 21% 21% 20% 17% 7%	180
	21st to end	Day	19% 13% 24% 22% 16% 6%	180
December	1st to 10th	Day	18% 16% 23% 18% 17% 8%	180
	11th to 20th	Day	14% 23% 24% 24% 12% 2	180
	21st to end	Day	20% 19% 23% 22% 14% 2	198
January	1st to 10th	Night	17% 18% 21% 27% 14% 3	760
	11th to 20th	Night	15% 14% 22% 28% 17% 3	760
	21st to end	Night	15% 10% 22% 35% 14% 4	836
February	1st to 10th	Night	12% 16% 24% 30% 15% 2	760
	11th to 20th	Night	13% 19% 23% 30% 14% 1	744
	21st to end	Night	14% 20% 25% 33% 7%	628
March	1st to 10th	Night	12% 19% 29% 27% 12% 1	760
	11th to 20th	Night	10% 17% 24% 32% 16% 1	760
	21st to end	Night	12% 22% 28% 26% 11% 1	836
April	1st to 10th	Night	13% 19% 24% 30% 12% 1	760
	11th to 20th	Night	10% 19% 26% 28% 13% 3	751
	21st to end	Night	10% 17% 26% 32% 14% 1	669
May	1st to 10th	Night	10% 11% 24% 34% 19% 2	394
	11th to 20th	Night	9% 10% 23% 35% 22% 1	374
	21st to end	Night	8% 7% 24% 40% 20% 2	411
June	1st to 10th	Night	13% 9% 26% 33% 17% 2	380
	11th to 20th	Night	9% 10% 28% 36% 17% 1	380
	21st to end	Night	5% 8% 21% 43% 23% 1	380
July	1st to 10th	Night	2 4 20% 48% 25% 1	370
	11th to 20th	Night	1 3 20% 55% 20% 1	368
	21st to end	Night	1 4 15% 48% 31% 2	416
August	1st to 10th	Night	2 2 13% 42% 36% 5%	510
	11th to 20th	Night	2 2 10% 38% 37% 10%	564
	21st to end	Night	3 5% 21% 41% 27% 3	826
September	1st to 10th	Night	2 7% 17% 38% 33% 4	760
	11th to 20th	Night	5% 5% 17% 39% 28% 6%	760
	21st to end	Night	9% 8% 17% 35% 27% 5%	760
October	1st to 10th	Night	6% 7% 23% 36% 23% 4	760
	11th to 20th	Night	8% 12% 19% 35% 21% 5%	760
	21st to end	Night	12% 13% 24% 31% 15% 5%	836
November	1st to 10th	Night	12% 13% 24% 37% 13% 1	760
	11th to 20th	Night	13% 18% 23% 31% 13% 1	760
	21st to end	Night	9% 15% 22% 35% 16% 3	760
December	1st to 10th	Night	11% 15% 23% 32% 16% 3	760
	11th to 20th	Night	14% 15% 25% 30% 14% 2	760
	21st to end	Night	15% 20% 24% 29% 10% 1	836

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