Baskin Engineering Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Baskin Engineering Observatory clear sky chart from 2005-11-06 to 2024-11-04.

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	7% 5% 2 5% 3 3 4 3 5% 8% 55%	104937
	Night	9% 6% 2 5% 4 3 4 3 6% 8% 50%	102828
Transparency	Day	27% 7% 10% 19% 22% 15%	104697
	Night	32% 7% 10% 17% 20% 14%	102658
Seeing	Day	9% 5% 18% 32% 28% 8%	15497
	Night	11% 3 11% 31% 33% 10%	24869

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	15% 6% 2 7% 4 4 3 4 6% 6% 43%	2763
	11th to 20th	Day	18% 7% 3 7% 5% 6% 4 4 6% 6% 35%	2860
	21st to end	Day	20% 8% 3 7% 5% 4 4 4 6% 7% 32%	3146
February	1st to 10th	Day	18% 5% 2 5% 4 3 4 3 5% 7% 45%	1710
	11th to 20th	Day	13% 5% 2 6% 5% 4 4 4 5% 7% 44%	1770
	21st to end	Day	14% 5% 3 6% 3 3 5% 4 4 6% 46%	1570
March	1st to 10th	Day	14% 10% 3 10% 6% 5% 6% 5% 7% 7% 28%	3384
	11th to 20th	Day	11% 5% 1 4 3 3 3 3 5% 8% 54%	3490
	21st to end	Day	13% 8% 3 7% 5% 4 6% 5% 7% 8% 33%	3881
April	1st to 10th	Day	11% 7% 2 4 5% 4 3 4 5% 8% 48%	2280
	11th to 20th	Day	8% 5% 2 5% 3 3 4 4 6% 8% 52%	2249
	21st to end	Day	5% 5% 2 6% 4 3 4 4 6% 8% 53%	2280
May	1st to 10th	Day	6% 3 1 3 2 2 2 2 4 7% 69%	3859
	11th to 20th	Day	3 6% 3 5% 3 3 3 3 5% 9% 57%	4116
	21st to end	Day	3 6% 2 5% 3 3 3 3 4 7% 61%	4813
June	1st to 10th	Day	4 5% 2 5% 4 3 4 4 6% 9% 55%	2660
	11th to 20th	Day	2 4 1 3 3 2 3 3 6% 8% 64%	2660
	21st to end	Day	2 3 1 4 3 3 3 3 5% 9% 64%	2660
July	1st to 10th	Day	1 3 1 3 3 2 2 3 4 8% 71%	4367
	11th to 20th	Day	2 3 2 5% 2 3 3 3 6% 8% 63%	4110
	21st to end	Day	4 1 3 2 2 3 4 6% 9% 64%	4455
August	1st to 10th	Day	1 3 1 5% 4 4 5% 5% 7% 10% 56%	4091
	11th to 20th	Day	2 1 2 2 3 3 3 6% 10% 67%	3791
	21st to end	Day	3 2 5% 3 2 3 3 6% 9% 64%	4180
September	1st to 10th	Day	2 3 1 2 2 2 2 3 4 7% 72%	2280
	11th to 20th	Day	3 4 2 4 3 3 4 3 5% 10% 58%	2280
	21st to end	Day	3 3 1 3 2 2 3 3 5% 6% 72%	2019
October	1st to 10th	Day	2 2 1 3 3 2 3 3 4 8% 69%	3180
	11th to 20th	Day	3 2 1 4 3 3 4 3 4 7% 66%	3161
	21st to end	Day	4 3 1 3 2 3 4 3 5% 9% 62%	3448
November	1st to 10th	Day	8% 5% 1 4 3 4 4 3 6% 7% 55%	1876
	11th to 20th	Day	9% 5% 2 5% 3 3 4 3 6% 7% 53%	1710
	21st to end	Day	11% 4 2 4 3 3 3 3 4 8% 57%	1596
December	1st to 10th	Day	15% 6% 2 5% 4 3 4 3 5% 9% 45%	1520
	11th to 20th	Day	28% 8% 2 5% 3 3 3 3 6% 6% 33%	1928
	21st to end	Day	21% 7% 2 5% 4 4 4 3 6% 7% 37%	2794
January	1st to 10th	Night	12% 7% 2 6% 3 3 3 3 5% 6% 48%	4186
	11th to 20th	Night	19% 7% 2 6% 4 5% 5% 4 6% 7% 34%	4110
	21st to end	Night	20% 8% 2 6% 4 4 5% 4 6% 7% 34%	4521
February	1st to 10th	Night	17% 5% 2 4 4 2 3 3 5% 6% 49%	2470
	11th to 20th	Night	13% 6% 2 4 3 4 4 5% 7% 7% 46%	2296
	21st to end	Night	12% 7% 3 4 2 3 3 3 6% 7% 51%	1884
March	1st to 10th	Night	16% 11% 3 8% 5% 4 4 4 5% 7% 33%	3475
	11th to 20th	Night	11% 5% 2 4 3 3 3 3 7% 7% 53%	3490
	21st to end	Night	16% 9% 3 5% 5% 4 4 4 6% 7% 37%	3771
April	1st to 10th	Night	11% 6% 2 4 4 3 4 4 6% 8% 48%	1900
	11th to 20th	Night	10% 5% 2 4 4 4 3 3 6% 7% 52%	1879
	21st to end	Night	5% 5% 1 4 3 3 3 3 6% 9% 56%	1900
May	1st to 10th	Night	3 4 1 3 2 2 2 2 5% 5% 70%	3102
	11th to 20th	Night	2 13% 5% 10% 5% 4 4 3 8% 7% 40%	2784
	21st to end	Night	2 5% 2 5% 3 3 5% 3 8% 9% 55%	2762
June	1st to 10th	Night	3 3 1 6% 4 4 3 4 6% 8% 58%	1520
	11th to 20th	Night	1 5% 2 5% 4 4 3 3 7% 7% 59%	1520
	21st to end	Night	2 3 2 5% 3 4 3 3 6% 10% 58%	1520
July	1st to 10th	Night	1 3 2 4 5% 3 3 3 5% 8% 64%	2590
	11th to 20th	Night	1 4 3 8% 4 5% 4 3 7% 12% 50%	2860
	21st to end	Night	8% 4 9% 5% 4 5% 4 8% 11% 43%	3109
August	1st to 10th	Night	1 5% 3 8% 6% 6% 5% 4 9% 13% 39%	2848
	11th to 20th	Night	1 3 1 4 4 5% 6% 4 9% 13% 51%	3056
	21st to end	Night	1 4 3 8% 3 3 3 2 6% 8% 57%	3498
September	1st to 10th	Night	3 1 3 3 3 4 4 6% 9% 64%	1900
	11th to 20th	Night	3 5% 2 6% 3 4 3 3 6% 7% 58%	1900
	21st to end	Night	2 5% 2 3 2 1 2 2 4 8% 68%	2157
October	1st to 10th	Night	2 3 1 4 3 3 3 3 5% 8% 66%	3800
	11th to 20th	Night	3 5% 2 5% 4 4 4 3 7% 7% 57%	3777
	21st to end	Night	5% 3 1 4 3 2 3 3 5% 7% 64%	4121
November	1st to 10th	Night	8% 5% 1 4 3 3 3 3 5% 7% 58%	2274
	11th to 20th	Night	9% 4 2 4 3 3 3 4 6% 10% 53%	2470
	21st to end	Night	7% 5% 1 5% 4 3 4 2 5% 5% 59%	2580
December	1st to 10th	Night	15% 6% 2 4 3 3 4 3 4 7% 50%	2660
	11th to 20th	Night	29% 8% 2 4 3 3 3 3 5% 6% 34%	3276
	21st to end	Night	21% 7% 2 5% 4 4 4 2 5% 6% 39%	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	38% 7% 15% 27% 10% 4	2763
	11th to 20th	Day	46% 8% 13% 15% 11% 8%	2860
	21st to end	Day	48% 7% 11% 15% 13% 5%	3146
February	1st to 10th	Day	37% 5% 8% 20% 20% 10%	1710
	11th to 20th	Day	36% 7% 11% 19% 19% 8%	1779
	21st to end	Day	36% 7% 10% 24% 17% 7%	1570
March	1st to 10th	Day	45% 14% 11% 14% 13% 3	3384
	11th to 20th	Day	28% 5% 15% 28% 13% 11%	3490
	21st to end	Day	39% 13% 17% 18% 10% 2	3881
April	1st to 10th	Day	33% 8% 14% 21% 19% 5%	2280
	11th to 20th	Day	27% 7% 15% 26% 18% 6%	2252
	21st to end	Day	27% 7% 15% 27% 19% 4	2280
May	1st to 10th	Day	17% 4 13% 27% 26% 12%	3859
	11th to 20th	Day	21% 8% 14% 29% 21% 7%	4119
	21st to end	Day	23% 7% 14% 26% 26% 3	4814
June	1st to 10th	Day	27% 8% 13% 24% 22% 5%	2660
	11th to 20th	Day	21% 4 12% 24% 28% 11%	2660
	21st to end	Day	22% 3 9% 17% 28% 21%	2660
July	1st to 10th	Day	16% 5% 3 10% 15% 50%	4299
	11th to 20th	Day	21% 7% 5% 10% 14% 43%	4041
	21st to end	Day	20% 5% 4 12% 32% 27%	4315
August	1st to 10th	Day	24% 7% 5% 14% 26% 24%	4076
	11th to 20th	Day	15% 9% 5% 13% 40% 17%	3828
	21st to end	Day	20% 6% 6% 14% 33% 21%	4179
September	1st to 10th	Day	18% 3 4 15% 27% 34%	2280
	11th to 20th	Day	23% 5% 11% 21% 28% 12%	2280
	21st to end	Day	16% 4 7% 22% 35% 17%	2019
October	1st to 10th	Day	15% 5% 6% 12% 27% 35%	3180
	11th to 20th	Day	19% 6% 8% 24% 26% 17%	3161
	21st to end	Day	21% 3 7% 24% 30% 15%	3448
November	1st to 10th	Day	27% 6% 9% 25% 22% 10%	1876
	11th to 20th	Day	29% 5% 12% 21% 24% 9%	1710
	21st to end	Day	26% 5% 11% 19% 27% 12%	1596
December	1st to 10th	Day	36% 6% 12% 19% 17% 11%	1520
	11th to 20th	Day	50% 6% 11% 14% 14% 6%	1928
	21st to end	Day	43% 6% 13% 22% 12% 4	2794
January	1st to 10th	Night	35% 6% 19% 26% 11% 4	4186
	11th to 20th	Night	46% 7% 15% 13% 10% 8%	4110
	21st to end	Night	48% 6% 13% 15% 11% 7%	4521
February	1st to 10th	Night	38% 5% 9% 17% 18% 13%	2470
	11th to 20th	Night	34% 6% 12% 19% 21% 8%	2298
	21st to end	Night	31% 5% 12% 30% 16% 6%	1884
March	1st to 10th	Night	48% 9% 14% 13% 13% 3	3475
	11th to 20th	Night	30% 7% 10% 23% 20% 10%	3490
	21st to end	Night	42% 10% 16% 19% 11% 3	3771
April	1st to 10th	Night	32% 7% 15% 22% 18% 5%	1900
	11th to 20th	Night	31% 6% 13% 28% 15% 7%	1879
	21st to end	Night	23% 8% 14% 29% 20% 6%	1900
May	1st to 10th	Night	17% 4 16% 24% 25% 14%	3102
	11th to 20th	Night	37% 13% 14% 13% 14% 9%	2785
	21st to end	Night	24% 9% 16% 21% 27% 3	2762
June	1st to 10th	Night	26% 8% 13% 23% 23% 8%	1520
	11th to 20th	Night	26% 6% 9% 16% 28% 16%	1520
	21st to end	Night	25% 7% 8% 12% 25% 23%	1520
July	1st to 10th	Night	21% 6% 2 7% 16% 48%	2549
	11th to 20th	Night	28% 12% 4 9% 14% 33%	2806
	21st to end	Night	36% 6% 4 10% 20% 25%	3011
August	1st to 10th	Night	37% 13% 4 11% 20% 15%	2839
	11th to 20th	Night	23% 14% 3 11% 31% 19%	3085
	21st to end	Night	27% 9% 6% 11% 33% 15%	3498
September	1st to 10th	Night	21% 4 4 11% 28% 31%	1900
	11th to 20th	Night	26% 5% 7% 21% 28% 13%	1900
	21st to end	Night	20% 4 5% 18% 33% 20%	2157
October	1st to 10th	Night	18% 5% 5% 11% 23% 37%	3800
	11th to 20th	Night	25% 10% 6% 22% 20% 18%	3777
	21st to end	Night	23% 4 6% 22% 29% 16%	4121
November	1st to 10th	Night	27% 5% 9% 24% 22% 13%	2274
	11th to 20th	Night	28% 5% 12% 22% 23% 10%	2470
	21st to end	Night	27% 5% 8% 21% 24% 15%	2580
December	1st to 10th	Night	35% 5% 10% 20% 18% 13%	2660
	11th to 20th	Night	51% 4 11% 14% 15% 5%	3276
	21st to end	Night	44% 7% 14% 17% 12% 5%	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	27% 7% 17% 25% 18% 6%	313
	11th to 20th	Day	16% 4 20% 27% 27% 5%	370
	21st to end	Day	14% 5% 20% 30% 25% 6%	407
February	1st to 10th	Day	19% 6% 22% 22% 21% 9%	370
	11th to 20th	Day	14% 12% 23% 29% 19% 4	416
	21st to end	Day	11% 9% 24% 35% 18% 3	382
March	1st to 10th	Day	22% 11% 21% 30% 15% 2	460
	11th to 20th	Day	20% 7% 22% 26% 19% 6%	460
	21st to end	Day	13% 9% 28% 31% 15% 3	506
April	1st to 10th	Day	13% 7% 27% 31% 17% 5%	460
	11th to 20th	Day	9% 11% 25% 31% 18% 6%	452
	21st to end	Day	5% 8% 30% 30% 21% 6%	460
May	1st to 10th	Day	8% 7% 28% 31% 21% 5%	463
	11th to 20th	Day	10% 5% 23% 31% 26% 6%	488
	21st to end	Day	9% 8% 21% 30% 26% 7%	529
June	1st to 10th	Day	6% 4 18% 41% 24% 7%	490
	11th to 20th	Day	4 4 23% 36% 28% 4	490
	21st to end	Day	2 2 13% 42% 33% 7%	490
July	1st to 10th	Day	6% 11% 39% 36% 9%	486
	11th to 20th	Day	4 1 6% 39% 39% 11%	484
	21st to end	Day	2 1 7% 37% 41% 12%	531
August	1st to 10th	Day	5% 11% 41% 36% 7%	487
	11th to 20th	Day	3 9% 42% 38% 8%	477
	21st to end	Day	4 1 8% 35% 39% 12%	539
September	1st to 10th	Day	2 2 10% 32% 40% 13%	490
	11th to 20th	Day	5% 3 16% 36% 30% 10%	490
	21st to end	Day	3 3 11% 30% 40% 12%	490
October	1st to 10th	Day	2 3 19% 28% 34% 14%	490
	11th to 20th	Day	6% 3 16% 28% 32% 15%	490
	21st to end	Day	9% 4 17% 28% 29% 14%	539
November	1st to 10th	Day	9% 6% 16% 24% 31% 14%	454
	11th to 20th	Day	9% 4 14% 31% 29% 13%	270
	21st to end	Day	9% 3 15% 33% 32% 9%	216
December	1st to 10th	Day	17% 7% 16% 23% 27% 9%	180
	11th to 20th	Day	16% 6% 19% 24% 25% 9%	180
	21st to end	Day	16% 12% 20% 26% 18% 8%	198
January	1st to 10th	Night	18% 6% 13% 32% 25% 6%	760
	11th to 20th	Night	16% 4 13% 33% 26% 9%	760
	21st to end	Night	16% 5% 10% 34% 29% 5%	836
February	1st to 10th	Night	20% 6% 12% 29% 26% 7%	760
	11th to 20th	Night	15% 6% 16% 33% 24% 6%	744
	21st to end	Night	14% 7% 17% 36% 23% 4	628
March	1st to 10th	Night	19% 8% 14% 33% 23% 4	760
	11th to 20th	Night	17% 4 14% 31% 27% 6%	760
	21st to end	Night	15% 5% 18% 35% 24% 3	836
April	1st to 10th	Night	13% 5% 16% 37% 26% 3	760
	11th to 20th	Night	11% 8% 16% 34% 24% 6%	751
	21st to end	Night	8% 4 20% 33% 26% 9%	760
May	1st to 10th	Night	8% 2 17% 34% 31% 7%	721
	11th to 20th	Night	7% 2 9% 36% 35% 11%	538
	21st to end	Night	8% 4 15% 34% 31% 8%	411
June	1st to 10th	Night	6% 2 10% 39% 35% 8%	380
	11th to 20th	Night	5% 2 10% 39% 40% 5%	380
	21st to end	Night	4 6% 32% 48% 10%	380
July	1st to 10th	Night	6% 4 25% 53% 12%	393
	11th to 20th	Night	7% 1 1 20% 48% 24%	552
	21st to end	Night	6% 1 2 25% 48% 18%	624
August	1st to 10th	Night	8% 1 6% 26% 43% 14%	567
	11th to 20th	Night	5% 1 4 28% 48% 13%	706
	21st to end	Night	6% 1 4 24% 46% 18%	836
September	1st to 10th	Night	3 5% 25% 48% 18%	760
	11th to 20th	Night	6% 2 6% 29% 43% 14%	760
	21st to end	Night	5% 2 7% 24% 45% 18%	760
October	1st to 10th	Night	6% 2 8% 31% 38% 16%	760
	11th to 20th	Night	8% 2 7% 28% 39% 15%	760
	21st to end	Night	8% 1 9% 29% 34% 18%	836
November	1st to 10th	Night	10% 2 11% 30% 36% 12%	754
	11th to 20th	Night	12% 2 8% 34% 36% 8%	760
	21st to end	Night	9% 2 13% 38% 30% 8%	760
December	1st to 10th	Night	16% 4 12% 33% 28% 7%	760
	11th to 20th	Night	21% 4 13% 35% 22% 4	760
	21st to end	Night	19% 6% 18% 34% 19% 4	836

Page generated at 2024-11-01 19:47:39. Version ac07

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