Santa Monica Canyon Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Santa Monica Canyon Observatory clear sky chart from 2005-11-06 to 2024-01-16.

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	5% 3 1 3 3 2 3 3 4 7% 66%	74959
	Night	6% 4 2 4 3 2 3 3 5% 7% 61%	74865
Transparency	Day	14% 36% 6% 13% 17% 14%	74685
	Night	17% 37% 6% 11% 14% 15%	74660
Seeing	Day	6% 6% 21% 35% 25% 7%	14480
	Night	6% 3 11% 34% 37% 9%	24408

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	8% 4 2 3 5% 2 4 4 5% 7% 57%	1519
	11th to 20th	Day	7% 5% 2 3 3 2 3 3 4 6% 62%	1658
	21st to end	Day	9% 5% 2 4 3 1 3 3 3 6% 61%	1952
February	1st to 10th	Day	8% 4 2 3 3 2 3 2 4 6% 64%	1800
	11th to 20th	Day	7% 2 1 2 3 2 3 3 5% 7% 63%	1750
	21st to end	Day	7% 4 2 4 3 2 3 4 5% 7% 61%	1480
March	1st to 10th	Day	7% 4 1 4 4 2 4 5% 6% 7% 55%	1800
	11th to 20th	Day	7% 4 2 3 3 2 3 4 6% 10% 56%	1860
	21st to end	Day	5% 3 1 3 3 2 4 4 5% 8% 61%	2376
April	1st to 10th	Day	5% 4 2 3 3 2 4 4 5% 8% 59%	2160
	11th to 20th	Day	3 3 1 3 3 1 3 3 4 7% 68%	2129
	21st to end	Day	3 3 2 3 3 1 3 3 4 8% 68%	2160
May	1st to 10th	Day	3 4 1 3 3 2 3 4 5% 9% 62%	2185
	11th to 20th	Day	4 5% 2 3 3 2 2 3 4 7% 64%	2301
	21st to end	Day	4 4 2 3 2 2 3 3 4 7% 66%	2530
June	1st to 10th	Day	5% 6% 1 4 3 1 2 3 4 7% 63%	2396
	11th to 20th	Day	3 4 1 3 2 1 2 2 4 7% 70%	2520
	21st to end	Day	2 4 2 3 2 1 3 2 4 6% 71%	2520
July	1st to 10th	Day	3 3 2 3 3 1 3 3 3 7% 69%	2520
	11th to 20th	Day	2 3 1 3 3 1 3 2 3 6% 73%	2506
	21st to end	Day	2 2 1 3 2 2 3 3 5% 8% 70%	2364
August	1st to 10th	Day	2 2 1 2 3 2 2 2 3 5% 75%	2149
	11th to 20th	Day	2 2 1 1 2 1 2 2 3 7% 77%	2122
	21st to end	Day	1 1 1 2 2 1 2 3 4 6% 76%	2376
September	1st to 10th	Day	3 2 1 2 2 1 2 2 4 5% 75%	2160
	11th to 20th	Day	2 2 1 2 2 1 2 2 3 6% 77%	2046
	21st to end	Day	2 2 1 2 2 2 2 2 4 6% 75%	1980
October	1st to 10th	Day	3 3 1 2 3 2 2 3 4 6% 72%	1980
	11th to 20th	Day	3 3 1 2 2 1 3 3 3 5% 74%	1832
	21st to end	Day	2 2 1 2 2 1 2 3 4 6% 73%	1969
November	1st to 10th	Day	3 2 1 3 3 2 3 3 5% 7% 69%	1674
	11th to 20th	Day	5% 3 1 3 3 1 2 3 5% 5% 69%	1710
	21st to end	Day	4 3 1 3 3 3 3 4 4 9% 63%	1710
December	1st to 10th	Day	7% 4 2 4 3 2 4 4 6% 6% 59%	1710
	11th to 20th	Day	16% 5% 2 5% 4 2 4 4 5% 8% 46%	2169
	21st to end	Day	12% 6% 2 5% 6% 4 4 4 6% 6% 45%	2886
January	1st to 10th	Night	9% 5% 1 3 3 2 3 4 4 8% 57%	2646
	11th to 20th	Night	7% 4 1 3 3 2 3 3 5% 7% 62%	2426
	21st to end	Night	10% 4 2 3 3 2 2 3 3 5% 63%	2399
February	1st to 10th	Night	6% 5% 2 4 3 2 3 3 3 6% 64%	2160
	11th to 20th	Night	8% 4 2 4 3 2 3 3 4 6% 62%	2098
	21st to end	Night	10% 3 2 3 4 2 4 3 3 5% 60%	1776
March	1st to 10th	Night	7% 5% 2 4 4 2 4 4 5% 9% 53%	2160
	11th to 20th	Night	7% 4 2 4 4 3 4 5% 6% 8% 52%	2094
	21st to end	Night	6% 5% 2 3 3 3 4 3 5% 7% 59%	1980
April	1st to 10th	Night	7% 5% 2 5% 4 2 3 3 4 8% 57%	1800
	11th to 20th	Night	4 5% 2 3 3 1 4 3 3 6% 65%	1779
	21st to end	Night	4 4 2 4 3 2 4 4 5% 8% 60%	1800
May	1st to 10th	Night	4 7% 2 4 4 2 3 4 6% 7% 57%	1774
	11th to 20th	Night	4 6% 4 5% 4 2 3 4 5% 8% 57%	1594
	21st to end	Night	3 6% 1 3 3 1 3 2 4 7% 65%	1746
June	1st to 10th	Night	2 8% 3 5% 3 3 5% 4 5% 9% 54%	1558
	11th to 20th	Night	3 6% 2 4 2 1 3 4 5% 9% 61%	1440
	21st to end	Night	1 7% 2 5% 3 2 3 3 6% 11% 57%	1440
July	1st to 10th	Night	2 4 1 4 4 2 3 3 4 11% 61%	1440
	11th to 20th	Night	1 3 2 4 3 3 4 4 6% 8% 61%	1449
	21st to end	Night	3 3 2 5% 4 2 5% 4 6% 9% 57%	1953
August	1st to 10th	Night	3 3 1 3 3 3 3 3 5% 9% 63%	1790
	11th to 20th	Night	3 6% 1 3 2 1 2 3 5% 10% 63%	1780
	21st to end	Night	1 2 2 3 3 2 3 4 4 8% 67%	1980
September	1st to 10th	Night	4 4 2 2 2 2 3 3 4 7% 67%	1800
	11th to 20th	Night	2 2 1 3 2 1 2 3 5% 6% 72%	1912
	21st to end	Night	1 3 1 2 2 1 3 4 4 6% 72%	1980
October	1st to 10th	Night	3 4 2 3 3 2 3 4 4 5% 68%	1980
	11th to 20th	Night	3 4 1 3 3 1 3 3 4 5% 69%	2124
	21st to end	Night	3 3 2 3 2 1 2 2 4 6% 72%	2384
November	1st to 10th	Night	2 3 1 3 3 2 3 3 4 6% 69%	2405
	11th to 20th	Night	3 3 2 3 4 2 3 3 3 6% 69%	2470
	21st to end	Night	4 3 1 4 3 2 4 3 5% 8% 61%	2470
December	1st to 10th	Night	6% 5% 2 5% 4 2 3 3 4 6% 60%	2470
	11th to 20th	Night	16% 6% 3 4 4 2 2 3 4 7% 47%	3041
	21st to end	Night	14% 6% 2 4 4 3 5% 5% 5% 6% 47%	4767

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	16% 39% 4 12% 15% 14%	1519
	11th to 20th	Day	12% 40% 5% 5% 16% 21%	1658
	21st to end	Day	18% 37% 6% 11% 10% 18%	1952
February	1st to 10th	Day	17% 35% 3 10% 17% 18%	1800
	11th to 20th	Day	15% 38% 5% 13% 17% 12%	1760
	21st to end	Day	16% 37% 5% 14% 15% 13%	1480
March	1st to 10th	Day	15% 36% 7% 15% 12% 14%	1800
	11th to 20th	Day	16% 37% 9% 16% 15% 8%	1860
	21st to end	Day	16% 37% 8% 15% 14% 9%	2376
April	1st to 10th	Day	15% 37% 10% 18% 12% 8%	2160
	11th to 20th	Day	12% 36% 7% 19% 16% 9%	2132
	21st to end	Day	12% 36% 7% 17% 20% 8%	2160
May	1st to 10th	Day	12% 37% 8% 15% 18% 10%	2185
	11th to 20th	Day	15% 37% 5% 16% 20% 7%	2304
	21st to end	Day	11% 38% 7% 18% 21% 4	2530
June	1st to 10th	Day	16% 38% 9% 13% 17% 7%	2396
	11th to 20th	Day	12% 37% 6% 11% 22% 13%	2520
	21st to end	Day	13% 35% 5% 6% 20% 21%	2520
July	1st to 10th	Day	12% 36% 5% 7% 14% 26%	2451
	11th to 20th	Day	11% 36% 4 12% 20% 17%	2431
	21st to end	Day	11% 38% 7% 15% 19% 9%	2233
August	1st to 10th	Day	9% 36% 4 12% 19% 19%	2135
	11th to 20th	Day	10% 34% 4 14% 22% 16%	2122
	21st to end	Day	9% 35% 5% 9% 21% 22%	2376
September	1st to 10th	Day	9% 35% 5% 9% 19% 23%	2160
	11th to 20th	Day	10% 35% 5% 10% 21% 19%	2046
	21st to end	Day	11% 36% 4 12% 19% 19%	1980
October	1st to 10th	Day	14% 35% 7% 15% 14% 15%	1980
	11th to 20th	Day	11% 36% 4 13% 17% 20%	1832
	21st to end	Day	10% 38% 4 11% 13% 24%	1969
November	1st to 10th	Day	14% 41% 4 13% 12% 15%	1674
	11th to 20th	Day	10% 39% 4 11% 13% 23%	1710
	21st to end	Day	13% 39% 6% 8% 15% 19%	1710
December	1st to 10th	Day	16% 40% 4 11% 13% 16%	1710
	11th to 20th	Day	30% 33% 6% 9% 13% 8%	2168
	21st to end	Day	32% 29% 10% 16% 9% 5%	2886
January	1st to 10th	Night	16% 39% 5% 11% 16% 13%	2646
	11th to 20th	Night	12% 40% 4 9% 14% 22%	2426
	21st to end	Night	17% 36% 6% 11% 10% 19%	2399
February	1st to 10th	Night	17% 36% 4 9% 16% 19%	2160
	11th to 20th	Night	18% 37% 5% 13% 14% 13%	2099
	21st to end	Night	19% 37% 6% 10% 13% 15%	1776
March	1st to 10th	Night	19% 36% 5% 14% 13% 12%	2160
	11th to 20th	Night	21% 38% 8% 12% 13% 9%	2094
	21st to end	Night	18% 37% 8% 13% 15% 9%	1980
April	1st to 10th	Night	18% 37% 8% 18% 11% 9%	1800
	11th to 20th	Night	16% 36% 6% 16% 15% 10%	1779
	21st to end	Night	20% 37% 6% 14% 16% 7%	1800
May	1st to 10th	Night	19% 37% 7% 13% 17% 8%	1774
	11th to 20th	Night	22% 38% 4 14% 16% 7%	1595
	21st to end	Night	13% 38% 6% 19% 19% 6%	1746
June	1st to 10th	Night	19% 39% 10% 12% 14% 6%	1558
	11th to 20th	Night	14% 38% 8% 10% 21% 9%	1440
	21st to end	Night	18% 36% 5% 7% 17% 18%	1440
July	1st to 10th	Night	15% 37% 4 7% 13% 25%	1400
	11th to 20th	Night	14% 38% 5% 10% 17% 16%	1401
	21st to end	Night	17% 39% 8% 14% 12% 9%	1844
August	1st to 10th	Night	16% 36% 4 10% 19% 15%	1780
	11th to 20th	Night	15% 36% 3 11% 19% 16%	1780
	21st to end	Night	13% 36% 5% 8% 16% 21%	1980
September	1st to 10th	Night	13% 36% 5% 6% 18% 22%	1800
	11th to 20th	Night	12% 36% 4 8% 20% 20%	1912
	21st to end	Night	15% 35% 3 10% 18% 20%	1980
October	1st to 10th	Night	16% 36% 5% 12% 15% 17%	1980
	11th to 20th	Night	15% 36% 4 8% 15% 21%	2124
	21st to end	Night	11% 37% 4 7% 14% 26%	2384
November	1st to 10th	Night	15% 41% 5% 10% 13% 17%	2405
	11th to 20th	Night	11% 39% 4 8% 13% 24%	2470
	21st to end	Night	16% 39% 4 9% 12% 20%	2470
December	1st to 10th	Night	17% 40% 5% 8% 13% 18%	2470
	11th to 20th	Night	30% 34% 5% 11% 13% 8%	3041
	21st to end	Night	31% 31% 9% 15% 9% 6%	4767

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	16% 6% 27% 33% 17% 2	180
	11th to 20th	Day	10% 8% 32% 32% 16% 1	346
	21st to end	Day	10% 11% 33% 30% 14% 2	450
February	1st to 10th	Day	9% 9% 30% 31% 16% 4	420
	11th to 20th	Day	10% 14% 33% 31% 10% 2	415
	21st to end	Day	8% 15% 34% 32% 11%	346
March	1st to 10th	Day	11% 16% 33% 26% 12% 2	420
	11th to 20th	Day	10% 12% 31% 31% 13% 2	420
	21st to end	Day	9% 15% 34% 30% 11% 2	462
April	1st to 10th	Day	7% 10% 30% 31% 17% 5%	420
	11th to 20th	Day	4 14% 37% 32% 10% 4	412
	21st to end	Day	3 12% 31% 31% 16% 7%	420
May	1st to 10th	Day	6% 11% 28% 35% 15% 4	423
	11th to 20th	Day	7% 6% 25% 36% 22% 4	448
	21st to end	Day	6% 5% 29% 37% 18% 5%	485
June	1st to 10th	Day	7% 3 18% 38% 28% 7%	450
	11th to 20th	Day	5% 3 14% 39% 30% 10%	450
	21st to end	Day	4 2 12% 39% 32% 12%	450
July	1st to 10th	Day	3 1 4 37% 42% 13%	446
	11th to 20th	Day	2 2 29% 49% 19%	444
	21st to end	Day	2 3 33% 46% 17%	487
August	1st to 10th	Day	2 1 7% 37% 39% 13%	447
	11th to 20th	Day	3 4 33% 45% 14%	437
	21st to end	Day	1 1 6% 39% 39% 14%	495
September	1st to 10th	Day	4 1 11% 43% 29% 12%	450
	11th to 20th	Day	3 2 15% 43% 29% 8%	450
	21st to end	Day	2 3 20% 39% 28% 9%	450
October	1st to 10th	Day	3 5% 20% 42% 26% 5%	450
	11th to 20th	Day	3 4 24% 42% 22% 5%	450
	21st to end	Day	4 6% 24% 33% 26% 6%	484
November	1st to 10th	Day	3 6% 18% 36% 30% 8%	270
	11th to 20th	Day	4 5% 21% 41% 23% 6%	270
	21st to end	Day	5% 6% 23% 31% 29% 6%	270
December	1st to 10th	Day	9% 6% 23% 34% 26% 3	270
	11th to 20th	Day	7% 7% 18% 37% 26% 4	270
	21st to end	Day	14% 13% 23% 35% 13% 2	223
January	1st to 10th	Night	11% 4 13% 43% 22% 6%	760
	11th to 20th	Night	8% 3 19% 41% 25% 5%	744
	21st to end	Night	11% 4 19% 39% 24% 3	792
February	1st to 10th	Night	8% 3 14% 39% 28% 7%	720
	11th to 20th	Night	9% 4 16% 40% 24% 7%	704
	21st to end	Night	11% 5% 18% 40% 22% 4	592
March	1st to 10th	Night	10% 5% 17% 44% 22% 3	720
	11th to 20th	Night	9% 4 14% 38% 29% 6%	720
	21st to end	Night	8% 5% 16% 43% 24% 4	792
April	1st to 10th	Night	9% 4 13% 43% 29% 4	720
	11th to 20th	Night	6% 4 16% 41% 30% 4	711
	21st to end	Night	5% 6% 15% 38% 29% 7%	720
May	1st to 10th	Night	7% 2 14% 38% 33% 5%	694
	11th to 20th	Night	4 2 15% 38% 37% 4	531
	21st to end	Night	4 1 16% 39% 35% 4	584
June	1st to 10th	Night	3 1 11% 37% 43% 5%	478
	11th to 20th	Night	3 1 3 31% 55% 7%	360
	21st to end	Night	5% 3 26% 59% 7%	360
July	1st to 10th	Night	2 2 12% 72% 11%	350
	11th to 20th	Night	1 9% 72% 17%	357
	21st to end	Night	3 1 1 15% 61% 19%	771
August	1st to 10th	Night	4 1 21% 58% 15%	716
	11th to 20th	Night	4 1 14% 63% 19%	712
	21st to end	Night	2 1 1 17% 60% 19%	792
September	1st to 10th	Night	6% 1 3 21% 52% 17%	720
	11th to 20th	Night	3 1 3 28% 53% 13%	720
	21st to end	Night	1 1 6% 29% 52% 12%	720
October	1st to 10th	Night	4 1 7% 40% 41% 7%	720
	11th to 20th	Night	5% 2 9% 34% 40% 10%	720
	21st to end	Night	4 2 12% 33% 35% 13%	792
November	1st to 10th	Night	3 4 11% 38% 34% 11%	740
	11th to 20th	Night	6% 2 9% 39% 34% 10%	760
	21st to end	Night	6% 2 14% 41% 29% 7%	760
December	1st to 10th	Night	8% 4 16% 40% 26% 6%	760
	11th to 20th	Night	12% 6% 14% 40% 24% 4	760
	21st to end	Night	11% 6% 18% 42% 19% 5%	836

Page generated at 2024-01-13 16:28:28. Version ac07

Copyright 2024 Attilla Danko