Mendocino
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Mendocino 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	11% 7% 2 5% 3 3 3 3 5% 8% 49%	105086
	Night	14% 9% 3 6% 4 3 3 3 4 6% 46%	102698
Transparency	Day	33% 3 9% 23% 20% 13%	104849
	Night	39% 3 9% 20% 18% 11%	102526
Seeing	Day	15% 11% 25% 28% 17% 5%	15382
	Night	16% 5% 14% 28% 28% 8%	24526

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	22% 10% 3 6% 3 4 3 3 4 6% 34%	2772
	11th to 20th	Day	31% 9% 3 8% 5% 3 3 2 4 5% 26%	2860
	21st to end	Day	30% 9% 3 7% 4 4 3 3 5% 6% 27%	3146
February	1st to 10th	Day	20% 8% 3 5% 4 3 4 3 4 5% 40%	1710
	11th to 20th	Day	18% 9% 3 6% 4 4 4 3 7% 8% 35%	1665
	21st to end	Day	20% 8% 2 6% 3 4 4 3 5% 7% 40%	1580
March	1st to 10th	Day	27% 14% 3 6% 4 3 3 2 4 5% 28%	3442
	11th to 20th	Day	14% 7% 3 5% 3 4 3 3 4 8% 46%	3490
	21st to end	Day	21% 11% 3 6% 4 4 5% 4 5% 7% 29%	3825
April	1st to 10th	Day	15% 8% 2 6% 4 4 4 3 7% 8% 37%	2242
	11th to 20th	Day	13% 8% 3 5% 4 4 4 3 6% 7% 42%	2249
	21st to end	Day	9% 6% 2 5% 3 3 4 3 7% 10% 47%	2356
May	1st to 10th	Day	8% 7% 2 4 2 2 2 2 4 7% 60%	4110
	11th to 20th	Day	5% 4 2 5% 3 2 3 2 4 8% 62%	4070
	21st to end	Day	6% 5% 1 3 2 2 2 2 4 6% 66%	4804
June	1st to 10th	Day	10% 10% 3 5% 3 3 3 3 6% 9% 46%	2660
	11th to 20th	Day	3 5% 2 3 3 3 2 2 4 8% 65%	2660
	21st to end	Day	5% 8% 3 5% 4 3 2 2 3 8% 57%	2660
July	1st to 10th	Day	1 4 1 3 2 2 2 2 3 8% 72%	4343
	11th to 20th	Day	2 5% 2 5% 3 3 2 3 5% 12% 58%	4110
	21st to end	Day	1 6% 3 6% 3 3 3 3 5% 12% 55%	4455
August	1st to 10th	Day	2 8% 4 6% 4 3 4 3 7% 11% 48%	4091
	11th to 20th	Day	4 6% 2 4 3 2 3 2 4 10% 59%	4026
	21st to end	Day	3 8% 2 5% 3 3 4 3 5% 9% 57%	4194
September	1st to 10th	Day	3 5% 2 4 3 3 3 2 4 9% 61%	2280
	11th to 20th	Day	6% 7% 2 4 3 3 4 3 5% 10% 53%	2184
	21st to end	Day	3 4 2 4 3 3 3 2 5% 11% 60%	2051
October	1st to 10th	Day	5% 2 1 3 2 3 3 2 4 5% 70%	3180
	11th to 20th	Day	11% 7% 2 5% 4 4 4 4 6% 7% 45%	3161
	21st to end	Day	11% 6% 3 7% 5% 4 4 3 5% 8% 44%	3448
November	1st to 10th	Day	14% 7% 3 6% 5% 3 4 3 6% 7% 43%	1900
	11th to 20th	Day	16% 7% 3 6% 3 3 4 3 6% 10% 40%	1600
	21st to end	Day	12% 7% 2 5% 3 4 5% 4 5% 7% 47%	1520
December	1st to 10th	Day	18% 10% 3 6% 4 4 3 3 4 6% 40%	1520
	11th to 20th	Day	31% 10% 3 6% 5% 4 3 3 5% 5% 26%	1928
	21st to end	Day	25% 10% 3 8% 5% 4 3 3 4 6% 29%	2794
January	1st to 10th	Night	21% 10% 3 6% 4 4 5% 4 5% 7% 31%	4177
	11th to 20th	Night	27% 11% 3 8% 5% 4 4 2 4 5% 26%	4110
	21st to end	Night	33% 12% 3 7% 4 3 3 3 3 5% 23%	4521
February	1st to 10th	Night	19% 7% 3 7% 3 3 3 4 4 5% 41%	2470
	11th to 20th	Night	17% 11% 3 7% 5% 4 4 3 5% 6% 34%	2402
	21st to end	Night	19% 7% 2 5% 3 3 3 2 5% 6% 45%	1867
March	1st to 10th	Night	25% 16% 3 6% 4 4 3 2 3 5% 28%	3432
	11th to 20th	Night	17% 11% 4 5% 3 2 2 2 3 4 45%	3490
	21st to end	Night	18% 15% 3 8% 4 4 4 4 5% 5% 30%	3828
April	1st to 10th	Night	16% 10% 3 6% 4 3 4 4 5% 7% 39%	1937
	11th to 20th	Night	13% 8% 3 6% 4 3 3 3 5% 7% 45%	1879
	21st to end	Night	8% 7% 1 3 3 3 4 3 5% 10% 53%	1819
May	1st to 10th	Night	9% 4 2 4 2 2 2 2 3 5% 65%	2860
	11th to 20th	Night	3 5% 2 7% 5% 3 3 2 4 6% 60%	2833
	21st to end	Night	5% 6% 2 3 2 1 2 1 3 4 70%	2767
June	1st to 10th	Night	8% 10% 3 5% 4 4 3 3 4 7% 48%	1520
	11th to 20th	Night	4 4 2 4 3 3 2 1 3 6% 69%	1520
	21st to end	Night	4 10% 2 5% 2 2 2 2 3 5% 64%	1520
July	1st to 10th	Night	1 4 1 3 3 2 1 2 3 4 73%	2601
	11th to 20th	Night	1 10% 4 6% 3 2 3 2 3 6% 59%	2860
	21st to end	Night	10% 4 7% 4 3 3 2 4 7% 57%	3109
August	1st to 10th	Night	1 14% 8% 12% 5% 4 4 4 4 6% 40%	2848
	11th to 20th	Night	3 7% 2 5% 3 3 3 3 3 6% 60%	2812
	21st to end	Night	5% 6% 2 6% 4 3 3 2 3 6% 61%	3484
September	1st to 10th	Night	2 7% 2 4 2 2 2 1 3 7% 68%	1900
	11th to 20th	Night	7% 9% 3 5% 3 3 3 2 4 6% 56%	1992
	21st to end	Night	4 6% 3 5% 3 3 3 3 4 6% 60%	2128
October	1st to 10th	Night	4 5% 2 4 3 3 2 2 3 4 71%	3800
	11th to 20th	Night	11% 14% 2 5% 3 3 3 2 3 5% 47%	3777
	21st to end	Night	13% 6% 3 5% 4 4 3 3 5% 7% 48%	4121
November	1st to 10th	Night	13% 9% 3 8% 3 4 4 4 5% 7% 39%	2279
	11th to 20th	Night	16% 10% 2 6% 3 4 4 3 5% 7% 39%	2577
	21st to end	Night	14% 6% 3 7% 3 4 2 3 5% 7% 46%	2660
December	1st to 10th	Night	21% 8% 3 6% 4 3 4 2 5% 7% 38%	2660
	11th to 20th	Night	33% 10% 2 5% 3 3 3 3 5% 6% 28%	3276
	21st to end	Night	23% 10% 4 7% 4 4 4 3 3 6% 31%	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	54% 3 15% 20% 5% 3	2772
	11th to 20th	Day	63% 2 12% 9% 8% 7%	2860
	21st to end	Day	60% 2 9% 15% 10% 5%	3146
February	1st to 10th	Day	47% 3 9% 17% 18% 6%	1710
	11th to 20th	Day	48% 3 8% 21% 16% 3	1674
	21st to end	Day	46% 4 13% 20% 12% 3	1580
March	1st to 10th	Day	62% 3 8% 18% 9% 1	3442
	11th to 20th	Day	38% 2 13% 23% 15% 8%	3490
	21st to end	Day	57% 3 13% 19% 6% 1	3825
April	1st to 10th	Day	47% 3 13% 24% 11% 1	2242
	11th to 20th	Day	42% 4 14% 25% 12% 3	2252
	21st to end	Day	32% 4 17% 29% 16% 2	2356
May	1st to 10th	Day	26% 4 14% 28% 19% 9%	4110
	11th to 20th	Day	20% 2 7% 30% 34% 7%	4073
	21st to end	Day	23% 2 13% 48% 15%	4805
June	1st to 10th	Day	35% 3 11% 29% 19% 3	2660
	11th to 20th	Day	18% 3 10% 28% 33% 7%	2660
	21st to end	Day	21% 2 5% 24% 35% 13%	2660
July	1st to 10th	Day	10% 1 3 12% 22% 52%	4276
	11th to 20th	Day	15% 2 5% 16% 22% 40%	4041
	21st to end	Day	15% 2 6% 13% 36% 27%	4315
August	1st to 10th	Day	22% 2 5% 19% 30% 22%	4076
	11th to 20th	Day	16% 1 4 31% 33% 14%	4065
	21st to end	Day	18% 4 5% 28% 26% 19%	4193
September	1st to 10th	Day	15% 2 4 18% 33% 28%	2280
	11th to 20th	Day	24% 3 7% 33% 28% 5%	2184
	21st to end	Day	16% 2 6% 29% 32% 16%	2051
October	1st to 10th	Day	17% 3 4 21% 18% 38%	3180
	11th to 20th	Day	30% 4 9% 24% 26% 7%	3161
	21st to end	Day	35% 5% 10% 24% 18% 8%	3448
November	1st to 10th	Day	40% 3 11% 26% 14% 7%	1900
	11th to 20th	Day	42% 4 13% 21% 13% 7%	1600
	21st to end	Day	37% 4 12% 20% 18% 9%	1520
December	1st to 10th	Day	47% 3 10% 18% 13% 10%	1520
	11th to 20th	Day	61% 3 8% 14% 11% 3	1928
	21st to end	Day	59% 4 9% 18% 8% 2	2794
January	1st to 10th	Night	53% 4 20% 14% 7% 2	4177
	11th to 20th	Night	64% 3 9% 12% 6% 6%	4110
	21st to end	Night	66% 2 6% 12% 10% 4	4521
February	1st to 10th	Night	45% 3 9% 18% 17% 6%	2470
	11th to 20th	Night	51% 4 7% 20% 13% 4	2404
	21st to end	Night	42% 4 13% 24% 14% 3	1867
March	1st to 10th	Night	62% 3 9% 17% 9% 1	3432
	11th to 20th	Night	45% 1 10% 21% 13% 9%	3490
	21st to end	Night	58% 2 13% 19% 7% 1	3828
April	1st to 10th	Night	46% 5% 13% 23% 11% 2	1937
	11th to 20th	Night	40% 3 15% 27% 13% 2	1879
	21st to end	Night	29% 4 16% 33% 16% 2	1819
May	1st to 10th	Night	25% 3 10% 29% 21% 11%	2860
	11th to 20th	Night	22% 5% 6% 20% 36% 11%	2834
	21st to end	Night	22% 2 11% 46% 19%	2767
June	1st to 10th	Night	34% 3 10% 28% 21% 3	1520
	11th to 20th	Night	18% 2 7% 28% 37% 8%	1520
	21st to end	Night	23% 2 4 16% 38% 18%	1520
July	1st to 10th	Night	12% 2 2 11% 20% 53%	2560
	11th to 20th	Night	23% 2 4 12% 21% 39%	2806
	21st to end	Night	25% 3 3 7% 31% 30%	3011
August	1st to 10th	Night	40% 3 5% 17% 21% 13%	2839
	11th to 20th	Night	19% 4 6% 24% 29% 18%	2839
	21st to end	Night	19% 3 6% 23% 28% 20%	3484
September	1st to 10th	Night	15% 3 2 18% 29% 33%	1900
	11th to 20th	Night	29% 3 5% 25% 31% 7%	1992
	21st to end	Night	23% 2 5% 22% 27% 20%	2128
October	1st to 10th	Night	18% 2 4 17% 21% 39%	3800
	11th to 20th	Night	39% 5% 6% 16% 28% 7%	3777
	21st to end	Night	35% 4 8% 26% 17% 10%	4121
November	1st to 10th	Night	44% 5% 12% 18% 15% 7%	2279
	11th to 20th	Night	45% 4 13% 19% 14% 5%	2577
	21st to end	Night	39% 3 11% 19% 17% 10%	2660
December	1st to 10th	Night	47% 4 9% 18% 14% 7%	2660
	11th to 20th	Night	59% 3 7% 15% 13% 3	3276
	21st to end	Night	57% 2 13% 19% 7% 2	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	37% 12% 23% 16% 11% 2	322
	11th to 20th	Day	30% 10% 23% 22% 11% 5%	370
	21st to end	Day	26% 11% 22% 22% 15% 4	407
February	1st to 10th	Day	23% 15% 21% 23% 14% 4	370
	11th to 20th	Day	26% 17% 24% 20% 12% 1	365
	21st to end	Day	22% 17% 25% 23% 10% 2	362
March	1st to 10th	Day	33% 16% 25% 18% 7% 1	460
	11th to 20th	Day	26% 13% 30% 19% 9% 2	460
	21st to end	Day	25% 18% 30% 18% 7% 2	506
April	1st to 10th	Day	22% 18% 29% 20% 9% 2	460
	11th to 20th	Day	22% 16% 28% 21% 10% 2	452
	21st to end	Day	12% 22% 32% 19% 11% 4	460
May	1st to 10th	Day	17% 12% 30% 27% 10% 3	463
	11th to 20th	Day	15% 16% 28% 24% 13% 4	488
	21st to end	Day	15% 15% 27% 26% 13% 4	529
June	1st to 10th	Day	12% 14% 27% 29% 14% 3	490
	11th to 20th	Day	8% 16% 33% 29% 11% 3	490
	21st to end	Day	6% 6% 28% 36% 20% 5%	490
July	1st to 10th	Day	5% 4 24% 44% 16% 7%	486
	11th to 20th	Day	3 2 23% 42% 24% 6%	484
	21st to end	Day	3 2 18% 42% 29% 7%	531
August	1st to 10th	Day	5% 3 26% 39% 20% 7%	487
	11th to 20th	Day	6% 4 22% 36% 26% 6%	477
	21st to end	Day	6% 3 22% 38% 23% 8%	539
September	1st to 10th	Day	5% 5% 23% 36% 22% 9%	490
	11th to 20th	Day	7% 6% 23% 36% 21% 5%	490
	21st to end	Day	5% 9% 21% 32% 24% 9%	490
October	1st to 10th	Day	8% 9% 22% 28% 24% 8%	490
	11th to 20th	Day	13% 9% 16% 26% 25% 10%	490
	21st to end	Day	16% 7% 22% 29% 19% 7%	539
November	1st to 10th	Day	16% 12% 21% 25% 21% 6%	472
	11th to 20th	Day	13% 8% 19% 29% 23% 8%	235
	21st to end	Day	16% 6% 23% 24% 23% 9%	180
December	1st to 10th	Day	25% 11% 20% 21% 13% 10%	180
	11th to 20th	Day	28% 12% 19% 22% 11% 8%	180
	21st to end	Day	26% 13% 19% 21% 17% 5%	198
January	1st to 10th	Night	26% 7% 18% 26% 19% 5%	760
	11th to 20th	Night	27% 5% 15% 27% 18% 8%	760
	21st to end	Night	26% 5% 14% 28% 22% 6%	836
February	1st to 10th	Night	22% 8% 14% 32% 20% 4	760
	11th to 20th	Night	22% 9% 18% 28% 19% 5%	744
	21st to end	Night	22% 8% 20% 32% 16% 2	628
March	1st to 10th	Night	29% 11% 15% 28% 14% 4	760
	11th to 20th	Night	28% 7% 11% 29% 21% 4	760
	21st to end	Night	24% 9% 19% 27% 17% 3	836
April	1st to 10th	Night	20% 7% 23% 27% 18% 4	760
	11th to 20th	Night	15% 13% 18% 29% 20% 5%	751
	21st to end	Night	12% 8% 19% 32% 24% 6%	679
May	1st to 10th	Night	11% 7% 23% 29% 24% 7%	570
	11th to 20th	Night	9% 4 16% 30% 33% 8%	561
	21st to end	Night	12% 7% 20% 28% 28% 5%	416
June	1st to 10th	Night	11% 6% 17% 32% 29% 5%	380
	11th to 20th	Night	4 6% 21% 37% 30% 2	380
	21st to end	Night	6% 1 8% 36% 42% 6%	380
July	1st to 10th	Night	3 1 10% 29% 47% 9%	404
	11th to 20th	Night	3 4 29% 48% 16%	552
	21st to end	Night	1 4 23% 51% 21%	624
August	1st to 10th	Night	4 1 4 28% 48% 14%	567
	11th to 20th	Night	5% 1 5% 27% 48% 15%	564
	21st to end	Night	6% 1 6% 26% 46% 14%	822
September	1st to 10th	Night	4 1 7% 27% 45% 16%	760
	11th to 20th	Night	9% 3 10% 29% 38% 12%	760
	21st to end	Night	6% 3 10% 28% 36% 17%	760
October	1st to 10th	Night	8% 4 14% 28% 34% 13%	760
	11th to 20th	Night	13% 3 10% 24% 36% 13%	760
	21st to end	Night	14% 4 11% 29% 31% 12%	836
November	1st to 10th	Night	17% 5% 15% 25% 29% 8%	760
	11th to 20th	Night	20% 5% 13% 30% 26% 6%	760
	21st to end	Night	16% 6% 15% 32% 24% 6%	760
December	1st to 10th	Night	24% 6% 15% 27% 21% 8%	760
	11th to 20th	Night	31% 8% 14% 27% 17% 4	760
	21st to end	Night	30% 8% 18% 24% 16% 4	836

Page generated at 2024-11-02 23:11:10. Version ac07

Copyright © 2024 Attilla Danko.