Gualala
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Gualala clear sky chart from 2005-11-06 to 2025-05-26.

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% 4 1 4 3 3 3 3 5% 7% 57%	118164
	Night	14% 5% 2 4 3 3 3 3 4 6% 54%	120000
Transparency	Day	28% 4 8% 20% 23% 18%	117928
	Night	32% 3 7% 19% 21% 17%	119827
Seeing	Day	14% 10% 25% 27% 19% 6%	16082
	Night	15% 6% 17% 28% 26% 8%	25388

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	17% 7% 2 6% 4 3 4 4 6% 7% 39%	4021
	11th to 20th	Day	21% 6% 2 5% 3 3 2 2 3 5% 47%	4100
	21st to end	Day	21% 7% 2 5% 3 3 3 3 5% 6% 43%	4510
February	1st to 10th	Day	22% 7% 3 5% 3 3 3 3 4 5% 42%	1800
	11th to 20th	Day	18% 6% 2 5% 3 3 4 4 7% 8% 38%	1755
	21st to end	Day	19% 5% 2 5% 4 3 4 3 5% 6% 44%	1676
March	1st to 10th	Day	21% 10% 2 5% 4 3 4 4 5% 8% 34%	4952
	11th to 20th	Day	19% 5% 1 4 3 3 3 3 5% 8% 45%	5000
	21st to end	Day	22% 10% 2 4 3 4 5% 4 7% 9% 30%	5486
April	1st to 10th	Day	16% 6% 2 4 4 3 4 4 6% 8% 42%	2370
	11th to 20th	Day	11% 5% 2 6% 4 4 4 3 6% 9% 47%	2369
	21st to end	Day	8% 3 1 3 3 4 4 4 7% 10% 53%	2439
May	1st to 10th	Day	5% 3 1 3 2 2 3 2 4 6% 68%	4240
	11th to 20th	Day	5% 2 1 3 2 2 3 2 4 7% 70%	4200
	21st to end	Day	4 2 1 2 2 2 2 2 4 7% 73%	4855
June	1st to 10th	Day	6% 5% 1 3 3 3 3 3 6% 10% 56%	2660
	11th to 20th	Day	2 2 1 3 2 2 2 2 3 7% 73%	2660
	21st to end	Day	3 1 1 2 2 1 2 2 4 5% 77%	2660
July	1st to 10th	Day	1 1 1 2 1 1 2 1 2 4 84%	4327
	11th to 20th	Day	1 2 1 4 3 2 2 2 3 7% 74%	4110
	21st to end	Day	1 1 2 2 3 2 2 3 6% 78%	4455
August	1st to 10th	Day	1 2 1 2 2 3 3 3 4 7% 73%	4091
	11th to 20th	Day	2 2 1 2 2 2 2 1 3 6% 79%	4000
	21st to end	Day	2 3 1 5% 2 2 3 2 4 8% 69%	4180
September	1st to 10th	Day	1 1 1 2 2 1 2 3 3 7% 77%	2280
	11th to 20th	Day	4 3 1 4 3 3 2 2 5% 9% 65%	2203
	21st to end	Day	5% 2 1 3 2 2 2 2 4 6% 73%	2040
October	1st to 10th	Day	4 2 1 3 2 2 2 2 3 6% 74%	3180
	11th to 20th	Day	11% 2 1 2 2 2 3 2 4 8% 63%	3161
	21st to end	Day	9% 5% 2 5% 3 3 4 3 6% 9% 52%	3448
November	1st to 10th	Day	11% 5% 2 4 3 3 4 3 5% 9% 49%	1959
	11th to 20th	Day	16% 6% 2 5% 3 2 4 3 5% 8% 45%	1725
	21st to end	Day	13% 4 1 4 4 4 4 4 5% 9% 49%	1600
December	1st to 10th	Day	12% 4 2 3 3 3 4 4 7% 9% 49%	2620
	11th to 20th	Day	30% 8% 2 6% 4 4 4 3 7% 7% 24%	3028
	21st to end	Day	28% 8% 3 6% 3 4 5% 4 6% 8% 25%	4004
January	1st to 10th	Night	17% 7% 1 4 4 4 4 4 7% 8% 39%	5938
	11th to 20th	Night	18% 7% 3 5% 3 3 3 2 3 5% 48%	5880
	21st to end	Night	23% 7% 2 5% 3 3 3 2 3 5% 43%	6468
February	1st to 10th	Night	20% 6% 2 4 3 3 3 4 5% 6% 44%	2600
	11th to 20th	Night	17% 8% 2 5% 3 4 4 4 7% 7% 39%	2532
	21st to end	Night	16% 7% 1 3 3 3 4 3 5% 6% 48%	1947
March	1st to 10th	Night	18% 12% 3 6% 4 4 4 4 6% 6% 33%	4942
	11th to 20th	Night	21% 5% 1 4 3 3 3 2 4 6% 49%	5000
	21st to end	Night	19% 11% 3 6% 4 4 4 3 5% 8% 33%	5489
April	1st to 10th	Night	13% 7% 2 6% 4 3 4 3 5% 7% 45%	2030
	11th to 20th	Night	11% 5% 3 5% 4 4 4 3 4 6% 52%	1979
	21st to end	Night	7% 4 1 3 3 3 4 3 5% 8% 60%	1957
May	1st to 10th	Night	6% 3 1 3 1 2 2 2 4 6% 71%	2950
	11th to 20th	Night	3 2 2 4 3 2 2 1 3 7% 71%	2923
	21st to end	Night	3 2 1 3 1 2 2 2 3 5% 76%	2819
June	1st to 10th	Night	5% 7% 2 4 4 3 4 2 6% 9% 55%	1520
	11th to 20th	Night	3 3 1 2 2 2 2 2 3 7% 75%	1520
	21st to end	Night	3 3 1 2 2 2 2 2 3 4 76%	1520
July	1st to 10th	Night	1 1 2 1 1 2 1 2 3 85%	2630
	11th to 20th	Night	1 3 2 5% 3 2 2 1 2 4 73%	2860
	21st to end	Night	1 2 1 2 2 2 2 2 3 6% 77%	3109
August	1st to 10th	Night	1 3 1 3 2 2 2 2 4 5% 74%	2848
	11th to 20th	Night	1 2 1 2 1 2 2 1 3 5% 81%	2836
	21st to end	Night	3 3 2 5% 2 2 2 2 2 4 73%	3498
September	1st to 10th	Night	1 1 1 3 1 1 2 3 3 6% 78%	1900
	11th to 20th	Night	5% 4 2 4 2 2 2 2 4 7% 66%	1973
	21st to end	Night	4 3 1 3 2 3 2 3 3 5% 71%	2139
October	1st to 10th	Night	3 3 1 3 2 2 2 2 3 4 75%	3800
	11th to 20th	Night	8% 5% 2 4 2 2 2 2 3 6% 64%	3777
	21st to end	Night	12% 3 1 3 3 3 4 3 5% 7% 57%	4121
November	1st to 10th	Night	13% 5% 2 4 3 3 4 4 6% 8% 49%	2340
	11th to 20th	Night	17% 4 2 4 4 4 4 4 6% 8% 44%	2667
	21st to end	Night	14% 5% 2 4 3 3 3 3 5% 7% 51%	2800
December	1st to 10th	Night	13% 5% 1 4 3 3 3 3 5% 8% 51%	4560
	11th to 20th	Night	31% 6% 2 5% 4 4 4 3 7% 7% 27%	5176
	21st to end	Night	36% 8% 2 5% 3 2 3 2 4 5% 30%	6952

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	43% 5% 15% 20% 10% 7%	4021
	11th to 20th	Day	42% 2 7% 15% 18% 16%	4100
	21st to end	Day	43% 3 7% 14% 17% 17%	4510
February	1st to 10th	Day	45% 3 8% 18% 18% 8%	1800
	11th to 20th	Day	42% 4 9% 20% 19% 5%	1764
	21st to end	Day	40% 4 11% 24% 16% 6%	1676
March	1st to 10th	Day	51% 3 7% 20% 18% 2	4952
	11th to 20th	Day	39% 4 15% 22% 12% 9%	5000
	21st to end	Day	51% 4 14% 21% 9% 1	5486
April	1st to 10th	Day	40% 3 14% 26% 14% 3	2370
	11th to 20th	Day	34% 4 15% 23% 18% 6%	2372
	21st to end	Day	25% 4 14% 30% 21% 5%	2439
May	1st to 10th	Day	18% 2 15% 28% 23% 13%	4240
	11th to 20th	Day	15% 5% 7% 24% 34% 15%	4203
	21st to end	Day	13% 3 10% 43% 30% 2	4856
June	1st to 10th	Day	24% 4 11% 28% 27% 6%	2660
	11th to 20th	Day	13% 3 8% 22% 38% 16%	2660
	21st to end	Day	10% 4 3 15% 38% 29%	2660
July	1st to 10th	Day	6% 3 2 7% 18% 64%	4261
	11th to 20th	Day	10% 4 2 9% 22% 54%	4041
	21st to end	Day	8% 4 2 9% 33% 45%	4315
August	1st to 10th	Day	13% 3 2 12% 26% 43%	4076
	11th to 20th	Day	9% 3 2 17% 40% 28%	4039
	21st to end	Day	12% 6% 4 19% 32% 28%	4179
September	1st to 10th	Day	8% 3 2 14% 33% 40%	2280
	11th to 20th	Day	19% 4 4 28% 34% 10%	2203
	21st to end	Day	14% 3 4 24% 31% 24%	2040
October	1st to 10th	Day	16% 2 3 16% 24% 40%	3180
	11th to 20th	Day	22% 4 8% 24% 30% 13%	3161
	21st to end	Day	30% 3 10% 23% 24% 11%	3448
November	1st to 10th	Day	31% 4 8% 29% 18% 9%	1959
	11th to 20th	Day	39% 3 12% 23% 15% 7%	1725
	21st to end	Day	33% 4 13% 19% 20% 12%	1600
December	1st to 10th	Day	31% 4 7% 23% 27% 8%	2620
	11th to 20th	Day	59% 3 9% 16% 10% 3	3028
	21st to end	Day	58% 3 10% 19% 8% 2	4004
January	1st to 10th	Night	42% 5% 19% 15% 13% 6%	5938
	11th to 20th	Night	43% 2 7% 19% 17% 12%	5880
	21st to end	Night	46% 2 5% 10% 18% 19%	6468
February	1st to 10th	Night	41% 3 8% 20% 18% 10%	2600
	11th to 20th	Night	42% 4 9% 20% 18% 6%	2534
	21st to end	Night	36% 3 12% 26% 18% 5%	1947
March	1st to 10th	Night	53% 3 7% 19% 14% 4	4942
	11th to 20th	Night	39% 3 10% 23% 17% 8%	5000
	21st to end	Night	50% 4 14% 21% 9% 2	5489
April	1st to 10th	Night	39% 4 12% 25% 17% 4	2030
	11th to 20th	Night	33% 5% 11% 25% 19% 7%	1979
	21st to end	Night	24% 4 10% 34% 21% 6%	1957
May	1st to 10th	Night	17% 3 7% 30% 28% 14%	2950
	11th to 20th	Night	15% 5% 7% 20% 31% 22%	2924
	21st to end	Night	13% 3 8% 42% 31% 3	2819
June	1st to 10th	Night	26% 6% 9% 22% 29% 9%	1520
	11th to 20th	Night	13% 4 8% 21% 37% 17%	1520
	21st to end	Night	13% 4 4 11% 32% 35%	1520
July	1st to 10th	Night	6% 4 1 5% 17% 67%	2588
	11th to 20th	Night	15% 4 3 6% 17% 54%	2806
	21st to end	Night	9% 4 1 7% 26% 53%	3011
August	1st to 10th	Night	14% 4 2 8% 26% 46%	2839
	11th to 20th	Night	8% 4 2 11% 40% 35%	2863
	21st to end	Night	14% 5% 1 13% 33% 33%	3498
September	1st to 10th	Night	9% 4 1 12% 29% 45%	1900
	11th to 20th	Night	18% 4 5% 20% 37% 16%	1973
	21st to end	Night	17% 3 3 20% 27% 30%	2139
October	1st to 10th	Night	16% 2 3 11% 22% 45%	3800
	11th to 20th	Night	24% 3 5% 22% 30% 17%	3777
	21st to end	Night	27% 2 5% 24% 27% 15%	4121
November	1st to 10th	Night	32% 5% 12% 23% 17% 11%	2340
	11th to 20th	Night	37% 4 14% 22% 18% 6%	2667
	21st to end	Night	34% 3 10% 20% 21% 12%	2800
December	1st to 10th	Night	32% 3 6% 26% 23% 11%	4560
	11th to 20th	Night	57% 3 8% 15% 14% 3	5176
	21st to end	Night	59% 2 9% 19% 8% 3	6952

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	31% 15% 22% 17% 13% 2	361
	11th to 20th	Day	28% 10% 23% 21% 16% 4	400
	21st to end	Day	23% 10% 20% 27% 16% 3	440
February	1st to 10th	Day	26% 12% 22% 19% 17% 4	400
	11th to 20th	Day	29% 14% 24% 18% 13% 2	395
	21st to end	Day	20% 14% 28% 23% 11% 4	405
March	1st to 10th	Day	29% 14% 27% 19% 9% 1	500
	11th to 20th	Day	29% 11% 29% 19% 10% 3	500
	21st to end	Day	24% 16% 30% 20% 7% 3	550
April	1st to 10th	Day	23% 16% 29% 21% 8% 3	500
	11th to 20th	Day	16% 17% 33% 21% 10% 4	492
	21st to end	Day	14% 17% 32% 21% 11% 4	500
May	1st to 10th	Day	10% 14% 34% 26% 13% 4	503
	11th to 20th	Day	16% 13% 28% 25% 14% 3	528
	21st to end	Day	11% 12% 29% 29% 13% 5%	550
June	1st to 10th	Day	9% 11% 33% 28% 14% 4	490
	11th to 20th	Day	6% 13% 35% 29% 16% 1	490
	21st to end	Day	1 4 29% 36% 23% 5%	490
July	1st to 10th	Day	3 6% 24% 42% 20% 6%	486
	11th to 20th	Day	2 25% 40% 26% 6%	484
	21st to end	Day	1 2 16% 44% 29% 8%	531
August	1st to 10th	Day	2 3 26% 39% 23% 7%	487
	11th to 20th	Day	3 4 23% 33% 29% 8%	477
	21st to end	Day	1 4 19% 36% 30% 9%	539
September	1st to 10th	Day	2 4 22% 34% 30% 8%	490
	11th to 20th	Day	5% 8% 21% 33% 24% 8%	490
	21st to end	Day	6% 7% 23% 28% 29% 8%	490
October	1st to 10th	Day	8% 7% 23% 24% 28% 10%	490
	11th to 20th	Day	12% 7% 18% 24% 27% 13%	490
	21st to end	Day	13% 6% 22% 27% 25% 7%	539
November	1st to 10th	Day	15% 9% 21% 25% 22% 8%	495
	11th to 20th	Day	19% 9% 16% 23% 24% 10%	280
	21st to end	Day	19% 5% 21% 22% 23% 12%	200
December	1st to 10th	Day	23% 10% 21% 20% 16% 12%	200
	11th to 20th	Day	31% 9% 17% 20% 14% 10%	200
	21st to end	Day	31% 10% 20% 17% 14% 8%	220
January	1st to 10th	Night	25% 7% 17% 27% 19% 6%	800
	11th to 20th	Night	23% 7% 16% 28% 20% 6%	800
	21st to end	Night	22% 7% 14% 28% 24% 6%	880
February	1st to 10th	Night	25% 7% 17% 26% 22% 4	800
	11th to 20th	Night	24% 9% 20% 23% 18% 6%	784
	21st to end	Night	21% 10% 20% 31% 15% 3	660
March	1st to 10th	Night	27% 11% 17% 25% 17% 4	800
	11th to 20th	Night	25% 8% 17% 29% 18% 4	800
	21st to end	Night	22% 10% 24% 26% 15% 3	880
April	1st to 10th	Night	18% 10% 24% 26% 17% 5%	800
	11th to 20th	Night	15% 12% 25% 27% 16% 5%	791
	21st to end	Night	11% 11% 30% 24% 18% 5%	757
May	1st to 10th	Night	8% 10% 28% 29% 20% 6%	600
	11th to 20th	Night	8% 5% 24% 35% 23% 6%	591
	21st to end	Night	8% 9% 27% 29% 22% 5%	436
June	1st to 10th	Night	9% 8% 30% 29% 21% 3	380
	11th to 20th	Night	3 11% 26% 38% 21% 2	380
	21st to end	Night	4 3 20% 42% 27% 4	380
July	1st to 10th	Night	2 3 19% 33% 33% 9%	419
	11th to 20th	Night	1 1 13% 33% 39% 13%	552
	21st to end	Night	2 1 10% 30% 40% 17%	624
August	1st to 10th	Night	2 2 13% 34% 37% 13%	567
	11th to 20th	Night	1 1 13% 32% 37% 15%	575
	21st to end	Night	3 2 10% 27% 45% 12%	836
September	1st to 10th	Night	1 3 14% 28% 39% 15%	760
	11th to 20th	Night	6% 4 13% 32% 35% 10%	760
	21st to end	Night	5% 6% 12% 28% 36% 13%	760
October	1st to 10th	Night	6% 7% 14% 29% 32% 12%	760
	11th to 20th	Night	10% 5% 12% 25% 37% 13%	760
	21st to end	Night	14% 4 13% 26% 31% 12%	836
November	1st to 10th	Night	15% 6% 16% 24% 30% 9%	780
	11th to 20th	Night	19% 6% 14% 28% 27% 6%	800
	21st to end	Night	17% 6% 16% 29% 25% 7%	800
December	1st to 10th	Night	26% 4 13% 28% 22% 8%	800
	11th to 20th	Night	30% 7% 15% 26% 18% 4	800
	21st to end	Night	28% 8% 19% 25% 16% 4	880

Page generated at 2025-05-23 06:21:01. Version ac07

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