Surf City
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Surf City 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% 6% 2 6% 4 4 4 4 6% 8% 44%	113464
	Night	12% 6% 2 6% 4 4 4 4 6% 8% 45%	115816
Transparency	Day	37% 6% 14% 21% 17% 5%	117107
	Night	37% 5% 13% 20% 19% 6%	120312
Seeing	Day	13% 3 15% 29% 29% 12%	16260
	Night	14% 4 20% 31% 24% 7%	26740

By Month

Percentage Cloud Cover SE (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	11% 5% 2 4 3 3 3 3 4 5% 57%	4056
	11th to 20th	Day	11% 5% 2 5% 3 4 3 3 5% 6% 54%	4060
	21st to end	Day	13% 10% 4 8% 4 3 4 3 4 5% 42%	4466
February	1st to 10th	Day	15% 5% 2 6% 6% 4 4 3 5% 6% 42%	1800
	11th to 20th	Day	19% 7% 3 5% 4 3 4 3 4 5% 45%	1889
	21st to end	Day	14% 6% 3 5% 4 4 4 4 5% 7% 43%	1716
March	1st to 10th	Day	21% 8% 2 6% 3 3 4 4 5% 6% 38%	4935
	11th to 20th	Day	8% 3 2 5% 3 4 4 4 5% 7% 55%	4980
	21st to end	Day	12% 5% 2 5% 4 4 4 3 4 6% 52%	5465
April	1st to 10th	Day	10% 4 2 5% 3 3 3 4 6% 6% 54%	2390
	11th to 20th	Day	8% 4 2 5% 4 3 3 4 5% 7% 54%	2374
	21st to end	Day	9% 4 1 4 3 3 3 4 6% 8% 55%	2400
May	1st to 10th	Day	6% 5% 2 6% 4 5% 6% 5% 8% 9% 43%	3885
	11th to 20th	Day	15% 7% 3 7% 5% 5% 5% 3 7% 8% 36%	4173
	21st to end	Day	6% 4 1 6% 4 5% 5% 5% 7% 10% 47%	4541
June	1st to 10th	Day	10% 6% 3 7% 5% 5% 6% 5% 7% 9% 38%	2470
	11th to 20th	Day	9% 3 2 4 4 5% 5% 5% 8% 12% 43%	2470
	21st to end	Day	8% 5% 2 5% 6% 5% 6% 6% 8% 11% 38%	2470
July	1st to 10th	Day	9% 5% 2 5% 5% 5% 6% 5% 8% 14% 37%	4120
	11th to 20th	Day	7% 6% 3 8% 7% 6% 6% 6% 9% 12% 31%	4120
	21st to end	Day	8% 6% 2 8% 6% 6% 7% 6% 9% 12% 29%	4466
August	1st to 10th	Day	18% 12% 4 8% 4 4 5% 4 6% 10% 24%	4083
	11th to 20th	Day	7% 4 2 6% 5% 5% 6% 4 8% 10% 41%	3730
	21st to end	Day	7% 5% 3 6% 4 5% 4 4 7% 9% 45%	4180
September	1st to 10th	Day	10% 5% 2 7% 4 5% 5% 5% 6% 10% 42%	2280
	11th to 20th	Day	15% 7% 2 6% 5% 4 5% 4 6% 8% 39%	2280
	21st to end	Day	15% 8% 3 7% 4 4 5% 4 5% 7% 39%	1981
October	1st to 10th	Day	15% 5% 3 6% 4 4 4 3 4 6% 46%	1900
	11th to 20th	Day	10% 3 2 5% 3 3 3 3 4 6% 58%	1900
	21st to end	Day	11% 5% 2 5% 3 2 3 3 4 6% 57%	2090
November	1st to 10th	Day	12% 4 2 4 3 4 3 3 5% 6% 52%	1957
	11th to 20th	Day	12% 5% 2 6% 4 4 3 3 5% 6% 50%	1981
	21st to end	Day	10% 5% 2 5% 3 5% 4 4 5% 7% 51%	1772
December	1st to 10th	Day	9% 5% 2 6% 3 4 4 3 4 7% 53%	2600
	11th to 20th	Day	13% 7% 3 8% 4 3 4 3 4 5% 45%	3018
	21st to end	Day	12% 7% 2 6% 4 4 4 3 5% 7% 46%	4466
January	1st to 10th	Night	11% 5% 2 5% 3 3 3 3 4 6% 56%	5889
	11th to 20th	Night	13% 6% 2 6% 3 3 4 3 5% 7% 48%	5900
	21st to end	Night	13% 7% 3 7% 4 4 4 3 5% 6% 45%	6490
February	1st to 10th	Night	17% 7% 2 5% 4 4 4 3 5% 5% 44%	2600
	11th to 20th	Night	19% 8% 3 5% 4 4 4 4 4 5% 40%	2394
	21st to end	Night	16% 6% 3 6% 4 4 4 3 5% 7% 43%	1910
March	1st to 10th	Night	17% 8% 3 7% 4 4 4 3 4 5% 40%	4918
	11th to 20th	Night	13% 5% 2 5% 3 3 4 4 5% 7% 50%	4980
	21st to end	Night	13% 5% 2 5% 3 3 3 3 4 7% 52%	5467
April	1st to 10th	Night	9% 6% 3 5% 4 3 4 4 6% 6% 49%	2010
	11th to 20th	Night	10% 5% 2 6% 4 4 4 4 5% 5% 51%	1975
	21st to end	Night	8% 3 1 5% 4 4 5% 4 5% 8% 55%	2000
May	1st to 10th	Night	7% 5% 2 6% 5% 5% 5% 4 6% 10% 43%	3230
	11th to 20th	Night	13% 6% 3 8% 6% 5% 5% 4 5% 8% 38%	2968
	21st to end	Night	8% 5% 2 5% 4 5% 4 4 7% 10% 47%	3130
June	1st to 10th	Night	11% 5% 2 7% 5% 6% 6% 4 7% 11% 35%	1710
	11th to 20th	Night	9% 4 2 5% 4 5% 5% 5% 8% 11% 41%	1710
	21st to end	Night	10% 5% 2 7% 5% 6% 5% 5% 8% 12% 35%	1710
July	1st to 10th	Night	7% 5% 3 6% 5% 6% 6% 6% 8% 12% 35%	2840
	11th to 20th	Night	7% 5% 2 8% 7% 6% 6% 5% 9% 13% 31%	2840
	21st to end	Night	8% 6% 3 7% 5% 5% 8% 6% 12% 12% 29%	3087
August	1st to 10th	Night	17% 10% 3 8% 5% 4 5% 5% 6% 10% 26%	2825
	11th to 20th	Night	7% 5% 2 7% 6% 5% 7% 6% 8% 11% 37%	3088
	21st to end	Night	7% 5% 2 7% 5% 4 5% 5% 7% 10% 43%	3476
September	1st to 10th	Night	12% 4 2 5% 5% 4 5% 4 7% 10% 41%	1900
	11th to 20th	Night	13% 6% 3 7% 5% 5% 5% 4 5% 9% 38%	1900
	21st to end	Night	16% 7% 3 8% 5% 4 4 4 5% 7% 37%	2193
October	1st to 10th	Night	13% 6% 3 5% 3 5% 4 3 6% 6% 46%	2280
	11th to 20th	Night	10% 5% 2 5% 3 4 3 3 4 5% 55%	2280
	21st to end	Night	10% 4 2 4 3 3 3 3 5% 7% 56%	2508
November	1st to 10th	Night	13% 5% 2 5% 3 4 4 4 4 5% 51%	2341
	11th to 20th	Night	13% 6% 3 7% 4 4 4 2 5% 6% 48%	2413
	21st to end	Night	11% 5% 2 5% 4 3 4 4 5% 7% 50%	2625
December	1st to 10th	Night	10% 6% 2 4 3 3 3 3 4 6% 55%	4580
	11th to 20th	Night	13% 7% 3 7% 4 4 3 3 5% 6% 43%	5159
	21st to end	Night	13% 5% 2 6% 3 4 4 3 5% 7% 48%	6490

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	31% 3 6% 19% 33% 8%	4057
	11th to 20th	Day	32% 3 6% 18% 32% 9%	4060
	21st to end	Day	46% 4 5% 16% 21% 8%	4466
February	1st to 10th	Day	43% 3 10% 22% 18% 5%	1800
	11th to 20th	Day	44% 3 8% 16% 22% 7%	1898
	21st to end	Day	40% 4 11% 19% 17% 8%	1716
March	1st to 10th	Day	48% 3 9% 14% 19% 7%	4935
	11th to 20th	Day	29% 4 10% 17% 24% 16%	4980
	21st to end	Day	35% 3 10% 24% 20% 7%	5465
April	1st to 10th	Day	30% 5% 13% 24% 21% 6%	2390
	11th to 20th	Day	28% 5% 12% 26% 20% 8%	2374
	21st to end	Day	27% 6% 16% 26% 22% 3	2400
May	1st to 10th	Day	34% 9% 23% 23% 9% 2	3920
	11th to 20th	Day	43% 7% 15% 23% 11%	4177
	21st to end	Day	28% 9% 19% 30% 12% 1	4554
June	1st to 10th	Day	40% 9% 16% 23% 10% 1	2470
	11th to 20th	Day	30% 10% 22% 25% 12% 1	2470
	21st to end	Day	37% 11% 21% 24% 8%	2470
July	1st to 10th	Day	35% 9% 29% 21% 4 1	4055
	11th to 20th	Day	42% 13% 27% 13% 4	4051
	21st to end	Day	43% 12% 21% 17% 7%	4324
August	1st to 10th	Day	55% 8% 22% 11% 3	4070
	11th to 20th	Day	36% 10% 20% 24% 10%	3766
	21st to end	Day	34% 7% 20% 32% 6% 1	4180
September	1st to 10th	Day	37% 9% 20% 18% 13% 3	2280
	11th to 20th	Day	42% 6% 14% 19% 15% 3	2280
	21st to end	Day	44% 5% 14% 19% 15% 3	1981
October	1st to 10th	Day	39% 4 7% 23% 23% 4	3160
	11th to 20th	Day	21% 3 6% 19% 25% 25%	3140
	21st to end	Day	26% 4 7% 28% 25% 10%	3428
November	1st to 10th	Day	32% 4 9% 21% 25% 8%	1957
	11th to 20th	Day	36% 4 9% 20% 24% 8%	1981
	21st to end	Day	34% 3 11% 23% 22% 7%	1772
December	1st to 10th	Day	32% 4 9% 18% 26% 11%	2600
	11th to 20th	Day	42% 4 9% 18% 20% 7%	3014
	21st to end	Day	38% 4 13% 26% 17% 2	4466
January	1st to 10th	Night	31% 3 6% 19% 34% 7%	5889
	11th to 20th	Night	36% 4 7% 16% 32% 6%	5900
	21st to end	Night	40% 3 6% 18% 25% 8%	6490
February	1st to 10th	Night	43% 3 9% 20% 19% 6%	2600
	11th to 20th	Night	45% 4 8% 16% 20% 7%	2396
	21st to end	Night	42% 4 9% 18% 19% 8%	1910
March	1st to 10th	Night	48% 3 8% 15% 21% 6%	4918
	11th to 20th	Night	35% 4 9% 13% 24% 16%	4980
	21st to end	Night	34% 3 11% 24% 21% 6%	5467
April	1st to 10th	Night	35% 4 13% 19% 22% 7%	2010
	11th to 20th	Night	35% 3 13% 24% 17% 8%	1975
	21st to end	Night	28% 6% 15% 28% 19% 4	2000
May	1st to 10th	Night	36% 7% 21% 24% 11% 2	3260
	11th to 20th	Night	44% 7% 13% 24% 12%	2969
	21st to end	Night	31% 8% 21% 26% 13% 1	3138
June	1st to 10th	Night	42% 5% 20% 22% 9% 1	1710
	11th to 20th	Night	33% 10% 20% 27% 9% 1	1710
	21st to end	Night	39% 10% 19% 24% 7%	1710
July	1st to 10th	Night	38% 10% 25% 21% 5%	2795
	11th to 20th	Night	41% 13% 30% 12% 4	2786
	21st to end	Night	41% 15% 20% 17% 7%	2988
August	1st to 10th	Night	52% 8% 24% 13% 2	2814
	11th to 20th	Night	37% 11% 22% 24% 6%	3118
	21st to end	Night	35% 8% 19% 32% 6% 1	3476
September	1st to 10th	Night	37% 8% 24% 17% 12% 3	1900
	11th to 20th	Night	43% 8% 13% 20% 12% 3	1900
	21st to end	Night	48% 5% 13% 20% 13% 1	2193
October	1st to 10th	Night	39% 5% 9% 19% 23% 5%	3800
	11th to 20th	Night	21% 3 5% 18% 21% 32%	3779
	21st to end	Night	25% 3 7% 28% 28% 10%	4120
November	1st to 10th	Night	35% 5% 9% 19% 24% 8%	2341
	11th to 20th	Night	39% 3 9% 17% 24% 8%	2413
	21st to end	Night	34% 4 10% 23% 24% 6%	2625
December	1st to 10th	Night	32% 3 8% 15% 31% 12%	4580
	11th to 20th	Night	41% 4 13% 17% 18% 7%	5162
	21st to end	Night	36% 4 12% 26% 19% 2	6490

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	15% 6% 34% 33% 12%	300
	11th to 20th	Day	9% 4 29% 41% 16% 1	300
	21st to end	Day	18% 4 28% 36% 13% 1	330
February	1st to 10th	Day	16% 4 22% 42% 15% 1	300
	11th to 20th	Day	25% 4 28% 30% 12%	437
	21st to end	Day	15% 5% 29% 35% 14% 2	414
March	1st to 10th	Day	14% 5% 30% 32% 17% 2	500
	11th to 20th	Day	14% 4 29% 37% 15% 2	500
	21st to end	Day	13% 3 27% 36% 16% 3	550
April	1st to 10th	Day	12% 7% 23% 34% 21% 3	500
	11th to 20th	Day	9% 3 21% 33% 29% 5%	492
	21st to end	Day	10% 3 17% 33% 27% 10%	500
May	1st to 10th	Day	6% 4 18% 39% 23% 9%	503
	11th to 20th	Day	15% 2 13% 30% 31% 8%	527
	21st to end	Day	11% 3 7% 25% 38% 17%	549
June	1st to 10th	Day	10% 3 6% 29% 37% 15%	490
	11th to 20th	Day	10% 2 6% 26% 38% 20%	490
	21st to end	Day	8% 3 4 25% 42% 17%	490
July	1st to 10th	Day	10% 3 2 16% 44% 25%	485
	11th to 20th	Day	10% 2 2 18% 45% 23%	484
	21st to end	Day	8% 4 4 22% 44% 18%	532
August	1st to 10th	Day	14% 3 4 23% 35% 21%	486
	11th to 20th	Day	11% 3 2 17% 40% 27%	479
	21st to end	Day	11% 2 4 15% 40% 27%	539
September	1st to 10th	Day	11% 3 5% 18% 37% 26%	490
	11th to 20th	Day	18% 3 5% 24% 33% 16%	490
	21st to end	Day	17% 3 9% 23% 32% 16%	490
October	1st to 10th	Day	19% 3 9% 23% 31% 16%	490
	11th to 20th	Day	11% 1 15% 30% 30% 13%	490
	21st to end	Day	11% 3 17% 26% 32% 12%	539
November	1st to 10th	Day	17% 4 15% 28% 25% 11%	495
	11th to 20th	Day	13% 3 25% 35% 21% 3	490
	21st to end	Day	12% 3 25% 33% 22% 5%	372
December	1st to 10th	Day	16% 2 25% 37% 18% 3	200
	11th to 20th	Day	19% 1 19% 33% 20% 6%	207
	21st to end	Day	17% 5% 20% 36% 17% 5%	330
January	1st to 10th	Night	15% 12% 34% 28% 10% 1	800
	11th to 20th	Night	14% 6% 32% 36% 12% 1	800
	21st to end	Night	18% 7% 34% 35% 5% 1	880
February	1st to 10th	Night	21% 4 30% 35% 9%	800
	11th to 20th	Night	22% 7% 33% 32% 5%	783
	21st to end	Night	17% 6% 30% 36% 10%	660
March	1st to 10th	Night	15% 6% 32% 35% 11% 1	800
	11th to 20th	Night	14% 6% 27% 36% 14% 3	800
	21st to end	Night	16% 3 30% 36% 13% 2	880
April	1st to 10th	Night	11% 5% 30% 36% 16% 2	800
	11th to 20th	Night	11% 4 24% 35% 22% 5%	791
	21st to end	Night	9% 4 18% 41% 24% 5%	800
May	1st to 10th	Night	8% 4 21% 39% 24% 4	800
	11th to 20th	Night	15% 3 18% 33% 25% 6%	631
	21st to end	Night	10% 3 7% 25% 37% 17%	634
June	1st to 10th	Night	11% 2 7% 34% 37% 9%	570
	11th to 20th	Night	11% 2 5% 26% 41% 15%	570
	21st to end	Night	10% 3 5% 29% 44% 10%	570
July	1st to 10th	Night	8% 2 4 23% 47% 15%	555
	11th to 20th	Night	6% 2 3 20% 51% 19%	552
	21st to end	Night	8% 2 4 27% 46% 13%	624
August	1st to 10th	Night	12% 4 3 24% 41% 16%	567
	11th to 20th	Night	11% 3 4 23% 43% 17%	741
	21st to end	Night	12% 3 3 19% 43% 19%	836
September	1st to 10th	Night	13% 2 4 23% 41% 17%	760
	11th to 20th	Night	14% 3 7% 27% 36% 12%	760
	21st to end	Night	19% 2 10% 25% 32% 11%	760
October	1st to 10th	Night	16% 2 12% 29% 30% 11%	760
	11th to 20th	Night	12% 4 20% 32% 27% 5%	760
	21st to end	Night	12% 4 19% 31% 26% 8%	836
November	1st to 10th	Night	14% 4 20% 36% 21% 5%	780
	11th to 20th	Night	16% 5% 26% 33% 17% 3	800
	21st to end	Night	13% 5% 27% 33% 18% 4	800
December	1st to 10th	Night	18% 7% 27% 34% 13% 1	800
	11th to 20th	Night	15% 5% 28% 34% 15% 2	800
	21st to end	Night	17% 6% 29% 34% 13% 2	880

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