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 2024-11-02.

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 5% 4 6% 8% 43%	100294
	Night	12% 6% 2 6% 4 4 4 4 6% 8% 43%	98617
Transparency	Day	38% 7% 15% 21% 15% 4	100099
	Night	39% 6% 14% 21% 16% 4	98482
Seeing	Day	13% 3 15% 28% 29% 12%	15547
	Night	14% 4 19% 31% 25% 7%	25932

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	13% 5% 2 4 3 4 4 3 5% 6% 51%	2836
	11th to 20th	Day	11% 5% 2 5% 4 4 4 3 5% 7% 49%	2840
	21st to end	Day	14% 8% 3 8% 4 3 4 3 4 5% 43%	3124
February	1st to 10th	Day	15% 5% 2 6% 6% 4 4 4 5% 6% 43%	1710
	11th to 20th	Day	18% 6% 3 5% 4 3 4 3 4 5% 45%	1792
	21st to end	Day	15% 6% 3 6% 4 4 4 4 5% 7% 42%	1632
March	1st to 10th	Day	22% 9% 2 6% 3 3 4 3 5% 5% 37%	3435
	11th to 20th	Day	9% 3 2 5% 4 4 3 3 5% 7% 55%	3480
	21st to end	Day	15% 6% 2 6% 4 4 3 3 4 6% 47%	3815
April	1st to 10th	Day	10% 4 2 5% 3 3 3 4 6% 6% 54%	2270
	11th to 20th	Day	9% 4 2 5% 4 4 3 4 6% 7% 53%	2254
	21st to end	Day	9% 4 1 4 3 3 3 4 6% 8% 55%	2280
May	1st to 10th	Day	7% 5% 2 6% 4 5% 6% 5% 8% 10% 43%	3765
	11th to 20th	Day	15% 6% 3 7% 5% 5% 5% 3 7% 8% 37%	4044
	21st to end	Day	6% 4 1 6% 4 5% 5% 5% 8% 10% 47%	4476
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 3 3 3 5% 6% 53%	1867
	11th to 20th	Day	12% 5% 2 6% 4 4 3 3 4 7% 51%	1882
	21st to end	Day	11% 5% 2 5% 3 5% 4 4 5% 7% 50%	1684
December	1st to 10th	Day	14% 6% 3 7% 4 5% 5% 4 5% 8% 40%	1520
	11th to 20th	Day	14% 5% 2 5% 3 3 3 2 4 5% 53%	1924
	21st to end	Day	13% 9% 3 6% 4 4 4 3 5% 7% 43%	3124
January	1st to 10th	Night	14% 6% 2 5% 4 3 3 4 5% 7% 47%	4109
	11th to 20th	Night	13% 7% 2 6% 4 4 4 4 7% 8% 41%	4120
	21st to end	Night	14% 8% 3 7% 4 4 4 3 5% 6% 43%	4532
February	1st to 10th	Night	17% 7% 2 5% 5% 4 4 3 5% 5% 44%	2470
	11th to 20th	Night	19% 8% 3 5% 4 4 4 4 4 6% 41%	2272
	21st to end	Night	16% 6% 3 6% 4 5% 4 3 5% 7% 41%	1818
March	1st to 10th	Night	22% 10% 4 7% 4 4 4 3 4 6% 32%	3418
	11th to 20th	Night	12% 5% 2 6% 4 4 4 3 5% 6% 49%	3480
	21st to end	Night	15% 4 2 4 3 3 4 3 5% 7% 50%	3817
April	1st to 10th	Night	9% 6% 2 5% 4 3 4 4 6% 6% 49%	1910
	11th to 20th	Night	11% 5% 2 7% 4 4 4 4 5% 5% 50%	1875
	21st to end	Night	8% 3 1 5% 4 4 4 3 5% 7% 56%	1900
May	1st to 10th	Night	7% 5% 2 6% 5% 5% 5% 4 6% 10% 44%	3130
	11th to 20th	Night	13% 6% 3 8% 6% 5% 5% 4 5% 8% 38%	2876
	21st to end	Night	8% 4 2 5% 4 5% 4 4 7% 10% 47%	3079
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% 6% 56%	2508
November	1st to 10th	Night	13% 5% 2 5% 3 4 4 3 4 5% 52%	2234
	11th to 20th	Night	13% 6% 3 7% 4 4 4 2 5% 6% 48%	2292
	21st to end	Night	11% 5% 2 5% 3 3 4 4 4 8% 50%	2493
December	1st to 10th	Night	15% 8% 3 6% 5% 4 4 4 5% 7% 41%	2660
	11th to 20th	Night	15% 6% 2 5% 3 3 3 3 5% 6% 49%	3253
	21st to end	Night	15% 6% 2 6% 3 4 4 3 4 6% 46%	4532

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	34% 5% 8% 22% 26% 5%	2837
	11th to 20th	Day	35% 3 8% 21% 25% 9%	2840
	21st to end	Day	43% 5% 7% 18% 19% 8%	3124
February	1st to 10th	Day	42% 3 10% 22% 18% 4	1710
	11th to 20th	Day	43% 3 8% 16% 22% 7%	1801
	21st to end	Day	41% 5% 12% 18% 16% 8%	1632
March	1st to 10th	Day	49% 3 10% 15% 14% 8%	3435
	11th to 20th	Day	28% 4 11% 18% 25% 13%	3480
	21st to end	Day	39% 4 8% 26% 17% 6%	3815
April	1st to 10th	Day	30% 5% 13% 24% 22% 6%	2270
	11th to 20th	Day	29% 5% 13% 24% 20% 8%	2254
	21st to end	Day	27% 6% 15% 26% 23% 3	2280
May	1st to 10th	Day	34% 9% 23% 22% 10% 2	3800
	11th to 20th	Day	43% 7% 14% 23% 12%	4048
	21st to end	Day	28% 10% 19% 30% 12% 1	4489
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	40% 4 8% 23% 22% 3	1900
	11th to 20th	Day	29% 4 10% 25% 22% 10%	1900
	21st to end	Day	30% 3 7% 24% 28% 8%	2090
November	1st to 10th	Day	32% 4 9% 21% 25% 8%	1867
	11th to 20th	Day	36% 4 9% 19% 24% 8%	1882
	21st to end	Day	35% 3 11% 23% 21% 7%	1684
December	1st to 10th	Day	43% 6% 13% 19% 14% 5%	1520
	11th to 20th	Day	35% 3 8% 21% 24% 9%	1920
	21st to end	Day	42% 3 11% 21% 20% 2	3124
January	1st to 10th	Night	37% 5% 8% 24% 20% 6%	4109
	11th to 20th	Night	40% 5% 9% 18% 23% 5%	4120
	21st to end	Night	42% 4 7% 18% 22% 7%	4532
February	1st to 10th	Night	42% 3 9% 20% 20% 6%	2470
	11th to 20th	Night	45% 4 8% 16% 20% 7%	2274
	21st to end	Night	43% 4 9% 18% 17% 8%	1818
March	1st to 10th	Night	55% 4 10% 15% 12% 5%	3418
	11th to 20th	Night	37% 4 10% 13% 22% 14%	3480
	21st to end	Night	35% 4 12% 26% 17% 6%	3817
April	1st to 10th	Night	34% 4 13% 19% 23% 7%	1910
	11th to 20th	Night	36% 3 13% 22% 17% 8%	1875
	21st to end	Night	28% 5% 15% 28% 19% 4	1900
May	1st to 10th	Night	36% 7% 20% 24% 11% 2	3160
	11th to 20th	Night	44% 7% 13% 24% 12%	2877
	21st to end	Night	31% 8% 21% 26% 13% 1	3087
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% 10% 22% 19% 6%	2280
	11th to 20th	Night	32% 4 8% 24% 23% 9%	2280
	21st to end	Night	29% 3 9% 24% 27% 9%	2508
November	1st to 10th	Night	35% 5% 9% 18% 25% 8%	2234
	11th to 20th	Night	39% 3 10% 17% 23% 8%	2292
	21st to end	Night	35% 4 10% 22% 24% 6%	2493
December	1st to 10th	Night	43% 5% 12% 17% 18% 5%	2660
	11th to 20th	Night	37% 3 8% 20% 25% 7%	3256
	21st to end	Night	39% 3 9% 23% 22% 3	4532

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% 7% 31% 33% 14%	270
	11th to 20th	Day	9% 4 28% 41% 17% 1	270
	21st to end	Day	19% 4 27% 35% 14% 1	297
February	1st to 10th	Day	15% 4 24% 41% 15% 1	270
	11th to 20th	Day	24% 4 29% 31% 13% 1	400
	21st to end	Day	16% 5% 30% 33% 13% 2	382
March	1st to 10th	Day	14% 5% 29% 32% 18% 2	460
	11th to 20th	Day	14% 4 30% 36% 15% 2	460
	21st to end	Day	15% 3 27% 36% 16% 3	506
April	1st to 10th	Day	12% 7% 24% 33% 20% 4	460
	11th to 20th	Day	10% 3 21% 33% 28% 6%	452
	21st to end	Day	10% 3 18% 35% 25% 9%	460
May	1st to 10th	Day	6% 4 20% 38% 23% 9%	463
	11th to 20th	Day	15% 2 12% 29% 33% 9%	487
	21st to end	Day	11% 3 6% 24% 39% 18%	529
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% 5% 15% 29% 24% 10%	459
	11th to 20th	Day	14% 4 25% 35% 20% 3	451
	21st to end	Day	12% 3 24% 35% 21% 5%	344
December	1st to 10th	Day	18% 2 24% 35% 19% 3	180
	11th to 20th	Day	19% 2 21% 32% 20% 6%	186
	21st to end	Day	18% 4 19% 35% 18% 6%	297
January	1st to 10th	Night	15% 12% 32% 29% 11% 1	760
	11th to 20th	Night	14% 6% 31% 36% 12% 1	760
	21st to end	Night	18% 7% 34% 34% 6% 1	836
February	1st to 10th	Night	20% 4 31% 35% 9%	760
	11th to 20th	Night	22% 7% 33% 32% 5%	743
	21st to end	Night	18% 6% 31% 34% 10%	628
March	1st to 10th	Night	16% 6% 31% 35% 11% 1	760
	11th to 20th	Night	14% 6% 28% 36% 14% 3	760
	21st to end	Night	16% 3 30% 36% 14% 2	836
April	1st to 10th	Night	11% 5% 31% 36% 15% 2	760
	11th to 20th	Night	12% 4 23% 33% 22% 5%	751
	21st to end	Night	9% 4 19% 41% 22% 4	760
May	1st to 10th	Night	8% 5% 21% 39% 23% 4	760
	11th to 20th	Night	15% 3 18% 32% 26% 7%	599
	21st to end	Night	10% 3 6% 25% 38% 17%	617
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 21% 35% 21% 5%	745
	11th to 20th	Night	16% 5% 26% 33% 17% 3	760
	21st to end	Night	13% 5% 27% 33% 19% 4	760
December	1st to 10th	Night	19% 6% 26% 34% 14% 1	760
	11th to 20th	Night	16% 5% 28% 34% 15% 2	760
	21st to end	Night	17% 6% 29% 33% 12% 2	836

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