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 2024-03-06.

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	12% 5% 2 5% 5% 3 4 5% 6% 8% 45%	78376
	Night	12% 6% 2 5% 5% 3 4 5% 5% 8% 44%	81129
Transparency	Day	37% 6% 15% 22% 16% 4	78097
	Night	38% 6% 13% 21% 17% 5%	80927
Seeing	Day	13% 3 15% 28% 29% 12%	14583
	Night	14% 4 19% 31% 24% 7%	25060

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% 4 2 3 4 3 4 5% 5% 6% 51%	2836
	11th to 20th	Day	11% 5% 2 4 5% 3 4 5% 5% 8% 49%	2840
	21st to end	Day	14% 8% 3 6% 6% 3 3 4 4 6% 43%	3124
February	1st to 10th	Day	15% 5% 2 6% 6% 3 4 4 5% 6% 43%	1710
	11th to 20th	Day	18% 6% 3 4 5% 2 4 4 3 5% 46%	1792
	21st to end	Day	15% 6% 3 4 5% 3 4 5% 6% 7% 42%	1632
March	1st to 10th	Day	14% 6% 2 4 3 2 4 4 3 6% 52%	2035
	11th to 20th	Day	13% 4 2 6% 6% 3 4 4 5% 7% 44%	1980
	21st to end	Day	13% 5% 3 5% 6% 3 4 5% 5% 7% 43%	2178
April	1st to 10th	Day	11% 4 2 4 4 2 3 4 5% 6% 55%	2150
	11th to 20th	Day	9% 4 2 4 5% 2 4 5% 5% 8% 53%	2134
	21st to end	Day	9% 4 1 4 3 2 4 5% 6% 8% 54%	2160
May	1st to 10th	Day	8% 4 2 4 3 3 4 5% 7% 8% 50%	2160
	11th to 20th	Day	12% 4 3 5% 6% 3 5% 4 6% 8% 43%	2278
	21st to end	Day	9% 4 1 5% 5% 4 6% 7% 7% 10% 43%	2531
June	1st to 10th	Day	10% 5% 3 6% 6% 3 6% 6% 7% 9% 37%	2340
	11th to 20th	Day	9% 3 2 4 4 4 6% 6% 8% 12% 41%	2340
	21st to end	Day	8% 4 2 4 7% 4 6% 7% 7% 12% 38%	2340
July	1st to 10th	Day	9% 5% 2 5% 6% 3 6% 6% 8% 12% 38%	2340
	11th to 20th	Day	9% 4 2 4 5% 4 5% 8% 8% 12% 38%	2340
	21st to end	Day	7% 5% 3 5% 6% 4 6% 7% 7% 13% 36%	2547
August	1st to 10th	Day	10% 6% 2 6% 6% 4 6% 6% 8% 12% 34%	2319
	11th to 20th	Day	11% 4 3 6% 6% 4 5% 5% 8% 10% 38%	2126
	21st to end	Day	10% 5% 3 7% 6% 4 5% 7% 8% 10% 35%	2376
September	1st to 10th	Day	10% 4 2 6% 5% 4 5% 7% 6% 10% 42%	2160
	11th to 20th	Day	14% 6% 2 5% 6% 3 5% 5% 6% 8% 40%	2160
	21st to end	Day	15% 7% 3 6% 4 4 4 5% 5% 7% 39%	1877
October	1st to 10th	Day	16% 5% 3 5% 4 3 4 4 4 6% 46%	1800
	11th to 20th	Day	10% 3 2 5% 4 2 3 4 4 6% 56%	1800
	21st to end	Day	11% 5% 2 4 4 2 3 4 3 6% 57%	1980
November	1st to 10th	Day	12% 4 2 4 4 2 4 4 5% 6% 54%	1857
	11th to 20th	Day	12% 4 2 5% 5% 3 3 4 4 7% 51%	1882
	21st to end	Day	11% 4 2 5% 4 3 5% 5% 5% 7% 50%	1684
December	1st to 10th	Day	14% 6% 3 7% 5% 3 5% 5% 5% 8% 40%	1520
	11th to 20th	Day	14% 5% 2 5% 4 2 3 3 3 5% 53%	1924
	21st to end	Day	13% 8% 3 6% 4 3 4 4 5% 7% 43%	3124
January	1st to 10th	Night	14% 6% 2 5% 4 2 4 4 4 7% 47%	4109
	11th to 20th	Night	13% 6% 2 6% 5% 3 5% 5% 6% 8% 41%	4120
	21st to end	Night	14% 7% 3 6% 5% 3 4 4 5% 6% 43%	4532
February	1st to 10th	Night	17% 6% 2 4 5% 3 4 4 5% 6% 45%	2470
	11th to 20th	Night	19% 7% 3 4 4 2 4 4 4 6% 41%	2272
	21st to end	Night	16% 6% 3 5% 5% 3 4 4 5% 7% 41%	1818
March	1st to 10th	Night	14% 4 2 4 4 2 4 4 5% 7% 49%	2042
	11th to 20th	Night	13% 6% 3 6% 6% 4 6% 5% 5% 7% 40%	1980
	21st to end	Night	13% 5% 3 5% 4 3 4 4 5% 8% 46%	2178
April	1st to 10th	Night	10% 6% 3 4 4 2 5% 4 5% 7% 50%	1810
	11th to 20th	Night	11% 4 2 6% 5% 3 4 5% 5% 5% 50%	1775
	21st to end	Night	8% 3 1 4 4 3 5% 4 4 8% 56%	1800
May	1st to 10th	Night	8% 5% 2 5% 5% 3 3 6% 6% 9% 48%	1800
	11th to 20th	Night	12% 4 3 5% 6% 4 5% 4 5% 10% 42%	1628
	21st to end	Night	9% 6% 2 4 4 4 4 5% 7% 9% 44%	1744
June	1st to 10th	Night	11% 5% 2 5% 6% 4 6% 6% 6% 11% 36%	1620
	11th to 20th	Night	10% 4 2 4 5% 3 6% 6% 8% 11% 41%	1620
	21st to end	Night	10% 5% 2 5% 6% 4 5% 6% 8% 12% 35%	1620
July	1st to 10th	Night	7% 5% 3 5% 6% 5% 7% 6% 9% 11% 36%	1620
	11th to 20th	Night	6% 5% 2 4 6% 4 5% 6% 8% 12% 41%	1620
	21st to end	Night	6% 5% 3 5% 5% 3 7% 7% 9% 12% 36%	1771
August	1st to 10th	Night	9% 6% 2 5% 7% 4 5% 6% 7% 10% 38%	1611
	11th to 20th	Night	9% 6% 3 7% 7% 3 6% 6% 7% 10% 36%	1765
	21st to end	Night	11% 6% 3 7% 6% 3 6% 7% 7% 11% 34%	1980
September	1st to 10th	Night	11% 4 2 4 6% 4 5% 6% 7% 10% 42%	1800
	11th to 20th	Night	12% 6% 3 6% 5% 4 5% 5% 5% 9% 40%	1800
	21st to end	Night	16% 7% 3 6% 6% 3 4 4 5% 6% 37%	2077
October	1st to 10th	Night	13% 6% 3 5% 4 4 4 4 6% 6% 46%	2160
	11th to 20th	Night	11% 5% 3 4 4 3 4 4 4 6% 53%	2160
	21st to end	Night	10% 4 2 4 4 3 4 4 5% 6% 55%	2376
November	1st to 10th	Night	13% 5% 2 5% 4 2 4 4 4 5% 52%	2221
	11th to 20th	Night	13% 6% 3 6% 5% 2 4 3 4 6% 48%	2292
	21st to end	Night	11% 5% 2 5% 4 2 4 4 4 8% 50%	2493
December	1st to 10th	Night	15% 7% 3 5% 5% 3 4 4 5% 7% 41%	2660
	11th to 20th	Night	15% 6% 2 5% 3 2 3 4 4 6% 49%	3253
	21st to end	Night	15% 5% 2 5% 4 3 4 4 4 6% 47%	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	36% 4 11% 19% 23% 8%	2035
	11th to 20th	Day	39% 5% 13% 20% 17% 6%	1980
	21st to end	Day	40% 5% 12% 19% 19% 4	2178
April	1st to 10th	Day	30% 5% 13% 24% 22% 6%	2150
	11th to 20th	Day	30% 5% 13% 25% 19% 8%	2134
	21st to end	Day	28% 6% 14% 25% 23% 3	2160
May	1st to 10th	Day	30% 6% 19% 27% 15% 3	2160
	11th to 20th	Day	38% 6% 18% 26% 11% 1	2282
	21st to end	Day	34% 10% 19% 26% 11% 1	2531
June	1st to 10th	Day	41% 10% 16% 23% 10% 1	2340
	11th to 20th	Day	31% 11% 23% 24% 10% 1	2340
	21st to end	Day	37% 11% 21% 23% 8% 1	2340
July	1st to 10th	Day	37% 10% 25% 20% 7% 1	2275
	11th to 20th	Day	33% 11% 25% 23% 8%	2271
	21st to end	Day	35% 10% 24% 26% 4	2405
August	1st to 10th	Day	40% 10% 27% 19% 5%	2306
	11th to 20th	Day	39% 10% 23% 20% 7%	2126
	21st to end	Day	41% 9% 23% 21% 6% 1	2376
September	1st to 10th	Day	36% 9% 20% 18% 13% 2	2160
	11th to 20th	Day	41% 7% 15% 19% 16% 3	2160
	21st to end	Day	44% 5% 13% 20% 15% 3	1877
October	1st to 10th	Day	40% 4 8% 23% 22% 3	1800
	11th to 20th	Day	30% 4 10% 26% 21% 8%	1800
	21st to end	Day	30% 3 7% 24% 28% 8%	1980
November	1st to 10th	Day	32% 4 9% 21% 26% 8%	1857
	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	35% 4 10% 22% 20% 8%	2042
	11th to 20th	Night	44% 5% 12% 17% 16% 6%	1980
	21st to end	Night	37% 5% 14% 23% 17% 5%	2178
April	1st to 10th	Night	35% 4 14% 18% 24% 6%	1810
	11th to 20th	Night	37% 3 13% 22% 17% 8%	1775
	21st to end	Night	28% 5% 15% 28% 20% 4	1800
May	1st to 10th	Night	33% 6% 17% 24% 17% 3	1800
	11th to 20th	Night	38% 7% 17% 24% 13% 1	1629
	21st to end	Night	34% 8% 21% 24% 12% 1	1745
June	1st to 10th	Night	43% 5% 20% 22% 9% 1	1620
	11th to 20th	Night	34% 11% 21% 25% 9% 1	1620
	21st to end	Night	40% 10% 20% 24% 7%	1620
July	1st to 10th	Night	38% 10% 23% 19% 9% 1	1575
	11th to 20th	Night	34% 11% 28% 20% 6%	1566
	21st to end	Night	35% 11% 25% 23% 6%	1672
August	1st to 10th	Night	38% 9% 28% 21% 3	1600
	11th to 20th	Night	40% 11% 22% 21% 5% 1	1765
	21st to end	Night	42% 10% 22% 20% 5% 1	1980
September	1st to 10th	Night	36% 8% 24% 17% 12% 3	1800
	11th to 20th	Night	42% 8% 14% 21% 13% 3	1800
	21st to end	Night	48% 5% 12% 20% 13% 1	2077
October	1st to 10th	Night	39% 5% 10% 22% 19% 5%	2160
	11th to 20th	Night	34% 4 8% 25% 23% 6%	2160
	21st to end	Night	30% 4 9% 23% 26% 9%	2376
November	1st to 10th	Night	35% 5% 9% 18% 25% 8%	2221
	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% 33% 17% 2	440
	11th to 20th	Day	15% 4 30% 35% 14% 2	420
	21st to end	Day	14% 3 28% 34% 17% 3	462
April	1st to 10th	Day	13% 7% 23% 32% 22% 4	420
	11th to 20th	Day	10% 3 20% 33% 28% 6%	412
	21st to end	Day	10% 3 18% 36% 25% 8%	420
May	1st to 10th	Day	7% 4 21% 39% 23% 7%	423
	11th to 20th	Day	14% 2 12% 29% 34% 9%	447
	21st to end	Day	12% 3 6% 23% 38% 19%	485
June	1st to 10th	Day	10% 3 6% 30% 37% 14%	450
	11th to 20th	Day	10% 2 6% 25% 35% 21%	450
	21st to end	Day	8% 3 4 26% 41% 17%	450
July	1st to 10th	Day	10% 3 2 17% 44% 24%	445
	11th to 20th	Day	10% 2 2 18% 45% 23%	444
	21st to end	Day	7% 4 3 23% 44% 18%	488
August	1st to 10th	Day	12% 3 4 24% 35% 22%	446
	11th to 20th	Day	11% 3 1 15% 41% 28%	439
	21st to end	Day	11% 2 4 15% 41% 27%	495
September	1st to 10th	Day	9% 3 5% 17% 38% 28%	450
	11th to 20th	Day	17% 3 5% 25% 34% 17%	450
	21st to end	Day	18% 2 8% 23% 32% 17%	450
October	1st to 10th	Day	19% 2 9% 23% 30% 16%	450
	11th to 20th	Day	11% 2 15% 29% 30% 14%	450
	21st to end	Day	11% 3 18% 28% 31% 10%	495
November	1st to 10th	Day	17% 5% 15% 30% 23% 10%	455
	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% 12% 1	743
	11th to 20th	Night	14% 6% 28% 35% 14% 3	720
	21st to end	Night	16% 3 29% 35% 14% 2	792
April	1st to 10th	Night	11% 6% 30% 35% 15% 3	720
	11th to 20th	Night	12% 4 24% 33% 22% 5%	711
	21st to end	Night	9% 4 19% 41% 22% 4	720
May	1st to 10th	Night	8% 5% 22% 38% 23% 3	720
	11th to 20th	Night	14% 2 18% 32% 27% 7%	567
	21st to end	Night	11% 3 6% 24% 38% 17%	584
June	1st to 10th	Night	11% 2 7% 35% 36% 9%	540
	11th to 20th	Night	11% 2 6% 26% 40% 16%	540
	21st to end	Night	10% 3 5% 29% 43% 9%	540
July	1st to 10th	Night	7% 2 4 24% 47% 15%	525
	11th to 20th	Night	6% 2 2 20% 51% 19%	522
	21st to end	Night	7% 2 4 27% 45% 14%	591
August	1st to 10th	Night	11% 3 2 25% 42% 17%	537
	11th to 20th	Night	11% 3 2 23% 44% 18%	701
	21st to end	Night	13% 3 3 18% 44% 20%	792
September	1st to 10th	Night	13% 2 3 22% 43% 17%	720
	11th to 20th	Night	13% 3 7% 28% 37% 13%	720
	21st to end	Night	20% 2 10% 24% 32% 12%	720
October	1st to 10th	Night	16% 2 12% 29% 30% 11%	720
	11th to 20th	Night	13% 4 19% 32% 27% 6%	720
	21st to end	Night	12% 4 20% 32% 25% 7%	792
November	1st to 10th	Night	14% 4 21% 35% 21% 5%	740
	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

Page generated at 2024-03-03 06:29:01. Version ac07

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