Big Sable Point
Clear Sky Chart
History

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

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	13% 12% 5% 10% 5% 4 4 3 5% 6% 33%	113691
	Night	14% 14% 5% 12% 6% 5% 4 3 4 5% 27%	115462
Transparency	Day	52% 5% 11% 20% 11% 1	117238
	Night	58% 4 10% 17% 9% 1	120058
Seeing	Day	17% 10% 28% 27% 14% 3	16542
	Night	21% 10% 26% 28% 13% 2	26550

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	9% 26% 14% 28% 6% 4 2 1 1 2 6%	3617
	11th to 20th	Day	10% 19% 8% 25% 16% 10% 5% 1 2 1 2	3620
	21st to end	Day	14% 19% 10% 18% 9% 5% 6% 3 2 3 11%	3982
February	1st to 10th	Day	11% 17% 8% 18% 14% 6% 3 3 3 4 13%	1752
	11th to 20th	Day	13% 16% 8% 16% 12% 6% 4 3 4 3 14%	1948
	21st to end	Day	13% 16% 7% 14% 8% 5% 5% 3 4 5% 20%	1650
March	1st to 10th	Day	12% 10% 4 13% 6% 5% 5% 4 5% 5% 32%	4480
	11th to 20th	Day	12% 10% 6% 10% 5% 4 4 4 6% 7% 32%	4745
	21st to end	Day	22% 12% 6% 12% 5% 4 3 3 4 5% 25%	5819
April	1st to 10th	Day	17% 13% 4 8% 5% 4 4 3 5% 6% 31%	2400
	11th to 20th	Day	18% 11% 3 7% 4 4 4 3 4 5% 36%	2412
	21st to end	Day	15% 10% 4 7% 5% 5% 5% 4 5% 7% 34%	2600
May	1st to 10th	Day	13% 8% 3 6% 4 4 4 4 5% 7% 43%	4212
	11th to 20th	Day	11% 7% 2 6% 4 4 5% 4 5% 6% 47%	4289
	21st to end	Day	10% 6% 3 6% 4 4 4 4 6% 9% 45%	4824
June	1st to 10th	Day	11% 6% 2 6% 4 4 4 4 6% 9% 45%	2660
	11th to 20th	Day	12% 6% 2 6% 4 4 3 4 6% 8% 45%	2660
	21st to end	Day	11% 5% 3 5% 4 4 5% 4 6% 9% 45%	2660
July	1st to 10th	Day	15% 7% 2 7% 4 3 4 4 6% 8% 41%	4440
	11th to 20th	Day	6% 4 2 4 3 3 4 3 7% 9% 57%	4440
	21st to end	Day	7% 5% 2 6% 4 3 5% 4 6% 8% 50%	4813
August	1st to 10th	Day	9% 5% 2 6% 4 5% 5% 4 6% 9% 43%	4301
	11th to 20th	Day	11% 6% 2 5% 3 4 3 2 5% 6% 53%	4044
	21st to end	Day	10% 7% 2 6% 4 4 4 4 5% 9% 46%	4187
September	1st to 10th	Day	14% 5% 2 6% 4 4 4 3 5% 7% 45%	2280
	11th to 20th	Day	12% 5% 2 5% 4 3 4 3 5% 8% 47%	2104
	21st to end	Day	15% 8% 3 7% 4 5% 5% 3 4 8% 39%	2090
October	1st to 10th	Day	14% 9% 3 7% 5% 3 3 3 5% 7% 41%	2090
	11th to 20th	Day	23% 13% 3 10% 5% 4 4 4 5% 7% 22%	1804
	21st to end	Day	23% 14% 4 9% 5% 4 4 2 5% 6% 23%	1881
November	1st to 10th	Day	18% 14% 4 8% 5% 4 3 3 5% 6% 31%	1762
	11th to 20th	Day	16% 23% 7% 11% 5% 4 4 4 4 5% 17%	1800
	21st to end	Day	20% 22% 7% 13% 5% 4 3 3 3 5% 16%	1725
December	1st to 10th	Day	13% 28% 17% 17% 5% 3 2 1 1 3 9%	2610
	11th to 20th	Day	13% 27% 13% 16% 10% 3 3 2 3 3 6%	3008
	21st to end	Day	21% 23% 10% 15% 6% 5% 3 2 3 3 10%	3982
January	1st to 10th	Night	12% 23% 11% 28% 7% 3 3 1 2 2 9%	6348
	11th to 20th	Night	12% 21% 9% 24% 11% 12% 3 2 2 1 4	6360
	21st to end	Night	12% 22% 10% 18% 8% 6% 6% 2 2 3 11%	6996
February	1st to 10th	Night	12% 19% 7% 16% 12% 6% 4 3 4 3 14%	2642
	11th to 20th	Night	12% 17% 6% 17% 11% 6% 4 3 3 4 16%	2338
	21st to end	Night	14% 17% 5% 15% 6% 7% 4 3 4 5% 20%	1980
March	1st to 10th	Night	16% 10% 4 12% 4 3 4 3 5% 6% 33%	5373
	11th to 20th	Night	11% 10% 4 9% 4 4 4 4 5% 8% 37%	5215
	21st to end	Night	18% 12% 4 13% 6% 4 4 3 5% 6% 27%	5151
April	1st to 10th	Night	16% 13% 4 8% 5% 4 3 4 5% 7% 32%	2000
	11th to 20th	Night	19% 11% 3 6% 4 4 5% 3 4 5% 36%	1936
	21st to end	Night	17% 10% 3 8% 4 4 3 3 5% 5% 37%	1800
May	1st to 10th	Night	13% 8% 3 7% 6% 4 5% 5% 5% 8% 38%	2903
	11th to 20th	Night	13% 7% 3 6% 4 5% 5% 4 6% 7% 40%	2616
	21st to end	Night	18% 6% 2 6% 4 3 4 3 6% 6% 42%	2743
June	1st to 10th	Night	11% 8% 3 6% 4 3 4 4 7% 8% 42%	1520
	11th to 20th	Night	11% 7% 3 7% 4 4 5% 4 6% 8% 43%	1520
	21st to end	Night	10% 6% 2 6% 4 5% 4 5% 6% 8% 44%	1520
July	1st to 10th	Night	12% 8% 2 5% 4 5% 5% 5% 6% 8% 40%	2530
	11th to 20th	Night	5% 5% 2 4 4 3 4 3 5% 9% 56%	2530
	21st to end	Night	6% 6% 3 6% 4 4 5% 4 6% 8% 48%	2750
August	1st to 10th	Night	11% 5% 2 6% 4 4 5% 4 6% 10% 42%	2631
	11th to 20th	Night	12% 5% 2 5% 3 4 3 3 5% 7% 52%	2785
	21st to end	Night	9% 6% 2 6% 4 4 4 4 6% 8% 46%	3466
September	1st to 10th	Night	11% 6% 3 5% 4 4 4 3 5% 6% 49%	1900
	11th to 20th	Night	12% 5% 2 5% 3 3 4 3 6% 8% 49%	2057
	21st to end	Night	16% 6% 2 6% 5% 4 5% 4 5% 7% 40%	2090
October	1st to 10th	Night	16% 8% 3 7% 3 3 4 3 4 6% 43%	2090
	11th to 20th	Night	23% 12% 4 7% 4 4 3 3 3 5% 30%	2374
	21st to end	Night	26% 14% 4 9% 4 4 4 3 4 6% 24%	2717
November	1st to 10th	Night	15% 17% 4 9% 5% 4 4 2 3 5% 32%	2536
	11th to 20th	Night	17% 22% 6% 12% 5% 5% 4 3 4 4 19%	2600
	21st to end	Night	18% 23% 7% 11% 5% 3 4 3 4 4 18%	2670
December	1st to 10th	Night	14% 22% 11% 20% 6% 4 3 2 3 3 11%	4580
	11th to 20th	Night	15% 27% 11% 15% 9% 3 2 2 3 3 9%	5199
	21st to end	Night	23% 23% 8% 12% 5% 4 4 3 4 4 11%	6996

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	88% 2 4 5% 1	3618
	11th to 20th	Day	92% 3 2 2 1	3620
	21st to end	Day	81% 4 7% 7% 1	3982
February	1st to 10th	Day	76% 4 7% 11% 2	1752
	11th to 20th	Day	75% 4 8% 8% 4	1958
	21st to end	Day	67% 5% 10% 13% 5%	1650
March	1st to 10th	Day	54% 4 15% 18% 9% 1	4480
	11th to 20th	Day	50% 4 16% 20% 9% 1	4745
	21st to end	Day	63% 3 10% 15% 8%	5821
April	1st to 10th	Day	53% 5% 11% 20% 11%	2400
	11th to 20th	Day	49% 5% 8% 22% 14% 2	2412
	21st to end	Day	48% 6% 12% 19% 13% 2	2600
May	1st to 10th	Day	40% 6% 11% 25% 15% 3	4250
	11th to 20th	Day	35% 9% 11% 25% 17% 3	4293
	21st to end	Day	35% 8% 12% 24% 20% 2	4837
June	1st to 10th	Day	35% 7% 11% 27% 17% 2	2660
	11th to 20th	Day	36% 6% 13% 26% 18% 1	2660
	21st to end	Day	34% 8% 16% 25% 15% 1	2660
July	1st to 10th	Day	42% 4 13% 25% 14% 2	4371
	11th to 20th	Day	24% 4 16% 35% 19% 2	4365
	21st to end	Day	32% 5% 14% 28% 20% 2	4662
August	1st to 10th	Day	38% 4 12% 30% 14% 1	4286
	11th to 20th	Day	33% 5% 14% 32% 16% 1	4083
	21st to end	Day	38% 4 14% 29% 15% 1	4186
September	1st to 10th	Day	39% 5% 12% 27% 14% 1	2280
	11th to 20th	Day	35% 6% 15% 29% 14% 1	2104
	21st to end	Day	43% 6% 13% 27% 10%	2090
October	1st to 10th	Day	30% 3 8% 38% 18% 2	3480
	11th to 20th	Day	53% 3 11% 22% 11%	2968
	21st to end	Day	58% 3 15% 17% 6%	3081
November	1st to 10th	Day	55% 6% 11% 19% 9%	1762
	11th to 20th	Day	69% 6% 11% 10% 4	1800
	21st to end	Day	74% 4 12% 7% 3	1725
December	1st to 10th	Day	85% 2 5% 7% 1	2610
	11th to 20th	Day	85% 4 7% 4 1	3005
	21st to end	Day	80% 5% 5% 8% 2	3982
January	1st to 10th	Night	84% 3 5% 6% 2	6348
	11th to 20th	Night	90% 3 4 2 1	6360
	21st to end	Night	82% 3 8% 7% 1	6996
February	1st to 10th	Night	74% 5% 6% 11% 4	2642
	11th to 20th	Night	73% 4 8% 10% 4	2339
	21st to end	Night	67% 5% 11% 13% 4	1980
March	1st to 10th	Night	52% 4 16% 21% 7%	5373
	11th to 20th	Night	47% 4 18% 21% 9% 1	5215
	21st to end	Night	58% 4 9% 19% 8% 1	5151
April	1st to 10th	Night	52% 6% 10% 20% 12% 1	2000
	11th to 20th	Night	50% 4 8% 21% 14% 3	1936
	21st to end	Night	48% 6% 9% 20% 14% 3	1800
May	1st to 10th	Night	43% 7% 13% 19% 15% 4	2930
	11th to 20th	Night	41% 7% 11% 26% 14% 2	2617
	21st to end	Night	42% 6% 10% 20% 15% 7%	2751
June	1st to 10th	Night	38% 7% 11% 26% 16% 2	1520
	11th to 20th	Night	38% 6% 12% 24% 19% 2	1520
	21st to end	Night	35% 8% 14% 24% 16% 3	1520
July	1st to 10th	Night	43% 5% 11% 23% 12% 6%	2490
	11th to 20th	Night	26% 4 14% 34% 19% 3	2482
	21st to end	Night	33% 6% 13% 22% 23% 3	2662
August	1st to 10th	Night	38% 5% 13% 27% 16% 1	2622
	11th to 20th	Night	34% 4 10% 34% 18% 1	2812
	21st to end	Night	36% 3 12% 25% 22% 2	3466
September	1st to 10th	Night	36% 5% 11% 26% 21% 2	1900
	11th to 20th	Night	32% 6% 13% 32% 14% 2	2057
	21st to end	Night	42% 6% 13% 27% 11% 1	2090
October	1st to 10th	Night	38% 3 8% 35% 14% 1	3480
	11th to 20th	Night	48% 3 10% 26% 12%	3949
	21st to end	Night	53% 3 13% 23% 9%	4467
November	1st to 10th	Night	56% 5% 10% 19% 9% 1	2536
	11th to 20th	Night	70% 4 10% 10% 6% 1	2600
	21st to end	Night	71% 5% 13% 10% 2 1	2670
December	1st to 10th	Night	80% 4 8% 7% 1	4580
	11th to 20th	Night	83% 3 6% 6% 1	5201
	21st to end	Night	77% 4 9% 6% 3	6996

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	16% 17% 34% 25% 7% 1	300
	11th to 20th	Day	22% 16% 37% 21% 3 1	300
	21st to end	Day	24% 13% 33% 25% 5%	330
February	1st to 10th	Day	20% 20% 35% 18% 5% 2	300
	11th to 20th	Day	19% 19% 41% 19% 2	300
	21st to end	Day	20% 21% 42% 16%	249
March	1st to 10th	Day	18% 18% 46% 15% 3	300
	11th to 20th	Day	21% 15% 32% 20% 11% 2	395
	21st to end	Day	27% 12% 30% 23% 8% 1	550
April	1st to 10th	Day	23% 10% 37% 24% 5% 1	500
	11th to 20th	Day	23% 16% 29% 20% 9% 3	492
	21st to end	Day	18% 12% 31% 26% 11% 2	500
May	1st to 10th	Day	19% 8% 37% 25% 9% 1	503
	11th to 20th	Day	16% 6% 27% 33% 16% 2	604
	21st to end	Day	13% 5% 26% 32% 19% 5%	734
June	1st to 10th	Day	13% 4 27% 34% 19% 3	680
	11th to 20th	Day	16% 4 26% 33% 17% 4	680
	21st to end	Day	13% 6% 24% 34% 19% 5%	680
July	1st to 10th	Day	8% 4 19% 36% 28% 6%	671
	11th to 20th	Day	9% 5% 20% 38% 23% 5%	668
	21st to end	Day	8% 3 21% 38% 24% 6%	739
August	1st to 10th	Day	9% 3 20% 34% 27% 6%	606
	11th to 20th	Day	11% 3 17% 32% 26% 11%	479
	21st to end	Day	15% 4 21% 32% 23% 5%	539
September	1st to 10th	Day	15% 6% 20% 31% 20% 7%	490
	11th to 20th	Day	11% 6% 18% 35% 22% 9%	490
	21st to end	Day	15% 9% 24% 27% 18% 7%	490
October	1st to 10th	Day	17% 9% 29% 24% 17% 4	490
	11th to 20th	Day	27% 13% 30% 24% 5%	323
	21st to end	Day	34% 11% 34% 17% 4 1	330
November	1st to 10th	Day	25% 16% 33% 17% 8% 1	300
	11th to 20th	Day	24% 19% 35% 17% 4	300
	21st to end	Day	26% 15% 37% 18% 4	300
December	1st to 10th	Day	24% 21% 32% 19% 4	300
	11th to 20th	Day	27% 22% 32% 15% 2 2	300
	21st to end	Day	32% 19% 33% 12% 4 1	330
January	1st to 10th	Night	23% 18% 33% 21% 5% 1	1000
	11th to 20th	Night	27% 16% 33% 19% 5% 1	1000
	21st to end	Night	23% 14% 33% 24% 7%	1100
February	1st to 10th	Night	22% 15% 33% 25% 4 1	927
	11th to 20th	Night	22% 17% 31% 22% 7%	783
	21st to end	Night	25% 15% 34% 23% 3	660
March	1st to 10th	Night	20% 12% 32% 26% 10% 1	800
	11th to 20th	Night	16% 11% 34% 28% 9% 1	800
	21st to end	Night	22% 9% 24% 34% 10% 1	745
April	1st to 10th	Night	25% 9% 30% 29% 7% 1	600
	11th to 20th	Night	25% 10% 24% 28% 11% 2	593
	21st to end	Night	21% 6% 28% 32% 12% 1	600
May	1st to 10th	Night	16% 4 28% 36% 15% 1	600
	11th to 20th	Night	17% 3 20% 38% 21% 2	563
	21st to end	Night	16% 3 18% 35% 23% 4	617
June	1st to 10th	Night	13% 4 18% 41% 19% 4	570
	11th to 20th	Night	14% 5% 21% 33% 22% 5%	570
	21st to end	Night	11% 3 15% 41% 26% 3	570
July	1st to 10th	Night	9% 2 12% 41% 30% 7%	555
	11th to 20th	Night	8% 3 14% 38% 32% 5%	552
	21st to end	Night	7% 3 17% 36% 33% 4	624
August	1st to 10th	Night	8% 2 14% 40% 30% 6%	567
	11th to 20th	Night	9% 2 14% 34% 32% 8%	564
	21st to end	Night	13% 3 16% 36% 29% 3	627
September	1st to 10th	Night	14% 5% 18% 34% 22% 7%	570
	11th to 20th	Night	13% 4 16% 35% 25% 7%	727
	21st to end	Night	18% 7% 21% 27% 22% 5%	760
October	1st to 10th	Night	21% 7% 21% 28% 19% 3	760
	11th to 20th	Night	31% 10% 25% 24% 10% 1	760
	21st to end	Night	34% 11% 26% 21% 7%	836
November	1st to 10th	Night	25% 14% 26% 27% 8% 1	780
	11th to 20th	Night	28% 19% 28% 20% 5%	800
	21st to end	Night	30% 15% 29% 21% 4	870
December	1st to 10th	Night	30% 19% 29% 18% 3	1000
	11th to 20th	Night	31% 17% 30% 18% 4	1000
	21st to end	Night	33% 15% 32% 19% 2	1100

Page generated at 2025-05-08 09:34:00. Version ac07

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