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 2026-09-14.

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% 11% 5% 10% 5% 4 4 3 5% 7% 35%	149159
	Night	13% 13% 5% 12% 6% 5% 4 3 4 6% 28%	142241
Transparency	Day	50% 4 11% 22% 12% 1	152659
	Night	57% 4 10% 18% 10% 1	146818
Seeing	Day	17% 10% 28% 27% 14% 3	18519
	Night	21% 11% 25% 28% 13% 2	28288

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	12% 26% 13% 27% 7% 4 2 2 1 2 5%	4691
	11th to 20th	Day	10% 19% 10% 25% 14% 11% 4 1 1 1 2	4710
	21st to end	Day	11% 16% 9% 18% 13% 8% 7% 2 2 3 11%	5156
February	1st to 10th	Day	11% 17% 8% 18% 14% 6% 3 3 3 4 13%	1840
	11th to 20th	Day	13% 15% 8% 17% 12% 6% 4 3 4 4 15%	2048
	21st to end	Day	12% 17% 8% 15% 8% 5% 5% 3 4 4 19%	1730
March	1st to 10th	Day	12% 10% 4 13% 6% 5% 5% 4 5% 5% 32%	4580
	11th to 20th	Day	12% 10% 6% 10% 5% 4 4 4 6% 7% 32%	4850
	21st to end	Day	22% 11% 6% 12% 5% 4 3 3 4 5% 25%	5948
April	1st to 10th	Day	17% 13% 4 8% 4 4 4 3 5% 6% 31%	2520
	11th to 20th	Day	18% 11% 3 7% 4 4 4 3 5% 6% 36%	2534
	21st to end	Day	15% 10% 4 7% 5% 5% 5% 4 5% 7% 34%	2730
May	1st to 10th	Day	11% 7% 3 6% 4 4 4 4 6% 8% 45%	7616
	11th to 20th	Day	12% 9% 3 7% 4 4 5% 4 5% 7% 42%	8002
	21st to end	Day	12% 6% 3 6% 3 3 4 4 5% 7% 48%	9047
June	1st to 10th	Day	11% 6% 2 6% 4 4 4 4 6% 8% 45%	2940
	11th to 20th	Day	12% 6% 2 6% 4 5% 4 4 6% 8% 44%	2940
	21st to end	Day	11% 5% 3 5% 4 4 5% 4 6% 9% 46%	2940
July	1st to 10th	Day	12% 7% 2 6% 4 4 4 4 6% 9% 42%	8280
	11th to 20th	Day	7% 4 1 4 3 3 4 3 6% 9% 55%	8280
	21st to end	Day	8% 6% 2 6% 4 4 4 4 6% 9% 48%	8990
August	1st to 10th	Day	10% 6% 2 6% 4 4 4 4 6% 10% 44%	6301
	11th to 20th	Day	11% 6% 2 5% 4 3 4 3 5% 7% 50%	5951
	21st to end	Day	10% 7% 2 7% 4 4 5% 4 6% 9% 42%	6087
September	1st to 10th	Day	14% 6% 2 6% 4 4 4 3 5% 7% 45%	2520
	11th to 20th	Day	12% 5% 2 5% 4 3 4 3 5% 8% 48%	2248
	21st to end	Day	14% 8% 3 7% 5% 5% 5% 3 5% 8% 39%	2200
October	1st to 10th	Day	14% 9% 3 7% 5% 4 3 3 5% 7% 42%	2200
	11th to 20th	Day	22% 13% 3 10% 5% 4 4 4 5% 7% 22%	1899
	21st to end	Day	22% 14% 4 9% 5% 4 4 2 5% 6% 24%	1980
November	1st to 10th	Day	17% 14% 4 7% 5% 5% 3 3 5% 6% 31%	1852
	11th to 20th	Day	16% 23% 7% 11% 5% 4 4 3 4 5% 18%	1890
	21st to end	Day	19% 22% 8% 13% 5% 3 3 3 3 5% 16%	1811
December	1st to 10th	Day	13% 28% 17% 18% 6% 3 2 1 1 3 9%	2690
	11th to 20th	Day	13% 26% 13% 17% 10% 3 3 2 3 3 6%	3088
	21st to end	Day	21% 23% 10% 15% 6% 5% 3 2 3 3 10%	4070
January	1st to 10th	Night	15% 22% 10% 26% 7% 3 2 2 2 2 9%	8232
	11th to 20th	Night	10% 22% 10% 26% 10% 11% 2 1 2 1 4	8280
	21st to end	Night	9% 18% 10% 19% 13% 9% 6% 2 2 2 9%	9058
February	1st to 10th	Night	12% 18% 7% 17% 12% 6% 4 3 4 3 14%	2774
	11th to 20th	Night	12% 17% 6% 17% 11% 6% 4 3 3 4 17%	2458
	21st to end	Night	14% 17% 5% 15% 6% 6% 4 3 4 5% 20%	2076
March	1st to 10th	Night	16% 11% 4 12% 4 3 4 3 5% 6% 33%	5493
	11th to 20th	Night	11% 10% 4 9% 4 4 4 4 5% 8% 36%	5330
	21st to end	Night	17% 11% 4 13% 6% 4 4 3 5% 6% 27%	5265
April	1st to 10th	Night	17% 13% 4 8% 5% 4 3 4 5% 7% 31%	2100
	11th to 20th	Night	20% 11% 3 6% 4 4 4 3 4 5% 35%	2034
	21st to end	Night	17% 10% 3 8% 4 4 3 3 5% 6% 37%	1890
May	1st to 10th	Night	11% 7% 3 7% 5% 4 5% 4 6% 8% 41%	5237
	11th to 20th	Night	10% 7% 3 6% 5% 5% 5% 4 6% 8% 42%	4863
	21st to end	Night	16% 6% 2 6% 4 3 4 3 5% 6% 44%	5139
June	1st to 10th	Night	11% 7% 3 6% 5% 3 5% 4 6% 8% 42%	1680
	11th to 20th	Night	11% 7% 3 7% 4 4 5% 4 6% 8% 41%	1680
	21st to end	Night	10% 6% 3 6% 4 5% 4 5% 6% 8% 43%	1680
July	1st to 10th	Night	12% 8% 2 7% 5% 5% 5% 4 6% 9% 37%	4708
	11th to 20th	Night	5% 5% 1 4 3 3 4 3 5% 10% 56%	4707
	21st to end	Night	6% 7% 3 7% 4 4 4 4 6% 8% 47%	5117
August	1st to 10th	Night	14% 6% 3 6% 4 4 4 4 6% 8% 41%	3857
	11th to 20th	Night	11% 5% 2 6% 3 4 4 3 6% 9% 47%	4095
	21st to end	Night	9% 6% 2 6% 4 5% 5% 4 7% 9% 42%	5023
September	1st to 10th	Night	11% 6% 3 5% 4 4 4 3 5% 6% 48%	2100
	11th to 20th	Night	11% 5% 2 5% 3 3 4 3 6% 8% 50%	2197
	21st to end	Night	15% 6% 2 6% 5% 4 5% 4 5% 6% 40%	2200
October	1st to 10th	Night	16% 8% 3 7% 3 3 4 3 4 6% 43%	2200
	11th to 20th	Night	23% 12% 4 7% 4 4 3 3 3 5% 30%	2499
	21st to end	Night	25% 13% 4 9% 4 4 4 3 4 6% 25%	2860
November	1st to 10th	Night	15% 17% 4 9% 5% 4 4 2 3 5% 32%	2666
	11th to 20th	Night	16% 22% 6% 12% 5% 5% 4 3 4 4 20%	2730
	21st to end	Night	18% 23% 7% 11% 4 3 4 2 4 4 18%	2804
December	1st to 10th	Night	14% 22% 11% 21% 6% 4 3 2 3 3 10%	4720
	11th to 20th	Night	15% 27% 11% 16% 9% 3 2 2 3 3 8%	5339
	21st to end	Night	23% 23% 8% 13% 5% 3 3 3 4 4 11%	7150

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	89% 2 4 4 1	4692
	11th to 20th	Day	93% 2 2 2 1	4710
	21st to end	Day	81% 3 6% 8% 2	5156
February	1st to 10th	Day	76% 4 7% 11% 2	1840
	11th to 20th	Day	74% 4 9% 8% 5%	2058
	21st to end	Day	68% 5% 10% 13% 4	1730
March	1st to 10th	Day	54% 4 15% 18% 9% 1	4580
	11th to 20th	Day	50% 4 16% 19% 9% 1	4850
	21st to end	Day	63% 3 10% 15% 8%	5950
April	1st to 10th	Day	53% 5% 11% 20% 11%	2520
	11th to 20th	Day	50% 5% 9% 22% 14% 2	2534
	21st to end	Day	49% 5% 12% 19% 13% 2	2730
May	1st to 10th	Day	38% 3 10% 30% 16% 3	7651
	11th to 20th	Day	42% 5% 9% 24% 17% 2	8006
	21st to end	Day	37% 4 8% 25% 22% 3	9061
June	1st to 10th	Day	36% 6% 11% 27% 18% 2	2940
	11th to 20th	Day	38% 5% 13% 26% 17% 1	2940
	21st to end	Day	34% 7% 17% 26% 15% 1	2940
July	1st to 10th	Day	40% 3 13% 27% 14% 1	8211
	11th to 20th	Day	27% 2 12% 34% 23% 2	8205
	21st to end	Day	34% 3 14% 30% 18% 1	8794
August	1st to 10th	Day	38% 3 13% 31% 14% 1	6286
	11th to 20th	Day	35% 4 16% 32% 13% 1	5990
	21st to end	Day	41% 3 14% 31% 11% 1	6086
September	1st to 10th	Day	40% 5% 13% 27% 13% 1	2520
	11th to 20th	Day	34% 6% 15% 30% 14% 1	2248
	21st to end	Day	43% 6% 13% 28% 11%	2200
October	1st to 10th	Day	30% 3 8% 38% 18% 2	3590
	11th to 20th	Day	53% 3 11% 22% 10%	3063
	21st to end	Day	57% 3 15% 18% 7%	3180
November	1st to 10th	Day	55% 6% 11% 20% 9%	1852
	11th to 20th	Day	68% 6% 11% 11% 4	1890
	21st to end	Day	74% 4 11% 8% 3	1811
December	1st to 10th	Day	85% 2 5% 7% 1	2690
	11th to 20th	Day	85% 4 7% 4 1	3085
	21st to end	Day	81% 5% 5% 8% 2	4070
January	1st to 10th	Night	85% 2 6% 5% 2	8233
	11th to 20th	Night	91% 2 4 2 1	8280
	21st to end	Night	84% 2 6% 6% 1	9058
February	1st to 10th	Night	75% 5% 6% 11% 4	2774
	11th to 20th	Night	72% 4 8% 12% 5%	2459
	21st to end	Night	67% 4 11% 13% 4	2076
March	1st to 10th	Night	52% 4 15% 21% 7%	5493
	11th to 20th	Night	47% 4 18% 21% 9% 1	5330
	21st to end	Night	58% 4 9% 19% 8% 1	5265
April	1st to 10th	Night	53% 5% 10% 19% 12% 1	2100
	11th to 20th	Night	51% 4 8% 21% 14% 3	2034
	21st to end	Night	48% 5% 10% 21% 13% 3	1890
May	1st to 10th	Night	41% 4 12% 26% 15% 2	5264
	11th to 20th	Night	39% 5% 11% 27% 17% 1	4864
	21st to end	Night	42% 3 8% 23% 17% 7%	5149
June	1st to 10th	Night	38% 7% 10% 25% 18% 2	1680
	11th to 20th	Night	40% 5% 11% 23% 18% 2	1680
	21st to end	Night	36% 8% 14% 24% 15% 3	1680
July	1st to 10th	Night	44% 3 12% 23% 14% 4	4670
	11th to 20th	Night	26% 2 11% 35% 23% 3	4662
	21st to end	Night	35% 4 12% 27% 20% 2	5002
August	1st to 10th	Night	42% 3 11% 25% 17% 1	3848
	11th to 20th	Night	35% 3 17% 33% 13%	4122
	21st to end	Night	38% 3 13% 28% 17% 1	5023
September	1st to 10th	Night	37% 5% 11% 26% 19% 1	2100
	11th to 20th	Night	31% 5% 14% 33% 15% 2	2197
	21st to end	Night	42% 6% 12% 26% 12% 1	2200
October	1st to 10th	Night	38% 3 8% 36% 14% 1	3590
	11th to 20th	Night	49% 3 10% 26% 12%	4074
	21st to end	Night	52% 3 12% 23% 9%	4610
November	1st to 10th	Night	56% 5% 10% 19% 9% 1	2666
	11th to 20th	Night	68% 4 10% 11% 5% 1	2730
	21st to end	Night	71% 4 12% 10% 2 1	2804
December	1st to 10th	Night	80% 4 8% 7% 1	4720
	11th to 20th	Night	83% 3 6% 6% 1	5341
	21st to end	Night	77% 4 9% 6% 3	7150

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	17% 19% 33% 24% 7% 1	330
	11th to 20th	Day	22% 19% 37% 19% 3 1	330
	21st to end	Day	23% 15% 34% 23% 4	363
February	1st to 10th	Day	21% 21% 35% 18% 5% 2	330
	11th to 20th	Day	18% 19% 41% 19% 2	330
	21st to end	Day	21% 23% 41% 15%	273
March	1st to 10th	Day	18% 18% 46% 15% 3	330
	11th to 20th	Day	22% 16% 31% 19% 10% 1	430
	21st to end	Day	26% 14% 30% 22% 7% 1	594
April	1st to 10th	Day	23% 12% 37% 23% 4 1	540
	11th to 20th	Day	23% 17% 29% 20% 8% 3	532
	21st to end	Day	18% 12% 31% 26% 11% 2	540
May	1st to 10th	Day	18% 8% 39% 24% 9% 1	543
	11th to 20th	Day	15% 9% 28% 30% 15% 2	696
	21st to end	Day	13% 5% 28% 31% 18% 4	844
June	1st to 10th	Day	12% 4 28% 35% 18% 3	780
	11th to 20th	Day	15% 6% 27% 32% 15% 4	780
	21st to end	Day	12% 7% 25% 34% 17% 4	780
July	1st to 10th	Day	8% 4 19% 38% 26% 6%	771
	11th to 20th	Day	9% 5% 21% 38% 22% 5%	768
	21st to end	Day	8% 3 23% 38% 23% 5%	849
August	1st to 10th	Day	9% 4 20% 34% 26% 7%	698
	11th to 20th	Day	12% 4 17% 34% 24% 10%	559
	21st to end	Day	14% 5% 22% 32% 22% 5%	627
September	1st to 10th	Day	15% 7% 21% 30% 19% 7%	570
	11th to 20th	Day	10% 6% 17% 34% 24% 10%	542
	21st to end	Day	14% 9% 24% 28% 19% 7%	530
October	1st to 10th	Day	16% 9% 29% 26% 17% 4	530
	11th to 20th	Day	26% 13% 32% 25% 5%	354
	21st to end	Day	31% 11% 34% 18% 5% 1	363
November	1st to 10th	Day	24% 18% 32% 17% 8% 1	330
	11th to 20th	Day	24% 22% 34% 17% 4	330
	21st to end	Day	27% 17% 35% 18% 3	330
December	1st to 10th	Day	24% 22% 32% 18% 4	330
	11th to 20th	Day	29% 23% 31% 14% 2 2	330
	21st to end	Day	32% 19% 34% 11% 4 1	363
January	1st to 10th	Night	24% 17% 33% 20% 5%	1050
	11th to 20th	Night	26% 17% 32% 19% 5%	1050
	21st to end	Night	23% 15% 33% 23% 6%	1155
February	1st to 10th	Night	22% 15% 33% 25% 4 1	973
	11th to 20th	Night	21% 17% 31% 23% 7%	823
	21st to end	Night	25% 15% 34% 23% 3	692
March	1st to 10th	Night	20% 12% 31% 26% 10% 1	840
	11th to 20th	Night	18% 12% 33% 27% 9% 1	840
	21st to end	Night	21% 11% 24% 33% 9% 1	782
April	1st to 10th	Night	25% 10% 29% 28% 7% 1	630
	11th to 20th	Night	26% 10% 24% 28% 11% 2	623
	21st to end	Night	20% 6% 28% 31% 13% 1	630
May	1st to 10th	Night	16% 4 28% 36% 14% 1	630
	11th to 20th	Night	17% 4 21% 36% 20% 2	621
	21st to end	Night	16% 4 20% 35% 21% 4	683
June	1st to 10th	Night	13% 4 20% 40% 20% 4	630
	11th to 20th	Night	15% 5% 22% 33% 20% 4	630
	21st to end	Night	12% 4 16% 41% 25% 2	630
July	1st to 10th	Night	9% 2 13% 41% 29% 6%	615
	11th to 20th	Night	8% 3 14% 40% 31% 5%	612
	21st to end	Night	7% 3 18% 38% 31% 3	690
August	1st to 10th	Night	9% 3 15% 40% 29% 6%	627
	11th to 20th	Night	10% 3 13% 36% 31% 7%	624
	21st to end	Night	13% 4 16% 35% 28% 4	693
September	1st to 10th	Night	14% 6% 18% 34% 22% 7%	630
	11th to 20th	Night	13% 4 16% 34% 26% 8%	776
	21st to end	Night	17% 7% 21% 27% 22% 5%	800
October	1st to 10th	Night	21% 7% 22% 29% 19% 3	800
	11th to 20th	Night	30% 11% 25% 23% 10% 1	800
	21st to end	Night	33% 11% 25% 22% 8% 1	880
November	1st to 10th	Night	25% 15% 26% 26% 7% 1	820
	11th to 20th	Night	28% 20% 28% 20% 5%	840
	21st to end	Night	31% 15% 29% 21% 4	914
December	1st to 10th	Night	30% 19% 29% 18% 3	1050
	11th to 20th	Night	31% 17% 30% 17% 4	1050
	21st to end	Night	33% 16% 32% 18% 2	1155

Page generated at 2026-09-11 04:11:56. Version ac07

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