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 2024-11-01.

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% 11% 4 9% 5% 4 4 3 5% 6% 35%	101346
	Night	14% 14% 5% 10% 6% 5% 4 3 4 6% 29%	97678
Transparency	Day	50% 5% 12% 21% 11% 1	101137
	Night	56% 5% 10% 18% 9% 1	97559
Seeing	Day	17% 9% 28% 28% 15% 4	15913
	Night	21% 10% 26% 28% 13% 2	25762

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% 30% 14% 17% 8% 4 3 1 2 2 7%	2527
	11th to 20th	Day	13% 21% 9% 23% 12% 11% 4 1 2 2 3	2530
	21st to end	Day	18% 23% 10% 15% 8% 5% 4 3 3 3 8%	2783
February	1st to 10th	Day	11% 17% 8% 17% 14% 6% 3 3 3 4 13%	1663
	11th to 20th	Day	13% 16% 8% 16% 12% 6% 4 3 4 3 14%	1848
	21st to end	Day	13% 16% 7% 14% 9% 5% 5% 3 4 4 20%	1570
March	1st to 10th	Day	12% 12% 6% 9% 5% 5% 5% 4 5% 5% 32%	3120
	11th to 20th	Day	12% 10% 7% 12% 5% 4 3 4 5% 6% 31%	3315
	21st to end	Day	19% 11% 6% 13% 6% 4 4 3 4 5% 26%	4059
April	1st to 10th	Day	17% 13% 4 8% 4 4 4 3 5% 6% 32%	2280
	11th to 20th	Day	19% 11% 3 7% 4 4 4 3 4 5% 36%	2290
	21st to end	Day	15% 11% 3 7% 5% 4 4 3 5% 7% 34%	2470
May	1st to 10th	Day	13% 8% 3 6% 4 4 4 4 5% 7% 43%	4082
	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% 5% 9% 5% 4 4 2 5% 6% 23%	1881
November	1st to 10th	Day	18% 14% 4 7% 5% 4 4 3 5% 6% 31%	1672
	11th to 20th	Day	16% 24% 7% 11% 5% 4 4 4 4 5% 17%	1710
	21st to end	Day	20% 22% 7% 13% 5% 3 3 3 3 5% 16%	1639
December	1st to 10th	Day	15% 27% 12% 16% 6% 4 3 2 2 3 10%	1520
	11th to 20th	Day	15% 25% 10% 16% 8% 3 4 3 4 5% 9%	1918
	21st to end	Day	19% 24% 10% 14% 6% 5% 4 2 4 3 9%	2783
January	1st to 10th	Night	14% 25% 10% 17% 8% 4 3 2 2 3 11%	4428
	11th to 20th	Night	12% 20% 9% 22% 11% 11% 3 2 2 2 6%	4440
	21st to end	Night	16% 24% 10% 17% 9% 6% 4 2 2 3 7%	4884
February	1st to 10th	Night	12% 18% 7% 17% 11% 6% 4 3 4 3 14%	2511
	11th to 20th	Night	12% 17% 6% 18% 11% 6% 4 3 3 4 17%	2218
	21st to end	Night	15% 17% 5% 15% 6% 6% 4 3 4 4 20%	1884
March	1st to 10th	Night	16% 11% 4 8% 4 3 4 3 5% 6% 35%	3733
	11th to 20th	Night	8% 11% 5% 11% 5% 5% 4 4 5% 7% 37%	3645
	21st to end	Night	16% 11% 4 14% 6% 4 4 3 5% 6% 26%	3599
April	1st to 10th	Night	16% 13% 4 8% 5% 4 3 4 5% 7% 32%	1900
	11th to 20th	Night	20% 11% 3 6% 4 4 5% 3 4 5% 36%	1838
	21st to end	Night	17% 10% 3 8% 4 4 3 3 5% 5% 36%	1710
May	1st to 10th	Night	13% 8% 3 7% 6% 4 5% 5% 5% 8% 37%	2813
	11th to 20th	Night	13% 7% 3 6% 4 5% 5% 4 6% 7% 40%	2610
	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	14% 17% 4 9% 5% 4 4 2 3 5% 32%	2413
	11th to 20th	Night	17% 23% 6% 12% 5% 5% 3 3 4 4 19%	2470
	21st to end	Night	18% 23% 6% 11% 4 4 4 3 4 4 19%	2536
December	1st to 10th	Night	17% 25% 10% 14% 7% 4 3 2 3 3 12%	2660
	11th to 20th	Night	16% 24% 10% 15% 6% 4 3 3 3 3 12%	3279
	21st to end	Night	23% 26% 8% 10% 5% 4 3 2 4 4 10%	4884

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	87% 3 5% 4 1	2528
	11th to 20th	Day	90% 3 3 3 1	2530
	21st to end	Day	83% 6% 8% 3 1	2783
February	1st to 10th	Day	76% 5% 6% 12% 1	1663
	11th to 20th	Day	74% 4 8% 8% 5%	1858
	21st to end	Day	67% 5% 10% 13% 4	1570
March	1st to 10th	Day	52% 5% 14% 20% 9%	3120
	11th to 20th	Day	51% 6% 16% 18% 8% 1	3315
	21st to end	Day	60% 4 10% 19% 6% 1	4059
April	1st to 10th	Day	53% 6% 11% 20% 11%	2280
	11th to 20th	Day	49% 5% 8% 21% 14% 2	2290
	21st to end	Day	48% 6% 11% 19% 14% 2	2470
May	1st to 10th	Day	40% 6% 11% 25% 15% 3	4120
	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	43% 6% 11% 27% 12%	2090
	11th to 20th	Day	62% 6% 11% 16% 5%	1804
	21st to end	Day	63% 5% 12% 14% 6%	1881
November	1st to 10th	Day	54% 6% 11% 20% 9%	1672
	11th to 20th	Day	69% 6% 11% 10% 4	1710
	21st to end	Day	72% 4 12% 8% 4	1639
December	1st to 10th	Day	82% 4 6% 7% 2	1520
	11th to 20th	Day	79% 6% 10% 5% 1	1915
	21st to end	Day	80% 7% 7% 5% 1	2783
January	1st to 10th	Night	81% 4 7% 8% 1	4428
	11th to 20th	Night	87% 4 4 3 1	4440
	21st to end	Night	84% 5% 8% 3	4884
February	1st to 10th	Night	74% 5% 5% 11% 4	2511
	11th to 20th	Night	72% 4 8% 11% 5%	2219
	21st to end	Night	67% 5% 11% 13% 4	1884
March	1st to 10th	Night	48% 6% 14% 24% 7%	3733
	11th to 20th	Night	47% 6% 13% 23% 10% 1	3645
	21st to end	Night	58% 6% 8% 21% 6% 1	3599
April	1st to 10th	Night	52% 6% 10% 19% 12% 1	1900
	11th to 20th	Night	50% 4 9% 21% 14% 3	1838
	21st to end	Night	48% 6% 9% 20% 13% 3	1710
May	1st to 10th	Night	43% 7% 13% 19% 15% 4	2840
	11th to 20th	Night	41% 7% 11% 26% 14% 2	2611
	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	43% 5% 9% 28% 14% 1	2090
	11th to 20th	Night	57% 5% 11% 19% 7% 1	2374
	21st to end	Night	62% 5% 11% 15% 6%	2717
November	1st to 10th	Night	55% 5% 11% 19% 9% 1	2413
	11th to 20th	Night	70% 4 10% 10% 5%	2470
	21st to end	Night	69% 5% 13% 10% 2 1	2536
December	1st to 10th	Night	78% 6% 7% 7% 2	2660
	11th to 20th	Night	78% 5% 9% 5% 2	3281
	21st to end	Night	77% 6% 11% 5% 1	4884

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% 17% 33% 24% 8% 1	270
	11th to 20th	Day	24% 12% 38% 22% 3 1	270
	21st to end	Day	25% 11% 32% 27% 5%	297
February	1st to 10th	Day	19% 20% 35% 19% 6% 2	270
	11th to 20th	Day	17% 18% 43% 20% 2	270
	21st to end	Day	21% 21% 41% 16%	225
March	1st to 10th	Day	17% 16% 47% 16% 4	270
	11th to 20th	Day	20% 14% 31% 21% 13% 2	360
	21st to end	Day	26% 12% 29% 24% 8% 1	506
April	1st to 10th	Day	22% 10% 38% 25% 5% 1	460
	11th to 20th	Day	24% 15% 28% 21% 9% 3	452
	21st to end	Day	19% 11% 31% 26% 12% 2	460
May	1st to 10th	Day	19% 8% 36% 26% 10% 1	463
	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	33% 11% 34% 17% 4 1	330
November	1st to 10th	Day	23% 15% 34% 19% 9% 1	270
	11th to 20th	Day	23% 19% 38% 16% 4	270
	21st to end	Day	26% 16% 36% 18% 4	270
December	1st to 10th	Day	23% 21% 33% 19% 3	270
	11th to 20th	Day	28% 21% 31% 15% 3 2	270
	21st to end	Day	29% 20% 35% 12% 3	297
January	1st to 10th	Night	24% 17% 32% 21% 6% 1	950
	11th to 20th	Night	27% 15% 33% 20% 6% 1	950
	21st to end	Night	22% 13% 33% 24% 7%	1045
February	1st to 10th	Night	21% 15% 34% 26% 4 1	881
	11th to 20th	Night	21% 16% 32% 23% 7%	743
	21st to end	Night	25% 14% 34% 23% 3	628
March	1st to 10th	Night	19% 11% 32% 27% 11% 1	760
	11th to 20th	Night	16% 11% 34% 28% 10% 1	760
	21st to end	Night	22% 9% 24% 35% 10% 1	708
April	1st to 10th	Night	24% 8% 31% 29% 7% 1	570
	11th to 20th	Night	25% 9% 25% 29% 11% 1	563
	21st to end	Night	21% 5% 27% 32% 13% 1	570
May	1st to 10th	Night	17% 4 27% 36% 15% 1	570
	11th to 20th	Night	17% 3 20% 38% 21% 2	561
	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% 12% 25% 21% 7%	836
November	1st to 10th	Night	24% 13% 27% 27% 8% 1	743
	11th to 20th	Night	28% 19% 28% 20% 5%	760
	21st to end	Night	30% 15% 29% 21% 5%	826
December	1st to 10th	Night	31% 18% 30% 18% 3	950
	11th to 20th	Night	30% 16% 31% 18% 4	950
	21st to end	Night	33% 15% 32% 19% 2	1045

Page generated at 2024-10-29 11:20:50. Version ac07

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