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 2024-03-01.

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	14% 11% 5% 8% 6% 3 4 4 5% 6% 33%	78380
	Night	15% 14% 6% 10% 7% 4 4 4 4 6% 27%	81078
Transparency	Day	52% 6% 11% 19% 10% 1	78081
	Night	59% 6% 10% 16% 8% 1	80898
Seeing	Day	17% 9% 28% 28% 15% 4	14883
	Night	21% 10% 26% 28% 13% 2	24953

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% 29% 15% 16% 9% 3 3 2 1 2 7%	2527
	11th to 20th	Day	14% 19% 10% 20% 14% 9% 5% 2 2 2 3	2530
	21st to end	Day	19% 22% 11% 13% 10% 4 4 3 3 3 8%	2783
February	1st to 10th	Day	11% 15% 9% 14% 17% 5% 4 4 3 4 13%	1663
	11th to 20th	Day	13% 14% 9% 14% 13% 5% 5% 4 4 3 15%	1848
	21st to end	Day	13% 14% 8% 13% 9% 4 5% 4 4 4 20%	1570
March	1st to 10th	Day	14% 11% 6% 10% 8% 4 6% 5% 5% 6% 27%	1800
	11th to 20th	Day	12% 10% 4 8% 7% 3 4 5% 6% 7% 33%	1885
	21st to end	Day	16% 11% 4 8% 6% 4 5% 4 5% 7% 31%	2312
April	1st to 10th	Day	18% 11% 5% 7% 5% 3 5% 4 4 7% 31%	2160
	11th to 20th	Day	19% 11% 3 6% 4 3 4 4 5% 5% 35%	2168
	21st to end	Day	15% 10% 4 7% 5% 4 5% 4 5% 7% 34%	2340
May	1st to 10th	Day	14% 8% 4 5% 5% 3 4 5% 5% 7% 41%	2340
	11th to 20th	Day	15% 6% 2 5% 5% 3 4 5% 5% 6% 43%	2411
	21st to end	Day	10% 5% 3 4 4 3 5% 5% 6% 10% 45%	2725
June	1st to 10th	Day	11% 5% 2 5% 5% 3 4 5% 6% 9% 46%	2520
	11th to 20th	Day	12% 6% 2 5% 4 3 4 5% 6% 8% 45%	2520
	21st to end	Day	10% 4 3 4 4 3 5% 5% 6% 10% 46%	2520
July	1st to 10th	Day	7% 4 1 4 4 2 4 5% 6% 10% 55%	2520
	11th to 20th	Day	9% 4 2 4 4 2 4 4 7% 8% 52%	2520
	21st to end	Day	7% 4 3 5% 4 2 5% 5% 6% 8% 52%	2743
August	1st to 10th	Day	9% 4 1 4 4 3 4 5% 6% 10% 49%	2441
	11th to 20th	Day	9% 4 3 4 4 3 4 3 6% 7% 51%	2303
	21st to end	Day	11% 6% 2 4 4 3 4 5% 5% 8% 48%	2383
September	1st to 10th	Day	14% 5% 2 5% 5% 3 4 4 4 7% 44%	2160
	11th to 20th	Day	13% 6% 2 4 5% 3 4 4 5% 8% 46%	1994
	21st to end	Day	15% 7% 3 6% 5% 4 5% 4 4 9% 38%	1980
October	1st to 10th	Day	15% 9% 3 6% 6% 2 4 4 5% 7% 39%	1980
	11th to 20th	Day	24% 12% 4 9% 7% 4 4 5% 4 7% 20%	1710
	21st to end	Day	25% 14% 5% 8% 6% 3 4 3 4 6% 22%	1782
November	1st to 10th	Day	18% 13% 4 7% 5% 4 4 4 4 7% 31%	1672
	11th to 20th	Day	16% 21% 8% 10% 6% 3 5% 4 4 5% 17%	1710
	21st to end	Day	21% 20% 8% 12% 6% 3 3 3 3 5% 16%	1639
December	1st to 10th	Day	15% 24% 14% 16% 6% 3 3 2 2 3 10%	1520
	11th to 20th	Day	15% 22% 12% 15% 9% 3 3 4 4 5% 9%	1918
	21st to end	Day	20% 23% 10% 13% 8% 4 4 3 3 3 9%	2783
January	1st to 10th	Night	15% 24% 11% 16% 10% 3 3 3 2 3 11%	4428
	11th to 20th	Night	13% 18% 10% 18% 14% 10% 4 3 2 2 6%	4440
	21st to end	Night	16% 23% 11% 15% 11% 4 5% 3 2 3 7%	4884
February	1st to 10th	Night	12% 16% 8% 14% 13% 5% 4 4 4 3 14%	2511
	11th to 20th	Night	12% 15% 7% 16% 13% 4 5% 3 3 5% 17%	2218
	21st to end	Night	16% 15% 6% 13% 7% 4 5% 4 4 4 21%	1884
March	1st to 10th	Night	15% 10% 5% 9% 7% 3 4 4 6% 7% 30%	2167
	11th to 20th	Night	12% 9% 4 8% 6% 3 5% 5% 5% 7% 35%	2075
	21st to end	Night	19% 9% 3 8% 6% 3 4 4 5% 7% 32%	2057
April	1st to 10th	Night	16% 12% 6% 7% 6% 3 3 5% 5% 7% 31%	1800
	11th to 20th	Night	20% 10% 3 5% 4 3 5% 4 4 6% 36%	1740
	21st to end	Night	17% 9% 4 7% 5% 3 3 3 5% 6% 37%	1620
May	1st to 10th	Night	15% 7% 3 6% 7% 3 5% 6% 5% 8% 34%	1620
	11th to 20th	Night	14% 8% 3 6% 5% 3 5% 5% 5% 7% 38%	1481
	21st to end	Night	13% 5% 2 5% 5% 3 4 4 7% 9% 44%	1551
June	1st to 10th	Night	11% 6% 3 5% 5% 3 4 5% 6% 9% 43%	1440
	11th to 20th	Night	11% 6% 3 6% 5% 4 5% 5% 5% 8% 44%	1440
	21st to end	Night	10% 5% 2 5% 5% 4 4 6% 6% 9% 45%	1440
July	1st to 10th	Night	8% 3 1 3 4 3 5% 6% 7% 10% 51%	1440
	11th to 20th	Night	6% 5% 3 5% 5% 2 5% 4 5% 10% 50%	1440
	21st to end	Night	7% 4 2 5% 5% 3 5% 5% 6% 9% 49%	1575
August	1st to 10th	Night	7% 5% 2 4 5% 3 4 5% 7% 11% 46%	1494
	11th to 20th	Night	7% 4 2 4 4 3 4 4 5% 9% 53%	1598
	21st to end	Night	11% 6% 3 5% 5% 3 3 4 5% 8% 48%	1970
September	1st to 10th	Night	12% 6% 3 5% 5% 3 4 4 4 7% 48%	1800
	11th to 20th	Night	13% 5% 2 5% 4 2 4 4 5% 8% 49%	1948
	21st to end	Night	16% 6% 2 6% 5% 3 5% 5% 5% 7% 40%	1980
October	1st to 10th	Night	17% 8% 3 6% 4 2 4 4 4 6% 42%	1980
	11th to 20th	Night	25% 12% 4 7% 5% 3 3 4 3 5% 29%	2248
	21st to end	Night	27% 13% 5% 8% 5% 3 4 4 4 5% 23%	2574
November	1st to 10th	Night	14% 16% 5% 8% 5% 3 4 3 3 5% 32%	2406
	11th to 20th	Night	17% 21% 7% 11% 6% 3 4 4 4 4 19%	2470
	21st to end	Night	19% 21% 7% 10% 5% 3 4 3 4 5% 19%	2536
December	1st to 10th	Night	18% 22% 12% 13% 8% 3 3 3 3 3 12%	2660
	11th to 20th	Night	16% 23% 10% 15% 7% 3 3 4 3 4 12%	3279
	21st to end	Night	24% 25% 9% 9% 6% 3 3 3 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	58% 6% 13% 17% 6%	1800
	11th to 20th	Day	49% 7% 14% 18% 11% 2	1885
	21st to end	Day	53% 5% 13% 21% 8% 1	2312
April	1st to 10th	Day	54% 5% 11% 19% 11%	2160
	11th to 20th	Day	50% 5% 9% 20% 14% 2	2168
	21st to end	Day	49% 6% 11% 18% 14% 2	2340
May	1st to 10th	Day	43% 5% 11% 26% 13% 1	2340
	11th to 20th	Day	40% 7% 12% 22% 16% 3	2415
	21st to end	Day	35% 9% 14% 27% 14% 1	2725
June	1st to 10th	Day	35% 7% 11% 27% 17% 2	2520
	11th to 20th	Day	36% 6% 14% 26% 18% 1	2520
	21st to end	Day	33% 8% 17% 25% 16% 1	2520
July	1st to 10th	Day	26% 7% 13% 32% 20% 3	2451
	11th to 20th	Day	29% 6% 15% 31% 17% 2	2445
	21st to end	Day	29% 7% 14% 29% 17% 3	2591
August	1st to 10th	Day	30% 8% 16% 33% 12% 2	2426
	11th to 20th	Day	31% 7% 16% 31% 13% 2	2303
	21st to end	Day	35% 7% 13% 28% 17% 2	2383
September	1st to 10th	Day	40% 6% 12% 26% 15% 1	2160
	11th to 20th	Day	36% 7% 15% 30% 11%	1994
	21st to end	Day	44% 6% 14% 27% 9%	1980
October	1st to 10th	Day	45% 6% 11% 25% 12%	1980
	11th to 20th	Day	64% 6% 11% 15% 4	1710
	21st to end	Day	65% 5% 12% 13% 5%	1782
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% 10% 13% 5%	1884
March	1st to 10th	Night	53% 6% 12% 20% 8% 1	2167
	11th to 20th	Night	48% 6% 13% 19% 11% 2	2075
	21st to end	Night	51% 5% 10% 24% 9% 1	2057
April	1st to 10th	Night	52% 6% 10% 19% 12% 1	1800
	11th to 20th	Night	50% 4 9% 20% 14% 3	1740
	21st to end	Night	47% 6% 10% 20% 13% 3	1620
May	1st to 10th	Night	47% 7% 11% 21% 12% 2	1620
	11th to 20th	Night	44% 6% 10% 21% 15% 3	1482
	21st to end	Night	36% 7% 12% 27% 15% 3	1552
June	1st to 10th	Night	37% 7% 11% 26% 17% 2	1440
	11th to 20th	Night	38% 6% 12% 24% 19% 2	1440
	21st to end	Night	33% 9% 15% 24% 16% 3	1440
July	1st to 10th	Night	26% 9% 13% 29% 20% 4	1400
	11th to 20th	Night	29% 6% 14% 28% 20% 3	1392
	21st to end	Night	31% 10% 12% 27% 17% 3	1487
August	1st to 10th	Night	30% 8% 16% 29% 14% 2	1485
	11th to 20th	Night	29% 6% 15% 33% 16% 1	1598
	21st to end	Night	35% 6% 12% 26% 18% 2	1970
September	1st to 10th	Night	37% 6% 11% 25% 20% 2	1800
	11th to 20th	Night	33% 6% 14% 32% 12% 2	1948
	21st to end	Night	43% 7% 13% 27% 9% 1	1980
October	1st to 10th	Night	44% 6% 9% 26% 14% 1	1980
	11th to 20th	Night	58% 5% 12% 18% 6% 1	2248
	21st to end	Night	64% 5% 10% 14% 6%	2574
November	1st to 10th	Night	55% 5% 11% 19% 9% 1	2406
	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% 20% 41% 16%	225
March	1st to 10th	Day	18% 17% 45% 15% 4	240
	11th to 20th	Day	19% 12% 32% 22% 14% 2	325
	21st to end	Day	26% 11% 29% 23% 9% 1	462
April	1st to 10th	Day	22% 9% 37% 26% 5% 1	420
	11th to 20th	Day	24% 14% 28% 21% 9% 3	412
	21st to end	Day	19% 10% 31% 26% 12% 2	420
May	1st to 10th	Day	20% 9% 35% 25% 10% 1	423
	11th to 20th	Day	16% 6% 27% 33% 16% 2	557
	21st to end	Day	13% 4 26% 31% 20% 5%	679
June	1st to 10th	Day	12% 3 26% 35% 20% 3	630
	11th to 20th	Day	16% 3 24% 34% 18% 5%	630
	21st to end	Day	12% 5% 23% 35% 20% 5%	630
July	1st to 10th	Day	7% 3 18% 36% 29% 7%	621
	11th to 20th	Day	9% 5% 20% 39% 22% 5%	618
	21st to end	Day	8% 3 21% 38% 24% 6%	684
August	1st to 10th	Day	9% 3 19% 34% 28% 7%	560
	11th to 20th	Day	11% 3 16% 31% 27% 12%	439
	21st to end	Day	15% 4 21% 32% 23% 5%	495
September	1st to 10th	Day	16% 5% 20% 31% 20% 8%	450
	11th to 20th	Day	12% 6% 18% 34% 22% 8%	450
	21st to end	Day	15% 10% 25% 24% 19% 8%	450
October	1st to 10th	Day	17% 8% 28% 24% 18% 4	450
	11th to 20th	Day	29% 13% 28% 24% 5%	292
	21st to end	Day	35% 9% 34% 16% 5% 1	297
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% 10% 32% 27% 11% 1	723
	11th to 20th	Night	17% 10% 34% 28% 10% 2	720
	21st to end	Night	22% 8% 23% 35% 11% 1	671
April	1st to 10th	Night	24% 9% 30% 29% 7% 1	540
	11th to 20th	Night	25% 8% 25% 30% 11% 2	533
	21st to end	Night	21% 5% 27% 33% 13% 1	540
May	1st to 10th	Night	17% 4 27% 36% 15% 1	540
	11th to 20th	Night	18% 2 20% 37% 21% 2	531
	21st to end	Night	16% 3 19% 35% 23% 4	584
June	1st to 10th	Night	13% 4 18% 41% 20% 4	540
	11th to 20th	Night	14% 4 21% 33% 23% 5%	540
	21st to end	Night	11% 3 14% 42% 27% 3	540
July	1st to 10th	Night	9% 1 12% 41% 31% 7%	525
	11th to 20th	Night	8% 2 14% 39% 32% 5%	522
	21st to end	Night	7% 3 17% 37% 32% 3	591
August	1st to 10th	Night	8% 2 14% 41% 30% 6%	537
	11th to 20th	Night	9% 2 13% 35% 32% 9%	534
	21st to end	Night	14% 3 16% 35% 28% 3	594
September	1st to 10th	Night	14% 5% 18% 35% 21% 7%	540
	11th to 20th	Night	14% 5% 17% 34% 24% 7%	688
	21st to end	Night	18% 7% 21% 26% 23% 5%	720
October	1st to 10th	Night	22% 7% 21% 28% 19% 3	720
	11th to 20th	Night	32% 10% 24% 23% 10% 1	720
	21st to end	Night	35% 11% 25% 21% 7% 1	792
November	1st to 10th	Night	24% 13% 27% 27% 8% 1	740
	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 2024-02-27 06:30:13. Version ac07

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