Climax Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Climax Observatory clear sky chart from 2005-11-06 to 2024-07-16.

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	4 8% 5% 11% 6% 5% 4 3 5% 6% 42%	89901
	Night	2 5% 3 10% 6% 5% 4 4 5% 7% 49%	89761
Transparency	Day	39% 6% 10% 21% 18% 6%	89613
	Night	31% 6% 14% 25% 19% 6%	89571
Seeing	Day	16% 25% 29% 19% 10% 2	15109
	Night	8% 18% 29% 29% 14% 1	25182

By Month

Percentage Cloud Cover SW (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	4 4 12% 12% 11% 5% 3 4 7% 38%	2538
	11th to 20th	Day	5% 5% 19% 8% 8% 6% 3 3 4 38%	2773
	21st to end	Day	7% 5% 16% 7% 5% 3 3 4 6% 44%	3146
February	1st to 10th	Day	5% 6% 19% 8% 6% 4 4 4 4 39%	1710
	11th to 20th	Day	5% 5% 15% 10% 6% 4 3 4 6% 43%	1767
	21st to end	Day	5% 5% 19% 7% 7% 4 3 4 5% 41%	1570
March	1st to 10th	Day	7% 7% 19% 7% 3 3 2 4 4 43%	3226
	11th to 20th	Day	1 8% 8% 17% 6% 5% 4 3 5% 6% 36%	3490
	21st to end	Day	1 12% 8% 19% 8% 6% 4 2 4 5% 30%	3969
April	1st to 10th	Day	2 11% 5% 12% 6% 4 4 3 5% 6% 43%	2280
	11th to 20th	Day	1 15% 8% 15% 7% 4 4 3 4 6% 34%	2251
	21st to end	Day	2 17% 6% 13% 7% 4 5% 3 4 5% 33%	2280
May	1st to 10th	Day	3 15% 10% 13% 6% 6% 5% 4 5% 5% 28%	3967
	11th to 20th	Day	3 13% 4 9% 5% 5% 6% 5% 6% 7% 38%	4388
	21st to end	Day	3 8% 3 8% 4 4 5% 4 7% 8% 46%	4825
June	1st to 10th	Day	6% 7% 2 6% 5% 4 5% 4 7% 8% 45%	2660
	11th to 20th	Day	7% 8% 2 5% 4 4 5% 3 5% 6% 50%	2660
	21st to end	Day	6% 5% 3 7% 5% 5% 5% 4 6% 7% 47%	2660
July	1st to 10th	Day	10% 7% 3 8% 5% 4 6% 3 6% 6% 43%	2660
	11th to 20th	Day	9% 7% 2 8% 6% 5% 5% 6% 7% 7% 36%	2593
	21st to end	Day	14% 9% 4 9% 7% 6% 6% 5% 5% 7% 27%	2583
August	1st to 10th	Day	16% 9% 3 8% 6% 5% 5% 4 6% 6% 31%	2328
	11th to 20th	Day	11% 8% 3 8% 6% 4 5% 4 5% 6% 40%	2177
	21st to end	Day	10% 8% 4 9% 6% 6% 4 4 6% 6% 37%	2376
September	1st to 10th	Day	10% 7% 2 6% 5% 5% 3 3 4 5% 50%	2160
	11th to 20th	Day	9% 8% 3 6% 4 5% 4 3 4 5% 49%	2160
	21st to end	Day	6% 9% 3 6% 4 3 2 2 4 6% 54%	1942
October	1st to 10th	Day	6% 10% 4 7% 5% 3 4 3 4 5% 49%	1800
	11th to 20th	Day	3 9% 2 5% 3 3 3 3 4 6% 61%	1800
	21st to end	Day	3 8% 3 11% 3 3 3 2 4 5% 54%	1980
November	1st to 10th	Day	1 6% 2 8% 3 4 3 3 4 5% 61%	1683
	11th to 20th	Day	9% 3 7% 4 3 3 3 4 8% 57%	1710
	21st to end	Day	1 6% 3 9% 8% 3 2 2 5% 6% 55%	1549
December	1st to 10th	Day	4 3 15% 9% 5% 5% 3 4 8% 43%	1520
	11th to 20th	Day	6% 4 12% 6% 5% 4 4 6% 9% 45%	1926
	21st to end	Day	5% 4 14% 9% 6% 5% 3 5% 7% 41%	2794
January	1st to 10th	Night	2 3 16% 12% 7% 5% 3 4 7% 42%	4417
	11th to 20th	Night	3 5% 17% 11% 6% 7% 3 3 5% 41%	4226
	21st to end	Night	4 5% 16% 9% 6% 5% 3 5% 5% 42%	4521
February	1st to 10th	Night	3 4 16% 9% 6% 4 3 5% 6% 43%	2470
	11th to 20th	Night	4 4 13% 9% 6% 5% 4 5% 6% 44%	2298
	21st to end	Night	4 4 13% 8% 8% 5% 4 5% 6% 43%	1884
March	1st to 10th	Night	4 7% 13% 7% 4 4 4 6% 7% 44%	3624
	11th to 20th	Night	7% 6% 15% 6% 4 3 3 5% 6% 45%	3490
	21st to end	Night	1 8% 6% 13% 7% 6% 5% 5% 5% 6% 37%	3678
April	1st to 10th	Night	1 5% 3 10% 6% 5% 5% 3 5% 7% 50%	1900
	11th to 20th	Night	1 10% 3 11% 7% 5% 5% 3 6% 5% 44%	1877
	21st to end	Night	2 10% 4 9% 5% 4 4 4 5% 7% 46%	1900
May	1st to 10th	Night	3 10% 5% 10% 4 4 4 4 6% 7% 43%	2999
	11th to 20th	Night	3 9% 3 8% 6% 5% 6% 5% 7% 8% 41%	2517
	21st to end	Night	2 8% 3 5% 4 4 4 4 6% 7% 55%	2762
June	1st to 10th	Night	2 3 2 4 4 3 4 4 6% 10% 59%	1520
	11th to 20th	Night	4 5% 1 4 3 3 4 3 4 7% 62%	1520
	21st to end	Night	3 3 2 4 3 4 3 4 6% 9% 59%	1520
July	1st to 10th	Night	6% 5% 2 6% 4 4 5% 5% 6% 9% 47%	1520
	11th to 20th	Night	2 3 2 5% 4 5% 5% 3 7% 11% 53%	1488
	21st to end	Night	6% 5% 2 7% 5% 6% 6% 5% 7% 10% 42%	1731
August	1st to 10th	Night	7% 6% 2 7% 4 3 5% 5% 7% 9% 46%	1611
	11th to 20th	Night	6% 6% 2 4 4 3 4 4 6% 8% 53%	1722
	21st to end	Night	5% 5% 2 6% 4 4 4 4 7% 7% 50%	1980
September	1st to 10th	Night	4 5% 2 6% 3 3 4 5% 6% 8% 54%	1800
	11th to 20th	Night	4 4 2 6% 3 3 4 3 5% 6% 59%	1800
	21st to end	Night	3 5% 2 5% 3 3 4 4 4 8% 60%	2013
October	1st to 10th	Night	4 6% 2 5% 4 4 4 4 5% 7% 56%	2160
	11th to 20th	Night	1 5% 2 4 4 2 3 2 4 5% 67%	2160
	21st to end	Night	2 7% 2 8% 3 3 4 3 4 6% 58%	2376
November	1st to 10th	Night	4 2 7% 3 3 3 3 4 6% 64%	2377
	11th to 20th	Night	4 3 8% 5% 4 3 3 4 6% 59%	2470
	21st to end	Night	5% 3 10% 7% 4 3 3 5% 7% 54%	2626
December	1st to 10th	Night	3 3 11% 8% 5% 4 3 4 6% 53%	2660
	11th to 20th	Night	5% 3 9% 7% 6% 4 4 6% 7% 46%	3271
	21st to end	Night	4 3 12% 9% 7% 4 4 4 7% 45%	4873

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	36% 7% 14% 20% 18% 5%	2539
	11th to 20th	Day	46% 6% 15% 20% 10% 3	2773
	21st to end	Day	39% 5% 12% 24% 14% 6%	3146
February	1st to 10th	Day	45% 5% 15% 17% 13% 5%	1710
	11th to 20th	Day	39% 3 12% 22% 18% 7%	1776
	21st to end	Day	42% 3 10% 19% 18% 7%	1570
March	1st to 10th	Day	41% 4 7% 22% 19% 7%	3226
	11th to 20th	Day	43% 8% 10% 26% 10% 2	3490
	21st to end	Day	51% 4 10% 22% 11% 2	3969
April	1st to 10th	Day	40% 5% 12% 20% 17% 6%	2280
	11th to 20th	Day	50% 3 12% 17% 15% 3	2254
	21st to end	Day	50% 4 9% 25% 11% 1	2280
May	1st to 10th	Day	52% 5% 9% 17% 16% 2	3967
	11th to 20th	Day	38% 7% 10% 26% 17% 1	4392
	21st to end	Day	31% 7% 8% 23% 27% 5%	4825
June	1st to 10th	Day	33% 6% 12% 24% 18% 5%	2660
	11th to 20th	Day	33% 5% 8% 18% 23% 13%	2660
	21st to end	Day	33% 7% 7% 19% 24% 11%	2660
July	1st to 10th	Day	39% 8% 8% 14% 19% 12%	2591
	11th to 20th	Day	41% 9% 12% 17% 12% 8%	2518
	21st to end	Day	52% 8% 14% 14% 10% 2	2439
August	1st to 10th	Day	51% 8% 10% 13% 14% 4	2313
	11th to 20th	Day	43% 6% 8% 18% 18% 7%	2177
	21st to end	Day	45% 7% 8% 20% 16% 5%	2376
September	1st to 10th	Day	37% 5% 6% 15% 26% 11%	2160
	11th to 20th	Day	36% 4 9% 19% 24% 8%	2160
	21st to end	Day	32% 3 6% 27% 27% 6%	1942
October	1st to 10th	Day	36% 5% 7% 21% 25% 7%	1800
	11th to 20th	Day	25% 4 7% 29% 28% 8%	1800
	21st to end	Day	32% 3 11% 26% 21% 7%	1980
November	1st to 10th	Day	23% 5% 12% 24% 31% 5%	1683
	11th to 20th	Day	24% 3 16% 30% 21% 7%	1710
	21st to end	Day	30% 3 10% 28% 17% 11%	1549
December	1st to 10th	Day	37% 6% 16% 22% 15% 4	1520
	11th to 20th	Day	32% 8% 12% 28% 18% 2	1924
	21st to end	Day	35% 6% 12% 16% 22% 8%	2794
January	1st to 10th	Night	36% 5% 15% 25% 14% 5%	4417
	11th to 20th	Night	39% 6% 16% 23% 13% 4	4226
	21st to end	Night	35% 6% 14% 25% 15% 5%	4521
February	1st to 10th	Night	37% 4 16% 22% 16% 4	2470
	11th to 20th	Night	35% 4 14% 23% 19% 5%	2299
	21st to end	Night	34% 4 13% 22% 20% 7%	1884
March	1st to 10th	Night	34% 4 11% 24% 21% 7%	3624
	11th to 20th	Night	36% 4 13% 30% 13% 3	3490
	21st to end	Night	38% 7% 17% 26% 11% 1	3678
April	1st to 10th	Night	29% 5% 17% 24% 20% 4	1900
	11th to 20th	Night	36% 5% 14% 27% 16% 2	1877
	21st to end	Night	34% 5% 17% 29% 15% 1	1900
May	1st to 10th	Night	35% 7% 11% 26% 18% 3	2999
	11th to 20th	Night	35% 7% 13% 29% 15%	2518
	21st to end	Night	24% 5% 11% 30% 26% 3	2762
June	1st to 10th	Night	20% 6% 16% 30% 21% 6%	1520
	11th to 20th	Night	21% 5% 12% 22% 28% 13%	1520
	21st to end	Night	20% 6% 13% 23% 28% 11%	1520
July	1st to 10th	Night	30% 9% 13% 18% 19% 10%	1480
	11th to 20th	Night	24% 8% 19% 25% 17% 8%	1440
	21st to end	Night	32% 11% 25% 20% 9% 2	1635
August	1st to 10th	Night	34% 8% 20% 19% 14% 5%	1602
	11th to 20th	Night	28% 6% 17% 22% 21% 6%	1722
	21st to end	Night	30% 8% 14% 25% 19% 5%	1980
September	1st to 10th	Night	25% 7% 12% 20% 27% 9%	1800
	11th to 20th	Night	24% 5% 14% 23% 24% 10%	1800
	21st to end	Night	22% 5% 10% 34% 24% 4	2013
October	1st to 10th	Night	25% 6% 12% 26% 23% 9%	2160
	11th to 20th	Night	18% 4 11% 31% 28% 8%	2160
	21st to end	Night	26% 3 12% 29% 22% 7%	2376
November	1st to 10th	Night	20% 5% 13% 28% 27% 7%	2377
	11th to 20th	Night	22% 4 14% 31% 22% 6%	2470
	21st to end	Night	28% 4 10% 28% 21% 9%	2626
December	1st to 10th	Night	29% 6% 19% 24% 17% 6%	2660
	11th to 20th	Night	30% 7% 14% 22% 23% 4	3272
	21st to end	Night	33% 6% 12% 18% 20% 10%	4873

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	21% 27% 24% 19% 8% 2	270
	11th to 20th	Day	23% 30% 27% 16% 4	270
	21st to end	Day	14% 33% 31% 16% 6%	297
February	1st to 10th	Day	24% 41% 23% 10% 1 1	270
	11th to 20th	Day	29% 34% 24% 11% 1 1	270
	21st to end	Day	33% 33% 25% 8%	225
March	1st to 10th	Day	24% 32% 24% 17% 3	327
	11th to 20th	Day	19% 32% 31% 14% 4	460
	21st to end	Day	19% 41% 29% 8% 2	506
April	1st to 10th	Day	22% 37% 29% 9% 2 1	460
	11th to 20th	Day	28% 33% 26% 10% 2	452
	21st to end	Day	19% 39% 30% 9% 3 1	460
May	1st to 10th	Day	21% 36% 24% 14% 4 1	490
	11th to 20th	Day	15% 20% 34% 20% 10% 1	675
	21st to end	Day	15% 21% 30% 22% 10% 2	734
June	1st to 10th	Day	9% 20% 28% 24% 17% 2	680
	11th to 20th	Day	11% 21% 33% 21% 11% 1	680
	21st to end	Day	7% 21% 30% 24% 16% 2	680
July	1st to 10th	Day	10% 10% 26% 29% 22% 3	671
	11th to 20th	Day	8% 9% 24% 30% 23% 6%	645
	21st to end	Day	14% 11% 26% 27% 17% 5%	525
August	1st to 10th	Day	16% 14% 32% 24% 11% 3	447
	11th to 20th	Day	8% 12% 35% 26% 14% 5%	437
	21st to end	Day	11% 14% 30% 28% 13% 3	495
September	1st to 10th	Day	14% 16% 30% 23% 10% 6%	450
	11th to 20th	Day	12% 17% 37% 23% 10% 2	450
	21st to end	Day	13% 19% 29% 21% 14% 4	299
October	1st to 10th	Day	17% 20% 24% 20% 17% 3	270
	11th to 20th	Day	16% 31% 25% 18% 7% 3	270
	21st to end	Day	21% 29% 26% 15% 7% 2	297
November	1st to 10th	Day	22% 34% 23% 14% 7% 1	270
	11th to 20th	Day	18% 31% 30% 13% 6% 2	270
	21st to end	Day	12% 30% 35% 19% 4	270
December	1st to 10th	Day	22% 31% 25% 13% 8% 1	270
	11th to 20th	Day	19% 35% 28% 13% 5%	270
	21st to end	Day	22% 34% 26% 11% 6%	297
January	1st to 10th	Night	13% 23% 30% 22% 10% 2	950
	11th to 20th	Night	15% 23% 30% 23% 7% 1	824
	21st to end	Night	7% 22% 38% 25% 6% 1	836
February	1st to 10th	Night	10% 30% 35% 20% 5%	760
	11th to 20th	Night	9% 31% 33% 23% 4	744
	21st to end	Night	12% 27% 39% 19% 2	628
March	1st to 10th	Night	10% 24% 33% 26% 6% 1	760
	11th to 20th	Night	5% 18% 38% 29% 9% 1	760
	21st to end	Night	7% 26% 40% 23% 4	750
April	1st to 10th	Night	9% 25% 37% 24% 5%	570
	11th to 20th	Night	9% 25% 32% 26% 8%	563
	21st to end	Night	11% 18% 35% 28% 7% 1	570
May	1st to 10th	Night	10% 12% 40% 27% 10% 1	570
	11th to 20th	Night	8% 9% 31% 36% 15% 1	561
	21st to end	Night	8% 13% 27% 34% 16% 1	617
June	1st to 10th	Night	5% 7% 25% 40% 22% 1	570
	11th to 20th	Night	6% 11% 29% 40% 14% 1	570
	21st to end	Night	3 4 24% 42% 27% 1	570
July	1st to 10th	Night	6% 2 15% 41% 33% 3	555
	11th to 20th	Night	3 2 10% 40% 41% 4	540
	21st to end	Night	6% 3 9% 35% 43% 4	591
August	1st to 10th	Night	8% 1 12% 40% 37% 3	537
	11th to 20th	Night	6% 2 14% 40% 33% 4	534
	21st to end	Night	6% 2 14% 40% 36% 3	594
September	1st to 10th	Night	5% 3 16% 45% 27% 4	540
	11th to 20th	Night	6% 4 19% 44% 25% 3	540
	21st to end	Night	4 10% 23% 35% 23% 4	604
October	1st to 10th	Night	5% 16% 30% 29% 16% 4	720
	11th to 20th	Night	8% 20% 28% 29% 13% 2	720
	21st to end	Night	9% 18% 31% 29% 11% 2	792
November	1st to 10th	Night	7% 22% 32% 28% 10% 1	897
	11th to 20th	Night	11% 25% 33% 24% 6% 2	950
	21st to end	Night	8% 21% 33% 30% 8%	950
December	1st to 10th	Night	10% 28% 35% 21% 6%	950
	11th to 20th	Night	10% 27% 35% 20% 7% 1	950
	21st to end	Night	14% 25% 35% 21% 5% 1	1045

Page generated at 2024-07-13 08:19:54. Version ac07

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