Caxambas Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Caxambas Observatory clear sky chart from 2005-11-06 to 2026-07-16.

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	5% 4 2 6% 5% 5% 6% 5% 8% 11% 45%	137588
	Night	6% 5% 2 6% 5% 5% 5% 5% 7% 10% 43%	135111
Transparency	Day	20% 39% 15% 17% 7% 2	141319
	Night	22% 39% 13% 15% 8% 2	139452
Seeing	Day	6% 3 16% 28% 29% 16%	18048
	Night	7% 3 15% 31% 31% 12%	28123

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	5% 5% 2 4 3 3 3 3 6% 10% 57%	5258
	11th to 20th	Day	13% 8% 3 8% 5% 5% 5% 4 6% 9% 36%	5280
	21st to end	Day	10% 6% 2 7% 5% 5% 4 4 5% 8% 45%	6334
February	1st to 10th	Day	7% 5% 2 5% 3 4 4 4 6% 8% 52%	2100
	11th to 20th	Day	5% 4 1 3 2 3 3 4 5% 9% 62%	2048
	21st to end	Day	4 3 1 4 3 4 4 4 6% 8% 59%	1893
March	1st to 10th	Day	4 3 2 5% 4 4 5% 4 7% 9% 54%	5045
	11th to 20th	Day	2 2 1 3 2 2 3 3 6% 10% 66%	5090
	21st to end	Day	6% 3 1 4 3 3 4 3 6% 9% 56%	5586
April	1st to 10th	Day	2 2 1 3 3 3 4 3 6% 11% 60%	2310
	11th to 20th	Day	4 3 2 4 3 4 4 3 6% 9% 59%	2286
	21st to end	Day	4 3 1 4 3 3 3 3 6% 10% 59%	2492
May	1st to 10th	Day	3 2 1 2 2 2 4 3 6% 11% 65%	7076
	11th to 20th	Day	4 3 1 5% 4 4 5% 4 7% 9% 53%	7626
	21st to end	Day	3 3 1 4 3 4 4 4 7% 13% 55%	8391
June	1st to 10th	Day	11% 7% 3 7% 6% 6% 7% 6% 10% 11% 26%	2730
	11th to 20th	Day	7% 6% 3 6% 6% 6% 8% 6% 10% 15% 28%	2730
	21st to end	Day	4 6% 2 7% 7% 7% 8% 7% 11% 14% 27%	2730
July	1st to 10th	Day	4 5% 2 9% 8% 7% 9% 7% 11% 13% 25%	6030
	11th to 20th	Day	3 4 2 8% 7% 9% 9% 8% 12% 15% 25%	5965
	21st to end	Day	2 2 1 6% 6% 6% 8% 7% 11% 15% 35%	6424
August	1st to 10th	Day	4 5% 3 11% 7% 8% 9% 7% 10% 12% 25%	4210
	11th to 20th	Day	3 3 2 7% 6% 7% 10% 8% 12% 13% 28%	3652
	21st to end	Day	4 4 2 9% 7% 7% 9% 7% 10% 12% 28%	3949
September	1st to 10th	Day	5% 4 2 8% 7% 8% 8% 8% 9% 14% 27%	2200
	11th to 20th	Day	5% 6% 3 8% 6% 8% 8% 6% 9% 13% 29%	2200
	21st to end	Day	9% 6% 2 8% 7% 7% 9% 6% 10% 11% 26%	2200
October	1st to 10th	Day	6% 7% 3 8% 6% 6% 6% 5% 8% 11% 35%	2200
	11th to 20th	Day	6% 5% 2 7% 6% 5% 6% 5% 7% 11% 40%	2013
	21st to end	Day	7% 5% 2 6% 4 5% 4 4 6% 9% 47%	2200
November	1st to 10th	Day	5% 5% 2 6% 4 4 5% 4 6% 8% 50%	2057
	11th to 20th	Day	7% 3 2 5% 5% 5% 4 4 8% 8% 48%	2100
	21st to end	Day	5% 3 1 4 4 4 5% 4 7% 8% 53%	2100
December	1st to 10th	Day	4 3 1 3 2 2 3 3 6% 7% 64%	3055
	11th to 20th	Day	5% 5% 2 6% 5% 4 5% 4 7% 10% 48%	3463
	21st to end	Day	9% 6% 3 7% 5% 5% 6% 5% 8% 9% 37%	4565
January	1st to 10th	Night	4 4 2 5% 4 4 4 3 7% 10% 53%	7635
	11th to 20th	Night	13% 8% 3 9% 6% 5% 5% 4 6% 8% 33%	7680
	21st to end	Night	9% 6% 2 6% 4 4 4 4 7% 8% 46%	7830
February	1st to 10th	Night	7% 7% 2 6% 4 4 4 3 5% 8% 50%	2520
	11th to 20th	Night	5% 5% 2 4 3 4 4 3 5% 7% 57%	2458
	21st to end	Night	3 3 2 5% 3 3 3 3 6% 8% 61%	1911
March	1st to 10th	Night	4 5% 2 6% 5% 5% 5% 4 6% 7% 52%	5028
	11th to 20th	Night	5% 3 1 4 3 3 4 3 6% 8% 60%	5090
	21st to end	Night	5% 4 2 6% 4 5% 5% 4 6% 9% 50%	5588
April	1st to 10th	Night	4 4 1 4 4 2 4 4 7% 10% 56%	2310
	11th to 20th	Night	4 3 2 5% 3 4 4 4 6% 10% 56%	2283
	21st to end	Night	4 4 2 4 3 4 4 4 6% 9% 55%	2126
May	1st to 10th	Night	5% 3 1 5% 3 4 5% 4 7% 10% 54%	5817
	11th to 20th	Night	5% 3 2 5% 4 4 5% 4 6% 8% 53%	5234
	21st to end	Night	3 3 2 4 4 4 5% 5% 8% 12% 50%	5761
June	1st to 10th	Night	11% 9% 3 9% 5% 5% 6% 5% 9% 10% 28%	1890
	11th to 20th	Night	6% 7% 2 8% 5% 6% 7% 5% 9% 14% 31%	1890
	21st to end	Night	5% 5% 3 9% 7% 6% 8% 6% 9% 14% 29%	1890
July	1st to 10th	Night	3 5% 3 10% 9% 8% 9% 7% 10% 12% 24%	4148
	11th to 20th	Night	4 5% 3 10% 7% 7% 8% 8% 11% 12% 24%	4102
	21st to end	Night	3 4 2 7% 7% 7% 7% 6% 10% 13% 34%	4427
August	1st to 10th	Night	4 5% 3 9% 7% 7% 7% 7% 11% 13% 27%	2934
	11th to 20th	Night	5% 6% 3 9% 7% 8% 8% 6% 10% 14% 25%	3359
	21st to end	Night	5% 6% 2 9% 6% 7% 7% 7% 11% 14% 25%	3949
September	1st to 10th	Night	4 5% 3 8% 5% 6% 8% 8% 11% 15% 28%	2200
	11th to 20th	Night	6% 6% 3 8% 7% 7% 7% 6% 8% 13% 29%	2200
	21st to end	Night	7% 7% 3 9% 7% 7% 6% 7% 8% 11% 27%	2200
October	1st to 10th	Night	7% 6% 3 8% 6% 6% 6% 6% 8% 10% 35%	2200
	11th to 20th	Night	7% 6% 2 6% 5% 5% 5% 5% 6% 9% 44%	2385
	21st to end	Night	9% 6% 3 7% 5% 4 5% 3 6% 10% 43%	2640
November	1st to 10th	Night	6% 5% 2 5% 4 4 4 4 6% 8% 51%	2461
	11th to 20th	Night	6% 6% 3 5% 4 4 4 3 6% 10% 49%	2520
	21st to end	Night	6% 6% 2 4 5% 5% 5% 4 7% 9% 48%	2520
December	1st to 10th	Night	4 4 1 3 3 2 3 3 6% 9% 61%	4340
	11th to 20th	Night	8% 5% 2 5% 4 4 4 4 5% 8% 51%	4952
	21st to end	Night	8% 9% 3 8% 5% 6% 5% 5% 7% 10% 34%	6633

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	17% 22% 8% 32% 17% 4	5259
	11th to 20th	Day	37% 26% 10% 17% 7% 4	5280
	21st to end	Day	30% 25% 6% 23% 12% 5%	6334
February	1st to 10th	Day	8% 60% 7% 13% 7% 4	2100
	11th to 20th	Day	6% 58% 4 14% 13% 5%	2058
	21st to end	Day	9% 60% 7% 10% 11% 3	1893
March	1st to 10th	Day	19% 34% 11% 16% 17% 3	5045
	11th to 20th	Day	7% 31% 13% 20% 13% 15%	5090
	21st to end	Day	20% 30% 9% 22% 14% 6%	5586
April	1st to 10th	Day	7% 59% 7% 16% 8% 2	2310
	11th to 20th	Day	9% 61% 7% 8% 9% 6%	2286
	21st to end	Day	8% 59% 6% 14% 11% 1	2492
May	1st to 10th	Day	10% 24% 18% 33% 13% 1	7108
	11th to 20th	Day	18% 27% 15% 30% 8% 2	7630
	21st to end	Day	14% 26% 24% 29% 6%	8405
June	1st to 10th	Day	20% 63% 9% 7%	2730
	11th to 20th	Day	19% 65% 11% 5%	2730
	21st to end	Day	14% 63% 16% 6%	2730
July	1st to 10th	Day	33% 34% 27% 6%	5965
	11th to 20th	Day	32% 35% 25% 7%	5896
	21st to end	Day	22% 34% 27% 15% 1	6240
August	1st to 10th	Day	31% 43% 19% 6% 1	4197
	11th to 20th	Day	24% 44% 23% 9%	3688
	21st to end	Day	24% 44% 27% 4 1	3949
September	1st to 10th	Day	18% 64% 12% 6%	2200
	11th to 20th	Day	16% 62% 12% 8% 2	2200
	21st to end	Day	19% 62% 11% 5% 3	2200
October	1st to 10th	Day	35% 39% 13% 10% 2	3590
	11th to 20th	Day	22% 40% 14% 14% 9% 1	3253
	21st to end	Day	17% 38% 8% 23% 12% 3	3538
November	1st to 10th	Day	13% 56% 9% 14% 7% 2	2057
	11th to 20th	Day	16% 56% 6% 9% 9% 4	2100
	21st to end	Day	11% 56% 6% 11% 11% 4	2100
December	1st to 10th	Day	10% 36% 10% 21% 15% 8%	3055
	11th to 20th	Day	19% 36% 10% 17% 14% 5%	3460
	21st to end	Day	33% 31% 14% 15% 7%	4565
January	1st to 10th	Night	19% 24% 7% 28% 19% 3	7636
	11th to 20th	Night	40% 25% 12% 14% 7% 2	7680
	21st to end	Night	27% 25% 7% 24% 14% 3	7830
February	1st to 10th	Night	12% 60% 6% 13% 6% 3	2520
	11th to 20th	Night	8% 58% 4 12% 11% 6%	2459
	21st to end	Night	9% 59% 6% 9% 13% 4	1911
March	1st to 10th	Night	22% 34% 9% 14% 18% 4	5028
	11th to 20th	Night	14% 32% 13% 16% 15% 11%	5090
	21st to end	Night	23% 32% 10% 18% 13% 4	5588
April	1st to 10th	Night	10% 59% 6% 15% 7% 2	2310
	11th to 20th	Night	8% 61% 7% 9% 10% 5%	2283
	21st to end	Night	10% 61% 7% 13% 8% 1	2126
May	1st to 10th	Night	18% 28% 19% 27% 7% 1	5847
	11th to 20th	Night	20% 26% 15% 29% 8% 2	5235
	21st to end	Night	18% 28% 23% 22% 8%	5771
June	1st to 10th	Night	18% 63% 11% 7% 1	1890
	11th to 20th	Night	18% 64% 12% 6%	1890
	21st to end	Night	15% 63% 15% 6% 1	1890
July	1st to 10th	Night	36% 33% 27% 4	4105
	11th to 20th	Night	35% 36% 26% 4	4051
	21st to end	Night	27% 33% 26% 13% 2	4297
August	1st to 10th	Night	29% 43% 19% 8% 2	2923
	11th to 20th	Night	29% 45% 20% 5%	3389
	21st to end	Night	25% 47% 25% 3	3949
September	1st to 10th	Night	17% 64% 14% 6%	2200
	11th to 20th	Night	16% 62% 13% 7% 2	2200
	21st to end	Night	17% 65% 8% 8% 3	2200
October	1st to 10th	Night	37% 42% 13% 7% 2	3590
	11th to 20th	Night	26% 40% 13% 12% 9% 1	3884
	21st to end	Night	22% 37% 8% 19% 12% 3	4252
November	1st to 10th	Night	11% 57% 9% 13% 8% 1	2461
	11th to 20th	Night	16% 56% 6% 10% 9% 3	2520
	21st to end	Night	14% 57% 5% 9% 11% 4	2520
December	1st to 10th	Night	11% 36% 8% 27% 9% 9%	4340
	11th to 20th	Night	20% 33% 8% 19% 15% 5%	4954
	21st to end	Night	35% 32% 14% 11% 8% 1	6633

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	7% 6% 35% 33% 16% 3	330
	11th to 20th	Day	11% 11% 30% 30% 15% 3	330
	21st to end	Day	12% 10% 35% 33% 9% 1	363
February	1st to 10th	Day	6% 8% 24% 40% 18% 3	330
	11th to 20th	Day	4 5% 29% 38% 18% 4	330
	21st to end	Day	4 6% 25% 40% 24% 3	436
March	1st to 10th	Day	4 6% 29% 43% 16% 1	540
	11th to 20th	Day	6% 6% 28% 35% 23% 2	540
	21st to end	Day	4 3 26% 42% 20% 5%	594
April	1st to 10th	Day	3 6% 31% 39% 17% 3	540
	11th to 20th	Day	4 6% 27% 38% 24% 2	532
	21st to end	Day	4 2 23% 42% 25% 4	540
May	1st to 10th	Day	3 2 19% 40% 29% 7%	543
	11th to 20th	Day	8% 3 19% 33% 26% 10%	567
	21st to end	Day	8% 1 9% 30% 36% 16%	617
June	1st to 10th	Day	13% 3 8% 25% 35% 16%	570
	11th to 20th	Day	8% 2 7% 24% 32% 27%	570
	21st to end	Day	4 1 3 15% 37% 40%	570
July	1st to 10th	Day	3 1 2 12% 38% 44%	565
	11th to 20th	Day	5% 4 12% 35% 44%	544
	21st to end	Day	5% 1 4 15% 40% 35%	576
August	1st to 10th	Day	4 1 4 12% 42% 37%	526
	11th to 20th	Day	4 1 3 10% 41% 41%	519
	21st to end	Day	8% 1 6% 18% 34% 33%	583
September	1st to 10th	Day	6% 1 5% 14% 39% 36%	530
	11th to 20th	Day	5% 2 4 18% 38% 33%	530
	21st to end	Day	8% 2 5% 19% 36% 30%	530
October	1st to 10th	Day	9% 2 9% 30% 38% 12%	530
	11th to 20th	Day	9% 3 11% 29% 35% 12%	530
	21st to end	Day	8% 5% 16% 34% 28% 9%	583
November	1st to 10th	Day	6% 4 19% 31% 31% 8%	535
	11th to 20th	Day	9% 3 21% 33% 27% 6%	540
	21st to end	Day	4 2 23% 36% 30% 5%	540
December	1st to 10th	Day	7% 5% 24% 36% 23% 6%	352
	11th to 20th	Day	6% 7% 26% 32% 24% 5%	330
	21st to end	Day	7% 5% 25% 31% 25% 7%	363
January	1st to 10th	Night	7% 6% 24% 37% 24% 2	840
	11th to 20th	Night	10% 7% 26% 37% 20% 1	840
	21st to end	Night	9% 7% 29% 40% 15% 1	924
February	1st to 10th	Night	10% 5% 25% 40% 19% 2	840
	11th to 20th	Night	7% 5% 22% 41% 23% 2	823
	21st to end	Night	5% 3 18% 45% 27% 1	692
March	1st to 10th	Night	4 5% 25% 43% 22% 1	840
	11th to 20th	Night	8% 3 22% 40% 26% 1	840
	21st to end	Night	5% 4 23% 44% 23% 2	924
April	1st to 10th	Night	5% 5% 22% 40% 27% 2	840
	11th to 20th	Night	6% 3 23% 43% 23% 2	831
	21st to end	Night	7% 2 19% 43% 26% 2	840
May	1st to 10th	Night	3 1 13% 45% 33% 5%	837
	11th to 20th	Night	8% 2 13% 36% 36% 5%	621
	21st to end	Night	7% 1 7% 31% 43% 11%	683
June	1st to 10th	Night	15% 2 9% 17% 44% 12%	630
	11th to 20th	Night	7% 2 6% 14% 44% 27%	630
	21st to end	Night	6% 3 11% 41% 39%	630
July	1st to 10th	Night	4 1 2 9% 42% 41%	615
	11th to 20th	Night	5% 3 9% 40% 43%	597
	21st to end	Night	4 1 3 8% 40% 44%	657
August	1st to 10th	Night	6% 3 10% 44% 36%	597
	11th to 20th	Night	6% 1 2 8% 40% 45%	688
	21st to end	Night	10% 1 6% 16% 40% 27%	880
September	1st to 10th	Night	6% 1 4 13% 45% 32%	800
	11th to 20th	Night	9% 1 4 18% 39% 29%	800
	21st to end	Night	10% 2 9% 21% 36% 23%	800
October	1st to 10th	Night	10% 3 9% 34% 35% 10%	800
	11th to 20th	Night	8% 3 11% 33% 35% 10%	800
	21st to end	Night	11% 3 18% 36% 27% 6%	880
November	1st to 10th	Night	8% 3 22% 37% 26% 3	820
	11th to 20th	Night	8% 3 20% 36% 30% 4	840
	21st to end	Night	8% 3 21% 38% 28% 2	840
December	1st to 10th	Night	7% 3 18% 38% 31% 3	840
	11th to 20th	Night	9% 5% 22% 35% 27% 3	840
	21st to end	Night	7% 5% 21% 36% 28% 3	924

Page generated at 2026-07-13 03:14:51. Version ac07

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