Pedro-Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Pedro-Observatory clear sky chart from 2005-11-06 to 2026-02-01.

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	16% 10% 3 8% 5% 5% 5% 4 5% 7% 32%	127784
	Night	16% 11% 4 9% 5% 4 4 3 5% 6% 33%	124232
Transparency	Day	49% 6% 13% 20% 10% 1	131229
	Night	51% 6% 12% 19% 10% 1	128874
Seeing	Day	21% 16% 32% 21% 8% 2	15987
	Night	21% 11% 33% 26% 8% 1	25076

By Month

Percentage Cloud Cover NE (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	13% 20% 7% 13% 5% 4 3 3 5% 4 23%	3677
	11th to 20th	Day	11% 15% 6% 13% 6% 5% 4 4 4 5% 26%	3650
	21st to end	Day	9% 15% 6% 11% 6% 5% 5% 4 5% 5% 28%	4048
February	1st to 10th	Day	13% 15% 4 10% 8% 6% 4 3 4 5% 27%	1759
	11th to 20th	Day	11% 13% 5% 12% 7% 5% 5% 4 5% 7% 26%	1839
	21st to end	Day	17% 15% 4 10% 6% 4 5% 3 4 5% 27%	1650
March	1st to 10th	Day	18% 15% 5% 10% 6% 5% 4 3 4 4 25%	4476
	11th to 20th	Day	10% 13% 4 10% 5% 5% 5% 3 5% 7% 33%	4722
	21st to end	Day	18% 10% 4 9% 5% 5% 4 3 4 5% 34%	5959
April	1st to 10th	Day	20% 13% 3 7% 4 5% 4 3 4 5% 33%	2400
	11th to 20th	Day	21% 8% 2 6% 5% 4 4 3 5% 6% 35%	2374
	21st to end	Day	20% 10% 4 7% 5% 4 4 3 5% 5% 33%	2556
May	1st to 10th	Day	26% 10% 3 8% 5% 5% 5% 4 5% 6% 23%	6318
	11th to 20th	Day	21% 8% 3 7% 4 4 5% 3 6% 8% 30%	6318
	21st to end	Day	22% 8% 2 7% 4 5% 5% 4 6% 7% 31%	6949
June	1st to 10th	Day	21% 7% 3 6% 6% 5% 5% 4 6% 7% 30%	2800
	11th to 20th	Day	14% 6% 3 7% 5% 5% 5% 5% 7% 7% 35%	2800
	21st to end	Day	19% 8% 4 7% 5% 6% 5% 5% 6% 7% 29%	2800
July	1st to 10th	Day	14% 6% 2 8% 6% 6% 6% 5% 7% 8% 32%	6360
	11th to 20th	Day	12% 5% 2 6% 4 5% 6% 5% 7% 9% 39%	6360
	21st to end	Day	10% 5% 2 5% 4 4 5% 4 6% 9% 46%	6926
August	1st to 10th	Day	13% 5% 3 7% 5% 6% 6% 5% 7% 8% 34%	4563
	11th to 20th	Day	14% 6% 3 7% 4 5% 5% 4 7% 8% 37%	4149
	21st to end	Day	16% 4 2 6% 5% 4 5% 4 6% 8% 40%	4312
September	1st to 10th	Day	13% 5% 2 5% 4 4 4 4 6% 10% 43%	2400
	11th to 20th	Day	12% 4 2 6% 4 3 4 3 5% 6% 50%	2325
	21st to end	Day	17% 7% 1 6% 4 3 4 4 6% 7% 42%	2200
October	1st to 10th	Day	19% 6% 2 6% 4 4 4 3 5% 7% 38%	2048
	11th to 20th	Day	19% 9% 3 8% 6% 5% 5% 3 6% 6% 31%	1961
	21st to end	Day	22% 11% 3 7% 5% 4 4 3 5% 5% 31%	1980
November	1st to 10th	Day	14% 10% 3 7% 5% 5% 5% 4 5% 8% 34%	1851
	11th to 20th	Day	17% 12% 3 8% 5% 5% 4 4 5% 7% 31%	1780
	21st to end	Day	20% 13% 4 7% 6% 5% 4 4 5% 7% 25%	1680
December	1st to 10th	Day	18% 17% 6% 12% 6% 5% 4 4 4 4 20%	2680
	11th to 20th	Day	17% 16% 5% 9% 5% 4 4 3 5% 4 29%	3066
	21st to end	Day	22% 14% 4 9% 4 4 5% 3 4 4 26%	4048
January	1st to 10th	Night	12% 20% 7% 13% 6% 4 4 3 4 5% 22%	6489
	11th to 20th	Night	9% 14% 7% 17% 7% 6% 4 3 5% 5% 24%	6455
	21st to end	Night	10% 13% 5% 13% 7% 6% 5% 4 5% 5% 27%	7150
February	1st to 10th	Night	12% 13% 4 12% 7% 4 6% 3 6% 6% 27%	2641
	11th to 20th	Night	12% 11% 4 11% 5% 5% 5% 4 5% 5% 31%	2445
	21st to end	Night	14% 13% 4 9% 6% 5% 5% 3 4 5% 32%	1980
March	1st to 10th	Night	21% 14% 4 9% 5% 4 4 3 4 4 29%	5364
	11th to 20th	Night	11% 14% 4 7% 5% 4 5% 4 6% 8% 32%	5222
	21st to end	Night	15% 10% 4 9% 6% 5% 5% 3 5% 5% 34%	4972
April	1st to 10th	Night	23% 9% 3 7% 4 4 4 3 5% 6% 32%	2000
	11th to 20th	Night	19% 8% 2 7% 5% 4 4 4 5% 6% 37%	1975
	21st to end	Night	21% 8% 3 6% 3 4 5% 3 5% 6% 36%	1842
May	1st to 10th	Night	25% 9% 3 8% 5% 5% 4 3 5% 5% 26%	3651
	11th to 20th	Night	21% 8% 3 7% 4 4 4 3 6% 7% 33%	3575
	21st to end	Night	20% 9% 3 8% 5% 4 5% 3 6% 6% 31%	3926
June	1st to 10th	Night	20% 6% 3 7% 5% 4 4 4 6% 8% 34%	1600
	11th to 20th	Night	16% 8% 2 7% 3 5% 4 4 6% 7% 39%	1600
	21st to end	Night	19% 6% 2 6% 5% 4 5% 4 5% 7% 37%	1600
July	1st to 10th	Night	13% 7% 3 7% 5% 5% 6% 5% 7% 8% 35%	3600
	11th to 20th	Night	13% 6% 2 6% 4 4 4 4 5% 7% 44%	3600
	21st to end	Night	9% 5% 2 6% 4 5% 5% 4 6% 7% 47%	3926
August	1st to 10th	Night	13% 6% 3 7% 5% 5% 5% 4 6% 8% 40%	2586
	11th to 20th	Night	15% 7% 2 6% 4 4 4 3 5% 7% 43%	2863
	21st to end	Night	18% 5% 2 5% 4 4 4 3 5% 7% 42%	3586
September	1st to 10th	Night	10% 4 2 6% 5% 5% 4 4 6% 7% 47%	2000
	11th to 20th	Night	12% 5% 2 5% 4 3 4 3 4 7% 52%	2074
	21st to end	Night	17% 5% 2 6% 3 4 3 3 6% 7% 46%	2200
October	1st to 10th	Night	17% 6% 3 6% 4 4 4 3 4 6% 42%	2350
	11th to 20th	Night	19% 7% 3 6% 4 4 4 3 5% 6% 38%	2437
	21st to end	Night	21% 8% 2 8% 5% 4 4 3 5% 6% 32%	2860
November	1st to 10th	Night	18% 9% 3 8% 5% 5% 4 4 5% 7% 33%	2667
	11th to 20th	Night	17% 9% 3 8% 5% 4 4 3 5% 5% 35%	2838
	21st to end	Night	19% 14% 4 8% 5% 4 4 3 4 6% 29%	2940
December	1st to 10th	Night	16% 14% 5% 9% 6% 6% 5% 3 6% 6% 22%	4720
	11th to 20th	Night	22% 13% 4 8% 5% 4 4 3 4 4 28%	5348
	21st to end	Night	22% 17% 5% 8% 4 3 3 2 4 4 28%	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	63% 6% 10% 17% 4 1	3678
	11th to 20th	Day	58% 7% 10% 16% 7% 3	3680
	21st to end	Day	56% 6% 10% 15% 11% 1	4048
February	1st to 10th	Day	59% 5% 8% 17% 8% 2	1759
	11th to 20th	Day	58% 5% 12% 15% 10% 1	1848
	21st to end	Day	59% 4 9% 15% 10% 3	1650
March	1st to 10th	Day	63% 4 8% 11% 10% 3	4479
	11th to 20th	Day	49% 6% 18% 14% 11% 2	4722
	21st to end	Day	52% 5% 7% 16% 18% 2	5959
April	1st to 10th	Day	55% 4 8% 18% 12% 3	2400
	11th to 20th	Day	48% 6% 9% 22% 14% 2	2374
	21st to end	Day	53% 6% 9% 17% 13% 3	2556
May	1st to 10th	Day	60% 6% 8% 18% 7% 1	6329
	11th to 20th	Day	51% 7% 16% 16% 8% 2	6322
	21st to end	Day	50% 7% 12% 17% 12% 1	6949
June	1st to 10th	Day	51% 7% 11% 18% 12% 2	2800
	11th to 20th	Day	43% 8% 12% 22% 12% 3	2800
	21st to end	Day	53% 8% 12% 17% 9% 1	2800
July	1st to 10th	Day	46% 7% 14% 24% 8%	6290
	11th to 20th	Day	38% 8% 15% 29% 11%	6285
	21st to end	Day	33% 6% 17% 34% 10%	6728
August	1st to 10th	Day	44% 8% 19% 21% 8%	4549
	11th to 20th	Day	41% 9% 17% 26% 6%	4191
	21st to end	Day	41% 7% 17% 21% 13% 1	4312
September	1st to 10th	Day	36% 8% 16% 29% 13%	2400
	11th to 20th	Day	33% 6% 15% 32% 13% 1	2325
	21st to end	Day	41% 6% 15% 25% 12% 1	2200
October	1st to 10th	Day	43% 6% 14% 26% 10%	3334
	11th to 20th	Day	43% 6% 16% 27% 8%	3177
	21st to end	Day	43% 6% 21% 21% 10% 1	3180
November	1st to 10th	Day	48% 7% 14% 21% 9% 1	1851
	11th to 20th	Day	51% 7% 13% 17% 10% 1	1780
	21st to end	Day	58% 7% 15% 14% 6% 1	1680
December	1st to 10th	Day	68% 5% 9% 14% 4	2680
	11th to 20th	Day	58% 5% 10% 17% 10%	3066
	21st to end	Day	61% 5% 10% 15% 9%	4048
January	1st to 10th	Night	64% 6% 11% 14% 4	6489
	11th to 20th	Night	62% 6% 12% 15% 5% 1	6500
	21st to end	Night	57% 7% 10% 11% 14% 1	7150
February	1st to 10th	Night	57% 5% 10% 18% 8% 1	2641
	11th to 20th	Night	53% 6% 11% 20% 10% 1	2447
	21st to end	Night	53% 5% 10% 18% 13% 2	1980
March	1st to 10th	Night	58% 5% 8% 13% 12% 4	5374
	11th to 20th	Night	48% 7% 15% 16% 11% 3	5223
	21st to end	Night	52% 5% 7% 21% 12% 3	4972
April	1st to 10th	Night	52% 5% 8% 19% 14% 2	2000
	11th to 20th	Night	48% 5% 9% 21% 15% 2	1975
	21st to end	Night	49% 5% 8% 20% 14% 3	1842
May	1st to 10th	Night	58% 6% 10% 17% 7% 2	3657
	11th to 20th	Night	49% 7% 14% 18% 10% 2	3576
	21st to end	Night	51% 7% 11% 16% 13% 1	3927
June	1st to 10th	Night	48% 7% 12% 19% 14% 1	1600
	11th to 20th	Night	44% 7% 12% 21% 14% 3	1600
	21st to end	Night	47% 8% 12% 19% 14% 1	1600
July	1st to 10th	Night	44% 7% 18% 22% 9%	3560
	11th to 20th	Night	37% 6% 18% 31% 8%	3552
	21st to end	Night	34% 6% 17% 30% 13%	3809
August	1st to 10th	Night	42% 8% 14% 27% 9%	2576
	11th to 20th	Night	41% 5% 19% 26% 8%	2887
	21st to end	Night	41% 7% 15% 23% 13% 1	3586
September	1st to 10th	Night	33% 8% 16% 27% 15% 1	2000
	11th to 20th	Night	33% 5% 15% 33% 12% 1	2074
	21st to end	Night	38% 6% 12% 28% 15%	2200
October	1st to 10th	Night	43% 5% 14% 25% 12% 1	3844
	11th to 20th	Night	41% 6% 13% 29% 11%	3960
	21st to end	Night	43% 5% 19% 19% 13% 2	4610
November	1st to 10th	Night	49% 7% 13% 22% 8% 1	2667
	11th to 20th	Night	50% 5% 13% 20% 10% 2	2838
	21st to end	Night	57% 5% 12% 18% 7% 1	2940
December	1st to 10th	Night	62% 6% 13% 15% 5%	4720
	11th to 20th	Night	59% 5% 9% 16% 11% 1	5348
	21st to end	Night	61% 4 8% 15% 13%	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	19% 20% 38% 20% 4	220
	11th to 20th	Day	26% 20% 36% 14% 4	220
	21st to end	Day	17% 21% 36% 21% 4 1	242
February	1st to 10th	Day	26% 26% 37% 9% 1	280
	11th to 20th	Day	21% 24% 41% 12% 2	386
	21st to end	Day	27% 19% 34% 18% 2	414
March	1st to 10th	Day	27% 18% 33% 18% 4	500
	11th to 20th	Day	21% 23% 35% 17% 3 1	500
	21st to end	Day	28% 20% 30% 15% 7% 1	550
April	1st to 10th	Day	27% 19% 32% 16% 6% 1	500
	11th to 20th	Day	31% 20% 26% 15% 7% 1	492
	21st to end	Day	27% 21% 31% 16% 4 1	500
May	1st to 10th	Day	25% 16% 36% 16% 5% 1	503
	11th to 20th	Day	21% 16% 34% 21% 7% 1	527
	21st to end	Day	22% 19% 30% 22% 6% 1	573
June	1st to 10th	Day	22% 17% 32% 21% 7% 1	530
	11th to 20th	Day	18% 15% 32% 25% 9% 2	530
	21st to end	Day	26% 11% 32% 21% 8% 2	530
July	1st to 10th	Day	12% 11% 35% 27% 12% 3	525
	11th to 20th	Day	14% 11% 34% 28% 11% 2	524
	21st to end	Day	13% 10% 33% 30% 13% 2	576
August	1st to 10th	Day	13% 9% 28% 33% 15% 2	526
	11th to 20th	Day	12% 7% 27% 31% 16% 7%	519
	21st to end	Day	17% 11% 26% 26% 14% 6%	583
September	1st to 10th	Day	16% 7% 35% 23% 13% 6%	530
	11th to 20th	Day	11% 9% 25% 29% 19% 7%	530
	21st to end	Day	20% 12% 27% 25% 12% 4	530
October	1st to 10th	Day	22% 13% 30% 21% 12% 2	530
	11th to 20th	Day	20% 16% 34% 21% 7% 1	508
	21st to end	Day	28% 16% 31% 20% 5%	462
November	1st to 10th	Day	26% 20% 28% 19% 6%	425
	11th to 20th	Day	23% 19% 34% 18% 6%	320
	21st to end	Day	30% 20% 31% 14% 4	220
December	1st to 10th	Day	25% 18% 28% 22% 6% 1	220
	11th to 20th	Day	25% 22% 39% 13% 1 1	220
	21st to end	Day	28% 24% 27% 13% 7% 1	242
January	1st to 10th	Night	22% 14% 36% 23% 4	840
	11th to 20th	Night	22% 15% 34% 23% 5%	840
	21st to end	Night	15% 13% 41% 24% 6% 1	924
February	1st to 10th	Night	18% 13% 43% 22% 3	801
	11th to 20th	Night	20% 15% 42% 19% 4	783
	21st to end	Night	22% 13% 35% 27% 3	660
March	1st to 10th	Night	24% 15% 34% 23% 4	800
	11th to 20th	Night	22% 16% 36% 21% 6%	800
	21st to end	Night	20% 14% 36% 24% 5%	880
April	1st to 10th	Night	27% 14% 33% 22% 4	800
	11th to 20th	Night	24% 13% 35% 24% 4 1	791
	21st to end	Night	28% 12% 33% 20% 6%	642
May	1st to 10th	Night	23% 13% 33% 24% 5% 2	431
	11th to 20th	Night	22% 11% 29% 29% 8%	394
	21st to end	Night	20% 8% 40% 24% 8%	433
June	1st to 10th	Night	24% 9% 32% 28% 8%	400
	11th to 20th	Night	21% 7% 31% 31% 11%	400
	21st to end	Night	22% 7% 27% 31% 13% 1	400
July	1st to 10th	Night	10% 6% 36% 35% 12% 1	390
	11th to 20th	Night	11% 5% 25% 44% 14%	388
	21st to end	Night	13% 4 27% 43% 12% 1	438
August	1st to 10th	Night	15% 4 19% 44% 17% 1	398
	11th to 20th	Night	14% 4 25% 32% 23% 2	579
	21st to end	Night	16% 5% 26% 34% 17% 2	880
September	1st to 10th	Night	13% 6% 28% 38% 14% 1	800
	11th to 20th	Night	15% 5% 24% 34% 21% 2	800
	21st to end	Night	19% 7% 27% 31% 15% 2	800
October	1st to 10th	Night	20% 10% 29% 30% 11% 1	800
	11th to 20th	Night	22% 9% 34% 26% 8% 1	800
	21st to end	Night	26% 11% 33% 25% 5%	880
November	1st to 10th	Night	23% 14% 32% 25% 6%	820
	11th to 20th	Night	23% 12% 34% 22% 8% 1	840
	21st to end	Night	27% 16% 32% 18% 6% 1	840
December	1st to 10th	Night	25% 13% 34% 21% 6%	840
	11th to 20th	Night	26% 16% 33% 20% 4 1	840
	21st to end	Night	31% 15% 31% 18% 4	924

Page generated at 2026-01-29 01:21:45. Version ac07

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