Don Pedro Reservoir
Clear Sky Chart
History

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

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	7% 3 1 3 2 2 2 2 3 5% 69%	135705
	Night	9% 4 1 3 2 2 3 2 3 5% 64%	133100
Transparency	Day	20% 3 7% 17% 26% 27%	130687
	Night	24% 3 8% 19% 24% 22%	129098
Seeing	Day	10% 8% 26% 34% 17% 5%	16697
	Night	11% 2 14% 38% 28% 6%	26165

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	15% 6% 2 4 3 3 3 2 4 6% 52%	3647
	11th to 20th	Day	14% 5% 2 6% 3 4 3 2 2 4 54%	3980
	21st to end	Day	16% 7% 2 5% 4 3 4 3 5% 7% 44%	4510
February	1st to 10th	Day	20% 7% 1 4 3 3 3 3 4 4 48%	1812
	11th to 20th	Day	15% 6% 3 4 3 3 4 3 5% 7% 47%	1950
	21st to end	Day	17% 6% 2 5% 4 4 4 3 4 5% 45%	1650
March	1st to 10th	Day	16% 9% 3 6% 4 4 5% 4 7% 7% 34%	4552
	11th to 20th	Day	17% 6% 1 4 3 3 3 3 5% 6% 49%	5000
	21st to end	Day	16% 6% 2 6% 3 4 5% 3 6% 8% 41%	5783
April	1st to 10th	Day	13% 6% 1 4 3 3 4 4 4 6% 52%	2400
	11th to 20th	Day	11% 4 2 3 3 3 3 4 5% 7% 56%	2369
	21st to end	Day	8% 4 2 3 3 2 3 2 4 5% 63%	2400
May	1st to 10th	Day	5% 3 1 2 1 2 2 2 4 4 74%	5518
	11th to 20th	Day	2 2 1 2 2 2 2 2 3 5% 78%	6101
	21st to end	Day	3 1 1 2 1 1 2 1 3 3 82%	6902
June	1st to 10th	Day	3 2 1 3 2 2 2 3 4 6% 70%	2800
	11th to 20th	Day	1 1 2 1 1 2 2 2 4 84%	2800
	21st to end	Day	2 2 1 1 1 1 1 1 2 3 85%	2800
July	1st to 10th	Day	1 1 1 1 1 94%	6319
	11th to 20th	Day	1 1 1 1 1 2 1 2 2 88%	6320
	21st to end	Day	1 1 1 1 1 1 2 3 88%	6454
August	1st to 10th	Day	1 1 1 1 1 1 1 2 2 88%	5675
	11th to 20th	Day	1 1 1 1 2 93%	5364
	21st to end	Day	1 1 1 2 1 1 2 1 3 3 83%	5984
September	1st to 10th	Day	2 1 1 1 1 1 1 2 3 88%	2400
	11th to 20th	Day	3 2 1 1 2 2 2 2 3 4 79%	2385
	21st to end	Day	3 2 1 2 1 2 2 1 3 3 81%	2200
October	1st to 10th	Day	3 2 1 2 2 2 2 2 4 5% 76%	3288
	11th to 20th	Day	4 2 1 2 1 2 2 2 2 3 79%	3261
	21st to end	Day	5% 3 1 3 2 3 3 3 5% 6% 67%	3558
November	1st to 10th	Day	9% 4 2 4 3 3 4 3 5% 6% 58%	1869
	11th to 20th	Day	11% 5% 1 4 3 3 3 3 4 6% 55%	1890
	21st to end	Day	13% 4 1 3 3 2 3 3 5% 7% 56%	1864
December	1st to 10th	Day	8% 3 1 3 3 4 3 3 4 7% 60%	2700
	11th to 20th	Day	24% 7% 2 6% 3 3 3 2 4 7% 38%	3108
	21st to end	Day	19% 7% 3 6% 4 4 4 4 6% 8% 33%	4092
January	1st to 10th	Night	12% 6% 2 4 3 3 3 3 6% 8% 51%	6320
	11th to 20th	Night	15% 6% 2 4 3 3 3 2 4 5% 54%	5992
	21st to end	Night	17% 6% 2 5% 3 3 4 3 4 6% 48%	6468
February	1st to 10th	Night	18% 6% 2 5% 3 3 3 2 4 5% 50%	2585
	11th to 20th	Night	16% 6% 1 4 2 3 2 4 4 7% 50%	2338
	21st to end	Night	17% 9% 2 4 3 3 3 2 3 6% 50%	1980
March	1st to 10th	Night	19% 9% 2 5% 4 3 4 4 5% 6% 40%	5340
	11th to 20th	Night	18% 8% 2 5% 3 3 3 2 3 5% 50%	5000
	21st to end	Night	21% 6% 1 5% 3 3 3 3 5% 7% 43%	5192
April	1st to 10th	Night	13% 4 1 4 3 4 4 3 4 7% 54%	2000
	11th to 20th	Night	9% 4 1 4 2 3 3 3 4 5% 61%	1979
	21st to end	Night	7% 4 1 3 2 3 3 3 4 7% 64%	2000
May	1st to 10th	Night	3 3 1 2 2 2 2 2 3 5% 76%	4475
	11th to 20th	Night	2 2 1 2 2 1 2 2 3 5% 79%	3782
	21st to end	Night	2 2 1 1 2 1 2 1 2 3 84%	3972
June	1st to 10th	Night	4 3 1 2 1 2 2 2 4 6% 74%	1600
	11th to 20th	Night	1 1 2 2 3 4 86%	1600
	21st to end	Night	1 2 1 1 1 1 1 2 2 3 85%	1600
July	1st to 10th	Night	1 1 1 1 96%	3640
	11th to 20th	Night	2 1 1 2 1 1 2 1 1 2 86%	3640
	21st to end	Night	1 1 1 1 1 2 2 2 3 84%	4414
August	1st to 10th	Night	1 1 1 1 1 1 1 2 3 86%	4139
	11th to 20th	Night	1 1 1 1 1 2 2 92%	4506
	21st to end	Night	2 1 1 2 1 1 2 2 2 3 84%	5015
September	1st to 10th	Night	1 1 1 1 1 1 2 2 90%	2000
	11th to 20th	Night	3 1 1 1 1 2 1 2 4 82%	2013
	21st to end	Night	2 1 1 2 1 1 1 2 3 4 82%	2200
October	1st to 10th	Night	3 1 2 2 2 2 2 3 4 80%	3909
	11th to 20th	Night	3 1 1 2 1 1 2 2 3 4 81%	3897
	21st to end	Night	6% 2 1 3 2 2 2 2 4 5% 70%	4253
November	1st to 10th	Night	10% 4 1 3 2 2 2 2 4 7% 63%	2648
	11th to 20th	Night	10% 4 2 4 2 3 4 2 5% 6% 57%	2730
	21st to end	Night	11% 4 1 3 3 3 3 3 4 7% 57%	2751
December	1st to 10th	Night	9% 3 1 3 2 2 4 3 5% 5% 63%	4700
	11th to 20th	Night	22% 7% 2 5% 3 3 4 4 6% 9% 36%	5316
	21st to end	Night	19% 8% 3 8% 6% 5% 5% 4 5% 6% 31%	7106

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	34% 4 17% 24% 15% 5%	3647
	11th to 20th	Day	35% 5% 6% 14% 24% 16%	3980
	21st to end	Day	38% 7% 8% 15% 26% 6%	4510
February	1st to 10th	Day	40% 3 7% 25% 16% 9%	1812
	11th to 20th	Day	36% 4 9% 23% 23% 6%	1960
	21st to end	Day	40% 3 10% 23% 20% 5%	1650
March	1st to 10th	Day	44% 7% 12% 17% 18% 3	4552
	11th to 20th	Day	34% 5% 15% 28% 11% 7%	5000
	21st to end	Day	39% 5% 17% 24% 13% 2	5783
April	1st to 10th	Day	33% 4 12% 26% 18% 8%	2400
	11th to 20th	Day	28% 3 13% 29% 19% 7%	2372
	21st to end	Day	24% 3 10% 31% 27% 5%	2400
May	1st to 10th	Day	15% 2 6% 27% 35% 14%	5518
	11th to 20th	Day	11% 2 5% 28% 40% 13%	6104
	21st to end	Day	10% 2 6% 20% 51% 12%	6904
June	1st to 10th	Day	16% 3 9% 23% 33% 17%	2800
	11th to 20th	Day	7% 1 5% 19% 35% 33%	2800
	21st to end	Day	9% 1 1 9% 30% 50%	2800
July	1st to 10th	Day	2 1 1 3 15% 78%	6251
	11th to 20th	Day	5% 1 1 4 11% 78%	6245
	21st to end	Day	5% 1 1 7% 35% 51%	6267
August	1st to 10th	Day	8% 1 1 6% 21% 62%	4126
	11th to 20th	Day	4 1 1 6% 24% 65%	3880
	21st to end	Day	6% 1 2 5% 31% 54%	4311
September	1st to 10th	Day	6% 1 2 8% 28% 56%	2400
	11th to 20th	Day	11% 2 3 20% 38% 25%	2385
	21st to end	Day	11% 1 3 17% 36% 32%	2200
October	1st to 10th	Day	13% 2 4 10% 20% 51%	3288
	11th to 20th	Day	13% 2 4 18% 42% 21%	3261
	21st to end	Day	19% 2 5% 15% 39% 18%	3558
November	1st to 10th	Day	27% 3 10% 24% 24% 13%	1869
	11th to 20th	Day	30% 4 10% 23% 25% 8%	1890
	21st to end	Day	29% 4 9% 22% 26% 12%	1864
December	1st to 10th	Day	25% 4 8% 27% 25% 11%	2700
	11th to 20th	Day	48% 3 9% 16% 18% 7%	3108
	21st to end	Day	46% 7% 15% 21% 7% 4	4092
January	1st to 10th	Night	30% 5% 19% 25% 15% 5%	6320
	11th to 20th	Night	34% 4 9% 15% 27% 11%	5992
	21st to end	Night	37% 4 8% 18% 23% 9%	6468
February	1st to 10th	Night	38% 3 8% 21% 20% 10%	2585
	11th to 20th	Night	33% 3 10% 25% 21% 7%	2339
	21st to end	Night	38% 3 11% 24% 19% 6%	1980
March	1st to 10th	Night	45% 4 10% 18% 18% 5%	5340
	11th to 20th	Night	39% 4 11% 27% 12% 8%	5000
	21st to end	Night	40% 4 16% 24% 14% 3	5192
April	1st to 10th	Night	31% 4 15% 24% 20% 7%	2000
	11th to 20th	Night	26% 4 13% 27% 21% 9%	1979
	21st to end	Night	22% 4 12% 32% 24% 6%	2000
May	1st to 10th	Night	13% 3 9% 29% 32% 14%	4472
	11th to 20th	Night	10% 2 7% 29% 39% 13%	3782
	21st to end	Night	9% 2 5% 27% 50% 7%	3972
June	1st to 10th	Night	14% 3 12% 25% 32% 15%	1600
	11th to 20th	Night	4 2 6% 21% 35% 32%	1600
	21st to end	Night	8% 1 2 10% 31% 49%	1600
July	1st to 10th	Night	2 3 16% 79%	3600
	11th to 20th	Night	8% 1 2 3 13% 73%	3592
	21st to end	Night	7% 2 2 7% 33% 50%	4289
August	1st to 10th	Night	9% 1 2 7% 21% 60%	3009
	11th to 20th	Night	5% 1 1 6% 25% 62%	3256
	21st to end	Night	7% 1 1 8% 30% 53%	3608
September	1st to 10th	Night	5% 1 2 7% 28% 57%	2000
	11th to 20th	Night	10% 2 4 18% 39% 28%	2013
	21st to end	Night	10% 2 2 17% 38% 31%	2200
October	1st to 10th	Night	11% 2 4 11% 19% 53%	3909
	11th to 20th	Night	10% 2 3 24% 38% 23%	3897
	21st to end	Night	18% 3 4 17% 36% 21%	4253
November	1st to 10th	Night	24% 2 9% 25% 21% 18%	2648
	11th to 20th	Night	27% 3 9% 24% 25% 12%	2730
	21st to end	Night	28% 3 7% 23% 29% 10%	2751
December	1st to 10th	Night	24% 3 7% 28% 26% 12%	4700
	11th to 20th	Night	44% 5% 11% 16% 20% 5%	5316
	21st to end	Night	51% 8% 12% 19% 7% 4	7106

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	30% 6% 22% 25% 16%	202
	11th to 20th	Day	20% 4 20% 35% 16% 5%	345
	21st to end	Day	18% 7% 23% 29% 20% 4	440
February	1st to 10th	Day	26% 9% 21% 23% 18% 3	407
	11th to 20th	Day	20% 8% 33% 25% 13% 2	495
	21st to end	Day	18% 11% 29% 33% 9% 1	414
March	1st to 10th	Day	25% 12% 29% 27% 7% 1	500
	11th to 20th	Day	22% 14% 27% 22% 13% 2	500
	21st to end	Day	19% 11% 34% 25% 10% 1	550
April	1st to 10th	Day	18% 15% 28% 25% 13% 2	500
	11th to 20th	Day	15% 16% 30% 28% 10% 2	492
	21st to end	Day	8% 14% 33% 27% 15% 4	500
May	1st to 10th	Day	9% 17% 32% 28% 10% 4	503
	11th to 20th	Day	9% 14% 28% 28% 16% 5%	528
	21st to end	Day	8% 10% 27% 32% 16% 6%	573
June	1st to 10th	Day	4 9% 29% 36% 15% 7%	530
	11th to 20th	Day	3 11% 31% 36% 13% 6%	530
	21st to end	Day	3 6% 26% 38% 19% 7%	530
July	1st to 10th	Day	3 25% 47% 17% 7%	526
	11th to 20th	Day	2 18% 49% 22% 10%	524
	21st to end	Day	1 2 19% 48% 19% 11%	575
August	1st to 10th	Day	3 4 22% 46% 17% 8%	527
	11th to 20th	Day	1 3 28% 40% 19% 10%	517
	21st to end	Day	1 3 22% 44% 22% 8%	583
September	1st to 10th	Day	2 3 24% 44% 22% 5%	530
	11th to 20th	Day	6% 7% 28% 35% 21% 4	530
	21st to end	Day	3 7% 25% 43% 20% 2	530
October	1st to 10th	Day	4 10% 26% 34% 23% 3	530
	11th to 20th	Day	8% 7% 22% 34% 24% 4	530
	21st to end	Day	8% 7% 23% 35% 23% 3	583
November	1st to 10th	Day	10% 8% 21% 31% 26% 5%	345
	11th to 20th	Day	14% 7% 22% 28% 23% 5%	330
	21st to end	Day	14% 5% 22% 32% 21% 5%	316
December	1st to 10th	Day	14% 5% 22% 33% 18% 8%	220
	11th to 20th	Day	20% 5% 22% 26% 24% 3	220
	21st to end	Day	24% 7% 25% 24% 16% 4	242
January	1st to 10th	Night	20% 2 19% 31% 19% 9%	804
	11th to 20th	Night	15% 4 16% 37% 22% 6%	800
	21st to end	Night	20% 3 15% 35% 21% 7%	880
February	1st to 10th	Night	21% 3 18% 34% 20% 5%	800
	11th to 20th	Night	19% 4 17% 33% 19% 8%	784
	21st to end	Night	22% 3 15% 42% 15% 3	660
March	1st to 10th	Night	23% 5% 18% 34% 17% 4	800
	11th to 20th	Night	20% 5% 17% 30% 22% 7%	800
	21st to end	Night	19% 3 17% 39% 20% 2	880
April	1st to 10th	Night	14% 4 17% 41% 22% 3	800
	11th to 20th	Night	12% 4 20% 37% 21% 6%	791
	21st to end	Night	8% 4 17% 40% 25% 6%	800
May	1st to 10th	Night	7% 4 21% 42% 21% 6%	767
	11th to 20th	Night	5% 3 20% 38% 31% 3	469
	21st to end	Night	4 2 14% 43% 33% 4	433
June	1st to 10th	Night	6% 2 13% 42% 32% 5%	400
	11th to 20th	Night	1 1 14% 46% 35% 4	400
	21st to end	Night	1 1 10% 45% 40% 4	400
July	1st to 10th	Night	6% 47% 43% 5%	390
	11th to 20th	Night	2 3 43% 45% 6%	388
	21st to end	Night	2 3 33% 51% 10%	625
August	1st to 10th	Night	2 6% 37% 45% 10%	638
	11th to 20th	Night	1 1 7% 43% 41% 7%	792
	21st to end	Night	2 5% 39% 47% 7%	880
September	1st to 10th	Night	1 6% 43% 41% 8%	800
	11th to 20th	Night	3 1 10% 42% 35% 9%	800
	21st to end	Night	2 1 10% 42% 36% 9%	800
October	1st to 10th	Night	5% 1 12% 46% 30% 7%	800
	11th to 20th	Night	6% 3 12% 38% 33% 9%	800
	21st to end	Night	5% 1 15% 37% 29% 13%	880
November	1st to 10th	Night	12% 3 9% 37% 29% 10%	820
	11th to 20th	Night	12% 3 16% 37% 26% 7%	840
	21st to end	Night	13% 2 15% 39% 23% 7%	840
December	1st to 10th	Night	17% 2 14% 40% 20% 6%	840
	11th to 20th	Night	24% 2 12% 37% 20% 4	840
	21st to end	Night	23% 6% 18% 32% 17% 3	924

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