Cordova
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Cordova clear sky chart from 2005-11-06 to 2025-04-11.

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	10% 7% 2 6% 4 4 4 3 5% 7% 47%	113842
	Night	9% 6% 2 6% 4 3 4 3 5% 7% 50%	114638
Transparency	Day	36% 4 13% 26% 18% 3	117527
	Night	33% 3 12% 27% 20% 4	119074
Seeing	Day	14% 7% 31% 30% 15% 3	16242
	Night	13% 8% 34% 34% 11% 1	26322

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	10% 11% 5% 14% 7% 5% 5% 3 4 6% 30%	4077
	11th to 20th	Day	5% 10% 4 7% 5% 5% 5% 4 4 6% 46%	4080
	21st to end	Day	5% 8% 4 11% 5% 5% 4 3 5% 5% 44%	4488
February	1st to 10th	Day	9% 11% 4 9% 5% 4 3 3 7% 8% 36%	1800
	11th to 20th	Day	8% 10% 3 8% 4 4 4 4 4 8% 43%	1875
	21st to end	Day	8% 8% 2 7% 4 4 4 3 4 7% 48%	1650
March	1st to 10th	Day	12% 8% 3 5% 3 2 3 2 3 4 55%	4754
	11th to 20th	Day	11% 6% 2 5% 3 4 4 3 5% 6% 52%	4980
	21st to end	Day	15% 11% 3 8% 4 3 4 3 5% 8% 36%	5462
April	1st to 10th	Day	14% 7% 2 6% 4 4 3 3 4 6% 48%	2200
	11th to 20th	Day	14% 7% 3 6% 5% 4 4 3 5% 7% 43%	2433
	21st to end	Day	20% 7% 2 6% 4 4 4 3 6% 7% 39%	2470
May	1st to 10th	Day	15% 7% 2 6% 4 4 4 3 6% 8% 40%	4082
	11th to 20th	Day	14% 7% 3 6% 4 4 3 3 5% 6% 46%	4082
	21st to end	Day	14% 5% 2 7% 5% 4 4 4 5% 7% 42%	4477
June	1st to 10th	Day	7% 3 2 5% 3 4 4 4 6% 9% 54%	2470
	11th to 20th	Day	10% 5% 2 5% 4 4 4 4 6% 8% 49%	2471
	21st to end	Day	6% 4 2 5% 5% 4 5% 4 7% 8% 50%	2660
July	1st to 10th	Day	11% 6% 2 6% 4 4 4 4 6% 8% 46%	4275
	11th to 20th	Day	7% 4 2 5% 4 4 4 4 6% 8% 52%	4120
	21st to end	Day	5% 3 2 4 4 4 4 5% 7% 9% 53%	4465
August	1st to 10th	Day	8% 5% 2 6% 5% 4 5% 5% 6% 10% 45%	4104
	11th to 20th	Day	13% 6% 2 6% 4 4 4 4 6% 8% 45%	4041
	21st to end	Day	6% 4 2 4 3 4 4 4 6% 7% 55%	4532
September	1st to 10th	Day	13% 4 2 4 3 3 4 3 5% 6% 55%	2113
	11th to 20th	Day	9% 4 2 5% 3 3 4 3 3 8% 56%	2090
	21st to end	Day	9% 4 1 4 2 3 3 3 5% 6% 60%	2090
October	1st to 10th	Day	13% 6% 2 5% 3 3 3 2 4 5% 54%	2004
	11th to 20th	Day	10% 5% 2 5% 2 2 2 3 4 5% 60%	1900
	21st to end	Day	13% 7% 2 6% 3 3 2 3 3 6% 52%	2047
November	1st to 10th	Day	9% 6% 1 5% 4 4 3 2 4 7% 55%	1763
	11th to 20th	Day	8% 7% 2 5% 4 3 3 3 4 6% 53%	1800
	21st to end	Day	12% 9% 2 5% 4 3 4 2 5% 7% 48%	1745
December	1st to 10th	Day	5% 5% 2 5% 4 3 4 4 5% 7% 56%	2610
	11th to 20th	Day	7% 8% 3 8% 5% 4 4 3 5% 7% 46%	3144
	21st to end	Day	15% 10% 4 12% 5% 4 4 3 4 5% 34%	4488
January	1st to 10th	Night	9% 11% 5% 15% 5% 4 5% 4 5% 6% 32%	5888
	11th to 20th	Night	6% 7% 2 6% 4 5% 6% 4 6% 6% 48%	5900
	21st to end	Night	8% 9% 4 11% 4 3 3 3 4 5% 46%	6490
February	1st to 10th	Night	11% 11% 4 6% 5% 4 5% 4 5% 6% 41%	2600
	11th to 20th	Night	8% 8% 3 7% 5% 5% 5% 4 7% 7% 42%	2430
	21st to end	Night	8% 8% 2 5% 4 5% 2 3 4 6% 54%	1980
March	1st to 10th	Night	11% 5% 2 5% 3 3 4 3 4 5% 55%	5107
	11th to 20th	Night	10% 5% 2 4 3 3 3 3 4 6% 59%	4980
	21st to end	Night	13% 9% 2 7% 4 4 4 4 6% 8% 39%	5467
April	1st to 10th	Night	12% 7% 2 5% 4 4 4 3 5% 6% 49%	2199
	11th to 20th	Night	13% 7% 2 5% 4 3 3 3 6% 7% 47%	1700
	21st to end	Night	15% 6% 3 5% 4 4 3 3 5% 7% 46%	1710
May	1st to 10th	Night	21% 7% 2 4 3 3 3 3 4 6% 46%	2823
	11th to 20th	Night	11% 6% 2 6% 3 3 4 3 5% 7% 50%	2823
	21st to end	Night	15% 6% 2 5% 3 4 3 3 6% 8% 44%	3090
June	1st to 10th	Night	5% 5% 1 4 4 4 4 5% 5% 9% 56%	1710
	11th to 20th	Night	8% 4 2 5% 3 3 3 4 6% 8% 55%	1699
	21st to end	Night	4 4 2 4 3 3 4 4 5% 9% 59%	1520
July	1st to 10th	Night	9% 5% 2 4 4 3 4 3 5% 7% 54%	2685
	11th to 20th	Night	6% 3 1 4 3 3 3 3 6% 10% 57%	2850
	21st to end	Night	3 3 1 3 3 3 3 4 6% 9% 63%	3098
August	1st to 10th	Night	3 4 1 4 4 4 4 4 6% 10% 56%	2836
	11th to 20th	Night	12% 5% 2 4 3 3 4 4 5% 8% 50%	2798
	21st to end	Night	6% 3 1 5% 3 3 4 3 5% 9% 57%	3135
September	1st to 10th	Night	8% 3 2 3 2 3 3 2 4 6% 64%	2061
	11th to 20th	Night	8% 3 2 3 3 3 4 3 4 8% 59%	2090
	21st to end	Night	8% 4 2 4 3 3 3 3 4 6% 60%	2090
October	1st to 10th	Night	13% 4 2 4 3 3 4 4 5% 6% 52%	2156
	11th to 20th	Night	11% 5% 1 5% 3 2 3 2 4 4 60%	2280
	21st to end	Night	13% 6% 2 4 3 3 3 3 4 5% 56%	2546
November	1st to 10th	Night	7% 5% 1 5% 3 3 3 3 5% 7% 59%	2535
	11th to 20th	Night	8% 6% 3 4 3 3 3 3 4 6% 57%	2600
	21st to end	Night	10% 6% 2 4 3 3 3 3 4 7% 55%	2648
December	1st to 10th	Night	4 5% 1 4 4 3 4 3 5% 6% 60%	4580
	11th to 20th	Night	8% 6% 3 7% 4 3 3 3 5% 7% 51%	5044
	21st to end	Night	15% 11% 4 9% 4 4 4 3 4 5% 37%	6490

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	56% 3 10% 21% 9% 1	4078
	11th to 20th	Day	40% 3 13% 21% 20% 2	4080
	21st to end	Day	43% 3 12% 26% 15% 2	4488
February	1st to 10th	Day	46% 4 15% 23% 11% 2	1800
	11th to 20th	Day	41% 4 13% 24% 15% 3	1884
	21st to end	Day	37% 4 12% 25% 18% 4	1650
March	1st to 10th	Day	36% 2 8% 25% 21% 8%	4754
	11th to 20th	Day	33% 4 7% 24% 26% 6%	4980
	21st to end	Day	48% 4 22% 19% 6% 2	5464
April	1st to 10th	Day	38% 3 13% 26% 17% 2	2200
	11th to 20th	Day	42% 3 13% 25% 15% 3	2433
	21st to end	Day	45% 5% 11% 26% 13% 1	2470
May	1st to 10th	Day	40% 6% 12% 24% 15% 4	4120
	11th to 20th	Day	39% 4 12% 26% 18% 1	4086
	21st to end	Day	40% 6% 13% 28% 12% 1	4489
June	1st to 10th	Day	26% 6% 18% 34% 14% 2	2470
	11th to 20th	Day	32% 5% 12% 31% 16% 2	2471
	21st to end	Day	30% 5% 15% 30% 16% 4	2660
July	1st to 10th	Day	35% 4 12% 29% 18% 1	4211
	11th to 20th	Day	30% 4 13% 31% 18% 3	4051
	21st to end	Day	24% 5% 16% 28% 22% 5%	4325
August	1st to 10th	Day	33% 5% 17% 25% 16% 4	4090
	11th to 20th	Day	37% 5% 16% 24% 17% 1	4080
	21st to end	Day	28% 4 15% 25% 20% 7%	4531
September	1st to 10th	Day	31% 3 11% 30% 19% 6%	2113
	11th to 20th	Day	29% 4 12% 30% 23% 2	2090
	21st to end	Day	25% 3 9% 34% 27% 2	2090
October	1st to 10th	Day	21% 3 6% 20% 45% 5%	3329
	11th to 20th	Day	21% 2 11% 32% 25% 9%	3140
	21st to end	Day	31% 3 11% 29% 23% 3	3352
November	1st to 10th	Day	31% 2 13% 30% 21% 3	1763
	11th to 20th	Day	32% 3 12% 27% 24% 2	1800
	21st to end	Day	38% 3 11% 29% 16% 3	1745
December	1st to 10th	Day	28% 3 15% 33% 19% 2	2610
	11th to 20th	Day	39% 2 18% 29% 11% 1	3142
	21st to end	Day	54% 3 9% 24% 10% 1	4488
January	1st to 10th	Night	52% 4 10% 19% 14% 1	5888
	11th to 20th	Night	36% 4 11% 27% 20% 2	5900
	21st to end	Night	43% 3 10% 20% 21% 3	6490
February	1st to 10th	Night	44% 4 13% 22% 14% 3	2600
	11th to 20th	Night	39% 4 13% 25% 16% 3	2431
	21st to end	Night	33% 3 10% 24% 24% 7%	1980
March	1st to 10th	Night	32% 3 7% 27% 26% 4	5107
	11th to 20th	Night	29% 2 6% 23% 31% 9%	4980
	21st to end	Night	43% 5% 20% 25% 6% 1	5467
April	1st to 10th	Night	36% 3 10% 27% 20% 3	2199
	11th to 20th	Night	36% 3 13% 28% 17% 3	1700
	21st to end	Night	39% 4 12% 26% 18% 1	1710
May	1st to 10th	Night	41% 4 10% 26% 17% 2	2850
	11th to 20th	Night	34% 4 12% 28% 22%	2824
	21st to end	Night	38% 5% 15% 23% 18% 2	3099
June	1st to 10th	Night	24% 6% 18% 31% 18% 2	1710
	11th to 20th	Night	27% 5% 15% 31% 18% 4	1699
	21st to end	Night	22% 4 15% 33% 21% 4	1520
July	1st to 10th	Night	31% 3 13% 31% 18% 4	2641
	11th to 20th	Night	23% 4 14% 33% 23% 4	2796
	21st to end	Night	17% 4 18% 30% 27% 4	2999
August	1st to 10th	Night	24% 5% 18% 28% 19% 5%	2826
	11th to 20th	Night	33% 4 17% 30% 15% 2	2825
	21st to end	Night	25% 3 17% 30% 17% 8%	3135
September	1st to 10th	Night	24% 3 11% 30% 24% 9%	2061
	11th to 20th	Night	25% 4 11% 32% 23% 5%	2090
	21st to end	Night	26% 3 8% 30% 29% 4	2090
October	1st to 10th	Night	21% 3 6% 18% 45% 7%	3598
	11th to 20th	Night	21% 2 8% 33% 26% 10%	3779
	21st to end	Night	29% 2 8% 33% 24% 3	4182
November	1st to 10th	Night	26% 3 13% 28% 25% 5%	2535
	11th to 20th	Night	30% 3 10% 30% 23% 4	2600
	21st to end	Night	31% 2 13% 29% 22% 3	2648
December	1st to 10th	Night	25% 3 15% 36% 20% 2	4580
	11th to 20th	Night	34% 3 14% 33% 16% 1	5045
	21st to end	Night	51% 3 10% 26% 9% 1	6490

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% 11% 35% 25% 10% 2	300
	11th to 20th	Day	18% 15% 34% 24% 8% 1	300
	21st to end	Day	13% 7% 48% 24% 8% 1	330
February	1st to 10th	Day	16% 17% 43% 22% 3	300
	11th to 20th	Day	16% 11% 40% 24% 7% 2	300
	21st to end	Day	11% 15% 47% 22% 4	249
March	1st to 10th	Day	15% 13% 42% 23% 6% 1	300
	11th to 20th	Day	21% 9% 39% 21% 8% 2	300
	21st to end	Day	28% 14% 38% 15% 4	330
April	1st to 10th	Day	20% 14% 46% 17% 3	300
	11th to 20th	Day	18% 15% 37% 22% 8%	631
	21st to end	Day	24% 12% 33% 20% 9% 2	650
May	1st to 10th	Day	19% 7% 36% 27% 10% 1	653
	11th to 20th	Day	19% 7% 31% 27% 12% 4	675
	21st to end	Day	20% 5% 30% 29% 13% 3	734
June	1st to 10th	Day	6% 5% 25% 34% 23% 7%	680
	11th to 20th	Day	9% 5% 31% 35% 16% 4	680
	21st to end	Day	8% 6% 34% 34% 17% 2	680
July	1st to 10th	Day	11% 1 16% 36% 27% 8%	671
	11th to 20th	Day	6% 1 18% 41% 27% 6%	668
	21st to end	Day	8% 1 17% 38% 31% 6%	739
August	1st to 10th	Day	10% 2 16% 41% 27% 5%	676
	11th to 20th	Day	11% 2 17% 43% 23% 4	665
	21st to end	Day	12% 2 19% 36% 27% 5%	748
September	1st to 10th	Day	15% 1 24% 39% 17% 4	323
	11th to 20th	Day	7% 1 28% 44% 14% 6%	300
	21st to end	Day	16% 5% 29% 31% 15% 4	300
October	1st to 10th	Day	19% 4 22% 35% 14% 5%	300
	11th to 20th	Day	9% 15% 39% 25% 11% 1	300
	21st to end	Day	19% 12% 39% 21% 8% 2	330
November	1st to 10th	Day	18% 11% 36% 26% 8% 2	300
	11th to 20th	Day	14% 12% 45% 20% 8% 1	300
	21st to end	Day	21% 11% 34% 22% 10% 2	300
December	1st to 10th	Day	8% 10% 44% 28% 7% 2	300
	11th to 20th	Day	19% 8% 41% 24% 7% 1	300
	21st to end	Day	21% 13% 41% 23% 3	330
January	1st to 10th	Night	14% 11% 36% 32% 7% 1	1000
	11th to 20th	Night	12% 12% 38% 30% 8% 1	1000
	21st to end	Night	14% 8% 41% 30% 6% 1	1100
February	1st to 10th	Night	16% 10% 41% 28% 5%	1000
	11th to 20th	Night	12% 10% 42% 31% 4	876
	21st to end	Night	13% 12% 43% 26% 5%	660
March	1st to 10th	Night	13% 12% 39% 29% 5% 1	689
	11th to 20th	Night	17% 10% 39% 28% 6% 1	600
	21st to end	Night	22% 8% 40% 24% 5%	660
April	1st to 10th	Night	17% 12% 42% 24% 5%	600
	11th to 20th	Night	17% 12% 41% 26% 4 1	565
	21st to end	Night	20% 6% 39% 25% 9% 1	570
May	1st to 10th	Night	21% 6% 34% 31% 8%	570
	11th to 20th	Night	16% 6% 33% 33% 11%	561
	21st to end	Night	17% 6% 29% 36% 12% 1	617
June	1st to 10th	Night	8% 3 24% 48% 15% 1	570
	11th to 20th	Night	10% 2 32% 42% 14% 1	570
	21st to end	Night	4 4 32% 45% 15%	570
July	1st to 10th	Night	10% 2 15% 43% 30% 1	555
	11th to 20th	Night	6% 1 17% 53% 23% 1	552
	21st to end	Night	5% 14% 54% 25% 1	624
August	1st to 10th	Night	7% 1 16% 52% 24% 1	567
	11th to 20th	Night	9% 2 17% 50% 21% 1	564
	21st to end	Night	9% 1 22% 41% 25% 1	627
September	1st to 10th	Night	10% 1 25% 42% 21% 1	570
	11th to 20th	Night	10% 4 27% 41% 16% 1	570
	21st to end	Night	10% 4 35% 36% 16% 1	570
October	1st to 10th	Night	16% 7% 29% 33% 14% 2	636
	11th to 20th	Night	14% 9% 38% 31% 9%	760
	21st to end	Night	17% 10% 30% 32% 10%	874
November	1st to 10th	Night	11% 9% 35% 36% 9%	975
	11th to 20th	Night	12% 12% 39% 30% 7%	1000
	21st to end	Night	14% 10% 35% 31% 9% 1	1000
December	1st to 10th	Night	11% 11% 41% 30% 7%	1000
	11th to 20th	Night	15% 10% 36% 33% 7%	1000
	21st to end	Night	18% 11% 36% 30% 6%	1100

Page generated at 2025-04-08 08:17:30. Version ac07

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