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 2024-10-24.

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	11% 7% 2 6% 4 4 4 3 5% 7% 47%	101136
	Night	10% 6% 2 6% 3 3 4 3 5% 7% 51%	97717
Transparency	Day	37% 4 13% 26% 17% 3	100949
	Night	34% 4 13% 28% 19% 3	97576
Seeing	Day	14% 7% 30% 30% 15% 3	15734
	Night	13% 7% 33% 34% 11% 1	25574

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	9% 11% 5% 12% 7% 5% 6% 3 5% 6% 31%	2847
	11th to 20th	Day	7% 13% 5% 8% 5% 4 5% 4 4 6% 40%	2850
	21st to end	Day	8% 11% 6% 13% 5% 4 4 3 4 5% 38%	3135
February	1st to 10th	Day	10% 11% 4 9% 5% 4 3 3 7% 8% 36%	1710
	11th to 20th	Day	8% 8% 3 8% 4 4 4 4 5% 8% 44%	1778
	21st to end	Day	9% 9% 2 7% 5% 4 4 3 5% 6% 46%	1570
March	1st to 10th	Day	10% 7% 3 6% 4 3 3 2 3 5% 53%	3306
	11th to 20th	Day	12% 6% 2 6% 4 3 3 3 5% 5% 51%	3480
	21st to end	Day	18% 11% 3 8% 4 3 4 3 5% 7% 34%	3814
April	1st to 10th	Day	13% 7% 2 6% 4 4 3 3 4 6% 48%	2090
	11th to 20th	Day	14% 7% 3 6% 5% 4 4 3 5% 7% 43%	2432
	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 3 3 3 5% 52%	1970
November	1st to 10th	Day	8% 5% 1 5% 3 3 3 3 5% 7% 57%	1673
	11th to 20th	Day	8% 7% 2 5% 4 3 3 3 5% 6% 53%	1710
	21st to end	Day	12% 9% 2 5% 4 3 4 2 5% 7% 48%	1658
December	1st to 10th	Day	8% 7% 2 6% 4 3 4 4 6% 8% 48%	1520
	11th to 20th	Day	8% 10% 3 7% 5% 4 4 3 5% 8% 44%	2012
	21st to end	Day	14% 11% 4 13% 6% 5% 4 3 4 5% 30%	3135
January	1st to 10th	Night	7% 11% 5% 14% 4 4 5% 4 5% 6% 35%	4108
	11th to 20th	Night	7% 9% 3 6% 4 5% 7% 4 5% 5% 45%	4120
	21st to end	Night	10% 11% 5% 11% 4 3 3 3 4 6% 40%	4532
February	1st to 10th	Night	11% 10% 4 6% 4 4 5% 4 5% 5% 41%	2470
	11th to 20th	Night	8% 8% 2 6% 5% 5% 5% 4 7% 8% 43%	2306
	21st to end	Night	8% 8% 2 5% 4 5% 2 3 4 6% 53%	1884
March	1st to 10th	Night	11% 5% 2 4 3 3 3 3 4 5% 57%	3551
	11th to 20th	Night	11% 6% 2 4 3 3 3 3 4 6% 58%	3480
	21st to end	Night	18% 7% 2 6% 4 4 4 4 5% 7% 39%	3817
April	1st to 10th	Night	12% 7% 2 5% 4 4 4 3 5% 6% 49%	2089
	11th to 20th	Night	13% 7% 2 5% 4 3 3 3 6% 7% 47%	1695
	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 2 4 5% 56%	2449
November	1st to 10th	Night	5% 4 1 5% 3 3 2 3 5% 8% 60%	2405
	11th to 20th	Night	8% 6% 3 4 3 3 3 3 4 6% 56%	2470
	21st to end	Night	11% 6% 2 4 3 3 3 3 4 7% 55%	2515
December	1st to 10th	Night	7% 7% 2 6% 4 4 3 3 5% 6% 52%	2660
	11th to 20th	Night	9% 7% 3 6% 3 3 3 2 4 7% 54%	3180
	21st to end	Night	17% 12% 4 10% 4 3 3 3 4 5% 36%	4532

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	54% 3 13% 20% 9% 1	2848
	11th to 20th	Day	46% 3 18% 20% 12% 2	2850
	21st to end	Day	49% 4 12% 21% 13% 1	3135
February	1st to 10th	Day	45% 4 15% 23% 10% 2	1710
	11th to 20th	Day	39% 4 13% 25% 15% 3	1787
	21st to end	Day	39% 4 12% 25% 17% 4	1570
March	1st to 10th	Day	36% 3 8% 27% 23% 4	3306
	11th to 20th	Day	35% 4 10% 29% 20% 1	3480
	21st to end	Day	50% 4 23% 17% 5% 1	3814
April	1st to 10th	Day	38% 3 13% 25% 18% 2	2090
	11th to 20th	Day	42% 3 13% 25% 15% 3	2432
	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	34% 3 9% 25% 27% 2	2004
	11th to 20th	Day	29% 2 8% 30% 22% 8%	1900
	21st to end	Day	35% 3 11% 24% 22% 4	1970
November	1st to 10th	Day	28% 2 13% 31% 22% 3	1673
	11th to 20th	Day	32% 3 12% 27% 23% 2	1710
	21st to end	Day	38% 3 10% 29% 16% 3	1658
December	1st to 10th	Day	34% 4 15% 31% 14% 2	1520
	11th to 20th	Day	40% 3 14% 31% 11%	2010
	21st to end	Day	56% 4 10% 20% 10% 1	3135
January	1st to 10th	Night	48% 5% 12% 22% 13% 1	4108
	11th to 20th	Night	40% 4 13% 28% 14% 1	4120
	21st to end	Night	47% 4 12% 20% 16% 1	4532
February	1st to 10th	Night	44% 4 13% 22% 14% 3	2470
	11th to 20th	Night	38% 4 14% 26% 16% 3	2307
	21st to end	Night	34% 3 10% 23% 23% 7%	1884
March	1st to 10th	Night	30% 4 8% 28% 26% 4	3551
	11th to 20th	Night	30% 3 8% 29% 26% 5%	3480
	21st to end	Night	44% 5% 22% 21% 6% 1	3817
April	1st to 10th	Night	36% 3 11% 27% 20% 3	2089
	11th to 20th	Night	37% 3 13% 28% 17% 2	1695
	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	32% 4 10% 26% 25% 3	2156
	11th to 20th	Night	29% 3 7% 27% 26% 8%	2280
	21st to end	Night	32% 2 10% 26% 24% 5%	2449
November	1st to 10th	Night	24% 3 13% 29% 26% 6%	2405
	11th to 20th	Night	30% 3 10% 30% 23% 4	2470
	21st to end	Night	31% 2 12% 29% 22% 3	2515
December	1st to 10th	Night	33% 4 14% 32% 16% 2	2660
	11th to 20th	Night	32% 3 12% 38% 14% 1	3181
	21st to end	Night	52% 4 10% 25% 9% 1	4532

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	16% 11% 34% 26% 10% 2	270
	11th to 20th	Day	20% 14% 32% 24% 9% 1	270
	21st to end	Day	14% 6% 46% 25% 8% 1	297
February	1st to 10th	Day	15% 16% 43% 23% 3	270
	11th to 20th	Day	15% 10% 40% 26% 7% 2	270
	21st to end	Day	12% 14% 49% 21% 4	225
March	1st to 10th	Day	14% 13% 43% 23% 7% 1	270
	11th to 20th	Day	22% 9% 39% 21% 7% 2	270
	21st to end	Day	29% 14% 38% 15% 5%	297
April	1st to 10th	Day	19% 13% 47% 18% 3	270
	11th to 20th	Day	18% 15% 37% 22% 8%	630
	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	20% 11% 39% 21% 8% 2	306
November	1st to 10th	Day	16% 11% 37% 25% 9% 3	270
	11th to 20th	Day	13% 10% 47% 20% 9% 1	270
	21st to end	Day	23% 11% 32% 23% 9% 2	270
December	1st to 10th	Day	9% 10% 44% 28% 8% 2	270
	11th to 20th	Day	20% 8% 39% 25% 7% 1	270
	21st to end	Day	20% 13% 42% 23% 2	297
January	1st to 10th	Night	13% 11% 35% 32% 8% 1	950
	11th to 20th	Night	13% 11% 37% 30% 8% 1	950
	21st to end	Night	14% 8% 40% 31% 6% 1	1045
February	1st to 10th	Night	16% 9% 41% 28% 5%	950
	11th to 20th	Night	12% 9% 43% 32% 4	832
	21st to end	Night	14% 12% 43% 26% 5%	628
March	1st to 10th	Night	13% 12% 39% 30% 5% 1	655
	11th to 20th	Night	18% 9% 38% 28% 6% 1	570
	21st to end	Night	22% 8% 39% 25% 6%	627
April	1st to 10th	Night	16% 13% 42% 24% 5%	570
	11th to 20th	Night	17% 12% 40% 26% 4 1	563
	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% 31% 32% 10%	841
November	1st to 10th	Night	9% 9% 35% 36% 10%	925
	11th to 20th	Night	12% 11% 39% 30% 7%	950
	21st to end	Night	14% 10% 34% 31% 9% 1	950
December	1st to 10th	Night	12% 11% 41% 29% 7%	950
	11th to 20th	Night	15% 9% 35% 33% 7%	950
	21st to end	Night	18% 11% 36% 30% 5%	1045

Page generated at 2024-10-21 01:20:04. Version ac07

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