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 2026-08-15.

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%	143515
	Night	9% 6% 2 6% 4 3 4 3 5% 7% 50%	138702
Transparency	Day	36% 4 13% 26% 18% 3	147159
	Night	34% 3 12% 27% 20% 4	143117
Seeing	Day	14% 7% 31% 29% 15% 3	18254
	Night	13% 8% 34% 34% 11% 1	28051

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% 4 12% 6% 5% 5% 3 4 5% 35%	5289
	11th to 20th	Day	4 9% 3 7% 6% 6% 5% 4 5% 6% 45%	5310
	21st to end	Day	6% 11% 5% 10% 4 4 4 3 5% 5% 42%	5812
February	1st to 10th	Day	9% 11% 4 8% 5% 4 3 3 7% 8% 37%	1890
	11th to 20th	Day	8% 10% 3 7% 4 4 4 4 5% 8% 44%	1971
	21st to end	Day	8% 8% 2 6% 4 4 4 3 4 7% 49%	1730
March	1st to 10th	Day	12% 8% 3 5% 3 2 3 2 3 4 55%	4859
	11th to 20th	Day	11% 6% 2 5% 3 3 4 3 5% 6% 53%	5090
	21st to end	Day	15% 11% 3 8% 4 3 4 3 5% 8% 36%	5583
April	1st to 10th	Day	14% 7% 2 6% 4 4 4 3 4 6% 47%	2310
	11th to 20th	Day	14% 7% 2 6% 5% 4 4 3 5% 7% 44%	2692
	21st to end	Day	20% 8% 2 6% 4 4 3 3 5% 6% 38%	2730
May	1st to 10th	Day	12% 6% 2 5% 4 4 4 3 6% 7% 48%	7617
	11th to 20th	Day	12% 5% 2 5% 4 3 4 3 5% 6% 51%	7627
	21st to end	Day	17% 7% 3 7% 4 4 4 3 5% 7% 39%	8392
June	1st to 10th	Day	7% 3 2 5% 4 4 4 4 6% 9% 52%	2730
	11th to 20th	Day	9% 4 2 5% 4 4 4 3 6% 8% 50%	2731
	21st to end	Day	7% 5% 2 5% 5% 4 5% 4 7% 8% 49%	2940
July	1st to 10th	Day	8% 4 2 5% 4 4 5% 5% 6% 9% 47%	7965
	11th to 20th	Day	6% 3 2 5% 3 3 4 4 5% 7% 58%	7680
	21st to end	Day	9% 5% 2 6% 4 4 5% 4 7% 9% 44%	8337
August	1st to 10th	Day	8% 5% 2 6% 5% 4 4 5% 6% 10% 45%	4364
	11th to 20th	Day	12% 5% 2 6% 4 4 4 4 6% 8% 45%	4224
	21st to end	Day	7% 4 2 4 3 4 4 4 6% 7% 54%	4675
September	1st to 10th	Day	13% 4 2 4 3 2 4 3 5% 6% 54%	2224
	11th to 20th	Day	10% 4 2 5% 3 3 4 3 4 8% 55%	2200
	21st to end	Day	9% 4 1 4 2 3 3 3 5% 6% 60%	2200
October	1st to 10th	Day	13% 6% 2 4 3 3 3 2 4 5% 55%	2109
	11th to 20th	Day	11% 5% 2 5% 3 2 2 3 4 5% 59%	2000
	21st to end	Day	13% 7% 2 6% 3 3 3 3 3 6% 51%	2155
November	1st to 10th	Day	9% 5% 1 5% 4 4 3 2 4 7% 56%	1853
	11th to 20th	Day	8% 7% 2 5% 4 3 3 3 5% 6% 54%	1890
	21st to end	Day	12% 9% 2 5% 4 3 3 2 4 7% 47%	1832
December	1st to 10th	Day	5% 5% 2 5% 4 3 4 4 5% 7% 56%	2690
	11th to 20th	Day	6% 8% 3 7% 5% 4 4 3 5% 7% 47%	3227
	21st to end	Day	15% 10% 4 12% 5% 4 4 3 4 5% 35%	4587
January	1st to 10th	Night	8% 11% 4 13% 5% 4 5% 4 5% 6% 36%	7634
	11th to 20th	Night	4 6% 2 6% 4 5% 6% 4 6% 7% 48%	7680
	21st to end	Night	8% 10% 4 11% 4 3 3 3 4 5% 45%	8402
February	1st to 10th	Night	10% 10% 4 6% 4 4 5% 4 5% 6% 42%	2730
	11th to 20th	Night	8% 8% 3 7% 5% 4 5% 4 7% 8% 42%	2555
	21st to end	Night	8% 8% 2 5% 4 5% 2 3 4 6% 54%	2076
March	1st to 10th	Night	11% 6% 2 5% 3 3 4 3 4 5% 55%	5221
	11th to 20th	Night	10% 5% 2 4 3 3 3 3 4 6% 59%	5090
	21st to end	Night	13% 8% 2 6% 4 4 4 4 6% 8% 40%	5588
April	1st to 10th	Night	12% 7% 2 5% 3 4 4 3 5% 6% 49%	2309
	11th to 20th	Night	12% 6% 2 5% 4 3 3 3 6% 7% 48%	1875
	21st to end	Night	16% 6% 3 5% 4 4 3 3 4 7% 45%	1890
May	1st to 10th	Night	13% 6% 2 5% 3 3 3 3 4 6% 52%	5266
	11th to 20th	Night	11% 5% 2 5% 3 3 4 3 4 6% 55%	5265
	21st to end	Night	18% 6% 2 6% 3 4 3 3 5% 7% 43%	5793
June	1st to 10th	Night	6% 5% 1 4 4 3 4 5% 5% 9% 54%	1890
	11th to 20th	Night	7% 4 1 4 3 3 3 4 6% 8% 56%	1877
	21st to end	Night	5% 4 2 4 3 3 3 4 5% 9% 58%	1680
July	1st to 10th	Night	8% 5% 2 5% 4 3 4 3 5% 8% 52%	5000
	11th to 20th	Night	6% 3 1 4 3 3 3 3 6% 8% 60%	5307
	21st to end	Night	7% 5% 2 5% 4 3 4 4 7% 10% 49%	5770
August	1st to 10th	Night	4 4 2 4 4 4 4 4 6% 10% 56%	3016
	11th to 20th	Night	12% 5% 2 4 3 3 4 4 5% 8% 50%	2924
	21st to end	Night	6% 3 1 5% 3 3 4 3 5% 9% 57%	3234
September	1st to 10th	Night	9% 4 2 3 2 3 3 2 4 6% 63%	2170
	11th to 20th	Night	8% 3 2 4 3 3 4 3 4 8% 58%	2200
	21st to end	Night	8% 4 2 4 3 3 3 3 4 6% 60%	2200
October	1st to 10th	Night	13% 4 2 4 3 3 4 4 5% 6% 52%	2270
	11th to 20th	Night	11% 5% 2 5% 3 3 3 2 4 4 59%	2400
	21st to end	Night	13% 6% 2 4 3 3 3 2 4 5% 55%	2680
November	1st to 10th	Night	6% 5% 1 5% 3 3 3 3 5% 8% 59%	2665
	11th to 20th	Night	8% 6% 3 4 3 3 3 3 4 6% 57%	2730
	21st to end	Night	11% 6% 2 4 3 3 3 3 4 7% 53%	2781
December	1st to 10th	Night	4 5% 2 5% 4 3 4 3 5% 6% 60%	4720
	11th to 20th	Night	9% 6% 3 7% 4 3 3 3 5% 7% 51%	5181
	21st to end	Night	15% 11% 4 9% 4 4 4 3 4 5% 37%	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	53% 2 10% 22% 12% 1	5290
	11th to 20th	Day	41% 3 14% 20% 20% 2	5310
	21st to end	Day	45% 3 11% 25% 15% 1	5812
February	1st to 10th	Day	44% 4 15% 23% 11% 2	1890
	11th to 20th	Day	40% 4 13% 25% 15% 4	1980
	21st to end	Day	36% 4 12% 26% 19% 4	1730
March	1st to 10th	Day	36% 2 7% 25% 21% 8%	4859
	11th to 20th	Day	33% 4 7% 24% 25% 6%	5090
	21st to end	Day	48% 4 21% 19% 6% 2	5585
April	1st to 10th	Day	40% 3 13% 25% 17% 2	2310
	11th to 20th	Day	41% 3 12% 25% 16% 3	2692
	21st to end	Day	45% 4 11% 25% 13% 1	2730
May	1st to 10th	Day	35% 4 10% 27% 22% 2	7655
	11th to 20th	Day	35% 3 11% 23% 22% 6%	7631
	21st to end	Day	46% 5% 10% 26% 13% 1	8405
June	1st to 10th	Day	28% 6% 18% 33% 14% 2	2730
	11th to 20th	Day	31% 5% 12% 31% 18% 2	2731
	21st to end	Day	32% 5% 14% 29% 17% 4	2940
July	1st to 10th	Day	32% 4 14% 32% 17% 1	7901
	11th to 20th	Day	26% 3 13% 31% 20% 7%	7611
	21st to end	Day	35% 5% 16% 27% 14% 3	8155
August	1st to 10th	Day	33% 5% 17% 25% 16% 4	4350
	11th to 20th	Day	37% 5% 16% 25% 17% 1	4263
	21st to end	Day	29% 4 15% 25% 20% 7%	4674
September	1st to 10th	Day	32% 3 11% 30% 18% 6%	2224
	11th to 20th	Day	29% 4 12% 30% 22% 2	2200
	21st to end	Day	26% 3 9% 34% 27% 2	2200
October	1st to 10th	Day	21% 3 6% 21% 44% 5%	3434
	11th to 20th	Day	22% 2 11% 32% 25% 9%	3240
	21st to end	Day	32% 3 11% 29% 23% 3	3460
November	1st to 10th	Day	30% 2 13% 30% 22% 3	1853
	11th to 20th	Day	32% 3 12% 28% 24% 2	1890
	21st to end	Day	38% 3 11% 29% 16% 3	1832
December	1st to 10th	Day	29% 3 15% 33% 18% 2	2690
	11th to 20th	Day	38% 2 18% 29% 11% 1	3225
	21st to end	Day	53% 3 10% 24% 10% 1	4587
January	1st to 10th	Night	49% 3 11% 19% 15% 2	7635
	11th to 20th	Night	33% 4 12% 29% 20% 2	7680
	21st to end	Night	44% 3 11% 20% 20% 3	8402
February	1st to 10th	Night	43% 4 13% 22% 15% 3	2730
	11th to 20th	Night	39% 4 13% 25% 15% 3	2556
	21st to end	Night	33% 3 10% 24% 25% 7%	2076
March	1st to 10th	Night	33% 3 7% 27% 26% 4	5221
	11th to 20th	Night	29% 2 6% 22% 31% 9%	5090
	21st to end	Night	42% 5% 20% 25% 7% 1	5588
April	1st to 10th	Night	37% 3 11% 28% 19% 3	2309
	11th to 20th	Night	36% 3 12% 28% 18% 3	1875
	21st to end	Night	40% 4 11% 26% 17% 1	1890
May	1st to 10th	Night	35% 3 8% 27% 24% 3	5293
	11th to 20th	Night	31% 3 11% 25% 24% 7%	5266
	21st to end	Night	42% 4 12% 24% 17% 1	5805
June	1st to 10th	Night	26% 6% 17% 30% 18% 2	1890
	11th to 20th	Night	26% 4 14% 31% 20% 5%	1877
	21st to end	Night	24% 4 16% 31% 21% 3	1680
July	1st to 10th	Night	32% 3 14% 33% 15% 2	4958
	11th to 20th	Night	24% 4 11% 30% 24% 8%	5256
	21st to end	Night	31% 4 18% 25% 20% 2	5641
August	1st to 10th	Night	24% 4 19% 29% 19% 5%	3006
	11th to 20th	Night	33% 4 17% 30% 15% 2	2951
	21st to end	Night	26% 3 16% 30% 17% 8%	3234
September	1st to 10th	Night	25% 3 11% 29% 24% 8%	2170
	11th to 20th	Night	26% 4 12% 31% 23% 5%	2200
	21st to end	Night	27% 3 8% 30% 29% 4	2200
October	1st to 10th	Night	22% 3 6% 18% 44% 7%	3712
	11th to 20th	Night	22% 2 8% 32% 26% 10%	3899
	21st to end	Night	30% 2 8% 33% 24% 3	4316
November	1st to 10th	Night	26% 3 13% 29% 25% 5%	2665
	11th to 20th	Night	30% 3 11% 31% 22% 4	2730
	21st to end	Night	33% 2 12% 28% 21% 3	2781
December	1st to 10th	Night	26% 3 15% 36% 19% 2	4720
	11th to 20th	Night	34% 3 14% 33% 16% 1	5182
	21st to end	Night	50% 3 10% 27% 10% 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	17% 11% 36% 26% 9% 2	330
	11th to 20th	Day	18% 15% 35% 23% 7% 1	330
	21st to end	Day	13% 7% 47% 25% 7% 1	363
February	1st to 10th	Day	14% 16% 44% 23% 3	330
	11th to 20th	Day	16% 11% 41% 25% 7% 2	330
	21st to end	Day	11% 14% 50% 21% 3	273
March	1st to 10th	Day	16% 12% 43% 21% 7% 1	330
	11th to 20th	Day	21% 10% 39% 20% 8% 2	330
	21st to end	Day	28% 15% 38% 15% 4	363
April	1st to 10th	Day	21% 15% 46% 15% 3	330
	11th to 20th	Day	18% 16% 37% 21% 7%	730
	21st to end	Day	25% 12% 34% 20% 8% 1	750
May	1st to 10th	Day	17% 8% 35% 27% 11% 2	753
	11th to 20th	Day	19% 8% 32% 26% 13% 3	775
	21st to end	Day	20% 5% 31% 28% 13% 3	844
June	1st to 10th	Day	8% 5% 26% 33% 22% 7%	780
	11th to 20th	Day	9% 6% 31% 34% 16% 4	780
	21st to end	Day	10% 6% 34% 33% 15% 2	780
July	1st to 10th	Day	10% 1 18% 36% 27% 8%	771
	11th to 20th	Day	6% 1 17% 39% 29% 8%	768
	21st to end	Day	9% 2 17% 38% 29% 6%	849
August	1st to 10th	Day	10% 2 17% 41% 25% 5%	776
	11th to 20th	Day	10% 2 17% 43% 23% 5%	736
	21st to end	Day	12% 2 19% 36% 27% 5%	803
September	1st to 10th	Day	16% 2 24% 37% 17% 4	354
	11th to 20th	Day	7% 2 28% 43% 13% 6%	330
	21st to end	Day	16% 5% 28% 30% 16% 5%	330
October	1st to 10th	Day	18% 5% 24% 35% 13% 5%	330
	11th to 20th	Day	10% 15% 40% 24% 10% 1	330
	21st to end	Day	21% 13% 38% 20% 8% 1	363
November	1st to 10th	Day	16% 12% 38% 25% 7% 2	330
	11th to 20th	Day	13% 11% 46% 21% 8% 1	330
	21st to end	Day	23% 12% 34% 21% 9% 2	330
December	1st to 10th	Day	8% 11% 45% 28% 7% 2	330
	11th to 20th	Day	18% 9% 42% 23% 7% 1	330
	21st to end	Day	20% 12% 40% 24% 3	363
January	1st to 10th	Night	14% 10% 36% 32% 7% 1	1050
	11th to 20th	Night	12% 12% 38% 29% 7% 1	1050
	21st to end	Night	14% 9% 42% 30% 6% 1	1155
February	1st to 10th	Night	16% 10% 42% 28% 5%	1050
	11th to 20th	Night	12% 10% 43% 31% 4	921
	21st to end	Night	13% 12% 44% 26% 5%	692
March	1st to 10th	Night	14% 13% 39% 29% 5% 1	723
	11th to 20th	Night	17% 10% 40% 27% 5% 1	630
	21st to end	Night	21% 9% 41% 24% 5%	693
April	1st to 10th	Night	17% 13% 42% 23% 5%	630
	11th to 20th	Night	16% 13% 41% 25% 4	623
	21st to end	Night	20% 7% 39% 25% 8% 1	630
May	1st to 10th	Night	20% 6% 34% 32% 8%	630
	11th to 20th	Night	16% 7% 33% 32% 11%	621
	21st to end	Night	17% 5% 28% 37% 12% 1	683
June	1st to 10th	Night	9% 3 24% 47% 15% 1	630
	11th to 20th	Night	9% 2 33% 41% 14% 1	630
	21st to end	Night	5% 4 33% 43% 14%	630
July	1st to 10th	Night	9% 2 16% 43% 29% 1	615
	11th to 20th	Night	6% 17% 51% 25% 1	612
	21st to end	Night	5% 1 15% 52% 25% 1	690
August	1st to 10th	Night	7% 1 17% 51% 23% 1	627
	11th to 20th	Night	9% 2 17% 50% 21% 1	606
	21st to end	Night	10% 2 22% 41% 25% 2	660
September	1st to 10th	Night	10% 2 25% 42% 20% 1	600
	11th to 20th	Night	10% 4 28% 42% 16% 1	600
	21st to end	Night	9% 4 33% 36% 17% 1	600
October	1st to 10th	Night	16% 7% 29% 33% 14% 1	670
	11th to 20th	Night	13% 9% 39% 31% 8%	800
	21st to end	Night	18% 10% 30% 32% 10%	920
November	1st to 10th	Night	10% 9% 37% 35% 9%	1025
	11th to 20th	Night	12% 11% 40% 31% 7%	1050
	21st to end	Night	14% 10% 34% 31% 9% 1	1050
December	1st to 10th	Night	12% 10% 42% 30% 7%	1050
	11th to 20th	Night	15% 10% 36% 32% 7%	1050
	21st to end	Night	17% 10% 37% 30% 6%	1155

Page generated at 2026-08-12 02:37:19. Version ac07

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