Center Valley Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Center Valley Observatory clear sky chart from 2005-11-06 to 2024-11-28.

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	13% 9% 3 7% 4 4 4 4 6% 7% 38%	101249
	Night	14% 10% 3 7% 4 4 4 3 5% 6% 39%	98307
Transparency	Day	44% 6% 11% 23% 14% 2	104888
	Night	44% 5% 10% 22% 16% 2	102807
Seeing	Day	16% 9% 25% 25% 18% 7%	15653
	Night	17% 8% 27% 30% 15% 2	25477

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	14% 16% 8% 10% 5% 5% 3 4 4 5% 26%	2527
	11th to 20th	Day	16% 12% 6% 14% 6% 6% 7% 5% 5% 4 19%	2530
	21st to end	Day	26% 19% 8% 8% 4 4 3 2 3 4 18%	2913
February	1st to 10th	Day	18% 13% 6% 9% 6% 4 4 3 5% 5% 29%	1900
	11th to 20th	Day	14% 11% 4 10% 5% 6% 3 3 6% 6% 32%	1848
	21st to end	Day	17% 15% 4 8% 4 4 4 3 4 6% 32%	1570
March	1st to 10th	Day	21% 18% 4 7% 4 3 3 3 3 4 31%	3120
	11th to 20th	Day	13% 8% 3 6% 4 3 4 3 5% 7% 45%	3339
	21st to end	Day	15% 10% 4 9% 5% 5% 5% 4 5% 7% 31%	4026
April	1st to 10th	Day	14% 11% 3 8% 5% 4 4 3 6% 7% 36%	2280
	11th to 20th	Day	16% 9% 3 7% 4 4 5% 3 6% 6% 39%	2254
	21st to end	Day	20% 8% 3 7% 4 5% 4 3 5% 7% 35%	2420
May	1st to 10th	Day	18% 9% 3 8% 5% 5% 5% 4 7% 9% 28%	4082
	11th to 20th	Day	20% 7% 2 6% 4 4 4 3 5% 6% 39%	4081
	21st to end	Day	9% 7% 3 6% 4 5% 6% 5% 7% 10% 39%	4604
June	1st to 10th	Day	11% 7% 2 6% 4 5% 4 4 5% 8% 43%	2660
	11th to 20th	Day	9% 5% 2 5% 4 5% 5% 5% 7% 8% 45%	2660
	21st to end	Day	9% 5% 3 6% 5% 5% 5% 4 6% 9% 42%	2660
July	1st to 10th	Day	13% 6% 2 6% 4 4 5% 4 7% 10% 38%	4440
	11th to 20th	Day	6% 4 2 5% 4 5% 5% 4 8% 12% 46%	4440
	21st to end	Day	9% 6% 2 8% 5% 6% 7% 5% 8% 10% 34%	4701
August	1st to 10th	Day	8% 5% 2 5% 4 4 4 4 7% 10% 48%	4104
	11th to 20th	Day	9% 4 2 6% 4 4 5% 5% 7% 11% 41%	3806
	21st to end	Day	6% 4 2 5% 4 4 4 3 6% 9% 54%	4180
September	1st to 10th	Day	11% 6% 2 6% 4 4 5% 4 6% 8% 44%	2263
	11th to 20th	Day	9% 5% 2 4 4 4 5% 4 6% 7% 49%	2090
	21st to end	Day	13% 5% 2 5% 4 4 3 4 5% 6% 49%	2090
October	1st to 10th	Day	11% 6% 2 5% 5% 4 4 3 5% 8% 49%	2090
	11th to 20th	Day	12% 6% 2 6% 4 4 4 4 5% 6% 44%	1939
	21st to end	Day	18% 9% 3 7% 3 5% 5% 4 4 5% 37%	1881
November	1st to 10th	Day	9% 6% 2 6% 4 3 4 3 4 7% 51%	1762
	11th to 20th	Day	16% 10% 3 7% 4 3 5% 3 4 6% 38%	1800
	21st to end	Day	18% 12% 4 8% 5% 4 3 2 5% 5% 35%	1773
December	1st to 10th	Day	18% 15% 4 9% 5% 4 4 3 3 5% 31%	1710
	11th to 20th	Day	15% 16% 6% 11% 4 3 3 3 5% 6% 29%	1923
	21st to end	Day	20% 22% 8% 10% 4 3 4 2 4 5% 17%	2783
January	1st to 10th	Night	17% 16% 7% 10% 5% 4 4 3 4 5% 24%	4428
	11th to 20th	Night	14% 18% 6% 14% 6% 6% 5% 3 4 4 20%	4440
	21st to end	Night	25% 17% 5% 9% 4 3 3 3 4 4 23%	4747
February	1st to 10th	Night	19% 11% 5% 10% 5% 4 4 3 5% 5% 29%	2280
	11th to 20th	Night	13% 11% 4 10% 5% 5% 4 3 5% 6% 33%	2218
	21st to end	Night	18% 13% 5% 8% 4 4 3 3 4 5% 31%	1884
March	1st to 10th	Night	20% 15% 4 6% 4 3 3 3 4 5% 33%	3733
	11th to 20th	Night	13% 7% 2 5% 4 4 4 3 5% 6% 47%	3619
	21st to end	Night	17% 8% 3 7% 5% 4 4 3 5% 6% 38%	3635
April	1st to 10th	Night	12% 9% 4 7% 5% 4 4 4 5% 6% 39%	1900
	11th to 20th	Night	16% 8% 2 6% 5% 4 4 3 4 7% 41%	1875
	21st to end	Night	16% 7% 3 7% 4 4 4 4 5% 6% 38%	1758
May	1st to 10th	Night	18% 12% 3 8% 5% 4 4 4 6% 7% 29%	2813
	11th to 20th	Night	19% 7% 2 6% 4 3 4 3 5% 7% 40%	2812
	21st to end	Night	10% 5% 2 6% 5% 3 5% 4 6% 9% 45%	2939
June	1st to 10th	Night	9% 5% 2 7% 4 3 4 4 4 8% 49%	1520
	11th to 20th	Night	8% 6% 2 6% 4 4 4 4 5% 8% 50%	1520
	21st to end	Night	6% 3 2 5% 5% 4 6% 5% 8% 9% 46%	1520
July	1st to 10th	Night	10% 5% 2 5% 4 4 4 3 6% 8% 49%	2530
	11th to 20th	Night	5% 3 2 5% 3 4 5% 4 6% 9% 55%	2530
	21st to end	Night	9% 6% 3 7% 5% 4 5% 4 7% 10% 40%	2858
August	1st to 10th	Night	8% 4 2 6% 4 4 4 3 5% 8% 51%	2825
	11th to 20th	Night	6% 5% 1 6% 4 4 6% 4 6% 9% 48%	3007
	21st to end	Night	5% 3 2 5% 4 4 4 3 6% 8% 56%	3476
September	1st to 10th	Night	11% 6% 2 6% 4 4 4 4 6% 6% 49%	1900
	11th to 20th	Night	8% 5% 1 5% 4 3 4 3 5% 8% 55%	2087
	21st to end	Night	12% 6% 2 5% 4 3 4 3 5% 6% 49%	2090
October	1st to 10th	Night	8% 4 1 5% 4 4 4 4 4 5% 55%	2090
	11th to 20th	Night	16% 7% 2 5% 3 3 3 3 4 6% 49%	2235
	21st to end	Night	18% 7% 3 6% 4 4 4 3 4 7% 41%	2717
November	1st to 10th	Night	11% 8% 3 5% 4 3 3 3 5% 5% 50%	2536
	11th to 20th	Night	14% 8% 3 8% 4 4 4 4 5% 7% 40%	2600
	21st to end	Night	19% 12% 4 6% 5% 4 3 4 4 5% 33%	2562
December	1st to 10th	Night	17% 12% 5% 8% 6% 3 3 3 5% 7% 30%	2470
	11th to 20th	Night	17% 12% 4 9% 4 3 4 3 4 6% 33%	3269
	21st to end	Night	23% 19% 6% 10% 5% 4 4 3 4 4 18%	4884

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	60% 4 7% 20% 7%	2528
	11th to 20th	Day	65% 6% 12% 11% 6%	2530
	21st to end	Day	72% 3 7% 15% 3 1	2913
February	1st to 10th	Day	57% 5% 10% 16% 10% 2	1900
	11th to 20th	Day	53% 5% 11% 21% 10% 1	1858
	21st to end	Day	54% 4 10% 21% 9% 2	1570
March	1st to 10th	Day	58% 5% 6% 18% 11% 2	3120
	11th to 20th	Day	40% 5% 11% 29% 14% 1	3339
	21st to end	Day	51% 7% 14% 22% 6% 1	4026
April	1st to 10th	Day	47% 6% 12% 20% 14% 1	2280
	11th to 20th	Day	45% 6% 10% 24% 11% 3	2254
	21st to end	Day	49% 6% 11% 21% 11% 3	2420
May	1st to 10th	Day	50% 8% 13% 23% 6%	4120
	11th to 20th	Day	45% 7% 12% 26% 10%	4085
	21st to end	Day	37% 9% 13% 20% 19% 2	4617
June	1st to 10th	Day	38% 7% 12% 25% 15% 3	2660
	11th to 20th	Day	33% 9% 11% 23% 21% 3	2660
	21st to end	Day	36% 9% 15% 19% 17% 4	2660
July	1st to 10th	Day	41% 6% 12% 25% 15% 2	4371
	11th to 20th	Day	30% 5% 16% 29% 18% 1	4365
	21st to end	Day	43% 6% 15% 19% 14% 3	4552
August	1st to 10th	Day	30% 6% 15% 32% 15% 1	4091
	11th to 20th	Day	35% 6% 12% 31% 15% 1	3844
	21st to end	Day	28% 4 15% 31% 17% 4	4179
September	1st to 10th	Day	37% 6% 11% 24% 18% 4	2263
	11th to 20th	Day	33% 5% 11% 25% 22% 3	2090
	21st to end	Day	36% 5% 11% 24% 22% 2	2090
October	1st to 10th	Day	23% 3 8% 32% 32% 2	3480
	11th to 20th	Day	32% 4 8% 27% 27% 2	3194
	21st to end	Day	41% 3 9% 22% 23% 1	3081
November	1st to 10th	Day	34% 4 12% 27% 18% 5%	1762
	11th to 20th	Day	48% 5% 8% 21% 15% 4	1800
	21st to end	Day	52% 4 9% 21% 13% 1	1773
December	1st to 10th	Day	58% 4 10% 18% 10%	1710
	11th to 20th	Day	58% 5% 6% 22% 8% 1	1920
	21st to end	Day	70% 5% 9% 10% 5%	2783
January	1st to 10th	Night	62% 5% 10% 15% 7%	4428
	11th to 20th	Night	68% 4 9% 13% 6%	4440
	21st to end	Night	66% 4 8% 14% 8% 1	4747
February	1st to 10th	Night	58% 4 12% 17% 8% 1	2280
	11th to 20th	Night	52% 5% 10% 19% 13% 1	2219
	21st to end	Night	54% 4 11% 18% 11% 2	1884
March	1st to 10th	Night	55% 4 8% 22% 10% 2	3733
	11th to 20th	Night	36% 7% 11% 22% 21% 2	3619
	21st to end	Night	46% 5% 11% 29% 8% 1	3635
April	1st to 10th	Night	44% 6% 11% 24% 13% 2	1900
	11th to 20th	Night	44% 5% 9% 20% 17% 5%	1875
	21st to end	Night	46% 6% 10% 20% 14% 4	1758
May	1st to 10th	Night	52% 9% 11% 19% 7% 1	2840
	11th to 20th	Night	42% 7% 13% 27% 10% 1	2813
	21st to end	Night	34% 8% 14% 22% 18% 4	2947
June	1st to 10th	Night	33% 6% 11% 26% 21% 3	1520
	11th to 20th	Night	32% 7% 11% 24% 20% 5%	1520
	21st to end	Night	31% 8% 15% 23% 19% 4	1520
July	1st to 10th	Night	33% 6% 10% 28% 18% 4	2490
	11th to 20th	Night	25% 5% 13% 32% 23% 2	2482
	21st to end	Night	39% 4 17% 21% 15% 4	2767
August	1st to 10th	Night	31% 5% 15% 34% 14% 1	2814
	11th to 20th	Night	32% 6% 12% 31% 18% 1	3034
	21st to end	Night	26% 5% 13% 31% 21% 4	3476
September	1st to 10th	Night	34% 5% 12% 24% 20% 6%	1900
	11th to 20th	Night	28% 5% 9% 27% 26% 5%	2087
	21st to end	Night	35% 6% 10% 22% 23% 4	2090
October	1st to 10th	Night	20% 5% 6% 25% 42% 2	3480
	11th to 20th	Night	28% 3 7% 26% 35% 2	3719
	21st to end	Night	35% 2 9% 24% 24% 5%	4467
November	1st to 10th	Night	36% 4 9% 25% 21% 4	2536
	11th to 20th	Night	43% 4 10% 23% 17% 4	2600
	21st to end	Night	54% 4 9% 21% 11% 1	2562
December	1st to 10th	Night	54% 5% 10% 19% 11% 1	2470
	11th to 20th	Night	53% 4 9% 20% 13% 1	3271
	21st to end	Night	70% 5% 9% 10% 6%	4884

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	24% 14% 32% 22% 7% 1	270
	11th to 20th	Day	23% 19% 36% 17% 4 1	270
	21st to end	Day	24% 19% 31% 20% 6%	297
February	1st to 10th	Day	28% 12% 35% 20% 5%	270
	11th to 20th	Day	23% 20% 34% 17% 6% 1	270
	21st to end	Day	25% 14% 40% 18% 4	225
March	1st to 10th	Day	23% 23% 32% 18% 4	270
	11th to 20th	Day	23% 16% 35% 18% 7% 1	371
	21st to end	Day	27% 14% 33% 18% 8%	506
April	1st to 10th	Day	17% 17% 32% 22% 11% 1	460
	11th to 20th	Day	19% 17% 26% 22% 13% 3	452
	21st to end	Day	25% 13% 33% 19% 8% 3	460
May	1st to 10th	Day	21% 13% 27% 26% 10% 3	463
	11th to 20th	Day	21% 7% 26% 25% 15% 6%	487
	21st to end	Day	11% 5% 25% 27% 20% 11%	605
June	1st to 10th	Day	12% 4 26% 32% 19% 7%	680
	11th to 20th	Day	10% 5% 24% 31% 22% 8%	680
	21st to end	Day	12% 6% 26% 28% 20% 9%	680
July	1st to 10th	Day	12% 2 16% 26% 24% 21%	671
	11th to 20th	Day	7% 3 18% 34% 25% 14%	668
	21st to end	Day	10% 1 16% 29% 31% 12%	676
August	1st to 10th	Day	10% 2 13% 24% 33% 19%	486
	11th to 20th	Day	14% 3 15% 28% 29% 11%	479
	21st to end	Day	8% 2 10% 26% 36% 17%	539
September	1st to 10th	Day	10% 3 14% 28% 32% 12%	490
	11th to 20th	Day	8% 3 14% 25% 34% 17%	490
	21st to end	Day	17% 8% 19% 22% 24% 11%	490
October	1st to 10th	Day	11% 5% 23% 30% 22% 8%	490
	11th to 20th	Day	12% 13% 36% 22% 14% 3	400
	21st to end	Day	25% 14% 34% 22% 4	330
November	1st to 10th	Day	13% 12% 35% 24% 13% 3	300
	11th to 20th	Day	22% 16% 29% 20% 11% 2	300
	21st to end	Day	23% 14% 33% 23% 6%	291
December	1st to 10th	Day	15% 22% 35% 21% 5% 1	270
	11th to 20th	Day	22% 13% 36% 20% 6% 2	270
	21st to end	Day	30% 15% 31% 19% 4	297
January	1st to 10th	Night	21% 15% 33% 26% 5%	950
	11th to 20th	Night	24% 14% 37% 21% 4	950
	21st to end	Night	20% 15% 36% 26% 3	988
February	1st to 10th	Night	23% 12% 37% 25% 3	760
	11th to 20th	Night	19% 15% 38% 25% 3	743
	21st to end	Night	26% 12% 38% 21% 3	628
March	1st to 10th	Night	22% 14% 33% 26% 5%	760
	11th to 20th	Night	19% 13% 37% 25% 6% 1	760
	21st to end	Night	24% 10% 34% 27% 5% 1	731
April	1st to 10th	Night	15% 12% 36% 29% 8% 1	570
	11th to 20th	Night	19% 10% 30% 30% 11% 1	563
	21st to end	Night	21% 8% 38% 25% 9%	570
May	1st to 10th	Night	19% 7% 32% 32% 10%	570
	11th to 20th	Night	18% 6% 22% 34% 17% 3	561
	21st to end	Night	9% 4 22% 39% 23% 3	617
June	1st to 10th	Night	11% 3 21% 43% 20% 1	570
	11th to 20th	Night	10% 3 20% 43% 22% 1	570
	21st to end	Night	9% 1 22% 38% 29% 2	570
July	1st to 10th	Night	10% 1 10% 36% 36% 7%	555
	11th to 20th	Night	6% 2 16% 37% 35% 4	552
	21st to end	Night	9% 1 9% 46% 31% 4	624
August	1st to 10th	Night	8% 2 10% 37% 40% 3	567
	11th to 20th	Night	7% 1 11% 43% 34% 4	564
	21st to end	Night	8% 2 10% 32% 42% 6%	627
September	1st to 10th	Night	13% 3 12% 35% 32% 5%	570
	11th to 20th	Night	10% 3 14% 33% 36% 4	757
	21st to end	Night	13% 6% 18% 35% 25% 3	760
October	1st to 10th	Night	9% 4 23% 35% 24% 4	760
	11th to 20th	Night	20% 9% 26% 29% 15% 1	760
	21st to end	Night	21% 10% 33% 28% 8%	836
November	1st to 10th	Night	15% 8% 33% 31% 12% 1	780
	11th to 20th	Night	17% 12% 33% 29% 8% 1	800
	21st to end	Night	24% 13% 27% 28% 8%	789
December	1st to 10th	Night	23% 11% 37% 24% 5% 1	760
	11th to 20th	Night	23% 10% 32% 26% 7% 1	940
	21st to end	Night	30% 13% 31% 21% 5%	1045

Page generated at 2024-11-25 00:22:19. Version ac07

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