CSI Astrophysical Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the CSI Astrophysical Observatory clear sky chart from 2005-11-06 to 2024-11-05.

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	16% 7% 2 6% 4 4 4 4 6% 7% 40%	101293
	Night	17% 7% 2 6% 4 4 4 3 5% 6% 41%	97761
Transparency	Day	42% 3 11% 24% 17% 2	104838
	Night	43% 3 10% 24% 17% 3	102305
Seeing	Day	19% 7% 26% 27% 16% 5%	15021
	Night	20% 9% 29% 29% 12% 1	24168

By Month

Percentage Cloud Cover NE (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% 8% 2 4 4 3 3 3 5% 5% 48%	2517
	11th to 20th	Day	15% 9% 3 6% 4 5% 5% 3 6% 6% 37%	2520
	21st to end	Day	22% 13% 4 7% 4 4 3 3 3 5% 33%	3033
February	1st to 10th	Day	16% 8% 2 7% 4 4 4 4 5% 5% 40%	1719
	11th to 20th	Day	15% 8% 2 6% 5% 4 4 2 5% 5% 44%	1848
	21st to end	Day	19% 8% 2 6% 5% 4 4 4 5% 6% 37%	1570
March	1st to 10th	Day	27% 8% 2 5% 3 3 3 3 3 6% 36%	3116
	11th to 20th	Day	9% 5% 2 6% 5% 5% 5% 4 6% 8% 45%	3347
	21st to end	Day	20% 7% 2 5% 4 3 3 3 4 5% 44%	4128
April	1st to 10th	Day	17% 8% 2 6% 4 4 4 4 5% 6% 39%	2280
	11th to 20th	Day	17% 6% 2 5% 4 4 4 4 5% 8% 41%	2254
	21st to end	Day	18% 5% 2 6% 4 4 5% 4 6% 7% 39%	2289
May	1st to 10th	Day	27% 9% 2 6% 4 4 4 4 5% 7% 29%	4106
	11th to 20th	Day	24% 8% 3 7% 4 4 4 4 6% 6% 31%	4361
	21st to end	Day	13% 5% 2 5% 4 5% 4 4 6% 8% 44%	4837
June	1st to 10th	Day	14% 6% 2 5% 5% 4 5% 5% 7% 9% 37%	2660
	11th to 20th	Day	14% 7% 2 6% 5% 4 5% 4 6% 8% 38%	2660
	21st to end	Day	10% 6% 2 7% 5% 4 5% 4 7% 10% 40%	2660
July	1st to 10th	Day	8% 6% 3 7% 6% 6% 6% 5% 7% 11% 36%	4440
	11th to 20th	Day	10% 6% 2 6% 5% 5% 5% 5% 7% 10% 38%	4440
	21st to end	Day	12% 8% 3 8% 6% 6% 7% 5% 7% 8% 31%	4814
August	1st to 10th	Day	18% 6% 3 7% 4 5% 6% 4 7% 9% 32%	4130
	11th to 20th	Day	12% 6% 2 6% 4 4 4 4 6% 8% 43%	3730
	21st to end	Day	9% 5% 2 6% 4 4 4 4 6% 9% 45%	4180
September	1st to 10th	Day	14% 6% 2 5% 4 5% 4 4 5% 7% 46%	2280
	11th to 20th	Day	13% 4 2 5% 3 3 4 3 5% 7% 51%	2200
	21st to end	Day	18% 6% 2 6% 4 4 4 3 4 6% 41%	2090
October	1st to 10th	Day	19% 6% 2 5% 4 3 4 4 5% 6% 42%	1981
	11th to 20th	Day	15% 5% 2 5% 3 3 4 4 5% 6% 49%	1900
	21st to end	Day	19% 5% 2 5% 3 4 4 3 4 6% 45%	1948
November	1st to 10th	Day	15% 5% 2 5% 4 3 2 3 4 5% 52%	1708
	11th to 20th	Day	17% 5% 2 5% 3 3 4 3 5% 5% 48%	1710
	21st to end	Day	16% 7% 2 4 4 3 4 3 5% 7% 45%	1639
December	1st to 10th	Day	18% 7% 3 6% 4 3 4 3 7% 7% 38%	1520
	11th to 20th	Day	21% 6% 2 3 4 3 3 3 5% 6% 45%	1906
	21st to end	Day	18% 9% 3 8% 4 5% 5% 4 6% 7% 32%	2772
January	1st to 10th	Night	16% 7% 2 5% 4 3 3 3 4 6% 47%	4429
	11th to 20th	Night	16% 10% 2 6% 4 4 3 3 4 5% 43%	4440
	21st to end	Night	24% 10% 3 6% 3 3 4 3 4 5% 34%	4619
February	1st to 10th	Night	16% 8% 3 6% 4 4 4 3 4 6% 42%	2459
	11th to 20th	Night	17% 9% 2 6% 4 4 3 3 5% 5% 42%	2218
	21st to end	Night	20% 8% 2 5% 3 3 3 3 5% 5% 42%	1884
March	1st to 10th	Night	23% 10% 2 6% 4 3 3 2 4 5% 37%	3724
	11th to 20th	Night	12% 7% 2 7% 4 4 4 3 5% 7% 47%	3609
	21st to end	Night	20% 9% 3 6% 4 3 3 3 4 4 42%	3503
April	1st to 10th	Night	18% 7% 3 6% 5% 4 4 4 5% 6% 38%	1900
	11th to 20th	Night	18% 7% 2 6% 4 4 4 3 5% 6% 41%	1875
	21st to end	Night	19% 7% 2 5% 4 4 4 3 4 6% 43%	1889
May	1st to 10th	Night	26% 9% 3 8% 5% 4 3 3 4 6% 29%	2834
	11th to 20th	Night	25% 8% 3 7% 4 4 3 3 4 6% 33%	2560
	21st to end	Night	16% 8% 2 5% 3 4 4 3 6% 9% 40%	2738
June	1st to 10th	Night	16% 7% 1 5% 4 4 4 4 6% 9% 40%	1520
	11th to 20th	Night	13% 6% 2 6% 4 5% 4 4 7% 9% 40%	1520
	21st to end	Night	9% 5% 2 7% 5% 5% 4 3 7% 11% 42%	1520
July	1st to 10th	Night	9% 6% 2 8% 5% 5% 6% 5% 6% 10% 38%	2520
	11th to 20th	Night	11% 7% 2 6% 6% 5% 5% 5% 8% 9% 37%	2520
	21st to end	Night	17% 7% 2 6% 5% 5% 5% 4 6% 8% 34%	2739
August	1st to 10th	Night	22% 7% 2 6% 5% 5% 5% 4 7% 6% 32%	2764
	11th to 20th	Night	14% 6% 2 8% 5% 5% 4 4 6% 6% 40%	3097
	21st to end	Night	9% 5% 2 4 3 4 4 4 5% 8% 51%	3476
September	1st to 10th	Night	13% 6% 2 7% 4 4 5% 4 5% 6% 44%	1900
	11th to 20th	Night	13% 5% 1 4 2 3 3 3 6% 8% 51%	1978
	21st to end	Night	18% 7% 3 6% 4 4 3 2 4 6% 43%	2090
October	1st to 10th	Night	19% 6% 2 5% 4 4 4 3 4 7% 42%	2196
	11th to 20th	Night	14% 4 2 5% 3 3 4 3 4 6% 51%	2280
	21st to end	Night	20% 7% 2 5% 3 2 3 3 4 5% 45%	2649
November	1st to 10th	Night	12% 5% 2 5% 4 4 4 2 4 5% 52%	2470
	11th to 20th	Night	18% 6% 3 5% 4 3 3 2 5% 5% 47%	2470
	21st to end	Night	15% 5% 2 5% 4 4 4 3 5% 7% 46%	2539
December	1st to 10th	Night	20% 7% 2 6% 4 3 4 4 5% 5% 40%	2660
	11th to 20th	Night	19% 7% 2 5% 3 4 4 3 5% 6% 43%	3288
	21st to end	Night	19% 10% 3 7% 4 4 4 3 5% 6% 36%	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	40% 1 9% 32% 15% 3	2518
	11th to 20th	Day	48% 2 10% 23% 15% 2	2520
	21st to end	Day	56% 2 8% 22% 10% 2	3033
February	1st to 10th	Day	45% 3 13% 24% 13% 2	1719
	11th to 20th	Day	44% 2 8% 26% 18% 3	1857
	21st to end	Day	48% 2 9% 22% 15% 4	1570
March	1st to 10th	Day	50% 2 8% 27% 10% 2	3119
	11th to 20th	Day	37% 2 10% 31% 18% 2	3347
	21st to end	Day	44% 2 8% 17% 24% 5%	4128
April	1st to 10th	Day	45% 3 9% 21% 17% 5%	2280
	11th to 20th	Day	41% 3 11% 23% 18% 4	2254
	21st to end	Day	43% 2 10% 22% 19% 4	2289
May	1st to 10th	Day	56% 2 12% 16% 12% 1	4120
	11th to 20th	Day	53% 2 12% 21% 9% 1	4365
	21st to end	Day	38% 3 10% 27% 20% 2	4837
June	1st to 10th	Day	41% 4 13% 24% 16% 2	2660
	11th to 20th	Day	42% 4 14% 25% 12% 3	2660
	21st to end	Day	38% 5% 13% 26% 17% 1	2660
July	1st to 10th	Day	41% 8% 12% 22% 16% 1	4370
	11th to 20th	Day	39% 6% 16% 23% 14% 1	4365
	21st to end	Day	48% 6% 11% 18% 16% 2	4661
August	1st to 10th	Day	47% 6% 14% 23% 10% 1	4116
	11th to 20th	Day	38% 4 13% 30% 14% 1	3766
	21st to end	Day	33% 4 11% 28% 22% 2	4180
September	1st to 10th	Day	38% 4 12% 23% 21% 3	2280
	11th to 20th	Day	34% 3 10% 26% 25% 2	2200
	21st to end	Day	45% 3 9% 19% 20% 3	2090
October	1st to 10th	Day	36% 3 11% 21% 23% 5%	3293
	11th to 20th	Day	25% 2 10% 25% 32% 5%	3140
	21st to end	Day	28% 2 13% 26% 27% 4	3186
November	1st to 10th	Day	36% 2 11% 26% 22% 3	1708
	11th to 20th	Day	38% 3 8% 24% 23% 3	1710
	21st to end	Day	39% 2 12% 31% 13% 3	1639
December	1st to 10th	Day	45% 3 15% 22% 15% 1	1520
	11th to 20th	Day	42% 2 13% 25% 14% 2	1906
	21st to end	Day	51% 3 9% 26% 10% 1	2772
January	1st to 10th	Night	41% 2 9% 33% 12% 4	4429
	11th to 20th	Night	46% 2 11% 25% 14% 3	4440
	21st to end	Night	54% 1 7% 23% 13% 2	4619
February	1st to 10th	Night	45% 3 12% 25% 13% 2	2459
	11th to 20th	Night	45% 3 8% 20% 19% 5%	2220
	21st to end	Night	44% 2 6% 26% 19% 4	1884
March	1st to 10th	Night	52% 1 7% 24% 12% 3	3734
	11th to 20th	Night	39% 2 11% 26% 19% 3	3610
	21st to end	Night	47% 2 5% 16% 23% 7%	3503
April	1st to 10th	Night	47% 3 8% 20% 18% 4	1900
	11th to 20th	Night	45% 3 9% 20% 21% 2	1875
	21st to end	Night	42% 3 9% 22% 19% 4	1889
May	1st to 10th	Night	58% 2 10% 18% 11% 1	2840
	11th to 20th	Night	54% 3 14% 16% 11% 2	2561
	21st to end	Night	42% 3 14% 24% 15% 3	2739
June	1st to 10th	Night	41% 5% 10% 23% 20% 2	1520
	11th to 20th	Night	39% 4 15% 27% 13% 1	1520
	21st to end	Night	38% 5% 14% 26% 15% 2	1520
July	1st to 10th	Night	41% 7% 16% 20% 14% 2	2480
	11th to 20th	Night	40% 7% 15% 25% 12% 1	2472
	21st to end	Night	46% 6% 13% 17% 16% 2	2651
August	1st to 10th	Night	50% 5% 17% 18% 9% 1	2754
	11th to 20th	Night	43% 5% 10% 30% 12% 1	3127
	21st to end	Night	32% 4 10% 32% 21% 2	3476
September	1st to 10th	Night	40% 4 10% 25% 20% 2	1900
	11th to 20th	Night	33% 3 10% 25% 26% 3	1978
	21st to end	Night	43% 3 7% 23% 21% 2	2090
October	1st to 10th	Night	38% 4 10% 24% 22% 2	3664
	11th to 20th	Night	25% 2 9% 28% 31% 4	3779
	21st to end	Night	30% 3 10% 31% 24% 2	4361
November	1st to 10th	Night	35% 2 10% 25% 22% 4	2470
	11th to 20th	Night	41% 2 8% 25% 19% 5%	2470
	21st to end	Night	39% 2 13% 29% 16% 1	2539
December	1st to 10th	Night	46% 2 12% 24% 14% 2	2660
	11th to 20th	Night	42% 3 12% 21% 18% 4	3288
	21st to end	Night	50% 2 10% 24% 13% 1	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	20% 12% 37% 23% 6% 2	180
	11th to 20th	Day	19% 24% 37% 16% 4	180
	21st to end	Day	23% 10% 36% 20% 9% 1	273
February	1st to 10th	Day	25% 10% 36% 24% 5% 1	279
	11th to 20th	Day	23% 16% 37% 22% 2	456
	21st to end	Day	26% 13% 33% 23% 4 1	382
March	1st to 10th	Day	19% 16% 35% 23% 7%	460
	11th to 20th	Day	17% 15% 39% 20% 7% 2	460
	21st to end	Day	25% 10% 34% 23% 7% 1	506
April	1st to 10th	Day	25% 11% 34% 21% 8% 2	460
	11th to 20th	Day	21% 11% 32% 23% 10% 3	452
	21st to end	Day	24% 12% 29% 25% 8% 2	460
May	1st to 10th	Day	28% 7% 29% 23% 9% 4	463
	11th to 20th	Day	23% 3 28% 28% 15% 3	487
	21st to end	Day	20% 3 18% 26% 26% 8%	529
June	1st to 10th	Day	15% 4 21% 32% 21% 6%	490
	11th to 20th	Day	13% 4 23% 34% 20% 6%	490
	21st to end	Day	14% 2 19% 34% 23% 6%	490
July	1st to 10th	Day	13% 2 14% 33% 27% 11%	485
	11th to 20th	Day	11% 1 13% 32% 30% 12%	484
	21st to end	Day	14% 2 17% 33% 28% 6%	532
August	1st to 10th	Day	12% 1 15% 33% 29% 10%	486
	11th to 20th	Day	13% 2 13% 32% 31% 9%	479
	21st to end	Day	15% 2 17% 32% 23% 12%	539
September	1st to 10th	Day	16% 3 22% 27% 19% 13%	490
	11th to 20th	Day	16% 2 18% 32% 20% 12%	490
	21st to end	Day	25% 3 23% 27% 17% 5%	490
October	1st to 10th	Day	26% 5% 20% 23% 19% 7%	490
	11th to 20th	Day	17% 7% 29% 24% 20% 3	490
	21st to end	Day	23% 7% 30% 25% 13% 3	464
November	1st to 10th	Day	16% 9% 29% 25% 17% 4	378
	11th to 20th	Day	19% 14% 35% 21% 11%	370
	21st to end	Day	18% 11% 36% 23% 11% 1	299
December	1st to 10th	Day	21% 12% 38% 18% 9% 2	180
	11th to 20th	Day	25% 16% 31% 21% 7%	180
	21st to end	Day	24% 10% 37% 19% 10%	198
January	1st to 10th	Night	19% 17% 39% 22% 3	760
	11th to 20th	Night	25% 14% 35% 23% 4	760
	21st to end	Night	19% 16% 39% 23% 3	836
February	1st to 10th	Night	23% 13% 37% 25% 2	760
	11th to 20th	Night	23% 16% 42% 19% 1	743
	21st to end	Night	24% 16% 32% 25% 4	628
March	1st to 10th	Night	22% 14% 34% 25% 5%	760
	11th to 20th	Night	21% 12% 39% 22% 5% 1	760
	21st to end	Night	21% 11% 37% 24% 6%	836
April	1st to 10th	Night	22% 12% 35% 25% 6%	760
	11th to 20th	Night	22% 7% 34% 30% 7%	751
	21st to end	Night	21% 8% 32% 31% 7% 1	749
May	1st to 10th	Night	26% 9% 27% 28% 9% 1	570
	11th to 20th	Night	22% 7% 31% 28% 10% 1	413
	21st to end	Night	19% 3 16% 39% 19% 3	411
June	1st to 10th	Night	19% 3 23% 36% 17% 1	380
	11th to 20th	Night	15% 2 20% 41% 21% 1	380
	21st to end	Night	9% 2 23% 44% 19% 1	380
July	1st to 10th	Night	14% 3 15% 38% 29% 2	370
	11th to 20th	Night	11% 2 15% 42% 26% 3	368
	21st to end	Night	12% 1 17% 47% 21% 1	416
August	1st to 10th	Night	13% 2 13% 44% 25% 3	519
	11th to 20th	Night	14% 2 14% 36% 31% 4	750
	21st to end	Night	16% 2 12% 38% 28% 4	836
September	1st to 10th	Night	16% 3 21% 35% 20% 5%	760
	11th to 20th	Night	16% 3 16% 36% 24% 6%	760
	21st to end	Night	22% 5% 21% 34% 17% 3	760
October	1st to 10th	Night	22% 5% 25% 25% 20% 3	760
	11th to 20th	Night	17% 8% 27% 35% 12% 1	760
	21st to end	Night	23% 6% 32% 27% 11% 1	836
November	1st to 10th	Night	15% 8% 34% 30% 12% 1	760
	11th to 20th	Night	21% 13% 32% 25% 9%	760
	21st to end	Night	17% 15% 35% 25% 7% 1	760
December	1st to 10th	Night	25% 15% 32% 20% 7% 1	760
	11th to 20th	Night	21% 12% 39% 23% 3	760
	21st to end	Night	24% 11% 36% 26% 3	836

Page generated at 2024-11-03 02:11:22. Version ac07

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