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 2024-04-25.

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% 6% 2 5% 5% 3 4 5% 5% 7% 41%	83234
	Night	17% 7% 3 5% 4 3 4 4 5% 6% 42%	85864
Transparency	Day	43% 3 11% 24% 17% 2	82939
	Night	44% 3 10% 24% 17% 3	85693
Seeing	Day	19% 7% 26% 26% 16% 5%	14257
	Night	20% 9% 29% 29% 11% 1	23576

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 2 3 4 5% 5% 48%	2517
	11th to 20th	Day	16% 9% 3 5% 5% 3 5% 5% 5% 6% 38%	2520
	21st to end	Day	22% 13% 4 6% 5% 3 3 4 3 5% 33%	3033
February	1st to 10th	Day	17% 8% 3 6% 4 3 4 5% 4 6% 41%	1719
	11th to 20th	Day	15% 7% 3 5% 5% 3 4 3 5% 5% 45%	1848
	21st to end	Day	19% 7% 2 6% 5% 3 4 5% 5% 6% 37%	1570
March	1st to 10th	Day	27% 8% 2 5% 4 2 4 3 3 6% 36%	3116
	11th to 20th	Day	9% 5% 2 5% 6% 4 5% 6% 6% 8% 45%	3347
	21st to end	Day	20% 6% 3 5% 4 2 3 3 4 5% 44%	4128
April	1st to 10th	Day	17% 8% 3 5% 5% 3 4 4 5% 6% 40%	2280
	11th to 20th	Day	17% 5% 3 5% 4 3 4 5% 5% 8% 41%	2254
	21st to end	Day	19% 6% 2 5% 5% 3 5% 5% 5% 7% 39%	2218
May	1st to 10th	Day	21% 7% 3 5% 5% 3 5% 5% 5% 7% 35%	2340
	11th to 20th	Day	21% 5% 2 4 5% 3 5% 5% 6% 7% 37%	2455
	21st to end	Day	15% 6% 2 5% 5% 3 4 4 5% 8% 42%	2725
June	1st to 10th	Day	15% 6% 2 4 5% 3 5% 6% 7% 9% 37%	2520
	11th to 20th	Day	15% 7% 3 5% 6% 3 6% 5% 6% 8% 38%	2520
	21st to end	Day	10% 5% 2 6% 6% 3 5% 5% 6% 10% 41%	2520
July	1st to 10th	Day	9% 6% 3 6% 6% 4 6% 6% 7% 10% 39%	2520
	11th to 20th	Day	9% 5% 2 4 5% 4 6% 7% 7% 10% 42%	2520
	21st to end	Day	10% 6% 3 6% 6% 4 7% 7% 6% 8% 37%	2744
August	1st to 10th	Day	8% 5% 2 6% 6% 4 7% 5% 8% 10% 38%	2352
	11th to 20th	Day	11% 6% 2 5% 6% 3 5% 7% 6% 8% 40%	2126
	21st to end	Day	13% 6% 2 5% 5% 3 4 5% 5% 7% 43%	2376
September	1st to 10th	Day	14% 5% 2 4 5% 3 5% 5% 5% 7% 44%	2160
	11th to 20th	Day	14% 4 3 4 3 3 3 3 5% 8% 51%	2085
	21st to end	Day	16% 6% 2 5% 6% 3 4 4 4 6% 43%	1980
October	1st to 10th	Day	20% 5% 2 4 4 2 4 4 5% 6% 42%	1877
	11th to 20th	Day	16% 5% 2 5% 4 2 4 5% 5% 6% 47%	1800
	21st to end	Day	20% 5% 2 4 4 3 4 4 4 6% 43%	1846
November	1st to 10th	Day	16% 5% 2 4 4 2 3 3 4 5% 52%	1671
	11th to 20th	Day	17% 5% 2 4 4 2 3 4 5% 5% 48%	1710
	21st to end	Day	16% 6% 2 4 4 3 4 4 5% 7% 46%	1639
December	1st to 10th	Day	18% 7% 3 5% 5% 2 4 4 6% 8% 38%	1520
	11th to 20th	Day	21% 6% 2 3 4 2 3 3 4 6% 45%	1906
	21st to end	Day	18% 8% 3 7% 5% 3 5% 6% 6% 7% 32%	2772
January	1st to 10th	Night	16% 7% 3 4 4 3 4 3 4 6% 47%	4429
	11th to 20th	Night	17% 9% 3 5% 4 3 3 4 4 5% 43%	4440
	21st to end	Night	24% 10% 3 5% 4 2 4 4 4 5% 35%	4619
February	1st to 10th	Night	16% 8% 3 5% 5% 3 4 4 4 6% 42%	2459
	11th to 20th	Night	17% 8% 3 6% 4 3 4 3 5% 5% 42%	2218
	21st to end	Night	20% 7% 2 5% 4 2 3 4 5% 5% 43%	1884
March	1st to 10th	Night	23% 10% 2 5% 5% 3 3 3 3 5% 37%	3724
	11th to 20th	Night	12% 6% 2 6% 5% 2 5% 4 4 7% 47%	3609
	21st to end	Night	20% 8% 3 5% 4 2 3 3 4 5% 42%	3503
April	1st to 10th	Night	18% 7% 3 6% 5% 3 5% 5% 5% 6% 39%	1900
	11th to 20th	Night	18% 7% 2 5% 4 3 4 4 5% 7% 41%	1875
	21st to end	Night	19% 6% 2 4 4 3 4 4 4 6% 43%	1840
May	1st to 10th	Night	22% 7% 3 6% 6% 3 3 3 4 6% 36%	1620
	11th to 20th	Night	20% 6% 3 5% 5% 3 4 4 6% 6% 38%	1452
	21st to end	Night	17% 7% 2 4 4 3 4 4 5% 8% 40%	1550
June	1st to 10th	Night	16% 6% 2 5% 5% 3 4 5% 5% 9% 39%	1440
	11th to 20th	Night	14% 6% 2 6% 5% 4 4 5% 7% 9% 39%	1440
	21st to end	Night	9% 5% 2 5% 6% 4 5% 4 6% 12% 43%	1440
July	1st to 10th	Night	12% 5% 2 5% 5% 3 5% 7% 6% 10% 40%	1440
	11th to 20th	Night	10% 5% 2 5% 6% 4 5% 6% 7% 9% 41%	1440
	21st to end	Night	9% 5% 2 5% 5% 3 5% 6% 6% 11% 42%	1574
August	1st to 10th	Night	9% 5% 2 5% 6% 4 5% 6% 8% 8% 44%	1564
	11th to 20th	Night	11% 6% 3 7% 7% 4 5% 6% 6% 7% 38%	1774
	21st to end	Night	14% 6% 2 4 5% 3 5% 5% 6% 8% 42%	1980
September	1st to 10th	Night	14% 5% 3 6% 5% 3 5% 5% 6% 6% 43%	1800
	11th to 20th	Night	14% 5% 2 4 3 2 3 3 5% 7% 52%	1873
	21st to end	Night	17% 6% 3 5% 5% 3 3 3 4 7% 45%	1980
October	1st to 10th	Night	19% 6% 2 4 5% 2 4 4 4 7% 42%	2080
	11th to 20th	Night	15% 4 2 5% 4 3 4 4 4 6% 49%	2160
	21st to end	Night	21% 7% 2 4 4 2 3 4 4 5% 44%	2509
November	1st to 10th	Night	12% 4 2 5% 4 2 5% 3 4 5% 52%	2407
	11th to 20th	Night	18% 6% 3 5% 4 2 3 3 4 5% 48%	2470
	21st to end	Night	15% 5% 3 5% 4 3 4 4 4 8% 46%	2539
December	1st to 10th	Night	20% 6% 3 5% 5% 2 4 4 5% 5% 40%	2660
	11th to 20th	Night	19% 6% 2 4 3 3 4 4 5% 6% 43%	3288
	21st to end	Night	19% 9% 3 6% 5% 3 4 4 4 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% 3 9% 22% 19% 4	2218
May	1st to 10th	Day	49% 3 9% 20% 17% 2	2340
	11th to 20th	Day	45% 4 10% 22% 16% 2	2459
	21st to end	Day	41% 4 15% 23% 15% 2	2725
June	1st to 10th	Day	41% 5% 14% 24% 15% 2	2520
	11th to 20th	Day	44% 4 13% 24% 12% 3	2520
	21st to end	Day	39% 5% 12% 27% 16% 1	2520
July	1st to 10th	Day	40% 5% 12% 24% 17% 1	2450
	11th to 20th	Day	34% 5% 15% 27% 16% 2	2445
	21st to end	Day	41% 5% 12% 22% 18% 3	2591
August	1st to 10th	Day	37% 5% 14% 27% 15% 1	2338
	11th to 20th	Day	39% 4 14% 26% 15% 2	2126
	21st to end	Day	39% 3 11% 23% 20% 3	2376
September	1st to 10th	Day	39% 4 12% 23% 20% 3	2160
	11th to 20th	Day	34% 3 10% 26% 25% 2	2085
	21st to end	Day	43% 3 9% 20% 21% 3	1980
October	1st to 10th	Day	43% 3 10% 24% 18% 2	1877
	11th to 20th	Day	38% 2 10% 27% 20% 2	1800
	21st to end	Day	43% 2 9% 24% 19% 2	1846
November	1st to 10th	Day	37% 2 11% 26% 22% 3	1671
	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	43% 3 9% 22% 19% 5%	1840
May	1st to 10th	Night	51% 3 9% 18% 17% 2	1620
	11th to 20th	Night	46% 5% 10% 17% 19% 3	1453
	21st to end	Night	43% 5% 15% 21% 13% 2	1551
June	1st to 10th	Night	42% 5% 10% 22% 19% 2	1440
	11th to 20th	Night	41% 5% 15% 25% 13% 1	1440
	21st to end	Night	37% 5% 14% 27% 16% 2	1440
July	1st to 10th	Night	39% 5% 15% 23% 16% 2	1400
	11th to 20th	Night	38% 5% 13% 28% 14% 2	1392
	21st to end	Night	34% 6% 16% 25% 16% 4	1486
August	1st to 10th	Night	37% 5% 17% 25% 15% 2	1554
	11th to 20th	Night	44% 5% 12% 26% 13% 1	1774
	21st to end	Night	40% 4 12% 22% 19% 3	1980
September	1st to 10th	Night	41% 4 11% 24% 18% 2	1800
	11th to 20th	Night	33% 2 11% 25% 26% 3	1873
	21st to end	Night	42% 3 6% 24% 23% 2	1980
October	1st to 10th	Night	43% 4 10% 25% 16% 2	2080
	11th to 20th	Night	38% 2 11% 29% 18% 2	2160
	21st to end	Night	44% 2 9% 25% 18% 1	2509
November	1st to 10th	Night	36% 2 10% 25% 23% 4	2407
	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% 30% 24% 8% 2	437
May	1st to 10th	Day	27% 8% 29% 23% 8% 4	423
	11th to 20th	Day	22% 4 30% 27% 14% 3	447
	21st to end	Day	21% 3 17% 25% 26% 8%	485
June	1st to 10th	Day	16% 4 22% 31% 21% 6%	450
	11th to 20th	Day	15% 4 24% 34% 19% 4	450
	21st to end	Day	15% 1 18% 36% 24% 6%	450
July	1st to 10th	Day	14% 2 13% 33% 27% 12%	445
	11th to 20th	Day	11% 1 12% 31% 31% 13%	444
	21st to end	Day	14% 1 17% 32% 29% 6%	488
August	1st to 10th	Day	10% 1 15% 34% 30% 11%	446
	11th to 20th	Day	13% 2 12% 33% 32% 9%	439
	21st to end	Day	16% 1 16% 31% 23% 12%	495
September	1st to 10th	Day	16% 2 22% 27% 19% 13%	450
	11th to 20th	Day	17% 3 19% 32% 19% 12%	450
	21st to end	Day	22% 3 24% 28% 18% 5%	450
October	1st to 10th	Day	28% 4 19% 22% 20% 7%	450
	11th to 20th	Day	18% 6% 28% 24% 21% 3	450
	21st to end	Day	25% 7% 31% 23% 11% 3	428
November	1st to 10th	Day	16% 8% 29% 25% 17% 4	365
	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	22% 8% 32% 31% 7% 1	730
May	1st to 10th	Night	25% 9% 27% 28% 9% 1	540
	11th to 20th	Night	21% 7% 32% 28% 11% 1	391
	21st to end	Night	20% 4 16% 38% 20% 3	389
June	1st to 10th	Night	20% 3 23% 35% 18% 1	360
	11th to 20th	Night	15% 3 20% 41% 20% 1	360
	21st to end	Night	9% 2 22% 45% 20% 1	360
July	1st to 10th	Night	14% 2 16% 37% 29% 3	350
	11th to 20th	Night	11% 2 15% 42% 27% 3	348
	21st to end	Night	10% 1 17% 48% 22% 2	394
August	1st to 10th	Night	11% 1 13% 45% 26% 3	490
	11th to 20th	Night	14% 2 13% 36% 31% 4	710
	21st to end	Night	17% 2 12% 38% 27% 4	792
September	1st to 10th	Night	17% 3 21% 35% 20% 5%	720
	11th to 20th	Night	17% 3 17% 36% 22% 6%	720
	21st to end	Night	21% 4 21% 34% 18% 3	720
October	1st to 10th	Night	23% 5% 24% 25% 20% 3	720
	11th to 20th	Night	18% 8% 26% 36% 12% 1	720
	21st to end	Night	24% 6% 33% 26% 10% 1	792
November	1st to 10th	Night	15% 9% 33% 30% 12% 1	740
	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 2024-04-22 09:25:44. Version ac07

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