Observatoire Saint-Raymond
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Observatoire Saint-Raymond clear sky chart from 2005-11-06 to 2025-04-26.

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	19% 11% 3 8% 5% 4 4 4 5% 6% 30%	113016
	Night	19% 12% 4 9% 5% 4 4 3 5% 6% 29%	115618
Transparency	Day	56% 3 12% 19% 10% 1	116506
	Night	57% 3 11% 19% 9% 1	120293
Seeing	Day	28% 14% 29% 20% 8% 2	15584
	Night	27% 11% 26% 26% 9% 1	24365

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	18% 20% 5% 12% 6% 4 4 3 4 5% 20%	3597
	11th to 20th	Day	10% 15% 7% 20% 8% 5% 4 3 4 4 22%	3570
	21st to end	Day	9% 13% 5% 12% 6% 4 5% 4 5% 7% 30%	3960
February	1st to 10th	Day	12% 16% 6% 12% 7% 6% 5% 2 4 4 25%	1612
	11th to 20th	Day	13% 17% 6% 12% 6% 5% 4 4 4 5% 24%	1918
	21st to end	Day	14% 15% 5% 12% 6% 4 4 3 5% 6% 26%	1650
March	1st to 10th	Day	24% 15% 5% 10% 6% 4 3 2 3 3 25%	4476
	11th to 20th	Day	15% 16% 4 8% 6% 4 4 3 4 5% 29%	4699
	21st to end	Day	20% 14% 3 7% 4 4 4 3 4 4 33%	5876
April	1st to 10th	Day	23% 12% 4 8% 5% 5% 4 3 2 5% 29%	2400
	11th to 20th	Day	22% 8% 3 6% 4 5% 4 3 4 5% 35%	2448
	21st to end	Day	24% 10% 3 7% 5% 4 4 3 3 6% 30%	2535
May	1st to 10th	Day	22% 8% 3 7% 4 4 4 3 5% 6% 35%	4259
	11th to 20th	Day	18% 7% 3 7% 5% 4 5% 4 7% 8% 33%	4398
	21st to end	Day	19% 7% 3 8% 5% 5% 5% 4 5% 7% 31%	4837
June	1st to 10th	Day	21% 8% 2 7% 5% 6% 6% 4 6% 8% 27%	2817
	11th to 20th	Day	20% 7% 2 6% 4 4 5% 4 6% 8% 34%	2850
	21st to end	Day	25% 9% 3 8% 5% 5% 4 4 5% 6% 26%	2825
July	1st to 10th	Day	17% 7% 3 8% 6% 5% 6% 4 6% 8% 30%	4440
	11th to 20th	Day	19% 7% 2 7% 5% 5% 6% 5% 7% 9% 29%	4440
	21st to end	Day	16% 6% 2 6% 4 5% 5% 5% 6% 8% 39%	4814
August	1st to 10th	Day	17% 7% 2 7% 5% 6% 6% 5% 7% 9% 29%	4423
	11th to 20th	Day	21% 7% 3 6% 5% 5% 5% 4 6% 9% 28%	4058
	21st to end	Day	23% 7% 2 7% 3 4 4 3 5% 7% 35%	4286
September	1st to 10th	Day	20% 6% 2 6% 3 4 5% 4 6% 7% 37%	2280
	11th to 20th	Day	19% 5% 2 5% 3 4 4 3 5% 6% 44%	2132
	21st to end	Day	24% 7% 2 6% 4 3 3 3 5% 6% 37%	2090
October	1st to 10th	Day	24% 9% 2 5% 4 5% 5% 4 5% 6% 31%	2057
	11th to 20th	Day	26% 10% 3 9% 5% 4 4 5% 5% 6% 23%	1758
	21st to end	Day	28% 10% 3 7% 5% 4 4 3 4 6% 25%	1881
November	1st to 10th	Day	21% 11% 3 8% 6% 4 3 3 4 5% 31%	1761
	11th to 20th	Day	22% 13% 4 9% 6% 5% 4 3 3 4 26%	1770
	21st to end	Day	22% 18% 4 8% 6% 5% 4 4 4 5% 20%	1485
December	1st to 10th	Day	20% 16% 5% 10% 5% 5% 5% 4 5% 5% 20%	2280
	11th to 20th	Day	21% 16% 5% 9% 5% 4 3 2 3 4 27%	2618
	21st to end	Day	20% 18% 4 7% 4 3 5% 3 5% 4 25%	3716
January	1st to 10th	Night	16% 22% 7% 15% 6% 4 3 2 3 4 18%	6349
	11th to 20th	Night	11% 20% 8% 16% 6% 5% 4 3 3 4 20%	6315
	21st to end	Night	9% 13% 5% 12% 7% 6% 5% 4 6% 6% 28%	6996
February	1st to 10th	Night	12% 15% 5% 12% 7% 5% 4 3 4 5% 28%	2785
	11th to 20th	Night	13% 16% 5% 12% 5% 6% 4 4 5% 5% 25%	2368
	21st to end	Night	16% 14% 5% 9% 5% 5% 5% 3 5% 5% 28%	1980
March	1st to 10th	Night	23% 13% 4 11% 5% 4 5% 3 4 5% 23%	5364
	11th to 20th	Night	15% 15% 4 9% 6% 5% 5% 4 5% 7% 24%	5259
	21st to end	Night	19% 15% 4 8% 4 4 4 3 4 5% 30%	5054
April	1st to 10th	Night	22% 14% 3 7% 4 4 3 3 5% 6% 29%	2000
	11th to 20th	Night	22% 8% 3 6% 5% 4 4 3 5% 6% 32%	1900
	21st to end	Night	22% 10% 3 6% 4 3 4 3 4 6% 34%	1762
May	1st to 10th	Night	24% 7% 2 6% 5% 4 4 3 5% 6% 33%	2710
	11th to 20th	Night	22% 7% 2 6% 3 4 3 3 5% 7% 37%	2495
	21st to end	Night	19% 6% 3 6% 5% 5% 5% 3 6% 8% 35%	2738
June	1st to 10th	Night	22% 8% 2 6% 5% 5% 5% 4 7% 7% 29%	1359
	11th to 20th	Night	20% 7% 2 5% 5% 4 4 3 5% 8% 36%	1330
	21st to end	Night	23% 7% 3 6% 6% 4 4 3 5% 6% 31%	1348
July	1st to 10th	Night	16% 6% 2 8% 6% 5% 5% 5% 7% 7% 32%	2520
	11th to 20th	Night	20% 7% 3 6% 5% 3 4 4 5% 8% 35%	2520
	21st to end	Night	14% 5% 2 5% 5% 4 4 3 6% 7% 44%	2739
August	1st to 10th	Night	18% 7% 3 8% 4 4 5% 3 6% 8% 35%	2506
	11th to 20th	Night	21% 6% 2 7% 5% 6% 5% 4 5% 7% 32%	2739
	21st to end	Night	19% 8% 3 9% 5% 5% 4 3 5% 6% 34%	3368
September	1st to 10th	Night	19% 6% 2 6% 4 3 3 4 6% 5% 42%	1900
	11th to 20th	Night	18% 5% 2 6% 4 4 4 3 4 6% 45%	2047
	21st to end	Night	22% 7% 2 6% 3 3 4 3 4 6% 41%	2090
October	1st to 10th	Night	21% 8% 2 6% 4 4 4 3 5% 6% 38%	2119
	11th to 20th	Night	25% 9% 3 7% 4 4 5% 3 3 5% 31%	2421
	21st to end	Night	28% 9% 2 6% 4 4 3 3 5% 6% 28%	2717
November	1st to 10th	Night	20% 12% 3 8% 5% 4 4 3 4 6% 31%	2537
	11th to 20th	Night	21% 12% 3 7% 5% 4 4 3 4 6% 31%	2625
	21st to end	Night	25% 15% 4 8% 5% 4 4 3 4 5% 24%	2911
December	1st to 10th	Night	18% 16% 6% 12% 8% 5% 4 3 4 4 20%	4910
	11th to 20th	Night	24% 15% 4 9% 6% 5% 4 3 4 5% 22%	5591
	21st to end	Night	23% 17% 5% 10% 4 3 3 2 3 3 26%	7246

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	70% 1 7% 14% 7%	3598
	11th to 20th	Day	69% 2 6% 16% 7% 1	3600
	21st to end	Day	54% 2 8% 20% 15% 1	3960
February	1st to 10th	Day	64% 2 8% 15% 9% 2	1612
	11th to 20th	Day	64% 2 10% 13% 10% 1	1927
	21st to end	Day	60% 2 8% 18% 10% 3	1650
March	1st to 10th	Day	67% 1 7% 12% 10% 3	4479
	11th to 20th	Day	59% 3 12% 15% 10% 1	4699
	21st to end	Day	56% 2 6% 17% 16% 4	5876
April	1st to 10th	Day	61% 2 9% 14% 11% 4	2400
	11th to 20th	Day	53% 2 9% 22% 12% 3	2448
	21st to end	Day	58% 2 8% 17% 13% 2	2535
May	1st to 10th	Day	52% 1 11% 18% 16% 2	4273
	11th to 20th	Day	50% 2 17% 22% 8% 1	4402
	21st to end	Day	53% 2 8% 20% 16% 1	4837
June	1st to 10th	Day	56% 3 11% 21% 8% 2	2817
	11th to 20th	Day	48% 3 14% 21% 12% 2	2850
	21st to end	Day	58% 4 11% 17% 9% 1	2825
July	1st to 10th	Day	51% 4 15% 22% 8%	4370
	11th to 20th	Day	49% 6% 20% 20% 4	4365
	21st to end	Day	44% 4 20% 25% 7%	4661
August	1st to 10th	Day	49% 6% 19% 20% 5%	4409
	11th to 20th	Day	52% 5% 19% 19% 5%	4097
	21st to end	Day	49% 4 14% 18% 14%	4286
September	1st to 10th	Day	46% 3 15% 24% 11% 1	2280
	11th to 20th	Day	42% 2 17% 28% 11% 1	2132
	21st to end	Day	50% 2 14% 26% 9%	2090
October	1st to 10th	Day	55% 6% 10% 22% 6%	3421
	11th to 20th	Day	57% 5% 16% 20% 2	2896
	21st to end	Day	54% 5% 17% 17% 7%	3081
November	1st to 10th	Day	57% 3 11% 20% 9%	1761
	11th to 20th	Day	63% 2 8% 18% 7% 1	1770
	21st to end	Day	67% 3 11% 14% 5% 1	1485
December	1st to 10th	Day	66% 3 10% 15% 6%	2280
	11th to 20th	Day	63% 2 8% 17% 10%	2618
	21st to end	Day	63% 3 8% 14% 11% 1	3716
January	1st to 10th	Night	73% 2 9% 11% 6%	6349
	11th to 20th	Night	70% 2 7% 16% 4	6360
	21st to end	Night	57% 2 9% 18% 13%	6996
February	1st to 10th	Night	60% 2 8% 19% 10% 1	2785
	11th to 20th	Night	62% 2 9% 16% 10% 1	2370
	21st to end	Night	58% 2 7% 18% 13% 2	1980
March	1st to 10th	Night	65% 2 9% 11% 11% 2	5374
	11th to 20th	Night	61% 3 10% 15% 9% 2	5260
	21st to end	Night	58% 2 5% 22% 10% 2	5054
April	1st to 10th	Night	58% 1 8% 17% 14% 2	2000
	11th to 20th	Night	53% 2 7% 22% 14% 2	1900
	21st to end	Night	52% 2 8% 20% 15% 2	1762
May	1st to 10th	Night	54% 1 9% 22% 11% 2	2716
	11th to 20th	Night	49% 1 15% 22% 12% 1	2496
	21st to end	Night	49% 2 11% 20% 17% 1	2739
June	1st to 10th	Night	52% 3 11% 23% 10% 1	1359
	11th to 20th	Night	47% 4 12% 22% 13% 3	1330
	21st to end	Night	55% 3 12% 18% 12% 1	1348
July	1st to 10th	Night	48% 5% 19% 21% 7%	2480
	11th to 20th	Night	48% 4 21% 22% 5%	2472
	21st to end	Night	38% 5% 22% 26% 8%	2651
August	1st to 10th	Night	48% 5% 17% 23% 8%	2496
	11th to 20th	Night	51% 6% 20% 17% 6%	2766
	21st to end	Night	51% 4 11% 22% 11%	3368
September	1st to 10th	Night	43% 3 13% 27% 12% 1	1900
	11th to 20th	Night	42% 2 17% 29% 9% 1	2047
	21st to end	Night	46% 3 11% 28% 11%	2090
October	1st to 10th	Night	52% 4 12% 23% 8%	3535
	11th to 20th	Night	51% 4 16% 25% 4	4022
	21st to end	Night	49% 3 19% 17% 11%	4467
November	1st to 10th	Night	56% 3 11% 21% 8% 1	2537
	11th to 20th	Night	56% 3 11% 20% 10%	2625
	21st to end	Night	64% 3 9% 17% 7%	2911
December	1st to 10th	Night	68% 4 11% 13% 4	4910
	11th to 20th	Night	66% 3 6% 19% 7%	5592
	21st to end	Night	65% 2 7% 17% 9% 1	7246

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	35% 17% 31% 16% 3	200
	11th to 20th	Day	30% 21% 24% 18% 7% 2	200
	21st to end	Day	19% 21% 38% 15% 8%	220
February	1st to 10th	Day	32% 19% 33% 13% 3	207
	11th to 20th	Day	29% 23% 31% 14% 3	466
	21st to end	Day	29% 23% 29% 16% 3	414
March	1st to 10th	Day	30% 19% 28% 17% 6%	500
	11th to 20th	Day	31% 19% 29% 16% 4 1	500
	21st to end	Day	30% 21% 26% 16% 7% 1	550
April	1st to 10th	Day	33% 16% 32% 14% 5% 1	500
	11th to 20th	Day	36% 14% 27% 15% 5% 2	492
	21st to end	Day	34% 17% 30% 12% 5% 1	480
May	1st to 10th	Day	32% 16% 32% 14% 6%	463
	11th to 20th	Day	26% 14% 30% 22% 8% 1	487
	21st to end	Day	24% 21% 32% 16% 7%	529
June	1st to 10th	Day	26% 11% 32% 23% 7% 1	647
	11th to 20th	Day	24% 13% 28% 23% 11% 1	680
	21st to end	Day	27% 10% 28% 22% 11% 2	655
July	1st to 10th	Day	22% 12% 33% 21% 11% 1	485
	11th to 20th	Day	21% 8% 35% 24% 10% 2	484
	21st to end	Day	21% 8% 31% 27% 10% 3	532
August	1st to 10th	Day	20% 7% 29% 29% 11% 3	486
	11th to 20th	Day	24% 6% 22% 30% 15% 3	479
	21st to end	Day	23% 13% 24% 20% 15% 6%	539
September	1st to 10th	Day	25% 9% 26% 24% 12% 4	490
	11th to 20th	Day	22% 9% 24% 26% 15% 5%	490
	21st to end	Day	26% 13% 23% 21% 13% 4	490
October	1st to 10th	Day	27% 14% 25% 21% 12% 2	490
	11th to 20th	Day	32% 12% 27% 19% 8% 2	415
	21st to end	Day	38% 11% 26% 19% 6%	429
November	1st to 10th	Day	36% 13% 23% 21% 7% 1	395
	11th to 20th	Day	33% 13% 28% 19% 7%	370
	21st to end	Day	36% 19% 29% 14% 3 1	200
December	1st to 10th	Day	35% 9% 33% 17% 6% 1	200
	11th to 20th	Day	33% 17% 30% 16% 4 2	200
	21st to end	Day	35% 17% 28% 13% 5% 1	220
January	1st to 10th	Night	30% 13% 31% 22% 4 1	800
	11th to 20th	Night	29% 16% 26% 21% 8%	800
	21st to end	Night	17% 13% 31% 31% 8% 1	880
February	1st to 10th	Night	19% 15% 35% 25% 6%	800
	11th to 20th	Night	23% 16% 35% 19% 6%	783
	21st to end	Night	27% 14% 28% 26% 5%	660
March	1st to 10th	Night	25% 13% 31% 25% 6%	800
	11th to 20th	Night	27% 15% 33% 19% 6% 1	800
	21st to end	Night	28% 13% 28% 23% 7% 1	880
April	1st to 10th	Night	32% 12% 28% 22% 6%	800
	11th to 20th	Night	28% 12% 28% 25% 6%	716
	21st to end	Night	32% 14% 28% 21% 5%	588
May	1st to 10th	Night	31% 10% 32% 19% 6%	498
	11th to 20th	Night	26% 8% 28% 29% 8% 1	374
	21st to end	Night	25% 8% 30% 27% 9%	411
June	1st to 10th	Night	27% 5% 28% 33% 8% 1	380
	11th to 20th	Night	24% 7% 22% 32% 15% 1	380
	21st to end	Night	26% 2 20% 38% 13% 1	380
July	1st to 10th	Night	21% 2 25% 37% 14% 1	370
	11th to 20th	Night	20% 3 19% 42% 15% 2	368
	21st to end	Night	18% 4 20% 40% 18% 1	416
August	1st to 10th	Night	18% 3 12% 44% 22%	378
	11th to 20th	Night	19% 3 20% 38% 19%	531
	21st to end	Night	21% 7% 21% 32% 18% 1	767
September	1st to 10th	Night	22% 5% 24% 34% 14% 1	760
	11th to 20th	Night	23% 5% 19% 32% 19% 2	760
	21st to end	Night	25% 6% 23% 30% 14% 1	760
October	1st to 10th	Night	25% 8% 24% 31% 11%	760
	11th to 20th	Night	31% 9% 23% 27% 9% 1	760
	21st to end	Night	34% 9% 28% 24% 4 1	836
November	1st to 10th	Night	30% 10% 26% 26% 7% 1	780
	11th to 20th	Night	30% 13% 26% 23% 8% 1	800
	21st to end	Night	34% 14% 24% 20% 7% 1	856
December	1st to 10th	Night	34% 11% 24% 22% 8%	900
	11th to 20th	Night	31% 15% 25% 21% 7% 1	900
	21st to end	Night	37% 12% 27% 18% 5% 1	933

Page generated at 2025-04-23 09:25:03. Version ac07

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