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 2026-08-30.

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% 10% 3 8% 5% 5% 5% 4 5% 6% 30%	143730
	Night	18% 12% 4 9% 5% 4 4 3 5% 6% 29%	138533
Transparency	Day	54% 4 12% 19% 9% 1	147174
	Night	57% 3 11% 19% 9% 1	143179
Seeing	Day	28% 14% 29% 19% 8% 2	17396
	Night	27% 11% 27% 27% 9% 1	25912

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	16% 17% 5% 12% 6% 3 4 3 4 5% 24%	4661
	11th to 20th	Day	12% 17% 8% 19% 8% 5% 4 3 3 4 19%	4650
	21st to end	Day	7% 13% 6% 11% 5% 4 5% 6% 6% 8% 29%	5124
February	1st to 10th	Day	11% 16% 6% 12% 7% 6% 5% 2 4 5% 27%	1693
	11th to 20th	Day	13% 17% 6% 12% 5% 5% 4 4 4 5% 25%	2017
	21st to end	Day	13% 15% 5% 12% 6% 4 4 3 5% 6% 27%	1730
March	1st to 10th	Day	23% 15% 5% 10% 6% 4 3 2 3 3 25%	4576
	11th to 20th	Day	16% 16% 5% 9% 6% 4 3 3 4 5% 29%	4803
	21st to end	Day	19% 15% 3 7% 4 4 4 3 4 4 33%	6006
April	1st to 10th	Day	23% 12% 4 8% 6% 5% 4 3 2 5% 29%	2520
	11th to 20th	Day	22% 8% 3 7% 4 5% 4 3 4 5% 34%	2572
	21st to end	Day	24% 10% 3 7% 5% 5% 4 3 4 6% 30%	2730
May	1st to 10th	Day	28% 9% 3 7% 4 4 4 4 5% 6% 27%	7930
	11th to 20th	Day	22% 7% 3 7% 5% 4 4 4 6% 7% 32%	8221
	21st to end	Day	21% 9% 3 8% 5% 5% 6% 4 5% 6% 28%	9060
June	1st to 10th	Day	21% 8% 2 7% 5% 6% 6% 5% 6% 8% 28%	3113
	11th to 20th	Day	20% 7% 2 6% 4 4 5% 4 6% 8% 33%	3150
	21st to end	Day	24% 9% 3 7% 5% 5% 4 4 5% 6% 26%	3122
July	1st to 10th	Day	17% 6% 3 7% 5% 5% 5% 4 7% 9% 33%	8280
	11th to 20th	Day	16% 6% 2 6% 4 5% 5% 4 7% 9% 35%	8280
	21st to end	Day	14% 5% 2 7% 5% 5% 5% 5% 7% 8% 37%	8993
August	1st to 10th	Day	16% 6% 2 7% 5% 6% 6% 5% 7% 9% 30%	4703
	11th to 20th	Day	21% 7% 3 6% 5% 5% 5% 4 6% 9% 29%	4320
	21st to end	Day	23% 7% 2 7% 3 4 4 4 5% 7% 35%	4532
September	1st to 10th	Day	19% 6% 2 6% 3 4 5% 4 6% 7% 38%	2400
	11th to 20th	Day	18% 5% 2 5% 3 4 4 3 5% 6% 46%	2244
	21st to end	Day	24% 7% 2 6% 4 3 3 3 5% 6% 37%	2200
October	1st to 10th	Day	23% 8% 2 5% 4 5% 5% 4 5% 6% 33%	2165
	11th to 20th	Day	25% 10% 3 9% 5% 4 5% 5% 5% 6% 24%	1850
	21st to end	Day	28% 10% 3 7% 5% 4 4 3 4 6% 25%	1980
November	1st to 10th	Day	21% 11% 3 9% 6% 4 3 3 4 5% 30%	1851
	11th to 20th	Day	22% 14% 4 9% 6% 5% 4 3 3 4 26%	1858
	21st to end	Day	21% 19% 4 9% 6% 5% 4 4 4 5% 20%	1559
December	1st to 10th	Day	20% 16% 5% 10% 5% 5% 5% 4 5% 5% 20%	2350
	11th to 20th	Day	21% 15% 6% 10% 5% 4 3 2 3 4 27%	2688
	21st to end	Day	20% 18% 4 8% 4 4 5% 3 5% 4 25%	3799
January	1st to 10th	Night	14% 19% 7% 15% 6% 5% 4 3 4 4 20%	8234
	11th to 20th	Night	11% 24% 8% 17% 6% 5% 4 3 3 3 17%	8235
	21st to end	Night	7% 12% 6% 13% 8% 6% 5% 5% 6% 6% 26%	9057
February	1st to 10th	Night	11% 14% 5% 12% 7% 5% 4 3 4 4 29%	2924
	11th to 20th	Night	13% 16% 5% 11% 5% 6% 4 4 5% 5% 26%	2489
	21st to end	Night	15% 14% 5% 9% 5% 5% 5% 3 5% 5% 29%	2076
March	1st to 10th	Night	23% 13% 4 11% 5% 4 5% 3 4 5% 23%	5484
	11th to 20th	Night	16% 15% 4 10% 7% 5% 5% 4 5% 7% 23%	5375
	21st to end	Night	19% 15% 4 8% 4 4 4 3 4 5% 30%	5166
April	1st to 10th	Night	23% 14% 3 7% 4 4 3 3 5% 5% 29%	2100
	11th to 20th	Night	22% 9% 3 7% 5% 4 5% 3 5% 6% 32%	1996
	21st to end	Night	22% 10% 3 6% 4 3 5% 3 5% 6% 34%	1890
May	1st to 10th	Night	26% 8% 3 6% 4 4 4 3 5% 6% 30%	5024
	11th to 20th	Night	24% 6% 2 6% 4 4 4 3 5% 7% 34%	4639
	21st to end	Night	20% 8% 3 7% 4 5% 5% 4 5% 7% 33%	5114
June	1st to 10th	Night	21% 8% 2 6% 5% 5% 5% 4 7% 7% 31%	1502
	11th to 20th	Night	21% 7% 2 5% 5% 4 4 3 5% 8% 35%	1470
	21st to end	Night	23% 7% 3 6% 6% 5% 4 3 5% 7% 32%	1490
July	1st to 10th	Night	16% 7% 2 7% 5% 5% 5% 4 6% 7% 35%	4680
	11th to 20th	Night	18% 6% 3 6% 4 4 5% 4 6% 7% 39%	4680
	21st to end	Night	15% 5% 3 6% 5% 5% 4 4 6% 8% 40%	5084
August	1st to 10th	Night	18% 7% 3 8% 4 3 5% 3 5% 8% 36%	2666
	11th to 20th	Night	20% 6% 2 7% 5% 5% 5% 4 5% 7% 34%	2915
	21st to end	Night	19% 8% 3 9% 4 5% 4 3 4 6% 34%	3562
September	1st to 10th	Night	18% 6% 2 6% 4 3 3 3 6% 6% 43%	2000
	11th to 20th	Night	17% 5% 2 6% 4 4 4 3 4 6% 45%	2155
	21st to end	Night	22% 6% 2 6% 3 3 4 3 4 6% 41%	2200
October	1st to 10th	Night	20% 7% 2 6% 4 3 3 3 5% 6% 39%	2231
	11th to 20th	Night	24% 8% 3 7% 4 4 5% 4 3 6% 32%	2549
	21st to end	Night	28% 10% 2 6% 4 4 3 3 5% 6% 28%	2860
November	1st to 10th	Night	21% 12% 3 8% 5% 4 4 3 4 6% 30%	2667
	11th to 20th	Night	21% 12% 3 7% 5% 4 4 3 4 6% 30%	2756
	21st to end	Night	24% 16% 4 8% 5% 4 4 3 4 5% 23%	3057
December	1st to 10th	Night	17% 16% 6% 12% 8% 5% 4 3 4 4 21%	5060
	11th to 20th	Night	24% 15% 5% 9% 6% 5% 4 3 4 4 22%	5741
	21st to end	Night	22% 17% 5% 9% 4 3 3 2 3 3 26%	7405

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	64% 2 9% 17% 8%	4662
	11th to 20th	Day	72% 2 5% 14% 7% 1	4680
	21st to end	Day	52% 3 10% 21% 14%	5124
February	1st to 10th	Day	62% 2 8% 16% 10% 2	1693
	11th to 20th	Day	63% 2 10% 14% 10% 1	2026
	21st to end	Day	60% 2 8% 18% 10% 3	1730
March	1st to 10th	Day	66% 1 8% 12% 10% 3	4579
	11th to 20th	Day	59% 3 12% 15% 10% 1	4803
	21st to end	Day	56% 2 6% 17% 16% 4	6006
April	1st to 10th	Day	61% 2 9% 15% 10% 3	2520
	11th to 20th	Day	53% 2 9% 22% 12% 3	2572
	21st to end	Day	57% 2 8% 17% 13% 2	2730
May	1st to 10th	Day	58% 3 9% 17% 12% 1	7942
	11th to 20th	Day	51% 3 14% 22% 7% 2	8225
	21st to end	Day	56% 4 9% 17% 13% 2	9061
June	1st to 10th	Day	55% 3 11% 21% 8% 2	3113
	11th to 20th	Day	49% 4 13% 21% 11% 1	3150
	21st to end	Day	57% 4 12% 17% 9% 1	3122
July	1st to 10th	Day	47% 5% 15% 23% 11%	8210
	11th to 20th	Day	43% 6% 16% 26% 8%	8205
	21st to end	Day	43% 6% 20% 24% 7%	8795
August	1st to 10th	Day	48% 6% 20% 20% 6%	4689
	11th to 20th	Day	51% 5% 19% 20% 5%	4359
	21st to end	Day	49% 4 14% 18% 14%	4532
September	1st to 10th	Day	45% 3 16% 25% 10% 1	2400
	11th to 20th	Day	41% 2 16% 29% 11%	2244
	21st to end	Day	49% 2 14% 26% 9%	2200
October	1st to 10th	Day	53% 6% 11% 23% 7%	3529
	11th to 20th	Day	56% 5% 16% 21% 2	2988
	21st to end	Day	54% 5% 17% 17% 7%	3180
November	1st to 10th	Day	58% 3 11% 20% 9%	1851
	11th to 20th	Day	64% 2 8% 18% 7% 1	1858
	21st to end	Day	67% 3 11% 14% 5% 1	1559
December	1st to 10th	Day	66% 3 10% 15% 6%	2350
	11th to 20th	Day	63% 2 8% 17% 10%	2688
	21st to end	Day	63% 3 8% 14% 11% 1	3799
January	1st to 10th	Night	69% 2 9% 13% 6%	8234
	11th to 20th	Night	74% 2 6% 14% 4	8280
	21st to end	Night	57% 3 10% 17% 13%	9057
February	1st to 10th	Night	59% 2 7% 20% 10% 1	2924
	11th to 20th	Night	62% 2 9% 16% 11% 1	2491
	21st to end	Night	57% 2 7% 19% 13% 1	2076
March	1st to 10th	Night	65% 2 9% 11% 11% 2	5494
	11th to 20th	Night	61% 3 10% 14% 9% 1	5376
	21st to end	Night	59% 2 5% 22% 11% 2	5166
April	1st to 10th	Night	58% 1 8% 16% 14% 2	2100
	11th to 20th	Night	53% 3 8% 22% 13% 2	1996
	21st to end	Night	52% 3 8% 20% 15% 2	1890
May	1st to 10th	Night	55% 3 9% 20% 11% 1	5030
	11th to 20th	Night	51% 3 13% 22% 10% 1	4640
	21st to end	Night	52% 3 10% 17% 16% 2	5115
June	1st to 10th	Night	51% 3 11% 23% 11% 1	1502
	11th to 20th	Night	48% 4 12% 21% 13% 2	1470
	21st to end	Night	53% 3 13% 19% 11%	1490
July	1st to 10th	Night	46% 6% 17% 21% 10%	4640
	11th to 20th	Night	42% 5% 19% 25% 7%	4632
	21st to end	Night	41% 6% 19% 26% 7%	4967
August	1st to 10th	Night	48% 4 17% 23% 8%	2656
	11th to 20th	Night	50% 6% 20% 18% 6% 1	2942
	21st to end	Night	51% 4 12% 22% 11%	3562
September	1st to 10th	Night	43% 3 14% 28% 12% 1	2000
	11th to 20th	Night	41% 3 17% 30% 9% 1	2155
	21st to end	Night	46% 3 11% 28% 12%	2200
October	1st to 10th	Night	51% 4 12% 24% 9%	3647
	11th to 20th	Night	50% 4 16% 26% 4	4150
	21st to end	Night	50% 3 18% 18% 11%	4610
November	1st to 10th	Night	57% 3 11% 20% 8% 1	2667
	11th to 20th	Night	57% 3 11% 19% 10%	2756
	21st to end	Night	65% 3 9% 16% 7%	3057
December	1st to 10th	Night	67% 4 11% 14% 4	5060
	11th to 20th	Night	66% 3 6% 18% 7%	5742
	21st to end	Night	65% 2 7% 16% 9% 1	7405

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	33% 16% 32% 16% 3	220
	11th to 20th	Day	31% 20% 24% 16% 6% 1	220
	21st to end	Day	20% 21% 36% 15% 7%	242
February	1st to 10th	Day	30% 19% 32% 13% 6%	228
	11th to 20th	Day	28% 22% 31% 15% 4	505
	21st to end	Day	28% 22% 30% 16% 3	446
March	1st to 10th	Day	30% 19% 28% 16% 6%	540
	11th to 20th	Day	32% 19% 29% 16% 4 1	540
	21st to end	Day	30% 22% 25% 16% 6% 1	594
April	1st to 10th	Day	33% 17% 31% 14% 4 1	540
	11th to 20th	Day	37% 14% 28% 15% 4 2	532
	21st to end	Day	34% 17% 30% 12% 5% 2	540
May	1st to 10th	Day	33% 16% 31% 14% 5%	543
	11th to 20th	Day	28% 15% 29% 21% 7% 1	567
	21st to end	Day	25% 21% 31% 16% 6%	617
June	1st to 10th	Day	25% 11% 32% 24% 7% 1	743
	11th to 20th	Day	26% 13% 27% 22% 11% 1	780
	21st to end	Day	26% 11% 29% 21% 11% 2	752
July	1st to 10th	Day	22% 13% 32% 21% 11% 1	565
	11th to 20th	Day	21% 10% 37% 22% 9% 2	564
	21st to end	Day	20% 10% 33% 25% 10% 3	620
August	1st to 10th	Day	19% 7% 30% 30% 11% 3	566
	11th to 20th	Day	21% 6% 25% 29% 14% 3	559
	21st to end	Day	23% 12% 24% 21% 14% 5%	619
September	1st to 10th	Day	24% 10% 26% 25% 12% 4	530
	11th to 20th	Day	21% 9% 24% 25% 15% 5%	530
	21st to end	Day	25% 13% 24% 21% 13% 4	530
October	1st to 10th	Day	26% 14% 26% 21% 12% 2	530
	11th to 20th	Day	31% 12% 28% 20% 8% 2	447
	21st to end	Day	37% 10% 26% 20% 6% 1	462
November	1st to 10th	Day	37% 13% 22% 20% 7%	425
	11th to 20th	Day	32% 14% 28% 18% 7% 1	398
	21st to end	Day	34% 21% 28% 14% 3	220
December	1st to 10th	Day	32% 11% 33% 16% 6% 1	220
	11th to 20th	Day	32% 18% 30% 15% 4 1	220
	21st to end	Day	34% 17% 29% 13% 5% 1	242
January	1st to 10th	Night	29% 13% 31% 23% 4	840
	11th to 20th	Night	30% 16% 25% 21% 8%	840
	21st to end	Night	16% 14% 31% 30% 8% 1	924
February	1st to 10th	Night	18% 14% 34% 27% 7% 1	840
	11th to 20th	Night	23% 16% 35% 20% 6%	823
	21st to end	Night	25% 14% 28% 27% 5%	692
March	1st to 10th	Night	26% 13% 32% 24% 6%	840
	11th to 20th	Night	28% 15% 32% 19% 6%	840
	21st to end	Night	27% 13% 29% 22% 7% 1	924
April	1st to 10th	Night	32% 12% 29% 21% 6%	840
	11th to 20th	Night	28% 12% 30% 24% 6%	752
	21st to end	Night	31% 14% 29% 20% 6%	630
May	1st to 10th	Night	31% 10% 32% 21% 6%	550
	11th to 20th	Night	25% 8% 29% 29% 8%	414
	21st to end	Night	25% 8% 30% 28% 9%	455
June	1st to 10th	Night	26% 4 28% 34% 8%	420
	11th to 20th	Night	25% 7% 21% 32% 14%	420
	21st to end	Night	26% 2 20% 40% 12%	420
July	1st to 10th	Night	20% 2 26% 39% 12%	410
	11th to 20th	Night	20% 4 20% 42% 13% 1	408
	21st to end	Night	18% 4 20% 39% 18% 1	460
August	1st to 10th	Night	18% 3 13% 44% 22%	418
	11th to 20th	Night	18% 3 20% 40% 19%	587
	21st to end	Night	22% 7% 21% 32% 18% 1	841
September	1st to 10th	Night	21% 5% 24% 34% 15% 1	800
	11th to 20th	Night	21% 6% 19% 33% 20% 2	800
	21st to end	Night	25% 6% 23% 31% 14% 1	800
October	1st to 10th	Night	25% 8% 24% 33% 11%	800
	11th to 20th	Night	29% 9% 24% 28% 9% 1	800
	21st to end	Night	34% 9% 28% 24% 5% 1	880
November	1st to 10th	Night	31% 10% 27% 25% 7% 1	820
	11th to 20th	Night	29% 13% 26% 23% 8% 1	840
	21st to end	Night	34% 15% 24% 20% 7% 1	902
December	1st to 10th	Night	33% 11% 24% 23% 8%	950
	11th to 20th	Night	31% 16% 26% 20% 6% 1	950
	21st to end	Night	36% 13% 28% 18% 5% 1	982

Page generated at 2026-08-27 04:07:09. Version ac07

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