Portail Étoilé de Saint-Pierre
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Portail Étoilé de Saint-Pierre 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	18% 11% 4 9% 5% 5% 4 3 5% 6% 30%	143981
	Night	17% 14% 5% 10% 5% 4 4 3 4 5% 28%	138313
Transparency	Day	54% 6% 13% 19% 8% 1	147423
	Night	58% 5% 11% 17% 8% 1	142948
Seeing	Day	26% 17% 30% 19% 6% 1	17792
	Night	25% 15% 31% 22% 6%	26053

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	14% 19% 5% 13% 6% 4 3 2 4 5% 24%	4637
	11th to 20th	Day	10% 17% 8% 19% 9% 7% 5% 2 3 4 16%	4650
	21st to end	Day	5% 10% 8% 14% 7% 5% 5% 4 7% 6% 30%	5124
February	1st to 10th	Day	12% 15% 5% 11% 8% 6% 4 3 5% 5% 25%	1717
	11th to 20th	Day	13% 17% 6% 12% 6% 5% 4 2 4 4 26%	1993
	21st to end	Day	11% 15% 5% 12% 7% 5% 4 3 5% 5% 28%	1730
March	1st to 10th	Day	19% 16% 6% 10% 6% 5% 4 3 4 5% 23%	4576
	11th to 20th	Day	15% 16% 4 8% 6% 5% 4 4 6% 6% 27%	4935
	21st to end	Day	18% 17% 4 8% 4 4 3 3 4 4 30%	5838
April	1st to 10th	Day	24% 14% 3 8% 5% 3 4 3 3 6% 27%	2520
	11th to 20th	Day	21% 13% 3 7% 4 3 3 3 4 5% 35%	2629
	21st to end	Day	23% 11% 3 8% 4 4 3 3 4 5% 31%	2730
May	1st to 10th	Day	24% 11% 3 7% 5% 4 4 3 5% 7% 26%	7693
	11th to 20th	Day	21% 9% 3 8% 5% 5% 5% 3 5% 6% 29%	8221
	21st to end	Day	20% 10% 3 8% 5% 5% 5% 4 6% 7% 28%	9411
June	1st to 10th	Day	22% 7% 3 6% 5% 5% 5% 5% 7% 8% 27%	3150
	11th to 20th	Day	21% 7% 2 6% 5% 4 5% 4 5% 8% 33%	3150
	21st to end	Day	23% 10% 4 8% 5% 4 5% 5% 5% 7% 26%	3150
July	1st to 10th	Day	17% 8% 3 7% 5% 5% 5% 4 6% 8% 32%	8650
	11th to 20th	Day	17% 7% 3 7% 5% 4 5% 4 6% 7% 35%	8280
	21st to end	Day	13% 7% 2 7% 5% 5% 5% 4 6% 8% 38%	8993
August	1st to 10th	Day	16% 7% 2 7% 5% 5% 6% 5% 7% 9% 32%	4614
	11th to 20th	Day	19% 7% 3 7% 6% 5% 5% 4 7% 8% 29%	4305
	21st to end	Day	21% 8% 2 6% 4 4 4 3 4 6% 38%	4666
September	1st to 10th	Day	19% 6% 3 6% 4 4 4 3 6% 8% 39%	2393
	11th to 20th	Day	19% 5% 2 5% 3 3 3 2 4 5% 48%	2200
	21st to end	Day	23% 7% 2 5% 3 3 3 3 5% 7% 39%	2200
October	1st to 10th	Day	19% 10% 3 6% 4 3 5% 3 5% 7% 36%	2198
	11th to 20th	Day	23% 13% 3 8% 5% 5% 4 4 4 5% 26%	1838
	21st to end	Day	28% 14% 3 8% 4 3 4 3 4 6% 24%	1980
November	1st to 10th	Day	19% 15% 5% 9% 5% 4 4 3 5% 4 28%	1851
	11th to 20th	Day	20% 17% 5% 11% 5% 4 4 2 4 5% 24%	1853
	21st to end	Day	21% 21% 6% 9% 5% 4 4 3 3 4 21%	1515
December	1st to 10th	Day	17% 17% 6% 12% 5% 5% 5% 3 4 4 21%	2350
	11th to 20th	Day	20% 17% 6% 9% 6% 4 3 3 4 4 25%	2688
	21st to end	Day	19% 16% 5% 11% 5% 4 4 3 4 6% 23%	3553
January	1st to 10th	Night	14% 18% 6% 12% 7% 5% 5% 3 4 4 21%	8256
	11th to 20th	Night	10% 20% 9% 20% 8% 5% 4 3 3 3 15%	8235
	21st to end	Night	5% 10% 7% 17% 8% 6% 6% 4 6% 6% 26%	9057
February	1st to 10th	Night	10% 15% 6% 13% 7% 5% 4 3 5% 5% 27%	2901
	11th to 20th	Night	13% 17% 6% 12% 6% 5% 4 3 4 4 25%	2510
	21st to end	Night	13% 17% 5% 10% 6% 5% 4 3 3 5% 30%	2076
March	1st to 10th	Night	20% 16% 5% 11% 4 3 5% 2 3 5% 25%	5484
	11th to 20th	Night	14% 16% 4 10% 6% 6% 6% 4 6% 6% 22%	5243
	21st to end	Night	19% 17% 5% 9% 5% 3 3 2 3 5% 28%	5319
April	1st to 10th	Night	23% 17% 4 8% 4 3 3 3 4 5% 27%	2100
	11th to 20th	Night	22% 12% 2 6% 4 4 4 4 6% 6% 31%	1939
	21st to end	Night	23% 13% 3 7% 4 3 4 3 4 4 33%	1890
May	1st to 10th	Night	24% 10% 3 8% 4 4 4 3 5% 6% 29%	5259
	11th to 20th	Night	22% 10% 3 8% 5% 4 4 3 4 5% 31%	4641
	21st to end	Night	19% 9% 3 7% 4 4 4 4 5% 6% 35%	4778
June	1st to 10th	Night	22% 8% 3 6% 7% 6% 5% 4 6% 6% 27%	1470
	11th to 20th	Night	18% 8% 3 7% 5% 4 4 4 6% 7% 35%	1470
	21st to end	Night	22% 11% 3 6% 6% 5% 4 4 5% 6% 30%	1470
July	1st to 10th	Night	18% 9% 3 8% 4 4 4 4 5% 7% 33%	4311
	11th to 20th	Night	21% 7% 3 6% 4 4 5% 4 6% 7% 34%	4680
	21st to end	Night	13% 7% 2 8% 6% 5% 6% 4 6% 7% 36%	5084
August	1st to 10th	Night	20% 8% 3 6% 5% 4 5% 4 5% 7% 33%	2721
	11th to 20th	Night	18% 9% 3 9% 5% 6% 4 4 6% 7% 29%	2962
	21st to end	Night	18% 9% 3 7% 4 4 4 3 5% 6% 37%	3428
September	1st to 10th	Night	19% 8% 2 7% 4 4 4 3 5% 6% 40%	2006
	11th to 20th	Night	17% 8% 3 5% 4 3 4 3 5% 6% 43%	2200
	21st to end	Night	21% 8% 2 6% 4 4 4 3 4 5% 40%	2200
October	1st to 10th	Night	19% 10% 3 6% 4 3 4 3 5% 5% 38%	2201
	11th to 20th	Night	25% 12% 3 7% 4 4 3 2 4 5% 30%	2560
	21st to end	Night	25% 14% 4 6% 4 4 4 3 4 6% 27%	2860
November	1st to 10th	Night	21% 15% 4 8% 5% 4 4 3 4 5% 26%	2667
	11th to 20th	Night	18% 14% 5% 10% 6% 4 4 2 4 5% 28%	2764
	21st to end	Night	19% 21% 7% 10% 4 4 3 3 4 4 22%	3103
December	1st to 10th	Night	15% 17% 8% 15% 8% 5% 4 3 5% 4 16%	5060
	11th to 20th	Night	19% 18% 6% 11% 6% 4 3 3 3 5% 22%	5741
	21st to end	Night	18% 19% 6% 10% 5% 4 4 2 3 3 26%	7667

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	61% 6% 8% 17% 8%	4638
	11th to 20th	Day	71% 4 7% 11% 5% 1	4680
	21st to end	Day	53% 6% 11% 18% 13%	5124
February	1st to 10th	Day	61% 4 11% 16% 8% 1	1717
	11th to 20th	Day	62% 3 10% 16% 7% 1	2002
	21st to end	Day	58% 4 8% 20% 8% 2	1730
March	1st to 10th	Day	63% 6% 8% 10% 10% 3	4579
	11th to 20th	Day	55% 6% 16% 15% 8%	4935
	21st to end	Day	58% 3 7% 16% 12% 3	5838
April	1st to 10th	Day	61% 3 10% 15% 10% 2	2520
	11th to 20th	Day	52% 4 10% 21% 12% 2	2629
	21st to end	Day	54% 4 10% 17% 12% 2	2730
May	1st to 10th	Day	57% 6% 9% 17% 10% 1	7705
	11th to 20th	Day	53% 7% 14% 19% 6% 2	8225
	21st to end	Day	54% 7% 11% 18% 9% 1	9412
June	1st to 10th	Day	51% 9% 13% 19% 7% 1	3150
	11th to 20th	Day	48% 7% 14% 20% 9% 1	3150
	21st to end	Day	57% 7% 12% 17% 7%	3150
July	1st to 10th	Day	49% 6% 14% 23% 8%	8578
	11th to 20th	Day	45% 6% 16% 27% 5%	8205
	21st to end	Day	44% 7% 20% 23% 6%	8795
August	1st to 10th	Day	47% 8% 20% 20% 5%	4600
	11th to 20th	Day	51% 8% 22% 15% 5%	4344
	21st to end	Day	48% 6% 17% 18% 10% 1	4666
September	1st to 10th	Day	43% 5% 17% 24% 10% 1	2393
	11th to 20th	Day	40% 4 16% 29% 11%	2200
	21st to end	Day	46% 5% 14% 25% 11%	2200
October	1st to 10th	Day	51% 5% 12% 26% 5%	3575
	11th to 20th	Day	54% 5% 16% 23% 2	2963
	21st to end	Day	53% 5% 16% 20% 6%	3180
November	1st to 10th	Day	59% 6% 13% 17% 6%	1851
	11th to 20th	Day	62% 5% 11% 16% 6%	1853
	21st to end	Day	68% 5% 11% 13% 4	1515
December	1st to 10th	Day	66% 5% 10% 11% 7%	2350
	11th to 20th	Day	64% 3 9% 17% 7%	2688
	21st to end	Day	63% 5% 11% 10% 9% 2	3553
January	1st to 10th	Night	66% 5% 9% 14% 6%	8256
	11th to 20th	Night	75% 3 7% 11% 4	8280
	21st to end	Night	58% 5% 10% 14% 12%	9057
February	1st to 10th	Night	59% 5% 10% 17% 9% 1	2901
	11th to 20th	Night	62% 4 8% 15% 9% 1	2512
	21st to end	Night	58% 4 7% 18% 12% 1	2076
March	1st to 10th	Night	63% 4 8% 12% 12% 1	5494
	11th to 20th	Night	61% 7% 12% 12% 7% 1	5244
	21st to end	Night	60% 3 6% 19% 11% 1	5319
April	1st to 10th	Night	61% 3 8% 14% 13% 2	2100
	11th to 20th	Night	53% 5% 9% 20% 11% 2	1939
	21st to end	Night	56% 4 8% 17% 13% 2	1890
May	1st to 10th	Night	55% 5% 10% 18% 12% 1	5265
	11th to 20th	Night	53% 7% 10% 21% 8%	4642
	21st to end	Night	48% 7% 13% 17% 14% 2	4779
June	1st to 10th	Night	54% 7% 11% 20% 7%	1470
	11th to 20th	Night	47% 7% 11% 22% 9% 3	1470
	21st to end	Night	54% 7% 14% 15% 10%	1470
July	1st to 10th	Night	50% 6% 16% 19% 9%	4273
	11th to 20th	Night	49% 6% 17% 24% 4	4632
	21st to end	Night	45% 8% 19% 21% 6%	4967
August	1st to 10th	Night	49% 6% 16% 23% 4	2711
	11th to 20th	Night	52% 9% 19% 16% 5%	2989
	21st to end	Night	47% 6% 14% 21% 11% 1	3428
September	1st to 10th	Night	45% 6% 13% 24% 10% 1	2006
	11th to 20th	Night	42% 6% 16% 27% 8%	2200
	21st to end	Night	47% 5% 11% 25% 11%	2200
October	1st to 10th	Night	49% 4 12% 28% 7%	3604
	11th to 20th	Night	56% 5% 13% 24% 3	4161
	21st to end	Night	53% 4 17% 17% 8%	4610
November	1st to 10th	Night	60% 5% 12% 18% 5%	2667
	11th to 20th	Night	59% 6% 11% 16% 8%	2764
	21st to end	Night	67% 5% 10% 13% 5%	3103
December	1st to 10th	Night	71% 6% 10% 11% 3	5060
	11th to 20th	Night	66% 4 6% 19% 4	5742
	21st to end	Night	64% 4 9% 14% 9% 1	7667

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	29% 27% 30% 13% 2	220
	11th to 20th	Day	32% 25% 30% 10% 3	220
	21st to end	Day	17% 32% 34% 14% 3	242
February	1st to 10th	Day	27% 26% 29% 14% 3	257
	11th to 20th	Day	25% 28% 33% 12% 3	508
	21st to end	Day	25% 23% 33% 17% 2	446
March	1st to 10th	Day	31% 23% 26% 16% 3 1	540
	11th to 20th	Day	28% 22% 29% 16% 5% 1	540
	21st to end	Day	28% 23% 27% 15% 6% 1	594
April	1st to 10th	Day	35% 19% 28% 13% 4	540
	11th to 20th	Day	33% 21% 25% 17% 5% 1	532
	21st to end	Day	28% 22% 30% 15% 4 1	540
May	1st to 10th	Day	32% 15% 34% 14% 4 1	543
	11th to 20th	Day	26% 14% 30% 23% 7% 1	567
	21st to end	Day	23% 18% 36% 17% 6%	734
June	1st to 10th	Day	24% 14% 32% 22% 7%	780
	11th to 20th	Day	24% 13% 29% 25% 8%	780
	21st to end	Day	27% 11% 30% 22% 9% 1	780
July	1st to 10th	Day	22% 13% 32% 24% 8% 1	699
	11th to 20th	Day	21% 16% 34% 21% 7% 1	564
	21st to end	Day	19% 12% 35% 24% 9% 1	620
August	1st to 10th	Day	19% 11% 33% 25% 10% 2	566
	11th to 20th	Day	19% 10% 29% 28% 12% 1	559
	21st to end	Day	21% 14% 24% 25% 12% 3	619
September	1st to 10th	Day	23% 12% 30% 23% 9% 3	530
	11th to 20th	Day	21% 11% 32% 24% 10% 3	530
	21st to end	Day	22% 14% 29% 21% 9% 5%	530
October	1st to 10th	Day	23% 18% 31% 20% 7% 2	528
	11th to 20th	Day	31% 15% 29% 17% 8% 1	420
	21st to end	Day	35% 19% 30% 12% 3	462
November	1st to 10th	Day	33% 18% 32% 14% 2	425
	11th to 20th	Day	29% 20% 29% 15% 7%	430
	21st to end	Day	35% 22% 32% 11%	265
December	1st to 10th	Day	31% 17% 30% 17% 3 1	220
	11th to 20th	Day	35% 26% 25% 11% 2 1	220
	21st to end	Day	35% 20% 29% 14% 2	242
January	1st to 10th	Night	27% 21% 34% 15% 2	844
	11th to 20th	Night	25% 22% 33% 17% 3	840
	21st to end	Night	17% 22% 36% 20% 4	924
February	1st to 10th	Night	18% 23% 34% 19% 5%	840
	11th to 20th	Night	25% 21% 38% 12% 4	823
	21st to end	Night	24% 18% 34% 20% 4	692
March	1st to 10th	Night	26% 16% 37% 18% 3	840
	11th to 20th	Night	24% 17% 36% 18% 5% 1	840
	21st to end	Night	24% 16% 32% 22% 6% 1	924
April	1st to 10th	Night	33% 15% 27% 20% 5%	840
	11th to 20th	Night	28% 13% 32% 21% 5%	695
	21st to end	Night	30% 14% 27% 22% 7%	630
May	1st to 10th	Night	28% 10% 30% 25% 7%	630
	11th to 20th	Night	24% 9% 28% 30% 9% 1	416
	21st to end	Night	26% 10% 33% 25% 6%	455
June	1st to 10th	Night	25% 6% 30% 33% 6%	420
	11th to 20th	Night	21% 7% 25% 37% 10%	420
	21st to end	Night	24% 10% 30% 28% 8%	420
July	1st to 10th	Night	20% 6% 35% 29% 9%	410
	11th to 20th	Night	20% 6% 31% 32% 10% 1	408
	21st to end	Night	17% 6% 30% 35% 11%	460
August	1st to 10th	Night	17% 5% 29% 34% 14%	447
	11th to 20th	Night	19% 7% 26% 35% 12% 1	622
	21st to end	Night	20% 8% 29% 30% 11% 2	759
September	1st to 10th	Night	23% 8% 29% 30% 10% 1	800
	11th to 20th	Night	21% 8% 30% 28% 13% 1	800
	21st to end	Night	23% 11% 28% 26% 12%	800
October	1st to 10th	Night	24% 12% 31% 25% 7% 1	800
	11th to 20th	Night	30% 15% 26% 22% 6% 1	800
	21st to end	Night	33% 14% 31% 18% 5%	880
November	1st to 10th	Night	32% 16% 28% 20% 3	820
	11th to 20th	Night	27% 19% 28% 19% 7% 1	859
	21st to end	Night	30% 19% 31% 16% 4 1	950
December	1st to 10th	Night	31% 18% 31% 15% 5%	950
	11th to 20th	Night	29% 23% 28% 14% 5%	950
	21st to end	Night	31% 21% 29% 16% 3	1045

Page generated at 2026-08-27 04:07:12. Version ac07

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