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 2024-10-25.

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	19% 11% 4 8% 5% 4 4 3 5% 6% 30%	101363
	Night	18% 14% 4 9% 5% 4 4 3 5% 5% 28%	97477
Transparency	Day	54% 6% 14% 18% 8% 1	101119
	Night	57% 6% 12% 17% 8% 1	97342
Seeing	Day	26% 17% 30% 20% 7% 1	15407
	Night	25% 15% 31% 22% 7%	23728

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	13% 18% 7% 15% 8% 5% 4 3 4 5% 17%	2493
	11th to 20th	Day	12% 14% 6% 17% 9% 6% 5% 2 3 5% 23%	2520
	21st to end	Day	9% 11% 8% 14% 6% 5% 4 3 5% 6% 29%	2772
February	1st to 10th	Day	12% 16% 5% 11% 8% 5% 4 3 5% 5% 24%	1553
	11th to 20th	Day	14% 17% 6% 12% 6% 5% 4 3 5% 5% 25%	1797
	21st to end	Day	12% 16% 5% 11% 6% 5% 4 3 5% 5% 28%	1570
March	1st to 10th	Day	18% 13% 5% 10% 7% 5% 4 3 4 5% 25%	3116
	11th to 20th	Day	16% 21% 5% 9% 6% 5% 3 3 4 5% 24%	3371
	21st to end	Day	16% 16% 4 8% 4 4 4 3 4 5% 34%	3992
April	1st to 10th	Day	24% 14% 3 8% 6% 3 4 3 4 6% 27%	2280
	11th to 20th	Day	20% 12% 3 6% 4 3 3 3 4 5% 37%	2375
	21st to end	Day	23% 11% 3 7% 4 4 3 3 4 5% 31%	2470
May	1st to 10th	Day	20% 10% 3 7% 5% 4 4 3 4 8% 32%	4133
	11th to 20th	Day	19% 9% 3 7% 5% 5% 5% 4 6% 7% 28%	4398
	21st to end	Day	18% 9% 3 8% 6% 5% 5% 4 6% 7% 30%	5020
June	1st to 10th	Day	22% 8% 3 6% 5% 4 5% 5% 7% 8% 27%	2850
	11th to 20th	Day	20% 7% 2 5% 5% 5% 5% 4 5% 8% 33%	2850
	21st to end	Day	23% 10% 4 8% 5% 4 4 5% 5% 7% 25%	2850
July	1st to 10th	Day	16% 8% 3 8% 5% 5% 5% 5% 6% 8% 31%	4642
	11th to 20th	Day	17% 8% 2 7% 5% 5% 5% 4 7% 8% 32%	4440
	21st to end	Day	15% 7% 2 6% 4 4 5% 4 6% 7% 40%	4814
August	1st to 10th	Day	17% 7% 2 7% 5% 5% 6% 5% 7% 9% 29%	4339
	11th to 20th	Day	19% 7% 3 7% 6% 5% 5% 4 7% 8% 28%	4045
	21st to end	Day	21% 8% 2 6% 4 4 4 3 4 6% 38%	4412
September	1st to 10th	Day	19% 6% 3 6% 4 4 4 3 5% 8% 38%	2274
	11th to 20th	Day	20% 5% 2 5% 3 3 3 2 4 5% 46%	2090
	21st to end	Day	23% 7% 2 6% 3 3 3 3 5% 7% 38%	2090
October	1st to 10th	Day	20% 10% 3 6% 4 3 5% 3 5% 6% 34%	2088
	11th to 20th	Day	24% 13% 3 8% 5% 5% 4 4 4 5% 25%	1746
	21st to end	Day	28% 14% 3 8% 4 3 4 3 4 6% 24%	1825
November	1st to 10th	Day	18% 14% 5% 9% 5% 4 4 3 5% 4 29%	1671
	11th to 20th	Day	21% 17% 4 10% 5% 4 4 2 4 5% 24%	1677
	21st to end	Day	20% 19% 6% 9% 5% 4 3 3 3 4 23%	1371
December	1st to 10th	Day	23% 19% 5% 11% 5% 5% 4 2 4 4 18%	1330
	11th to 20th	Day	20% 18% 5% 9% 6% 5% 3 3 4 3 25%	1668
	21st to end	Day	23% 15% 5% 11% 5% 3 3 2 4 5% 23%	2431
January	1st to 10th	Night	14% 21% 7% 13% 8% 5% 4 2 3 3 20%	4451
	11th to 20th	Night	12% 17% 7% 15% 7% 6% 4 3 4 4 21%	4440
	21st to end	Night	10% 14% 6% 13% 7% 6% 5% 4 5% 5% 24%	4884
February	1st to 10th	Night	11% 15% 6% 13% 7% 5% 4 4 5% 5% 25%	2625
	11th to 20th	Night	13% 17% 6% 12% 7% 5% 5% 3 4 4 24%	2266
	21st to end	Night	14% 17% 5% 10% 6% 5% 4 3 3 5% 29%	1884
March	1st to 10th	Night	21% 16% 4 7% 4 3 6% 2 4 5% 27%	3724
	11th to 20th	Night	14% 20% 5% 10% 6% 5% 5% 3 4 5% 22%	3587
	21st to end	Night	18% 15% 5% 10% 5% 3 3 3 3 5% 30%	3637
April	1st to 10th	Night	22% 17% 4 8% 4 3 3 3 4 4 28%	1900
	11th to 20th	Night	21% 11% 2 6% 4 4 4 4 6% 6% 31%	1753
	21st to end	Night	24% 13% 3 7% 4 3 4 3 4 4 33%	1710
May	1st to 10th	Night	23% 9% 2 7% 4 4 4 3 6% 6% 32%	2834
	11th to 20th	Night	20% 10% 3 8% 6% 4 4 4 5% 6% 31%	2497
	21st to end	Night	18% 6% 2 6% 4 5% 5% 4 7% 7% 35%	2558
June	1st to 10th	Night	23% 8% 3 6% 7% 6% 5% 4 6% 6% 26%	1330
	11th to 20th	Night	18% 8% 2 7% 5% 4 4 4 6% 7% 37%	1330
	21st to end	Night	22% 11% 3 6% 5% 5% 4 4 5% 6% 30%	1330
July	1st to 10th	Night	14% 9% 3 10% 6% 5% 5% 4 6% 8% 32%	2320
	11th to 20th	Night	22% 8% 3 6% 4 5% 4 3 6% 7% 31%	2520
	21st to end	Night	14% 7% 2 6% 5% 4 5% 4 6% 8% 39%	2739
August	1st to 10th	Night	21% 8% 3 6% 5% 4 5% 4 5% 7% 33%	2558
	11th to 20th	Night	18% 9% 3 9% 5% 6% 5% 4 6% 7% 28%	2782
	21st to end	Night	18% 9% 3 7% 4 4 5% 3 5% 6% 36%	3242
September	1st to 10th	Night	19% 8% 2 7% 5% 4 4 3 5% 6% 38%	1905
	11th to 20th	Night	18% 8% 3 5% 3 3 3 3 5% 6% 42%	2090
	21st to end	Night	21% 8% 2 6% 4 4 3 3 4 5% 40%	2090
October	1st to 10th	Night	20% 10% 3 6% 4 3 4 3 5% 5% 37%	2091
	11th to 20th	Night	26% 13% 3 7% 4 3 3 2 4 5% 30%	2432
	21st to end	Night	25% 13% 4 6% 4 4 4 3 4 7% 27%	2637
November	1st to 10th	Night	20% 15% 4 8% 5% 4 4 3 4 5% 27%	2407
	11th to 20th	Night	19% 13% 5% 10% 6% 4 4 2 4 5% 28%	2500
	21st to end	Night	20% 19% 6% 9% 4 4 3 3 4 4 23%	2807
December	1st to 10th	Night	21% 19% 6% 10% 6% 4 4 3 5% 4 18%	2850
	11th to 20th	Night	18% 18% 6% 11% 6% 4 3 3 3 5% 22%	3531
	21st to end	Night	22% 20% 5% 9% 4 3 3 2 3 3 26%	5236

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	66% 7% 12% 12% 3	2494
	11th to 20th	Day	63% 4 11% 16% 6% 1	2520
	21st to end	Day	55% 8% 10% 19% 8%	2772
February	1st to 10th	Day	62% 4 11% 14% 7% 1	1553
	11th to 20th	Day	63% 4 10% 15% 8% 1	1806
	21st to end	Day	59% 4 9% 19% 8% 2	1570
March	1st to 10th	Day	59% 8% 9% 14% 8% 2	3119
	11th to 20th	Day	61% 6% 13% 14% 6%	3371
	21st to end	Day	54% 4 9% 18% 11% 4	3992
April	1st to 10th	Day	61% 3 11% 14% 9% 2	2280
	11th to 20th	Day	50% 4 10% 22% 12% 2	2375
	21st to end	Day	55% 4 10% 16% 12% 3	2470
May	1st to 10th	Day	50% 8% 10% 19% 12% 1	4147
	11th to 20th	Day	50% 9% 19% 17% 6%	4402
	21st to end	Day	51% 9% 10% 20% 10%	5020
June	1st to 10th	Day	52% 9% 13% 19% 7% 1	2850
	11th to 20th	Day	48% 7% 15% 20% 9% 1	2850
	21st to end	Day	57% 7% 11% 17% 7%	2850
July	1st to 10th	Day	49% 7% 16% 22% 6%	4570
	11th to 20th	Day	47% 7% 20% 22% 4	4365
	21st to end	Day	43% 7% 19% 23% 8%	4661
August	1st to 10th	Day	49% 8% 19% 20% 4	4325
	11th to 20th	Day	51% 8% 22% 14% 4	4084
	21st to end	Day	48% 6% 17% 18% 11% 1	4412
September	1st to 10th	Day	44% 5% 16% 23% 10% 1	2274
	11th to 20th	Day	41% 4 16% 28% 11%	2090
	21st to end	Day	47% 5% 14% 25% 10%	2090
October	1st to 10th	Day	50% 5% 12% 25% 8%	2088
	11th to 20th	Day	61% 6% 15% 16% 2	1746
	21st to end	Day	62% 5% 12% 16% 4 1	1825
November	1st to 10th	Day	57% 6% 13% 17% 6%	1671
	11th to 20th	Day	62% 5% 12% 15% 5%	1677
	21st to end	Day	66% 5% 12% 13% 4	1371
December	1st to 10th	Day	69% 6% 9% 12% 4	1330
	11th to 20th	Day	64% 3 9% 18% 6%	1668
	21st to end	Day	65% 6% 11% 12% 5% 2	2431
January	1st to 10th	Night	69% 6% 9% 11% 5%	4451
	11th to 20th	Night	65% 4 11% 15% 5%	4440
	21st to end	Night	59% 6% 11% 14% 9% 1	4884
February	1st to 10th	Night	60% 5% 10% 15% 9% 1	2625
	11th to 20th	Night	63% 4 8% 15% 9% 1	2268
	21st to end	Night	58% 4 8% 17% 12% 1	1884
March	1st to 10th	Night	60% 6% 10% 15% 8% 1	3734
	11th to 20th	Night	63% 7% 11% 12% 6% 1	3588
	21st to end	Night	59% 3 8% 20% 8% 2	3637
April	1st to 10th	Night	60% 3 8% 14% 12% 2	1900
	11th to 20th	Night	51% 6% 10% 21% 11% 2	1753
	21st to end	Night	56% 4 7% 17% 13% 2	1710
May	1st to 10th	Night	51% 5% 11% 20% 11% 1	2840
	11th to 20th	Night	50% 10% 12% 18% 10%	2498
	21st to end	Night	44% 9% 15% 19% 13% 1	2559
June	1st to 10th	Night	56% 8% 11% 19% 6%	1330
	11th to 20th	Night	46% 8% 11% 23% 10% 3	1330
	21st to end	Night	55% 6% 13% 15% 10%	1330
July	1st to 10th	Night	49% 7% 18% 20% 5%	2282
	11th to 20th	Night	51% 7% 18% 20% 3	2472
	21st to end	Night	41% 9% 21% 21% 8%	2651
August	1st to 10th	Night	50% 7% 16% 23% 4	2548
	11th to 20th	Night	54% 9% 18% 15% 5%	2809
	21st to end	Night	47% 6% 14% 20% 12% 1	3242
September	1st to 10th	Night	46% 6% 13% 22% 11% 1	1905
	11th to 20th	Night	43% 6% 16% 26% 8%	2090
	21st to end	Night	47% 6% 11% 25% 11%	2090
October	1st to 10th	Night	49% 5% 11% 25% 10% 1	2091
	11th to 20th	Night	58% 6% 12% 20% 4	2432
	21st to end	Night	58% 5% 14% 15% 7%	2637
November	1st to 10th	Night	59% 5% 12% 18% 5%	2407
	11th to 20th	Night	58% 6% 11% 16% 8%	2500
	21st to end	Night	65% 5% 11% 14% 5%	2807
December	1st to 10th	Night	69% 5% 10% 12% 3	2850
	11th to 20th	Night	65% 4 7% 17% 6%	3532
	21st to end	Night	65% 4 10% 14% 7% 1	5236

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	27% 27% 31% 13% 2 1	180
	11th to 20th	Day	32% 24% 32% 9% 3	180
	21st to end	Day	16% 28% 35% 16% 4 1	198
February	1st to 10th	Day	29% 27% 31% 11% 2	213
	11th to 20th	Day	23% 30% 33% 12% 2	432
	21st to end	Day	26% 23% 31% 18% 3	382
March	1st to 10th	Day	29% 20% 29% 18% 3 1	460
	11th to 20th	Day	26% 20% 30% 18% 5% 1	460
	21st to end	Day	24% 23% 29% 17% 7% 1	506
April	1st to 10th	Day	33% 19% 27% 15% 5%	460
	11th to 20th	Day	30% 21% 24% 19% 5% 1	452
	21st to end	Day	27% 23% 30% 14% 4 2	460
May	1st to 10th	Day	30% 15% 35% 15% 4 1	463
	11th to 20th	Day	23% 13% 31% 24% 8% 1	487
	21st to end	Day	23% 17% 37% 17% 6%	634
June	1st to 10th	Day	25% 15% 31% 23% 7%	680
	11th to 20th	Day	22% 14% 29% 26% 9%	680
	21st to end	Day	28% 10% 30% 23% 9% 1	680
July	1st to 10th	Day	21% 12% 33% 26% 8%	607
	11th to 20th	Day	19% 14% 35% 24% 7% 1	484
	21st to end	Day	19% 9% 36% 27% 8% 1	532
August	1st to 10th	Day	20% 11% 32% 25% 11% 2	486
	11th to 20th	Day	20% 10% 28% 28% 13% 1	479
	21st to end	Day	22% 14% 23% 25% 13% 4	539
September	1st to 10th	Day	23% 12% 29% 23% 10% 3	490
	11th to 20th	Day	22% 10% 32% 23% 10% 2	490
	21st to end	Day	23% 13% 29% 21% 9% 5%	490
October	1st to 10th	Day	24% 17% 29% 20% 8% 2	488
	11th to 20th	Day	32% 15% 28% 17% 7% 1	390
	21st to end	Day	35% 18% 29% 13% 4	411
November	1st to 10th	Day	31% 18% 34% 15% 2 1	365
	11th to 20th	Day	29% 21% 26% 16% 7% 1	370
	21st to end	Day	32% 21% 34% 12%	221
December	1st to 10th	Day	33% 16% 27% 19% 3 1	180
	11th to 20th	Day	34% 26% 24% 12% 2 1	180
	21st to end	Day	39% 21% 27% 13% 1	198
January	1st to 10th	Night	27% 21% 34% 15% 2	764
	11th to 20th	Night	25% 22% 33% 17% 3	760
	21st to end	Night	17% 21% 36% 21% 5%	836
February	1st to 10th	Night	18% 23% 35% 18% 5%	760
	11th to 20th	Night	24% 22% 37% 12% 4	743
	21st to end	Night	25% 18% 33% 21% 4	628
March	1st to 10th	Night	24% 15% 38% 20% 4	760
	11th to 20th	Night	23% 16% 37% 18% 5% 1	760
	21st to end	Night	23% 14% 32% 23% 6% 1	836
April	1st to 10th	Night	31% 15% 27% 21% 5%	760
	11th to 20th	Night	28% 12% 32% 21% 6%	629
	21st to end	Night	31% 13% 27% 22% 7%	570
May	1st to 10th	Night	28% 11% 30% 24% 7%	570
	11th to 20th	Night	24% 7% 28% 31% 9% 1	376
	21st to end	Night	26% 9% 33% 25% 7%	411
June	1st to 10th	Night	26% 6% 29% 32% 7%	380
	11th to 20th	Night	20% 7% 25% 37% 11%	380
	21st to end	Night	24% 11% 29% 28% 8%	380
July	1st to 10th	Night	20% 6% 35% 30% 9%	370
	11th to 20th	Night	19% 5% 31% 33% 10% 1	368
	21st to end	Night	17% 7% 30% 36% 11%	416
August	1st to 10th	Night	18% 4 29% 35% 14%	404
	11th to 20th	Night	20% 7% 27% 33% 13% 1	562
	21st to end	Night	20% 8% 29% 30% 12% 2	693
September	1st to 10th	Night	23% 7% 30% 29% 10% 1	760
	11th to 20th	Night	22% 9% 30% 27% 12% 1	760
	21st to end	Night	23% 11% 27% 26% 12%	760
October	1st to 10th	Night	25% 12% 30% 25% 7% 1	760
	11th to 20th	Night	32% 15% 26% 21% 6% 1	760
	21st to end	Night	33% 14% 30% 18% 5%	812
November	1st to 10th	Night	30% 17% 28% 21% 4	740
	11th to 20th	Night	27% 20% 27% 19% 7% 1	775
	21st to end	Night	29% 18% 32% 16% 4 1	850
December	1st to 10th	Night	32% 18% 30% 16% 5%	850
	11th to 20th	Night	28% 22% 29% 14% 6%	850
	21st to end	Night	33% 21% 27% 16% 3	935

Page generated at 2024-10-22 20:21:04. Version ac07

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