Observatoire de la Pourvoirie St-Zénon
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Observatoire de la Pourvoirie St-Zénon clear sky chart from 2005-11-06 to 2024-11-11.

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% 12% 4 9% 6% 5% 5% 4 5% 6% 28%	101648
	Night	15% 12% 4 10% 6% 5% 4 3 5% 6% 29%	97524
Transparency	Day	52% 8% 12% 18% 9% 1	105085
	Night	52% 8% 13% 17% 9% 1	102150
Seeing	Day	24% 20% 31% 17% 6% 2	14513
	Night	22% 17% 31% 23% 7% 1	23430

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	11% 18% 6% 14% 7% 7% 5% 3 4 5% 19%	2517
	11th to 20th	Day	9% 16% 7% 16% 11% 6% 4 3 4 4 21%	2520
	21st to end	Day	10% 12% 7% 16% 8% 6% 7% 4 5% 7% 18%	2772
February	1st to 10th	Day	10% 17% 6% 12% 8% 8% 4 3 4 6% 21%	1634
	11th to 20th	Day	10% 17% 5% 12% 6% 7% 5% 4 5% 5% 24%	1743
	21st to end	Day	12% 19% 6% 11% 8% 5% 4 4 4 4 23%	1570
March	1st to 10th	Day	14% 20% 5% 12% 6% 5% 4 3 4 3 23%	3116
	11th to 20th	Day	10% 19% 7% 14% 6% 4 4 3 4 5% 24%	3275
	21st to end	Day	11% 14% 4 11% 4 4 5% 4 5% 6% 34%	4166
April	1st to 10th	Day	18% 18% 5% 9% 5% 4 3 3 4 5% 26%	2280
	11th to 20th	Day	21% 11% 4 8% 5% 3 4 2 5% 5% 32%	2254
	21st to end	Day	19% 14% 4 8% 5% 5% 3 4 4 4 29%	2456
May	1st to 10th	Day	20% 12% 3 8% 5% 4 4 4 5% 5% 29%	4421
	11th to 20th	Day	18% 8% 3 8% 5% 5% 5% 4 6% 7% 31%	4398
	21st to end	Day	18% 9% 3 8% 6% 6% 5% 4 5% 6% 31%	4837
June	1st to 10th	Day	23% 10% 3 8% 5% 5% 5% 4 5% 6% 27%	2660
	11th to 20th	Day	17% 8% 4 7% 5% 5% 5% 5% 6% 8% 31%	2660
	21st to end	Day	24% 9% 3 9% 5% 6% 5% 4 5% 6% 24%	2660
July	1st to 10th	Day	14% 8% 3 9% 7% 6% 6% 4 6% 8% 28%	4440
	11th to 20th	Day	14% 7% 3 7% 5% 6% 6% 5% 7% 7% 31%	4440
	21st to end	Day	12% 7% 3 8% 5% 4 5% 4 6% 7% 39%	4814
August	1st to 10th	Day	15% 8% 3 8% 6% 6% 7% 5% 7% 8% 28%	4423
	11th to 20th	Day	17% 8% 3 7% 5% 5% 5% 5% 7% 7% 31%	4089
	21st to end	Day	15% 8% 3 8% 4 5% 5% 4 6% 7% 34%	4180
September	1st to 10th	Day	16% 7% 3 7% 5% 4 4 3 5% 8% 38%	2280
	11th to 20th	Day	14% 8% 3 7% 5% 4 4 4 4 6% 41%	2201
	21st to end	Day	20% 11% 3 5% 4 3 4 3 4 6% 36%	2090
October	1st to 10th	Day	22% 10% 3 7% 5% 5% 4 4 5% 6% 30%	1954
	11th to 20th	Day	21% 15% 4 9% 6% 5% 4 4 4 4 24%	1842
	21st to end	Day	24% 14% 4 9% 5% 5% 4 3 4 5% 24%	1881
November	1st to 10th	Day	16% 16% 4 9% 6% 4 4 3 5% 5% 29%	1761
	11th to 20th	Day	17% 17% 6% 11% 6% 5% 5% 3 4 6% 21%	1596
	21st to end	Day	16% 20% 7% 11% 6% 5% 4 3 4 5% 20%	1520
December	1st to 10th	Day	22% 18% 6% 12% 5% 4 4 3 3 4 18%	1520
	11th to 20th	Day	19% 16% 5% 14% 5% 4 4 3 4 5% 20%	1906
	21st to end	Day	18% 18% 7% 13% 6% 5% 4 2 4 5% 19%	2772
January	1st to 10th	Night	12% 19% 6% 15% 7% 6% 5% 3 4 4 19%	4429
	11th to 20th	Night	8% 13% 6% 14% 12% 8% 6% 5% 5% 6% 18%	4440
	21st to end	Night	9% 13% 7% 17% 9% 8% 6% 4 5% 5% 18%	4884
February	1st to 10th	Night	9% 15% 5% 13% 7% 6% 6% 4 5% 6% 23%	2542
	11th to 20th	Night	9% 14% 5% 13% 8% 7% 5% 4 6% 6% 23%	2323
	21st to end	Night	11% 14% 5% 11% 6% 5% 5% 5% 5% 6% 27%	1884
March	1st to 10th	Night	17% 17% 5% 9% 5% 4 5% 3 4 5% 25%	3724
	11th to 20th	Night	13% 21% 6% 13% 6% 4 3 2 4 4 25%	3681
	21st to end	Night	12% 10% 5% 11% 6% 7% 5% 4 4 4 33%	3466
April	1st to 10th	Night	21% 13% 4 9% 5% 5% 4 3 5% 5% 27%	1900
	11th to 20th	Night	17% 11% 3 6% 5% 5% 4 3 5% 6% 35%	1875
	21st to end	Night	20% 10% 4 9% 4 4 3 3 5% 4 34%	1724
May	1st to 10th	Night	18% 11% 3 8% 6% 5% 3 3 5% 6% 31%	2547
	11th to 20th	Night	20% 9% 2 6% 4 4 4 3 5% 5% 37%	2495
	21st to end	Night	19% 8% 2 8% 5% 5% 5% 4 5% 7% 31%	2738
June	1st to 10th	Night	20% 8% 3 7% 5% 3 5% 4 6% 9% 32%	1520
	11th to 20th	Night	18% 8% 4 6% 5% 3 5% 4 5% 7% 36%	1520
	21st to end	Night	20% 8% 2 6% 5% 5% 4 3 6% 6% 35%	1520
July	1st to 10th	Night	13% 8% 3 8% 6% 6% 5% 4 7% 8% 32%	2520
	11th to 20th	Night	14% 5% 3 7% 4 5% 5% 4 6% 8% 40%	2520
	21st to end	Night	10% 5% 2 5% 4 4 4 4 6% 8% 48%	2739
August	1st to 10th	Night	12% 8% 3 8% 5% 5% 5% 4 6% 7% 37%	2506
	11th to 20th	Night	16% 9% 3 8% 4 4 5% 3 5% 6% 38%	2689
	21st to end	Night	16% 8% 3 7% 5% 5% 4 3 5% 6% 38%	3476
September	1st to 10th	Night	13% 9% 2 6% 5% 4 3 3 5% 6% 44%	1900
	11th to 20th	Night	15% 6% 2 6% 4 4 4 4 5% 5% 47%	1978
	21st to end	Night	16% 9% 3 5% 4 3 4 3 4 7% 42%	2090
October	1st to 10th	Night	16% 10% 4 7% 5% 4 3 2 4 6% 38%	2223
	11th to 20th	Night	19% 14% 4 9% 4 3 4 2 5% 6% 29%	2337
	21st to end	Night	22% 12% 4 10% 6% 5% 4 3 5% 5% 24%	2717
November	1st to 10th	Night	15% 13% 5% 9% 5% 5% 4 4 5% 6% 28%	2537
	11th to 20th	Night	15% 14% 5% 12% 5% 5% 5% 4 4 6% 25%	2588
	21st to end	Night	18% 16% 6% 11% 5% 4 5% 4 5% 5% 21%	2660
December	1st to 10th	Night	17% 17% 6% 15% 7% 5% 4 4 4 5% 15%	2660
	11th to 20th	Night	18% 16% 5% 12% 6% 5% 4 3 5% 4 20%	3288
	21st to end	Night	19% 18% 6% 12% 8% 4 4 3 4 4 18%	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	62% 10% 11% 13% 5%	2518
	11th to 20th	Day	63% 8% 7% 15% 7% 1	2520
	21st to end	Day	60% 10% 9% 14% 7% 1	2772
February	1st to 10th	Day	63% 5% 7% 16% 8% 2	1634
	11th to 20th	Day	58% 7% 11% 13% 10% 1	1752
	21st to end	Day	61% 6% 7% 14% 8% 3	1570
March	1st to 10th	Day	63% 6% 7% 12% 10% 2	3119
	11th to 20th	Day	59% 8% 9% 10% 10% 3	3275
	21st to end	Day	46% 8% 10% 19% 15% 3	4166
April	1st to 10th	Day	58% 5% 10% 14% 10% 2	2280
	11th to 20th	Day	53% 5% 9% 19% 11% 2	2254
	21st to end	Day	55% 7% 8% 15% 12% 3	2456
May	1st to 10th	Day	52% 8% 10% 17% 11% 1	4435
	11th to 20th	Day	45% 12% 18% 17% 8% 1	4402
	21st to end	Day	49% 9% 10% 16% 14% 1	4837
June	1st to 10th	Day	55% 9% 10% 16% 9% 1	2660
	11th to 20th	Day	48% 8% 13% 19% 10% 2	2660
	21st to end	Day	58% 8% 10% 15% 8%	2660
July	1st to 10th	Day	49% 9% 14% 21% 7%	4370
	11th to 20th	Day	44% 10% 19% 22% 5%	4365
	21st to end	Day	41% 9% 15% 25% 10%	4661
August	1st to 10th	Day	49% 9% 16% 19% 6%	4409
	11th to 20th	Day	47% 9% 19% 21% 5%	4131
	21st to end	Day	46% 8% 13% 20% 13% 1	4180
September	1st to 10th	Day	42% 8% 15% 24% 11% 1	2280
	11th to 20th	Day	41% 8% 14% 26% 10% 1	2201
	21st to end	Day	47% 7% 12% 24% 10%	2090
October	1st to 10th	Day	49% 8% 13% 24% 5% 1	3240
	11th to 20th	Day	53% 6% 14% 21% 5%	3032
	21st to end	Day	51% 7% 20% 15% 6% 1	3081
November	1st to 10th	Day	55% 7% 12% 17% 9% 1	1761
	11th to 20th	Day	60% 8% 11% 13% 8% 1	1596
	21st to end	Day	63% 8% 12% 11% 4 1	1520
December	1st to 10th	Day	67% 6% 10% 12% 6%	1520
	11th to 20th	Day	61% 7% 11% 14% 8%	1906
	21st to end	Day	64% 7% 8% 12% 8%	2772
January	1st to 10th	Night	61% 10% 12% 12% 5%	4429
	11th to 20th	Night	58% 12% 12% 12% 4 1	4440
	21st to end	Night	62% 9% 9% 10% 8% 1	4884
February	1st to 10th	Night	57% 8% 11% 15% 8% 2	2542
	11th to 20th	Night	55% 9% 11% 15% 9% 1	2325
	21st to end	Night	52% 7% 11% 16% 12% 2	1884
March	1st to 10th	Night	58% 8% 11% 11% 10% 3	3734
	11th to 20th	Night	60% 8% 7% 12% 12% 2	3682
	21st to end	Night	48% 8% 11% 19% 11% 4	3466
April	1st to 10th	Night	56% 6% 10% 15% 12% 2	1900
	11th to 20th	Night	47% 8% 10% 21% 12% 2	1875
	21st to end	Night	50% 6% 10% 19% 13% 2	1724
May	1st to 10th	Night	51% 10% 14% 16% 8% 2	2553
	11th to 20th	Night	44% 11% 15% 19% 10% 2	2496
	21st to end	Night	49% 8% 13% 17% 12% 1	2739
June	1st to 10th	Night	47% 9% 13% 20% 10% 1	1520
	11th to 20th	Night	45% 9% 12% 21% 11% 3	1520
	21st to end	Night	48% 8% 14% 17% 12%	1520
July	1st to 10th	Night	47% 8% 19% 18% 7% 1	2480
	11th to 20th	Night	39% 8% 22% 25% 5%	2472
	21st to end	Night	33% 8% 20% 28% 11%	2651
August	1st to 10th	Night	44% 10% 17% 23% 7%	2496
	11th to 20th	Night	43% 8% 21% 22% 6%	2713
	21st to end	Night	43% 8% 15% 22% 10% 1	3476
September	1st to 10th	Night	38% 9% 16% 24% 13%	1900
	11th to 20th	Night	35% 8% 18% 29% 9% 1	1978
	21st to end	Night	41% 7% 13% 27% 12%	2090
October	1st to 10th	Night	46% 6% 15% 23% 10%	3704
	11th to 20th	Night	49% 7% 13% 23% 8%	3873
	21st to end	Night	50% 7% 18% 15% 8% 2	4467
November	1st to 10th	Night	52% 9% 13% 19% 6% 1	2537
	11th to 20th	Night	54% 10% 13% 14% 7% 1	2588
	21st to end	Night	59% 9% 12% 13% 5% 1	2660
December	1st to 10th	Night	66% 9% 11% 10% 4	2660
	11th to 20th	Night	62% 8% 9% 12% 8% 1	3288
	21st to end	Night	65% 7% 8% 13% 6% 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	26% 23% 36% 12% 3	180
	11th to 20th	Day	27% 19% 36% 13% 5%	180
	21st to end	Day	16% 24% 40% 15% 4 1	198
February	1st to 10th	Day	29% 31% 31% 7% 2	234
	11th to 20th	Day	25% 27% 37% 10%	350
	21st to end	Day	27% 28% 31% 12% 2	382
March	1st to 10th	Day	25% 24% 32% 15% 3	460
	11th to 20th	Day	26% 25% 33% 12% 3	460
	21st to end	Day	29% 27% 25% 11% 6% 2	506
April	1st to 10th	Day	30% 21% 30% 14% 5%	460
	11th to 20th	Day	35% 21% 23% 13% 8% 1	452
	21st to end	Day	32% 22% 32% 9% 4 1	460
May	1st to 10th	Day	29% 20% 33% 13% 4 1	463
	11th to 20th	Day	23% 22% 31% 18% 5% 1	487
	21st to end	Day	24% 22% 34% 15% 4 1	529
June	1st to 10th	Day	25% 18% 37% 13% 6%	490
	11th to 20th	Day	22% 19% 32% 16% 10% 1	490
	21st to end	Day	29% 15% 30% 18% 6% 2	490
July	1st to 10th	Day	16% 13% 39% 24% 6% 2	485
	11th to 20th	Day	16% 14% 38% 27% 5% 1	484
	21st to end	Day	15% 11% 34% 30% 9% 2	532
August	1st to 10th	Day	17% 13% 34% 26% 9% 2	486
	11th to 20th	Day	17% 9% 32% 26% 12% 4	479
	21st to end	Day	16% 18% 31% 19% 12% 4	539
September	1st to 10th	Day	20% 16% 30% 20% 10% 4	490
	11th to 20th	Day	17% 13% 28% 24% 13% 5%	490
	21st to end	Day	22% 18% 27% 18% 11% 4	490
October	1st to 10th	Day	25% 18% 25% 19% 9% 3	490
	11th to 20th	Day	27% 24% 26% 14% 7% 2	459
	21st to end	Day	32% 19% 31% 15% 3	429
November	1st to 10th	Day	29% 23% 26% 17% 4 1	395
	11th to 20th	Day	30% 21% 32% 13% 4	256
	21st to end	Day	28% 30% 30% 9% 3	180
December	1st to 10th	Day	33% 18% 29% 12% 7% 1	180
	11th to 20th	Day	29% 33% 24% 11% 3	180
	21st to end	Day	31% 26% 28% 11% 4 1	198
January	1st to 10th	Night	25% 20% 37% 15% 4	760
	11th to 20th	Night	19% 23% 36% 18% 5%	760
	21st to end	Night	14% 19% 40% 22% 4	836
February	1st to 10th	Night	17% 22% 38% 19% 4	760
	11th to 20th	Night	21% 22% 36% 18% 3	743
	21st to end	Night	21% 21% 34% 21% 3	628
March	1st to 10th	Night	25% 20% 33% 19% 3	760
	11th to 20th	Night	25% 25% 29% 15% 5% 1	760
	21st to end	Night	22% 18% 33% 21% 6% 1	836
April	1st to 10th	Night	29% 18% 28% 21% 5%	760
	11th to 20th	Night	24% 19% 31% 20% 7%	751
	21st to end	Night	28% 19% 29% 19% 5%	584
May	1st to 10th	Night	26% 14% 32% 20% 8% 1	400
	11th to 20th	Night	23% 12% 32% 25% 8%	374
	21st to end	Night	20% 13% 39% 21% 7%	411
June	1st to 10th	Night	21% 12% 34% 26% 7%	380
	11th to 20th	Night	21% 10% 27% 31% 11% 1	380
	21st to end	Night	23% 8% 26% 32% 11% 1	380
July	1st to 10th	Night	14% 6% 33% 37% 9% 1	370
	11th to 20th	Night	13% 6% 30% 37% 13% 1	368
	21st to end	Night	13% 6% 29% 38% 13% 1	416
August	1st to 10th	Night	11% 7% 21% 45% 16% 1	378
	11th to 20th	Night	15% 7% 24% 34% 19% 1	504
	21st to end	Night	16% 10% 30% 28% 14% 3	836
September	1st to 10th	Night	16% 11% 30% 33% 10% 1	760
	11th to 20th	Night	17% 9% 27% 28% 17% 1	760
	21st to end	Night	21% 12% 28% 24% 14% 1	760
October	1st to 10th	Night	22% 16% 28% 24% 11% 1	760
	11th to 20th	Night	28% 16% 28% 20% 7% 1	760
	21st to end	Night	27% 19% 28% 21% 4	836
November	1st to 10th	Night	24% 20% 28% 22% 5% 1	780
	11th to 20th	Night	25% 19% 30% 17% 8% 1	763
	21st to end	Night	27% 23% 26% 18% 5% 1	760
December	1st to 10th	Night	27% 19% 30% 19% 4	760
	11th to 20th	Night	27% 19% 33% 15% 6% 1	760
	21st to end	Night	31% 21% 29% 17% 3	836

Page generated at 2024-11-08 06:44:51. Version ac07

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