Saint-Zénon
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Saint-Zénon clear sky chart from 2005-11-06 to 2025-08-05.

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 10% 6% 5% 5% 4 5% 6% 27%	126071
	Night	14% 13% 5% 11% 6% 5% 5% 3 5% 6% 27%	121987
Transparency	Day	55% 6% 11% 18% 9% 1	129503
	Night	56% 6% 11% 17% 9% 1	126642
Seeing	Day	26% 20% 31% 16% 6% 2	15392
	Night	23% 17% 29% 22% 8% 1	24295

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	10% 20% 7% 15% 8% 7% 8% 4 4 4 13%	3597
	11th to 20th	Day	7% 16% 7% 17% 13% 6% 4 3 4 4 19%	3570
	21st to end	Day	7% 12% 7% 18% 7% 5% 6% 4 4 7% 22%	3960
February	1st to 10th	Day	9% 17% 6% 13% 9% 8% 4 3 4 5% 21%	1725
	11th to 20th	Day	10% 18% 6% 13% 5% 6% 6% 3 5% 4 23%	1830
	21st to end	Day	12% 18% 7% 12% 7% 5% 4 3 4 4 23%	1650
March	1st to 10th	Day	15% 19% 6% 14% 8% 5% 4 2 3 4 21%	4476
	11th to 20th	Day	10% 17% 6% 12% 6% 4 4 3 5% 6% 27%	4699
	21st to end	Day	13% 16% 5% 10% 5% 5% 4 3 4 4 31%	5965
April	1st to 10th	Day	18% 18% 4 10% 5% 4 4 3 4 5% 26%	2400
	11th to 20th	Day	21% 12% 4 8% 4 4 3 3 4 4 32%	2374
	21st to end	Day	19% 15% 3 9% 5% 4 4 3 4 5% 29%	2585
May	1st to 10th	Day	22% 14% 4 9% 5% 4 4 3 4 6% 24%	6346
	11th to 20th	Day	21% 10% 3 8% 5% 5% 5% 4 6% 6% 29%	6318
	21st to end	Day	22% 11% 3 9% 5% 5% 5% 3 4 5% 28%	6949
June	1st to 10th	Day	22% 10% 3 8% 6% 4 5% 4 5% 6% 27%	2800
	11th to 20th	Day	17% 9% 3 8% 5% 6% 6% 5% 6% 8% 30%	2800
	21st to end	Day	23% 10% 3 8% 5% 6% 5% 3 6% 7% 24%	2800
July	1st to 10th	Day	17% 9% 4 9% 6% 6% 6% 4 6% 8% 25%	6360
	11th to 20th	Day	12% 7% 3 7% 5% 5% 6% 5% 7% 9% 34%	6360
	21st to end	Day	11% 6% 2 7% 4 5% 5% 4 7% 9% 39%	6926
August	1st to 10th	Day	15% 8% 3 8% 5% 6% 6% 4 7% 8% 28%	4479
	11th to 20th	Day	17% 8% 3 7% 5% 6% 5% 4 7% 7% 32%	4090
	21st to end	Day	16% 7% 3 8% 5% 5% 5% 4 6% 8% 34%	4180
September	1st to 10th	Day	16% 7% 3 8% 4 3 5% 4 5% 9% 37%	2280
	11th to 20th	Day	14% 9% 3 6% 5% 4 4 3 5% 7% 40%	2207
	21st to end	Day	21% 11% 3 6% 4 4 4 3 4 6% 36%	2090
October	1st to 10th	Day	22% 11% 3 7% 5% 5% 4 4 6% 5% 29%	1948
	11th to 20th	Day	21% 15% 5% 9% 5% 5% 4 3 5% 4 24%	1847
	21st to end	Day	24% 14% 5% 10% 5% 4 2 3 3 5% 23%	1881
November	1st to 10th	Day	16% 16% 4 10% 5% 4 4 3 4 5% 29%	1761
	11th to 20th	Day	16% 18% 5% 11% 6% 5% 4 2 5% 5% 21%	1672
	21st to end	Day	16% 21% 7% 12% 7% 4 4 3 4 4 19%	1600
December	1st to 10th	Day	17% 18% 9% 16% 7% 5% 4 3 3 3 14%	2600
	11th to 20th	Day	16% 16% 5% 16% 7% 4 5% 3 4 5% 20%	2986
	21st to end	Day	15% 16% 8% 14% 6% 5% 4 3 4 4 21%	3960
January	1st to 10th	Night	10% 22% 9% 18% 8% 5% 5% 3 4 3 14%	6349
	11th to 20th	Night	7% 14% 8% 20% 12% 8% 5% 4 4 4 13%	6315
	21st to end	Night	6% 11% 7% 18% 10% 7% 6% 4 5% 5% 20%	6996
February	1st to 10th	Night	9% 15% 6% 13% 8% 6% 5% 4 5% 6% 22%	2670
	11th to 20th	Night	9% 15% 6% 13% 8% 7% 5% 5% 6% 5% 21%	2454
	21st to end	Night	11% 15% 5% 12% 6% 5% 5% 4 5% 6% 26%	1980
March	1st to 10th	Night	17% 17% 5% 12% 7% 4 6% 3 4 4 21%	5364
	11th to 20th	Night	10% 16% 5% 12% 7% 5% 5% 3 5% 6% 26%	5258
	21st to end	Night	14% 12% 6% 11% 6% 6% 5% 4 5% 4 28%	4967
April	1st to 10th	Night	21% 13% 4 10% 5% 4 4 3 5% 5% 27%	2000
	11th to 20th	Night	16% 12% 4 6% 4 5% 4 3 5% 6% 35%	1975
	21st to end	Night	20% 11% 4 9% 4 3 3 4 4 5% 33%	1820
May	1st to 10th	Night	21% 13% 3 8% 6% 5% 4 3 5% 6% 26%	3607
	11th to 20th	Night	22% 10% 3 7% 4 4 4 3 5% 7% 32%	3575
	21st to end	Night	22% 10% 3 9% 5% 5% 4 3 5% 6% 27%	3926
June	1st to 10th	Night	20% 9% 3 6% 5% 3 4 4 5% 8% 32%	1600
	11th to 20th	Night	16% 9% 3 6% 4 4 5% 4 6% 6% 36%	1600
	21st to end	Night	20% 8% 2 6% 4 5% 4 4 6% 7% 34%	1600
July	1st to 10th	Night	14% 7% 3 7% 6% 6% 6% 5% 7% 9% 31%	3600
	11th to 20th	Night	14% 7% 2 7% 4 4 4 4 5% 7% 41%	3600
	21st to end	Night	9% 5% 2 6% 4 4 4 4 6% 8% 46%	3926
August	1st to 10th	Night	12% 8% 2 8% 5% 5% 5% 4 6% 7% 37%	2538
	11th to 20th	Night	17% 10% 3 9% 4 4 4 3 5% 6% 36%	2705
	21st to end	Night	17% 8% 3 7% 5% 4 5% 3 5% 7% 37%	3476
September	1st to 10th	Night	14% 9% 2 6% 5% 4 3 4 5% 7% 43%	1900
	11th to 20th	Night	15% 6% 2 6% 3 4 4 3 5% 6% 46%	1972
	21st to end	Night	16% 8% 3 6% 5% 3 4 3 4 7% 41%	2090
October	1st to 10th	Night	16% 10% 3 8% 5% 4 3 3 4 6% 38%	2229
	11th to 20th	Night	19% 16% 4 9% 4 3 3 2 5% 6% 29%	2332
	21st to end	Night	22% 14% 4 11% 5% 5% 3 3 4 5% 23%	2717
November	1st to 10th	Night	15% 14% 5% 9% 6% 4 5% 4 5% 6% 27%	2537
	11th to 20th	Night	15% 13% 5% 13% 6% 5% 5% 3 4 5% 24%	2725
	21st to end	Night	17% 18% 7% 13% 6% 3 4 3 5% 5% 19%	2800
December	1st to 10th	Night	13% 17% 7% 17% 10% 7% 4 3 5% 5% 13%	4580
	11th to 20th	Night	19% 18% 6% 12% 7% 5% 4 3 4 4 20%	5208
	21st to end	Night	16% 19% 7% 12% 7% 4 3 3 5% 5% 20%	6996

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	71% 6% 8% 12% 4	3598
	11th to 20th	Day	68% 4 5% 13% 8% 2	3600
	21st to end	Day	59% 6% 6% 14% 14% 1	3960
February	1st to 10th	Day	64% 3 7% 15% 9% 2	1725
	11th to 20th	Day	62% 4 9% 14% 10% 1	1839
	21st to end	Day	64% 3 7% 14% 9% 3	1650
March	1st to 10th	Day	68% 4 5% 9% 11% 3	4479
	11th to 20th	Day	56% 5% 13% 11% 12% 3	4699
	21st to end	Day	55% 3 6% 16% 17% 2	5965
April	1st to 10th	Day	60% 4 8% 15% 11% 3	2400
	11th to 20th	Day	55% 4 7% 20% 12% 2	2374
	21st to end	Day	58% 5% 7% 15% 12% 3	2585
May	1st to 10th	Day	60% 6% 8% 17% 10% 1	6357
	11th to 20th	Day	53% 7% 12% 18% 7% 2	6322
	21st to end	Day	58% 5% 8% 15% 12% 1	6949
June	1st to 10th	Day	55% 7% 9% 18% 10% 1	2800
	11th to 20th	Day	50% 7% 12% 21% 10% 2	2800
	21st to end	Day	57% 7% 11% 16% 8%	2800
July	1st to 10th	Day	53% 7% 13% 21% 5%	6290
	11th to 20th	Day	42% 7% 18% 27% 5%	6285
	21st to end	Day	38% 7% 17% 29% 9%	6728
August	1st to 10th	Day	49% 8% 17% 20% 6%	4465
	11th to 20th	Day	47% 8% 17% 23% 5%	4132
	21st to end	Day	46% 7% 13% 21% 13% 1	4180
September	1st to 10th	Day	44% 6% 14% 25% 11% 1	2280
	11th to 20th	Day	42% 5% 14% 27% 10% 1	2207
	21st to end	Day	49% 5% 11% 25% 10%	2090
October	1st to 10th	Day	51% 7% 13% 23% 6% 1	3234
	11th to 20th	Day	54% 6% 12% 22% 5%	3050
	21st to end	Day	54% 6% 18% 14% 6% 1	3081
November	1st to 10th	Day	57% 4 11% 17% 9% 1	1761
	11th to 20th	Day	63% 5% 9% 15% 8% 1	1672
	21st to end	Day	67% 5% 11% 12% 4 1	1600
December	1st to 10th	Day	73% 4 7% 12% 4	2600
	11th to 20th	Day	64% 4 7% 16% 9%	2986
	21st to end	Day	65% 4 7% 13% 11% 1	3960
January	1st to 10th	Night	73% 4 8% 12% 3	6349
	11th to 20th	Night	70% 6% 9% 11% 4 1	6360
	21st to end	Night	64% 5% 7% 11% 14% 1	6996
February	1st to 10th	Night	59% 5% 9% 17% 8% 2	2670
	11th to 20th	Night	60% 5% 9% 16% 9% 1	2456
	21st to end	Night	56% 4 9% 18% 12% 2	1980
March	1st to 10th	Night	66% 5% 7% 10% 10% 2	5374
	11th to 20th	Night	58% 5% 10% 14% 10% 3	5259
	21st to end	Night	56% 5% 6% 20% 10% 3	4967
April	1st to 10th	Night	58% 4 9% 16% 12% 2	2000
	11th to 20th	Night	50% 5% 9% 21% 13% 2	1975
	21st to end	Night	52% 5% 9% 20% 12% 2	1820
May	1st to 10th	Night	57% 6% 11% 16% 9% 1	3613
	11th to 20th	Night	51% 8% 12% 18% 10% 2	3576
	21st to end	Night	56% 6% 11% 17% 10% 1	3927
June	1st to 10th	Night	49% 7% 12% 20% 11% 1	1600
	11th to 20th	Night	46% 7% 12% 22% 11% 3	1600
	21st to end	Night	48% 7% 14% 19% 12%	1600
July	1st to 10th	Night	47% 8% 21% 19% 5%	3560
	11th to 20th	Night	40% 8% 20% 28% 4	3552
	21st to end	Night	33% 8% 19% 30% 10%	3809
August	1st to 10th	Night	44% 7% 19% 24% 7%	2528
	11th to 20th	Night	46% 8% 19% 21% 6%	2729
	21st to end	Night	44% 7% 15% 23% 9% 2	3476
September	1st to 10th	Night	40% 6% 16% 25% 13%	1900
	11th to 20th	Night	38% 5% 16% 31% 9% 1	1972
	21st to end	Night	42% 5% 14% 28% 11%	2090
October	1st to 10th	Night	46% 5% 14% 23% 11%	3723
	11th to 20th	Night	52% 5% 13% 22% 8%	3868
	21st to end	Night	53% 6% 16% 15% 8% 2	4467
November	1st to 10th	Night	55% 7% 12% 19% 6% 1	2537
	11th to 20th	Night	59% 6% 11% 14% 8% 2	2725
	21st to end	Night	64% 5% 11% 14% 5%	2800
December	1st to 10th	Night	70% 7% 11% 9% 3	4580
	11th to 20th	Night	67% 4 6% 14% 8% 1	5208
	21st to end	Night	65% 3 5% 13% 12% 1	6996

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	22% 26% 39% 11% 3	200
	11th to 20th	Day	29% 16% 38% 12% 6% 1	200
	21st to end	Day	19% 25% 37% 15% 3	220
February	1st to 10th	Day	32% 30% 30% 7% 2	263
	11th to 20th	Day	27% 29% 35% 8% 1	377
	21st to end	Day	30% 26% 30% 11% 2	414
March	1st to 10th	Day	27% 23% 33% 13% 3	500
	11th to 20th	Day	28% 25% 31% 12% 2 1	500
	21st to end	Day	32% 23% 26% 12% 6% 1	550
April	1st to 10th	Day	31% 20% 31% 13% 5%	500
	11th to 20th	Day	35% 22% 21% 13% 8% 2	492
	21st to end	Day	32% 23% 31% 9% 4 1	500
May	1st to 10th	Day	30% 24% 30% 12% 3 2	503
	11th to 20th	Day	27% 19% 31% 17% 5% 1	527
	21st to end	Day	27% 20% 31% 16% 5% 1	573
June	1st to 10th	Day	27% 19% 36% 13% 5% 1	530
	11th to 20th	Day	22% 19% 32% 17% 10% 1	530
	21st to end	Day	29% 15% 32% 18% 5% 2	530
July	1st to 10th	Day	18% 14% 39% 20% 6% 2	525
	11th to 20th	Day	16% 16% 36% 26% 5% 1	524
	21st to end	Day	14% 14% 36% 25% 9% 2	576
August	1st to 10th	Day	18% 13% 33% 25% 10% 2	502
	11th to 20th	Day	17% 11% 32% 25% 11% 5%	479
	21st to end	Day	18% 17% 29% 19% 12% 6%	539
September	1st to 10th	Day	21% 14% 32% 18% 11% 5%	490
	11th to 20th	Day	18% 12% 29% 22% 14% 6%	490
	21st to end	Day	23% 17% 25% 19% 12% 4	490
October	1st to 10th	Day	25% 18% 26% 17% 10% 4	490
	11th to 20th	Day	29% 23% 27% 13% 6% 2	462
	21st to end	Day	33% 20% 26% 15% 5%	429
November	1st to 10th	Day	31% 20% 28% 16% 4 1	395
	11th to 20th	Day	30% 24% 30% 14% 3	272
	21st to end	Day	33% 23% 33% 8% 4 1	200
December	1st to 10th	Day	30% 20% 30% 13% 7% 1	200
	11th to 20th	Day	31% 30% 26% 11% 3	200
	21st to end	Day	31% 24% 29% 10% 5% 1	220
January	1st to 10th	Night	25% 22% 34% 15% 4	800
	11th to 20th	Night	20% 23% 33% 19% 5%	800
	21st to end	Night	14% 19% 39% 22% 5% 1	880
February	1st to 10th	Night	17% 24% 36% 19% 4 1	800
	11th to 20th	Night	21% 25% 34% 16% 3 1	783
	21st to end	Night	21% 22% 34% 20% 3	660
March	1st to 10th	Night	27% 19% 32% 18% 4	800
	11th to 20th	Night	26% 23% 28% 17% 5% 1	800
	21st to end	Night	24% 19% 30% 21% 7%	880
April	1st to 10th	Night	31% 17% 27% 20% 5% 1	800
	11th to 20th	Night	25% 18% 29% 20% 7% 1	791
	21st to end	Night	29% 17% 30% 19% 5% 1	620
May	1st to 10th	Night	26% 14% 29% 22% 8% 1	413
	11th to 20th	Night	23% 13% 29% 25% 8% 1	394
	21st to end	Night	21% 14% 34% 22% 9%	433
June	1st to 10th	Night	23% 11% 30% 29% 6% 1	400
	11th to 20th	Night	22% 10% 25% 30% 12% 1	400
	21st to end	Night	24% 8% 23% 33% 12% 1	400
July	1st to 10th	Night	14% 6% 31% 35% 13% 1	390
	11th to 20th	Night	13% 7% 25% 39% 13% 2	388
	21st to end	Night	13% 7% 26% 38% 15% 1	438
August	1st to 10th	Night	12% 7% 18% 44% 19%	386
	11th to 20th	Night	16% 6% 23% 34% 20% 1	507
	21st to end	Night	19% 11% 25% 26% 16% 3	836
September	1st to 10th	Night	17% 9% 29% 33% 12% 1	760
	11th to 20th	Night	17% 10% 25% 28% 18% 2	760
	21st to end	Night	21% 11% 28% 23% 16% 1	760
October	1st to 10th	Night	22% 17% 25% 23% 11% 1	760
	11th to 20th	Night	28% 17% 27% 19% 8% 1	760
	21st to end	Night	30% 18% 26% 22% 5%	836
November	1st to 10th	Night	24% 20% 28% 20% 7% 1	780
	11th to 20th	Night	26% 19% 30% 16% 9% 1	800
	21st to end	Night	29% 24% 24% 17% 5% 1	800
December	1st to 10th	Night	27% 20% 29% 18% 5% 1	800
	11th to 20th	Night	28% 20% 30% 16% 6% 1	800
	21st to end	Night	30% 22% 26% 17% 4 1	880

Page generated at 2025-08-02 01:32:26. Version ac07

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