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 2024-03-23.

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	17% 12% 5% 8% 7% 4 5% 5% 5% 6% 27%	78510
	Night	15% 12% 5% 9% 7% 4 5% 4 5% 6% 27%	81373
Transparency	Day	56% 5% 10% 18% 9% 1	78215
	Night	56% 5% 11% 18% 9% 1	81202
Seeing	Day	25% 19% 31% 16% 7% 2	13596
	Night	23% 17% 29% 22% 8% 1	22722

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% 7% 12% 10% 6% 5% 4 4 5% 17%	2517
	11th to 20th	Day	9% 16% 7% 15% 13% 4 4 3 4 4 20%	2520
	21st to end	Day	10% 11% 7% 13% 11% 5% 6% 7% 5% 7% 18%	2772
February	1st to 10th	Day	9% 17% 7% 10% 10% 6% 6% 4 4 5% 22%	1638
	11th to 20th	Day	10% 16% 6% 12% 7% 5% 6% 4 5% 5% 24%	1736
	21st to end	Day	12% 18% 7% 11% 8% 3 5% 4 4 4 23%	1570
March	1st to 10th	Day	12% 14% 6% 10% 10% 4 5% 4 5% 5% 24%	1897
	11th to 20th	Day	13% 15% 7% 9% 7% 3 5% 4 4 6% 26%	1971
	21st to end	Day	16% 13% 5% 9% 6% 3 5% 3 4 5% 30%	2395
April	1st to 10th	Day	19% 16% 5% 9% 6% 3 4 4 4 6% 25%	2160
	11th to 20th	Day	21% 11% 4 7% 5% 3 3 4 4 4 33%	2134
	21st to end	Day	20% 14% 4 7% 6% 3 4 4 4 5% 29%	2326
May	1st to 10th	Day	20% 12% 4 7% 5% 3 4 4 4 6% 31%	2520
	11th to 20th	Day	19% 9% 4 6% 6% 4 5% 4 5% 6% 32%	2478
	21st to end	Day	20% 10% 3 6% 5% 3 5% 5% 5% 5% 32%	2725
June	1st to 10th	Day	23% 10% 3 6% 6% 3 5% 5% 5% 7% 27%	2520
	11th to 20th	Day	17% 8% 3 6% 5% 4 6% 6% 6% 8% 31%	2520
	21st to end	Day	23% 9% 4 8% 6% 4 6% 5% 5% 7% 24%	2520
July	1st to 10th	Day	15% 7% 4 5% 7% 5% 6% 6% 6% 8% 31%	2520
	11th to 20th	Day	15% 7% 3 6% 6% 4 7% 7% 6% 9% 30%	2520
	21st to end	Day	14% 8% 3 8% 7% 4 6% 5% 6% 9% 31%	2744
August	1st to 10th	Day	15% 8% 4 8% 7% 5% 6% 6% 7% 9% 26%	2506
	11th to 20th	Day	16% 6% 3 6% 7% 5% 6% 6% 7% 7% 33%	2338
	21st to end	Day	14% 8% 3 6% 6% 3 5% 5% 6% 9% 33%	2376
September	1st to 10th	Day	17% 6% 3 6% 5% 3 4 5% 5% 9% 37%	2160
	11th to 20th	Day	15% 9% 3 6% 5% 3 4 4 5% 7% 39%	2091
	21st to end	Day	21% 10% 3 5% 5% 3 4 4 4 6% 36%	1980
October	1st to 10th	Day	22% 11% 3 5% 6% 4 4 5% 5% 5% 29%	1846
	11th to 20th	Day	22% 15% 5% 9% 6% 4 5% 3 5% 4 23%	1750
	21st to end	Day	25% 14% 5% 9% 7% 3 3 4 3 5% 22%	1782
November	1st to 10th	Day	16% 15% 5% 8% 6% 3 5% 4 4 5% 29%	1671
	11th to 20th	Day	17% 17% 6% 10% 7% 4 4 3 5% 6% 20%	1589
	21st to end	Day	16% 19% 8% 11% 8% 3 4 3 4 4 20%	1520
December	1st to 10th	Day	22% 16% 7% 11% 8% 3 4 4 3 4 18%	1520
	11th to 20th	Day	19% 15% 6% 12% 8% 2 4 4 4 6% 20%	1906
	21st to end	Day	17% 18% 8% 12% 8% 4 4 3 3 4 18%	2772
January	1st to 10th	Night	12% 18% 8% 14% 9% 4 5% 4 4 4 18%	4429
	11th to 20th	Night	9% 12% 6% 13% 14% 7% 6% 6% 5% 5% 16%	4440
	21st to end	Night	8% 13% 8% 15% 11% 6% 7% 5% 5% 5% 17%	4884
February	1st to 10th	Night	9% 14% 7% 11% 9% 5% 6% 5% 5% 6% 22%	2537
	11th to 20th	Night	9% 14% 7% 11% 9% 5% 5% 6% 6% 5% 22%	2328
	21st to end	Night	11% 13% 5% 10% 8% 4 6% 5% 5% 6% 26%	1884
March	1st to 10th	Night	14% 13% 7% 8% 8% 4 6% 4 5% 5% 25%	2270
	11th to 20th	Night	14% 17% 5% 8% 7% 4 4 4 4 5% 26%	2206
	21st to end	Night	14% 11% 5% 9% 5% 4 5% 4 5% 4 34%	2006
April	1st to 10th	Night	21% 12% 5% 9% 6% 3 4 4 4 5% 26%	1800
	11th to 20th	Night	16% 10% 4 5% 5% 3 4 4 5% 6% 36%	1775
	21st to end	Night	20% 10% 5% 8% 5% 2 3 4 4 5% 33%	1638
May	1st to 10th	Night	19% 9% 4 8% 6% 2 4 3 5% 5% 36%	1453
	11th to 20th	Night	19% 9% 3 6% 5% 3 3 4 5% 7% 36%	1415
	21st to end	Night	18% 7% 4 6% 5% 3 5% 4 4 7% 37%	1550
June	1st to 10th	Night	20% 9% 4 5% 6% 3 5% 4 5% 9% 31%	1440
	11th to 20th	Night	17% 8% 3 5% 5% 3 6% 5% 6% 7% 36%	1440
	21st to end	Night	19% 7% 3 6% 4 3 5% 5% 6% 7% 35%	1440
July	1st to 10th	Night	12% 6% 3 5% 6% 4 5% 5% 6% 9% 39%	1440
	11th to 20th	Night	12% 5% 3 6% 6% 4 4 5% 5% 9% 41%	1440
	21st to end	Night	10% 7% 3 7% 5% 3 5% 4 7% 9% 41%	1574
August	1st to 10th	Night	11% 6% 3 6% 6% 3 5% 6% 7% 9% 39%	1432
	11th to 20th	Night	13% 8% 3 7% 5% 3 4 4 6% 7% 40%	1543
	21st to end	Night	15% 8% 3 5% 6% 3 4 4 5% 7% 40%	1980
September	1st to 10th	Night	14% 9% 2 5% 5% 3 4 4 5% 7% 42%	1800
	11th to 20th	Night	16% 6% 2 6% 4 3 5% 4 5% 6% 44%	1868
	21st to end	Night	17% 8% 3 5% 4 2 3 4 5% 7% 42%	1980
October	1st to 10th	Night	17% 10% 4 7% 5% 3 4 3 3 6% 38%	2111
	11th to 20th	Night	20% 15% 5% 8% 5% 3 3 3 4 6% 28%	2209
	21st to end	Night	23% 13% 4 10% 6% 4 3 4 4 5% 23%	2574
November	1st to 10th	Night	15% 13% 6% 8% 7% 3 5% 4 5% 6% 28%	2407
	11th to 20th	Night	16% 12% 6% 12% 7% 4 5% 5% 4 5% 24%	2588
	21st to end	Night	18% 15% 7% 11% 8% 3 5% 4 4 5% 20%	2660
December	1st to 10th	Night	18% 17% 8% 14% 9% 4 4 4 4 5% 15%	2660
	11th to 20th	Night	18% 16% 6% 11% 8% 4 5% 4 4 4 20%	3288
	21st to end	Night	18% 19% 7% 11% 9% 4 4 4 3 4 16%	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	68% 4 10% 13% 5%	2518
	11th to 20th	Day	67% 4 6% 15% 7% 1	2520
	21st to end	Day	63% 8% 8% 14% 7% 1	2772
February	1st to 10th	Day	64% 3 8% 16% 8% 2	1638
	11th to 20th	Day	61% 4 10% 14% 11% 1	1745
	21st to end	Day	64% 3 7% 15% 9% 3	1570
March	1st to 10th	Day	60% 4 8% 15% 10% 2	1900
	11th to 20th	Day	58% 5% 9% 12% 13% 3	1971
	21st to end	Day	55% 4 8% 18% 12% 4	2395
April	1st to 10th	Day	61% 3 9% 15% 10% 3	2160
	11th to 20th	Day	55% 4 7% 20% 12% 2	2134
	21st to end	Day	58% 4 7% 15% 12% 3	2326
May	1st to 10th	Day	54% 5% 8% 19% 13% 2	2520
	11th to 20th	Day	53% 5% 8% 18% 14% 2	2482
	21st to end	Day	53% 6% 10% 18% 13% 1	2725
June	1st to 10th	Day	56% 7% 9% 18% 10% 1	2520
	11th to 20th	Day	50% 7% 11% 21% 10% 2	2520
	21st to end	Day	58% 7% 11% 16% 8%	2520
July	1st to 10th	Day	46% 8% 14% 22% 9%	2450
	11th to 20th	Day	47% 7% 13% 23% 9%	2445
	21st to end	Day	49% 8% 14% 21% 8%	2591
August	1st to 10th	Day	52% 10% 15% 20% 4	2492
	11th to 20th	Day	47% 8% 15% 22% 8%	2338
	21st to end	Day	45% 7% 13% 23% 11%	2376
September	1st to 10th	Day	44% 5% 14% 24% 11% 1	2160
	11th to 20th	Day	44% 5% 14% 26% 10% 1	2091
	21st to end	Day	49% 5% 11% 25% 9%	1980
October	1st to 10th	Day	54% 5% 12% 19% 9% 1	1846
	11th to 20th	Day	64% 5% 11% 16% 4 1	1750
	21st to end	Day	65% 4 9% 13% 7% 1	1782
November	1st to 10th	Day	57% 5% 11% 17% 9% 1	1671
	11th to 20th	Day	64% 5% 9% 14% 7% 1	1589
	21st to end	Day	66% 4 11% 13% 5% 1	1520
December	1st to 10th	Day	69% 4 9% 12% 6%	1520
	11th to 20th	Day	65% 4 9% 14% 8%	1906
	21st to end	Day	68% 4 6% 13% 8%	2772
January	1st to 10th	Night	67% 5% 10% 13% 5%	4429
	11th to 20th	Night	65% 6% 11% 12% 4 1	4440
	21st to end	Night	67% 5% 8% 11% 8% 1	4884
February	1st to 10th	Night	60% 4 9% 17% 7% 2	2537
	11th to 20th	Night	59% 5% 9% 17% 10% 1	2330
	21st to end	Night	55% 4 9% 18% 12% 2	1884
March	1st to 10th	Night	59% 4 9% 15% 10% 2	2280
	11th to 20th	Night	59% 5% 8% 15% 12% 2	2207
	21st to end	Night	51% 5% 8% 20% 13% 3	2006
April	1st to 10th	Night	58% 4 9% 16% 12% 2	1800
	11th to 20th	Night	47% 5% 10% 22% 13% 2	1775
	21st to end	Night	52% 4 9% 20% 12% 2	1638
May	1st to 10th	Night	51% 4 9% 19% 14% 3	1453
	11th to 20th	Night	48% 5% 9% 20% 15% 3	1416
	21st to end	Night	47% 6% 12% 21% 13% 1	1551
June	1st to 10th	Night	49% 7% 13% 21% 10% 1	1440
	11th to 20th	Night	46% 8% 11% 22% 11% 3	1440
	21st to end	Night	46% 8% 15% 20% 11%	1440
July	1st to 10th	Night	40% 7% 18% 25% 9% 1	1400
	11th to 20th	Night	40% 7% 17% 27% 8% 1	1392
	21st to end	Night	39% 9% 18% 26% 9%	1486
August	1st to 10th	Night	38% 8% 21% 27% 6%	1422
	11th to 20th	Night	41% 8% 17% 25% 9%	1543
	21st to end	Night	41% 7% 15% 27% 9%	1980
September	1st to 10th	Night	40% 6% 16% 24% 13% 1	1800
	11th to 20th	Night	39% 6% 15% 30% 9% 1	1868
	21st to end	Night	42% 5% 14% 28% 11%	1980
October	1st to 10th	Night	48% 4 10% 26% 12% 1	2111
	11th to 20th	Night	57% 5% 14% 18% 7%	2209
	21st to end	Night	61% 6% 9% 15% 7% 1	2574
November	1st to 10th	Night	55% 7% 12% 19% 6% 1	2407
	11th to 20th	Night	59% 5% 11% 15% 8% 2	2588
	21st to end	Night	63% 5% 11% 15% 5%	2660
December	1st to 10th	Night	71% 4 10% 11% 5%	2660
	11th to 20th	Night	65% 4 8% 13% 8% 1	3288
	21st to end	Night	70% 4 6% 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	21% 27% 37% 12% 3	180
	11th to 20th	Day	29% 15% 38% 12% 6% 1	180
	21st to end	Day	18% 25% 38% 16% 3 1	198
February	1st to 10th	Day	31% 31% 29% 8% 2	236
	11th to 20th	Day	26% 29% 36% 8% 1	343
	21st to end	Day	31% 27% 28% 12% 2	382
March	1st to 10th	Day	26% 23% 32% 14% 3	460
	11th to 20th	Day	27% 25% 32% 13% 3 1	460
	21st to end	Day	30% 22% 27% 13% 6% 2	470
April	1st to 10th	Day	29% 19% 33% 13% 5%	420
	11th to 20th	Day	34% 21% 20% 15% 8% 2	412
	21st to end	Day	30% 23% 32% 10% 5% 1	420
May	1st to 10th	Day	30% 24% 29% 13% 3 2	423
	11th to 20th	Day	26% 20% 31% 16% 5% 2	447
	21st to end	Day	25% 21% 31% 16% 5% 1	485
June	1st to 10th	Day	28% 19% 36% 12% 5% 1	450
	11th to 20th	Day	22% 19% 30% 17% 11% 1	450
	21st to end	Day	27% 13% 33% 19% 6% 2	450
July	1st to 10th	Day	17% 12% 41% 21% 7% 2	445
	11th to 20th	Day	16% 15% 35% 27% 5% 2	444
	21st to end	Day	14% 13% 35% 27% 9% 2	488
August	1st to 10th	Day	18% 13% 31% 26% 10% 2	446
	11th to 20th	Day	16% 10% 32% 25% 11% 5%	439
	21st to end	Day	19% 17% 29% 18% 12% 6%	495
September	1st to 10th	Day	20% 14% 32% 18% 11% 5%	450
	11th to 20th	Day	19% 13% 30% 20% 12% 5%	450
	21st to end	Day	23% 17% 25% 19% 12% 4	450
October	1st to 10th	Day	26% 18% 26% 16% 10% 4	450
	11th to 20th	Day	29% 22% 27% 13% 7% 2	425
	21st to end	Day	34% 19% 26% 16% 5%	396
November	1st to 10th	Day	29% 21% 28% 17% 5% 1	365
	11th to 20th	Day	31% 23% 30% 13% 3	249
	21st to end	Day	30% 25% 32% 9% 4 1	180
December	1st to 10th	Day	32% 19% 29% 13% 6% 1	180
	11th to 20th	Day	29% 32% 24% 12% 3	180
	21st to end	Day	34% 25% 26% 9% 5% 1	198
January	1st to 10th	Night	25% 21% 34% 16% 4	760
	11th to 20th	Night	21% 23% 32% 19% 5%	760
	21st to end	Night	14% 19% 39% 22% 5% 1	836
February	1st to 10th	Night	17% 24% 36% 19% 4 1	760
	11th to 20th	Night	20% 24% 34% 17% 3 1	743
	21st to end	Night	21% 21% 34% 20% 3	628
March	1st to 10th	Night	26% 19% 32% 19% 4	760
	11th to 20th	Night	26% 24% 28% 16% 5% 1	760
	21st to end	Night	24% 19% 29% 21% 7%	801
April	1st to 10th	Night	30% 17% 26% 20% 6% 1	720
	11th to 20th	Night	24% 18% 29% 21% 8% 1	711
	21st to end	Night	28% 16% 29% 19% 6% 1	558
May	1st to 10th	Night	25% 15% 29% 22% 9% 1	373
	11th to 20th	Night	23% 13% 31% 25% 7% 1	354
	21st to end	Night	20% 14% 34% 23% 8%	389
June	1st to 10th	Night	23% 11% 31% 28% 6% 1	360
	11th to 20th	Night	22% 10% 24% 31% 12% 1	360
	21st to end	Night	21% 8% 23% 34% 13% 1	360
July	1st to 10th	Night	13% 7% 31% 35% 13% 1	350
	11th to 20th	Night	13% 7% 26% 37% 14% 2	348
	21st to end	Night	14% 6% 26% 38% 15% 1	394
August	1st to 10th	Night	12% 7% 17% 44% 19%	358
	11th to 20th	Night	15% 5% 23% 34% 20% 1	479
	21st to end	Night	18% 12% 25% 26% 16% 3	792
September	1st to 10th	Night	17% 9% 28% 33% 12% 1	720
	11th to 20th	Night	18% 10% 26% 28% 16% 2	720
	21st to end	Night	21% 12% 29% 23% 15% 1	720
October	1st to 10th	Night	23% 17% 25% 24% 11% 1	720
	11th to 20th	Night	29% 17% 27% 19% 8% 1	720
	21st to end	Night	30% 17% 26% 22% 5%	792
November	1st to 10th	Night	24% 20% 28% 20% 7% 1	740
	11th to 20th	Night	25% 19% 30% 16% 9% 1	760
	21st to end	Night	29% 23% 24% 18% 5% 1	760
December	1st to 10th	Night	28% 21% 29% 18% 5% 1	760
	11th to 20th	Night	27% 21% 31% 16% 6% 1	760
	21st to end	Night	31% 22% 27% 16% 3 1	836

Page generated at 2024-03-19 23:31:09. Version ac07

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