Astro-chalet West
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Astro-chalet West clear sky chart from 2005-11-06 to 2024-11-01.

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	4 5% 1 3 2 2 3 2 4 5% 68%	100850
	Night	5% 7% 2 4 2 2 3 2 4 5% 64%	98334
Transparency	Day	18% 3 6% 15% 27% 30%	100605
	Night	22% 4 6% 16% 26% 25%	98168
Seeing	Day	12% 13% 36% 27% 9% 3	15456
	Night	10% 7% 22% 35% 22% 4	25154

By Month

Percentage Cloud Cover SW (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	5% 15% 4 6% 4 3 3 3 5% 6% 46%	2539
	11th to 20th	Day	9% 7% 3 6% 4 4 3 5% 7% 9% 43%	2762
	21st to end	Day	11% 10% 2 8% 4 4 4 4 6% 9% 37%	3280
February	1st to 10th	Day	8% 12% 3 5% 4 3 3 3 4 4 51%	1900
	11th to 20th	Day	8% 12% 3 3 3 3 3 3 5% 8% 49%	1850
	21st to end	Day	8% 12% 3 6% 3 4 4 4 5% 4 48%	1570
March	1st to 10th	Day	10% 16% 3 7% 4 4 4 4 4 8% 38%	3138
	11th to 20th	Day	5% 8% 2 5% 3 3 4 4 6% 8% 50%	3294
	21st to end	Day	7% 16% 3 5% 4 4 5% 5% 6% 7% 37%	4165
April	1st to 10th	Day	8% 7% 1 4 3 3 4 3 5% 7% 54%	2280
	11th to 20th	Day	6% 7% 2 4 3 2 3 3 5% 7% 60%	2249
	21st to end	Day	5% 7% 1 3 3 2 3 3 5% 7% 62%	2280
May	1st to 10th	Day	3 4 1 2 2 2 2 2 3 5% 73%	3911
	11th to 20th	Day	3 2 1 2 2 2 2 4 6% 77%	4071
	21st to end	Day	3 3 1 1 1 1 1 2 2 4 80%	4477
June	1st to 10th	Day	2 2 1 2 2 2 2 3 5% 6% 73%	2643
	11th to 20th	Day	1 1 1 1 1 1 2 3 88%	2660
	21st to end	Day	1 1 1 2 1 1 1 2 3 87%	2660
July	1st to 10th	Day	1 1 1 1 1 2 3 91%	4420
	11th to 20th	Day	1 1 1 1 1 2 2 2 2 3 84%	4420
	21st to end	Day	1 1 1 1 1 1 1 3 4 86%	4345
August	1st to 10th	Day	1 1 1 1 2 1 2 2 3 85%	3783
	11th to 20th	Day	1 1 1 1 1 1 2 2 92%	3724
	21st to end	Day	1 1 1 1 1 2 92%	4180
September	1st to 10th	Day	1 1 1 1 1 2 1 3 4 85%	2280
	11th to 20th	Day	1 1 1 1 1 1 1 2 3 89%	2171
	21st to end	Day	1 1 1 2 1 1 2 1 2 4 84%	2090
October	1st to 10th	Day	4 3 1 3 2 3 3 2 4 5% 71%	2090
	11th to 20th	Day	3 3 1 3 1 3 3 2 3 4 74%	1905
	21st to end	Day	4 3 1 3 2 2 2 2 5% 7% 69%	2055
November	1st to 10th	Day	5% 9% 2 3 3 2 2 3 4 6% 62%	1674
	11th to 20th	Day	4 5% 1 4 3 3 4 2 4 7% 62%	1710
	21st to end	Day	5% 9% 2 3 3 4 3 3 5% 6% 57%	1710
December	1st to 10th	Day	7% 6% 2 5% 3 3 3 4 5% 7% 54%	1710
	11th to 20th	Day	10% 10% 2 7% 5% 4 4 4 5% 8% 41%	2060
	21st to end	Day	10% 10% 3 8% 6% 5% 6% 4 5% 6% 38%	2794
January	1st to 10th	Night	7% 16% 3 7% 3 3 4 3 5% 6% 43%	4406
	11th to 20th	Night	7% 11% 3 7% 4 4 4 4 6% 9% 42%	4203
	21st to end	Night	16% 14% 3 5% 4 3 4 3 5% 8% 36%	4387
February	1st to 10th	Night	8% 14% 3 6% 4 3 3 2 4 5% 49%	2280
	11th to 20th	Night	8% 11% 2 4 3 3 3 2 6% 6% 52%	2218
	21st to end	Night	9% 12% 3 5% 4 3 3 3 4 6% 48%	1884
March	1st to 10th	Night	10% 21% 2 4 3 3 3 3 6% 9% 37%	3736
	11th to 20th	Night	7% 11% 2 4 3 3 3 3 5% 7% 52%	3667
	21st to end	Night	8% 19% 2 5% 3 3 3 2 4 6% 43%	3488
April	1st to 10th	Night	7% 9% 3 5% 3 3 3 3 5% 6% 53%	1900
	11th to 20th	Night	6% 8% 1 4 2 3 3 3 4 6% 61%	1879
	21st to end	Night	8% 6% 1 2 1 2 2 3 4 7% 64%	1900
May	1st to 10th	Night	7% 4 1 2 1 1 1 1 3 4 76%	3062
	11th to 20th	Night	3 2 1 1 1 2 1 3 5% 80%	2834
	21st to end	Night	3 2 1 2 1 1 1 1 3 3 83%	3110
June	1st to 10th	Night	3 2 1 2 2 1 3 3 4 5% 75%	1532
	11th to 20th	Night	1 1 1 2 1 1 2 3 87%	1520
	21st to end	Night	1 1 1 1 1 2 3 89%	1520
July	1st to 10th	Night	1 1 1 1 1 2 2 90%	2540
	11th to 20th	Night	1 1 1 1 1 1 2 2 2 88%	2540
	21st to end	Night	1 1 1 1 1 1 1 1 3 88%	3213
August	1st to 10th	Night	1 1 1 1 1 1 1 1 2 3 86%	3166
	11th to 20th	Night	1 1 1 2 2 92%	3126
	21st to end	Night	1 1 1 1 1 1 2 93%	3498
September	1st to 10th	Night	1 2 1 1 1 1 2 3 88%	1900
	11th to 20th	Night	1 1 1 1 1 2 1 2 3 85%	2009
	21st to end	Night	1 1 1 1 2 1 1 2 3 85%	2090
October	1st to 10th	Night	3 3 1 3 2 2 2 2 5% 4 73%	2090
	11th to 20th	Night	5% 3 1 3 2 2 2 2 3 4 72%	2270
	21st to end	Night	4 3 1 2 2 1 2 2 3 5% 73%	2541
November	1st to 10th	Night	6% 7% 2 4 3 2 3 3 4 7% 60%	2411
	11th to 20th	Night	4 6% 2 4 3 3 4 3 4 6% 62%	2470
	21st to end	Night	8% 8% 2 5% 3 3 3 3 6% 7% 52%	2470
December	1st to 10th	Night	7% 9% 2 4 3 3 4 3 5% 6% 53%	2470
	11th to 20th	Night	10% 9% 2 6% 4 4 4 4 5% 9% 42%	3142
	21st to end	Night	7% 13% 4 9% 6% 5% 5% 5% 6% 7% 34%	4862

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	28% 4 14% 27% 20% 7%	2539
	11th to 20th	Day	31% 7% 14% 19% 20% 9%	2762
	21st to end	Day	38% 6% 11% 19% 16% 10%	3280
February	1st to 10th	Day	34% 4 5% 17% 21% 19%	1900
	11th to 20th	Day	31% 4 6% 18% 26% 15%	1860
	21st to end	Day	36% 4 9% 19% 26% 7%	1570
March	1st to 10th	Day	38% 5% 10% 16% 19% 12%	3138
	11th to 20th	Day	25% 8% 12% 27% 17% 11%	3294
	21st to end	Day	34% 10% 13% 22% 16% 5%	4165
April	1st to 10th	Day	29% 5% 12% 22% 23% 11%	2280
	11th to 20th	Day	22% 3 9% 28% 25% 12%	2252
	21st to end	Day	18% 4 13% 26% 31% 8%	2280
May	1st to 10th	Day	13% 4 7% 19% 39% 18%	3911
	11th to 20th	Day	10% 3 4 18% 44% 21%	4074
	21st to end	Day	12% 2 4 17% 47% 19%	4477
June	1st to 10th	Day	13% 3 7% 19% 35% 22%	2643
	11th to 20th	Day	5% 1 5% 13% 35% 40%	2660
	21st to end	Day	7% 1 3 6% 30% 53%	2660
July	1st to 10th	Day	4 1 2 5% 12% 77%	4351
	11th to 20th	Day	10% 1 1 8% 22% 58%	4345
	21st to end	Day	7% 2 2 16% 29% 44%	4207
August	1st to 10th	Day	8% 1 2 6% 34% 49%	3770
	11th to 20th	Day	4 1 1 4 25% 64%	3760
	21st to end	Day	4 1 2 6% 29% 58%	4179
September	1st to 10th	Day	7% 3 3 6% 31% 51%	2280
	11th to 20th	Day	5% 1 2 12% 37% 42%	2171
	21st to end	Day	8% 1 3 9% 38% 40%	2090
October	1st to 10th	Day	17% 2 5% 15% 24% 36%	2090
	11th to 20th	Day	14% 2 5% 13% 31% 35%	1905
	21st to end	Day	15% 3 5% 12% 29% 36%	2055
November	1st to 10th	Day	22% 3 8% 12% 31% 23%	1674
	11th to 20th	Day	21% 3 8% 17% 24% 28%	1710
	21st to end	Day	28% 4 7% 12% 25% 24%	1710
December	1st to 10th	Day	27% 5% 7% 18% 22% 20%	1710
	11th to 20th	Day	40% 6% 9% 15% 18% 12%	2059
	21st to end	Day	43% 5% 7% 19% 18% 9%	2794
January	1st to 10th	Night	33% 4 9% 22% 22% 10%	4406
	11th to 20th	Night	33% 7% 11% 19% 19% 10%	4203
	21st to end	Night	41% 4 10% 17% 17% 11%	4387
February	1st to 10th	Night	38% 2 6% 13% 21% 20%	2280
	11th to 20th	Night	32% 3 7% 16% 26% 17%	2219
	21st to end	Night	37% 4 8% 20% 22% 9%	1884
March	1st to 10th	Night	37% 7% 8% 19% 19% 11%	3736
	11th to 20th	Night	29% 6% 10% 29% 18% 9%	3667
	21st to end	Night	34% 9% 14% 23% 17% 4	3488
April	1st to 10th	Night	31% 4 11% 24% 22% 9%	1900
	11th to 20th	Night	24% 3 11% 23% 29% 11%	1879
	21st to end	Night	21% 3 8% 33% 28% 6%	1900
May	1st to 10th	Night	15% 2 5% 22% 40% 16%	3062
	11th to 20th	Night	10% 4 3 20% 47% 16%	2835
	21st to end	Night	10% 2 5% 20% 49% 14%	3110
June	1st to 10th	Night	14% 3 8% 21% 36% 19%	1532
	11th to 20th	Night	6% 2 5% 15% 37% 35%	1520
	21st to end	Night	5% 1 3 7% 33% 50%	1520
July	1st to 10th	Night	4 1 2 4 15% 75%	2500
	11th to 20th	Night	7% 1 2 7% 19% 63%	2492
	21st to end	Night	6% 1 2 19% 26% 45%	3113
August	1st to 10th	Night	7% 1 2 9% 37% 44%	3156
	11th to 20th	Night	3 1 1 5% 30% 59%	3156
	21st to end	Night	4 1 1 8% 32% 54%	3498
September	1st to 10th	Night	6% 2 3 8% 31% 50%	1900
	11th to 20th	Night	7% 2 2 12% 40% 36%	2009
	21st to end	Night	8% 1 2 15% 37% 37%	2090
October	1st to 10th	Night	15% 2 4 16% 26% 36%	2090
	11th to 20th	Night	16% 2 4 15% 30% 32%	2270
	21st to end	Night	16% 3 4 11% 31% 35%	2541
November	1st to 10th	Night	24% 2 5% 15% 29% 24%	2411
	11th to 20th	Night	22% 3 7% 14% 26% 28%	2470
	21st to end	Night	29% 4 6% 13% 21% 26%	2470
December	1st to 10th	Night	30% 4 7% 15% 24% 21%	2470
	11th to 20th	Night	39% 10% 7% 15% 17% 12%	3142
	21st to end	Night	43% 6% 7% 17% 18% 9%	4862

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	24% 17% 33% 21% 4 1	180
	11th to 20th	Day	21% 19% 36% 19% 5% 1	311
	21st to end	Day	19% 19% 39% 17% 5% 1	447
February	1st to 10th	Day	19% 17% 40% 19% 4 2	460
	11th to 20th	Day	22% 23% 30% 19% 5% 1	455
	21st to end	Day	23% 21% 35% 17% 3	382
March	1st to 10th	Day	26% 23% 30% 17% 4	460
	11th to 20th	Day	23% 20% 32% 18% 5% 1	460
	21st to end	Day	26% 22% 34% 13% 4	506
April	1st to 10th	Day	20% 19% 31% 21% 8% 1	460
	11th to 20th	Day	22% 20% 32% 19% 5% 1	452
	21st to end	Day	14% 20% 33% 20% 10% 3	460
May	1st to 10th	Day	15% 18% 37% 21% 8% 1	463
	11th to 20th	Day	12% 16% 38% 23% 8% 3	488
	21st to end	Day	15% 14% 33% 25% 9% 3	529
June	1st to 10th	Day	6% 13% 37% 31% 9% 4	490
	11th to 20th	Day	3 12% 41% 30% 10% 3	490
	21st to end	Day	3 11% 42% 29% 11% 4	490
July	1st to 10th	Day	1 4 40% 37% 11% 7%	486
	11th to 20th	Day	2 3 29% 43% 14% 10%	484
	21st to end	Day	2 3 33% 37% 16% 9%	531
August	1st to 10th	Day	2 6% 42% 31% 12% 7%	487
	11th to 20th	Day	3 4 35% 37% 15% 6%	477
	21st to end	Day	1 4 39% 37% 12% 6%	539
September	1st to 10th	Day	1 5% 42% 36% 12% 4	490
	11th to 20th	Day	4 12% 40% 32% 10% 1	490
	21st to end	Day	6% 9% 40% 30% 13% 2	490
October	1st to 10th	Day	7% 13% 35% 32% 12%	490
	11th to 20th	Day	9% 11% 37% 34% 7% 1	490
	21st to end	Day	9% 14% 33% 33% 8% 2	504
November	1st to 10th	Day	15% 8% 37% 27% 12% 1	270
	11th to 20th	Day	10% 12% 37% 29% 10% 1	270
	21st to end	Day	14% 15% 39% 21% 10% 1	270
December	1st to 10th	Day	16% 16% 38% 24% 5%	270
	11th to 20th	Day	20% 11% 33% 24% 9% 1	237
	21st to end	Day	26% 22% 27% 18% 8%	198
January	1st to 10th	Night	16% 8% 31% 29% 11% 5%	760
	11th to 20th	Night	11% 9% 32% 33% 12% 3	760
	21st to end	Night	18% 9% 27% 31% 12% 2	836
February	1st to 10th	Night	16% 9% 28% 30% 13% 4	760
	11th to 20th	Night	15% 9% 29% 29% 15% 4	744
	21st to end	Night	17% 11% 25% 32% 12% 3	628
March	1st to 10th	Night	17% 10% 27% 32% 12% 2	760
	11th to 20th	Night	16% 11% 23% 28% 18% 4	760
	21st to end	Night	19% 13% 22% 31% 14% 2	836
April	1st to 10th	Night	14% 13% 27% 29% 15% 2	760
	11th to 20th	Night	13% 12% 24% 34% 14% 3	751
	21st to end	Night	12% 14% 23% 30% 17% 4	760
May	1st to 10th	Night	11% 11% 29% 32% 16% 1	694
	11th to 20th	Night	8% 12% 24% 36% 20% 1	561
	21st to end	Night	11% 10% 28% 33% 17% 1	617
June	1st to 10th	Night	6% 6% 25% 41% 21% 1	392
	11th to 20th	Night	1 5% 25% 43% 24% 2	380
	21st to end	Night	1 2 24% 45% 29% 1	380
July	1st to 10th	Night	1 8% 44% 44% 3	370
	11th to 20th	Night	2 4 40% 51% 2	368
	21st to end	Night	2 8% 39% 44% 7%	679
August	1st to 10th	Night	2 1 14% 42% 35% 6%	756
	11th to 20th	Night	1 11% 40% 39% 9%	752
	21st to end	Night	1 1 8% 41% 39% 10%	836
September	1st to 10th	Night	2 1 8% 36% 43% 9%	760
	11th to 20th	Night	2 2 15% 42% 31% 8%	760
	21st to end	Night	3 3 18% 37% 31% 8%	760
October	1st to 10th	Night	4 5% 17% 47% 23% 3	760
	11th to 20th	Night	8% 5% 18% 39% 23% 7%	760
	21st to end	Night	8% 5% 22% 35% 21% 10%	836
November	1st to 10th	Night	12% 4 19% 38% 20% 7%	742
	11th to 20th	Night	7% 6% 26% 36% 21% 4	760
	21st to end	Night	11% 8% 28% 33% 17% 4	760
December	1st to 10th	Night	13% 9% 30% 31% 14% 3	760
	11th to 20th	Night	18% 8% 29% 31% 13% 2	760
	21st to end	Night	18% 9% 29% 31% 11% 2	836

Page generated at 2024-10-29 08:20:50. Version ac07

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