West Mountain
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the West Mountain 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	5% 6% 2 5% 4 4 4 4 6% 8% 52%	100870
	Night	6% 8% 3 6% 4 4 4 4 6% 7% 48%	98324
Transparency	Day	29% 4 9% 20% 21% 16%	100635
	Night	32% 5% 10% 22% 19% 12%	98147
Seeing	Day	8% 8% 20% 31% 25% 8%	14737
	Night	9% 5% 15% 40% 27% 4	25262

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	9% 16% 5% 11% 6% 5% 4 3 8% 8% 26%	2858
	11th to 20th	Day	10% 20% 5% 11% 5% 5% 4 4 5% 7% 24%	2860
	21st to end	Day	8% 15% 4 8% 4 5% 5% 4 9% 8% 30%	3146
February	1st to 10th	Day	10% 11% 3 8% 5% 5% 5% 4 6% 8% 35%	1710
	11th to 20th	Day	9% 12% 3 7% 5% 4 5% 3 6% 8% 37%	1744
	21st to end	Day	7% 11% 4 8% 5% 4 4 4 7% 9% 38%	1570
March	1st to 10th	Day	3 11% 4 8% 5% 4 5% 4 7% 8% 41%	3371
	11th to 20th	Day	5% 9% 3 6% 4 4 5% 5% 7% 8% 44%	3490
	21st to end	Day	8% 13% 4 9% 7% 6% 6% 5% 7% 8% 27%	3825
April	1st to 10th	Day	7% 8% 3 5% 4 5% 5% 5% 6% 7% 45%	2101
	11th to 20th	Day	7% 8% 2 7% 5% 5% 5% 3 6% 6% 46%	2386
	21st to end	Day	6% 7% 2 6% 5% 4 4 4 5% 7% 51%	2470
May	1st to 10th	Day	8% 8% 2 5% 5% 5% 5% 5% 6% 8% 43%	4110
	11th to 20th	Day	4 3 1 4 3 3 4 3 7% 9% 59%	4071
	21st to end	Day	5% 4 2 4 4 4 4 4 7% 8% 54%	4477
June	1st to 10th	Day	2 3 1 4 3 4 4 4 6% 9% 60%	2470
	11th to 20th	Day	3 3 1 4 3 3 4 3 5% 7% 66%	2470
	21st to end	Day	1 2 1 3 2 2 4 3 4 6% 71%	2470
July	1st to 10th	Day	1 1 1 2 2 2 2 2 3 5% 79%	4110
	11th to 20th	Day	1 2 1 4 4 4 5% 6% 7% 10% 57%	4110
	21st to end	Day	2 2 1 3 3 3 4 3 6% 7% 67%	4454
August	1st to 10th	Day	1 2 1 3 3 3 4 4 6% 9% 65%	4092
	11th to 20th	Day	1 1 1 3 3 3 4 4 6% 6% 68%	4028
	21st to end	Day	2 2 1 2 2 2 3 3 5% 6% 72%	4469
September	1st to 10th	Day	2 2 1 2 2 2 4 3 5% 7% 71%	2136
	11th to 20th	Day	3 2 1 3 2 3 4 2 5% 7% 68%	2090
	21st to end	Day	4 2 1 3 2 2 3 2 4 6% 71%	2090
October	1st to 10th	Day	6% 5% 2 4 3 4 4 4 5% 6% 60%	2000
	11th to 20th	Day	6% 4 2 4 3 3 3 3 4 7% 64%	1900
	21st to end	Day	5% 6% 2 4 3 3 3 3 5% 7% 59%	2090
November	1st to 10th	Day	7% 6% 2 5% 4 3 4 4 6% 7% 52%	1684
	11th to 20th	Day	11% 6% 2 5% 4 4 4 4 5% 8% 47%	1710
	21st to end	Day	5% 10% 3 7% 4 4 4 4 6% 8% 45%	1640
December	1st to 10th	Day	8% 12% 3 8% 4 4 4 4 5% 9% 40%	1520
	11th to 20th	Day	8% 12% 3 8% 5% 5% 5% 5% 9% 10% 30%	2002
	21st to end	Day	8% 13% 4 8% 4 5% 6% 5% 9% 9% 29%	3146
January	1st to 10th	Night	7% 18% 5% 9% 5% 4 5% 4 8% 7% 27%	4097
	11th to 20th	Night	13% 17% 6% 10% 5% 5% 4 5% 7% 6% 21%	4110
	21st to end	Night	9% 13% 4 9% 5% 5% 5% 5% 9% 8% 27%	4521
February	1st to 10th	Night	8% 11% 4 7% 5% 4 5% 4 8% 9% 34%	2470
	11th to 20th	Night	8% 12% 3 7% 5% 3 3 4 8% 9% 38%	2320
	21st to end	Night	7% 11% 4 8% 4 5% 4 4 7% 8% 38%	1884
March	1st to 10th	Night	4 13% 5% 8% 5% 5% 5% 5% 9% 7% 34%	3503
	11th to 20th	Night	4 7% 2 6% 4 4 4 4 6% 8% 50%	3490
	21st to end	Night	8% 14% 4 9% 6% 4 5% 4 5% 7% 35%	3828
April	1st to 10th	Night	9% 9% 2 5% 4 3 3 4 4 6% 51%	2078
	11th to 20th	Night	6% 6% 2 6% 4 3 5% 4 6% 7% 49%	1739
	21st to end	Night	8% 7% 2 6% 4 3 4 3 6% 7% 50%	1710
May	1st to 10th	Night	6% 8% 2 7% 4 4 4 4 6% 9% 45%	2860
	11th to 20th	Night	3 4 1 5% 3 4 3 3 6% 7% 62%	2834
	21st to end	Night	5% 4 1 4 4 3 4 4 5% 7% 58%	3110
June	1st to 10th	Night	3 3 1 3 3 4 5% 3 5% 8% 60%	1710
	11th to 20th	Night	3 3 1 3 3 3 3 3 5% 5% 69%	1710
	21st to end	Night	2 2 1 3 3 3 4 3 5% 7% 69%	1710
July	1st to 10th	Night	3 1 1 2 2 2 3 3 4 5% 73%	2860
	11th to 20th	Night	2 2 1 4 4 5% 7% 6% 10% 9% 48%	2860
	21st to end	Night	2 3 1 5% 4 5% 5% 4 5% 8% 58%	3109
August	1st to 10th	Night	2 2 1 4 4 4 5% 4 6% 8% 61%	2847
	11th to 20th	Night	2 3 1 4 4 4 5% 4 5% 7% 62%	2811
	21st to end	Night	1 2 1 3 3 3 3 3 4 6% 72%	3197
September	1st to 10th	Night	2 1 1 2 2 3 2 3 5% 5% 71%	2041
	11th to 20th	Night	3 3 1 3 3 3 3 2 5% 7% 68%	2090
	21st to end	Night	5% 3 1 3 2 3 2 2 4 5% 71%	2090
October	1st to 10th	Night	5% 3 1 4 3 3 3 4 4 6% 63%	2178
	11th to 20th	Night	6% 5% 1 4 3 3 3 3 4 5% 64%	2280
	21st to end	Night	5% 6% 2 4 3 3 3 3 4 6% 62%	2508
November	1st to 10th	Night	6% 6% 2 5% 3 3 3 3 5% 8% 56%	2397
	11th to 20th	Night	8% 6% 2 4 3 4 3 3 6% 8% 53%	2470
	21st to end	Night	6% 11% 4 6% 3 4 4 3 7% 6% 46%	2513
December	1st to 10th	Night	9% 11% 3 5% 4 4 4 3 7% 6% 44%	2660
	11th to 20th	Night	11% 13% 4 6% 4 4 5% 5% 8% 10% 31%	3208
	21st to end	Night	9% 12% 5% 10% 6% 5% 6% 6% 12% 8% 22%	4521

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	55% 4 15% 18% 7%	2859
	11th to 20th	Day	56% 6% 18% 14% 6% 1	2860
	21st to end	Day	48% 4 21% 18% 8% 2	3146
February	1st to 10th	Day	45% 5% 16% 22% 10% 1	1710
	11th to 20th	Day	46% 4 13% 24% 12% 1	1753
	21st to end	Day	42% 5% 12% 27% 14% 1	1570
March	1st to 10th	Day	38% 6% 12% 28% 15% 1	3371
	11th to 20th	Day	35% 5% 12% 33% 14% 2	3490
	21st to end	Day	52% 5% 14% 19% 8% 1	3825
April	1st to 10th	Day	39% 4 11% 23% 17% 6%	2101
	11th to 20th	Day	39% 4 10% 21% 20% 6%	2389
	21st to end	Day	33% 3 9% 26% 23% 4	2470
May	1st to 10th	Day	35% 8% 8% 22% 22% 6%	4110
	11th to 20th	Day	21% 5% 5% 30% 32% 6%	4074
	21st to end	Day	25% 6% 8% 25% 29% 8%	4477
June	1st to 10th	Day	20% 4 6% 20% 33% 16%	2470
	11th to 20th	Day	18% 3 5% 15% 31% 27%	2470
	21st to end	Day	14% 4 1 10% 28% 43%	2470
July	1st to 10th	Day	10% 3 2 7% 14% 65%	4046
	11th to 20th	Day	18% 5% 5% 12% 26% 33%	4041
	21st to end	Day	15% 3 6% 13% 21% 41%	4314
August	1st to 10th	Day	16% 4 5% 18% 30% 27%	4078
	11th to 20th	Day	16% 5% 4 14% 31% 30%	4067
	21st to end	Day	13% 3 4 14% 29% 38%	4468
September	1st to 10th	Day	14% 4 5% 14% 29% 35%	2136
	11th to 20th	Day	17% 3 6% 20% 27% 27%	2090
	21st to end	Day	16% 3 3 20% 35% 23%	2090
October	1st to 10th	Day	27% 4 7% 18% 32% 12%	2000
	11th to 20th	Day	23% 3 7% 26% 32% 9%	1900
	21st to end	Day	26% 3 11% 31% 25% 5%	2090
November	1st to 10th	Day	32% 3 10% 28% 22% 5%	1684
	11th to 20th	Day	35% 5% 10% 29% 19% 2	1710
	21st to end	Day	35% 4 14% 29% 16% 3	1640
December	1st to 10th	Day	38% 4 18% 26% 10% 3	1520
	11th to 20th	Day	46% 4 15% 25% 9%	2000
	21st to end	Day	43% 7% 17% 18% 15% 1	3146
January	1st to 10th	Night	51% 4 14% 21% 8%	4097
	11th to 20th	Night	57% 6% 15% 15% 6% 1	4110
	21st to end	Night	45% 5% 24% 17% 7% 2	4521
February	1st to 10th	Night	42% 7% 17% 24% 9% 1	2470
	11th to 20th	Night	42% 4 12% 25% 15% 2	2321
	21st to end	Night	41% 5% 10% 28% 14% 2	1884
March	1st to 10th	Night	40% 7% 12% 27% 13%	3503
	11th to 20th	Night	31% 4 10% 37% 16% 2	3490
	21st to end	Night	46% 6% 9% 22% 16% 2	3828
April	1st to 10th	Night	34% 4 11% 25% 18% 8%	2078
	11th to 20th	Night	32% 5% 10% 26% 23% 5%	1739
	21st to end	Night	32% 5% 11% 27% 21% 4	1710
May	1st to 10th	Night	34% 6% 6% 24% 24% 6%	2860
	11th to 20th	Night	22% 4 5% 30% 32% 7%	2835
	21st to end	Night	24% 4 8% 30% 29% 5%	3110
June	1st to 10th	Night	21% 5% 7% 23% 30% 15%	1710
	11th to 20th	Night	18% 2 5% 17% 31% 27%	1710
	21st to end	Night	14% 4 3 11% 25% 43%	1710
July	1st to 10th	Night	13% 4 2 7% 11% 62%	2815
	11th to 20th	Night	24% 6% 6% 12% 24% 28%	2806
	21st to end	Night	24% 4 6% 12% 20% 34%	3011
August	1st to 10th	Night	18% 5% 8% 19% 24% 25%	2838
	11th to 20th	Night	21% 5% 6% 15% 23% 30%	2838
	21st to end	Night	14% 3 5% 12% 30% 36%	3197
September	1st to 10th	Night	15% 3 5% 14% 28% 35%	2041
	11th to 20th	Night	18% 3 5% 20% 26% 28%	2090
	21st to end	Night	18% 2 3 16% 32% 28%	2090
October	1st to 10th	Night	23% 3 8% 20% 31% 15%	2178
	11th to 20th	Night	23% 3 6% 25% 33% 10%	2280
	21st to end	Night	24% 4 8% 31% 27% 6%	2508
November	1st to 10th	Night	28% 3 9% 29% 24% 7%	2397
	11th to 20th	Night	28% 5% 12% 32% 20% 3	2470
	21st to end	Night	35% 4 9% 29% 18% 4	2513
December	1st to 10th	Night	38% 4 15% 29% 11% 3	2660
	11th to 20th	Night	44% 5% 14% 25% 11%	3208
	21st to end	Night	49% 5% 14% 18% 13%	4521

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% 7% 11% 30% 22% 5%	270
	11th to 20th	Day	15% 9% 17% 33% 22% 3	270
	21st to end	Day	14% 6% 16% 33% 24% 5%	297
February	1st to 10th	Day	16% 11% 20% 35% 16% 3	270
	11th to 20th	Day	14% 9% 23% 33% 18% 2	349
	21st to end	Day	10% 11% 27% 35% 15% 1	382
March	1st to 10th	Day	12% 15% 22% 32% 16% 3	460
	11th to 20th	Day	8% 9% 31% 31% 18% 3	460
	21st to end	Day	16% 16% 29% 24% 13% 2	506
April	1st to 10th	Day	12% 14% 24% 27% 18% 5%	460
	11th to 20th	Day	12% 19% 23% 27% 15% 5%	452
	21st to end	Day	11% 17% 23% 29% 17% 4	460
May	1st to 10th	Day	8% 12% 28% 33% 16% 4	463
	11th to 20th	Day	8% 8% 25% 30% 22% 7%	488
	21st to end	Day	8% 9% 22% 27% 27% 8%	529
June	1st to 10th	Day	2 9% 20% 34% 27% 7%	490
	11th to 20th	Day	4 9% 26% 33% 22% 6%	490
	21st to end	Day	3 6% 25% 34% 26% 7%	490
July	1st to 10th	Day	1 2 21% 35% 31% 10%	486
	11th to 20th	Day	4 2 16% 36% 34% 9%	484
	21st to end	Day	2 1 10% 34% 41% 11%	531
August	1st to 10th	Day	3 2 17% 33% 32% 12%	487
	11th to 20th	Day	2 3 18% 31% 35% 12%	477
	21st to end	Day	2 3 18% 31% 35% 12%	539
September	1st to 10th	Day	3 4 15% 30% 30% 18%	490
	11th to 20th	Day	6% 6% 21% 27% 29% 12%	490
	21st to end	Day	5% 7% 16% 24% 34% 14%	490
October	1st to 10th	Day	6% 7% 19% 24% 27% 18%	400
	11th to 20th	Day	7% 7% 16% 23% 31% 17%	300
	21st to end	Day	10% 5% 18% 33% 27% 8%	330
November	1st to 10th	Day	13% 13% 16% 26% 21% 11%	270
	11th to 20th	Day	10% 6% 14% 34% 24% 12%	270
	21st to end	Day	10% 6% 13% 33% 29% 9%	270
December	1st to 10th	Day	13% 7% 13% 37% 20% 10%	270
	11th to 20th	Day	15% 5% 11% 39% 26% 3	270
	21st to end	Day	20% 8% 14% 34% 21% 3	297
January	1st to 10th	Night	15% 5% 12% 39% 23% 6%	760
	11th to 20th	Night	13% 7% 14% 35% 26% 4	760
	21st to end	Night	14% 6% 13% 38% 25% 4	836
February	1st to 10th	Night	13% 6% 19% 43% 16% 4	760
	11th to 20th	Night	13% 4 19% 43% 19% 2	744
	21st to end	Night	11% 6% 20% 44% 17% 1	628
March	1st to 10th	Night	13% 11% 16% 43% 17% 2	760
	11th to 20th	Night	8% 5% 18% 44% 23% 1	760
	21st to end	Night	11% 9% 22% 41% 15% 2	836
April	1st to 10th	Night	13% 10% 19% 38% 18% 2	748
	11th to 20th	Night	9% 8% 25% 41% 17%	563
	21st to end	Night	10% 10% 17% 39% 22% 2	570
May	1st to 10th	Night	9% 6% 21% 41% 22% 1	570
	11th to 20th	Night	6% 5% 17% 40% 29% 3	561
	21st to end	Night	6% 6% 16% 36% 30% 4	617
June	1st to 10th	Night	4 7% 16% 41% 30% 2	570
	11th to 20th	Night	5% 6% 22% 40% 25% 1	570
	21st to end	Night	2 2 17% 43% 34% 2	570
July	1st to 10th	Night	2 1 15% 35% 43% 5%	555
	11th to 20th	Night	5% 1 8% 42% 41% 3	552
	21st to end	Night	3 2 6% 35% 51% 2	624
August	1st to 10th	Night	4 1 10% 43% 40% 2	567
	11th to 20th	Night	2 2 12% 44% 38% 2	564
	21st to end	Night	2 2 12% 40% 42% 3	627
September	1st to 10th	Night	3 2 10% 39% 40% 7%	711
	11th to 20th	Night	5% 3 14% 35% 36% 7%	760
	21st to end	Night	7% 3 11% 33% 35% 10%	760
October	1st to 10th	Night	7% 3 16% 41% 28% 5%	760
	11th to 20th	Night	7% 4 13% 41% 31% 4	760
	21st to end	Night	8% 4 16% 40% 29% 4	836
November	1st to 10th	Night	8% 7% 15% 36% 28% 5%	742
	11th to 20th	Night	10% 5% 15% 42% 23% 5%	760
	21st to end	Night	11% 5% 15% 36% 26% 6%	803
December	1st to 10th	Night	14% 4 14% 44% 21% 3	950
	11th to 20th	Night	18% 6% 13% 40% 21% 2	912
	21st to end	Night	20% 6% 14% 41% 17% 3	836

Page generated at 2024-10-29 09:20:48. Version ac07

Copyright © 2024 Attilla Danko.