WestVale Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the WestVale Observatory clear sky chart from 2005-11-06 to 2024-06-30.

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	15% 6% 2 5% 4 4 4 4 6% 7% 43%	89670
	Night	15% 6% 2 5% 4 4 4 4 5% 7% 45%	89425
Transparency	Day	38% 7% 12% 20% 18% 5%	89444
	Night	38% 7% 11% 19% 19% 6%	89255
Seeing	Day	18% 10% 22% 25% 17% 8%	14686
	Night	17% 7% 23% 30% 20% 3	24794

By Month

Percentage Cloud Cover SE (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	17% 4 1 4 2 2 3 2 4 5% 55%	2836
	11th to 20th	Day	15% 6% 2 5% 3 3 3 2 4 4 52%	2840
	21st to end	Day	25% 4 2 4 2 3 3 3 4 5% 45%	3124
February	1st to 10th	Day	15% 6% 1 4 5% 3 3 4 6% 8% 43%	1710
	11th to 20th	Day	19% 7% 2 4 4 3 3 3 5% 5% 45%	1848
	21st to end	Day	18% 7% 2 6% 4 4 4 3 4 7% 41%	1582
March	1st to 10th	Day	25% 6% 2 5% 3 3 3 3 5% 6% 41%	3435
	11th to 20th	Day	12% 5% 2 5% 3 4 4 3 5% 6% 53%	3480
	21st to end	Day	22% 6% 2 4 4 3 3 3 5% 6% 43%	3815
April	1st to 10th	Day	11% 4 1 5% 4 3 4 4 6% 8% 50%	2090
	11th to 20th	Day	15% 4 1 5% 4 4 3 3 5% 7% 48%	2239
	21st to end	Day	14% 6% 2 5% 5% 4 4 4 6% 6% 47%	2470
May	1st to 10th	Day	12% 7% 2 7% 5% 5% 6% 5% 7% 9% 36%	4082
	11th to 20th	Day	17% 9% 3 6% 4 5% 5% 3 5% 8% 36%	4081
	21st to end	Day	9% 4 2 5% 3 4 5% 5% 7% 10% 47%	4476
June	1st to 10th	Day	12% 6% 2 6% 4 5% 5% 6% 8% 9% 36%	2470
	11th to 20th	Day	7% 5% 2 6% 5% 6% 6% 5% 8% 10% 40%	2470
	21st to end	Day	8% 5% 2 5% 5% 5% 5% 6% 9% 11% 38%	2457
July	1st to 10th	Day	9% 7% 2 7% 6% 7% 5% 6% 8% 11% 32%	2340
	11th to 20th	Day	9% 6% 3 7% 7% 7% 7% 5% 9% 10% 31%	2340
	21st to end	Day	9% 5% 2 7% 7% 5% 7% 6% 8% 10% 34%	2547
August	1st to 10th	Day	12% 6% 2 7% 6% 7% 6% 6% 8% 9% 30%	2327
	11th to 20th	Day	12% 6% 3 8% 6% 6% 7% 5% 8% 9% 30%	2303
	21st to end	Day	11% 6% 2 7% 5% 4 6% 4 7% 10% 37%	2437
September	1st to 10th	Day	11% 5% 2 7% 5% 6% 4 4 6% 9% 42%	1980
	11th to 20th	Day	16% 6% 2 6% 4 4 5% 3 5% 7% 41%	1980
	21st to end	Day	20% 5% 3 5% 4 5% 4 3 5% 5% 41%	1980
October	1st to 10th	Day	16% 4 2 5% 3 2 3 2 4 5% 54%	1892
	11th to 20th	Day	14% 4 2 5% 3 2 3 2 3 5% 57%	1800
	21st to end	Day	16% 5% 2 4 2 2 3 2 3 4 57%	1980
November	1st to 10th	Day	13% 4 2 4 3 3 3 3 4 5% 56%	1852
	11th to 20th	Day	14% 4 2 4 3 3 3 2 4 6% 54%	1710
	21st to end	Day	16% 5% 2 4 3 3 3 4 4 6% 51%	1710
December	1st to 10th	Day	19% 7% 2 6% 4 4 4 3 4 5% 42%	1710
	11th to 20th	Day	15% 5% 2 4 3 2 3 3 5% 7% 53%	2153
	21st to end	Day	20% 6% 2 5% 3 4 3 3 5% 6% 44%	3124
January	1st to 10th	Night	16% 5% 2 4 3 3 3 3 4 6% 51%	4109
	11th to 20th	Night	12% 6% 2 6% 4 3 3 3 4 6% 51%	4120
	21st to end	Night	25% 6% 1 4 3 3 3 3 3 5% 43%	4532
February	1st to 10th	Night	16% 5% 2 5% 3 4 4 3 5% 6% 46%	2466
	11th to 20th	Night	19% 6% 2 5% 3 4 3 3 5% 5% 45%	2218
	21st to end	Night	17% 6% 2 5% 4 4 5% 3 5% 6% 43%	1870
March	1st to 10th	Night	23% 8% 3 6% 3 4 4 3 4 6% 38%	3418
	11th to 20th	Night	10% 4 2 4 3 3 4 3 5% 7% 54%	3480
	21st to end	Night	20% 5% 2 4 4 3 4 4 5% 6% 44%	3817
April	1st to 10th	Night	12% 5% 1 4 4 4 5% 4 5% 6% 50%	2090
	11th to 20th	Night	15% 5% 2 5% 4 3 3 3 5% 7% 48%	1904
	21st to end	Night	12% 5% 2 6% 4 4 3 4 3 6% 51%	1710
May	1st to 10th	Night	14% 7% 2 6% 5% 4 4 3 5% 8% 41%	2813
	11th to 20th	Night	18% 7% 2 7% 4 5% 4 4 4 7% 38%	2812
	21st to end	Night	11% 5% 2 5% 4 4 4 4 7% 10% 45%	3079
June	1st to 10th	Night	11% 6% 2 5% 5% 5% 6% 5% 7% 11% 36%	1710
	11th to 20th	Night	11% 6% 2 6% 5% 5% 5% 4 8% 9% 39%	1710
	21st to end	Night	7% 4 2 6% 6% 5% 6% 7% 9% 10% 38%	1701
July	1st to 10th	Night	9% 6% 3 7% 6% 6% 7% 5% 9% 10% 31%	1620
	11th to 20th	Night	10% 5% 2 8% 5% 7% 5% 5% 8% 11% 34%	1620
	21st to end	Night	6% 6% 2 6% 7% 6% 7% 6% 11% 12% 31%	1771
August	1st to 10th	Night	14% 6% 3 7% 6% 5% 7% 5% 7% 9% 30%	1611
	11th to 20th	Night	13% 7% 2 7% 4 4 6% 6% 8% 9% 34%	1598
	21st to end	Night	11% 6% 2 7% 5% 5% 6% 5% 7% 11% 35%	1895
September	1st to 10th	Night	12% 5% 1 5% 5% 5% 5% 4 6% 8% 43%	1980
	11th to 20th	Night	16% 5% 2 7% 5% 4 4 4 5% 8% 40%	1980
	21st to end	Night	18% 6% 2 6% 5% 4 4 4 5% 6% 40%	1980
October	1st to 10th	Night	18% 4 2 4 3 3 3 3 4 6% 51%	2066
	11th to 20th	Night	15% 4 2 4 3 3 4 3 4 5% 53%	2160
	21st to end	Night	15% 3 1 4 3 3 3 2 3 4 59%	2376
November	1st to 10th	Night	15% 5% 2 5% 3 3 3 2 4 4 55%	2225
	11th to 20th	Night	13% 5% 2 4 3 3 4 3 4 6% 54%	2470
	21st to end	Night	14% 4 2 4 4 3 3 4 6% 6% 50%	2470
December	1st to 10th	Night	20% 6% 2 6% 4 3 3 4 5% 6% 42%	2470
	11th to 20th	Night	16% 6% 2 4 3 3 3 3 4 5% 52%	3042
	21st to end	Night	20% 5% 2 5% 3 3 4 3 5% 7% 42%	4532

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	33% 3 6% 25% 24% 8%	2837
	11th to 20th	Day	36% 4 6% 16% 32% 6%	2840
	21st to end	Day	42% 3 7% 18% 25% 5%	3124
February	1st to 10th	Day	38% 6% 10% 21% 19% 5%	1710
	11th to 20th	Day	41% 5% 8% 20% 21% 6%	1858
	21st to end	Day	45% 5% 9% 15% 19% 8%	1582
March	1st to 10th	Day	45% 5% 7% 18% 17% 9%	3435
	11th to 20th	Day	31% 6% 8% 19% 24% 12%	3480
	21st to end	Day	43% 4 8% 22% 20% 3	3815
April	1st to 10th	Day	30% 7% 11% 22% 24% 6%	2090
	11th to 20th	Day	35% 6% 10% 20% 22% 8%	2239
	21st to end	Day	36% 6% 12% 24% 17% 4	2470
May	1st to 10th	Day	42% 10% 15% 19% 12% 2	4120
	11th to 20th	Day	45% 8% 12% 20% 13% 1	4085
	21st to end	Day	30% 10% 18% 22% 18% 3	4489
June	1st to 10th	Day	39% 10% 17% 23% 10% 1	2470
	11th to 20th	Day	35% 11% 18% 21% 13% 1	2470
	21st to end	Day	34% 13% 17% 20% 14% 2	2457
July	1st to 10th	Day	42% 13% 16% 15% 10% 3	2275
	11th to 20th	Day	40% 14% 19% 15% 10% 1	2271
	21st to end	Day	38% 13% 19% 20% 9% 1	2405
August	1st to 10th	Day	45% 12% 17% 18% 7%	2314
	11th to 20th	Day	46% 14% 15% 16% 8% 1	2303
	21st to end	Day	39% 11% 17% 22% 8% 3	2437
September	1st to 10th	Day	37% 11% 12% 21% 16% 3	1980
	11th to 20th	Day	40% 8% 12% 18% 19% 3	1980
	21st to end	Day	45% 6% 9% 19% 16% 5%	1980
October	1st to 10th	Day	33% 5% 10% 20% 27% 5%	1892
	11th to 20th	Day	31% 5% 10% 24% 23% 8%	1800
	21st to end	Day	33% 3 7% 22% 25% 10%	1980
November	1st to 10th	Day	31% 5% 7% 19% 29% 8%	1852
	11th to 20th	Day	33% 4 8% 23% 26% 8%	1710
	21st to end	Day	35% 4 8% 23% 25% 6%	1710
December	1st to 10th	Day	45% 5% 8% 20% 17% 5%	1710
	11th to 20th	Day	33% 4 8% 21% 23% 11%	2150
	21st to end	Day	41% 4 9% 23% 20% 3	3124
January	1st to 10th	Night	35% 4 9% 18% 28% 7%	4109
	11th to 20th	Night	36% 4 8% 16% 29% 7%	4120
	21st to end	Night	44% 4 6% 17% 23% 6%	4532
February	1st to 10th	Night	38% 5% 11% 19% 21% 5%	2466
	11th to 20th	Night	43% 4 8% 17% 22% 7%	2219
	21st to end	Night	42% 5% 9% 16% 21% 7%	1870
March	1st to 10th	Night	47% 7% 8% 15% 17% 7%	3418
	11th to 20th	Night	29% 5% 8% 20% 22% 15%	3480
	21st to end	Night	41% 6% 7% 21% 17% 7%	3817
April	1st to 10th	Night	34% 6% 11% 20% 23% 5%	2090
	11th to 20th	Night	34% 5% 9% 22% 22% 8%	1904
	21st to end	Night	36% 6% 11% 23% 21% 4	1710
May	1st to 10th	Night	42% 8% 14% 24% 12% 2	2840
	11th to 20th	Night	44% 9% 12% 20% 14% 1	2813
	21st to end	Night	31% 9% 16% 28% 15% 1	3087
June	1st to 10th	Night	39% 11% 17% 21% 11% 1	1710
	11th to 20th	Night	39% 10% 19% 21% 10% 1	1710
	21st to end	Night	36% 12% 16% 18% 13% 4	1701
July	1st to 10th	Night	42% 13% 18% 15% 8% 3	1575
	11th to 20th	Night	40% 13% 19% 19% 6% 2	1566
	21st to end	Night	37% 15% 21% 19% 8% 1	1672
August	1st to 10th	Night	45% 14% 19% 15% 8%	1600
	11th to 20th	Night	43% 13% 17% 16% 10% 1	1598
	21st to end	Night	38% 15% 18% 19% 8% 2	1895
September	1st to 10th	Night	37% 11% 15% 19% 14% 4	1980
	11th to 20th	Night	41% 11% 13% 16% 18% 2	1980
	21st to end	Night	43% 7% 11% 18% 17% 4	1980
October	1st to 10th	Night	35% 5% 10% 22% 24% 4	2066
	11th to 20th	Night	33% 6% 8% 24% 21% 8%	2160
	21st to end	Night	31% 4 7% 20% 28% 11%	2376
November	1st to 10th	Night	35% 4 7% 19% 25% 11%	2225
	11th to 20th	Night	33% 4 8% 18% 25% 12%	2470
	21st to end	Night	34% 5% 7% 22% 26% 6%	2470
December	1st to 10th	Night	43% 5% 10% 18% 18% 6%	2470
	11th to 20th	Night	35% 4 8% 16% 26% 9%	3044
	21st to end	Night	41% 6% 9% 20% 21% 3	4532

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% 21% 32% 20% 3	270
	11th to 20th	Day	27% 19% 32% 19% 3	270
	21st to end	Day	21% 23% 37% 15% 3	297
February	1st to 10th	Day	23% 20% 36% 16% 5%	270
	11th to 20th	Day	35% 21% 32% 11% 1	270
	21st to end	Day	30% 27% 26% 14% 2	237
March	1st to 10th	Day	21% 17% 30% 25% 6% 1	460
	11th to 20th	Day	21% 20% 34% 21% 4 1	460
	21st to end	Day	23% 18% 32% 21% 5%	506
April	1st to 10th	Day	19% 18% 32% 20% 10% 1	460
	11th to 20th	Day	17% 17% 25% 23% 14% 2	452
	21st to end	Day	18% 12% 32% 22% 12% 5%	460
May	1st to 10th	Day	13% 15% 31% 25% 11% 5%	463
	11th to 20th	Day	18% 6% 22% 29% 18% 8%	487
	21st to end	Day	16% 5% 16% 28% 23% 12%	529
June	1st to 10th	Day	12% 5% 18% 33% 21% 11%	490
	11th to 20th	Day	11% 2 19% 26% 26% 15%	490
	21st to end	Day	11% 3 14% 34% 26% 13%	486
July	1st to 10th	Day	13% 1 10% 23% 30% 24%	445
	11th to 20th	Day	7% 1 12% 28% 30% 22%	444
	21st to end	Day	9% 2 9% 29% 29% 22%	488
August	1st to 10th	Day	15% 3 13% 29% 20% 20%	446
	11th to 20th	Day	12% 5% 9% 28% 28% 18%	439
	21st to end	Day	13% 3 11% 21% 31% 21%	495
September	1st to 10th	Day	15% 1 11% 24% 29% 20%	450
	11th to 20th	Day	18% 3 11% 22% 31% 14%	450
	21st to end	Day	24% 5% 17% 26% 23% 6%	450
October	1st to 10th	Day	20% 5% 18% 27% 22% 9%	450
	11th to 20th	Day	16% 9% 23% 27% 20% 5%	450
	21st to end	Day	19% 9% 19% 35% 15% 4	495
November	1st to 10th	Day	21% 9% 25% 27% 14% 4	450
	11th to 20th	Day	18% 15% 34% 24% 7% 1	270
	21st to end	Day	12% 15% 36% 24% 12% 2	270
December	1st to 10th	Day	27% 15% 30% 21% 6%	270
	11th to 20th	Day	19% 14% 32% 27% 8%	270
	21st to end	Day	26% 17% 33% 18% 5% 1	297
January	1st to 10th	Night	19% 13% 34% 26% 7%	760
	11th to 20th	Night	20% 13% 33% 30% 5%	760
	21st to end	Night	20% 11% 36% 30% 4	836
February	1st to 10th	Night	18% 11% 36% 32% 3	760
	11th to 20th	Night	23% 14% 39% 23% 2	743
	21st to end	Night	20% 16% 36% 25% 3	628
March	1st to 10th	Night	18% 11% 31% 34% 5%	760
	11th to 20th	Night	19% 12% 34% 26% 8% 1	760
	21st to end	Night	19% 10% 34% 29% 7%	836
April	1st to 10th	Night	15% 13% 34% 28% 9%	760
	11th to 20th	Night	17% 12% 27% 30% 14%	751
	21st to end	Night	14% 7% 27% 35% 16%	570
May	1st to 10th	Night	14% 5% 28% 34% 18% 1	570
	11th to 20th	Night	18% 4 20% 32% 25% 2	561
	21st to end	Night	16% 1 13% 30% 34% 5%	617
June	1st to 10th	Night	12% 2 14% 34% 32% 6%	570
	11th to 20th	Night	11% 4 12% 29% 34% 10%	570
	21st to end	Night	8% 1 11% 32% 41% 6%	567
July	1st to 10th	Night	11% 2 7% 23% 49% 8%	525
	11th to 20th	Night	11% 2 5% 27% 44% 11%	522
	21st to end	Night	7% 1 6% 30% 46% 10%	591
August	1st to 10th	Night	15% 2 6% 28% 41% 7%	537
	11th to 20th	Night	15% 2 6% 29% 38% 10%	534
	21st to end	Night	13% 2 10% 22% 45% 9%	698
September	1st to 10th	Night	13% 3 9% 27% 38% 10%	720
	11th to 20th	Night	18% 3 11% 23% 38% 8%	720
	21st to end	Night	21% 3 15% 29% 29% 2	720
October	1st to 10th	Night	18% 4 19% 25% 27% 6%	720
	11th to 20th	Night	19% 6% 22% 30% 21% 2	720
	21st to end	Night	16% 7% 22% 36% 17% 3	792
November	1st to 10th	Night	17% 5% 23% 34% 18% 3	740
	11th to 20th	Night	16% 8% 28% 36% 12% 1	760
	21st to end	Night	15% 8% 26% 35% 15% 1	760
December	1st to 10th	Night	21% 9% 26% 35% 9%	760
	11th to 20th	Night	20% 7% 32% 33% 8% 1	760
	21st to end	Night	24% 8% 29% 32% 7%	836

Page generated at 2024-06-26 22:18:46. Version ac07

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