Wilson Hill Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Wilson Hill Observatory clear sky chart from 2005-11-06 to 2024-11-10.

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% 8% 3 6% 5% 4 4 4 6% 7% 37%	101319
	Night	17% 8% 3 6% 4 4 4 3 5% 6% 39%	97830
Transparency	Day	45% 3 11% 23% 16% 2	104844
	Night	45% 3 11% 23% 15% 2	102394
Seeing	Day	25% 14% 30% 19% 9% 3	14971
	Night	23% 13% 30% 25% 8% 1	23869

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	13% 8% 2 6% 5% 4 4 3 6% 5% 43%	2517
	11th to 20th	Day	16% 7% 3 9% 4 4 5% 4 4 5% 38%	2520
	21st to end	Day	18% 12% 3 8% 5% 4 4 3 5% 5% 33%	2772
February	1st to 10th	Day	18% 8% 2 6% 5% 6% 5% 3 6% 6% 35%	1730
	11th to 20th	Day	12% 8% 3 7% 5% 4 5% 4 6% 8% 38%	1848
	21st to end	Day	16% 11% 4 8% 5% 4 3 3 4 5% 37%	1570
March	1st to 10th	Day	22% 14% 3 7% 4 4 4 3 4 4 29%	3116
	11th to 20th	Day	13% 8% 2 6% 4 5% 5% 4 7% 7% 39%	3310
	21st to end	Day	20% 10% 3 7% 5% 3 4 3 5% 7% 34%	4065
April	1st to 10th	Day	18% 10% 2 7% 5% 4 4 2 5% 6% 36%	2280
	11th to 20th	Day	17% 7% 2 6% 4 5% 4 4 7% 7% 38%	2263
	21st to end	Day	20% 8% 3 7% 5% 4 4 3 5% 6% 35%	2470
May	1st to 10th	Day	22% 11% 3 7% 5% 5% 4 4 5% 6% 28%	4106
	11th to 20th	Day	22% 7% 3 8% 5% 4 4 4 5% 7% 32%	4237
	21st to end	Day	14% 4 2 5% 4 4 4 4 6% 8% 43%	4837
June	1st to 10th	Day	18% 7% 3 6% 5% 5% 4 4 7% 8% 33%	2660
	11th to 20th	Day	16% 6% 2 6% 5% 5% 5% 4 6% 8% 37%	2660
	21st to end	Day	18% 7% 3 6% 5% 5% 5% 4 6% 7% 33%	2660
July	1st to 10th	Day	13% 6% 2 6% 5% 5% 6% 5% 6% 10% 36%	4440
	11th to 20th	Day	10% 6% 2 6% 5% 5% 6% 5% 8% 11% 37%	4440
	21st to end	Day	16% 8% 3 7% 4 4 4 4 6% 7% 35%	4814
August	1st to 10th	Day	14% 6% 2 7% 5% 5% 6% 5% 7% 8% 34%	4215
	11th to 20th	Day	14% 8% 3 7% 5% 5% 5% 4 7% 7% 36%	3986
	21st to end	Day	8% 5% 2 6% 4 5% 6% 5% 8% 10% 42%	4180
September	1st to 10th	Day	13% 5% 2 5% 4 4 4 4 5% 7% 46%	2280
	11th to 20th	Day	14% 6% 3 4 3 3 3 3 3 5% 52%	2104
	21st to end	Day	16% 5% 2 6% 4 4 4 3 4 7% 44%	2090
October	1st to 10th	Day	23% 6% 3 5% 5% 3 4 3 4 5% 38%	2090
	11th to 20th	Day	15% 7% 2 5% 4 3 4 3 4 7% 46%	1831
	21st to end	Day	22% 7% 2 5% 4 4 4 3 4 5% 39%	1881
November	1st to 10th	Day	14% 6% 2 6% 4 3 3 3 4 5% 49%	1752
	11th to 20th	Day	19% 6% 2 4 3 4 4 4 4 5% 46%	1710
	21st to end	Day	19% 6% 2 6% 4 4 4 3 5% 6% 41%	1687
December	1st to 10th	Day	18% 8% 3 6% 5% 5% 4 4 6% 6% 35%	1520
	11th to 20th	Day	22% 6% 2 5% 4 3 4 4 3 5% 42%	1906
	21st to end	Day	22% 12% 3 6% 4 4 5% 4 5% 6% 31%	2772
January	1st to 10th	Night	17% 8% 2 4 3 4 4 3 5% 5% 46%	4429
	11th to 20th	Night	13% 8% 3 9% 5% 5% 4 4 6% 6% 38%	4440
	21st to end	Night	21% 13% 5% 7% 4 4 4 3 4 5% 31%	4884
February	1st to 10th	Night	15% 9% 4 6% 5% 4 4 4 5% 6% 38%	2447
	11th to 20th	Night	12% 9% 2 6% 5% 5% 5% 4 6% 6% 40%	2218
	21st to end	Night	15% 9% 2 6% 4 4 4 4 5% 6% 41%	1884
March	1st to 10th	Night	26% 11% 2 5% 4 4 3 3 4 6% 33%	3724
	11th to 20th	Night	12% 8% 3 8% 5% 5% 5% 4 5% 7% 37%	3649
	21st to end	Night	23% 9% 2 5% 3 3 4 4 6% 7% 34%	3562
April	1st to 10th	Night	18% 8% 3 7% 4 4 3 5% 4 6% 37%	1900
	11th to 20th	Night	19% 8% 2 5% 4 4 4 3 6% 5% 40%	1866
	21st to end	Night	21% 6% 3 6% 4 4 3 3 5% 6% 39%	1710
May	1st to 10th	Night	25% 11% 3 7% 4 4 4 3 6% 7% 26%	2834
	11th to 20th	Night	19% 8% 3 9% 5% 6% 6% 5% 6% 6% 27%	2671
	21st to end	Night	15% 6% 2 6% 5% 4 4 4 6% 8% 41%	2738
June	1st to 10th	Night	18% 9% 3 6% 4 3 4 3 5% 7% 37%	1520
	11th to 20th	Night	20% 6% 2 5% 4 3 5% 4 5% 8% 38%	1520
	21st to end	Night	18% 6% 2 5% 5% 4 5% 4 5% 8% 39%	1520
July	1st to 10th	Night	11% 5% 2 6% 6% 6% 6% 4 7% 9% 39%	2520
	11th to 20th	Night	12% 6% 3 6% 5% 4 4 4 6% 9% 42%	2520
	21st to end	Night	15% 7% 3 6% 4 4 4 3 6% 7% 41%	2739
August	1st to 10th	Night	20% 6% 2 7% 5% 5% 5% 4 5% 7% 34%	2681
	11th to 20th	Night	12% 8% 2 8% 4 5% 5% 4 6% 8% 37%	2838
	21st to end	Night	9% 4 1 4 3 3 4 3 6% 9% 55%	3476
September	1st to 10th	Night	12% 5% 2 5% 4 3 3 3 5% 7% 51%	1900
	11th to 20th	Night	14% 6% 2 5% 3 2 3 3 4 6% 53%	2076
	21st to end	Night	16% 5% 2 6% 3 4 4 3 4 7% 48%	2090
October	1st to 10th	Night	21% 6% 2 6% 5% 4 3 4 4 5% 40%	2090
	11th to 20th	Night	15% 5% 2 5% 4 4 5% 4 5% 7% 45%	2345
	21st to end	Night	22% 7% 3 5% 4 4 3 4 5% 5% 39%	2717
November	1st to 10th	Night	14% 7% 2 6% 3 3 5% 3 5% 6% 47%	2531
	11th to 20th	Night	17% 7% 2 5% 4 4 3 3 4 5% 46%	2470
	21st to end	Night	15% 8% 2 5% 4 4 3 3 5% 6% 44%	2489
December	1st to 10th	Night	19% 9% 3 6% 4 4 4 3 6% 6% 36%	2660
	11th to 20th	Night	19% 8% 2 5% 4 3 4 4 6% 5% 40%	3288
	21st to end	Night	21% 10% 3 7% 5% 4 4 3 5% 6% 33%	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	43% 2 8% 33% 12% 1	2518
	11th to 20th	Day	48% 3 11% 26% 11% 2	2520
	21st to end	Day	54% 2 9% 23% 10% 2	2772
February	1st to 10th	Day	50% 2 11% 22% 12% 3	1730
	11th to 20th	Day	44% 4 10% 21% 16% 3	1857
	21st to end	Day	51% 2 9% 20% 15% 3	1570
March	1st to 10th	Day	60% 2 9% 15% 12% 3	3119
	11th to 20th	Day	44% 2 12% 23% 17% 3	3310
	21st to end	Day	51% 2 4 17% 19% 7%	4065
April	1st to 10th	Day	49% 3 7% 20% 17% 4	2280
	11th to 20th	Day	45% 3 10% 22% 18% 3	2263
	21st to end	Day	52% 3 7% 17% 18% 4	2470
May	1st to 10th	Day	59% 2 9% 17% 11% 1	4120
	11th to 20th	Day	54% 2 14% 18% 11% 2	4241
	21st to end	Day	39% 2 11% 27% 19% 2	4837
June	1st to 10th	Day	47% 4 11% 24% 13% 1	2660
	11th to 20th	Day	45% 4 11% 21% 16% 3	2660
	21st to end	Day	48% 5% 11% 23% 13% 1	2660
July	1st to 10th	Day	42% 6% 12% 21% 18% 1	4370
	11th to 20th	Day	39% 6% 15% 26% 13% 1	4365
	21st to end	Day	47% 3 12% 21% 15% 2	4661
August	1st to 10th	Day	46% 5% 15% 23% 11% 1	4201
	11th to 20th	Day	45% 5% 13% 26% 10% 1	4025
	21st to end	Day	33% 6% 12% 30% 17% 2	4180
September	1st to 10th	Day	37% 4 11% 26% 20% 2	2280
	11th to 20th	Day	36% 3 7% 27% 24% 3	2104
	21st to end	Day	41% 3 8% 24% 21% 3	2090
October	1st to 10th	Day	44% 5% 8% 22% 18% 2	3480
	11th to 20th	Day	33% 3 8% 30% 23% 3	3008
	21st to end	Day	35% 3 7% 31% 20% 4	3081
November	1st to 10th	Day	39% 2 12% 27% 18% 2	1752
	11th to 20th	Day	42% 3 8% 24% 20% 3	1710
	21st to end	Day	45% 2 16% 22% 14% 2	1687
December	1st to 10th	Day	49% 3 14% 18% 15% 1	1520
	11th to 20th	Day	47% 2 10% 19% 18% 3	1906
	21st to end	Day	56% 3 11% 19% 11% 1	2772
January	1st to 10th	Night	41% 2 13% 30% 11% 3	4429
	11th to 20th	Night	47% 4 11% 23% 13% 3	4440
	21st to end	Night	59% 2 9% 18% 11% 2	4884
February	1st to 10th	Night	46% 4 12% 21% 14% 2	2447
	11th to 20th	Night	45% 3 10% 22% 17% 3	2220
	21st to end	Night	45% 3 10% 24% 15% 5%	1884
March	1st to 10th	Night	55% 1 8% 20% 12% 3	3734
	11th to 20th	Night	48% 2 11% 21% 16% 2	3650
	21st to end	Night	50% 3 5% 14% 21% 7%	3562
April	1st to 10th	Night	49% 2 10% 19% 18% 3	1900
	11th to 20th	Night	47% 2 8% 21% 19% 2	1866
	21st to end	Night	47% 2 10% 20% 17% 4	1710
May	1st to 10th	Night	59% 1 10% 18% 8% 2	2840
	11th to 20th	Night	57% 2 14% 16% 10% 2	2672
	21st to end	Night	42% 3 16% 22% 15% 2	2739
June	1st to 10th	Night	48% 3 11% 25% 12% 1	1520
	11th to 20th	Night	45% 6% 13% 21% 14% 3	1520
	21st to end	Night	44% 5% 13% 22% 14% 1	1520
July	1st to 10th	Night	40% 7% 14% 23% 15% 1	2480
	11th to 20th	Night	40% 6% 14% 24% 16%	2472
	21st to end	Night	42% 5% 11% 25% 16% 1	2651
August	1st to 10th	Night	50% 5% 13% 20% 12% 1	2671
	11th to 20th	Night	44% 6% 14% 24% 11% 1	2865
	21st to end	Night	26% 5% 16% 31% 21% 1	3476
September	1st to 10th	Night	34% 4 12% 28% 20% 1	1900
	11th to 20th	Night	34% 3 9% 28% 25% 2	2076
	21st to end	Night	39% 3 9% 29% 18% 2	2090
October	1st to 10th	Night	41% 5% 14% 24% 14% 2	3480
	11th to 20th	Night	29% 2 10% 27% 26% 4	3907
	21st to end	Night	36% 4 10% 33% 15% 2	4467
November	1st to 10th	Night	40% 3 10% 24% 20% 3	2531
	11th to 20th	Night	42% 2 9% 24% 19% 3	2470
	21st to end	Night	42% 3 14% 26% 14% 1	2489
December	1st to 10th	Night	48% 4 11% 23% 13% 1	2660
	11th to 20th	Night	45% 3 13% 18% 19% 2	3288
	21st to end	Night	54% 2 7% 26% 10% 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	34% 17% 28% 16% 4	180
	11th to 20th	Day	31% 21% 33% 11% 2 2	180
	21st to end	Day	28% 19% 35% 13% 5% 1	198
February	1st to 10th	Day	32% 22% 30% 14% 2	330
	11th to 20th	Day	34% 24% 28% 12% 2	456
	21st to end	Day	32% 20% 29% 15% 4	382
March	1st to 10th	Day	32% 16% 33% 15% 3	460
	11th to 20th	Day	33% 22% 28% 12% 3 1	460
	21st to end	Day	33% 17% 31% 12% 5% 2	506
April	1st to 10th	Day	33% 18% 29% 13% 5% 2	460
	11th to 20th	Day	32% 19% 30% 13% 5% 2	452
	21st to end	Day	32% 15% 30% 14% 7% 2	460
May	1st to 10th	Day	36% 14% 28% 16% 5% 2	463
	11th to 20th	Day	24% 14% 36% 19% 6% 1	487
	21st to end	Day	20% 13% 35% 23% 7% 2	529
June	1st to 10th	Day	20% 14% 37% 16% 10% 2	490
	11th to 20th	Day	17% 14% 36% 22% 9% 2	490
	21st to end	Day	21% 12% 36% 20% 8% 3	490
July	1st to 10th	Day	20% 7% 29% 27% 13% 5%	485
	11th to 20th	Day	14% 5% 35% 30% 12% 3	484
	21st to end	Day	13% 10% 32% 32% 11% 3	532
August	1st to 10th	Day	15% 8% 29% 29% 16% 3	486
	11th to 20th	Day	19% 7% 29% 25% 15% 5%	479
	21st to end	Day	15% 8% 30% 26% 16% 5%	539
September	1st to 10th	Day	19% 11% 25% 22% 16% 7%	490
	11th to 20th	Day	22% 10% 24% 18% 16% 10%	490
	21st to end	Day	19% 10% 33% 21% 12% 5%	490
October	1st to 10th	Day	31% 11% 22% 20% 11% 5%	490
	11th to 20th	Day	23% 12% 31% 20% 11% 2	437
	21st to end	Day	31% 13% 28% 21% 6% 1	429
November	1st to 10th	Day	22% 17% 28% 21% 10% 2	392
	11th to 20th	Day	34% 14% 25% 19% 7% 1	370
	21st to end	Day	31% 17% 26% 18% 7% 1	347
December	1st to 10th	Day	27% 24% 31% 12% 6% 1	180
	11th to 20th	Day	36% 20% 30% 13% 2	180
	21st to end	Day	35% 16% 28% 17% 3 1	198
January	1st to 10th	Night	24% 20% 33% 20% 3	760
	11th to 20th	Night	30% 17% 30% 20% 3	760
	21st to end	Night	22% 18% 36% 20% 3	836
February	1st to 10th	Night	24% 17% 34% 22% 3	760
	11th to 20th	Night	24% 21% 35% 18% 2	743
	21st to end	Night	27% 19% 31% 20% 2	628
March	1st to 10th	Night	28% 17% 32% 20% 2	760
	11th to 20th	Night	25% 19% 31% 20% 4	760
	21st to end	Night	27% 17% 33% 18% 5%	836
April	1st to 10th	Night	29% 16% 31% 20% 5%	760
	11th to 20th	Night	26% 17% 31% 20% 6%	742
	21st to end	Night	27% 16% 31% 21% 4 1	570
May	1st to 10th	Night	28% 12% 32% 22% 6%	570
	11th to 20th	Night	22% 13% 31% 28% 6%	485
	21st to end	Night	21% 7% 33% 31% 8%	411
June	1st to 10th	Night	20% 9% 32% 29% 9% 1	380
	11th to 20th	Night	21% 7% 30% 33% 9% 1	380
	21st to end	Night	19% 4 31% 37% 9%	380
July	1st to 10th	Night	17% 5% 28% 38% 11% 1	370
	11th to 20th	Night	14% 2 24% 43% 15% 1	368
	21st to end	Night	14% 4 27% 42% 13%	416
August	1st to 10th	Night	16% 3 26% 39% 16%	475
	11th to 20th	Night	15% 6% 27% 36% 14% 2	592
	21st to end	Night	16% 4 22% 37% 19% 1	836
September	1st to 10th	Night	16% 6% 31% 29% 17% 1	760
	11th to 20th	Night	18% 7% 25% 28% 20% 3	760
	21st to end	Night	20% 7% 28% 29% 14% 2	760
October	1st to 10th	Night	26% 8% 24% 29% 12% 1	760
	11th to 20th	Night	21% 9% 31% 26% 12% 1	760
	21st to end	Night	27% 14% 28% 24% 6% 1	836
November	1st to 10th	Night	21% 12% 31% 27% 8% 1	779
	11th to 20th	Night	24% 16% 29% 22% 8% 1	760
	21st to end	Night	27% 15% 30% 23% 6% 1	760
December	1st to 10th	Night	26% 18% 33% 19% 4	760
	11th to 20th	Night	27% 18% 32% 20% 3	760
	21st to end	Night	28% 18% 31% 20% 3	836

Page generated at 2024-11-07 06:55:47. Version ac07

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