Colliers Mills WMA
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Colliers Mills WMA clear sky chart from 2005-11-06 to 2024-11-11.

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% 7% 2 6% 4 4 5% 4 6% 7% 39%	101324
	Night	16% 7% 2 6% 4 4 4 3 5% 7% 42%	97817
Transparency	Day	42% 6% 12% 22% 16% 2	104882
	Night	41% 5% 11% 23% 17% 3	102348
Seeing	Day	20% 13% 29% 23% 11% 3	15063
	Night	18% 11% 31% 29% 10% 1	24265

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	15% 9% 3 6% 4 3 3 3 4 4 47%	2517
	11th to 20th	Day	15% 9% 3 9% 5% 4 3 3 4 6% 38%	2520
	21st to end	Day	23% 10% 3 7% 4 4 3 3 4 5% 34%	3103
February	1st to 10th	Day	15% 8% 2 7% 5% 4 4 3 5% 6% 40%	1710
	11th to 20th	Day	16% 7% 3 6% 5% 4 4 3 4 6% 42%	1848
	21st to end	Day	18% 9% 3 8% 5% 3 4 3 6% 5% 38%	1570
March	1st to 10th	Day	27% 8% 2 5% 3 3 3 2 3 5% 37%	3116
	11th to 20th	Day	9% 5% 2 6% 4 4 5% 5% 6% 7% 47%	3402
	21st to end	Day	21% 6% 2 5% 4 3 3 3 4 5% 43%	4097
April	1st to 10th	Day	17% 8% 2 5% 4 5% 4 3 5% 6% 39%	2280
	11th to 20th	Day	15% 6% 2 5% 5% 4 4 3 6% 8% 42%	2254
	21st to end	Day	17% 6% 2 6% 5% 5% 5% 4 5% 6% 40%	2280
May	1st to 10th	Day	25% 9% 3 6% 4 4 4 3 5% 7% 29%	4067
	11th to 20th	Day	24% 8% 3 7% 4 4 4 3 5% 6% 30%	4366
	21st to end	Day	12% 6% 2 5% 5% 5% 4 4 6% 8% 43%	4837
June	1st to 10th	Day	13% 5% 2 6% 5% 5% 5% 4 7% 9% 38%	2660
	11th to 20th	Day	12% 7% 3 6% 5% 4 5% 4 6% 9% 39%	2660
	21st to end	Day	11% 5% 1 7% 5% 5% 6% 4 6% 8% 41%	2660
July	1st to 10th	Day	8% 5% 2 7% 6% 7% 7% 5% 8% 10% 35%	4440
	11th to 20th	Day	11% 6% 3 6% 5% 5% 6% 5% 7% 10% 35%	4440
	21st to end	Day	12% 9% 3 8% 6% 5% 6% 4 7% 9% 31%	4814
August	1st to 10th	Day	19% 6% 3 8% 5% 5% 6% 4 7% 8% 30%	4046
	11th to 20th	Day	13% 7% 2 6% 5% 5% 6% 5% 6% 9% 38%	3730
	21st to end	Day	10% 5% 2 6% 5% 4 5% 5% 7% 10% 42%	4180
September	1st to 10th	Day	13% 6% 2 7% 4 5% 4 3 5% 7% 44%	2280
	11th to 20th	Day	11% 6% 2 6% 4 4 4 4 5% 8% 48%	2216
	21st to end	Day	18% 7% 3 6% 3 4 5% 4 5% 6% 39%	2090
October	1st to 10th	Day	18% 7% 2 6% 4 3 3 2 5% 6% 44%	1957
	11th to 20th	Day	14% 6% 2 4 3 3 4 3 4 6% 50%	1900
	21st to end	Day	17% 6% 2 6% 3 3 3 3 5% 6% 47%	1980
November	1st to 10th	Day	13% 5% 2 5% 3 3 3 2 4 6% 53%	1761
	11th to 20th	Day	16% 6% 2 5% 4 3 3 3 5% 5% 47%	1710
	21st to end	Day	14% 5% 2 6% 4 4 3 3 4 7% 47%	1635
December	1st to 10th	Day	17% 8% 3 6% 4 3 4 4 5% 6% 40%	1520
	11th to 20th	Day	20% 8% 3 4 3 3 4 3 4 5% 43%	1906
	21st to end	Day	17% 7% 2 6% 4 5% 5% 5% 6% 7% 37%	2772
January	1st to 10th	Night	16% 7% 2 5% 3 4 3 3 5% 6% 46%	4429
	11th to 20th	Night	18% 9% 2 6% 4 3 4 3 4 4 44%	4440
	21st to end	Night	23% 10% 2 6% 4 4 3 3 4 6% 35%	4550
February	1st to 10th	Night	15% 9% 3 6% 4 4 3 3 5% 7% 41%	2469
	11th to 20th	Night	17% 9% 2 6% 4 3 3 3 5% 6% 41%	2218
	21st to end	Night	18% 8% 2 6% 3 3 4 3 5% 6% 42%	1884
March	1st to 10th	Night	23% 11% 2 6% 3 3 3 2 4 5% 38%	3724
	11th to 20th	Night	12% 6% 2 7% 4 4 3 3 4 5% 48%	3556
	21st to end	Night	18% 9% 3 7% 3 3 3 3 4 4 43%	3534
April	1st to 10th	Night	16% 8% 2 7% 4 3 3 3 5% 7% 41%	1900
	11th to 20th	Night	15% 7% 2 7% 4 4 4 3 5% 6% 42%	1875
	21st to end	Night	18% 6% 2 4 3 3 4 3 6% 7% 43%	1900
May	1st to 10th	Night	22% 10% 3 9% 4 4 3 4 6% 8% 29%	2871
	11th to 20th	Night	25% 9% 3 6% 5% 3 4 3 5% 6% 31%	2541
	21st to end	Night	13% 8% 2 6% 4 4 5% 3 5% 9% 41%	2738
June	1st to 10th	Night	14% 6% 2 5% 4 4 4 4 6% 8% 42%	1520
	11th to 20th	Night	10% 7% 3 6% 5% 5% 5% 4 6% 8% 41%	1520
	21st to end	Night	8% 5% 3 6% 6% 5% 6% 5% 7% 11% 40%	1520
July	1st to 10th	Night	7% 5% 3 8% 6% 5% 6% 5% 8% 10% 35%	2520
	11th to 20th	Night	11% 6% 2 6% 4 5% 5% 4 7% 11% 38%	2520
	21st to end	Night	15% 8% 3 7% 4 4 5% 4 7% 9% 34%	2739
August	1st to 10th	Night	23% 7% 2 6% 4 4 5% 4 7% 8% 31%	2822
	11th to 20th	Night	12% 6% 3 7% 4 4 5% 5% 5% 7% 43%	3097
	21st to end	Night	9% 5% 2 5% 4 4 4 3 5% 8% 51%	3476
September	1st to 10th	Night	13% 6% 2 6% 5% 4 5% 3 5% 6% 45%	1900
	11th to 20th	Night	10% 5% 2 4 3 3 4 3 4 7% 52%	1962
	21st to end	Night	18% 7% 2 7% 3 3 4 3 5% 7% 41%	2090
October	1st to 10th	Night	18% 6% 2 5% 4 4 4 4 4 6% 44%	2218
	11th to 20th	Night	14% 4 2 5% 4 3 4 3 4 6% 51%	2280
	21st to end	Night	17% 7% 2 5% 3 2 4 3 5% 5% 47%	2617
November	1st to 10th	Night	11% 5% 2 5% 4 3 3 3 5% 6% 53%	2537
	11th to 20th	Night	17% 7% 2 6% 4 3 3 2 4 5% 47%	2477
	21st to end	Night	13% 6% 2 6% 4 4 4 3 6% 7% 46%	2541
December	1st to 10th	Night	21% 7% 2 5% 3 4 4 3 6% 6% 40%	2660
	11th to 20th	Night	18% 6% 2 6% 5% 4 4 3 5% 6% 42%	3288
	21st to end	Night	18% 8% 3 6% 4 4 4 3 5% 6% 39%	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	40% 3 11% 26% 15% 4	2518
	11th to 20th	Day	47% 5% 9% 23% 14% 2	2520
	21st to end	Day	53% 4 10% 21% 10% 2	3103
February	1st to 10th	Day	45% 4 13% 24% 12% 2	1710
	11th to 20th	Day	44% 5% 9% 24% 16% 3	1857
	21st to end	Day	47% 4 9% 21% 14% 5%	1570
March	1st to 10th	Day	50% 4 8% 27% 9% 2	3119
	11th to 20th	Day	33% 6% 10% 32% 17% 2	3402
	21st to end	Day	45% 3 8% 19% 21% 5%	4097
April	1st to 10th	Day	44% 6% 9% 21% 16% 5%	2280
	11th to 20th	Day	39% 6% 12% 23% 17% 3	2254
	21st to end	Day	43% 5% 10% 20% 18% 4	2280
May	1st to 10th	Day	55% 5% 12% 17% 10% 1	4081
	11th to 20th	Day	54% 5% 13% 19% 9% 1	4370
	21st to end	Day	37% 6% 12% 26% 16% 2	4837
June	1st to 10th	Day	41% 7% 14% 22% 15% 2	2660
	11th to 20th	Day	41% 7% 12% 25% 12% 2	2660
	21st to end	Day	38% 8% 13% 22% 17% 1	2660
July	1st to 10th	Day	41% 9% 16% 19% 13% 2	4370
	11th to 20th	Day	41% 8% 17% 20% 14% 1	4365
	21st to end	Day	48% 7% 10% 19% 15% 1	4661
August	1st to 10th	Day	50% 8% 13% 19% 9% 1	4032
	11th to 20th	Day	41% 7% 12% 25% 13% 1	3766
	21st to end	Day	35% 6% 13% 25% 18% 2	4180
September	1st to 10th	Day	40% 6% 12% 19% 21% 3	2280
	11th to 20th	Day	34% 5% 10% 23% 25% 3	2216
	21st to end	Day	46% 5% 9% 18% 20% 2	2090
October	1st to 10th	Day	37% 4 11% 18% 26% 5%	3256
	11th to 20th	Day	25% 3 9% 23% 33% 7%	3140
	21st to end	Day	27% 3 13% 26% 27% 5%	3244
November	1st to 10th	Day	34% 3 13% 27% 20% 3	1761
	11th to 20th	Day	38% 4 9% 23% 23% 3	1710
	21st to end	Day	38% 4 13% 30% 13% 3	1635
December	1st to 10th	Day	45% 4 15% 21% 14% 1	1520
	11th to 20th	Day	42% 5% 11% 26% 13% 2	1906
	21st to end	Day	44% 6% 12% 24% 13% 1	2772
January	1st to 10th	Night	39% 4 9% 31% 13% 4	4429
	11th to 20th	Night	44% 3 11% 25% 14% 2	4440
	21st to end	Night	51% 4 7% 23% 13% 2	4550
February	1st to 10th	Night	44% 4 14% 23% 13% 2	2469
	11th to 20th	Night	44% 4 9% 20% 19% 5%	2220
	21st to end	Night	43% 4 8% 23% 18% 5%	1884
March	1st to 10th	Night	50% 3 8% 24% 12% 3	3734
	11th to 20th	Night	36% 5% 13% 27% 16% 3	3557
	21st to end	Night	46% 3 7% 17% 22% 5%	3534
April	1st to 10th	Night	43% 5% 9% 21% 18% 5%	1900
	11th to 20th	Night	43% 5% 9% 21% 20% 3	1875
	21st to end	Night	40% 5% 10% 20% 21% 4	1900
May	1st to 10th	Night	53% 5% 11% 19% 10% 1	2877
	11th to 20th	Night	54% 5% 13% 16% 10% 2	2542
	21st to end	Night	39% 6% 15% 21% 16% 2	2739
June	1st to 10th	Night	39% 8% 12% 21% 19% 1	1520
	11th to 20th	Night	40% 7% 14% 25% 13% 2	1520
	21st to end	Night	35% 8% 17% 23% 15% 2	1520
July	1st to 10th	Night	42% 9% 18% 18% 12% 2	2480
	11th to 20th	Night	38% 8% 17% 25% 11% 1	2472
	21st to end	Night	46% 6% 15% 18% 14% 2	2651
August	1st to 10th	Night	50% 7% 18% 16% 9% 1	2812
	11th to 20th	Night	39% 6% 13% 30% 12% 1	3127
	21st to end	Night	32% 5% 11% 29% 21% 2	3476
September	1st to 10th	Night	40% 6% 11% 21% 20% 2	1900
	11th to 20th	Night	32% 5% 11% 23% 25% 4	1962
	21st to end	Night	43% 5% 7% 22% 20% 2	2090
October	1st to 10th	Night	38% 5% 10% 24% 22% 2	3699
	11th to 20th	Night	24% 3 10% 27% 30% 6%	3779
	21st to end	Night	27% 3 11% 30% 24% 4	4303
November	1st to 10th	Night	33% 5% 11% 25% 22% 4	2537
	11th to 20th	Night	40% 4 8% 23% 19% 5%	2477
	21st to end	Night	37% 5% 13% 27% 17% 2	2541
December	1st to 10th	Night	45% 4 12% 23% 14% 2	2660
	11th to 20th	Night	41% 5% 12% 20% 18% 4	3288
	21st to end	Night	46% 4 13% 25% 12% 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	23% 24% 34% 14% 4 1	180
	11th to 20th	Day	32% 27% 26% 14% 1	180
	21st to end	Day	26% 23% 31% 16% 4 1	294
February	1st to 10th	Day	26% 27% 33% 11% 3	270
	11th to 20th	Day	29% 21% 36% 12% 2	456
	21st to end	Day	30% 19% 31% 17% 2	382
March	1st to 10th	Day	25% 20% 32% 18% 5%	460
	11th to 20th	Day	24% 24% 32% 14% 4 1	460
	21st to end	Day	26% 20% 32% 17% 5% 1	506
April	1st to 10th	Day	23% 23% 34% 13% 6% 1	460
	11th to 20th	Day	22% 17% 35% 17% 8% 2	452
	21st to end	Day	28% 17% 31% 18% 4 2	460
May	1st to 10th	Day	29% 17% 28% 16% 8% 2	463
	11th to 20th	Day	23% 13% 33% 21% 8% 2	487
	21st to end	Day	20% 7% 23% 29% 17% 4	529
June	1st to 10th	Day	16% 10% 29% 28% 13% 3	490
	11th to 20th	Day	14% 12% 31% 27% 14% 3	490
	21st to end	Day	13% 8% 29% 32% 14% 3	490
July	1st to 10th	Day	12% 5% 22% 33% 21% 7%	485
	11th to 20th	Day	8% 5% 25% 32% 24% 6%	484
	21st to end	Day	13% 9% 26% 32% 15% 5%	532
August	1st to 10th	Day	12% 4 26% 33% 17% 8%	486
	11th to 20th	Day	14% 4 21% 32% 22% 7%	479
	21st to end	Day	12% 4 27% 29% 17% 10%	539
September	1st to 10th	Day	17% 8% 26% 23% 18% 9%	490
	11th to 20th	Day	12% 6% 28% 31% 14% 9%	490
	21st to end	Day	24% 12% 24% 23% 12% 4	490
October	1st to 10th	Day	24% 9% 24% 23% 13% 7%	490
	11th to 20th	Day	18% 14% 27% 28% 11% 3	490
	21st to end	Day	19% 14% 33% 20% 11% 2	481
November	1st to 10th	Day	15% 13% 34% 24% 12% 2	395
	11th to 20th	Day	24% 16% 30% 22% 8%	370
	21st to end	Day	20% 13% 36% 22% 8% 1	295
December	1st to 10th	Day	25% 26% 31% 9% 8% 1	180
	11th to 20th	Day	33% 18% 30% 14% 5%	180
	21st to end	Day	27% 16% 31% 21% 4 1	198
January	1st to 10th	Night	19% 18% 38% 21% 4	760
	11th to 20th	Night	25% 14% 34% 22% 4	760
	21st to end	Night	19% 17% 39% 23% 2	836
February	1st to 10th	Night	20% 15% 37% 26% 2	760
	11th to 20th	Night	24% 20% 38% 17% 1	743
	21st to end	Night	24% 20% 35% 19% 3	628
March	1st to 10th	Night	22% 16% 37% 21% 4	760
	11th to 20th	Night	22% 17% 36% 20% 4 1	760
	21st to end	Night	20% 13% 39% 22% 5%	836
April	1st to 10th	Night	20% 18% 38% 18% 5%	760
	11th to 20th	Night	18% 12% 38% 27% 4	751
	21st to end	Night	21% 11% 36% 26% 5%	760
May	1st to 10th	Night	20% 14% 33% 27% 6%	594
	11th to 20th	Night	22% 10% 35% 29% 5%	407
	21st to end	Night	16% 5% 23% 40% 15% 1	411
June	1st to 10th	Night	17% 4 27% 40% 11% 1	380
	11th to 20th	Night	12% 4 28% 41% 14%	380
	21st to end	Night	10% 4 25% 49% 13%	380
July	1st to 10th	Night	10% 4 22% 44% 19% 1	370
	11th to 20th	Night	7% 4 21% 46% 21% 1	368
	21st to end	Night	11% 3 22% 47% 16% 1	416
August	1st to 10th	Night	12% 2 19% 44% 20% 2	564
	11th to 20th	Night	12% 4 18% 41% 24% 2	750
	21st to end	Night	13% 5% 17% 40% 24% 2	836
September	1st to 10th	Night	16% 2 25% 35% 19% 3	760
	11th to 20th	Night	13% 5% 20% 35% 23% 5%	760
	21st to end	Night	22% 5% 21% 35% 17% 1	760
October	1st to 10th	Night	22% 5% 26% 26% 16% 4	760
	11th to 20th	Night	16% 10% 28% 33% 12% 1	760
	21st to end	Night	21% 7% 34% 27% 9%	836
November	1st to 10th	Night	14% 8% 36% 29% 12% 1	780
	11th to 20th	Night	19% 14% 29% 27% 9% 1	763
	21st to end	Night	16% 13% 36% 26% 8% 1	760
December	1st to 10th	Night	25% 14% 34% 19% 7% 1	760
	11th to 20th	Night	20% 14% 37% 24% 5%	760
	21st to end	Night	21% 14% 36% 27% 2	836

Page generated at 2024-11-08 06:44:45. Version ac07

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