Chi'Cheemaun 1/3rd Point
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Chi'Cheemaun 1/3rd Point clear sky chart from 2005-11-06 to 2025-05-26.

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	14% 11% 4 9% 5% 4 4 4 5% 6% 34%	113645
	Night	15% 13% 5% 11% 5% 5% 4 3 5% 6% 28%	115692
Transparency	Day	49% 8% 12% 19% 10% 1	117205
	Night	57% 8% 10% 16% 9% 1	120295
Seeing	Day	18% 8% 24% 30% 17% 3	15926
	Night	21% 10% 27% 26% 13% 3	25320

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	14% 18% 10% 13% 7% 3 5% 4 6% 5% 15%	3184
	11th to 20th	Day	12% 19% 9% 23% 11% 6% 4 3 3 3 6%	3589
	21st to end	Day	15% 18% 8% 15% 7% 7% 4 3 4 5% 13%	4312
February	1st to 10th	Day	12% 17% 6% 16% 8% 5% 4 3 5% 6% 18%	1800
	11th to 20th	Day	11% 14% 5% 12% 7% 6% 5% 4 6% 5% 23%	1753
	21st to end	Day	13% 14% 5% 12% 6% 5% 4 3 5% 7% 26%	1630
March	1st to 10th	Day	16% 10% 3 7% 5% 4 5% 4 5% 7% 34%	4704
	11th to 20th	Day	11% 12% 5% 11% 6% 6% 6% 5% 6% 6% 28%	4980
	21st to end	Day	17% 9% 4 8% 5% 4 4 4 5% 7% 34%	5465
April	1st to 10th	Day	17% 10% 3 7% 5% 3 5% 4 5% 6% 34%	2335
	11th to 20th	Day	19% 6% 3 5% 5% 4 4 3 4 6% 41%	2572
	21st to end	Day	18% 9% 3 6% 4 3 3 3 5% 8% 38%	2600
May	1st to 10th	Day	16% 7% 3 7% 4 4 3 3 5% 6% 43%	4238
	11th to 20th	Day	13% 8% 2 7% 5% 4 4 3 5% 7% 41%	4373
	21st to end	Day	14% 6% 2 7% 5% 5% 4 3 4 6% 44%	5002
June	1st to 10th	Day	12% 7% 2 6% 6% 4 5% 4 6% 7% 40%	2850
	11th to 20th	Day	11% 6% 3 6% 4 3 5% 4 7% 8% 43%	2850
	21st to end	Day	14% 7% 2 6% 4 4 5% 4 5% 7% 40%	2850
July	1st to 10th	Day	12% 7% 3 8% 5% 4 5% 4 5% 7% 39%	4760
	11th to 20th	Day	8% 4 2 5% 4 4 5% 4 5% 8% 50%	4670
	21st to end	Day	8% 5% 2 5% 4 4 4 3 5% 7% 54%	4602
August	1st to 10th	Day	10% 5% 2 5% 4 4 5% 4 7% 9% 44%	4104
	11th to 20th	Day	14% 6% 2 5% 3 4 3 3 6% 8% 46%	4044
	21st to end	Day	8% 5% 2 6% 4 5% 5% 4 6% 8% 47%	4532
September	1st to 10th	Day	11% 6% 3 6% 5% 4 4 4 5% 7% 45%	2243
	11th to 20th	Day	11% 5% 2 5% 4 3 4 4 5% 8% 48%	2090
	21st to end	Day	17% 7% 2 6% 4 4 4 4 5% 7% 39%	2090
October	1st to 10th	Day	18% 9% 3 6% 4 4 5% 3 6% 7% 35%	1948
	11th to 20th	Day	23% 10% 2 9% 5% 5% 5% 4 4 7% 26%	1900
	21st to end	Day	25% 14% 4 8% 5% 4 4 4 5% 6% 21%	1964
November	1st to 10th	Day	18% 16% 4 9% 6% 5% 5% 3 4 6% 25%	1731
	11th to 20th	Day	17% 18% 5% 10% 6% 4 5% 3 6% 7% 19%	1600
	21st to end	Day	24% 23% 4 10% 7% 5% 4 3 5% 4 12%	1600
December	1st to 10th	Day	16% 27% 7% 13% 6% 4 4 3 5% 4 11%	2583
	11th to 20th	Day	20% 22% 8% 16% 5% 4 4 3 3 4 11%	2621
	21st to end	Day	27% 24% 8% 15% 6% 3 5% 2 2 2 4	3476
January	1st to 10th	Night	12% 20% 10% 14% 7% 4 5% 3 5% 4 15%	6780
	11th to 20th	Night	13% 19% 8% 21% 7% 5% 4 3 4 4 12%	6316
	21st to end	Night	12% 18% 8% 17% 8% 7% 4 3 4 4 16%	6648
February	1st to 10th	Night	11% 18% 6% 16% 7% 5% 4 3 5% 5% 19%	2600
	11th to 20th	Night	12% 15% 5% 12% 7% 6% 4 4 6% 6% 23%	2533
	21st to end	Night	14% 16% 5% 10% 6% 5% 5% 4 5% 4 27%	1999
March	1st to 10th	Night	15% 9% 3 8% 5% 4 4 3 5% 6% 37%	5135
	11th to 20th	Night	11% 10% 4 8% 5% 5% 5% 4 6% 8% 33%	4979
	21st to end	Night	18% 10% 4 10% 5% 4 4 3 4 5% 32%	5467
April	1st to 10th	Night	21% 9% 3 7% 5% 4 4 3 6% 6% 34%	2080
	11th to 20th	Night	18% 7% 3 6% 4 4 4 3 6% 7% 38%	1777
	21st to end	Night	18% 9% 4 8% 5% 5% 3 4 5% 5% 34%	1800
May	1st to 10th	Night	15% 7% 3 9% 5% 4 5% 3 5% 6% 39%	2923
	11th to 20th	Night	11% 7% 2 8% 5% 4 5% 3 6% 7% 41%	2726
	21st to end	Night	13% 8% 3 8% 5% 4 4 3 5% 6% 42%	2676
June	1st to 10th	Night	12% 7% 3 8% 6% 4 5% 4 5% 7% 40%	1330
	11th to 20th	Night	9% 6% 2 4 4 5% 6% 4 7% 8% 45%	1330
	21st to end	Night	12% 6% 2 8% 5% 4 5% 4 6% 8% 40%	1330
July	1st to 10th	Night	11% 6% 2 8% 4 4 4 3 4 7% 46%	2210
	11th to 20th	Night	10% 4 2 5% 4 4 4 3 6% 7% 50%	2296
	21st to end	Night	8% 5% 2 6% 4 4 4 3 5% 7% 51%	2952
August	1st to 10th	Night	9% 6% 2 6% 5% 4 5% 4 7% 8% 45%	2825
	11th to 20th	Night	12% 5% 2 7% 4 4 5% 4 6% 9% 43%	2785
	21st to end	Night	8% 5% 2 7% 4 3 5% 4 6% 7% 48%	3124
September	1st to 10th	Night	13% 4 2 5% 4 5% 4 4 5% 7% 47%	1914
	11th to 20th	Night	12% 5% 2 5% 4 3 5% 4 5% 6% 49%	2090
	21st to end	Night	19% 7% 2 5% 4 5% 4 4 6% 7% 38%	2090
October	1st to 10th	Night	21% 9% 3 7% 5% 5% 4 3 5% 6% 34%	2232
	11th to 20th	Night	25% 11% 3 9% 4 5% 4 4 5% 6% 24%	2280
	21st to end	Night	25% 13% 4 9% 5% 4 4 4 5% 6% 20%	2631
November	1st to 10th	Night	19% 17% 3 7% 5% 4 3 3 6% 6% 26%	2566
	11th to 20th	Night	18% 19% 6% 11% 6% 5% 4 4 4 6% 18%	2800
	21st to end	Night	22% 23% 6% 9% 5% 5% 4 3 5% 4 13%	2800
December	1st to 10th	Night	19% 23% 6% 11% 6% 4 4 3 4 5% 14%	4580
	11th to 20th	Night	18% 22% 8% 17% 7% 5% 4 3 4 3 10%	5586
	21st to end	Night	25% 23% 7% 14% 5% 6% 4 2 3 4 8%	7502

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	75% 8% 8% 7% 1 2	3185
	11th to 20th	Day	87% 5% 3 4 1	3620
	21st to end	Day	73% 9% 8% 6% 3	4312
February	1st to 10th	Day	70% 7% 10% 11% 2	1800
	11th to 20th	Day	63% 9% 12% 11% 5%	1762
	21st to end	Day	59% 8% 12% 17% 4	1630
March	1st to 10th	Day	49% 7% 15% 12% 14% 3	4707
	11th to 20th	Day	53% 8% 14% 17% 7% 1	4980
	21st to end	Day	48% 9% 15% 18% 8% 2	5465
April	1st to 10th	Day	49% 6% 13% 20% 11% 1	2335
	11th to 20th	Day	44% 6% 9% 25% 15% 2	2572
	21st to end	Day	44% 6% 14% 20% 13% 3	2600
May	1st to 10th	Day	39% 8% 12% 20% 19% 2	4250
	11th to 20th	Day	37% 10% 14% 23% 15% 1	4377
	21st to end	Day	38% 8% 13% 16% 22% 3	5002
June	1st to 10th	Day	40% 9% 12% 25% 13% 1	2850
	11th to 20th	Day	36% 7% 11% 28% 17% 1	2850
	21st to end	Day	40% 9% 12% 24% 13% 2	2850
July	1st to 10th	Day	42% 7% 14% 23% 13% 1	4686
	11th to 20th	Day	29% 7% 16% 34% 13% 1	4589
	21st to end	Day	29% 7% 11% 29% 24% 1	4456
August	1st to 10th	Day	33% 7% 16% 29% 14% 1	4091
	11th to 20th	Day	35% 7% 17% 29% 11%	4083
	21st to end	Day	33% 7% 15% 34% 10% 1	4531
September	1st to 10th	Day	38% 8% 14% 27% 12% 1	2243
	11th to 20th	Day	34% 8% 16% 30% 11% 1	2090
	21st to end	Day	45% 9% 14% 23% 9%	2090
October	1st to 10th	Day	39% 6% 11% 26% 18%	3234
	11th to 20th	Day	50% 7% 13% 22% 8%	3140
	21st to end	Day	58% 6% 14% 17% 6%	3214
November	1st to 10th	Day	60% 8% 14% 14% 5%	1731
	11th to 20th	Day	65% 10% 10% 10% 4	1600
	21st to end	Day	76% 8% 9% 5% 1	1600
December	1st to 10th	Day	78% 7% 9% 4 1	2583
	11th to 20th	Day	79% 7% 8% 6%	2621
	21st to end	Day	86% 7% 5% 2	3476
January	1st to 10th	Night	75% 11% 6% 6% 1	6780
	11th to 20th	Night	79% 7% 5% 7% 3	6360
	21st to end	Night	73% 9% 6% 6% 4 1	6648
February	1st to 10th	Night	70% 6% 9% 11% 3 1	2600
	11th to 20th	Night	64% 8% 9% 13% 6%	2535
	21st to end	Night	59% 9% 12% 14% 7%	1999
March	1st to 10th	Night	48% 8% 14% 15% 12% 3	5145
	11th to 20th	Night	46% 8% 16% 19% 8% 1	4980
	21st to end	Night	52% 11% 8% 15% 12% 2	5467
April	1st to 10th	Night	51% 6% 10% 19% 12% 2	2080
	11th to 20th	Night	44% 6% 9% 21% 18% 2	1777
	21st to end	Night	51% 6% 9% 15% 15% 3	1800
May	1st to 10th	Night	43% 8% 12% 19% 17% 2	2930
	11th to 20th	Night	38% 9% 11% 22% 18% 2	2727
	21st to end	Night	40% 8% 12% 19% 16% 5%	2677
June	1st to 10th	Night	41% 7% 10% 22% 18% 2	1330
	11th to 20th	Night	33% 8% 15% 22% 21% 2	1330
	21st to end	Night	41% 7% 14% 22% 14% 2	1330
July	1st to 10th	Night	37% 6% 12% 24% 16% 5%	2175
	11th to 20th	Night	32% 6% 11% 36% 15% 1	2254
	21st to end	Night	32% 7% 11% 25% 25% 1	2858
August	1st to 10th	Night	35% 7% 13% 30% 14% 1	2814
	11th to 20th	Night	38% 8% 17% 23% 13% 1	2812
	21st to end	Night	34% 8% 13% 32% 13% 1	3124
September	1st to 10th	Night	36% 8% 13% 27% 14% 2	1914
	11th to 20th	Night	34% 9% 15% 30% 12%	2090
	21st to end	Night	46% 8% 14% 23% 10%	2090
October	1st to 10th	Night	38% 6% 9% 30% 17%	3726
	11th to 20th	Night	52% 6% 14% 20% 8%	3779
	21st to end	Night	56% 7% 15% 17% 5%	4331
November	1st to 10th	Night	59% 7% 12% 17% 5%	2566
	11th to 20th	Night	68% 9% 11% 8% 4 1	2800
	21st to end	Night	75% 9% 10% 6% 1	2800
December	1st to 10th	Night	76% 7% 10% 6% 2	4580
	11th to 20th	Night	80% 7% 7% 5% 1	5585
	21st to end	Night	81% 8% 7% 3 1	7502

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	21% 16% 32% 24% 7%	207
	11th to 20th	Day	23% 11% 35% 24% 8%	300
	21st to end	Day	25% 11% 28% 27% 9%	330
February	1st to 10th	Day	18% 15% 39% 23% 5%	300
	11th to 20th	Day	19% 14% 37% 24% 5%	300
	21st to end	Day	21% 20% 34% 20% 4	249
March	1st to 10th	Day	18% 11% 38% 26% 7% 1	397
	11th to 20th	Day	17% 13% 30% 30% 9% 1	500
	21st to end	Day	24% 9% 28% 29% 9% 1	550
April	1st to 10th	Day	20% 7% 31% 30% 10% 1	500
	11th to 20th	Day	23% 9% 28% 23% 12% 4	492
	21st to end	Day	22% 10% 27% 30% 11% 1	500
May	1st to 10th	Day	21% 3 24% 36% 14% 2	503
	11th to 20th	Day	15% 5% 19% 34% 23% 4	527
	21st to end	Day	14% 3 19% 37% 21% 6%	605
June	1st to 10th	Day	14% 3 21% 39% 21% 2	680
	11th to 20th	Day	12% 4 19% 39% 23% 3	680
	21st to end	Day	17% 3 17% 39% 20% 3	680
July	1st to 10th	Day	8% 2 14% 45% 27% 4	671
	11th to 20th	Day	10% 3 17% 38% 26% 6%	668
	21st to end	Day	11% 3 15% 39% 28% 4	616
August	1st to 10th	Day	14% 4 15% 32% 30% 6%	486
	11th to 20th	Day	11% 3 13% 34% 30% 10%	479
	21st to end	Day	13% 6% 18% 32% 25% 6%	539
September	1st to 10th	Day	14% 5% 22% 27% 27% 6%	490
	11th to 20th	Day	10% 5% 20% 25% 29% 11%	490
	21st to end	Day	19% 8% 19% 25% 23% 6%	490
October	1st to 10th	Day	22% 10% 24% 22% 18% 3	490
	11th to 20th	Day	24% 14% 30% 25% 7% 1	490
	21st to end	Day	31% 15% 28% 21% 4 1	413
November	1st to 10th	Day	26% 13% 33% 20% 8%	284
	11th to 20th	Day	26% 17% 36% 18% 5%	200
	21st to end	Day	31% 18% 33% 16% 3	200
December	1st to 10th	Day	27% 19% 30% 18% 6% 2	200
	11th to 20th	Day	32% 20% 30% 15% 4	200
	21st to end	Day	35% 20% 30% 11% 2 1	220
January	1st to 10th	Night	25% 17% 31% 23% 5% 1	1000
	11th to 20th	Night	25% 16% 30% 23% 5% 1	1000
	21st to end	Night	20% 10% 35% 25% 8% 1	947
February	1st to 10th	Night	20% 14% 38% 23% 5%	800
	11th to 20th	Night	19% 11% 36% 25% 8%	783
	21st to end	Night	21% 10% 38% 25% 5% 1	660
March	1st to 10th	Night	17% 10% 38% 28% 7% 1	800
	11th to 20th	Night	17% 11% 36% 26% 9% 2	800
	21st to end	Night	19% 7% 31% 30% 12% 1	880
April	1st to 10th	Night	24% 9% 31% 28% 7% 1	756
	11th to 20th	Night	22% 9% 24% 29% 12% 4	593
	21st to end	Night	22% 8% 25% 30% 14% 1	600
May	1st to 10th	Night	15% 4 23% 38% 18% 3	600
	11th to 20th	Night	15% 3 20% 38% 21% 2	493
	21st to end	Night	17% 3 16% 37% 22% 4	423
June	1st to 10th	Night	15% 3 23% 38% 18% 3	380
	11th to 20th	Night	11% 4 18% 41% 24% 4	380
	21st to end	Night	13% 2 16% 37% 28% 3	380
July	1st to 10th	Night	7% 3 11% 47% 28% 4	370
	11th to 20th	Night	10% 2 16% 36% 29% 7%	415
	21st to end	Night	9% 2 15% 41% 30% 4	624
August	1st to 10th	Night	10% 3 16% 35% 29% 7%	567
	11th to 20th	Night	12% 3 14% 31% 32% 9%	564
	21st to end	Night	12% 4 19% 32% 27% 6%	627
September	1st to 10th	Night	14% 4 20% 30% 23% 9%	722
	11th to 20th	Night	14% 5% 20% 29% 22% 11%	760
	21st to end	Night	20% 7% 19% 24% 23% 6%	760
October	1st to 10th	Night	24% 8% 24% 25% 18% 2	760
	11th to 20th	Night	31% 11% 25% 22% 11% 1	760
	21st to end	Night	32% 13% 27% 23% 5% 1	836
November	1st to 10th	Night	28% 13% 26% 25% 7% 1	780
	11th to 20th	Night	27% 18% 31% 16% 8%	800
	21st to end	Night	32% 15% 30% 18% 4	800
December	1st to 10th	Night	34% 18% 28% 14% 6%	800
	11th to 20th	Night	28% 20% 34% 14% 4 1	1000
	21st to end	Night	33% 16% 30% 16% 5% 1	1100

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