Point MacKenzie
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Point MacKenzie clear sky chart from 2005-11-06 to 2026-03-03.

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	19% 13% 4 10% 6% 5% 5% 4 5% 6% 24%	134346
	Night	17% 16% 5% 10% 6% 5% 5% 3 5% 5% 24%	135670
Transparency	Day	39% 39% 9% 9% 3	133989
	Night	41% 37% 7% 8% 5% 1	135608
Seeing	Day	22% 7% 19% 25% 20% 7%	19668
	Night	25% 7% 21% 26% 17% 3	24299

By Month

Percentage Cloud Cover NW (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	11% 19% 5% 10% 5% 6% 5% 3 5% 5% 27%	2395
	11th to 20th	Day	16% 18% 4 9% 5% 4 4 4 5% 5% 25%	3099
	21st to end	Day	15% 15% 5% 10% 6% 5% 5% 3 4 4 28%	3871
February	1st to 10th	Day	13% 17% 3 8% 5% 4 4 2 5% 6% 34%	1447
	11th to 20th	Day	18% 22% 5% 9% 6% 5% 4 2 4 4 21%	1628
	21st to end	Day	10% 16% 4 8% 6% 4 4 4 4 6% 34%	1512
March	1st to 10th	Day	8% 20% 6% 14% 6% 5% 4 3 4 4 27%	4399
	11th to 20th	Day	9% 16% 6% 11% 6% 6% 5% 4 5% 6% 23%	4699
	21st to end	Day	15% 17% 4 8% 5% 5% 5% 4 6% 5% 27%	5918
April	1st to 10th	Day	10% 17% 6% 10% 6% 5% 5% 4 5% 6% 26%	2449
	11th to 20th	Day	9% 12% 4 8% 6% 6% 6% 5% 5% 6% 33%	2766
	21st to end	Day	12% 13% 4 9% 6% 6% 5% 4 6% 6% 28%	2820
May	1st to 10th	Day	18% 18% 5% 11% 7% 5% 5% 4 5% 6% 16%	7210
	11th to 20th	Day	14% 14% 4 11% 6% 5% 5% 4 5% 7% 25%	7213
	21st to end	Day	19% 12% 4 10% 7% 6% 5% 4 6% 6% 21%	8591
June	1st to 10th	Day	16% 13% 4 9% 6% 5% 6% 4 6% 8% 24%	3600
	11th to 20th	Day	15% 9% 3 9% 6% 5% 5% 4 7% 7% 29%	3600
	21st to end	Day	17% 10% 3 9% 6% 5% 6% 5% 6% 7% 26%	3600
July	1st to 10th	Day	23% 10% 3 10% 6% 5% 6% 4 5% 6% 22%	8160
	11th to 20th	Day	23% 11% 4 10% 6% 6% 5% 4 6% 6% 20%	7941
	21st to end	Day	26% 9% 3 8% 5% 5% 5% 3 5% 7% 24%	7955
August	1st to 10th	Day	31% 9% 3 8% 6% 4 5% 4 5% 6% 19%	5160
	11th to 20th	Day	30% 9% 4 7% 5% 4 4 3 4 6% 24%	4589
	21st to end	Day	28% 10% 4 8% 5% 5% 5% 3 5% 7% 21%	5038
September	1st to 10th	Day	33% 12% 5% 9% 6% 4 4 4 4 4 16%	2469
	11th to 20th	Day	34% 12% 5% 8% 4 4 4 3 4 4 17%	2400
	21st to end	Day	25% 11% 4 9% 4 5% 4 3 5% 4 26%	2125
October	1st to 10th	Day	20% 9% 4 10% 6% 7% 7% 5% 6% 6% 19%	3242
	11th to 20th	Day	15% 10% 3 7% 4 5% 4 3 5% 6% 39%	2870
	21st to end	Day	19% 13% 3 6% 3 2 4 2 4 5% 38%	2779
November	1st to 10th	Day	17% 17% 5% 13% 5% 5% 4 3 4 4 25%	1424
	11th to 20th	Day	13% 13% 4 7% 5% 4 4 2 5% 5% 38%	1260
	21st to end	Day	15% 16% 6% 9% 8% 5% 5% 3 4 4 26%	1092
December	1st to 10th	Day	20% 18% 7% 12% 6% 4 4 2 3 4 19%	1422
	11th to 20th	Day	13% 23% 7% 12% 6% 4 4 2 4 5% 19%	1557
	21st to end	Day	9% 18% 6% 11% 7% 5% 5% 3 5% 7% 24%	2046
January	1st to 10th	Night	13% 17% 4 10% 6% 5% 5% 3 4 4 29%	10529
	11th to 20th	Night	17% 18% 5% 12% 6% 5% 4 3 4 4 23%	9849
	21st to end	Night	15% 13% 4 9% 6% 5% 5% 3 4 5% 31%	10342
February	1st to 10th	Night	12% 17% 4 9% 4 3 4 3 5% 5% 33%	3171
	11th to 20th	Night	17% 23% 6% 10% 5% 4 4 3 4 4 20%	2879
	21st to end	Night	11% 16% 4 10% 5% 5% 4 3 4 5% 32%	2291
March	1st to 10th	Night	9% 21% 6% 11% 5% 5% 4 3 5% 5% 26%	5500
	11th to 20th	Night	10% 18% 6% 12% 6% 5% 6% 4 5% 6% 22%	5256
	21st to end	Night	12% 19% 5% 10% 4 5% 5% 4 5% 6% 24%	5013
April	1st to 10th	Night	11% 21% 6% 10% 7% 5% 4 3 5% 4 25%	1950
	11th to 20th	Night	13% 14% 4 8% 5% 4 5% 4 5% 6% 31%	1583
	21st to end	Night	11% 12% 5% 10% 7% 5% 5% 4 6% 6% 28%	1580
May	1st to 10th	Night	17% 18% 5% 13% 7% 6% 5% 4 5% 6% 14%	2767
	11th to 20th	Night	17% 16% 5% 11% 6% 5% 5% 3 4 5% 22%	2702
	21st to end	Night	22% 14% 4 9% 6% 6% 5% 4 6% 6% 19%	2298
June	1st to 10th	Night	20% 13% 4 10% 5% 7% 6% 6% 7% 5% 20%	800
	11th to 20th	Night	16% 10% 4 8% 6% 6% 6% 4 5% 8% 26%	800
	21st to end	Night	17% 11% 4 10% 8% 7% 7% 3 5% 7% 21%	800
July	1st to 10th	Night	26% 12% 4 10% 7% 7% 5% 4 5% 6% 13%	1820
	11th to 20th	Night	28% 13% 4 9% 5% 4 5% 4 5% 6% 17%	2046
	21st to end	Night	26% 8% 4 8% 6% 5% 5% 3 6% 7% 22%	2914
August	1st to 10th	Night	31% 10% 4 9% 4 4 3 3 5% 6% 22%	1985
	11th to 20th	Night	33% 6% 2 6% 4 4 4 3 5% 6% 27%	2469
	21st to end	Night	32% 9% 3 9% 5% 5% 5% 4 4 4 19%	2871
September	1st to 10th	Night	37% 12% 4 8% 6% 5% 3 3 4 4 15%	1930
	11th to 20th	Night	35% 11% 4 9% 5% 4 4 3 4 4 18%	2000
	21st to end	Night	27% 11% 3 8% 5% 4 5% 3 4 5% 24%	2274
October	1st to 10th	Night	23% 12% 4 10% 7% 6% 6% 4 5% 5% 17%	3938
	11th to 20th	Night	15% 11% 3 8% 4 5% 4 4 5% 7% 34%	4274
	21st to end	Night	18% 14% 4 8% 5% 4 4 3 5% 5% 30%	5022
November	1st to 10th	Night	18% 17% 5% 9% 4 5% 4 4 4 5% 26%	3093
	11th to 20th	Night	12% 13% 4 9% 5% 4 4 3 5% 5% 36%	3360
	21st to end	Night	16% 17% 5% 10% 4 4 4 3 4 5% 28%	3528
December	1st to 10th	Night	22% 19% 6% 11% 6% 5% 4 3 4 4 16%	5982
	11th to 20th	Night	11% 22% 7% 14% 6% 5% 4 3 4 5% 18%	6880
	21st to end	Night	9% 17% 6% 13% 7% 5% 6% 5% 6% 6% 21%	9174

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	47% 25% 5% 7% 15% 1	2395
	11th to 20th	Day	46% 25% 8% 12% 8% 1	3114
	21st to end	Day	46% 23% 7% 12% 10% 2	3872
February	1st to 10th	Day	16% 60% 6% 9% 6% 3	1447
	11th to 20th	Day	27% 58% 5% 5% 4 1	1635
	21st to end	Day	20% 60% 6% 8% 6%	1512
March	1st to 10th	Day	46% 30% 4 6% 11% 3	4399
	11th to 20th	Day	47% 31% 8% 6% 7% 1	4699
	21st to end	Day	41% 31% 8% 13% 6% 1	5918
April	1st to 10th	Day	22% 63% 5% 8% 3 1	2449
	11th to 20th	Day	19% 64% 5% 9% 3	2766
	21st to end	Day	23% 62% 4 7% 2	2820
May	1st to 10th	Day	50% 31% 5% 10% 3	7210
	11th to 20th	Day	42% 31% 9% 15% 3	7216
	21st to end	Day	47% 33% 10% 9% 1	8592
June	1st to 10th	Day	21% 66% 6% 6% 1	3600
	11th to 20th	Day	18% 64% 8% 8% 2	3600
	21st to end	Day	22% 63% 9% 6%	3600
July	1st to 10th	Day	47% 30% 16% 6%	8071
	11th to 20th	Day	50% 29% 17% 4	7842
	21st to end	Day	44% 29% 16% 10%	7732
August	1st to 10th	Day	43% 40% 13% 5%	5141
	11th to 20th	Day	38% 39% 11% 11%	4633
	21st to end	Day	40% 38% 11% 9% 2	5037
September	1st to 10th	Day	30% 58% 5% 6% 1	2469
	11th to 20th	Day	33% 58% 6% 3	2400
	21st to end	Day	26% 59% 6% 9% 1	2125
October	1st to 10th	Day	40% 38% 10% 10% 2	3242
	11th to 20th	Day	25% 37% 14% 14% 10%	2870
	21st to end	Day	31% 36% 8% 22% 3	2779
November	1st to 10th	Day	32% 54% 5% 5% 3	1424
	11th to 20th	Day	24% 55% 5% 12% 4	1260
	21st to end	Day	32% 55% 3 6% 4 1	1092
December	1st to 10th	Day	48% 36% 5% 10% 1	1422
	11th to 20th	Day	50% 33% 7% 6% 2 1	1560
	21st to end	Day	43% 29% 9% 12% 7% 1	2046
January	1st to 10th	Night	47% 24% 5% 6% 14% 4	10529
	11th to 20th	Night	53% 23% 8% 10% 6% 1	9897
	21st to end	Night	41% 25% 8% 11% 12% 3	10342
February	1st to 10th	Night	17% 59% 5% 10% 5% 4	3171
	11th to 20th	Night	27% 58% 4 5% 5% 1	2883
	21st to end	Night	23% 60% 3 6% 7%	2291
March	1st to 10th	Night	44% 30% 6% 9% 7% 4	5500
	11th to 20th	Night	49% 32% 8% 5% 6% 1	5258
	21st to end	Night	43% 32% 5% 14% 5%	5013
April	1st to 10th	Night	24% 63% 3 6% 3	1950
	11th to 20th	Night	21% 64% 4 8% 3	1583
	21st to end	Night	24% 63% 4 6% 2	1580
May	1st to 10th	Night	50% 32% 6% 10% 2	2764
	11th to 20th	Night	48% 30% 8% 9% 4	2703
	21st to end	Night	49% 34% 9% 7% 1	2298
June	1st to 10th	Night	26% 65% 3 6%	800
	11th to 20th	Night	19% 64% 7% 8% 2	800
	21st to end	Night	25% 65% 6% 4	800
July	1st to 10th	Night	54% 31% 12% 4	1800
	11th to 20th	Night	52% 29% 13% 5%	2022
	21st to end	Night	46% 28% 18% 8%	2832
August	1st to 10th	Night	43% 38% 12% 7%	1979
	11th to 20th	Night	35% 39% 12% 9% 4	2491
	21st to end	Night	46% 38% 8% 5% 3	2871
September	1st to 10th	Night	31% 59% 4 4 2	1930
	11th to 20th	Night	33% 59% 4 3 1	2000
	21st to end	Night	25% 58% 8% 8% 1	2274
October	1st to 10th	Night	45% 37% 6% 10% 2	3938
	11th to 20th	Night	28% 38% 12% 11% 10%	4274
	21st to end	Night	36% 37% 8% 15% 4	5022
November	1st to 10th	Night	30% 54% 6% 7% 2	3093
	11th to 20th	Night	24% 56% 4 12% 5%	3360
	21st to end	Night	29% 55% 4 7% 5% 1	3528
December	1st to 10th	Night	50% 36% 4 7% 2 1	5982
	11th to 20th	Night	50% 33% 9% 5% 2 1	6876
	21st to end	Night	45% 29% 11% 10% 4 1	9174

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	14% 14% 16% 30% 21% 5%	118
	11th to 20th	Day	25% 9% 23% 23% 16% 4	320
	21st to end	Day	26% 12% 19% 23% 16% 5%	352
February	1st to 10th	Day	19% 5% 21% 31% 14% 10%	320
	11th to 20th	Day	28% 10% 25% 24% 10% 3	420
	21st to end	Day	20% 8% 29% 27% 12% 5%	355
March	1st to 10th	Day	17% 9% 26% 22% 21% 4	407
	11th to 20th	Day	12% 8% 21% 32% 19% 9%	475
	21st to end	Day	17% 7% 20% 26% 22% 9%	660
April	1st to 10th	Day	15% 9% 27% 25% 19% 5%	608
	11th to 20th	Day	13% 7% 19% 26% 25% 9%	690
	21st to end	Day	17% 6% 16% 30% 25% 7%	700
May	1st to 10th	Day	23% 9% 20% 25% 19% 4	703
	11th to 20th	Day	18% 9% 20% 26% 20% 7%	725
	21st to end	Day	22% 7% 19% 30% 17% 5%	907
June	1st to 10th	Day	19% 9% 16% 25% 23% 8%	930
	11th to 20th	Day	15% 5% 17% 31% 25% 6%	930
	21st to end	Day	16% 6% 17% 26% 27% 9%	930
July	1st to 10th	Day	20% 6% 14% 30% 25% 5%	916
	11th to 20th	Day	23% 3 15% 30% 23% 5%	912
	21st to end	Day	27% 4 15% 24% 22% 8%	824
August	1st to 10th	Day	29% 4 15% 25% 20% 6%	726
	11th to 20th	Day	30% 7% 18% 21% 18% 6%	715
	21st to end	Day	32% 7% 13% 21% 19% 7%	803
September	1st to 10th	Day	33% 7% 18% 16% 19% 7%	636
	11th to 20th	Day	36% 7% 13% 17% 19% 8%	620
	21st to end	Day	26% 6% 16% 24% 18% 9%	435
October	1st to 10th	Day	32% 7% 20% 19% 16% 6%	420
	11th to 20th	Day	26% 9% 20% 25% 13% 7%	420
	21st to end	Day	23% 8% 23% 25% 15% 7%	462
November	1st to 10th	Day	23% 8% 29% 21% 15% 4	416
	11th to 20th	Day	18% 8% 25% 28% 19% 3	320
	21st to end	Day	22% 8% 26% 24% 16% 5%	152
December	1st to 10th	Day	30% 11% 18% 21% 17% 3	110
	11th to 20th	Day	23% 15% 25% 20% 14% 3	110
	21st to end	Day	23% 13% 25% 26% 10% 2	121
January	1st to 10th	Night	16% 8% 21% 35% 16% 3	1060
	11th to 20th	Night	24% 8% 26% 26% 13% 3	1033
	21st to end	Night	27% 7% 23% 29% 13% 2	1045
February	1st to 10th	Night	19% 6% 25% 31% 15% 4	950
	11th to 20th	Night	27% 11% 25% 26% 10% 1	934
	21st to end	Night	21% 10% 25% 30% 11% 3	652
March	1st to 10th	Night	17% 11% 25% 27% 17% 3	708
	11th to 20th	Night	13% 6% 29% 28% 19% 4	700
	21st to end	Night	16% 8% 20% 25% 25% 7%	672
April	1st to 10th	Night	20% 9% 21% 26% 18% 7%	600
	11th to 20th	Night	20% 6% 14% 26% 27% 6%	593
	21st to end	Night	14% 5% 17% 30% 30% 4	600
May	1st to 10th	Night	18% 8% 17% 28% 25% 3	421
	11th to 20th	Night	20% 7% 16% 29% 26% 2	394
	21st to end	Night	19% 7% 18% 33% 22% 1	260
June	1st to 10th	Night	22% 9% 12% 30% 28% 1	200
	11th to 20th	Night	18% 2 19% 36% 25% 1	200
	21st to end	Night	18% 5% 15% 36% 25% 2	200
July	1st to 10th	Night	27% 5% 15% 32% 19% 1	195
	11th to 20th	Night	30% 3 11% 30% 23% 3	290
	21st to end	Night	32% 4 14% 21% 25% 5%	438
August	1st to 10th	Night	34% 5% 14% 23% 21% 3	398
	11th to 20th	Night	37% 5% 15% 21% 19% 4	531
	21st to end	Night	38% 6% 13% 17% 20% 5%	660
September	1st to 10th	Night	40% 4 15% 21% 16% 4	600
	11th to 20th	Night	41% 7% 9% 16% 22% 6%	600
	21st to end	Night	31% 6% 17% 19% 22% 5%	650
October	1st to 10th	Night	37% 7% 16% 21% 16% 3	715
	11th to 20th	Night	27% 5% 20% 24% 19% 4	910
	21st to end	Night	27% 7% 23% 25% 17% 2	1001
November	1st to 10th	Night	26% 8% 25% 26% 13% 2	930
	11th to 20th	Night	18% 10% 25% 31% 14% 2	950
	21st to end	Night	26% 8% 24% 25% 16% 2	950
December	1st to 10th	Night	31% 10% 21% 25% 11% 2	1033
	11th to 20th	Night	22% 8% 29% 27% 12% 3	1060
	21st to end	Night	23% 10% 28% 23% 13% 3	1166

Page generated at 2026-02-27 21:40:18. Version ac07

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