Sachs Harbour
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sachs Harbour clear sky chart from 2005-11-06 to 2026-04-02.

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
Transparency	Day	56% 5% 17% 16% 5%	140166
	Night	51% 5% 13% 22% 8%	142376
Seeing	Day	13% 3 13% 27% 29% 14%	21570
	Night	8% 3 13% 30% 31% 15%	25043

By Month

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	21st to end	Day	35% 3 26% 28% 6% 1	206
	February	1st to 10th	Day	48% 6% 21% 19% 7%	696
11th to 20th		Day	45% 9% 13% 27% 7%	1134
21st to end		Day	43% 8% 15% 27% 6%	1211
March	1st to 10th	Day	39% 6% 9% 22% 22% 2	4088
	11th to 20th	Day	39% 5% 6% 25% 24% 1	4847
	21st to end	Day	29% 4 8% 25% 33% 1	6131
April	1st to 10th	Day	45% 6% 18% 24% 7%	2756
	11th to 20th	Day	50% 7% 16% 21% 6%	3052
	21st to end	Day	51% 6% 15% 23% 6%	3496
May	1st to 10th	Day	66% 4 10% 15% 4	9184
	11th to 20th	Day	61% 5% 16% 17% 2	10813
	21st to end	Day	59% 4 17% 16% 3	11880
June	1st to 10th	Day	48% 5% 17% 25% 4	4800
	11th to 20th	Day	51% 9% 20% 17% 2	4800
	21st to end	Day	42% 8% 25% 24% 1	4800
July	1st to 10th	Day	60% 4 18% 17% 1	10761
	11th to 20th	Day	59% 5% 18% 14% 4	10745
	21st to end	Day	49% 5% 30% 16%	11513
August	1st to 10th	Day	55% 7% 20% 15% 3	6707
	11th to 20th	Day	72% 6% 16% 6%	5734
	21st to end	Day	78% 5% 14% 3	5625
September	1st to 10th	Day	75% 4 15% 6%	2777
	11th to 20th	Day	68% 7% 20% 5%	2472
	21st to end	Day	76% 6% 14% 4	2114
October	1st to 10th	Day	65% 5% 15% 13% 1	2956
	11th to 20th	Day	77% 5% 11% 7%	2364
	21st to end	Day	70% 4 16% 9%	1862
November	1st to 10th	Day	59% 6% 18% 17%	607
	11th to 20th	Day	77% 11% 11%	35
January	1st to 10th	Night	46% 3 11% 37% 4	14090
	11th to 20th	Night	46% 4 11% 22% 15% 1	14160
	21st to end	Night	47% 5% 11% 26% 10%	14841
February	1st to 10th	Night	49% 8% 15% 21% 8%	3922
	11th to 20th	Night	44% 7% 15% 26% 8%	3402
	21st to end	Night	45% 7% 17% 26% 6%	2595
March	1st to 10th	Night	39% 6% 10% 24% 18% 4	6003
	11th to 20th	Night	35% 4 6% 25% 28% 1	5366
	21st to end	Night	29% 3 10% 25% 31% 1	5076
April	1st to 10th	Night	44% 7% 19% 24% 6% 1	1668
	11th to 20th	Night	45% 7% 17% 25% 6%	1295
	21st to end	Night	49% 6% 14% 24% 7%	902
May	1st to 10th	Night	65% 4 9% 18% 4	817
	August	1st to 10th	Night	50% 6% 16% 22% 6%	517
11th to 20th		Night	73% 5% 15% 6% 1	1378
21st to end		Night	77% 6% 13% 4	2273
September	1st to 10th	Night	74% 3 15% 7%	1622
	11th to 20th	Night	69% 7% 17% 7%	1926
	21st to end	Night	78% 6% 13% 3	2286
October	1st to 10th	Night	61% 9% 16% 13% 2	4234
	11th to 20th	Night	77% 5% 12% 7%	4742
	21st to end	Night	74% 4 15% 7%	5928
November	1st to 10th	Night	57% 6% 21% 14% 1	3907
	11th to 20th	Night	67% 9% 12% 10% 2	4879
	21st to end	Night	64% 7% 14% 11% 3	5040
December	1st to 10th	Night	48% 7% 16% 27% 2	8080
	11th to 20th	Night	35% 5% 17% 31% 12%	9195
	21st to end	Night	56% 6% 12% 21% 4	12232

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
February	1st to 10th	Day	2 3 10% 27% 35% 23%	124
	11th to 20th	Day	4 2 9% 31% 35% 19%	220
	21st to end	Day	2 2 9% 26% 36% 25%	182
March	1st to 10th	Day	2 1 12% 26% 37% 22%	416
	11th to 20th	Day	3 3 13% 27% 36% 19%	510
	21st to end	Day	4 1 13% 32% 30% 21%	594
April	1st to 10th	Day	4 1 11% 21% 34% 28%	545
	11th to 20th	Day	3 3 14% 30% 33% 16%	771
	21st to end	Day	4 2 11% 30% 33% 20%	900
May	1st to 10th	Day	8% 2 12% 26% 34% 17%	999
	11th to 20th	Day	7% 4 12% 29% 32% 16%	1316
	21st to end	Day	7% 3 10% 25% 37% 18%	1439
June	1st to 10th	Day	9% 3 12% 28% 31% 18%	1330
	11th to 20th	Day	12% 3 17% 31% 29% 8%	1330
	21st to end	Day	13% 3 14% 31% 29% 10%	1330
July	1st to 10th	Day	15% 3 13% 26% 30% 12%	1306
	11th to 20th	Day	17% 4 13% 28% 27% 11%	1300
	21st to end	Day	20% 4 13% 27% 27% 9%	1451
August	1st to 10th	Day	25% 5% 13% 27% 21% 9%	1084
	11th to 20th	Day	27% 4 14% 27% 21% 8%	913
	21st to end	Day	28% 4 12% 23% 24% 9%	903
September	1st to 10th	Day	29% 5% 14% 21% 19% 12%	581
	11th to 20th	Day	24% 6% 14% 27% 21% 8%	530
	21st to end	Day	25% 8% 15% 27% 18% 8%	530
October	1st to 10th	Day	15% 4 15% 30% 26% 9%	399
	11th to 20th	Day	14% 4 17% 24% 25% 16%	220
	21st to end	Day	11% 7% 19% 24% 28% 12%	242
November	1st to 10th	Day	10% 4 12% 35% 23% 16%	105
	January	1st to 10th	Night	4 1 16% 33% 30% 16%	1380
11th to 20th		Night	5% 3 17% 33% 30% 12%	1380
21st to end		Night	3 1 12% 32% 33% 19%	1476
February	1st to 10th	Night	2 2 13% 31% 32% 20%	1171
	11th to 20th	Night	4 2 13% 30% 35% 16%	1086
	21st to end	Night	3 2 11% 30% 34% 20%	783
March	1st to 10th	Night	2 1 9% 32% 38% 18%	853
	11th to 20th	Night	2 2 9% 27% 38% 22%	840
	21st to end	Night	2 1 10% 32% 36% 19%	824
April	1st to 10th	Night	2 3 9% 31% 35% 21%	502
	11th to 20th	Night	6% 2 12% 33% 34% 14%	395
	21st to end	Night	5% 2 12% 30% 37% 13%	387
May	1st to 10th	Night	5% 7% 29% 37% 21%	75
	August	1st to 10th	Night	26% 1 9% 25% 29% 10%	69
11th to 20th		Night	29% 5% 11% 24% 27% 5%	333
21st to end		Night	26% 4 9% 25% 25% 10%	440
September	1st to 10th	Night	28% 3 9% 26% 27% 7%	472
	11th to 20th	Night	22% 5% 13% 29% 23% 8%	720
	21st to end	Night	25% 4 15% 27% 23% 7%	800
October	1st to 10th	Night	17% 4 13% 31% 28% 7%	800
	11th to 20th	Night	15% 5% 16% 28% 25% 10%	880
	21st to end	Night	16% 4 13% 27% 29% 10%	1221
November	1st to 10th	Night	8% 3 15% 30% 32% 12%	1135
	11th to 20th	Night	5% 2 16% 31% 31% 14%	1363
	21st to end	Night	7% 2 13% 27% 34% 17%	1380
December	1st to 10th	Night	5% 2 17% 29% 29% 18%	1380
	11th to 20th	Night	4 4 14% 31% 30% 17%	1380
	21st to end	Night	3 3 13% 33% 35% 13%	1518

Page generated at 2026-03-30 00:18:46. Version ac07

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