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 2024-07-08.

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	54% 7% 18% 17% 4	92040
	Night	51% 7% 15% 20% 7%	94513
Seeing	Day	13% 3 13% 27% 30% 14%	19404
	Night	8% 2 13% 30% 32% 15%	22402

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	36% 5% 14% 36% 7% 2	102
	February	1st to 10th	Day	48% 6% 21% 19% 5%	629
11th to 20th		Day	45% 10% 14% 26% 5%	1022
21st to end		Day	45% 8% 14% 27% 6% 1	1099
March	1st to 10th	Day	47% 6% 14% 19% 14%	2774
	11th to 20th	Day	39% 6% 9% 27% 19%	3314
	21st to end	Day	38% 5% 11% 24% 21% 1	4181
April	1st to 10th	Day	43% 6% 19% 25% 7%	2605
	11th to 20th	Day	50% 7% 16% 21% 6%	2897
	21st to end	Day	50% 6% 15% 23% 7%	3321
May	1st to 10th	Day	65% 5% 13% 14% 3	6433
	11th to 20th	Day	56% 6% 20% 15% 3	7533
	21st to end	Day	49% 5% 20% 21% 5%	8272
June	1st to 10th	Day	47% 5% 18% 25% 4	4560
	11th to 20th	Day	49% 10% 21% 18% 2	4560
	21st to end	Day	44% 8% 25% 22% 1	4560
July	1st to 10th	Day	46% 7% 20% 24% 3	4382
	11th to 20th	Day	56% 9% 21% 13% 1	4185
	21st to end	Day	58% 8% 22% 12%	4449
August	1st to 10th	Day	65% 8% 18% 8% 1	3701
	11th to 20th	Day	67% 9% 17% 6% 1	3145
	21st to end	Day	70% 8% 17% 5%	3111
September	1st to 10th	Day	74% 4 15% 6%	2501
	11th to 20th	Day	66% 7% 21% 6%	2226
	21st to end	Day	75% 7% 15% 4	1904
October	1st to 10th	Day	68% 8% 16% 8% 1	1626
	11th to 20th	Day	65% 9% 18% 9% 1	1316
	21st to end	Day	67% 6% 21% 7%	1050
November	1st to 10th	Day	62% 6% 18% 14%	549
	11th to 20th	Day	79% 12% 9%	33
January	1st to 10th	Night	35% 5% 16% 41% 4	7585
	11th to 20th	Night	41% 5% 13% 20% 20% 1	7600
	21st to end	Night	43% 9% 10% 27% 12%	8027
February	1st to 10th	Night	49% 9% 15% 20% 6%	3549
	11th to 20th	Night	45% 7% 16% 26% 6%	3072
	21st to end	Night	47% 7% 16% 25% 6%	2355
March	1st to 10th	Night	46% 6% 15% 23% 11%	4087
	11th to 20th	Night	39% 5% 9% 27% 20% 1	3662
	21st to end	Night	40% 4 14% 24% 17% 1	3467
April	1st to 10th	Night	41% 8% 19% 25% 6% 1	1576
	11th to 20th	Night	45% 7% 17% 25% 6%	1230
	21st to end	Night	48% 7% 14% 24% 8%	857
May	1st to 10th	Night	63% 5% 10% 18% 3	566
	August	1st to 10th	Night	67% 9% 18% 5% 1	276
11th to 20th		Night	66% 8% 18% 6% 1	753
21st to end		Night	68% 10% 19% 4	1246
September	1st to 10th	Night	72% 3 16% 8%	1458
	11th to 20th	Night	68% 7% 17% 7%	1732
	21st to end	Night	77% 7% 13% 3	2056
October	1st to 10th	Night	64% 12% 16% 8%	2334
	11th to 20th	Night	64% 7% 19% 9%	2626
	21st to end	Night	70% 5% 17% 8%	3306
November	1st to 10th	Night	59% 7% 21% 12% 1	3525
	11th to 20th	Night	66% 10% 12% 10% 2	4413
	21st to end	Night	63% 8% 15% 11% 3	4560
December	1st to 10th	Night	50% 10% 19% 16% 4	4560
	11th to 20th	Night	43% 8% 16% 29% 6%	5675
	21st to end	Night	56% 7% 13% 20% 4	8360

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	1 3 8% 26% 38% 25%	101
	11th to 20th	Day	4 2 8% 29% 36% 20%	180
	21st to end	Day	2 1 9% 29% 33% 26%	150
March	1st to 10th	Day	2 1 13% 24% 36% 23%	357
	11th to 20th	Day	4 3 14% 27% 35% 17%	436
	21st to end	Day	5% 1 12% 33% 31% 18%	506
April	1st to 10th	Day	4 1 11% 21% 35% 29%	498
	11th to 20th	Day	3 3 12% 30% 35% 17%	717
	21st to end	Day	4 2 11% 30% 33% 20%	840
May	1st to 10th	Day	9% 3 12% 25% 34% 17%	934
	11th to 20th	Day	6% 4 12% 29% 33% 15%	1236
	21st to end	Day	6% 2 10% 25% 38% 19%	1351
June	1st to 10th	Day	9% 2 13% 28% 31% 18%	1250
	11th to 20th	Day	11% 3 17% 30% 30% 9%	1250
	21st to end	Day	13% 4 14% 30% 29% 10%	1250
July	1st to 10th	Day	15% 3 11% 26% 32% 14%	1207
	11th to 20th	Day	17% 4 13% 26% 29% 12%	1140
	21st to end	Day	21% 4 11% 26% 28% 9%	1275
August	1st to 10th	Day	27% 5% 13% 25% 21% 9%	949
	11th to 20th	Day	27% 4 13% 26% 22% 8%	793
	21st to end	Day	25% 3 12% 23% 26% 10%	783
September	1st to 10th	Day	29% 3 12% 21% 21% 13%	497
	11th to 20th	Day	24% 5% 16% 27% 22% 7%	450
	21st to end	Day	24% 8% 16% 27% 17% 8%	450
October	1st to 10th	Day	16% 4 17% 29% 24% 10%	339
	11th to 20th	Day	14% 3 17% 24% 25% 17%	180
	21st to end	Day	12% 7% 20% 25% 27% 10%	198
November	1st to 10th	Day	11% 2 13% 32% 25% 16%	87
	January	1st to 10th	Night	5% 1 17% 32% 29% 16%	1220
11th to 20th		Night	4 2 15% 32% 32% 14%	1220
21st to end		Night	2 1 9% 33% 35% 20%	1308
February	1st to 10th	Night	2 2 11% 31% 33% 21%	1049
	11th to 20th	Night	5% 2 12% 29% 35% 17%	972
	21st to end	Night	3 2 11% 30% 33% 21%	703
March	1st to 10th	Night	3 1 10% 31% 38% 18%	771
	11th to 20th	Night	2 2 10% 27% 37% 22%	760
	21st to end	Night	3 1 10% 32% 34% 20%	746
April	1st to 10th	Night	2 2 9% 30% 36% 21%	474
	11th to 20th	Night	6% 1 10% 33% 35% 15%	375
	21st to end	Night	6% 2 12% 31% 36% 14%	368
May	1st to 10th	Night	6% 7% 30% 35% 23%	71
	August	1st to 10th	Night	28% 2 10% 20% 30% 11%	61
11th to 20th		Night	29% 5% 11% 23% 27% 5%	299
21st to end		Night	24% 4 10% 24% 28% 11%	396
September	1st to 10th	Night	26% 3 9% 27% 28% 7%	424
	11th to 20th	Night	21% 5% 14% 29% 23% 8%	648
	21st to end	Night	24% 5% 16% 26% 22% 7%	720
October	1st to 10th	Night	17% 3 13% 31% 27% 8%	720
	11th to 20th	Night	16% 5% 16% 29% 24% 10%	786
	21st to end	Night	17% 4 14% 27% 28% 10%	1089
November	1st to 10th	Night	8% 2 15% 30% 33% 12%	1015
	11th to 20th	Night	6% 3 17% 29% 31% 15%	1205
	21st to end	Night	7% 2 12% 27% 34% 19%	1220
December	1st to 10th	Night	5% 3 17% 28% 29% 19%	1220
	11th to 20th	Night	4 4 12% 31% 30% 20%	1220
	21st to end	Night	3 3 13% 33% 35% 13%	1342

Page generated at 2024-07-05 09:05:38. Version ac07

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