Terrace Bay
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Terrace Bay clear sky chart from 2005-11-06 to 2026-07-01.

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 8% 5% 5% 5% 4 6% 7% 33%	138125
	Night	13% 12% 5% 10% 6% 5% 5% 4 6% 6% 29%	134526
Transparency	Day	51% 6% 12% 21% 9% 1	141525
	Night	56% 6% 10% 19% 7% 1	139212
Seeing	Day	20% 7% 25% 31% 15% 3	17980
	Night	20% 8% 26% 30% 14% 2	27451

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	7% 17% 7% 12% 6% 5% 7% 5% 6% 6% 21%	4553
	11th to 20th	Day	6% 16% 7% 14% 8% 5% 6% 6% 9% 7% 17%	4679
	21st to end	Day	6% 17% 7% 14% 7% 6% 6% 6% 9% 6% 17%	5156
February	1st to 10th	Day	8% 11% 5% 10% 6% 5% 7% 6% 9% 8% 24%	1680
	11th to 20th	Day	7% 13% 5% 12% 8% 6% 5% 5% 6% 7% 27%	1931
	21st to end	Day	8% 12% 6% 10% 6% 7% 4 4 6% 6% 29%	1730
March	1st to 10th	Day	10% 13% 4 8% 6% 5% 5% 4 5% 6% 32%	4578
	11th to 20th	Day	9% 13% 4 10% 6% 6% 5% 4 5% 6% 31%	4776
	21st to end	Day	19% 14% 4 8% 4 3 3 3 4 6% 32%	6054
April	1st to 10th	Day	13% 11% 3 8% 5% 4 5% 4 6% 7% 34%	2520
	11th to 20th	Day	17% 10% 3 7% 5% 4 4 4 6% 8% 31%	2597
	21st to end	Day	17% 9% 3 6% 5% 4 5% 4 5% 6% 35%	2730
May	1st to 10th	Day	13% 7% 3 8% 4 4 4 4 5% 6% 42%	8155
	11th to 20th	Day	18% 9% 3 6% 4 4 4 3 4 6% 39%	8222
	21st to end	Day	13% 6% 3 6% 4 4 4 3 5% 7% 45%	9478
June	1st to 10th	Day	17% 8% 3 8% 6% 5% 5% 4 5% 7% 33%	3150
	11th to 20th	Day	13% 9% 4 8% 5% 5% 5% 4 7% 7% 34%	3150
	21st to end	Day	16% 9% 3 6% 4 5% 5% 4 6% 8% 33%	3150
July	1st to 10th	Day	14% 9% 4 7% 4 4 5% 3 5% 7% 39%	6739
	11th to 20th	Day	12% 6% 2 7% 4 4 5% 4 6% 9% 39%	6360
	21st to end	Day	13% 7% 3 6% 4 4 4 3 6% 9% 40%	6926
August	1st to 10th	Day	11% 6% 2 7% 6% 6% 6% 6% 8% 9% 34%	4563
	11th to 20th	Day	13% 4 2 5% 3 4 4 4 6% 9% 47%	4335
	21st to end	Day	17% 10% 3 6% 3 3 4 3 5% 7% 38%	4478
September	1st to 10th	Day	15% 8% 2 7% 5% 5% 4 3 5% 7% 38%	2400
	11th to 20th	Day	18% 8% 3 6% 5% 5% 4 3 5% 8% 36%	2265
	21st to end	Day	17% 9% 4 8% 5% 5% 5% 4 5% 8% 32%	2200
October	1st to 10th	Day	18% 9% 4 9% 4 4 4 4 6% 6% 30%	2125
	11th to 20th	Day	21% 11% 3 8% 6% 5% 6% 5% 5% 8% 23%	1838
	21st to end	Day	22% 14% 3 11% 5% 4 4 3 4 5% 22%	1980
November	1st to 10th	Day	17% 13% 4 9% 7% 5% 5% 5% 6% 7% 22%	1852
	11th to 20th	Day	20% 16% 5% 11% 6% 6% 5% 4 4 5% 19%	1711
	21st to end	Day	18% 17% 4 8% 7% 5% 5% 5% 6% 6% 19%	1470
December	1st to 10th	Day	11% 17% 6% 10% 6% 6% 7% 5% 7% 7% 17%	2350
	11th to 20th	Day	14% 17% 8% 11% 5% 4 4 4 5% 7% 19%	2691
	21st to end	Day	21% 22% 8% 11% 5% 3 3 3 4 4 15%	3553
January	1st to 10th	Night	8% 14% 6% 13% 5% 6% 5% 5% 6% 7% 24%	8355
	11th to 20th	Night	6% 17% 8% 16% 8% 6% 5% 5% 8% 6% 15%	8236
	21st to end	Night	6% 13% 7% 14% 8% 7% 6% 5% 9% 7% 19%	9058
February	1st to 10th	Night	9% 13% 4 11% 6% 6% 6% 6% 7% 7% 24%	2940
	11th to 20th	Night	8% 13% 4 11% 8% 6% 6% 5% 6% 6% 26%	2575
	21st to end	Night	7% 14% 6% 12% 7% 5% 5% 4 6% 7% 29%	2076
March	1st to 10th	Night	11% 11% 3 9% 5% 5% 5% 4 6% 7% 33%	5482
	11th to 20th	Night	12% 13% 4 9% 5% 5% 5% 4 5% 7% 30%	5402
	21st to end	Night	15% 13% 4 10% 5% 5% 4 4 5% 5% 29%	5150
April	1st to 10th	Night	15% 11% 3 9% 5% 5% 5% 4 6% 6% 32%	2100
	11th to 20th	Night	16% 11% 3 8% 4 4 4 3 6% 7% 34%	1972
	21st to end	Night	18% 9% 2 8% 4 3 4 3 5% 6% 37%	1890
May	1st to 10th	Night	12% 7% 3 7% 5% 4 5% 4 6% 6% 41%	4768
	11th to 20th	Night	18% 7% 3 7% 5% 4 5% 3 5% 7% 37%	4670
	21st to end	Night	14% 8% 3 6% 4 3 4 4 6% 7% 43%	4730
June	1st to 10th	Night	16% 8% 3 7% 5% 5% 5% 4 6% 5% 37%	1470
	11th to 20th	Night	17% 8% 3 8% 5% 4 5% 3 5% 7% 36%	1470
	21st to end	Night	16% 9% 3 7% 4 4 4 5% 6% 8% 34%	1470
July	1st to 10th	Night	10% 10% 4 11% 6% 5% 5% 3 4 6% 35%	3223
	11th to 20th	Night	12% 8% 3 9% 4 4 5% 4 7% 9% 35%	3620
	21st to end	Night	15% 7% 3 7% 4 4 4 3 5% 8% 40%	3948
August	1st to 10th	Night	13% 7% 2 8% 5% 5% 5% 5% 6% 8% 37%	2597
	11th to 20th	Night	12% 4 2 6% 5% 4 3 3 5% 7% 48%	2717
	21st to end	Night	17% 11% 3 6% 3 3 3 2 5% 5% 42%	3416
September	1st to 10th	Night	13% 7% 2 7% 4 4 4 4 5% 5% 44%	2000
	11th to 20th	Night	16% 7% 2 5% 4 4 3 4 6% 7% 41%	2115
	21st to end	Night	20% 8% 2 6% 4 4 3 3 5% 6% 38%	2200
October	1st to 10th	Night	16% 10% 3 8% 4 5% 3 3 6% 7% 35%	2273
	11th to 20th	Night	19% 10% 4 9% 6% 4 4 4 6% 6% 28%	2561
	21st to end	Night	21% 13% 4 11% 5% 5% 5% 3 5% 5% 23%	2860
November	1st to 10th	Night	19% 13% 3 9% 5% 4 5% 4 6% 7% 25%	2666
	11th to 20th	Night	18% 17% 5% 10% 6% 5% 4 4 5% 5% 20%	2903
	21st to end	Night	16% 17% 6% 11% 7% 5% 4 3 5% 6% 19%	3150
December	1st to 10th	Night	11% 15% 8% 14% 6% 6% 6% 5% 7% 6% 17%	5060
	11th to 20th	Night	13% 14% 6% 15% 8% 6% 6% 4 5% 6% 18%	5736
	21st to end	Night	25% 20% 7% 10% 5% 3 3 3 4 5% 15%	7667

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	65% 9% 7% 12% 5% 1	4554
	11th to 20th	Day	66% 11% 6% 15% 2	4710
	21st to end	Day	64% 9% 7% 15% 4 1	5156
February	1st to 10th	Day	57% 15% 9% 13% 5% 1	1680
	11th to 20th	Day	56% 11% 11% 16% 5% 1	1940
	21st to end	Day	56% 5% 10% 16% 12% 1	1730
March	1st to 10th	Day	52% 6% 9% 17% 13% 4	4580
	11th to 20th	Day	55% 4 10% 20% 10% 1	4776
	21st to end	Day	55% 4 8% 19% 12% 2	6054
April	1st to 10th	Day	48% 6% 11% 22% 12% 2	2520
	11th to 20th	Day	51% 5% 13% 21% 9% 1	2597
	21st to end	Day	49% 4 12% 19% 13% 3	2730
May	1st to 10th	Day	42% 4 9% 27% 15% 3	8164
	11th to 20th	Day	46% 5% 9% 23% 15% 2	8226
	21st to end	Day	38% 5% 12% 25% 17% 4	9478
June	1st to 10th	Day	47% 7% 11% 19% 14% 1	3150
	11th to 20th	Day	48% 6% 12% 23% 10% 1	3150
	21st to end	Day	48% 8% 13% 23% 7% 1	3150
July	1st to 10th	Day	45% 5% 13% 29% 8%	6667
	11th to 20th	Day	42% 4 21% 27% 6%	6285
	21st to end	Day	42% 5% 17% 28% 8%	6728
August	1st to 10th	Day	44% 5% 18% 26% 7%	4548
	11th to 20th	Day	35% 5% 20% 32% 8%	4377
	21st to end	Day	46% 4 14% 26% 9%	4477
September	1st to 10th	Day	45% 7% 15% 25% 8%	2400
	11th to 20th	Day	47% 7% 22% 22% 3	2265
	21st to end	Day	50% 6% 16% 20% 8%	2200
October	1st to 10th	Day	42% 4 16% 24% 13% 1	3463
	11th to 20th	Day	53% 5% 16% 20% 5%	2963
	21st to end	Day	61% 4 15% 15% 4	3180
November	1st to 10th	Day	61% 6% 13% 15% 5%	1852
	11th to 20th	Day	70% 8% 9% 8% 4	1711
	21st to end	Day	69% 8% 10% 9% 4	1470
December	1st to 10th	Day	69% 8% 11% 11% 1	2350
	11th to 20th	Day	67% 10% 6% 11% 5% 1	2691
	21st to end	Day	77% 6% 4 11% 2	3553
January	1st to 10th	Night	61% 9% 8% 15% 5% 2	8355
	11th to 20th	Night	69% 10% 5% 14% 2	8280
	21st to end	Night	63% 8% 8% 17% 4 1	9058
February	1st to 10th	Night	59% 12% 9% 13% 6%	2940
	11th to 20th	Night	60% 9% 9% 17% 5%	2576
	21st to end	Night	56% 6% 10% 18% 9% 1	2076
March	1st to 10th	Night	50% 6% 11% 16% 13% 4	5493
	11th to 20th	Night	54% 5% 11% 20% 8% 1	5403
	21st to end	Night	57% 5% 7% 18% 12% 1	5150
April	1st to 10th	Night	53% 5% 8% 20% 13% 1	2100
	11th to 20th	Night	50% 4 10% 21% 13% 2	1972
	21st to end	Night	48% 4 9% 20% 14% 4	1890
May	1st to 10th	Night	43% 4 10% 29% 12% 3	4775
	11th to 20th	Night	47% 5% 10% 26% 11% 1	4671
	21st to end	Night	41% 4 8% 29% 16% 3	4731
June	1st to 10th	Night	49% 7% 9% 20% 14% 1	1470
	11th to 20th	Night	50% 4 9% 22% 14% 1	1470
	21st to end	Night	47% 9% 13% 21% 10%	1470
July	1st to 10th	Night	52% 4 10% 23% 11%	3187
	11th to 20th	Night	47% 4 19% 24% 5% 1	3572
	21st to end	Night	43% 5% 14% 28% 11%	3832
August	1st to 10th	Night	44% 6% 14% 28% 8%	2588
	11th to 20th	Night	37% 4 17% 33% 8%	2741
	21st to end	Night	46% 4 13% 28% 10%	3416
September	1st to 10th	Night	43% 5% 14% 29% 9% 1	2000
	11th to 20th	Night	41% 8% 20% 27% 4	2115
	21st to end	Night	49% 5% 13% 26% 7%	2200
October	1st to 10th	Night	41% 4 16% 26% 13%	3715
	11th to 20th	Night	50% 5% 14% 24% 7%	4175
	21st to end	Night	64% 5% 15% 14% 3	4610
November	1st to 10th	Night	60% 8% 10% 17% 5% 1	2666
	11th to 20th	Night	68% 9% 9% 11% 3	2903
	21st to end	Night	69% 9% 10% 8% 3	3150
December	1st to 10th	Night	70% 7% 12% 9% 2	5060
	11th to 20th	Night	69% 8% 8% 12% 3	5735
	21st to end	Night	75% 7% 5% 10% 2	7667

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	16% 10% 30% 35% 9% 1	305
	11th to 20th	Day	17% 11% 26% 33% 12% 2	330
	21st to end	Day	16% 9% 31% 31% 12% 2	363
February	1st to 10th	Day	17% 8% 38% 27% 9% 1	330
	11th to 20th	Day	13% 12% 38% 26% 9% 1	330
	21st to end	Day	15% 14% 41% 23% 6%	273
March	1st to 10th	Day	17% 11% 32% 30% 10% 1	330
	11th to 20th	Day	18% 10% 34% 29% 7% 2	395
	21st to end	Day	19% 9% 34% 25% 11% 2	594
April	1st to 10th	Day	19% 9% 27% 34% 10% 1	540
	11th to 20th	Day	24% 9% 25% 27% 13% 2	532
	21st to end	Day	23% 8% 27% 25% 14% 3	540
May	1st to 10th	Day	18% 4 28% 30% 17% 3	719
	11th to 20th	Day	19% 4 27% 34% 13% 3	775
	21st to end	Day	21% 5% 22% 33% 17% 3	844
June	1st to 10th	Day	22% 2 20% 38% 15% 3	780
	11th to 20th	Day	18% 4 24% 36% 16% 2	780
	21st to end	Day	21% 4 18% 36% 18% 4	780
July	1st to 10th	Day	16% 3 17% 39% 22% 2	722
	11th to 20th	Day	18% 4 19% 35% 20% 3	718
	21st to end	Day	13% 3 15% 39% 25% 4	794
August	1st to 10th	Day	17% 3 18% 39% 21% 3	726
	11th to 20th	Day	17% 3 15% 32% 27% 5%	619
	21st to end	Day	22% 4 20% 30% 19% 4	583
September	1st to 10th	Day	19% 8% 20% 31% 18% 5%	530
	11th to 20th	Day	22% 6% 22% 26% 17% 6%	530
	21st to end	Day	21% 7% 18% 31% 19% 4	530
October	1st to 10th	Day	23% 11% 28% 24% 13% 1	455
	11th to 20th	Day	22% 10% 33% 25% 8% 2	330
	21st to end	Day	32% 10% 29% 21% 7% 1	363
November	1st to 10th	Day	22% 17% 29% 24% 8%	330
	11th to 20th	Day	30% 14% 28% 20% 8%	308
	21st to end	Day	24% 17% 32% 21% 5%	220
December	1st to 10th	Day	24% 9% 31% 26% 9% 2	220
	11th to 20th	Day	23% 16% 31% 23% 6%	220
	21st to end	Day	22% 13% 36% 20% 9%	242
January	1st to 10th	Night	19% 11% 35% 27% 8%	1050
	11th to 20th	Night	19% 13% 32% 28% 8% 1	1050
	21st to end	Night	19% 7% 35% 29% 9% 1	1155
February	1st to 10th	Night	16% 9% 33% 30% 11% 2	1050
	11th to 20th	Night	15% 10% 32% 29% 12% 2	915
	21st to end	Night	13% 8% 36% 34% 8% 1	692
March	1st to 10th	Night	13% 7% 34% 32% 13% 2	840
	11th to 20th	Night	20% 8% 32% 30% 10% 1	840
	21st to end	Night	18% 9% 27% 31% 13% 3	732
April	1st to 10th	Night	21% 5% 26% 34% 11% 2	630
	11th to 20th	Night	23% 6% 23% 35% 11% 3	623
	21st to end	Night	20% 4 21% 36% 16% 3	630
May	1st to 10th	Night	21% 4 19% 35% 19% 3	630
	11th to 20th	Night	20% 2 20% 35% 19% 3	621
	21st to end	Night	22% 4 15% 39% 19% 2	538
June	1st to 10th	Night	19% 2 17% 40% 20% 3	420
	11th to 20th	Night	20% 4 13% 39% 20% 3	420
	21st to end	Night	20% 3 11% 41% 22% 3	420
July	1st to 10th	Night	17% 3 11% 40% 26% 3	413
	11th to 20th	Night	15% 4 13% 36% 27% 4	582
	21st to end	Night	14% 3 11% 36% 32% 3	657
August	1st to 10th	Night	14% 3 10% 39% 32% 3	597
	11th to 20th	Night	14% 2 13% 31% 33% 7%	594
	21st to end	Night	19% 3 17% 32% 25% 4	660
September	1st to 10th	Night	17% 4 17% 34% 22% 7%	600
	11th to 20th	Night	20% 4 23% 31% 18% 4	715
	21st to end	Night	24% 6% 18% 30% 19% 3	800
October	1st to 10th	Night	23% 9% 24% 28% 14% 2	800
	11th to 20th	Night	26% 10% 28% 24% 11% 1	800
	21st to end	Night	29% 9% 25% 26% 10% 1	880
November	1st to 10th	Night	25% 12% 29% 25% 8% 1	820
	11th to 20th	Night	27% 12% 30% 20% 10% 2	972
	21st to end	Night	26% 12% 33% 22% 7%	1050
December	1st to 10th	Night	18% 13% 36% 24% 8% 1	1050
	11th to 20th	Night	22% 13% 34% 22% 7% 2	1050
	21st to end	Night	28% 12% 28% 24% 7% 1	1155

Page generated at 2026-06-28 02:10:45. Version ac07

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