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 2025-02-25.

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% 31%	108394
	Night	14% 12% 5% 10% 5% 5% 5% 4 6% 6% 28%	110453
Transparency	Day	51% 7% 13% 20% 8% 1	111842
	Night	56% 7% 11% 18% 7% 1	115167
Seeing	Day	20% 7% 25% 31% 15% 2	16078
	Night	20% 8% 26% 30% 14% 2	25756

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	9% 14% 5% 11% 6% 6% 6% 6% 7% 7% 23%	3505
	11th to 20th	Day	7% 15% 6% 12% 7% 6% 6% 6% 10% 8% 17%	3589
	21st to end	Day	8% 21% 8% 15% 7% 5% 5% 4 7% 5% 15%	3982
February	1st to 10th	Day	8% 11% 5% 10% 6% 5% 7% 6% 9% 9% 24%	1600
	11th to 20th	Day	6% 13% 6% 12% 8% 6% 4 5% 6% 7% 27%	1836
	21st to end	Day	8% 12% 6% 10% 7% 7% 4 4 6% 7% 30%	1610
March	1st to 10th	Day	9% 10% 3 8% 6% 5% 5% 4 6% 7% 37%	3118
	11th to 20th	Day	8% 12% 4 10% 6% 6% 5% 4 5% 6% 33%	3271
	21st to end	Day	17% 11% 3 9% 6% 4 3 3 5% 5% 32%	4133
April	1st to 10th	Day	13% 11% 3 8% 6% 4 5% 4 6% 7% 33%	2280
	11th to 20th	Day	17% 11% 3 7% 5% 4 3 4 6% 7% 31%	2347
	21st to end	Day	16% 9% 3 6% 5% 4 5% 4 5% 6% 37%	2470
May	1st to 10th	Day	17% 8% 3 8% 4 4 4 4 5% 7% 38%	4384
	11th to 20th	Day	14% 9% 3 7% 5% 4 4 4 5% 7% 38%	4399
	21st to end	Day	18% 8% 3 7% 5% 4 4 4 5% 7% 36%	5058
June	1st to 10th	Day	17% 7% 3 9% 6% 5% 5% 4 5% 7% 32%	2850
	11th to 20th	Day	14% 8% 3 8% 5% 5% 5% 4 7% 7% 34%	2850
	21st to end	Day	16% 9% 3 6% 5% 6% 5% 4 6% 8% 33%	2850
July	1st to 10th	Day	13% 10% 5% 7% 5% 4 5% 4 6% 8% 32%	4707
	11th to 20th	Day	10% 5% 2 7% 4 4 5% 5% 7% 10% 42%	4440
	21st to end	Day	15% 7% 3 7% 4 4 4 3 6% 9% 38%	4814
August	1st to 10th	Day	11% 6% 2 7% 6% 6% 6% 6% 8% 9% 33%	4423
	11th to 20th	Day	12% 4 1 5% 4 4 4 4 6% 9% 47%	4200
	21st to end	Day	18% 10% 3 7% 3 3 4 3 5% 7% 38%	4341
September	1st to 10th	Day	15% 8% 2 7% 5% 5% 4 3 5% 7% 39%	2280
	11th to 20th	Day	18% 8% 3 6% 5% 5% 4 3 5% 8% 35%	2152
	21st to end	Day	17% 8% 4 8% 6% 6% 5% 4 5% 8% 31%	2090
October	1st to 10th	Day	19% 10% 4 9% 4 4 4 4 6% 6% 29%	2019
	11th to 20th	Day	21% 12% 3 8% 5% 5% 6% 5% 5% 8% 23%	1746
	21st to end	Day	23% 14% 3 11% 6% 5% 4 3 4 5% 21%	1881
November	1st to 10th	Day	17% 13% 4 9% 7% 5% 5% 5% 6% 7% 22%	1762
	11th to 20th	Day	20% 17% 5% 11% 6% 6% 5% 3 4 5% 18%	1630
	21st to end	Day	19% 18% 4 9% 7% 5% 5% 4 6% 6% 18%	1400
December	1st to 10th	Day	12% 18% 6% 10% 6% 6% 7% 5% 7% 7% 17%	2280
	11th to 20th	Day	14% 17% 8% 11% 5% 4 4 4 5% 7% 19%	2621
	21st to end	Day	22% 22% 8% 12% 5% 3 3 3 4 3 15%	3476
January	1st to 10th	Night	8% 14% 5% 12% 6% 6% 6% 6% 7% 8% 23%	6444
	11th to 20th	Night	5% 15% 8% 15% 8% 7% 6% 5% 8% 7% 15%	6316
	21st to end	Night	8% 16% 9% 14% 6% 6% 5% 5% 8% 6% 17%	6996
February	1st to 10th	Night	8% 13% 4 11% 6% 6% 6% 6% 7% 8% 24%	2800
	11th to 20th	Night	8% 13% 4 11% 8% 6% 6% 5% 6% 6% 27%	2450
	21st to end	Night	7% 14% 6% 11% 7% 5% 5% 4 6% 7% 30%	1939
March	1st to 10th	Night	11% 10% 4 10% 6% 6% 6% 4 7% 7% 30%	3722
	11th to 20th	Night	10% 13% 4 9% 5% 4 4 4 5% 6% 36%	3687
	21st to end	Night	16% 11% 4 9% 5% 5% 4 4 5% 5% 33%	3514
April	1st to 10th	Night	15% 10% 3 9% 5% 5% 5% 4 6% 6% 32%	1900
	11th to 20th	Night	15% 11% 3 9% 4 4 4 3 6% 7% 33%	1782
	21st to end	Night	17% 9% 2 7% 5% 3 3 3 5% 6% 39%	1710
May	1st to 10th	Night	17% 9% 2 7% 4 3 4 4 5% 5% 40%	2564
	11th to 20th	Night	16% 7% 3 8% 5% 4 5% 4 6% 8% 34%	2506
	21st to end	Night	20% 9% 3 6% 4 3 3 3 5% 6% 39%	2528
June	1st to 10th	Night	16% 7% 3 7% 5% 6% 5% 4 6% 5% 36%	1330
	11th to 20th	Night	17% 8% 3 8% 4 4 5% 3 5% 6% 36%	1330
	21st to end	Night	16% 9% 3 7% 5% 4 4 5% 5% 9% 34%	1330
July	1st to 10th	Night	12% 12% 4 10% 5% 5% 5% 4 5% 6% 32%	2259
	11th to 20th	Night	9% 6% 2 7% 4 4 5% 4 7% 10% 41%	2530
	21st to end	Night	12% 7% 3 7% 4 4 3 3 5% 9% 43%	2750
August	1st to 10th	Night	13% 7% 2 8% 5% 5% 5% 5% 6% 8% 37%	2517
	11th to 20th	Night	12% 4 2 6% 5% 4 3 3 5% 7% 48%	2632
	21st to end	Night	17% 11% 3 6% 3 3 2 2 4 5% 42%	3311
September	1st to 10th	Night	12% 6% 2 7% 4 4 4 4 5% 5% 46%	1900
	11th to 20th	Night	16% 7% 2 5% 4 4 4 4 7% 7% 40%	2009
	21st to end	Night	20% 8% 2 6% 4 4 4 3 5% 6% 37%	2090
October	1st to 10th	Night	17% 11% 3 8% 4 5% 3 3 6% 6% 34%	2159
	11th to 20th	Night	19% 10% 4 10% 6% 4 4 4 6% 6% 27%	2433
	21st to end	Night	21% 13% 4 10% 5% 5% 5% 3 5% 6% 22%	2717
November	1st to 10th	Night	19% 13% 3 9% 5% 4 5% 4 6% 7% 25%	2536
	11th to 20th	Night	19% 17% 4 10% 6% 5% 5% 4 5% 5% 20%	2764
	21st to end	Night	16% 17% 6% 11% 6% 5% 5% 4 5% 7% 19%	3000
December	1st to 10th	Night	11% 15% 8% 14% 6% 6% 6% 5% 7% 6% 17%	4910
	11th to 20th	Night	13% 14% 6% 15% 8% 6% 6% 4 5% 6% 18%	5586
	21st to end	Night	25% 20% 7% 9% 5% 3 3 3 4 5% 15%	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	60% 11% 8% 14% 5% 1	3506
	11th to 20th	Day	63% 14% 6% 17% 1	3620
	21st to end	Day	69% 11% 5% 9% 4 1	3982
February	1st to 10th	Day	57% 16% 9% 13% 5% 1	1600
	11th to 20th	Day	56% 12% 11% 16% 5% 1	1845
	21st to end	Day	55% 5% 11% 16% 12% 1	1610
March	1st to 10th	Day	46% 8% 12% 20% 13% 1	3120
	11th to 20th	Day	51% 5% 12% 22% 7% 1	3271
	21st to end	Day	54% 6% 10% 16% 13% 1	4133
April	1st to 10th	Day	48% 6% 11% 21% 12% 2	2280
	11th to 20th	Day	51% 5% 13% 21% 10% 1	2347
	21st to end	Day	47% 4 12% 19% 14% 4	2470
May	1st to 10th	Day	45% 6% 9% 25% 14% 1	4396
	11th to 20th	Day	43% 7% 11% 27% 12% 1	4403
	21st to end	Day	45% 8% 13% 21% 12% 1	5058
June	1st to 10th	Day	48% 8% 12% 18% 13% 1	2850
	11th to 20th	Day	47% 6% 12% 23% 11% 1	2850
	21st to end	Day	47% 9% 13% 22% 7% 1	2850
July	1st to 10th	Day	49% 6% 15% 21% 7% 1	4634
	11th to 20th	Day	36% 6% 23% 27% 8% 1	4365
	21st to end	Day	43% 6% 15% 29% 8%	4662
August	1st to 10th	Day	44% 5% 18% 25% 7%	4408
	11th to 20th	Day	35% 5% 20% 32% 9%	4242
	21st to end	Day	47% 4 14% 26% 9%	4340
September	1st to 10th	Day	43% 7% 15% 26% 9%	2280
	11th to 20th	Day	47% 7% 22% 21% 3	2152
	21st to end	Day	51% 6% 16% 19% 7%	2090
October	1st to 10th	Day	42% 4 16% 24% 13% 1	3357
	11th to 20th	Day	53% 5% 16% 20% 5%	2871
	21st to end	Day	62% 4 15% 14% 5%	3081
November	1st to 10th	Day	61% 7% 13% 15% 4	1762
	11th to 20th	Day	70% 9% 9% 8% 3	1630
	21st to end	Day	70% 9% 10% 8% 3	1400
December	1st to 10th	Day	70% 8% 11% 10% 1	2280
	11th to 20th	Day	68% 11% 6% 10% 5% 1	2621
	21st to end	Day	77% 6% 4 11% 2	3476
January	1st to 10th	Night	61% 12% 9% 13% 4 2	6444
	11th to 20th	Night	67% 13% 5% 13% 1	6360
	21st to end	Night	67% 10% 7% 13% 3 1	6996
February	1st to 10th	Night	59% 13% 10% 13% 6%	2800
	11th to 20th	Night	59% 10% 10% 17% 5%	2451
	21st to end	Night	55% 6% 10% 18% 10% 1	1939
March	1st to 10th	Night	50% 8% 13% 18% 10% 1	3733
	11th to 20th	Night	49% 6% 12% 24% 8% 1	3688
	21st to end	Night	53% 6% 8% 15% 15% 2	3514
April	1st to 10th	Night	52% 5% 8% 20% 13% 1	1900
	11th to 20th	Night	50% 4 10% 21% 13% 2	1782
	21st to end	Night	47% 4 10% 20% 15% 4	1710
May	1st to 10th	Night	46% 5% 8% 27% 13% 1	2571
	11th to 20th	Night	45% 7% 10% 28% 8% 2	2507
	21st to end	Night	47% 6% 9% 23% 15% 1	2529
June	1st to 10th	Night	49% 7% 10% 20% 12% 1	1330
	11th to 20th	Night	50% 5% 9% 21% 14% 1	1330
	21st to end	Night	46% 9% 14% 20% 10%	1330
July	1st to 10th	Night	54% 5% 12% 17% 11%	2223
	11th to 20th	Night	39% 5% 19% 28% 7% 2	2482
	21st to end	Night	39% 6% 13% 29% 13%	2662
August	1st to 10th	Night	44% 6% 14% 28% 8%	2508
	11th to 20th	Night	37% 4 17% 33% 9%	2656
	21st to end	Night	46% 4 12% 28% 10%	3311
September	1st to 10th	Night	41% 5% 15% 29% 9% 1	1900
	11th to 20th	Night	42% 8% 20% 26% 4	2009
	21st to end	Night	50% 5% 13% 25% 7%	2090
October	1st to 10th	Night	41% 4 15% 26% 13%	3601
	11th to 20th	Night	50% 5% 14% 24% 6%	4047
	21st to end	Night	65% 5% 15% 13% 3	4467
November	1st to 10th	Night	60% 8% 10% 17% 4 1	2536
	11th to 20th	Night	68% 9% 9% 11% 3	2764
	21st to end	Night	70% 9% 10% 8% 3	3000
December	1st to 10th	Night	71% 7% 12% 9% 1	4910
	11th to 20th	Night	69% 8% 8% 12% 3	5585
	21st to end	Night	75% 8% 5% 10% 2	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	16% 9% 30% 35% 9% 1	277
	11th to 20th	Day	17% 11% 25% 33% 12% 2	300
	21st to end	Day	18% 10% 31% 29% 11% 2	330
February	1st to 10th	Day	16% 8% 38% 27% 9% 1	300
	11th to 20th	Day	11% 13% 41% 25% 9% 1	300
	21st to end	Day	14% 14% 43% 24% 5%	237
March	1st to 10th	Day	14% 11% 31% 32% 11% 1	270
	11th to 20th	Day	18% 11% 31% 31% 8% 2	329
	21st to end	Day	17% 10% 33% 26% 11% 2	506
April	1st to 10th	Day	18% 8% 28% 34% 10% 1	460
	11th to 20th	Day	25% 10% 25% 25% 13% 2	452
	21st to end	Day	22% 8% 28% 24% 14% 3	460
May	1st to 10th	Day	20% 4 29% 30% 15% 2	622
	11th to 20th	Day	19% 4 26% 34% 14% 3	675
	21st to end	Day	23% 5% 22% 33% 15% 1	734
June	1st to 10th	Day	23% 3 21% 38% 14% 2	680
	11th to 20th	Day	19% 4 24% 35% 16% 2	680
	21st to end	Day	21% 4 18% 35% 19% 3	680
July	1st to 10th	Day	16% 4 18% 39% 21% 3	671
	11th to 20th	Day	18% 4 17% 35% 21% 4	668
	21st to end	Day	13% 4 14% 39% 26% 4	739
August	1st to 10th	Day	16% 3 19% 39% 21% 3	676
	11th to 20th	Day	16% 3 15% 32% 28% 6%	574
	21st to end	Day	24% 5% 21% 28% 18% 4	539
September	1st to 10th	Day	18% 8% 20% 31% 17% 5%	490
	11th to 20th	Day	23% 7% 24% 26% 16% 5%	490
	21st to end	Day	21% 8% 19% 31% 19% 3	490
October	1st to 10th	Day	24% 11% 28% 22% 14% 1	419
	11th to 20th	Day	23% 10% 34% 24% 8% 2	300
	21st to end	Day	33% 11% 31% 20% 5%	330
November	1st to 10th	Day	22% 17% 30% 23% 8%	300
	11th to 20th	Day	30% 14% 26% 21% 8%	280
	21st to end	Day	25% 17% 31% 21% 6% 1	200
December	1st to 10th	Day	26% 9% 29% 28% 8% 2	200
	11th to 20th	Day	23% 17% 31% 23% 7% 1	200
	21st to end	Day	21% 13% 37% 20% 10%	220
January	1st to 10th	Night	19% 10% 34% 28% 8%	1000
	11th to 20th	Night	18% 13% 31% 28% 9% 1	1000
	21st to end	Night	19% 8% 35% 28% 9% 1	1100
February	1st to 10th	Night	15% 9% 34% 30% 10% 2	1000
	11th to 20th	Night	15% 11% 32% 29% 11% 2	871
	21st to end	Night	13% 8% 37% 34% 7% 1	647
March	1st to 10th	Night	11% 8% 34% 31% 14% 2	760
	11th to 20th	Night	20% 7% 32% 29% 10% 1	760
	21st to end	Night	18% 8% 27% 32% 13% 3	662
April	1st to 10th	Night	21% 5% 25% 34% 11% 2	570
	11th to 20th	Night	23% 6% 23% 35% 11% 3	563
	21st to end	Night	20% 4 22% 36% 16% 3	570
May	1st to 10th	Night	22% 5% 19% 36% 17% 2	570
	11th to 20th	Night	19% 2 19% 36% 20% 4	561
	21st to end	Night	22% 4 15% 38% 19% 2	486
June	1st to 10th	Night	19% 2 17% 41% 19% 2	380
	11th to 20th	Night	21% 4 13% 38% 20% 3	380
	21st to end	Night	19% 3 12% 41% 22% 3	380
July	1st to 10th	Night	17% 3 11% 40% 25% 3	392
	11th to 20th	Night	15% 4 12% 36% 28% 5%	552
	21st to end	Night	15% 3 11% 34% 33% 3	624
August	1st to 10th	Night	14% 3 11% 40% 31% 3	567
	11th to 20th	Night	14% 2 13% 30% 33% 7%	564
	21st to end	Night	19% 4 16% 33% 24% 4	627
September	1st to 10th	Night	16% 4 17% 35% 22% 7%	570
	11th to 20th	Night	20% 4 24% 31% 17% 3	679
	21st to end	Night	25% 6% 18% 30% 18% 3	760
October	1st to 10th	Night	23% 9% 25% 26% 14% 2	760
	11th to 20th	Night	26% 10% 28% 24% 11% 1	760
	21st to end	Night	30% 9% 26% 25% 9% 1	836
November	1st to 10th	Night	25% 12% 29% 25% 8% 1	780
	11th to 20th	Night	27% 12% 29% 20% 10% 2	925
	21st to end	Night	26% 13% 32% 23% 7%	1000
December	1st to 10th	Night	19% 13% 36% 23% 8% 1	1000
	11th to 20th	Night	22% 14% 33% 23% 7% 2	1000
	21st to end	Night	28% 12% 28% 24% 8% 1	1100

Page generated at 2025-02-22 06:51:36. Version ac07

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