Cégep de Thetford
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Cégep de Thetford clear sky chart from 2005-11-06 to 2025-02-06.

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	18% 13% 4 10% 6% 5% 5% 4 5% 6% 25%	107905
	Night	16% 14% 5% 11% 6% 5% 4 3 4 5% 26%	110351
Transparency	Day	59% 6% 10% 17% 8% 1	111421
	Night	60% 5% 10% 16% 8% 1	115000
Seeing	Day	28% 18% 29% 17% 7% 1	15292
	Night	26% 15% 28% 22% 8% 1	24113

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	13% 20% 9% 19% 10% 7% 7% 3 3 2 8%	3597
	11th to 20th	Day	8% 17% 8% 23% 15% 6% 3 2 2 2 14%	3570
	21st to end	Day	7% 12% 9% 17% 8% 8% 8% 3 4 5% 18%	3960
February	1st to 10th	Day	12% 18% 7% 13% 10% 7% 5% 4 3 3 18%	1585
	11th to 20th	Day	13% 20% 8% 14% 7% 5% 5% 3 4 5% 16%	1848
	21st to end	Day	13% 19% 5% 12% 7% 5% 4 3 4 5% 20%	1570
March	1st to 10th	Day	17% 16% 6% 10% 7% 4 4 2 4 5% 24%	3116
	11th to 20th	Day	14% 23% 6% 14% 5% 4 4 2 3 3 21%	3317
	21st to end	Day	16% 16% 5% 11% 5% 3 3 2 3 4 31%	4057
April	1st to 10th	Day	21% 17% 4 10% 6% 4 3 3 4 5% 24%	2280
	11th to 20th	Day	19% 13% 4 7% 4 4 4 3 4 5% 33%	2333
	21st to end	Day	22% 14% 4 8% 5% 4 3 3 4 6% 27%	2470
May	1st to 10th	Day	21% 10% 4 8% 5% 5% 5% 3 5% 6% 27%	4160
	11th to 20th	Day	19% 9% 3 9% 5% 5% 5% 5% 6% 8% 26%	4398
	21st to end	Day	17% 8% 3 7% 6% 6% 6% 5% 6% 7% 28%	4837
June	1st to 10th	Day	24% 9% 2 6% 5% 5% 5% 4 5% 8% 26%	2777
	11th to 20th	Day	19% 6% 2 7% 5% 4 6% 5% 6% 9% 31%	2850
	21st to end	Day	25% 9% 3 8% 6% 5% 4 4 5% 6% 24%	2776
July	1st to 10th	Day	16% 8% 3 9% 6% 6% 6% 5% 6% 8% 28%	4440
	11th to 20th	Day	17% 8% 3 8% 6% 5% 5% 5% 6% 8% 29%	4440
	21st to end	Day	18% 7% 2 5% 4 4 5% 4 5% 7% 39%	4814
August	1st to 10th	Day	19% 7% 2 8% 6% 5% 6% 5% 7% 9% 25%	4367
	11th to 20th	Day	20% 8% 3 8% 6% 6% 6% 5% 7% 7% 25%	4045
	21st to end	Day	21% 7% 2 6% 4 5% 5% 3 6% 6% 34%	4294
September	1st to 10th	Day	17% 9% 3 7% 4 4 4 5% 5% 7% 35%	2280
	11th to 20th	Day	20% 7% 2 6% 3 3 4 3 6% 6% 40%	2109
	21st to end	Day	20% 8% 3 6% 4 4 5% 4 6% 9% 33%	2090
October	1st to 10th	Day	22% 11% 3 6% 4 4 4 4 5% 7% 30%	2090
	11th to 20th	Day	22% 16% 3 8% 5% 5% 5% 3 5% 4 24%	1753
	21st to end	Day	25% 19% 5% 9% 4 3 4 2 4 5% 21%	1881
November	1st to 10th	Day	19% 17% 4 9% 5% 4 3 3 3 4 28%	1761
	11th to 20th	Day	18% 18% 7% 12% 5% 3 3 3 4 5% 22%	1800
	21st to end	Day	19% 21% 6% 11% 5% 4 4 3 3 5% 17%	1542
December	1st to 10th	Day	16% 19% 8% 15% 9% 5% 4 2 4 4 13%	2280
	11th to 20th	Day	19% 16% 8% 12% 5% 4 4 3 3 3 23%	2618
	21st to end	Day	18% 21% 6% 13% 6% 4 4 3 3 4 19%	3800
January	1st to 10th	Night	11% 18% 9% 21% 10% 7% 4 2 3 3 11%	6349
	11th to 20th	Night	9% 21% 9% 21% 12% 6% 4 3 3 3 11%	6315
	21st to end	Night	6% 13% 8% 17% 8% 8% 6% 4 5% 5% 20%	6996
February	1st to 10th	Night	11% 17% 6% 13% 9% 6% 5% 3 4 4 22%	2703
	11th to 20th	Night	11% 19% 7% 15% 7% 6% 6% 3 4 3 20%	2218
	21st to end	Night	13% 16% 6% 11% 7% 5% 4 3 4 4 27%	1884
March	1st to 10th	Night	21% 16% 4 8% 5% 4 6% 3 3 4 28%	3724
	11th to 20th	Night	13% 20% 7% 15% 6% 4 4 3 3 3 23%	3641
	21st to end	Night	16% 16% 4 11% 6% 5% 3 3 4 4 29%	3572
April	1st to 10th	Night	21% 15% 3 9% 4 3 4 3 4 5% 28%	1900
	11th to 20th	Night	19% 10% 3 7% 5% 4 3 4 5% 6% 32%	1796
	21st to end	Night	22% 12% 3 7% 4 3 5% 3 5% 5% 30%	1710
May	1st to 10th	Night	23% 8% 4 8% 6% 4 5% 3 5% 6% 28%	2810
	11th to 20th	Night	19% 10% 3 7% 5% 4 4 4 4 7% 33%	2495
	21st to end	Night	18% 7% 2 6% 4 4 5% 4 7% 9% 35%	2738
June	1st to 10th	Night	23% 10% 3 7% 5% 4 5% 4 4 7% 29%	1397
	11th to 20th	Night	18% 6% 3 5% 5% 4 5% 3 6% 8% 36%	1330
	21st to end	Night	22% 8% 2 7% 5% 5% 5% 4 5% 7% 29%	1397
July	1st to 10th	Night	13% 8% 4 8% 7% 5% 6% 5% 6% 7% 31%	2520
	11th to 20th	Night	20% 8% 3 7% 5% 4 4 4 5% 6% 34%	2520
	21st to end	Night	15% 7% 2 6% 4 4 4 4 6% 7% 41%	2739
August	1st to 10th	Night	23% 8% 3 6% 4 4 4 3 6% 8% 32%	2530
	11th to 20th	Night	18% 11% 3 9% 6% 4 5% 4 5% 6% 29%	2782
	21st to end	Night	18% 7% 3 8% 4 4 4 3 5% 6% 38%	3346
September	1st to 10th	Night	19% 6% 2 6% 4 3 4 3 5% 6% 39%	1900
	11th to 20th	Night	16% 7% 2 5% 3 3 4 4 4 5% 46%	2071
	21st to end	Night	17% 8% 2 6% 4 4 4 3 4 7% 41%	2090
October	1st to 10th	Night	19% 9% 2 6% 4 4 5% 3 5% 7% 36%	2090
	11th to 20th	Night	21% 12% 3 7% 5% 5% 5% 3 5% 6% 29%	2424
	21st to end	Night	24% 14% 4 7% 5% 4 4 3 5% 4 26%	2717
November	1st to 10th	Night	19% 16% 4 8% 5% 5% 4 3 5% 5% 26%	2537
	11th to 20th	Night	17% 14% 5% 11% 6% 5% 4 3 4 4 27%	2600
	21st to end	Night	17% 20% 7% 12% 6% 4 3 3 3 4 21%	2851
December	1st to 10th	Night	15% 18% 10% 20% 10% 4 3 2 3 4 11%	4910
	11th to 20th	Night	19% 19% 6% 15% 7% 4 3 2 4 4 17%	5591
	21st to end	Night	18% 20% 6% 11% 5% 3 3 3 3 4 24%	7158

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	84% 4 4 6% 2	3598
	11th to 20th	Day	79% 3 4 10% 4 1	3600
	21st to end	Day	68% 5% 6% 9% 11% 1	3960
February	1st to 10th	Day	71% 4 6% 11% 7% 2	1585
	11th to 20th	Day	72% 3 8% 9% 7% 1	1857
	21st to end	Day	65% 5% 8% 14% 6% 2	1570
March	1st to 10th	Day	62% 6% 7% 13% 10% 2	3119
	11th to 20th	Day	69% 4 8% 11% 7% 1	3317
	21st to end	Day	58% 3 6% 16% 13% 3	4057
April	1st to 10th	Day	64% 4 8% 14% 8% 2	2280
	11th to 20th	Day	54% 4 9% 20% 12% 2	2333
	21st to end	Day	60% 4 8% 15% 11% 2	2470
May	1st to 10th	Day	55% 6% 10% 17% 10% 1	4174
	11th to 20th	Day	53% 9% 16% 15% 7% 1	4402
	21st to end	Day	51% 8% 10% 18% 12%	4837
June	1st to 10th	Day	55% 7% 10% 20% 6% 1	2777
	11th to 20th	Day	48% 6% 14% 20% 10% 1	2850
	21st to end	Day	60% 7% 9% 16% 8%	2776
July	1st to 10th	Day	52% 8% 13% 22% 6%	4370
	11th to 20th	Day	50% 8% 16% 22% 4	4365
	21st to end	Day	44% 7% 14% 28% 7%	4661
August	1st to 10th	Day	53% 8% 15% 20% 4	4353
	11th to 20th	Day	55% 9% 16% 16% 5%	4084
	21st to end	Day	50% 5% 14% 19% 12% 1	4294
September	1st to 10th	Day	47% 7% 14% 23% 9% 1	2280
	11th to 20th	Day	44% 5% 12% 27% 12%	2109
	21st to end	Day	46% 7% 13% 23% 10%	2090
October	1st to 10th	Day	53% 6% 13% 23% 5%	3480
	11th to 20th	Day	58% 4 12% 22% 3	2891
	21st to end	Day	58% 4 16% 16% 7%	3081
November	1st to 10th	Day	61% 5% 10% 18% 7%	1761
	11th to 20th	Day	65% 4 9% 13% 7% 1	1800
	21st to end	Day	71% 6% 9% 11% 3	1542
December	1st to 10th	Day	77% 3 8% 7% 5%	2280
	11th to 20th	Day	68% 4 6% 14% 9%	2618
	21st to end	Day	70% 3 5% 10% 10% 2	3800
January	1st to 10th	Night	79% 5% 7% 7% 3	6349
	11th to 20th	Night	80% 4 5% 7% 2	6360
	21st to end	Night	65% 5% 7% 11% 11% 1	6996
February	1st to 10th	Night	66% 4 9% 12% 8% 1	2703
	11th to 20th	Night	70% 4 7% 11% 7% 1	2220
	21st to end	Night	61% 4 8% 14% 11% 2	1884
March	1st to 10th	Night	58% 7% 10% 14% 8% 2	3734
	11th to 20th	Night	67% 5% 7% 13% 7% 1	3642
	21st to end	Night	61% 3 7% 18% 9% 2	3572
April	1st to 10th	Night	59% 4 9% 15% 12% 2	1900
	11th to 20th	Night	51% 5% 10% 20% 12% 2	1796
	21st to end	Night	55% 5% 10% 16% 11% 2	1710
May	1st to 10th	Night	56% 6% 12% 16% 8% 1	2816
	11th to 20th	Night	49% 9% 11% 19% 10% 1	2496
	21st to end	Night	44% 7% 15% 18% 15% 1	2739
June	1st to 10th	Night	52% 7% 12% 20% 7%	1397
	11th to 20th	Night	46% 6% 11% 24% 12% 2	1330
	21st to end	Night	54% 7% 12% 19% 9%	1397
July	1st to 10th	Night	49% 8% 16% 19% 7%	2480
	11th to 20th	Night	48% 7% 19% 20% 6%	2472
	21st to end	Night	42% 7% 18% 26% 6%	2651
August	1st to 10th	Night	50% 7% 15% 24% 4	2520
	11th to 20th	Night	55% 8% 15% 17% 5%	2809
	21st to end	Night	47% 6% 13% 21% 13%	3346
September	1st to 10th	Night	45% 6% 14% 25% 10% 1	1900
	11th to 20th	Night	39% 6% 15% 30% 9% 1	2071
	21st to end	Night	43% 8% 12% 24% 13% 1	2090
October	1st to 10th	Night	50% 5% 11% 24% 10%	3480
	11th to 20th	Night	55% 4 10% 25% 5%	4025
	21st to end	Night	53% 5% 17% 16% 9% 1	4467
November	1st to 10th	Night	60% 5% 12% 17% 5% 1	2537
	11th to 20th	Night	61% 4 11% 14% 9% 1	2600
	21st to end	Night	68% 5% 10% 13% 5%	2851
December	1st to 10th	Night	80% 3 7% 7% 2	4910
	11th to 20th	Night	73% 4 5% 13% 5%	5592
	21st to end	Night	66% 3 6% 14% 10%	7158

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	33% 19% 37% 10% 2	200
	11th to 20th	Day	31% 26% 29% 11% 3	200
	21st to end	Day	25% 26% 32% 14% 2 1	220
February	1st to 10th	Day	39% 24% 27% 7% 2 1	210
	11th to 20th	Day	30% 28% 32% 10% 1	456
	21st to end	Day	32% 23% 27% 15% 3	382
March	1st to 10th	Day	29% 22% 30% 15% 4	460
	11th to 20th	Day	32% 24% 27% 12% 4 1	460
	21st to end	Day	31% 24% 27% 11% 7% 1	506
April	1st to 10th	Day	38% 20% 25% 11% 5% 2	460
	11th to 20th	Day	34% 21% 24% 13% 6% 1	452
	21st to end	Day	33% 23% 27% 12% 3 2	460
May	1st to 10th	Day	34% 16% 30% 15% 5% 1	463
	11th to 20th	Day	24% 15% 32% 19% 8% 2	487
	21st to end	Day	23% 21% 36% 14% 6% 1	529
June	1st to 10th	Day	30% 14% 29% 17% 9% 1	607
	11th to 20th	Day	22% 14% 29% 24% 10% 1	680
	21st to end	Day	27% 12% 30% 20% 9% 2	606
July	1st to 10th	Day	21% 13% 31% 27% 7% 1	485
	11th to 20th	Day	19% 13% 41% 19% 8%	484
	21st to end	Day	23% 10% 34% 26% 6% 2	532
August	1st to 10th	Day	23% 14% 29% 22% 10% 2	486
	11th to 20th	Day	22% 9% 29% 27% 11% 2	479
	21st to end	Day	25% 13% 25% 20% 12% 5%	539
September	1st to 10th	Day	21% 16% 29% 22% 8% 4	490
	11th to 20th	Day	23% 11% 24% 24% 14% 5%	490
	21st to end	Day	22% 17% 26% 21% 10% 5%	490
October	1st to 10th	Day	26% 17% 28% 18% 10% 2	490
	11th to 20th	Day	32% 16% 27% 15% 8% 1	410
	21st to end	Day	39% 19% 22% 16% 3	429
November	1st to 10th	Day	36% 16% 29% 15% 4	395
	11th to 20th	Day	30% 22% 26% 15% 7% 1	400
	21st to end	Day	34% 23% 30% 11% 1	235
December	1st to 10th	Day	35% 18% 30% 13% 4 1	200
	11th to 20th	Day	38% 25% 26% 10% 3	200
	21st to end	Day	35% 22% 28% 12% 3 1	220
January	1st to 10th	Night	28% 23% 32% 14% 2 1	800
	11th to 20th	Night	28% 22% 31% 15% 5%	800
	21st to end	Night	19% 20% 36% 20% 4 1	880
February	1st to 10th	Night	22% 24% 33% 17% 4	781
	11th to 20th	Night	25% 22% 35% 15% 3	743
	21st to end	Night	25% 17% 34% 19% 5%	628
March	1st to 10th	Night	26% 18% 35% 19% 3	760
	11th to 20th	Night	26% 21% 31% 18% 4 1	760
	21st to end	Night	25% 17% 28% 25% 5% 1	836
April	1st to 10th	Night	32% 16% 27% 20% 5%	760
	11th to 20th	Night	27% 15% 30% 21% 7%	672
	21st to end	Night	30% 16% 27% 20% 6%	570
May	1st to 10th	Night	28% 13% 29% 24% 6% 1	559
	11th to 20th	Night	23% 8% 31% 30% 6% 1	374
	21st to end	Night	23% 8% 34% 27% 7% 1	411
June	1st to 10th	Night	26% 12% 25% 28% 8% 1	380
	11th to 20th	Night	22% 8% 25% 33% 13%	380
	21st to end	Night	23% 8% 29% 29% 11% 1	380
July	1st to 10th	Night	15% 6% 32% 35% 12% 1	370
	11th to 20th	Night	15% 7% 26% 39% 13% 1	368
	21st to end	Night	18% 7% 24% 41% 10%	416
August	1st to 10th	Night	20% 4 20% 38% 18% 1	389
	11th to 20th	Night	19% 7% 23% 33% 18% 1	562
	21st to end	Night	21% 7% 24% 28% 17% 3	758
September	1st to 10th	Night	21% 8% 26% 30% 12% 2	760
	11th to 20th	Night	21% 8% 22% 28% 20% 2	760
	21st to end	Night	22% 9% 28% 25% 15% 1	760
October	1st to 10th	Night	24% 12% 26% 26% 11% 1	760
	11th to 20th	Night	28% 15% 25% 22% 9% 1	760
	21st to end	Night	34% 17% 25% 19% 4	836
November	1st to 10th	Night	31% 18% 26% 21% 5%	780
	11th to 20th	Night	28% 18% 27% 18% 10% 1	800
	21st to end	Night	32% 20% 26% 17% 5%	845
December	1st to 10th	Night	34% 19% 27% 15% 5%	900
	11th to 20th	Night	30% 23% 24% 17% 5% 1	900
	21st to end	Night	35% 20% 25% 15% 5%	915

Page generated at 2025-02-03 03:05:52. Version ac07

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