Petawawa
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Petawawa 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	16% 10% 4 9% 5% 5% 5% 4 5% 6% 31%	108810
	Night	16% 12% 4 10% 5% 5% 4 3 5% 6% 29%	109845
Transparency	Day	51% 7% 12% 20% 9% 1	112375
	Night	54% 7% 12% 18% 9% 1	114444
Seeing	Day	21% 13% 29% 22% 11% 4	14622
	Night	23% 10% 27% 28% 11% 1	23947

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	14% 15% 7% 18% 8% 6% 4 2 4 4 18%	3597
	11th to 20th	Day	11% 16% 6% 16% 9% 6% 4 3 4 5% 19%	3570
	21st to end	Day	10% 19% 8% 14% 7% 5% 4 3 5% 5% 21%	4278
February	1st to 10th	Day	11% 16% 7% 13% 6% 6% 7% 4 5% 5% 20%	1800
	11th to 20th	Day	11% 16% 6% 11% 6% 6% 5% 4 5% 6% 24%	1753
	21st to end	Day	17% 14% 4 9% 6% 5% 4 4 5% 6% 24%	1535
March	1st to 10th	Day	21% 15% 5% 9% 5% 4 3 2 4 6% 28%	3244
	11th to 20th	Day	12% 15% 6% 10% 7% 5% 5% 3 4 5% 27%	3480
	21st to end	Day	12% 7% 4 7% 5% 5% 3 3 5% 6% 43%	3932
April	1st to 10th	Day	22% 13% 3 6% 4 4 5% 3 4 6% 30%	2280
	11th to 20th	Day	22% 10% 3 6% 4 4 4 3 5% 4 35%	2254
	21st to end	Day	22% 10% 3 7% 5% 4 4 3 4 5% 32%	2465
May	1st to 10th	Day	19% 9% 3 7% 4 5% 4 4 5% 7% 32%	4418
	11th to 20th	Day	16% 9% 3 7% 4 4 4 4 5% 8% 37%	4398
	21st to end	Day	17% 7% 2 7% 5% 4 4 4 4 7% 38%	4837
June	1st to 10th	Day	20% 8% 3 8% 5% 5% 5% 4 6% 6% 31%	2660
	11th to 20th	Day	14% 6% 2 6% 4 5% 5% 4 6% 7% 40%	2660
	21st to end	Day	16% 8% 3 6% 6% 5% 5% 4 6% 8% 33%	2660
July	1st to 10th	Day	12% 6% 3 8% 5% 5% 6% 4 7% 8% 34%	4440
	11th to 20th	Day	12% 5% 2 6% 6% 5% 6% 5% 7% 9% 39%	4440
	21st to end	Day	10% 5% 2 7% 4 4 4 3 6% 8% 46%	4814
August	1st to 10th	Day	12% 5% 3 8% 6% 6% 7% 5% 6% 8% 34%	4235
	11th to 20th	Day	16% 7% 2 6% 5% 4 5% 4 6% 8% 38%	4044
	21st to end	Day	9% 5% 2 6% 5% 5% 5% 4 6% 10% 42%	4254
September	1st to 10th	Day	14% 6% 3 6% 4 4 4 4 7% 7% 41%	2280
	11th to 20th	Day	13% 6% 2 7% 4 5% 4 3 5% 6% 45%	2280
	21st to end	Day	18% 7% 3 7% 5% 4 4 3 5% 8% 36%	1995
October	1st to 10th	Day	19% 9% 2 7% 5% 5% 4 4 5% 6% 34%	1900
	11th to 20th	Day	23% 11% 4 8% 7% 4 4 3 5% 6% 25%	1900
	21st to end	Day	26% 11% 3 8% 6% 5% 5% 3 5% 6% 23%	1995
November	1st to 10th	Day	16% 11% 3 7% 5% 5% 6% 4 6% 6% 32%	1666
	11th to 20th	Day	18% 14% 4 12% 6% 5% 5% 3 5% 5% 24%	1600
	21st to end	Day	26% 16% 5% 9% 6% 5% 5% 3 4 5% 17%	1600
December	1st to 10th	Day	18% 21% 5% 11% 6% 7% 6% 4 4 4 14%	2600
	11th to 20th	Day	16% 17% 7% 13% 6% 5% 3 3 3 4 22%	2986
	21st to end	Day	22% 18% 5% 15% 4 4 4 3 3 3 18%	3960
January	1st to 10th	Night	13% 21% 8% 17% 6% 4 4 3 4 4 16%	6349
	11th to 20th	Night	11% 14% 6% 16% 8% 6% 6% 4 4 5% 20%	6315
	21st to end	Night	10% 19% 8% 13% 7% 7% 5% 3 4 5% 19%	6674
February	1st to 10th	Night	13% 15% 6% 12% 7% 5% 6% 4 4 6% 22%	2600
	11th to 20th	Night	13% 15% 5% 12% 6% 5% 5% 3 5% 5% 26%	2533
	21st to end	Night	15% 15% 5% 10% 7% 5% 4 4 5% 5% 26%	2013
March	1st to 10th	Night	19% 13% 4 9% 5% 4 4 3 4 5% 31%	3580
	11th to 20th	Night	16% 17% 5% 9% 6% 4 4 4 5% 6% 24%	3479
	21st to end	Night	13% 9% 3 9% 5% 4 5% 3 5% 7% 36%	3700
April	1st to 10th	Night	20% 12% 3 9% 5% 4 4 3 4 5% 31%	1900
	11th to 20th	Night	21% 10% 3 7% 4 3 4 2 4 5% 36%	1875
	21st to end	Night	22% 10% 3 8% 5% 5% 4 2 4 6% 32%	1731
May	1st to 10th	Night	21% 8% 3 8% 5% 4 4 3 5% 6% 33%	2520
	11th to 20th	Night	18% 9% 2 7% 5% 4 5% 4 5% 6% 35%	2495
	21st to end	Night	14% 6% 2 8% 5% 4 5% 3 5% 6% 40%	2738
June	1st to 10th	Night	17% 7% 3 8% 5% 5% 5% 3 6% 7% 35%	1520
	11th to 20th	Night	15% 6% 2 5% 4 5% 4 5% 6% 7% 42%	1520
	21st to end	Night	18% 8% 2 5% 5% 4 4 4 6% 8% 36%	1520
July	1st to 10th	Night	11% 6% 3 9% 6% 6% 5% 4 7% 6% 37%	2520
	11th to 20th	Night	14% 6% 3 6% 5% 4 5% 4 7% 7% 40%	2520
	21st to end	Night	9% 6% 2 6% 4 4 4 4 6% 7% 48%	2739
August	1st to 10th	Night	12% 5% 2 6% 3 4 5% 4 7% 8% 43%	2691
	11th to 20th	Night	16% 6% 2 6% 3 4 4 4 7% 7% 42%	2785
	21st to end	Night	12% 6% 2 5% 4 4 5% 4 6% 8% 42%	3370
September	1st to 10th	Night	11% 6% 3 7% 5% 4 4 3 4 8% 45%	1900
	11th to 20th	Night	14% 6% 2 6% 3 3 4 3 5% 6% 48%	1900
	21st to end	Night	19% 7% 2 6% 5% 4 4 2 5% 6% 41%	2182
October	1st to 10th	Night	21% 7% 2 6% 4 4 3 3 4 6% 38%	2280
	11th to 20th	Night	21% 12% 3 7% 6% 5% 4 3 5% 5% 30%	2280
	21st to end	Night	23% 13% 4 7% 5% 5% 4 3 4 6% 25%	2603
November	1st to 10th	Night	19% 11% 3 8% 5% 5% 5% 3 4 6% 32%	2629
	11th to 20th	Night	17% 13% 5% 9% 7% 4 4 4 5% 5% 27%	2800
	21st to end	Night	23% 16% 5% 11% 5% 4 5% 3 4 5% 19%	2800
December	1st to 10th	Night	19% 20% 6% 12% 6% 5% 5% 4 5% 5% 13%	4580
	11th to 20th	Night	19% 16% 6% 12% 5% 4 4 3 4 4 22%	5208
	21st to end	Night	25% 18% 4 13% 5% 4 4 3 3 4 17%	6996

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	70% 6% 9% 10% 6%	3598
	11th to 20th	Day	67% 5% 10% 10% 7%	3600
	21st to end	Day	65% 5% 9% 13% 7% 1	4278
February	1st to 10th	Day	65% 5% 9% 14% 5% 1	1800
	11th to 20th	Day	59% 7% 13% 12% 8% 1	1762
	21st to end	Day	61% 6% 8% 14% 10% 1	1535
March	1st to 10th	Day	59% 5% 10% 15% 10% 1	3247
	11th to 20th	Day	57% 7% 12% 14% 9% 1	3480
	21st to end	Day	41% 6% 11% 22% 17% 4	3932
April	1st to 10th	Day	56% 5% 8% 18% 10% 3	2280
	11th to 20th	Day	52% 4 9% 21% 13% 2	2254
	21st to end	Day	53% 6% 8% 15% 15% 3	2465
May	1st to 10th	Day	48% 8% 10% 21% 10% 3	4432
	11th to 20th	Day	44% 8% 13% 24% 10% 1	4402
	21st to end	Day	44% 7% 12% 18% 16% 3	4837
June	1st to 10th	Day	52% 7% 11% 19% 11% 1	2660
	11th to 20th	Day	41% 7% 12% 23% 13% 2	2660
	21st to end	Day	48% 8% 13% 19% 12% 1	2660
July	1st to 10th	Day	42% 9% 14% 25% 9% 1	4370
	11th to 20th	Day	38% 8% 16% 28% 9%	4365
	21st to end	Day	35% 7% 14% 34% 11%	4661
August	1st to 10th	Day	45% 8% 14% 23% 9%	4221
	11th to 20th	Day	42% 7% 18% 25% 7% 1	4083
	21st to end	Day	36% 8% 15% 30% 10% 1	4254
September	1st to 10th	Day	39% 8% 16% 25% 12%	2280
	11th to 20th	Day	39% 8% 12% 30% 11% 1	2280
	21st to end	Day	48% 7% 14% 22% 9%	1995
October	1st to 10th	Day	51% 7% 10% 25% 6%	3160
	11th to 20th	Day	52% 7% 14% 22% 5%	3140
	21st to end	Day	56% 8% 17% 14% 4 1	3272
November	1st to 10th	Day	50% 8% 15% 20% 6%	1666
	11th to 20th	Day	60% 8% 12% 13% 6% 1	1600
	21st to end	Day	70% 7% 10% 8% 5%	1600
December	1st to 10th	Day	73% 7% 9% 9% 2	2600
	11th to 20th	Day	66% 5% 6% 14% 8%	2986
	21st to end	Day	71% 5% 7% 13% 4	3960
January	1st to 10th	Night	72% 6% 9% 10% 3	6349
	11th to 20th	Night	64% 9% 11% 11% 6%	6360
	21st to end	Night	68% 5% 8% 9% 10%	6674
February	1st to 10th	Night	61% 8% 11% 13% 6% 1	2600
	11th to 20th	Night	60% 5% 11% 17% 6% 1	2535
	21st to end	Night	58% 6% 9% 18% 7% 1	2013
March	1st to 10th	Night	55% 7% 13% 16% 8% 1	3590
	11th to 20th	Night	58% 7% 13% 14% 7% 1	3480
	21st to end	Night	44% 8% 11% 21% 14% 3	3700
April	1st to 10th	Night	55% 6% 8% 17% 11% 2	1900
	11th to 20th	Night	50% 5% 9% 22% 12% 2	1875
	21st to end	Night	54% 5% 7% 16% 15% 2	1731
May	1st to 10th	Night	47% 9% 12% 19% 10% 2	2526
	11th to 20th	Night	45% 9% 13% 21% 10% 2	2496
	21st to end	Night	42% 9% 10% 21% 15% 2	2739
June	1st to 10th	Night	46% 8% 13% 21% 10% 1	1520
	11th to 20th	Night	37% 9% 12% 25% 15% 2	1520
	21st to end	Night	45% 8% 14% 20% 13% 1	1520
July	1st to 10th	Night	42% 9% 15% 20% 13% 1	2480
	11th to 20th	Night	38% 8% 15% 30% 8% 1	2472
	21st to end	Night	33% 8% 14% 32% 13%	2651
August	1st to 10th	Night	36% 8% 15% 27% 13%	2681
	11th to 20th	Night	38% 8% 17% 28% 9%	2812
	21st to end	Night	36% 8% 16% 25% 11% 2	3370
September	1st to 10th	Night	37% 7% 13% 30% 13%	1900
	11th to 20th	Night	36% 7% 16% 31% 10%	1900
	21st to end	Night	43% 8% 14% 26% 9%	2182
October	1st to 10th	Night	40% 7% 13% 29% 11%	3800
	11th to 20th	Night	49% 7% 17% 20% 7%	3779
	21st to end	Night	52% 9% 17% 16% 6%	4276
November	1st to 10th	Night	53% 7% 14% 18% 7%	2629
	11th to 20th	Night	58% 8% 13% 14% 7% 1	2800
	21st to end	Night	66% 7% 12% 12% 2	2800
December	1st to 10th	Night	71% 7% 11% 8% 2	4580
	11th to 20th	Night	64% 5% 9% 11% 10%	5208
	21st to end	Night	71% 5% 6% 11% 7%	6996

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	21% 15% 35% 24% 5% 1	200
	11th to 20th	Day	27% 14% 33% 21% 4 3	200
	21st to end	Day	22% 14% 34% 21% 8% 1	288
February	1st to 10th	Day	27% 20% 35% 14% 4 1	300
	11th to 20th	Day	23% 24% 38% 15% 1	300
	21st to end	Day	30% 17% 30% 21% 1	323
March	1st to 10th	Day	24% 16% 34% 22% 4 1	460
	11th to 20th	Day	23% 17% 30% 23% 6% 1	460
	21st to end	Day	28% 16% 31% 18% 7% 1	506
April	1st to 10th	Day	27% 17% 31% 14% 9% 2	460
	11th to 20th	Day	32% 15% 22% 17% 10% 4	452
	21st to end	Day	29% 13% 32% 16% 8% 2	460
May	1st to 10th	Day	26% 11% 28% 24% 8% 3	463
	11th to 20th	Day	20% 16% 27% 23% 11% 3	487
	21st to end	Day	17% 12% 34% 22% 12% 3	529
June	1st to 10th	Day	24% 9% 33% 21% 12% 1	490
	11th to 20th	Day	17% 11% 28% 26% 14% 5%	490
	21st to end	Day	19% 12% 31% 23% 12% 4	490
July	1st to 10th	Day	11% 6% 26% 39% 14% 4	485
	11th to 20th	Day	15% 6% 28% 31% 16% 4	484
	21st to end	Day	11% 8% 28% 30% 17% 6%	532
August	1st to 10th	Day	13% 7% 26% 30% 18% 6%	486
	11th to 20th	Day	15% 5% 22% 29% 22% 8%	479
	21st to end	Day	15% 9% 26% 24% 19% 8%	539
September	1st to 10th	Day	15% 7% 29% 24% 18% 8%	490
	11th to 20th	Day	14% 8% 24% 22% 20% 13%	490
	21st to end	Day	16% 11% 28% 22% 17% 6%	490
October	1st to 10th	Day	24% 13% 23% 20% 16% 4	490
	11th to 20th	Day	27% 18% 29% 17% 8% 2	490
	21st to end	Day	30% 15% 25% 21% 7% 1	489
November	1st to 10th	Day	25% 15% 29% 21% 9%	300
	11th to 20th	Day	25% 16% 38% 14% 7% 2	200
	21st to end	Day	33% 20% 29% 13% 3 3	200
December	1st to 10th	Day	28% 13% 35% 17% 7% 1	200
	11th to 20th	Day	28% 18% 33% 15% 5% 2	200
	21st to end	Day	30% 15% 30% 16% 6% 2	220
January	1st to 10th	Night	27% 12% 32% 24% 5%	800
	11th to 20th	Night	28% 11% 26% 26% 8% 1	800
	21st to end	Night	19% 10% 31% 30% 9% 1	880
February	1st to 10th	Night	21% 12% 35% 26% 6% 1	800
	11th to 20th	Night	23% 13% 33% 26% 5%	783
	21st to end	Night	21% 16% 30% 27% 6%	647
March	1st to 10th	Night	22% 14% 31% 28% 5%	760
	11th to 20th	Night	22% 16% 30% 24% 7% 1	760
	21st to end	Night	20% 12% 31% 26% 9%	836
April	1st to 10th	Night	28% 12% 28% 26% 6%	760
	11th to 20th	Night	26% 11% 29% 25% 9%	751
	21st to end	Night	25% 10% 27% 26% 12% 1	591
May	1st to 10th	Night	21% 6% 28% 33% 11% 1	386
	11th to 20th	Night	21% 9% 28% 32% 10% 1	374
	21st to end	Night	15% 5% 34% 32% 12%	411
June	1st to 10th	Night	17% 4 31% 39% 8% 1	380
	11th to 20th	Night	16% 7% 24% 35% 17% 1	380
	21st to end	Night	21% 6% 22% 36% 16% 1	380
July	1st to 10th	Night	9% 5% 27% 41% 17% 1	370
	11th to 20th	Night	12% 4 22% 42% 20% 1	368
	21st to end	Night	9% 4 22% 44% 20% 1	416
August	1st to 10th	Night	10% 3 20% 38% 28% 1	485
	11th to 20th	Night	12% 3 16% 36% 30% 3	564
	21st to end	Night	13% 5% 23% 35% 20% 3	769
September	1st to 10th	Night	14% 4 27% 31% 22% 2	760
	11th to 20th	Night	18% 5% 20% 29% 26% 4	760
	21st to end	Night	22% 7% 21% 28% 20% 2	760
October	1st to 10th	Night	23% 7% 28% 25% 15% 2	760
	11th to 20th	Night	29% 8% 27% 24% 10% 1	760
	21st to end	Night	30% 11% 27% 27% 6%	836
November	1st to 10th	Night	25% 13% 24% 28% 9% 1	780
	11th to 20th	Night	25% 14% 32% 20% 9% 1	800
	21st to end	Night	32% 15% 24% 23% 6%	800
December	1st to 10th	Night	32% 14% 29% 18% 7%	800
	11th to 20th	Night	27% 12% 30% 24% 6%	800
	21st to end	Night	34% 13% 25% 23% 6%	880

Page generated at 2025-02-22 06:51:40. Version ac07

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