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 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	15% 10% 4 9% 5% 5% 5% 4 5% 7% 32%	138400
	Night	16% 12% 4 10% 6% 5% 5% 4 5% 6% 29%	133937
Transparency	Day	51% 7% 12% 20% 9% 1	141919
	Night	54% 7% 11% 18% 9% 1	138507
Seeing	Day	22% 13% 29% 22% 11% 3	16386
	Night	22% 10% 27% 28% 11% 1	25557

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% 16% 7% 5% 4 3 4 5% 19%	4661
	11th to 20th	Day	10% 19% 7% 18% 8% 5% 4 3 4 5% 17%	4650
	21st to end	Day	8% 15% 7% 16% 9% 6% 4 3 5% 5% 20%	5537
February	1st to 10th	Day	11% 16% 6% 13% 6% 6% 7% 4 5% 5% 21%	1890
	11th to 20th	Day	11% 16% 6% 11% 6% 6% 5% 4 5% 7% 24%	1843
	21st to end	Day	16% 15% 5% 10% 6% 5% 4 4 5% 6% 23%	1652
March	1st to 10th	Day	20% 13% 5% 10% 6% 4 4 3 5% 6% 25%	4764
	11th to 20th	Day	13% 12% 5% 10% 6% 5% 5% 4 5% 7% 28%	5090
	21st to end	Day	16% 12% 4 8% 5% 5% 3 2 4 5% 37%	5762
April	1st to 10th	Day	21% 13% 3 7% 4 4 5% 3 4 6% 30%	2520
	11th to 20th	Day	22% 10% 3 6% 4 3 4 3 5% 4 34%	2494
	21st to end	Day	21% 10% 3 7% 5% 4 4 4 4 5% 33%	2725
May	1st to 10th	Day	17% 9% 3 8% 5% 6% 5% 4 6% 8% 30%	8229
	11th to 20th	Day	16% 8% 3 7% 5% 4 4 4 5% 7% 35%	8221
	21st to end	Day	18% 9% 3 7% 5% 4 4 3 4 6% 37%	9060
June	1st to 10th	Day	19% 8% 3 8% 5% 5% 4 4 6% 6% 32%	2940
	11th to 20th	Day	15% 6% 2 6% 4 5% 6% 4 6% 7% 39%	2940
	21st to end	Day	16% 7% 3 6% 6% 5% 5% 4 6% 8% 33%	2940
July	1st to 10th	Day	13% 6% 3 7% 5% 5% 6% 5% 7% 8% 34%	6360
	11th to 20th	Day	10% 4 2 6% 5% 4 5% 4 6% 8% 44%	6360
	21st to end	Day	8% 4 2 6% 4 4 4 4 7% 10% 47%	6926
August	1st to 10th	Day	12% 5% 3 8% 6% 6% 7% 5% 6% 8% 35%	4369
	11th to 20th	Day	16% 7% 2 6% 5% 4 5% 4 6% 8% 38%	4174
	21st to end	Day	9% 5% 2 6% 5% 5% 5% 5% 6% 10% 42%	4388
September	1st to 10th	Day	13% 6% 3 6% 4 4 5% 4 7% 7% 41%	2400
	11th to 20th	Day	12% 5% 2 7% 5% 5% 4 4 5% 6% 46%	2400
	21st to end	Day	18% 7% 2 7% 6% 4 4 3 5% 7% 36%	2100
October	1st to 10th	Day	19% 8% 2 7% 5% 5% 4 4 5% 6% 36%	2000
	11th to 20th	Day	22% 11% 4 8% 7% 5% 4 3 5% 6% 26%	2000
	21st to end	Day	26% 12% 3 9% 6% 5% 5% 3 5% 5% 23%	2100
November	1st to 10th	Day	16% 11% 4 7% 5% 5% 6% 4 6% 6% 31%	1751
	11th to 20th	Day	17% 15% 4 12% 6% 5% 5% 3 5% 5% 24%	1680
	21st to end	Day	25% 16% 6% 9% 6% 5% 5% 3 4 5% 16%	1680
December	1st to 10th	Day	18% 21% 5% 11% 6% 7% 6% 4 4 4 14%	2680
	11th to 20th	Day	16% 17% 7% 14% 6% 5% 4 3 3 4 22%	3066
	21st to end	Day	21% 18% 5% 15% 4 4 4 3 3 3 18%	4048
January	1st to 10th	Night	11% 19% 9% 17% 7% 5% 5% 3 4 4 16%	8234
	11th to 20th	Night	11% 16% 7% 17% 8% 6% 6% 4 4 4 18%	8235
	21st to end	Night	8% 16% 8% 14% 8% 7% 5% 4 5% 5% 20%	8640
February	1st to 10th	Night	12% 14% 6% 12% 7% 5% 6% 5% 4 6% 23%	2730
	11th to 20th	Night	12% 15% 5% 13% 6% 5% 5% 3 5% 5% 25%	2663
	21st to end	Night	14% 15% 5% 11% 7% 5% 4 4 5% 5% 25%	2153
March	1st to 10th	Night	18% 16% 4 10% 5% 4 4 3 4 4 28%	5280
	11th to 20th	Night	12% 13% 4 9% 6% 5% 6% 5% 7% 8% 26%	5089
	21st to end	Night	16% 11% 4 10% 5% 4 4 3 5% 6% 31%	5412
April	1st to 10th	Night	19% 12% 4 9% 5% 4 4 3 4 5% 30%	2100
	11th to 20th	Night	20% 11% 3 7% 4 3 4 3 5% 5% 35%	2075
	21st to end	Night	21% 10% 3 7% 5% 5% 4 3 4 6% 33%	1913
May	1st to 10th	Night	20% 8% 3 8% 5% 4 5% 4 6% 7% 31%	4666
	11th to 20th	Night	15% 7% 2 7% 4 5% 5% 4 5% 6% 39%	4639
	21st to end	Night	19% 6% 2 6% 5% 5% 5% 4 5% 6% 37%	5114
June	1st to 10th	Night	16% 7% 3 8% 5% 4 4 3 6% 7% 36%	1680
	11th to 20th	Night	15% 6% 2 5% 4 5% 4 5% 6% 7% 42%	1680
	21st to end	Night	17% 8% 2 5% 5% 4 5% 4 6% 8% 36%	1680
July	1st to 10th	Night	13% 6% 3 8% 5% 5% 5% 4 7% 7% 36%	3600
	11th to 20th	Night	12% 5% 2 6% 5% 4 4 4 6% 8% 44%	3600
	21st to end	Night	8% 6% 2 6% 4 4 4 4 6% 8% 49%	3926
August	1st to 10th	Night	12% 5% 2 6% 3 4 5% 4 6% 8% 44%	2777
	11th to 20th	Night	16% 6% 2 6% 3 4 4 3 7% 7% 43%	2875
	21st to end	Night	13% 6% 2 6% 4 4 5% 4 6% 8% 42%	3477
September	1st to 10th	Night	11% 6% 3 7% 5% 4 4 3 4 8% 45%	2000
	11th to 20th	Night	14% 6% 2 6% 3 3 4 3 5% 6% 49%	2000
	21st to end	Night	18% 7% 2 6% 5% 4 4 3 5% 6% 41%	2297
October	1st to 10th	Night	20% 7% 2 6% 4 4 3 3 4 7% 40%	2400
	11th to 20th	Night	21% 11% 3 7% 6% 5% 5% 3 5% 5% 30%	2400
	21st to end	Night	23% 13% 4 7% 6% 5% 4 3 4 6% 26%	2740
November	1st to 10th	Night	19% 12% 3 8% 5% 5% 5% 3 4 6% 31%	2764
	11th to 20th	Night	17% 13% 6% 9% 6% 4 4 4 5% 5% 26%	2940
	21st to end	Night	22% 16% 5% 11% 5% 4 5% 3 4 5% 19%	2940
December	1st to 10th	Night	18% 20% 6% 12% 6% 5% 5% 4 5% 5% 13%	4720
	11th to 20th	Night	19% 16% 5% 12% 6% 4 4 3 4 5% 22%	5348
	21st to end	Night	24% 18% 4 13% 5% 4 4 3 3 4 17%	7150

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	66% 6% 10% 13% 5%	4662
	11th to 20th	Day	69% 5% 8% 9% 8%	4680
	21st to end	Day	66% 5% 9% 13% 8% 1	5537
February	1st to 10th	Day	64% 5% 10% 15% 5% 1	1890
	11th to 20th	Day	59% 7% 12% 13% 8% 1	1852
	21st to end	Day	61% 6% 8% 14% 10% 1	1652
March	1st to 10th	Day	59% 4 10% 12% 12% 2	4767
	11th to 20th	Day	53% 7% 16% 15% 8% 1	5090
	21st to end	Day	50% 5% 8% 20% 15% 3	5762
April	1st to 10th	Day	55% 5% 8% 18% 11% 2	2520
	11th to 20th	Day	53% 4 8% 20% 13% 2	2494
	21st to end	Day	53% 6% 7% 16% 15% 3	2725
May	1st to 10th	Day	48% 8% 10% 21% 9% 4	8241
	11th to 20th	Day	45% 7% 12% 24% 11% 1	8225
	21st to end	Day	48% 6% 10% 21% 14% 2	9061
June	1st to 10th	Day	51% 7% 10% 20% 12% 1	2940
	11th to 20th	Day	42% 8% 12% 24% 13% 2	2940
	21st to end	Day	47% 8% 13% 20% 11% 1	2940
July	1st to 10th	Day	43% 9% 13% 26% 8%	6290
	11th to 20th	Day	35% 8% 14% 32% 11%	6285
	21st to end	Day	31% 7% 17% 35% 10%	6728
August	1st to 10th	Day	44% 8% 15% 23% 9%	4355
	11th to 20th	Day	42% 7% 18% 25% 7%	4213
	21st to end	Day	35% 8% 15% 30% 10% 1	4388
September	1st to 10th	Day	39% 8% 17% 25% 12%	2400
	11th to 20th	Day	38% 8% 12% 31% 11% 1	2400
	21st to end	Day	48% 7% 14% 22% 10%	2100
October	1st to 10th	Day	50% 7% 10% 26% 6%	3260
	11th to 20th	Day	52% 7% 13% 21% 6%	3240
	21st to end	Day	57% 7% 17% 14% 4 1	3377
November	1st to 10th	Day	51% 8% 14% 20% 6%	1751
	11th to 20th	Day	61% 7% 12% 13% 5% 1	1680
	21st to end	Day	70% 7% 10% 8% 5%	1680
December	1st to 10th	Day	73% 7% 9% 9% 2	2680
	11th to 20th	Day	67% 5% 6% 14% 8%	3066
	21st to end	Day	71% 5% 7% 13% 4	4048
January	1st to 10th	Night	71% 6% 9% 11% 3	8234
	11th to 20th	Night	67% 7% 9% 10% 6%	8280
	21st to end	Night	65% 5% 8% 11% 11%	8640
February	1st to 10th	Night	61% 7% 11% 14% 6% 1	2730
	11th to 20th	Night	60% 5% 11% 18% 6% 1	2665
	21st to end	Night	59% 6% 9% 18% 7% 1	2153
March	1st to 10th	Night	58% 5% 10% 13% 10% 3	5290
	11th to 20th	Night	53% 8% 17% 14% 8% 1	5090
	21st to end	Night	51% 6% 9% 19% 12% 2	5412
April	1st to 10th	Night	55% 6% 9% 17% 11% 2	2100
	11th to 20th	Night	51% 5% 8% 22% 12% 2	2075
	21st to end	Night	52% 5% 7% 18% 15% 2	1913
May	1st to 10th	Night	49% 8% 10% 21% 10% 3	4672
	11th to 20th	Night	42% 8% 13% 21% 13% 3	4640
	21st to end	Night	46% 8% 11% 21% 13% 1	5115
June	1st to 10th	Night	45% 8% 12% 21% 12% 1	1680
	11th to 20th	Night	37% 9% 12% 25% 15% 2	1680
	21st to end	Night	44% 9% 14% 20% 12% 1	1680
July	1st to 10th	Night	42% 9% 15% 22% 11% 1	3560
	11th to 20th	Night	35% 7% 15% 31% 12%	3552
	21st to end	Night	31% 7% 13% 37% 12%	3809
August	1st to 10th	Night	35% 8% 15% 28% 13%	2767
	11th to 20th	Night	38% 8% 16% 28% 10%	2902
	21st to end	Night	37% 8% 17% 26% 11% 2	3477
September	1st to 10th	Night	37% 7% 13% 30% 13%	2000
	11th to 20th	Night	35% 6% 16% 32% 11%	2000
	21st to end	Night	43% 8% 14% 26% 10%	2297
October	1st to 10th	Night	40% 7% 13% 29% 11%	3920
	11th to 20th	Night	49% 6% 16% 20% 8%	3899
	21st to end	Night	52% 9% 17% 17% 6%	4413
November	1st to 10th	Night	53% 7% 14% 18% 7%	2764
	11th to 20th	Night	58% 8% 13% 14% 6% 1	2940
	21st to end	Night	67% 7% 11% 12% 2	2940
December	1st to 10th	Night	70% 7% 11% 9% 2	4720
	11th to 20th	Night	64% 5% 9% 11% 10%	5348
	21st to end	Night	71% 5% 6% 11% 7%	7150

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% 14% 36% 24% 5%	220
	11th to 20th	Day	27% 15% 31% 20% 4 2	220
	21st to end	Day	21% 14% 34% 22% 9% 1	317
February	1st to 10th	Day	25% 19% 34% 15% 5% 1	330
	11th to 20th	Day	22% 22% 39% 15% 1	330
	21st to end	Day	28% 17% 30% 22% 3	368
March	1st to 10th	Day	25% 16% 35% 21% 3 1	540
	11th to 20th	Day	26% 16% 30% 22% 5% 1	540
	21st to end	Day	29% 16% 30% 18% 6% 1	594
April	1st to 10th	Day	29% 18% 30% 14% 8% 1	540
	11th to 20th	Day	32% 16% 23% 16% 10% 3	532
	21st to end	Day	27% 14% 33% 16% 7% 2	540
May	1st to 10th	Day	24% 12% 30% 23% 8% 3	543
	11th to 20th	Day	20% 15% 29% 22% 11% 3	567
	21st to end	Day	19% 13% 33% 21% 11% 3	617
June	1st to 10th	Day	24% 10% 32% 21% 12% 2	570
	11th to 20th	Day	17% 11% 29% 26% 13% 5%	570
	21st to end	Day	18% 11% 32% 23% 12% 4	570
July	1st to 10th	Day	11% 6% 26% 38% 14% 4	525
	11th to 20th	Day	14% 7% 27% 32% 16% 4	524
	21st to end	Day	10% 9% 30% 29% 17% 5%	576
August	1st to 10th	Day	12% 7% 25% 32% 18% 7%	526
	11th to 20th	Day	15% 5% 22% 29% 22% 8%	519
	21st to end	Day	15% 9% 26% 24% 19% 7%	583
September	1st to 10th	Day	15% 7% 28% 23% 19% 8%	530
	11th to 20th	Day	13% 7% 23% 23% 21% 14%	530
	21st to end	Day	16% 11% 28% 22% 16% 6%	530
October	1st to 10th	Day	23% 13% 23% 20% 17% 4	530
	11th to 20th	Day	25% 18% 30% 17% 8% 2	530
	21st to end	Day	29% 15% 24% 23% 7% 1	528
November	1st to 10th	Day	26% 17% 28% 20% 9%	325
	11th to 20th	Day	25% 15% 38% 13% 7% 2	220
	21st to end	Day	34% 20% 30% 12% 3 2	220
December	1st to 10th	Day	27% 13% 36% 17% 6%	220
	11th to 20th	Day	28% 17% 34% 15% 5% 2	220
	21st to end	Day	32% 15% 30% 15% 6% 2	242
January	1st to 10th	Night	27% 11% 33% 24% 5%	840
	11th to 20th	Night	28% 12% 26% 26% 8% 1	840
	21st to end	Night	19% 10% 31% 30% 9% 1	924
February	1st to 10th	Night	20% 12% 35% 27% 6%	840
	11th to 20th	Night	22% 13% 33% 26% 6%	823
	21st to end	Night	21% 16% 30% 27% 6%	692
March	1st to 10th	Night	22% 15% 31% 27% 5%	840
	11th to 20th	Night	22% 16% 31% 25% 6%	840
	21st to end	Night	21% 13% 31% 26% 9%	924
April	1st to 10th	Night	28% 13% 27% 26% 6%	840
	11th to 20th	Night	26% 12% 28% 26% 9%	831
	21st to end	Night	25% 10% 26% 27% 11% 1	653
May	1st to 10th	Night	22% 7% 27% 33% 11% 1	426
	11th to 20th	Night	21% 9% 28% 32% 9%	414
	21st to end	Night	17% 5% 33% 33% 12%	455
June	1st to 10th	Night	17% 5% 30% 40% 8% 1	420
	11th to 20th	Night	16% 8% 25% 34% 17% 1	420
	21st to end	Night	20% 5% 21% 38% 15%	420
July	1st to 10th	Night	9% 5% 26% 41% 17% 1	390
	11th to 20th	Night	11% 4 22% 43% 19% 1	388
	21st to end	Night	9% 4 22% 44% 20% 1	438
August	1st to 10th	Night	10% 3 19% 38% 29% 1	511
	11th to 20th	Night	12% 3 15% 37% 29% 3	594
	21st to end	Night	14% 5% 24% 34% 20% 3	810
September	1st to 10th	Night	13% 5% 27% 31% 22% 2	800
	11th to 20th	Night	17% 5% 19% 30% 26% 4	800
	21st to end	Night	22% 7% 21% 29% 20% 2	800
October	1st to 10th	Night	22% 7% 28% 27% 15% 2	800
	11th to 20th	Night	29% 8% 28% 24% 10% 1	800
	21st to end	Night	29% 11% 26% 28% 6%	880
November	1st to 10th	Night	25% 13% 24% 28% 9% 1	820
	11th to 20th	Night	25% 15% 32% 20% 9% 1	840
	21st to end	Night	32% 15% 24% 23% 6%	840
December	1st to 10th	Night	31% 15% 30% 19% 6%	840
	11th to 20th	Night	26% 12% 31% 24% 6%	840
	21st to end	Night	34% 13% 25% 23% 6%	924

Page generated at 2026-06-28 02:10:47. Version ac07

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