Ottawa
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Ottawa clear sky chart from 2005-11-06 to 2024-11-06.

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	17% 9% 3 8% 5% 5% 5% 4 6% 7% 33%	101587
	Night	18% 11% 4 8% 5% 4 4 3 5% 6% 31%	97478
Transparency	Day	48% 8% 13% 20% 9% 1	105070
	Night	51% 8% 12% 19% 9% 1	102084
Seeing	Day	21% 15% 30% 21% 10% 3	14485
	Night	22% 12% 30% 26% 9% 1	23543

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	16% 16% 5% 12% 6% 5% 5% 4 5% 4 21%	2517
	11th to 20th	Day	14% 12% 6% 12% 8% 7% 5% 3 5% 5% 23%	2520
	21st to end	Day	14% 17% 6% 11% 7% 7% 5% 4 6% 5% 18%	2876
February	1st to 10th	Day	13% 15% 5% 11% 7% 6% 5% 4 5% 6% 25%	1710
	11th to 20th	Day	13% 14% 5% 10% 6% 5% 4 4 6% 5% 29%	1672
	21st to end	Day	18% 13% 3 9% 6% 5% 6% 4 6% 5% 26%	1570
March	1st to 10th	Day	20% 13% 4 9% 5% 5% 4 4 5% 5% 26%	3116
	11th to 20th	Day	12% 14% 5% 11% 6% 5% 5% 3 5% 5% 28%	3470
	21st to end	Day	14% 7% 3 7% 6% 4 4 4 6% 6% 40%	4033
April	1st to 10th	Day	22% 10% 3 7% 5% 3 4 3 5% 5% 33%	2280
	11th to 20th	Day	21% 9% 3 6% 4 4 4 3 4 5% 37%	2254
	21st to end	Day	23% 9% 3 8% 6% 5% 4 2 5% 4 31%	2413
May	1st to 10th	Day	20% 8% 2 7% 4 5% 4 4 6% 7% 30%	4426
	11th to 20th	Day	17% 9% 3 8% 5% 4 5% 4 5% 7% 33%	4398
	21st to end	Day	15% 7% 2 7% 5% 5% 5% 4 6% 7% 37%	4837
June	1st to 10th	Day	21% 8% 3 7% 5% 5% 4 4 5% 7% 30%	2660
	11th to 20th	Day	13% 6% 2 6% 5% 5% 5% 4 6% 9% 37%	2660
	21st to end	Day	19% 7% 2 7% 5% 4 5% 5% 7% 8% 31%	2660
July	1st to 10th	Day	12% 6% 2 7% 5% 5% 5% 5% 7% 10% 35%	4440
	11th to 20th	Day	13% 5% 2 6% 4 5% 5% 4 7% 8% 40%	4440
	21st to end	Day	11% 5% 2 5% 4 5% 5% 4 7% 8% 44%	4814
August	1st to 10th	Day	14% 6% 3 8% 5% 4 6% 4 6% 8% 36%	4369
	11th to 20th	Day	15% 7% 2 6% 4 4 5% 4 7% 9% 37%	3987
	21st to end	Day	14% 5% 3 6% 4 5% 4 4 6% 9% 40%	4180
September	1st to 10th	Day	13% 5% 2 6% 5% 3 5% 5% 6% 8% 43%	2280
	11th to 20th	Day	12% 5% 2 5% 4 4 4 4 6% 7% 47%	2276
	21st to end	Day	17% 6% 2 6% 4 4 3 4 5% 8% 40%	2033
October	1st to 10th	Day	20% 9% 3 6% 4 4 4 3 6% 7% 35%	1900
	11th to 20th	Day	21% 9% 3 8% 5% 5% 5% 4 6% 6% 29%	1900
	21st to end	Day	25% 10% 3 7% 5% 4 4 4 4 6% 28%	1931
November	1st to 10th	Day	16% 9% 3 6% 4 4 5% 5% 6% 7% 34%	1717
	11th to 20th	Day	19% 13% 3 8% 4 5% 4 4 6% 6% 27%	1530
	21st to end	Day	21% 14% 4 9% 6% 6% 6% 4 5% 5% 21%	1520
December	1st to 10th	Day	22% 16% 5% 10% 7% 4 4 4 6% 6% 17%	1520
	11th to 20th	Day	21% 14% 4 9% 6% 5% 4 3 4 5% 25%	1906
	21st to end	Day	29% 17% 5% 10% 5% 3 3 2 3 3 19%	2772
January	1st to 10th	Night	17% 18% 6% 13% 6% 4 4 3 4 5% 21%	4429
	11th to 20th	Night	13% 14% 5% 13% 8% 6% 6% 4 5% 5% 22%	4440
	21st to end	Night	16% 21% 6% 11% 5% 5% 4 3 4 5% 20%	4779
February	1st to 10th	Night	14% 14% 5% 12% 6% 6% 5% 4 5% 5% 24%	2470
	11th to 20th	Night	13% 13% 5% 11% 6% 5% 4 3 4 5% 29%	2394
	21st to end	Night	16% 13% 4 9% 6% 4 5% 3 5% 6% 29%	1884
March	1st to 10th	Night	21% 12% 4 9% 5% 4 4 3 4 4 31%	3724
	11th to 20th	Night	17% 16% 5% 10% 6% 4 3 3 5% 5% 26%	3484
	21st to end	Night	16% 9% 3 7% 4 3 4 3 5% 6% 40%	3599
April	1st to 10th	Night	21% 11% 3 7% 4 4 4 4 5% 6% 33%	1900
	11th to 20th	Night	19% 9% 3 7% 5% 4 4 4 4 6% 36%	1875
	21st to end	Night	21% 8% 3 7% 5% 4 4 3 4 7% 34%	1780
May	1st to 10th	Night	20% 8% 3 8% 5% 4 5% 5% 6% 7% 28%	2514
	11th to 20th	Night	20% 8% 3 7% 4 4 4 4 5% 7% 34%	2495
	21st to end	Night	14% 8% 2 7% 5% 4 5% 4 6% 7% 38%	2738
June	1st to 10th	Night	16% 6% 2 7% 6% 5% 6% 5% 7% 7% 34%	1520
	11th to 20th	Night	15% 6% 2 6% 4 4 4 4 7% 7% 41%	1520
	21st to end	Night	18% 7% 2 7% 4 4 4 4 6% 7% 35%	1520
July	1st to 10th	Night	13% 7% 3 8% 6% 6% 6% 5% 6% 7% 34%	2520
	11th to 20th	Night	13% 6% 2 7% 4 5% 4 5% 6% 7% 41%	2520
	21st to end	Night	10% 6% 3 6% 5% 4 5% 4 6% 7% 43%	2739
August	1st to 10th	Night	12% 7% 3 8% 4 5% 5% 4 5% 9% 38%	2558
	11th to 20th	Night	14% 6% 2 7% 4 4 5% 4 6% 7% 41%	2808
	21st to end	Night	12% 6% 3 7% 5% 5% 4 4 6% 7% 41%	3476
September	1st to 10th	Night	12% 4 2 6% 4 5% 4 4 5% 6% 47%	1900
	11th to 20th	Night	14% 5% 1 6% 4 3 4 3 5% 6% 50%	1903
	21st to end	Night	17% 6% 2 7% 4 3 4 2 4 6% 44%	2143
October	1st to 10th	Night	18% 8% 2 6% 4 4 4 3 5% 6% 39%	2280
	11th to 20th	Night	20% 8% 3 7% 6% 5% 4 3 5% 6% 32%	2280
	21st to end	Night	22% 9% 3 7% 5% 5% 4 4 4 7% 28%	2666
November	1st to 10th	Night	20% 10% 4 6% 5% 4 4 4 5% 6% 34%	2483
	11th to 20th	Night	19% 11% 3 9% 5% 5% 5% 4 5% 6% 30%	2645
	21st to end	Night	22% 13% 4 9% 6% 4 4 3 5% 6% 24%	2660
December	1st to 10th	Night	21% 17% 4 10% 7% 5% 5% 4 5% 5% 18%	2660
	11th to 20th	Night	23% 15% 4 9% 5% 3 3 3 4 5% 27%	3288
	21st to end	Night	31% 17% 4 8% 4 4 4 3 3 3 18%	4884

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% 14% 11% 9% 5% 1	2518
	11th to 20th	Day	62% 8% 12% 12% 6%	2520
	21st to end	Day	66% 9% 11% 9% 5%	2876
February	1st to 10th	Day	60% 6% 11% 17% 4 2	1710
	11th to 20th	Day	56% 7% 11% 16% 8% 1	1681
	21st to end	Day	58% 7% 11% 13% 9% 2	1570
March	1st to 10th	Day	58% 8% 10% 16% 8% 1	3119
	11th to 20th	Day	53% 10% 13% 14% 9% 1	3470
	21st to end	Day	40% 7% 10% 24% 16% 3	4033
April	1st to 10th	Day	52% 6% 8% 19% 11% 3	2280
	11th to 20th	Day	50% 5% 8% 22% 14% 2	2254
	21st to end	Day	54% 6% 9% 14% 14% 4	2413
May	1st to 10th	Day	48% 9% 11% 20% 10% 2	4440
	11th to 20th	Day	47% 11% 13% 18% 9% 2	4402
	21st to end	Day	42% 10% 12% 21% 14% 2	4837
June	1st to 10th	Day	52% 9% 10% 18% 11% 1	2660
	11th to 20th	Day	41% 10% 12% 23% 12% 2	2660
	21st to end	Day	48% 10% 13% 19% 10% 1	2660
July	1st to 10th	Day	41% 8% 15% 23% 12%	4370
	11th to 20th	Day	38% 8% 15% 30% 9%	4365
	21st to end	Day	35% 9% 14% 31% 11%	4661
August	1st to 10th	Day	45% 7% 16% 23% 9%	4355
	11th to 20th	Day	41% 8% 16% 27% 8%	4026
	21st to end	Day	39% 7% 17% 25% 11% 1	4180
September	1st to 10th	Day	38% 9% 15% 27% 11%	2280
	11th to 20th	Day	34% 8% 14% 30% 13% 1	2276
	21st to end	Day	42% 8% 15% 25% 10%	2033
October	1st to 10th	Day	47% 6% 12% 29% 6%	3160
	11th to 20th	Day	46% 7% 16% 24% 7%	3140
	21st to end	Day	49% 6% 18% 20% 7%	3156
November	1st to 10th	Day	46% 9% 16% 21% 6% 1	1717
	11th to 20th	Day	56% 7% 14% 15% 8% 1	1530
	21st to end	Day	64% 8% 11% 10% 6% 1	1520
December	1st to 10th	Day	68% 7% 13% 9% 3 1	1520
	11th to 20th	Day	61% 8% 14% 13% 4	1906
	21st to end	Day	70% 6% 7% 14% 3	2772
January	1st to 10th	Night	64% 9% 14% 10% 3	4429
	11th to 20th	Night	59% 11% 14% 11% 5%	4440
	21st to end	Night	65% 8% 10% 10% 6% 1	4779
February	1st to 10th	Night	61% 7% 11% 15% 6% 1	2470
	11th to 20th	Night	57% 7% 10% 19% 7% 1	2396
	21st to end	Night	55% 6% 10% 18% 10% 1	1884
March	1st to 10th	Night	54% 7% 10% 18% 9% 2	3734
	11th to 20th	Night	57% 8% 13% 14% 7% 1	3485
	21st to end	Night	42% 7% 8% 23% 16% 3	3599
April	1st to 10th	Night	52% 7% 9% 17% 13% 2	1900
	11th to 20th	Night	49% 7% 8% 20% 15% 1	1875
	21st to end	Night	51% 5% 9% 17% 14% 4	1780
May	1st to 10th	Night	48% 12% 11% 17% 9% 3	2520
	11th to 20th	Night	45% 11% 12% 19% 11% 2	2496
	21st to end	Night	39% 11% 13% 18% 17% 1	2739
June	1st to 10th	Night	45% 9% 13% 22% 9% 1	1520
	11th to 20th	Night	39% 9% 11% 23% 16% 2	1520
	21st to end	Night	46% 9% 13% 18% 13% 1	1520
July	1st to 10th	Night	46% 8% 14% 18% 13% 1	2480
	11th to 20th	Night	39% 8% 14% 31% 8%	2472
	21st to end	Night	38% 8% 15% 25% 15%	2651
August	1st to 10th	Night	42% 8% 15% 23% 11%	2548
	11th to 20th	Night	41% 7% 15% 30% 7%	2835
	21st to end	Night	40% 8% 15% 24% 12% 2	3476
September	1st to 10th	Night	36% 7% 12% 29% 15% 1	1900
	11th to 20th	Night	33% 9% 14% 33% 10% 1	1903
	21st to end	Night	41% 6% 12% 29% 11%	2143
October	1st to 10th	Night	40% 6% 14% 27% 12%	3800
	11th to 20th	Night	46% 6% 15% 25% 9%	3779
	21st to end	Night	48% 7% 18% 19% 9%	4391
November	1st to 10th	Night	51% 6% 15% 19% 8%	2483
	11th to 20th	Night	55% 6% 12% 17% 8% 1	2645
	21st to end	Night	60% 8% 13% 15% 5%	2660
December	1st to 10th	Night	67% 7% 11% 11% 3	2660
	11th to 20th	Night	61% 6% 10% 15% 7% 1	3288
	21st to end	Night	71% 6% 7% 12% 3	4884

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	23% 20% 29% 23% 4 1	180
	11th to 20th	Day	27% 15% 38% 15% 4 1	180
	21st to end	Day	23% 16% 34% 22% 6%	229
February	1st to 10th	Day	30% 20% 35% 13% 1	270
	11th to 20th	Day	25% 28% 36% 10% 1	279
	21st to end	Day	28% 21% 32% 16% 3	382
March	1st to 10th	Day	25% 16% 36% 18% 5%	460
	11th to 20th	Day	26% 17% 35% 18% 3 1	460
	21st to end	Day	28% 22% 26% 15% 8% 1	506
April	1st to 10th	Day	27% 21% 30% 16% 5% 1	460
	11th to 20th	Day	32% 19% 22% 16% 10% 1	452
	21st to end	Day	30% 20% 30% 12% 7% 2	460
May	1st to 10th	Day	24% 14% 33% 21% 8% 2	463
	11th to 20th	Day	17% 17% 33% 19% 11% 2	487
	21st to end	Day	18% 16% 31% 23% 12% 1	529
June	1st to 10th	Day	23% 12% 31% 23% 9% 1	490
	11th to 20th	Day	15% 14% 31% 26% 11% 3	490
	21st to end	Day	22% 13% 31% 22% 11% 2	490
July	1st to 10th	Day	12% 8% 27% 36% 13% 4	485
	11th to 20th	Day	11% 9% 33% 28% 16% 3	484
	21st to end	Day	12% 6% 31% 31% 14% 5%	532
August	1st to 10th	Day	14% 6% 27% 32% 17% 4	486
	11th to 20th	Day	13% 8% 23% 29% 19% 8%	479
	21st to end	Day	13% 10% 29% 26% 15% 7%	539
September	1st to 10th	Day	16% 10% 30% 20% 15% 9%	490
	11th to 20th	Day	11% 9% 25% 22% 21% 12%	490
	21st to end	Day	18% 12% 28% 23% 14% 5%	490
October	1st to 10th	Day	23% 14% 25% 21% 11% 5%	490
	11th to 20th	Day	23% 19% 31% 18% 8% 1	490
	21st to end	Day	31% 13% 29% 22% 5%	454
November	1st to 10th	Day	23% 17% 30% 20% 8% 1	381
	11th to 20th	Day	26% 21% 34% 12% 5% 1	190
	21st to end	Day	28% 19% 32% 16% 4 1	180
December	1st to 10th	Day	29% 16% 34% 18% 2	180
	11th to 20th	Day	27% 24% 32% 15% 1 1	180
	21st to end	Day	32% 21% 33% 12% 2 1	198
January	1st to 10th	Night	25% 15% 35% 21% 3	760
	11th to 20th	Night	26% 17% 30% 21% 6%	760
	21st to end	Night	19% 11% 36% 28% 5%	836
February	1st to 10th	Night	24% 13% 36% 24% 3	760
	11th to 20th	Night	20% 17% 40% 19% 4	743
	21st to end	Night	25% 16% 30% 26% 3	628
March	1st to 10th	Night	23% 15% 36% 23% 4	760
	11th to 20th	Night	22% 19% 33% 20% 5%	760
	21st to end	Night	23% 16% 29% 24% 8%	836
April	1st to 10th	Night	26% 14% 30% 24% 5%	760
	11th to 20th	Night	24% 15% 31% 22% 7%	751
	21st to end	Night	25% 14% 29% 24% 7% 1	640
May	1st to 10th	Night	22% 8% 32% 28% 9% 2	380
	11th to 20th	Night	22% 10% 28% 32% 9%	374
	21st to end	Night	14% 7% 40% 27% 11%	411
June	1st to 10th	Night	18% 4 31% 37% 10%	380
	11th to 20th	Night	14% 8% 30% 34% 12% 2	380
	21st to end	Night	21% 4 31% 30% 14% 1	380
July	1st to 10th	Night	11% 5% 28% 42% 15%	370
	11th to 20th	Night	11% 5% 25% 43% 15% 1	368
	21st to end	Night	9% 3 28% 42% 16% 2	416
August	1st to 10th	Night	13% 4 22% 40% 21% 1	404
	11th to 20th	Night	13% 4 19% 37% 24% 2	574
	21st to end	Night	12% 7% 25% 36% 18% 2	836
September	1st to 10th	Night	13% 6% 29% 33% 18% 1	760
	11th to 20th	Night	16% 6% 20% 31% 23% 3	760
	21st to end	Night	19% 10% 24% 26% 20% 2	760
October	1st to 10th	Night	21% 9% 28% 25% 16% 1	760
	11th to 20th	Night	24% 12% 29% 25% 8% 1	760
	21st to end	Night	26% 14% 28% 26% 6%	836
November	1st to 10th	Night	25% 13% 28% 24% 8% 1	764
	11th to 20th	Night	24% 16% 34% 16% 9% 1	760
	21st to end	Night	29% 16% 27% 22% 6%	760
December	1st to 10th	Night	31% 14% 30% 21% 3	760
	11th to 20th	Night	28% 16% 31% 20% 5% 1	760
	21st to end	Night	33% 15% 30% 19% 3	836

Page generated at 2024-11-03 13:19:00. Version ac07

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