Rideau Ferry Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Rideau Ferry Observatory clear sky chart from 2005-11-06 to 2024-11-04.

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% 10% 3 8% 5% 4 5% 4 5% 7% 33%	101560
	Night	17% 11% 4 8% 5% 4 4 3 5% 6% 32%	97445
Transparency	Day	50% 4 12% 22% 10% 1	105069
	Night	52% 4 12% 21% 10% 1	102025
Seeing	Day	23% 16% 30% 20% 9% 3	14503
	Night	23% 14% 30% 24% 9% 1	23610

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	15% 17% 6% 10% 6% 6% 4 3 5% 4 25%	2517
	11th to 20th	Day	13% 16% 6% 13% 7% 5% 5% 3 4 5% 22%	2520
	21st to end	Day	17% 18% 6% 13% 7% 5% 5% 3 4 4 17%	2946
February	1st to 10th	Day	16% 15% 4 12% 7% 4 5% 4 5% 5% 23%	1710
	11th to 20th	Day	12% 16% 5% 10% 6% 5% 5% 2 4 5% 28%	1663
	21st to end	Day	20% 14% 4 9% 6% 6% 4 3 6% 5% 23%	1569
March	1st to 10th	Day	20% 14% 4 9% 6% 4 4 3 4 5% 28%	3163
	11th to 20th	Day	12% 16% 4 8% 6% 5% 5% 3 5% 5% 30%	3480
	21st to end	Day	13% 10% 3 7% 5% 4 4 3 4 6% 42%	4000
April	1st to 10th	Day	20% 13% 4 6% 5% 3 4 3 4 6% 32%	2280
	11th to 20th	Day	21% 10% 3 7% 4 4 4 2 4 5% 36%	2254
	21st to end	Day	23% 9% 3 8% 5% 3 4 3 5% 5% 31%	2384
May	1st to 10th	Day	20% 8% 3 8% 5% 4 4 4 5% 6% 32%	4426
	11th to 20th	Day	17% 9% 4 8% 5% 4 5% 3 5% 8% 33%	4398
	21st to end	Day	14% 6% 2 6% 4 5% 5% 4 5% 8% 40%	4837
June	1st to 10th	Day	22% 8% 3 7% 4 5% 5% 4 5% 7% 30%	2660
	11th to 20th	Day	15% 5% 3 6% 5% 5% 5% 4 6% 9% 37%	2660
	21st to end	Day	18% 8% 3 7% 5% 6% 5% 4 5% 7% 32%	2660
July	1st to 10th	Day	12% 6% 2 7% 5% 4 6% 4 7% 9% 37%	4440
	11th to 20th	Day	14% 5% 2 6% 4 4 5% 4 6% 9% 40%	4440
	21st to end	Day	11% 5% 2 6% 4 5% 6% 4 7% 9% 41%	4814
August	1st to 10th	Day	17% 7% 3 7% 5% 4 5% 4 5% 7% 36%	4277
	11th to 20th	Day	18% 6% 3 5% 4 4 4 4 6% 9% 38%	3994
	21st to end	Day	15% 5% 2 6% 5% 4 4 4 6% 8% 40%	4180
September	1st to 10th	Day	14% 5% 2 7% 4 5% 5% 5% 5% 7% 42%	2280
	11th to 20th	Day	12% 5% 2 6% 4 4 4 3 6% 7% 47%	2280
	21st to end	Day	18% 6% 2 7% 5% 4 4 3 5% 6% 40%	2021
October	1st to 10th	Day	20% 8% 3 7% 4 4 3 3 5% 5% 37%	1900
	11th to 20th	Day	21% 10% 3 8% 5% 4 4 4 5% 7% 30%	1900
	21st to end	Day	25% 11% 3 7% 6% 4 3 4 5% 5% 27%	1964
November	1st to 10th	Day	15% 9% 3 7% 6% 5% 6% 4 5% 6% 34%	1698
	11th to 20th	Day	18% 13% 4 9% 6% 4 4 3 5% 5% 29%	1527
	21st to end	Day	21% 16% 4 9% 6% 5% 5% 3 5% 5% 21%	1520
December	1st to 10th	Day	23% 17% 5% 10% 6% 4 4 4 5% 6% 17%	1520
	11th to 20th	Day	21% 15% 5% 10% 5% 4 4 3 4 5% 25%	1906
	21st to end	Day	26% 17% 6% 11% 5% 4 3 2 3 3 20%	2772
January	1st to 10th	Night	17% 15% 7% 11% 6% 5% 4 3 4 5% 21%	4429
	11th to 20th	Night	14% 16% 5% 14% 7% 6% 5% 3 4 5% 20%	4440
	21st to end	Night	19% 18% 6% 11% 7% 6% 4 3 3 4 20%	4692
February	1st to 10th	Night	15% 16% 5% 10% 6% 5% 4 3 6% 6% 22%	2470
	11th to 20th	Night	14% 15% 5% 10% 6% 5% 4 3 4 5% 29%	2403
	21st to end	Night	16% 15% 5% 8% 6% 5% 4 3 5% 6% 29%	1884
March	1st to 10th	Night	21% 12% 4 8% 5% 4 4 3 3 4 32%	3674
	11th to 20th	Night	18% 17% 4 8% 5% 4 4 3 4 6% 26%	3479
	21st to end	Night	15% 10% 3 7% 4 3 3 3 5% 6% 40%	3631
April	1st to 10th	Night	21% 9% 4 7% 4 4 4 3 5% 5% 33%	1900
	11th to 20th	Night	20% 8% 3 7% 5% 4 3 3 4 5% 37%	1875
	21st to end	Night	20% 11% 3 7% 4 4 4 3 5% 6% 33%	1809
May	1st to 10th	Night	22% 9% 3 8% 5% 4 4 5% 5% 6% 29%	2514
	11th to 20th	Night	20% 9% 3 6% 4 4 3 3 5% 6% 37%	2495
	21st to end	Night	14% 7% 3 5% 4 4 4 4 6% 8% 42%	2738
June	1st to 10th	Night	17% 6% 2 7% 5% 5% 6% 4 6% 7% 34%	1520
	11th to 20th	Night	14% 7% 2 6% 4 4 4 4 6% 7% 41%	1520
	21st to end	Night	18% 6% 3 7% 5% 4 5% 5% 6% 8% 35%	1520
July	1st to 10th	Night	11% 7% 3 8% 6% 5% 5% 5% 6% 8% 37%	2520
	11th to 20th	Night	14% 5% 2 5% 4 4 5% 4 6% 7% 44%	2520
	21st to end	Night	11% 5% 2 6% 5% 5% 5% 4 6% 7% 44%	2739
August	1st to 10th	Night	12% 6% 2 7% 4 5% 4 3 6% 7% 43%	2650
	11th to 20th	Night	12% 7% 3 6% 4 5% 4 3 6% 7% 43%	2802
	21st to end	Night	11% 4 2 6% 4 5% 5% 4 6% 9% 43%	3476
September	1st to 10th	Night	12% 6% 2 7% 5% 4 3 3 4 7% 47%	1900
	11th to 20th	Night	14% 5% 2 4 3 3 3 3 5% 7% 52%	1900
	21st to end	Night	17% 6% 2 6% 4 4 3 3 5% 7% 43%	2157
October	1st to 10th	Night	17% 8% 3 7% 4 4 4 3 5% 7% 37%	2280
	11th to 20th	Night	22% 8% 2 7% 5% 4 4 4 5% 7% 33%	2280
	21st to end	Night	23% 10% 3 7% 5% 4 4 3 5% 6% 28%	2633
November	1st to 10th	Night	19% 11% 3 5% 4 4 4 4 4 5% 36%	2453
	11th to 20th	Night	17% 12% 4 7% 5% 4 4 4 5% 5% 32%	2650
	21st to end	Night	21% 14% 4 8% 6% 4 5% 3 5% 7% 24%	2660
December	1st to 10th	Night	20% 19% 5% 11% 6% 4 4 3 5% 4 19%	2660
	11th to 20th	Night	22% 15% 4 9% 5% 4 4 2 4 4 27%	3288
	21st to end	Night	30% 16% 4 11% 5% 4 3 3 4 4 16%	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	63% 2 16% 12% 6% 2	2518
	11th to 20th	Day	66% 3 10% 12% 8% 1	2520
	21st to end	Day	72% 3 9% 10% 5% 1	2946
February	1st to 10th	Day	63% 4 8% 20% 5% 1	1710
	11th to 20th	Day	58% 3 10% 17% 10% 1	1672
	21st to end	Day	64% 3 10% 12% 10% 1	1569
March	1st to 10th	Day	61% 2 9% 18% 9% 1	3166
	11th to 20th	Day	56% 3 12% 16% 10% 2	3480
	21st to end	Day	45% 3 6% 26% 17% 4	4000
April	1st to 10th	Day	54% 4 7% 19% 13% 3	2280
	11th to 20th	Day	52% 2 7% 21% 17% 2	2254
	21st to end	Day	55% 3 8% 16% 14% 4	2384
May	1st to 10th	Day	53% 4 9% 22% 11% 2	4440
	11th to 20th	Day	51% 3 13% 23% 9% 1	4402
	21st to end	Day	42% 4 13% 25% 15% 2	4837
June	1st to 10th	Day	53% 4 9% 20% 12% 1	2660
	11th to 20th	Day	43% 5% 12% 26% 13% 2	2660
	21st to end	Day	50% 5% 13% 20% 11% 1	2660
July	1st to 10th	Day	41% 6% 13% 27% 12% 1	4370
	11th to 20th	Day	38% 6% 15% 32% 9%	4365
	21st to end	Day	38% 6% 13% 31% 11%	4661
August	1st to 10th	Day	47% 4 15% 23% 11% 1	4263
	11th to 20th	Day	42% 5% 15% 28% 10% 1	4033
	21st to end	Day	40% 5% 15% 28% 11%	4180
September	1st to 10th	Day	41% 5% 13% 28% 13% 1	2280
	11th to 20th	Day	36% 5% 12% 31% 16%	2280
	21st to end	Day	45% 5% 13% 26% 11%	2021
October	1st to 10th	Day	44% 4 13% 31% 8%	3160
	11th to 20th	Day	46% 4 15% 26% 9%	3140
	21st to end	Day	49% 5% 16% 23% 7%	3215
November	1st to 10th	Day	50% 4 15% 23% 8% 1	1698
	11th to 20th	Day	56% 4 12% 16% 10% 1	1527
	21st to end	Day	65% 5% 12% 11% 7%	1520
December	1st to 10th	Day	69% 4 12% 11% 4	1520
	11th to 20th	Day	65% 4 13% 13% 4	1906
	21st to end	Day	72% 3 7% 14% 4	2772
January	1st to 10th	Night	66% 3 15% 13% 4	4429
	11th to 20th	Night	68% 3 12% 11% 5%	4440
	21st to end	Night	70% 3 10% 11% 6% 1	4692
February	1st to 10th	Night	63% 4 10% 17% 6% 1	2470
	11th to 20th	Night	58% 3 9% 21% 8%	2405
	21st to end	Night	58% 4 8% 18% 10% 1	1884
March	1st to 10th	Night	57% 2 9% 22% 9% 1	3684
	11th to 20th	Night	60% 3 13% 15% 9% 1	3480
	21st to end	Night	46% 4 5% 24% 17% 3	3631
April	1st to 10th	Night	53% 3 7% 21% 13% 2	1900
	11th to 20th	Night	51% 3 7% 20% 17% 2	1875
	21st to end	Night	53% 4 8% 16% 16% 3	1809
May	1st to 10th	Night	55% 3 9% 20% 10% 3	2520
	11th to 20th	Night	49% 4 11% 24% 11% 2	2496
	21st to end	Night	41% 3 13% 22% 18% 2	2739
June	1st to 10th	Night	47% 6% 13% 22% 12% 1	1520
	11th to 20th	Night	41% 4 12% 23% 18% 2	1520
	21st to end	Night	46% 7% 13% 21% 12% 1	1520
July	1st to 10th	Night	42% 7% 14% 21% 15% 2	2480
	11th to 20th	Night	38% 6% 13% 34% 9%	2472
	21st to end	Night	38% 7% 14% 24% 15% 1	2651
August	1st to 10th	Night	40% 6% 14% 27% 13% 1	2640
	11th to 20th	Night	40% 4 15% 31% 9%	2829
	21st to end	Night	36% 7% 16% 28% 11% 1	3476
September	1st to 10th	Night	37% 6% 11% 31% 14% 1	1900
	11th to 20th	Night	33% 4 14% 35% 12% 1	1900
	21st to end	Night	41% 4 11% 31% 11% 1	2157
October	1st to 10th	Night	41% 5% 11% 30% 12%	3800
	11th to 20th	Night	44% 4 15% 27% 9%	3779
	21st to end	Night	48% 5% 15% 24% 8%	4332
November	1st to 10th	Night	49% 5% 13% 22% 10% 1	2453
	11th to 20th	Night	53% 4 12% 20% 10% 2	2650
	21st to end	Night	61% 5% 11% 17% 5%	2660
December	1st to 10th	Night	69% 4 10% 13% 4	2660
	11th to 20th	Night	62% 3 11% 16% 8% 1	3288
	21st to end	Night	73% 3 9% 13% 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	27% 22% 33% 13% 4 1	180
	11th to 20th	Day	34% 18% 30% 16% 2 1	180
	21st to end	Day	26% 19% 33% 18% 4	249
February	1st to 10th	Day	33% 22% 33% 11% 1	270
	11th to 20th	Day	29% 27% 36% 6% 1	270
	21st to end	Day	34% 20% 34% 10% 2	381
March	1st to 10th	Day	27% 20% 33% 15% 5%	460
	11th to 20th	Day	30% 18% 33% 15% 4	460
	21st to end	Day	31% 22% 28% 11% 7%	506
April	1st to 10th	Day	30% 22% 29% 13% 6%	460
	11th to 20th	Day	33% 19% 23% 15% 8% 3	452
	21st to end	Day	29% 20% 31% 13% 6% 2	460
May	1st to 10th	Day	24% 17% 30% 20% 6% 3	463
	11th to 20th	Day	18% 17% 34% 20% 8% 2	487
	21st to end	Day	19% 14% 32% 24% 9% 2	529
June	1st to 10th	Day	24% 13% 32% 22% 8% 2	490
	11th to 20th	Day	15% 18% 31% 22% 12% 2	490
	21st to end	Day	21% 13% 31% 21% 10% 3	490
July	1st to 10th	Day	13% 8% 31% 31% 14% 3	485
	11th to 20th	Day	14% 12% 31% 25% 14% 4	484
	21st to end	Day	14% 9% 31% 32% 11% 4	532
August	1st to 10th	Day	16% 9% 28% 29% 13% 4	486
	11th to 20th	Day	15% 6% 27% 29% 15% 6%	479
	21st to end	Day	16% 10% 33% 24% 11% 7%	539
September	1st to 10th	Day	14% 11% 32% 24% 12% 7%	490
	11th to 20th	Day	12% 9% 24% 25% 19% 11%	490
	21st to end	Day	20% 11% 26% 25% 14% 3	490
October	1st to 10th	Day	26% 16% 25% 18% 11% 4	490
	11th to 20th	Day	28% 20% 28% 16% 7% 2	490
	21st to end	Day	29% 21% 26% 19% 4	472
November	1st to 10th	Day	26% 18% 29% 18% 8%	374
	11th to 20th	Day	28% 19% 33% 13% 5% 3	187
	21st to end	Day	29% 23% 34% 11% 3	180
December	1st to 10th	Day	30% 24% 30% 14% 2	180
	11th to 20th	Day	34% 24% 29% 9% 3 1	180
	21st to end	Day	35% 18% 32% 12% 3 1	198
January	1st to 10th	Night	29% 19% 31% 18% 3	760
	11th to 20th	Night	30% 17% 29% 19% 4 1	760
	21st to end	Night	20% 16% 34% 24% 5%	836
February	1st to 10th	Night	25% 21% 33% 19% 2	760
	11th to 20th	Night	22% 19% 38% 17% 3	743
	21st to end	Night	25% 19% 33% 19% 4	628
March	1st to 10th	Night	26% 16% 32% 22% 4	760
	11th to 20th	Night	26% 20% 29% 20% 4 1	760
	21st to end	Night	23% 16% 31% 21% 8%	836
April	1st to 10th	Night	28% 15% 31% 23% 3	760
	11th to 20th	Night	26% 20% 29% 18% 7% 1	751
	21st to end	Night	26% 14% 27% 24% 9% 1	669
May	1st to 10th	Night	25% 9% 26% 27% 11% 2	380
	11th to 20th	Night	16% 11% 33% 32% 7%	374
	21st to end	Night	12% 10% 38% 27% 11%	411
June	1st to 10th	Night	15% 9% 28% 37% 10% 1	380
	11th to 20th	Night	16% 10% 29% 31% 13% 1	380
	21st to end	Night	19% 5% 28% 33% 14% 1	380
July	1st to 10th	Night	9% 8% 31% 36% 15% 1	370
	11th to 20th	Night	13% 5% 27% 37% 17% 1	368
	21st to end	Night	11% 5% 29% 41% 13% 1	416
August	1st to 10th	Night	12% 6% 26% 37% 18% 1	457
	11th to 20th	Night	11% 5% 22% 35% 24% 2	568
	21st to end	Night	11% 8% 30% 32% 16% 3	836
September	1st to 10th	Night	14% 7% 32% 30% 16% 1	760
	11th to 20th	Night	16% 7% 21% 28% 23% 5%	760
	21st to end	Night	19% 10% 25% 26% 18% 2	760
October	1st to 10th	Night	22% 13% 26% 22% 15% 2	760
	11th to 20th	Night	26% 12% 30% 23% 8% 1	760
	21st to end	Night	30% 14% 27% 23% 6%	836
November	1st to 10th	Night	28% 13% 29% 21% 8%	755
	11th to 20th	Night	26% 18% 31% 17% 9%	760
	21st to end	Night	29% 17% 28% 19% 6%	760
December	1st to 10th	Night	31% 18% 30% 18% 3	760
	11th to 20th	Night	28% 19% 31% 19% 3 1	760
	21st to end	Night	34% 17% 29% 18% 2	836

Page generated at 2024-11-01 22:47:45. Version ac07

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