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 2024-01-16.

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 7% 6% 3 5% 5% 5% 7% 33%	74760
	Night	18% 10% 4 7% 6% 3 4 4 5% 6% 32%	75026
Transparency	Day	50% 8% 12% 19% 10% 1	74465
	Night	52% 7% 11% 19% 10% 1	74855
Seeing	Day	21% 15% 30% 21% 10% 3	13367
	Night	22% 12% 30% 26% 9% 1	22579

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	17% 16% 6% 11% 6% 3 5% 5% 5% 4 22%	1517
	11th to 20th	Day	19% 15% 5% 8% 8% 4 4 3 4 5% 24%	1480
	21st to end	Day	13% 13% 5% 9% 7% 5% 5% 5% 6% 6% 26%	1646
February	1st to 10th	Day	14% 15% 5% 11% 7% 4 5% 5% 5% 6% 24%	1620
	11th to 20th	Day	14% 14% 6% 8% 6% 3 4 5% 5% 5% 29%	1582
	21st to end	Day	18% 13% 4 9% 7% 4 6% 5% 5% 5% 25%	1480
March	1st to 10th	Day	15% 9% 5% 8% 7% 5% 6% 5% 6% 5% 30%	1797
	11th to 20th	Day	16% 11% 4 8% 6% 4 6% 4 5% 5% 31%	1970
	21st to end	Day	19% 7% 4 6% 5% 3 4 5% 5% 6% 37%	2299
April	1st to 10th	Day	22% 10% 3 6% 5% 2 4 4 5% 6% 33%	2160
	11th to 20th	Day	21% 8% 3 6% 5% 3 4 4 4 5% 38%	2134
	21st to end	Day	23% 9% 3 6% 6% 4 4 3 5% 5% 32%	2286
May	1st to 10th	Day	20% 7% 3 7% 5% 3 4 5% 5% 6% 34%	2520
	11th to 20th	Day	16% 7% 2 6% 6% 3 5% 5% 4 6% 40%	2478
	21st to end	Day	16% 6% 3 6% 6% 4 5% 5% 6% 7% 37%	2725
June	1st to 10th	Day	21% 7% 3 6% 6% 4 4 5% 5% 7% 30%	2520
	11th to 20th	Day	14% 6% 2 5% 6% 4 6% 5% 6% 9% 38%	2520
	21st to end	Day	18% 7% 2 6% 6% 3 6% 6% 7% 8% 31%	2520
July	1st to 10th	Day	12% 5% 3 6% 5% 3 6% 6% 6% 9% 40%	2520
	11th to 20th	Day	11% 6% 3 6% 6% 3 6% 5% 7% 10% 39%	2520
	21st to end	Day	12% 5% 3 6% 5% 4 5% 6% 7% 8% 40%	2744
August	1st to 10th	Day	11% 6% 2 6% 6% 3 5% 6% 7% 8% 40%	2480
	11th to 20th	Day	11% 6% 2 5% 6% 4 6% 6% 6% 9% 39%	2274
	21st to end	Day	13% 5% 3 5% 6% 3 5% 5% 6% 9% 41%	2376
September	1st to 10th	Day	14% 5% 3 5% 5% 2 5% 6% 6% 8% 42%	2160
	11th to 20th	Day	13% 5% 2 4 5% 3 4 5% 6% 7% 46%	2157
	21st to end	Day	17% 6% 3 6% 5% 3 5% 4 5% 8% 39%	1926
October	1st to 10th	Day	20% 8% 3 6% 4 3 5% 4 5% 6% 35%	1800
	11th to 20th	Day	22% 8% 3 7% 6% 3 6% 5% 5% 7% 28%	1800
	21st to end	Day	26% 9% 3 6% 6% 4 4 4 4 6% 28%	1830
November	1st to 10th	Day	16% 8% 4 6% 5% 3 5% 6% 6% 7% 34%	1671
	11th to 20th	Day	20% 11% 4 7% 5% 3 5% 5% 5% 6% 28%	1530
	21st to end	Day	21% 13% 4 8% 8% 4 6% 5% 4 5% 22%	1520
December	1st to 10th	Day	22% 15% 6% 9% 8% 3 5% 5% 6% 6% 17%	1520
	11th to 20th	Day	21% 13% 5% 8% 7% 4 4 5% 4 5% 25%	1906
	21st to end	Day	29% 17% 5% 9% 6% 3 3 3 3 3 19%	2772
January	1st to 10th	Night	18% 17% 6% 12% 7% 4 5% 4 4 5% 19%	2649
	11th to 20th	Night	18% 16% 5% 9% 8% 4 5% 4 4 4 22%	2591
	21st to end	Night	12% 15% 6% 9% 6% 4 4 4 4 7% 29%	2709
February	1st to 10th	Night	15% 13% 6% 12% 7% 5% 6% 4 5% 5% 23%	2340
	11th to 20th	Night	14% 12% 6% 9% 8% 4 4 4 4 5% 29%	2264
	21st to end	Night	17% 12% 5% 8% 6% 3 5% 5% 5% 6% 29%	1776
March	1st to 10th	Night	16% 13% 5% 7% 7% 3 5% 4 5% 5% 29%	2150
	11th to 20th	Night	17% 11% 5% 9% 6% 3 4 4 4 5% 33%	1984
	21st to end	Night	18% 9% 3 6% 6% 3 3 4 4 5% 39%	2057
April	1st to 10th	Night	22% 9% 4 6% 4 3 4 4 4 7% 33%	1800
	11th to 20th	Night	19% 8% 3 6% 6% 3 4 5% 4 6% 36%	1775
	21st to end	Night	21% 8% 3 6% 6% 3 4 4 4 7% 33%	1688
May	1st to 10th	Night	20% 6% 3 6% 5% 3 5% 4 5% 7% 36%	1440
	11th to 20th	Night	18% 7% 3 5% 4 2 4 5% 5% 7% 39%	1415
	21st to end	Night	13% 6% 3 5% 5% 3 4 5% 5% 7% 44%	1550
June	1st to 10th	Night	17% 5% 2 6% 6% 4 6% 6% 7% 8% 34%	1440
	11th to 20th	Night	15% 6% 2 6% 5% 2 4 5% 7% 7% 42%	1440
	21st to end	Night	17% 7% 2 6% 5% 2 5% 5% 6% 8% 35%	1440
July	1st to 10th	Night	11% 3 3 4 5% 4 5% 5% 6% 7% 45%	1440
	11th to 20th	Night	12% 6% 2 5% 4 3 5% 6% 6% 9% 43%	1440
	21st to end	Night	10% 4 3 5% 6% 4 5% 5% 6% 9% 43%	1574
August	1st to 10th	Night	9% 7% 3 5% 5% 3 5% 5% 5% 9% 43%	1456
	11th to 20th	Night	10% 6% 2 6% 5% 2 5% 5% 6% 7% 45%	1607
	21st to end	Night	11% 5% 3 5% 5% 4 5% 5% 6% 7% 44%	1980
September	1st to 10th	Night	12% 4 3 6% 5% 4 5% 5% 5% 6% 46%	1800
	11th to 20th	Night	15% 5% 2 5% 4 2 3 4 5% 7% 49%	1802
	21st to end	Night	17% 5% 3 7% 4 3 4 4 4 6% 44%	2030
October	1st to 10th	Night	19% 7% 3 5% 5% 3 4 5% 5% 6% 38%	2160
	11th to 20th	Night	21% 8% 3 6% 7% 4 5% 4 5% 7% 31%	2160
	21st to end	Night	23% 9% 4 6% 6% 4 4 5% 4 6% 28%	2525
November	1st to 10th	Night	20% 9% 4 5% 5% 3 3 4 5% 6% 35%	2407
	11th to 20th	Night	19% 10% 3 8% 6% 4 5% 5% 5% 6% 30%	2645
	21st to end	Night	22% 12% 4 8% 7% 3 4 4 4 6% 25%	2660
December	1st to 10th	Night	22% 16% 5% 8% 8% 3 5% 5% 4 5% 18%	2660
	11th to 20th	Night	23% 14% 4 8% 6% 2 3 4 4 5% 27%	3288
	21st to end	Night	31% 17% 4 8% 5% 2 4 4 3 4 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	65% 7% 9% 13% 5%	1518
	11th to 20th	Day	64% 5% 9% 11% 10% 1	1480
	21st to end	Day	59% 8% 12% 13% 8% 1	1646
February	1st to 10th	Day	61% 6% 11% 17% 4 2	1620
	11th to 20th	Day	56% 7% 11% 17% 8% 1	1591
	21st to end	Day	60% 6% 11% 14% 9% 1	1480
March	1st to 10th	Day	56% 6% 11% 17% 9% 1	1800
	11th to 20th	Day	53% 6% 12% 14% 11% 3	1970
	21st to end	Day	48% 7% 9% 18% 13% 5%	2299
April	1st to 10th	Day	53% 6% 8% 19% 11% 3	2160
	11th to 20th	Day	49% 5% 8% 22% 14% 2	2134
	21st to end	Day	54% 6% 9% 13% 14% 4	2286
May	1st to 10th	Day	49% 7% 8% 18% 14% 4	2520
	11th to 20th	Day	45% 7% 9% 21% 16% 3	2482
	21st to end	Day	44% 9% 13% 19% 13% 3	2725
June	1st to 10th	Day	52% 8% 10% 17% 11% 1	2520
	11th to 20th	Day	41% 10% 11% 23% 13% 2	2520
	21st to end	Day	48% 11% 13% 18% 10% 1	2520
July	1st to 10th	Day	37% 9% 14% 24% 14% 1	2450
	11th to 20th	Day	38% 9% 16% 25% 11%	2445
	21st to end	Day	39% 11% 16% 24% 10%	2591
August	1st to 10th	Day	39% 10% 16% 24% 10%	2466
	11th to 20th	Day	39% 9% 17% 25% 9% 1	2274
	21st to end	Day	38% 8% 16% 26% 11% 1	2376
September	1st to 10th	Day	38% 9% 15% 26% 12%	2160
	11th to 20th	Day	35% 8% 14% 30% 12% 1	2157
	21st to end	Day	43% 8% 15% 26% 8%	1926
October	1st to 10th	Day	48% 7% 13% 21% 10% 1	1800
	11th to 20th	Day	54% 9% 15% 14% 6% 1	1800
	21st to end	Day	59% 7% 12% 14% 8%	1830
November	1st to 10th	Day	47% 9% 16% 21% 6% 1	1671
	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	68% 6% 10% 11% 5%	2649
	11th to 20th	Night	66% 6% 9% 10% 8% 1	2591
	21st to end	Night	56% 6% 10% 17% 11% 1	2709
February	1st to 10th	Night	62% 6% 10% 14% 6% 1	2340
	11th to 20th	Night	57% 6% 10% 19% 7% 1	2266
	21st to end	Night	56% 6% 10% 18% 10% 1	1776
March	1st to 10th	Night	56% 7% 10% 16% 9% 2	2160
	11th to 20th	Night	54% 4 11% 18% 11% 2	1985
	21st to end	Night	48% 5% 7% 20% 15% 4	2057
April	1st to 10th	Night	52% 6% 9% 18% 14% 2	1800
	11th to 20th	Night	49% 7% 8% 20% 16% 1	1775
	21st to end	Night	52% 5% 9% 16% 14% 4	1688
May	1st to 10th	Night	47% 6% 9% 18% 15% 5%	1440
	11th to 20th	Night	44% 6% 9% 21% 18% 3	1416
	21st to end	Night	37% 9% 15% 19% 18% 2	1551
June	1st to 10th	Night	45% 9% 13% 23% 9% 1	1440
	11th to 20th	Night	39% 9% 11% 22% 17% 2	1440
	21st to end	Night	45% 9% 13% 19% 13% 1	1440
July	1st to 10th	Night	34% 9% 13% 26% 16% 2	1400
	11th to 20th	Night	36% 7% 14% 30% 13%	1392
	21st to end	Night	36% 10% 15% 25% 14%	1486
August	1st to 10th	Night	36% 10% 18% 21% 13% 1	1446
	11th to 20th	Night	37% 8% 16% 28% 10%	1607
	21st to end	Night	36% 9% 16% 28% 11%	1980
September	1st to 10th	Night	37% 8% 12% 28% 14% 1	1800
	11th to 20th	Night	34% 9% 14% 32% 9% 1	1802
	21st to end	Night	41% 7% 12% 30% 10%	2030
October	1st to 10th	Night	46% 8% 12% 21% 13% 1	2160
	11th to 20th	Night	54% 7% 11% 20% 8%	2160
	21st to end	Night	56% 7% 13% 15% 8%	2525
November	1st to 10th	Night	50% 6% 15% 20% 8%	2407
	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	29% 16% 35% 15% 4 1	170
	21st to end	Day	24% 16% 34% 20% 6%	204
February	1st to 10th	Day	33% 22% 34% 11%	240
	11th to 20th	Day	27% 25% 37% 10% 1	249
	21st to end	Day	28% 21% 32% 16% 3	346
March	1st to 10th	Day	24% 17% 36% 18% 5%	420
	11th to 20th	Day	27% 17% 33% 19% 3 1	420
	21st to end	Day	29% 21% 25% 16% 8% 1	462
April	1st to 10th	Day	27% 20% 31% 16% 6% 1	420
	11th to 20th	Day	30% 19% 22% 17% 10% 1	412
	21st to end	Day	31% 19% 29% 13% 6% 2	420
May	1st to 10th	Day	24% 13% 33% 20% 8% 2	423
	11th to 20th	Day	18% 18% 33% 19% 10% 2	447
	21st to end	Day	18% 15% 32% 22% 12% 1	485
June	1st to 10th	Day	24% 12% 32% 22% 9% 2	450
	11th to 20th	Day	16% 14% 30% 26% 11% 3	450
	21st to end	Day	20% 13% 30% 23% 12% 3	450
July	1st to 10th	Day	11% 8% 27% 36% 13% 5%	445
	11th to 20th	Day	11% 8% 32% 28% 16% 3	444
	21st to end	Day	12% 7% 32% 30% 14% 5%	488
August	1st to 10th	Day	13% 7% 28% 32% 17% 4	446
	11th to 20th	Day	12% 8% 24% 29% 19% 8%	439
	21st to end	Day	13% 11% 30% 25% 14% 7%	495
September	1st to 10th	Day	16% 10% 29% 20% 16% 9%	450
	11th to 20th	Day	12% 10% 27% 23% 18% 10%	450
	21st to end	Day	18% 13% 29% 22% 13% 6%	450
October	1st to 10th	Day	24% 14% 25% 20% 12% 5%	450
	11th to 20th	Day	24% 19% 31% 18% 7% 1	450
	21st to end	Day	32% 13% 28% 22% 5%	419
November	1st to 10th	Day	23% 18% 29% 20% 9% 1	365
	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% 20% 6%	741
	21st to end	Night	19% 11% 37% 27% 5% 1	792
February	1st to 10th	Night	25% 13% 37% 23% 3	720
	11th to 20th	Night	21% 16% 40% 19% 4	703
	21st to end	Night	26% 16% 29% 26% 3	592
March	1st to 10th	Night	22% 16% 36% 23% 3	720
	11th to 20th	Night	22% 19% 33% 20% 5%	720
	21st to end	Night	23% 15% 28% 25% 8%	792
April	1st to 10th	Night	26% 15% 30% 24% 5%	720
	11th to 20th	Night	24% 14% 31% 23% 8%	711
	21st to end	Night	25% 13% 29% 24% 7% 1	608
May	1st to 10th	Night	23% 8% 30% 28% 9% 2	360
	11th to 20th	Night	22% 10% 27% 31% 9%	354
	21st to end	Night	15% 6% 40% 27% 12%	389
June	1st to 10th	Night	19% 3 31% 37% 9%	360
	11th to 20th	Night	14% 8% 29% 34% 13% 2	360
	21st to end	Night	19% 4 31% 31% 14% 1	360
July	1st to 10th	Night	10% 5% 29% 42% 15%	350
	11th to 20th	Night	11% 4 25% 42% 16% 1	348
	21st to end	Night	8% 3 29% 42% 15% 2	394
August	1st to 10th	Night	13% 4 22% 40% 21% 1	382
	11th to 20th	Night	13% 4 19% 38% 24% 2	543
	21st to end	Night	12% 7% 25% 36% 18% 2	792
September	1st to 10th	Night	13% 6% 29% 33% 18% 1	720
	11th to 20th	Night	17% 7% 21% 33% 20% 3	720
	21st to end	Night	18% 10% 24% 25% 20% 2	720
October	1st to 10th	Night	21% 9% 28% 24% 15% 1	720
	11th to 20th	Night	25% 12% 30% 25% 8% 1	720
	21st to end	Night	27% 13% 28% 26% 5%	792
November	1st to 10th	Night	25% 13% 28% 24% 9% 1	740
	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 2024-01-13 01:38:13. Version ac07

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