Ontario(OR)
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Ontario(OR) clear sky chart from 2005-11-06 to 2024-11-02.

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	8% 6% 2 6% 4 4 4 3 5% 6% 53%	101340
	Night	11% 8% 3 7% 4 4 4 4 5% 6% 45%	97783
Transparency	Day	30% 7% 11% 19% 19% 14%	101084
	Night	37% 8% 12% 18% 15% 11%	97628
Seeing	Day	10% 5% 16% 26% 27% 16%	14456
	Night	13% 3 18% 39% 24% 3	23696

By Month

Percentage Cloud Cover SW (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% 5% 12% 7% 6% 5% 4 5% 5% 20%	2539
	11th to 20th	Day	19% 17% 6% 11% 5% 5% 6% 4 5% 5% 19%	2540
	21st to end	Day	24% 14% 7% 12% 6% 5% 5% 3 4 5% 16%	2794
February	1st to 10th	Day	14% 12% 4 9% 6% 6% 4 4 4 6% 32%	1648
	11th to 20th	Day	12% 10% 3 8% 7% 6% 5% 5% 5% 6% 33%	1850
	21st to end	Day	9% 9% 3 8% 6% 5% 6% 4 6% 8% 35%	1570
March	1st to 10th	Day	8% 13% 3 9% 5% 5% 5% 5% 6% 9% 31%	3138
	11th to 20th	Day	8% 7% 2 5% 3 3 4 3 4 5% 57%	3300
	21st to end	Day	9% 8% 2 8% 6% 6% 6% 5% 7% 8% 34%	4086
April	1st to 10th	Day	10% 8% 3 7% 5% 4 5% 4 6% 7% 41%	2280
	11th to 20th	Day	7% 6% 3 7% 5% 5% 5% 4 6% 7% 47%	2266
	21st to end	Day	8% 6% 2 6% 4 4 5% 4 5% 8% 49%	2470
May	1st to 10th	Day	8% 6% 2 5% 4 4 4 3 5% 6% 52%	4110
	11th to 20th	Day	6% 3 1 3 2 2 3 2 4 6% 67%	4312
	21st to end	Day	5% 4 2 5% 4 4 4 3 6% 8% 54%	4813
June	1st to 10th	Day	8% 6% 2 6% 4 4 5% 5% 7% 8% 46%	2660
	11th to 20th	Day	7% 3 1 4 3 3 3 3 6% 7% 59%	2660
	21st to end	Day	2 4 1 3 3 3 2 3 4 5% 71%	2660
July	1st to 10th	Day	2 1 1 2 2 2 2 2 2 4 82%	4420
	11th to 20th	Day	2 2 1 2 2 2 2 2 3 4 80%	4420
	21st to end	Day	1 2 1 2 2 2 2 2 4 5% 77%	4790
August	1st to 10th	Day	4 4 2 4 3 3 3 2 4 7% 64%	4318
	11th to 20th	Day	2 1 1 2 2 2 2 2 3 5% 79%	3978
	21st to end	Day	2 2 1 3 2 2 2 2 3 4 77%	4180
September	1st to 10th	Day	2 2 1 2 2 3 3 2 4 5% 74%	2280
	11th to 20th	Day	4 4 1 4 2 3 4 4 4 7% 63%	2138
	21st to end	Day	5% 3 1 4 4 3 4 3 4 6% 65%	2090
October	1st to 10th	Day	7% 5% 2 5% 4 4 3 3 5% 6% 57%	2084
	11th to 20th	Day	7% 5% 2 4 4 3 3 3 5% 8% 55%	1819
	21st to end	Day	9% 7% 2 8% 5% 4 4 4 5% 6% 46%	1881
November	1st to 10th	Day	15% 7% 3 6% 5% 4 6% 4 5% 7% 39%	1683
	11th to 20th	Day	13% 9% 3 7% 6% 5% 5% 4 6% 7% 35%	1710
	21st to end	Day	10% 10% 4 9% 8% 6% 7% 4 7% 7% 29%	1611
December	1st to 10th	Day	17% 13% 6% 9% 4 5% 5% 4 6% 6% 25%	1520
	11th to 20th	Day	18% 14% 6% 15% 8% 5% 4 3 5% 5% 17%	1928
	21st to end	Day	13% 12% 5% 12% 8% 6% 6% 5% 5% 5% 22%	2794
January	1st to 10th	Night	16% 17% 5% 12% 7% 6% 6% 5% 5% 6% 15%	4406
	11th to 20th	Night	23% 16% 5% 11% 7% 5% 5% 3 4 4 16%	4420
	21st to end	Night	25% 16% 7% 11% 5% 5% 4 3 4 5% 17%	4862
February	1st to 10th	Night	15% 11% 3 8% 7% 6% 6% 5% 6% 6% 27%	2527
	11th to 20th	Night	13% 9% 2 8% 6% 5% 6% 4 7% 7% 33%	2218
	21st to end	Night	11% 12% 3 8% 5% 6% 6% 5% 7% 8% 29%	1884
March	1st to 10th	Night	10% 11% 3 9% 6% 8% 7% 4 5% 7% 30%	3736
	11th to 20th	Night	10% 8% 2 5% 4 3 3 3 4 5% 53%	3679
	21st to end	Night	10% 8% 3 8% 7% 6% 6% 5% 7% 8% 33%	3564
April	1st to 10th	Night	11% 7% 3 7% 4 4 5% 3 5% 6% 44%	1900
	11th to 20th	Night	10% 6% 3 6% 4 4 5% 4 6% 6% 46%	1861
	21st to end	Night	8% 5% 2 5% 4 3 5% 4 6% 7% 51%	1710
May	1st to 10th	Night	10% 6% 2 5% 3 4 4 4 6% 7% 48%	2860
	11th to 20th	Night	4 3 1 4 3 3 3 3 7% 6% 63%	2566
	21st to end	Night	8% 6% 2 6% 5% 4 4 3 5% 8% 50%	2762
June	1st to 10th	Night	9% 5% 2 7% 5% 4 5% 4 6% 7% 47%	1520
	11th to 20th	Night	7% 4 1 5% 3 4 3 3 4 6% 59%	1520
	21st to end	Night	3 3 2 3 3 2 4 3 5% 6% 66%	1520
July	1st to 10th	Night	1 1 2 1 2 2 2 3 4 82%	2540
	11th to 20th	Night	1 2 2 2 2 3 4 5% 79%	2540
	21st to end	Night	3 3 1 3 2 3 3 3 5% 5% 69%	2761
August	1st to 10th	Night	4 3 2 5% 4 4 4 3 5% 7% 59%	2614
	11th to 20th	Night	1 2 1 2 2 2 2 2 4 5% 76%	2860
	21st to end	Night	4 3 1 2 1 2 2 2 3 3 77%	3498
September	1st to 10th	Night	3 3 1 2 2 2 2 2 4 5% 75%	1900
	11th to 20th	Night	4 4 2 4 3 3 3 3 5% 6% 64%	2041
	21st to end	Night	7% 3 1 4 2 3 2 3 4 5% 67%	2090
October	1st to 10th	Night	8% 5% 2 4 3 3 3 3 4 6% 61%	2095
	11th to 20th	Night	7% 4 2 4 4 4 3 3 6% 7% 57%	2361
	21st to end	Night	8% 5% 2 6% 4 4 5% 4 6% 7% 47%	2717
November	1st to 10th	Night	14% 8% 3 6% 4 4 4 4 6% 6% 42%	2418
	11th to 20th	Night	17% 8% 3 7% 4 4 5% 4 5% 6% 36%	2470
	21st to end	Night	13% 8% 3 7% 5% 5% 6% 5% 5% 7% 36%	2565
December	1st to 10th	Night	17% 11% 4 9% 5% 5% 5% 4 5% 7% 28%	2660
	11th to 20th	Night	19% 12% 5% 10% 7% 6% 6% 4 4 6% 21%	3276
	21st to end	Night	15% 13% 3 10% 8% 7% 7% 5% 6% 6% 21%	4862

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% 13% 16% 10% 1	2539
	11th to 20th	Day	64% 11% 14% 9% 1	2540
	21st to end	Day	68% 14% 11% 5% 1	2794
February	1st to 10th	Day	53% 11% 18% 14% 3	1648
	11th to 20th	Day	47% 11% 17% 19% 6%	1860
	21st to end	Day	43% 10% 19% 18% 9% 1	1570
March	1st to 10th	Day	44% 12% 15% 20% 8% 1	3138
	11th to 20th	Day	28% 7% 13% 36% 15% 1	3300
	21st to end	Day	39% 13% 19% 19% 8% 2	4086
April	1st to 10th	Day	39% 7% 17% 22% 13% 3	2280
	11th to 20th	Day	32% 7% 14% 26% 17% 4	2269
	21st to end	Day	32% 6% 14% 27% 18% 3	2470
May	1st to 10th	Day	29% 7% 10% 24% 25% 5%	4110
	11th to 20th	Day	18% 4 8% 26% 30% 14%	4315
	21st to end	Day	23% 8% 14% 33% 18% 4	4814
June	1st to 10th	Day	32% 9% 12% 23% 21% 2	2660
	11th to 20th	Day	22% 6% 9% 25% 27% 11%	2660
	21st to end	Day	16% 4 7% 19% 32% 22%	2660
July	1st to 10th	Day	9% 2 3 9% 21% 57%	4351
	11th to 20th	Day	10% 2 2 7% 21% 58%	4345
	21st to end	Day	10% 2 2 8% 31% 46%	4639
August	1st to 10th	Day	21% 4 5% 10% 26% 35%	4302
	11th to 20th	Day	10% 2 3 17% 36% 32%	4017
	21st to end	Day	13% 2 4 21% 35% 24%	4179
September	1st to 10th	Day	13% 3 5% 19% 32% 28%	2280
	11th to 20th	Day	20% 5% 10% 23% 30% 13%	2138
	21st to end	Day	21% 4 9% 28% 30% 8%	2090
October	1st to 10th	Day	28% 5% 12% 27% 24% 4	2084
	11th to 20th	Day	28% 6% 14% 32% 18% 3	1819
	21st to end	Day	36% 7% 17% 27% 12% 1	1881
November	1st to 10th	Day	42% 10% 17% 23% 8%	1683
	11th to 20th	Day	47% 9% 19% 18% 6% 1	1710
	21st to end	Day	50% 12% 17% 15% 6%	1611
December	1st to 10th	Day	57% 11% 17% 11% 4	1520
	11th to 20th	Day	67% 11% 12% 7% 3	1928
	21st to end	Day	56% 14% 16% 10% 3	2794
January	1st to 10th	Night	61% 15% 16% 6% 1	4406
	11th to 20th	Night	66% 10% 13% 9% 2	4420
	21st to end	Night	65% 11% 14% 9% 2	4862
February	1st to 10th	Night	51% 11% 17% 16% 4 1	2527
	11th to 20th	Night	45% 11% 18% 19% 8%	2219
	21st to end	Night	46% 10% 16% 20% 7% 1	1884
March	1st to 10th	Night	42% 13% 14% 21% 9% 1	3736
	11th to 20th	Night	33% 5% 11% 34% 18%	3679
	21st to end	Night	41% 12% 18% 21% 7%	3564
April	1st to 10th	Night	37% 8% 12% 24% 17% 2	1900
	11th to 20th	Night	35% 8% 11% 24% 18% 4	1861
	21st to end	Night	29% 6% 13% 25% 24% 3	1710
May	1st to 10th	Night	28% 9% 11% 23% 24% 4	2860
	11th to 20th	Night	19% 5% 9% 25% 34% 8%	2566
	21st to end	Night	31% 7% 11% 31% 19% 2	2762
June	1st to 10th	Night	34% 7% 14% 23% 20% 2	1520
	11th to 20th	Night	26% 6% 8% 22% 29% 10%	1520
	21st to end	Night	18% 4 6% 18% 33% 21%	1520
July	1st to 10th	Night	8% 2 3 10% 18% 60%	2500
	11th to 20th	Night	7% 3 3 8% 20% 59%	2492
	21st to end	Night	16% 3 2 8% 27% 44%	2674
August	1st to 10th	Night	24% 4 5% 10% 22% 35%	2606
	11th to 20th	Night	11% 3 4 12% 28% 42%	2887
	21st to end	Night	14% 2 3 15% 33% 33%	3498
September	1st to 10th	Night	13% 2 5% 14% 29% 36%	1900
	11th to 20th	Night	21% 4 7% 20% 25% 22%	2041
	21st to end	Night	20% 3 6% 22% 33% 16%	2090
October	1st to 10th	Night	26% 4 8% 25% 28% 8%	2095
	11th to 20th	Night	26% 5% 12% 28% 24% 4	2361
	21st to end	Night	33% 7% 14% 25% 19% 1	2717
November	1st to 10th	Night	40% 7% 14% 25% 14% 1	2418
	11th to 20th	Night	45% 9% 15% 23% 8%	2470
	21st to end	Night	43% 8% 18% 21% 8% 1	2565
December	1st to 10th	Night	52% 11% 16% 15% 6%	2660
	11th to 20th	Night	59% 11% 16% 11% 3	3276
	21st to end	Night	52% 16% 18% 11% 4	4862

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% 6% 12% 33% 23% 7%	180
	11th to 20th	Day	23% 4 15% 27% 19% 11%	180
	21st to end	Day	21% 4 12% 31% 25% 9%	198
February	1st to 10th	Day	17% 5% 24% 28% 20% 6%	286
	11th to 20th	Day	17% 5% 19% 31% 22% 7%	455
	21st to end	Day	14% 6% 26% 29% 19% 6%	382
March	1st to 10th	Day	18% 10% 21% 32% 17% 2	460
	11th to 20th	Day	14% 7% 18% 31% 22% 9%	460
	21st to end	Day	14% 11% 20% 30% 20% 6%	506
April	1st to 10th	Day	14% 13% 18% 22% 20% 12%	460
	11th to 20th	Day	8% 12% 25% 27% 19% 10%	452
	21st to end	Day	8% 8% 26% 26% 23% 8%	460
May	1st to 10th	Day	7% 12% 23% 25% 22% 11%	463
	11th to 20th	Day	15% 9% 16% 25% 22% 14%	488
	21st to end	Day	8% 5% 16% 22% 30% 19%	529
June	1st to 10th	Day	9% 4 16% 27% 25% 19%	490
	11th to 20th	Day	8% 6% 22% 27% 26% 12%	490
	21st to end	Day	3 2 16% 29% 31% 19%	490
July	1st to 10th	Day	3 1 11% 28% 36% 21%	486
	11th to 20th	Day	2 1 9% 30% 39% 18%	484
	21st to end	Day	3 1 6% 26% 42% 22%	531
August	1st to 10th	Day	6% 1 7% 26% 38% 22%	487
	11th to 20th	Day	2 1 7% 24% 35% 31%	477
	21st to end	Day	4 2 11% 22% 33% 28%	539
September	1st to 10th	Day	5% 1 9% 18% 35% 31%	490
	11th to 20th	Day	6% 2 11% 22% 31% 26%	490
	21st to end	Day	5% 3 14% 25% 29% 24%	490
October	1st to 10th	Day	8% 4 13% 21% 28% 25%	490
	11th to 20th	Day	9% 3 14% 26% 27% 20%	409
	21st to end	Day	12% 5% 18% 26% 28% 11%	330
November	1st to 10th	Day	17% 4 16% 27% 31% 6%	273
	11th to 20th	Day	14% 3 18% 27% 29% 9%	270
	21st to end	Day	17% 2 12% 26% 35% 9%	223
December	1st to 10th	Day	23% 3 13% 28% 21% 13%	180
	11th to 20th	Day	24% 4 21% 28% 19% 4	180
	21st to end	Day	18% 4 17% 32% 21% 8%	198
January	1st to 10th	Night	21% 4 17% 34% 19% 4	760
	11th to 20th	Night	21% 4 17% 32% 22% 4	760
	21st to end	Night	20% 3 13% 38% 23% 4	836
February	1st to 10th	Night	21% 2 20% 37% 18% 2	760
	11th to 20th	Night	17% 2 19% 39% 21% 2	744
	21st to end	Night	15% 4 25% 37% 17% 2	628
March	1st to 10th	Night	15% 5% 23% 39% 15% 3	760
	11th to 20th	Night	14% 5% 20% 39% 20% 2	760
	21st to end	Night	15% 6% 22% 39% 17% 1	836
April	1st to 10th	Night	12% 5% 22% 37% 21% 1	760
	11th to 20th	Night	12% 6% 26% 35% 19% 2	733
	21st to end	Night	9% 5% 27% 40% 18% 2	570
May	1st to 10th	Night	8% 7% 23% 42% 19% 1	570
	11th to 20th	Night	8% 5% 21% 35% 27% 4	411
	21st to end	Night	9% 5% 18% 38% 25% 5%	411
June	1st to 10th	Night	9% 5% 23% 36% 24% 4	380
	11th to 20th	Night	9% 4 28% 34% 22% 2	380
	21st to end	Night	3 2 24% 44% 26% 1	380
July	1st to 10th	Night	2 3 18% 50% 26% 1	370
	11th to 20th	Night	1 1 20% 58% 20%	368
	21st to end	Night	3 1 15% 52% 28% 2	416
August	1st to 10th	Night	5% 14% 47% 31% 2	424
	11th to 20th	Night	2 1 13% 48% 34% 3	587
	21st to end	Night	4 2 13% 41% 35% 4	836
September	1st to 10th	Night	4 1 11% 42% 37% 5%	760
	11th to 20th	Night	5% 2 12% 35% 40% 6%	760
	21st to end	Night	8% 3 13% 37% 33% 7%	760
October	1st to 10th	Night	10% 1 16% 40% 29% 5%	760
	11th to 20th	Night	9% 3 15% 37% 30% 6%	760
	21st to end	Night	11% 2 17% 40% 26% 3	836
November	1st to 10th	Night	17% 3 15% 39% 24% 2	744
	11th to 20th	Night	20% 2 16% 38% 21% 2	760
	21st to end	Night	17% 4 16% 36% 24% 4	760
December	1st to 10th	Night	21% 2 17% 38% 19% 2	760
	11th to 20th	Night	24% 2 15% 39% 17% 2	760
	21st to end	Night	26% 4 18% 37% 12% 2	836

Page generated at 2024-10-29 22:23:00. Version ac07

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