Oshawa
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Oshawa clear sky chart from 2005-11-06 to 2024-03-23.

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% 8% 3 7% 6% 3 5% 5% 6% 7% 34%	78651
	Night	17% 9% 3 6% 6% 3 5% 5% 5% 7% 33%	81224
Transparency	Day	47% 7% 14% 20% 10% 1	78363
	Night	50% 6% 14% 19% 10% 1	81046
Seeing	Day	18% 10% 27% 26% 14% 4	13549
	Night	20% 8% 28% 30% 13% 2	23076

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% 12% 3 8% 7% 3 4 4 4 6% 31%	2517
	11th to 20th	Day	12% 18% 7% 13% 9% 4 5% 4 4 5% 18%	2682
	21st to end	Day	21% 17% 6% 9% 7% 3 5% 4 4 5% 18%	3124
February	1st to 10th	Day	16% 13% 5% 10% 8% 5% 6% 5% 5% 5% 22%	1710
	11th to 20th	Day	13% 12% 7% 11% 7% 4 5% 4 5% 7% 27%	1663
	21st to end	Day	18% 12% 5% 8% 7% 3 4 4 4 5% 29%	1456
March	1st to 10th	Day	15% 9% 3 8% 8% 3 6% 4 5% 7% 32%	2087
	11th to 20th	Day	14% 11% 5% 6% 6% 4 5% 5% 5% 6% 33%	2090
	21st to end	Day	18% 9% 4 6% 6% 3 5% 3 5% 5% 36%	2200
April	1st to 10th	Day	17% 9% 4 7% 6% 3 5% 4 6% 7% 31%	2150
	11th to 20th	Day	19% 7% 4 5% 4 3 4 5% 5% 6% 37%	2169
	21st to end	Day	19% 7% 3 6% 7% 3 5% 4 5% 6% 35%	2340
May	1st to 10th	Day	15% 8% 3 7% 5% 4 5% 5% 6% 8% 34%	2365
	11th to 20th	Day	14% 6% 3 5% 5% 2 4 5% 6% 7% 42%	2478
	21st to end	Day	11% 4 2 5% 6% 2 5% 5% 7% 8% 44%	2725
June	1st to 10th	Day	15% 5% 3 6% 5% 3 5% 6% 7% 9% 37%	2520
	11th to 20th	Day	12% 5% 3 5% 5% 3 5% 5% 6% 9% 42%	2520
	21st to end	Day	13% 5% 2 5% 5% 3 5% 5% 7% 10% 42%	2520
July	1st to 10th	Day	7% 4 2 4 5% 3 5% 5% 8% 9% 48%	2520
	11th to 20th	Day	10% 4 2 5% 5% 3 6% 5% 7% 10% 43%	2520
	21st to end	Day	9% 5% 2 5% 6% 4 6% 7% 7% 10% 40%	2623
August	1st to 10th	Day	7% 4 2 6% 6% 3 6% 6% 8% 9% 43%	2327
	11th to 20th	Day	9% 4 2 5% 6% 3 5% 6% 7% 10% 43%	2303
	21st to end	Day	10% 5% 2 5% 5% 3 5% 6% 6% 9% 44%	2456
September	1st to 10th	Day	13% 5% 2 5% 5% 3 4 5% 7% 7% 44%	2160
	11th to 20th	Day	11% 4 2 4 4 3 5% 4 6% 8% 48%	2093
	21st to end	Day	13% 5% 3 5% 6% 4 5% 5% 5% 8% 41%	1919
October	1st to 10th	Day	17% 7% 4 5% 6% 4 5% 5% 5% 6% 36%	1800
	11th to 20th	Day	20% 8% 3 7% 6% 3 4 5% 6% 7% 31%	1800
	21st to end	Day	23% 10% 3 8% 6% 4 4 4 5% 6% 26%	1980
November	1st to 10th	Day	16% 7% 3 8% 7% 4 5% 5% 5% 8% 33%	1596
	11th to 20th	Day	16% 9% 5% 8% 8% 5% 5% 5% 7% 7% 27%	1520
	21st to end	Day	21% 10% 4 8% 7% 3 5% 5% 4 8% 26%	1520
December	1st to 10th	Day	17% 14% 5% 9% 8% 5% 6% 6% 5% 7% 19%	1520
	11th to 20th	Day	19% 13% 5% 7% 6% 2 5% 5% 6% 7% 26%	1906
	21st to end	Day	29% 14% 5% 11% 7% 4 5% 3 4 4 14%	2772
January	1st to 10th	Night	19% 14% 4 8% 7% 4 5% 5% 5% 6% 24%	4429
	11th to 20th	Night	15% 12% 4 11% 11% 5% 5% 6% 5% 9% 18%	4276
	21st to end	Night	21% 13% 5% 8% 7% 3 5% 5% 5% 6% 23%	4532
February	1st to 10th	Night	15% 13% 5% 9% 8% 4 5% 6% 5% 6% 24%	2470
	11th to 20th	Night	15% 12% 5% 8% 7% 4 5% 4 6% 6% 28%	2403
	21st to end	Night	16% 10% 4 8% 7% 4 5% 5% 5% 7% 30%	1993
March	1st to 10th	Night	14% 8% 3 7% 7% 4 6% 5% 5% 6% 35%	2080
	11th to 20th	Night	17% 10% 5% 7% 6% 3 4 4 5% 6% 33%	2089
	21st to end	Night	16% 8% 3 5% 6% 3 4 5% 4 5% 41%	2201
April	1st to 10th	Night	19% 9% 3 5% 5% 4 4 4 4 7% 35%	1810
	11th to 20th	Night	15% 6% 3 7% 6% 3 6% 4 5% 6% 39%	1754
	21st to end	Night	18% 7% 3 6% 5% 3 5% 4 5% 7% 35%	1620
May	1st to 10th	Night	17% 5% 3 5% 6% 3 4 5% 6% 7% 39%	1594
	11th to 20th	Night	14% 4 2 6% 5% 3 4 5% 5% 8% 45%	1415
	21st to end	Night	9% 4 2 4 5% 3 4 5% 5% 8% 52%	1550
June	1st to 10th	Night	12% 4 2 5% 5% 3 5% 5% 7% 8% 42%	1440
	11th to 20th	Night	9% 4 2 6% 6% 3 5% 6% 5% 10% 45%	1440
	21st to end	Night	13% 4 3 4 5% 3 4 6% 7% 9% 43%	1440
July	1st to 10th	Night	5% 4 2 4 4 3 4 5% 5% 8% 55%	1440
	11th to 20th	Night	10% 5% 2 4 4 3 4 5% 6% 8% 49%	1440
	21st to end	Night	9% 3 2 4 4 3 4 6% 7% 9% 49%	1691
August	1st to 10th	Night	8% 4 1 5% 5% 2 5% 4 7% 8% 50%	1611
	11th to 20th	Night	7% 5% 2 4 5% 3 5% 4 6% 9% 51%	1598
	21st to end	Night	9% 6% 2 6% 5% 3 5% 4 5% 8% 48%	1881
September	1st to 10th	Night	11% 6% 2 5% 4 3 5% 5% 6% 7% 46%	1800
	11th to 20th	Night	12% 3 2 4 3 3 4 3 5% 8% 53%	1862
	21st to end	Night	15% 6% 2 6% 5% 2 4 4 4 6% 45%	2039
October	1st to 10th	Night	16% 6% 3 6% 6% 3 4 5% 5% 6% 39%	2160
	11th to 20th	Night	20% 8% 3 6% 6% 3 5% 5% 5% 6% 32%	2160
	21st to end	Night	23% 8% 3 6% 6% 4 5% 6% 5% 6% 30%	2376
November	1st to 10th	Night	17% 7% 2 6% 5% 4 4 4 5% 6% 38%	2478
	11th to 20th	Night	18% 9% 3 6% 6% 4 5% 6% 6% 7% 31%	2660
	21st to end	Night	21% 9% 4 6% 6% 4 5% 5% 6% 8% 26%	2660
December	1st to 10th	Night	20% 13% 5% 8% 6% 4 6% 5% 5% 6% 23%	2660
	11th to 20th	Night	17% 15% 4 8% 7% 4 6% 5% 6% 6% 23%	3288
	21st to end	Night	31% 14% 4 7% 5% 4 6% 5% 5% 5% 15%	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	54% 6% 21% 12% 6% 1	2518
	11th to 20th	Day	69% 6% 13% 8% 3	2682
	21st to end	Day	68% 6% 11% 10% 4	3124
February	1st to 10th	Day	63% 6% 12% 14% 4 1	1710
	11th to 20th	Day	57% 7% 11% 17% 7% 1	1672
	21st to end	Day	56% 6% 12% 18% 7%	1456
March	1st to 10th	Day	51% 7% 15% 17% 10% 1	2090
	11th to 20th	Day	50% 7% 11% 17% 12% 2	2090
	21st to end	Day	50% 5% 8% 19% 16% 3	2200
April	1st to 10th	Day	51% 7% 11% 19% 11% 2	2150
	11th to 20th	Day	46% 6% 10% 21% 15% 2	2169
	21st to end	Day	48% 6% 11% 20% 12% 3	2340
May	1st to 10th	Day	47% 6% 10% 21% 14% 2	2365
	11th to 20th	Day	41% 6% 11% 26% 15% 2	2482
	21st to end	Day	36% 6% 18% 25% 13% 2	2725
June	1st to 10th	Day	41% 8% 13% 22% 14% 1	2520
	11th to 20th	Day	36% 7% 14% 26% 15% 2	2520
	21st to end	Day	36% 8% 16% 25% 14% 1	2520
July	1st to 10th	Day	29% 9% 13% 28% 19% 2	2450
	11th to 20th	Day	34% 9% 15% 30% 11% 1	2445
	21st to end	Day	36% 10% 17% 24% 13% 1	2476
August	1st to 10th	Day	33% 10% 17% 25% 12% 2	2314
	11th to 20th	Day	34% 8% 18% 28% 12%	2303
	21st to end	Day	34% 9% 15% 29% 12% 1	2456
September	1st to 10th	Day	36% 8% 15% 28% 11% 1	2160
	11th to 20th	Day	33% 7% 15% 30% 15% 1	2093
	21st to end	Day	39% 8% 16% 26% 9% 1	1919
October	1st to 10th	Day	48% 7% 15% 19% 11% 1	1800
	11th to 20th	Day	50% 7% 16% 20% 7% 1	1800
	21st to end	Day	58% 7% 14% 15% 6% 1	1980
November	1st to 10th	Day	48% 8% 14% 20% 9% 1	1596
	11th to 20th	Day	54% 7% 15% 15% 8% 1	1520
	21st to end	Day	57% 7% 15% 17% 4	1520
December	1st to 10th	Day	64% 7% 14% 13% 2	1520
	11th to 20th	Day	57% 9% 15% 13% 6%	1906
	21st to end	Day	73% 6% 10% 9% 2	2772
January	1st to 10th	Night	60% 7% 15% 14% 3 1	4429
	11th to 20th	Night	63% 11% 16% 7% 3 1	4276
	21st to end	Night	63% 5% 16% 11% 4 1	4532
February	1st to 10th	Night	60% 6% 12% 18% 4 1	2470
	11th to 20th	Night	56% 6% 11% 18% 9%	2405
	21st to end	Night	52% 6% 14% 19% 7% 1	1993
March	1st to 10th	Night	50% 5% 12% 21% 9% 2	2090
	11th to 20th	Night	51% 4 10% 22% 11% 2	2090
	21st to end	Night	45% 5% 10% 21% 16% 3	2201
April	1st to 10th	Night	50% 6% 8% 21% 13% 2	1810
	11th to 20th	Night	46% 6% 10% 19% 17% 2	1754
	21st to end	Night	48% 5% 11% 20% 14% 2	1620
May	1st to 10th	Night	44% 6% 10% 22% 15% 3	1594
	11th to 20th	Night	37% 5% 11% 25% 17% 4	1416
	21st to end	Night	31% 5% 16% 24% 19% 4	1551
June	1st to 10th	Night	38% 8% 12% 24% 16% 3	1440
	11th to 20th	Night	36% 6% 12% 22% 22% 2	1440
	21st to end	Night	36% 8% 13% 26% 16% 1	1440
July	1st to 10th	Night	27% 6% 13% 27% 24% 3	1400
	11th to 20th	Night	31% 6% 13% 31% 18% 2	1392
	21st to end	Night	29% 7% 15% 30% 16% 2	1597
August	1st to 10th	Night	32% 4 20% 29% 14% 1	1600
	11th to 20th	Night	30% 6% 17% 32% 14% 1	1598
	21st to end	Night	35% 5% 13% 30% 15% 1	1881
September	1st to 10th	Night	35% 6% 16% 27% 14% 2	1800
	11th to 20th	Night	31% 5% 14% 32% 18%	1862
	21st to end	Night	41% 5% 13% 28% 12% 1	2039
October	1st to 10th	Night	44% 5% 12% 23% 14% 1	2160
	11th to 20th	Night	51% 7% 14% 22% 7%	2160
	21st to end	Night	54% 7% 13% 17% 10% 1	2376
November	1st to 10th	Night	45% 5% 13% 24% 12% 1	2478
	11th to 20th	Night	52% 5% 15% 17% 10% 1	2660
	21st to end	Night	55% 7% 18% 15% 4	2660
December	1st to 10th	Night	62% 5% 14% 14% 4	2660
	11th to 20th	Night	61% 7% 14% 14% 4	3288
	21st to end	Night	69% 7% 13% 8% 2	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	25% 14% 33% 18% 9% 1	180
	11th to 20th	Day	25% 22% 31% 15% 5% 1	227
	21st to end	Day	25% 20% 33% 18% 4 1	297
February	1st to 10th	Day	24% 23% 35% 13% 5%	270
	11th to 20th	Day	22% 21% 41% 14% 1	270
	21st to end	Day	32% 19% 35% 13% 1	268
March	1st to 10th	Day	23% 16% 34% 21% 6%	460
	11th to 20th	Day	23% 17% 32% 22% 6%	460
	21st to end	Day	30% 11% 29% 21% 9% 1	470
April	1st to 10th	Day	20% 14% 35% 25% 6%	420
	11th to 20th	Day	25% 11% 27% 23% 10% 4	412
	21st to end	Day	23% 13% 33% 20% 9% 2	420
May	1st to 10th	Day	22% 9% 26% 26% 11% 5%	423
	11th to 20th	Day	16% 7% 25% 32% 15% 4	447
	21st to end	Day	13% 4 23% 32% 21% 7%	485
June	1st to 10th	Day	14% 8% 28% 32% 16% 2	450
	11th to 20th	Day	14% 6% 25% 31% 22% 3	450
	21st to end	Day	15% 6% 24% 33% 17% 5%	450
July	1st to 10th	Day	9% 3 19% 33% 27% 9%	445
	11th to 20th	Day	14% 4 18% 33% 23% 8%	444
	21st to end	Day	8% 3 25% 39% 18% 7%	488
August	1st to 10th	Day	8% 3 20% 35% 22% 11%	446
	11th to 20th	Day	10% 4 18% 30% 29% 9%	439
	21st to end	Day	12% 4 21% 30% 22% 10%	495
September	1st to 10th	Day	13% 5% 22% 30% 20% 10%	450
	11th to 20th	Day	10% 4 21% 28% 23% 13%	450
	21st to end	Day	14% 8% 28% 27% 15% 8%	450
October	1st to 10th	Day	20% 9% 25% 25% 15% 6%	450
	11th to 20th	Day	19% 16% 33% 24% 8% 1	450
	21st to end	Day	29% 11% 31% 21% 8%	495
November	1st to 10th	Day	21% 17% 26% 25% 10% 1	270
	11th to 20th	Day	18% 19% 36% 21% 6% 1	180
	21st to end	Day	29% 12% 36% 18% 5% 1	180
December	1st to 10th	Day	21% 16% 34% 19% 7% 2	180
	11th to 20th	Day	29% 18% 28% 17% 7%	180
	21st to end	Day	26% 22% 36% 15% 1	198
January	1st to 10th	Night	25% 14% 37% 17% 6%	760
	11th to 20th	Night	29% 13% 32% 22% 4 1	760
	21st to end	Night	21% 10% 34% 27% 7%	836
February	1st to 10th	Night	21% 15% 38% 23% 3	760
	11th to 20th	Night	22% 13% 36% 23% 6%	743
	21st to end	Night	22% 12% 39% 22% 4	628
March	1st to 10th	Night	21% 12% 34% 27% 5% 1	760
	11th to 20th	Night	22% 12% 34% 27% 5% 1	760
	21st to end	Night	20% 8% 30% 29% 11%	801
April	1st to 10th	Night	23% 10% 32% 29% 6%	720
	11th to 20th	Night	17% 9% 32% 30% 10% 2	690
	21st to end	Night	21% 7% 27% 33% 12%	540
May	1st to 10th	Night	21% 3 26% 29% 18% 2	514
	11th to 20th	Night	15% 3 28% 37% 16%	354
	21st to end	Night	11% 3 18% 43% 23% 3	389
June	1st to 10th	Night	15% 2 22% 41% 19% 1	360
	11th to 20th	Night	9% 4 21% 42% 21% 1	360
	21st to end	Night	12% 5% 20% 40% 22% 1	360
July	1st to 10th	Night	6% 3 15% 44% 29% 3	350
	11th to 20th	Night	11% 4 16% 38% 29% 2	348
	21st to end	Night	11% 2 13% 47% 24% 3	511
August	1st to 10th	Night	9% 2 11% 41% 32% 4	537
	11th to 20th	Night	7% 2 13% 42% 31% 6%	534
	21st to end	Night	13% 3 18% 37% 27% 3	693
September	1st to 10th	Night	13% 5% 18% 36% 24% 5%	720
	11th to 20th	Night	14% 4 18% 31% 26% 7%	720
	21st to end	Night	20% 5% 18% 31% 21% 5%	720
October	1st to 10th	Night	19% 4 27% 28% 20% 2	720
	11th to 20th	Night	23% 11% 28% 27% 10% 1	720
	21st to end	Night	28% 7% 29% 30% 6% 1	792
November	1st to 10th	Night	21% 10% 24% 32% 12% 1	740
	11th to 20th	Night	23% 12% 29% 27% 7% 2	760
	21st to end	Night	25% 10% 31% 27% 7%	760
December	1st to 10th	Night	29% 13% 31% 22% 5%	760
	11th to 20th	Night	23% 12% 36% 24% 4 1	760
	21st to end	Night	32% 10% 35% 21% 2	836

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