Port Burwell Provincial Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Port Burwell Provincial Park clear sky chart from 2005-11-06 to 2026-05-17.

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% 9% 4 8% 5% 5% 4 4 5% 7% 33%	132488
	Night	16% 11% 4 9% 5% 5% 4 4 5% 6% 32%	130290
Transparency	Day	33% 38% 8% 13% 7% 1	136101
	Night	34% 37% 8% 13% 8% 1	134766
Seeing	Day	19% 11% 28% 25% 13% 5%	16716
	Night	20% 9% 28% 29% 13% 2	26065

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% 14% 7% 16% 6% 5% 4 3 4 4 22%	5003
	11th to 20th	Day	11% 21% 9% 22% 10% 8% 4 2 3 3 8%	5246
	21st to end	Day	16% 17% 6% 13% 6% 6% 5% 3 5% 4 19%	5780
February	1st to 10th	Day	16% 16% 6% 12% 5% 6% 5% 4 5% 5% 21%	1890
	11th to 20th	Day	15% 12% 8% 12% 7% 5% 4 4 4 5% 23%	1843
	21st to end	Day	18% 13% 4 11% 6% 4 5% 4 6% 6% 22%	1709
March	1st to 10th	Day	19% 10% 5% 12% 6% 4 4 3 5% 5% 27%	4982
	11th to 20th	Day	12% 12% 4 9% 5% 4 4 3 6% 8% 33%	5090
	21st to end	Day	21% 9% 3 8% 5% 5% 4 3 5% 5% 32%	5586
April	1st to 10th	Day	17% 10% 3 8% 5% 4 5% 4 6% 7% 31%	2404
	11th to 20th	Day	17% 10% 4 8% 5% 4 4 3 6% 6% 34%	2644
	21st to end	Day	18% 8% 3 7% 4 4 4 4 5% 6% 36%	2730
May	1st to 10th	Day	21% 8% 3 7% 5% 5% 5% 3 5% 6% 31%	6018
	11th to 20th	Day	17% 9% 3 7% 5% 4 4 4 5% 8% 33%	5980
	21st to end	Day	17% 6% 2 6% 4 4 4 3 5% 7% 40%	6949
June	1st to 10th	Day	12% 6% 2 6% 4 4 5% 4 7% 7% 41%	2800
	11th to 20th	Day	10% 6% 2 6% 5% 5% 5% 5% 8% 9% 39%	2833
	21st to end	Day	10% 5% 2 6% 4 4 5% 4 7% 10% 44%	3000
July	1st to 10th	Day	8% 5% 2 6% 4 5% 5% 4 6% 9% 46%	6617
	11th to 20th	Day	9% 5% 2 6% 4 4 5% 4 7% 9% 46%	5949
	21st to end	Day	8% 4 2 6% 4 4 5% 4 6% 9% 48%	6424
August	1st to 10th	Day	16% 5% 2 4 4 4 5% 4 7% 9% 41%	4234
	11th to 20th	Day	11% 5% 2 6% 5% 5% 5% 5% 8% 10% 37%	4174
	21st to end	Day	9% 6% 2 6% 5% 4 5% 4 6% 9% 44%	4576
September	1st to 10th	Day	11% 5% 2 6% 4 5% 5% 4 5% 9% 44%	2370
	11th to 20th	Day	9% 5% 2 5% 4 4 4 4 6% 8% 50%	2200
	21st to end	Day	16% 6% 2 6% 4 5% 5% 4 6% 7% 38%	2200
October	1st to 10th	Day	15% 7% 2 6% 5% 4 5% 4 5% 7% 40%	2025
	11th to 20th	Day	19% 8% 3 7% 4 5% 5% 4 6% 7% 31%	2000
	21st to end	Day	23% 10% 3 9% 5% 4 5% 4 5% 6% 26%	2200
November	1st to 10th	Day	15% 8% 2 7% 5% 5% 5% 4 6% 7% 35%	1852
	11th to 20th	Day	17% 12% 4 8% 4 4 4 3 6% 7% 30%	1706
	21st to end	Day	21% 14% 5% 9% 6% 6% 4 5% 5% 6% 19%	1680
December	1st to 10th	Day	20% 17% 5% 11% 6% 5% 4 4 5% 7% 16%	2680
	11th to 20th	Day	22% 18% 5% 10% 6% 5% 4 3 5% 5% 17%	3066
	21st to end	Day	28% 19% 5% 9% 5% 4 4 4 4 5% 13%	4048
January	1st to 10th	Night	16% 16% 6% 13% 5% 5% 5% 4 5% 5% 20%	7874
	11th to 20th	Night	13% 19% 7% 17% 8% 9% 4 3 4 4 13%	7639
	21st to end	Night	17% 15% 7% 15% 7% 5% 4 2 4 4 20%	8401
February	1st to 10th	Night	16% 15% 4 11% 7% 5% 5% 3 5% 5% 23%	2730
	11th to 20th	Night	16% 14% 4 9% 5% 5% 5% 4 6% 6% 25%	2663
	21st to end	Night	18% 13% 4 10% 6% 5% 4 4 5% 7% 24%	2095
March	1st to 10th	Night	17% 10% 3 8% 6% 4 4 4 5% 6% 33%	5076
	11th to 20th	Night	12% 8% 3 6% 5% 4 5% 4 5% 8% 40%	5089
	21st to end	Night	17% 10% 3 8% 4 4 4 4 4 4 37%	5588
April	1st to 10th	Night	20% 9% 3 7% 5% 4 4 4 5% 6% 31%	2216
	11th to 20th	Night	17% 9% 3 8% 5% 4 4 4 5% 7% 35%	1941
	21st to end	Night	16% 6% 2 8% 5% 5% 5% 4 5% 7% 37%	1890
May	1st to 10th	Night	22% 10% 3 8% 4 4 4 3 4 5% 33%	4143
	11th to 20th	Night	14% 7% 3 8% 6% 5% 5% 4 5% 6% 37%	4045
	21st to end	Night	18% 5% 2 5% 3 3 4 4 6% 8% 41%	3926
June	1st to 10th	Night	12% 6% 2 5% 5% 4 5% 4 6% 8% 44%	1600
	11th to 20th	Night	10% 5% 2 5% 5% 4 5% 4 7% 10% 42%	1556
	21st to end	Night	10% 5% 3 6% 3 4 4 4 6% 9% 46%	1400
July	1st to 10th	Night	7% 4 2 5% 5% 4 4 5% 6% 10% 47%	3331
	11th to 20th	Night	9% 4 2 5% 4 4 4 4 6% 9% 48%	4006
	21st to end	Night	7% 5% 2 6% 4 4 5% 4 5% 8% 50%	4428
August	1st to 10th	Night	12% 6% 2 6% 4 4 4 4 6% 9% 44%	2915
	11th to 20th	Night	11% 5% 2 5% 4 4 4 3 5% 9% 48%	2875
	21st to end	Night	8% 4 2 6% 5% 4 4 4 6% 8% 49%	3289
September	1st to 10th	Night	9% 6% 2 6% 4 4 5% 4 5% 8% 47%	2025
	11th to 20th	Night	9% 4 1 4 3 4 4 4 6% 7% 54%	2200
	21st to end	Night	16% 5% 2 7% 5% 5% 4 4 5% 7% 39%	2200
October	1st to 10th	Night	14% 6% 2 6% 4 4 4 3 6% 7% 44%	2375
	11th to 20th	Night	18% 9% 3 8% 4 5% 4 3 5% 6% 36%	2400
	21st to end	Night	22% 9% 3 7% 5% 4 4 4 5% 6% 31%	2640
November	1st to 10th	Night	16% 7% 2 7% 4 4 4 3 7% 6% 40%	2663
	11th to 20th	Night	17% 10% 3 8% 6% 5% 5% 5% 6% 7% 28%	2913
	21st to end	Night	22% 14% 4 7% 6% 5% 5% 4 5% 7% 23%	2940
December	1st to 10th	Night	17% 17% 5% 12% 6% 5% 5% 4 5% 7% 17%	4720
	11th to 20th	Night	19% 18% 6% 11% 6% 4 4 3 4 5% 20%	5348
	21st to end	Night	26% 18% 5% 10% 5% 4 4 3 5% 5% 16%	7150

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	55% 23% 7% 9% 5%	5004
	11th to 20th	Day	69% 23% 3 3 2	5280
	21st to end	Day	55% 24% 8% 7% 5% 1	5780
February	1st to 10th	Day	28% 59% 3 7% 3	1890
	11th to 20th	Day	27% 58% 3 9% 3	1852
	21st to end	Day	25% 60% 5% 7% 3 1	1709
March	1st to 10th	Day	45% 30% 9% 12% 4	4985
	11th to 20th	Day	34% 30% 16% 15% 4 1	5090
	21st to end	Day	40% 29% 7% 16% 8% 1	5586
April	1st to 10th	Day	26% 59% 4 7% 4	2404
	11th to 20th	Day	22% 60% 4 9% 5% 1	2644
	21st to end	Day	21% 60% 5% 9% 5% 1	2730
May	1st to 10th	Day	40% 30% 8% 12% 6% 4	6027
	11th to 20th	Day	37% 33% 9% 15% 5% 1	5984
	21st to end	Day	34% 30% 7% 14% 11% 4	6949
June	1st to 10th	Day	16% 62% 4 10% 7% 1	2800
	11th to 20th	Day	17% 63% 6% 8% 6% 1	2833
	21st to end	Day	14% 61% 5% 11% 8%	3000
July	1st to 10th	Day	27% 27% 10% 22% 13% 2	6548
	11th to 20th	Day	25% 27% 11% 24% 13% 1	5878
	21st to end	Day	23% 27% 11% 20% 17% 1	6240
August	1st to 10th	Day	27% 37% 10% 15% 10% 1	4221
	11th to 20th	Day	27% 39% 10% 19% 4	4213
	21st to end	Day	23% 38% 8% 22% 8%	4576
September	1st to 10th	Day	15% 58% 7% 14% 6%	2370
	11th to 20th	Day	13% 58% 6% 15% 9%	2200
	21st to end	Day	19% 57% 6% 11% 6%	2200
October	1st to 10th	Day	22% 37% 10% 17% 14% 1	3298
	11th to 20th	Day	21% 36% 10% 20% 13%	3240
	21st to end	Day	27% 36% 12% 19% 5%	3538
November	1st to 10th	Day	26% 54% 6% 10% 3 1	1852
	11th to 20th	Day	25% 55% 7% 9% 5%	1706
	21st to end	Day	30% 56% 7% 5% 2	1680
December	1st to 10th	Day	45% 37% 9% 7% 2	2680
	11th to 20th	Day	49% 32% 8% 6% 5%	3066
	21st to end	Day	56% 29% 6% 7% 2	4048
January	1st to 10th	Night	52% 26% 8% 12% 3	7874
	11th to 20th	Night	58% 26% 5% 7% 4	7680
	21st to end	Night	54% 23% 5% 10% 7%	8401
February	1st to 10th	Night	25% 59% 4 8% 3	2730
	11th to 20th	Night	24% 58% 5% 9% 4	2665
	21st to end	Night	25% 60% 4 7% 3	2095
March	1st to 10th	Night	38% 29% 10% 12% 9% 1	5086
	11th to 20th	Night	29% 30% 15% 17% 9%	5090
	21st to end	Night	36% 29% 9% 11% 12% 1	5588
April	1st to 10th	Night	26% 59% 4 7% 4	2216
	11th to 20th	Night	21% 60% 4 9% 6% 1	1941
	21st to end	Night	18% 59% 5% 12% 5% 1	1890
May	1st to 10th	Night	40% 29% 7% 9% 8% 7%	4150
	11th to 20th	Night	37% 31% 8% 17% 6% 1	4046
	21st to end	Night	32% 30% 8% 16% 13% 1	3927
June	1st to 10th	Night	14% 62% 4 12% 6% 3	1600
	11th to 20th	Night	14% 62% 6% 12% 5% 1	1556
	21st to end	Night	14% 62% 5% 9% 10% 1	1400
July	1st to 10th	Night	24% 28% 11% 20% 13% 3	3293
	11th to 20th	Night	25% 27% 9% 24% 13% 1	3954
	21st to end	Night	25% 27% 10% 15% 21% 3	4297
August	1st to 10th	Night	24% 37% 8% 16% 12% 2	2904
	11th to 20th	Night	25% 37% 11% 21% 6%	2902
	21st to end	Night	21% 38% 8% 23% 10%	3289
September	1st to 10th	Night	14% 57% 6% 14% 8%	2025
	11th to 20th	Night	11% 57% 5% 15% 11% 1	2200
	21st to end	Night	19% 57% 5% 12% 7% 1	2200
October	1st to 10th	Night	16% 36% 4 22% 19% 1	3882
	11th to 20th	Night	25% 36% 9% 17% 13%	3899
	21st to end	Night	21% 36% 12% 20% 11%	4252
November	1st to 10th	Night	24% 54% 6% 10% 6%	2663
	11th to 20th	Night	22% 54% 5% 13% 5%	2913
	21st to end	Night	29% 55% 7% 6% 2	2940
December	1st to 10th	Night	41% 37% 11% 8% 2	4720
	11th to 20th	Night	45% 33% 6% 10% 5%	5348
	21st to end	Night	52% 28% 8% 8% 4	7150

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% 19% 35% 14% 6% 2	283
	11th to 20th	Day	27% 18% 37% 13% 4 1	330
	21st to end	Day	26% 18% 32% 19% 3 1	363
February	1st to 10th	Day	20% 19% 40% 16% 4	330
	11th to 20th	Day	25% 22% 36% 14% 2	330
	21st to end	Day	26% 23% 40% 10% 1	273
March	1st to 10th	Day	24% 14% 34% 21% 7% 1	504
	11th to 20th	Day	23% 16% 35% 21% 4 1	540
	21st to end	Day	28% 15% 33% 18% 5% 1	594
April	1st to 10th	Day	22% 18% 32% 21% 6% 1	540
	11th to 20th	Day	25% 15% 29% 19% 9% 3	532
	21st to end	Day	23% 10% 34% 24% 8% 2	540
May	1st to 10th	Day	25% 12% 30% 21% 9% 3	543
	11th to 20th	Day	18% 9% 26% 27% 15% 4	551
	21st to end	Day	15% 6% 23% 30% 20% 5%	573
June	1st to 10th	Day	13% 6% 32% 32% 14% 3	530
	11th to 20th	Day	11% 9% 24% 34% 18% 4	563
	21st to end	Day	13% 6% 29% 35% 14% 3	730
July	1st to 10th	Day	8% 4 22% 32% 25% 10%	640
	11th to 20th	Day	14% 4 23% 31% 18% 10%	524
	21st to end	Day	11% 3 20% 36% 23% 7%	576
August	1st to 10th	Day	9% 4 18% 33% 24% 13%	526
	11th to 20th	Day	12% 4 16% 33% 23% 11%	519
	21st to end	Day	13% 3 18% 34% 23% 10%	583
September	1st to 10th	Day	12% 5% 22% 28% 22% 13%	530
	11th to 20th	Day	6% 5% 15% 27% 31% 16%	530
	21st to end	Day	17% 9% 22% 30% 16% 7%	530
October	1st to 10th	Day	18% 8% 23% 26% 19% 6%	530
	11th to 20th	Day	18% 15% 31% 26% 7% 3	530
	21st to end	Day	25% 14% 31% 22% 8% 1	583
November	1st to 10th	Day	20% 17% 35% 18% 7% 2	330
	11th to 20th	Day	26% 22% 26% 17% 7% 1	234
	21st to end	Day	29% 18% 34% 16% 3	220
December	1st to 10th	Day	30% 17% 30% 18% 5% 1	220
	11th to 20th	Day	29% 22% 30% 16% 3	220
	21st to end	Day	31% 19% 30% 17% 4	242
January	1st to 10th	Night	24% 17% 36% 16% 6%	840
	11th to 20th	Night	28% 16% 32% 20% 3	840
	21st to end	Night	22% 14% 36% 22% 6%	924
February	1st to 10th	Night	24% 15% 34% 23% 3	840
	11th to 20th	Night	23% 13% 35% 25% 4	823
	21st to end	Night	25% 14% 37% 21% 3	692
March	1st to 10th	Night	21% 11% 35% 26% 7%	840
	11th to 20th	Night	21% 9% 38% 25% 7%	840
	21st to end	Night	22% 10% 31% 27% 9% 1	924
April	1st to 10th	Night	23% 11% 33% 27% 5% 1	840
	11th to 20th	Night	22% 10% 31% 28% 9% 1	697
	21st to end	Night	17% 7% 31% 35% 9% 1	630
May	1st to 10th	Night	23% 4 26% 31% 14% 1	630
	11th to 20th	Night	15% 4 25% 40% 13% 2	594
	21st to end	Night	13% 3 24% 35% 21% 3	433
June	1st to 10th	Night	15% 1 26% 41% 16% 1	400
	11th to 20th	Night	12% 3 24% 42% 19%	400
	21st to end	Night	13% 4 22% 40% 20% 1	400
July	1st to 10th	Night	7% 3 18% 43% 26% 4	390
	11th to 20th	Night	11% 3 14% 40% 28% 4	556
	21st to end	Night	9% 2 16% 45% 26% 2	657
August	1st to 10th	Night	9% 2 13% 41% 31% 4	597
	11th to 20th	Night	11% 2 14% 37% 33% 4	594
	21st to end	Night	9% 3 16% 40% 27% 4	700
September	1st to 10th	Night	13% 4 18% 33% 26% 5%	800
	11th to 20th	Night	11% 3 13% 36% 33% 5%	800
	21st to end	Night	17% 5% 21% 32% 19% 5%	800
October	1st to 10th	Night	17% 7% 22% 32% 18% 4	800
	11th to 20th	Night	20% 12% 30% 27% 11% 2	800
	21st to end	Night	24% 11% 30% 29% 6%	880
November	1st to 10th	Night	19% 12% 28% 28% 11% 1	820
	11th to 20th	Night	22% 16% 32% 22% 8% 1	840
	21st to end	Night	29% 12% 31% 22% 6%	840
December	1st to 10th	Night	30% 16% 30% 17% 6%	840
	11th to 20th	Night	26% 17% 35% 19% 4	840
	21st to end	Night	31% 12% 32% 23% 2	924

Page generated at 2026-05-14 01:58:55. Version ac07

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