Port Colborne
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Port Colborne clear sky chart from 2005-11-06 to 2025-01-22.

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% 10% 3 8% 5% 5% 5% 4 6% 7% 32%	105153
	Night	17% 12% 4 8% 5% 5% 4 4 5% 6% 31%	104210
Transparency	Day	28% 47% 8% 11% 6%	108759
	Night	30% 46% 7% 11% 6%	108692
Seeing	Day	19% 11% 26% 24% 14% 5%	14692
	Night	21% 9% 27% 28% 13% 1	24247

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% 20% 7% 12% 6% 4 3 3 5% 5% 17%	2597
	11th to 20th	Day	14% 22% 7% 20% 10% 5% 4 3 4 4 9%	2899
	21st to end	Day	22% 19% 8% 13% 7% 5% 4 3 4 4 12%	3133
February	1st to 10th	Day	18% 16% 5% 14% 7% 6% 5% 3 4 5% 16%	1710
	11th to 20th	Day	14% 17% 6% 14% 7% 5% 4 4 5% 5% 20%	1663
	21st to end	Day	21% 13% 4 12% 8% 4 5% 3 6% 4 21%	1489
March	1st to 10th	Day	20% 12% 3 8% 6% 5% 4 3 4 5% 29%	3432
	11th to 20th	Day	10% 18% 5% 9% 6% 5% 4 3 5% 6% 29%	3480
	21st to end	Day	17% 11% 4 9% 5% 4 4 4 5% 6% 31%	3815
April	1st to 10th	Day	19% 13% 3 7% 4 4 4 4 5% 6% 31%	2247
	11th to 20th	Day	18% 10% 2 7% 4 5% 4 3 5% 7% 35%	2291
	21st to end	Day	19% 10% 3 7% 5% 5% 5% 3 4 6% 34%	2470
May	1st to 10th	Day	19% 8% 3 7% 5% 5% 5% 4 5% 7% 32%	4108
	11th to 20th	Day	13% 10% 4 9% 6% 5% 5% 4 6% 7% 31%	4329
	21st to end	Day	11% 6% 2 5% 4 4 4 4 6% 8% 46%	4837
June	1st to 10th	Day	14% 8% 2 6% 4 4 4 4 7% 8% 39%	2660
	11th to 20th	Day	11% 5% 2 6% 5% 5% 5% 5% 7% 10% 40%	2660
	21st to end	Day	14% 6% 2 5% 4 3 4 4 7% 8% 43%	2660
July	1st to 10th	Day	8% 5% 2 5% 4 4 5% 5% 6% 9% 47%	4440
	11th to 20th	Day	11% 6% 2 5% 4 4 5% 4 7% 10% 43%	4418
	21st to end	Day	6% 5% 3 6% 4 5% 5% 4 7% 9% 43%	4466
August	1st to 10th	Day	16% 6% 3 6% 4 4 4 4 7% 8% 39%	4104
	11th to 20th	Day	12% 6% 3 7% 5% 5% 5% 5% 7% 11% 35%	4044
	21st to end	Day	10% 5% 2 5% 4 4 5% 4 6% 9% 46%	4317
September	1st to 10th	Day	13% 7% 2 6% 4 5% 5% 4 6% 7% 43%	2280
	11th to 20th	Day	10% 5% 2 5% 4 5% 4 4 7% 8% 47%	2176
	21st to end	Day	15% 7% 4 9% 6% 5% 5% 4 6% 7% 33%	2044
October	1st to 10th	Day	18% 7% 3 7% 4 5% 5% 3 5% 6% 36%	1900
	11th to 20th	Day	19% 10% 3 7% 6% 4 5% 3 5% 7% 30%	1900
	21st to end	Day	23% 11% 4 10% 6% 5% 5% 3 5% 6% 22%	2090
November	1st to 10th	Day	14% 9% 4 9% 5% 5% 5% 4 5% 7% 33%	1748
	11th to 20th	Day	15% 12% 4 8% 6% 4 5% 4 5% 8% 29%	1600
	21st to end	Day	21% 14% 4 9% 5% 4 4 4 6% 7% 22%	1600
December	1st to 10th	Day	21% 15% 5% 12% 7% 5% 5% 4 6% 5% 15%	2600
	11th to 20th	Day	21% 17% 5% 10% 5% 4 4 3 5% 5% 21%	2986
	21st to end	Day	25% 20% 5% 11% 6% 4 4 3 5% 6% 12%	3960
January	1st to 10th	Night	18% 19% 5% 11% 6% 5% 4 3 4 5% 20%	4569
	11th to 20th	Night	15% 18% 7% 13% 8% 6% 5% 4 5% 6% 13%	4278
	21st to end	Night	24% 19% 6% 14% 6% 5% 3 3 3 4 14%	4546
February	1st to 10th	Night	18% 18% 6% 11% 7% 5% 4 3 4 5% 20%	2470
	11th to 20th	Night	16% 15% 5% 10% 6% 5% 5% 4 6% 6% 22%	2403
	21st to end	Night	19% 14% 4 10% 6% 6% 4 4 5% 6% 22%	1959
March	1st to 10th	Night	20% 12% 3 8% 6% 4 3 3 3 5% 32%	3408
	11th to 20th	Night	17% 13% 3 8% 4 4 5% 3 5% 6% 31%	3479
	21st to end	Night	16% 8% 3 7% 4 3 3 3 4 6% 42%	3817
April	1st to 10th	Night	21% 10% 3 8% 5% 4 5% 3 5% 5% 31%	1933
	11th to 20th	Night	19% 8% 3 7% 5% 4 4 4 4 7% 35%	1852
	21st to end	Night	16% 9% 3 7% 5% 4 5% 5% 5% 5% 35%	1710
May	1st to 10th	Night	20% 10% 4 8% 4 4 4 2 5% 6% 32%	2833
	11th to 20th	Night	12% 6% 3 6% 5% 6% 6% 5% 6% 8% 36%	2561
	21st to end	Night	12% 5% 2 5% 4 4 4 3 6% 8% 46%	2738
June	1st to 10th	Night	11% 7% 2 8% 5% 5% 5% 6% 7% 8% 36%	1520
	11th to 20th	Night	10% 5% 2 7% 5% 5% 6% 4 6% 8% 42%	1520
	21st to end	Night	13% 6% 2 6% 6% 4 5% 4 6% 7% 41%	1520
July	1st to 10th	Night	7% 5% 2 6% 5% 4 5% 4 6% 10% 45%	2520
	11th to 20th	Night	10% 5% 2 5% 4 4 4 4 6% 9% 46%	2539
	21st to end	Night	8% 5% 2 5% 5% 4 5% 4 7% 8% 47%	3087
August	1st to 10th	Night	9% 7% 3 6% 4 4 5% 4 6% 8% 42%	2825
	11th to 20th	Night	11% 8% 3 7% 4 3 5% 5% 6% 8% 39%	2785
	21st to end	Night	8% 4 2 5% 5% 4 5% 5% 7% 9% 46%	3306
September	1st to 10th	Night	13% 6% 2 6% 4 4 4 3 5% 7% 46%	1900
	11th to 20th	Night	12% 4 2 4 3 3 3 4 5% 8% 53%	2000
	21st to end	Night	16% 7% 3 8% 6% 4 5% 3 6% 6% 36%	2135
October	1st to 10th	Night	17% 6% 2 7% 5% 4 5% 4 5% 6% 39%	2280
	11th to 20th	Night	20% 8% 3 8% 5% 5% 4 4 5% 6% 31%	2280
	21st to end	Night	23% 8% 3 8% 5% 5% 4 4 6% 6% 29%	2508
November	1st to 10th	Night	17% 8% 3 7% 4 4 4 3 5% 6% 39%	2545
	11th to 20th	Night	15% 12% 4 8% 5% 5% 5% 4 5% 8% 30%	2800
	21st to end	Night	20% 13% 3 9% 5% 4 5% 4 5% 7% 25%	2800
December	1st to 10th	Night	18% 19% 5% 10% 5% 5% 5% 4 6% 6% 16%	4580
	11th to 20th	Night	18% 20% 6% 10% 5% 5% 4 3 4 5% 20%	5208
	21st to end	Night	26% 16% 5% 9% 5% 5% 5% 3 5% 5% 14%	6996

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	45% 41% 6% 5% 3	2598
	11th to 20th	Day	54% 39% 3 2 1	2899
	21st to end	Day	48% 42% 6% 2 1	3133
February	1st to 10th	Day	26% 66% 5% 3	1710
	11th to 20th	Day	23% 65% 4 7% 1	1672
	21st to end	Day	20% 67% 4 6% 3	1489
March	1st to 10th	Day	32% 44% 7% 13% 4	3435
	11th to 20th	Day	31% 43% 13% 10% 3	3480
	21st to end	Day	29% 44% 9% 14% 5% 1	3815
April	1st to 10th	Day	23% 65% 4 6% 2	2247
	11th to 20th	Day	18% 67% 3 8% 4 1	2291
	21st to end	Day	19% 66% 5% 4 5% 1	2470
May	1st to 10th	Day	31% 44% 8% 11% 5% 1	4120
	11th to 20th	Day	32% 45% 11% 11% 1	4333
	21st to end	Day	21% 43% 8% 16% 11% 2	4837
June	1st to 10th	Day	16% 66% 4 7% 6% 1	2660
	11th to 20th	Day	14% 67% 5% 8% 6% 1	2660
	21st to end	Day	15% 64% 4 10% 7%	2660
July	1st to 10th	Day	23% 37% 8% 19% 11% 1	4370
	11th to 20th	Day	22% 38% 9% 22% 9%	4343
	21st to end	Day	21% 38% 13% 13% 13% 1	4324
August	1st to 10th	Day	29% 39% 9% 14% 9% 1	4091
	11th to 20th	Day	29% 41% 11% 15% 4	4083
	21st to end	Day	21% 39% 8% 24% 8%	4317
September	1st to 10th	Day	14% 61% 7% 12% 5%	2280
	11th to 20th	Day	12% 61% 6% 11% 9% 1	2176
	21st to end	Day	19% 61% 7% 9% 4	2044
October	1st to 10th	Day	20% 39% 10% 18% 12% 1	3160
	11th to 20th	Day	24% 38% 12% 14% 11%	3140
	21st to end	Day	29% 38% 11% 16% 5%	3428
November	1st to 10th	Day	26% 57% 7% 7% 2	1748
	11th to 20th	Day	23% 58% 7% 10% 2	1600
	21st to end	Day	28% 59% 8% 5% 1	1600
December	1st to 10th	Day	46% 38% 11% 4 1	2600
	11th to 20th	Day	45% 33% 7% 7% 7%	2986
	21st to end	Day	56% 28% 8% 6% 2	3960
January	1st to 10th	Night	44% 39% 9% 6% 1	4569
	11th to 20th	Night	45% 46% 4 3 1	4278
	21st to end	Night	50% 41% 5% 3 1	4546
February	1st to 10th	Night	24% 66% 4 5% 1	2470
	11th to 20th	Night	22% 65% 4 7% 2	2405
	21st to end	Night	22% 66% 4 5% 3	1959
March	1st to 10th	Night	34% 41% 6% 15% 4	3418
	11th to 20th	Night	31% 45% 12% 8% 4 1	3480
	21st to end	Night	22% 42% 8% 17% 10%	3817
April	1st to 10th	Night	23% 65% 3 6% 3	1933
	11th to 20th	Night	18% 66% 4 7% 5% 1	1852
	21st to end	Night	16% 65% 4 8% 5% 1	1710
May	1st to 10th	Night	33% 44% 6% 10% 5% 2	2840
	11th to 20th	Night	28% 45% 13% 13% 1	2562
	21st to end	Night	21% 42% 7% 15% 14% 1	2739
June	1st to 10th	Night	16% 66% 3 7% 7% 1	1520
	11th to 20th	Night	15% 66% 4 9% 6% 1	1520
	21st to end	Night	16% 64% 4 8% 7% 1	1520
July	1st to 10th	Night	25% 37% 8% 14% 14% 2	2480
	11th to 20th	Night	23% 37% 9% 22% 9%	2491
	21st to end	Night	22% 38% 12% 15% 12% 1	2988
August	1st to 10th	Night	25% 39% 9% 18% 8% 2	2814
	11th to 20th	Night	30% 39% 10% 17% 4	2812
	21st to end	Night	19% 40% 9% 23% 9%	3306
September	1st to 10th	Night	13% 61% 7% 11% 7%	1900
	11th to 20th	Night	11% 61% 6% 12% 10% 1	2000
	21st to end	Night	19% 61% 5% 10% 6%	2135
October	1st to 10th	Night	24% 38% 6% 17% 16%	3800
	11th to 20th	Night	29% 38% 8% 15% 10%	3779
	21st to end	Night	22% 38% 14% 20% 7%	4120
November	1st to 10th	Night	25% 57% 6% 8% 5%	2545
	11th to 20th	Night	21% 59% 7% 10% 3	2800
	21st to end	Night	26% 60% 7% 6% 1	2800
December	1st to 10th	Night	45% 38% 11% 5% 1	4580
	11th to 20th	Night	46% 33% 6% 7% 7% 1	5208
	21st to end	Night	52% 29% 9% 8% 3	6996

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	22% 19% 35% 17% 7% 2	200
	11th to 20th	Day	25% 21% 35% 13% 5% 1	292
	21st to end	Day	25% 18% 30% 19% 8% 1	300
February	1st to 10th	Day	25% 17% 37% 17% 3	270
	11th to 20th	Day	22% 25% 35% 16% 2	270
	21st to end	Day	28% 22% 32% 16% 2	263
March	1st to 10th	Day	22% 14% 35% 21% 6% 1	460
	11th to 20th	Day	23% 15% 34% 21% 6% 1	460
	21st to end	Day	28% 10% 30% 23% 7% 2	506
April	1st to 10th	Day	23% 13% 30% 24% 8% 2	460
	11th to 20th	Day	27% 14% 27% 17% 11% 4	452
	21st to end	Day	23% 11% 30% 23% 10% 3	460
May	1st to 10th	Day	24% 12% 23% 26% 11% 5%	463
	11th to 20th	Day	16% 9% 23% 28% 19% 5%	487
	21st to end	Day	12% 7% 24% 28% 22% 7%	529
June	1st to 10th	Day	16% 8% 29% 30% 14% 2	490
	11th to 20th	Day	12% 8% 25% 31% 20% 4	490
	21st to end	Day	17% 6% 27% 31% 15% 4	490
July	1st to 10th	Day	8% 5% 18% 30% 29% 9%	485
	11th to 20th	Day	14% 6% 19% 29% 22% 11%	484
	21st to end	Day	10% 5% 24% 33% 21% 7%	532
August	1st to 10th	Day	10% 6% 20% 29% 23% 12%	486
	11th to 20th	Day	13% 5% 17% 28% 24% 12%	479
	21st to end	Day	12% 5% 20% 29% 22% 11%	539
September	1st to 10th	Day	14% 8% 19% 27% 23% 10%	490
	11th to 20th	Day	11% 5% 14% 25% 27% 18%	490
	21st to end	Day	16% 11% 23% 23% 18% 8%	490
October	1st to 10th	Day	21% 9% 25% 19% 18% 8%	490
	11th to 20th	Day	23% 14% 29% 23% 9% 2	490
	21st to end	Day	31% 15% 25% 20% 9%	539
November	1st to 10th	Day	22% 15% 30% 22% 8% 3	336
	11th to 20th	Day	26% 19% 27% 22% 6% 2	200
	21st to end	Day	30% 20% 35% 13% 3	200
December	1st to 10th	Day	25% 20% 33% 16% 5% 1	200
	11th to 20th	Day	29% 21% 31% 15% 5% 1	200
	21st to end	Day	26% 21% 33% 14% 4 1	220
January	1st to 10th	Night	27% 17% 33% 16% 7%	800
	11th to 20th	Night	28% 17% 31% 20% 4	800
	21st to end	Night	24% 11% 34% 25% 6%	841
February	1st to 10th	Night	27% 17% 32% 21% 3	760
	11th to 20th	Night	23% 14% 36% 22% 4	743
	21st to end	Night	27% 11% 35% 24% 3	628
March	1st to 10th	Night	21% 11% 34% 27% 6%	760
	11th to 20th	Night	24% 13% 31% 24% 8%	760
	21st to end	Night	21% 8% 33% 27% 11% 1	836
April	1st to 10th	Night	24% 10% 32% 29% 5%	760
	11th to 20th	Night	22% 9% 31% 29% 8% 2	728
	21st to end	Night	22% 7% 26% 33% 12%	570
May	1st to 10th	Night	21% 5% 24% 33% 14% 3	570
	11th to 20th	Night	15% 4 25% 41% 14% 1	414
	21st to end	Night	14% 4 22% 36% 22% 2	411
June	1st to 10th	Night	14% 4 29% 36% 17% 1	380
	11th to 20th	Night	12% 4 24% 41% 18% 1	380
	21st to end	Night	13% 6% 22% 43% 17%	380
July	1st to 10th	Night	7% 3 17% 44% 26% 2	370
	11th to 20th	Night	11% 3 20% 37% 26% 3	374
	21st to end	Night	11% 2 18% 43% 24% 2	624
August	1st to 10th	Night	10% 3 13% 40% 30% 4	567
	11th to 20th	Night	9% 3 16% 32% 36% 4	564
	21st to end	Night	11% 2 16% 40% 27% 4	731
September	1st to 10th	Night	15% 4 18% 34% 23% 5%	760
	11th to 20th	Night	13% 4 15% 30% 30% 7%	760
	21st to end	Night	18% 6% 20% 30% 21% 5%	760
October	1st to 10th	Night	19% 6% 23% 29% 20% 3	760
	11th to 20th	Night	26% 11% 25% 26% 10% 2	760
	21st to end	Night	29% 10% 28% 28% 6%	836
November	1st to 10th	Night	21% 10% 28% 28% 11% 2	780
	11th to 20th	Night	22% 14% 34% 19% 10% 2	800
	21st to end	Night	27% 12% 35% 20% 7%	800
December	1st to 10th	Night	32% 15% 29% 19% 5%	800
	11th to 20th	Night	26% 19% 32% 19% 5%	800
	21st to end	Night	31% 13% 31% 22% 3	880

Page generated at 2025-01-19 03:06:48. Version ac07

Copyright © 2025 Attilla Danko.