Port Elgin
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Port Elgin clear sky chart from 2005-11-06 to 2025-10-19.

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% 12% 4 10% 5% 4 4 3 5% 6% 31%	126609
	Night	15% 14% 6% 13% 6% 4 4 3 4 5% 25%	123147
Transparency	Day	53% 4 11% 19% 10% 1	130155
	Night	60% 4 10% 16% 9% 1	127688
Seeing	Day	19% 10% 28% 26% 13% 4	16456
	Night	22% 10% 27% 28% 12% 1	25636

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	12% 21% 12% 23% 12% 6% 3 1 2 2 6%	3267
	11th to 20th	Day	9% 22% 11% 27% 14% 5% 3 1 2 2 3	3676
	21st to end	Day	14% 20% 11% 23% 8% 6% 5% 2 2 3 6%	4466
February	1st to 10th	Day	13% 20% 8% 20% 9% 6% 4 2 4 4 11%	1800
	11th to 20th	Day	13% 14% 9% 20% 10% 5% 4 4 4 4 13%	1753
	21st to end	Day	15% 19% 6% 13% 7% 5% 4 3 5% 5% 18%	1625
March	1st to 10th	Day	16% 13% 4 14% 7% 5% 4 3 4 5% 24%	4768
	11th to 20th	Day	12% 16% 7% 11% 5% 4 5% 4 6% 6% 25%	4980
	21st to end	Day	18% 15% 6% 11% 5% 3 4 3 5% 5% 26%	5465
April	1st to 10th	Day	17% 14% 5% 9% 5% 4 4 3 5% 6% 29%	2302
	11th to 20th	Day	18% 11% 3 6% 4 3 4 3 5% 6% 37%	2572
	21st to end	Day	19% 9% 3 7% 4 3 4 4 5% 7% 35%	2600
May	1st to 10th	Day	17% 10% 2 6% 4 4 4 3 6% 7% 38%	5888
	11th to 20th	Day	14% 9% 3 7% 4 4 4 3 5% 7% 40%	6039
	21st to end	Day	19% 9% 2 5% 3 3 3 3 5% 7% 41%	6949
June	1st to 10th	Day	14% 7% 3 6% 4 4 5% 4 6% 7% 41%	2947
	11th to 20th	Day	11% 5% 2 6% 5% 4 4 4 6% 9% 44%	3000
	21st to end	Day	14% 7% 2 5% 4 4 3 4 5% 8% 42%	3000
July	1st to 10th	Day	13% 7% 2 6% 4 4 4 4 6% 8% 42%	6819
	11th to 20th	Day	12% 5% 2 4 3 3 3 3 5% 8% 52%	6583
	21st to end	Day	8% 5% 2 5% 4 4 4 3 6% 9% 51%	6424
August	1st to 10th	Day	12% 5% 2 6% 4 4 5% 5% 7% 9% 42%	4234
	11th to 20th	Day	14% 6% 2 6% 4 4 4 4 6% 9% 40%	4174
	21st to end	Day	11% 5% 2 6% 4 4 5% 4 6% 10% 45%	4652
September	1st to 10th	Day	13% 6% 2 7% 5% 4 5% 4 6% 9% 39%	2355
	11th to 20th	Day	13% 6% 2 5% 4 4 4 3 6% 8% 46%	2200
	21st to end	Day	17% 9% 2 7% 4 5% 5% 4 6% 6% 35%	2200
October	1st to 10th	Day	19% 8% 3 8% 5% 4 4 4 5% 6% 35%	2040
	11th to 20th	Day	24% 15% 4 9% 5% 5% 5% 3 4 6% 21%	1980
	21st to end	Day	29% 17% 5% 9% 5% 4 3 2 4 4 18%	2009
November	1st to 10th	Day	17% 20% 5% 9% 6% 5% 4 3 5% 5% 22%	1745
	11th to 20th	Day	17% 23% 6% 11% 4 4 5% 4 4 6% 16%	1600
	21st to end	Day	20% 28% 10% 12% 4 4 4 2 4 4 9%	1600
December	1st to 10th	Day	17% 34% 13% 17% 5% 4 3 2 2 2 4	2600
	11th to 20th	Day	19% 26% 7% 18% 6% 4 4 2 3 3 7%	2821
	21st to end	Day	25% 23% 7% 12% 6% 5% 4 3 3 3 9%	3476
January	1st to 10th	Night	12% 21% 11% 26% 11% 4 3 2 2 3 4	6698
	11th to 20th	Night	12% 19% 10% 29% 11% 6% 3 2 2 2 4	6208
	21st to end	Night	12% 19% 10% 20% 9% 8% 5% 2 3 4 8%	6490
February	1st to 10th	Night	12% 21% 8% 19% 9% 5% 4 3 4 3 11%	2600
	11th to 20th	Night	14% 16% 8% 18% 8% 4 5% 3 4 4 15%	2533
	21st to end	Night	14% 16% 6% 15% 7% 5% 4 3 5% 6% 20%	2000
March	1st to 10th	Night	15% 14% 5% 11% 7% 5% 4 3 5% 6% 26%	5071
	11th to 20th	Night	10% 14% 6% 9% 5% 4 5% 4 6% 7% 30%	4979
	21st to end	Night	20% 12% 6% 13% 5% 4 3 2 4 4 26%	5467
April	1st to 10th	Night	19% 14% 4 9% 5% 4 3 3 4 6% 29%	2113
	11th to 20th	Night	18% 10% 3 7% 4 4 4 3 5% 6% 36%	1777
	21st to end	Night	19% 10% 4 8% 5% 3 4 4 4 6% 31%	1800
May	1st to 10th	Night	16% 9% 3 8% 5% 4 4 4 4 7% 36%	4053
	11th to 20th	Night	14% 7% 2 8% 5% 5% 4 3 4 7% 41%	3851
	21st to end	Night	20% 6% 2 6% 4 3 4 3 5% 6% 40%	3926
June	1st to 10th	Night	14% 7% 2 7% 4 4 4 4 5% 8% 39%	1449
	11th to 20th	Night	11% 7% 2 6% 4 4 6% 5% 7% 10% 39%	1400
	21st to end	Night	14% 6% 2 7% 5% 5% 4 4 6% 7% 41%	1400
July	1st to 10th	Night	12% 9% 4 7% 4 4 3 3 4 8% 43%	3160
	11th to 20th	Night	11% 6% 2 5% 3 3 4 4 6% 7% 48%	3376
	21st to end	Night	9% 7% 2 5% 3 4 4 4 5% 8% 50%	4428
August	1st to 10th	Night	11% 6% 2 8% 4 4 4 4 6% 6% 44%	2915
	11th to 20th	Night	14% 6% 3 8% 4 4 5% 3 6% 8% 41%	2875
	21st to end	Night	11% 6% 2 6% 4 3 4 4 5% 7% 47%	3223
September	1st to 10th	Night	11% 5% 2 7% 4 4 4 5% 6% 8% 46%	2030
	11th to 20th	Night	11% 5% 2 5% 4 4 4 3 5% 7% 50%	2200
	21st to end	Night	17% 9% 3 7% 5% 5% 5% 3 5% 5% 37%	2200
October	1st to 10th	Night	18% 7% 3 7% 5% 4 4 4 5% 6% 36%	2360
	11th to 20th	Night	25% 12% 3 10% 5% 4 4 3 5% 5% 24%	2377
	21st to end	Night	28% 15% 3 10% 5% 4 5% 3 4 5% 18%	2588
November	1st to 10th	Night	18% 18% 4 8% 4 5% 3 4 4 6% 24%	2551
	11th to 20th	Night	18% 22% 5% 12% 6% 4 4 3 4 4 17%	2800
	21st to end	Night	22% 24% 8% 12% 6% 4 3 3 4 4 12%	2800
December	1st to 10th	Night	17% 29% 10% 20% 6% 4 4 2 3 2 4	4580
	11th to 20th	Night	13% 26% 10% 20% 6% 4 4 2 3 2 9%	5367
	21st to end	Night	22% 23% 9% 14% 6% 5% 4 3 3 4 9%	7502

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	86% 2 7% 4 2	3268
	11th to 20th	Day	91% 2 3 3 1	3707
	21st to end	Day	85% 3 7% 4 2	4466
February	1st to 10th	Day	78% 3 9% 9% 1	1800
	11th to 20th	Day	75% 5% 8% 8% 4	1762
	21st to end	Day	70% 3 10% 13% 4	1625
March	1st to 10th	Day	62% 4 14% 13% 6% 1	4771
	11th to 20th	Day	58% 4 12% 18% 6% 1	4980
	21st to end	Day	60% 5% 10% 16% 8% 1	5465
April	1st to 10th	Day	56% 5% 9% 19% 10%	2302
	11th to 20th	Day	48% 5% 8% 23% 15% 1	2572
	21st to end	Day	50% 5% 11% 20% 12% 2	2600
May	1st to 10th	Day	45% 5% 12% 18% 15% 5%	5897
	11th to 20th	Day	45% 5% 13% 18% 18% 1	6043
	21st to end	Day	44% 4 11% 21% 16% 4	6949
June	1st to 10th	Day	41% 5% 12% 25% 16% 1	2947
	11th to 20th	Day	37% 5% 12% 27% 18% 1	3000
	21st to end	Day	41% 5% 14% 24% 14% 2	3000
July	1st to 10th	Day	39% 5% 15% 23% 17% 1	6746
	11th to 20th	Day	32% 4 12% 36% 16% 1	6502
	21st to end	Day	30% 6% 13% 33% 17% 1	6240
August	1st to 10th	Day	37% 6% 14% 26% 16% 1	4221
	11th to 20th	Day	41% 6% 15% 26% 11%	4213
	21st to end	Day	35% 6% 15% 32% 12% 1	4652
September	1st to 10th	Day	40% 6% 13% 27% 12% 2	2355
	11th to 20th	Day	36% 5% 15% 31% 13%	2200
	21st to end	Day	48% 5% 13% 24% 9% 1	2200
October	1st to 10th	Day	45% 4 13% 26% 11% 1	3326
	11th to 20th	Day	53% 4 11% 22% 9%	3220
	21st to end	Day	64% 4 12% 16% 4	3285
November	1st to 10th	Day	64% 4 10% 16% 6%	1745
	11th to 20th	Day	70% 5% 11% 9% 5% 1	1600
	21st to end	Day	80% 3 9% 7% 1	1600
December	1st to 10th	Day	90% 3 4 3 1	2600
	11th to 20th	Day	82% 3 8% 5% 1	2820
	21st to end	Day	81% 3 8% 6% 2	3476
January	1st to 10th	Night	88% 2 6% 4	6698
	11th to 20th	Night	88% 3 6% 2 1	6252
	21st to end	Night	81% 3 10% 5% 2	6490
February	1st to 10th	Night	79% 3 7% 9% 2	2600
	11th to 20th	Night	73% 4 9% 11% 3	2535
	21st to end	Night	65% 4 12% 12% 6%	2000
March	1st to 10th	Night	60% 4 14% 16% 6%	5081
	11th to 20th	Night	53% 4 16% 18% 8% 1	4980
	21st to end	Night	62% 3 9% 16% 10% 1	5467
April	1st to 10th	Night	58% 3 8% 19% 11% 1	2113
	11th to 20th	Night	49% 4 7% 21% 18% 1	1777
	21st to end	Night	54% 4 8% 17% 15% 2	1800
May	1st to 10th	Night	48% 4 9% 18% 14% 6%	4060
	11th to 20th	Night	43% 5% 10% 23% 18% 2	3852
	21st to end	Night	45% 3 11% 24% 15% 2	3927
June	1st to 10th	Night	42% 4 10% 23% 18% 3	1449
	11th to 20th	Night	37% 6% 14% 24% 17% 2	1400
	21st to end	Night	40% 5% 13% 24% 16% 2	1400
July	1st to 10th	Night	41% 3 11% 23% 18% 4	3125
	11th to 20th	Night	33% 5% 11% 31% 18% 1	3334
	21st to end	Night	33% 5% 11% 30% 20% 1	4297
August	1st to 10th	Night	40% 4 12% 28% 15% 1	2904
	11th to 20th	Night	41% 5% 16% 23% 14% 1	2902
	21st to end	Night	36% 5% 12% 32% 13% 1	3223
September	1st to 10th	Night	34% 6% 13% 31% 14% 2	2030
	11th to 20th	Night	35% 3 15% 31% 17%	2200
	21st to end	Night	49% 4 12% 24% 9% 1	2200
October	1st to 10th	Night	40% 4 12% 26% 17% 1	3854
	11th to 20th	Night	51% 4 16% 18% 11%	3876
	21st to end	Night	56% 4 15% 19% 5%	4262
November	1st to 10th	Night	60% 3 11% 19% 5%	2551
	11th to 20th	Night	70% 3 11% 11% 4 1	2800
	21st to end	Night	76% 4 12% 7% 1	2800
December	1st to 10th	Night	88% 3 6% 3 1	4580
	11th to 20th	Night	82% 3 9% 5% 1	5367
	21st to end	Night	80% 3 8% 6% 2	7502

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	19% 20% 37% 15% 8%	223
	11th to 20th	Day	19% 19% 40% 15% 7% 1	300
	21st to end	Day	25% 12% 32% 25% 5%	330
February	1st to 10th	Day	24% 24% 33% 13% 5%	300
	11th to 20th	Day	22% 16% 44% 15% 3	300
	21st to end	Day	22% 29% 33% 14% 3	249
March	1st to 10th	Day	22% 17% 37% 18% 6% 1	422
	11th to 20th	Day	22% 16% 32% 25% 5% 1	500
	21st to end	Day	27% 10% 32% 23% 7% 1	550
April	1st to 10th	Day	24% 15% 33% 20% 8% 1	500
	11th to 20th	Day	29% 14% 26% 16% 9% 6%	492
	21st to end	Day	25% 9% 29% 25% 9% 2	500
May	1st to 10th	Day	21% 9% 31% 26% 10% 3	503
	11th to 20th	Day	19% 7% 27% 26% 17% 5%	527
	21st to end	Day	16% 7% 26% 28% 16% 6%	573
June	1st to 10th	Day	14% 9% 30% 31% 14% 2	677
	11th to 20th	Day	13% 7% 30% 31% 15% 3	730
	21st to end	Day	17% 7% 30% 32% 13% 2	730
July	1st to 10th	Day	11% 5% 26% 33% 21% 5%	721
	11th to 20th	Day	13% 4 27% 32% 17% 7%	714
	21st to end	Day	11% 5% 22% 38% 18% 6%	576
August	1st to 10th	Day	11% 4 19% 35% 21% 10%	526
	11th to 20th	Day	14% 5% 15% 32% 22% 12%	519
	21st to end	Day	15% 5% 20% 30% 22% 7%	583
September	1st to 10th	Day	14% 7% 20% 32% 19% 8%	530
	11th to 20th	Day	10% 5% 18% 26% 26% 14%	530
	21st to end	Day	16% 7% 25% 28% 17% 7%	530
October	1st to 10th	Day	20% 10% 26% 24% 14% 6%	530
	11th to 20th	Day	26% 14% 31% 21% 6% 1	522
	21st to end	Day	34% 15% 29% 17% 5%	458
November	1st to 10th	Day	26% 18% 29% 20% 5% 1	291
	11th to 20th	Day	28% 19% 32% 17% 4 3	200
	21st to end	Day	30% 20% 34% 15% 2	200
December	1st to 10th	Day	29% 20% 33% 15% 4 1	200
	11th to 20th	Day	29% 19% 31% 17% 4 1	200
	21st to end	Day	38% 15% 32% 12% 3	220
January	1st to 10th	Night	25% 16% 33% 19% 6% 1	1000
	11th to 20th	Night	26% 15% 33% 20% 5% 1	957
	21st to end	Night	21% 11% 34% 26% 7% 1	880
February	1st to 10th	Night	22% 15% 36% 22% 5%	800
	11th to 20th	Night	22% 13% 35% 25% 5% 1	783
	21st to end	Night	21% 15% 36% 23% 4	660
March	1st to 10th	Night	19% 13% 37% 24% 6%	800
	11th to 20th	Night	19% 14% 35% 25% 6% 1	800
	21st to end	Night	23% 11% 27% 28% 10% 1	880
April	1st to 10th	Night	24% 10% 32% 27% 7%	797
	11th to 20th	Night	23% 9% 27% 28% 10% 2	593
	21st to end	Night	26% 9% 22% 31% 12% 1	600
May	1st to 10th	Night	19% 5% 24% 37% 14% 2	600
	11th to 20th	Night	19% 5% 20% 40% 15% 1	514
	21st to end	Night	15% 3 22% 40% 19% 1	433
June	1st to 10th	Night	14% 6% 24% 41% 14% 2	400
	11th to 20th	Night	13% 5% 25% 40% 17% 1	400
	21st to end	Night	17% 4 19% 39% 21% 1	400
July	1st to 10th	Night	11% 3 18% 46% 19% 2	390
	11th to 20th	Night	10% 2 20% 39% 27% 2	474
	21st to end	Night	10% 3 16% 44% 25% 1	657
August	1st to 10th	Night	11% 3 16% 38% 31% 1	597
	11th to 20th	Night	12% 2 13% 38% 29% 4	594
	21st to end	Night	15% 3 17% 35% 28% 2	660
September	1st to 10th	Night	12% 4 21% 36% 21% 6%	788
	11th to 20th	Night	13% 3 16% 37% 26% 4	800
	21st to end	Night	18% 7% 21% 30% 20% 4	800
October	1st to 10th	Night	21% 7% 24% 32% 15% 2	800
	11th to 20th	Night	28% 10% 25% 28% 8% 1	793
	21st to end	Night	35% 12% 25% 24% 4	836
November	1st to 10th	Night	29% 13% 26% 23% 8% 1	780
	11th to 20th	Night	27% 20% 27% 20% 6%	800
	21st to end	Night	34% 14% 30% 20% 3	800
December	1st to 10th	Night	33% 15% 31% 17% 4	800
	11th to 20th	Night	26% 16% 38% 17% 3	870
	21st to end	Night	32% 14% 32% 19% 3	1100

Page generated at 2025-10-16 01:50:23. Version ac07

Copyright © 2025 Attilla Danko.