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 2026-08-30.

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	18% 11% 3 8% 5% 4 4 4 5% 7% 31%	144907
	Night	18% 12% 4 8% 5% 4 4 3 5% 6% 31%	137494
Transparency	Day	52% 6% 12% 20% 9% 1	148466
	Night	53% 6% 12% 19% 10% 1	142025
Seeing	Day	26% 19% 32% 17% 5% 1	19545
	Night	25% 17% 32% 21% 5%	26870

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	13% 21% 5% 11% 6% 5% 5% 4 4 5% 21%	4093
	11th to 20th	Day	16% 17% 8% 12% 5% 4 4 2 3 4 25%	4630
	21st to end	Day	10% 10% 4 12% 4 4 4 3 4 7% 38%	5781
February	1st to 10th	Day	15% 15% 5% 10% 5% 5% 4 4 4 4 28%	1890
	11th to 20th	Day	15% 16% 4 10% 7% 4 4 3 4 4 28%	1843
	21st to end	Day	11% 13% 5% 8% 5% 5% 4 3 6% 7% 32%	1563
March	1st to 10th	Day	19% 14% 4 13% 5% 4 4 3 4 5% 24%	4995
	11th to 20th	Day	14% 17% 4 11% 5% 5% 5% 4 5% 6% 24%	5090
	21st to end	Day	25% 17% 5% 8% 5% 4 4 3 5% 5% 20%	5587
April	1st to 10th	Day	22% 14% 4 8% 5% 3 4 3 3 5% 28%	2515
	11th to 20th	Day	20% 13% 3 6% 5% 5% 4 4 5% 7% 30%	2607
	21st to end	Day	21% 13% 3 7% 4 4 4 3 5% 6% 30%	2730
May	1st to 10th	Day	29% 12% 3 7% 4 4 4 3 4 5% 25%	7935
	11th to 20th	Day	21% 9% 3 6% 5% 4 4 3 5% 6% 33%	8220
	21st to end	Day	24% 10% 3 7% 4 3 4 3 5% 7% 30%	9059
June	1st to 10th	Day	25% 10% 3 6% 5% 4 4 4 6% 8% 26%	3028
	11th to 20th	Day	19% 8% 3 8% 5% 5% 5% 4 6% 6% 33%	3150
	21st to end	Day	25% 9% 3 7% 4 5% 4 3 5% 7% 29%	3150
July	1st to 10th	Day	15% 8% 2 8% 5% 5% 6% 5% 7% 9% 31%	8880
	11th to 20th	Day	13% 5% 2 7% 4 5% 5% 4 6% 8% 42%	8529
	21st to end	Day	13% 5% 2 6% 4 4 5% 4 7% 9% 40%	8884
August	1st to 10th	Day	17% 8% 3 8% 5% 5% 5% 4 6% 8% 32%	4365
	11th to 20th	Day	13% 6% 2 7% 5% 5% 5% 5% 7% 8% 38%	4305
	21st to end	Day	12% 5% 2 5% 4 4 4 4 6% 10% 44%	4640
September	1st to 10th	Day	17% 6% 2 5% 3 4 4 3 6% 9% 42%	2400
	11th to 20th	Day	17% 7% 3 7% 5% 4 4 4 5% 7% 39%	2323
	21st to end	Day	18% 6% 2 7% 4 3 4 3 5% 7% 41%	2136
October	1st to 10th	Day	19% 7% 3 6% 4 4 4 4 6% 7% 36%	2000
	11th to 20th	Day	19% 10% 3 8% 4 4 6% 3 5% 7% 32%	2000
	21st to end	Day	21% 10% 4 7% 5% 5% 5% 3 5% 6% 30%	2190
November	1st to 10th	Day	20% 14% 4 9% 5% 5% 3 3 4 5% 29%	1645
	11th to 20th	Day	21% 15% 3 7% 5% 4 4 4 4 6% 28%	1680
	21st to end	Day	18% 15% 5% 8% 6% 4 5% 3 5% 5% 26%	1680
December	1st to 10th	Day	18% 14% 4 8% 5% 4 4 3 5% 7% 29%	2690
	11th to 20th	Day	19% 14% 4 9% 5% 4 3 2 3 4 31%	3076
	21st to end	Day	16% 14% 7% 16% 4 4 4 3 3 4 23%	3618
January	1st to 10th	Night	14% 17% 4 9% 5% 5% 5% 3 5% 5% 28%	8831
	11th to 20th	Night	19% 17% 7% 10% 5% 4 4 3 3 5% 25%	8274
	21st to end	Night	9% 13% 5% 9% 6% 4 4 3 4 5% 37%	8400
February	1st to 10th	Night	17% 15% 4 9% 5% 4 5% 3 5% 5% 28%	2730
	11th to 20th	Night	17% 15% 3 10% 6% 5% 4 3 4 5% 28%	2663
	21st to end	Night	13% 14% 4 9% 5% 4 5% 4 5% 5% 33%	2242
March	1st to 10th	Night	25% 13% 4 11% 6% 4 4 2 3 4 24%	5049
	11th to 20th	Night	19% 18% 6% 9% 4 4 4 3 4 5% 25%	5089
	21st to end	Night	26% 14% 4 9% 4 4 4 3 3 3 25%	5587
April	1st to 10th	Night	23% 13% 4 8% 6% 4 5% 3 4 4 26%	2105
	11th to 20th	Night	22% 14% 3 7% 5% 4 3 2 4 5% 32%	1961
	21st to end	Night	22% 14% 4 8% 4 3 4 3 5% 6% 28%	1890
May	1st to 10th	Night	29% 13% 3 7% 5% 4 4 4 5% 6% 21%	4976
	11th to 20th	Night	21% 10% 3 7% 5% 4 4 4 4 6% 31%	4670
	21st to end	Night	21% 10% 3 8% 5% 4 4 3 5% 7% 31%	5147
June	1st to 10th	Night	25% 8% 2 6% 5% 4 4 2 6% 7% 29%	1608
	11th to 20th	Night	20% 8% 2 5% 4 4 4 4 5% 7% 35%	1470
	21st to end	Night	22% 10% 3 6% 6% 4 4 4 5% 7% 29%	1470
July	1st to 10th	Night	15% 7% 3 8% 6% 6% 5% 4 6% 8% 31%	4110
	11th to 20th	Night	11% 6% 3 7% 5% 5% 5% 5% 6% 8% 40%	4386
	21st to end	Night	15% 6% 2 7% 4 5% 4 4 6% 8% 40%	5205
August	1st to 10th	Night	16% 9% 3 8% 5% 5% 6% 4 7% 7% 31%	3005
	11th to 20th	Night	10% 7% 3 7% 5% 6% 6% 5% 6% 9% 38%	2962
	21st to end	Night	14% 5% 2 5% 4 4 4 4 5% 9% 44%	3457
September	1st to 10th	Night	15% 6% 2 7% 3 3 4 3 5% 8% 44%	2000
	11th to 20th	Night	16% 6% 2 7% 4 4 4 2 4 6% 45%	2074
	21st to end	Night	17% 7% 2 6% 3 5% 4 3 4 7% 41%	2263
October	1st to 10th	Night	19% 7% 3 7% 4 4 3 3 5% 6% 39%	2400
	11th to 20th	Night	18% 7% 4 7% 5% 5% 4 4 5% 6% 35%	2400
	21st to end	Night	25% 10% 3 6% 5% 4 4 3 5% 6% 30%	2649
November	1st to 10th	Night	21% 14% 3 7% 5% 5% 4 3 4 6% 29%	2871
	11th to 20th	Night	20% 14% 3 7% 5% 5% 4 3 5% 5% 28%	2940
	21st to end	Night	23% 13% 3 7% 4 5% 4 4 5% 6% 25%	2940
December	1st to 10th	Night	15% 12% 4 8% 5% 4 4 4 5% 6% 34%	4720
	11th to 20th	Night	22% 13% 4 8% 4 3 3 3 4 4 32%	5353
	21st to end	Night	21% 14% 5% 13% 4 3 4 3 4 5% 24%	7597

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	63% 3 13% 12% 8%	4094
	11th to 20th	Day	65% 5% 8% 13% 8% 1	4659
	21st to end	Day	47% 5% 9% 20% 16% 3	5781
February	1st to 10th	Day	60% 4 10% 14% 10% 1	1890
	11th to 20th	Day	59% 5% 10% 17% 9% 1	1851
	21st to end	Day	52% 5% 11% 19% 11% 2	1563
March	1st to 10th	Day	62% 5% 8% 15% 9% 1	4999
	11th to 20th	Day	58% 8% 13% 15% 5% 1	5090
	21st to end	Day	65% 5% 7% 16% 7% 1	5587
April	1st to 10th	Day	60% 5% 7% 15% 10% 2	2515
	11th to 20th	Day	55% 6% 9% 18% 11% 1	2607
	21st to end	Day	54% 6% 10% 17% 11% 2	2730
May	1st to 10th	Day	62% 6% 9% 15% 8%	7947
	11th to 20th	Day	51% 7% 13% 22% 7%	8224
	21st to end	Day	53% 9% 10% 16% 10% 1	9060
June	1st to 10th	Day	56% 7% 13% 19% 5%	3028
	11th to 20th	Day	50% 8% 12% 21% 8% 1	3150
	21st to end	Day	55% 7% 12% 16% 8% 1	3150
July	1st to 10th	Day	47% 8% 16% 18% 11%	8805
	11th to 20th	Day	40% 6% 15% 29% 8% 1	8448
	21st to end	Day	40% 8% 15% 28% 9%	8688
August	1st to 10th	Day	50% 8% 12% 24% 6%	4352
	11th to 20th	Day	42% 8% 15% 23% 11%	4344
	21st to end	Day	36% 7% 15% 26% 15%	4640
September	1st to 10th	Day	39% 7% 16% 25% 13%	2400
	11th to 20th	Day	43% 6% 14% 24% 12% 1	2323
	21st to end	Day	42% 6% 10% 27% 14% 1	2136
October	1st to 10th	Day	44% 7% 12% 28% 8%	3260
	11th to 20th	Day	47% 4 10% 30% 8%	3240
	21st to end	Day	45% 5% 14% 20% 15%	3517
November	1st to 10th	Day	56% 6% 11% 19% 8%	1645
	11th to 20th	Day	57% 5% 14% 15% 8%	1680
	21st to end	Day	59% 5% 14% 16% 6%	1680
December	1st to 10th	Day	54% 4 14% 23% 4	2690
	11th to 20th	Day	57% 4 10% 18% 9% 1	3075
	21st to end	Day	63% 5% 12% 13% 6% 1	3618
January	1st to 10th	Night	57% 5% 11% 21% 6%	8831
	11th to 20th	Night	63% 6% 9% 15% 7%	8320
	21st to end	Night	48% 4 10% 19% 16% 3	8400
February	1st to 10th	Night	59% 4 10% 13% 12% 2	2730
	11th to 20th	Night	57% 5% 10% 16% 10% 1	2666
	21st to end	Night	53% 5% 9% 19% 12% 2	2242
March	1st to 10th	Night	66% 4 5% 12% 12% 2	5058
	11th to 20th	Night	61% 6% 11% 13% 8% 1	5090
	21st to end	Night	63% 4 6% 15% 10% 1	5587
April	1st to 10th	Night	61% 5% 8% 13% 10% 3	2105
	11th to 20th	Night	54% 5% 9% 20% 11% 1	1961
	21st to end	Night	57% 5% 10% 15% 12% 2	1890
May	1st to 10th	Night	63% 6% 11% 13% 6% 1	4982
	11th to 20th	Night	53% 7% 12% 20% 6% 1	4671
	21st to end	Night	53% 8% 14% 15% 9% 1	5148
June	1st to 10th	Night	55% 7% 12% 18% 8%	1608
	11th to 20th	Night	49% 7% 11% 23% 8% 1	1470
	21st to end	Night	55% 8% 15% 14% 8% 1	1470
July	1st to 10th	Night	50% 8% 12% 19% 11%	4075
	11th to 20th	Night	41% 8% 15% 27% 8%	4344
	21st to end	Night	42% 8% 15% 24% 10%	5087
August	1st to 10th	Night	51% 9% 14% 20% 6%	2993
	11th to 20th	Night	42% 11% 18% 18% 11%	2989
	21st to end	Night	36% 7% 19% 26% 13%	3456
September	1st to 10th	Night	39% 7% 13% 29% 12%	2000
	11th to 20th	Night	41% 5% 13% 27% 12% 1	2074
	21st to end	Night	43% 6% 11% 27% 13% 1	2263
October	1st to 10th	Night	49% 5% 13% 24% 8%	3920
	11th to 20th	Night	39% 5% 12% 31% 13%	3899
	21st to end	Night	46% 5% 14% 22% 14%	4273
November	1st to 10th	Night	56% 6% 12% 18% 8% 1	2871
	11th to 20th	Night	56% 6% 14% 16% 8% 1	2940
	21st to end	Night	56% 6% 14% 19% 5%	2940
December	1st to 10th	Night	49% 4 13% 24% 9%	4720
	11th to 20th	Night	55% 4 10% 19% 10% 2	5355
	21st to end	Night	60% 4 12% 14% 8% 1	7597

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	32% 25% 30% 11% 1	220
	11th to 20th	Day	30% 23% 28% 15% 4	395
	21st to end	Day	21% 20% 38% 18% 3 1	473
February	1st to 10th	Day	25% 23% 32% 15% 4	430
	11th to 20th	Day	26% 28% 30% 12% 4	426
	21st to end	Day	23% 22% 35% 17% 3	355
March	1st to 10th	Day	28% 25% 35% 10% 2 1	529
	11th to 20th	Day	25% 24% 33% 13% 4	540
	21st to end	Day	32% 25% 29% 10% 3 1	594
April	1st to 10th	Day	36% 28% 27% 8% 1	540
	11th to 20th	Day	33% 25% 28% 11% 3	532
	21st to end	Day	29% 24% 29% 14% 4 1	540
May	1st to 10th	Day	35% 20% 28% 13% 4	646
	11th to 20th	Day	29% 18% 28% 18% 6% 1	774
	21st to end	Day	27% 18% 36% 16% 3	845
June	1st to 10th	Day	31% 16% 32% 15% 5%	780
	11th to 20th	Day	25% 16% 35% 19% 5% 1	780
	21st to end	Day	29% 14% 30% 21% 6% 1	780
July	1st to 10th	Day	21% 15% 39% 18% 6% 1	770
	11th to 20th	Day	19% 11% 37% 24% 8% 1	768
	21st to end	Day	20% 11% 39% 23% 7%	815
August	1st to 10th	Day	15% 11% 39% 28% 7%	566
	11th to 20th	Day	18% 10% 35% 27% 9% 2	559
	21st to end	Day	16% 16% 33% 24% 8% 2	619
September	1st to 10th	Day	16% 13% 42% 19% 8% 1	530
	11th to 20th	Day	21% 17% 31% 22% 7% 2	530
	21st to end	Day	21% 16% 32% 21% 8% 2	494
October	1st to 10th	Day	22% 16% 31% 20% 9% 2	420
	11th to 20th	Day	22% 21% 29% 20% 7% 1	420
	21st to end	Day	26% 23% 28% 17% 4 1	462
November	1st to 10th	Day	30% 23% 29% 12% 6%	425
	11th to 20th	Day	31% 25% 26% 13% 4 1	430
	21st to end	Day	31% 27% 27% 12% 3 1	430
December	1st to 10th	Day	33% 20% 31% 13% 3	430
	11th to 20th	Day	31% 28% 28% 11% 1	430
	21st to end	Day	25% 24% 34% 13% 3	268
January	1st to 10th	Night	27% 21% 31% 17% 4	950
	11th to 20th	Night	27% 22% 29% 18% 4	942
	21st to end	Night	20% 20% 37% 18% 4	924
February	1st to 10th	Night	27% 18% 33% 18% 3 1	840
	11th to 20th	Night	27% 23% 32% 15% 3 1	823
	21st to end	Night	23% 16% 37% 20% 3 1	692
March	1st to 10th	Night	27% 19% 35% 17% 2	840
	11th to 20th	Night	24% 20% 30% 20% 5% 1	840
	21st to end	Night	27% 19% 32% 17% 5%	924
April	1st to 10th	Night	31% 19% 30% 17% 2	635
	11th to 20th	Night	31% 16% 29% 19% 5%	624
	21st to end	Night	30% 15% 30% 19% 6%	630
May	1st to 10th	Night	31% 16% 28% 20% 5%	630
	11th to 20th	Night	25% 15% 29% 25% 5%	622
	21st to end	Night	23% 14% 42% 18% 2	682
June	1st to 10th	Night	32% 10% 32% 23% 4	558
	11th to 20th	Night	25% 8% 37% 25% 5%	420
	21st to end	Night	24% 10% 32% 27% 6% 1	420
July	1st to 10th	Night	18% 10% 43% 23% 6%	410
	11th to 20th	Night	16% 11% 41% 27% 5%	502
	21st to end	Night	19% 9% 36% 30% 6%	689
August	1st to 10th	Night	16% 7% 39% 30% 8%	628
	11th to 20th	Night	15% 9% 36% 30% 9% 1	622
	21st to end	Night	17% 9% 32% 32% 10%	688
September	1st to 10th	Night	19% 10% 38% 26% 7%	600
	11th to 20th	Night	18% 12% 29% 31% 9% 1	674
	21st to end	Night	21% 13% 32% 25% 9% 1	800
October	1st to 10th	Night	22% 13% 30% 26% 9%	800
	11th to 20th	Night	21% 16% 34% 21% 8% 1	800
	21st to end	Night	29% 21% 30% 17% 3	886
November	1st to 10th	Night	28% 21% 29% 17% 5%	930
	11th to 20th	Night	28% 24% 26% 17% 4 1	950
	21st to end	Night	30% 21% 29% 16% 3	950
December	1st to 10th	Night	31% 20% 29% 18% 3	950
	11th to 20th	Night	29% 25% 31% 12% 2	950
	21st to end	Night	28% 24% 26% 18% 3 1	1045

Page generated at 2026-08-27 05:07:10. Version ac07

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