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 2025-04-26.

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% 4 8% 5% 4 4 4 5% 7% 30%	113831
	Night	18% 12% 4 8% 5% 4 4 3 5% 6% 31%	114889
Transparency	Day	52% 7% 12% 19% 9% 1	117435
	Night	53% 6% 12% 19% 9% 1	119450
Seeing	Day	25% 19% 33% 17% 5% 1	17587
	Night	25% 17% 32% 21% 5%	25200

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	14% 23% 5% 11% 6% 6% 5% 4 4 4 18%	3157
	11th to 20th	Day	12% 16% 8% 12% 5% 4 4 3 4 5% 28%	3541
	21st to end	Day	10% 10% 4 13% 4 4 4 4 4 7% 36%	4466
February	1st to 10th	Day	16% 14% 4 10% 6% 5% 4 4 4 4 30%	1800
	11th to 20th	Day	15% 15% 3 10% 7% 4 4 4 5% 5% 28%	1753
	21st to end	Day	11% 13% 5% 8% 5% 5% 4 3 6% 7% 32%	1491
March	1st to 10th	Day	20% 15% 4 13% 5% 4 4 3 4 5% 24%	4886
	11th to 20th	Day	14% 17% 4 10% 5% 5% 5% 4 5% 6% 24%	4980
	21st to end	Day	25% 17% 5% 8% 5% 4 4 3 5% 5% 20%	5466
April	1st to 10th	Day	22% 14% 4 9% 5% 3 4 3 3 5% 28%	2395
	11th to 20th	Day	20% 13% 3 6% 5% 5% 4 4 5% 7% 30%	2482
	21st to end	Day	21% 13% 3 7% 4 4 4 4 5% 6% 30%	2535
May	1st to 10th	Day	26% 15% 3 7% 4 4 4 3 4 5% 24%	4264
	11th to 20th	Day	17% 8% 3 6% 4 4 5% 3 5% 7% 37%	4398
	21st to end	Day	17% 9% 3 8% 5% 5% 5% 4 7% 8% 28%	4836
June	1st to 10th	Day	26% 10% 3 7% 5% 4 4 3 6% 7% 25%	2740
	11th to 20th	Day	20% 8% 3 8% 4 5% 5% 4 6% 6% 33%	2850
	21st to end	Day	26% 9% 3 7% 4 5% 4 3 5% 7% 29%	2850
July	1st to 10th	Day	16% 8% 3 7% 5% 5% 6% 5% 6% 9% 31%	4760
	11th to 20th	Day	15% 6% 2 7% 5% 5% 6% 4 7% 9% 35%	4577
	21st to end	Day	12% 7% 3 7% 5% 4 5% 5% 7% 9% 36%	4760
August	1st to 10th	Day	18% 8% 3 8% 5% 5% 5% 4 6% 8% 30%	4105
	11th to 20th	Day	13% 6% 2 7% 5% 5% 5% 5% 7% 8% 37%	4045
	21st to end	Day	12% 5% 2 5% 3 4 4 4 6% 10% 45%	4386
September	1st to 10th	Day	17% 6% 2 5% 3 4 4 3 6% 9% 41%	2280
	11th to 20th	Day	17% 7% 3 7% 5% 4 4 4 5% 6% 38%	2207
	21st to end	Day	19% 6% 2 7% 4 3 4 3 5% 7% 40%	2029
October	1st to 10th	Day	19% 7% 3 6% 4 4 4 4 6% 8% 35%	1900
	11th to 20th	Day	19% 10% 3 8% 4 4 5% 2 5% 7% 33%	1900
	21st to end	Day	20% 10% 4 7% 5% 5% 5% 3 5% 6% 30%	2081
November	1st to 10th	Day	19% 14% 4 9% 5% 5% 3 3 4 5% 29%	1565
	11th to 20th	Day	21% 14% 4 7% 5% 4 4 4 4 6% 28%	1600
	21st to end	Day	18% 15% 5% 8% 6% 4 5% 4 5% 5% 26%	1600
December	1st to 10th	Day	18% 13% 4 8% 5% 4 4 3 5% 7% 29%	2610
	11th to 20th	Day	20% 14% 4 9% 5% 4 3 2 3 4 31%	2996
	21st to end	Day	17% 14% 7% 16% 4 4 4 3 3 4 23%	3540
January	1st to 10th	Night	14% 18% 4 9% 5% 4 5% 3 5% 5% 27%	6808
	11th to 20th	Night	15% 16% 7% 10% 5% 4 4 3 4 5% 26%	6354
	21st to end	Night	10% 13% 5% 10% 6% 4 4 3 4 5% 37%	6490
February	1st to 10th	Night	17% 14% 4 9% 6% 4 5% 3 6% 5% 28%	2600
	11th to 20th	Night	17% 15% 3 10% 6% 5% 4 3 4 5% 28%	2533
	21st to end	Night	13% 14% 4 9% 5% 4 5% 4 5% 5% 33%	2138
March	1st to 10th	Night	26% 14% 4 12% 6% 4 4 2 3 4 23%	4938
	11th to 20th	Night	19% 18% 6% 9% 4 4 4 3 4 5% 25%	4979
	21st to end	Night	27% 14% 4 9% 4 4 4 3 3 3 25%	5466
April	1st to 10th	Night	23% 14% 3 8% 6% 4 5% 3 4 3 26%	2005
	11th to 20th	Night	21% 13% 3 7% 5% 4 3 2 4 5% 32%	1867
	21st to end	Night	21% 14% 4 8% 4 3 4 3 5% 5% 28%	1762
May	1st to 10th	Night	25% 14% 3 6% 5% 4 4 4 5% 6% 25%	2679
	11th to 20th	Night	16% 10% 2 6% 4 4 4 3 4 7% 39%	2506
	21st to end	Night	16% 10% 3 9% 6% 5% 5% 4 6% 8% 29%	2749
June	1st to 10th	Night	26% 9% 3 6% 6% 4 4 2 5% 7% 27%	1455
	11th to 20th	Night	20% 9% 2 6% 5% 4 4 4 5% 7% 35%	1330
	21st to end	Night	23% 10% 3 6% 6% 4 4 4 5% 7% 29%	1330
July	1st to 10th	Night	15% 8% 3 8% 6% 6% 5% 5% 7% 7% 29%	2210
	11th to 20th	Night	13% 7% 2 7% 5% 5% 6% 5% 8% 10% 32%	2360
	21st to end	Night	13% 7% 2 6% 5% 5% 4 3 6% 8% 41%	2800
August	1st to 10th	Night	16% 9% 3 8% 6% 5% 6% 4 7% 7% 29%	2825
	11th to 20th	Night	9% 7% 3 8% 5% 6% 6% 5% 6% 9% 38%	2782
	21st to end	Night	14% 5% 2 5% 3 4 4 4 5% 9% 45%	3270
September	1st to 10th	Night	15% 6% 2 7% 4 3 4 3 5% 7% 43%	1900
	11th to 20th	Night	16% 6% 2 7% 4 4 4 2 4 6% 44%	1970
	21st to end	Night	18% 7% 2 6% 3 5% 4 3 4 7% 41%	2150
October	1st to 10th	Night	20% 7% 3 7% 4 4 3 3 4 6% 38%	2280
	11th to 20th	Night	18% 7% 4 7% 5% 4 4 4 5% 7% 36%	2280
	21st to end	Night	25% 10% 3 6% 5% 4 4 2 5% 6% 30%	2516
November	1st to 10th	Night	21% 14% 4 7% 5% 5% 4 3 4 6% 29%	2731
	11th to 20th	Night	20% 14% 3 7% 5% 5% 4 3 5% 5% 28%	2800
	21st to end	Night	23% 13% 3 7% 4 5% 4 4 5% 6% 25%	2800
December	1st to 10th	Night	16% 12% 4 8% 5% 4 4 4 5% 6% 34%	4580
	11th to 20th	Night	22% 13% 4 8% 4 3 3 3 4 4 33%	5213
	21st to end	Night	22% 14% 5% 13% 4 3 3 3 4 5% 24%	7433

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	66% 4 13% 12% 4	3158
	11th to 20th	Day	61% 6% 9% 15% 8% 1	3570
	21st to end	Day	48% 5% 10% 17% 15% 4	4466
February	1st to 10th	Day	59% 4 11% 15% 11% 1	1800
	11th to 20th	Day	59% 5% 10% 16% 9% 1	1761
	21st to end	Day	52% 5% 11% 19% 10% 2	1491
March	1st to 10th	Day	62% 5% 8% 14% 9% 1	4890
	11th to 20th	Day	58% 8% 13% 15% 5% 1	4980
	21st to end	Day	65% 5% 7% 16% 7% 1	5466
April	1st to 10th	Day	61% 5% 7% 15% 10% 3	2395
	11th to 20th	Day	55% 6% 9% 18% 11% 1	2482
	21st to end	Day	55% 6% 10% 16% 11% 2	2535
May	1st to 10th	Day	60% 7% 9% 16% 6% 1	4278
	11th to 20th	Day	46% 9% 14% 24% 7%	4402
	21st to end	Day	49% 12% 16% 16% 7%	4836
June	1st to 10th	Day	58% 6% 12% 19% 5%	2740
	11th to 20th	Day	51% 7% 12% 21% 8% 1	2850
	21st to end	Day	55% 7% 12% 16% 8% 1	2850
July	1st to 10th	Day	48% 7% 16% 18% 11%	4685
	11th to 20th	Day	46% 7% 15% 25% 6%	4496
	21st to end	Day	43% 11% 17% 24% 6%	4608
August	1st to 10th	Day	52% 8% 12% 23% 5%	4092
	11th to 20th	Day	43% 9% 14% 23% 11%	4084
	21st to end	Day	36% 7% 15% 26% 16%	4386
September	1st to 10th	Day	40% 7% 16% 25% 12%	2280
	11th to 20th	Day	44% 6% 13% 24% 12% 1	2207
	21st to end	Day	43% 6% 11% 27% 13% 1	2029
October	1st to 10th	Day	45% 7% 13% 27% 8%	3160
	11th to 20th	Day	47% 4 11% 30% 8%	3140
	21st to end	Day	45% 5% 15% 20% 15%	3408
November	1st to 10th	Day	56% 6% 11% 18% 8%	1565
	11th to 20th	Day	57% 5% 14% 15% 9%	1600
	21st to end	Day	59% 5% 14% 16% 6%	1600
December	1st to 10th	Day	54% 4 14% 23% 4	2610
	11th to 20th	Day	57% 4 10% 18% 10% 1	2995
	21st to end	Day	63% 5% 12% 13% 6% 1	3540
January	1st to 10th	Night	57% 5% 13% 22% 3	6808
	11th to 20th	Night	60% 7% 11% 16% 6%	6400
	21st to end	Night	49% 5% 10% 20% 14% 2	6490
February	1st to 10th	Night	58% 5% 10% 13% 12% 2	2600
	11th to 20th	Night	58% 5% 10% 15% 10% 1	2536
	21st to end	Night	53% 5% 9% 19% 13% 2	2138
March	1st to 10th	Night	66% 4 5% 12% 12% 2	4947
	11th to 20th	Night	61% 6% 11% 13% 8% 1	4980
	21st to end	Night	63% 4 6% 15% 10% 1	5466
April	1st to 10th	Night	60% 6% 8% 13% 10% 3	2005
	11th to 20th	Night	53% 5% 10% 20% 11% 1	1867
	21st to end	Night	57% 5% 10% 14% 12% 2	1762
May	1st to 10th	Night	59% 8% 13% 13% 6% 1	2685
	11th to 20th	Night	43% 9% 18% 23% 7% 1	2507
	21st to end	Night	51% 10% 19% 15% 5%	2750
June	1st to 10th	Night	57% 7% 12% 16% 7%	1455
	11th to 20th	Night	50% 7% 11% 23% 8% 1	1330
	21st to end	Night	55% 8% 14% 14% 8% 1	1330
July	1st to 10th	Night	51% 9% 13% 17% 10% 1	2175
	11th to 20th	Night	46% 10% 17% 19% 7%	2318
	21st to end	Night	41% 10% 17% 21% 11%	2712
August	1st to 10th	Night	53% 9% 14% 19% 5%	2813
	11th to 20th	Night	42% 11% 18% 18% 11%	2809
	21st to end	Night	35% 7% 19% 25% 13%	3269
September	1st to 10th	Night	40% 7% 13% 28% 11%	1900
	11th to 20th	Night	41% 5% 13% 27% 12% 1	1970
	21st to end	Night	43% 7% 11% 27% 12% 1	2150
October	1st to 10th	Night	50% 6% 13% 24% 8%	3800
	11th to 20th	Night	38% 5% 12% 32% 13%	3779
	21st to end	Night	45% 5% 14% 22% 14%	4140
November	1st to 10th	Night	56% 6% 12% 18% 8% 1	2731
	11th to 20th	Night	56% 6% 14% 16% 8% 1	2800
	21st to end	Night	57% 6% 14% 18% 5%	2800
December	1st to 10th	Night	49% 4 13% 24% 9%	4580
	11th to 20th	Night	56% 4 10% 19% 10% 2	5215
	21st to end	Night	60% 4 13% 14% 8% 1	7433

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% 26% 31% 11% 1	200
	11th to 20th	Day	28% 22% 30% 16% 4	366
	21st to end	Day	20% 20% 39% 18% 3 1	440
February	1st to 10th	Day	27% 24% 32% 14% 4 1	400
	11th to 20th	Day	28% 28% 30% 11% 3 1	396
	21st to end	Day	22% 21% 35% 18% 3	331
March	1st to 10th	Day	28% 24% 35% 10% 2 1	490
	11th to 20th	Day	22% 24% 35% 14% 4	500
	21st to end	Day	30% 25% 30% 11% 3 1	550
April	1st to 10th	Day	35% 27% 27% 8% 2	500
	11th to 20th	Day	31% 25% 29% 11% 3	492
	21st to end	Day	29% 25% 28% 14% 4 1	480
May	1st to 10th	Day	33% 19% 29% 14% 4 1	556
	11th to 20th	Day	27% 17% 29% 20% 6% 1	674
	21st to end	Day	25% 17% 37% 17% 3	735
June	1st to 10th	Day	33% 16% 31% 15% 5%	680
	11th to 20th	Day	25% 14% 35% 21% 5% 1	680
	21st to end	Day	29% 12% 30% 22% 6% 1	680
July	1st to 10th	Day	22% 13% 38% 19% 7% 1	670
	11th to 20th	Day	19% 9% 37% 26% 8% 1	668
	21st to end	Day	19% 11% 39% 23% 7%	709
August	1st to 10th	Day	15% 11% 38% 29% 7%	486
	11th to 20th	Day	18% 10% 34% 25% 10% 2	479
	21st to end	Day	16% 15% 33% 25% 9% 3	539
September	1st to 10th	Day	17% 13% 43% 19% 8% 1	490
	11th to 20th	Day	21% 17% 30% 22% 8% 2	490
	21st to end	Day	22% 16% 30% 22% 9% 2	457
October	1st to 10th	Day	23% 15% 30% 20% 9% 2	390
	11th to 20th	Day	23% 21% 29% 19% 7% 1	390
	21st to end	Day	25% 24% 29% 17% 4 1	429
November	1st to 10th	Day	28% 23% 30% 13% 6% 1	395
	11th to 20th	Day	30% 25% 27% 13% 4 1	400
	21st to end	Day	31% 26% 29% 12% 2	400
December	1st to 10th	Day	32% 21% 31% 14% 3	400
	11th to 20th	Day	30% 29% 28% 12% 2	400
	21st to end	Day	24% 24% 35% 13% 3	245
January	1st to 10th	Night	27% 20% 32% 16% 4	900
	11th to 20th	Night	26% 22% 29% 19% 4	893
	21st to end	Night	20% 21% 37% 18% 5%	880
February	1st to 10th	Night	27% 19% 33% 19% 2	800
	11th to 20th	Night	28% 23% 33% 13% 3 1	783
	21st to end	Night	22% 17% 36% 21% 3 1	660
March	1st to 10th	Night	27% 18% 35% 17% 2	800
	11th to 20th	Night	24% 20% 30% 21% 5% 1	800
	21st to end	Night	27% 19% 31% 17% 6%	880
April	1st to 10th	Night	31% 19% 29% 18% 2	605
	11th to 20th	Night	30% 16% 29% 19% 5% 1	594
	21st to end	Night	29% 15% 31% 18% 6% 1	588
May	1st to 10th	Night	30% 15% 28% 21% 5% 1	570
	11th to 20th	Night	24% 14% 29% 27% 6%	562
	21st to end	Night	21% 14% 43% 19% 2	616
June	1st to 10th	Night	32% 10% 32% 23% 4	505
	11th to 20th	Night	25% 8% 37% 25% 5%	380
	21st to end	Night	24% 10% 32% 29% 5% 1	380
July	1st to 10th	Night	19% 8% 43% 24% 7%	370
	11th to 20th	Night	16% 9% 41% 28% 5%	453
	21st to end	Night	19% 8% 37% 31% 5%	623
August	1st to 10th	Night	16% 6% 40% 30% 8%	568
	11th to 20th	Night	15% 9% 35% 30% 9% 1	562
	21st to end	Night	17% 9% 31% 32% 11%	627
September	1st to 10th	Night	19% 10% 38% 25% 8%	570
	11th to 20th	Night	19% 12% 29% 31% 8% 1	640
	21st to end	Night	21% 14% 30% 25% 9%	760
October	1st to 10th	Night	22% 12% 30% 27% 9%	760
	11th to 20th	Night	20% 16% 34% 21% 8% 1	760
	21st to end	Night	29% 21% 29% 17% 3	841
November	1st to 10th	Night	28% 20% 29% 18% 5%	880
	11th to 20th	Night	27% 24% 26% 17% 5% 1	900
	21st to end	Night	31% 22% 28% 16% 3	900
December	1st to 10th	Night	31% 20% 29% 18% 3	900
	11th to 20th	Night	28% 25% 32% 12% 2	900
	21st to end	Night	29% 23% 26% 19% 3 1	990

Page generated at 2025-04-23 10:25:06. Version ac07

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