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 2024-10-25.

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%	101739
	Night	19% 12% 3 8% 5% 4 4 3 5% 6% 31%	97137
Transparency	Day	52% 7% 13% 19% 8% 1	101487
	Night	53% 6% 13% 18% 8% 1	97009
Seeing	Day	25% 19% 33% 18% 5% 1	17007
	Night	25% 17% 32% 21% 5%	24413

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% 14% 4 11% 6% 6% 6% 4 5% 5% 25%	2207
	11th to 20th	Day	13% 13% 4 11% 5% 4 4 3 4 5% 34%	2481
	21st to end	Day	13% 10% 5% 15% 4 4 4 4 4 7% 30%	3124
February	1st to 10th	Day	17% 14% 4 10% 5% 4 4 4 4 5% 30%	1710
	11th to 20th	Day	15% 15% 3 10% 7% 4 4 4 5% 5% 28%	1663
	21st to end	Day	11% 13% 5% 8% 5% 6% 4 3 6% 7% 32%	1418
March	1st to 10th	Day	22% 16% 4 8% 4 4 4 3 4 5% 26%	3400
	11th to 20th	Day	13% 21% 5% 12% 6% 5% 4 4 4 5% 21%	3480
	21st to end	Day	28% 16% 5% 8% 4 4 4 3 4 4 20%	3816
April	1st to 10th	Day	21% 14% 4 8% 5% 4 4 3 3 5% 28%	2275
	11th to 20th	Day	20% 13% 3 6% 4 5% 4 4 5% 7% 30%	2356
	21st to end	Day	21% 13% 3 7% 4 4 4 4 5% 6% 30%	2470
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	21% 10% 4 7% 5% 5% 5% 3 5% 6% 29%	2020
November	1st to 10th	Day	19% 14% 4 9% 5% 5% 3 3 4 5% 29%	1485
	11th to 20th	Day	19% 13% 3 7% 5% 4 4 4 5% 6% 30%	1520
	21st to end	Day	17% 15% 5% 8% 6% 4 5% 3 5% 5% 27%	1520
December	1st to 10th	Day	23% 16% 4 7% 5% 5% 3 3 5% 6% 22%	1520
	11th to 20th	Day	19% 18% 6% 10% 5% 5% 4 3 3 5% 22%	1906
	21st to end	Day	19% 14% 8% 14% 4 4 4 3 3 4 22%	2481
January	1st to 10th	Night	14% 12% 4 8% 5% 5% 5% 4 5% 6% 34%	4748
	11th to 20th	Night	17% 13% 5% 9% 5% 5% 4 3 4 5% 30%	4480
	21st to end	Night	14% 13% 4 12% 6% 4 4 3 4 6% 30%	4532
February	1st to 10th	Night	18% 14% 4 9% 6% 4 5% 3 6% 6% 28%	2470
	11th to 20th	Night	17% 15% 3 10% 6% 5% 4 3 4 5% 27%	2403
	21st to end	Night	13% 14% 4 9% 5% 4 5% 4 5% 5% 33%	2035
March	1st to 10th	Night	24% 14% 4 12% 5% 5% 4 2 3 4 23%	3424
	11th to 20th	Night	19% 21% 6% 11% 5% 5% 4 3 4 4 20%	3479
	21st to end	Night	26% 14% 5% 9% 4 4 5% 3 3 3 24%	3816
April	1st to 10th	Night	23% 13% 3 8% 6% 4 5% 4 4 3 26%	1905
	11th to 20th	Night	20% 13% 3 7% 5% 4 3 2 4 5% 33%	1773
	21st to end	Night	21% 14% 4 8% 4 3 4 3 5% 5% 28%	1710
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	26% 10% 3 7% 5% 4 4 2 4 6% 30%	2441
November	1st to 10th	Night	21% 13% 4 7% 4 5% 4 3 4 6% 29%	2591
	11th to 20th	Night	19% 12% 3 7% 5% 5% 4 4 5% 6% 29%	2660
	21st to end	Night	22% 13% 3 7% 4 5% 4 4 5% 6% 25%	2660
December	1st to 10th	Night	23% 14% 4 8% 5% 5% 4 4 5% 6% 23%	2660
	11th to 20th	Night	24% 17% 5% 9% 4 3 3 3 4 4 23%	3293
	21st to end	Night	25% 15% 5% 11% 4 3 3 3 4 4 24%	5181

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	56% 4 18% 16% 6%	2208
	11th to 20th	Day	55% 7% 7% 19% 12% 1	2481
	21st to end	Day	54% 6% 13% 14% 13% 1	3124
February	1st to 10th	Day	59% 4 11% 15% 10% 1	1710
	11th to 20th	Day	59% 6% 10% 16% 9% 1	1671
	21st to end	Day	52% 5% 11% 19% 11% 2	1418
March	1st to 10th	Day	60% 5% 10% 18% 5% 2	3404
	11th to 20th	Day	63% 8% 9% 14% 6% 1	3480
	21st to end	Day	67% 6% 7% 13% 6% 1	3816
April	1st to 10th	Day	60% 5% 7% 16% 9% 2	2275
	11th to 20th	Day	54% 6% 9% 19% 11% 1	2356
	21st to end	Day	54% 6% 11% 16% 11% 2	2470
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	46% 6% 12% 27% 9% 1	1900
	11th to 20th	Day	50% 5% 13% 25% 7%	1900
	21st to end	Day	54% 6% 12% 19% 8%	2020
November	1st to 10th	Day	56% 6% 11% 18% 9%	1485
	11th to 20th	Day	54% 6% 15% 15% 9%	1520
	21st to end	Day	57% 6% 14% 17% 6%	1520
December	1st to 10th	Day	59% 6% 16% 14% 4	1520
	11th to 20th	Day	63% 5% 10% 16% 5% 1	1905
	21st to end	Day	65% 6% 14% 10% 5% 1	2481
January	1st to 10th	Night	48% 5% 17% 25% 4	4748
	11th to 20th	Night	54% 7% 11% 19% 8% 1	4480
	21st to end	Night	55% 5% 13% 19% 8% 1	4532
February	1st to 10th	Night	58% 5% 11% 13% 12% 2	2470
	11th to 20th	Night	58% 5% 10% 15% 11% 1	2406
	21st to end	Night	53% 5% 9% 18% 13% 2	2035
March	1st to 10th	Night	65% 5% 6% 15% 7% 1	3433
	11th to 20th	Night	66% 6% 8% 12% 6% 1	3480
	21st to end	Night	65% 4 6% 15% 8% 1	3816
April	1st to 10th	Night	60% 6% 8% 13% 10% 3	1905
	11th to 20th	Night	53% 5% 9% 20% 12% 1	1773
	21st to end	Night	56% 5% 10% 15% 12% 2	1710
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	45% 6% 14% 24% 11%	2280
	11th to 20th	Night	46% 6% 14% 27% 7%	2280
	21st to end	Night	56% 6% 11% 17% 10%	2441
November	1st to 10th	Night	56% 6% 11% 17% 8% 1	2591
	11th to 20th	Night	54% 6% 15% 16% 9% 1	2660
	21st to end	Night	55% 6% 15% 19% 5%	2660
December	1st to 10th	Night	60% 5% 15% 15% 5%	2660
	11th to 20th	Night	63% 4 10% 17% 6%	3295
	21st to end	Night	63% 4 15% 12% 5% 1	5181

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	30% 24% 32% 12% 1	180
	11th to 20th	Day	28% 24% 30% 14% 4	337
	21st to end	Day	20% 20% 39% 17% 3 1	407
February	1st to 10th	Day	26% 23% 32% 14% 4 1	370
	11th to 20th	Day	27% 27% 30% 11% 3 1	366
	21st to end	Day	21% 21% 36% 18% 3	307
March	1st to 10th	Day	27% 24% 35% 10% 3 1	451
	11th to 20th	Day	22% 25% 34% 15% 4	460
	21st to end	Day	29% 25% 31% 11% 3 1	506
April	1st to 10th	Day	33% 27% 28% 9% 2	460
	11th to 20th	Day	29% 25% 31% 12% 3	452
	21st to end	Day	28% 23% 28% 14% 5% 1	460
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% 23% 30% 17% 4 1	411
November	1st to 10th	Day	27% 23% 30% 14% 6% 1	365
	11th to 20th	Day	26% 26% 29% 14% 4 1	370
	21st to end	Day	29% 27% 29% 12% 2	370
December	1st to 10th	Day	32% 21% 30% 14% 3	370
	11th to 20th	Day	29% 31% 28% 11% 1	370
	21st to end	Day	25% 25% 34% 13% 3	222
January	1st to 10th	Night	26% 20% 32% 17% 4	850
	11th to 20th	Night	26% 22% 30% 18% 4	844
	21st to end	Night	20% 20% 36% 18% 5%	836
February	1st to 10th	Night	27% 18% 33% 19% 2	760
	11th to 20th	Night	26% 24% 33% 14% 3 1	743
	21st to end	Night	21% 17% 37% 20% 4 1	628
March	1st to 10th	Night	26% 18% 36% 17% 3	760
	11th to 20th	Night	24% 20% 30% 21% 5% 1	760
	21st to end	Night	27% 19% 31% 17% 6%	836
April	1st to 10th	Night	31% 18% 30% 18% 3	575
	11th to 20th	Night	30% 16% 30% 19% 5% 1	564
	21st to end	Night	29% 16% 31% 18% 6% 1	570
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	30% 21% 30% 17% 3	816
November	1st to 10th	Night	28% 20% 28% 18% 5%	830
	11th to 20th	Night	25% 24% 27% 18% 5% 1	850
	21st to end	Night	29% 22% 29% 17% 3	850
December	1st to 10th	Night	31% 20% 29% 17% 3	850
	11th to 20th	Night	28% 25% 32% 12% 2	850
	21st to end	Night	30% 23% 26% 17% 3 1	935

Page generated at 2024-10-22 21:21:04. Version ac07

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