Earlton
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Earlton clear sky chart from 2005-11-06 to 2026-07-01.

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% 11% 4 10% 6% 5% 5% 4 5% 7% 29%	138113
	Night	15% 13% 5% 11% 6% 5% 5% 4 5% 6% 26%	134381
Transparency	Day	55% 4 11% 20% 8% 1	141600
	Night	59% 4 10% 18% 8% 1	138983
Seeing	Day	21% 8% 26% 27% 13% 5%	17319
	Night	22% 6% 26% 33% 12% 1	26330

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% 19% 8% 17% 7% 8% 5% 3 5% 4 12%	4094
	11th to 20th	Day	9% 19% 7% 18% 8% 6% 5% 3 5% 6% 14%	4083
	21st to end	Day	7% 13% 7% 16% 7% 6% 6% 4 6% 6% 20%	5544
February	1st to 10th	Day	7% 17% 7% 12% 9% 6% 7% 4 6% 7% 20%	1890
	11th to 20th	Day	10% 18% 6% 11% 7% 6% 5% 4 5% 7% 21%	1843
	21st to end	Day	10% 18% 5% 10% 7% 5% 5% 4 4 5% 25%	1557
March	1st to 10th	Day	18% 15% 5% 9% 5% 5% 5% 3 5% 6% 25%	4944
	11th to 20th	Day	16% 15% 4 13% 7% 5% 4 3 4 5% 23%	5090
	21st to end	Day	14% 13% 6% 12% 5% 5% 5% 3 4 5% 28%	5586
April	1st to 10th	Day	18% 13% 4 10% 6% 4 4 4 5% 5% 26%	2497
	11th to 20th	Day	21% 11% 3 9% 5% 3 4 3 5% 6% 31%	2689
	21st to end	Day	21% 12% 4 8% 4 4 3 3 4 5% 32%	2730
May	1st to 10th	Day	15% 11% 4 9% 6% 5% 5% 4 5% 6% 30%	8000
	11th to 20th	Day	15% 8% 3 8% 5% 5% 5% 4 6% 7% 36%	8221
	21st to end	Day	17% 8% 3 6% 4 4 4 4 5% 7% 38%	9297
June	1st to 10th	Day	17% 9% 3 8% 5% 5% 5% 4 6% 8% 31%	3150
	11th to 20th	Day	13% 7% 3 8% 6% 5% 5% 5% 7% 8% 35%	3150
	21st to end	Day	15% 9% 3 7% 6% 5% 5% 4 7% 7% 31%	3150
July	1st to 10th	Day	14% 7% 2 7% 5% 5% 6% 5% 7% 10% 33%	6820
	11th to 20th	Day	13% 5% 2 5% 5% 5% 5% 4 7% 10% 36%	6820
	21st to end	Day	12% 6% 2 7% 5% 5% 5% 4 7% 10% 37%	7118
August	1st to 10th	Day	11% 6% 3 8% 5% 5% 5% 5% 6% 10% 35%	4237
	11th to 20th	Day	16% 6% 3 6% 5% 4 5% 5% 6% 7% 37%	4174
	21st to end	Day	12% 6% 3 8% 5% 4 5% 4 6% 8% 39%	4619
September	1st to 10th	Day	17% 7% 3 6% 5% 5% 5% 4 5% 8% 35%	2400
	11th to 20th	Day	17% 7% 3 6% 5% 4 5% 3 6% 8% 36%	2289
	21st to end	Day	20% 9% 3 8% 5% 3 5% 3 5% 6% 33%	2160
October	1st to 10th	Day	19% 10% 3 8% 6% 4 5% 3 4 6% 32%	2000
	11th to 20th	Day	24% 15% 4 10% 5% 4 4 3 4 5% 22%	2000
	21st to end	Day	25% 15% 4 11% 6% 5% 4 3 5% 5% 17%	2092
November	1st to 10th	Day	21% 15% 4 8% 6% 5% 5% 3 4 7% 22%	1646
	11th to 20th	Day	18% 17% 6% 13% 8% 6% 5% 4 3 5% 16%	1680
	21st to end	Day	22% 21% 6% 14% 7% 5% 5% 3 4 4 10%	1680
December	1st to 10th	Day	13% 23% 9% 16% 8% 5% 4 3 5% 4 10%	2619
	11th to 20th	Day	14% 19% 5% 14% 7% 6% 5% 3 4 5% 19%	2691
	21st to end	Day	19% 21% 6% 16% 7% 5% 3 3 4 5% 11%	3553
January	1st to 10th	Night	10% 17% 9% 18% 9% 6% 6% 3 4 4 13%	8831
	11th to 20th	Night	10% 19% 7% 16% 8% 5% 6% 4 6% 5% 14%	8832
	21st to end	Night	7% 13% 7% 15% 8% 8% 7% 5% 7% 6% 18%	8627
February	1st to 10th	Night	10% 16% 5% 12% 9% 7% 6% 4 6% 6% 19%	2730
	11th to 20th	Night	10% 16% 7% 12% 8% 5% 5% 4 4 5% 22%	2663
	21st to end	Night	10% 17% 7% 12% 7% 6% 6% 3 5% 6% 21%	2249
March	1st to 10th	Night	18% 16% 5% 9% 4 4 5% 4 4 4 26%	5111
	11th to 20th	Night	17% 17% 5% 11% 7% 5% 5% 4 4 5% 19%	5089
	21st to end	Night	16% 14% 5% 11% 5% 5% 4 3 4 5% 28%	5588
April	1st to 10th	Night	19% 15% 5% 9% 6% 3 3 3 5% 6% 27%	2122
	11th to 20th	Night	17% 11% 2 9% 5% 5% 4 3 5% 6% 32%	1898
	21st to end	Night	18% 9% 4 7% 5% 4 4 4 5% 6% 34%	1890
May	1st to 10th	Night	14% 10% 3 9% 5% 5% 5% 4 5% 5% 32%	4899
	11th to 20th	Night	15% 8% 3 7% 4 5% 4 3 5% 6% 39%	4639
	21st to end	Night	15% 7% 3 6% 4 4 4 4 5% 8% 40%	4886
June	1st to 10th	Night	16% 8% 3 7% 5% 4 5% 4 7% 8% 33%	1470
	11th to 20th	Night	16% 6% 2 5% 4 4 4 4 5% 8% 41%	1470
	21st to end	Night	15% 6% 2 6% 6% 5% 4 4 7% 7% 37%	1470
July	1st to 10th	Night	16% 7% 3 8% 5% 5% 5% 3 5% 7% 37%	3160
	11th to 20th	Night	13% 6% 2 7% 5% 4 5% 4 6% 9% 39%	3160
	21st to end	Night	12% 5% 2 5% 4 4 5% 5% 6% 9% 44%	3739
August	1st to 10th	Night	8% 5% 2 7% 5% 6% 5% 5% 7% 10% 40%	2909
	11th to 20th	Night	14% 7% 3 6% 4 4 5% 5% 6% 7% 39%	2875
	21st to end	Night	14% 6% 3 6% 4 4 5% 3 5% 6% 43%	3246
September	1st to 10th	Night	15% 7% 3 6% 3 4 5% 4 5% 7% 40%	2000
	11th to 20th	Night	15% 7% 2 6% 5% 3 4 3 4 8% 43%	2110
	21st to end	Night	18% 9% 2 7% 3 3 4 4 6% 6% 39%	2240
October	1st to 10th	Night	20% 10% 3 8% 4 4 4 3 6% 7% 31%	2400
	11th to 20th	Night	24% 12% 4 9% 6% 6% 5% 3 4 5% 22%	2400
	21st to end	Night	21% 15% 4 9% 5% 5% 4 4 5% 6% 23%	2745
November	1st to 10th	Night	18% 14% 4 9% 6% 5% 5% 4 4 6% 24%	2872
	11th to 20th	Night	19% 16% 6% 12% 7% 6% 5% 3 4 5% 18%	2940
	21st to end	Night	22% 19% 6% 12% 6% 5% 5% 3 4 5% 13%	2940
December	1st to 10th	Night	14% 22% 9% 16% 8% 6% 4 3 4 4 9%	4778
	11th to 20th	Night	15% 17% 6% 13% 8% 6% 5% 4 5% 4 17%	5736
	21st to end	Night	21% 21% 6% 14% 5% 4 4 3 4 5% 15%	7667

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	76% 3 8% 9% 3	4095
	11th to 20th	Day	73% 2 6% 12% 7%	4110
	21st to end	Day	63% 3 8% 18% 8%	5544
February	1st to 10th	Day	64% 3 10% 16% 7%	1890
	11th to 20th	Day	62% 3 10% 17% 7%	1852
	21st to end	Day	61% 2 7% 21% 8% 1	1557
March	1st to 10th	Day	61% 3 9% 14% 12% 2	4947
	11th to 20th	Day	63% 3 11% 14% 7% 1	5090
	21st to end	Day	59% 3 7% 20% 9% 1	5586
April	1st to 10th	Day	59% 4 9% 18% 10% 1	2497
	11th to 20th	Day	55% 3 7% 23% 10% 1	2689
	21st to end	Day	54% 3 8% 18% 14% 2	2730
May	1st to 10th	Day	53% 4 8% 18% 15% 2	8009
	11th to 20th	Day	48% 5% 12% 23% 10% 2	8225
	21st to end	Day	46% 3 11% 22% 15% 3	9298
June	1st to 10th	Day	50% 4 11% 22% 11% 1	3150
	11th to 20th	Day	46% 6% 11% 24% 14% 1	3150
	21st to end	Day	50% 6% 12% 22% 9% 1	3150
July	1st to 10th	Day	44% 6% 16% 28% 6%	6747
	11th to 20th	Day	40% 7% 18% 27% 7%	6739
	21st to end	Day	41% 6% 14% 31% 7%	6916
August	1st to 10th	Day	43% 6% 17% 27% 7%	4223
	11th to 20th	Day	44% 6% 15% 26% 8% 1	4213
	21st to end	Day	43% 5% 13% 30% 7% 2	4619
September	1st to 10th	Day	47% 5% 16% 24% 8%	2400
	11th to 20th	Day	46% 5% 17% 26% 5%	2289
	21st to end	Day	52% 4 15% 22% 7%	2160
October	1st to 10th	Day	55% 5% 11% 23% 6%	3260
	11th to 20th	Day	57% 4 12% 19% 8%	3240
	21st to end	Day	65% 4 14% 10% 6%	3356
November	1st to 10th	Day	63% 4 14% 14% 5%	1646
	11th to 20th	Day	73% 4 7% 12% 4	1680
	21st to end	Day	79% 3 9% 7% 2	1680
December	1st to 10th	Day	78% 4 8% 7% 3	2619
	11th to 20th	Day	69% 4 9% 16% 2	2691
	21st to end	Day	77% 2 8% 9% 4	3553
January	1st to 10th	Night	75% 3 8% 10% 3	8831
	11th to 20th	Night	72% 3 8% 11% 6%	8880
	21st to end	Night	65% 3 7% 17% 7%	8627
February	1st to 10th	Night	64% 4 9% 14% 8% 1	2730
	11th to 20th	Night	65% 3 10% 16% 6%	2665
	21st to end	Night	64% 3 8% 17% 8%	2249
March	1st to 10th	Night	62% 3 9% 14% 9% 3	5121
	11th to 20th	Night	68% 3 9% 12% 6% 1	5090
	21st to end	Night	58% 4 7% 17% 11% 3	5588
April	1st to 10th	Night	59% 3 7% 18% 12% 1	2122
	11th to 20th	Night	53% 3 7% 20% 15% 2	1898
	21st to end	Night	50% 4 10% 17% 17% 2	1890
May	1st to 10th	Night	52% 5% 6% 20% 16% 1	4906
	11th to 20th	Night	45% 4 13% 24% 12% 2	4640
	21st to end	Night	43% 3 10% 26% 16% 2	4887
June	1st to 10th	Night	49% 5% 9% 22% 12% 2	1470
	11th to 20th	Night	40% 5% 12% 26% 15% 2	1470
	21st to end	Night	44% 6% 13% 23% 13% 1	1470
July	1st to 10th	Night	45% 6% 12% 27% 10%	3125
	11th to 20th	Night	42% 6% 14% 29% 9%	3118
	21st to end	Night	36% 5% 17% 32% 9%	3627
August	1st to 10th	Night	37% 6% 17% 32% 8%	2899
	11th to 20th	Night	41% 7% 15% 31% 5%	2902
	21st to end	Night	42% 5% 15% 26% 10% 1	3246
September	1st to 10th	Night	43% 6% 17% 25% 8% 1	2000
	11th to 20th	Night	42% 5% 17% 28% 8%	2110
	21st to end	Night	45% 5% 15% 26% 8%	2240
October	1st to 10th	Night	48% 5% 12% 25% 10%	3920
	11th to 20th	Night	56% 4 12% 23% 4	3899
	21st to end	Night	59% 5% 16% 14% 6%	4431
November	1st to 10th	Night	61% 5% 14% 17% 4	2872
	11th to 20th	Night	70% 4 11% 12% 4	2940
	21st to end	Night	76% 3 10% 8% 2	2940
December	1st to 10th	Night	78% 5% 6% 9% 2	4778
	11th to 20th	Night	70% 4 8% 13% 6%	5735
	21st to end	Night	74% 3 7% 12% 4	7667

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	25% 9% 26% 28% 9% 4	220
	11th to 20th	Day	22% 7% 27% 29% 10% 5%	220
	21st to end	Day	15% 5% 32% 31% 13% 3	350
February	1st to 10th	Day	18% 13% 32% 26% 9% 1	330
	11th to 20th	Day	20% 9% 37% 25% 7% 2	330
	21st to end	Day	22% 12% 37% 22% 6% 1	273
March	1st to 10th	Day	20% 9% 35% 27% 8% 1	494
	11th to 20th	Day	21% 11% 30% 28% 9% 1	540
	21st to end	Day	23% 11% 29% 26% 9% 1	594
April	1st to 10th	Day	24% 10% 28% 24% 11% 3	540
	11th to 20th	Day	29% 11% 22% 23% 11% 4	532
	21st to end	Day	29% 12% 24% 20% 12% 4	540
May	1st to 10th	Day	23% 6% 26% 28% 13% 4	543
	11th to 20th	Day	20% 8% 28% 25% 13% 5%	567
	21st to end	Day	20% 7% 29% 26% 15% 3	698
June	1st to 10th	Day	20% 7% 28% 30% 12% 3	780
	11th to 20th	Day	17% 9% 29% 28% 14% 3	780
	21st to end	Day	19% 7% 21% 30% 18% 5%	780
July	1st to 10th	Day	15% 5% 26% 32% 17% 5%	722
	11th to 20th	Day	15% 6% 25% 31% 16% 7%	718
	21st to end	Day	14% 5% 21% 32% 20% 8%	664
August	1st to 10th	Day	13% 5% 23% 25% 24% 10%	526
	11th to 20th	Day	15% 4 16% 27% 24% 14%	519
	21st to end	Day	17% 6% 22% 26% 16% 13%	583
September	1st to 10th	Day	19% 5% 24% 27% 17% 9%	530
	11th to 20th	Day	18% 5% 18% 31% 19% 8%	530
	21st to end	Day	23% 7% 21% 23% 18% 8%	530
October	1st to 10th	Day	26% 8% 23% 25% 13% 5%	530
	11th to 20th	Day	30% 10% 28% 23% 8% 1	530
	21st to end	Day	31% 10% 26% 24% 7% 2	484
November	1st to 10th	Day	31% 12% 32% 20% 4 1	220
	11th to 20th	Day	24% 12% 29% 25% 8% 2	220
	21st to end	Day	36% 10% 31% 15% 6% 2	220
December	1st to 10th	Day	22% 14% 28% 23% 12% 1	220
	11th to 20th	Day	25% 13% 30% 21% 8% 3	220
	21st to end	Day	24% 10% 27% 26% 10% 4	242
January	1st to 10th	Night	24% 5% 28% 33% 10% 1	1050
	11th to 20th	Night	24% 7% 26% 32% 10% 1	1050
	21st to end	Night	18% 4 23% 38% 15% 2	986
February	1st to 10th	Night	18% 8% 29% 35% 10%	840
	11th to 20th	Night	18% 7% 31% 35% 9% 1	823
	21st to end	Night	19% 7% 32% 32% 10%	692
March	1st to 10th	Night	20% 8% 33% 30% 8% 1	840
	11th to 20th	Night	24% 9% 29% 31% 7%	840
	21st to end	Night	20% 7% 30% 35% 8%	924
April	1st to 10th	Night	25% 10% 24% 33% 7% 1	840
	11th to 20th	Night	23% 7% 28% 31% 11% 1	654
	21st to end	Night	24% 5% 28% 33% 9% 1	630
May	1st to 10th	Night	20% 4 26% 39% 11%	504
	11th to 20th	Night	20% 7% 25% 38% 10% 1	414
	21st to end	Night	19% 5% 25% 39% 11%	455
June	1st to 10th	Night	20% 5% 25% 40% 10%	420
	11th to 20th	Night	18% 5% 27% 36% 14%	420
	21st to end	Night	17% 3 22% 41% 15% 1	420
July	1st to 10th	Night	14% 3 23% 48% 12%	390
	11th to 20th	Night	15% 3 21% 44% 17%	388
	21st to end	Night	13% 2 20% 46% 18% 1	438
August	1st to 10th	Night	13% 2 19% 40% 24% 2	591
	11th to 20th	Night	14% 2 16% 40% 25% 2	594
	21st to end	Night	20% 4 19% 34% 20% 2	670
September	1st to 10th	Night	19% 4 22% 35% 18% 2	800
	11th to 20th	Night	19% 4 20% 34% 22% 2	800
	21st to end	Night	21% 5% 20% 33% 18% 2	800
October	1st to 10th	Night	25% 5% 23% 34% 12% 1	800
	11th to 20th	Night	31% 7% 26% 26% 9% 1	800
	21st to end	Night	28% 6% 26% 31% 8% 1	880
November	1st to 10th	Night	25% 8% 30% 29% 7% 1	820
	11th to 20th	Night	28% 8% 29% 25% 9% 1	840
	21st to end	Night	33% 7% 24% 29% 6%	840
December	1st to 10th	Night	28% 6% 28% 28% 9% 2	872
	11th to 20th	Night	27% 7% 26% 31% 8% 1	1050
	21st to end	Night	29% 8% 25% 26% 10% 2	1155

Page generated at 2026-06-28 02:10:45. Version ac07

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