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 2025-02-25.

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	15% 12% 4 10% 6% 5% 5% 4 5% 7% 28%	108402
	Night	15% 13% 5% 11% 6% 5% 5% 4 5% 6% 25%	110356
Transparency	Day	55% 4 12% 20% 8% 1	111935
	Night	59% 4 11% 18% 8% 1	114987
Seeing	Day	21% 7% 26% 27% 14% 5%	15478
	Night	23% 6% 25% 33% 12% 1	24689

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	10% 19% 9% 19% 9% 9% 6% 3 4 4 10%	3158
	11th to 20th	Day	10% 17% 6% 18% 9% 6% 4 3 5% 6% 16%	3133
	21st to end	Day	9% 17% 8% 15% 7% 6% 5% 3 5% 6% 18%	4283
February	1st to 10th	Day	7% 17% 7% 12% 9% 6% 7% 4 6% 7% 20%	1800
	11th to 20th	Day	10% 17% 6% 11% 7% 6% 5% 4 5% 7% 22%	1753
	21st to end	Day	11% 19% 5% 10% 8% 5% 5% 4 4 5% 25%	1449
March	1st to 10th	Day	19% 13% 4 9% 5% 5% 4 3 4 6% 26%	3364
	11th to 20th	Day	9% 17% 5% 16% 6% 5% 5% 3 4 4 26%	3480
	21st to end	Day	13% 13% 5% 11% 6% 5% 5% 4 4 5% 30%	3815
April	1st to 10th	Day	19% 13% 4 9% 6% 4 4 3 6% 6% 27%	2259
	11th to 20th	Day	20% 10% 3 8% 5% 3 4 4 5% 6% 31%	2430
	21st to end	Day	21% 11% 4 7% 4 4 3 3 4 6% 32%	2470
May	1st to 10th	Day	18% 10% 3 7% 5% 4 4 5% 6% 7% 31%	4300
	11th to 20th	Day	15% 8% 4 8% 5% 5% 5% 4 5% 7% 35%	4398
	21st to end	Day	17% 7% 2 6% 4 4 4 4 6% 7% 37%	4962
June	1st to 10th	Day	17% 9% 3 8% 5% 5% 5% 4 6% 8% 29%	2850
	11th to 20th	Day	13% 7% 3 7% 6% 5% 5% 4 6% 8% 36%	2850
	21st to end	Day	16% 9% 3 7% 6% 5% 5% 4 7% 7% 31%	2850
July	1st to 10th	Day	16% 8% 3 7% 5% 5% 5% 4 7% 9% 32%	4760
	11th to 20th	Day	12% 6% 2 6% 6% 6% 5% 4 7% 10% 37%	4760
	21st to end	Day	13% 6% 2 7% 5% 4 4 4 6% 9% 39%	4950
August	1st to 10th	Day	12% 7% 3 8% 5% 5% 5% 5% 6% 10% 34%	4107
	11th to 20th	Day	17% 6% 3 6% 5% 4 5% 4 6% 7% 37%	4044
	21st to end	Day	12% 6% 3 8% 5% 4 5% 4 6% 8% 40%	4478
September	1st to 10th	Day	17% 7% 3 6% 5% 5% 5% 4 5% 8% 36%	2280
	11th to 20th	Day	18% 7% 3 6% 5% 4 5% 3 6% 7% 36%	2175
	21st to end	Day	21% 9% 2 8% 5% 3 5% 3 4 6% 32%	2052
October	1st to 10th	Day	19% 10% 4 8% 6% 4 5% 3 4 6% 31%	1900
	11th to 20th	Day	24% 15% 4 10% 5% 4 5% 3 4 5% 21%	1900
	21st to end	Day	25% 15% 4 10% 6% 5% 4 3 5% 5% 17%	1988
November	1st to 10th	Day	21% 15% 5% 8% 6% 4 5% 3 4 8% 22%	1566
	11th to 20th	Day	18% 17% 6% 13% 8% 6% 5% 3 3 5% 16%	1600
	21st to end	Day	21% 21% 6% 14% 7% 5% 5% 3 4 4 11%	1600
December	1st to 10th	Day	13% 23% 9% 16% 8% 5% 4 3 5% 4 10%	2541
	11th to 20th	Day	14% 19% 5% 14% 7% 6% 5% 3 4 5% 20%	2621
	21st to end	Day	19% 21% 6% 16% 7% 5% 4 3 4 5% 11%	3476
January	1st to 10th	Night	11% 17% 9% 18% 8% 6% 6% 3 4 4 13%	6808
	11th to 20th	Night	11% 16% 6% 16% 8% 6% 6% 5% 6% 5% 15%	6772
	21st to end	Night	9% 16% 8% 15% 7% 6% 7% 4 5% 5% 18%	6660
February	1st to 10th	Night	10% 16% 5% 12% 9% 7% 6% 4 6% 6% 19%	2600
	11th to 20th	Night	11% 16% 7% 12% 9% 5% 5% 4 4 5% 22%	2533
	21st to end	Night	10% 17% 7% 13% 7% 6% 5% 3 5% 6% 22%	2100
March	1st to 10th	Night	16% 15% 5% 8% 4 4 4 3 4 5% 31%	3471
	11th to 20th	Night	14% 18% 5% 12% 7% 5% 5% 3 4 4 23%	3479
	21st to end	Night	14% 11% 5% 12% 5% 5% 4 4 5% 5% 30%	3817
April	1st to 10th	Night	19% 15% 4 8% 6% 3 3 3 5% 6% 27%	1920
	11th to 20th	Night	18% 11% 2 9% 5% 5% 4 3 5% 5% 32%	1716
	21st to end	Night	18% 9% 4 6% 5% 4 4 5% 5% 6% 35%	1710
May	1st to 10th	Night	17% 10% 3 10% 6% 5% 4 4 5% 5% 32%	2641
	11th to 20th	Night	15% 7% 2 7% 4 5% 4 4 6% 8% 37%	2495
	21st to end	Night	14% 7% 3 6% 5% 4 6% 4 6% 8% 38%	2614
June	1st to 10th	Night	17% 8% 3 7% 6% 4 5% 4 7% 8% 32%	1330
	11th to 20th	Night	17% 5% 2 5% 3 4 4 4 5% 8% 42%	1330
	21st to end	Night	15% 7% 2 6% 5% 5% 4 5% 7% 7% 38%	1330
July	1st to 10th	Night	15% 6% 3 7% 4 5% 5% 3 6% 7% 40%	2210
	11th to 20th	Night	13% 7% 2 7% 6% 4 5% 5% 6% 9% 35%	2210
	21st to end	Night	14% 5% 2 5% 4 4 5% 5% 6% 8% 42%	2604
August	1st to 10th	Night	8% 5% 2 7% 5% 6% 5% 5% 7% 10% 40%	2819
	11th to 20th	Night	15% 6% 3 6% 4 4 5% 5% 6% 7% 39%	2785
	21st to end	Night	14% 6% 3 6% 4 4 5% 3 5% 6% 43%	3146
September	1st to 10th	Night	15% 7% 3 6% 3 4 5% 4 5% 7% 42%	1900
	11th to 20th	Night	16% 7% 2 6% 5% 3 4 3 4 8% 42%	2004
	21st to end	Night	18% 9% 2 7% 3 3 4 4 6% 6% 38%	2128
October	1st to 10th	Night	20% 10% 3 8% 4 4 4 3 6% 7% 30%	2280
	11th to 20th	Night	24% 12% 4 9% 6% 5% 5% 3 4 5% 22%	2280
	21st to end	Night	21% 16% 4 9% 5% 4 4 3 5% 6% 23%	2608
November	1st to 10th	Night	18% 14% 4 9% 6% 5% 5% 4 4 6% 25%	2732
	11th to 20th	Night	19% 15% 5% 12% 7% 6% 5% 3 4 5% 19%	2800
	21st to end	Night	22% 19% 6% 11% 6% 5% 5% 3 4 5% 13%	2800
December	1st to 10th	Night	14% 22% 10% 16% 8% 6% 4 3 4 4 9%	4636
	11th to 20th	Night	16% 18% 6% 13% 8% 6% 5% 4 5% 4 17%	5586
	21st to end	Night	21% 21% 6% 14% 5% 4 4 3 4 5% 15%	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	79% 3 8% 7% 2	3159
	11th to 20th	Day	70% 3 7% 14% 6%	3160
	21st to end	Day	66% 3 8% 16% 6%	4283
February	1st to 10th	Day	63% 3 10% 16% 7%	1800
	11th to 20th	Day	63% 3 11% 16% 8%	1762
	21st to end	Day	61% 3 7% 20% 8% 1	1449
March	1st to 10th	Day	60% 4 10% 19% 7% 1	3367
	11th to 20th	Day	62% 4 9% 18% 7% 1	3480
	21st to end	Day	56% 4 7% 20% 11% 2	3815
April	1st to 10th	Day	58% 4 9% 17% 11% 1	2259
	11th to 20th	Day	54% 3 8% 25% 9% 2	2430
	21st to end	Day	54% 3 8% 17% 14% 2	2470
May	1st to 10th	Day	50% 5% 10% 22% 12% 1	4312
	11th to 20th	Day	48% 5% 13% 24% 10% 1	4402
	21st to end	Day	46% 4 12% 19% 16% 3	4962
June	1st to 10th	Day	52% 4 12% 22% 9% 1	2850
	11th to 20th	Day	44% 5% 11% 24% 14% 1	2850
	21st to end	Day	51% 6% 12% 21% 10% 1	2850
July	1st to 10th	Day	47% 6% 17% 25% 6%	4686
	11th to 20th	Day	40% 6% 17% 28% 9%	4679
	21st to end	Day	43% 5% 13% 33% 7%	4793
August	1st to 10th	Day	44% 6% 17% 27% 6%	4093
	11th to 20th	Day	45% 6% 15% 26% 8% 1	4083
	21st to end	Day	43% 5% 13% 31% 7% 2	4478
September	1st to 10th	Day	47% 5% 16% 24% 8%	2280
	11th to 20th	Day	47% 5% 18% 25% 5%	2175
	21st to end	Day	54% 4 15% 21% 7%	2052
October	1st to 10th	Day	56% 5% 11% 23% 6%	3160
	11th to 20th	Day	58% 4 12% 19% 7%	3140
	21st to end	Day	65% 4 15% 10% 6%	3252
November	1st to 10th	Day	63% 4 15% 13% 4	1566
	11th to 20th	Day	73% 4 8% 12% 4	1600
	21st to end	Day	78% 4 9% 8% 2	1600
December	1st to 10th	Day	78% 4 8% 7% 2	2541
	11th to 20th	Day	68% 4 9% 16% 2	2621
	21st to end	Day	78% 2 8% 9% 4	3476
January	1st to 10th	Night	75% 3 9% 9% 3	6808
	11th to 20th	Night	70% 4 9% 11% 6%	6820
	21st to end	Night	68% 3 7% 14% 8%	6660
February	1st to 10th	Night	64% 4 9% 14% 8% 1	2600
	11th to 20th	Night	64% 3 11% 15% 6%	2535
	21st to end	Night	64% 3 8% 16% 8% 1	2100
March	1st to 10th	Night	56% 3 11% 18% 10% 2	3481
	11th to 20th	Night	65% 3 9% 14% 7% 1	3480
	21st to end	Night	55% 5% 8% 16% 13% 3	3817
April	1st to 10th	Night	58% 3 7% 18% 13% 1	1920
	11th to 20th	Night	53% 3 6% 20% 15% 2	1716
	21st to end	Night	49% 4 10% 16% 18% 2	1710
May	1st to 10th	Night	52% 5% 7% 20% 13% 2	2648
	11th to 20th	Night	43% 5% 14% 25% 12% 1	2496
	21st to end	Night	44% 4 12% 21% 15% 3	2615
June	1st to 10th	Night	50% 6% 9% 22% 11% 2	1330
	11th to 20th	Night	39% 5% 12% 26% 15% 2	1330
	21st to end	Night	43% 6% 13% 23% 13% 2	1330
July	1st to 10th	Night	42% 6% 14% 27% 11%	2175
	11th to 20th	Night	43% 6% 17% 26% 9%	2168
	21st to end	Night	39% 5% 15% 30% 12%	2521
August	1st to 10th	Night	37% 6% 16% 32% 8%	2809
	11th to 20th	Night	41% 7% 15% 31% 5%	2812
	21st to end	Night	41% 5% 15% 26% 10% 1	3146
September	1st to 10th	Night	42% 6% 17% 25% 9% 2	1900
	11th to 20th	Night	42% 5% 18% 26% 8%	2004
	21st to end	Night	46% 5% 16% 26% 8%	2128
October	1st to 10th	Night	49% 5% 12% 24% 10%	3800
	11th to 20th	Night	56% 4 13% 23% 4	3779
	21st to end	Night	59% 5% 16% 14% 6%	4294
November	1st to 10th	Night	60% 5% 14% 17% 4	2732
	11th to 20th	Night	69% 4 11% 12% 4	2800
	21st to end	Night	76% 3 10% 9% 2	2800
December	1st to 10th	Night	79% 5% 6% 9% 2	4636
	11th to 20th	Night	70% 4 8% 13% 5%	5585
	21st to end	Night	74% 3 7% 12% 4	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	24% 10% 26% 29% 9% 4	200
	11th to 20th	Day	20% 8% 28% 30% 11% 5%	200
	21st to end	Day	17% 5% 32% 31% 13% 3	318
February	1st to 10th	Day	17% 13% 35% 27% 7% 1	300
	11th to 20th	Day	20% 9% 37% 25% 6% 3	300
	21st to end	Day	24% 12% 38% 22% 5%	237
March	1st to 10th	Day	18% 7% 35% 30% 9% 1	418
	11th to 20th	Day	18% 10% 30% 31% 10% 2	460
	21st to end	Day	24% 8% 30% 27% 9% 1	506
April	1st to 10th	Day	24% 8% 27% 25% 12% 3	460
	11th to 20th	Day	28% 10% 22% 25% 12% 4	452
	21st to end	Day	28% 11% 24% 20% 12% 4	460
May	1st to 10th	Day	24% 6% 25% 26% 14% 5%	463
	11th to 20th	Day	21% 7% 27% 25% 14% 5%	487
	21st to end	Day	19% 6% 30% 26% 16% 3	602
June	1st to 10th	Day	21% 6% 28% 31% 12% 3	680
	11th to 20th	Day	17% 8% 29% 28% 15% 3	680
	21st to end	Day	19% 6% 20% 31% 19% 5%	680
July	1st to 10th	Day	15% 5% 26% 32% 17% 5%	671
	11th to 20th	Day	15% 5% 24% 31% 17% 7%	668
	21st to end	Day	14% 4 21% 31% 21% 8%	616
August	1st to 10th	Day	14% 5% 23% 25% 24% 9%	486
	11th to 20th	Day	16% 3 15% 27% 24% 14%	479
	21st to end	Day	17% 5% 23% 26% 16% 13%	539
September	1st to 10th	Day	18% 4 23% 27% 18% 9%	490
	11th to 20th	Day	19% 6% 18% 32% 18% 7%	490
	21st to end	Day	24% 7% 21% 23% 18% 7%	490
October	1st to 10th	Day	28% 8% 22% 25% 13% 4	490
	11th to 20th	Day	30% 9% 28% 23% 9% 1	490
	21st to end	Day	31% 10% 28% 24% 6% 2	446
November	1st to 10th	Day	33% 11% 31% 21% 4 2	200
	11th to 20th	Day	23% 12% 29% 26% 9% 2	200
	21st to end	Day	36% 10% 31% 16% 7% 2	200
December	1st to 10th	Day	22% 13% 29% 23% 13% 2	200
	11th to 20th	Day	23% 14% 30% 21% 9% 4	200
	21st to end	Day	24% 8% 28% 26% 10% 4	220
January	1st to 10th	Night	24% 5% 28% 32% 10% 1	1000
	11th to 20th	Night	25% 6% 26% 32% 10% 1	1000
	21st to end	Night	19% 4 23% 38% 15% 2	939
February	1st to 10th	Night	18% 8% 29% 36% 9% 1	800
	11th to 20th	Night	18% 7% 32% 34% 9% 1	783
	21st to end	Night	20% 6% 32% 33% 9%	647
March	1st to 10th	Night	19% 8% 33% 31% 9% 1	760
	11th to 20th	Night	22% 9% 29% 32% 8%	760
	21st to end	Night	19% 7% 29% 36% 8%	836
April	1st to 10th	Night	25% 9% 24% 34% 7% 1	760
	11th to 20th	Night	23% 6% 29% 31% 11% 1	592
	21st to end	Night	25% 5% 27% 32% 10% 1	570
May	1st to 10th	Night	21% 4 27% 39% 10%	456
	11th to 20th	Night	19% 7% 24% 39% 10% 1	374
	21st to end	Night	19% 6% 24% 41% 10%	411
June	1st to 10th	Night	21% 5% 24% 40% 9%	380
	11th to 20th	Night	19% 4 26% 37% 14%	380
	21st to end	Night	17% 3 22% 42% 15% 1	380
July	1st to 10th	Night	15% 2 22% 48% 12%	370
	11th to 20th	Night	15% 3 20% 44% 18%	368
	21st to end	Night	14% 2 19% 46% 18% 1	416
August	1st to 10th	Night	14% 2 20% 40% 23% 2	561
	11th to 20th	Night	15% 2 16% 40% 25% 2	564
	21st to end	Night	20% 4 20% 33% 20% 2	636
September	1st to 10th	Night	19% 4 21% 36% 18% 2	760
	11th to 20th	Night	19% 4 20% 33% 21% 2	760
	21st to end	Night	22% 6% 20% 33% 17% 2	760
October	1st to 10th	Night	26% 5% 23% 34% 12% 1	760
	11th to 20th	Night	31% 7% 26% 26% 10% 1	760
	21st to end	Night	29% 7% 27% 30% 7% 1	836
November	1st to 10th	Night	25% 7% 30% 30% 7% 1	780
	11th to 20th	Night	28% 8% 30% 24% 9% 1	800
	21st to end	Night	33% 7% 24% 29% 7%	800
December	1st to 10th	Night	29% 6% 27% 27% 9% 2	830
	11th to 20th	Night	28% 7% 26% 30% 8% 1	1000
	21st to end	Night	29% 8% 24% 26% 10% 2	1100

Page generated at 2025-02-22 06:51:39. Version ac07

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