Alberton
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Alberton clear sky chart from 2005-11-06 to 2026-04-17.

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	17% 10% 4 9% 5% 4 4 3 5% 6% 32%	131767
	Night	17% 12% 4 9% 5% 5% 4 3 5% 6% 29%	130569
Transparency	Day	34% 39% 9% 13% 5%	135298
	Night	37% 38% 8% 11% 5%	135126
Seeing	Day	22% 8% 25% 29% 14% 3	18789
	Night	24% 10% 27% 27% 10% 1	26385

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% 19% 7% 15% 8% 7% 5% 4 5% 4 12%	4093
	11th to 20th	Day	16% 15% 9% 14% 7% 5% 5% 3 3 4 20%	4323
	21st to end	Day	7% 10% 4 10% 6% 4 7% 4 6% 7% 35%	5707
February	1st to 10th	Day	14% 13% 4 9% 6% 4 4 3 5% 6% 31%	1890
	11th to 20th	Day	14% 14% 5% 9% 6% 4 3 3 5% 6% 31%	1843
	21st to end	Day	11% 12% 3 8% 5% 4 5% 4 5% 5% 35%	1557
March	1st to 10th	Day	17% 13% 5% 12% 4 7% 5% 3 4 5% 25%	4982
	11th to 20th	Day	14% 14% 5% 11% 6% 5% 5% 4 5% 6% 23%	5090
	21st to end	Day	24% 14% 4 8% 5% 4 4 3 4 6% 23%	5600
April	1st to 10th	Day	19% 11% 4 8% 5% 4 4 3 5% 6% 32%	2520
	11th to 20th	Day	19% 10% 3 7% 4 4 4 3 4 8% 35%	2571
	21st to end	Day	22% 12% 3 7% 4 3 4 3 5% 6% 31%	2600
May	1st to 10th	Day	23% 13% 4 7% 5% 4 4 3 5% 6% 27%	6194
	11th to 20th	Day	18% 10% 3 7% 4 4 4 3 4 6% 36%	6318
	21st to end	Day	20% 9% 2 7% 4 4 4 3 5% 7% 35%	6948
June	1st to 10th	Day	24% 9% 3 7% 4 4 5% 4 6% 7% 28%	2958
	11th to 20th	Day	17% 8% 2 7% 5% 4 5% 4 5% 7% 36%	3000
	21st to end	Day	24% 8% 3 6% 5% 5% 4 3 5% 6% 32%	3000
July	1st to 10th	Day	14% 7% 3 8% 5% 5% 5% 5% 7% 9% 31%	6820
	11th to 20th	Day	13% 6% 2 6% 4 4 4 4 6% 8% 43%	6692
	21st to end	Day	11% 6% 2 6% 5% 4 5% 4 6% 8% 43%	6927
August	1st to 10th	Day	15% 7% 3 8% 5% 4 5% 4 6% 8% 36%	4244
	11th to 20th	Day	13% 6% 2 6% 4 5% 5% 5% 6% 8% 40%	4175
	21st to end	Day	15% 5% 1 5% 3 3 4 4 6% 8% 47%	4548
September	1st to 10th	Day	16% 6% 2 4 3 4 4 4 6% 8% 44%	2400
	11th to 20th	Day	17% 7% 3 6% 4 4 4 4 5% 5% 44%	2330
	21st to end	Day	17% 7% 2 6% 4 3 4 3 5% 7% 44%	2134
October	1st to 10th	Day	17% 8% 3 6% 4 4 4 3 5% 8% 38%	2000
	11th to 20th	Day	18% 11% 4 9% 5% 5% 4 3 5% 6% 29%	2000
	21st to end	Day	20% 12% 4 9% 5% 5% 5% 3 5% 6% 26%	2147
November	1st to 10th	Day	20% 14% 3 9% 5% 5% 4 3 5% 5% 27%	1645
	11th to 20th	Day	20% 15% 7% 10% 7% 5% 3 3 4 6% 21%	1680
	21st to end	Day	19% 16% 5% 12% 6% 5% 5% 4 5% 5% 19%	1680
December	1st to 10th	Day	16% 13% 7% 16% 9% 5% 4 3 4 3 19%	2690
	11th to 20th	Day	18% 15% 5% 14% 7% 6% 4 2 2 3 25%	2908
	21st to end	Day	15% 14% 9% 19% 9% 5% 4 2 3 4 17%	3553
January	1st to 10th	Night	14% 17% 6% 15% 8% 6% 4 3 4 4 19%	8831
	11th to 20th	Night	18% 17% 7% 11% 6% 4 4 3 3 5% 22%	8577
	21st to end	Night	6% 12% 4 9% 7% 5% 5% 4 6% 7% 35%	8462
February	1st to 10th	Night	14% 15% 5% 8% 5% 4 4 3 6% 6% 29%	2730
	11th to 20th	Night	16% 14% 5% 9% 5% 5% 4 4 5% 4 29%	2663
	21st to end	Night	12% 14% 3 8% 5% 5% 4 3 5% 6% 35%	2249
March	1st to 10th	Night	21% 13% 4 11% 7% 5% 4 3 4 4 25%	5076
	11th to 20th	Night	19% 17% 4 9% 5% 5% 4 3 4 5% 24%	5089
	21st to end	Night	27% 13% 4 10% 5% 4 3 3 4 5% 23%	5573
April	1st to 10th	Night	21% 14% 4 9% 5% 4 4 3 4 5% 27%	2100
	11th to 20th	Night	22% 12% 4 7% 3 4 4 4 4 5% 32%	1910
	21st to end	Night	23% 11% 3 8% 4 4 4 3 5% 6% 30%	1800
May	1st to 10th	Night	27% 11% 3 7% 5% 4 4 3 4 5% 26%	3758
	11th to 20th	Night	19% 8% 3 7% 4 4 4 4 5% 6% 36%	3596
	21st to end	Night	19% 8% 3 7% 5% 5% 4 4 6% 7% 33%	3948
June	1st to 10th	Night	24% 10% 2 7% 5% 3 4 3 5% 7% 29%	1458
	11th to 20th	Night	18% 7% 3 7% 5% 5% 4 4 6% 6% 36%	1400
	21st to end	Night	23% 8% 4 9% 6% 4 5% 4 5% 6% 28%	1400
July	1st to 10th	Night	14% 8% 4 8% 6% 5% 5% 5% 7% 9% 29%	3160
	11th to 20th	Night	11% 6% 3 8% 6% 5% 5% 4 6% 8% 36%	3238
	21st to end	Night	12% 6% 2 6% 4 5% 4 5% 7% 8% 40%	3948
August	1st to 10th	Night	16% 7% 3 9% 6% 6% 5% 4 6% 7% 30%	2904
	11th to 20th	Night	10% 6% 3 8% 5% 5% 5% 4 6% 8% 40%	2872
	21st to end	Night	12% 5% 2 6% 4 4 5% 4 5% 7% 45%	3349
September	1st to 10th	Night	16% 5% 3 6% 4 3 5% 3 4 8% 43%	2000
	11th to 20th	Night	16% 7% 2 6% 3 3 4 3 5% 6% 46%	2068
	21st to end	Night	16% 7% 2 7% 4 3 3 3 4 6% 44%	2265
October	1st to 10th	Night	19% 7% 2 6% 4 4 4 3 5% 7% 39%	2400
	11th to 20th	Night	19% 11% 3 8% 5% 4 4 3 5% 6% 33%	2400
	21st to end	Night	23% 11% 4 8% 5% 4 5% 3 4 6% 28%	2689
November	1st to 10th	Night	21% 13% 3 9% 5% 4 4 3 4 5% 28%	2873
	11th to 20th	Night	21% 15% 5% 9% 5% 5% 4 3 4 5% 24%	2940
	21st to end	Night	22% 14% 5% 11% 5% 5% 5% 3 5% 5% 20%	2940
December	1st to 10th	Night	15% 11% 5% 12% 7% 6% 6% 4 5% 5% 23%	4720
	11th to 20th	Night	17% 15% 5% 12% 6% 4 4 3 4 4 25%	5516
	21st to end	Night	21% 13% 6% 15% 6% 5% 4 3 3 4 19%	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	61% 26% 7% 3 3	4094
	11th to 20th	Day	55% 25% 7% 7% 5% 1	4350
	21st to end	Day	38% 27% 11% 15% 9%	5707
February	1st to 10th	Day	24% 59% 3 8% 5% 1	1890
	11th to 20th	Day	22% 58% 5% 9% 5%	1851
	21st to end	Day	19% 59% 3 10% 7% 1	1557
March	1st to 10th	Day	46% 30% 7% 11% 5% 1	4986
	11th to 20th	Day	43% 33% 12% 8% 3 1	5090
	21st to end	Day	47% 31% 5% 10% 6% 1	5600
April	1st to 10th	Day	23% 60% 3 6% 7% 2	2520
	11th to 20th	Day	21% 61% 5% 9% 5% 1	2571
	21st to end	Day	22% 62% 4 5% 5% 1	2600
May	1st to 10th	Day	42% 32% 7% 13% 6%	6206
	11th to 20th	Day	35% 32% 12% 18% 3	6322
	21st to end	Day	33% 34% 9% 17% 8%	6948
June	1st to 10th	Day	19% 63% 5% 9% 4	2958
	11th to 20th	Day	16% 63% 5% 11% 4	3000
	21st to end	Day	19% 61% 5% 8% 6%	3000
July	1st to 10th	Day	37% 28% 15% 14% 6%	6745
	11th to 20th	Day	28% 28% 13% 25% 5%	6611
	21st to end	Day	26% 29% 16% 24% 5%	6730
August	1st to 10th	Day	30% 38% 10% 16% 5%	4230
	11th to 20th	Day	25% 39% 9% 16% 9%	4214
	21st to end	Day	22% 38% 11% 18% 10% 1	4548
September	1st to 10th	Day	13% 58% 8% 14% 6%	2400
	11th to 20th	Day	19% 58% 8% 11% 4	2330
	21st to end	Day	16% 58% 5% 14% 6% 1	2134
October	1st to 10th	Day	29% 38% 11% 17% 5%	3260
	11th to 20th	Day	35% 37% 7% 16% 5%	3240
	21st to end	Day	30% 39% 15% 12% 4	3451
November	1st to 10th	Day	30% 54% 6% 7% 3	1645
	11th to 20th	Day	35% 55% 5% 2 2	1680
	21st to end	Day	33% 56% 6% 4 2	1680
December	1st to 10th	Day	46% 37% 5% 10% 1	2690
	11th to 20th	Day	47% 32% 7% 7% 7%	2907
	21st to end	Day	54% 30% 7% 7% 3	3553
January	1st to 10th	Night	55% 27% 7% 9% 2	8831
	11th to 20th	Night	52% 25% 8% 9% 5%	8624
	21st to end	Night	38% 29% 10% 14% 9% 1	8462
February	1st to 10th	Night	23% 59% 4 7% 6% 1	2730
	11th to 20th	Night	24% 58% 4 9% 5%	2666
	21st to end	Night	20% 59% 3 8% 8% 2	2249
March	1st to 10th	Night	45% 31% 4 9% 9% 1	5085
	11th to 20th	Night	46% 31% 9% 7% 6% 1	5090
	21st to end	Night	49% 30% 4 9% 7% 1	5573
April	1st to 10th	Night	24% 59% 4 7% 4 2	2100
	11th to 20th	Night	23% 61% 3 8% 3 1	1910
	21st to end	Night	24% 62% 3 6% 4 2	1800
May	1st to 10th	Night	45% 32% 5% 10% 9%	3763
	11th to 20th	Night	34% 32% 10% 16% 6% 1	3597
	21st to end	Night	34% 34% 12% 14% 5%	3949
June	1st to 10th	Night	19% 63% 4 9% 5%	1458
	11th to 20th	Night	16% 63% 5% 11% 5%	1400
	21st to end	Night	21% 61% 4 9% 5%	1400
July	1st to 10th	Night	39% 29% 11% 13% 8%	3125
	11th to 20th	Night	32% 29% 15% 20% 5%	3196
	21st to end	Night	28% 30% 17% 19% 6%	3831
August	1st to 10th	Night	36% 40% 9% 11% 4	2893
	11th to 20th	Night	25% 40% 11% 15% 9% 1	2899
	21st to end	Night	24% 39% 10% 16% 11%	3348
September	1st to 10th	Night	15% 58% 6% 16% 5%	2000
	11th to 20th	Night	19% 57% 7% 13% 4	2068
	21st to end	Night	17% 58% 5% 14% 6%	2265
October	1st to 10th	Night	33% 38% 10% 14% 5%	3920
	11th to 20th	Night	31% 39% 7% 17% 6%	3899
	21st to end	Night	32% 37% 11% 14% 6%	4337
November	1st to 10th	Night	30% 54% 6% 7% 3	2873
	11th to 20th	Night	31% 56% 5% 5% 2	2940
	21st to end	Night	34% 55% 5% 4 2	2940
December	1st to 10th	Night	41% 39% 8% 11% 2	4720
	11th to 20th	Night	44% 33% 7% 11% 5% 1	5518
	21st to end	Night	53% 28% 7% 8% 3	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% 18% 29% 22% 5%	220
	11th to 20th	Day	24% 18% 32% 19% 6% 1	304
	21st to end	Day	15% 9% 40% 29% 7%	473
February	1st to 10th	Day	23% 11% 34% 23% 6% 2	430
	11th to 20th	Day	20% 15% 35% 23% 7% 1	426
	21st to end	Day	17% 10% 31% 30% 12% 1	355
March	1st to 10th	Day	20% 12% 33% 25% 9% 1	524
	11th to 20th	Day	15% 12% 33% 27% 11% 1	540
	21st to end	Day	25% 12% 27% 25% 9% 2	594
April	1st to 10th	Day	26% 9% 32% 24% 8%	540
	11th to 20th	Day	22% 8% 29% 30% 9% 2	516
	21st to end	Day	24% 11% 21% 28% 14% 2	500
May	1st to 10th	Day	30% 4 24% 27% 13% 2	630
	11th to 20th	Day	22% 6% 20% 30% 20% 3	724
	21st to end	Day	22% 4 25% 35% 13% 2	790
June	1st to 10th	Day	26% 5% 20% 32% 15% 3	730
	11th to 20th	Day	20% 3 21% 35% 18% 3	730
	21st to end	Day	26% 3 17% 32% 18% 4	730
July	1st to 10th	Day	18% 4 19% 32% 24% 3	720
	11th to 20th	Day	13% 4 16% 37% 25% 4	718
	21st to end	Day	16% 4 13% 41% 23% 4	795
August	1st to 10th	Day	12% 2 15% 37% 27% 7%	535
	11th to 20th	Day	16% 4 14% 28% 29% 9%	519
	21st to end	Day	16% 3 20% 30% 24% 7%	583
September	1st to 10th	Day	14% 4 23% 36% 19% 4	530
	11th to 20th	Day	21% 7% 20% 27% 20% 5%	530
	21st to end	Day	20% 7% 25% 28% 17% 4	493
October	1st to 10th	Day	21% 9% 21% 27% 20% 3	420
	11th to 20th	Day	25% 10% 24% 23% 15% 2	420
	21st to end	Day	26% 12% 30% 23% 8% 1	462
November	1st to 10th	Day	28% 12% 30% 25% 4 1	425
	11th to 20th	Day	33% 16% 28% 17% 6% 1	430
	21st to end	Day	30% 14% 33% 19% 4	430
December	1st to 10th	Day	28% 15% 34% 19% 4	430
	11th to 20th	Day	26% 24% 31% 17% 3	351
	21st to end	Day	17% 20% 33% 25% 6%	242
January	1st to 10th	Night	27% 13% 32% 22% 6%	950
	11th to 20th	Night	25% 13% 34% 20% 8%	950
	21st to end	Night	17% 14% 37% 23% 7% 1	935
February	1st to 10th	Night	23% 11% 34% 23% 8% 2	840
	11th to 20th	Night	23% 12% 33% 25% 4 2	823
	21st to end	Night	18% 9% 30% 33% 9% 1	692
March	1st to 10th	Night	23% 10% 34% 29% 5%	840
	11th to 20th	Night	21% 10% 31% 27% 9% 2	840
	21st to end	Night	25% 10% 28% 25% 9% 1	922
April	1st to 10th	Night	26% 10% 30% 26% 8%	630
	11th to 20th	Night	26% 7% 26% 29% 10% 2	613
	21st to end	Night	28% 6% 25% 27% 13% 1	600
May	1st to 10th	Night	29% 4 24% 29% 12% 3	600
	11th to 20th	Night	22% 3 23% 29% 18% 4	592
	21st to end	Night	19% 5% 27% 37% 10% 1	649
June	1st to 10th	Night	30% 3 19% 36% 12%	458
	11th to 20th	Night	20% 4 19% 36% 19% 1	400
	21st to end	Night	24% 2 18% 40% 13% 3	400
July	1st to 10th	Night	19% 2 19% 39% 17% 3	390
	11th to 20th	Night	13% 2 22% 41% 20% 1	414
	21st to end	Night	20% 3 18% 40% 18% 2	656
August	1st to 10th	Night	18% 2 18% 39% 22% 1	598
	11th to 20th	Night	19% 2 18% 35% 24% 2	592
	21st to end	Night	16% 3 17% 38% 23% 3	660
September	1st to 10th	Night	19% 5% 25% 34% 15% 1	600
	11th to 20th	Night	20% 8% 20% 33% 17% 2	668
	21st to end	Night	21% 7% 25% 32% 13% 2	800
October	1st to 10th	Night	24% 6% 26% 29% 14% 1	800
	11th to 20th	Night	25% 11% 26% 23% 12% 2	800
	21st to end	Night	31% 15% 27% 21% 6%	898
November	1st to 10th	Night	29% 15% 29% 21% 5% 1	930
	11th to 20th	Night	31% 17% 26% 18% 6% 1	950
	21st to end	Night	33% 15% 28% 21% 4 1	950
December	1st to 10th	Night	30% 15% 32% 18% 4	950
	11th to 20th	Night	28% 21% 32% 16% 3	950
	21st to end	Night	29% 16% 28% 21% 5% 1	1045

Page generated at 2026-04-14 03:44:28. Version ac07

Copyright © 2026 Attilla Danko.