Aladdin Valley
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Aladdin Valley clear sky chart from 2005-11-06 to 2025-08-05.

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	10% 11% 3 8% 5% 4 4 4 5% 7% 39%	129543
	Night	11% 12% 4 8% 5% 4 4 3 5% 6% 37%	127220
Transparency	Day	43% 7% 12% 21% 13% 4	129268
	Night	46% 7% 12% 20% 11% 3	127073
Seeing	Day	18% 13% 27% 26% 13% 3	15849
	Night	20% 6% 20% 34% 19% 2	24869

By Month

Percentage Cloud Cover NW (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% 26% 10% 15% 5% 4 3 2 3 3 13%	3637
	11th to 20th	Day	12% 12% 4 8% 5% 5% 4 3 4 6% 37%	3616
	21st to end	Day	20% 23% 4 6% 3 2 2 2 4 5% 28%	4004
February	1st to 10th	Day	15% 17% 5% 11% 6% 4 5% 3 4 5% 26%	1600
	11th to 20th	Day	12% 19% 5% 9% 6% 5% 4 3 6% 6% 26%	1823
	21st to end	Day	13% 18% 4 10% 6% 5% 5% 3 5% 5% 25%	1650
March	1st to 10th	Day	9% 14% 5% 8% 6% 6% 5% 4 6% 7% 29%	4518
	11th to 20th	Day	9% 15% 3 8% 4 4 4 3 4 6% 38%	4662
	21st to end	Day	14% 17% 5% 11% 6% 6% 5% 4 6% 7% 20%	5959
April	1st to 10th	Day	14% 15% 5% 10% 6% 5% 5% 3 5% 7% 24%	2400
	11th to 20th	Day	11% 13% 4 9% 6% 6% 6% 5% 5% 6% 28%	2448
	21st to end	Day	12% 13% 4 9% 5% 5% 5% 4 5% 7% 32%	2600
May	1st to 10th	Day	8% 8% 3 8% 6% 6% 6% 4 6% 7% 39%	6320
	11th to 20th	Day	10% 12% 4 12% 7% 6% 6% 5% 7% 8% 25%	6277
	21st to end	Day	9% 9% 4 9% 7% 6% 6% 4 6% 8% 33%	7123
June	1st to 10th	Day	18% 8% 3 9% 5% 5% 5% 3 6% 6% 33%	3000
	11th to 20th	Day	14% 8% 4 9% 6% 6% 6% 5% 6% 7% 30%	3000
	21st to end	Day	8% 6% 2 6% 5% 6% 5% 4 6% 7% 46%	3000
July	1st to 10th	Day	3 3 1 3 3 3 3 3 4 6% 68%	6581
	11th to 20th	Day	3 2 1 3 3 3 3 2 4 4 73%	6320
	21st to end	Day	5% 2 1 3 3 3 3 3 5% 7% 65%	6874
August	1st to 10th	Day	3 3 1 3 3 3 4 3 5% 8% 64%	4458
	11th to 20th	Day	4 3 1 3 3 3 4 4 6% 7% 61%	4212
	21st to end	Day	4 4 2 6% 4 4 5% 4 7% 8% 52%	4281
September	1st to 10th	Day	4 4 2 5% 3 3 4 3 5% 7% 60%	2280
	11th to 20th	Day	8% 6% 2 6% 5% 4 4 3 5% 7% 48%	2190
	21st to end	Day	10% 7% 2 7% 5% 4 4 4 5% 8% 45%	2090
October	1st to 10th	Day	8% 6% 2 6% 4 4 5% 4 6% 7% 49%	3315
	11th to 20th	Day	10% 8% 2 7% 5% 5% 5% 4 6% 8% 40%	2970
	21st to end	Day	17% 12% 3 7% 5% 5% 5% 4 6% 6% 30%	3101
November	1st to 10th	Day	23% 14% 4 9% 5% 3 4 3 4 7% 23%	1764
	11th to 20th	Day	21% 17% 4 10% 5% 4 4 3 4 5% 24%	1640
	21st to end	Day	19% 19% 6% 9% 5% 4 3 4 4 5% 21%	1400
December	1st to 10th	Day	12% 11% 4 9% 4 4 5% 5% 6% 8% 31%	2290
	11th to 20th	Day	17% 26% 6% 12% 4 4 4 3 5% 5% 15%	2642
	21st to end	Day	15% 27% 9% 12% 5% 4 4 3 4 4 12%	3498
January	1st to 10th	Night	19% 26% 7% 12% 4 3 3 2 3 4 16%	6352
	11th to 20th	Night	11% 12% 5% 7% 4 4 4 4 7% 8% 34%	6282
	21st to end	Night	18% 22% 4 7% 4 3 3 3 3 4 29%	6952
February	1st to 10th	Night	16% 17% 5% 10% 5% 4 4 3 4 6% 26%	2800
	11th to 20th	Night	13% 17% 4 10% 5% 4 4 3 5% 6% 29%	2462
	21st to end	Night	12% 15% 4 9% 5% 4 5% 3 6% 7% 30%	1980
March	1st to 10th	Night	7% 13% 3 9% 6% 5% 5% 4 5% 8% 36%	5376
	11th to 20th	Night	10% 13% 5% 8% 4 4 3 3 4 6% 41%	5336
	21st to end	Night	12% 14% 4 11% 7% 7% 7% 5% 7% 7% 20%	5011
April	1st to 10th	Night	10% 12% 3 7% 5% 6% 6% 5% 7% 8% 32%	2000
	11th to 20th	Night	10% 10% 4 9% 5% 6% 4 3 4 7% 38%	1902
	21st to end	Night	9% 10% 4 9% 6% 5% 5% 4 6% 6% 36%	1796
May	1st to 10th	Night	8% 5% 2 6% 5% 5% 6% 6% 6% 7% 44%	3640
	11th to 20th	Night	9% 8% 3 8% 5% 7% 6% 5% 6% 7% 35%	3616
	21st to end	Night	10% 8% 3 8% 5% 5% 4 4 7% 8% 38%	3747
June	1st to 10th	Night	12% 7% 2 8% 6% 4 4 5% 6% 9% 37%	1400
	11th to 20th	Night	11% 7% 3 7% 6% 5% 6% 5% 7% 9% 34%	1400
	21st to end	Night	7% 4 2 4 5% 4 5% 4 7% 8% 51%	1400
July	1st to 10th	Night	3 2 1 2 2 2 2 2 4 6% 74%	3361
	11th to 20th	Night	3 2 1 3 2 2 2 2 4 5% 74%	3640
	21st to end	Night	4 2 1 2 2 2 3 3 4 6% 70%	3969
August	1st to 10th	Night	3 4 2 4 2 2 3 3 4 7% 67%	2561
	11th to 20th	Night	2 2 2 5% 3 3 4 4 6% 9% 61%	2617
	21st to end	Night	3 3 2 5% 4 5% 4 4 7% 7% 57%	3392
September	1st to 10th	Night	4 3 1 4 3 3 4 3 6% 7% 61%	1900
	11th to 20th	Night	7% 6% 2 5% 4 4 6% 4 6% 7% 49%	1990
	21st to end	Night	8% 6% 3 5% 3 3 4 4 5% 8% 51%	2090
October	1st to 10th	Night	7% 4 2 5% 4 3 4 4 6% 8% 54%	3662
	11th to 20th	Night	12% 7% 2 6% 4 4 4 4 5% 8% 44%	3962
	21st to end	Night	14% 9% 3 6% 4 5% 5% 4 5% 5% 38%	4457
November	1st to 10th	Night	22% 16% 4 7% 5% 4 5% 3 5% 5% 24%	2535
	11th to 20th	Night	20% 17% 4 8% 5% 5% 4 2 4 6% 25%	2757
	21st to end	Night	21% 19% 5% 9% 5% 4 3 3 5% 5% 23%	2977
December	1st to 10th	Night	11% 13% 4 10% 6% 4 4 3 5% 6% 34%	4890
	11th to 20th	Night	17% 23% 8% 12% 6% 4 3 3 4 4 15%	5550
	21st to end	Night	16% 25% 7% 13% 6% 4 4 3 4 3 13%	7458

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% 6% 7% 9% 2	3637
	11th to 20th	Day	47% 7% 20% 18% 6% 3	3640
	21st to end	Day	59% 6% 12% 16% 7%	4004
February	1st to 10th	Day	61% 7% 13% 10% 7% 2	1600
	11th to 20th	Day	58% 8% 14% 13% 7% 1	1832
	21st to end	Day	59% 8% 12% 13% 8% 1	1650
March	1st to 10th	Day	52% 6% 10% 16% 15%	4518
	11th to 20th	Day	46% 6% 17% 25% 6%	4662
	21st to end	Day	62% 9% 12% 13% 4	5959
April	1st to 10th	Day	59% 6% 15% 16% 4	2400
	11th to 20th	Day	54% 7% 13% 17% 8% 1	2448
	21st to end	Day	52% 7% 12% 19% 8% 2	2600
May	1st to 10th	Day	39% 6% 13% 23% 18% 1	6320
	11th to 20th	Day	52% 7% 13% 21% 7%	6280
	21st to end	Day	46% 9% 16% 23% 6%	7124
June	1st to 10th	Day	50% 6% 10% 18% 14% 3	3000
	11th to 20th	Day	51% 7% 13% 17% 11% 2	3000
	21st to end	Day	36% 7% 15% 23% 17% 3	3000
July	1st to 10th	Day	18% 4 10% 22% 28% 18%	6511
	11th to 20th	Day	15% 3 8% 25% 26% 23%	6245
	21st to end	Day	19% 4 8% 30% 25% 14%	6681
August	1st to 10th	Day	18% 4 7% 34% 28% 9%	4441
	11th to 20th	Day	21% 5% 11% 40% 20% 3	4254
	21st to end	Day	26% 7% 15% 32% 19% 2	4280
September	1st to 10th	Day	25% 5% 12% 30% 21% 7%	2280
	11th to 20th	Day	35% 7% 12% 25% 18% 3	2190
	21st to end	Day	37% 8% 17% 23% 11% 3	2090
October	1st to 10th	Day	33% 7% 17% 35% 9%	3315
	11th to 20th	Day	40% 8% 15% 22% 15%	2970
	21st to end	Day	49% 10% 15% 18% 7% 1	3101
November	1st to 10th	Day	61% 9% 13% 12% 4 1	1764
	11th to 20th	Day	64% 9% 10% 12% 3 2	1640
	21st to end	Day	64% 8% 13% 11% 3	1400
December	1st to 10th	Day	49% 10% 22% 16% 3	2290
	11th to 20th	Day	71% 7% 11% 8% 3	2644
	21st to end	Day	75% 7% 9% 7% 3	3498
January	1st to 10th	Night	73% 6% 6% 13% 2	6352
	11th to 20th	Night	45% 10% 16% 20% 8% 2	6320
	21st to end	Night	60% 6% 13% 15% 6%	6952
February	1st to 10th	Night	60% 7% 14% 10% 8% 2	2800
	11th to 20th	Night	57% 6% 14% 16% 7% 1	2464
	21st to end	Night	52% 7% 17% 14% 9% 1	1980
March	1st to 10th	Night	45% 6% 15% 18% 15% 1	5376
	11th to 20th	Night	44% 4 16% 27% 8%	5337
	21st to end	Night	57% 12% 13% 14% 4	5011
April	1st to 10th	Night	46% 9% 17% 21% 7% 1	2000
	11th to 20th	Night	45% 6% 13% 22% 12% 1	1902
	21st to end	Night	45% 7% 12% 23% 12% 1	1796
May	1st to 10th	Night	33% 7% 11% 25% 23% 2	3637
	11th to 20th	Night	42% 8% 11% 26% 11% 1	3616
	21st to end	Night	39% 10% 15% 29% 8%	3747
June	1st to 10th	Night	42% 7% 13% 20% 15% 4	1400
	11th to 20th	Night	42% 7% 15% 20% 13% 3	1400
	21st to end	Night	28% 7% 13% 26% 23% 4	1400
July	1st to 10th	Night	13% 3 8% 23% 30% 23%	3323
	11th to 20th	Night	14% 3 6% 27% 20% 30%	3592
	21st to end	Night	15% 4 5% 31% 27% 19%	3857
August	1st to 10th	Night	17% 4 6% 29% 30% 14%	2553
	11th to 20th	Night	20% 4 10% 34% 27% 4	2641
	21st to end	Night	23% 6% 15% 28% 25% 4	3392
September	1st to 10th	Night	22% 4 8% 30% 27% 10%	1900
	11th to 20th	Night	34% 6% 11% 24% 20% 5%	1990
	21st to end	Night	31% 6% 18% 28% 13% 5%	2090
October	1st to 10th	Night	28% 5% 15% 39% 12%	3662
	11th to 20th	Night	38% 6% 13% 26% 16%	3962
	21st to end	Night	45% 8% 15% 25% 7% 1	4457
November	1st to 10th	Night	61% 9% 14% 11% 5% 1	2535
	11th to 20th	Night	61% 8% 14% 11% 5% 1	2757
	21st to end	Night	63% 7% 13% 12% 4	2977
December	1st to 10th	Night	51% 8% 16% 21% 4	4890
	11th to 20th	Night	73% 7% 11% 8% 2	5547
	21st to end	Night	74% 7% 9% 8% 3	7458

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	28% 12% 28% 20% 10% 4	200
	11th to 20th	Day	28% 5% 26% 20% 17% 5%	200
	21st to end	Day	28% 6% 29% 27% 9% 2	220
February	1st to 10th	Day	21% 13% 35% 25% 7% 2	200
	11th to 20th	Day	21% 15% 29% 25% 9% 1	421
	21st to end	Day	21% 13% 31% 25% 10%	414
March	1st to 10th	Day	23% 19% 25% 22% 8% 2	500
	11th to 20th	Day	25% 15% 22% 21% 16% 1	500
	21st to end	Day	27% 17% 29% 18% 8% 2	550
April	1st to 10th	Day	27% 17% 28% 19% 8% 2	500
	11th to 20th	Day	21% 22% 27% 18% 9% 2	492
	21st to end	Day	19% 17% 29% 23% 10% 2	500
May	1st to 10th	Day	16% 15% 34% 24% 8% 3	503
	11th to 20th	Day	23% 11% 29% 24% 10% 2	528
	21st to end	Day	17% 12% 25% 25% 17% 4	663
June	1st to 10th	Day	19% 13% 26% 26% 13% 3	730
	11th to 20th	Day	17% 16% 28% 25% 11% 3	730
	21st to end	Day	10% 9% 25% 32% 19% 4	730
July	1st to 10th	Day	7% 10% 30% 32% 18% 3	643
	11th to 20th	Day	7% 13% 33% 29% 15% 3	524
	21st to end	Day	5% 10% 32% 33% 17% 4	575
August	1st to 10th	Day	6% 9% 28% 34% 19% 5%	504
	11th to 20th	Day	7% 6% 27% 33% 20% 7%	477
	21st to end	Day	7% 14% 26% 28% 19% 5%	539
September	1st to 10th	Day	10% 11% 26% 29% 19% 5%	490
	11th to 20th	Day	13% 12% 27% 27% 17% 3	490
	21st to end	Day	16% 16% 28% 22% 14% 3	490
October	1st to 10th	Day	13% 12% 29% 27% 15% 3	490
	11th to 20th	Day	20% 11% 25% 23% 16% 5%	376
	21st to end	Day	29% 10% 25% 26% 7% 3	330
November	1st to 10th	Day	26% 11% 22% 30% 11%	300
	11th to 20th	Day	35% 11% 18% 26% 8% 2	220
	21st to end	Day	30% 10% 20% 24% 14% 3	200
December	1st to 10th	Day	26% 9% 21% 22% 18% 5%	200
	11th to 20th	Day	25% 9% 29% 24% 13% 2	200
	21st to end	Day	29% 8% 23% 28% 11% 1	220
January	1st to 10th	Night	38% 7% 21% 24% 9% 1	820
	11th to 20th	Night	28% 7% 21% 31% 12% 2	800
	21st to end	Night	26% 5% 23% 33% 12%	880
February	1st to 10th	Night	22% 8% 28% 30% 11% 1	800
	11th to 20th	Night	23% 4 25% 34% 13% 1	784
	21st to end	Night	21% 7% 22% 33% 16% 2	660
March	1st to 10th	Night	23% 8% 22% 30% 17% 1	800
	11th to 20th	Night	21% 6% 22% 33% 17% 1	800
	21st to end	Night	20% 7% 26% 33% 13% 1	880
April	1st to 10th	Night	17% 5% 24% 34% 19% 2	800
	11th to 20th	Night	17% 7% 27% 35% 13% 2	714
	21st to end	Night	15% 8% 23% 36% 17% 1	596
May	1st to 10th	Night	12% 5% 23% 35% 24% 1	400
	11th to 20th	Night	14% 7% 17% 31% 29% 1	394
	21st to end	Night	14% 6% 18% 35% 24% 3	433
June	1st to 10th	Night	14% 3 22% 40% 19% 2	400
	11th to 20th	Night	13% 7% 20% 37% 20% 3	400
	21st to end	Night	9% 4 15% 42% 28% 3	400
July	1st to 10th	Night	5% 2 13% 42% 37% 2	390
	11th to 20th	Night	3 3 16% 45% 31% 2	388
	21st to end	Night	2 3 10% 47% 35% 3	438
August	1st to 10th	Night	4 2 9% 35% 44% 5%	386
	11th to 20th	Night	4 2 13% 36% 39% 6%	444
	21st to end	Night	6% 4 12% 40% 35% 3	769
September	1st to 10th	Night	5% 3 17% 38% 29% 7%	760
	11th to 20th	Night	10% 4 15% 30% 37% 5%	760
	21st to end	Night	13% 5% 16% 39% 22% 5%	760
October	1st to 10th	Night	15% 4 16% 39% 25% 1	760
	11th to 20th	Night	19% 4 19% 32% 24% 2	760
	21st to end	Night	23% 5% 23% 35% 13% 3	836
November	1st to 10th	Night	30% 7% 19% 36% 8%	780
	11th to 20th	Night	33% 6% 22% 26% 12% 1	800
	21st to end	Night	30% 6% 19% 31% 13% 2	977
December	1st to 10th	Night	26% 5% 21% 32% 15% 2	1000
	11th to 20th	Night	32% 7% 20% 33% 9%	1000
	21st to end	Night	32% 9% 22% 31% 6%	1100

Page generated at 2025-08-01 22:32:23. Version ac07

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