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 2024-11-04.

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	11% 11% 3 7% 5% 4 4 4 5% 7% 39%	105288
	Night	13% 12% 4 7% 5% 4 4 4 5% 6% 37%	102296
Transparency	Day	44% 7% 12% 20% 13% 5%	105055
	Night	47% 6% 12% 19% 11% 4	102176
Seeing	Day	18% 13% 27% 26% 13% 3	14905
	Night	20% 6% 20% 34% 19% 2	23940

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	17% 28% 8% 14% 5% 5% 4 3 3 4 11%	2537
	11th to 20th	Day	18% 17% 5% 9% 6% 5% 4 3 4 6% 24%	2516
	21st to end	Day	26% 28% 5% 8% 4 3 3 3 4 6% 12%	2794
February	1st to 10th	Day	16% 17% 4 11% 6% 4 5% 3 4 5% 25%	1520
	11th to 20th	Day	13% 19% 4 9% 6% 5% 4 3 6% 6% 26%	1728
	21st to end	Day	13% 17% 4 10% 7% 5% 5% 3 5% 5% 25%	1570
March	1st to 10th	Day	12% 17% 5% 9% 6% 6% 4 3 5% 7% 25%	3138
	11th to 20th	Day	10% 12% 3 6% 4 4 3 3 4 6% 46%	3256
	21st to end	Day	15% 17% 5% 12% 7% 6% 6% 4 5% 5% 18%	4155
April	1st to 10th	Day	15% 15% 5% 10% 7% 5% 5% 3 5% 7% 23%	2280
	11th to 20th	Day	12% 14% 4 10% 6% 6% 6% 5% 5% 6% 26%	2324
	21st to end	Day	12% 13% 4 9% 6% 5% 5% 4 5% 7% 30%	2470
May	1st to 10th	Day	10% 10% 3 9% 7% 6% 6% 4 6% 7% 31%	4420
	11th to 20th	Day	8% 9% 3 9% 5% 6% 5% 5% 8% 9% 32%	4377
	21st to end	Day	12% 11% 4 11% 8% 7% 7% 5% 6% 7% 23%	4963
June	1st to 10th	Day	19% 8% 3 9% 5% 5% 5% 4 6% 6% 31%	2850
	11th to 20th	Day	14% 9% 4 9% 6% 6% 6% 5% 6% 7% 28%	2850
	21st to end	Day	8% 5% 2 6% 5% 6% 5% 4 6% 6% 46%	2850
July	1st to 10th	Day	3 3 1 3 3 3 3 3 4 6% 70%	4597
	11th to 20th	Day	3 2 1 2 2 2 3 2 4 4 74%	4420
	21st to end	Day	2 2 1 3 3 3 3 3 5% 7% 69%	4790
August	1st to 10th	Day	3 3 1 3 3 3 4 3 5% 8% 65%	4401
	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 8% 5% 3 4 3 5% 7% 23%	1701
	11th to 20th	Day	22% 16% 4 10% 5% 4 4 3 4 5% 25%	1558
	21st to end	Day	20% 18% 5% 9% 5% 4 3 4 4 6% 22%	1330
December	1st to 10th	Day	16% 15% 7% 10% 5% 4 5% 5% 4 5% 24%	1330
	11th to 20th	Day	20% 26% 6% 10% 5% 4 3 3 4 5% 15%	1682
	21st to end	Day	17% 23% 7% 9% 5% 5% 4 3 5% 6% 17%	2442
January	1st to 10th	Night	23% 26% 7% 11% 4 3 3 2 3 4 13%	4438
	11th to 20th	Night	16% 17% 7% 10% 5% 4 4 3 5% 6% 23%	4382
	21st to end	Night	25% 28% 6% 9% 4 3 3 3 3 3 13%	4862
February	1st to 10th	Night	16% 17% 5% 10% 5% 4 4 3 4 6% 26%	2660
	11th to 20th	Night	14% 17% 4 10% 5% 4 4 3 5% 6% 29%	2337
	21st to end	Night	11% 15% 4 9% 5% 4 5% 3 6% 7% 31%	1884
March	1st to 10th	Night	9% 14% 4 9% 5% 4 5% 4 6% 8% 31%	3736
	11th to 20th	Night	11% 9% 3 6% 4 3 3 2 4 5% 49%	3722
	21st to end	Night	13% 14% 4 11% 8% 7% 5% 4 6% 6% 22%	3493
April	1st to 10th	Night	10% 12% 3 7% 5% 5% 6% 5% 6% 8% 32%	1900
	11th to 20th	Night	11% 10% 4 9% 5% 6% 4 3 4 7% 36%	1806
	21st to end	Night	9% 11% 4 9% 6% 5% 5% 4 6% 6% 35%	1706
May	1st to 10th	Night	10% 6% 3 7% 6% 5% 6% 6% 7% 8% 35%	2540
	11th to 20th	Night	7% 6% 2 6% 4 5% 5% 5% 6% 8% 45%	2516
	21st to end	Night	14% 10% 4 10% 5% 6% 5% 5% 7% 8% 27%	2607
June	1st to 10th	Night	13% 7% 2 8% 6% 5% 4 5% 6% 9% 35%	1330
	11th to 20th	Night	11% 7% 3 7% 6% 5% 7% 6% 7% 9% 32%	1330
	21st to end	Night	7% 4 2 4 5% 4 4 4 7% 8% 52%	1330
July	1st to 10th	Night	2 1 1 2 3 2 2 2 4 6% 74%	2345
	11th to 20th	Night	1 2 1 2 2 2 2 2 5% 5% 76%	2540
	21st to end	Night	3 1 2 2 2 3 3 4 6% 75%	2762
August	1st to 10th	Night	3 4 2 3 2 2 3 3 4 7% 68%	2529
	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	23% 15% 4 7% 5% 4 5% 3 5% 5% 23%	2450
	11th to 20th	Night	20% 17% 4 8% 5% 5% 4 2 5% 6% 26%	2619
	21st to end	Night	21% 18% 5% 9% 5% 4 3 3 5% 5% 24%	2828
December	1st to 10th	Night	17% 18% 5% 12% 6% 4 3 3 4 4 24%	2850
	11th to 20th	Night	21% 24% 7% 11% 6% 3 3 3 4 4 15%	3510
	21st to end	Night	18% 22% 6% 10% 6% 5% 5% 4 5% 4 16%	5214

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% 7% 9% 6% 2	2537
	11th to 20th	Day	63% 5% 13% 12% 3 4	2540
	21st to end	Day	75% 7% 10% 6% 2	2794
February	1st to 10th	Day	62% 7% 14% 10% 5% 2	1520
	11th to 20th	Day	58% 9% 15% 12% 7% 1	1737
	21st to end	Day	59% 8% 12% 12% 8% 1	1570
March	1st to 10th	Day	59% 6% 11% 13% 11%	3138
	11th to 20th	Day	41% 6% 21% 28% 5%	3256
	21st to end	Day	66% 9% 10% 11% 5%	4155
April	1st to 10th	Day	61% 5% 14% 15% 4	2280
	11th to 20th	Day	56% 7% 13% 15% 7% 1	2324
	21st to end	Day	54% 7% 13% 18% 7% 2	2470
May	1st to 10th	Day	46% 6% 16% 22% 10% 1	4420
	11th to 20th	Day	42% 7% 15% 25% 10% 1	4380
	21st to end	Day	55% 10% 14% 17% 4	4964
June	1st to 10th	Day	52% 6% 10% 17% 12% 3	2850
	11th to 20th	Day	53% 7% 13% 16% 9% 2	2850
	21st to end	Day	35% 6% 15% 22% 18% 4	2850
July	1st to 10th	Day	17% 4 8% 19% 31% 21%	4527
	11th to 20th	Day	15% 3 6% 13% 30% 34%	4345
	21st to end	Day	16% 4 7% 24% 29% 19%	4639
August	1st to 10th	Day	17% 4 7% 34% 28% 9%	4384
	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	62% 9% 13% 12% 4 1	1701
	11th to 20th	Day	63% 9% 10% 12% 4 2	1558
	21st to end	Day	62% 8% 14% 12% 3	1330
December	1st to 10th	Day	61% 8% 12% 13% 5%	1330
	11th to 20th	Day	73% 6% 12% 7% 3	1684
	21st to end	Day	66% 9% 12% 10% 4	2442
January	1st to 10th	Night	76% 6% 7% 9% 2	4438
	11th to 20th	Night	59% 6% 13% 15% 5% 2	4420
	21st to end	Night	76% 7% 10% 6% 2 1	4862
February	1st to 10th	Night	60% 7% 15% 11% 6% 1	2660
	11th to 20th	Night	57% 6% 14% 16% 7% 1	2339
	21st to end	Night	52% 8% 16% 14% 10% 1	1884
March	1st to 10th	Night	49% 7% 17% 17% 9% 1	3736
	11th to 20th	Night	39% 4 21% 30% 6%	3723
	21st to end	Night	58% 12% 13% 13% 5%	3493
April	1st to 10th	Night	47% 9% 17% 21% 7% 1	1900
	11th to 20th	Night	47% 6% 13% 21% 11% 1	1806
	21st to end	Night	47% 7% 13% 22% 10% 1	1706
May	1st to 10th	Night	40% 8% 13% 23% 15% 1	2540
	11th to 20th	Night	32% 7% 13% 31% 15% 2	2516
	21st to end	Night	48% 11% 14% 18% 8%	2607
June	1st to 10th	Night	44% 6% 13% 19% 13% 4	1330
	11th to 20th	Night	43% 7% 15% 20% 11% 3	1330
	21st to end	Night	27% 6% 13% 26% 23% 4	1330
July	1st to 10th	Night	13% 3 6% 22% 30% 27%	2307
	11th to 20th	Night	11% 3 6% 14% 23% 43%	2492
	21st to end	Night	11% 3 5% 24% 31% 27%	2674
August	1st to 10th	Night	16% 4 6% 30% 30% 14%	2521
	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% 8% 14% 11% 5% 1	2450
	11th to 20th	Night	61% 8% 14% 11% 5% 1	2619
	21st to end	Night	62% 7% 14% 13% 4	2828
December	1st to 10th	Night	65% 6% 10% 15% 4	2850
	11th to 20th	Night	73% 8% 10% 6% 2	3507
	21st to end	Night	69% 7% 11% 8% 4	5214

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% 13% 26% 18% 10% 4	180
	11th to 20th	Day	31% 6% 24% 18% 16% 5%	180
	21st to end	Day	30% 6% 28% 28% 8% 1	198
February	1st to 10th	Day	23% 12% 34% 25% 5% 1	180
	11th to 20th	Day	22% 16% 29% 24% 8% 2	386
	21st to end	Day	20% 13% 31% 25% 10% 1	382
March	1st to 10th	Day	24% 20% 25% 21% 8% 2	460
	11th to 20th	Day	25% 14% 21% 22% 17% 1	460
	21st to end	Day	25% 17% 30% 19% 8% 2	506
April	1st to 10th	Day	28% 16% 29% 18% 7% 2	460
	11th to 20th	Day	22% 21% 28% 17% 9% 2	452
	21st to end	Day	20% 17% 30% 22% 9% 2	460
May	1st to 10th	Day	16% 14% 35% 24% 9% 2	463
	11th to 20th	Day	22% 11% 29% 25% 11% 2	488
	21st to end	Day	18% 11% 26% 25% 17% 3	614
June	1st to 10th	Day	20% 13% 26% 26% 12% 3	680
	11th to 20th	Day	17% 17% 27% 25% 11% 3	680
	21st to end	Day	10% 9% 25% 32% 20% 4	680
July	1st to 10th	Day	7% 10% 30% 32% 18% 3	597
	11th to 20th	Day	7% 13% 33% 29% 14% 3	484
	21st to end	Day	4 11% 32% 33% 18% 3	531
August	1st to 10th	Day	6% 9% 28% 34% 19% 5%	487
	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% 10% 24% 29% 11%	279
	11th to 20th	Day	33% 9% 19% 28% 9% 3	198
	21st to end	Day	29% 10% 19% 23% 16% 3	180
December	1st to 10th	Day	27% 9% 23% 21% 14% 5%	180
	11th to 20th	Day	25% 7% 28% 25% 13% 1	180
	21st to end	Day	28% 8% 24% 29% 10% 1	198
January	1st to 10th	Night	39% 7% 20% 24% 9% 1	779
	11th to 20th	Night	29% 7% 21% 30% 12% 2	760
	21st to end	Night	27% 6% 23% 32% 12%	836
February	1st to 10th	Night	23% 8% 28% 30% 10% 1	760
	11th to 20th	Night	24% 4 25% 33% 13% 1	744
	21st to end	Night	20% 7% 22% 33% 17% 2	628
March	1st to 10th	Night	24% 8% 21% 30% 16% 1	760
	11th to 20th	Night	21% 6% 22% 33% 17% 1	760
	21st to end	Night	20% 7% 25% 33% 14% 1	836
April	1st to 10th	Night	17% 5% 23% 34% 19% 2	760
	11th to 20th	Night	17% 7% 27% 34% 13% 2	678
	21st to end	Night	16% 8% 23% 36% 16% 1	566
May	1st to 10th	Night	12% 4 23% 35% 24% 1	380
	11th to 20th	Night	13% 7% 17% 32% 30% 1	374
	21st to end	Night	14% 6% 18% 35% 23% 3	411
June	1st to 10th	Night	14% 3 23% 39% 19% 2	380
	11th to 20th	Night	13% 7% 20% 36% 20% 3	380
	21st to end	Night	8% 4 15% 42% 27% 3	380
July	1st to 10th	Night	5% 2 13% 42% 37% 2	370
	11th to 20th	Night	2 3 15% 45% 32% 2	368
	21st to end	Night	2 3 11% 47% 35% 4	416
August	1st to 10th	Night	4 2 10% 35% 44% 5%	378
	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	31% 6% 19% 35% 8%	754
	11th to 20th	Night	32% 6% 23% 27% 13% 1	760
	21st to end	Night	30% 6% 18% 31% 13% 2	928
December	1st to 10th	Night	27% 5% 21% 32% 14% 2	950
	11th to 20th	Night	32% 7% 19% 34% 8%	950
	21st to end	Night	32% 8% 22% 31% 6%	1045

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