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 2024-04-03.

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	13% 11% 4 7% 6% 3 5% 4 5% 7% 35%	78458
	Night	15% 13% 4 7% 5% 3 4 4 5% 6% 33%	81614
Transparency	Day	49% 7% 13% 18% 11% 3	78183
	Night	51% 7% 12% 17% 10% 3	81470
Seeing	Day	18% 12% 27% 26% 13% 3	14026
	Night	20% 5% 20% 34% 19% 2	23316

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% 27% 8% 12% 6% 4 4 3 3 4 11%	2537
	11th to 20th	Day	18% 16% 5% 8% 7% 4 4 3 4 6% 24%	2516
	21st to end	Day	26% 27% 5% 7% 4 2 3 3 3 6% 12%	2794
February	1st to 10th	Day	17% 16% 5% 10% 7% 3 4 5% 4 5% 25%	1520
	11th to 20th	Day	13% 18% 5% 8% 6% 4 4 4 6% 7% 26%	1728
	21st to end	Day	14% 16% 5% 8% 8% 4 5% 4 5% 5% 25%	1570
March	1st to 10th	Day	17% 16% 5% 8% 7% 4 6% 4 5% 8% 22%	1900
	11th to 20th	Day	16% 15% 4 7% 5% 3 5% 5% 4 7% 29%	1940
	21st to end	Day	18% 16% 5% 10% 7% 4 6% 4 5% 5% 19%	2498
April	1st to 10th	Day	15% 14% 6% 9% 8% 4 5% 5% 5% 7% 23%	2185
	11th to 20th	Day	12% 13% 5% 8% 7% 5% 6% 7% 5% 6% 26%	2200
	21st to end	Day	13% 12% 5% 8% 6% 3 5% 5% 5% 7% 31%	2340
May	1st to 10th	Day	11% 8% 3 6% 7% 4 5% 6% 6% 8% 36%	2520
	11th to 20th	Day	13% 9% 4 8% 7% 4 6% 6% 6% 8% 30%	2477
	21st to end	Day	15% 8% 4 9% 7% 5% 7% 6% 6% 8% 26%	2803
June	1st to 10th	Day	19% 7% 4 8% 6% 3 5% 5% 6% 6% 31%	2700
	11th to 20th	Day	15% 8% 4 8% 8% 5% 6% 6% 6% 7% 27%	2700
	21st to end	Day	8% 5% 3 5% 5% 4 5% 5% 6% 7% 46%	2700
July	1st to 10th	Day	4 4 2 4 5% 3 5% 5% 6% 7% 55%	2627
	11th to 20th	Day	5% 3 1 3 4 2 4 4 5% 6% 61%	2520
	21st to end	Day	3 1 1 3 4 2 3 3 4 6% 70%	2741
August	1st to 10th	Day	4 4 2 3 4 3 4 4 5% 8% 60%	2507
	11th to 20th	Day	5% 3 1 2 3 2 3 4 4 7% 65%	2409
	21st to end	Day	5% 4 2 5% 5% 3 5% 5% 6% 8% 54%	2438
September	1st to 10th	Day	5% 5% 2 4 4 2 4 4 5% 7% 59%	2160
	11th to 20th	Day	8% 6% 3 5% 6% 3 4 4 5% 8% 48%	2075
	21st to end	Day	11% 7% 2 6% 6% 3 4 5% 5% 7% 44%	1980
October	1st to 10th	Day	12% 7% 3 6% 6% 3 4 5% 6% 7% 40%	1883
	11th to 20th	Day	15% 7% 3 7% 5% 3 3 4 5% 8% 39%	1692
	21st to end	Day	21% 11% 3 6% 5% 3 4 4 5% 6% 31%	1782
November	1st to 10th	Day	24% 13% 5% 7% 6% 2 4 4 5% 7% 23%	1674
	11th to 20th	Day	22% 15% 5% 9% 6% 3 3 4 4 5% 25%	1558
	21st to end	Day	20% 16% 6% 8% 6% 3 4 4 4 6% 22%	1330
December	1st to 10th	Day	16% 15% 7% 10% 5% 3 5% 5% 4 6% 24%	1330
	11th to 20th	Day	20% 25% 7% 9% 6% 3 3 4 4 5% 15%	1682
	21st to end	Day	17% 22% 7% 8% 6% 3 4 4 5% 6% 17%	2442
January	1st to 10th	Night	23% 25% 7% 10% 6% 3 3 3 3 4 13%	4438
	11th to 20th	Night	17% 16% 7% 9% 6% 3 4 4 5% 6% 23%	4382
	21st to end	Night	25% 27% 6% 8% 5% 2 3 4 3 3 13%	4862
February	1st to 10th	Night	17% 16% 5% 9% 6% 3 4 4 4 6% 26%	2660
	11th to 20th	Night	14% 16% 4 9% 6% 3 4 4 5% 6% 29%	2337
	21st to end	Night	12% 14% 4 8% 6% 3 5% 4 5% 7% 31%	1884
March	1st to 10th	Night	15% 15% 4 8% 5% 3 5% 5% 5% 6% 28%	2280
	11th to 20th	Night	16% 10% 4 7% 6% 3 4 4 5% 7% 34%	2238
	21st to end	Night	13% 12% 5% 8% 8% 5% 6% 6% 6% 6% 27%	2095
April	1st to 10th	Night	11% 11% 4 6% 5% 4 6% 6% 7% 8% 32%	1820
	11th to 20th	Night	11% 9% 4 8% 6% 4 5% 4 4 7% 36%	1710
	21st to end	Night	9% 11% 4 8% 6% 4 5% 5% 5% 7% 35%	1617
May	1st to 10th	Night	11% 6% 3 5% 7% 3 5% 7% 6% 9% 38%	1440
	11th to 20th	Night	10% 7% 3 5% 5% 3 6% 6% 6% 9% 41%	1416
	21st to end	Night	13% 8% 4 9% 6% 4 5% 6% 6% 8% 31%	1467
June	1st to 10th	Night	13% 7% 3 7% 6% 4 5% 6% 6% 9% 35%	1260
	11th to 20th	Night	12% 7% 3 6% 8% 4 6% 6% 6% 9% 33%	1260
	21st to end	Night	7% 3 2 3 5% 3 4 4 7% 9% 52%	1260
July	1st to 10th	Night	3 2 1 3 5% 2 4 5% 6% 8% 60%	1329
	11th to 20th	Night	2 2 1 3 3 3 4 4 6% 8% 63%	1440
	21st to end	Night	1 1 2 2 1 3 3 5% 6% 75%	1576
August	1st to 10th	Night	4 3 2 3 2 2 2 3 4 6% 69%	1432
	11th to 20th	Night	3 2 2 2 3 2 3 4 4 8% 67%	1488
	21st to end	Night	4 2 1 3 3 2 4 4 7% 8% 62%	1916
September	1st to 10th	Night	4 3 2 4 4 2 4 4 5% 7% 61%	1800
	11th to 20th	Night	8% 6% 3 5% 5% 3 5% 5% 6% 7% 49%	1885
	21st to end	Night	9% 6% 3 4 4 3 3 6% 5% 8% 50%	1980
October	1st to 10th	Night	12% 7% 3 7% 5% 3 4 4 5% 6% 45%	2074
	11th to 20th	Night	15% 7% 3 6% 5% 3 4 4 6% 8% 40%	2268
	21st to end	Night	17% 10% 3 6% 5% 3 4 4 5% 6% 37%	2574
November	1st to 10th	Night	23% 15% 4 6% 5% 3 5% 4 5% 5% 23%	2405
	11th to 20th	Night	20% 15% 5% 7% 6% 3 5% 3 4 6% 26%	2619
	21st to end	Night	21% 15% 6% 8% 6% 3 4 3 5% 5% 24%	2828
December	1st to 10th	Night	18% 17% 6% 11% 6% 3 4 4 4 5% 24%	2850
	11th to 20th	Night	21% 24% 7% 10% 7% 2 3 3 4 4 15%	3510
	21st to end	Night	19% 21% 7% 9% 7% 4 5% 5% 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	62% 7% 14% 10% 6%	1900
	11th to 20th	Day	55% 8% 14% 18% 5%	1940
	21st to end	Day	67% 7% 12% 10% 3	2498
April	1st to 10th	Day	61% 5% 14% 15% 4	2185
	11th to 20th	Day	57% 7% 13% 15% 7% 1	2200
	21st to end	Day	54% 6% 12% 19% 7% 2	2340
May	1st to 10th	Day	45% 6% 16% 22% 9% 1	2520
	11th to 20th	Day	50% 7% 14% 20% 8% 1	2480
	21st to end	Day	54% 8% 16% 16% 6%	2804
June	1st to 10th	Day	53% 6% 11% 17% 11% 3	2700
	11th to 20th	Day	54% 8% 14% 15% 8% 1	2700
	21st to end	Day	35% 7% 15% 22% 17% 4	2700
July	1st to 10th	Day	27% 5% 12% 23% 22% 10%	2557
	11th to 20th	Day	23% 5% 10% 22% 29% 12%	2445
	21st to end	Day	17% 3 7% 25% 34% 14%	2589
August	1st to 10th	Day	23% 6% 10% 26% 24% 11%	2490
	11th to 20th	Day	19% 5% 11% 29% 31% 5%	2409
	21st to end	Day	26% 7% 13% 30% 21% 3	2438
September	1st to 10th	Day	25% 5% 12% 30% 21% 6%	2160
	11th to 20th	Day	35% 7% 11% 24% 19% 3	2075
	21st to end	Day	39% 8% 17% 22% 11% 3	1980
October	1st to 10th	Day	41% 7% 15% 27% 9%	1883
	11th to 20th	Day	43% 8% 16% 24% 9%	1692
	21st to end	Day	52% 7% 16% 18% 6% 1	1782
November	1st to 10th	Day	61% 9% 13% 12% 4 1	1674
	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	54% 8% 15% 15% 7% 1	2280
	11th to 20th	Night	51% 6% 13% 21% 8% 1	2239
	21st to end	Night	55% 10% 14% 14% 6% 1	2095
April	1st to 10th	Night	46% 9% 17% 21% 7% 1	1820
	11th to 20th	Night	48% 6% 13% 21% 11% 1	1710
	21st to end	Night	47% 7% 13% 22% 10% 1	1617
May	1st to 10th	Night	39% 7% 13% 26% 14% 1	1440
	11th to 20th	Night	39% 8% 15% 25% 12% 2	1416
	21st to end	Night	47% 8% 13% 22% 9% 1	1467
June	1st to 10th	Night	45% 6% 13% 19% 13% 5%	1260
	11th to 20th	Night	44% 7% 16% 20% 11% 2	1260
	21st to end	Night	27% 7% 13% 27% 22% 4	1260
July	1st to 10th	Night	22% 4 10% 27% 24% 14%	1291
	11th to 20th	Night	18% 5% 11% 25% 25% 17%	1392
	21st to end	Night	10% 3 7% 23% 36% 21%	1488
August	1st to 10th	Night	17% 4 8% 25% 31% 15%	1424
	11th to 20th	Night	17% 4 10% 27% 35% 7%	1488
	21st to end	Night	19% 5% 13% 25% 31% 6%	1916
September	1st to 10th	Night	23% 4 8% 30% 26% 9%	1800
	11th to 20th	Night	34% 6% 10% 23% 21% 5%	1885
	21st to end	Night	32% 6% 17% 27% 13% 5%	1980
October	1st to 10th	Night	41% 5% 14% 29% 11% 1	2074
	11th to 20th	Night	42% 6% 16% 22% 12% 1	2268
	21st to end	Night	48% 7% 14% 22% 7% 1	2574
November	1st to 10th	Night	61% 9% 14% 11% 5% 1	2405
	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	27% 14% 30% 19% 8% 2	429
	11th to 20th	Day	24% 22% 27% 17% 8% 3	412
	21st to end	Day	21% 18% 27% 23% 9% 2	420
May	1st to 10th	Day	17% 14% 34% 25% 8% 2	423
	11th to 20th	Day	22% 11% 29% 25% 10% 2	448
	21st to end	Day	18% 10% 25% 25% 18% 4	565
June	1st to 10th	Day	20% 14% 26% 25% 13% 3	630
	11th to 20th	Day	17% 16% 27% 26% 11% 3	630
	21st to end	Day	10% 8% 25% 32% 21% 4	630
July	1st to 10th	Day	8% 9% 29% 32% 18% 3	552
	11th to 20th	Day	8% 14% 34% 28% 14% 2	444
	21st to end	Day	4 11% 32% 31% 18% 4	487
August	1st to 10th	Day	6% 9% 29% 34% 18% 4	447
	11th to 20th	Day	7% 6% 28% 33% 20% 6%	437
	21st to end	Day	7% 14% 26% 29% 20% 5%	495
September	1st to 10th	Day	11% 12% 27% 28% 19% 3	450
	11th to 20th	Day	14% 12% 27% 27% 17% 4	450
	21st to end	Day	17% 15% 28% 22% 14% 4	450
October	1st to 10th	Day	14% 11% 30% 27% 14% 3	450
	11th to 20th	Day	21% 11% 26% 24% 14% 4	342
	21st to end	Day	30% 10% 25% 26% 6% 3	297
November	1st to 10th	Day	26% 10% 23% 29% 11%	270
	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% 4 23% 34% 20% 2	728
	11th to 20th	Night	18% 7% 26% 34% 13% 2	642
	21st to end	Night	16% 8% 23% 36% 16% 1	537
May	1st to 10th	Night	13% 4 23% 36% 23% 1	360
	11th to 20th	Night	13% 6% 18% 31% 31% 1	354
	21st to end	Night	15% 6% 17% 35% 24% 3	389
June	1st to 10th	Night	15% 3 22% 39% 20% 2	360
	11th to 20th	Night	14% 6% 20% 36% 21% 3	360
	21st to end	Night	8% 4 14% 42% 28% 3	360
July	1st to 10th	Night	5% 2 13% 41% 38% 2	350
	11th to 20th	Night	3 3 16% 46% 30% 2	348
	21st to end	Night	2 2 10% 47% 36% 4	394
August	1st to 10th	Night	4 2 9% 34% 45% 5%	358
	11th to 20th	Night	4 2 12% 37% 40% 6%	420
	21st to end	Night	6% 4 12% 40% 36% 3	728
September	1st to 10th	Night	5% 3 18% 39% 28% 6%	720
	11th to 20th	Night	10% 4 15% 29% 38% 5%	720
	21st to end	Night	13% 4 16% 39% 23% 5%	720
October	1st to 10th	Night	16% 3 15% 38% 26% 1	720
	11th to 20th	Night	19% 4 19% 33% 24% 2	720
	21st to end	Night	23% 5% 22% 34% 13% 3	792
November	1st to 10th	Night	31% 6% 19% 35% 9%	740
	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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