Stanley
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Stanley clear sky chart from 2005-11-06 to 2024-04-25.

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	4 10% 5% 9% 6% 3 5% 4 5% 6% 42%	82933
	Night	3 10% 5% 8% 6% 3 4 5% 5% 7% 43%	86220
Transparency	Day	43% 6% 10% 19% 16% 6%	82636
	Night	40% 7% 12% 21% 15% 5%	86039
Seeing	Day	14% 20% 33% 21% 9% 2	13824
	Night	9% 10% 26% 35% 17% 3	23587

By Month

Percentage Cloud Cover SW (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% 7% 19% 11% 4 6% 6% 6% 6% 24%	2539
	11th to 20th	Day	2 12% 7% 13% 11% 4 4 4 5% 6% 33%	2540
	21st to end	Day	2 20% 8% 9% 7% 3 5% 4 5% 7% 31%	2794
February	1st to 10th	Day	2 14% 7% 12% 7% 3 6% 4 6% 7% 32%	1680
	11th to 20th	Day	2 12% 9% 16% 8% 4 5% 5% 5% 6% 29%	1821
	21st to end	Day	2 15% 9% 16% 9% 4 6% 4 6% 6% 23%	1570
March	1st to 10th	Day	1 9% 8% 15% 10% 4 5% 5% 6% 7% 30%	3138
	11th to 20th	Day	2 12% 6% 10% 4 3 3 3 3 5% 49%	3445
	21st to end	Day	3 21% 9% 14% 9% 5% 6% 6% 5% 5% 17%	3876
April	1st to 10th	Day	4 17% 8% 11% 7% 4 5% 5% 5% 7% 27%	2280
	11th to 20th	Day	3 16% 6% 10% 6% 4 5% 4 4 6% 35%	2359
	21st to end	Day	7% 14% 6% 9% 7% 4 5% 5% 5% 7% 34%	2394
May	1st to 10th	Day	6% 13% 5% 8% 6% 4 5% 5% 6% 6% 37%	2340
	11th to 20th	Day	8% 11% 4 8% 8% 5% 6% 5% 6% 8% 32%	2317
	21st to end	Day	11% 15% 6% 8% 7% 5% 6% 4 5% 7% 26%	2723
June	1st to 10th	Day	12% 9% 3 6% 6% 4 6% 5% 7% 7% 34%	2542
	11th to 20th	Day	9% 9% 3 6% 6% 3 5% 5% 4 7% 44%	2699
	21st to end	Day	3 4 1 5% 5% 3 3 4 4 5% 62%	2520
July	1st to 10th	Day	2 2 1 3 4 2 4 4 6% 7% 63%	2520
	11th to 20th	Day	3 2 1 3 3 2 3 3 3 6% 72%	2520
	21st to end	Day	4 3 2 3 4 3 3 4 4 5% 64%	2741
August	1st to 10th	Day	4 4 2 4 5% 3 5% 5% 5% 6% 56%	2360
	11th to 20th	Day	2 2 1 3 4 3 3 4 4 6% 68%	2299
	21st to end	Day	3 3 2 4 4 2 4 4 4 6% 65%	2484
September	1st to 10th	Day	4 4 1 3 3 2 3 3 4 5% 67%	2129
	11th to 20th	Day	7% 5% 2 4 4 3 4 5% 5% 7% 55%	1980
	21st to end	Day	6% 8% 1 3 3 2 3 4 4 7% 58%	1980
October	1st to 10th	Day	8% 9% 3 6% 5% 2 4 5% 4 6% 48%	1980
	11th to 20th	Day	6% 11% 3 5% 5% 2 3 4 4 7% 49%	1745
	21st to end	Day	3 9% 4 8% 5% 4 4 4 6% 9% 44%	1782
November	1st to 10th	Day	5% 13% 5% 9% 5% 4 4 3 5% 7% 39%	1674
	11th to 20th	Day	3 12% 5% 10% 7% 3 4 4 6% 7% 38%	1710
	21st to end	Day	2 9% 7% 8% 7% 4 5% 5% 6% 9% 39%	1647
December	1st to 10th	Day	3 10% 6% 12% 8% 3 5% 4 4 7% 37%	1354
	11th to 20th	Day	2 13% 6% 13% 8% 5% 6% 6% 7% 8% 28%	1685
	21st to end	Day	2 11% 5% 11% 9% 4 5% 5% 6% 6% 36%	2766
January	1st to 10th	Night	1 13% 7% 15% 8% 4 4 5% 5% 8% 28%	4406
	11th to 20th	Night	3 14% 8% 13% 9% 3 4 4 4 6% 31%	4420
	21st to end	Night	2 17% 7% 11% 7% 4 4 5% 5% 6% 31%	4862
February	1st to 10th	Night	2 13% 8% 10% 7% 4 6% 6% 7% 9% 30%	2499
	11th to 20th	Night	2 11% 7% 12% 7% 4 4 5% 6% 7% 34%	2246
	21st to end	Night	2 10% 7% 16% 9% 5% 7% 5% 5% 7% 27%	1884
March	1st to 10th	Night	1 10% 7% 10% 8% 4 5% 5% 5% 9% 36%	3736
	11th to 20th	Night	1 10% 5% 9% 5% 2 4 4 5% 6% 48%	3534
	21st to end	Night	2 12% 9% 12% 8% 4 6% 6% 7% 8% 27%	3772
April	1st to 10th	Night	3 11% 7% 9% 5% 3 6% 7% 6% 8% 36%	1900
	11th to 20th	Night	3 11% 6% 8% 6% 3 5% 6% 6% 6% 41%	1767
	21st to end	Night	4 10% 5% 7% 5% 3 4 5% 6% 9% 43%	1665
May	1st to 10th	Night	3 9% 3 6% 5% 3 4 5% 5% 9% 48%	1620
	11th to 20th	Night	5% 8% 2 4 5% 3 6% 7% 7% 11% 42%	1574
	21st to end	Night	7% 11% 3 7% 6% 4 5% 6% 6% 10% 35%	1552
June	1st to 10th	Night	8% 6% 2 5% 5% 3 5% 5% 7% 10% 43%	1404
	11th to 20th	Night	8% 7% 2 4 5% 2 4 4 5% 7% 52%	1260
	21st to end	Night	2 3 1 3 4 3 4 4 5% 7% 65%	1428
July	1st to 10th	Night	1 2 1 2 2 2 3 4 5% 6% 70%	1440
	11th to 20th	Night	1 1 1 2 2 2 2 3 4 6% 76%	1440
	21st to end	Night	2 2 1 2 3 2 3 3 4 6% 72%	1576
August	1st to 10th	Night	3 3 1 4 4 3 4 4 6% 6% 62%	1579
	11th to 20th	Night	1 1 1 2 2 2 3 3 5% 7% 74%	1602
	21st to end	Night	3 2 1 3 3 2 3 4 4 6% 69%	1868
September	1st to 10th	Night	3 3 1 2 2 2 2 3 4 6% 72%	1831
	11th to 20th	Night	4 4 1 3 4 2 4 4 5% 6% 63%	1980
	21st to end	Night	6% 5% 1 3 3 1 2 3 4 6% 64%	1980
October	1st to 10th	Night	5% 8% 2 4 4 3 4 4 5% 7% 54%	1980
	11th to 20th	Night	5% 9% 3 4 4 2 4 4 5% 7% 53%	2212
	21st to end	Night	4 10% 4 6% 5% 3 4 5% 6% 8% 46%	2574
November	1st to 10th	Night	5% 11% 6% 8% 5% 3 4 5% 6% 8% 39%	2405
	11th to 20th	Night	4 12% 4 8% 5% 4 5% 6% 6% 9% 38%	2470
	21st to end	Night	3 7% 5% 8% 7% 4 7% 5% 5% 8% 42%	2510
December	1st to 10th	Night	1 11% 6% 11% 8% 4 5% 5% 6% 8% 35%	2821
	11th to 20th	Night	3 13% 5% 12% 8% 4 5% 7% 6% 7% 30%	3506
	21st to end	Night	1 10% 6% 12% 9% 4 5% 5% 5% 8% 34%	4917

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	58% 9% 11% 16% 5% 1	2539
	11th to 20th	Day	51% 7% 11% 15% 12% 4	2540
	21st to end	Day	54% 6% 13% 19% 7% 2	2794
February	1st to 10th	Day	52% 9% 13% 19% 6% 2	1680
	11th to 20th	Day	57% 7% 11% 15% 7% 3	1831
	21st to end	Day	62% 6% 8% 13% 9% 2	1570
March	1st to 10th	Day	53% 6% 10% 12% 19% 1	3138
	11th to 20th	Day	41% 5% 11% 30% 14%	3445
	21st to end	Day	67% 8% 11% 11% 3	3876
April	1st to 10th	Day	59% 7% 12% 14% 7% 1	2280
	11th to 20th	Day	49% 6% 14% 18% 11% 1	2362
	21st to end	Day	51% 6% 13% 22% 8%	2394
May	1st to 10th	Day	48% 6% 14% 21% 11% 1	2340
	11th to 20th	Day	49% 6% 17% 22% 6% 1	2320
	21st to end	Day	58% 7% 13% 16% 6% 1	2724
June	1st to 10th	Day	47% 8% 12% 24% 9%	2542
	11th to 20th	Day	41% 6% 9% 21% 17% 7%	2699
	21st to end	Day	25% 4 7% 21% 34% 8%	2520
July	1st to 10th	Day	19% 5% 5% 23% 28% 20%	2451
	11th to 20th	Day	16% 2 5% 14% 30% 33%	2445
	21st to end	Day	22% 3 5% 11% 31% 28%	2589
August	1st to 10th	Day	28% 5% 9% 17% 26% 16%	2343
	11th to 20th	Day	18% 4 6% 24% 33% 15%	2299
	21st to end	Day	23% 3 6% 21% 32% 15%	2484
September	1st to 10th	Day	21% 4 5% 20% 30% 20%	2129
	11th to 20th	Day	29% 5% 9% 23% 23% 10%	1980
	21st to end	Day	27% 4 10% 26% 27% 6%	1980
October	1st to 10th	Day	38% 6% 10% 24% 18% 4	1980
	11th to 20th	Day	37% 4 12% 28% 16% 3	1745
	21st to end	Day	38% 8% 13% 25% 15% 2	1782
November	1st to 10th	Day	46% 7% 12% 19% 14% 3	1674
	11th to 20th	Day	46% 8% 13% 23% 9% 2	1710
	21st to end	Day	42% 7% 12% 19% 13% 7%	1647
December	1st to 10th	Day	49% 6% 14% 17% 11% 4	1354
	11th to 20th	Day	54% 9% 15% 13% 9% 1	1684
	21st to end	Day	47% 7% 8% 19% 13% 5%	2766
January	1st to 10th	Night	53% 8% 9% 21% 8% 1	4406
	11th to 20th	Night	55% 5% 10% 16% 11% 3	4420
	21st to end	Night	51% 10% 10% 19% 7% 3	4862
February	1st to 10th	Night	52% 8% 13% 18% 8% 2	2499
	11th to 20th	Night	48% 9% 14% 17% 9% 3	2247
	21st to end	Night	57% 8% 8% 15% 9% 3	1884
March	1st to 10th	Night	45% 9% 9% 14% 21% 2	3736
	11th to 20th	Night	36% 7% 13% 30% 12% 1	3534
	21st to end	Night	51% 12% 15% 18% 4	3772
April	1st to 10th	Night	46% 8% 13% 22% 9% 1	1900
	11th to 20th	Night	42% 8% 15% 22% 12% 1	1767
	21st to end	Night	38% 7% 18% 27% 9%	1665
May	1st to 10th	Night	32% 8% 15% 31% 13% 1	1620
	11th to 20th	Night	34% 10% 19% 28% 8%	1575
	21st to end	Night	44% 9% 17% 24% 6%	1552
June	1st to 10th	Night	35% 11% 18% 27% 9%	1404
	11th to 20th	Night	33% 5% 12% 25% 18% 6%	1260
	21st to end	Night	18% 5% 8% 25% 35% 8%	1428
July	1st to 10th	Night	14% 4 8% 21% 34% 19%	1400
	11th to 20th	Night	11% 3 5% 18% 29% 35%	1392
	21st to end	Night	14% 3 6% 12% 34% 31%	1488
August	1st to 10th	Night	23% 4 7% 20% 27% 19%	1571
	11th to 20th	Night	11% 4 6% 24% 37% 18%	1602
	21st to end	Night	16% 4 8% 22% 32% 18%	1868
September	1st to 10th	Night	16% 3 6% 21% 34% 20%	1831
	11th to 20th	Night	22% 5% 11% 25% 24% 13%	1980
	21st to end	Night	22% 4 9% 31% 27% 8%	1980
October	1st to 10th	Night	29% 7% 13% 27% 20% 5%	1980
	11th to 20th	Night	31% 5% 12% 29% 19% 3	2212
	21st to end	Night	36% 8% 14% 25% 16% 2	2574
November	1st to 10th	Night	42% 8% 13% 20% 15% 3	2405
	11th to 20th	Night	43% 9% 14% 22% 11% 1	2470
	21st to end	Night	41% 8% 12% 18% 15% 7%	2510
December	1st to 10th	Night	46% 8% 17% 15% 9% 5%	2821
	11th to 20th	Night	51% 9% 13% 16% 10% 1	3507
	21st to end	Night	47% 7% 10% 18% 12% 6%	4917

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	17% 18% 28% 27% 7% 3	180
	11th to 20th	Day	13% 25% 28% 17% 11% 6%	180
	21st to end	Day	14% 25% 29% 19% 10% 3	198
February	1st to 10th	Day	20% 30% 32% 12% 5%	256
	11th to 20th	Day	19% 27% 31% 15% 6% 1	426
	21st to end	Day	19% 24% 35% 18% 3 1	382
March	1st to 10th	Day	17% 31% 36% 13% 3	460
	11th to 20th	Day	13% 24% 35% 18% 8% 1	460
	21st to end	Day	20% 25% 33% 18% 4	506
April	1st to 10th	Day	23% 23% 30% 17% 6% 1	460
	11th to 20th	Day	21% 27% 31% 15% 6% 1	452
	21st to end	Day	18% 25% 31% 19% 5% 2	437
May	1st to 10th	Day	14% 21% 33% 21% 10% 1	423
	11th to 20th	Day	20% 20% 29% 20% 9% 2	448
	21st to end	Day	19% 17% 27% 21% 11% 4	485
June	1st to 10th	Day	16% 21% 28% 24% 9% 3	472
	11th to 20th	Day	19% 18% 31% 19% 11% 2	629
	21st to end	Day	8% 19% 36% 26% 8% 3	450
July	1st to 10th	Day	5% 18% 41% 24% 9% 3	446
	11th to 20th	Day	5% 18% 44% 22% 10% 1	444
	21st to end	Day	6% 16% 35% 29% 11% 3	487
August	1st to 10th	Day	6% 14% 41% 24% 12% 2	447
	11th to 20th	Day	3 13% 35% 29% 15% 4	437
	21st to end	Day	7% 18% 33% 27% 12% 4	495
September	1st to 10th	Day	8% 16% 34% 23% 16% 3	450
	11th to 20th	Day	14% 14% 30% 28% 11% 4	450
	21st to end	Day	11% 16% 33% 25% 14% 2	450
October	1st to 10th	Day	17% 16% 28% 24% 13% 2	450
	11th to 20th	Day	13% 22% 25% 20% 14% 6%	287
	21st to end	Day	14% 23% 30% 23% 7% 2	297
November	1st to 10th	Day	19% 20% 28% 20% 11% 1	270
	11th to 20th	Day	13% 20% 31% 24% 10% 3	270
	21st to end	Day	10% 17% 36% 25% 11% 1	270
December	1st to 10th	Day	16% 16% 28% 21% 13% 6%	192
	11th to 20th	Day	19% 24% 34% 13% 8% 1	180
	21st to end	Day	17% 20% 30% 22% 10% 2	198
January	1st to 10th	Night	9% 16% 30% 32% 12% 1	760
	11th to 20th	Night	10% 13% 31% 30% 14% 3	760
	21st to end	Night	6% 12% 35% 32% 13% 2	836
February	1st to 10th	Night	11% 17% 37% 25% 9% 2	760
	11th to 20th	Night	9% 15% 35% 28% 12% 1	744
	21st to end	Night	9% 13% 37% 30% 8% 3	628
March	1st to 10th	Night	9% 16% 34% 30% 9% 1	760
	11th to 20th	Night	11% 13% 28% 34% 12% 2	760
	21st to end	Night	10% 13% 32% 34% 11% 1	836
April	1st to 10th	Night	10% 13% 28% 33% 13% 3	760
	11th to 20th	Night	11% 14% 33% 29% 11% 2	639
	21st to end	Night	10% 12% 26% 37% 13% 3	555
May	1st to 10th	Night	9% 8% 23% 37% 21% 3	540
	11th to 20th	Night	8% 7% 20% 37% 25% 3	512
	21st to end	Night	12% 6% 19% 30% 29% 4	389
June	1st to 10th	Night	13% 6% 16% 39% 23% 3	360
	11th to 20th	Night	12% 6% 22% 40% 19% 2	360
	21st to end	Night	4 1 15% 43% 35% 2	360
July	1st to 10th	Night	2 1 10% 47% 37% 4	350
	11th to 20th	Night	2 1 12% 57% 27% 1	348
	21st to end	Night	2 1 10% 47% 36% 4	394
August	1st to 10th	Night	4 2 14% 46% 32% 2	505
	11th to 20th	Night	1 3 9% 46% 38% 2	534
	21st to end	Night	4 3 15% 46% 29% 4	680
September	1st to 10th	Night	5% 2 14% 42% 32% 4	720
	11th to 20th	Night	7% 3 14% 38% 33% 6%	720
	21st to end	Night	9% 4 19% 36% 25% 7%	720
October	1st to 10th	Night	10% 6% 23% 36% 23% 3	720
	11th to 20th	Night	11% 11% 22% 35% 17% 5%	720
	21st to end	Night	11% 9% 30% 35% 12% 4	792
November	1st to 10th	Night	14% 11% 28% 32% 14% 1	740
	11th to 20th	Night	13% 13% 34% 32% 8% 1	760
	21st to end	Night	9% 13% 32% 29% 13% 4	800
December	1st to 10th	Night	10% 14% 32% 33% 9% 1	950
	11th to 20th	Night	13% 15% 31% 31% 9% 1	950
	21st to end	Night	11% 18% 34% 25% 10% 2	865

Page generated at 2024-04-22 07:25:44. Version ac07

Copyright © 2024 Attilla Danko.