Steve's Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Steve's Observatory clear sky chart from 2005-11-06 to 2024-10-20.

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	12% 7% 2 7% 5% 5% 5% 4 6% 7% 40%	99921
	Night	12% 7% 2 6% 4 4 4 4 6% 7% 44%	98695
Transparency	Day	42% 5% 11% 19% 18% 5%	99734
	Night	39% 5% 12% 19% 19% 7%	98553
Seeing	Day	15% 8% 20% 25% 22% 10%	14882
	Night	15% 8% 23% 29% 21% 5%	24565

By Month

Percentage Cloud Cover SE (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% 10% 3 7% 3 3 3 3 4 5% 41%	2847
	11th to 20th	Day	16% 6% 2 5% 3 3 3 2 3 5% 51%	2850
	21st to end	Day	23% 9% 2 5% 3 4 3 3 4 4 39%	3234
February	1st to 10th	Day	18% 10% 3 6% 4 4 4 3 4 6% 38%	1900
	11th to 20th	Day	19% 7% 3 6% 4 4 4 3 5% 6% 41%	1848
	21st to end	Day	15% 8% 4 8% 5% 4 4 4 4 6% 37%	1570
March	1st to 10th	Day	22% 11% 3 7% 5% 5% 4 5% 5% 6% 28%	3312
	11th to 20th	Day	16% 9% 3 9% 4 4 4 4 6% 7% 34%	3480
	21st to end	Day	14% 8% 3 7% 6% 5% 5% 3 4 5% 41%	3968
April	1st to 10th	Day	10% 8% 2 6% 5% 4 5% 5% 6% 7% 41%	2280
	11th to 20th	Day	16% 8% 2 7% 5% 4 5% 3 5% 7% 39%	2254
	21st to end	Day	8% 5% 2 6% 5% 4 5% 5% 6% 8% 45%	2280
May	1st to 10th	Day	13% 6% 2 7% 5% 5% 6% 5% 7% 8% 34%	3765
	11th to 20th	Day	13% 7% 2 6% 5% 4 5% 4 5% 6% 43%	3764
	21st to end	Day	7% 5% 2 6% 5% 5% 6% 5% 8% 11% 39%	4129
June	1st to 10th	Day	9% 6% 3 7% 6% 7% 7% 7% 8% 8% 32%	2446
	11th to 20th	Day	6% 5% 2 8% 7% 7% 7% 5% 8% 9% 37%	2535
	21st to end	Day	7% 6% 2 8% 8% 7% 7% 7% 9% 10% 30%	2470
July	1st to 10th	Day	6% 7% 3 9% 8% 9% 8% 6% 8% 10% 26%	4120
	11th to 20th	Day	8% 6% 2 8% 8% 7% 9% 7% 9% 11% 25%	4120
	21st to end	Day	11% 10% 4 11% 8% 6% 7% 5% 7% 8% 24%	4277
August	1st to 10th	Day	3 3 1 5% 4 4 5% 4 5% 8% 59%	3785
	11th to 20th	Day	6% 4 2 6% 5% 6% 6% 5% 6% 10% 46%	3729
	21st to end	Day	11% 5% 2 8% 5% 6% 5% 5% 6% 7% 39%	4180
September	1st to 10th	Day	10% 6% 3 7% 6% 6% 7% 5% 6% 8% 35%	2280
	11th to 20th	Day	12% 6% 2 7% 6% 5% 6% 4 5% 6% 42%	2247
	21st to end	Day	11% 5% 2 5% 4 4 4 3 5% 7% 51%	2090
October	1st to 10th	Day	7% 4 2 5% 4 3 4 4 6% 7% 56%	1950
	11th to 20th	Day	9% 4 2 6% 4 3 3 2 5% 7% 55%	1890
	21st to end	Day	12% 5% 2 4 3 4 4 2 3 6% 55%	1980
November	1st to 10th	Day	11% 5% 2 5% 4 2 4 3 5% 6% 54%	1858
	11th to 20th	Day	12% 6% 2 5% 4 3 3 3 4 6% 52%	1801
	21st to end	Day	14% 7% 2 6% 4 3 4 3 4 6% 47%	1710
December	1st to 10th	Day	15% 8% 3 6% 4 4 3 3 5% 6% 42%	1710
	11th to 20th	Day	15% 11% 4 6% 5% 4 3 3 4 5% 41%	2149
	21st to end	Day	15% 7% 3 6% 3 4 4 4 5% 7% 42%	3113
January	1st to 10th	Night	19% 10% 2 4 3 3 3 3 5% 5% 44%	4108
	11th to 20th	Night	16% 7% 2 5% 3 2 3 2 4 4 51%	4120
	21st to end	Night	27% 10% 2 4 2 2 2 2 3 4 42%	4425
February	1st to 10th	Night	16% 9% 3 6% 4 4 4 3 5% 6% 40%	2280
	11th to 20th	Night	19% 10% 3 5% 3 3 3 2 4 6% 43%	2218
	21st to end	Night	20% 10% 3 7% 5% 4 4 3 5% 6% 36%	1884
March	1st to 10th	Night	21% 13% 3 7% 4 4 3 3 5% 7% 30%	3555
	11th to 20th	Night	14% 8% 3 6% 5% 5% 5% 4 6% 8% 37%	3480
	21st to end	Night	16% 8% 2 6% 4 5% 5% 5% 5% 6% 39%	3661
April	1st to 10th	Night	12% 7% 2 5% 5% 4 4 4 6% 7% 44%	1900
	11th to 20th	Night	12% 7% 2 6% 5% 4 4 4 5% 7% 45%	1875
	21st to end	Night	7% 5% 2 4 4 4 4 4 5% 8% 54%	1900
May	1st to 10th	Night	11% 7% 3 7% 3 4 4 3 5% 8% 44%	3130
	11th to 20th	Night	16% 7% 3 6% 3 3 4 3 5% 8% 43%	3129
	21st to end	Night	6% 5% 2 6% 6% 5% 6% 5% 7% 11% 41%	3426
June	1st to 10th	Night	7% 7% 2 7% 5% 5% 5% 5% 7% 11% 39%	1697
	11th to 20th	Night	3 5% 1 5% 5% 5% 4 6% 7% 11% 48%	1611
	21st to end	Night	5% 5% 2 5% 5% 5% 6% 6% 10% 10% 41%	1710
July	1st to 10th	Night	6% 6% 3 8% 7% 7% 6% 5% 9% 10% 34%	2850
	11th to 20th	Night	6% 5% 2 6% 6% 8% 7% 7% 11% 12% 30%	2850
	21st to end	Night	8% 8% 4 9% 7% 6% 6% 5% 8% 11% 29%	3277
August	1st to 10th	Night	2 2 1 3 2 3 4 4 6% 11% 62%	3144
	11th to 20th	Night	4 3 1 5% 5% 5% 6% 5% 8% 13% 44%	3100
	21st to end	Night	7% 5% 3 8% 5% 5% 5% 5% 6% 8% 43%	3476
September	1st to 10th	Night	7% 5% 2 6% 4 5% 6% 6% 9% 10% 40%	1900
	11th to 20th	Night	9% 6% 2 6% 4 4 4 3 6% 9% 46%	1914
	21st to end	Night	9% 5% 2 5% 3 3 4 3 5% 7% 54%	2090
October	1st to 10th	Night	6% 4 2 5% 3 4 4 3 5% 6% 59%	2225
	11th to 20th	Night	8% 5% 2 5% 4 3 3 3 4 5% 58%	2275
	21st to end	Night	13% 6% 2 5% 3 3 3 2 4 4 56%	2376
November	1st to 10th	Night	12% 4 1 4 3 3 3 3 4 5% 57%	2220
	11th to 20th	Night	11% 6% 2 4 3 3 3 3 4 6% 55%	2375
	21st to end	Night	14% 8% 2 4 4 3 4 3 5% 5% 48%	2470
December	1st to 10th	Night	17% 7% 2 5% 3 3 3 3 4 6% 46%	2470
	11th to 20th	Night	15% 9% 3 6% 4 3 4 3 5% 5% 43%	3042
	21st to end	Night	17% 11% 3 6% 3 4 3 2 4 5% 42%	4532

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	44% 4 3 17% 26% 6%	2848
	11th to 20th	Day	36% 2 5% 20% 26% 10%	2850
	21st to end	Day	48% 3 4 14% 22% 9%	3234
February	1st to 10th	Day	48% 2 6% 15% 17% 11%	1900
	11th to 20th	Day	45% 3 6% 15% 22% 9%	1858
	21st to end	Day	48% 4 6% 15% 17% 10%	1570
March	1st to 10th	Day	56% 3 8% 14% 13% 5%	3312
	11th to 20th	Day	49% 4 8% 18% 17% 5%	3480
	21st to end	Day	47% 3 8% 15% 20% 7%	3968
April	1st to 10th	Day	41% 4 10% 19% 18% 9%	2280
	11th to 20th	Day	45% 3 8% 17% 20% 7%	2254
	21st to end	Day	35% 5% 11% 23% 22% 4	2280
May	1st to 10th	Day	45% 4 14% 21% 13% 3	3800
	11th to 20th	Day	41% 3 12% 19% 21% 3	3768
	21st to end	Day	36% 4 18% 29% 11% 2	4141
June	1st to 10th	Day	45% 5% 14% 23% 11% 2	2446
	11th to 20th	Day	40% 5% 15% 23% 14% 3	2535
	21st to end	Day	44% 8% 17% 20% 10% 2	2470
July	1st to 10th	Day	47% 10% 20% 17% 5%	4056
	11th to 20th	Day	46% 11% 25% 14% 3 1	4051
	21st to end	Day	55% 8% 13% 16% 6% 1	4141
August	1st to 10th	Day	24% 4 13% 30% 28% 1	3773
	11th to 20th	Day	33% 6% 19% 29% 12% 1	3765
	21st to end	Day	43% 6% 15% 18% 16% 3	4179
September	1st to 10th	Day	46% 5% 14% 17% 14% 5%	2280
	11th to 20th	Day	43% 5% 10% 18% 18% 7%	2247
	21st to end	Day	33% 3 10% 24% 19% 10%	2090
October	1st to 10th	Day	28% 4 8% 20% 26% 14%	1950
	11th to 20th	Day	30% 3 6% 17% 29% 15%	1890
	21st to end	Day	33% 3 4 16% 31% 13%	1980
November	1st to 10th	Day	33% 2 7% 18% 28% 12%	1858
	11th to 20th	Day	35% 3 6% 15% 29% 13%	1801
	21st to end	Day	39% 2 7% 18% 22% 11%	1710
December	1st to 10th	Day	42% 3 10% 19% 18% 8%	1710
	11th to 20th	Day	47% 3 5% 14% 24% 8%	2146
	21st to end	Day	43% 2 7% 21% 24% 3	3113
January	1st to 10th	Night	42% 3 5% 15% 27% 9%	4108
	11th to 20th	Night	38% 3 6% 18% 23% 12%	4120
	21st to end	Night	48% 2 4 16% 23% 7%	4425
February	1st to 10th	Night	45% 3 6% 17% 20% 9%	2280
	11th to 20th	Night	45% 3 5% 16% 21% 11%	2219
	21st to end	Night	50% 3 7% 14% 14% 12%	1884
March	1st to 10th	Night	54% 3 9% 14% 14% 6%	3555
	11th to 20th	Night	45% 4 10% 17% 17% 6%	3480
	21st to end	Night	44% 3 9% 18% 21% 5%	3661
April	1st to 10th	Night	39% 4 11% 18% 19% 10%	1900
	11th to 20th	Night	38% 3 10% 20% 19% 10%	1875
	21st to end	Night	29% 3 11% 23% 27% 7%	1900
May	1st to 10th	Night	39% 4 14% 22% 17% 4	3160
	11th to 20th	Night	40% 4 12% 24% 19% 1	3130
	21st to end	Night	35% 5% 18% 27% 13% 2	3435
June	1st to 10th	Night	38% 6% 18% 25% 13% 1	1697
	11th to 20th	Night	30% 6% 19% 28% 14% 3	1611
	21st to end	Night	32% 8% 23% 22% 13% 2	1710
July	1st to 10th	Night	41% 11% 25% 17% 5% 1	2805
	11th to 20th	Night	40% 13% 30% 14% 3 1	2796
	21st to end	Night	49% 10% 18% 17% 5% 1	3173
August	1st to 10th	Night	16% 6% 20% 31% 25% 1	3132
	11th to 20th	Night	28% 10% 21% 31% 9% 1	3130
	21st to end	Night	40% 7% 14% 18% 17% 4	3476
September	1st to 10th	Night	34% 8% 20% 18% 14% 6%	1900
	11th to 20th	Night	35% 5% 16% 17% 18% 9%	1914
	21st to end	Night	30% 3 11% 25% 21% 10%	2090
October	1st to 10th	Night	26% 3 10% 18% 26% 17%	2225
	11th to 20th	Night	28% 4 5% 20% 27% 17%	2275
	21st to end	Night	32% 2 6% 16% 26% 17%	2376
November	1st to 10th	Night	29% 3 8% 18% 26% 15%	2220
	11th to 20th	Night	32% 3 5% 17% 29% 15%	2375
	21st to end	Night	38% 2 6% 20% 21% 13%	2470
December	1st to 10th	Night	41% 2 9% 22% 20% 7%	2470
	11th to 20th	Night	44% 3 5% 13% 24% 11%	3044
	21st to end	Night	47% 2 6% 18% 21% 6%	4532

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% 22% 33% 16% 3 1	270
	11th to 20th	Day	26% 17% 34% 17% 4 1	270
	21st to end	Day	27% 23% 36% 12% 2	297
February	1st to 10th	Day	30% 19% 33% 13% 4	270
	11th to 20th	Day	34% 14% 34% 14% 3	270
	21st to end	Day	29% 27% 35% 9%	225
March	1st to 10th	Day	31% 15% 33% 16% 4	270
	11th to 20th	Day	27% 17% 39% 14% 3	270
	21st to end	Day	24% 15% 33% 21% 6%	387
April	1st to 10th	Day	18% 19% 30% 22% 9% 1	460
	11th to 20th	Day	24% 14% 30% 21% 10% 1	452
	21st to end	Day	13% 10% 32% 30% 13% 2	460
May	1st to 10th	Day	15% 11% 27% 29% 15% 3	463
	11th to 20th	Day	14% 6% 24% 29% 20% 8%	487
	21st to end	Day	7% 4 22% 32% 24% 10%	529
June	1st to 10th	Day	12% 4 12% 35% 25% 12%	612
	11th to 20th	Day	8% 3 14% 34% 32% 9%	680
	21st to end	Day	10% 3 12% 27% 30% 18%	680
July	1st to 10th	Day	7% 2 7% 28% 42% 15%	671
	11th to 20th	Day	8% 2 5% 23% 40% 22%	668
	21st to end	Day	7% 3 7% 25% 39% 19%	626
August	1st to 10th	Day	6% 2 5% 26% 34% 27%	486
	11th to 20th	Day	9% 1 4 20% 43% 23%	479
	21st to end	Day	14% 2 7% 22% 33% 21%	539
September	1st to 10th	Day	13% 1 6% 25% 35% 19%	490
	11th to 20th	Day	12% 4 12% 22% 35% 14%	490
	21st to end	Day	13% 4 11% 32% 28% 13%	490
October	1st to 10th	Day	7% 7% 23% 37% 18% 8%	350
	11th to 20th	Day	11% 5% 26% 30% 23% 5%	297
	21st to end	Day	22% 10% 21% 30% 13% 4	297
November	1st to 10th	Day	18% 8% 23% 34% 13% 4	270
	11th to 20th	Day	20% 11% 31% 27% 10% 1	270
	21st to end	Day	16% 17% 35% 20% 9% 3	270
December	1st to 10th	Day	23% 10% 37% 24% 6% 1	270
	11th to 20th	Day	23% 17% 36% 18% 6% 1	270
	21st to end	Day	27% 16% 32% 19% 5% 1	297
January	1st to 10th	Night	25% 14% 33% 23% 5%	950
	11th to 20th	Night	23% 15% 32% 23% 7%	950
	21st to end	Night	24% 17% 32% 24% 4	977
February	1st to 10th	Night	23% 15% 34% 24% 4	760
	11th to 20th	Night	28% 15% 29% 23% 5%	743
	21st to end	Night	23% 21% 35% 19% 2	628
March	1st to 10th	Night	20% 14% 33% 27% 5%	660
	11th to 20th	Night	18% 14% 34% 28% 6% 1	570
	21st to end	Night	17% 10% 37% 28% 8%	627
April	1st to 10th	Night	19% 11% 34% 26% 9% 1	570
	11th to 20th	Night	17% 12% 33% 27% 10% 1	563
	21st to end	Night	9% 9% 33% 35% 14% 1	570
May	1st to 10th	Night	11% 5% 30% 35% 17% 2	570
	11th to 20th	Night	11% 3 24% 37% 21% 3	561
	21st to end	Night	5% 4 20% 40% 26% 5%	617
June	1st to 10th	Night	10% 3 10% 40% 30% 8%	570
	11th to 20th	Night	4 2 11% 35% 41% 7%	570
	21st to end	Night	6% 2 8% 31% 38% 15%	570
July	1st to 10th	Night	5% 2 3 29% 47% 14%	555
	11th to 20th	Night	6% 1 4 25% 45% 20%	552
	21st to end	Night	5% 2 5% 28% 46% 14%	624
August	1st to 10th	Night	3 1 4 23% 49% 20%	567
	11th to 20th	Night	7% 1 4 23% 48% 17%	564
	21st to end	Night	10% 2 6% 24% 39% 19%	627
September	1st to 10th	Night	9% 2 5% 30% 42% 11%	570
	11th to 20th	Night	10% 3 9% 28% 41% 9%	584
	21st to end	Night	10% 2 11% 34% 36% 6%	760
October	1st to 10th	Night	8% 2 18% 34% 33% 5%	760
	11th to 20th	Night	10% 4 24% 36% 22% 3	759
	21st to end	Night	17% 6% 21% 32% 22% 2	792
November	1st to 10th	Night	12% 6% 21% 37% 20% 3	740
	11th to 20th	Night	15% 9% 28% 33% 14% 1	760
	21st to end	Night	17% 10% 29% 28% 15% 2	760
December	1st to 10th	Night	21% 9% 29% 30% 10%	760
	11th to 20th	Night	22% 9% 34% 26% 9%	760
	21st to end	Night	27% 12% 29% 27% 5%	1045

Page generated at 2024-10-17 12:09:41. Version ac07

Copyright © 2024 Attilla Danko.