Summit View Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Summit View Observatory clear sky chart from 2005-11-06 to 2024-01-15.

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	7% 4 2 4 4 2 3 4 5% 7% 58%	74706
	Night	8% 5% 2 4 4 3 4 4 5% 8% 53%	75075
Transparency	Day	26% 6% 9% 19% 24% 17%	74427
	Night	29% 7% 10% 18% 21% 15%	74876
Seeing	Day	8% 9% 22% 32% 22% 7%	14324
	Night	9% 4 14% 33% 32% 8%	23801

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	18% 7% 3 6% 5% 3 4 5% 6% 8% 36%	1637
	11th to 20th	Day	11% 5% 2 5% 5% 3 4 5% 6% 6% 48%	1657
	21st to end	Day	15% 7% 3 5% 5% 3 5% 5% 5% 7% 41%	1782
February	1st to 10th	Day	17% 7% 2 4 4 2 3 4 5% 6% 45%	1620
	11th to 20th	Day	12% 6% 3 5% 4 3 4 5% 5% 7% 46%	1677
	21st to end	Day	14% 6% 4 6% 5% 2 4 4 4 6% 45%	1480
March	1st to 10th	Day	15% 8% 4 7% 6% 4 5% 5% 5% 7% 35%	1935
	11th to 20th	Day	16% 7% 3 6% 6% 4 5% 5% 5% 9% 35%	1980
	21st to end	Day	11% 6% 3 7% 6% 3 5% 4 4 6% 45%	2214
April	1st to 10th	Day	14% 7% 3 5% 4 3 4 3 5% 7% 46%	2160
	11th to 20th	Day	9% 5% 2 4 4 2 3 4 5% 8% 54%	2129
	21st to end	Day	6% 4 2 5% 4 2 4 4 5% 8% 57%	2160
May	1st to 10th	Day	5% 5% 2 4 4 2 4 4 5% 8% 58%	2191
	11th to 20th	Day	5% 3 2 3 4 2 3 3 4 7% 64%	2336
	21st to end	Day	4 5% 3 5% 5% 2 3 4 6% 7% 55%	2723
June	1st to 10th	Day	5% 4 2 4 3 2 3 4 5% 8% 62%	2520
	11th to 20th	Day	2 2 2 2 2 2 4 5% 7% 72%	2520
	21st to end	Day	2 2 1 2 2 2 2 3 3 6% 76%	2520
July	1st to 10th	Day	1 1 1 1 2 2 3 4 4 7% 75%	2515
	11th to 20th	Day	2 2 1 1 2 2 2 4 4 8% 72%	2340
	21st to end	Day	1 1 1 1 1 2 2 4 4 7% 76%	2546
August	1st to 10th	Day	1 2 1 3 3 2 3 4 4 7% 70%	2328
	11th to 20th	Day	1 1 2 2 2 2 3 4 7% 76%	2163
	21st to end	Day	1 1 2 2 1 3 4 4 7% 74%	2376
September	1st to 10th	Day	1 2 1 1 2 1 2 3 3 5% 80%	2160
	11th to 20th	Day	2 3 1 3 3 2 3 4 5% 9% 64%	2160
	21st to end	Day	3 2 1 2 2 2 2 3 4 6% 75%	1918
October	1st to 10th	Day	3 3 2 3 3 2 4 4 4 6% 68%	1800
	11th to 20th	Day	5% 3 1 3 4 2 3 4 5% 7% 63%	1800
	21st to end	Day	6% 4 2 3 4 2 3 4 4 7% 62%	1980
November	1st to 10th	Day	9% 4 2 4 4 3 4 5% 5% 6% 54%	1831
	11th to 20th	Day	7% 6% 2 4 5% 2 4 5% 6% 7% 51%	1710
	21st to end	Day	11% 4 2 3 4 2 4 4 5% 7% 54%	1596
December	1st to 10th	Day	11% 6% 3 6% 4 4 4 4 5% 7% 44%	1520
	11th to 20th	Day	26% 9% 3 6% 5% 3 3 4 5% 5% 30%	1928
	21st to end	Day	15% 12% 4 6% 5% 3 5% 5% 6% 6% 34%	2794
January	1st to 10th	Night	14% 7% 3 7% 7% 2 4 5% 6% 6% 39%	2525
	11th to 20th	Night	11% 7% 3 5% 5% 4 5% 5% 4 7% 44%	2392
	21st to end	Night	14% 7% 2 5% 4 3 5% 5% 4 7% 44%	2574
February	1st to 10th	Night	13% 7% 3 5% 4 3 3 3 4 6% 48%	2340
	11th to 20th	Night	11% 5% 2 5% 5% 2 5% 5% 6% 8% 46%	2170
	21st to end	Night	13% 7% 2 5% 3 2 3 3 5% 7% 49%	1776
March	1st to 10th	Night	15% 9% 3 7% 6% 3 4 5% 5% 6% 37%	2021
	11th to 20th	Night	13% 7% 3 6% 5% 3 4 3 6% 9% 41%	1980
	21st to end	Night	11% 7% 3 5% 5% 2 5% 4 5% 6% 47%	2141
April	1st to 10th	Night	11% 6% 3 4 4 4 5% 4 4 9% 46%	1800
	11th to 20th	Night	8% 5% 2 6% 4 3 3 4 5% 6% 53%	1779
	21st to end	Night	4 3 2 3 3 3 4 5% 6% 11% 56%	1800
May	1st to 10th	Night	3 3 2 4 5% 3 4 4 6% 8% 58%	1764
	11th to 20th	Night	3 3 1 4 3 2 5% 6% 7% 11% 55%	1554
	21st to end	Night	3 3 2 4 5% 3 6% 5% 6% 10% 53%	1552
June	1st to 10th	Night	3 2 2 3 4 2 3 3 6% 9% 62%	1440
	11th to 20th	Night	1 1 3 3 2 4 5% 7% 9% 65%	1440
	21st to end	Night	1 2 1 2 3 2 3 4 5% 7% 70%	1440
July	1st to 10th	Night	2 3 2 4 4 6% 9% 70%	1441
	11th to 20th	Night	1 1 2 3 2 4 4 6% 10% 66%	1620
	21st to end	Night	1 2 1 3 3 3 5% 6% 8% 13% 55%	1773
August	1st to 10th	Night	1 2 1 5% 4 3 5% 6% 7% 10% 55%	1611
	11th to 20th	Night	1 1 2 4 2 4 6% 6% 10% 64%	1736
	21st to end	Night	1 1 3 4 3 5% 5% 6% 9% 63%	1980
September	1st to 10th	Night	1 1 1 2 2 3 4 4 10% 73%	1800
	11th to 20th	Night	3 2 1 4 4 2 3 4 6% 9% 62%	1800
	21st to end	Night	2 2 1 3 2 1 3 3 3 7% 73%	2038
October	1st to 10th	Night	3 3 1 3 3 2 4 3 4 6% 67%	2160
	11th to 20th	Night	4 4 2 4 3 2 4 4 5% 7% 61%	2160
	21st to end	Night	5% 3 2 3 3 2 3 3 4 7% 64%	2376
November	1st to 10th	Night	7% 4 2 4 4 2 4 3 5% 8% 57%	2245
	11th to 20th	Night	8% 5% 2 4 4 3 4 5% 6% 8% 51%	2470
	21st to end	Night	7% 4 2 4 4 3 4 4 4 7% 56%	2579
December	1st to 10th	Night	13% 7% 3 5% 5% 3 4 4 4 6% 46%	2660
	11th to 20th	Night	25% 10% 3 5% 4 3 3 3 5% 6% 32%	3276
	21st to end	Night	16% 9% 3 7% 7% 4 5% 5% 5% 6% 34%	4862

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	45% 6% 12% 20% 12% 6%	1637
	11th to 20th	Day	34% 6% 12% 18% 17% 14%	1657
	21st to end	Day	41% 4 9% 13% 23% 9%	1782
February	1st to 10th	Day	38% 3 7% 21% 19% 11%	1620
	11th to 20th	Day	37% 6% 8% 19% 23% 8%	1686
	21st to end	Day	40% 5% 7% 22% 19% 7%	1480
March	1st to 10th	Day	45% 6% 9% 20% 15% 5%	1935
	11th to 20th	Day	45% 5% 10% 18% 18% 4	1980
	21st to end	Day	39% 6% 13% 21% 18% 4	2214
April	1st to 10th	Day	38% 5% 13% 19% 20% 5%	2160
	11th to 20th	Day	28% 6% 13% 25% 21% 7%	2132
	21st to end	Day	27% 5% 12% 28% 23% 5%	2160
May	1st to 10th	Day	24% 4 10% 25% 30% 6%	2191
	11th to 20th	Day	21% 6% 8% 30% 27% 8%	2339
	21st to end	Day	28% 9% 12% 25% 22% 4	2724
June	1st to 10th	Day	21% 7% 12% 26% 25% 8%	2520
	11th to 20th	Day	13% 7% 10% 22% 32% 16%	2520
	21st to end	Day	13% 6% 6% 13% 32% 30%	2520
July	1st to 10th	Day	11% 5% 6% 11% 23% 45%	2446
	11th to 20th	Day	13% 6% 10% 10% 22% 39%	2271
	21st to end	Day	11% 7% 4 9% 32% 37%	2405
August	1st to 10th	Day	16% 7% 6% 11% 31% 30%	2312
	11th to 20th	Day	10% 6% 6% 11% 32% 35%	2163
	21st to end	Day	12% 8% 6% 12% 29% 33%	2376
September	1st to 10th	Day	10% 4 5% 9% 30% 43%	2160
	11th to 20th	Day	17% 7% 6% 22% 31% 18%	2160
	21st to end	Day	13% 4 5% 21% 35% 22%	1918
October	1st to 10th	Day	18% 3 9% 18% 28% 25%	1800
	11th to 20th	Day	21% 5% 8% 19% 23% 25%	1800
	21st to end	Day	23% 5% 7% 21% 23% 21%	1980
November	1st to 10th	Day	29% 4 9% 22% 24% 13%	1831
	11th to 20th	Day	30% 5% 10% 21% 24% 9%	1710
	21st to end	Day	30% 3 10% 17% 29% 11%	1596
December	1st to 10th	Day	37% 6% 10% 18% 17% 11%	1520
	11th to 20th	Day	53% 5% 9% 14% 14% 6%	1928
	21st to end	Day	46% 6% 12% 21% 12% 4	2794
January	1st to 10th	Night	41% 5% 13% 21% 14% 6%	2525
	11th to 20th	Night	37% 5% 12% 17% 15% 14%	2392
	21st to end	Night	37% 6% 12% 14% 18% 13%	2574
February	1st to 10th	Night	37% 3 8% 18% 20% 14%	2340
	11th to 20th	Night	34% 6% 10% 18% 24% 9%	2172
	21st to end	Night	33% 4 11% 28% 18% 6%	1776
March	1st to 10th	Night	45% 6% 11% 16% 15% 6%	2021
	11th to 20th	Night	39% 5% 9% 21% 20% 6%	1980
	21st to end	Night	35% 6% 14% 20% 18% 6%	2141
April	1st to 10th	Night	35% 5% 14% 22% 19% 6%	1800
	11th to 20th	Night	30% 6% 13% 25% 17% 8%	1779
	21st to end	Night	21% 9% 12% 29% 22% 7%	1800
May	1st to 10th	Night	25% 6% 10% 22% 25% 11%	1764
	11th to 20th	Night	21% 12% 12% 22% 25% 8%	1555
	21st to end	Night	24% 13% 15% 22% 22% 4	1552
June	1st to 10th	Night	19% 12% 11% 25% 24% 10%	1440
	11th to 20th	Night	15% 7% 13% 15% 28% 22%	1440
	21st to end	Night	19% 9% 6% 13% 25% 29%	1440
July	1st to 10th	Night	12% 7% 9% 9% 22% 40%	1401
	11th to 20th	Night	16% 10% 10% 10% 20% 34%	1566
	21st to end	Night	22% 12% 10% 8% 20% 27%	1674
August	1st to 10th	Night	26% 9% 10% 10% 20% 25%	1602
	11th to 20th	Night	17% 9% 6% 9% 26% 33%	1736
	21st to end	Night	17% 11% 10% 9% 24% 29%	1980
September	1st to 10th	Night	9% 6% 9% 9% 26% 41%	1800
	11th to 20th	Night	18% 9% 6% 20% 29% 18%	1800
	21st to end	Night	14% 5% 5% 17% 34% 25%	2038
October	1st to 10th	Night	19% 7% 9% 14% 24% 28%	2160
	11th to 20th	Night	21% 7% 8% 19% 21% 24%	2160
	21st to end	Night	21% 6% 6% 20% 24% 23%	2376
November	1st to 10th	Night	25% 5% 9% 23% 22% 15%	2245
	11th to 20th	Night	28% 6% 11% 21% 24% 10%	2470
	21st to end	Night	28% 4 9% 20% 24% 16%	2579
December	1st to 10th	Night	37% 5% 8% 19% 18% 13%	2660
	11th to 20th	Night	52% 4 10% 14% 15% 5%	3276
	21st to end	Night	45% 8% 14% 17% 12% 4	4862

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% 20% 23% 15% 2	298
	11th to 20th	Day	15% 12% 24% 29% 17% 4	353
	21st to end	Day	15% 10% 22% 29% 21% 4	374
February	1st to 10th	Day	18% 16% 20% 23% 17% 6%	340
	11th to 20th	Day	17% 15% 26% 28% 12% 2	381
	21st to end	Day	13% 16% 29% 28% 12% 2	346
March	1st to 10th	Day	21% 16% 27% 23% 11% 1	420
	11th to 20th	Day	20% 16% 23% 23% 14% 5%	420
	21st to end	Day	13% 17% 31% 27% 10% 2	462
April	1st to 10th	Day	18% 14% 27% 26% 14% 2	420
	11th to 20th	Day	13% 16% 32% 24% 12% 3	412
	21st to end	Day	6% 17% 27% 31% 13% 6%	420
May	1st to 10th	Day	8% 13% 31% 28% 15% 5%	423
	11th to 20th	Day	8% 13% 29% 28% 15% 6%	448
	21st to end	Day	7% 13% 24% 32% 19% 6%	485
June	1st to 10th	Day	6% 10% 25% 31% 21% 8%	450
	11th to 20th	Day	2 9% 30% 36% 20% 4	450
	21st to end	Day	1 4 20% 40% 26% 8%	450
July	1st to 10th	Day	2 1 18% 40% 32% 8%	446
	11th to 20th	Day	1 1 10% 45% 32% 11%	444
	21st to end	Day	1 10% 41% 33% 14%	487
August	1st to 10th	Day	2 1 20% 38% 33% 6%	447
	11th to 20th	Day	1 14% 43% 28% 14%	437
	21st to end	Day	1 2 12% 41% 33% 11%	495
September	1st to 10th	Day	1 4 12% 41% 29% 12%	450
	11th to 20th	Day	2 3 26% 35% 23% 10%	450
	21st to end	Day	3 6% 17% 34% 32% 8%	450
October	1st to 10th	Day	2 7% 22% 30% 28% 10%	450
	11th to 20th	Day	5% 7% 20% 28% 28% 11%	450
	21st to end	Day	7% 7% 19% 31% 26% 9%	495
November	1st to 10th	Day	8% 12% 17% 25% 29% 9%	427
	11th to 20th	Day	6% 8% 20% 27% 29% 10%	270
	21st to end	Day	8% 6% 22% 30% 29% 6%	216
December	1st to 10th	Day	13% 12% 17% 28% 21% 8%	180
	11th to 20th	Day	15% 15% 19% 20% 20% 11%	180
	21st to end	Day	13% 21% 25% 18% 17% 6%	198
January	1st to 10th	Night	17% 7% 15% 31% 24% 6%	760
	11th to 20th	Night	14% 5% 15% 33% 24% 8%	736
	21st to end	Night	17% 4 13% 35% 26% 5%	792
February	1st to 10th	Night	17% 8% 13% 32% 26% 5%	720
	11th to 20th	Night	13% 7% 19% 33% 21% 6%	704
	21st to end	Night	16% 7% 21% 33% 21% 3	592
March	1st to 10th	Night	18% 8% 18% 30% 23% 3	720
	11th to 20th	Night	16% 7% 17% 29% 26% 5%	720
	21st to end	Night	13% 7% 20% 35% 21% 3	792
April	1st to 10th	Night	13% 6% 20% 36% 23% 3	720
	11th to 20th	Night	11% 10% 20% 33% 21% 5%	711
	21st to end	Night	6% 7% 25% 32% 24% 7%	720
May	1st to 10th	Night	5% 5% 22% 36% 28% 5%	684
	11th to 20th	Night	4 3 13% 35% 38% 8%	492
	21st to end	Night	3 5% 21% 34% 32% 5%	389
June	1st to 10th	Night	3 4 14% 41% 32% 6%	360
	11th to 20th	Night	1 3 13% 44% 37% 3	360
	21st to end	Night	2 1 9% 38% 46% 5%	360
July	1st to 10th	Night	5% 30% 58% 5%	351
	11th to 20th	Night	1 3 26% 53% 16%	522
	21st to end	Night	1 5% 23% 56% 15%	591
August	1st to 10th	Night	2 9% 31% 50% 7%	537
	11th to 20th	Night	1 1 7% 35% 47% 10%	668
	21st to end	Night	2 7% 29% 49% 13%	792
September	1st to 10th	Night	1 1 8% 28% 49% 14%	720
	11th to 20th	Night	4 1 8% 34% 43% 10%	720
	21st to end	Night	3 2 12% 30% 41% 12%	720
October	1st to 10th	Night	4 3 12% 34% 35% 12%	720
	11th to 20th	Night	6% 3 10% 29% 41% 11%	720
	21st to end	Night	7% 4 9% 32% 32% 16%	792
November	1st to 10th	Night	7% 4 14% 30% 35% 10%	740
	11th to 20th	Night	10% 2 14% 33% 34% 7%	760
	21st to end	Night	9% 4 14% 39% 27% 7%	760
December	1st to 10th	Night	17% 4 15% 33% 26% 6%	760
	11th to 20th	Night	19% 5% 15% 34% 23% 4	760
	21st to end	Night	17% 10% 20% 31% 19% 3	836

Page generated at 2024-01-11 19:33:47. Version ac07

Copyright 2024 Attilla Danko