Summit Crossing Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Summit Crossing Observatory clear sky chart from 2005-11-06 to 2025-06-10.

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	14% 6% 2 6% 4 4 4 4 6% 8% 42%	119497
	Night	14% 6% 2 6% 4 4 4 3 5% 7% 45%	118717
Transparency	Day	38% 7% 12% 22% 17% 4	123136
	Night	37% 6% 11% 22% 19% 5%	123215
Seeing	Day	18% 11% 27% 25% 14% 5%	15789
	Night	17% 10% 29% 30% 13% 1	25456

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	16% 5% 2 4 3 4 3 3 5% 5% 51%	3855
	11th to 20th	Day	14% 8% 2 5% 4 3 3 3 4 5% 49%	4060
	21st to end	Day	14% 8% 3 6% 4 4 4 3 5% 5% 45%	4466
February	1st to 10th	Day	15% 8% 3 6% 5% 6% 4 4 5% 7% 39%	1800
	11th to 20th	Day	19% 7% 2 5% 4 4 3 3 4 6% 41%	1811
	21st to end	Day	17% 8% 2 7% 4 5% 4 3 5% 6% 39%	1650
March	1st to 10th	Day	18% 6% 2 6% 5% 4 5% 4 5% 7% 38%	4925
	11th to 20th	Day	11% 5% 2 6% 4 3 4 3 5% 7% 51%	4980
	21st to end	Day	17% 6% 2 6% 4 4 4 3 5% 7% 40%	5510
April	1st to 10th	Day	12% 6% 2 5% 4 4 4 4 6% 7% 46%	2400
	11th to 20th	Day	12% 6% 2 5% 4 3 4 3 5% 7% 48%	2374
	21st to end	Day	16% 7% 2 6% 4 4 4 3 5% 7% 42%	2400
May	1st to 10th	Day	17% 7% 2 7% 4 5% 5% 4 7% 9% 32%	5726
	11th to 20th	Day	21% 6% 2 6% 4 4 4 4 6% 10% 32%	5997
	21st to end	Day	15% 5% 2 6% 4 4 5% 4 7% 9% 40%	6934
June	1st to 10th	Day	11% 5% 2 5% 4 4 4 4 7% 9% 44%	2786
	11th to 20th	Day	10% 4 2 5% 5% 5% 6% 4 7% 11% 42%	2660
	21st to end	Day	8% 4 2 6% 5% 5% 6% 4 7% 10% 44%	2660
July	1st to 10th	Day	6% 3 2 6% 5% 4 6% 6% 8% 13% 41%	4440
	11th to 20th	Day	10% 6% 2 5% 4 4 5% 6% 9% 13% 35%	4161
	21st to end	Day	11% 6% 2 7% 6% 6% 6% 5% 8% 9% 35%	4466
August	1st to 10th	Day	15% 7% 2 7% 5% 4 6% 5% 8% 10% 31%	4104
	11th to 20th	Day	9% 5% 2 7% 5% 5% 6% 5% 7% 10% 38%	3862
	21st to end	Day	10% 3 2 5% 4 4 4 3 6% 9% 49%	4180
September	1st to 10th	Day	14% 5% 1 4 4 5% 5% 3 5% 8% 46%	2280
	11th to 20th	Day	12% 5% 2 6% 3 4 4 3 5% 8% 48%	2280
	21st to end	Day	22% 6% 2 7% 4 4 4 3 5% 6% 38%	1989
October	1st to 10th	Day	17% 5% 2 5% 4 3 4 3 4 5% 48%	1900
	11th to 20th	Day	17% 5% 1 4 3 3 3 3 4 5% 53%	1900
	21st to end	Day	13% 6% 2 5% 2 3 4 2 4 7% 51%	2090
November	1st to 10th	Day	12% 5% 2 4 4 4 4 3 4 6% 53%	1904
	11th to 20th	Day	15% 6% 2 4 3 3 3 3 4 7% 50%	1797
	21st to end	Day	15% 5% 2 5% 4 3 3 3 5% 5% 51%	1600
December	1st to 10th	Day	11% 5% 2 6% 4 4 4 4 6% 6% 50%	2600
	11th to 20th	Day	18% 9% 2 6% 3 2 2 2 4 6% 46%	2990
	21st to end	Day	15% 6% 2 6% 4 5% 4 3 6% 7% 41%	3960
January	1st to 10th	Night	13% 7% 2 4 3 3 3 3 4 5% 53%	6073
	11th to 20th	Night	14% 6% 2 5% 3 3 3 2 4 4 54%	5900
	21st to end	Night	15% 7% 2 6% 4 3 3 2 4 5% 48%	6490
February	1st to 10th	Night	15% 8% 2 5% 4 4 5% 4 5% 6% 42%	2600
	11th to 20th	Night	21% 7% 2 5% 4 4 3 2 4 5% 43%	2473
	21st to end	Night	16% 7% 3 6% 3 3 4 3 5% 6% 45%	1980
March	1st to 10th	Night	16% 6% 2 5% 3 4 3 3 4 5% 48%	4925
	11th to 20th	Night	12% 6% 2 5% 3 3 3 3 6% 7% 50%	4980
	21st to end	Night	13% 7% 2 6% 4 4 4 3 5% 7% 46%	5408
April	1st to 10th	Night	16% 6% 2 5% 5% 3 4 3 5% 6% 45%	2000
	11th to 20th	Night	11% 6% 2 6% 4 4 4 4 4 7% 49%	1975
	21st to end	Night	16% 5% 2 5% 4 4 3 4 6% 7% 44%	2000
May	1st to 10th	Night	17% 8% 3 8% 5% 5% 5% 4 6% 8% 32%	4197
	11th to 20th	Night	22% 8% 2 6% 5% 4 4 4 6% 7% 32%	3895
	21st to end	Night	15% 7% 3 6% 5% 4 4 4 5% 9% 36%	3920
June	1st to 10th	Night	9% 5% 2 6% 5% 5% 5% 5% 6% 9% 44%	1598
	11th to 20th	Night	11% 6% 1 7% 5% 5% 5% 4 6% 9% 41%	1520
	21st to end	Night	9% 5% 2 5% 5% 4 6% 5% 6% 10% 44%	1520
July	1st to 10th	Night	6% 5% 2 8% 4 6% 6% 4 8% 10% 40%	2520
	11th to 20th	Night	8% 6% 2 8% 5% 5% 6% 5% 7% 11% 38%	2794
	21st to end	Night	10% 7% 3 8% 6% 6% 6% 5% 8% 8% 33%	3087
August	1st to 10th	Night	15% 7% 3 7% 5% 5% 6% 4 6% 9% 32%	2825
	11th to 20th	Night	10% 7% 3 8% 6% 5% 6% 5% 7% 8% 36%	2934
	21st to end	Night	10% 5% 2 6% 4 4 4 3 6% 9% 48%	3476
September	1st to 10th	Night	15% 5% 2 5% 4 4 5% 4 6% 8% 43%	1900
	11th to 20th	Night	11% 7% 3 6% 4 3 4 4 5% 6% 48%	1900
	21st to end	Night	22% 7% 2 6% 4 4 4 4 4 6% 37%	2187
October	1st to 10th	Night	17% 6% 2 4 3 4 4 3 4 6% 46%	2280
	11th to 20th	Night	17% 5% 2 5% 3 2 3 3 5% 5% 50%	2280
	21st to end	Night	14% 5% 1 5% 4 3 4 3 5% 6% 51%	2508
November	1st to 10th	Night	12% 6% 3 5% 3 4 3 3 4 5% 54%	2391
	11th to 20th	Night	15% 7% 2 5% 3 3 4 3 4 5% 49%	2600
	21st to end	Night	13% 4 2 4 3 4 4 3 6% 6% 51%	2800
December	1st to 10th	Night	10% 6% 2 5% 3 3 3 3 5% 6% 55%	4580
	11th to 20th	Night	20% 7% 2 6% 4 4 4 3 5% 5% 41%	5205
	21st to end	Night	15% 7% 2 5% 4 4 4 3 6% 7% 42%	6996

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	35% 3 6% 25% 22% 8%	3856
	11th to 20th	Day	38% 5% 6% 20% 23% 9%	4060
	21st to end	Day	41% 4 9% 25% 18% 3	4466
February	1st to 10th	Day	44% 6% 10% 25% 13% 2	1800
	11th to 20th	Day	44% 4 8% 21% 18% 4	1820
	21st to end	Day	45% 4 12% 17% 17% 4	1650
March	1st to 10th	Day	43% 6% 8% 19% 16% 8%	4925
	11th to 20th	Day	31% 6% 9% 25% 22% 8%	4980
	21st to end	Day	43% 6% 11% 17% 17% 6%	5510
April	1st to 10th	Day	36% 6% 11% 21% 19% 7%	2400
	11th to 20th	Day	36% 6% 11% 19% 23% 6%	2374
	21st to end	Day	41% 6% 11% 24% 13% 5%	2400
May	1st to 10th	Day	45% 9% 15% 18% 11% 1	5759
	11th to 20th	Day	46% 8% 13% 23% 10% 1	6001
	21st to end	Day	38% 9% 14% 22% 16% 2	6949
June	1st to 10th	Day	34% 8% 15% 26% 15% 1	2786
	11th to 20th	Day	34% 9% 15% 23% 17% 1	2660
	21st to end	Day	34% 9% 15% 24% 17% 1	2660
July	1st to 10th	Day	31% 12% 23% 18% 11% 5%	4370
	11th to 20th	Day	36% 9% 20% 26% 8% 1	4090
	21st to end	Day	42% 10% 12% 19% 16% 1	4324
August	1st to 10th	Day	44% 9% 17% 23% 7%	4091
	11th to 20th	Day	36% 9% 15% 24% 15% 1	3901
	21st to end	Day	30% 7% 17% 27% 18% 2	4180
September	1st to 10th	Day	36% 9% 13% 18% 20% 4	2280
	11th to 20th	Day	35% 6% 9% 27% 20% 4	2280
	21st to end	Day	47% 7% 9% 19% 15% 4	1989
October	1st to 10th	Day	36% 6% 7% 17% 29% 5%	3160
	11th to 20th	Day	26% 3 6% 22% 32% 11%	3140
	21st to end	Day	21% 3 10% 28% 26% 12%	3428
November	1st to 10th	Day	33% 4 9% 26% 23% 5%	1904
	11th to 20th	Day	35% 5% 10% 21% 23% 7%	1797
	21st to end	Day	35% 3 10% 25% 23% 4	1600
December	1st to 10th	Day	34% 5% 10% 26% 18% 7%	2600
	11th to 20th	Day	41% 3 13% 25% 15% 4	2986
	21st to end	Day	40% 6% 13% 25% 16% 1	3960
January	1st to 10th	Night	33% 4 7% 22% 27% 7%	6073
	11th to 20th	Night	34% 3 6% 24% 25% 8%	5900
	21st to end	Night	40% 3 7% 27% 20% 3	6490
February	1st to 10th	Night	41% 5% 11% 24% 16% 2	2600
	11th to 20th	Night	44% 3 8% 20% 19% 6%	2475
	21st to end	Night	40% 5% 9% 21% 18% 7%	1980
March	1st to 10th	Night	37% 5% 8% 22% 20% 7%	4925
	11th to 20th	Night	32% 6% 9% 21% 25% 8%	4980
	21st to end	Night	38% 5% 9% 21% 20% 7%	5408
April	1st to 10th	Night	39% 6% 9% 18% 23% 5%	2000
	11th to 20th	Night	35% 6% 11% 22% 21% 6%	1975
	21st to end	Night	38% 6% 11% 25% 15% 5%	2000
May	1st to 10th	Night	47% 9% 15% 18% 8% 3	4226
	11th to 20th	Night	49% 8% 12% 20% 10% 1	3896
	21st to end	Night	42% 8% 14% 22% 12% 1	3927
June	1st to 10th	Night	35% 10% 13% 25% 16% 2	1598
	11th to 20th	Night	37% 9% 16% 22% 15% 2	1520
	21st to end	Night	33% 9% 16% 20% 19% 3	1520
July	1st to 10th	Night	36% 11% 21% 18% 11% 3	2480
	11th to 20th	Night	39% 10% 22% 21% 7% 1	2742
	21st to end	Night	45% 10% 15% 17% 13%	2988
August	1st to 10th	Night	46% 9% 15% 22% 7%	2814
	11th to 20th	Night	40% 9% 14% 22% 13% 1	2961
	21st to end	Night	32% 7% 12% 27% 20% 1	3476
September	1st to 10th	Night	38% 8% 12% 20% 15% 6%	1900
	11th to 20th	Night	34% 7% 10% 24% 22% 3	1900
	21st to end	Night	47% 6% 10% 17% 16% 3	2187
October	1st to 10th	Night	39% 6% 9% 19% 20% 6%	3800
	11th to 20th	Night	24% 4 9% 22% 32% 10%	3779
	21st to end	Night	21% 3 7% 31% 26% 11%	4120
November	1st to 10th	Night	33% 4 10% 24% 23% 5%	2391
	11th to 20th	Night	38% 4 8% 20% 22% 7%	2600
	21st to end	Night	33% 4 10% 26% 22% 5%	2800
December	1st to 10th	Night	29% 4 11% 28% 24% 4	4580
	11th to 20th	Night	46% 4 11% 19% 15% 5%	5208
	21st to end	Night	38% 6% 13% 26% 16% 1	6996

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	27% 21% 30% 18% 4	257
	11th to 20th	Day	25% 27% 28% 17% 3	300
	21st to end	Day	23% 21% 38% 14% 3	330
February	1st to 10th	Day	23% 24% 36% 13% 4	300
	11th to 20th	Day	33% 21% 33% 11% 1	358
	21st to end	Day	28% 18% 30% 21% 4	414
March	1st to 10th	Day	23% 19% 33% 19% 4	500
	11th to 20th	Day	23% 19% 34% 18% 6% 1	500
	21st to end	Day	25% 17% 33% 20% 5% 1	550
April	1st to 10th	Day	24% 17% 32% 20% 6% 1	500
	11th to 20th	Day	18% 17% 30% 22% 10% 4	492
	21st to end	Day	22% 13% 32% 23% 9% 1	500
May	1st to 10th	Day	22% 14% 31% 19% 11% 3	503
	11th to 20th	Day	21% 10% 28% 25% 13% 2	527
	21st to end	Day	20% 6% 22% 28% 20% 4	573
June	1st to 10th	Day	13% 5% 26% 31% 19% 6%	526
	11th to 20th	Day	12% 5% 24% 32% 19% 8%	490
	21st to end	Day	10% 5% 23% 36% 20% 6%	490
July	1st to 10th	Day	10% 4 17% 31% 28% 11%	485
	11th to 20th	Day	5% 3 15% 37% 29% 11%	484
	21st to end	Day	11% 4 20% 34% 22% 10%	532
August	1st to 10th	Day	14% 3 19% 27% 28% 9%	486
	11th to 20th	Day	11% 3 18% 31% 26% 11%	479
	21st to end	Day	11% 3 17% 30% 24% 16%	539
September	1st to 10th	Day	16% 4 17% 28% 18% 17%	490
	11th to 20th	Day	13% 4 18% 32% 22% 11%	490
	21st to end	Day	28% 11% 20% 27% 10% 5%	490
October	1st to 10th	Day	19% 7% 22% 25% 19% 7%	490
	11th to 20th	Day	17% 12% 22% 28% 18% 3	490
	21st to end	Day	15% 13% 33% 26% 10% 3	539
November	1st to 10th	Day	16% 10% 32% 27% 13% 3	468
	11th to 20th	Day	18% 11% 36% 23% 12% 1	397
	21st to end	Day	21% 16% 34% 19% 10% 2	200
December	1st to 10th	Day	20% 15% 41% 18% 6% 1	200
	11th to 20th	Day	24% 12% 36% 19% 10%	200
	21st to end	Day	26% 15% 28% 20% 10% 1	220
January	1st to 10th	Night	20% 17% 40% 19% 3	800
	11th to 20th	Night	21% 15% 34% 26% 4	800
	21st to end	Night	20% 15% 38% 25% 2	880
February	1st to 10th	Night	20% 14% 37% 25% 3	800
	11th to 20th	Night	26% 18% 37% 17% 2	783
	21st to end	Night	22% 17% 36% 21% 3	660
March	1st to 10th	Night	20% 17% 35% 26% 3	800
	11th to 20th	Night	22% 14% 37% 21% 6%	800
	21st to end	Night	18% 16% 38% 23% 5%	880
April	1st to 10th	Night	19% 16% 38% 22% 4	800
	11th to 20th	Night	15% 12% 36% 28% 8%	791
	21st to end	Night	19% 9% 33% 31% 7%	800
May	1st to 10th	Night	19% 9% 32% 29% 11%	675
	11th to 20th	Night	17% 5% 30% 35% 13%	532
	21st to end	Night	14% 5% 19% 39% 22%	433
June	1st to 10th	Night	10% 5% 20% 44% 21% 1	400
	11th to 20th	Night	13% 3 20% 42% 20% 1	380
	21st to end	Night	9% 3 21% 47% 18% 2	380
July	1st to 10th	Night	10% 4 17% 37% 29% 4	370
	11th to 20th	Night	6% 2 12% 39% 35% 6%	521
	21st to end	Night	8% 2 15% 45% 27% 3	624
August	1st to 10th	Night	12% 1 14% 39% 32% 2	567
	11th to 20th	Night	11% 2 15% 41% 27% 4	648
	21st to end	Night	11% 3 14% 37% 30% 6%	836
September	1st to 10th	Night	16% 3 14% 35% 28% 5%	760
	11th to 20th	Night	14% 3 15% 35% 29% 4	760
	21st to end	Night	24% 5% 18% 34% 18% 1	760
October	1st to 10th	Night	20% 4 19% 32% 21% 4	760
	11th to 20th	Night	18% 8% 27% 29% 16% 1	760
	21st to end	Night	17% 7% 32% 30% 13% 1	836
November	1st to 10th	Night	15% 9% 29% 31% 13% 2	780
	11th to 20th	Night	18% 11% 34% 29% 9%	800
	21st to end	Night	15% 11% 35% 29% 10% 1	800
December	1st to 10th	Night	20% 11% 38% 23% 9%	800
	11th to 20th	Night	21% 10% 35% 29% 5%	800
	21st to end	Night	19% 12% 32% 31% 5%	880

Page generated at 2025-06-07 10:28:15. Version ac07

Copyright © 2025 Attilla Danko.