Spring Gulch
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Spring Gulch clear sky chart from 2005-11-06 to 2025-07-21.

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	2 5% 2 6% 5% 5% 5% 5% 7% 8% 50%	124262
	Night	2 5% 2 6% 4 4 5% 4 6% 8% 54%	123797
Transparency	Day	29% 10% 13% 21% 19% 8%	124018
	Night	28% 9% 14% 23% 20% 6%	123629
Seeing	Day	9% 14% 29% 29% 15% 2	16437
	Night	6% 7% 26% 40% 20% 1	26522

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	4 3 12% 8% 7% 8% 6% 8% 7% 37%	3712
	11th to 20th	Day	1 6% 5% 10% 6% 6% 5% 5% 7% 7% 42%	4100
	21st to end	Day	1 6% 3 6% 5% 4 5% 4 5% 6% 54%	4510
February	1st to 10th	Day	2 10% 4 11% 6% 6% 5% 4 6% 7% 40%	1800
	11th to 20th	Day	1 11% 4 9% 6% 6% 5% 5% 5% 7% 40%	1800
	21st to end	Day	1 9% 5% 10% 6% 5% 6% 5% 7% 6% 41%	1650
March	1st to 10th	Day	1 9% 5% 8% 5% 5% 6% 5% 5% 6% 45%	4836
	11th to 20th	Day	1 7% 3 8% 6% 5% 7% 5% 8% 9% 40%	5000
	21st to end	Day	1 8% 3 7% 5% 7% 8% 8% 9% 9% 36%	5568
April	1st to 10th	Day	3 8% 3 7% 5% 5% 4 5% 6% 7% 46%	2400
	11th to 20th	Day	4 9% 2 8% 6% 5% 6% 6% 7% 8% 40%	2371
	21st to end	Day	3 7% 3 8% 6% 6% 6% 5% 7% 7% 43%	2400
May	1st to 10th	Day	3 7% 3 8% 6% 6% 6% 5% 7% 9% 40%	5790
	11th to 20th	Day	3 4 1 5% 4 5% 6% 5% 8% 9% 48%	6159
	21st to end	Day	3 4 1 4 4 4 6% 5% 7% 10% 53%	6925
June	1st to 10th	Day	3 3 1 4 3 4 4 4 7% 10% 57%	2800
	11th to 20th	Day	2 3 1 3 3 4 5% 4 6% 8% 62%	2800
	21st to end	Day	2 2 1 3 3 4 5% 4 7% 8% 62%	2800
July	1st to 10th	Day	3 2 1 3 3 3 4 4 5% 7% 66%	4570
	11th to 20th	Day	2 2 1 3 4 4 6% 6% 10% 14% 49%	4450
	21st to end	Day	3 3 2 5% 4 5% 5% 4 7% 9% 53%	4455
August	1st to 10th	Day	4 3 1 5% 5% 5% 8% 6% 9% 11% 42%	4092
	11th to 20th	Day	3 2 1 4 5% 5% 7% 6% 8% 9% 48%	3912
	21st to end	Day	2 2 1 5% 4 4 5% 5% 8% 11% 53%	4180
September	1st to 10th	Day	5% 2 1 5% 3 4 5% 4 5% 8% 58%	2280
	11th to 20th	Day	4 2 1 4 4 4 5% 3 6% 8% 58%	2280
	21st to end	Day	5% 3 1 5% 2 3 4 3 5% 6% 63%	2010
October	1st to 10th	Day	4 2 1 3 2 2 2 3 4 5% 72%	3170
	11th to 20th	Day	3 3 1 3 4 4 5% 5% 8% 11% 53%	3150
	21st to end	Day	3 5% 2 4 2 3 3 3 4 6% 64%	3438
November	1st to 10th	Day	2 5% 2 4 3 3 3 4 6% 6% 61%	1849
	11th to 20th	Day	2 8% 2 6% 3 3 3 3 5% 5% 59%	1755
	21st to end	Day	2 7% 3 8% 4 4 3 3 4 5% 57%	1600
December	1st to 10th	Day	1 6% 2 7% 4 4 4 4 3 5% 60%	2620
	11th to 20th	Day	1 6% 3 7% 4 4 4 3 5% 7% 57%	3026
	21st to end	Day	1 8% 4 9% 6% 6% 6% 5% 7% 8% 42%	4004
January	1st to 10th	Night	8% 5% 13% 7% 5% 6% 4 5% 7% 40%	6281
	11th to 20th	Night	1 8% 3 9% 8% 6% 5% 3 5% 6% 46%	5880
	21st to end	Night	1 8% 4 8% 4 4 4 4 5% 5% 53%	6468
February	1st to 10th	Night	1 7% 4 9% 6% 5% 5% 5% 6% 7% 46%	2600
	11th to 20th	Night	1 7% 5% 8% 6% 5% 6% 5% 7% 8% 43%	2487
	21st to end	Night	2 9% 5% 9% 4 5% 5% 4 5% 7% 46%	1980
March	1st to 10th	Night	7% 3 8% 5% 6% 7% 5% 6% 7% 46%	5038
	11th to 20th	Night	1 6% 4 7% 4 4 5% 4 6% 7% 54%	5000
	21st to end	Night	1 7% 2 6% 4 5% 6% 7% 9% 10% 41%	5401
April	1st to 10th	Night	3 7% 3 6% 5% 5% 5% 5% 6% 7% 48%	2000
	11th to 20th	Night	4 10% 3 7% 4 4 4 5% 6% 8% 47%	1977
	21st to end	Night	5% 7% 2 6% 4 4 4 4 6% 7% 51%	2000
May	1st to 10th	Night	4 6% 2 6% 4 4 5% 5% 7% 10% 47%	4175
	11th to 20th	Night	4 3 2 5% 4 4 5% 5% 8% 10% 52%	3755
	21st to end	Night	2 2 1 3 3 3 5% 3 7% 9% 62%	3972
June	1st to 10th	Night	2 2 1 3 3 3 3 4 6% 9% 64%	1600
	11th to 20th	Night	4 2 1 3 3 3 4 3 6% 6% 64%	1600
	21st to end	Night	1 1 1 2 2 3 3 4 6% 8% 69%	1600
July	1st to 10th	Night	3 2 1 3 4 3 4 3 5% 6% 67%	2620
	11th to 20th	Night	1 1 1 3 3 4 5% 5% 9% 12% 56%	2735
	21st to end	Night	3 2 1 4 4 4 5% 4 8% 8% 57%	3109
August	1st to 10th	Night	3 2 1 4 4 4 6% 7% 10% 12% 47%	2847
	11th to 20th	Night	2 3 1 3 3 4 5% 4 7% 10% 58%	2925
	21st to end	Night	2 2 1 4 4 4 5% 4 7% 9% 57%	3487
September	1st to 10th	Night	3 3 2 4 4 4 3 4 5% 6% 63%	1900
	11th to 20th	Night	3 2 1 4 4 2 4 3 6% 9% 62%	1900
	21st to end	Night	3 2 1 3 2 3 3 2 4 6% 69%	2166
October	1st to 10th	Night	3 2 1 2 2 2 2 2 3 5% 76%	3800
	11th to 20th	Night	2 2 1 3 2 2 3 4 7% 10% 63%	3778
	21st to end	Night	4 5% 1 3 2 2 3 2 4 6% 67%	4120
November	1st to 10th	Night	2 6% 2 4 3 2 3 3 7% 6% 62%	2429
	11th to 20th	Night	2 8% 2 4 4 3 3 4 4 6% 59%	2642
	21st to end	Night	2 7% 3 6% 3 4 3 4 5% 6% 57%	2800
December	1st to 10th	Night	1 5% 2 5% 4 3 3 3 4 5% 65%	4570
	11th to 20th	Night	2 6% 2 5% 4 4 4 4 6% 10% 54%	5181
	21st to end	Night	1 8% 4 10% 7% 7% 7% 5% 6% 6% 40%	6974

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	40% 13% 14% 20% 11% 2	3713
	11th to 20th	Day	38% 12% 16% 13% 19% 3	4100
	21st to end	Day	30% 9% 15% 21% 21% 4	4510
February	1st to 10th	Day	45% 9% 16% 17% 10% 3	1800
	11th to 20th	Day	48% 6% 11% 21% 13% 2	1809
	21st to end	Day	45% 8% 12% 18% 13% 4	1650
March	1st to 10th	Day	31% 13% 13% 20% 18% 5%	4836
	11th to 20th	Day	31% 15% 18% 26% 9% 1	5000
	21st to end	Day	39% 14% 17% 21% 7% 1	5568
April	1st to 10th	Day	37% 8% 14% 19% 17% 5%	2400
	11th to 20th	Day	42% 9% 12% 17% 16% 3	2374
	21st to end	Day	37% 8% 14% 23% 16% 1	2400
May	1st to 10th	Day	33% 12% 15% 20% 18% 2	5790
	11th to 20th	Day	24% 13% 14% 24% 20% 5%	6163
	21st to end	Day	22% 9% 12% 24% 28% 4	6926
June	1st to 10th	Day	23% 7% 12% 22% 26% 10%	2800
	11th to 20th	Day	21% 7% 8% 15% 26% 22%	2800
	21st to end	Day	19% 6% 9% 18% 27% 21%	2800
July	1st to 10th	Day	19% 5% 9% 10% 21% 37%	4501
	11th to 20th	Day	22% 9% 13% 20% 24% 12%	4375
	21st to end	Day	25% 9% 12% 15% 19% 19%	4315
August	1st to 10th	Day	32% 12% 18% 12% 16% 11%	4078
	11th to 20th	Day	30% 12% 14% 13% 21% 10%	3951
	21st to end	Day	26% 10% 14% 18% 22% 11%	4179
September	1st to 10th	Day	26% 7% 10% 17% 22% 18%	2280
	11th to 20th	Day	26% 7% 11% 18% 26% 12%	2280
	21st to end	Day	25% 5% 7% 23% 32% 8%	2010
October	1st to 10th	Day	18% 5% 8% 19% 33% 16%	3170
	11th to 20th	Day	24% 9% 10% 33% 19% 4	3150
	21st to end	Day	21% 8% 11% 34% 23% 2	3438
November	1st to 10th	Day	25% 7% 13% 25% 27% 2	1849
	11th to 20th	Day	28% 6% 15% 28% 20% 4	1755
	21st to end	Day	33% 5% 12% 30% 16% 4	1600
December	1st to 10th	Day	30% 6% 11% 35% 15% 2	2620
	11th to 20th	Day	29% 8% 20% 28% 16%	3024
	21st to end	Day	37% 12% 15% 19% 15% 2	4004
January	1st to 10th	Night	38% 14% 15% 19% 13% 2	6281
	11th to 20th	Night	39% 9% 13% 16% 20% 4	5880
	21st to end	Night	33% 8% 15% 17% 22% 5%	6468
February	1st to 10th	Night	38% 10% 16% 22% 12% 2	2600
	11th to 20th	Night	40% 9% 14% 23% 13% 2	2488
	21st to end	Night	40% 7% 12% 22% 16% 4	1980
March	1st to 10th	Night	30% 12% 13% 19% 21% 5%	5038
	11th to 20th	Night	26% 10% 15% 29% 19% 2	5000
	21st to end	Night	33% 15% 20% 25% 7% 1	5401
April	1st to 10th	Night	35% 8% 13% 23% 18% 3	2000
	11th to 20th	Night	35% 10% 13% 22% 17% 3	1977
	21st to end	Night	32% 9% 13% 24% 20% 2	2000
May	1st to 10th	Night	29% 11% 15% 28% 15% 2	4172
	11th to 20th	Night	23% 10% 15% 33% 17% 2	3756
	21st to end	Night	16% 10% 14% 26% 29% 4	3972
June	1st to 10th	Night	18% 7% 12% 24% 27% 11%	1600
	11th to 20th	Night	20% 7% 8% 15% 23% 27%	1600
	21st to end	Night	14% 5% 11% 17% 27% 26%	1600
July	1st to 10th	Night	18% 7% 8% 10% 22% 35%	2580
	11th to 20th	Night	16% 10% 15% 29% 16% 15%	2687
	21st to end	Night	20% 8% 16% 19% 18% 18%	3011
August	1st to 10th	Night	26% 10% 24% 15% 15% 11%	2838
	11th to 20th	Night	22% 10% 20% 15% 20% 13%	2952
	21st to end	Night	24% 10% 11% 17% 22% 16%	3487
September	1st to 10th	Night	23% 6% 11% 16% 24% 20%	1900
	11th to 20th	Night	21% 7% 13% 18% 26% 14%	1900
	21st to end	Night	18% 5% 8% 23% 36% 10%	2166
October	1st to 10th	Night	14% 5% 7% 18% 41% 16%	3800
	11th to 20th	Night	16% 8% 13% 36% 22% 4	3778
	21st to end	Night	20% 6% 11% 33% 27% 3	4120
November	1st to 10th	Night	23% 7% 13% 26% 27% 4	2429
	11th to 20th	Night	27% 7% 13% 28% 21% 4	2642
	21st to end	Night	30% 6% 10% 28% 21% 4	2800
December	1st to 10th	Night	24% 5% 11% 40% 18% 1	4570
	11th to 20th	Night	27% 9% 15% 33% 15%	5182
	21st to end	Night	41% 11% 11% 18% 18% 1	6974

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	10% 14% 25% 35% 15% 1	300
	11th to 20th	Day	12% 12% 33% 32% 11%	300
	21st to end	Day	6% 11% 34% 34% 14% 1	330
February	1st to 10th	Day	15% 19% 35% 25% 5% 1	300
	11th to 20th	Day	15% 21% 30% 28% 5% 1	300
	21st to end	Day	18% 19% 33% 21% 8% 1	249
March	1st to 10th	Day	19% 23% 29% 21% 7% 1	443
	11th to 20th	Day	12% 23% 33% 25% 7%	500
	21st to end	Day	16% 30% 34% 16% 4	550
April	1st to 10th	Day	16% 27% 31% 18% 8% 1	500
	11th to 20th	Day	19% 29% 30% 17% 5% 1	492
	21st to end	Day	13% 27% 33% 20% 5% 1	500
May	1st to 10th	Day	15% 22% 36% 19% 7% 1	503
	11th to 20th	Day	10% 14% 29% 31% 13% 2	664
	21st to end	Day	7% 15% 28% 32% 16% 2	789
June	1st to 10th	Day	5% 12% 28% 31% 21% 2	730
	11th to 20th	Day	5% 14% 32% 32% 16% 1	730
	21st to end	Day	4 12% 31% 31% 21% 2	730
July	1st to 10th	Day	4 5% 23% 36% 29% 4	721
	11th to 20th	Day	2 4 23% 38% 30% 4	650
	21st to end	Day	5% 5% 24% 38% 22% 6%	532
August	1st to 10th	Day	7% 6% 26% 35% 21% 5%	487
	11th to 20th	Day	3 5% 30% 38% 20% 4	477
	21st to end	Day	3 6% 24% 39% 23% 5%	539
September	1st to 10th	Day	6% 8% 25% 32% 23% 6%	490
	11th to 20th	Day	6% 11% 33% 31% 14% 4	490
	21st to end	Day	12% 11% 23% 29% 19% 6%	381
October	1st to 10th	Day	10% 12% 20% 31% 18% 9%	300
	11th to 20th	Day	9% 16% 25% 29% 17% 4	300
	21st to end	Day	12% 13% 34% 27% 13% 2	330
November	1st to 10th	Day	14% 18% 29% 26% 13% 1	300
	11th to 20th	Day	7% 15% 29% 33% 13% 2	300
	21st to end	Day	10% 13% 31% 30% 14% 2	300
December	1st to 10th	Day	9% 12% 33% 28% 15% 2	300
	11th to 20th	Day	9% 11% 32% 35% 12%	300
	21st to end	Day	11% 15% 36% 28% 9%	330
January	1st to 10th	Night	6% 9% 30% 38% 16% 2	980
	11th to 20th	Night	6% 7% 32% 38% 15% 1	800
	21st to end	Night	7% 5% 30% 43% 13% 2	880
February	1st to 10th	Night	6% 9% 36% 41% 8%	800
	11th to 20th	Night	6% 8% 36% 39% 10%	784
	21st to end	Night	8% 8% 41% 37% 5%	660
March	1st to 10th	Night	6% 11% 35% 38% 10% 1	800
	11th to 20th	Night	5% 9% 27% 44% 15%	800
	21st to end	Night	8% 9% 33% 39% 11%	843
April	1st to 10th	Night	8% 12% 36% 36% 8%	600
	11th to 20th	Night	9% 11% 34% 34% 11% 1	593
	21st to end	Night	10% 10% 29% 36% 15% 2	600
May	1st to 10th	Night	9% 7% 31% 40% 13% 1	600
	11th to 20th	Night	7% 5% 23% 41% 22% 2	591
	21st to end	Night	7% 7% 23% 37% 23% 2	650
June	1st to 10th	Night	4 4 18% 45% 29% 1	600
	11th to 20th	Night	5% 6% 25% 45% 19% 1	600
	21st to end	Night	1 2 20% 44% 32% 1	600
July	1st to 10th	Night	4 1 13% 41% 39% 3	585
	11th to 20th	Night	2 1 7% 44% 43% 4	582
	21st to end	Night	3 1 5% 36% 52% 3	624
August	1st to 10th	Night	7% 1 8% 41% 42% 2	567
	11th to 20th	Night	4 1 12% 43% 38% 3	564
	21st to end	Night	2 1 11% 40% 42% 3	627
September	1st to 10th	Night	4 2 12% 46% 35% 1	570
	11th to 20th	Night	4 3 15% 45% 32% 2	570
	21st to end	Night	4 3 18% 39% 33% 4	727
October	1st to 10th	Night	6% 4 22% 42% 25% 2	760
	11th to 20th	Night	5% 4 26% 40% 22% 2	760
	21st to end	Night	9% 7% 24% 39% 19% 2	836
November	1st to 10th	Night	5% 7% 32% 36% 19% 1	869
	11th to 20th	Night	8% 9% 29% 38% 14% 2	1000
	21st to end	Night	7% 9% 26% 39% 17% 1	1000
December	1st to 10th	Night	7% 7% 32% 41% 13% 1	1000
	11th to 20th	Night	8% 11% 32% 35% 14% 1	1000
	21st to end	Night	9% 9% 33% 38% 10% 1	1100

Page generated at 2025-07-17 23:09:58. Version ac07

Copyright © 2025 Attilla Danko.