Shot Rock
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Shot Rock clear sky chart from 2005-11-06 to 2026-01-17.

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	5% 7% 2 4 2 2 3 2 4 5% 64%	135907
	Night	5% 8% 2 4 3 3 3 3 4 5% 61%	133184
Transparency	Day	24% 3 7% 19% 26% 21%	130886
	Night	27% 4 6% 18% 26% 20%	129198
Seeing	Day	16% 17% 33% 21% 10% 3	16620
	Night	13% 9% 24% 33% 18% 4	26075

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	6% 14% 3 5% 3 2 3 3 5% 6% 49%	3719
	11th to 20th	Day	7% 11% 2 5% 3 3 3 2 3 5% 57%	3899
	21st to end	Day	9% 12% 3 6% 3 4 3 3 4 5% 46%	4510
February	1st to 10th	Day	12% 12% 4 7% 2 3 3 3 4 5% 45%	1800
	11th to 20th	Day	7% 14% 5% 6% 3 4 4 3 4 6% 44%	1950
	21st to end	Day	9% 15% 5% 8% 3 3 3 3 3 5% 43%	1650
March	1st to 10th	Day	6% 18% 9% 11% 4 3 3 3 5% 6% 33%	4518
	11th to 20th	Day	6% 16% 4 5% 3 3 4 2 4 5% 48%	4990
	21st to end	Day	8% 23% 6% 6% 3 2 3 2 4 5% 37%	5793
April	1st to 10th	Day	8% 15% 3 5% 3 3 3 3 5% 6% 45%	2400
	11th to 20th	Day	8% 13% 3 5% 3 3 3 3 4 6% 50%	2369
	21st to end	Day	8% 10% 1 4 2 2 3 3 6% 7% 54%	2400
May	1st to 10th	Day	5% 7% 2 3 2 2 2 1 3 5% 69%	5611
	11th to 20th	Day	3 8% 2 3 2 2 2 2 3 5% 68%	6176
	21st to end	Day	4 4 1 3 2 2 3 2 4 4 72%	6902
June	1st to 10th	Day	6% 5% 2 4 3 3 3 3 5% 6% 61%	2800
	11th to 20th	Day	3 3 1 2 2 2 2 2 4 5% 76%	2800
	21st to end	Day	3 2 1 2 1 2 2 2 3 3 78%	2800
July	1st to 10th	Day	1 1 1 1 1 2 2 91%	6319
	11th to 20th	Day	1 1 2 1 1 2 2 3 3 83%	6320
	21st to end	Day	1 2 1 2 1 2 2 2 3 4 81%	6589
August	1st to 10th	Day	1 1 2 1 1 2 2 2 3 84%	5704
	11th to 20th	Day	1 1 1 1 1 1 2 2 90%	5364
	21st to end	Day	2 2 1 3 3 2 2 2 3 4 76%	5984
September	1st to 10th	Day	2 1 2 2 2 1 2 3 3 83%	2400
	11th to 20th	Day	5% 3 1 3 2 2 3 2 4 4 70%	2380
	21st to end	Day	4 3 1 3 2 2 2 2 2 4 75%	2200
October	1st to 10th	Day	5% 4 1 3 2 2 2 3 4 5% 69%	3295
	11th to 20th	Day	6% 2 1 2 2 2 2 2 3 3 75%	3261
	21st to end	Day	4 6% 1 4 3 3 3 3 4 6% 64%	3528
November	1st to 10th	Day	8% 9% 2 3 3 4 3 3 5% 6% 54%	1854
	11th to 20th	Day	8% 8% 2 4 3 3 4 3 5% 6% 53%	1890
	21st to end	Day	7% 9% 3 5% 3 2 3 3 6% 6% 55%	1832
December	1st to 10th	Day	6% 5% 1 4 3 3 4 4 5% 8% 58%	2700
	11th to 20th	Day	13% 14% 4 7% 4 4 4 3 5% 5% 36%	3108
	21st to end	Day	13% 13% 3 5% 3 3 4 5% 6% 9% 35%	4092
January	1st to 10th	Night	5% 9% 3 5% 4 5% 4 4 6% 8% 48%	6446
	11th to 20th	Night	8% 10% 3 5% 3 3 4 3 4 4 52%	6200
	21st to end	Night	6% 14% 3 6% 4 4 4 3 4 5% 48%	6468
February	1st to 10th	Night	10% 11% 4 6% 3 3 3 3 4 6% 46%	2598
	11th to 20th	Night	6% 13% 4 6% 4 4 4 3 6% 7% 44%	2338
	21st to end	Night	8% 13% 4 8% 3 3 3 3 4 5% 48%	1980
March	1st to 10th	Night	6% 17% 8% 9% 3 3 3 3 5% 6% 37%	5376
	11th to 20th	Night	7% 16% 4 7% 3 3 3 2 3 5% 48%	5006
	21st to end	Night	8% 20% 5% 6% 4 4 4 3 5% 7% 35%	5169
April	1st to 10th	Night	8% 11% 4 6% 3 3 4 3 5% 7% 47%	2000
	11th to 20th	Night	6% 11% 3 5% 3 2 3 3 4 6% 52%	1979
	21st to end	Night	6% 9% 2 3 2 3 3 3 3 7% 57%	2000
May	1st to 10th	Night	2 4 2 4 2 2 2 3 3 5% 71%	4379
	11th to 20th	Night	2 5% 2 3 2 2 2 2 3 5% 72%	3718
	21st to end	Night	3 3 1 3 2 2 2 2 3 4 76%	3972
June	1st to 10th	Night	6% 5% 1 2 3 3 3 3 4 5% 66%	1600
	11th to 20th	Night	2 2 1 2 1 2 2 3 3 83%	1600
	21st to end	Night	3 2 1 1 2 2 2 1 2 3 81%	1600
July	1st to 10th	Night	1 1 1 1 1 1 1 1 93%	3640
	11th to 20th	Night	3 3 1 3 2 2 2 1 2 3 80%	3640
	21st to end	Night	2 2 1 2 2 2 2 2 4 5% 76%	4259
August	1st to 10th	Night	2 2 1 2 1 1 2 2 3 3 82%	4097
	11th to 20th	Night	1 1 1 1 1 1 1 1 2 2 89%	4506
	21st to end	Night	2 2 1 2 2 2 2 1 2 3 80%	5015
September	1st to 10th	Night	1 1 1 1 1 1 1 2 4 86%	2000
	11th to 20th	Night	3 3 2 2 2 2 2 3 5% 78%	2020
	21st to end	Night	3 2 1 3 2 2 2 2 2 5% 76%	2200
October	1st to 10th	Night	3 3 1 2 2 2 2 2 3 3 77%	3901
	11th to 20th	Night	3 2 1 3 2 2 2 2 3 4 77%	3897
	21st to end	Night	5% 5% 1 2 3 3 3 3 4 6% 65%	4280
November	1st to 10th	Night	7% 8% 2 3 2 2 3 3 5% 7% 57%	2665
	11th to 20th	Night	7% 7% 2 4 3 4 3 3 5% 7% 55%	2730
	21st to end	Night	7% 8% 2 4 3 3 3 2 4 6% 56%	2783
December	1st to 10th	Night	7% 6% 2 4 2 3 3 3 4 6% 62%	4700
	11th to 20th	Night	10% 14% 3 6% 4 4 5% 5% 7% 9% 32%	5316
	21st to end	Night	12% 13% 5% 7% 5% 4 4 4 5% 7% 35%	7106

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	36% 5% 13% 18% 20% 8%	3719
	11th to 20th	Day	33% 2 6% 14% 26% 19%	3899
	21st to end	Day	40% 5% 6% 14% 18% 18%	4510
February	1st to 10th	Day	41% 3 8% 17% 18% 13%	1800
	11th to 20th	Day	40% 4 7% 18% 23% 8%	1960
	21st to end	Day	45% 3 6% 19% 18% 8%	1650
March	1st to 10th	Day	52% 4 7% 13% 17% 7%	4518
	11th to 20th	Day	38% 4 11% 27% 17% 4	4990
	21st to end	Day	50% 5% 10% 22% 11% 3	5793
April	1st to 10th	Day	39% 5% 13% 21% 18% 4	2400
	11th to 20th	Day	36% 5% 11% 24% 17% 7%	2372
	21st to end	Day	29% 5% 15% 29% 20% 3	2400
May	1st to 10th	Day	20% 3 9% 30% 27% 11%	5611
	11th to 20th	Day	20% 3 8% 33% 29% 6%	6179
	21st to end	Day	16% 4 8% 34% 33% 6%	6904
June	1st to 10th	Day	23% 5% 11% 28% 27% 7%	2800
	11th to 20th	Day	13% 3 8% 24% 34% 19%	2800
	21st to end	Day	11% 3 3 16% 36% 31%	2800
July	1st to 10th	Day	3 1 1 5% 22% 67%	6251
	11th to 20th	Day	7% 2 2 8% 19% 62%	6245
	21st to end	Day	8% 2 3 16% 34% 37%	6399
August	1st to 10th	Day	11% 2 3 10% 32% 42%	4155
	11th to 20th	Day	5% 2 2 7% 36% 48%	3880
	21st to end	Day	9% 1 2 12% 43% 33%	4311
September	1st to 10th	Day	9% 1 2 12% 38% 36%	2400
	11th to 20th	Day	17% 3 4 22% 37% 17%	2380
	21st to end	Day	16% 2 4 21% 36% 22%	2200
October	1st to 10th	Day	18% 2 4 11% 38% 27%	3295
	11th to 20th	Day	16% 2 4 20% 43% 16%	3261
	21st to end	Day	21% 3 5% 23% 34% 13%	3528
November	1st to 10th	Day	31% 3 7% 23% 23% 13%	1854
	11th to 20th	Day	31% 5% 9% 19% 25% 11%	1890
	21st to end	Day	30% 4 7% 20% 27% 13%	1832
December	1st to 10th	Day	24% 4 8% 21% 26% 18%	2700
	11th to 20th	Day	50% 4 8% 12% 15% 11%	3108
	21st to end	Day	44% 6% 11% 17% 16% 7%	4092
January	1st to 10th	Night	32% 6% 13% 23% 19% 7%	6446
	11th to 20th	Night	35% 4 5% 12% 25% 20%	6200
	21st to end	Night	38% 5% 6% 11% 20% 21%	6468
February	1st to 10th	Night	40% 4 6% 17% 18% 15%	2598
	11th to 20th	Night	38% 4 7% 19% 21% 10%	2339
	21st to end	Night	39% 4 7% 21% 20% 10%	1980
March	1st to 10th	Night	48% 3 6% 14% 20% 9%	5376
	11th to 20th	Night	40% 4 5% 27% 20% 4	5006
	21st to end	Night	48% 6% 11% 21% 11% 3	5169
April	1st to 10th	Night	36% 5% 12% 22% 20% 6%	2000
	11th to 20th	Night	31% 6% 12% 23% 19% 8%	1979
	21st to end	Night	27% 5% 11% 34% 19% 5%	2000
May	1st to 10th	Night	16% 4 9% 33% 28% 10%	4376
	11th to 20th	Night	15% 3 8% 31% 34% 9%	3718
	21st to end	Night	12% 3 8% 28% 39% 10%	3972
June	1st to 10th	Night	21% 5% 10% 26% 30% 9%	1600
	11th to 20th	Night	9% 3 6% 27% 34% 22%	1600
	21st to end	Night	11% 2 3 15% 35% 34%	1600
July	1st to 10th	Night	3 1 1 4 23% 68%	3600
	11th to 20th	Night	12% 2 2 6% 18% 61%	3592
	21st to end	Night	11% 2 3 16% 27% 41%	4138
August	1st to 10th	Night	13% 2 2 9% 32% 41%	2979
	11th to 20th	Night	6% 2 2 8% 30% 52%	3256
	21st to end	Night	9% 1 1 11% 41% 36%	3608
September	1st to 10th	Night	6% 1 2 12% 40% 39%	2000
	11th to 20th	Night	12% 3 4 23% 38% 20%	2020
	21st to end	Night	13% 2 4 23% 34% 24%	2200
October	1st to 10th	Night	14% 2 3 11% 38% 31%	3901
	11th to 20th	Night	12% 2 4 19% 43% 20%	3897
	21st to end	Night	21% 3 5% 20% 34% 16%	4280
November	1st to 10th	Night	27% 4 7% 23% 23% 16%	2665
	11th to 20th	Night	28% 5% 7% 21% 27% 12%	2730
	21st to end	Night	30% 3 5% 20% 26% 15%	2783
December	1st to 10th	Night	25% 3 6% 19% 23% 23%	4700
	11th to 20th	Night	45% 6% 7% 13% 21% 9%	5316
	21st to end	Night	48% 6% 8% 15% 16% 8%	7106

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	40% 15% 24% 15% 6%	220
	11th to 20th	Day	26% 15% 28% 17% 11% 3	306
	21st to end	Day	25% 16% 23% 22% 12% 2	440
February	1st to 10th	Day	32% 17% 24% 17% 8% 3	400
	11th to 20th	Day	25% 22% 29% 16% 6% 1	495
	21st to end	Day	23% 21% 33% 18% 4 1	414
March	1st to 10th	Day	32% 25% 24% 14% 4 2	500
	11th to 20th	Day	31% 20% 23% 15% 9% 1	500
	21st to end	Day	30% 23% 28% 15% 5%	550
April	1st to 10th	Day	21% 23% 31% 17% 7% 1	500
	11th to 20th	Day	28% 19% 26% 19% 6% 1	492
	21st to end	Day	17% 18% 30% 21% 10% 4	500
May	1st to 10th	Day	21% 20% 30% 18% 8% 3	503
	11th to 20th	Day	20% 19% 27% 20% 11% 3	528
	21st to end	Day	18% 15% 27% 21% 14% 5%	573
June	1st to 10th	Day	11% 16% 35% 21% 12% 5%	530
	11th to 20th	Day	10% 22% 35% 20% 9% 3	530
	21st to end	Day	4 17% 38% 25% 10% 5%	530
July	1st to 10th	Day	3 12% 50% 19% 12% 4	526
	11th to 20th	Day	2 11% 45% 26% 12% 4	524
	21st to end	Day	2 11% 45% 24% 12% 7%	575
August	1st to 10th	Day	4 16% 42% 23% 12% 4	527
	11th to 20th	Day	3 15% 40% 25% 11% 5%	517
	21st to end	Day	5% 10% 45% 25% 13% 3	583
September	1st to 10th	Day	4 16% 42% 23% 13% 2	530
	11th to 20th	Day	11% 17% 37% 25% 9% 2	530
	21st to end	Day	9% 17% 36% 30% 6% 2	530
October	1st to 10th	Day	12% 18% 28% 31% 9% 2	530
	11th to 20th	Day	12% 14% 32% 27% 12% 3	530
	21st to end	Day	14% 17% 29% 26% 10% 3	565
November	1st to 10th	Day	19% 14% 23% 25% 15% 5%	330
	11th to 20th	Day	21% 13% 28% 22% 11% 5%	330
	21st to end	Day	20% 13% 28% 22% 14% 3	300
December	1st to 10th	Day	21% 12% 23% 20% 16% 7%	220
	11th to 20th	Day	21% 20% 25% 17% 14% 4	220
	21st to end	Day	33% 12% 25% 18% 10% 2	242
January	1st to 10th	Night	23% 13% 25% 21% 13% 5%	840
	11th to 20th	Night	18% 13% 30% 27% 9% 3	824
	21st to end	Night	19% 14% 26% 24% 13% 3	880
February	1st to 10th	Night	21% 14% 24% 24% 14% 2	800
	11th to 20th	Night	18% 13% 25% 26% 12% 4	784
	21st to end	Night	21% 11% 29% 27% 10% 2	660
March	1st to 10th	Night	23% 13% 29% 23% 11% 2	800
	11th to 20th	Night	21% 12% 26% 22% 18% 3	800
	21st to end	Night	20% 12% 29% 28% 10% 1	880
April	1st to 10th	Night	16% 11% 26% 34% 12% 2	800
	11th to 20th	Night	13% 13% 27% 30% 13% 3	791
	21st to end	Night	12% 10% 26% 31% 17% 4	800
May	1st to 10th	Night	10% 12% 26% 31% 18% 3	723
	11th to 20th	Night	6% 10% 22% 39% 21% 2	444
	21st to end	Night	10% 4 24% 34% 25% 3	433
June	1st to 10th	Night	8% 4 22% 41% 22% 4	400
	11th to 20th	Night	3 5% 25% 43% 23% 2	400
	21st to end	Night	4 4 19% 45% 27% 2	400
July	1st to 10th	Night	1 15% 47% 34% 3	390
	11th to 20th	Night	2 3 13% 47% 32% 3	388
	21st to end	Night	3 1 12% 36% 41% 7%	561
August	1st to 10th	Night	4 1 15% 48% 29% 4	621
	11th to 20th	Night	2 2 20% 44% 27% 5%	792
	21st to end	Night	3 2 14% 50% 30% 2	880
September	1st to 10th	Night	2 3 18% 46% 28% 4	800
	11th to 20th	Night	5% 3 20% 37% 27% 7%	800
	21st to end	Night	4 6% 25% 35% 23% 7%	800
October	1st to 10th	Night	9% 8% 20% 38% 20% 5%	800
	11th to 20th	Night	9% 9% 22% 36% 20% 5%	800
	21st to end	Night	10% 8% 25% 30% 19% 8%	880
November	1st to 10th	Night	13% 9% 19% 35% 19% 5%	820
	11th to 20th	Night	14% 11% 28% 30% 14% 4	840
	21st to end	Night	16% 13% 28% 27% 14% 3	840
December	1st to 10th	Night	19% 11% 27% 29% 11% 3	840
	11th to 20th	Night	22% 12% 25% 27% 11% 3	840
	21st to end	Night	26% 15% 25% 23% 9% 2	924

Page generated at 2026-01-13 22:14:24. Version ac07

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