Trapshoot
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Trapshoot clear sky chart from 2005-11-06 to 2026-02-16.

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	3 5% 2 4 3 3 3 3 5% 6% 63%	139604
	Night	3 6% 2 5% 3 3 4 3 5% 6% 59%	138625
Transparency	Day	21% 5% 8% 19% 27% 20%	134556
	Night	24% 6% 9% 21% 24% 15%	134657
Seeing	Day	10% 15% 26% 25% 18% 6%	16575
	Night	7% 8% 17% 39% 25% 4	25994

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	3 9% 3 8% 5% 5% 6% 5% 7% 9% 42%	4722
	11th to 20th	Day	4 6% 2 5% 3 4 4 3 4 6% 59%	4856
	21st to end	Day	5% 8% 3 7% 5% 5% 5% 4 6% 9% 44%	5843
February	1st to 10th	Day	4 7% 3 6% 5% 5% 4 4 6% 7% 49%	1890
	11th to 20th	Day	3 7% 3 7% 4 5% 6% 3 6% 8% 47%	1967
	21st to end	Day	1 7% 2 6% 5% 4 5% 5% 7% 8% 50%	1650
March	1st to 10th	Day	3 13% 6% 11% 6% 5% 5% 4 6% 8% 33%	4518
	11th to 20th	Day	2 7% 2 6% 3 3 4 3 6% 8% 55%	4956
	21st to end	Day	3 12% 4 7% 4 4 4 3 5% 8% 46%	5810
April	1st to 10th	Day	4 7% 3 7% 6% 4 4 5% 7% 8% 45%	2400
	11th to 20th	Day	3 6% 2 6% 4 4 4 4 5% 7% 54%	2369
	21st to end	Day	5% 7% 2 5% 3 4 4 3 4 7% 56%	2400
May	1st to 10th	Day	3 5% 2 4 2 2 2 2 3 5% 69%	5720
	11th to 20th	Day	3 4 1 4 3 3 3 3 4 5% 68%	6277
	21st to end	Day	2 3 1 3 3 2 2 2 4 5% 71%	6902
June	1st to 10th	Day	4 3 1 4 4 4 3 3 6% 8% 60%	2800
	11th to 20th	Day	2 2 1 2 2 2 2 2 4 5% 76%	2800
	21st to end	Day	2 2 1 3 2 2 2 2 4 4 77%	2800
July	1st to 10th	Day	1 1 1 1 2 1 2 2 88%	6319
	11th to 20th	Day	1 1 1 2 2 2 2 2 2 3 82%	6320
	21st to end	Day	2 2 1 2 2 3 3 3 4 6% 72%	6738
August	1st to 10th	Day	1 1 2 2 2 2 2 3 4 80%	5777
	11th to 20th	Day	1 1 1 1 1 1 1 2 3 89%	5373
	21st to end	Day	2 2 1 3 3 3 3 2 3 3 76%	5984
September	1st to 10th	Day	2 1 1 1 1 2 2 1 4 4 82%	2400
	11th to 20th	Day	3 2 1 2 2 2 3 2 3 5% 73%	2382
	21st to end	Day	4 2 1 3 2 2 2 2 3 6% 74%	2200
October	1st to 10th	Day	2 3 1 3 2 2 2 2 4 7% 71%	3285
	11th to 20th	Day	4 4 1 3 2 2 2 2 3 6% 70%	3261
	21st to end	Day	2 3 1 4 3 3 4 4 5% 7% 63%	3472
November	1st to 10th	Day	4 5% 2 4 5% 3 4 3 5% 7% 58%	1854
	11th to 20th	Day	3 6% 2 4 4 4 6% 5% 7% 10% 50%	1890
	21st to end	Day	2 7% 2 4 3 4 4 4 6% 8% 54%	1769
December	1st to 10th	Day	3 4 1 4 3 3 4 4 6% 9% 59%	2700
	11th to 20th	Day	9% 9% 3 8% 5% 6% 7% 5% 7% 10% 31%	3108
	21st to end	Day	4 10% 4 10% 5% 5% 6% 4 7% 11% 32%	4092
January	1st to 10th	Night	3 8% 3 8% 5% 5% 6% 5% 8% 10% 40%	8172
	11th to 20th	Night	3 7% 2 5% 4 3 4 3 4 7% 58%	8106
	21st to end	Night	5% 9% 3 8% 5% 5% 5% 3 5% 6% 46%	8371
February	1st to 10th	Night	3 7% 3 6% 4 4 4 4 6% 9% 50%	2730
	11th to 20th	Night	2 7% 2 7% 4 5% 4 5% 8% 10% 47%	2430
	21st to end	Night	2 7% 2 6% 4 5% 4 4 6% 9% 51%	1980
March	1st to 10th	Night	3 14% 6% 8% 4 4 5% 4 5% 7% 40%	5376
	11th to 20th	Night	2 8% 3 8% 4 4 4 3 6% 7% 51%	5028
	21st to end	Night	3 13% 4 10% 5% 5% 5% 5% 6% 7% 38%	5165
April	1st to 10th	Night	2 6% 2 6% 5% 4 5% 5% 6% 10% 49%	2000
	11th to 20th	Night	3 6% 1 5% 4 3 5% 3 6% 8% 56%	1979
	21st to end	Night	5% 4 2 5% 3 3 3 3 5% 8% 59%	2000
May	1st to 10th	Night	3 5% 1 5% 3 2 2 2 3 5% 70%	4250
	11th to 20th	Night	3 4 1 3 3 2 3 2 4 5% 69%	3616
	21st to end	Night	2 3 1 3 2 2 2 2 4 5% 73%	3972
June	1st to 10th	Night	4 4 2 4 3 3 3 4 6% 8% 61%	1600
	11th to 20th	Night	2 2 1 3 2 2 3 2 4 4 76%	1600
	21st to end	Night	2 2 1 2 3 3 2 2 3 3 78%	1600
July	1st to 10th	Night	1 1 1 1 1 1 2 2 90%	3640
	11th to 20th	Night	1 2 2 2 1 2 2 2 3 84%	3640
	21st to end	Night	3 2 1 2 2 2 3 2 4 5% 72%	4101
August	1st to 10th	Night	2 2 1 2 2 1 2 2 3 4 80%	4035
	11th to 20th	Night	1 1 1 1 1 1 1 2 3 88%	4497
	21st to end	Night	3 2 1 3 2 2 2 2 3 4 76%	5015
September	1st to 10th	Night	2 1 2 1 1 2 2 3 4 82%	2000
	11th to 20th	Night	3 3 1 3 2 2 2 1 3 5% 74%	2017
	21st to end	Night	2 3 1 2 3 2 3 2 3 5% 76%	2200
October	1st to 10th	Night	2 2 1 2 2 2 3 2 3 4 77%	3910
	11th to 20th	Night	2 3 1 3 2 2 2 2 3 5% 75%	3897
	21st to end	Night	5% 4 1 3 2 4 4 3 4 7% 62%	4335
November	1st to 10th	Night	4 5% 2 5% 3 3 3 4 6% 8% 56%	2665
	11th to 20th	Night	3 5% 2 5% 4 4 4 4 7% 9% 53%	2730
	21st to end	Night	2 5% 2 5% 4 4 4 4 6% 8% 55%	2846
December	1st to 10th	Night	3 5% 1 3 3 3 3 3 5% 7% 63%	4700
	11th to 20th	Night	7% 8% 3 9% 5% 5% 6% 5% 8% 12% 31%	5316
	21st to end	Night	6% 10% 4 10% 5% 6% 6% 5% 7% 9% 31%	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	33% 11% 16% 28% 12%	4723
	11th to 20th	Day	24% 6% 8% 21% 28% 14%	4856
	21st to end	Day	34% 6% 8% 19% 25% 8%	5843
February	1st to 10th	Day	33% 5% 13% 24% 19% 6%	1890
	11th to 20th	Day	33% 5% 13% 28% 18% 3	1977
	21st to end	Day	28% 8% 15% 27% 16% 6%	1650
March	1st to 10th	Day	43% 7% 10% 19% 16% 4	4518
	11th to 20th	Day	24% 6% 14% 34% 21% 2	4956
	21st to end	Day	33% 8% 14% 24% 18% 2	5810
April	1st to 10th	Day	32% 8% 15% 26% 16% 4	2400
	11th to 20th	Day	27% 6% 12% 28% 21% 6%	2372
	21st to end	Day	27% 5% 12% 28% 24% 4	2400
May	1st to 10th	Day	18% 5% 5% 24% 41% 7%	5720
	11th to 20th	Day	17% 5% 8% 21% 37% 12%	6280
	21st to end	Day	15% 4 5% 23% 44% 8%	6904
June	1st to 10th	Day	22% 5% 8% 24% 31% 10%	2800
	11th to 20th	Day	12% 3 5% 20% 38% 22%	2800
	21st to end	Day	11% 3 3 13% 35% 35%	2800
July	1st to 10th	Day	5% 2 2 5% 19% 68%	6251
	11th to 20th	Day	8% 1 3 4 14% 69%	6245
	21st to end	Day	13% 3 4 13% 28% 39%	6542
August	1st to 10th	Day	13% 2 4 6% 23% 52%	4206
	11th to 20th	Day	6% 1 1 6% 32% 53%	3889
	21st to end	Day	8% 2 2 8% 43% 38%	4311
September	1st to 10th	Day	8% 2 2 12% 29% 47%	2400
	11th to 20th	Day	15% 3 4 18% 36% 24%	2382
	21st to end	Day	14% 3 5% 18% 36% 25%	2200
October	1st to 10th	Day	14% 2 5% 12% 37% 29%	3285
	11th to 20th	Day	17% 3 5% 23% 39% 12%	3261
	21st to end	Day	19% 5% 8% 29% 29% 11%	3472
November	1st to 10th	Day	26% 6% 12% 24% 24% 9%	1854
	11th to 20th	Day	26% 8% 15% 27% 21% 3	1890
	21st to end	Day	25% 6% 11% 27% 25% 6%	1769
December	1st to 10th	Day	22% 6% 8% 30% 28% 6%	2700
	11th to 20th	Day	45% 9% 10% 22% 12% 3	3108
	21st to end	Day	41% 10% 18% 21% 9% 1	4092
January	1st to 10th	Night	34% 10% 19% 25% 12%	8172
	11th to 20th	Night	23% 8% 9% 18% 28% 15%	8106
	21st to end	Night	37% 5% 8% 17% 27% 6%	8371
February	1st to 10th	Night	30% 7% 11% 26% 20% 5%	2730
	11th to 20th	Night	29% 6% 13% 32% 18% 2	2431
	21st to end	Night	28% 8% 14% 28% 16% 6%	1980
March	1st to 10th	Night	38% 9% 10% 24% 14% 4	5376
	11th to 20th	Night	27% 8% 13% 34% 16% 2	5028
	21st to end	Night	39% 11% 17% 23% 10% 1	5165
April	1st to 10th	Night	27% 9% 16% 29% 16% 4	2000
	11th to 20th	Night	25% 6% 17% 29% 18% 5%	1979
	21st to end	Night	22% 7% 16% 35% 18% 3	2000
May	1st to 10th	Night	17% 6% 7% 29% 37% 5%	4247
	11th to 20th	Night	17% 4 11% 26% 33% 9%	3616
	21st to end	Night	13% 5% 7% 30% 40% 6%	3972
June	1st to 10th	Night	21% 5% 12% 25% 29% 8%	1600
	11th to 20th	Night	12% 3 9% 21% 36% 20%	1600
	21st to end	Night	14% 2 4 16% 33% 31%	1600
July	1st to 10th	Night	4 1 2 6% 23% 64%	3600
	11th to 20th	Night	8% 1 2 5% 20% 64%	3592
	21st to end	Night	14% 3 4 15% 28% 37%	3986
August	1st to 10th	Night	14% 3 3 8% 29% 45%	2929
	11th to 20th	Night	6% 2 1 7% 35% 48%	3247
	21st to end	Night	9% 2 2 10% 39% 39%	3608
September	1st to 10th	Night	8% 2 3 8% 34% 45%	2000
	11th to 20th	Night	14% 3 4 20% 36% 23%	2017
	21st to end	Night	13% 2 4 20% 35% 25%	2200
October	1st to 10th	Night	13% 2 5% 13% 35% 31%	3910
	11th to 20th	Night	14% 3 5% 23% 45% 11%	3897
	21st to end	Night	21% 3 7% 30% 27% 11%	4335
November	1st to 10th	Night	24% 7% 12% 27% 20% 10%	2665
	11th to 20th	Night	25% 7% 14% 27% 23% 4	2730
	21st to end	Night	25% 7% 11% 27% 23% 7%	2846
December	1st to 10th	Night	20% 6% 8% 28% 27% 10%	4700
	11th to 20th	Night	40% 11% 11% 21% 16% 2	5316
	21st to end	Night	43% 11% 15% 20% 10% 1	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	22% 13% 29% 20% 13% 3	220
	11th to 20th	Day	14% 14% 25% 26% 16% 5%	258
	21st to end	Day	10% 13% 30% 23% 20% 4	473
February	1st to 10th	Day	19% 16% 25% 24% 14% 2	430
	11th to 20th	Day	16% 17% 26% 29% 12% 1	500
	21st to end	Day	14% 16% 25% 33% 11% 1	414
March	1st to 10th	Day	19% 23% 26% 20% 10% 2	500
	11th to 20th	Day	22% 18% 25% 19% 15% 2	500
	21st to end	Day	18% 24% 27% 19% 10% 1	550
April	1st to 10th	Day	15% 23% 27% 22% 10% 3	500
	11th to 20th	Day	16% 24% 24% 21% 12% 3	492
	21st to end	Day	15% 20% 23% 24% 14% 4	500
May	1st to 10th	Day	13% 23% 26% 22% 12% 4	503
	11th to 20th	Day	13% 18% 30% 19% 12% 8%	528
	21st to end	Day	12% 15% 24% 24% 17% 8%	573
June	1st to 10th	Day	8% 16% 25% 23% 18% 10%	530
	11th to 20th	Day	9% 17% 33% 22% 13% 5%	530
	21st to end	Day	3 12% 30% 27% 19% 8%	530
July	1st to 10th	Day	3 9% 33% 24% 21% 9%	526
	11th to 20th	Day	1 9% 29% 30% 20% 11%	524
	21st to end	Day	3 8% 26% 30% 23% 11%	575
August	1st to 10th	Day	3 8% 29% 24% 24% 11%	527
	11th to 20th	Day	2 12% 26% 26% 21% 13%	517
	21st to end	Day	3 9% 26% 30% 23% 9%	583
September	1st to 10th	Day	3 8% 27% 29% 24% 8%	530
	11th to 20th	Day	7% 13% 23% 29% 23% 5%	530
	21st to end	Day	6% 12% 26% 30% 21% 5%	530
October	1st to 10th	Day	7% 14% 25% 26% 20% 8%	530
	11th to 20th	Day	9% 16% 19% 27% 23% 6%	530
	21st to end	Day	10% 16% 20% 28% 21% 5%	533
November	1st to 10th	Day	13% 12% 16% 28% 24% 6%	330
	11th to 20th	Day	12% 9% 24% 27% 20% 9%	330
	21st to end	Day	11% 15% 18% 29% 19% 7%	267
December	1st to 10th	Day	11% 11% 21% 25% 22% 10%	220
	11th to 20th	Day	14% 13% 22% 24% 19% 9%	220
	21st to end	Day	24% 10% 21% 28% 14% 2	242
January	1st to 10th	Night	12% 10% 22% 33% 19% 5%	840
	11th to 20th	Night	7% 10% 19% 41% 19% 3	840
	21st to end	Night	9% 6% 22% 40% 19% 4	924
February	1st to 10th	Night	12% 8% 19% 39% 19% 2	840
	11th to 20th	Night	8% 10% 20% 40% 17% 4	804
	21st to end	Night	10% 13% 18% 42% 15% 2	660
March	1st to 10th	Night	10% 13% 24% 35% 16% 2	800
	11th to 20th	Night	11% 13% 20% 31% 22% 2	800
	21st to end	Night	10% 16% 24% 31% 16% 2	880
April	1st to 10th	Night	8% 11% 24% 37% 19% 1	800
	11th to 20th	Night	12% 11% 20% 35% 19% 3	791
	21st to end	Night	8% 10% 22% 36% 22% 3	800
May	1st to 10th	Night	9% 10% 23% 35% 19% 2	672
	11th to 20th	Night	7% 4 19% 43% 25% 3	394
	21st to end	Night	7% 4 15% 41% 31% 2	433
June	1st to 10th	Night	5% 3 17% 44% 30% 3	400
	11th to 20th	Night	2 4 18% 47% 27% 2	400
	21st to end	Night	3 2 12% 51% 30% 3	400
July	1st to 10th	Night	1 1 11% 50% 35% 2	390
	11th to 20th	Night	1 2 10% 52% 36%	388
	21st to end	Night	3 1 6% 45% 40% 5%	494
August	1st to 10th	Night	4 1 5% 45% 41% 4	597
	11th to 20th	Night	2 2 15% 41% 36% 5%	783
	21st to end	Night	3 2 13% 45% 34% 3	880
September	1st to 10th	Night	2 2 14% 42% 35% 5%	800
	11th to 20th	Night	5% 4 11% 38% 37% 6%	800
	21st to end	Night	3 4 13% 42% 31% 8%	800
October	1st to 10th	Night	6% 5% 16% 40% 28% 6%	800
	11th to 20th	Night	6% 6% 12% 40% 31% 5%	800
	21st to end	Night	7% 7% 14% 36% 27% 9%	880
November	1st to 10th	Night	8% 8% 18% 33% 27% 6%	820
	11th to 20th	Night	7% 8% 20% 43% 19% 4	840
	21st to end	Night	8% 9% 17% 40% 23% 3	840
December	1st to 10th	Night	9% 9% 17% 42% 19% 3	840
	11th to 20th	Night	12% 11% 15% 40% 18% 4	840
	21st to end	Night	14% 12% 22% 37% 14% 1	924

Page generated at 2026-02-12 22:42:16. Version ac07

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