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 2024-11-30.

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 5% 3 3 4 3 5% 6% 62%	105380
	Night	3 6% 2 5% 4 3 4 3 5% 7% 58%	102917
Transparency	Day	21% 5% 8% 19% 25% 21%	105125
	Night	24% 7% 10% 21% 23% 16%	102762
Seeing	Day	10% 15% 26% 26% 17% 6%	15088
	Night	7% 8% 17% 39% 25% 4	24404

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 11% 3 9% 6% 5% 6% 5% 8% 8% 37%	2539
	11th to 20th	Day	7% 10% 4 9% 6% 6% 6% 5% 5% 7% 36%	2600
	21st to end	Day	8% 11% 4 9% 6% 6% 6% 5% 6% 7% 32%	3146
February	1st to 10th	Day	4 8% 3 6% 5% 5% 4 4 6% 6% 49%	1710
	11th to 20th	Day	3 7% 3 6% 5% 5% 6% 3 6% 8% 48%	1818
	21st to end	Day	1 7% 2 6% 5% 4 5% 5% 7% 9% 49%	1570
March	1st to 10th	Day	3 13% 6% 13% 7% 6% 5% 4 6% 7% 29%	3138
	11th to 20th	Day	3 7% 2 5% 3 2 4 3 5% 7% 60%	3459
	21st to end	Day	3 12% 4 8% 4 4 5% 4 6% 8% 43%	4058
April	1st to 10th	Day	4 7% 3 7% 6% 4 4 5% 7% 8% 45%	2280
	11th to 20th	Day	3 6% 2 6% 4 4 4 4 5% 7% 54%	2249
	21st to end	Day	5% 7% 2 5% 4 4 4 3 4 7% 56%	2280
May	1st to 10th	Day	4 4 2 5% 3 3 3 3 4 5% 66%	4002
	11th to 20th	Day	3 3 1 3 3 2 3 3 3 5% 72%	4377
	21st to end	Day	3 4 1 4 3 3 3 3 5% 6% 64%	4813
June	1st to 10th	Day	4 3 2 4 5% 4 3 3 6% 8% 59%	2660
	11th to 20th	Day	2 2 1 2 2 2 2 2 4 5% 75%	2660
	21st to end	Day	2 2 1 3 2 2 2 2 4 4 76%	2660
July	1st to 10th	Day	1 1 1 1 2 1 2 2 89%	4420
	11th to 20th	Day	2 2 1 3 2 2 2 2 3 4 77%	4420
	21st to end	Day	1 1 1 2 1 2 2 2 3 4 80%	4687
August	1st to 10th	Day	2 2 1 3 2 2 3 2 4 5% 74%	4091
	11th to 20th	Day	1 1 1 1 1 1 1 2 3 87%	3733
	21st to end	Day	1 1 1 1 1 1 1 1 2 2 87%	4180
September	1st to 10th	Day	2 1 1 1 1 2 1 3 4 83%	2280
	11th to 20th	Day	3 2 1 2 2 2 3 3 3 5% 74%	2263
	21st to end	Day	4 2 1 3 2 2 2 2 3 7% 74%	2090
October	1st to 10th	Day	2 3 1 3 2 2 2 2 4 7% 71%	3185
	11th to 20th	Day	4 4 1 3 2 2 2 2 3 6% 70%	3161
	21st to end	Day	2 3 1 4 3 3 4 4 5% 7% 64%	3365
November	1st to 10th	Day	5% 5% 2 4 5% 4 4 3 5% 7% 57%	1764
	11th to 20th	Day	3 5% 2 4 4 4 5% 5% 7% 10% 51%	1800
	21st to end	Day	2 7% 2 5% 3 4 4 4 6% 9% 53%	1680
December	1st to 10th	Day	6% 6% 2 7% 4 5% 4 4 8% 9% 45%	1520
	11th to 20th	Day	10% 8% 3 9% 6% 7% 6% 5% 7% 9% 30%	1928
	21st to end	Day	3 7% 3 9% 6% 5% 7% 5% 7% 12% 36%	2794
January	1st to 10th	Night	3 7% 3 8% 6% 6% 7% 5% 8% 9% 38%	4406
	11th to 20th	Night	6% 13% 4 9% 6% 5% 6% 5% 6% 8% 32%	4358
	21st to end	Night	8% 14% 3 9% 6% 5% 6% 4 7% 7% 32%	4521
February	1st to 10th	Night	3 7% 3 6% 5% 4 4 4 6% 9% 50%	2470
	11th to 20th	Night	2 7% 2 6% 4 5% 4 5% 7% 10% 48%	2248
	21st to end	Night	2 7% 2 6% 4 5% 4 4 6% 9% 50%	1884
March	1st to 10th	Night	3 15% 7% 8% 5% 4 5% 4 6% 8% 35%	3736
	11th to 20th	Night	2 8% 2 5% 4 4 4 3 6% 6% 57%	3505
	21st to end	Night	4 13% 3 9% 6% 5% 5% 5% 6% 8% 35%	3595
April	1st to 10th	Night	2 6% 2 5% 5% 4 5% 4 6% 10% 49%	1900
	11th to 20th	Night	3 6% 1 5% 4 3 5% 3 6% 8% 56%	1879
	21st to end	Night	4 4 2 5% 3 3 3 3 5% 7% 60%	1900
May	1st to 10th	Night	3 6% 2 6% 3 3 3 3 3 5% 64%	2968
	11th to 20th	Night	3 3 1 3 2 2 3 2 4 5% 72%	2516
	21st to end	Night	3 3 1 3 2 3 3 3 5% 6% 66%	2762
June	1st to 10th	Night	4 4 2 4 3 3 3 4 6% 7% 60%	1520
	11th to 20th	Night	2 2 1 3 2 3 3 2 4 4 76%	1520
	21st to end	Night	2 2 1 2 3 3 2 2 3 3 77%	1520
July	1st to 10th	Night	1 1 1 1 1 1 1 2 2 89%	2540
	11th to 20th	Night	2 3 1 2 2 1 2 2 3 4 78%	2540
	21st to end	Night	2 2 1 2 2 1 1 2 2 3 82%	2850
August	1st to 10th	Night	3 2 1 3 2 2 2 2 4 5% 73%	2848
	11th to 20th	Night	1 1 1 1 1 1 1 2 3 86%	3117
	21st to end	Night	2 2 2 1 1 1 1 2 3 86%	3498
September	1st to 10th	Night	2 1 2 1 1 2 1 2 4 83%	1900
	11th to 20th	Night	3 3 1 3 2 2 2 1 3 5% 75%	1916
	21st to end	Night	2 3 1 2 2 2 3 2 3 5% 76%	2090
October	1st to 10th	Night	2 2 1 2 2 2 3 2 3 4 76%	3790
	11th to 20th	Night	2 2 1 3 2 2 2 2 3 5% 75%	3777
	21st to end	Night	5% 4 1 3 2 4 4 3 4 8% 62%	4200
November	1st to 10th	Night	4 6% 2 5% 3 3 4 4 6% 8% 56%	2535
	11th to 20th	Night	2 4 2 5% 4 4 4 4 7% 9% 55%	2600
	21st to end	Night	2 5% 2 6% 4 4 4 4 6% 8% 55%	2710
December	1st to 10th	Night	5% 7% 2 5% 5% 4 4 4 8% 9% 48%	2660
	11th to 20th	Night	11% 8% 3 7% 6% 5% 5% 5% 8% 11% 31%	3276
	21st to end	Night	5% 9% 4 9% 6% 7% 7% 5% 7% 9% 32%	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	36% 12% 14% 26% 10% 1	2539
	11th to 20th	Day	40% 11% 13% 23% 9% 3	2600
	21st to end	Day	47% 10% 10% 22% 10% 1	3146
February	1st to 10th	Day	34% 5% 13% 25% 18% 5%	1710
	11th to 20th	Day	32% 5% 14% 27% 19% 3	1828
	21st to end	Day	28% 8% 16% 27% 17% 4	1570
March	1st to 10th	Day	47% 9% 12% 18% 12% 1	3138
	11th to 20th	Day	22% 6% 13% 34% 23% 2	3459
	21st to end	Day	33% 10% 16% 24% 15% 2	4058
April	1st to 10th	Day	32% 8% 15% 25% 16% 4	2280
	11th to 20th	Day	27% 6% 12% 29% 21% 5%	2252
	21st to end	Day	27% 6% 12% 29% 23% 3	2280
May	1st to 10th	Day	19% 6% 6% 29% 33% 6%	4002
	11th to 20th	Day	15% 4 6% 19% 40% 15%	4380
	21st to end	Day	20% 6% 7% 30% 33% 4	4814
June	1st to 10th	Day	23% 5% 8% 24% 30% 10%	2660
	11th to 20th	Day	13% 3 5% 21% 37% 21%	2660
	21st to end	Day	11% 3 3 13% 34% 35%	2660
July	1st to 10th	Day	5% 2 2 5% 14% 72%	4351
	11th to 20th	Day	11% 2 4 6% 18% 60%	4345
	21st to end	Day	8% 2 3 6% 27% 54%	4539
August	1st to 10th	Day	13% 2 4 6% 22% 53%	4076
	11th to 20th	Day	6% 1 1 6% 31% 54%	3769
	21st to end	Day	7% 1 2 8% 43% 39%	4179
September	1st to 10th	Day	8% 2 2 10% 29% 50%	2280
	11th to 20th	Day	14% 3 5% 18% 36% 25%	2263
	21st to end	Day	13% 3 5% 19% 36% 25%	2090
October	1st to 10th	Day	14% 2 5% 12% 36% 30%	3185
	11th to 20th	Day	17% 3 6% 23% 39% 13%	3161
	21st to end	Day	18% 5% 8% 29% 29% 12%	3365
November	1st to 10th	Day	26% 6% 11% 23% 24% 9%	1764
	11th to 20th	Day	25% 8% 15% 27% 22% 4	1800
	21st to end	Day	26% 6% 12% 27% 24% 6%	1680
December	1st to 10th	Day	32% 8% 11% 26% 18% 4	1520
	11th to 20th	Day	46% 10% 9% 22% 12% 2	1928
	21st to end	Day	36% 11% 16% 24% 12% 1	2794
January	1st to 10th	Night	33% 12% 20% 25% 10% 1	4406
	11th to 20th	Night	39% 15% 15% 17% 10% 4	4358
	21st to end	Night	47% 8% 12% 20% 11% 2	4521
February	1st to 10th	Night	30% 8% 12% 27% 19% 4	2470
	11th to 20th	Night	28% 6% 13% 32% 19% 2	2249
	21st to end	Night	29% 9% 15% 28% 16% 4	1884
March	1st to 10th	Night	39% 12% 13% 22% 12% 2	3736
	11th to 20th	Night	23% 9% 11% 36% 19% 2	3505
	21st to end	Night	39% 12% 18% 20% 10% 1	3595
April	1st to 10th	Night	28% 9% 16% 29% 15% 4	1900
	11th to 20th	Night	25% 7% 17% 29% 17% 5%	1879
	21st to end	Night	22% 7% 16% 34% 18% 4	1900
May	1st to 10th	Night	20% 7% 9% 30% 30% 5%	2968
	11th to 20th	Night	15% 4 10% 22% 37% 13%	2516
	21st to end	Night	16% 7% 10% 39% 25% 4	2762
June	1st to 10th	Night	22% 5% 12% 24% 27% 8%	1520
	11th to 20th	Night	13% 3 9% 22% 35% 19%	1520
	21st to end	Night	14% 2 4 16% 32% 32%	1520
July	1st to 10th	Night	4 1 2 5% 16% 71%	2500
	11th to 20th	Night	12% 1 2 7% 17% 60%	2492
	21st to end	Night	9% 2 3 7% 30% 50%	2761
August	1st to 10th	Night	14% 3 3 7% 28% 45%	2839
	11th to 20th	Night	6% 2 1 6% 35% 49%	3147
	21st to end	Night	8% 2 2 10% 39% 39%	3498
September	1st to 10th	Night	8% 2 3 6% 33% 48%	1900
	11th to 20th	Night	14% 3 4 20% 36% 24%	1916
	21st to end	Night	13% 2 4 20% 35% 26%	2090
October	1st to 10th	Night	13% 2 5% 13% 35% 32%	3790
	11th to 20th	Night	14% 3 5% 22% 45% 11%	3777
	21st to end	Night	22% 3 7% 29% 28% 11%	4200
November	1st to 10th	Night	25% 7% 12% 25% 21% 10%	2535
	11th to 20th	Night	24% 7% 14% 28% 24% 4	2600
	21st to end	Night	26% 7% 11% 26% 23% 7%	2710
December	1st to 10th	Night	30% 9% 12% 24% 20% 4	2660
	11th to 20th	Night	40% 11% 12% 20% 16% 2	3276
	21st to end	Night	40% 12% 15% 19% 12% 2	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	24% 13% 26% 21% 13% 3	180
	11th to 20th	Day	16% 17% 24% 24% 14% 4	214
	21st to end	Day	12% 13% 31% 23% 18% 3	407
February	1st to 10th	Day	16% 16% 26% 25% 13% 3	370
	11th to 20th	Day	15% 17% 26% 29% 12% 1	441
	21st to end	Day	14% 17% 26% 33% 10% 1	382
March	1st to 10th	Day	20% 23% 26% 20% 9% 2	460
	11th to 20th	Day	22% 17% 25% 19% 15% 2	460
	21st to end	Day	17% 25% 29% 20% 9%	506
April	1st to 10th	Day	15% 23% 27% 23% 9% 2	460
	11th to 20th	Day	17% 23% 24% 22% 12% 2	452
	21st to end	Day	15% 20% 23% 24% 15% 3	460
May	1st to 10th	Day	14% 23% 26% 23% 11% 3	463
	11th to 20th	Day	13% 18% 31% 18% 12% 8%	488
	21st to end	Day	13% 15% 24% 24% 16% 8%	529
June	1st to 10th	Day	8% 17% 25% 23% 17% 9%	490
	11th to 20th	Day	9% 18% 33% 23% 13% 5%	490
	21st to end	Day	2 13% 30% 28% 19% 8%	490
July	1st to 10th	Day	3 9% 34% 24% 22% 9%	486
	11th to 20th	Day	1 10% 30% 29% 20% 11%	484
	21st to end	Day	2 8% 26% 31% 22% 10%	531
August	1st to 10th	Day	3 8% 29% 24% 23% 11%	487
	11th to 20th	Day	2 13% 26% 27% 21% 11%	477
	21st to end	Day	3 10% 27% 30% 23% 7%	539
September	1st to 10th	Day	4 8% 27% 30% 24% 8%	490
	11th to 20th	Day	7% 14% 24% 29% 23% 4	490
	21st to end	Day	6% 13% 27% 29% 21% 4	490
October	1st to 10th	Day	7% 13% 26% 26% 20% 8%	490
	11th to 20th	Day	9% 16% 19% 28% 23% 5%	490
	21st to end	Day	9% 17% 21% 29% 20% 5%	492
November	1st to 10th	Day	13% 13% 17% 29% 23% 6%	300
	11th to 20th	Day	9% 10% 23% 27% 21% 9%	300
	21st to end	Day	12% 16% 19% 29% 16% 7%	242
December	1st to 10th	Day	13% 13% 21% 26% 17% 9%	180
	11th to 20th	Day	12% 13% 26% 25% 18% 7%	180
	21st to end	Day	19% 11% 21% 30% 17% 3	198
January	1st to 10th	Night	11% 9% 22% 33% 21% 5%	760
	11th to 20th	Night	8% 11% 18% 41% 19% 3	760
	21st to end	Night	10% 6% 22% 39% 19% 4	836
February	1st to 10th	Night	10% 9% 20% 38% 21% 2	760
	11th to 20th	Night	8% 10% 20% 39% 18% 4	744
	21st to end	Night	10% 14% 18% 41% 15% 2	628
March	1st to 10th	Night	10% 13% 24% 35% 16% 3	760
	11th to 20th	Night	11% 12% 19% 32% 23% 3	760
	21st to end	Night	10% 16% 25% 32% 16% 2	836
April	1st to 10th	Night	8% 11% 24% 37% 19% 1	760
	11th to 20th	Night	12% 12% 19% 35% 19% 3	751
	21st to end	Night	8% 10% 22% 35% 22% 3	760
May	1st to 10th	Night	10% 11% 23% 35% 19% 2	639
	11th to 20th	Night	7% 4 18% 42% 26% 3	374
	21st to end	Night	8% 4 15% 40% 31% 2	411
June	1st to 10th	Night	5% 3 18% 42% 30% 3	380
	11th to 20th	Night	2 4 18% 46% 28% 2	380
	21st to end	Night	3 2 12% 50% 30% 3	380
July	1st to 10th	Night	1 1 11% 49% 36% 2	370
	11th to 20th	Night	1 2 10% 52% 35%	368
	21st to end	Night	3 1 6% 45% 41% 5%	469
August	1st to 10th	Night	4 1 5% 45% 40% 5%	567
	11th to 20th	Night	2 3 15% 40% 36% 4	743
	21st to end	Night	3 2 13% 46% 33% 3	836
September	1st to 10th	Night	2 2 14% 41% 36% 5%	760
	11th to 20th	Night	4 4 11% 38% 36% 6%	760
	21st to end	Night	3 4 12% 41% 30% 8%	760
October	1st to 10th	Night	6% 5% 15% 40% 28% 6%	760
	11th to 20th	Night	6% 6% 12% 40% 32% 5%	760
	21st to end	Night	7% 7% 14% 36% 27% 9%	836
November	1st to 10th	Night	8% 8% 18% 33% 27% 6%	780
	11th to 20th	Night	6% 8% 20% 42% 20% 4	800
	21st to end	Night	8% 9% 17% 38% 25% 3	800
December	1st to 10th	Night	10% 10% 17% 41% 17% 4	760
	11th to 20th	Night	11% 11% 16% 40% 18% 4	760
	21st to end	Night	13% 11% 21% 39% 15% 1	836

Page generated at 2024-11-27 14:30:52. Version ac07

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