Boktuklo Trail Head
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Boktuklo Trail Head clear sky chart from 2005-11-06 to 2026-05-17.

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	14% 6% 2 6% 4 4 4 3 5% 6% 45%	132341
	Night	13% 6% 2 5% 3 3 3 3 4 6% 51%	130787
Transparency	Day	38% 5% 10% 23% 19% 6%	135953
	Night	34% 4 9% 22% 22% 8%	135239
Seeing	Day	19% 12% 26% 25% 15% 3	17314
	Night	18% 11% 24% 29% 17% 2	27229

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	13% 8% 5% 6% 3 3 3 2 4 6% 47%	5289
	11th to 20th	Day	5% 5% 3 5% 3 3 4 3 4 5% 60%	5310
	21st to end	Day	20% 8% 2 5% 3 3 3 2 3 4 46%	5812
February	1st to 10th	Day	22% 10% 3 6% 4 4 2 2 2 4 41%	1890
	11th to 20th	Day	19% 10% 2 6% 4 4 4 3 4 5% 40%	1953
	21st to end	Day	21% 8% 3 6% 3 3 3 2 4 5% 42%	1872
March	1st to 10th	Day	22% 8% 2 6% 3 3 3 3 3 5% 43%	5046
	11th to 20th	Day	11% 6% 2 6% 4 4 4 3 5% 6% 49%	5090
	21st to end	Day	18% 9% 3 6% 4 4 4 3 5% 6% 39%	5583
April	1st to 10th	Day	17% 8% 4 5% 5% 3 3 3 4 6% 42%	2364
	11th to 20th	Day	20% 6% 2 6% 4 5% 4 3 4 5% 41%	2494
	21st to end	Day	21% 9% 3 6% 5% 4 4 3 4 5% 36%	2520
May	1st to 10th	Day	22% 8% 2 6% 4 4 3 3 5% 6% 37%	5990
	11th to 20th	Day	15% 6% 2 8% 5% 4 5% 4 6% 6% 39%	5941
	21st to end	Day	20% 8% 3 8% 5% 4 4 3 5% 6% 34%	6434
June	1st to 10th	Day	11% 6% 2 6% 5% 5% 5% 4 6% 9% 42%	2600
	11th to 20th	Day	9% 7% 2 6% 6% 6% 5% 5% 6% 7% 42%	2600
	21st to end	Day	5% 5% 2 4 4 5% 5% 5% 7% 9% 50%	2600
July	1st to 10th	Day	9% 5% 2 8% 5% 5% 6% 4 7% 10% 37%	5900
	11th to 20th	Day	6% 3 1 5% 3 4 4 3 5% 8% 58%	5900
	21st to end	Day	8% 5% 2 6% 5% 5% 5% 5% 6% 9% 43%	6422
August	1st to 10th	Day	4 3 1 5% 4 4 5% 4 6% 8% 55%	4234
	11th to 20th	Day	9% 4 2 5% 4 4 5% 4 7% 10% 47%	4121
	21st to end	Day	6% 4 2 6% 4 5% 6% 4 7% 8% 48%	4312
September	1st to 10th	Day	11% 6% 2 6% 4 4 4 4 5% 6% 48%	2334
	11th to 20th	Day	10% 4 2 6% 5% 5% 4 5% 6% 7% 45%	2200
	21st to end	Day	10% 4 2 5% 4 4 5% 4 5% 6% 53%	2200
October	1st to 10th	Day	9% 5% 2 6% 3 2 4 3 5% 6% 56%	2017
	11th to 20th	Day	15% 4 2 4 3 3 2 2 3 3 59%	2000
	21st to end	Day	20% 7% 2 4 2 3 3 2 4 4 49%	2200
November	1st to 10th	Day	15% 6% 2 5% 3 3 2 2 4 6% 51%	2058
	11th to 20th	Day	13% 6% 2 4 3 2 3 2 4 6% 55%	2067
	21st to end	Day	19% 6% 2 4 3 4 3 2 4 5% 48%	1890
December	1st to 10th	Day	19% 7% 2 4 2 3 3 2 3 4 50%	3030
	11th to 20th	Day	22% 8% 2 5% 3 3 3 2 4 5% 43%	3481
	21st to end	Day	23% 11% 3 5% 3 3 3 3 4 5% 39%	4587
January	1st to 10th	Night	13% 7% 3 6% 4 3 3 3 4 6% 49%	7634
	11th to 20th	Night	7% 5% 2 4 2 2 2 2 3 5% 67%	7680
	21st to end	Night	22% 8% 3 6% 3 3 2 2 3 4 44%	8402
February	1st to 10th	Night	19% 9% 3 5% 3 3 3 3 4 4 43%	2730
	11th to 20th	Night	19% 9% 3 6% 4 3 3 3 4 5% 43%	2572
	21st to end	Night	17% 7% 2 6% 2 3 3 3 4 5% 49%	1934
March	1st to 10th	Night	22% 9% 3 5% 3 3 2 2 3 4 43%	5029
	11th to 20th	Night	12% 7% 2 5% 4 3 3 3 4 5% 53%	5090
	21st to end	Night	16% 7% 2 6% 4 3 3 3 5% 7% 43%	5588
April	1st to 10th	Night	15% 7% 3 5% 4 3 3 3 4 6% 46%	2254
	11th to 20th	Night	16% 7% 2 6% 4 3 3 3 4 6% 47%	2075
	21st to end	Night	15% 8% 2 6% 4 3 3 3 5% 7% 44%	2097
May	1st to 10th	Night	22% 8% 2 4 4 3 3 4 5% 7% 38%	4143
	11th to 20th	Night	15% 6% 2 6% 3 4 5% 4 6% 7% 42%	4107
	21st to end	Night	17% 7% 2 6% 3 4 4 3 6% 7% 41%	4443
June	1st to 10th	Night	7% 5% 2 5% 3 3 3 4 6% 8% 54%	1800
	11th to 20th	Night	7% 6% 2 4 4 2 3 4 5% 9% 55%	1800
	21st to end	Night	5% 4 1 3 2 3 3 3 6% 9% 63%	1800
July	1st to 10th	Night	8% 4 2 6% 4 5% 5% 5% 8% 11% 44%	4078
	11th to 20th	Night	6% 3 1 3 3 2 3 2 5% 7% 66%	4077
	21st to end	Night	7% 5% 2 5% 3 4 4 4 6% 8% 52%	4449
August	1st to 10th	Night	3 2 1 3 2 4 3 3 5% 7% 68%	2926
	11th to 20th	Night	5% 3 2 4 3 3 3 3 6% 9% 60%	2933
	21st to end	Night	4 3 1 4 4 3 3 3 5% 10% 60%	3586
September	1st to 10th	Night	6% 6% 2 4 3 3 3 4 6% 7% 57%	2060
	11th to 20th	Night	9% 4 2 5% 4 4 4 4 6% 8% 50%	2200
	21st to end	Night	9% 4 1 4 3 3 3 3 4 5% 59%	2200
October	1st to 10th	Night	8% 4 2 4 3 3 3 3 5% 7% 60%	2361
	11th to 20th	Night	13% 4 2 4 2 2 3 2 3 5% 60%	2400
	21st to end	Night	18% 7% 2 5% 3 3 2 2 3 3 53%	2640
November	1st to 10th	Night	12% 6% 2 4 3 3 3 3 3 5% 57%	2460
	11th to 20th	Night	11% 6% 2 4 3 3 3 3 4 5% 57%	2550
	21st to end	Night	16% 8% 3 5% 3 2 2 2 4 5% 49%	2730
December	1st to 10th	Night	14% 9% 3 6% 3 3 3 2 4 5% 49%	4380
	11th to 20th	Night	21% 6% 3 6% 4 3 2 2 3 3 48%	4946
	21st to end	Night	19% 11% 4 6% 4 3 3 2 3 5% 42%	6633

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% 2 9% 25% 20% 3	5290
	11th to 20th	Day	27% 2 9% 22% 34% 6%	5310
	21st to end	Day	44% 2 4 18% 22% 10%	5812
February	1st to 10th	Day	49% 2 8% 16% 20% 4	1890
	11th to 20th	Day	47% 4 6% 19% 19% 5%	1962
	21st to end	Day	45% 3 6% 15% 22% 9%	1872
March	1st to 10th	Day	46% 2 6% 13% 17% 15%	5046
	11th to 20th	Day	36% 4 8% 15% 19% 18%	5090
	21st to end	Day	46% 5% 9% 23% 16% 1	5585
April	1st to 10th	Day	44% 4 9% 18% 19% 6%	2364
	11th to 20th	Day	46% 4 7% 19% 18% 5%	2494
	21st to end	Day	50% 5% 7% 19% 16% 3	2520
May	1st to 10th	Day	48% 5% 9% 23% 14% 1	6028
	11th to 20th	Day	43% 7% 12% 19% 17% 2	5945
	21st to end	Day	50% 6% 11% 17% 14% 3	6447
June	1st to 10th	Day	37% 8% 13% 26% 14% 2	2600
	11th to 20th	Day	39% 8% 12% 22% 17% 2	2600
	21st to end	Day	29% 7% 15% 28% 19% 2	2600
July	1st to 10th	Day	39% 8% 19% 25% 8% 1	5836
	11th to 20th	Day	24% 5% 13% 38% 18% 1	5831
	21st to end	Day	34% 8% 13% 33% 11% 1	6240
August	1st to 10th	Day	24% 6% 13% 28% 24% 4	4220
	11th to 20th	Day	32% 6% 18% 32% 11% 1	4160
	21st to end	Day	31% 7% 14% 34% 12% 2	4311
September	1st to 10th	Day	35% 5% 10% 22% 18% 9%	2334
	11th to 20th	Day	34% 7% 11% 23% 17% 6%	2200
	21st to end	Day	32% 6% 9% 18% 27% 9%	2200
October	1st to 10th	Day	18% 2 6% 11% 36% 27%	3277
	11th to 20th	Day	22% 1 5% 18% 36% 19%	3240
	21st to end	Day	33% 3 5% 28% 23% 7%	3538
November	1st to 10th	Day	36% 3 7% 23% 25% 7%	2058
	11th to 20th	Day	32% 4 7% 22% 25% 10%	2067
	21st to end	Day	40% 3 6% 20% 26% 7%	1890
December	1st to 10th	Day	39% 4 6% 27% 20% 3	3030
	11th to 20th	Day	45% 2 5% 19% 25% 5%	3479
	21st to end	Day	49% 3 6% 20% 18% 4	4587
January	1st to 10th	Night	37% 3 8% 26% 23% 3	7635
	11th to 20th	Night	23% 3 6% 18% 37% 13%	7680
	21st to end	Night	46% 3 5% 14% 23% 9%	8402
February	1st to 10th	Night	44% 4 8% 19% 18% 7%	2730
	11th to 20th	Night	45% 3 6% 20% 20% 6%	2573
	21st to end	Night	38% 4 8% 17% 22% 11%	1934
March	1st to 10th	Night	46% 3 5% 13% 19% 14%	5029
	11th to 20th	Night	34% 4 6% 20% 18% 18%	5090
	21st to end	Night	41% 5% 10% 20% 21% 3	5588
April	1st to 10th	Night	40% 4 9% 19% 19% 10%	2254
	11th to 20th	Night	39% 4 8% 20% 20% 8%	2075
	21st to end	Night	40% 6% 9% 22% 21% 2	2097
May	1st to 10th	Night	46% 6% 11% 22% 12% 4	4170
	11th to 20th	Night	39% 7% 14% 22% 16% 2	4108
	21st to end	Night	41% 7% 15% 19% 13% 6%	4452
June	1st to 10th	Night	27% 7% 16% 29% 19% 3	1800
	11th to 20th	Night	26% 6% 11% 31% 22% 3	1800
	21st to end	Night	19% 5% 15% 29% 27% 4	1800
July	1st to 10th	Night	32% 7% 22% 25% 12% 1	4035
	11th to 20th	Night	19% 5% 13% 41% 21% 1	4026
	21st to end	Night	29% 7% 15% 33% 16% 1	4320
August	1st to 10th	Night	15% 5% 14% 30% 30% 6%	2916
	11th to 20th	Night	21% 5% 20% 36% 17% 2	2960
	21st to end	Night	22% 6% 15% 35% 20% 2	3586
September	1st to 10th	Night	27% 5% 11% 24% 23% 10%	2060
	11th to 20th	Night	31% 6% 12% 22% 20% 8%	2200
	21st to end	Night	27% 4 7% 22% 29% 9%	2200
October	1st to 10th	Night	15% 3 7% 13% 28% 35%	3868
	11th to 20th	Night	20% 2 4 15% 39% 19%	3899
	21st to end	Night	31% 3 5% 26% 25% 10%	4252
November	1st to 10th	Night	32% 3 7% 21% 26% 11%	2460
	11th to 20th	Night	30% 3 8% 21% 25% 12%	2550
	21st to end	Night	39% 3 6% 18% 27% 7%	2730
December	1st to 10th	Night	39% 3 7% 24% 23% 5%	4380
	11th to 20th	Night	44% 3 4 17% 22% 11%	4947
	21st to end	Night	46% 3 9% 18% 20% 5%	6633

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	29% 20% 35% 11% 5%	330
	11th to 20th	Day	26% 26% 34% 11% 3	330
	21st to end	Day	28% 26% 31% 13% 3	363
February	1st to 10th	Day	34% 20% 32% 10% 4	330
	11th to 20th	Day	37% 27% 27% 7% 1	330
	21st to end	Day	36% 27% 25% 10% 2	273
March	1st to 10th	Day	35% 22% 29% 13% 1	330
	11th to 20th	Day	40% 23% 26% 9% 2	330
	21st to end	Day	28% 23% 37% 10% 2	363
April	1st to 10th	Day	30% 19% 32% 13% 5%	384
	11th to 20th	Day	35% 16% 30% 12% 6%	532
	21st to end	Day	29% 20% 28% 17% 5% 1	540
May	1st to 10th	Day	23% 17% 36% 20% 3 1	751
	11th to 20th	Day	20% 13% 34% 24% 8% 2	756
	21st to end	Day	16% 11% 36% 20% 15% 2	789
June	1st to 10th	Day	13% 9% 24% 31% 20% 5%	730
	11th to 20th	Day	11% 5% 28% 35% 17% 4	730
	21st to end	Day	5% 5% 25% 37% 20% 8%	730
July	1st to 10th	Day	9% 3 17% 36% 28% 7%	721
	11th to 20th	Day	5% 2 17% 36% 32% 9%	718
	21st to end	Day	6% 3 14% 35% 33% 10%	794
August	1st to 10th	Day	6% 3 14% 42% 31% 5%	726
	11th to 20th	Day	11% 3 14% 37% 29% 7%	691
	21st to end	Day	10% 2 9% 31% 37% 11%	583
September	1st to 10th	Day	9% 2 11% 38% 32% 8%	464
	11th to 20th	Day	5% 4 23% 38% 27% 5%	330
	21st to end	Day	17% 7% 21% 31% 20% 5%	330
October	1st to 10th	Day	6% 6% 35% 30% 20% 2	330
	11th to 20th	Day	16% 13% 36% 28% 6% 1	330
	21st to end	Day	30% 16% 30% 18% 6% 1	363
November	1st to 10th	Day	19% 19% 32% 22% 6% 1	330
	11th to 20th	Day	21% 18% 38% 18% 5% 1	330
	21st to end	Day	29% 21% 29% 15% 5%	330
December	1st to 10th	Day	28% 22% 31% 15% 3 1	330
	11th to 20th	Day	31% 23% 31% 10% 5%	330
	21st to end	Day	29% 21% 35% 11% 3 1	363
January	1st to 10th	Night	22% 16% 31% 26% 5%	1050
	11th to 20th	Night	23% 19% 29% 24% 5% 1	1050
	21st to end	Night	22% 16% 31% 27% 4	1155
February	1st to 10th	Night	26% 17% 29% 22% 5%	1050
	11th to 20th	Night	28% 20% 28% 21% 2	938
	21st to end	Night	28% 18% 29% 21% 4	550
March	1st to 10th	Night	27% 15% 26% 28% 4	630
	11th to 20th	Night	24% 15% 28% 28% 4	630
	21st to end	Night	21% 19% 32% 22% 5%	693
April	1st to 10th	Night	20% 18% 30% 26% 6%	630
	11th to 20th	Night	22% 17% 27% 26% 8%	623
	21st to end	Night	20% 16% 31% 22% 10% 1	630
May	1st to 10th	Night	16% 10% 31% 34% 9%	630
	11th to 20th	Night	15% 9% 30% 29% 16% 1	609
	21st to end	Night	15% 6% 28% 28% 20% 2	650
June	1st to 10th	Night	8% 5% 17% 35% 32% 3	600
	11th to 20th	Night	9% 3 21% 37% 29% 1	600
	21st to end	Night	5% 2 18% 34% 36% 6%	600
July	1st to 10th	Night	5% 2 10% 31% 46% 6%	585
	11th to 20th	Night	5% 1 10% 33% 45% 6%	582
	21st to end	Night	5% 2 8% 33% 45% 7%	657
August	1st to 10th	Night	3 1 9% 37% 45% 5%	597
	11th to 20th	Night	8% 2 7% 37% 39% 7%	594
	21st to end	Night	7% 1 10% 36% 39% 7%	660
September	1st to 10th	Night	7% 4 10% 37% 37% 5%	600
	11th to 20th	Night	12% 2 10% 34% 36% 5%	600
	21st to end	Night	11% 3 17% 33% 33% 4	600
October	1st to 10th	Night	9% 4 19% 38% 28% 3	761
	11th to 20th	Night	15% 9% 27% 31% 16% 1	800
	21st to end	Night	22% 12% 24% 27% 13% 2	880
November	1st to 10th	Night	16% 10% 29% 33% 12% 1	820
	11th to 20th	Night	16% 13% 28% 31% 11%	870
	21st to end	Night	25% 16% 26% 24% 9%	1050
December	1st to 10th	Night	22% 13% 28% 31% 6%	1050
	11th to 20th	Night	27% 14% 26% 27% 5%	1050
	21st to end	Night	25% 16% 28% 25% 7%	1155

Page generated at 2026-05-14 00:58:59. Version ac07

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