Little Piney Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Little Piney Observatory 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 5% 4 4 4 3 5% 7% 46%	131311
	Night	15% 6% 2 5% 3 3 3 3 5% 6% 49%	131787
Transparency	Day	36% 6% 11% 24% 18% 5%	134919
	Night	34% 6% 11% 23% 20% 6%	136256
Seeing	Day	16% 10% 23% 26% 20% 5%	17408
	Night	16% 8% 23% 33% 18% 2	27303

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	17% 9% 2 5% 3 3 3 3 4 5% 47%	5289
	11th to 20th	Day	9% 8% 2 5% 3 3 3 3 3 4 57%	5310
	21st to end	Day	20% 6% 2 5% 3 2 3 2 3 4 49%	5812
February	1st to 10th	Day	24% 8% 1 5% 3 2 2 2 3 4 45%	1890
	11th to 20th	Day	21% 7% 2 5% 3 3 3 3 4 5% 44%	1904
	21st to end	Day	19% 9% 3 6% 3 3 3 2 3 5% 43%	1849
March	1st to 10th	Day	21% 9% 2 5% 3 3 4 2 4 5% 41%	5046
	11th to 20th	Day	12% 5% 2 4 3 3 4 4 4 7% 52%	5090
	21st to end	Day	17% 8% 2 6% 4 4 3 3 5% 7% 42%	5583
April	1st to 10th	Day	19% 6% 2 6% 4 3 4 3 5% 6% 43%	2471
	11th to 20th	Day	21% 7% 2 5% 3 3 3 3 5% 6% 41%	2494
	21st to end	Day	23% 7% 2 6% 4 4 4 3 4 6% 37%	2520
May	1st to 10th	Day	21% 8% 3 6% 5% 4 4 3 5% 6% 35%	5746
	11th to 20th	Day	14% 7% 3 8% 5% 5% 4 4 5% 7% 38%	5941
	21st to end	Day	20% 7% 3 7% 4 4 4 4 5% 7% 34%	6434
June	1st to 10th	Day	11% 6% 2 5% 4 4 5% 5% 7% 9% 42%	2600
	11th to 20th	Day	8% 5% 2 5% 5% 5% 6% 5% 8% 10% 42%	2600
	21st to end	Day	5% 4 1 4 4 4 6% 5% 7% 9% 51%	2600
July	1st to 10th	Day	8% 4 2 5% 4 5% 5% 5% 7% 12% 41%	5900
	11th to 20th	Day	5% 4 1 4 4 4 4 4 6% 9% 55%	5900
	21st to end	Day	7% 5% 3 6% 5% 5% 6% 5% 7% 9% 43%	6422
August	1st to 10th	Day	4 3 1 4 3 3 4 4 5% 9% 60%	4234
	11th to 20th	Day	12% 5% 2 5% 4 4 4 3 7% 10% 45%	3989
	21st to end	Day	5% 3 1 4 4 4 5% 4 6% 8% 57%	4312
September	1st to 10th	Day	11% 5% 3 5% 3 4 5% 4 5% 7% 50%	2400
	11th to 20th	Day	12% 4 2 5% 4 4 5% 3 6% 8% 47%	2318
	21st to end	Day	10% 4 2 5% 4 3 4 3 5% 6% 54%	2125
October	1st to 10th	Day	9% 4 2 4 3 4 4 3 4 5% 59%	2000
	11th to 20th	Day	15% 4 2 4 2 2 3 2 4 5% 58%	2000
	21st to end	Day	22% 6% 2 4 2 3 3 3 3 4 49%	2200
November	1st to 10th	Day	15% 5% 2 4 3 2 3 2 4 5% 56%	2058
	11th to 20th	Day	14% 5% 1 4 3 3 3 3 4 5% 55%	2100
	21st to end	Day	21% 6% 2 4 2 3 3 3 3 5% 48%	1744
December	1st to 10th	Day	16% 8% 2 5% 2 3 2 2 4 4 51%	2690
	11th to 20th	Day	21% 7% 2 4 4 3 3 2 3 5% 45%	3153
	21st to end	Day	24% 11% 3 7% 3 3 3 2 4 5% 36%	4587
January	1st to 10th	Night	15% 7% 2 5% 3 3 4 3 5% 5% 47%	7634
	11th to 20th	Night	9% 5% 1 3 2 2 2 2 3 4 65%	7680
	21st to end	Night	24% 7% 2 4 2 2 3 2 3 4 45%	8402
February	1st to 10th	Night	21% 8% 2 4 3 3 3 2 4 5% 44%	2730
	11th to 20th	Night	19% 7% 2 5% 3 3 3 3 5% 6% 45%	2601
	21st to end	Night	19% 5% 2 5% 3 2 3 2 4 5% 50%	1975
March	1st to 10th	Night	22% 7% 2 6% 3 3 3 2 3 4 43%	5029
	11th to 20th	Night	14% 6% 2 5% 3 3 3 2 4 6% 51%	5090
	21st to end	Night	17% 6% 2 6% 3 4 3 3 4 7% 45%	5588
April	1st to 10th	Night	17% 6% 2 4 3 3 4 3 5% 6% 48%	2147
	11th to 20th	Night	16% 5% 2 5% 4 4 3 3 4 6% 47%	2075
	21st to end	Night	19% 7% 2 5% 4 4 3 3 5% 7% 42%	2100
May	1st to 10th	Night	21% 6% 2 5% 3 4 3 3 6% 7% 40%	4374
	11th to 20th	Night	16% 7% 3 7% 4 4 4 3 6% 8% 36%	4107
	21st to end	Night	19% 7% 2 6% 4 4 4 3 6% 7% 38%	4443
June	1st to 10th	Night	7% 4 1 4 4 4 4 4 6% 10% 52%	1800
	11th to 20th	Night	5% 4 1 4 3 3 3 4 7% 11% 55%	1800
	21st to end	Night	5% 4 1 4 3 3 3 4 6% 9% 59%	1800
July	1st to 10th	Night	7% 5% 2 6% 5% 5% 5% 4 7% 11% 42%	4078
	11th to 20th	Night	4 3 2 4 3 3 3 3 6% 9% 59%	4077
	21st to end	Night	5% 5% 2 6% 4 5% 5% 4 7% 10% 47%	4449
August	1st to 10th	Night	2 2 1 4 3 3 4 3 6% 9% 62%	2926
	11th to 20th	Night	5% 4 2 5% 4 4 4 4 6% 9% 53%	3061
	21st to end	Night	4 3 2 4 3 3 4 4 6% 8% 58%	3586
September	1st to 10th	Night	8% 5% 2 4 3 3 3 4 6% 7% 56%	2000
	11th to 20th	Night	9% 4 2 5% 4 4 5% 3 6% 8% 50%	2077
	21st to end	Night	9% 4 1 4 3 3 3 3 6% 6% 57%	2253
October	1st to 10th	Night	8% 3 1 3 2 2 3 3 6% 7% 60%	2400
	11th to 20th	Night	14% 3 1 4 3 3 2 2 3 5% 60%	2400
	21st to end	Night	20% 6% 2 4 3 2 2 2 3 4 52%	2640
November	1st to 10th	Night	14% 5% 2 5% 3 3 3 2 3 5% 56%	2460
	11th to 20th	Night	15% 4 1 3 3 2 2 3 4 5% 57%	2520
	21st to end	Night	20% 6% 2 3 2 3 3 2 3 6% 50%	2864
December	1st to 10th	Night	15% 6% 2 5% 3 3 3 2 3 5% 52%	4720
	11th to 20th	Night	22% 6% 2 5% 3 2 3 2 3 4 48%	5268
	21st to end	Night	26% 8% 2 6% 4 3 3 2 3 4 38%	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	41% 4 9% 26% 18% 2	5290
	11th to 20th	Day	32% 3 8% 23% 27% 7%	5310
	21st to end	Day	41% 3 5% 20% 24% 7%	5812
February	1st to 10th	Day	45% 3 11% 22% 16% 4	1890
	11th to 20th	Day	43% 5% 9% 21% 19% 3	1913
	21st to end	Day	45% 3 8% 15% 19% 9%	1849
March	1st to 10th	Day	44% 6% 7% 16% 14% 14%	5046
	11th to 20th	Day	31% 5% 8% 20% 23% 12%	5090
	21st to end	Day	42% 5% 9% 28% 15% 1	5585
April	1st to 10th	Day	42% 6% 9% 19% 21% 3	2471
	11th to 20th	Day	42% 6% 9% 20% 17% 6%	2494
	21st to end	Day	47% 6% 9% 20% 16% 2	2520
May	1st to 10th	Day	47% 8% 9% 19% 15% 1	5781
	11th to 20th	Day	43% 9% 12% 22% 13% 1	5945
	21st to end	Day	47% 9% 11% 16% 15% 2	6447
June	1st to 10th	Day	35% 10% 14% 26% 14% 1	2600
	11th to 20th	Day	34% 10% 16% 22% 17% 2	2600
	21st to end	Day	26% 9% 16% 28% 17% 4	2600
July	1st to 10th	Day	32% 8% 19% 28% 11% 2	5836
	11th to 20th	Day	25% 7% 15% 36% 15% 1	5831
	21st to end	Day	33% 9% 16% 30% 10% 1	6240
August	1st to 10th	Day	21% 7% 17% 31% 19% 5%	4220
	11th to 20th	Day	34% 7% 17% 29% 12% 1	4028
	21st to end	Day	25% 7% 15% 35% 15% 3	4311
September	1st to 10th	Day	32% 8% 12% 23% 18% 8%	2400
	11th to 20th	Day	32% 8% 12% 23% 21% 4	2318
	21st to end	Day	30% 7% 10% 20% 28% 6%	2125
October	1st to 10th	Day	17% 3 6% 13% 39% 22%	3260
	11th to 20th	Day	19% 3 5% 21% 36% 17%	3240
	21st to end	Day	33% 4 7% 29% 21% 5%	3538
November	1st to 10th	Day	32% 5% 9% 26% 21% 8%	2058
	11th to 20th	Day	32% 4 9% 24% 22% 9%	2100
	21st to end	Day	40% 4 8% 21% 23% 5%	1744
December	1st to 10th	Day	38% 4 7% 28% 21% 2	2690
	11th to 20th	Day	42% 4 8% 22% 21% 3	3150
	21st to end	Day	49% 6% 8% 21% 12% 3	4587
January	1st to 10th	Night	37% 5% 11% 29% 16% 2	7635
	11th to 20th	Night	24% 3 9% 20% 36% 9%	7680
	21st to end	Night	44% 3 8% 16% 24% 6%	8402
February	1st to 10th	Night	44% 4 8% 23% 17% 4	2730
	11th to 20th	Night	41% 4 9% 22% 19% 5%	2602
	21st to end	Night	38% 4 8% 20% 21% 10%	1975
March	1st to 10th	Night	44% 5% 7% 14% 17% 13%	5029
	11th to 20th	Night	34% 4 8% 23% 19% 12%	5090
	21st to end	Night	37% 6% 11% 26% 17% 3	5588
April	1st to 10th	Night	36% 6% 11% 22% 19% 7%	2147
	11th to 20th	Night	36% 6% 9% 22% 19% 8%	2075
	21st to end	Night	41% 7% 9% 22% 18% 2	2100
May	1st to 10th	Night	41% 9% 14% 21% 14% 2	4404
	11th to 20th	Night	43% 9% 13% 22% 11% 2	4108
	21st to end	Night	42% 10% 13% 18% 13% 4	4452
June	1st to 10th	Night	26% 9% 15% 29% 18% 3	1800
	11th to 20th	Night	22% 7% 16% 32% 21% 2	1800
	21st to end	Night	20% 6% 18% 27% 23% 6%	1800
July	1st to 10th	Night	34% 9% 19% 24% 14% 1	4035
	11th to 20th	Night	20% 7% 16% 39% 17% 1	4026
	21st to end	Night	29% 9% 17% 29% 15% 1	4320
August	1st to 10th	Night	18% 6% 18% 32% 24% 2	2916
	11th to 20th	Night	26% 7% 21% 29% 15% 2	3088
	21st to end	Night	22% 7% 14% 32% 23% 2	3586
September	1st to 10th	Night	25% 8% 10% 30% 18% 9%	2000
	11th to 20th	Night	30% 7% 13% 21% 22% 6%	2077
	21st to end	Night	26% 7% 11% 21% 29% 8%	2253
October	1st to 10th	Night	14% 4 9% 13% 31% 29%	3920
	11th to 20th	Night	18% 3 4 16% 39% 20%	3899
	21st to end	Night	31% 4 6% 24% 27% 9%	4252
November	1st to 10th	Night	31% 4 9% 23% 24% 9%	2460
	11th to 20th	Night	29% 4 8% 25% 25% 9%	2520
	21st to end	Night	37% 4 8% 21% 25% 5%	2864
December	1st to 10th	Night	36% 3 8% 31% 19% 3	4720
	11th to 20th	Night	42% 3 6% 20% 21% 8%	5270
	21st to end	Night	46% 6% 11% 22% 11% 4	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	27% 15% 32% 21% 5%	330
	11th to 20th	Day	24% 23% 34% 14% 4 1	330
	21st to end	Day	22% 21% 34% 17% 5%	363
February	1st to 10th	Day	29% 16% 34% 16% 4 1	330
	11th to 20th	Day	28% 22% 34% 14% 2	330
	21st to end	Day	32% 22% 31% 12% 3	273
March	1st to 10th	Day	26% 19% 35% 15% 5%	330
	11th to 20th	Day	28% 23% 35% 12% 2	330
	21st to end	Day	24% 21% 39% 11% 4	363
April	1st to 10th	Day	24% 17% 33% 19% 8%	491
	11th to 20th	Day	27% 15% 31% 20% 6% 1	532
	21st to end	Day	22% 17% 31% 20% 7% 1	540
May	1st to 10th	Day	20% 19% 29% 24% 8% 1	634
	11th to 20th	Day	17% 9% 26% 29% 16% 3	756
	21st to end	Day	13% 8% 26% 33% 15% 4	789
June	1st to 10th	Day	12% 6% 17% 31% 28% 7%	730
	11th to 20th	Day	9% 2 17% 35% 31% 6%	730
	21st to end	Day	4 3 20% 37% 28% 8%	730
July	1st to 10th	Day	7% 3 12% 33% 35% 10%	721
	11th to 20th	Day	6% 2 11% 31% 36% 14%	718
	21st to end	Day	6% 2 9% 30% 39% 13%	794
August	1st to 10th	Day	6% 1 12% 36% 35% 9%	726
	11th to 20th	Day	14% 2 10% 29% 36% 10%	611
	21st to end	Day	11% 1 7% 26% 40% 14%	583
September	1st to 10th	Day	10% 2 7% 31% 39% 10%	530
	11th to 20th	Day	9% 3 14% 31% 33% 11%	448
	21st to end	Day	13% 6% 19% 32% 23% 7%	330
October	1st to 10th	Day	6% 4 25% 37% 24% 4	330
	11th to 20th	Day	12% 14% 24% 32% 17% 1	330
	21st to end	Day	29% 14% 25% 22% 8% 1	363
November	1st to 10th	Day	18% 12% 29% 28% 12% 2	330
	11th to 20th	Day	16% 15% 35% 26% 6% 2	330
	21st to end	Day	26% 17% 22% 25% 8% 2	330
December	1st to 10th	Day	25% 15% 32% 19% 6% 2	330
	11th to 20th	Day	26% 15% 31% 22% 7%	330
	21st to end	Day	28% 18% 33% 17% 4	363
January	1st to 10th	Night	22% 12% 29% 32% 5%	1050
	11th to 20th	Night	20% 13% 34% 29% 4	1050
	21st to end	Night	21% 11% 33% 30% 4	1155
February	1st to 10th	Night	24% 12% 30% 30% 4	1050
	11th to 20th	Night	23% 15% 35% 24% 3	967
	21st to end	Night	22% 15% 35% 27% 1	591
March	1st to 10th	Night	23% 11% 30% 33% 3	630
	11th to 20th	Night	23% 11% 26% 34% 5%	630
	21st to end	Night	21% 11% 33% 29% 7%	693
April	1st to 10th	Night	19% 11% 34% 30% 7%	630
	11th to 20th	Night	17% 11% 32% 32% 8%	623
	21st to end	Night	20% 10% 29% 31% 10%	630
May	1st to 10th	Night	17% 7% 26% 40% 10%	630
	11th to 20th	Night	14% 7% 24% 32% 21% 1	609
	21st to end	Night	11% 4 21% 39% 22% 3	650
June	1st to 10th	Night	7% 4 11% 37% 39% 2	600
	11th to 20th	Night	5% 2 10% 44% 38% 2	600
	21st to end	Night	5% 1 11% 35% 44% 5%	600
July	1st to 10th	Night	6% 1 10% 32% 44% 8%	585
	11th to 20th	Night	4 1 7% 31% 46% 10%	582
	21st to end	Night	6% 1 4 32% 47% 10%	657
August	1st to 10th	Night	5% 1 7% 33% 48% 6%	597
	11th to 20th	Night	9% 2 8% 35% 40% 6%	594
	21st to end	Night	7% 2 6% 33% 45% 7%	660
September	1st to 10th	Night	9% 2 6% 36% 43% 4	600
	11th to 20th	Night	11% 3 11% 35% 37% 4	600
	21st to end	Night	11% 3 12% 37% 34% 4	653
October	1st to 10th	Night	10% 3 16% 39% 30% 4	800
	11th to 20th	Night	14% 7% 24% 38% 18%	800
	21st to end	Night	22% 9% 23% 31% 14% 2	880
November	1st to 10th	Night	15% 8% 24% 36% 16% 1	820
	11th to 20th	Night	16% 10% 26% 38% 10%	840
	21st to end	Night	21% 11% 26% 29% 13%	992
December	1st to 10th	Night	22% 8% 30% 34% 6%	1050
	11th to 20th	Night	24% 11% 24% 36% 5%	1050
	21st to end	Night	24% 14% 25% 32% 5%	1155

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

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