Lake Somerville State Park - Birch Creek Unit
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lake Somerville State Park - Birch Creek Unit clear sky chart from 2005-11-06 to 2024-11-11.

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	11% 6% 2 6% 4 4 4 4 6% 8% 44%	101107
	Night	12% 6% 2 5% 4 3 4 3 5% 7% 49%	98142
Transparency	Day	37% 5% 11% 21% 18% 8%	104850
	Night	34% 5% 11% 21% 19% 10%	102513
Seeing	Day	12% 7% 19% 27% 25% 10%	14893
	Night	13% 7% 25% 35% 17% 2	24760

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	15% 10% 2 4 3 3 3 3 5% 6% 45%	2847
	11th to 20th	Day	16% 6% 2 4 2 2 3 1 4 7% 52%	2850
	21st to end	Day	22% 10% 3 7% 4 2 2 2 4 7% 38%	3135
February	1st to 10th	Day	20% 10% 3 5% 4 3 3 3 4 5% 40%	1895
	11th to 20th	Day	19% 9% 2 6% 3 4 3 2 4 5% 43%	1849
	21st to end	Day	17% 8% 2 7% 3 5% 3 4 5% 5% 42%	1646
March	1st to 10th	Day	16% 8% 3 7% 5% 4 5% 4 5% 7% 36%	3436
	11th to 20th	Day	19% 9% 3 7% 5% 5% 5% 3 6% 6% 32%	3480
	21st to end	Day	16% 7% 3 6% 4 4 4 3 4 6% 42%	3814
April	1st to 10th	Day	13% 8% 3 7% 5% 4 4 4 5% 8% 39%	2090
	11th to 20th	Day	14% 7% 3 8% 5% 4 4 4 5% 5% 40%	2134
	21st to end	Day	12% 6% 2 6% 4 5% 4 3 5% 7% 45%	2294
May	1st to 10th	Day	17% 8% 3 7% 6% 5% 4 4 7% 8% 31%	4082
	11th to 20th	Day	13% 6% 2 6% 4 4 5% 4 5% 7% 43%	4082
	21st to end	Day	9% 6% 2 6% 6% 5% 6% 5% 9% 10% 36%	4477
June	1st to 10th	Day	5% 4 2 5% 4 6% 6% 5% 8% 10% 46%	2470
	11th to 20th	Day	6% 4 2 5% 4 5% 6% 5% 7% 10% 47%	2470
	21st to end	Day	5% 6% 2 7% 6% 6% 8% 5% 9% 10% 37%	2470
July	1st to 10th	Day	8% 4 1 4 5% 4 5% 4 7% 12% 45%	4120
	11th to 20th	Day	5% 5% 2 7% 5% 5% 6% 5% 8% 12% 41%	4120
	21st to end	Day	10% 7% 3 7% 6% 5% 6% 5% 7% 11% 33%	4465
August	1st to 10th	Day	2 1 1 3 2 3 3 3 4 9% 69%	4104
	11th to 20th	Day	3 2 1 4 3 4 4 5% 8% 13% 53%	4041
	21st to end	Day	4 4 2 6% 5% 6% 5% 5% 9% 10% 44%	3848
September	1st to 10th	Day	5% 6% 2 6% 6% 6% 6% 5% 6% 10% 43%	2090
	11th to 20th	Day	12% 6% 2 7% 5% 5% 6% 4 5% 7% 42%	2090
	21st to end	Day	6% 4 2 5% 5% 5% 5% 4 6% 7% 50%	2090
October	1st to 10th	Day	5% 4 2 4 4 4 4 4 6% 7% 58%	2049
	11th to 20th	Day	12% 5% 2 4 3 2 4 3 4 5% 55%	1900
	21st to end	Day	12% 5% 1 4 3 3 3 2 4 6% 56%	2090
November	1st to 10th	Day	12% 7% 2 6% 3 4 4 4 6% 7% 47%	1958
	11th to 20th	Day	11% 7% 2 5% 3 3 4 3 5% 6% 52%	1900
	21st to end	Day	18% 7% 3 6% 4 4 4 3 4 5% 42%	1715
December	1st to 10th	Day	15% 9% 2 6% 5% 3 3 3 4 6% 44%	1710
	11th to 20th	Day	18% 7% 2 6% 4 3 4 2 5% 6% 43%	2161
	21st to end	Day	15% 8% 3 5% 4 3 3 2 4 5% 48%	3135
January	1st to 10th	Night	18% 8% 2 4 3 3 3 2 4 5% 49%	4108
	11th to 20th	Night	15% 7% 1 4 2 2 2 2 3 4 58%	4120
	21st to end	Night	21% 8% 2 6% 4 3 3 2 4 6% 42%	4532
February	1st to 10th	Night	17% 9% 3 7% 3 3 3 3 4 5% 44%	2300
	11th to 20th	Night	20% 8% 2 5% 3 2 2 2 3 4 48%	2218
	21st to end	Night	19% 7% 3 5% 3 3 3 3 4 6% 44%	1806
March	1st to 10th	Night	19% 10% 3 7% 3 4 4 3 5% 7% 36%	3419
	11th to 20th	Night	22% 9% 3 7% 5% 4 4 3 4 6% 33%	3480
	21st to end	Night	14% 8% 2 6% 4 4 4 3 4 5% 45%	3817
April	1st to 10th	Night	12% 6% 2 5% 4 4 4 3 6% 7% 46%	2090
	11th to 20th	Night	13% 7% 2 6% 3 4 3 4 6% 8% 44%	1994
	21st to end	Night	13% 6% 2 5% 4 4 3 3 5% 6% 48%	1880
May	1st to 10th	Night	19% 8% 3 7% 5% 4 4 3 6% 8% 34%	2823
	11th to 20th	Night	11% 5% 2 6% 4 4 5% 3 6% 7% 47%	2823
	21st to end	Night	9% 6% 2 6% 5% 4 4 5% 6% 10% 42%	3090
June	1st to 10th	Night	4 2 2 4 3 3 4 3 6% 10% 58%	1710
	11th to 20th	Night	4 2 1 3 2 4 3 5% 7% 10% 60%	1710
	21st to end	Night	3 4 2 5% 5% 5% 5% 5% 8% 11% 49%	1710
July	1st to 10th	Night	4 3 1 4 4 4 5% 4 7% 13% 51%	2850
	11th to 20th	Night	3 4 1 5% 4 4 5% 5% 6% 11% 52%	2850
	21st to end	Night	7% 7% 3 7% 4 5% 5% 4 7% 10% 41%	3098
August	1st to 10th	Night	1 1 1 1 2 2 2 2 4 9% 74%	2836
	11th to 20th	Night	2 2 1 3 3 3 4 4 6% 14% 58%	2798
	21st to end	Night	3 3 1 4 3 4 5% 5% 8% 12% 52%	3787
September	1st to 10th	Night	6% 4 2 5% 3 4 5% 4 6% 9% 52%	2090
	11th to 20th	Night	10% 6% 2 6% 4 4 4 3 6% 8% 47%	2090
	21st to end	Night	7% 3 2 4 3 3 4 4 6% 8% 55%	2090
October	1st to 10th	Night	4 3 1 4 4 3 3 4 5% 7% 64%	2109
	11th to 20th	Night	10% 5% 1 4 3 2 3 3 4 6% 60%	2280
	21st to end	Night	11% 5% 2 4 3 2 2 3 4 4 61%	2508
November	1st to 10th	Night	12% 5% 1 5% 4 3 4 3 4 6% 53%	2340
	11th to 20th	Night	10% 7% 2 5% 4 4 4 3 4 6% 52%	2287
	21st to end	Night	16% 6% 3 5% 3 3 4 3 5% 7% 45%	2461
December	1st to 10th	Night	16% 8% 2 4 3 3 3 3 4 6% 46%	2470
	11th to 20th	Night	16% 8% 3 5% 4 3 3 3 4 6% 44%	3036
	21st to end	Night	16% 7% 2 5% 3 3 2 2 4 5% 51%	4532

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% 4 5% 19% 21% 11%	2848
	11th to 20th	Day	35% 3 5% 20% 28% 8%	2850
	21st to end	Day	49% 2 4 12% 21% 12%	3135
February	1st to 10th	Day	48% 4 5% 12% 19% 12%	1895
	11th to 20th	Day	46% 3 7% 15% 18% 10%	1859
	21st to end	Day	44% 4 8% 16% 16% 13%	1646
March	1st to 10th	Day	48% 5% 8% 15% 19% 5%	3436
	11th to 20th	Day	54% 5% 8% 11% 15% 7%	3480
	21st to end	Day	43% 4 8% 17% 23% 5%	3814
April	1st to 10th	Day	45% 6% 6% 18% 14% 11%	2090
	11th to 20th	Day	45% 4 8% 14% 19% 10%	2134
	21st to end	Day	39% 4 8% 20% 21% 7%	2294
May	1st to 10th	Day	50% 6% 12% 17% 11% 5%	4120
	11th to 20th	Day	41% 4 10% 18% 23% 4	4086
	21st to end	Day	39% 8% 12% 30% 10% 1	4489
June	1st to 10th	Day	31% 7% 14% 28% 17% 3	2470
	11th to 20th	Day	29% 8% 15% 26% 18% 4	2470
	21st to end	Day	38% 10% 13% 25% 12% 2	2470
July	1st to 10th	Day	31% 7% 24% 33% 5% 1	4056
	11th to 20th	Day	34% 7% 19% 25% 14% 1	4051
	21st to end	Day	43% 9% 19% 24% 6%	4325
August	1st to 10th	Day	14% 5% 13% 40% 26% 1	4090
	11th to 20th	Day	21% 7% 30% 32% 8% 2	4080
	21st to end	Day	32% 11% 18% 25% 13% 1	3847
September	1st to 10th	Day	36% 9% 12% 20% 16% 7%	2090
	11th to 20th	Day	40% 8% 13% 17% 18% 4	2090
	21st to end	Day	32% 6% 9% 22% 18% 13%	2090
October	1st to 10th	Day	16% 3 6% 13% 22% 40%	3400
	11th to 20th	Day	21% 3 7% 17% 34% 18%	3140
	21st to end	Day	26% 3 5% 21% 30% 15%	3428
November	1st to 10th	Day	36% 6% 8% 18% 21% 11%	1958
	11th to 20th	Day	33% 4 10% 18% 21% 13%	1900
	21st to end	Day	43% 4 8% 16% 18% 11%	1715
December	1st to 10th	Day	42% 3 10% 18% 19% 7%	1710
	11th to 20th	Day	44% 3 8% 12% 23% 10%	2159
	21st to end	Day	41% 3 5% 14% 26% 11%	3135
January	1st to 10th	Night	39% 4 5% 17% 20% 15%	4108
	11th to 20th	Night	32% 4 4 18% 29% 13%	4120
	21st to end	Night	46% 3 4 14% 22% 11%	4532
February	1st to 10th	Night	45% 3 5% 12% 19% 15%	2300
	11th to 20th	Night	42% 4 6% 16% 19% 14%	2218
	21st to end	Night	45% 4 6% 14% 16% 15%	1806
March	1st to 10th	Night	49% 6% 9% 14% 16% 7%	3419
	11th to 20th	Night	53% 5% 9% 15% 12% 6%	3480
	21st to end	Night	42% 5% 8% 14% 22% 9%	3817
April	1st to 10th	Night	36% 5% 10% 19% 16% 12%	2090
	11th to 20th	Night	39% 5% 10% 16% 16% 14%	1994
	21st to end	Night	38% 4 9% 22% 19% 8%	1880
May	1st to 10th	Night	49% 6% 9% 21% 11% 5%	2850
	11th to 20th	Night	37% 6% 10% 21% 20% 7%	2824
	21st to end	Night	37% 6% 13% 32% 10% 1	3099
June	1st to 10th	Night	23% 6% 17% 31% 22% 2	1710
	11th to 20th	Night	20% 7% 17% 33% 18% 5%	1710
	21st to end	Night	27% 9% 18% 30% 15% 2	1710
July	1st to 10th	Night	25% 8% 27% 34% 5%	2805
	11th to 20th	Night	26% 8% 21% 32% 12% 1	2796
	21st to end	Night	38% 8% 23% 24% 7%	2999
August	1st to 10th	Night	9% 4 16% 42% 28% 1	2826
	11th to 20th	Night	18% 5% 31% 34% 10% 1	2825
	21st to end	Night	23% 11% 23% 28% 12% 2	3787
September	1st to 10th	Night	28% 8% 18% 24% 15% 7%	2090
	11th to 20th	Night	36% 6% 15% 22% 14% 6%	2090
	21st to end	Night	26% 7% 15% 20% 18% 14%	2090
October	1st to 10th	Night	14% 3 8% 16% 18% 41%	3512
	11th to 20th	Night	17% 2 6% 20% 34% 22%	3779
	21st to end	Night	20% 3 5% 24% 31% 17%	4120
November	1st to 10th	Night	33% 5% 9% 19% 21% 12%	2340
	11th to 20th	Night	34% 4 9% 19% 21% 13%	2287
	21st to end	Night	39% 4 9% 17% 19% 13%	2461
December	1st to 10th	Night	39% 4 7% 22% 17% 10%	2470
	11th to 20th	Night	42% 4 6% 12% 20% 15%	3037
	21st to end	Night	38% 3 5% 15% 29% 11%	4532

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	23% 7% 37% 24% 7% 2	270
	11th to 20th	Day	20% 16% 28% 27% 7% 2	270
	21st to end	Day	20% 16% 33% 22% 7% 1	297
February	1st to 10th	Day	30% 13% 29% 20% 7%	270
	11th to 20th	Day	27% 16% 30% 20% 7%	270
	21st to end	Day	25% 18% 38% 16% 3	225
March	1st to 10th	Day	19% 18% 34% 22% 7%	270
	11th to 20th	Day	18% 15% 41% 19% 6% 1	270
	21st to end	Day	17% 14% 38% 23% 6% 1	297
April	1st to 10th	Day	17% 16% 41% 20% 6% 1	270
	11th to 20th	Day	18% 18% 31% 23% 8% 1	332
	21st to end	Day	14% 13% 35% 27% 11% 1	474
May	1st to 10th	Day	12% 11% 36% 30% 10% 1	653
	11th to 20th	Day	14% 7% 25% 34% 17% 3	675
	21st to end	Day	10% 6% 26% 35% 19% 3	734
June	1st to 10th	Day	4 2 13% 39% 33% 9%	680
	11th to 20th	Day	6% 2 13% 40% 32% 7%	680
	21st to end	Day	6% 2 11% 30% 38% 13%	680
July	1st to 10th	Day	6% 2 8% 28% 38% 18%	671
	11th to 20th	Day	4 3 29% 46% 18%	668
	21st to end	Day	5% 2 4 25% 46% 17%	739
August	1st to 10th	Day	3 3 23% 51% 21%	676
	11th to 20th	Day	5% 3 22% 50% 20%	665
	21st to end	Day	7% 1 3 18% 33% 37%	350
September	1st to 10th	Day	5% 1 6% 23% 36% 29%	300
	11th to 20th	Day	7% 2 5% 19% 37% 29%	300
	21st to end	Day	7% 1 7% 23% 40% 21%	300
October	1st to 10th	Day	3 2 11% 32% 38% 15%	300
	11th to 20th	Day	11% 4 17% 34% 26% 9%	300
	21st to end	Day	18% 10% 22% 22% 20% 8%	330
November	1st to 10th	Day	17% 7% 18% 33% 18% 7%	300
	11th to 20th	Day	19% 9% 23% 29% 16% 5%	270
	21st to end	Day	22% 16% 32% 19% 9% 3	270
December	1st to 10th	Day	19% 7% 31% 24% 14% 6%	270
	11th to 20th	Day	23% 15% 27% 25% 7% 2	270
	21st to end	Day	23% 7% 38% 23% 6% 2	297
January	1st to 10th	Night	20% 9% 32% 31% 8%	950
	11th to 20th	Night	21% 11% 30% 30% 8%	950
	21st to end	Night	19% 12% 31% 32% 6%	1045
February	1st to 10th	Night	23% 12% 33% 27% 4	780
	11th to 20th	Night	24% 11% 35% 26% 5%	744
	21st to end	Night	24% 13% 42% 18% 3	550
March	1st to 10th	Night	19% 13% 40% 25% 3	570
	11th to 20th	Night	15% 13% 36% 30% 5%	570
	21st to end	Night	14% 11% 42% 28% 5%	627
April	1st to 10th	Night	13% 11% 43% 30% 3	570
	11th to 20th	Night	14% 15% 37% 29% 6%	563
	21st to end	Night	13% 12% 39% 27% 8% 1	570
May	1st to 10th	Night	13% 11% 43% 29% 4	570
	11th to 20th	Night	9% 7% 34% 37% 12% 1	561
	21st to end	Night	5% 5% 33% 41% 16% 1	617
June	1st to 10th	Night	4 2 16% 51% 26% 2	570
	11th to 20th	Night	4 1 23% 51% 21% 1	570
	21st to end	Night	4 1 11% 48% 33% 4	570
July	1st to 10th	Night	5% 1 9% 46% 35% 3	555
	11th to 20th	Night	3 1 7% 51% 35% 3	552
	21st to end	Night	4 5% 52% 35% 3	624
August	1st to 10th	Night	1 4 54% 37% 3	567
	11th to 20th	Night	4 4 51% 35% 5%	564
	21st to end	Night	4 1 5% 37% 48% 6%	627
September	1st to 10th	Night	6% 1 8% 34% 45% 6%	570
	11th to 20th	Night	10% 1 8% 34% 43% 4	570
	21st to end	Night	8% 1 13% 34% 39% 4	570
October	1st to 10th	Night	4 1 11% 44% 35% 5%	589
	11th to 20th	Night	11% 3 22% 41% 21% 2	760
	21st to end	Night	12% 8% 27% 33% 19% 2	836
November	1st to 10th	Night	13% 4 22% 40% 19% 1	780
	11th to 20th	Night	11% 9% 25% 38% 15% 1	763
	21st to end	Night	17% 11% 29% 29% 14% 1	941
December	1st to 10th	Night	18% 8% 27% 33% 12% 1	950
	11th to 20th	Night	23% 11% 28% 30% 7% 1	950
	21st to end	Night	19% 9% 31% 31% 9%	1045

Page generated at 2024-11-08 05:44:51. Version ac07

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