Twin Pond
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Twin Pond clear sky chart from 2005-11-06 to 2025-12-18.

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	8% 6% 2 5% 3 3 4 3 5% 7% 55%	136043
	Night	7% 5% 2 5% 3 3 4 3 5% 7% 54%	132289
Transparency	Day	29% 4 12% 27% 22% 6%	130855
	Night	29% 4 12% 26% 22% 7%	128484
Seeing	Day	12% 6% 30% 32% 17% 3	17168
	Night	11% 7% 34% 38% 10% 1	27110

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	9% 9% 2 6% 4 3 3 4 5% 7% 48%	3638
	11th to 20th	Day	6% 8% 3 8% 6% 4 4 3 4 5% 49%	3884
	21st to end	Day	4 8% 3 6% 4 3 3 3 4 5% 57%	4488
February	1st to 10th	Day	7% 10% 2 8% 5% 3 4 3 6% 7% 44%	1910
	11th to 20th	Day	5% 7% 3 6% 5% 5% 5% 4 6% 7% 48%	1949
	21st to end	Day	6% 6% 1 6% 3 2 3 3 5% 7% 57%	1650
March	1st to 10th	Day	8% 7% 2 5% 3 3 3 2 3 5% 60%	4532
	11th to 20th	Day	7% 6% 2 4 3 3 3 2 4 5% 60%	4980
	21st to end	Day	7% 6% 2 4 4 4 3 3 6% 7% 54%	5464
April	1st to 10th	Day	9% 5% 2 4 4 3 3 3 5% 7% 54%	2350
	11th to 20th	Day	10% 6% 2 5% 4 4 3 4 5% 7% 49%	2423
	21st to end	Day	15% 6% 2 5% 4 4 3 3 5% 7% 46%	2600
May	1st to 10th	Day	11% 5% 2 5% 3 4 4 3 5% 7% 51%	5900
	11th to 20th	Day	9% 4 1 4 3 3 3 3 5% 7% 58%	5862
	21st to end	Day	18% 7% 2 5% 3 3 4 4 6% 7% 42%	6446
June	1st to 10th	Day	6% 3 1 3 3 2 4 3 5% 8% 60%	2629
	11th to 20th	Day	6% 5% 1 4 3 4 4 4 5% 8% 57%	2800
	21st to end	Day	4 4 1 3 4 3 5% 4 6% 8% 60%	2800
July	1st to 10th	Day	6% 4 2 5% 4 4 5% 4 6% 8% 53%	6339
	11th to 20th	Day	5% 3 1 4 3 3 5% 4 6% 10% 55%	6174
	21st to end	Day	6% 4 1 4 3 4 4 4 6% 9% 55%	6424
August	1st to 10th	Day	10% 6% 2 6% 4 4 4 4 5% 8% 48%	5801
	11th to 20th	Day	7% 4 2 5% 4 4 4 4 6% 9% 52%	5821
	21st to end	Day	13% 6% 2 5% 4 4 3 3 4 6% 50%	6012
September	1st to 10th	Day	10% 5% 2 4 3 3 3 2 5% 6% 59%	2302
	11th to 20th	Day	7% 5% 1 5% 4 3 3 2 5% 8% 57%	2200
	21st to end	Day	7% 4 2 5% 3 3 3 3 4 6% 61%	2200
October	1st to 10th	Day	9% 3 1 3 2 2 2 2 3 4 71%	3590
	11th to 20th	Day	5% 3 1 4 3 3 4 3 4 6% 64%	3288
	21st to end	Day	8% 5% 1 4 2 2 2 2 4 6% 63%	3268
November	1st to 10th	Day	7% 4 1 4 3 3 3 3 4 6% 62%	1853
	11th to 20th	Day	6% 5% 1 4 3 2 2 2 4 6% 64%	1890
	21st to end	Day	10% 6% 2 4 3 3 3 3 4 6% 58%	1890
December	1st to 10th	Day	4 5% 2 3 2 2 3 3 4 6% 65%	3030
	11th to 20th	Day	5% 5% 2 4 3 3 3 2 4 6% 63%	3454
	21st to end	Day	10% 12% 3 9% 4 4 4 3 5% 6% 40%	4202
January	1st to 10th	Night	7% 8% 4 11% 4 3 3 3 5% 6% 46%	6327
	11th to 20th	Night	3 6% 2 7% 5% 4 4 3 5% 6% 55%	6077
	21st to end	Night	6% 9% 3 7% 4 4 4 3 4 5% 53%	6490
February	1st to 10th	Night	7% 9% 3 7% 5% 4 4 3 5% 5% 48%	2509
	11th to 20th	Night	5% 8% 2 6% 5% 4 4 4 6% 7% 47%	2338
	21st to end	Night	5% 6% 2 7% 4 4 3 2 4 5% 58%	1980
March	1st to 10th	Night	7% 5% 1 4 3 2 3 2 4 5% 64%	5340
	11th to 20th	Night	7% 4 1 4 3 3 3 3 6% 7% 58%	4980
	21st to end	Night	8% 6% 2 6% 4 4 5% 5% 6% 8% 45%	5467
April	1st to 10th	Night	9% 6% 2 5% 2 4 3 4 6% 8% 52%	2045
	11th to 20th	Night	11% 6% 2 5% 4 4 4 3 6% 7% 49%	1924
	21st to end	Night	14% 5% 2 5% 4 4 3 3 4 7% 48%	1800
May	1st to 10th	Night	13% 6% 2 5% 4 4 4 4 6% 6% 47%	4080
	11th to 20th	Night	8% 5% 1 4 3 3 4 3 5% 7% 56%	4053
	21st to end	Night	18% 6% 2 5% 3 3 4 3 6% 8% 42%	4451
June	1st to 10th	Night	5% 3 1 4 3 4 3 4 8% 9% 56%	1766
	11th to 20th	Night	6% 4 1 4 3 4 4 4 6% 10% 55%	1600
	21st to end	Night	4 4 2 5% 4 4 4 5% 7% 9% 53%	1600
July	1st to 10th	Night	7% 3 1 4 4 4 4 4 6% 9% 53%	3640
	11th to 20th	Night	7% 5% 2 6% 4 6% 5% 5% 7% 10% 44%	3789
	21st to end	Night	5% 4 1 5% 3 3 5% 4 7% 9% 54%	4449
August	1st to 10th	Night	7% 4 2 5% 3 4 5% 5% 8% 12% 46%	4011
	11th to 20th	Night	7% 4 2 5% 3 4 4 4 7% 8% 52%	4028
	21st to end	Night	9% 6% 2 6% 4 4 4 4 7% 8% 45%	4961
September	1st to 10th	Night	6% 4 1 3 2 3 4 3 4 8% 62%	2096
	11th to 20th	Night	7% 3 1 4 3 3 3 4 5% 7% 59%	2200
	21st to end	Night	7% 4 1 4 3 3 2 3 5% 5% 64%	2200
October	1st to 10th	Night	6% 2 1 2 2 2 2 2 3 4 73%	3590
	11th to 20th	Night	6% 3 1 3 2 3 2 2 4 6% 67%	3818
	21st to end	Night	7% 3 1 3 2 2 3 2 4 7% 66%	4513
November	1st to 10th	Night	5% 3 2 3 3 3 3 3 4 6% 66%	2665
	11th to 20th	Night	7% 4 1 3 2 3 3 3 4 6% 65%	2730
	21st to end	Night	9% 6% 2 3 3 3 3 2 4 6% 60%	2730
December	1st to 10th	Night	3 5% 2 4 3 2 3 2 4 5% 67%	4380
	11th to 20th	Night	4 4 1 4 3 3 3 3 5% 7% 62%	4908
	21st to end	Night	10% 12% 3 7% 4 3 3 3 4 6% 44%	6754

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% 4 13% 27% 19% 2	3639
	11th to 20th	Day	38% 5% 9% 25% 19% 3	3884
	21st to end	Day	32% 3 12% 27% 21% 4	4488
February	1st to 10th	Day	39% 5% 14% 24% 14% 4	1910
	11th to 20th	Day	35% 5% 15% 24% 16% 5%	1959
	21st to end	Day	28% 4 11% 25% 24% 8%	1650
March	1st to 10th	Day	29% 3 6% 20% 29% 13%	4532
	11th to 20th	Day	27% 4 7% 22% 27% 14%	4980
	21st to end	Day	29% 6% 18% 35% 12% 1	5464
April	1st to 10th	Day	29% 5% 12% 28% 22% 5%	2350
	11th to 20th	Day	34% 5% 13% 25% 18% 5%	2426
	21st to end	Day	38% 5% 11% 27% 17% 2	2600
May	1st to 10th	Day	31% 6% 12% 28% 17% 6%	5900
	11th to 20th	Day	26% 6% 11% 23% 23% 10%	5866
	21st to end	Day	39% 7% 12% 22% 17% 2	6447
June	1st to 10th	Day	21% 7% 19% 34% 16% 4	2629
	11th to 20th	Day	25% 6% 13% 28% 21% 7%	2800
	21st to end	Day	21% 7% 11% 28% 26% 7%	2800
July	1st to 10th	Day	28% 5% 9% 27% 25% 6%	6271
	11th to 20th	Day	25% 4 17% 27% 23% 4	6099
	21st to end	Day	25% 5% 13% 26% 23% 7%	6240
August	1st to 10th	Day	34% 4 13% 27% 19% 3	4220
	11th to 20th	Day	33% 5% 17% 23% 19% 3	4210
	21st to end	Day	23% 4 12% 27% 24% 9%	4326
September	1st to 10th	Day	28% 4 9% 26% 24% 9%	2302
	11th to 20th	Day	27% 4 9% 27% 26% 6%	2200
	21st to end	Day	26% 3 9% 29% 27% 6%	2200
October	1st to 10th	Day	20% 2 5% 21% 41% 11%	3590
	11th to 20th	Day	22% 3 10% 36% 20% 9%	3288
	21st to end	Day	24% 2 7% 28% 33% 6%	3268
November	1st to 10th	Day	24% 4 10% 29% 27% 6%	1853
	11th to 20th	Day	24% 2 9% 29% 31% 5%	1890
	21st to end	Day	29% 3 11% 27% 26% 5%	1890
December	1st to 10th	Day	22% 3 12% 35% 22% 6%	3030
	11th to 20th	Day	25% 2 12% 41% 19% 1	3452
	21st to end	Day	46% 4 9% 24% 15% 2	4202
January	1st to 10th	Night	40% 4 12% 24% 17% 2	6327
	11th to 20th	Night	29% 5% 11% 25% 25% 5%	6077
	21st to end	Night	35% 4 10% 23% 20% 9%	6490
February	1st to 10th	Night	37% 5% 13% 22% 16% 6%	2509
	11th to 20th	Night	35% 5% 12% 28% 18% 3	2338
	21st to end	Night	29% 4 9% 22% 25% 11%	1980
March	1st to 10th	Night	24% 3 6% 22% 31% 14%	5340
	11th to 20th	Night	25% 4 7% 19% 26% 19%	4980
	21st to end	Night	35% 5% 16% 33% 10% 1	5467
April	1st to 10th	Night	30% 6% 13% 23% 23% 5%	2045
	11th to 20th	Night	34% 5% 13% 24% 20% 4	1924
	21st to end	Night	35% 6% 13% 26% 19% 2	1800
May	1st to 10th	Night	35% 6% 13% 25% 16% 5%	4080
	11th to 20th	Night	27% 6% 12% 25% 22% 7%	4054
	21st to end	Night	39% 7% 15% 22% 14% 2	4452
June	1st to 10th	Night	22% 8% 18% 29% 19% 4	1766
	11th to 20th	Night	25% 7% 14% 28% 21% 5%	1600
	21st to end	Night	24% 7% 14% 26% 24% 6%	1600
July	1st to 10th	Night	29% 4 17% 24% 23% 4	3600
	11th to 20th	Night	34% 4 16% 23% 20% 4	3741
	21st to end	Night	25% 4 16% 25% 22% 7%	4320
August	1st to 10th	Night	28% 5% 16% 25% 23% 3	2916
	11th to 20th	Night	32% 4 18% 26% 17% 3	2915
	21st to end	Night	26% 4 14% 29% 18% 9%	3578
September	1st to 10th	Night	22% 5% 11% 25% 26% 10%	2096
	11th to 20th	Night	24% 5% 10% 25% 27% 9%	2200
	21st to end	Night	24% 3 10% 24% 32% 8%	2200
October	1st to 10th	Night	18% 3 6% 18% 44% 12%	3590
	11th to 20th	Night	20% 2 10% 26% 30% 13%	3818
	21st to end	Night	21% 2 9% 26% 35% 8%	4513
November	1st to 10th	Night	20% 3 11% 29% 28% 10%	2665
	11th to 20th	Night	22% 3 9% 29% 29% 8%	2730
	21st to end	Night	27% 3 10% 28% 24% 7%	2730
December	1st to 10th	Night	22% 3 11% 36% 23% 5%	4380
	11th to 20th	Night	22% 3 10% 38% 24% 4	4909
	21st to end	Night	43% 4 9% 29% 14% 2	6754

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	10% 6% 38% 31% 12% 2	300
	11th to 20th	Day	14% 11% 34% 31% 11%	300
	21st to end	Day	11% 5% 43% 31% 9% 1	330
February	1st to 10th	Day	17% 10% 40% 27% 7%	300
	11th to 20th	Day	12% 11% 42% 25% 8% 3	300
	21st to end	Day	8% 13% 54% 20% 5%	249
March	1st to 10th	Day	15% 10% 39% 27% 8%	300
	11th to 20th	Day	19% 9% 35% 25% 9% 3	300
	21st to end	Day	18% 12% 42% 22% 5% 1	330
April	1st to 10th	Day	14% 18% 36% 25% 6% 1	450
	11th to 20th	Day	15% 15% 39% 25% 6%	544
	21st to end	Day	19% 12% 38% 21% 8% 1	700
May	1st to 10th	Day	15% 7% 30% 32% 14% 2	703
	11th to 20th	Day	17% 8% 30% 28% 15% 2	725
	21st to end	Day	17% 6% 30% 33% 11% 2	789
June	1st to 10th	Day	6% 3 26% 35% 20% 9%	730
	11th to 20th	Day	6% 3 33% 36% 19% 3	730
	21st to end	Day	7% 3 33% 39% 17% 2	730
July	1st to 10th	Day	8% 2 20% 37% 27% 6%	721
	11th to 20th	Day	5% 2 14% 44% 29% 6%	718
	21st to end	Day	8% 1 14% 40% 31% 6%	794
August	1st to 10th	Day	10% 2 15% 39% 30% 5%	726
	11th to 20th	Day	8% 1 17% 43% 27% 4	715
	21st to end	Day	10% 1 19% 39% 27% 6%	598
September	1st to 10th	Day	12% 3 20% 38% 22% 5%	432
	11th to 20th	Day	6% 4 25% 37% 22% 6%	330
	21st to end	Day	9% 5% 27% 31% 21% 7%	330
October	1st to 10th	Day	19% 4 19% 35% 15% 6%	330
	11th to 20th	Day	7% 11% 40% 26% 12% 4	330
	21st to end	Day	20% 8% 33% 24% 12% 3	363
November	1st to 10th	Day	14% 9% 34% 31% 10% 3	330
	11th to 20th	Day	12% 8% 39% 25% 14% 1	330
	21st to end	Day	19% 8% 32% 28% 12% 2	330
December	1st to 10th	Day	7% 7% 42% 31% 12% 2	330
	11th to 20th	Day	12% 9% 40% 29% 9%	321
	21st to end	Day	20% 8% 34% 29% 8%	330
January	1st to 10th	Night	10% 7% 36% 39% 7% 1	1000
	11th to 20th	Night	9% 9% 36% 37% 8% 1	1000
	21st to end	Night	11% 7% 43% 34% 6%	1100
February	1st to 10th	Night	12% 7% 41% 33% 7%	909
	11th to 20th	Night	9% 10% 41% 35% 4	784
	21st to end	Night	8% 11% 42% 35% 4	660
March	1st to 10th	Night	13% 12% 37% 33% 5%	792
	11th to 20th	Night	15% 9% 36% 33% 8% 1	600
	21st to end	Night	16% 12% 40% 27% 5%	660
April	1st to 10th	Night	13% 14% 41% 29% 3	600
	11th to 20th	Night	16% 14% 39% 27% 4	593
	21st to end	Night	18% 10% 33% 32% 7%	600
May	1st to 10th	Night	15% 6% 35% 37% 7% 1	600
	11th to 20th	Night	16% 8% 31% 35% 9% 1	591
	21st to end	Night	15% 7% 34% 34% 10% 1	650
June	1st to 10th	Night	7% 5% 35% 39% 13% 1	600
	11th to 20th	Night	8% 4 38% 39% 11%	600
	21st to end	Night	7% 5% 35% 42% 12%	600
July	1st to 10th	Night	8% 2 22% 47% 20% 1	585
	11th to 20th	Night	4 1 24% 52% 18% 1	582
	21st to end	Night	7% 16% 50% 25% 1	657
August	1st to 10th	Night	8% 1 19% 51% 21%	597
	11th to 20th	Night	10% 1 20% 47% 21% 1	594
	21st to end	Night	5% 1 22% 47% 23% 1	660
September	1st to 10th	Night	8% 2 29% 48% 13% 1	600
	11th to 20th	Night	9% 3 31% 41% 16% 1	600
	21st to end	Night	10% 5% 29% 40% 16% 1	600
October	1st to 10th	Night	11% 7% 31% 38% 13%	600
	11th to 20th	Night	12% 7% 38% 36% 7%	745
	21st to end	Night	15% 9% 30% 34% 12% 1	1040
November	1st to 10th	Night	8% 8% 32% 43% 9%	1025
	11th to 20th	Night	10% 8% 38% 35% 8%	1050
	21st to end	Night	12% 7% 32% 38% 10% 1	1050
December	1st to 10th	Night	9% 7% 38% 38% 7%	1050
	11th to 20th	Night	12% 8% 36% 37% 7%	1036
	21st to end	Night	15% 9% 33% 37% 7%	1100

Page generated at 2025-12-15 00:13:54. Version ac07

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