Thomaston
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Thomaston clear sky chart from 2005-11-06 to 2024-07-02.

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	13% 6% 2 6% 5% 5% 5% 4 6% 8% 41%	89653
	Night	13% 6% 2 6% 4 4 4 4 6% 7% 44%	89493
Transparency	Day	40% 6% 11% 19% 19% 6%	89427
	Night	37% 6% 10% 19% 20% 7%	89323
Seeing	Day	16% 10% 23% 25% 18% 9%	14418
	Night	15% 9% 22% 29% 21% 4	24472

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% 7% 2 5% 3 4 3 3 5% 6% 45%	2836
	11th to 20th	Day	13% 7% 1 4 2 2 3 2 4 6% 55%	2840
	21st to end	Day	24% 8% 3 6% 3 3 3 3 4 5% 40%	3321
February	1st to 10th	Day	15% 8% 3 7% 4 4 5% 4 6% 6% 38%	1900
	11th to 20th	Day	20% 7% 2 5% 3 3 4 3 6% 6% 42%	1848
	21st to end	Day	16% 8% 2 7% 5% 4 4 4 5% 6% 38%	1570
March	1st to 10th	Day	22% 9% 3 6% 5% 3 3 3 5% 6% 35%	3232
	11th to 20th	Day	11% 6% 2 5% 5% 5% 4 4 6% 8% 46%	3480
	21st to end	Day	17% 5% 2 6% 4 4 4 3 5% 6% 43%	3815
April	1st to 10th	Day	11% 6% 3 6% 5% 4 3 4 5% 7% 46%	2127
	11th to 20th	Day	12% 5% 2 5% 4 3 3 4 5% 7% 49%	2254
	21st to end	Day	8% 5% 1 5% 4 4 5% 3 5% 7% 53%	2403
May	1st to 10th	Day	8% 5% 2 6% 5% 4 5% 4 7% 8% 46%	4082
	11th to 20th	Day	16% 7% 3 6% 5% 4 5% 4 6% 7% 37%	4081
	21st to end	Day	7% 4 2 6% 5% 5% 5% 4 7% 10% 46%	4476
June	1st to 10th	Day	10% 7% 3 7% 6% 7% 7% 5% 7% 10% 31%	2470
	11th to 20th	Day	5% 4 2 6% 6% 6% 6% 6% 8% 11% 39%	2470
	21st to end	Day	5% 5% 2 7% 7% 7% 7% 6% 9% 9% 36%	2470
July	1st to 10th	Day	9% 5% 3 8% 7% 8% 8% 6% 9% 11% 26%	2353
	11th to 20th	Day	7% 7% 3 7% 7% 7% 8% 6% 9% 11% 28%	2340
	21st to end	Day	6% 5% 2 7% 7% 7% 8% 7% 10% 12% 28%	2547
August	1st to 10th	Day	8% 5% 3 8% 7% 7% 8% 7% 9% 11% 28%	2316
	11th to 20th	Day	10% 7% 2 7% 7% 7% 7% 5% 8% 10% 29%	2125
	21st to end	Day	13% 7% 2 7% 7% 7% 5% 6% 7% 9% 29%	2372
September	1st to 10th	Day	11% 6% 2 7% 6% 5% 6% 5% 7% 8% 36%	1980
	11th to 20th	Day	14% 6% 2 5% 4 4 5% 4 7% 9% 39%	1980
	21st to end	Day	13% 5% 3 7% 4 5% 4 4 5% 5% 46%	1980
October	1st to 10th	Day	13% 5% 1 4 3 4 4 3 4 5% 53%	1980
	11th to 20th	Day	12% 4 1 4 3 3 3 3 5% 6% 56%	1900
	21st to end	Day	12% 5% 1 5% 4 4 3 3 4 5% 54%	1980
November	1st to 10th	Day	11% 6% 2 4 3 4 3 3 4 4 54%	1718
	11th to 20th	Day	13% 5% 1 4 4 3 3 2 4 6% 55%	1710
	21st to end	Day	14% 4 2 5% 4 4 4 3 5% 8% 46%	1710
December	1st to 10th	Day	16% 7% 3 5% 4 4 4 4 5% 7% 41%	1710
	11th to 20th	Day	17% 9% 2 6% 3 4 3 2 4 6% 44%	2153
	21st to end	Day	21% 8% 2 6% 2 3 4 3 4 7% 40%	3124
January	1st to 10th	Night	18% 8% 2 6% 3 4 4 4 5% 6% 40%	4109
	11th to 20th	Night	11% 6% 2 5% 4 4 4 4 5% 7% 48%	4120
	21st to end	Night	23% 9% 2 6% 4 3 3 3 3 4 40%	4331
February	1st to 10th	Night	15% 8% 3 5% 4 4 4 3 5% 6% 43%	2280
	11th to 20th	Night	20% 7% 2 4 3 4 3 4 4 6% 44%	2218
	21st to end	Night	16% 7% 2 6% 4 4 4 4 5% 6% 42%	1884
March	1st to 10th	Night	24% 9% 2 7% 3 3 3 2 4 5% 37%	3619
	11th to 20th	Night	11% 5% 2 5% 4 4 4 4 5% 7% 48%	3480
	21st to end	Night	16% 6% 2 6% 4 4 4 3 5% 6% 43%	3817
April	1st to 10th	Night	11% 5% 2 5% 5% 3 4 4 6% 7% 47%	2067
	11th to 20th	Night	12% 4 2 5% 3 4 3 3 5% 8% 50%	1875
	21st to end	Night	6% 5% 2 5% 4 4 4 4 5% 7% 55%	1777
May	1st to 10th	Night	6% 4 2 6% 4 5% 4 5% 8% 11% 45%	2813
	11th to 20th	Night	15% 6% 3 5% 4 5% 5% 4 6% 7% 41%	2812
	21st to end	Night	6% 4 2 5% 4 4 4 4 7% 11% 51%	3079
June	1st to 10th	Night	7% 6% 2 7% 6% 5% 6% 5% 8% 11% 37%	1710
	11th to 20th	Night	4 4 2 6% 5% 4 5% 4 8% 13% 46%	1710
	21st to end	Night	6% 4 2 6% 5% 6% 6% 7% 9% 14% 36%	1710
July	1st to 10th	Night	7% 5% 2 6% 6% 7% 8% 7% 8% 12% 33%	1635
	11th to 20th	Night	6% 4 2 6% 5% 6% 7% 6% 10% 12% 35%	1620
	21st to end	Night	5% 4 2 5% 5% 6% 7% 7% 9% 13% 36%	1771
August	1st to 10th	Night	6% 5% 2 7% 5% 5% 6% 6% 8% 13% 36%	1619
	11th to 20th	Night	8% 6% 2 7% 5% 5% 7% 5% 8% 11% 35%	1776
	21st to end	Night	12% 7% 3 7% 5% 4 6% 5% 6% 9% 35%	1980
September	1st to 10th	Night	9% 6% 2 6% 4 5% 6% 5% 7% 10% 41%	1965
	11th to 20th	Night	11% 6% 2 6% 5% 5% 5% 3 6% 8% 43%	1980
	21st to end	Night	9% 6% 2 8% 4 4 4 3 6% 7% 47%	1980
October	1st to 10th	Night	11% 4 2 5% 3 3 3 3 5% 6% 55%	1980
	11th to 20th	Night	12% 4 2 4 3 3 3 3 4 5% 57%	2060
	21st to end	Night	12% 5% 1 4 3 3 3 3 4 5% 57%	2376
November	1st to 10th	Night	11% 5% 1 5% 2 3 3 4 4 5% 56%	2356
	11th to 20th	Night	14% 5% 2 5% 3 3 3 2 4 6% 54%	2470
	21st to end	Night	14% 5% 2 6% 4 4 4 2 5% 7% 47%	2470
December	1st to 10th	Night	15% 6% 2 6% 3 4 5% 3 5% 6% 45%	2470
	11th to 20th	Night	17% 6% 2 5% 3 3 3 3 4 6% 48%	3042
	21st to end	Night	19% 8% 3 7% 4 4 4 3 5% 6% 35%	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% 3 4 20% 24% 7%	2837
	11th to 20th	Day	31% 3 5% 21% 29% 11%	2840
	21st to end	Day	47% 4 4 14% 22% 10%	3321
February	1st to 10th	Day	45% 5% 6% 17% 20% 7%	1900
	11th to 20th	Day	43% 4 5% 17% 24% 8%	1858
	21st to end	Day	45% 6% 7% 13% 20% 9%	1570
March	1st to 10th	Day	50% 4 8% 14% 16% 7%	3232
	11th to 20th	Day	36% 6% 8% 17% 23% 11%	3480
	21st to end	Day	42% 5% 8% 20% 17% 9%	3815
April	1st to 10th	Day	38% 4 9% 21% 19% 9%	2127
	11th to 20th	Day	34% 5% 8% 19% 24% 11%	2254
	21st to end	Day	30% 5% 10% 24% 26% 5%	2403
May	1st to 10th	Day	34% 8% 12% 23% 21% 3	4120
	11th to 20th	Day	45% 6% 11% 23% 14% 1	4085
	21st to end	Day	31% 7% 15% 26% 20% 2	4489
June	1st to 10th	Day	45% 9% 14% 19% 11% 2	2470
	11th to 20th	Day	33% 9% 16% 25% 15% 1	2470
	21st to end	Day	39% 11% 17% 19% 12% 3	2470
July	1st to 10th	Day	44% 12% 21% 15% 6% 2	2288
	11th to 20th	Day	44% 12% 19% 16% 7% 1	2271
	21st to end	Day	40% 11% 22% 19% 7% 1	2405
August	1st to 10th	Day	44% 11% 21% 21% 4	2303
	11th to 20th	Day	46% 10% 18% 17% 8% 1	2125
	21st to end	Day	48% 9% 16% 16% 9% 2	2372
September	1st to 10th	Day	43% 9% 14% 15% 15% 5%	1980
	11th to 20th	Day	39% 7% 12% 19% 18% 4	1980
	21st to end	Day	39% 5% 7% 22% 21% 6%	1980
October	1st to 10th	Day	33% 4 10% 18% 25% 9%	1980
	11th to 20th	Day	29% 4 6% 25% 25% 10%	1900
	21st to end	Day	33% 4 5% 13% 32% 14%	1980
November	1st to 10th	Day	34% 4 5% 16% 27% 15%	1718
	11th to 20th	Day	31% 3 6% 20% 25% 15%	1710
	21st to end	Day	37% 4 9% 17% 23% 9%	1710
December	1st to 10th	Day	42% 6% 9% 16% 20% 8%	1710
	11th to 20th	Day	43% 3 5% 14% 26% 8%	2150
	21st to end	Day	45% 4 7% 18% 23% 4	3124
January	1st to 10th	Night	43% 5% 4 16% 24% 9%	4109
	11th to 20th	Night	34% 5% 5% 24% 23% 9%	4120
	21st to end	Night	49% 4 3 10% 26% 8%	4331
February	1st to 10th	Night	42% 4 6% 19% 19% 11%	2280
	11th to 20th	Night	42% 4 4 16% 22% 11%	2219
	21st to end	Night	42% 4 10% 15% 16% 13%	1884
March	1st to 10th	Night	51% 4 8% 15% 14% 8%	3619
	11th to 20th	Night	35% 5% 9% 14% 26% 12%	3480
	21st to end	Night	42% 4 7% 18% 20% 10%	3817
April	1st to 10th	Night	34% 6% 10% 19% 20% 11%	2067
	11th to 20th	Night	32% 4 6% 22% 24% 11%	1875
	21st to end	Night	28% 4 12% 24% 24% 8%	1777
May	1st to 10th	Night	29% 9% 16% 24% 20% 3	2840
	11th to 20th	Night	40% 8% 13% 25% 13% 2	2813
	21st to end	Night	25% 7% 16% 29% 20% 3	3087
June	1st to 10th	Night	38% 11% 17% 20% 14% 1	1710
	11th to 20th	Night	27% 8% 21% 30% 12% 2	1710
	21st to end	Night	33% 11% 22% 18% 13% 3	1710
July	1st to 10th	Night	38% 13% 21% 17% 8% 3	1590
	11th to 20th	Night	35% 13% 28% 15% 8% 2	1566
	21st to end	Night	31% 13% 26% 21% 7% 1	1672
August	1st to 10th	Night	35% 12% 24% 23% 6%	1608
	11th to 20th	Night	38% 11% 20% 19% 10% 1	1776
	21st to end	Night	43% 10% 18% 16% 11% 2	1980
September	1st to 10th	Night	36% 9% 18% 18% 15% 4	1965
	11th to 20th	Night	38% 7% 12% 19% 18% 5%	1980
	21st to end	Night	36% 6% 11% 18% 21% 9%	1980
October	1st to 10th	Night	31% 4 10% 22% 22% 11%	1980
	11th to 20th	Night	29% 4 6% 22% 28% 11%	2060
	21st to end	Night	30% 4 5% 17% 30% 15%	2376
November	1st to 10th	Night	30% 4 8% 16% 27% 15%	2356
	11th to 20th	Night	33% 3 5% 18% 26% 15%	2470
	21st to end	Night	38% 3 7% 18% 24% 10%	2470
December	1st to 10th	Night	40% 5% 8% 19% 21% 7%	2470
	11th to 20th	Night	39% 3 6% 14% 29% 8%	3044
	21st to end	Night	49% 5% 6% 19% 18% 4	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	24% 22% 40% 11% 2	270
	11th to 20th	Day	25% 20% 33% 13% 6% 2	270
	21st to end	Day	28% 24% 36% 9% 2 1	297
February	1st to 10th	Day	25% 22% 34% 16% 3	270
	11th to 20th	Day	33% 19% 34% 12% 1	270
	21st to end	Day	32% 14% 43% 11% 1	225
March	1st to 10th	Day	23% 18% 31% 21% 6% 1	330
	11th to 20th	Day	21% 17% 35% 18% 8% 1	460
	21st to end	Day	19% 20% 32% 21% 7%	506
April	1st to 10th	Day	23% 15% 31% 21% 9% 1	460
	11th to 20th	Day	16% 15% 32% 23% 11% 3	452
	21st to end	Day	13% 13% 28% 27% 15% 4	460
May	1st to 10th	Day	11% 13% 28% 29% 14% 6%	463
	11th to 20th	Day	12% 6% 26% 28% 19% 10%	487
	21st to end	Day	14% 5% 17% 30% 23% 11%	529
June	1st to 10th	Day	11% 3 18% 30% 24% 13%	490
	11th to 20th	Day	7% 3 17% 27% 27% 18%	490
	21st to end	Day	7% 5% 14% 32% 27% 15%	490
July	1st to 10th	Day	9% 2 8% 28% 30% 23%	449
	11th to 20th	Day	7% 4 6% 26% 31% 26%	444
	21st to end	Day	8% 1 6% 27% 36% 22%	488
August	1st to 10th	Day	10% 4 9% 28% 28% 21%	446
	11th to 20th	Day	10% 3 6% 23% 36% 22%	439
	21st to end	Day	16% 3 8% 31% 28% 14%	495
September	1st to 10th	Day	13% 3 10% 26% 34% 13%	450
	11th to 20th	Day	15% 3 12% 31% 29% 10%	450
	21st to end	Day	13% 2 15% 32% 26% 10%	450
October	1st to 10th	Day	16% 6% 22% 29% 19% 7%	450
	11th to 20th	Day	13% 9% 21% 32% 20% 6%	450
	21st to end	Day	17% 9% 26% 27% 17% 4	495
November	1st to 10th	Day	21% 9% 26% 29% 12% 3	316
	11th to 20th	Day	17% 17% 38% 21% 6% 1	270
	21st to end	Day	19% 10% 37% 24% 8% 1	270
December	1st to 10th	Day	24% 18% 33% 19% 6% 1	270
	11th to 20th	Day	27% 19% 34% 15% 5%	270
	21st to end	Day	33% 12% 31% 20% 3	297
January	1st to 10th	Night	24% 18% 29% 23% 5%	760
	11th to 20th	Night	21% 15% 28% 27% 9%	760
	21st to end	Night	23% 15% 34% 25% 3	836
February	1st to 10th	Night	21% 12% 31% 28% 8%	760
	11th to 20th	Night	25% 15% 29% 28% 3	743
	21st to end	Night	20% 16% 35% 25% 4	628
March	1st to 10th	Night	16% 14% 33% 31% 6%	760
	11th to 20th	Night	18% 13% 32% 26% 11% 1	760
	21st to end	Night	18% 13% 28% 30% 10% 1	836
April	1st to 10th	Night	14% 12% 32% 29% 13%	737
	11th to 20th	Night	15% 12% 25% 31% 16% 1	563
	21st to end	Night	8% 8% 24% 38% 20% 1	570
May	1st to 10th	Night	9% 8% 26% 31% 25% 2	570
	11th to 20th	Night	12% 4 21% 34% 24% 6%	561
	21st to end	Night	12% 3 14% 33% 32% 6%	617
June	1st to 10th	Night	10% 2 11% 41% 31% 6%	570
	11th to 20th	Night	4 1 13% 31% 36% 15%	570
	21st to end	Night	6% 3 8% 33% 39% 11%	570
July	1st to 10th	Night	8% 3 6% 25% 43% 15%	530
	11th to 20th	Night	7% 2 4 21% 48% 18%	522
	21st to end	Night	6% 1 6% 27% 48% 12%	591
August	1st to 10th	Night	9% 1 6% 25% 43% 17%	537
	11th to 20th	Night	10% 2 4 26% 45% 12%	534
	21st to end	Night	15% 3 7% 26% 36% 13%	594
September	1st to 10th	Night	10% 2 9% 27% 40% 11%	705
	11th to 20th	Night	13% 3 12% 30% 36% 6%	720
	21st to end	Night	12% 2 14% 36% 32% 4	720
October	1st to 10th	Night	14% 4 21% 30% 26% 5%	720
	11th to 20th	Night	14% 6% 24% 28% 25% 3	720
	21st to end	Night	15% 9% 22% 31% 20% 2	792
November	1st to 10th	Night	14% 8% 22% 36% 20% 1	740
	11th to 20th	Night	18% 11% 28% 28% 14% 2	760
	21st to end	Night	15% 11% 28% 31% 13% 1	760
December	1st to 10th	Night	20% 12% 28% 27% 12% 1	760
	11th to 20th	Night	22% 10% 30% 27% 9% 1	760
	21st to end	Night	28% 11% 26% 28% 7%	836

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