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 2026-02-16.

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	12% 6% 2 6% 5% 5% 5% 4 6% 8% 42%	131049
	Night	13% 6% 2 6% 4 4 4 4 6% 7% 44%	129808
Transparency	Day	38% 7% 11% 19% 18% 7%	134848
	Night	37% 6% 11% 19% 20% 8%	134079
Seeing	Day	16% 10% 23% 25% 18% 8%	16564
	Night	15% 9% 22% 30% 21% 4	26641

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% 7% 2 6% 4 3 3 3 4 5% 47%	5258
	11th to 20th	Day	12% 6% 2 4 2 2 3 2 4 6% 57%	5280
	21st to end	Day	21% 7% 3 7% 4 4 4 3 4 5% 37%	6170
February	1st to 10th	Day	14% 8% 2 7% 4 4 5% 4 6% 6% 40%	2100
	11th to 20th	Day	21% 6% 2 4 3 3 4 3 6% 6% 41%	1998
	21st to end	Day	15% 8% 2 7% 5% 4 4 4 5% 6% 39%	1650
March	1st to 10th	Day	20% 8% 3 6% 5% 4 4 3 5% 6% 36%	4634
	11th to 20th	Day	9% 5% 2 5% 4 4 4 3 5% 7% 51%	4980
	21st to end	Day	17% 6% 2 6% 4 4 4 3 4 6% 45%	5465
April	1st to 10th	Day	11% 6% 3 6% 5% 4 3 4 5% 7% 46%	2239
	11th to 20th	Day	11% 5% 2 5% 4 3 3 4 5% 7% 51%	2374
	21st to end	Day	8% 5% 1 5% 5% 4 5% 4 5% 7% 52%	2530
May	1st to 10th	Day	11% 5% 3 7% 6% 4 5% 4 7% 8% 40%	5862
	11th to 20th	Day	16% 7% 2 6% 5% 5% 5% 5% 7% 9% 33%	5861
	21st to end	Day	9% 4 2 6% 5% 5% 5% 4 7% 9% 43%	6433
June	1st to 10th	Day	10% 7% 3 7% 6% 7% 7% 5% 7% 10% 31%	2600
	11th to 20th	Day	5% 4 2 6% 6% 6% 6% 6% 9% 11% 39%	2600
	21st to end	Day	5% 5% 2 7% 7% 7% 7% 6% 9% 9% 36%	2600
July	1st to 10th	Day	11% 5% 2 8% 6% 7% 7% 6% 9% 11% 27%	5900
	11th to 20th	Day	5% 4 2 7% 6% 6% 7% 5% 9% 13% 36%	5900
	21st to end	Day	8% 6% 3 8% 6% 7% 8% 6% 10% 13% 24%	6424
August	1st to 10th	Day	9% 6% 2 7% 5% 6% 7% 6% 9% 11% 32%	4208
	11th to 20th	Day	6% 4 2 5% 5% 5% 5% 5% 6% 9% 47%	3849
	21st to end	Day	8% 5% 1 5% 5% 5% 5% 4 6% 9% 47%	4294
September	1st to 10th	Day	11% 5% 2 7% 6% 5% 6% 5% 7% 8% 37%	2200
	11th to 20th	Day	14% 5% 2 5% 4 4 5% 4 7% 9% 40%	2200
	21st to end	Day	13% 5% 3 7% 5% 5% 4 4 5% 6% 45%	2200
October	1st to 10th	Day	13% 5% 2 5% 3 4 4 3 4 6% 52%	2200
	11th to 20th	Day	11% 4 1 4 3 3 3 3 5% 5% 59%	2110
	21st to end	Day	12% 5% 1 5% 4 4 3 3 4 5% 55%	2200
November	1st to 10th	Day	11% 6% 2 4 3 4 3 3 4 4 53%	1902
	11th to 20th	Day	13% 4 1 4 3 3 3 2 4 6% 57%	1890
	21st to end	Day	14% 4 2 5% 4 3 4 3 6% 7% 47%	1890
December	1st to 10th	Day	18% 5% 2 4 3 3 3 3 5% 5% 48%	3020
	11th to 20th	Day	16% 8% 2 5% 3 3 3 2 4 5% 47%	3463
	21st to end	Day	22% 7% 2 5% 2 3 4 3 4 6% 43%	4565
January	1st to 10th	Night	15% 6% 2 6% 3 4 4 3 5% 5% 46%	7635
	11th to 20th	Night	13% 6% 3 6% 4 4 4 3 4 5% 48%	7680
	21st to end	Night	20% 9% 3 6% 4 3 4 3 4 5% 40%	8007
February	1st to 10th	Night	14% 7% 3 5% 4 4 4 3 5% 6% 45%	2520
	11th to 20th	Night	21% 7% 2 4 3 4 3 4 4 6% 44%	2399
	21st to end	Night	15% 6% 2 6% 4 4 4 4 5% 6% 43%	1980
March	1st to 10th	Night	21% 8% 2 6% 4 4 3 3 4 6% 38%	5217
	11th to 20th	Night	11% 5% 2 4 4 3 4 4 5% 6% 52%	4980
	21st to end	Night	14% 6% 2 5% 4 4 4 3 5% 5% 47%	5467
April	1st to 10th	Night	11% 5% 2 5% 4 4 4 4 6% 7% 48%	2176
	11th to 20th	Night	12% 4 2 5% 3 4 3 3 5% 8% 52%	1975
	21st to end	Night	6% 5% 2 5% 4 4 4 4 5% 7% 54%	1870
May	1st to 10th	Night	9% 6% 2 7% 4 5% 4 4 7% 11% 41%	4033
	11th to 20th	Night	17% 6% 2 5% 4 5% 5% 4 7% 9% 35%	4032
	21st to end	Night	8% 4 2 6% 4 4 4 4 7% 11% 46%	4421
June	1st to 10th	Night	7% 6% 2 7% 6% 5% 6% 5% 8% 11% 37%	1800
	11th to 20th	Night	4 5% 2 6% 5% 4 5% 4 8% 13% 45%	1800
	21st to end	Night	6% 4 2 6% 5% 6% 7% 7% 8% 13% 37%	1800
July	1st to 10th	Night	12% 6% 3 7% 6% 7% 7% 6% 8% 10% 28%	4058
	11th to 20th	Night	5% 4 2 6% 6% 6% 7% 6% 9% 13% 37%	4057
	21st to end	Night	9% 6% 2 9% 7% 7% 7% 6% 9% 12% 27%	4427
August	1st to 10th	Night	9% 6% 2 8% 6% 6% 6% 6% 8% 12% 31%	2938
	11th to 20th	Night	6% 4 2 6% 4 4 6% 4 7% 11% 46%	3200
	21st to end	Night	8% 5% 2 5% 4 3 4 4 5% 9% 52%	3586
September	1st to 10th	Night	9% 6% 2 7% 4 4 6% 5% 7% 9% 40%	2184
	11th to 20th	Night	12% 6% 2 6% 5% 5% 5% 3 6% 8% 43%	2200
	21st to end	Night	10% 6% 2 8% 5% 4 4 3 6% 7% 46%	2200
October	1st to 10th	Night	11% 5% 2 5% 3 3 3 3 5% 6% 55%	2200
	11th to 20th	Night	11% 4 1 4 3 3 3 3 4 5% 60%	2290
	21st to end	Night	11% 5% 1 4 3 3 3 3 4 5% 58%	2640
November	1st to 10th	Night	12% 5% 1 5% 2 3 3 4 4 5% 54%	2611
	11th to 20th	Night	13% 5% 2 4 3 3 3 2 4 5% 56%	2730
	21st to end	Night	13% 5% 2 6% 4 4 4 2 5% 7% 49%	2730
December	1st to 10th	Night	15% 6% 2 5% 2 3 3 2 4 5% 53%	4380
	11th to 20th	Night	16% 5% 1 5% 3 3 3 3 4 7% 49%	4952
	21st to end	Night	21% 7% 2 5% 4 3 4 3 4 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% 4 6% 21% 24% 6%	5259
	11th to 20th	Day	29% 3 4 18% 32% 14%	5280
	21st to end	Day	49% 4 5% 12% 20% 9%	6170
February	1st to 10th	Day	43% 5% 6% 17% 21% 7%	2100
	11th to 20th	Day	44% 4 5% 18% 23% 7%	2008
	21st to end	Day	44% 6% 7% 14% 21% 9%	1650
March	1st to 10th	Day	48% 4 7% 12% 22% 7%	4634
	11th to 20th	Day	32% 5% 7% 14% 22% 21%	4980
	21st to end	Day	41% 4 6% 20% 18% 10%	5465
April	1st to 10th	Day	37% 4 10% 22% 18% 9%	2239
	11th to 20th	Day	33% 5% 7% 20% 24% 11%	2374
	21st to end	Day	31% 5% 10% 23% 25% 5%	2530
May	1st to 10th	Day	39% 8% 13% 21% 17% 2	5897
	11th to 20th	Day	45% 8% 17% 20% 10% 1	5865
	21st to end	Day	35% 7% 13% 21% 21% 1	6447
June	1st to 10th	Day	44% 9% 14% 19% 12% 2	2600
	11th to 20th	Day	33% 10% 17% 24% 15% 1	2600
	21st to end	Day	38% 11% 17% 19% 12% 3	2600
July	1st to 10th	Day	44% 15% 19% 17% 4 1	5835
	11th to 20th	Day	35% 14% 29% 19% 3 1	5831
	21st to end	Day	46% 15% 19% 17% 3	6240
August	1st to 10th	Day	40% 9% 17% 26% 7%	4195
	11th to 20th	Day	31% 8% 15% 30% 15% 1	3885
	21st to end	Day	32% 8% 17% 26% 15% 2	4294
September	1st to 10th	Day	42% 8% 14% 16% 16% 4	2200
	11th to 20th	Day	39% 7% 12% 21% 18% 4	2200
	21st to end	Day	39% 5% 8% 22% 20% 6%	2200
October	1st to 10th	Day	29% 4 7% 14% 29% 16%	3590
	11th to 20th	Day	17% 3 4 17% 27% 33%	3415
	21st to end	Day	23% 4 4 16% 38% 15%	3538
November	1st to 10th	Day	34% 4 5% 15% 27% 14%	1902
	11th to 20th	Day	30% 3 7% 20% 26% 15%	1890
	21st to end	Day	36% 4 9% 18% 24% 9%	1890
December	1st to 10th	Day	38% 4 6% 17% 26% 9%	3020
	11th to 20th	Day	40% 4 8% 17% 22% 8%	3460
	21st to end	Day	42% 4 6% 22% 23% 3	4565
January	1st to 10th	Night	38% 5% 6% 21% 23% 6%	7636
	11th to 20th	Night	38% 4 4 18% 26% 10%	7680
	21st to end	Night	47% 3 4 14% 24% 7%	8007
February	1st to 10th	Night	40% 4 6% 19% 21% 11%	2520
	11th to 20th	Night	43% 4 4 17% 22% 10%	2400
	21st to end	Night	41% 4 9% 15% 17% 14%	1980
March	1st to 10th	Night	47% 4 8% 15% 15% 11%	5217
	11th to 20th	Night	32% 4 8% 12% 24% 19%	4980
	21st to end	Night	39% 4 6% 19% 21% 11%	5467
April	1st to 10th	Night	34% 6% 10% 20% 19% 11%	2176
	11th to 20th	Night	32% 4 6% 22% 25% 11%	1975
	21st to end	Night	30% 4 12% 24% 23% 7%	1870
May	1st to 10th	Night	35% 9% 17% 22% 15% 2	4060
	11th to 20th	Night	43% 9% 16% 22% 9% 1	4033
	21st to end	Night	30% 7% 15% 26% 19% 2	4429
June	1st to 10th	Night	37% 11% 17% 20% 14% 1	1800
	11th to 20th	Night	28% 9% 21% 29% 12% 2	1800
	21st to end	Night	33% 11% 21% 19% 13% 3	1800
July	1st to 10th	Night	46% 14% 20% 15% 4 1	4015
	11th to 20th	Night	33% 15% 31% 17% 4 1	4006
	21st to end	Night	46% 14% 22% 15% 3 1	4297
August	1st to 10th	Night	40% 11% 19% 24% 6%	2927
	11th to 20th	Night	29% 9% 18% 29% 14% 1	3230
	21st to end	Night	27% 8% 17% 28% 17% 2	3586
September	1st to 10th	Night	36% 10% 18% 18% 16% 3	2184
	11th to 20th	Night	38% 8% 11% 21% 18% 5%	2200
	21st to end	Night	36% 6% 11% 18% 21% 8%	2200
October	1st to 10th	Night	32% 4 9% 15% 25% 15%	3590
	11th to 20th	Night	17% 2 4 15% 29% 33%	3724
	21st to end	Night	20% 3 4 20% 33% 19%	4252
November	1st to 10th	Night	32% 4 8% 15% 28% 14%	2611
	11th to 20th	Night	32% 3 5% 18% 27% 15%	2730
	21st to end	Night	37% 4 7% 18% 25% 10%	2730
December	1st to 10th	Night	36% 3 6% 20% 27% 9%	4380
	11th to 20th	Night	36% 3 11% 17% 24% 8%	4954
	21st to end	Night	44% 4 5% 22% 22% 3	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	25% 22% 40% 11% 2	330
	11th to 20th	Day	26% 22% 32% 12% 6% 2	330
	21st to end	Day	28% 24% 35% 10% 2 1	363
February	1st to 10th	Day	23% 21% 38% 15% 3	330
	11th to 20th	Day	36% 19% 32% 11% 1	315
	21st to end	Day	30% 14% 43% 11% 2	249
March	1st to 10th	Day	25% 20% 30% 20% 5% 1	363
	11th to 20th	Day	22% 16% 34% 19% 8% 1	500
	21st to end	Day	20% 19% 33% 21% 7%	550
April	1st to 10th	Day	23% 15% 31% 21% 9% 1	500
	11th to 20th	Day	16% 15% 33% 24% 11% 3	492
	21st to end	Day	13% 13% 28% 26% 17% 4	500
May	1st to 10th	Day	12% 13% 29% 29% 13% 5%	503
	11th to 20th	Day	13% 6% 27% 27% 18% 9%	527
	21st to end	Day	15% 6% 18% 29% 21% 10%	573
June	1st to 10th	Day	11% 4 20% 29% 24% 12%	530
	11th to 20th	Day	7% 4 16% 30% 26% 17%	530
	21st to end	Day	6% 4 14% 31% 28% 17%	530
July	1st to 10th	Day	8% 2 8% 29% 30% 24%	525
	11th to 20th	Day	6% 4 5% 25% 34% 25%	524
	21st to end	Day	7% 2 7% 28% 36% 19%	576
August	1st to 10th	Day	12% 4 10% 29% 27% 18%	526
	11th to 20th	Day	9% 3 7% 24% 35% 21%	519
	21st to end	Day	14% 3 11% 31% 27% 13%	583
September	1st to 10th	Day	12% 3 14% 27% 32% 12%	530
	11th to 20th	Day	15% 3 12% 32% 29% 9%	530
	21st to end	Day	14% 4 16% 32% 25% 10%	530
October	1st to 10th	Day	15% 7% 24% 29% 18% 6%	530
	11th to 20th	Day	11% 9% 23% 32% 20% 5%	530
	21st to end	Day	17% 9% 26% 28% 16% 4	583
November	1st to 10th	Day	21% 9% 26% 29% 13% 2	380
	11th to 20th	Day	16% 16% 39% 21% 7% 1	330
	21st to end	Day	20% 13% 36% 22% 8% 1	330
December	1st to 10th	Day	26% 18% 33% 16% 5% 1	330
	11th to 20th	Day	25% 18% 32% 16% 6% 1	330
	21st to end	Day	31% 12% 31% 21% 4 1	363
January	1st to 10th	Night	24% 19% 29% 24% 5%	840
	11th to 20th	Night	22% 15% 29% 26% 8%	840
	21st to end	Night	23% 15% 34% 25% 3	924
February	1st to 10th	Night	20% 13% 32% 28% 8%	840
	11th to 20th	Night	25% 16% 29% 27% 3	804
	21st to end	Night	20% 16% 35% 25% 4	660
March	1st to 10th	Night	17% 14% 33% 31% 6%	800
	11th to 20th	Night	18% 13% 32% 27% 10% 1	800
	21st to end	Night	18% 13% 29% 30% 9% 1	880
April	1st to 10th	Night	14% 12% 33% 28% 13%	776
	11th to 20th	Night	15% 12% 25% 32% 16% 1	593
	21st to end	Night	8% 8% 24% 39% 20% 1	600
May	1st to 10th	Night	9% 8% 26% 32% 24% 2	600
	11th to 20th	Night	12% 4 21% 34% 24% 5%	591
	21st to end	Night	13% 3 15% 34% 30% 6%	650
June	1st to 10th	Night	11% 2 11% 40% 31% 6%	600
	11th to 20th	Night	4 2 13% 31% 36% 14%	600
	21st to end	Night	6% 3 7% 33% 40% 11%	600
July	1st to 10th	Night	8% 3 6% 27% 42% 15%	585
	11th to 20th	Night	7% 2 4 20% 49% 18%	582
	21st to end	Night	6% 2 6% 27% 47% 11%	657
August	1st to 10th	Night	10% 2 7% 26% 40% 15%	597
	11th to 20th	Night	9% 2 6% 27% 44% 12%	594
	21st to end	Night	15% 3 9% 27% 35% 12%	660
September	1st to 10th	Night	11% 3 10% 29% 38% 10%	784
	11th to 20th	Night	14% 3 12% 30% 36% 6%	800
	21st to end	Night	12% 3 13% 36% 31% 4	800
October	1st to 10th	Night	13% 4 22% 31% 25% 5%	800
	11th to 20th	Night	13% 6% 24% 30% 24% 2	800
	21st to end	Night	15% 9% 22% 33% 20% 2	880
November	1st to 10th	Night	15% 8% 21% 36% 19% 1	820
	11th to 20th	Night	17% 11% 28% 29% 14% 2	840
	21st to end	Night	15% 13% 27% 31% 13% 1	840
December	1st to 10th	Night	20% 12% 28% 27% 11% 1	840
	11th to 20th	Night	22% 11% 29% 28% 9% 1	840
	21st to end	Night	26% 12% 25% 29% 7%	924

Page generated at 2026-02-13 01:42:17. Version ac07

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