Southington Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Southington Observatory clear sky chart from 2005-11-06 to 2026-08-15.

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	17% 7% 2 6% 4 4 4 4 5% 7% 39%	143625
	Night	18% 8% 3 6% 4 4 4 3 5% 6% 41%	138257
Transparency	Day	43% 6% 12% 22% 15% 2	147157
	Night	43% 5% 11% 22% 16% 3	142814
Seeing	Day	23% 18% 31% 19% 7% 2	17273
	Night	22% 15% 32% 24% 6% 1	26231

By Month

Percentage Cloud Cover NE (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	11% 8% 3 9% 5% 5% 4 3 5% 5% 41%	4661
	11th to 20th	Day	15% 8% 3 6% 4 3 4 3 4 5% 43%	4650
	21st to end	Day	16% 9% 2 5% 3 4 4 3 5% 7% 43%	5262
February	1st to 10th	Day	16% 8% 2 7% 4 5% 4 5% 5% 6% 38%	1958
	11th to 20th	Day	14% 7% 3 6% 5% 5% 5% 3 6% 7% 39%	2048
	21st to end	Day	20% 9% 3 5% 4 3 4 3 4 5% 40%	1730
March	1st to 10th	Day	22% 9% 3 6% 3 3 4 3 4 5% 39%	4576
	11th to 20th	Day	15% 7% 2 6% 4 4 4 4 6% 8% 41%	4756
	21st to end	Day	19% 8% 3 6% 4 3 4 3 6% 7% 36%	6102
April	1st to 10th	Day	18% 9% 2 6% 5% 3 4 3 6% 7% 37%	2520
	11th to 20th	Day	18% 6% 2 6% 4 4 4 4 5% 7% 41%	2494
	21st to end	Day	21% 6% 2 5% 4 4 4 4 5% 6% 40%	2640
May	1st to 10th	Day	27% 8% 3 6% 4 4 3 3 5% 7% 31%	7639
	11th to 20th	Day	19% 7% 2 6% 4 4 4 4 5% 7% 37%	7998
	21st to end	Day	23% 7% 2 6% 4 4 4 4 6% 8% 32%	9060
June	1st to 10th	Day	16% 5% 2 6% 5% 5% 5% 4 7% 9% 35%	2940
	11th to 20th	Day	15% 6% 2 6% 5% 4 5% 5% 6% 9% 36%	2940
	21st to end	Day	14% 7% 2 7% 4 4 5% 4 7% 8% 38%	2940
July	1st to 10th	Day	16% 6% 2 6% 4 5% 6% 4 6% 9% 35%	8280
	11th to 20th	Day	10% 5% 2 6% 4 4 5% 4 7% 11% 41%	8280
	21st to end	Day	16% 6% 2 6% 4 4 4 4 5% 7% 42%	8993
August	1st to 10th	Day	19% 6% 3 7% 5% 6% 5% 4 6% 8% 31%	4540
	11th to 20th	Day	11% 6% 2 7% 4 4 5% 4 6% 8% 43%	3931
	21st to end	Day	9% 5% 2 6% 4 4 5% 4 7% 9% 43%	4312
September	1st to 10th	Day	13% 6% 2 6% 4 4 4 4 5% 6% 45%	2400
	11th to 20th	Day	12% 6% 2 5% 3 3 4 3 5% 6% 51%	2261
	21st to end	Day	19% 5% 2 6% 4 4 4 3 5% 6% 41%	2200
October	1st to 10th	Day	20% 7% 2 5% 4 2 3 4 4 5% 43%	2167
	11th to 20th	Day	15% 6% 2 5% 4 3 4 3 6% 7% 46%	1980
	21st to end	Day	21% 6% 2 6% 3 5% 4 3 4 6% 41%	1980
November	1st to 10th	Day	12% 6% 2 6% 5% 4 4 3 4 5% 49%	1851
	11th to 20th	Day	18% 5% 1 5% 3 3 4 3 5% 7% 47%	1890
	21st to end	Day	16% 9% 3 5% 4 3 4 3 5% 7% 41%	1852
December	1st to 10th	Day	15% 7% 2 5% 4 4 4 4 5% 6% 45%	2680
	11th to 20th	Day	21% 6% 2 5% 3 3 3 3 4 6% 45%	3066
	21st to end	Day	19% 10% 4 7% 4 4 3 3 4 5% 38%	4048
January	1st to 10th	Night	15% 8% 3 6% 4 3 4 4 5% 6% 43%	8234
	11th to 20th	Night	16% 9% 3 7% 4 4 3 3 4 5% 42%	8235
	21st to end	Night	16% 8% 3 7% 4 4 4 3 4 5% 41%	8901
February	1st to 10th	Night	16% 9% 3 6% 5% 3 4 3 5% 6% 41%	2662
	11th to 20th	Night	16% 9% 2 6% 3 5% 4 3 6% 6% 39%	2458
	21st to end	Night	18% 8% 2 6% 6% 4 4 3 4 5% 40%	2076
March	1st to 10th	Night	21% 9% 2 6% 3 3 3 3 4 6% 41%	5484
	11th to 20th	Night	16% 9% 3 6% 4 4 4 4 5% 6% 40%	5408
	21st to end	Night	22% 10% 3 6% 3 4 3 3 5% 6% 38%	5072
April	1st to 10th	Night	20% 8% 2 6% 4 4 5% 4 5% 6% 37%	2100
	11th to 20th	Night	19% 6% 2 6% 4 4 4 4 5% 7% 40%	2075
	21st to end	Night	20% 7% 2 7% 3 4 3 2 4 5% 42%	1979
May	1st to 10th	Night	27% 10% 3 6% 4 4 3 3 4 6% 31%	5259
	11th to 20th	Night	20% 8% 4 7% 4 4 4 3 5% 7% 34%	4904
	21st to end	Night	23% 8% 3 6% 5% 4 4 3 6% 6% 32%	5114
June	1st to 10th	Night	17% 7% 2 6% 4 5% 5% 4 5% 6% 40%	1680
	11th to 20th	Night	17% 6% 2 6% 5% 4 4 4 5% 8% 39%	1680
	21st to end	Night	14% 5% 3 6% 5% 3 4 4 5% 9% 43%	1680
July	1st to 10th	Night	17% 6% 2 6% 4 4 4 4 7% 9% 36%	4680
	11th to 20th	Night	14% 7% 2 7% 4 4 4 4 6% 9% 39%	4680
	21st to end	Night	14% 7% 2 6% 4 4 4 4 5% 7% 43%	5084
August	1st to 10th	Night	21% 6% 3 7% 4 5% 5% 4 6% 7% 31%	2797
	11th to 20th	Night	14% 7% 2 7% 5% 5% 4 3 5% 7% 41%	3201
	21st to end	Night	10% 4 1 4 3 4 3 4 5% 8% 53%	3586
September	1st to 10th	Night	14% 6% 2 6% 5% 4 4 3 4 6% 45%	2000
	11th to 20th	Night	13% 6% 2 4 3 4 3 3 4 6% 51%	2138
	21st to end	Night	17% 7% 3 5% 4 4 4 3 5% 6% 43%	2200
October	1st to 10th	Night	19% 7% 2 6% 4 4 3 3 5% 5% 44%	2230
	11th to 20th	Night	16% 5% 2 5% 4 3 4 4 4 5% 49%	2419
	21st to end	Night	22% 6% 2 5% 3 3 4 4 4 6% 41%	2860
November	1st to 10th	Night	13% 6% 2 5% 4 4 4 3 5% 6% 49%	2667
	11th to 20th	Night	18% 7% 2 5% 3 3 3 3 5% 5% 46%	2730
	21st to end	Night	16% 8% 1 4 4 4 4 3 5% 6% 45%	2766
December	1st to 10th	Night	16% 7% 2 6% 4 3 3 3 4 5% 47%	4720
	11th to 20th	Night	25% 7% 2 4 3 3 3 3 3 4 42%	5348
	21st to end	Night	19% 10% 3 7% 4 3 3 3 4 5% 40%	7150

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	44% 4 10% 25% 15% 2	4662
	11th to 20th	Day	43% 4 9% 21% 15% 8%	4680
	21st to end	Day	42% 4 10% 26% 17% 1	5262
February	1st to 10th	Day	46% 6% 12% 20% 15% 2	1958
	11th to 20th	Day	43% 5% 10% 24% 15% 3	2057
	21st to end	Day	47% 5% 12% 20% 14% 3	1730
March	1st to 10th	Day	48% 4 10% 16% 13% 9%	4579
	11th to 20th	Day	39% 7% 14% 28% 11% 2	4756
	21st to end	Day	47% 5% 9% 15% 19% 6%	6102
April	1st to 10th	Day	46% 5% 11% 19% 15% 4	2520
	11th to 20th	Day	42% 6% 11% 20% 18% 2	2494
	21st to end	Day	45% 5% 10% 20% 16% 4	2640
May	1st to 10th	Day	53% 6% 12% 16% 12% 1	7651
	11th to 20th	Day	46% 6% 12% 21% 13% 1	8002
	21st to end	Day	50% 6% 11% 20% 12% 1	9061
June	1st to 10th	Day	43% 8% 11% 22% 14% 1	2940
	11th to 20th	Day	43% 8% 14% 21% 13% 2	2940
	21st to end	Day	42% 8% 13% 22% 14% 1	2940
July	1st to 10th	Day	45% 8% 13% 19% 14% 1	8210
	11th to 20th	Day	35% 7% 16% 28% 13% 1	8205
	21st to end	Day	41% 6% 10% 23% 18% 1	8795
August	1st to 10th	Day	49% 7% 14% 20% 9% 1	4526
	11th to 20th	Day	38% 8% 13% 29% 11% 1	3968
	21st to end	Day	35% 7% 12% 27% 17% 2	4312
September	1st to 10th	Day	40% 8% 10% 22% 19% 2	2400
	11th to 20th	Day	34% 6% 11% 24% 24% 3	2261
	21st to end	Day	44% 6% 9% 21% 18% 3	2200
October	1st to 10th	Day	38% 5% 9% 19% 24% 5%	3531
	11th to 20th	Day	29% 4 9% 24% 30% 4	3208
	21st to end	Day	33% 4 12% 24% 23% 3	3180
November	1st to 10th	Day	38% 5% 12% 22% 21% 2	1851
	11th to 20th	Day	38% 4 11% 23% 21% 3	1890
	21st to end	Day	44% 4 12% 25% 12% 3	1852
December	1st to 10th	Day	40% 4 15% 27% 12% 1	2680
	11th to 20th	Day	41% 4 15% 19% 18% 3	3066
	21st to end	Day	49% 4 7% 20% 15% 4	4048
January	1st to 10th	Night	42% 3 11% 25% 16% 2	8234
	11th to 20th	Night	46% 4 11% 18% 15% 6%	8280
	21st to end	Night	45% 4 9% 20% 19% 3	8901
February	1st to 10th	Night	45% 5% 12% 23% 13% 2	2662
	11th to 20th	Night	45% 5% 9% 20% 17% 4	2460
	21st to end	Night	46% 5% 9% 22% 14% 4	2076
March	1st to 10th	Night	46% 4 10% 18% 15% 6%	5494
	11th to 20th	Night	43% 6% 16% 21% 11% 3	5409
	21st to end	Night	48% 4 7% 12% 24% 5%	5072
April	1st to 10th	Night	47% 6% 10% 19% 15% 3	2100
	11th to 20th	Night	44% 6% 10% 19% 20% 1	2075
	21st to end	Night	45% 5% 9% 21% 16% 4	1979
May	1st to 10th	Night	55% 5% 13% 15% 12% 1	5265
	11th to 20th	Night	50% 7% 12% 19% 10% 2	4905
	21st to end	Night	52% 5% 12% 21% 9% 1	5115
June	1st to 10th	Night	44% 6% 11% 21% 17% 1	1680
	11th to 20th	Night	42% 8% 14% 25% 11% 1	1680
	21st to end	Night	39% 7% 14% 25% 14% 1	1680
July	1st to 10th	Night	44% 8% 15% 20% 13% 1	4640
	11th to 20th	Night	41% 6% 14% 25% 12% 1	4632
	21st to end	Night	40% 7% 11% 24% 16% 1	4967
August	1st to 10th	Night	51% 9% 12% 18% 10% 1	2787
	11th to 20th	Night	42% 7% 13% 29% 9%	3230
	21st to end	Night	29% 6% 14% 33% 17% 1	3586
September	1st to 10th	Night	40% 6% 9% 26% 18% 1	2000
	11th to 20th	Night	34% 5% 11% 23% 25% 2	2138
	21st to end	Night	42% 7% 8% 21% 20% 2	2200
October	1st to 10th	Night	38% 5% 12% 22% 20% 2	3646
	11th to 20th	Night	27% 4 8% 28% 29% 3	3930
	21st to end	Night	33% 4 12% 29% 20% 2	4610
November	1st to 10th	Night	36% 6% 11% 22% 21% 4	2667
	11th to 20th	Night	40% 4 10% 22% 20% 4	2730
	21st to end	Night	40% 4 13% 29% 13% 1	2766
December	1st to 10th	Night	41% 4 11% 30% 13% 1	4720
	11th to 20th	Night	47% 4 12% 16% 18% 2	5348
	21st to end	Night	47% 3 9% 20% 17% 4	7150

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	30% 25% 30% 13% 2	220
	11th to 20th	Day	30% 30% 28% 10% 2	220
	21st to end	Day	27% 29% 32% 7% 4 1	267
February	1st to 10th	Day	32% 24% 31% 11% 2	398
	11th to 20th	Day	29% 26% 33% 10% 1	536
	21st to end	Day	31% 21% 33% 12% 3	446
March	1st to 10th	Day	28% 24% 33% 13% 3	540
	11th to 20th	Day	30% 25% 30% 11% 3 1	540
	21st to end	Day	34% 23% 30% 9% 3 1	594
April	1st to 10th	Day	32% 26% 26% 10% 4 1	540
	11th to 20th	Day	33% 19% 30% 13% 5% 1	532
	21st to end	Day	29% 21% 32% 12% 4 1	540
May	1st to 10th	Day	33% 22% 28% 12% 5% 1	543
	11th to 20th	Day	24% 20% 36% 14% 6% 1	567
	21st to end	Day	23% 15% 31% 22% 7% 2	617
June	1st to 10th	Day	19% 15% 32% 23% 9% 2	570
	11th to 20th	Day	18% 18% 37% 19% 7% 1	570
	21st to end	Day	17% 16% 33% 25% 9% 1	570
July	1st to 10th	Day	17% 9% 31% 28% 12% 2	565
	11th to 20th	Day	12% 10% 35% 29% 12% 2	564
	21st to end	Day	15% 10% 37% 28% 8% 1	620
August	1st to 10th	Day	12% 9% 30% 34% 11% 4	566
	11th to 20th	Day	12% 7% 34% 30% 12% 4	535
	21st to end	Day	11% 12% 34% 24% 13% 5%	583
September	1st to 10th	Day	19% 12% 26% 22% 17% 4	530
	11th to 20th	Day	15% 11% 28% 26% 12% 8%	530
	21st to end	Day	22% 11% 35% 19% 8% 4	530
October	1st to 10th	Day	27% 12% 26% 18% 12% 5%	530
	11th to 20th	Day	18% 20% 31% 22% 7% 2	519
	21st to end	Day	27% 16% 30% 18% 7% 1	462
November	1st to 10th	Day	20% 18% 31% 22% 7% 2	425
	11th to 20th	Day	29% 21% 24% 20% 5%	430
	21st to end	Day	29% 21% 27% 19% 4	392
December	1st to 10th	Day	25% 24% 30% 15% 6%	220
	11th to 20th	Day	36% 24% 28% 10% 2	220
	21st to end	Day	31% 22% 28% 17% 2 1	242
January	1st to 10th	Night	23% 20% 37% 17% 3	840
	11th to 20th	Night	28% 20% 31% 19% 2	840
	21st to end	Night	21% 22% 36% 19% 2	924
February	1st to 10th	Night	23% 19% 35% 21% 2	840
	11th to 20th	Night	25% 22% 36% 15% 2	823
	21st to end	Night	27% 19% 36% 15% 2	692
March	1st to 10th	Night	25% 21% 34% 18% 2	840
	11th to 20th	Night	23% 21% 34% 19% 3	840
	21st to end	Night	26% 22% 34% 16% 3	924
April	1st to 10th	Night	26% 20% 35% 16% 3	840
	11th to 20th	Night	24% 19% 35% 19% 3	831
	21st to end	Night	23% 20% 34% 18% 4	719
May	1st to 10th	Night	27% 15% 35% 18% 4	630
	11th to 20th	Night	22% 15% 38% 22% 3	512
	21st to end	Night	23% 8% 31% 31% 6% 1	455
June	1st to 10th	Night	20% 8% 33% 30% 9%	420
	11th to 20th	Night	20% 8% 33% 31% 8%	420
	21st to end	Night	15% 6% 34% 37% 8%	420
July	1st to 10th	Night	15% 5% 28% 38% 14%	410
	11th to 20th	Night	14% 4 27% 42% 12% 1	408
	21st to end	Night	13% 7% 29% 41% 9% 1	460
August	1st to 10th	Night	13% 5% 30% 41% 10% 1	497
	11th to 20th	Night	14% 5% 26% 38% 15% 2	782
	21st to end	Night	14% 5% 28% 35% 16% 2	880
September	1st to 10th	Night	17% 6% 31% 33% 12% 2	800
	11th to 20th	Night	17% 6% 27% 31% 17% 3	800
	21st to end	Night	20% 7% 29% 28% 15% 1	800
October	1st to 10th	Night	24% 10% 28% 25% 12% 2	800
	11th to 20th	Night	20% 14% 30% 27% 9% 1	800
	21st to end	Night	27% 14% 32% 21% 7%	880
November	1st to 10th	Night	18% 13% 34% 26% 8% 1	820
	11th to 20th	Night	23% 18% 34% 19% 6% 1	840
	21st to end	Night	23% 17% 31% 24% 5%	840
December	1st to 10th	Night	26% 17% 32% 20% 5% 1	840
	11th to 20th	Night	26% 20% 31% 21% 3	840
	21st to end	Night	28% 17% 34% 18% 2	924

Page generated at 2026-08-12 03:37:14. Version ac07

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