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 2025-04-11.

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	17% 7% 2 6% 4 4 4 4 5% 7% 39%	113165
	Night	18% 8% 2 6% 4 4 4 3 5% 6% 41%	115112
Transparency	Day	43% 6% 12% 21% 16% 3	116743
	Night	43% 5% 11% 22% 16% 3	119698
Seeing	Day	23% 18% 31% 19% 7% 2	15482
	Night	22% 15% 32% 24% 7% 1	24654

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	12% 7% 3 8% 5% 4 4 3 5% 5% 43%	3597
	11th to 20th	Day	14% 8% 3 7% 4 4 5% 4 5% 5% 41%	3570
	21st to end	Day	18% 9% 2 6% 4 4 4 3 4 5% 40%	4070
February	1st to 10th	Day	17% 8% 2 7% 4 5% 4 5% 6% 6% 36%	1865
	11th to 20th	Day	14% 7% 3 6% 5% 5% 5% 3 6% 7% 39%	1948
	21st to end	Day	20% 9% 2 5% 4 3 4 4 4 5% 39%	1650
March	1st to 10th	Day	22% 9% 3 6% 3 3 4 3 4 5% 39%	4476
	11th to 20th	Day	14% 7% 2 6% 4 4 4 4 6% 7% 41%	4653
	21st to end	Day	19% 8% 3 6% 4 3 4 3 6% 7% 36%	5970
April	1st to 10th	Day	18% 9% 2 6% 5% 3 4 4 6% 7% 37%	2400
	11th to 20th	Day	19% 6% 2 6% 4 4 4 4 5% 7% 41%	2254
	21st to end	Day	21% 6% 2 5% 4 4 4 4 5% 6% 39%	2388
May	1st to 10th	Day	26% 9% 3 6% 4 3 3 3 5% 7% 29%	4106
	11th to 20th	Day	23% 8% 2 7% 4 4 4 3 5% 7% 32%	4286
	21st to end	Day	15% 5% 2 5% 3 4 4 4 6% 8% 45%	4837
June	1st to 10th	Day	17% 6% 2 5% 5% 5% 5% 4 7% 9% 34%	2660
	11th to 20th	Day	15% 6% 2 6% 5% 4 5% 5% 6% 9% 36%	2660
	21st to end	Day	13% 7% 2 7% 5% 4 5% 4 7% 8% 38%	2660
July	1st to 10th	Day	12% 6% 2 7% 6% 6% 6% 5% 6% 9% 35%	4440
	11th to 20th	Day	13% 5% 2 6% 5% 5% 5% 4 6% 9% 39%	4440
	21st to end	Day	17% 8% 3 7% 5% 4 5% 4 6% 7% 34%	4814
August	1st to 10th	Day	19% 6% 3 7% 6% 5% 5% 4 6% 8% 30%	4270
	11th to 20th	Day	12% 6% 2 7% 4 4 5% 4 6% 8% 42%	3761
	21st to end	Day	10% 5% 2 6% 4 4 5% 4 7% 9% 43%	4180
September	1st to 10th	Day	13% 6% 2 6% 4 4 4 4 5% 6% 45%	2280
	11th to 20th	Day	12% 6% 2 5% 3 3 4 2 5% 6% 50%	2148
	21st to end	Day	19% 5% 2 6% 4 4 4 3 5% 6% 41%	2090
October	1st to 10th	Day	21% 7% 2 5% 4 2 4 4 4 5% 41%	2059
	11th to 20th	Day	14% 6% 2 5% 4 3 4 3 6% 7% 47%	1881
	21st to end	Day	21% 6% 2 6% 3 4 4 3 4 6% 41%	1881
November	1st to 10th	Day	12% 6% 2 5% 5% 4 4 3 4 5% 49%	1761
	11th to 20th	Day	19% 5% 1 5% 3 3 4 3 5% 7% 47%	1800
	21st to end	Day	17% 8% 2 5% 4 3 4 3 5% 7% 42%	1764
December	1st to 10th	Day	16% 7% 2 5% 4 4 4 4 5% 6% 45%	2600
	11th to 20th	Day	21% 6% 2 4 3 3 3 3 4 6% 45%	2986
	21st to end	Day	19% 10% 4 7% 4 4 3 3 4 5% 38%	3960
January	1st to 10th	Night	14% 6% 2 6% 4 3 4 4 5% 6% 46%	6349
	11th to 20th	Night	14% 8% 3 7% 4 4 3 3 4 5% 45%	6315
	21st to end	Night	18% 9% 3 7% 4 4 4 3 4 5% 38%	6882
February	1st to 10th	Night	17% 9% 3 6% 5% 3 4 3 5% 5% 40%	2535
	11th to 20th	Night	16% 9% 2 6% 3 5% 4 3 6% 6% 40%	2338
	21st to end	Night	19% 8% 2 6% 6% 4 4 3 4 5% 40%	1980
March	1st to 10th	Night	21% 9% 2 6% 3 3 3 3 4 6% 40%	5364
	11th to 20th	Night	16% 9% 3 6% 4 4 4 4 5% 6% 40%	5291
	21st to end	Night	22% 10% 3 6% 3 4 3 3 5% 6% 38%	4962
April	1st to 10th	Night	19% 8% 2 6% 5% 4 5% 4 5% 6% 37%	2000
	11th to 20th	Night	19% 6% 2 6% 4 4 4 4 5% 7% 40%	1882
	21st to end	Night	21% 7% 2 7% 4 4 3 2 4 5% 41%	1791
May	1st to 10th	Night	25% 9% 4 7% 5% 4 4 3 4 6% 29%	2834
	11th to 20th	Night	22% 8% 4 8% 5% 4 4 4 5% 6% 31%	2636
	21st to end	Night	18% 6% 2 4 4 3 4 4 6% 7% 42%	2738
June	1st to 10th	Night	18% 7% 2 6% 4 4 5% 4 5% 6% 39%	1520
	11th to 20th	Night	16% 6% 2 6% 5% 4 4 4 5% 8% 40%	1520
	21st to end	Night	14% 5% 3 6% 5% 4 3 4 5% 9% 42%	1520
July	1st to 10th	Night	14% 5% 2 6% 5% 5% 5% 5% 9% 9% 36%	2520
	11th to 20th	Night	16% 6% 2 8% 4 4 4 4 7% 9% 37%	2520
	21st to end	Night	18% 9% 3 7% 5% 5% 5% 4 6% 6% 33%	2739
August	1st to 10th	Night	21% 6% 3 7% 4 5% 5% 5% 6% 7% 30%	2629
	11th to 20th	Night	14% 7% 2 7% 5% 5% 4 3 5% 7% 41%	3062
	21st to end	Night	10% 4 1 4 3 4 3 4 5% 8% 53%	3476
September	1st to 10th	Night	14% 6% 2 6% 5% 4 4 3 4 6% 45%	1900
	11th to 20th	Night	13% 6% 2 4 3 4 3 3 4 6% 51%	2031
	21st to end	Night	17% 6% 3 5% 4 4 4 3 5% 6% 43%	2090
October	1st to 10th	Night	20% 7% 2 6% 4 4 3 3 5% 5% 42%	2118
	11th to 20th	Night	15% 5% 2 5% 4 3 4 4 4 5% 49%	2298
	21st to end	Night	23% 7% 2 5% 3 3 4 3 4 6% 40%	2717
November	1st to 10th	Night	13% 6% 2 5% 4 4 4 3 5% 6% 49%	2537
	11th to 20th	Night	18% 7% 2 5% 3 3 3 3 5% 5% 46%	2600
	21st to end	Night	16% 8% 1 4 4 4 4 3 5% 6% 46%	2634
December	1st to 10th	Night	17% 7% 2 6% 4 3 3 3 4 5% 47%	4580
	11th to 20th	Night	25% 7% 2 4 3 3 3 3 3 4 41%	5208
	21st to end	Night	19% 10% 3 7% 4 3 3 3 4 5% 41%	6996

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	42% 4 8% 28% 15% 3	3598
	11th to 20th	Day	44% 5% 10% 21% 13% 7%	3600
	21st to end	Day	47% 5% 8% 23% 15% 1	4070
February	1st to 10th	Day	46% 6% 13% 19% 14% 2	1865
	11th to 20th	Day	43% 6% 10% 23% 15% 3	1957
	21st to end	Day	47% 5% 11% 20% 14% 3	1650
March	1st to 10th	Day	48% 4 10% 16% 13% 10%	4479
	11th to 20th	Day	39% 7% 14% 28% 11% 2	4653
	21st to end	Day	47% 5% 8% 15% 19% 6%	5970
April	1st to 10th	Day	47% 5% 11% 19% 15% 4	2400
	11th to 20th	Day	42% 6% 10% 21% 18% 3	2254
	21st to end	Day	45% 5% 10% 20% 16% 4	2388
May	1st to 10th	Day	53% 7% 13% 15% 11% 1	4120
	11th to 20th	Day	50% 7% 13% 19% 9% 2	4290
	21st to end	Day	35% 8% 13% 24% 18% 2	4837
June	1st to 10th	Day	44% 8% 12% 23% 12% 1	2660
	11th to 20th	Day	43% 8% 14% 21% 12% 2	2660
	21st to end	Day	42% 8% 13% 22% 14% 1	2660
July	1st to 10th	Day	45% 9% 11% 19% 15% 1	4370
	11th to 20th	Day	40% 8% 16% 22% 13% 1	4365
	21st to end	Day	48% 7% 12% 17% 15% 1	4661
August	1st to 10th	Day	50% 7% 14% 20% 8%	4256
	11th to 20th	Day	38% 8% 13% 29% 11% 1	3798
	21st to end	Day	35% 7% 13% 27% 16% 2	4180
September	1st to 10th	Day	40% 8% 10% 22% 19% 2	2280
	11th to 20th	Day	34% 6% 11% 23% 23% 3	2148
	21st to end	Day	44% 6% 9% 21% 18% 3	2090
October	1st to 10th	Day	39% 5% 9% 18% 23% 5%	3423
	11th to 20th	Day	28% 4 9% 24% 31% 4	3109
	21st to end	Day	33% 4 13% 24% 23% 3	3081
November	1st to 10th	Day	37% 5% 12% 22% 21% 3	1761
	11th to 20th	Day	38% 4 11% 23% 21% 4	1800
	21st to end	Day	43% 4 12% 25% 12% 3	1764
December	1st to 10th	Day	40% 4 16% 27% 12% 1	2600
	11th to 20th	Day	41% 4 15% 19% 18% 3	2986
	21st to end	Day	49% 4 7% 20% 15% 4	3960
January	1st to 10th	Night	39% 3 9% 28% 18% 3	6349
	11th to 20th	Night	43% 4 13% 20% 14% 6%	6360
	21st to end	Night	48% 4 10% 18% 16% 4	6882
February	1st to 10th	Night	46% 5% 13% 23% 12% 2	2535
	11th to 20th	Night	44% 5% 9% 20% 18% 4	2340
	21st to end	Night	46% 5% 9% 22% 14% 5%	1980
March	1st to 10th	Night	46% 4 10% 18% 15% 6%	5374
	11th to 20th	Night	43% 6% 16% 21% 11% 3	5292
	21st to end	Night	48% 4 7% 12% 24% 5%	4962
April	1st to 10th	Night	47% 6% 10% 19% 15% 3	2000
	11th to 20th	Night	43% 7% 10% 19% 20% 1	1882
	21st to end	Night	45% 5% 9% 22% 15% 4	1791
May	1st to 10th	Night	55% 7% 12% 15% 9% 1	2840
	11th to 20th	Night	53% 9% 13% 15% 9% 2	2637
	21st to end	Night	40% 7% 15% 24% 13% 1	2739
June	1st to 10th	Night	44% 7% 12% 20% 16% 1	1520
	11th to 20th	Night	41% 8% 14% 25% 11% 1	1520
	21st to end	Night	39% 8% 14% 25% 14%	1520
July	1st to 10th	Night	42% 10% 15% 18% 13% 1	2480
	11th to 20th	Night	43% 7% 16% 23% 10% 1	2472
	21st to end	Night	49% 8% 12% 14% 15% 2	2651
August	1st to 10th	Night	52% 9% 13% 16% 9% 1	2619
	11th to 20th	Night	42% 7% 13% 28% 9% 1	3091
	21st to end	Night	29% 7% 14% 33% 17% 1	3476
September	1st to 10th	Night	41% 6% 9% 25% 17% 1	1900
	11th to 20th	Night	34% 5% 11% 23% 25% 2	2031
	21st to end	Night	42% 7% 7% 21% 20% 2	2090
October	1st to 10th	Night	39% 5% 13% 22% 19% 2	3534
	11th to 20th	Night	26% 4 8% 28% 30% 3	3809
	21st to end	Night	33% 4 13% 29% 20% 2	4467
November	1st to 10th	Night	36% 6% 11% 21% 21% 4	2537
	11th to 20th	Night	41% 4 10% 22% 20% 4	2600
	21st to end	Night	40% 4 13% 29% 12% 1	2634
December	1st to 10th	Night	41% 4 11% 30% 13% 1	4580
	11th to 20th	Night	47% 4 12% 16% 18% 2	5208
	21st to end	Night	47% 3 9% 19% 17% 4	6996

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	31% 27% 28% 13% 2	200
	11th to 20th	Day	30% 30% 27% 11% 3	200
	21st to end	Day	26% 28% 33% 8% 5% 1	243
February	1st to 10th	Day	34% 24% 30% 11% 1	365
	11th to 20th	Day	30% 27% 32% 10% 1	496
	21st to end	Day	31% 21% 33% 12% 3	414
March	1st to 10th	Day	28% 24% 33% 12% 3	500
	11th to 20th	Day	29% 26% 31% 11% 3 1	500
	21st to end	Day	33% 22% 31% 9% 3 1	550
April	1st to 10th	Day	31% 27% 26% 10% 5% 1	500
	11th to 20th	Day	31% 19% 31% 13% 5% 1	452
	21st to end	Day	29% 20% 33% 12% 4 1	460
May	1st to 10th	Day	33% 21% 26% 14% 6% 1	463
	11th to 20th	Day	24% 18% 37% 15% 6% 1	487
	21st to end	Day	21% 14% 31% 24% 8% 2	529
June	1st to 10th	Day	19% 16% 32% 22% 9% 2	490
	11th to 20th	Day	16% 18% 37% 19% 8% 1	490
	21st to end	Day	17% 16% 33% 24% 9% 1	490
July	1st to 10th	Day	17% 9% 31% 27% 14% 2	485
	11th to 20th	Day	13% 9% 35% 29% 13% 2	484
	21st to end	Day	15% 10% 38% 27% 8% 1	532
August	1st to 10th	Day	13% 9% 29% 35% 9% 4	486
	11th to 20th	Day	13% 8% 34% 28% 13% 5%	479
	21st to end	Day	12% 11% 33% 24% 14% 6%	539
September	1st to 10th	Day	19% 12% 25% 22% 17% 4	490
	11th to 20th	Day	16% 11% 28% 24% 12% 9%	490
	21st to end	Day	23% 12% 33% 19% 8% 4	490
October	1st to 10th	Day	28% 12% 26% 17% 13% 4	490
	11th to 20th	Day	16% 19% 33% 23% 7% 2	480
	21st to end	Day	27% 16% 29% 19% 7% 1	429
November	1st to 10th	Day	19% 17% 32% 23% 8% 2	395
	11th to 20th	Day	30% 21% 25% 20% 5%	400
	21st to end	Day	28% 20% 28% 20% 5%	364
December	1st to 10th	Day	24% 25% 31% 14% 7%	200
	11th to 20th	Day	35% 25% 29% 11% 2	200
	21st to end	Day	29% 20% 29% 18% 3 1	220
January	1st to 10th	Night	23% 21% 37% 16% 3	800
	11th to 20th	Night	27% 19% 32% 20% 2	800
	21st to end	Night	21% 22% 35% 19% 2	880
February	1st to 10th	Night	24% 19% 35% 21% 2	800
	11th to 20th	Night	25% 23% 37% 14% 2	783
	21st to end	Night	27% 19% 36% 15% 3	660
March	1st to 10th	Night	25% 22% 33% 18% 2	800
	11th to 20th	Night	22% 22% 35% 19% 3 1	800
	21st to end	Night	25% 21% 34% 16% 3	880
April	1st to 10th	Night	26% 20% 36% 16% 3	800
	11th to 20th	Night	24% 18% 34% 20% 3	754
	21st to end	Night	23% 20% 34% 17% 4	651
May	1st to 10th	Night	26% 15% 34% 19% 5%	570
	11th to 20th	Night	22% 15% 39% 21% 3	463
	21st to end	Night	21% 8% 30% 33% 7% 1	411
June	1st to 10th	Night	20% 8% 32% 30% 9%	380
	11th to 20th	Night	19% 7% 33% 33% 9%	380
	21st to end	Night	16% 7% 34% 36% 8%	380
July	1st to 10th	Night	14% 5% 29% 38% 15%	370
	11th to 20th	Night	14% 4 27% 43% 12% 1	368
	21st to end	Night	13% 7% 30% 40% 9% 1	416
August	1st to 10th	Night	12% 5% 32% 42% 9% 1	449
	11th to 20th	Night	14% 5% 26% 37% 16% 2	727
	21st to end	Night	14% 5% 27% 36% 17% 2	836
September	1st to 10th	Night	17% 6% 31% 33% 13% 2	760
	11th to 20th	Night	17% 6% 27% 31% 17% 3	760
	21st to end	Night	20% 7% 29% 28% 14% 1	760
October	1st to 10th	Night	24% 10% 28% 25% 11% 2	760
	11th to 20th	Night	19% 13% 31% 28% 9% 1	760
	21st to end	Night	28% 13% 32% 20% 7%	836
November	1st to 10th	Night	17% 14% 35% 26% 9% 1	780
	11th to 20th	Night	24% 17% 34% 19% 6% 1	800
	21st to end	Night	24% 17% 31% 23% 5% 1	800
December	1st to 10th	Night	26% 16% 32% 20% 5% 1	800
	11th to 20th	Night	25% 20% 31% 21% 3	800
	21st to end	Night	28% 17% 35% 19% 2	880

Page generated at 2025-04-08 09:17:23. Version ac07

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