Pawcatuck River Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Pawcatuck River Observatory clear sky chart from 2005-11-06 to 2026-09-14.

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	18% 7% 2 6% 4 4 4 3 5% 7% 40%	148595
	Night	19% 8% 2 6% 4 4 4 3 5% 6% 40%	142497
Transparency	Day	30% 34% 9% 16% 11% 2	152143
	Night	31% 33% 8% 15% 11% 2	147038
Seeing	Day	20% 15% 31% 23% 9% 2	17525
	Night	22% 11% 30% 26% 10% 1	26410

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	13% 9% 2 6% 3 4 4 3 5% 6% 45%	4661
	11th to 20th	Day	17% 8% 2 5% 3 4 3 3 4 5% 47%	4650
	21st to end	Day	16% 8% 3 5% 3 3 3 3 4 6% 46%	5124
February	1st to 10th	Day	17% 7% 3 5% 5% 4 4 4 6% 6% 39%	2036
	11th to 20th	Day	15% 7% 2 6% 4 4 4 4 6% 6% 41%	2048
	21st to end	Day	20% 9% 3 6% 3 3 3 4 4 7% 38%	1730
March	1st to 10th	Day	22% 9% 2 5% 3 3 3 2 4 5% 41%	4576
	11th to 20th	Day	14% 9% 2 6% 4 4 3 4 5% 7% 42%	4826
	21st to end	Day	23% 8% 2 6% 4 4 4 4 5% 7% 34%	5975
April	1st to 10th	Day	20% 7% 2 5% 3 4 4 3 5% 6% 40%	2520
	11th to 20th	Day	19% 6% 2 5% 3 4 3 3 5% 7% 42%	2494
	21st to end	Day	20% 6% 2 5% 4 4 4 4 5% 6% 39%	2693
May	1st to 10th	Day	27% 10% 3 6% 3 3 4 3 5% 7% 30%	7639
	11th to 20th	Day	20% 8% 3 7% 4 4 4 3 4 6% 38%	7698
	21st to end	Day	23% 8% 2 7% 4 4 4 3 5% 7% 32%	9060
June	1st to 10th	Day	17% 6% 2 5% 4 4 5% 4 7% 7% 38%	2940
	11th to 20th	Day	16% 6% 2 6% 4 4 4 4 6% 9% 38%	2940
	21st to end	Day	14% 6% 2 5% 4 5% 4 4 6% 9% 41%	2940
July	1st to 10th	Day	20% 7% 2 6% 3 4 4 4 6% 9% 35%	8280
	11th to 20th	Day	13% 6% 2 5% 4 4 4 4 6% 11% 42%	8280
	21st to end	Day	18% 6% 2 6% 4 3 4 3 5% 7% 43%	8993
August	1st to 10th	Day	16% 7% 3 7% 5% 5% 5% 4 7% 9% 33%	6063
	11th to 20th	Day	12% 4 2 6% 4 4 5% 4 6% 9% 45%	5700
	21st to end	Day	11% 4 2 5% 4 5% 5% 4 7% 9% 44%	6080
September	1st to 10th	Day	16% 6% 2 6% 3 3 4 4 5% 7% 44%	2520
	11th to 20th	Day	12% 6% 2 5% 3 3 3 3 5% 7% 51%	2244
	21st to end	Day	19% 7% 2 5% 4 4 5% 3 5% 5% 40%	2200
October	1st to 10th	Day	21% 6% 2 5% 3 3 3 2 5% 5% 45%	2200
	11th to 20th	Day	16% 5% 2 5% 3 3 4 3 5% 7% 47%	1978
	21st to end	Day	19% 5% 2 6% 3 3 3 4 4 5% 45%	1980
November	1st to 10th	Day	14% 6% 2 5% 4 3 4 2 4 4 50%	1851
	11th to 20th	Day	15% 5% 2 4 3 3 4 4 6% 6% 48%	1890
	21st to end	Day	18% 6% 2 6% 3 3 4 3 4 6% 45%	1890
December	1st to 10th	Day	15% 7% 2 5% 3 3 3 3 4 7% 47%	2782
	11th to 20th	Day	21% 7% 2 4 3 2 2 2 4 5% 48%	3066
	21st to end	Day	21% 10% 3 6% 4 2 3 2 4 5% 40%	4048
January	1st to 10th	Night	16% 7% 2 5% 3 3 3 2 4 6% 49%	8234
	11th to 20th	Night	17% 9% 3 7% 4 4 4 3 4 5% 43%	8235
	21st to end	Night	16% 9% 2 6% 4 4 5% 4 5% 6% 40%	9057
February	1st to 10th	Night	16% 9% 3 7% 4 4 3 3 4 6% 41%	2581
	11th to 20th	Night	19% 7% 2 5% 5% 3 3 3 5% 6% 42%	2458
	21st to end	Night	19% 10% 2 5% 4 5% 4 3 4 5% 40%	2076
March	1st to 10th	Night	23% 8% 2 4 3 4 3 3 4 6% 40%	5484
	11th to 20th	Night	17% 9% 3 6% 4 4 4 3 5% 6% 40%	5339
	21st to end	Night	22% 8% 3 5% 4 4 5% 4 5% 5% 35%	5195
April	1st to 10th	Night	21% 9% 2 4 4 4 4 3 4 6% 38%	2100
	11th to 20th	Night	19% 8% 2 5% 4 3 4 4 4 6% 41%	2075
	21st to end	Night	21% 7% 2 6% 5% 4 3 3 3 5% 40%	1925
May	1st to 10th	Night	27% 10% 3 6% 4 3 3 2 4 6% 32%	5259
	11th to 20th	Night	20% 9% 3 7% 4 4 4 3 6% 7% 33%	5217
	21st to end	Night	24% 9% 2 7% 4 5% 5% 4 6% 6% 28%	5114
June	1st to 10th	Night	18% 8% 3 5% 4 3 4 4 5% 6% 39%	1680
	11th to 20th	Night	21% 7% 2 5% 3 3 3 4 6% 9% 38%	1680
	21st to end	Night	16% 8% 2 5% 4 4 4 4 6% 9% 39%	1680
July	1st to 10th	Night	23% 10% 3 7% 4 4 4 4 5% 8% 29%	4680
	11th to 20th	Night	18% 10% 2 5% 4 3 4 4 6% 7% 37%	4680
	21st to end	Night	16% 7% 2 5% 4 4 5% 4 5% 7% 40%	5084
August	1st to 10th	Night	20% 8% 2 7% 5% 5% 5% 4 7% 8% 30%	4037
	11th to 20th	Night	11% 6% 3 7% 4 6% 6% 5% 6% 8% 38%	4342
	21st to end	Night	12% 5% 1 5% 4 3 4 4 6% 8% 48%	5045
September	1st to 10th	Night	15% 6% 3 6% 5% 5% 4 4 6% 7% 40%	2100
	11th to 20th	Night	13% 7% 2 5% 3 3 3 3 4 6% 52%	2222
	21st to end	Night	20% 7% 3 7% 5% 4 4 4 4 4 38%	2200
October	1st to 10th	Night	18% 8% 2 6% 4 3 3 2 4 6% 42%	2200
	11th to 20th	Night	15% 6% 2 5% 4 3 3 3 5% 7% 47%	2420
	21st to end	Night	19% 7% 2 6% 3 3 4 3 5% 6% 42%	2860
November	1st to 10th	Night	13% 6% 2 6% 4 4 4 3 5% 6% 47%	2667
	11th to 20th	Night	18% 6% 2 5% 3 3 3 3 4 5% 48%	2730
	21st to end	Night	15% 5% 2 5% 4 4 4 3 4 7% 46%	2730
December	1st to 10th	Night	18% 7% 2 5% 4 3 3 2 4 5% 48%	4613
	11th to 20th	Night	25% 7% 2 4 3 3 3 2 4 4 42%	5348
	21st to end	Night	19% 9% 3 6% 3 3 3 2 4 5% 43%	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	32% 21% 8% 20% 17% 2	4662
	11th to 20th	Day	31% 21% 7% 17% 15% 8%	4680
	21st to end	Day	33% 22% 8% 19% 16% 1	5124
February	1st to 10th	Day	19% 59% 7% 8% 6% 1	2036
	11th to 20th	Day	20% 58% 3 9% 9% 1	2057
	21st to end	Day	18% 59% 6% 9% 6% 2	1730
March	1st to 10th	Day	36% 28% 7% 10% 9% 10%	4579
	11th to 20th	Day	27% 30% 10% 23% 9% 1	4826
	21st to end	Day	39% 28% 6% 11% 12% 5%	5975
April	1st to 10th	Day	21% 59% 4 8% 7% 1	2520
	11th to 20th	Day	17% 60% 5% 9% 9% 1	2494
	21st to end	Day	19% 59% 3 10% 7% 1	2693
May	1st to 10th	Day	44% 24% 12% 11% 7% 1	7651
	11th to 20th	Day	39% 24% 12% 17% 8%	7702
	21st to end	Day	45% 24% 7% 16% 8%	9061
June	1st to 10th	Day	17% 60% 5% 10% 8%	2940
	11th to 20th	Day	17% 59% 6% 10% 6% 1	2940
	21st to end	Day	15% 59% 6% 11% 9% 1	2940
July	1st to 10th	Day	39% 25% 11% 16% 9% 1	8210
	11th to 20th	Day	30% 24% 12% 23% 10%	8205
	21st to end	Day	34% 22% 8% 20% 15% 1	8795
August	1st to 10th	Day	36% 29% 15% 14% 6%	6049
	11th to 20th	Day	25% 28% 14% 27% 4	5739
	21st to end	Day	24% 29% 13% 21% 11% 1	6080
September	1st to 10th	Day	18% 55% 5% 14% 8%	2520
	11th to 20th	Day	16% 56% 4 11% 12% 1	2244
	21st to end	Day	22% 57% 5% 9% 7%	2200
October	1st to 10th	Day	21% 36% 6% 16% 15% 5%	3590
	11th to 20th	Day	16% 36% 5% 15% 26% 3	3194
	21st to end	Day	17% 36% 10% 20% 15% 2	3180
November	1st to 10th	Day	19% 53% 7% 9% 10% 1	1851
	11th to 20th	Day	15% 54% 4 11% 13% 3	1890
	21st to end	Day	18% 54% 4 15% 7% 2	1890
December	1st to 10th	Day	24% 35% 10% 21% 10%	2782
	11th to 20th	Day	28% 30% 9% 12% 16% 4	3066
	21st to end	Day	38% 26% 4 16% 12% 4	4048
January	1st to 10th	Night	31% 20% 7% 24% 16% 2	8234
	11th to 20th	Night	36% 20% 8% 17% 14% 5%	8280
	21st to end	Night	39% 22% 7% 15% 14% 3	9057
February	1st to 10th	Night	19% 59% 5% 10% 5% 1	2581
	11th to 20th	Night	18% 57% 4 8% 11% 2	2460
	21st to end	Night	20% 59% 3 8% 7% 2	2076
March	1st to 10th	Night	37% 28% 7% 12% 9% 7%	5494
	11th to 20th	Night	34% 28% 11% 16% 9% 2	5340
	21st to end	Night	39% 28% 3 7% 18% 4	5195
April	1st to 10th	Night	22% 58% 4 8% 6% 2	2100
	11th to 20th	Night	18% 60% 6% 7% 8% 1	2075
	21st to end	Night	20% 59% 3 8% 8% 1	1925
May	1st to 10th	Night	44% 23% 12% 12% 8%	5265
	11th to 20th	Night	42% 24% 13% 15% 5% 2	5218
	21st to end	Night	47% 23% 8% 16% 5%	5115
June	1st to 10th	Night	17% 59% 3 11% 9% 1	1680
	11th to 20th	Night	17% 60% 5% 11% 6% 1	1680
	21st to end	Night	16% 58% 5% 13% 6% 1	1680
July	1st to 10th	Night	46% 22% 9% 14% 10%	4640
	11th to 20th	Night	38% 22% 10% 20% 10% 1	4632
	21st to end	Night	34% 22% 11% 20% 13%	4967
August	1st to 10th	Night	40% 30% 13% 10% 7% 1	4027
	11th to 20th	Night	30% 30% 13% 23% 3	4369
	21st to end	Night	24% 28% 13% 23% 12%	5045
September	1st to 10th	Night	19% 56% 4 14% 7% 1	2100
	11th to 20th	Night	16% 56% 5% 10% 12% 1	2222
	21st to end	Night	24% 58% 3 8% 8%	2200
October	1st to 10th	Night	24% 36% 7% 18% 13% 2	3590
	11th to 20th	Night	12% 36% 4 16% 28% 4	3943
	21st to end	Night	17% 36% 8% 20% 18% 1	4610
November	1st to 10th	Night	19% 54% 5% 10% 10% 2	2667
	11th to 20th	Night	17% 53% 4 9% 12% 4	2730
	21st to end	Night	17% 54% 6% 15% 7% 1	2730
December	1st to 10th	Night	27% 34% 7% 20% 11% 1	4613
	11th to 20th	Night	34% 30% 7% 11% 17% 2	5348
	21st to end	Night	35% 27% 6% 14% 15% 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	24% 27% 27% 16% 5%	220
	11th to 20th	Day	23% 34% 29% 12% 3	220
	21st to end	Day	24% 24% 36% 11% 5%	242
February	1st to 10th	Day	24% 20% 36% 17% 2	482
	11th to 20th	Day	24% 26% 37% 13% 1	536
	21st to end	Day	24% 24% 33% 15% 4	446
March	1st to 10th	Day	23% 22% 32% 19% 3	540
	11th to 20th	Day	20% 22% 38% 17% 3 1	540
	21st to end	Day	27% 22% 33% 13% 5% 1	594
April	1st to 10th	Day	25% 24% 29% 16% 5% 1	540
	11th to 20th	Day	24% 16% 36% 18% 6%	532
	21st to end	Day	25% 15% 36% 18% 5% 1	540
May	1st to 10th	Day	27% 17% 34% 16% 4 1	543
	11th to 20th	Day	19% 15% 35% 26% 4 1	567
	21st to end	Day	22% 10% 27% 29% 10% 3	617
June	1st to 10th	Day	16% 12% 31% 26% 13% 2	570
	11th to 20th	Day	18% 11% 32% 29% 9% 1	570
	21st to end	Day	17% 9% 30% 29% 13% 2	570
July	1st to 10th	Day	18% 8% 28% 29% 15% 2	565
	11th to 20th	Day	13% 8% 24% 35% 15% 4	564
	21st to end	Day	15% 8% 31% 34% 11% 2	620
August	1st to 10th	Day	13% 7% 28% 34% 14% 4	566
	11th to 20th	Day	15% 6% 28% 32% 15% 4	559
	21st to end	Day	12% 7% 30% 31% 14% 6%	627
September	1st to 10th	Day	19% 8% 27% 27% 14% 5%	570
	11th to 20th	Day	15% 5% 30% 29% 15% 6%	542
	21st to end	Day	22% 8% 31% 27% 10% 2	530
October	1st to 10th	Day	23% 10% 26% 22% 14% 5%	530
	11th to 20th	Day	18% 17% 27% 23% 13% 1	491
	21st to end	Day	24% 13% 32% 22% 8% 2	462
November	1st to 10th	Day	15% 16% 32% 24% 10% 2	425
	11th to 20th	Day	19% 23% 33% 20% 6%	430
	21st to end	Day	22% 22% 27% 20% 7% 1	430
December	1st to 10th	Day	22% 20% 37% 16% 5%	283
	11th to 20th	Day	28% 26% 28% 15% 4	220
	21st to end	Day	26% 19% 36% 12% 5% 2	242
January	1st to 10th	Night	21% 20% 36% 20% 3	840
	11th to 20th	Night	29% 18% 33% 18% 3	840
	21st to end	Night	23% 20% 34% 20% 2	924
February	1st to 10th	Night	22% 17% 36% 23% 2	840
	11th to 20th	Night	25% 17% 40% 16% 2	823
	21st to end	Night	25% 18% 36% 18% 3	692
March	1st to 10th	Night	26% 14% 33% 23% 4	840
	11th to 20th	Night	21% 14% 36% 23% 5% 1	840
	21st to end	Night	24% 14% 35% 20% 5% 1	924
April	1st to 10th	Night	27% 11% 31% 25% 5%	840
	11th to 20th	Night	23% 9% 34% 25% 8%	831
	21st to end	Night	24% 7% 34% 26% 8% 1	665
May	1st to 10th	Night	27% 8% 27% 27% 10% 1	630
	11th to 20th	Night	21% 8% 35% 29% 6% 1	617
	21st to end	Night	25% 3 22% 34% 15% 2	455
June	1st to 10th	Night	21% 4 23% 36% 16%	420
	11th to 20th	Night	24% 6% 19% 36% 13%	420
	21st to end	Night	20% 4 18% 40% 17%	420
July	1st to 10th	Night	20% 4 17% 34% 23% 2	410
	11th to 20th	Night	15% 5% 15% 40% 23% 1	408
	21st to end	Night	16% 4 15% 44% 19% 2	460
August	1st to 10th	Night	14% 4 17% 43% 21% 2	581
	11th to 20th	Night	15% 3 19% 40% 21% 3	729
	21st to end	Night	15% 4 17% 37% 23% 5%	924
September	1st to 10th	Night	18% 4 22% 35% 18% 3	840
	11th to 20th	Night	16% 4 23% 31% 22% 5%	813
	21st to end	Night	24% 6% 25% 29% 14% 3	800
October	1st to 10th	Night	22% 8% 26% 24% 16% 4	800
	11th to 20th	Night	18% 11% 33% 25% 11% 2	800
	21st to end	Night	23% 12% 35% 21% 8% 1	880
November	1st to 10th	Night	17% 11% 31% 27% 12% 1	820
	11th to 20th	Night	22% 19% 31% 21% 6%	840
	21st to end	Night	19% 19% 33% 22% 7% 1	840
December	1st to 10th	Night	26% 18% 32% 20% 4 1	840
	11th to 20th	Night	25% 18% 35% 18% 4	840
	21st to end	Night	25% 17% 35% 20% 3	924

Page generated at 2026-09-11 04:11:51. Version ac07

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