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 2025-05-11.

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	18% 7% 2 6% 4 4 4 3 5% 7% 41%	113431
	Night	18% 8% 2 6% 4 4 4 3 5% 6% 40%	115498
Transparency	Day	26% 42% 7% 13% 10% 2	117025
	Night	27% 40% 7% 13% 11% 2	120068
Seeing	Day	20% 14% 31% 24% 9% 2	15729
	Night	22% 11% 30% 26% 10% 1	24808

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 5% 3 4 3 3 5% 6% 48%	3597
	11th to 20th	Day	16% 8% 2 4 3 4 4 3 4 5% 47%	3570
	21st to end	Day	19% 8% 3 6% 4 4 3 3 3 5% 42%	3960
February	1st to 10th	Day	18% 7% 3 5% 5% 4 4 4 6% 7% 38%	1938
	11th to 20th	Day	14% 7% 2 6% 5% 4 4 4 6% 6% 41%	1948
	21st to end	Day	20% 8% 3 6% 3 3 3 4 4 7% 38%	1650
March	1st to 10th	Day	22% 8% 2 5% 3 3 3 2 4 5% 41%	4476
	11th to 20th	Day	14% 9% 2 6% 4 4 3 4 5% 7% 42%	4722
	21st to end	Day	23% 8% 2 6% 4 4 4 3 5% 7% 34%	5846
April	1st to 10th	Day	20% 7% 2 5% 3 4 4 3 5% 6% 40%	2400
	11th to 20th	Day	19% 6% 2 6% 3 4 3 3 5% 7% 42%	2374
	21st to end	Day	20% 6% 2 5% 4 4 4 4 5% 6% 39%	2565
May	1st to 10th	Day	27% 11% 3 6% 4 3 4 3 5% 7% 28%	4236
	11th to 20th	Day	23% 8% 3 7% 5% 4 4 3 5% 6% 33%	4126
	21st to end	Day	16% 6% 2 5% 4 3 4 4 5% 8% 44%	4837
June	1st to 10th	Day	18% 6% 2 5% 4 4 5% 4 7% 7% 37%	2660
	11th to 20th	Day	16% 6% 2 5% 4 4 4 4 6% 9% 38%	2660
	21st to end	Day	14% 7% 2 5% 4 5% 4 4 6% 9% 40%	2660
July	1st to 10th	Day	18% 8% 2 7% 4 5% 4 4 6% 8% 36%	4440
	11th to 20th	Day	17% 6% 2 5% 4 4 4 4 6% 10% 39%	4440
	21st to end	Day	21% 7% 3 7% 5% 4 5% 4 6% 7% 33%	4814
August	1st to 10th	Day	19% 7% 3 7% 5% 4 5% 4 6% 8% 32%	4138
	11th to 20th	Day	13% 5% 2 6% 4 4 5% 4 5% 9% 42%	3867
	21st to end	Day	7% 4 2 5% 5% 5% 6% 4 7% 9% 46%	4180
September	1st to 10th	Day	15% 6% 2 6% 3 3 4 4 5% 7% 45%	2280
	11th to 20th	Day	12% 6% 2 5% 3 3 3 3 5% 7% 51%	2100
	21st to end	Day	19% 7% 2 5% 3 4 5% 3 5% 5% 41%	2090
October	1st to 10th	Day	21% 7% 2 5% 3 3 3 2 5% 6% 43%	2090
	11th to 20th	Day	15% 5% 2 5% 3 3 4 3 5% 7% 48%	1880
	21st to end	Day	19% 5% 2 6% 4 3 4 4 5% 5% 45%	1881
November	1st to 10th	Day	14% 6% 2 5% 4 3 4 2 4 4 49%	1761
	11th to 20th	Day	16% 5% 2 4 3 3 3 4 6% 6% 49%	1800
	21st to end	Day	18% 6% 2 5% 3 3 4 3 5% 6% 45%	1800
December	1st to 10th	Day	15% 7% 2 5% 3 3 3 3 4 7% 47%	2699
	11th to 20th	Day	21% 7% 2 4 3 2 2 2 4 5% 47%	2986
	21st to end	Day	21% 10% 3 6% 4 2 3 2 4 5% 40%	3960
January	1st to 10th	Night	14% 5% 2 5% 3 3 4 3 5% 7% 51%	6349
	11th to 20th	Night	16% 9% 3 7% 4 4 4 2 3 4 45%	6315
	21st to end	Night	17% 9% 2 6% 5% 4 5% 4 5% 6% 36%	6996
February	1st to 10th	Night	16% 10% 3 7% 4 4 3 3 4 6% 41%	2459
	11th to 20th	Night	19% 7% 2 5% 5% 3 3 3 5% 6% 42%	2338
	21st to end	Night	19% 9% 2 5% 4 5% 4 3 4 5% 40%	1980
March	1st to 10th	Night	23% 8% 2 5% 3 4 3 3 4 6% 40%	5364
	11th to 20th	Night	17% 9% 3 6% 4 4 4 3 5% 6% 39%	5223
	21st to end	Night	22% 9% 3 5% 4 4 5% 3 5% 5% 35%	5082
April	1st to 10th	Night	21% 9% 3 4 4 4 4 3 3 6% 38%	2000
	11th to 20th	Night	20% 8% 2 5% 4 4 4 3 4 5% 41%	1975
	21st to end	Night	21% 7% 2 6% 5% 4 3 3 3 5% 40%	1833
May	1st to 10th	Night	25% 12% 4 7% 4 4 3 2 4 6% 28%	2924
	11th to 20th	Night	23% 10% 4 8% 4 5% 5% 4 6% 6% 25%	2802
	21st to end	Night	19% 8% 2 6% 4 4 4 4 6% 7% 36%	2738
June	1st to 10th	Night	19% 9% 3 5% 4 3 4 4 5% 7% 38%	1520
	11th to 20th	Night	20% 7% 2 5% 3 3 3 4 6% 8% 39%	1520
	21st to end	Night	16% 8% 2 5% 4 4 3 4 6% 9% 38%	1520
July	1st to 10th	Night	21% 10% 3 7% 4 4 5% 4 5% 8% 29%	2520
	11th to 20th	Night	19% 7% 2 6% 4 4 4 4 6% 9% 35%	2520
	21st to end	Night	21% 9% 3 7% 5% 4 4 4 5% 7% 31%	2739
August	1st to 10th	Night	24% 8% 3 7% 5% 5% 5% 4 7% 7% 27%	2757
	11th to 20th	Night	10% 6% 3 8% 4 6% 6% 5% 7% 9% 37%	2957
	21st to end	Night	8% 4 1 4 3 3 4 4 6% 9% 53%	3476
September	1st to 10th	Night	15% 6% 3 6% 5% 5% 4 4 6% 6% 40%	1900
	11th to 20th	Night	13% 7% 2 4 3 3 3 3 4 6% 52%	2079
	21st to end	Night	20% 7% 3 7% 5% 4 4 4 4 4 38%	2090
October	1st to 10th	Night	19% 9% 2 6% 4 3 3 2 4 6% 40%	2090
	11th to 20th	Night	15% 6% 2 5% 4 3 3 3 5% 7% 48%	2298
	21st to end	Night	19% 7% 2 6% 3 3 4 3 5% 6% 41%	2717
November	1st to 10th	Night	13% 6% 2 6% 4 4 4 3 5% 6% 47%	2537
	11th to 20th	Night	19% 6% 2 5% 3 3 3 3 4 5% 47%	2600
	21st to end	Night	15% 5% 2 5% 4 4 4 3 4 7% 46%	2600
December	1st to 10th	Night	18% 7% 2 5% 4 3 3 2 3 5% 48%	4476
	11th to 20th	Night	25% 7% 2 4 3 3 3 2 4 4 42%	5208
	21st to end	Night	19% 9% 3 6% 3 3 3 2 4 5% 43%	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	27% 26% 5% 21% 18% 3	3598
	11th to 20th	Day	27% 27% 7% 17% 14% 8%	3600
	21st to end	Day	37% 28% 6% 15% 14% 1	3960
February	1st to 10th	Day	18% 62% 7% 7% 4 1	1938
	11th to 20th	Day	19% 61% 2 8% 8% 1	1957
	21st to end	Day	17% 61% 6% 8% 6% 2	1650
March	1st to 10th	Day	35% 29% 7% 10% 9% 10%	4479
	11th to 20th	Day	27% 31% 10% 23% 9% 1	4722
	21st to end	Day	39% 29% 5% 11% 12% 5%	5846
April	1st to 10th	Day	20% 61% 4 7% 6% 1	2400
	11th to 20th	Day	16% 62% 3 8% 9% 1	2374
	21st to end	Day	18% 62% 3 9% 6% 1	2565
May	1st to 10th	Day	39% 39% 12% 7% 4	4250
	11th to 20th	Day	35% 39% 12% 9% 4	4130
	21st to end	Day	26% 40% 4 18% 12%	4837
June	1st to 10th	Day	15% 65% 4 9% 6%	2660
	11th to 20th	Day	14% 65% 5% 9% 6% 1	2660
	21st to end	Day	13% 64% 4 10% 8%	2660
July	1st to 10th	Day	34% 39% 6% 11% 9% 1	4370
	11th to 20th	Day	28% 38% 12% 14% 8% 1	4365
	21st to end	Day	36% 37% 9% 10% 7% 1	4661
August	1st to 10th	Day	34% 38% 10% 13% 4	4124
	11th to 20th	Day	24% 39% 11% 22% 4	3906
	21st to end	Day	16% 40% 12% 19% 12% 1	4180
September	1st to 10th	Day	16% 60% 5% 11% 7%	2280
	11th to 20th	Day	15% 60% 4 10% 10% 1	2100
	21st to end	Day	21% 60% 4 8% 7%	2090
October	1st to 10th	Day	22% 37% 6% 16% 14% 5%	3480
	11th to 20th	Day	15% 37% 4 15% 27% 3	3096
	21st to end	Day	17% 37% 10% 20% 14% 2	3081
November	1st to 10th	Day	18% 56% 7% 9% 9% 1	1761
	11th to 20th	Day	15% 56% 4 10% 12% 3	1800
	21st to end	Day	16% 57% 4 14% 7% 2	1800
December	1st to 10th	Day	24% 36% 10% 21% 10%	2699
	11th to 20th	Day	28% 31% 9% 12% 16% 4	2986
	21st to end	Day	38% 27% 4 16% 12% 4	3960
January	1st to 10th	Night	25% 25% 6% 25% 16% 3	6349
	11th to 20th	Night	32% 26% 8% 16% 13% 5%	6360
	21st to end	Night	39% 27% 7% 13% 10% 3	6996
February	1st to 10th	Night	19% 62% 5% 9% 4 1	2459
	11th to 20th	Night	17% 60% 4 7% 11% 2	2340
	21st to end	Night	18% 62% 3 7% 7% 2	1980
March	1st to 10th	Night	37% 28% 7% 12% 9% 7%	5374
	11th to 20th	Night	34% 29% 11% 16% 8% 2	5224
	21st to end	Night	39% 29% 3 7% 19% 4	5082
April	1st to 10th	Night	21% 61% 4 7% 6% 2	2000
	11th to 20th	Night	17% 62% 5% 7% 8% 1	1975
	21st to end	Night	19% 62% 3 8% 7% 1	1833
May	1st to 10th	Night	40% 38% 9% 9% 3	2930
	11th to 20th	Night	42% 40% 10% 7% 2	2803
	21st to end	Night	29% 40% 8% 16% 7%	2739
June	1st to 10th	Night	16% 65% 2 9% 8% 1	1520
	11th to 20th	Night	13% 65% 5% 10% 6% 1	1520
	21st to end	Night	14% 64% 4 12% 6% 1	1520
July	1st to 10th	Night	38% 37% 6% 10% 9%	2480
	11th to 20th	Night	31% 38% 11% 15% 6%	2472
	21st to end	Night	37% 37% 9% 8% 9% 1	2651
August	1st to 10th	Night	39% 39% 7% 9% 4 1	2747
	11th to 20th	Night	26% 40% 10% 20% 4	2984
	21st to end	Night	13% 38% 12% 22% 14%	3476
September	1st to 10th	Night	17% 61% 4 12% 7% 1	1900
	11th to 20th	Night	15% 60% 4 9% 11% 1	2079
	21st to end	Night	22% 61% 2 7% 8%	2090
October	1st to 10th	Night	25% 37% 7% 17% 12% 2	3480
	11th to 20th	Night	11% 37% 4 16% 29% 4	3821
	21st to end	Night	16% 37% 8% 20% 17% 1	4467
November	1st to 10th	Night	18% 56% 5% 9% 10% 1	2537
	11th to 20th	Night	17% 56% 4 8% 12% 4	2600
	21st to end	Night	16% 57% 6% 14% 6% 1	2600
December	1st to 10th	Night	26% 35% 7% 20% 11% 1	4476
	11th to 20th	Night	34% 31% 6% 11% 16% 1	5208
	21st to end	Night	34% 27% 6% 14% 15% 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	24% 27% 27% 17% 6%	200
	11th to 20th	Day	22% 33% 30% 13% 3	200
	21st to end	Day	22% 22% 38% 12% 6%	220
February	1st to 10th	Day	26% 20% 35% 17% 2	444
	11th to 20th	Day	24% 26% 36% 13% 1	496
	21st to end	Day	23% 24% 33% 15% 4	414
March	1st to 10th	Day	22% 23% 32% 19% 3	500
	11th to 20th	Day	18% 22% 38% 17% 3 1	500
	21st to end	Day	27% 19% 35% 13% 5% 1	550
April	1st to 10th	Day	24% 23% 30% 17% 6% 1	500
	11th to 20th	Day	24% 15% 36% 19% 6%	492
	21st to end	Day	25% 14% 34% 19% 5% 2	500
May	1st to 10th	Day	28% 15% 34% 17% 5% 1	503
	11th to 20th	Day	19% 13% 34% 27% 5% 1	487
	21st to end	Day	19% 6% 26% 33% 12% 3	529
June	1st to 10th	Day	17% 10% 30% 27% 15% 2	490
	11th to 20th	Day	16% 8% 31% 32% 11% 1	490
	21st to end	Day	16% 9% 29% 29% 14% 2	490
July	1st to 10th	Day	18% 7% 25% 30% 17% 3	485
	11th to 20th	Day	14% 6% 21% 37% 16% 5%	484
	21st to end	Day	14% 6% 30% 36% 12% 2	532
August	1st to 10th	Day	14% 6% 26% 36% 14% 4	486
	11th to 20th	Day	16% 4 25% 32% 17% 5%	479
	21st to end	Day	12% 4 28% 34% 16% 7%	539
September	1st to 10th	Day	19% 7% 23% 30% 16% 5%	490
	11th to 20th	Day	15% 6% 28% 29% 16% 6%	490
	21st to end	Day	23% 7% 31% 27% 10% 2	490
October	1st to 10th	Day	24% 10% 26% 23% 13% 4	490
	11th to 20th	Day	17% 16% 27% 25% 14% 2	455
	21st to end	Day	23% 12% 31% 23% 9% 1	429
November	1st to 10th	Day	14% 15% 33% 25% 10% 2	395
	11th to 20th	Day	19% 22% 33% 20% 6%	400
	21st to end	Day	21% 21% 29% 21% 8% 1	400
December	1st to 10th	Day	22% 19% 37% 17% 5%	260
	11th to 20th	Day	26% 26% 29% 16% 4	200
	21st to end	Day	23% 18% 38% 13% 5% 3	220
January	1st to 10th	Night	21% 20% 36% 21% 3	800
	11th to 20th	Night	28% 18% 34% 18% 3	800
	21st to end	Night	22% 20% 35% 21% 2	880
February	1st to 10th	Night	22% 17% 35% 24% 2	800
	11th to 20th	Night	25% 17% 40% 15% 2	783
	21st to end	Night	24% 18% 36% 18% 3	660
March	1st to 10th	Night	25% 15% 34% 22% 4 1	800
	11th to 20th	Night	21% 13% 37% 23% 5% 1	800
	21st to end	Night	24% 13% 36% 21% 6% 1	880
April	1st to 10th	Night	27% 10% 32% 26% 5%	800
	11th to 20th	Night	24% 9% 33% 26% 8%	791
	21st to end	Night	24% 7% 33% 26% 8% 1	633
May	1st to 10th	Night	28% 7% 27% 28% 10% 1	600
	11th to 20th	Night	22% 6% 35% 29% 7% 1	560
	21st to end	Night	23% 2 20% 36% 16% 3	411
June	1st to 10th	Night	22% 3 22% 36% 17% 1	380
	11th to 20th	Night	24% 5% 18% 38% 14% 1	380
	21st to end	Night	20% 5% 17% 40% 18% 1	380
July	1st to 10th	Night	19% 4 16% 34% 25% 2	370
	11th to 20th	Night	14% 4 14% 43% 24% 1	368
	21st to end	Night	16% 4 14% 43% 20% 2	416
August	1st to 10th	Night	13% 4 17% 43% 21% 2	525
	11th to 20th	Night	15% 2 18% 39% 23% 3	659
	21st to end	Night	15% 2 15% 38% 25% 5%	836
September	1st to 10th	Night	18% 3 22% 35% 19% 4	760
	11th to 20th	Night	17% 4 22% 29% 22% 6%	760
	21st to end	Night	23% 5% 25% 29% 15% 3	760
October	1st to 10th	Night	23% 8% 26% 24% 15% 4	760
	11th to 20th	Night	17% 11% 33% 26% 11% 2	760
	21st to end	Night	23% 11% 35% 22% 8% 1	836
November	1st to 10th	Night	16% 11% 31% 28% 12% 1	780
	11th to 20th	Night	22% 18% 32% 21% 7% 1	800
	21st to end	Night	19% 19% 34% 22% 7% 1	800
December	1st to 10th	Night	26% 17% 32% 21% 4 1	800
	11th to 20th	Night	24% 18% 35% 19% 4	800
	21st to end	Night	24% 16% 36% 21% 4	880

Page generated at 2025-05-08 09:34:01. Version ac07

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