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 2024-03-06.

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% 6% 2 5% 5% 3 4 4 5% 7% 41%	78393
	Night	18% 7% 3 5% 5% 3 4 4 5% 6% 41%	81115
Transparency	Day	29% 35% 8% 16% 10% 1	78098
	Night	32% 33% 8% 16% 10% 1	80944
Seeing	Day	20% 13% 30% 25% 10% 2	14173
	Night	21% 11% 30% 27% 10% 1	23293

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	16% 8% 2 4 4 3 3 4 4 5% 46%	2517
	11th to 20th	Day	19% 8% 2 4 5% 3 4 4 5% 5% 40%	2520
	21st to end	Day	23% 10% 4 5% 5% 2 3 3 3 6% 35%	2772
February	1st to 10th	Day	19% 7% 3 4 5% 3 5% 4 5% 7% 38%	1840
	11th to 20th	Day	14% 7% 3 5% 5% 3 4 4 6% 7% 42%	1848
	21st to end	Day	21% 8% 3 5% 4 3 4 4 4 7% 37%	1570
March	1st to 10th	Day	16% 6% 2 5% 4 3 4 4 5% 7% 44%	1847
	11th to 20th	Day	17% 6% 2 5% 4 3 4 5% 6% 8% 39%	1876
	21st to end	Day	19% 8% 3 5% 5% 3 4 3 4 6% 39%	2322
April	1st to 10th	Day	19% 6% 3 4 4 3 4 4 5% 7% 41%	2160
	11th to 20th	Day	19% 6% 3 4 4 3 3 4 4 7% 43%	2134
	21st to end	Day	21% 6% 2 4 5% 3 5% 5% 5% 6% 38%	2308
May	1st to 10th	Day	24% 8% 3 5% 5% 3 4 3 5% 6% 35%	2340
	11th to 20th	Day	20% 5% 2 4 5% 3 5% 4 5% 6% 41%	2318
	21st to end	Day	16% 7% 2 4 5% 3 4 5% 5% 7% 43%	2725
June	1st to 10th	Day	19% 6% 2 4 5% 3 5% 5% 6% 8% 36%	2520
	11th to 20th	Day	17% 5% 3 5% 5% 3 5% 5% 6% 9% 37%	2520
	21st to end	Day	13% 6% 2 5% 5% 3 5% 5% 6% 9% 41%	2520
July	1st to 10th	Day	14% 5% 2 5% 5% 3 4 5% 6% 8% 43%	2520
	11th to 20th	Day	14% 6% 2 4 5% 3 4 5% 6% 10% 41%	2520
	21st to end	Day	14% 5% 2 6% 5% 3 5% 6% 7% 8% 40%	2744
August	1st to 10th	Day	12% 6% 2 5% 5% 4 5% 5% 6% 10% 40%	2346
	11th to 20th	Day	14% 5% 2 5% 5% 3 5% 5% 6% 9% 41%	2210
	21st to end	Day	12% 5% 2 4 5% 3 5% 5% 7% 8% 43%	2376
September	1st to 10th	Day	16% 6% 2 5% 4 3 4 5% 5% 7% 43%	2160
	11th to 20th	Day	13% 6% 2 4 4 3 3 3 5% 7% 51%	1990
	21st to end	Day	19% 6% 2 4 4 3 5% 4 4 6% 43%	1980
October	1st to 10th	Day	22% 6% 3 4 4 2 3 3 5% 5% 42%	1980
	11th to 20th	Day	16% 5% 2 4 3 2 4 4 5% 8% 46%	1782
	21st to end	Day	20% 5% 2 5% 4 2 4 4 5% 5% 44%	1782
November	1st to 10th	Day	15% 6% 2 4 5% 3 4 3 4 5% 48%	1671
	11th to 20th	Day	17% 5% 3 4 4 2 4 4 6% 6% 47%	1710
	21st to end	Day	17% 6% 2 5% 4 2 4 4 5% 6% 45%	1710
December	1st to 10th	Day	22% 6% 2 4 5% 3 4 4 5% 7% 39%	1577
	11th to 20th	Day	23% 6% 3 4 3 2 3 2 3 6% 45%	1906
	21st to end	Day	21% 10% 3 5% 5% 2 3 4 4 5% 36%	2772
January	1st to 10th	Night	18% 6% 2 4 3 2 4 3 4 7% 48%	4429
	11th to 20th	Night	18% 9% 3 6% 4 3 4 3 3 4 43%	4440
	21st to end	Night	23% 11% 3 6% 5% 3 4 4 4 5% 31%	4884
February	1st to 10th	Night	16% 9% 3 6% 5% 3 3 4 3 6% 41%	2337
	11th to 20th	Night	19% 6% 3 4 5% 2 3 4 5% 6% 42%	2218
	21st to end	Night	20% 8% 3 4 4 3 4 4 4 5% 41%	1884
March	1st to 10th	Night	18% 7% 2 4 4 3 3 4 5% 7% 43%	2217
	11th to 20th	Night	17% 7% 3 6% 5% 3 5% 5% 6% 7% 39%	2083
	21st to end	Night	19% 9% 3 4 5% 2 4 4 4 6% 42%	2030
April	1st to 10th	Night	20% 9% 3 4 5% 3 4 4 3 6% 40%	1800
	11th to 20th	Night	20% 6% 3 4 5% 2 4 4 4 5% 42%	1775
	21st to end	Night	22% 7% 3 5% 5% 3 3 3 4 5% 39%	1651
May	1st to 10th	Night	23% 9% 3 6% 5% 3 4 4 5% 6% 32%	1620
	11th to 20th	Night	20% 7% 3 7% 5% 3 4 4 5% 7% 35%	1589
	21st to end	Night	20% 8% 2 5% 6% 3 5% 5% 5% 6% 34%	1550
June	1st to 10th	Night	20% 9% 3 4 4 3 4 4 5% 7% 37%	1440
	11th to 20th	Night	21% 6% 3 4 4 2 3 5% 6% 8% 38%	1440
	21st to end	Night	16% 8% 2 4 4 3 4 5% 6% 9% 40%	1440
July	1st to 10th	Night	15% 6% 3 6% 6% 4 6% 5% 6% 9% 35%	1440
	11th to 20th	Night	17% 5% 3 5% 5% 3 5% 5% 6% 10% 36%	1440
	21st to end	Night	13% 6% 3 7% 5% 3 5% 6% 5% 9% 39%	1574
August	1st to 10th	Night	9% 6% 3 5% 6% 4 6% 5% 8% 8% 40%	1571
	11th to 20th	Night	10% 6% 3 6% 6% 4 6% 6% 7% 9% 37%	1687
	21st to end	Night	13% 6% 2 4 4 3 3 5% 6% 9% 46%	1980
September	1st to 10th	Night	16% 6% 3 5% 6% 4 5% 4 6% 6% 39%	1800
	11th to 20th	Night	14% 7% 2 4 3 2 3 4 4 6% 52%	1969
	21st to end	Night	19% 7% 3 5% 5% 3 4 6% 4 5% 40%	1980
October	1st to 10th	Night	20% 8% 2 5% 5% 3 4 3 4 6% 40%	1980
	11th to 20th	Night	16% 6% 2 4 5% 2 3 3 5% 7% 46%	2176
	21st to end	Night	20% 7% 2 5% 4 3 4 4 5% 6% 40%	2574
November	1st to 10th	Night	14% 6% 3 5% 5% 2 4 4 4 6% 46%	2407
	11th to 20th	Night	19% 6% 2 4 4 2 4 3 4 5% 46%	2470
	21st to end	Night	16% 4 3 5% 5% 3 4 4 4 7% 46%	2470
December	1st to 10th	Night	22% 6% 3 4 5% 3 4 4 4 6% 40%	2598
	11th to 20th	Night	20% 6% 3 4 5% 2 4 4 5% 6% 42%	3288
	21st to end	Night	22% 10% 4 6% 4 2 3 3 3 5% 38%	4884

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	34% 24% 8% 25% 10%	2518
	11th to 20th	Day	37% 26% 8% 20% 9% 1	2520
	21st to end	Day	45% 20% 6% 20% 8% 1	2772
February	1st to 10th	Day	30% 33% 9% 16% 11% 1	1840
	11th to 20th	Day	26% 35% 8% 20% 9% 2	1857
	21st to end	Day	32% 33% 7% 14% 11% 2	1570
March	1st to 10th	Day	25% 35% 10% 18% 11% 2	1850
	11th to 20th	Day	29% 36% 8% 16% 9% 1	1876
	21st to end	Day	29% 36% 5% 13% 13% 3	2322
April	1st to 10th	Day	26% 36% 8% 16% 12% 2	2160
	11th to 20th	Day	29% 36% 7% 15% 12% 2	2134
	21st to end	Day	29% 36% 7% 14% 11% 3	2308
May	1st to 10th	Day	33% 36% 5% 15% 9% 2	2340
	11th to 20th	Day	29% 37% 7% 14% 11% 2	2322
	21st to end	Day	26% 37% 11% 15% 9% 2	2725
June	1st to 10th	Day	30% 37% 10% 16% 7%	2520
	11th to 20th	Day	28% 37% 12% 15% 7% 1	2520
	21st to end	Day	27% 38% 11% 17% 7% 1	2520
July	1st to 10th	Day	27% 38% 10% 17% 8% 1	2450
	11th to 20th	Day	25% 38% 9% 20% 7% 1	2445
	21st to end	Day	25% 39% 9% 15% 11% 1	2591
August	1st to 10th	Day	27% 36% 13% 16% 8%	2332
	11th to 20th	Day	28% 36% 9% 16% 10% 1	2210
	21st to end	Day	28% 37% 8% 14% 12% 1	2376
September	1st to 10th	Day	26% 37% 8% 14% 14% 1	2160
	11th to 20th	Day	21% 35% 8% 18% 15% 2	1990
	21st to end	Day	29% 36% 4 15% 14% 1	1980
October	1st to 10th	Day	28% 35% 6% 17% 13% 1	1980
	11th to 20th	Day	26% 35% 9% 20% 9% 1	1782
	21st to end	Day	28% 36% 8% 17% 9% 2	1782
November	1st to 10th	Day	25% 39% 9% 14% 12% 1	1671
	11th to 20th	Day	24% 39% 9% 15% 11% 2	1710
	21st to end	Day	28% 38% 9% 16% 7% 1	1710
December	1st to 10th	Day	29% 39% 9% 14% 8% 1	1577
	11th to 20th	Day	31% 31% 11% 12% 13% 3	1906
	21st to end	Day	41% 25% 8% 18% 7%	2772
January	1st to 10th	Night	31% 23% 9% 28% 7% 2	4429
	11th to 20th	Night	38% 24% 8% 20% 9% 2	4440
	21st to end	Night	48% 21% 7% 17% 7% 1	4884
February	1st to 10th	Night	31% 33% 8% 16% 10% 1	2337
	11th to 20th	Night	30% 35% 7% 17% 9% 2	2220
	21st to end	Night	33% 32% 5% 17% 10% 2	1884
March	1st to 10th	Night	28% 34% 7% 18% 11% 2	2227
	11th to 20th	Night	32% 36% 7% 14% 8% 2	2084
	21st to end	Night	30% 35% 5% 13% 13% 4	2030
April	1st to 10th	Night	30% 36% 6% 14% 12% 2	1800
	11th to 20th	Night	33% 34% 4 14% 13% 1	1775
	21st to end	Night	32% 35% 6% 13% 11% 3	1651
May	1st to 10th	Night	35% 35% 7% 11% 10% 2	1620
	11th to 20th	Night	31% 36% 6% 14% 9% 3	1590
	21st to end	Night	32% 38% 9% 11% 9%	1551
June	1st to 10th	Night	34% 35% 10% 13% 7% 1	1440
	11th to 20th	Night	30% 36% 10% 15% 8% 1	1440
	21st to end	Night	30% 36% 11% 16% 7%	1440
July	1st to 10th	Night	31% 39% 9% 15% 5% 1	1400
	11th to 20th	Night	29% 38% 10% 17% 6% 1	1392
	21st to end	Night	28% 38% 10% 15% 8% 2	1486
August	1st to 10th	Night	28% 37% 12% 16% 7% 1	1561
	11th to 20th	Night	28% 37% 9% 18% 8%	1687
	21st to end	Night	28% 37% 9% 15% 10% 1	1980
September	1st to 10th	Night	30% 36% 6% 15% 12% 1	1800
	11th to 20th	Night	24% 35% 8% 17% 15% 2	1969
	21st to end	Night	31% 36% 4 13% 13% 3	1980
October	1st to 10th	Night	29% 36% 6% 16% 11% 2	1980
	11th to 20th	Night	29% 35% 8% 19% 8%	2176
	21st to end	Night	31% 36% 9% 14% 9% 1	2574
November	1st to 10th	Night	23% 40% 8% 15% 11% 3	2407
	11th to 20th	Night	27% 38% 6% 17% 10% 1	2470
	21st to end	Night	26% 39% 9% 17% 8% 1	2470
December	1st to 10th	Night	29% 38% 10% 13% 8% 1	2598
	11th to 20th	Night	30% 32% 10% 13% 14% 1	3288
	21st to end	Night	41% 25% 7% 18% 9%	4884

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	22% 24% 28% 19% 7%	180
	11th to 20th	Day	21% 32% 29% 14% 3	180
	21st to end	Day	21% 21% 39% 13% 7%	198
February	1st to 10th	Day	26% 17% 35% 18% 2	406
	11th to 20th	Day	22% 25% 38% 14% 2	456
	21st to end	Day	24% 22% 33% 16% 5% 1	382
March	1st to 10th	Day	19% 21% 34% 21% 4	440
	11th to 20th	Day	19% 20% 40% 17% 4 1	420
	21st to end	Day	25% 18% 35% 16% 6% 1	462
April	1st to 10th	Day	23% 22% 30% 18% 6% 1	420
	11th to 20th	Day	22% 13% 37% 22% 7%	412
	21st to end	Day	27% 13% 34% 19% 5% 2	420
May	1st to 10th	Day	28% 13% 35% 17% 5% 1	423
	11th to 20th	Day	18% 14% 35% 27% 5% 1	447
	21st to end	Day	20% 6% 25% 33% 13% 3	485
June	1st to 10th	Day	18% 9% 30% 26% 16% 2	450
	11th to 20th	Day	18% 7% 30% 33% 11% 1	450
	21st to end	Day	16% 7% 27% 31% 15% 3	450
July	1st to 10th	Day	18% 6% 23% 32% 18% 3	445
	11th to 20th	Day	14% 5% 19% 40% 18% 6%	444
	21st to end	Day	12% 4 31% 38% 13% 2	488
August	1st to 10th	Day	13% 4 25% 38% 15% 4	446
	11th to 20th	Day	17% 3 24% 34% 18% 5%	439
	21st to end	Day	13% 3 27% 34% 17% 7%	495
September	1st to 10th	Day	20% 6% 22% 30% 17% 5%	450
	11th to 20th	Day	16% 5% 30% 28% 16% 6%	450
	21st to end	Day	22% 6% 30% 28% 11% 3	450
October	1st to 10th	Day	25% 9% 25% 23% 13% 4	450
	11th to 20th	Day	17% 15% 26% 26% 14% 1	419
	21st to end	Day	25% 12% 30% 22% 9% 1	396
November	1st to 10th	Day	14% 14% 32% 27% 11% 2	365
	11th to 20th	Day	19% 21% 32% 21% 6%	370
	21st to end	Day	19% 19% 29% 22% 8% 1	370
December	1st to 10th	Day	22% 19% 37% 16% 6%	237
	11th to 20th	Day	24% 26% 31% 16% 3	180
	21st to end	Day	23% 19% 39% 12% 5% 3	198
January	1st to 10th	Night	20% 18% 37% 22% 3	760
	11th to 20th	Night	28% 18% 33% 18% 3	760
	21st to end	Night	22% 19% 35% 21% 2	836
February	1st to 10th	Night	21% 16% 36% 24% 2	760
	11th to 20th	Night	23% 18% 41% 16% 2	743
	21st to end	Night	25% 17% 36% 19% 3	628
March	1st to 10th	Night	23% 15% 35% 22% 4	743
	11th to 20th	Night	21% 12% 38% 24% 5% 1	720
	21st to end	Night	23% 12% 35% 22% 6% 1	792
April	1st to 10th	Night	27% 10% 32% 27% 5%	720
	11th to 20th	Night	23% 7% 34% 28% 9%	711
	21st to end	Night	25% 6% 32% 26% 9% 1	571
May	1st to 10th	Night	27% 7% 26% 28% 10% 1	540
	11th to 20th	Night	22% 6% 35% 29% 7% 1	528
	21st to end	Night	24% 2 19% 35% 16% 3	389
June	1st to 10th	Night	23% 3 22% 35% 18% 1	360
	11th to 20th	Night	25% 5% 17% 38% 15%	360
	21st to end	Night	20% 3 17% 41% 19% 1	360
July	1st to 10th	Night	18% 3 17% 35% 25% 2	350
	11th to 20th	Night	14% 4 12% 44% 25% 1	348
	21st to end	Night	15% 4 14% 44% 21% 2	394
August	1st to 10th	Night	11% 4 17% 44% 22% 2	497
	11th to 20th	Night	14% 2 17% 39% 23% 3	623
	21st to end	Night	15% 2 14% 38% 25% 5%	792
September	1st to 10th	Night	18% 3 21% 35% 19% 4	720
	11th to 20th	Night	17% 4 23% 30% 21% 6%	720
	21st to end	Night	23% 4 25% 30% 15% 3	720
October	1st to 10th	Night	24% 8% 26% 23% 14% 4	720
	11th to 20th	Night	18% 10% 32% 27% 11% 2	720
	21st to end	Night	23% 11% 36% 21% 8% 1	792
November	1st to 10th	Night	16% 11% 31% 28% 13% 1	740
	11th to 20th	Night	23% 17% 32% 21% 7% 1	760
	21st to end	Night	17% 19% 34% 22% 7% 1	760
December	1st to 10th	Night	26% 16% 32% 21% 4 1	760
	11th to 20th	Night	23% 18% 35% 19% 4	760
	21st to end	Night	24% 16% 37% 20% 3	836

Page generated at 2024-03-03 06:28:54. Version ac07

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