Connecticut Star Party
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Connecticut Star Party clear sky chart from 2005-11-06 to 2024-01-15.

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	16% 7% 3 6% 5% 3 5% 5% 5% 7% 37%	74792
	Night	16% 8% 3 5% 5% 3 4 5% 5% 7% 39%	74975
Transparency	Day	45% 5% 11% 23% 14% 2	74497
	Night	45% 4 12% 23% 15% 2	74804
Seeing	Day	25% 19% 30% 18% 7% 2	13830
	Night	23% 18% 29% 22% 7% 1	23002

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% 8% 4 4 5% 3 6% 5% 6% 7% 38%	1517
	11th to 20th	Day	16% 10% 3 7% 7% 3 6% 5% 5% 7% 32%	1472
	21st to end	Day	12% 8% 4 5% 5% 3 5% 6% 6% 7% 38%	1638
February	1st to 10th	Day	17% 9% 3 6% 8% 4 5% 5% 5% 6% 31%	1648
	11th to 20th	Day	14% 8% 3 6% 7% 4 5% 5% 5% 7% 37%	1748
	21st to end	Day	18% 12% 3 7% 4 4 4 3 4 6% 34%	1480
March	1st to 10th	Day	14% 8% 3 6% 7% 4 4 4 6% 6% 38%	1797
	11th to 20th	Day	16% 8% 3 6% 7% 3 6% 6% 5% 7% 34%	1855
	21st to end	Day	19% 9% 3 5% 5% 3 4 4 5% 6% 37%	2376
April	1st to 10th	Day	18% 8% 3 6% 5% 3 6% 4 5% 6% 36%	2160
	11th to 20th	Day	16% 8% 2 5% 5% 4 5% 4 4 6% 40%	2134
	21st to end	Day	20% 7% 3 6% 5% 3 4 5% 5% 6% 36%	2249
May	1st to 10th	Day	25% 8% 2 6% 5% 3 5% 4 4 7% 31%	2340
	11th to 20th	Day	20% 6% 2 4 5% 3 4 5% 6% 7% 39%	2446
	21st to end	Day	14% 7% 3 5% 5% 3 4 6% 5% 8% 40%	2725
June	1st to 10th	Day	18% 6% 3 5% 6% 4 6% 6% 6% 8% 32%	2520
	11th to 20th	Day	17% 7% 3 5% 6% 3 5% 5% 7% 9% 34%	2520
	21st to end	Day	14% 7% 3 7% 6% 4 6% 5% 6% 9% 35%	2520
July	1st to 10th	Day	12% 6% 3 5% 6% 4 6% 6% 6% 7% 40%	2520
	11th to 20th	Day	12% 5% 2 5% 5% 3 5% 6% 6% 10% 40%	2520
	21st to end	Day	12% 6% 3 6% 6% 4 6% 6% 7% 7% 38%	2744
August	1st to 10th	Day	12% 7% 2 6% 6% 4 6% 6% 7% 9% 36%	2449
	11th to 20th	Day	13% 6% 2 5% 5% 5% 5% 6% 6% 9% 37%	2127
	21st to end	Day	13% 6% 2 6% 6% 3 4 5% 6% 8% 41%	2376
September	1st to 10th	Day	14% 7% 3 5% 6% 3 5% 5% 6% 7% 40%	2160
	11th to 20th	Day	13% 6% 3 5% 3 2 4 4 5% 7% 49%	2052
	21st to end	Day	17% 7% 2 5% 4 3 4 5% 6% 7% 41%	1980
October	1st to 10th	Day	22% 7% 2 6% 4 3 5% 4 4 4 39%	1923
	11th to 20th	Day	14% 7% 2 6% 4 3 4 5% 6% 7% 42%	1796
	21st to end	Day	23% 7% 2 5% 5% 3 4 5% 6% 5% 34%	1782
November	1st to 10th	Day	14% 6% 3 5% 4 2 3 4 5% 7% 46%	1671
	11th to 20th	Day	19% 7% 3 4 4 2 5% 5% 5% 6% 42%	1710
	21st to end	Day	18% 8% 3 5% 5% 3 4 4 5% 6% 41%	1639
December	1st to 10th	Day	18% 8% 4 7% 6% 3 5% 5% 6% 6% 33%	1520
	11th to 20th	Day	21% 7% 3 5% 4 3 4 4 5% 6% 38%	1906
	21st to end	Day	18% 12% 4 8% 7% 3 5% 4 5% 7% 26%	2772
January	1st to 10th	Night	14% 8% 3 5% 5% 3 4 5% 6% 7% 40%	2649
	11th to 20th	Night	19% 8% 3 5% 7% 4 5% 5% 5% 6% 33%	2583
	21st to end	Night	12% 9% 3 6% 5% 3 4 5% 7% 7% 39%	2715
February	1st to 10th	Night	17% 10% 3 6% 5% 3 5% 5% 5% 6% 35%	2310
	11th to 20th	Night	15% 8% 3 6% 6% 3 5% 5% 6% 6% 35%	2098
	21st to end	Night	19% 8% 3 7% 5% 4 3 4 5% 6% 37%	1776
March	1st to 10th	Night	14% 8% 3 5% 5% 3 6% 4 5% 7% 39%	2150
	11th to 20th	Night	15% 8% 3 6% 6% 3 5% 5% 7% 6% 37%	2098
	21st to end	Night	17% 7% 3 6% 5% 3 4 4 5% 5% 40%	1980
April	1st to 10th	Night	17% 9% 5% 6% 5% 3 5% 6% 5% 7% 33%	1800
	11th to 20th	Night	18% 7% 2 5% 7% 3 5% 4 5% 6% 39%	1775
	21st to end	Night	19% 8% 3 5% 5% 3 3 4 4 7% 38%	1710
May	1st to 10th	Night	21% 9% 3 7% 6% 4 4 4 4 7% 30%	1620
	11th to 20th	Night	18% 9% 3 6% 5% 3 5% 3 5% 8% 36%	1462
	21st to end	Night	16% 7% 3 5% 5% 3 4 4 6% 7% 40%	1550
June	1st to 10th	Night	18% 7% 3 5% 5% 3 4 4 5% 6% 42%	1440
	11th to 20th	Night	15% 7% 3 6% 5% 4 5% 5% 8% 9% 35%	1440
	21st to end	Night	13% 6% 2 5% 5% 2 5% 4 6% 8% 43%	1440
July	1st to 10th	Night	14% 6% 2 4 5% 3 6% 5% 5% 9% 43%	1440
	11th to 20th	Night	14% 5% 4 5% 5% 3 5% 5% 6% 10% 39%	1440
	21st to end	Night	10% 6% 1 5% 7% 3 5% 5% 6% 8% 43%	1574
August	1st to 10th	Night	10% 5% 3 5% 4 4 4 5% 8% 8% 45%	1470
	11th to 20th	Night	13% 6% 1 6% 6% 4 5% 6% 8% 7% 37%	1769
	21st to end	Night	16% 6% 2 4 4 3 4 4 5% 7% 45%	1980
September	1st to 10th	Night	14% 6% 4 5% 5% 3 4 3 5% 7% 44%	1800
	11th to 20th	Night	13% 6% 3 4 3 2 3 3 4 6% 54%	1908
	21st to end	Night	17% 7% 3 4 3 2 4 4 4 6% 45%	1980
October	1st to 10th	Night	20% 7% 3 6% 5% 3 4 3 4 5% 41%	2034
	11th to 20th	Night	15% 7% 2 5% 4 3 4 4 5% 6% 43%	2162
	21st to end	Night	22% 8% 3 5% 5% 3 4 4 5% 6% 36%	2574
November	1st to 10th	Night	15% 6% 2 5% 3 3 3 5% 5% 6% 46%	2407
	11th to 20th	Night	17% 8% 3 5% 3 3 4 4 5% 7% 40%	2470
	21st to end	Night	14% 7% 3 5% 5% 4 4 4 5% 6% 41%	2539
December	1st to 10th	Night	20% 8% 4 6% 6% 3 3 5% 5% 7% 34%	2660
	11th to 20th	Night	19% 8% 2 5% 5% 4 5% 5% 5% 6% 35%	3288
	21st to end	Night	21% 11% 4 6% 5% 3 4 5% 5% 6% 31%	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	42% 5% 11% 28% 12% 3	1518
	11th to 20th	Day	50% 6% 13% 19% 10% 2	1472
	21st to end	Day	43% 5% 11% 25% 14% 3	1638
February	1st to 10th	Day	52% 4 12% 18% 12% 2	1648
	11th to 20th	Day	45% 6% 9% 23% 15% 2	1757
	21st to end	Day	51% 4 9% 20% 13% 3	1480
March	1st to 10th	Day	46% 4 12% 21% 14% 3	1800
	11th to 20th	Day	48% 4 9% 23% 13% 2	1855
	21st to end	Day	49% 4 7% 18% 18% 5%	2376
April	1st to 10th	Day	48% 5% 8% 21% 14% 3	2160
	11th to 20th	Day	45% 4 9% 23% 17% 2	2134
	21st to end	Day	48% 4 9% 20% 15% 4	2249
May	1st to 10th	Day	53% 5% 8% 19% 13% 2	2340
	11th to 20th	Day	43% 5% 9% 24% 16% 2	2450
	21st to end	Day	43% 6% 15% 23% 12% 2	2725
June	1st to 10th	Day	47% 6% 13% 22% 11% 1	2520
	11th to 20th	Day	46% 5% 13% 24% 11% 1	2520
	21st to end	Day	45% 6% 13% 23% 12% 1	2520
July	1st to 10th	Day	43% 5% 12% 21% 16% 1	2450
	11th to 20th	Day	40% 5% 15% 27% 12% 1	2445
	21st to end	Day	43% 5% 13% 21% 16% 2	2591
August	1st to 10th	Day	44% 6% 13% 24% 13% 1	2435
	11th to 20th	Day	42% 6% 16% 26% 11% 1	2127
	21st to end	Day	40% 5% 12% 25% 17% 1	2376
September	1st to 10th	Day	43% 5% 11% 24% 15% 2	2160
	11th to 20th	Day	35% 4 10% 25% 24% 2	2052
	21st to end	Day	41% 5% 10% 23% 18% 3	1980
October	1st to 10th	Day	48% 4 8% 23% 13% 3	1923
	11th to 20th	Day	40% 5% 12% 28% 13% 2	1796
	21st to end	Day	51% 4 10% 19% 13% 3	1782
November	1st to 10th	Day	37% 4 13% 26% 17% 3	1671
	11th to 20th	Day	42% 4 11% 23% 17% 3	1710
	21st to end	Day	44% 3 13% 26% 12% 2	1639
December	1st to 10th	Day	51% 4 14% 18% 13% 1	1520
	11th to 20th	Day	46% 5% 14% 21% 12% 2	1906
	21st to end	Day	57% 3 9% 20% 11%	2772
January	1st to 10th	Night	42% 4 12% 24% 16% 3	2649
	11th to 20th	Night	50% 4 14% 20% 9% 2	2583
	21st to end	Night	43% 4 10% 23% 18% 2	2715
February	1st to 10th	Night	49% 4 12% 21% 11% 2	2310
	11th to 20th	Night	46% 5% 10% 19% 16% 3	2100
	21st to end	Night	48% 4 8% 23% 13% 4	1776
March	1st to 10th	Night	45% 4 11% 24% 14% 3	2160
	11th to 20th	Night	46% 4 11% 22% 14% 3	2099
	21st to end	Night	45% 4 9% 20% 18% 5%	1980
April	1st to 10th	Night	49% 4 9% 21% 14% 2	1800
	11th to 20th	Night	47% 4 9% 21% 19% 1	1775
	21st to end	Night	47% 3 9% 23% 15% 4	1710
May	1st to 10th	Night	54% 4 10% 17% 13% 2	1620
	11th to 20th	Night	48% 4 9% 21% 16% 3	1463
	21st to end	Night	43% 5% 17% 21% 12% 1	1551
June	1st to 10th	Night	45% 4 11% 26% 13% 1	1440
	11th to 20th	Night	44% 4 16% 25% 10% 1	1440
	21st to end	Night	38% 5% 15% 27% 14% 1	1440
July	1st to 10th	Night	39% 5% 15% 25% 15% 2	1400
	11th to 20th	Night	40% 5% 15% 31% 8% 1	1392
	21st to end	Night	38% 6% 16% 22% 16% 3	1486
August	1st to 10th	Night	35% 6% 18% 26% 14% 1	1460
	11th to 20th	Night	42% 7% 15% 25% 10%	1769
	21st to end	Night	38% 5% 11% 27% 18% 1	1980
September	1st to 10th	Night	41% 5% 10% 27% 16% 1	1800
	11th to 20th	Night	33% 3 12% 26% 25% 1	1908
	21st to end	Night	41% 4 8% 24% 21% 2	1980
October	1st to 10th	Night	46% 4 11% 23% 14% 2	2034
	11th to 20th	Night	40% 4 12% 29% 13% 1	2162
	21st to end	Night	48% 4 12% 21% 13% 1	2574
November	1st to 10th	Night	39% 4 11% 22% 21% 4	2407
	11th to 20th	Night	43% 4 11% 22% 18% 3	2470
	21st to end	Night	42% 3 14% 29% 11% 1	2539
December	1st to 10th	Night	49% 5% 11% 22% 12% 1	2660
	11th to 20th	Night	48% 5% 13% 18% 15% 2	3288
	21st to end	Night	54% 3 9% 22% 12%	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	31% 28% 26% 13% 2	180
	11th to 20th	Day	33% 29% 26% 11% 1	168
	21st to end	Day	20% 39% 30% 9% 3 1	200
February	1st to 10th	Day	37% 31% 24% 7% 1	268
	11th to 20th	Day	31% 29% 32% 7% 1	416
	21st to end	Day	36% 25% 28% 9% 2	346
March	1st to 10th	Day	28% 26% 34% 11% 1	420
	11th to 20th	Day	30% 28% 31% 9% 2 1	420
	21st to end	Day	34% 21% 31% 8% 5% 1	462
April	1st to 10th	Day	29% 26% 29% 9% 6% 1	420
	11th to 20th	Day	30% 26% 26% 13% 5% 1	412
	21st to end	Day	32% 18% 34% 12% 3 1	420
May	1st to 10th	Day	35% 21% 25% 12% 5% 2	423
	11th to 20th	Day	23% 22% 32% 19% 4 1	447
	21st to end	Day	24% 12% 30% 22% 9% 2	485
June	1st to 10th	Day	22% 13% 33% 19% 11% 2	450
	11th to 20th	Day	20% 14% 33% 23% 8% 2	450
	21st to end	Day	17% 15% 31% 27% 9% 2	450
July	1st to 10th	Day	15% 12% 32% 26% 13% 2	445
	11th to 20th	Day	14% 7% 32% 32% 12% 3	444
	21st to end	Day	14% 10% 37% 26% 12% 2	488
August	1st to 10th	Day	14% 9% 31% 30% 12% 5%	446
	11th to 20th	Day	15% 10% 29% 28% 11% 7%	439
	21st to end	Day	14% 13% 29% 25% 13% 6%	495
September	1st to 10th	Day	21% 12% 25% 20% 16% 6%	450
	11th to 20th	Day	16% 13% 28% 22% 11% 9%	450
	21st to end	Day	20% 14% 33% 19% 9% 4	450
October	1st to 10th	Day	30% 11% 27% 16% 12% 4	450
	11th to 20th	Day	21% 21% 28% 21% 7% 1	448
	21st to end	Day	30% 19% 26% 18% 6% 1	396
November	1st to 10th	Day	25% 18% 26% 21% 9% 1	365
	11th to 20th	Day	33% 22% 26% 14% 4 1	370
	21st to end	Day	27% 25% 27% 15% 4	299
December	1st to 10th	Day	28% 30% 28% 9% 5%	180
	11th to 20th	Day	38% 25% 27% 8% 2	180
	21st to end	Day	29% 29% 27% 13% 3	198
January	1st to 10th	Night	23% 26% 34% 14% 3	760
	11th to 20th	Night	29% 24% 30% 15% 2	739
	21st to end	Night	22% 26% 34% 15% 3	792
February	1st to 10th	Night	28% 23% 30% 16% 2	720
	11th to 20th	Night	25% 28% 35% 11% 1	703
	21st to end	Night	30% 26% 27% 15% 2	592
March	1st to 10th	Night	25% 25% 33% 15% 2	720
	11th to 20th	Night	23% 27% 30% 17% 3	720
	21st to end	Night	25% 26% 29% 16% 4 1	792
April	1st to 10th	Night	26% 21% 31% 19% 3	720
	11th to 20th	Night	24% 21% 33% 16% 6%	711
	21st to end	Night	26% 20% 32% 17% 4	630
May	1st to 10th	Night	30% 16% 29% 18% 6% 1	540
	11th to 20th	Night	22% 16% 37% 20% 4	401
	21st to end	Night	21% 9% 28% 32% 9% 1	389
June	1st to 10th	Night	22% 9% 29% 30% 9% 1	360
	11th to 20th	Night	21% 8% 29% 29% 13% 1	360
	21st to end	Night	18% 4 29% 35% 13% 1	360
July	1st to 10th	Night	18% 6% 21% 37% 18%	350
	11th to 20th	Night	16% 5% 24% 39% 16% 1	348
	21st to end	Night	12% 5% 27% 40% 16%	394
August	1st to 10th	Night	11% 4 28% 40% 16% 1	396
	11th to 20th	Night	16% 4 22% 36% 19% 2	705
	21st to end	Night	18% 5% 24% 34% 18% 2	792
September	1st to 10th	Night	18% 7% 29% 31% 13% 3	720
	11th to 20th	Night	17% 8% 26% 29% 18% 3	720
	21st to end	Night	23% 9% 25% 27% 14% 3	720
October	1st to 10th	Night	23% 15% 24% 25% 10% 2	720
	11th to 20th	Night	19% 17% 30% 24% 9% 1	720
	21st to end	Night	30% 16% 30% 18% 6%	792
November	1st to 10th	Night	21% 18% 31% 21% 8% 1	740
	11th to 20th	Night	24% 22% 30% 17% 7% 1	760
	21st to end	Night	23% 22% 31% 20% 5% 1	760
December	1st to 10th	Night	28% 22% 29% 16% 4 1	760
	11th to 20th	Night	25% 27% 28% 18% 3	760
	21st to end	Night	29% 23% 32% 13% 2	836

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