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 2026-03-03.

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% 8% 3 7% 5% 4 5% 4 6% 7% 36%	130801
	Night	16% 9% 3 7% 4 4 4 4 5% 6% 38%	130345
Transparency	Day	45% 5% 11% 22% 14% 2	134304
	Night	45% 5% 12% 22% 15% 2	134916
Seeing	Day	25% 19% 29% 17% 7% 2	16553
	Night	24% 18% 29% 21% 7% 1	25723

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	10% 10% 4 10% 6% 5% 5% 4 6% 6% 35%	4661
	11th to 20th	Day	13% 10% 4 10% 5% 4 4 3 4 5% 38%	4650
	21st to end	Day	15% 10% 4 6% 3 3 5% 3 6% 6% 40%	5304
February	1st to 10th	Day	15% 9% 3 7% 7% 5% 5% 4 5% 6% 34%	1923
	11th to 20th	Day	14% 8% 3 7% 6% 5% 5% 4 5% 7% 36%	2048
	21st to end	Day	17% 12% 2 7% 4 5% 3 3 4 6% 36%	1730
March	1st to 10th	Day	20% 10% 3 7% 4 4 4 3 5% 5% 36%	4496
	11th to 20th	Day	13% 8% 3 7% 5% 5% 5% 4 5% 7% 38%	4673
	21st to end	Day	19% 9% 3 7% 4 4 4 3 6% 7% 34%	5970
April	1st to 10th	Day	19% 10% 3 7% 4 5% 5% 3 5% 6% 34%	2400
	11th to 20th	Day	17% 8% 2 7% 4 5% 5% 3 5% 6% 39%	2374
	21st to end	Day	19% 8% 3 7% 4 4 4 4 5% 6% 37%	2499
May	1st to 10th	Day	31% 9% 2 6% 4 4 4 4 5% 8% 24%	5886
	11th to 20th	Day	19% 9% 3 8% 5% 4 5% 3 6% 6% 32%	6244
	21st to end	Day	20% 8% 2 6% 4 4 5% 4 6% 8% 32%	6949
June	1st to 10th	Day	17% 7% 2 6% 5% 5% 6% 5% 6% 8% 33%	2800
	11th to 20th	Day	17% 7% 2 6% 6% 5% 5% 4 7% 9% 34%	2800
	21st to end	Day	14% 7% 3 8% 5% 5% 5% 4 6% 9% 35%	2800
July	1st to 10th	Day	11% 8% 3 8% 5% 6% 6% 5% 6% 8% 34%	6360
	11th to 20th	Day	11% 6% 2 7% 5% 6% 6% 5% 8% 11% 33%	6360
	21st to end	Day	15% 7% 2 7% 4 4 5% 3 6% 8% 38%	6926
August	1st to 10th	Day	19% 8% 2 7% 5% 5% 5% 4 6% 8% 30%	4448
	11th to 20th	Day	13% 6% 3 7% 4 5% 5% 5% 7% 9% 37%	3851
	21st to end	Day	10% 5% 2 6% 5% 5% 5% 5% 7% 9% 41%	4312
September	1st to 10th	Day	13% 7% 3 6% 4 4 5% 4 6% 6% 42%	2400
	11th to 20th	Day	11% 6% 3 5% 3 3 4 3 5% 7% 49%	2280
	21st to end	Day	17% 7% 2 6% 4 4 4 4 6% 7% 39%	2200
October	1st to 10th	Day	20% 7% 2 6% 4 4 4 3 4 5% 41%	2136
	11th to 20th	Day	13% 7% 2 7% 3 3 4 4 6% 7% 42%	1995
	21st to end	Day	21% 7% 2 6% 4 4 4 3 6% 5% 36%	1980
November	1st to 10th	Day	13% 7% 3 6% 3 4 4 3 5% 7% 45%	1851
	11th to 20th	Day	17% 7% 2 5% 4 3 4 4 5% 6% 42%	1890
	21st to end	Day	17% 10% 3 7% 4 4 4 3 5% 5% 39%	1811
December	1st to 10th	Day	13% 9% 4 7% 4 4 4 3 5% 6% 41%	2680
	11th to 20th	Day	19% 9% 3 6% 3 3 3 3 5% 6% 39%	3066
	21st to end	Day	17% 12% 4 8% 5% 4 3 3 5% 7% 32%	4048
January	1st to 10th	Night	12% 9% 3 8% 6% 5% 5% 4 6% 6% 34%	8234
	11th to 20th	Night	14% 9% 4 10% 6% 5% 4 3 5% 6% 34%	8235
	21st to end	Night	13% 9% 3 7% 5% 5% 5% 3 5% 6% 38%	8860
February	1st to 10th	Night	15% 10% 3 6% 4 4 5% 4 5% 6% 37%	2695
	11th to 20th	Night	14% 9% 3 7% 5% 5% 5% 4 6% 6% 35%	2458
	21st to end	Night	17% 8% 3 8% 4 4 4 4 5% 6% 36%	2076
March	1st to 10th	Night	19% 10% 3 6% 4 4 4 3 5% 6% 38%	5389
	11th to 20th	Night	15% 8% 3 7% 5% 4 4 4 6% 6% 38%	5266
	21st to end	Night	19% 11% 3 7% 4 4 4 3 4 5% 36%	4962
April	1st to 10th	Night	18% 10% 4 7% 5% 4 5% 5% 5% 6% 32%	2000
	11th to 20th	Night	18% 8% 2 6% 6% 4 4 3 5% 6% 38%	1975
	21st to end	Night	18% 8% 3 6% 4 4 3 4 5% 6% 39%	1900
May	1st to 10th	Night	32% 9% 3 7% 4 4 3 3 4 7% 25%	4054
	11th to 20th	Night	19% 11% 3 9% 4 5% 4 3 5% 7% 30%	3678
	21st to end	Night	21% 8% 3 7% 5% 4 5% 4 5% 6% 33%	3926
June	1st to 10th	Night	18% 8% 2 6% 5% 4 4 3 5% 6% 41%	1600
	11th to 20th	Night	15% 8% 2 6% 5% 4 4 4 8% 9% 35%	1600
	21st to end	Night	14% 6% 2 6% 4 4 4 3 6% 9% 42%	1600
July	1st to 10th	Night	13% 8% 2 6% 4 4 5% 4 6% 9% 40%	3600
	11th to 20th	Night	14% 9% 3 8% 4 4 4 4 6% 9% 34%	3600
	21st to end	Night	12% 7% 2 6% 5% 3 4 4 5% 6% 46%	3926
August	1st to 10th	Night	22% 7% 3 7% 4 4 4 4 6% 7% 32%	2668
	11th to 20th	Night	15% 7% 2 6% 5% 5% 4 4 6% 7% 41%	3192
	21st to end	Night	10% 5% 2 5% 4 4 4 4 5% 8% 51%	3586
September	1st to 10th	Night	14% 6% 3 6% 4 4 3 3 5% 7% 45%	2000
	11th to 20th	Night	12% 5% 3 5% 2 3 4 2 4 6% 54%	2120
	21st to end	Night	18% 8% 3 5% 3 3 3 3 4 6% 44%	2200
October	1st to 10th	Night	19% 7% 2 6% 4 3 3 2 4 6% 43%	2260
	11th to 20th	Night	15% 7% 2 6% 3 4 4 3 5% 6% 45%	2403
	21st to end	Night	21% 8% 2 6% 4 3 4 3 5% 6% 38%	2860
November	1st to 10th	Night	14% 6% 2 5% 3 4 3 4 5% 6% 46%	2667
	11th to 20th	Night	16% 8% 2 6% 3 4 3 4 5% 6% 41%	2730
	21st to end	Night	14% 8% 3 6% 5% 5% 4 3 6% 7% 40%	2807
December	1st to 10th	Night	16% 9% 3 7% 5% 4 3 3 5% 6% 40%	4720
	11th to 20th	Night	22% 10% 2 5% 3 4 3 3 4 5% 37%	5348
	21st to end	Night	18% 11% 4 7% 4 4 4 3 4 6% 35%	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	45% 6% 10% 25% 12% 2	4662
	11th to 20th	Day	47% 4 8% 21% 14% 6%	4680
	21st to end	Day	44% 4 9% 25% 18% 1	5304
February	1st to 10th	Day	50% 3 11% 20% 13% 2	1923
	11th to 20th	Day	46% 6% 9% 23% 15% 2	2057
	21st to end	Day	49% 4 10% 21% 13% 2	1730
March	1st to 10th	Day	50% 4 10% 16% 13% 8%	4499
	11th to 20th	Day	44% 4 12% 29% 8% 3	4673
	21st to end	Day	49% 4 7% 14% 21% 6%	5970
April	1st to 10th	Day	50% 5% 8% 20% 14% 3	2400
	11th to 20th	Day	46% 4 9% 22% 16% 2	2374
	21st to end	Day	47% 4 9% 21% 16% 3	2499
May	1st to 10th	Day	59% 5% 12% 14% 9% 1	5897
	11th to 20th	Day	51% 4 12% 20% 12% 1	6248
	21st to end	Day	48% 5% 10% 24% 12% 1	6949
June	1st to 10th	Day	46% 6% 12% 23% 12% 1	2800
	11th to 20th	Day	45% 5% 14% 24% 11% 1	2800
	21st to end	Day	45% 6% 13% 23% 12% 1	2800
July	1st to 10th	Day	46% 8% 12% 20% 14% 1	6290
	11th to 20th	Day	41% 8% 17% 23% 11% 1	6285
	21st to end	Day	43% 5% 11% 24% 16% 1	6728
August	1st to 10th	Day	51% 6% 13% 21% 8% 1	4434
	11th to 20th	Day	41% 6% 15% 29% 9%	3887
	21st to end	Day	36% 6% 13% 31% 14% 1	4312
September	1st to 10th	Day	41% 5% 10% 25% 17% 1	2400
	11th to 20th	Day	34% 4 10% 26% 24% 2	2280
	21st to end	Day	43% 5% 10% 22% 17% 3	2200
October	1st to 10th	Day	40% 5% 8% 19% 25% 3	3474
	11th to 20th	Day	32% 4 9% 26% 25% 5%	3223
	21st to end	Day	34% 4 14% 26% 19% 3	3180
November	1st to 10th	Day	37% 4 13% 26% 18% 2	1851
	11th to 20th	Day	41% 4 10% 23% 19% 3	1890
	21st to end	Day	47% 3 13% 25% 11% 2	1811
December	1st to 10th	Day	44% 3 15% 28% 10% 1	2680
	11th to 20th	Day	46% 4 13% 20% 15% 2	3066
	21st to end	Day	52% 3 7% 19% 15% 5%	4048
January	1st to 10th	Night	44% 6% 13% 23% 13% 2	8234
	11th to 20th	Night	47% 6% 12% 18% 12% 5%	8280
	21st to end	Night	45% 4 10% 20% 19% 3	8860
February	1st to 10th	Night	47% 4 12% 23% 13% 2	2695
	11th to 20th	Night	46% 5% 9% 19% 17% 3	2460
	21st to end	Night	48% 4 8% 23% 13% 4	2076
March	1st to 10th	Night	47% 4 11% 19% 15% 4	5399
	11th to 20th	Night	45% 4 16% 21% 11% 3	5267
	21st to end	Night	49% 4 5% 15% 23% 4	4962
April	1st to 10th	Night	50% 4 9% 20% 13% 3	2000
	11th to 20th	Night	48% 4 9% 20% 18% 1	1975
	21st to end	Night	45% 3 9% 22% 17% 4	1900
May	1st to 10th	Night	60% 4 13% 12% 9% 1	4060
	11th to 20th	Night	54% 5% 12% 16% 11% 2	3679
	21st to end	Night	51% 5% 13% 20% 10% 1	3927
June	1st to 10th	Night	45% 4 10% 26% 14% 1	1600
	11th to 20th	Night	44% 4 16% 26% 9% 1	1600
	21st to end	Night	38% 6% 15% 26% 14% 1	1600
July	1st to 10th	Night	41% 6% 15% 21% 15% 1	3560
	11th to 20th	Night	46% 7% 14% 22% 10% 1	3552
	21st to end	Night	37% 5% 13% 25% 18% 1	3809
August	1st to 10th	Night	51% 6% 13% 19% 9% 1	2658
	11th to 20th	Night	42% 6% 14% 30% 8%	3222
	21st to end	Night	30% 5% 13% 36% 14% 1	3586
September	1st to 10th	Night	40% 4 10% 27% 18% 1	2000
	11th to 20th	Night	32% 4 11% 26% 25% 1	2120
	21st to end	Night	43% 5% 8% 24% 19% 2	2200
October	1st to 10th	Night	39% 5% 13% 22% 19% 2	3689
	11th to 20th	Night	30% 4 10% 26% 25% 4	3914
	21st to end	Night	35% 4 14% 29% 16% 2	4610
November	1st to 10th	Night	38% 4 11% 23% 21% 3	2667
	11th to 20th	Night	42% 4 11% 21% 19% 3	2730
	21st to end	Night	42% 4 13% 29% 11% 1	2807
December	1st to 10th	Night	43% 5% 12% 30% 9% 1	4720
	11th to 20th	Night	49% 4 12% 16% 17% 2	5348
	21st to end	Night	51% 3 8% 18% 16% 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	32% 31% 23% 11% 2	220
	11th to 20th	Day	37% 30% 24% 8% 1	220
	21st to end	Day	28% 34% 27% 8% 2 1	275
February	1st to 10th	Day	35% 30% 26% 7% 1	363
	11th to 20th	Day	32% 29% 32% 7% 1	536
	21st to end	Day	34% 27% 28% 9% 2	446
March	1st to 10th	Day	31% 25% 32% 10% 1	508
	11th to 20th	Day	30% 28% 30% 9% 2 1	500
	21st to end	Day	35% 23% 30% 7% 5% 1	550
April	1st to 10th	Day	33% 25% 28% 8% 5% 1	500
	11th to 20th	Day	33% 26% 26% 11% 4 1	492
	21st to end	Day	30% 19% 35% 12% 3 1	500
May	1st to 10th	Day	36% 20% 25% 13% 5% 1	503
	11th to 20th	Day	23% 22% 31% 19% 5% 1	527
	21st to end	Day	25% 13% 31% 20% 8% 2	573
June	1st to 10th	Day	22% 13% 34% 19% 10% 2	530
	11th to 20th	Day	20% 14% 32% 24% 8% 1	530
	21st to end	Day	17% 16% 32% 26% 8% 2	530
July	1st to 10th	Day	15% 12% 34% 26% 12% 2	525
	11th to 20th	Day	14% 7% 33% 31% 12% 3	524
	21st to end	Day	15% 11% 37% 26% 10% 2	576
August	1st to 10th	Day	14% 9% 31% 29% 11% 5%	526
	11th to 20th	Day	14% 11% 29% 29% 11% 6%	519
	21st to end	Day	13% 14% 30% 26% 12% 5%	583
September	1st to 10th	Day	21% 13% 27% 20% 14% 5%	530
	11th to 20th	Day	14% 12% 26% 27% 13% 8%	530
	21st to end	Day	21% 13% 33% 20% 9% 4	530
October	1st to 10th	Day	27% 12% 26% 18% 12% 4	530
	11th to 20th	Day	24% 21% 27% 20% 7% 2	527
	21st to end	Day	29% 19% 28% 18% 6% 1	462
November	1st to 10th	Day	25% 20% 26% 19% 8% 1	425
	11th to 20th	Day	32% 24% 26% 14% 4	430
	21st to end	Day	32% 26% 25% 14% 3	351
December	1st to 10th	Day	30% 29% 28% 10% 4	220
	11th to 20th	Day	40% 25% 26% 8% 1	220
	21st to end	Day	32% 27% 26% 12% 3	242
January	1st to 10th	Night	24% 27% 33% 13% 3	840
	11th to 20th	Night	30% 25% 29% 14% 2	840
	21st to end	Night	25% 25% 34% 14% 2	924
February	1st to 10th	Night	27% 25% 30% 17% 2	840
	11th to 20th	Night	27% 26% 35% 11% 1	823
	21st to end	Night	30% 25% 28% 14% 3	692
March	1st to 10th	Night	26% 24% 33% 14% 2	809
	11th to 20th	Night	23% 27% 30% 17% 2	800
	21st to end	Night	26% 26% 30% 15% 4	880
April	1st to 10th	Night	28% 21% 31% 18% 2	800
	11th to 20th	Night	26% 22% 32% 15% 5%	791
	21st to end	Night	25% 21% 31% 17% 5%	700
May	1st to 10th	Night	31% 16% 29% 18% 5% 1	600
	11th to 20th	Night	22% 17% 36% 20% 4	445
	21st to end	Night	21% 9% 29% 31% 8% 1	433
June	1st to 10th	Night	21% 10% 29% 31% 9% 1	400
	11th to 20th	Night	21% 9% 29% 29% 12% 1	400
	21st to end	Night	18% 6% 29% 34% 13% 1	400
July	1st to 10th	Night	18% 6% 23% 37% 16%	390
	11th to 20th	Night	14% 6% 25% 38% 15% 1	388
	21st to end	Night	13% 5% 28% 38% 16%	438
August	1st to 10th	Night	13% 4 26% 40% 16% 1	441
	11th to 20th	Night	16% 5% 23% 36% 19% 2	785
	21st to end	Night	17% 6% 25% 33% 18% 2	880
September	1st to 10th	Night	18% 8% 28% 31% 14% 2	800
	11th to 20th	Night	16% 7% 25% 31% 18% 4	800
	21st to end	Night	24% 8% 27% 26% 13% 2	800
October	1st to 10th	Night	22% 14% 25% 25% 12% 2	800
	11th to 20th	Night	21% 18% 30% 22% 9% 1	800
	21st to end	Night	28% 16% 31% 19% 6%	880
November	1st to 10th	Night	22% 18% 31% 20% 8% 1	820
	11th to 20th	Night	25% 22% 29% 17% 7% 1	840
	21st to end	Night	23% 22% 30% 20% 4	840
December	1st to 10th	Night	28% 22% 29% 16% 4	840
	11th to 20th	Night	27% 26% 27% 17% 3	840
	21st to end	Night	30% 23% 31% 13% 2	924

Page generated at 2026-02-28 01:40:22. Version ac07

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