East Hartford
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the East Hartford clear sky chart from 2005-11-06 to 2026-01-02.

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	17% 7% 2 6% 4 4 4 4 5% 7% 38%	127063
	Night	18% 8% 3 6% 4 4 4 3 5% 6% 39%	124300
Transparency	Day	44% 5% 11% 22% 15% 2	130595
	Night	44% 4 11% 22% 16% 2	128855
Seeing	Day	24% 16% 30% 19% 8% 2	16443
	Night	23% 14% 32% 24% 7% 1	25505

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 9% 5% 4 4 3 4 5% 41%	3605
	11th to 20th	Day	14% 8% 3 7% 4 3 4 4 5% 6% 42%	3570
	21st to end	Day	19% 8% 2 7% 4 3 4 3 5% 5% 40%	4022
February	1st to 10th	Day	18% 7% 2 6% 4 5% 5% 5% 6% 6% 36%	1877
	11th to 20th	Day	14% 7% 3 7% 5% 5% 5% 3 5% 7% 39%	1948
	21st to end	Day	20% 9% 2 5% 4 4 4 4 5% 6% 38%	1650
March	1st to 10th	Day	22% 10% 3 7% 3 3 3 3 4 5% 38%	4476
	11th to 20th	Day	15% 8% 2 6% 5% 5% 5% 3 5% 6% 40%	4646
	21st to end	Day	22% 7% 3 6% 4 4 4 4 5% 6% 35%	5970
April	1st to 10th	Day	19% 8% 3 7% 4 4 4 4 5% 7% 36%	2400
	11th to 20th	Day	20% 6% 1 6% 4 4 4 4 5% 6% 41%	2374
	21st to end	Day	20% 6% 2 6% 4 5% 4 3 5% 6% 39%	2532
May	1st to 10th	Day	30% 8% 3 6% 4 4 4 3 5% 8% 25%	5886
	11th to 20th	Day	20% 8% 3 7% 5% 4 5% 4 5% 6% 33%	6124
	21st to end	Day	20% 7% 2 6% 4 4 4 4 6% 8% 35%	6949
June	1st to 10th	Day	17% 7% 2 6% 5% 5% 5% 4 6% 9% 35%	2800
	11th to 20th	Day	16% 6% 3 6% 6% 4 5% 4 6% 9% 36%	2800
	21st to end	Day	13% 7% 3 7% 5% 5% 4 4 6% 9% 37%	2800
July	1st to 10th	Day	13% 8% 3 7% 6% 5% 6% 5% 7% 9% 33%	6360
	11th to 20th	Day	10% 6% 2 7% 5% 5% 5% 5% 7% 11% 35%	6360
	21st to end	Day	15% 7% 3 6% 4 4 4 4 5% 7% 41%	6926
August	1st to 10th	Day	16% 8% 3 8% 6% 5% 4 4 7% 9% 29%	4377
	11th to 20th	Day	10% 6% 3 8% 5% 4 5% 4 6% 8% 41%	3921
	21st to end	Day	8% 5% 2 7% 4 5% 5% 4 6% 9% 44%	4312
September	1st to 10th	Day	14% 6% 2 6% 4 4 4 3 6% 6% 45%	2400
	11th to 20th	Day	13% 6% 2 5% 3 3 3 3 4 6% 51%	2250
	21st to end	Day	18% 6% 3 6% 4 4 5% 3 5% 7% 41%	2200
October	1st to 10th	Day	21% 7% 3 5% 3 4 4 3 4 5% 42%	2185
	11th to 20th	Day	15% 6% 2 5% 3 4 4 3 5% 7% 45%	1964
	21st to end	Day	19% 7% 2 6% 4 3 3 4 5% 6% 41%	1980
November	1st to 10th	Day	13% 6% 3 6% 4 4 4 3 4 5% 47%	1851
	11th to 20th	Day	18% 6% 2 4 3 3 3 3 4 6% 46%	1890
	21st to end	Day	18% 8% 2 6% 5% 4 4 3 4 5% 41%	1864
December	1st to 10th	Day	15% 8% 3 6% 4 3 4 3 5% 7% 44%	2680
	11th to 20th	Day	20% 7% 2 4 3 3 4 3 4 5% 46%	3066
	21st to end	Day	21% 10% 3 8% 4 3 3 3 4 5% 37%	4048
January	1st to 10th	Night	15% 6% 3 8% 5% 4 4 3 5% 6% 42%	6364
	11th to 20th	Night	14% 8% 3 8% 5% 4 3 3 4 5% 42%	6315
	21st to end	Night	18% 9% 3 7% 4 4 4 3 4 6% 37%	6932
February	1st to 10th	Night	18% 9% 3 6% 4 3 4 3 5% 5% 39%	2521
	11th to 20th	Night	16% 8% 2 6% 5% 5% 4 4 5% 7% 39%	2338
	21st to end	Night	19% 9% 2 6% 5% 4 3 4 4 5% 40%	1980
March	1st to 10th	Night	23% 8% 3 5% 3 3 3 3 5% 5% 38%	5364
	11th to 20th	Night	17% 10% 3 6% 4 4 4 3 5% 6% 39%	5295
	21st to end	Night	23% 8% 2 7% 4 4 3 3 5% 5% 36%	4962
April	1st to 10th	Night	21% 7% 2 6% 5% 4 4 3 5% 6% 36%	2000
	11th to 20th	Night	20% 7% 3 6% 5% 4 4 4 5% 5% 39%	1975
	21st to end	Night	22% 7% 2 6% 4 3 3 3 4 5% 41%	1866
May	1st to 10th	Night	28% 11% 4 7% 4 4 3 3 5% 6% 26%	4054
	11th to 20th	Night	20% 11% 4 8% 5% 4 4 3 6% 6% 30%	3813
	21st to end	Night	21% 8% 4 7% 4 5% 4 4 5% 7% 32%	3926
June	1st to 10th	Night	17% 7% 2 6% 4 4 4 4 6% 8% 38%	1600
	11th to 20th	Night	17% 7% 2 6% 4 4 4 4 6% 7% 38%	1600
	21st to end	Night	13% 5% 2 6% 5% 4 4 4 6% 9% 42%	1600
July	1st to 10th	Night	14% 7% 2 7% 5% 4 4 4 6% 9% 37%	3600
	11th to 20th	Night	14% 8% 3 7% 5% 5% 5% 4 6% 9% 36%	3600
	21st to end	Night	12% 8% 3 7% 4 4 5% 4 6% 6% 43%	3926
August	1st to 10th	Night	21% 6% 2 7% 5% 5% 5% 4 6% 7% 30%	2738
	11th to 20th	Night	12% 8% 3 8% 4 4 5% 4 6% 7% 39%	3123
	21st to end	Night	9% 4 1 5% 4 3 4 3 6% 9% 51%	3586
September	1st to 10th	Night	14% 6% 3 7% 4 4 4 4 5% 6% 45%	2000
	11th to 20th	Night	12% 6% 2 5% 3 4 3 3 4 6% 52%	2150
	21st to end	Night	17% 7% 2 7% 4 3 4 3 5% 6% 43%	2200
October	1st to 10th	Night	20% 7% 2 5% 4 3 3 3 5% 6% 42%	2211
	11th to 20th	Night	17% 6% 1 6% 3 4 4 3 4 5% 47%	2435
	21st to end	Night	23% 6% 2 5% 4 4 3 4 5% 6% 40%	2860
November	1st to 10th	Night	14% 6% 2 5% 4 4 3 3 5% 6% 48%	2667
	11th to 20th	Night	19% 7% 2 6% 3 3 3 3 5% 5% 45%	2730
	21st to end	Night	16% 7% 2 6% 4 4 4 3 5% 7% 43%	2751
December	1st to 10th	Night	19% 8% 2 5% 4 4 3 3 4 5% 44%	4720
	11th to 20th	Night	24% 8% 2 5% 3 3 3 3 3 4 41%	5348
	21st to end	Night	19% 10% 3 6% 4 4 3 3 5% 5% 38%	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	44% 4 7% 29% 14% 2	3606
	11th to 20th	Day	43% 3 10% 23% 14% 7%	3600
	21st to end	Day	47% 3 10% 23% 16% 1	4022
February	1st to 10th	Day	47% 4 13% 21% 13% 2	1877
	11th to 20th	Day	45% 4 9% 23% 15% 3	1957
	21st to end	Day	48% 3 10% 22% 14% 3	1650
March	1st to 10th	Day	50% 3 10% 16% 12% 9%	4479
	11th to 20th	Day	43% 6% 12% 28% 11% 2	4646
	21st to end	Day	49% 5% 6% 16% 19% 5%	5970
April	1st to 10th	Day	48% 4 9% 21% 15% 3	2400
	11th to 20th	Day	45% 4 10% 21% 19% 3	2374
	21st to end	Day	47% 4 9% 21% 16% 4	2532
May	1st to 10th	Day	58% 4 14% 14% 8% 1	5897
	11th to 20th	Day	51% 4 12% 19% 12% 1	6128
	21st to end	Day	47% 6% 10% 23% 13% 1	6949
June	1st to 10th	Day	45% 5% 12% 24% 12% 1	2800
	11th to 20th	Day	45% 5% 14% 22% 13% 2	2800
	21st to end	Day	43% 6% 13% 22% 15% 1	2800
July	1st to 10th	Day	47% 7% 11% 20% 14% 1	6290
	11th to 20th	Day	41% 8% 17% 23% 11% 1	6285
	21st to end	Day	41% 5% 11% 23% 18% 1	6728
August	1st to 10th	Day	50% 6% 14% 20% 8% 1	4363
	11th to 20th	Day	39% 6% 14% 30% 10% 1	3959
	21st to end	Day	35% 7% 11% 29% 16% 2	4312
September	1st to 10th	Day	40% 4 11% 23% 20% 2	2400
	11th to 20th	Day	34% 4 10% 24% 24% 3	2250
	21st to end	Day	44% 4 8% 22% 19% 3	2200
October	1st to 10th	Day	38% 5% 9% 20% 24% 4	3562
	11th to 20th	Day	30% 3 8% 26% 29% 4	3180
	21st to end	Day	33% 4 13% 27% 21% 3	3180
November	1st to 10th	Day	40% 4 12% 22% 20% 2	1851
	11th to 20th	Day	40% 3 9% 24% 20% 4	1890
	21st to end	Day	45% 4 11% 27% 11% 3	1864
December	1st to 10th	Day	41% 3 15% 29% 12% 1	2680
	11th to 20th	Day	42% 3 14% 19% 19% 3	3066
	21st to end	Day	51% 3 8% 20% 15% 5%	4048
January	1st to 10th	Night	42% 3 9% 29% 15% 2	6364
	11th to 20th	Night	44% 4 13% 21% 14% 5%	6360
	21st to end	Night	49% 3 10% 18% 16% 3	6932
February	1st to 10th	Night	47% 4 13% 23% 12% 2	2521
	11th to 20th	Night	45% 4 9% 21% 17% 4	2340
	21st to end	Night	47% 4 7% 23% 15% 4	1980
March	1st to 10th	Night	49% 4 10% 18% 15% 5%	5374
	11th to 20th	Night	46% 4 15% 22% 11% 3	5296
	21st to end	Night	51% 3 5% 13% 23% 5%	4962
April	1st to 10th	Night	50% 4 8% 20% 15% 3	2000
	11th to 20th	Night	47% 4 9% 20% 19% 1	1975
	21st to end	Night	46% 4 9% 22% 14% 5%	1866
May	1st to 10th	Night	60% 4 14% 12% 9% 1	4060
	11th to 20th	Night	55% 5% 12% 15% 10% 3	3814
	21st to end	Night	50% 6% 13% 21% 10% 1	3927
June	1st to 10th	Night	45% 6% 11% 22% 15% 1	1600
	11th to 20th	Night	45% 4 14% 25% 11% 1	1600
	21st to end	Night	39% 7% 14% 25% 14% 1	1600
July	1st to 10th	Night	44% 6% 15% 21% 12% 1	3560
	11th to 20th	Night	44% 7% 18% 21% 9% 1	3552
	21st to end	Night	40% 5% 12% 24% 18% 1	3809
August	1st to 10th	Night	52% 7% 13% 18% 10% 1	2728
	11th to 20th	Night	43% 6% 14% 29% 8% 1	3151
	21st to end	Night	27% 6% 16% 33% 16% 1	3586
September	1st to 10th	Night	39% 5% 10% 27% 18% 1	2000
	11th to 20th	Night	34% 3 10% 24% 26% 2	2150
	21st to end	Night	43% 6% 8% 22% 20% 2	2200
October	1st to 10th	Night	39% 5% 12% 23% 19% 2	3614
	11th to 20th	Night	29% 3 9% 27% 30% 2	3958
	21st to end	Night	33% 3 13% 29% 20% 2	4610
November	1st to 10th	Night	37% 4 12% 24% 20% 4	2667
	11th to 20th	Night	42% 4 9% 22% 20% 4	2730
	21st to end	Night	41% 3 13% 28% 12% 1	2751
December	1st to 10th	Night	43% 4 12% 30% 12%	4720
	11th to 20th	Night	48% 3 12% 16% 19% 2	5348
	21st to end	Night	48% 3 8% 21% 17% 3	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% 25% 26% 14% 2	202
	11th to 20th	Day	31% 27% 28% 11% 4	200
	21st to end	Day	28% 26% 31% 9% 5% 1	233
February	1st to 10th	Day	34% 24% 27% 14% 1	377
	11th to 20th	Day	33% 26% 31% 9% 1	496
	21st to end	Day	30% 21% 33% 11% 4	414
March	1st to 10th	Day	29% 23% 31% 14% 3	500
	11th to 20th	Day	31% 23% 32% 12% 3	500
	21st to end	Day	33% 21% 30% 10% 4 2	550
April	1st to 10th	Day	34% 24% 26% 11% 4 1	500
	11th to 20th	Day	34% 19% 28% 14% 4	492
	21st to end	Day	31% 18% 33% 12% 4 2	500
May	1st to 10th	Day	35% 17% 28% 12% 7% 1	503
	11th to 20th	Day	26% 17% 35% 15% 6% 1	527
	21st to end	Day	22% 15% 31% 21% 8% 2	573
June	1st to 10th	Day	20% 13% 31% 23% 10% 3	530
	11th to 20th	Day	17% 15% 38% 21% 8% 1	530
	21st to end	Day	17% 18% 31% 24% 9% 2	530
July	1st to 10th	Day	19% 8% 29% 29% 12% 3	525
	11th to 20th	Day	15% 6% 31% 32% 12% 3	524
	21st to end	Day	16% 9% 35% 30% 9% 2	576
August	1st to 10th	Day	14% 7% 32% 33% 10% 4	526
	11th to 20th	Day	14% 8% 31% 27% 15% 5%	519
	21st to end	Day	13% 11% 31% 26% 13% 6%	583
September	1st to 10th	Day	19% 11% 25% 25% 15% 5%	530
	11th to 20th	Day	15% 11% 27% 25% 12% 10%	530
	21st to end	Day	21% 11% 34% 19% 9% 5%	530
October	1st to 10th	Day	29% 9% 24% 21% 12% 5%	530
	11th to 20th	Day	20% 18% 28% 25% 7% 2	510
	21st to end	Day	28% 14% 31% 18% 7% 2	462
November	1st to 10th	Day	22% 16% 31% 20% 9% 2	425
	11th to 20th	Day	30% 18% 29% 16% 7% 1	430
	21st to end	Day	30% 19% 29% 17% 5% 1	404
December	1st to 10th	Day	23% 28% 30% 15% 5%	220
	11th to 20th	Day	38% 22% 29% 8% 2	220
	21st to end	Day	31% 21% 29% 14% 4 2	242
January	1st to 10th	Night	23% 20% 38% 17% 3	805
	11th to 20th	Night	29% 19% 31% 19% 2	800
	21st to end	Night	22% 21% 34% 19% 3	880
February	1st to 10th	Night	24% 20% 34% 21% 2	800
	11th to 20th	Night	26% 21% 38% 14% 1	783
	21st to end	Night	27% 20% 35% 16% 2	660
March	1st to 10th	Night	27% 20% 34% 17% 3	800
	11th to 20th	Night	24% 20% 36% 17% 3	800
	21st to end	Night	27% 19% 35% 16% 3	880
April	1st to 10th	Night	26% 18% 34% 19% 3	800
	11th to 20th	Night	25% 19% 33% 19% 4	791
	21st to end	Night	25% 18% 34% 19% 4	666
May	1st to 10th	Night	30% 15% 30% 21% 4	600
	11th to 20th	Night	23% 14% 37% 21% 5%	502
	21st to end	Night	22% 7% 33% 30% 6% 1	433
June	1st to 10th	Night	21% 6% 32% 33% 8%	400
	11th to 20th	Night	21% 7% 30% 33% 9%	400
	21st to end	Night	16% 4 35% 37% 8% 1	400
July	1st to 10th	Night	14% 4 29% 39% 14%	390
	11th to 20th	Night	15% 3 26% 40% 15% 1	388
	21st to end	Night	12% 7% 31% 39% 11%	438
August	1st to 10th	Night	12% 6% 27% 42% 12% 1	485
	11th to 20th	Night	14% 4 25% 38% 17% 1	740
	21st to end	Night	15% 5% 26% 36% 17% 2	880
September	1st to 10th	Night	17% 5% 30% 34% 12% 2	800
	11th to 20th	Night	16% 7% 24% 34% 17% 2	800
	21st to end	Night	20% 7% 27% 30% 14% 2	800
October	1st to 10th	Night	24% 9% 27% 25% 13% 2	800
	11th to 20th	Night	22% 12% 29% 27% 9% 1	800
	21st to end	Night	27% 13% 30% 24% 6%	880
November	1st to 10th	Night	19% 12% 33% 26% 8% 1	820
	11th to 20th	Night	24% 15% 33% 21% 6% 1	840
	21st to end	Night	24% 17% 31% 22% 5%	840
December	1st to 10th	Night	28% 15% 33% 19% 5% 1	840
	11th to 20th	Night	26% 19% 31% 22% 2	840
	21st to end	Night	30% 16% 33% 19% 2	924

Page generated at 2025-12-30 01:14:05. Version ac07

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