Hartford
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Hartford clear sky chart from 2005-11-06 to 2024-11-04.

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% 3 6% 4 4 4 4 5% 7% 38%	101243
	Night	18% 8% 2 6% 4 4 4 3 5% 6% 39%	97782
Transparency	Day	43% 6% 12% 22% 15% 2	104793
	Night	43% 6% 12% 22% 15% 2	102321
Seeing	Day	23% 16% 30% 20% 8% 2	15005
	Night	22% 13% 32% 25% 7% 1	24002

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	15% 7% 3 6% 4 4 4 3 5% 6% 45%	2517
	11th to 20th	Day	17% 8% 3 8% 5% 4 5% 4 5% 5% 36%	2520
	21st to end	Day	22% 11% 3 7% 4 4 4 3 4 6% 32%	2810
February	1st to 10th	Day	18% 7% 2 6% 4 4 5% 5% 6% 6% 36%	1778
	11th to 20th	Day	14% 7% 2 7% 5% 5% 4 3 5% 7% 40%	1848
	21st to end	Day	21% 9% 2 5% 4 3 4 4 5% 5% 37%	1570
March	1st to 10th	Day	25% 11% 3 7% 4 3 3 3 3 4 33%	3116
	11th to 20th	Day	11% 6% 2 7% 6% 5% 5% 4 6% 7% 40%	3260
	21st to end	Day	21% 6% 3 6% 4 3 3 4 5% 6% 38%	4166
April	1st to 10th	Day	18% 8% 3 6% 4 4 4 4 6% 6% 36%	2280
	11th to 20th	Day	19% 6% 2 6% 4 4 4 3 6% 6% 41%	2254
	21st to end	Day	20% 6% 2 6% 4 4 4 3 5% 6% 39%	2401
May	1st to 10th	Day	26% 8% 3 7% 4 4 4 3 5% 8% 28%	4106
	11th to 20th	Day	22% 8% 2 7% 4 4 4 3 5% 7% 33%	4265
	21st to end	Day	14% 6% 2 4 4 4 4 3 6% 8% 44%	4837
June	1st to 10th	Day	16% 6% 3 5% 5% 4 5% 5% 6% 8% 35%	2660
	11th to 20th	Day	15% 6% 2 7% 5% 5% 4 4 6% 10% 37%	2660
	21st to end	Day	13% 7% 3 7% 5% 5% 4 5% 6% 9% 37%	2660
July	1st to 10th	Day	11% 6% 3 7% 6% 6% 5% 5% 7% 9% 36%	4440
	11th to 20th	Day	12% 5% 2 6% 5% 5% 5% 5% 6% 10% 38%	4440
	21st to end	Day	17% 8% 3 7% 5% 5% 5% 4 6% 6% 35%	4814
August	1st to 10th	Day	16% 8% 3 8% 5% 6% 4 4 7% 8% 29%	4248
	11th to 20th	Day	10% 6% 3 8% 5% 5% 4 4 6% 8% 41%	3792
	21st to end	Day	9% 5% 2 7% 5% 4 5% 5% 6% 9% 44%	4180
September	1st to 10th	Day	14% 6% 2 7% 4 4 5% 3 5% 6% 45%	2280
	11th to 20th	Day	14% 5% 2 5% 2 3 3 3 5% 6% 50%	2141
	21st to end	Day	18% 6% 2 6% 4 4 5% 3 5% 7% 41%	2090
October	1st to 10th	Day	22% 7% 3 5% 4 4 4 3 5% 5% 40%	2071
	11th to 20th	Day	14% 7% 2 5% 3 4 3 3 5% 7% 46%	1870
	21st to end	Day	21% 6% 2 5% 3 4 4 4 4 7% 40%	1881
November	1st to 10th	Day	13% 7% 2 6% 4 4 3 3 3 6% 48%	1698
	11th to 20th	Day	19% 6% 2 4 3 3 3 3 5% 6% 45%	1710
	21st to end	Day	18% 6% 2 6% 4 4 4 3 5% 6% 43%	1682
December	1st to 10th	Day	19% 6% 3 7% 5% 4 5% 4 6% 5% 37%	1520
	11th to 20th	Day	23% 7% 2 3 2 3 4 4 4 5% 44%	1906
	21st to end	Day	21% 12% 3 8% 5% 4 4 3 5% 5% 32%	2772
January	1st to 10th	Night	17% 7% 2 5% 4 4 3 4 5% 6% 45%	4429
	11th to 20th	Night	16% 9% 3 8% 4 4 3 3 4 5% 41%	4440
	21st to end	Night	24% 12% 4 7% 4 3 3 2 4 5% 31%	4843
February	1st to 10th	Night	17% 9% 3 6% 4 4 4 4 5% 5% 40%	2400
	11th to 20th	Night	15% 9% 2 6% 5% 5% 4 4 5% 6% 39%	2218
	21st to end	Night	19% 9% 2 7% 4 3 4 3 4 5% 40%	1884
March	1st to 10th	Night	28% 10% 2 5% 4 3 3 3 5% 5% 32%	3724
	11th to 20th	Night	12% 9% 3 7% 4 4 5% 4 5% 6% 41%	3696
	21st to end	Night	22% 7% 3 6% 4 3 4 3 6% 5% 38%	3466
April	1st to 10th	Night	19% 7% 2 6% 5% 4 4 4 6% 6% 37%	1900
	11th to 20th	Night	19% 7% 2 6% 5% 4 4 4 5% 5% 39%	1875
	21st to end	Night	22% 7% 2 6% 4 4 2 3 4 5% 41%	1777
May	1st to 10th	Night	24% 9% 3 8% 4 5% 4 4 5% 7% 28%	2834
	11th to 20th	Night	21% 9% 4 8% 5% 4 4 4 6% 6% 29%	2656
	21st to end	Night	17% 6% 2 5% 3 4 3 4 6% 9% 41%	2738
June	1st to 10th	Night	17% 7% 2 6% 4 3 5% 3 6% 8% 39%	1520
	11th to 20th	Night	17% 6% 3 6% 4 4 4 4 6% 8% 39%	1520
	21st to end	Night	14% 6% 2 6% 4 4 4 4 7% 9% 41%	1520
July	1st to 10th	Night	12% 7% 2 7% 5% 5% 5% 4 7% 11% 36%	2520
	11th to 20th	Night	15% 7% 3 6% 5% 4 5% 4 6% 9% 37%	2520
	21st to end	Night	16% 10% 3 7% 5% 4 4 4 7% 6% 33%	2739
August	1st to 10th	Night	21% 6% 3 7% 5% 5% 5% 4 6% 8% 30%	2648
	11th to 20th	Night	13% 7% 2 8% 5% 5% 5% 4 6% 7% 39%	3031
	21st to end	Night	9% 4 1 5% 4 4 4 3 6% 8% 51%	3476
September	1st to 10th	Night	14% 6% 2 7% 4 4 4 4 5% 6% 45%	1900
	11th to 20th	Night	13% 6% 2 5% 4 3 3 3 4 6% 52%	2038
	21st to end	Night	17% 6% 2 6% 3 3 4 4 5% 6% 44%	2090
October	1st to 10th	Night	21% 7% 2 5% 4 4 4 3 4 6% 41%	2106
	11th to 20th	Night	15% 5% 2 6% 4 3 4 3 4 6% 47%	2308
	21st to end	Night	23% 6% 2 5% 4 4 3 4 4 5% 40%	2717
November	1st to 10th	Night	14% 5% 2 5% 3 4 4 3 5% 6% 48%	2453
	11th to 20th	Night	20% 7% 2 5% 3 3 3 3 5% 5% 44%	2470
	21st to end	Night	16% 7% 2 5% 4 3 4 4 4 6% 44%	2494
December	1st to 10th	Night	20% 8% 2 6% 4 4 4 3 5% 6% 39%	2660
	11th to 20th	Night	21% 7% 2 5% 4 4 3 4 4 6% 41%	3288
	21st to end	Night	23% 11% 3 7% 4 4 3 3 4 5% 34%	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	40% 5% 10% 32% 10% 2	2518
	11th to 20th	Day	48% 6% 11% 24% 10% 1	2520
	21st to end	Day	53% 6% 8% 21% 10% 1	2810
February	1st to 10th	Day	46% 7% 12% 19% 13% 2	1778
	11th to 20th	Day	44% 5% 10% 22% 16% 3	1857
	21st to end	Day	47% 6% 11% 20% 14% 3	1570
March	1st to 10th	Day	55% 4 12% 17% 11% 2	3119
	11th to 20th	Day	38% 9% 13% 27% 12% 2	3260
	21st to end	Day	47% 4 7% 17% 20% 5%	4166
April	1st to 10th	Day	46% 6% 10% 20% 14% 3	2280
	11th to 20th	Day	43% 5% 10% 20% 19% 3	2254
	21st to end	Day	46% 5% 10% 20% 15% 4	2401
May	1st to 10th	Day	53% 7% 13% 14% 11% 1	4120
	11th to 20th	Day	50% 7% 13% 18% 10% 2	4269
	21st to end	Day	35% 8% 12% 25% 18% 2	4837
June	1st to 10th	Day	45% 7% 12% 24% 12% 1	2660
	11th to 20th	Day	43% 8% 13% 21% 13% 2	2660
	21st to end	Day	43% 8% 13% 20% 15% 1	2660
July	1st to 10th	Day	44% 8% 11% 19% 16% 1	4370
	11th to 20th	Day	40% 8% 15% 23% 13% 2	4365
	21st to end	Day	49% 7% 11% 17% 15% 1	4661
August	1st to 10th	Day	50% 8% 15% 19% 8%	4234
	11th to 20th	Day	38% 8% 13% 29% 10%	3830
	21st to end	Day	35% 8% 12% 28% 16% 2	4180
September	1st to 10th	Day	40% 6% 10% 21% 20% 2	2280
	11th to 20th	Day	34% 6% 10% 24% 23% 3	2141
	21st to end	Day	43% 5% 8% 21% 19% 3	2090
October	1st to 10th	Day	39% 6% 9% 19% 23% 4	3448
	11th to 20th	Day	29% 4 8% 26% 30% 3	3086
	21st to end	Day	32% 5% 13% 26% 21% 3	3081
November	1st to 10th	Day	39% 5% 12% 23% 19% 3	1698
	11th to 20th	Day	41% 4 10% 23% 19% 3	1710
	21st to end	Day	43% 4 12% 26% 12% 3	1682
December	1st to 10th	Day	47% 6% 14% 17% 15% 1	1520
	11th to 20th	Day	43% 4 15% 18% 18% 2	1906
	21st to end	Day	53% 5% 12% 19% 10% 1	2772
January	1st to 10th	Night	40% 4 11% 31% 11% 3	4429
	11th to 20th	Night	46% 5% 12% 22% 12% 3	4440
	21st to end	Night	56% 4 10% 18% 11% 1	4843
February	1st to 10th	Night	46% 6% 13% 23% 12% 2	2400
	11th to 20th	Night	45% 5% 10% 20% 16% 4	2220
	21st to end	Night	46% 5% 9% 22% 14% 4	1884
March	1st to 10th	Night	53% 5% 9% 19% 11% 2	3734
	11th to 20th	Night	40% 7% 15% 22% 14% 2	3697
	21st to end	Night	47% 4 8% 12% 23% 5%	3466
April	1st to 10th	Night	48% 6% 9% 19% 15% 3	1900
	11th to 20th	Night	45% 6% 9% 18% 20% 1	1875
	21st to end	Night	46% 5% 9% 21% 14% 5%	1777
May	1st to 10th	Night	54% 8% 13% 14% 9% 2	2840
	11th to 20th	Night	53% 9% 13% 15% 9% 2	2657
	21st to end	Night	38% 9% 15% 24% 13% 1	2739
June	1st to 10th	Night	43% 8% 12% 21% 15% 1	1520
	11th to 20th	Night	43% 8% 13% 25% 11% 1	1520
	21st to end	Night	38% 9% 14% 24% 14%	1520
July	1st to 10th	Night	42% 10% 15% 20% 13% 1	2480
	11th to 20th	Night	42% 8% 16% 23% 10% 1	2472
	21st to end	Night	49% 7% 12% 15% 15% 2	2651
August	1st to 10th	Night	51% 10% 13% 17% 9% 1	2638
	11th to 20th	Night	42% 8% 14% 27% 8%	3059
	21st to end	Night	28% 7% 16% 32% 16% 1	3476
September	1st to 10th	Night	40% 7% 9% 25% 18% 1	1900
	11th to 20th	Night	34% 5% 11% 22% 26% 2	2038
	21st to end	Night	41% 6% 9% 21% 20% 2	2090
October	1st to 10th	Night	39% 6% 13% 21% 18% 2	3509
	11th to 20th	Night	27% 4 8% 28% 30% 2	3831
	21st to end	Night	33% 3 13% 29% 19% 2	4467
November	1st to 10th	Night	37% 6% 12% 22% 20% 4	2453
	11th to 20th	Night	42% 5% 11% 21% 18% 3	2470
	21st to end	Night	41% 5% 14% 27% 12% 2	2494
December	1st to 10th	Night	46% 6% 13% 21% 14% 1	2660
	11th to 20th	Night	45% 4 15% 17% 17% 2	3288
	21st to end	Night	52% 3 11% 22% 12% 1	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	26% 22% 31% 18% 3	180
	11th to 20th	Day	28% 28% 29% 12% 3	180
	21st to end	Day	24% 25% 34% 11% 5%	211
February	1st to 10th	Day	31% 26% 27% 14% 2	338
	11th to 20th	Day	28% 27% 32% 11% 2	456
	21st to end	Day	31% 19% 34% 12% 4	382
March	1st to 10th	Day	27% 22% 33% 15% 3	460
	11th to 20th	Day	28% 24% 32% 14% 2	460
	21st to end	Day	30% 21% 32% 10% 5% 2	506
April	1st to 10th	Day	31% 23% 27% 13% 5% 1	460
	11th to 20th	Day	31% 19% 29% 16% 4 1	452
	21st to end	Day	30% 18% 33% 13% 4 2	460
May	1st to 10th	Day	34% 16% 29% 12% 7% 1	463
	11th to 20th	Day	24% 16% 36% 16% 7%	487
	21st to end	Day	21% 14% 33% 22% 9% 2	529
June	1st to 10th	Day	18% 17% 29% 23% 10% 3	490
	11th to 20th	Day	15% 17% 36% 22% 8% 2	490
	21st to end	Day	16% 17% 31% 26% 9% 2	490
July	1st to 10th	Day	18% 9% 28% 28% 14% 3	485
	11th to 20th	Day	14% 6% 32% 30% 14% 3	484
	21st to end	Day	16% 9% 35% 28% 11% 2	532
August	1st to 10th	Day	14% 8% 30% 33% 11% 4	486
	11th to 20th	Day	14% 9% 31% 27% 14% 5%	479
	21st to end	Day	13% 10% 28% 26% 17% 6%	539
September	1st to 10th	Day	19% 10% 25% 24% 17% 6%	490
	11th to 20th	Day	17% 11% 25% 24% 12% 10%	490
	21st to end	Day	21% 11% 31% 21% 10% 5%	490
October	1st to 10th	Day	28% 10% 25% 20% 12% 6%	490
	11th to 20th	Day	16% 17% 31% 26% 8% 3	473
	21st to end	Day	27% 15% 29% 19% 8% 2	429
November	1st to 10th	Day	19% 16% 30% 23% 10% 2	374
	11th to 20th	Day	29% 20% 26% 18% 7% 1	370
	21st to end	Day	25% 18% 30% 19% 7%	342
December	1st to 10th	Day	23% 25% 31% 16% 5%	180
	11th to 20th	Day	32% 23% 34% 9% 2	180
	21st to end	Day	26% 22% 32% 14% 4 2	198
January	1st to 10th	Night	21% 18% 39% 19% 3	760
	11th to 20th	Night	29% 18% 31% 20% 2	760
	21st to end	Night	22% 18% 37% 21% 2	836
February	1st to 10th	Night	22% 18% 36% 22% 2	760
	11th to 20th	Night	24% 20% 39% 16% 1	743
	21st to end	Night	27% 18% 36% 17% 2	628
March	1st to 10th	Night	26% 19% 34% 18% 3	760
	11th to 20th	Night	23% 20% 36% 18% 3	760
	21st to end	Night	26% 17% 34% 19% 4	836
April	1st to 10th	Night	24% 18% 35% 20% 3	760
	11th to 20th	Night	23% 19% 34% 19% 5%	751
	21st to end	Night	26% 18% 32% 19% 4	637
May	1st to 10th	Night	29% 15% 30% 22% 4	570
	11th to 20th	Night	21% 15% 39% 20% 4	470
	21st to end	Night	20% 9% 30% 33% 6% 1	411
June	1st to 10th	Night	21% 6% 34% 32% 7%	380
	11th to 20th	Night	19% 8% 32% 32% 9%	380
	21st to end	Night	14% 5% 36% 36% 8% 1	380
July	1st to 10th	Night	14% 5% 28% 39% 14%	370
	11th to 20th	Night	16% 4 23% 42% 15% 1	368
	21st to end	Night	12% 6% 30% 40% 12%	416
August	1st to 10th	Night	12% 7% 27% 44% 10% 1	455
	11th to 20th	Night	14% 5% 23% 38% 18% 2	708
	21st to end	Night	14% 4 25% 37% 18% 1	836
September	1st to 10th	Night	17% 5% 29% 34% 14% 1	760
	11th to 20th	Night	17% 5% 25% 32% 18% 2	760
	21st to end	Night	19% 8% 28% 30% 14% 2	760
October	1st to 10th	Night	25% 8% 26% 27% 12% 2	760
	11th to 20th	Night	20% 10% 31% 28% 10% 1	760
	21st to end	Night	28% 13% 30% 23% 7%	836
November	1st to 10th	Night	18% 12% 34% 26% 9% 1	755
	11th to 20th	Night	25% 13% 34% 21% 6% 1	760
	21st to end	Night	23% 15% 33% 23% 5% 1	760
December	1st to 10th	Night	26% 15% 34% 19% 5% 1	760
	11th to 20th	Night	25% 16% 33% 23% 3	760
	21st to end	Night	28% 14% 36% 19% 2	836

Page generated at 2024-11-01 22:47:51. Version ac07

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