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 2024-03-28.

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% 6% 3 5% 5% 3 5% 5% 5% 7% 40%	78624
	Night	18% 7% 3 5% 5% 3 4 4 5% 6% 40%	81358
Transparency	Day	44% 6% 11% 22% 15% 2	78329
	Night	44% 6% 11% 22% 15% 2	81187
Seeing	Day	23% 16% 30% 20% 8% 2	14137
	Night	22% 13% 32% 25% 7% 1	23309

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 5% 5% 2 4 4 4 6% 45%	2517
	11th to 20th	Day	17% 7% 4 7% 6% 3 5% 5% 5% 5% 36%	2520
	21st to end	Day	22% 10% 3 6% 4 3 4 4 4 6% 33%	2810
February	1st to 10th	Day	18% 6% 3 5% 5% 2 6% 6% 6% 6% 36%	1778
	11th to 20th	Day	14% 6% 3 7% 5% 3 5% 5% 4 7% 40%	1848
	21st to end	Day	21% 8% 3 4 5% 2 4 5% 5% 6% 37%	1570
March	1st to 10th	Day	16% 7% 3 5% 5% 3 4 5% 4 7% 41%	1897
	11th to 20th	Day	16% 5% 2 5% 7% 3 6% 5% 6% 7% 38%	1948
	21st to end	Day	19% 7% 3 5% 6% 2 4 4 4 5% 41%	2460
April	1st to 10th	Day	18% 7% 3 5% 5% 3 4 5% 6% 6% 38%	2160
	11th to 20th	Day	18% 5% 2 5% 4 3 4 4 6% 6% 42%	2134
	21st to end	Day	21% 6% 2 5% 5% 3 4 4 5% 6% 38%	2274
May	1st to 10th	Day	25% 7% 3 5% 5% 3 4 4 5% 7% 33%	2340
	11th to 20th	Day	19% 6% 2 5% 4 3 4 5% 6% 8% 40%	2401
	21st to end	Day	15% 6% 2 4 4 3 5% 4 5% 8% 43%	2725
June	1st to 10th	Day	17% 6% 3 4 6% 3 5% 6% 6% 8% 35%	2520
	11th to 20th	Day	16% 6% 3 6% 6% 3 5% 4 6% 10% 36%	2520
	21st to end	Day	13% 7% 3 6% 5% 3 5% 6% 6% 9% 37%	2520
July	1st to 10th	Day	12% 6% 3 6% 5% 4 6% 5% 7% 7% 40%	2520
	11th to 20th	Day	12% 4 2 5% 6% 3 6% 6% 6% 10% 39%	2520
	21st to end	Day	12% 5% 3 5% 6% 4 5% 6% 6% 8% 38%	2744
August	1st to 10th	Day	10% 7% 3 6% 6% 5% 5% 6% 8% 8% 36%	2414
	11th to 20th	Day	11% 6% 3 6% 7% 3 5% 5% 6% 8% 40%	2162
	21st to end	Day	12% 5% 3 6% 5% 3 5% 5% 5% 8% 44%	2376
September	1st to 10th	Day	14% 6% 2 6% 5% 3 5% 4 5% 6% 43%	2160
	11th to 20th	Day	15% 5% 2 4 3 3 3 4 5% 6% 50%	2029
	21st to end	Day	18% 5% 2 5% 4 3 4 4 4 7% 44%	1980
October	1st to 10th	Day	23% 7% 3 4 4 3 4 4 4 5% 40%	1962
	11th to 20th	Day	15% 6% 2 5% 4 3 4 4 5% 8% 45%	1772
	21st to end	Day	21% 6% 3 4 4 3 4 5% 4 6% 39%	1782
November	1st to 10th	Day	14% 7% 3 6% 4 2 5% 3 3 5% 48%	1671
	11th to 20th	Day	20% 6% 2 4 3 2 4 4 4 7% 45%	1710
	21st to end	Day	18% 5% 3 5% 5% 3 4 4 4 6% 43%	1682
December	1st to 10th	Day	19% 6% 3 7% 5% 3 4 5% 5% 6% 37%	1520
	11th to 20th	Day	23% 6% 2 3 3 2 3 4 4 5% 44%	1906
	21st to end	Day	21% 11% 3 7% 6% 3 4 4 5% 5% 32%	2772
January	1st to 10th	Night	17% 6% 2 4 5% 3 4 4 5% 6% 45%	4429
	11th to 20th	Night	16% 9% 3 7% 5% 3 4 4 4 5% 41%	4440
	21st to end	Night	24% 12% 4 6% 5% 3 3 3 4 5% 31%	4843
February	1st to 10th	Night	17% 9% 4 5% 5% 3 4 4 5% 6% 40%	2400
	11th to 20th	Night	15% 8% 2 5% 6% 4 4 5% 5% 7% 39%	2218
	21st to end	Night	19% 8% 2 6% 5% 3 4 4 4 5% 40%	1884
March	1st to 10th	Night	18% 7% 3 5% 5% 3 4 4 6% 7% 39%	2270
	11th to 20th	Night	16% 8% 3 5% 5% 3 5% 5% 5% 7% 39%	2228
	21st to end	Night	19% 7% 3 5% 5% 2 4 4 5% 6% 42%	2051
April	1st to 10th	Night	19% 7% 3 5% 5% 3 5% 4 5% 6% 38%	1800
	11th to 20th	Night	18% 6% 2 6% 6% 3 4 4 5% 6% 40%	1775
	21st to end	Night	23% 7% 3 5% 5% 2 3 4 4 5% 40%	1684
May	1st to 10th	Night	23% 7% 3 7% 5% 4 4 5% 4 6% 32%	1620
	11th to 20th	Night	19% 7% 2 6% 4 3 4 4 6% 7% 37%	1506
	21st to end	Night	17% 6% 2 4 4 3 4 4 6% 9% 40%	1550
June	1st to 10th	Night	18% 6% 2 5% 5% 3 4 5% 6% 8% 39%	1440
	11th to 20th	Night	18% 5% 3 6% 4 3 5% 5% 6% 7% 38%	1440
	21st to end	Night	14% 5% 2 5% 5% 3 4 5% 7% 9% 43%	1440
July	1st to 10th	Night	12% 6% 2 5% 5% 3 5% 4 7% 11% 39%	1440
	11th to 20th	Night	13% 6% 3 5% 5% 4 5% 5% 7% 9% 38%	1440
	21st to end	Night	10% 5% 3 5% 5% 4 5% 5% 8% 9% 40%	1574
August	1st to 10th	Night	9% 6% 2 5% 5% 4 5% 5% 6% 9% 43%	1504
	11th to 20th	Night	12% 5% 3 6% 6% 4 6% 5% 7% 7% 39%	1734
	21st to end	Night	14% 5% 2 5% 5% 3 5% 4 6% 8% 45%	1980
September	1st to 10th	Night	14% 5% 3 6% 5% 3 4 4 5% 6% 44%	1800
	11th to 20th	Night	14% 6% 2 4 4 2 3 4 4 5% 52%	1930
	21st to end	Night	17% 6% 2 5% 4 3 4 5% 5% 5% 45%	1980
October	1st to 10th	Night	22% 6% 2 4 5% 3 4 4 4 6% 41%	1995
	11th to 20th	Night	16% 5% 2 5% 5% 2 4 4 4 6% 46%	2186
	21st to end	Night	24% 6% 2 4 5% 3 4 5% 4 5% 38%	2574
November	1st to 10th	Night	15% 5% 2 5% 4 3 4 4 5% 6% 48%	2407
	11th to 20th	Night	20% 6% 2 5% 4 2 3 4 5% 5% 44%	2470
	21st to end	Night	17% 6% 2 5% 4 3 4 4 4 6% 44%	2494
December	1st to 10th	Night	21% 7% 3 5% 4 3 4 3 5% 6% 39%	2660
	11th to 20th	Night	21% 6% 2 4 4 3 4 4 4 6% 41%	3288
	21st to end	Night	23% 11% 3 6% 5% 3 4 3 4 5% 35%	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	45% 4 13% 21% 13% 4	1900
	11th to 20th	Day	43% 7% 11% 23% 13% 2	1948
	21st to end	Day	47% 4 8% 18% 18% 5%	2460
April	1st to 10th	Day	45% 6% 11% 20% 15% 4	2160
	11th to 20th	Day	42% 5% 10% 21% 19% 3	2134
	21st to end	Day	47% 5% 10% 20% 15% 4	2274
May	1st to 10th	Day	51% 6% 9% 19% 13% 2	2340
	11th to 20th	Day	43% 6% 10% 21% 17% 3	2405
	21st to end	Day	39% 9% 14% 22% 14% 2	2725
June	1st to 10th	Day	46% 7% 12% 23% 11% 1	2520
	11th to 20th	Day	45% 8% 12% 20% 14% 2	2520
	21st to end	Day	42% 8% 14% 21% 14% 1	2520
July	1st to 10th	Day	42% 9% 11% 19% 17% 2	2450
	11th to 20th	Day	39% 9% 13% 24% 13% 2	2445
	21st to end	Day	41% 9% 12% 19% 17% 2	2591
August	1st to 10th	Day	42% 9% 14% 22% 13% 1	2400
	11th to 20th	Day	39% 10% 13% 23% 14% 1	2162
	21st to end	Day	37% 8% 11% 23% 18% 2	2376
September	1st to 10th	Day	42% 6% 11% 21% 19% 2	2160
	11th to 20th	Day	34% 6% 11% 23% 23% 3	2029
	21st to end	Day	41% 5% 9% 22% 21% 3	1980
October	1st to 10th	Day	47% 6% 8% 21% 14% 4	1962
	11th to 20th	Day	38% 6% 12% 27% 16% 2	1772
	21st to end	Day	46% 6% 10% 21% 14% 3	1782
November	1st to 10th	Day	40% 5% 12% 22% 18% 3	1671
	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	44% 7% 11% 21% 15% 3	2280
	11th to 20th	Night	44% 6% 10% 22% 15% 3	2229
	21st to end	Night	44% 4 9% 17% 20% 5%	2051
April	1st to 10th	Night	47% 6% 9% 20% 15% 3	1800
	11th to 20th	Night	44% 6% 10% 19% 20% 1	1775
	21st to end	Night	47% 5% 9% 20% 13% 5%	1684
May	1st to 10th	Night	52% 8% 8% 16% 13% 3	1620
	11th to 20th	Night	45% 7% 10% 19% 16% 3	1507
	21st to end	Night	40% 11% 15% 19% 13% 1	1551
June	1st to 10th	Night	44% 8% 12% 20% 15% 1	1440
	11th to 20th	Night	45% 8% 12% 24% 11% 1	1440
	21st to end	Night	37% 10% 14% 25% 14%	1440
July	1st to 10th	Night	38% 10% 14% 20% 16% 1	1400
	11th to 20th	Night	40% 10% 15% 26% 9% 1	1392
	21st to end	Night	37% 9% 16% 21% 14% 2	1486
August	1st to 10th	Night	35% 11% 14% 24% 14% 2	1494
	11th to 20th	Night	42% 9% 13% 24% 11% 1	1734
	21st to end	Night	36% 7% 13% 25% 19% 1	1980
September	1st to 10th	Night	40% 8% 10% 24% 17% 1	1800
	11th to 20th	Night	34% 6% 11% 21% 26% 2	1930
	21st to end	Night	40% 6% 8% 22% 21% 2	1980
October	1st to 10th	Night	45% 6% 11% 21% 14% 3	1995
	11th to 20th	Night	38% 6% 12% 27% 15% 1	2186
	21st to end	Night	48% 5% 12% 20% 14% 1	2574
November	1st to 10th	Night	38% 6% 12% 22% 20% 4	2407
	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% 20% 32% 11% 5% 2	490
April	1st to 10th	Day	31% 23% 28% 13% 5% 1	420
	11th to 20th	Day	29% 18% 30% 17% 5% 1	412
	21st to end	Day	32% 18% 33% 12% 4 1	420
May	1st to 10th	Day	35% 16% 29% 12% 7% 1	423
	11th to 20th	Day	24% 16% 37% 16% 6%	447
	21st to end	Day	21% 14% 31% 22% 10% 2	485
June	1st to 10th	Day	18% 18% 28% 23% 10% 3	450
	11th to 20th	Day	16% 18% 36% 21% 7% 2	450
	21st to end	Day	16% 17% 30% 27% 10% 2	450
July	1st to 10th	Day	18% 9% 28% 27% 14% 3	445
	11th to 20th	Day	15% 6% 30% 31% 15% 3	444
	21st to end	Day	15% 9% 35% 29% 11% 2	488
August	1st to 10th	Day	13% 8% 30% 33% 12% 4	446
	11th to 20th	Day	13% 9% 31% 27% 15% 5%	439
	21st to end	Day	14% 10% 29% 25% 16% 5%	495
September	1st to 10th	Day	20% 10% 25% 23% 17% 5%	450
	11th to 20th	Day	18% 11% 26% 24% 10% 9%	450
	21st to end	Day	21% 12% 30% 20% 10% 6%	450
October	1st to 10th	Day	30% 10% 25% 19% 11% 6%	450
	11th to 20th	Day	17% 16% 30% 26% 8% 2	435
	21st to end	Day	29% 15% 29% 18% 7% 2	396
November	1st to 10th	Day	19% 16% 30% 23% 10% 2	365
	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	821
April	1st to 10th	Night	24% 18% 34% 20% 3	720
	11th to 20th	Night	23% 19% 34% 20% 5%	711
	21st to end	Night	27% 18% 32% 19% 4	604
May	1st to 10th	Night	30% 14% 31% 21% 4	540
	11th to 20th	Night	22% 15% 39% 20% 5%	445
	21st to end	Night	21% 8% 30% 34% 6% 1	389
June	1st to 10th	Night	22% 5% 34% 31% 8%	360
	11th to 20th	Night	20% 8% 32% 32% 9%	360
	21st to end	Night	14% 5% 36% 37% 8% 1	360
July	1st to 10th	Night	15% 4 28% 39% 15%	350
	11th to 20th	Night	15% 3 23% 42% 16% 1	348
	21st to end	Night	12% 6% 30% 41% 12%	394
August	1st to 10th	Night	10% 6% 28% 45% 10% 1	430
	11th to 20th	Night	14% 5% 23% 39% 17% 1	670
	21st to end	Night	15% 4 25% 37% 18% 1	792
September	1st to 10th	Night	18% 5% 30% 34% 13% 1	720
	11th to 20th	Night	18% 6% 26% 32% 17% 2	720
	21st to end	Night	20% 7% 28% 29% 14% 2	720
October	1st to 10th	Night	26% 8% 26% 26% 12% 2	720
	11th to 20th	Night	21% 10% 31% 28% 10%	720
	21st to end	Night	29% 13% 30% 21% 6%	792
November	1st to 10th	Night	18% 12% 34% 26% 9% 1	740
	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 2024-03-24 23:37:03. Version ac07

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