Danbury
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Danbury clear sky chart from 2005-11-06 to 2024-11-03.

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	17% 7% 2 6% 4 4 4 4 5% 7% 38%	101267
	Night	18% 8% 2 6% 4 4 4 3 5% 6% 40%	97711
Transparency	Day	44% 6% 12% 22% 14% 2	101022
	Night	43% 6% 12% 22% 14% 2	97576
Seeing	Day	23% 17% 30% 19% 8% 2	14982
	Night	22% 15% 30% 24% 8% 1	24043

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 4 5% 46%	2517
	11th to 20th	Day	16% 10% 3 7% 5% 5% 5% 3 4 5% 35%	2520
	21st to end	Day	21% 12% 4 8% 4 4 3 3 4 5% 31%	2909
February	1st to 10th	Day	18% 8% 2 6% 5% 5% 5% 4 5% 6% 37%	1740
	11th to 20th	Day	14% 8% 3 5% 5% 4 4 4 5% 7% 41%	1848
	21st to end	Day	20% 9% 3 6% 4 4 4 3 4 6% 37%	1570
March	1st to 10th	Day	27% 10% 2 6% 4 4 3 2 3 4 34%	3116
	11th to 20th	Day	10% 6% 2 5% 5% 5% 5% 5% 7% 8% 43%	3277
	21st to end	Day	21% 7% 2 6% 4 4 3 3 4 6% 39%	4166
April	1st to 10th	Day	18% 10% 2 7% 4 4 4 3 6% 6% 36%	2280
	11th to 20th	Day	17% 7% 2 6% 4 4 4 3 5% 7% 41%	2254
	21st to end	Day	20% 6% 2 5% 4 4 4 4 5% 6% 40%	2351
May	1st to 10th	Day	28% 9% 2 6% 3 4 4 3 5% 8% 30%	4106
	11th to 20th	Day	22% 8% 3 7% 5% 4 4 4 5% 7% 32%	4332
	21st to end	Day	14% 6% 2 5% 4 3 4 4 6% 8% 44%	4837
June	1st to 10th	Day	18% 6% 2 5% 4 5% 4 5% 6% 9% 36%	2660
	11th to 20th	Day	15% 7% 2 6% 5% 4 5% 5% 6% 9% 35%	2660
	21st to end	Day	13% 6% 3 6% 5% 5% 5% 3 7% 9% 37%	2660
July	1st to 10th	Day	11% 6% 2 7% 6% 6% 6% 5% 7% 10% 35%	4440
	11th to 20th	Day	13% 6% 2 6% 4 5% 5% 4 7% 9% 38%	4440
	21st to end	Day	15% 8% 3 7% 5% 5% 5% 5% 6% 7% 33%	4814
August	1st to 10th	Day	20% 7% 2 6% 5% 5% 5% 4 6% 8% 31%	4254
	11th to 20th	Day	11% 7% 2 7% 4 4 4 4 6% 9% 41%	3730
	21st to end	Day	10% 6% 3 5% 4 4 5% 4 6% 9% 45%	4180
September	1st to 10th	Day	13% 7% 2 6% 5% 4 5% 4 6% 5% 43%	2280
	11th to 20th	Day	13% 5% 2 5% 3 3 4 3 4 7% 49%	2173
	21st to end	Day	17% 7% 3 6% 4 4 4 3 5% 6% 40%	2090
October	1st to 10th	Day	22% 6% 2 6% 4 4 4 3 4 5% 41%	2022
	11th to 20th	Day	14% 6% 2 6% 4 4 3 3 6% 7% 46%	1900
	21st to end	Day	22% 5% 2 5% 4 3 5% 4 4 6% 40%	1895
November	1st to 10th	Day	13% 7% 2 6% 3 3 3 3 5% 6% 50%	1689
	11th to 20th	Day	19% 5% 2 5% 3 3 3 2 5% 7% 45%	1710
	21st to end	Day	17% 6% 2 5% 4 4 3 4 6% 7% 44%	1649
December	1st to 10th	Day	18% 7% 3 7% 6% 4 4 3 4 6% 37%	1520
	11th to 20th	Day	22% 5% 2 5% 3 3 3 3 4 6% 43%	1906
	21st to end	Day	19% 11% 4 7% 5% 5% 4 3 5% 7% 30%	2772
January	1st to 10th	Night	17% 7% 2 5% 3 3 3 3 5% 6% 45%	4429
	11th to 20th	Night	16% 9% 3 7% 4 3 4 3 5% 6% 41%	4440
	21st to end	Night	23% 12% 3 7% 4 3 3 3 4 5% 33%	4744
February	1st to 10th	Night	16% 9% 3 6% 5% 4 4 3 5% 6% 40%	2437
	11th to 20th	Night	16% 9% 3 5% 5% 4 3 4 5% 7% 40%	2218
	21st to end	Night	19% 8% 2 6% 4 3 4 3 5% 5% 41%	1884
March	1st to 10th	Night	24% 12% 2 6% 3 3 3 3 4 5% 34%	3724
	11th to 20th	Night	11% 6% 2 7% 4 4 4 3 5% 6% 45%	3663
	21st to end	Night	19% 10% 3 6% 3 3 3 3 5% 5% 41%	3466
April	1st to 10th	Night	18% 7% 3 5% 5% 5% 4 4 5% 7% 37%	1900
	11th to 20th	Night	18% 8% 2 6% 5% 4 4 4 4 8% 38%	1875
	21st to end	Night	20% 7% 3 6% 4 3 4 2 5% 6% 41%	1829
May	1st to 10th	Night	24% 9% 3 8% 5% 4 4 3 5% 8% 27%	2834
	11th to 20th	Night	23% 10% 3 7% 4 4 4 3 4 7% 32%	2577
	21st to end	Night	16% 7% 2 6% 3 3 4 3 6% 7% 43%	2738
June	1st to 10th	Night	18% 6% 2 5% 5% 4 4 4 5% 7% 41%	1520
	11th to 20th	Night	15% 5% 3 5% 4 4 4 5% 6% 9% 39%	1520
	21st to end	Night	12% 6% 2 6% 4 4 4 4 7% 10% 42%	1520
July	1st to 10th	Night	12% 6% 2 6% 5% 5% 6% 4 7% 9% 38%	2520
	11th to 20th	Night	15% 6% 2 7% 4 6% 4 4 6% 9% 37%	2520
	21st to end	Night	18% 8% 2 6% 5% 4 4 4 6% 7% 36%	2739
August	1st to 10th	Night	21% 7% 3 8% 5% 4 5% 4 5% 7% 30%	2641
	11th to 20th	Night	15% 7% 2 7% 5% 4 5% 3 6% 7% 40%	3097
	21st to end	Night	11% 5% 2 4 3 3 4 3 5% 7% 53%	3476
September	1st to 10th	Night	15% 7% 2 6% 4 4 3 3 4 6% 46%	1900
	11th to 20th	Night	13% 5% 2 5% 3 3 3 2 4 6% 54%	2005
	21st to end	Night	19% 7% 2 5% 3 3 4 4 4 5% 44%	2090
October	1st to 10th	Night	20% 6% 2 6% 4 3 3 3 4 6% 42%	2156
	11th to 20th	Night	15% 6% 2 6% 3 3 3 3 4 6% 48%	2280
	21st to end	Night	22% 7% 2 5% 3 4 4 3 5% 6% 41%	2702
November	1st to 10th	Night	12% 6% 2 5% 4 3 4 4 6% 6% 48%	2434
	11th to 20th	Night	19% 7% 2 4 3 3 3 2 5% 6% 45%	2470
	21st to end	Night	15% 6% 2 5% 4 4 4 3 5% 7% 45%	2531
December	1st to 10th	Night	19% 8% 2 6% 4 4 4 3 5% 6% 39%	2660
	11th to 20th	Night	20% 8% 2 5% 4 4 4 4 5% 7% 39%	3288
	21st to end	Night	21% 10% 3 7% 4 4 4 3 5% 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	39% 5% 10% 32% 10% 3	2518
	11th to 20th	Day	49% 6% 11% 23% 9% 1	2520
	21st to end	Day	56% 5% 8% 20% 10% 2	2909
February	1st to 10th	Day	47% 5% 12% 21% 13% 1	1740
	11th to 20th	Day	41% 5% 11% 22% 17% 3	1857
	21st to end	Day	49% 4 10% 22% 12% 3	1570
March	1st to 10th	Day	52% 5% 12% 18% 11% 2	3119
	11th to 20th	Day	33% 8% 17% 29% 11% 1	3277
	21st to end	Day	45% 5% 8% 16% 21% 5%	4166
April	1st to 10th	Day	46% 6% 10% 20% 15% 3	2280
	11th to 20th	Day	42% 6% 11% 21% 17% 3	2254
	21st to end	Day	43% 7% 10% 21% 16% 3	2351
May	1st to 10th	Day	53% 6% 13% 14% 12% 1	4120
	11th to 20th	Day	50% 8% 13% 17% 9% 1	4336
	21st to end	Day	35% 8% 13% 25% 17% 2	4837
June	1st to 10th	Day	43% 8% 14% 21% 13% 1	2660
	11th to 20th	Day	42% 9% 14% 23% 11% 2	2660
	21st to end	Day	41% 8% 14% 23% 13% 1	2660
July	1st to 10th	Day	44% 8% 12% 20% 15% 1	4370
	11th to 20th	Day	40% 7% 16% 22% 13% 1	4365
	21st to end	Day	48% 7% 12% 17% 14% 1	4661
August	1st to 10th	Day	49% 8% 15% 21% 8%	4240
	11th to 20th	Day	38% 7% 16% 29% 10%	3766
	21st to end	Day	35% 6% 12% 29% 17% 1	4180
September	1st to 10th	Day	40% 8% 10% 22% 18% 1	2280
	11th to 20th	Day	35% 5% 10% 23% 25% 2	2173
	21st to end	Day	44% 6% 10% 21% 16% 3	2090
October	1st to 10th	Day	45% 5% 9% 21% 16% 3	2022
	11th to 20th	Day	36% 6% 12% 26% 18% 2	1900
	21st to end	Day	44% 5% 11% 22% 16% 3	1895
November	1st to 10th	Day	36% 5% 12% 26% 19% 3	1689
	11th to 20th	Day	39% 4 12% 23% 19% 3	1710
	21st to end	Day	40% 4 14% 27% 12% 2	1649
December	1st to 10th	Day	48% 5% 14% 17% 14% 1	1520
	11th to 20th	Day	43% 4 15% 21% 15% 2	1906
	21st to end	Day	52% 7% 11% 21% 9% 1	2772
January	1st to 10th	Night	39% 5% 12% 30% 11% 4	4429
	11th to 20th	Night	44% 5% 13% 24% 11% 3	4440
	21st to end	Night	54% 4 9% 20% 11% 2	4744
February	1st to 10th	Night	46% 5% 12% 22% 13% 2	2437
	11th to 20th	Night	44% 5% 10% 19% 18% 4	2220
	21st to end	Night	45% 4 10% 23% 15% 4	1884
March	1st to 10th	Night	51% 5% 11% 19% 12% 2	3734
	11th to 20th	Night	36% 7% 15% 24% 15% 2	3664
	21st to end	Night	45% 4 8% 14% 24% 5%	3466
April	1st to 10th	Night	45% 7% 11% 20% 15% 3	1900
	11th to 20th	Night	44% 5% 12% 19% 19% 1	1875
	21st to end	Night	44% 6% 9% 22% 16% 4	1829
May	1st to 10th	Night	55% 7% 11% 16% 10% 1	2840
	11th to 20th	Night	52% 9% 13% 15% 10% 1	2578
	21st to end	Night	40% 7% 14% 25% 12% 2	2739
June	1st to 10th	Night	43% 7% 10% 22% 16% 2	1520
	11th to 20th	Night	39% 7% 17% 25% 10% 1	1520
	21st to end	Night	36% 9% 15% 25% 14% 1	1520
July	1st to 10th	Night	41% 9% 17% 18% 14% 1	2480
	11th to 20th	Night	44% 6% 15% 23% 12% 1	2472
	21st to end	Night	46% 7% 15% 14% 17% 2	2651
August	1st to 10th	Night	52% 8% 14% 17% 9% 1	2631
	11th to 20th	Night	43% 7% 14% 28% 8% 1	3127
	21st to end	Night	30% 6% 12% 34% 17% 1	3476
September	1st to 10th	Night	40% 5% 9% 26% 18% 1	1900
	11th to 20th	Night	32% 5% 11% 25% 25% 2	2005
	21st to end	Night	42% 6% 8% 21% 20% 2	2090
October	1st to 10th	Night	44% 6% 11% 23% 14% 3	2156
	11th to 20th	Night	36% 5% 12% 29% 16% 1	2280
	21st to end	Night	44% 5% 12% 22% 15% 1	2702
November	1st to 10th	Night	36% 6% 12% 22% 21% 4	2434
	11th to 20th	Night	41% 4 10% 23% 18% 4	2470
	21st to end	Night	39% 5% 13% 30% 12% 1	2531
December	1st to 10th	Night	45% 6% 12% 22% 14% 1	2660
	11th to 20th	Night	43% 6% 13% 19% 16% 3	3288
	21st to end	Night	49% 7% 12% 21% 11% 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	35% 21% 27% 14% 2	180
	11th to 20th	Day	32% 26% 31% 10% 1	180
	21st to end	Day	22% 32% 32% 9% 5%	238
February	1st to 10th	Day	35% 26% 28% 10% 1	300
	11th to 20th	Day	30% 29% 31% 10% 1	456
	21st to end	Day	32% 24% 30% 12% 2	382
March	1st to 10th	Day	30% 20% 33% 14% 3	460
	11th to 20th	Day	28% 27% 31% 11% 2 1	460
	21st to end	Day	31% 23% 31% 10% 3 1	506
April	1st to 10th	Day	32% 26% 24% 11% 6% 1	460
	11th to 20th	Day	29% 25% 27% 13% 6% 2	452
	21st to end	Day	30% 18% 32% 14% 5% 1	460
May	1st to 10th	Day	34% 19% 28% 13% 5% 2	463
	11th to 20th	Day	25% 16% 35% 18% 6% 1	487
	21st to end	Day	20% 11% 31% 25% 10% 3	529
June	1st to 10th	Day	21% 14% 31% 22% 10% 2	490
	11th to 20th	Day	18% 13% 34% 23% 11% 2	490
	21st to end	Day	16% 12% 31% 27% 12% 1	490
July	1st to 10th	Day	16% 8% 31% 26% 16% 3	485
	11th to 20th	Day	13% 6% 31% 32% 16% 2	484
	21st to end	Day	14% 10% 33% 29% 12% 1	532
August	1st to 10th	Day	15% 9% 27% 31% 13% 5%	486
	11th to 20th	Day	15% 7% 28% 31% 14% 5%	479
	21st to end	Day	11% 12% 28% 27% 14% 8%	539
September	1st to 10th	Day	19% 11% 27% 21% 17% 5%	490
	11th to 20th	Day	15% 10% 28% 27% 12% 9%	490
	21st to end	Day	21% 14% 31% 19% 10% 4	490
October	1st to 10th	Day	29% 11% 26% 17% 14% 3	490
	11th to 20th	Day	17% 21% 30% 21% 8% 2	490
	21st to end	Day	30% 13% 30% 18% 8% 1	436
November	1st to 10th	Day	20% 17% 28% 23% 9% 2	371
	11th to 20th	Day	27% 23% 27% 17% 5% 1	370
	21st to end	Day	26% 20% 29% 19% 5% 1	309
December	1st to 10th	Day	31% 22% 30% 14% 3 1	180
	11th to 20th	Day	36% 25% 26% 11% 2	180
	21st to end	Day	27% 23% 29% 15% 4 2	198
January	1st to 10th	Night	24% 19% 36% 18% 3	760
	11th to 20th	Night	27% 21% 31% 19% 2	760
	21st to end	Night	24% 22% 34% 18% 2	836
February	1st to 10th	Night	25% 19% 35% 20% 2	760
	11th to 20th	Night	25% 24% 36% 14% 1	743
	21st to end	Night	29% 20% 32% 17% 3	628
March	1st to 10th	Night	26% 21% 33% 18% 3	760
	11th to 20th	Night	24% 25% 32% 16% 3	760
	21st to end	Night	25% 21% 33% 17% 4	836
April	1st to 10th	Night	26% 21% 32% 18% 3	760
	11th to 20th	Night	22% 20% 34% 20% 4	751
	21st to end	Night	25% 19% 33% 18% 5%	689
May	1st to 10th	Night	27% 15% 33% 20% 5%	570
	11th to 20th	Night	22% 17% 34% 22% 5%	430
	21st to end	Night	22% 7% 25% 36% 9% 1	411
June	1st to 10th	Night	19% 9% 29% 32% 10% 1	380
	11th to 20th	Night	17% 7% 28% 34% 13%	380
	21st to end	Night	14% 5% 27% 45% 9%	380
July	1st to 10th	Night	15% 4 22% 41% 17% 1	370
	11th to 20th	Night	12% 5% 24% 41% 16% 2	368
	21st to end	Night	14% 5% 25% 40% 16% 1	416
August	1st to 10th	Night	12% 3 27% 41% 16% 1	448
	11th to 20th	Night	16% 5% 22% 35% 20% 2	750
	21st to end	Night	16% 5% 19% 38% 19% 2	836
September	1st to 10th	Night	17% 6% 29% 32% 14% 2	760
	11th to 20th	Night	16% 7% 22% 31% 19% 4	760
	21st to end	Night	22% 8% 25% 29% 14% 2	760
October	1st to 10th	Night	23% 11% 26% 26% 13% 1	760
	11th to 20th	Night	17% 14% 31% 27% 9% 1	760
	21st to end	Night	26% 12% 34% 20% 7%	836
November	1st to 10th	Night	16% 15% 33% 27% 8% 1	749
	11th to 20th	Night	24% 17% 31% 21% 6% 1	760
	21st to end	Night	23% 17% 31% 23% 6% 1	760
December	1st to 10th	Night	27% 19% 31% 18% 4 1	760
	11th to 20th	Night	26% 21% 29% 21% 3	760
	21st to end	Night	27% 17% 35% 19% 2	836

Page generated at 2024-10-31 03:39:27. Version ac07

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