Chestnut Branch Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Chestnut Branch Park clear sky chart from 2005-11-06 to 2025-03-27.

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	15% 6% 2 6% 4 4 4 4 6% 7% 41%	108920
	Night	16% 7% 2 6% 4 4 4 3 5% 7% 43%	110397
Transparency	Day	40% 6% 12% 23% 17% 3	112496
	Night	40% 5% 11% 23% 18% 3	114984
Seeing	Day	19% 14% 28% 23% 12% 4	15448
	Night	18% 10% 32% 29% 10% 1	24869

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	13% 7% 2 5% 4 4 4 3 5% 6% 48%	3597
	11th to 20th	Day	14% 8% 2 8% 6% 4 3 2 4 5% 43%	3687
	21st to end	Day	18% 8% 2 6% 4 3 4 3 4 5% 44%	4466
February	1st to 10th	Day	15% 8% 3 7% 4 5% 4 3 6% 6% 40%	1800
	11th to 20th	Day	18% 7% 2 5% 4 4 4 3 5% 6% 40%	1914
	21st to end	Day	17% 10% 3 6% 4 4 4 3 5% 6% 39%	1650
March	1st to 10th	Day	24% 7% 2 6% 3 3 3 3 4 6% 40%	3216
	11th to 20th	Day	10% 4 2 6% 4 5% 5% 4 6% 7% 49%	3585
	21st to end	Day	21% 5% 2 5% 4 4 3 3 5% 5% 44%	4122
April	1st to 10th	Day	15% 8% 2 5% 4 4 4 4 6% 7% 42%	2280
	11th to 20th	Day	14% 7% 2 5% 5% 4 4 3 5% 7% 44%	2254
	21st to end	Day	16% 6% 2 5% 5% 4 4 4 6% 6% 41%	2280
May	1st to 10th	Day	27% 9% 3 7% 4 4 4 4 5% 6% 28%	4008
	11th to 20th	Day	24% 8% 3 7% 6% 5% 4 4 5% 6% 29%	4398
	21st to end	Day	12% 5% 2 6% 4 4 4 3 6% 9% 45%	4837
June	1st to 10th	Day	12% 6% 2 6% 5% 4 5% 5% 8% 8% 40%	2660
	11th to 20th	Day	11% 6% 2 6% 5% 5% 5% 5% 7% 8% 39%	2660
	21st to end	Day	10% 4 2 6% 5% 4 6% 4 7% 10% 42%	2660
July	1st to 10th	Day	7% 5% 2 7% 6% 6% 7% 5% 8% 11% 36%	4440
	11th to 20th	Day	10% 5% 2 6% 5% 5% 6% 5% 7% 11% 38%	4440
	21st to end	Day	11% 7% 3 8% 6% 6% 6% 5% 7% 9% 31%	4725
August	1st to 10th	Day	17% 6% 2 7% 5% 6% 5% 4 7% 8% 34%	4083
	11th to 20th	Day	12% 6% 2 6% 4 4 5% 5% 6% 9% 41%	3730
	21st to end	Day	9% 5% 2 5% 4 4 5% 4 6% 9% 47%	4180
September	1st to 10th	Day	13% 6% 2 6% 5% 4 4 4 6% 6% 45%	2280
	11th to 20th	Day	12% 4 2 5% 4 3 5% 3 5% 7% 51%	2246
	21st to end	Day	18% 7% 3 7% 5% 3 4 3 5% 6% 39%	2090
October	1st to 10th	Day	18% 6% 2 5% 3 3 4 3 5% 6% 45%	1910
	11th to 20th	Day	15% 5% 2 4 3 3 4 2 5% 6% 50%	1900
	21st to end	Day	17% 6% 2 6% 3 3 3 3 4 6% 48%	2025
November	1st to 10th	Day	13% 5% 2 4 4 3 3 2 4 7% 52%	1761
	11th to 20th	Day	15% 6% 1 4 3 4 4 4 5% 7% 47%	1800
	21st to end	Day	15% 5% 2 5% 4 3 4 3 4 7% 48%	1690
December	1st to 10th	Day	14% 6% 2 5% 3 4 4 4 6% 7% 46%	2600
	11th to 20th	Day	19% 10% 2 5% 3 3 3 3 3 5% 44%	2986
	21st to end	Day	15% 6% 2 5% 3 5% 5% 4 6% 8% 41%	3960
January	1st to 10th	Night	14% 7% 2 5% 3 3 4 3 5% 5% 49%	6349
	11th to 20th	Night	15% 7% 2 6% 3 3 3 2 3 5% 50%	6195
	21st to end	Night	17% 7% 2 7% 4 3 4 3 4 6% 43%	6490
February	1st to 10th	Night	17% 8% 3 6% 4 4 3 3 5% 7% 40%	2600
	11th to 20th	Night	19% 9% 2 6% 4 4 3 3 4 6% 41%	2370
	21st to end	Night	17% 8% 2 6% 4 4 4 3 4 6% 42%	1980
March	1st to 10th	Night	22% 9% 2 6% 3 3 3 3 4 6% 38%	3844
	11th to 20th	Night	11% 6% 2 5% 4 4 3 3 4 6% 51%	3589
	21st to end	Night	17% 9% 2 6% 4 3 4 3 3 4 45%	3647
April	1st to 10th	Night	17% 7% 2 7% 4 4 4 4 6% 7% 41%	1900
	11th to 20th	Night	14% 6% 3 6% 5% 4 4 4 5% 7% 42%	1875
	21st to end	Night	18% 5% 2 5% 4 4 4 2 5% 7% 43%	1900
May	1st to 10th	Night	21% 9% 3 8% 4 4 4 4 5% 7% 30%	2946
	11th to 20th	Night	23% 8% 4 7% 5% 4 4 4 5% 6% 30%	2495
	21st to end	Night	13% 6% 2 6% 4 4 5% 4 6% 9% 42%	2738
June	1st to 10th	Night	14% 6% 2 5% 4 4 4 3 6% 9% 43%	1520
	11th to 20th	Night	9% 7% 2 7% 6% 4 4 4 7% 9% 41%	1520
	21st to end	Night	8% 6% 2 5% 4 5% 5% 4 8% 11% 42%	1520
July	1st to 10th	Night	8% 5% 3 8% 6% 6% 7% 5% 7% 9% 37%	2520
	11th to 20th	Night	11% 5% 2 6% 5% 5% 5% 5% 7% 10% 38%	2520
	21st to end	Night	15% 7% 2 8% 5% 5% 5% 4 7% 7% 36%	2824
August	1st to 10th	Night	20% 7% 2 6% 4 4 5% 5% 6% 8% 33%	2825
	11th to 20th	Night	13% 7% 2 6% 4 4 4 3 6% 7% 43%	3088
	21st to end	Night	10% 5% 2 6% 4 4 4 3 5% 7% 49%	3476
September	1st to 10th	Night	12% 6% 2 6% 5% 3 4 3 5% 7% 46%	1900
	11th to 20th	Night	10% 5% 2 5% 3 3 3 3 5% 7% 55%	1933
	21st to end	Night	19% 7% 2 6% 5% 3 4 3 5% 7% 40%	2090
October	1st to 10th	Night	18% 7% 2 6% 3 3 3 3 5% 6% 44%	2266
	11th to 20th	Night	15% 4 1 5% 3 3 3 3 5% 6% 51%	2280
	21st to end	Night	16% 6% 2 4 4 2 4 3 5% 6% 48%	2571
November	1st to 10th	Night	11% 5% 2 5% 3 3 4 3 5% 6% 53%	2537
	11th to 20th	Night	16% 6% 2 5% 4 3 3 3 4 5% 49%	2600
	21st to end	Night	12% 6% 1 5% 4 4 4 4 6% 6% 45%	2705
December	1st to 10th	Night	14% 6% 2 5% 3 3 4 3 5% 6% 49%	4580
	11th to 20th	Night	22% 7% 2 5% 3 3 3 3 5% 7% 41%	5208
	21st to end	Night	18% 7% 3 6% 4 4 4 4 5% 6% 40%	6996

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	37% 3 10% 25% 22% 3	3598
	11th to 20th	Day	44% 3 8% 23% 17% 5%	3717
	21st to end	Day	43% 4 12% 24% 14% 2	4466
February	1st to 10th	Day	43% 6% 13% 25% 12% 2	1800
	11th to 20th	Day	43% 6% 10% 23% 15% 3	1923
	21st to end	Day	46% 5% 9% 22% 14% 5%	1650
March	1st to 10th	Day	45% 4 8% 29% 11% 3	3219
	11th to 20th	Day	32% 5% 10% 31% 18% 3	3585
	21st to end	Day	43% 4 8% 19% 22% 4	4122
April	1st to 10th	Day	41% 6% 11% 20% 16% 6%	2280
	11th to 20th	Day	39% 6% 11% 23% 16% 5%	2254
	21st to end	Day	42% 6% 11% 18% 19% 4	2280
May	1st to 10th	Day	55% 5% 10% 17% 10% 2	4020
	11th to 20th	Day	54% 7% 14% 16% 8% 1	4402
	21st to end	Day	34% 8% 12% 27% 17% 2	4837
June	1st to 10th	Day	38% 8% 13% 23% 15% 2	2660
	11th to 20th	Day	38% 10% 13% 24% 13% 3	2660
	21st to end	Day	35% 9% 14% 23% 17% 1	2660
July	1st to 10th	Day	38% 11% 16% 17% 14% 2	4370
	11th to 20th	Day	38% 8% 17% 23% 13% 1	4365
	21st to end	Day	46% 8% 12% 19% 14% 1	4574
August	1st to 10th	Day	47% 8% 13% 23% 9% 1	4070
	11th to 20th	Day	38% 7% 13% 27% 14% 1	3766
	21st to end	Day	32% 7% 11% 27% 20% 2	4180
September	1st to 10th	Day	39% 7% 11% 19% 22% 3	2280
	11th to 20th	Day	33% 5% 11% 22% 25% 4	2246
	21st to end	Day	47% 5% 9% 18% 20% 2	2090
October	1st to 10th	Day	36% 4 9% 17% 29% 5%	3170
	11th to 20th	Day	25% 3 11% 22% 30% 9%	3140
	21st to end	Day	25% 3 11% 28% 29% 5%	3315
November	1st to 10th	Day	33% 4 12% 26% 21% 4	1761
	11th to 20th	Day	36% 6% 9% 24% 22% 3	1800
	21st to end	Day	37% 4 12% 31% 13% 3	1690
December	1st to 10th	Day	37% 5% 17% 25% 14% 3	2600
	11th to 20th	Day	45% 3 11% 29% 10% 3	2986
	21st to end	Day	40% 5% 13% 23% 18% 2	3960
January	1st to 10th	Night	36% 4 8% 24% 22% 6%	6349
	11th to 20th	Night	39% 3 9% 24% 18% 7%	6240
	21st to end	Night	43% 4 9% 24% 18% 2	6490
February	1st to 10th	Night	43% 4 13% 24% 13% 2	2600
	11th to 20th	Night	45% 4 9% 21% 17% 5%	2372
	21st to end	Night	43% 4 9% 21% 16% 6%	1980
March	1st to 10th	Night	48% 4 9% 24% 13% 3	3854
	11th to 20th	Night	34% 5% 12% 28% 17% 4	3590
	21st to end	Night	43% 4 7% 17% 24% 5%	3647
April	1st to 10th	Night	43% 5% 9% 20% 18% 4	1900
	11th to 20th	Night	41% 5% 10% 20% 19% 4	1875
	21st to end	Night	41% 5% 9% 20% 20% 5%	1900
May	1st to 10th	Night	51% 8% 10% 18% 12% 1	2953
	11th to 20th	Night	53% 8% 12% 15% 10% 2	2496
	21st to end	Night	37% 9% 15% 20% 16% 3	2739
June	1st to 10th	Night	38% 8% 11% 22% 20% 2	1520
	11th to 20th	Night	38% 8% 13% 26% 13% 2	1520
	21st to end	Night	33% 9% 15% 25% 15% 2	1520
July	1st to 10th	Night	41% 9% 19% 17% 12% 2	2480
	11th to 20th	Night	38% 9% 18% 23% 10% 1	2472
	21st to end	Night	45% 7% 13% 19% 14% 1	2734
August	1st to 10th	Night	48% 8% 18% 17% 9%	2814
	11th to 20th	Night	39% 7% 12% 27% 14% 1	3118
	21st to end	Night	33% 5% 10% 29% 20% 2	3476
September	1st to 10th	Night	38% 6% 13% 19% 21% 4	1900
	11th to 20th	Night	30% 6% 10% 23% 26% 4	1933
	21st to end	Night	44% 7% 7% 20% 20% 2	2090
October	1st to 10th	Night	40% 5% 10% 22% 21% 3	3786
	11th to 20th	Night	24% 3 11% 26% 30% 6%	3779
	21st to end	Night	26% 3 11% 31% 24% 5%	4231
November	1st to 10th	Night	33% 5% 12% 25% 20% 6%	2537
	11th to 20th	Night	39% 5% 9% 21% 21% 5%	2600
	21st to end	Night	37% 5% 12% 26% 18% 2	2705
December	1st to 10th	Night	36% 4 12% 30% 15% 2	4580
	11th to 20th	Night	44% 4 10% 23% 15% 4	5208
	21st to end	Night	44% 5% 11% 20% 17% 2	6996

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% 26% 29% 15% 3 2	200
	11th to 20th	Day	26% 33% 28% 13% 1	227
	21st to end	Day	23% 27% 27% 17% 5% 1	330
February	1st to 10th	Day	25% 25% 33% 14% 4	300
	11th to 20th	Day	31% 24% 32% 11% 2	462
	21st to end	Day	27% 20% 36% 15% 3	414
March	1st to 10th	Day	23% 22% 31% 18% 5%	500
	11th to 20th	Day	20% 25% 32% 16% 5% 1	500
	21st to end	Day	25% 19% 30% 20% 4 1	530
April	1st to 10th	Day	23% 20% 35% 14% 7% 1	460
	11th to 20th	Day	19% 19% 33% 20% 9% 2	452
	21st to end	Day	23% 17% 32% 21% 5% 1	460
May	1st to 10th	Day	27% 20% 27% 16% 9% 2	463
	11th to 20th	Day	20% 13% 30% 25% 10% 2	487
	21st to end	Day	16% 9% 23% 28% 19% 5%	529
June	1st to 10th	Day	12% 11% 27% 31% 14% 4	490
	11th to 20th	Day	14% 10% 28% 30% 16% 3	490
	21st to end	Day	12% 8% 30% 30% 16% 5%	490
July	1st to 10th	Day	11% 4 22% 32% 23% 8%	485
	11th to 20th	Day	7% 2 23% 37% 25% 7%	484
	21st to end	Day	11% 5% 25% 34% 19% 6%	532
August	1st to 10th	Day	11% 5% 25% 29% 22% 8%	486
	11th to 20th	Day	13% 4 19% 34% 23% 7%	479
	21st to end	Day	11% 6% 27% 28% 19% 10%	539
September	1st to 10th	Day	16% 9% 20% 28% 18% 9%	490
	11th to 20th	Day	13% 5% 26% 29% 17% 10%	490
	21st to end	Day	24% 11% 23% 25% 12% 5%	490
October	1st to 10th	Day	23% 7% 25% 24% 13% 8%	490
	11th to 20th	Day	17% 15% 27% 23% 15% 3	490
	21st to end	Day	19% 10% 36% 21% 11% 3	504
November	1st to 10th	Day	15% 11% 34% 26% 11% 3	395
	11th to 20th	Day	18% 17% 36% 21% 8%	400
	21st to end	Day	20% 17% 31% 25% 6% 1	290
December	1st to 10th	Day	22% 25% 36% 11% 7%	200
	11th to 20th	Day	29% 22% 33% 12% 6%	200
	21st to end	Day	26% 19% 30% 15% 8% 1	220
January	1st to 10th	Night	21% 16% 40% 20% 3	800
	11th to 20th	Night	22% 16% 34% 24% 3	800
	21st to end	Night	18% 15% 41% 24% 2	880
February	1st to 10th	Night	21% 13% 41% 24% 2	800
	11th to 20th	Night	27% 17% 38% 17% 1	783
	21st to end	Night	22% 17% 40% 19% 3	660
March	1st to 10th	Night	21% 15% 36% 24% 4	800
	11th to 20th	Night	20% 16% 38% 19% 6% 1	800
	21st to end	Night	21% 12% 42% 20% 5%	863
April	1st to 10th	Night	20% 19% 38% 19% 5%	760
	11th to 20th	Night	17% 14% 37% 28% 4	751
	21st to end	Night	20% 12% 33% 30% 5%	760
May	1st to 10th	Night	20% 10% 38% 26% 6%	644
	11th to 20th	Night	18% 7% 38% 30% 7%	374
	21st to end	Night	18% 3 24% 40% 14% 1	411
June	1st to 10th	Night	16% 4 28% 40% 12%	380
	11th to 20th	Night	11% 5% 27% 45% 12% 1	380
	21st to end	Night	9% 3 24% 52% 11%	380
July	1st to 10th	Night	10% 3 24% 44% 18% 1	370
	11th to 20th	Night	7% 4 18% 49% 21% 2	368
	21st to end	Night	9% 3 25% 42% 20% 1	465
August	1st to 10th	Night	12% 1 17% 44% 24% 2	567
	11th to 20th	Night	14% 3 17% 41% 23% 2	741
	21st to end	Night	14% 3 18% 39% 24% 3	836
September	1st to 10th	Night	14% 4 24% 37% 19% 2	760
	11th to 20th	Night	13% 3 19% 36% 25% 4	760
	21st to end	Night	22% 5% 24% 29% 18% 1	760
October	1st to 10th	Night	21% 6% 27% 27% 16% 4	760
	11th to 20th	Night	18% 9% 28% 33% 12% 1	760
	21st to end	Night	20% 9% 34% 28% 10%	836
November	1st to 10th	Night	14% 8% 37% 29% 12% 1	780
	11th to 20th	Night	18% 12% 35% 26% 8% 1	800
	21st to end	Night	15% 14% 37% 26% 7% 1	800
December	1st to 10th	Night	23% 13% 34% 22% 6% 1	800
	11th to 20th	Night	19% 14% 36% 26% 5%	800
	21st to end	Night	20% 13% 35% 29% 3	880

Page generated at 2025-03-24 09:04:30. Version ac07

Copyright © 2025 Attilla Danko.