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 2024-02-15.

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 5% 5% 3 5% 5% 5% 7% 42%	78295
	Night	16% 6% 2 5% 5% 3 4 4 5% 7% 43%	80767
Transparency	Day	41% 6% 12% 23% 16% 3	78003
	Night	41% 6% 11% 23% 16% 3	80593
Seeing	Day	18% 13% 28% 24% 12% 4	13985
	Night	18% 10% 32% 29% 10% 1	23423

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% 9% 3 4 5% 2 4 3 4 6% 46%	2517
	11th to 20th	Day	15% 8% 3 7% 8% 4 4 4 4 6% 39%	2595
	21st to end	Day	22% 8% 2 5% 5% 3 4 4 4 5% 37%	3124
February	1st to 10th	Day	15% 7% 3 6% 4 3 4 5% 5% 6% 40%	1710
	11th to 20th	Day	18% 7% 2 4 5% 3 5% 5% 5% 6% 40%	1755
	21st to end	Day	18% 10% 4 6% 5% 3 5% 4 4 5% 38%	1480
March	1st to 10th	Day	13% 6% 2 5% 4 3 4 4 4 6% 49%	1797
	11th to 20th	Day	17% 5% 3 5% 4 3 6% 4 6% 7% 40%	1975
	21st to end	Day	20% 6% 2 5% 4 3 5% 4 5% 6% 39%	2306
April	1st to 10th	Day	15% 7% 3 4 5% 3 4 5% 6% 6% 43%	2160
	11th to 20th	Day	14% 6% 2 5% 5% 2 5% 4 5% 8% 44%	2134
	21st to end	Day	17% 5% 3 4 6% 3 4 5% 6% 7% 40%	2160
May	1st to 10th	Day	18% 7% 3 6% 5% 3 5% 5% 6% 7% 36%	2282
	11th to 20th	Day	17% 6% 3 6% 5% 4 5% 5% 5% 7% 37%	2478
	21st to end	Day	13% 5% 2 6% 5% 3 4 5% 6% 9% 42%	2725
June	1st to 10th	Day	13% 5% 2 5% 6% 3 5% 6% 8% 8% 39%	2520
	11th to 20th	Day	12% 5% 2 6% 5% 3 6% 6% 7% 9% 38%	2520
	21st to end	Day	10% 4 2 5% 6% 3 6% 6% 7% 9% 42%	2520
July	1st to 10th	Day	9% 5% 2 6% 7% 3 6% 5% 7% 10% 40%	2520
	11th to 20th	Day	6% 4 2 5% 6% 3 6% 6% 7% 11% 43%	2520
	21st to end	Day	10% 6% 3 6% 5% 4 7% 5% 7% 10% 37%	2694
August	1st to 10th	Day	10% 5% 2 6% 7% 4 6% 6% 6% 8% 40%	2319
	11th to 20th	Day	11% 5% 3 5% 6% 3 5% 6% 5% 9% 41%	2126
	21st to end	Day	12% 6% 3 5% 6% 3 5% 5% 6% 9% 40%	2376
September	1st to 10th	Day	13% 6% 2 5% 5% 3 5% 4 6% 7% 43%	2160
	11th to 20th	Day	13% 4 2 4 4 3 4 4 5% 7% 51%	2128
	21st to end	Day	17% 7% 3 6% 5% 2 4 4 5% 7% 40%	1980
October	1st to 10th	Day	19% 6% 2 4 4 2 4 4 5% 6% 44%	1810
	11th to 20th	Day	16% 5% 2 3 3 2 4 3 5% 6% 49%	1800
	21st to end	Day	18% 6% 2 5% 4 2 4 3 4 6% 46%	1919
November	1st to 10th	Day	13% 5% 3 3 5% 2 3 3 4 7% 52%	1671
	11th to 20th	Day	15% 5% 2 4 4 3 4 5% 5% 7% 47%	1710
	21st to end	Day	14% 5% 2 4 5% 3 4 4 4 7% 48%	1606
December	1st to 10th	Day	19% 7% 2 5% 3 3 4 4 5% 9% 39%	1520
	11th to 20th	Day	19% 8% 3 4 5% 2 3 4 4 5% 44%	1906
	21st to end	Day	16% 7% 2 5% 5% 3 6% 6% 6% 8% 36%	2772
January	1st to 10th	Night	17% 7% 2 4 4 3 4 4 5% 5% 45%	4429
	11th to 20th	Night	19% 7% 3 5% 4 2 3 3 3 5% 44%	4362
	21st to end	Night	23% 7% 3 6% 5% 3 5% 3 4 6% 37%	4532
February	1st to 10th	Night	16% 8% 3 5% 5% 3 4 4 6% 7% 41%	2470
	11th to 20th	Night	19% 8% 3 5% 5% 3 3 3 4 6% 40%	2184
	21st to end	Night	18% 7% 3 5% 4 2 4 4 5% 5% 43%	1776
March	1st to 10th	Night	15% 5% 2 5% 4 2 4 4 5% 8% 47%	2150
	11th to 20th	Night	17% 7% 3 5% 5% 3 4 4 4 6% 44%	1979
	21st to end	Night	16% 7% 3 5% 5% 2 5% 4 4 6% 43%	2048
April	1st to 10th	Night	17% 6% 2 6% 4 3 4 4 6% 7% 41%	1800
	11th to 20th	Night	14% 6% 3 5% 5% 3 4 4 5% 7% 43%	1775
	21st to end	Night	19% 5% 2 4 5% 3 4 3 5% 7% 43%	1800
May	1st to 10th	Night	18% 7% 3 6% 5% 3 5% 5% 5% 7% 35%	1691
	11th to 20th	Night	17% 6% 4 5% 5% 2 4 5% 6% 8% 38%	1415
	21st to end	Night	15% 6% 2 6% 5% 3 5% 6% 5% 7% 39%	1550
June	1st to 10th	Night	14% 5% 2 5% 5% 3 5% 4 6% 9% 43%	1440
	11th to 20th	Night	10% 7% 3 6% 6% 3 5% 4 6% 10% 40%	1440
	21st to end	Night	9% 6% 2 4 4 4 5% 5% 7% 11% 43%	1440
July	1st to 10th	Night	10% 5% 3 6% 6% 4 7% 6% 6% 9% 38%	1440
	11th to 20th	Night	7% 4 3 4 6% 4 7% 7% 7% 9% 44%	1440
	21st to end	Night	9% 5% 2 6% 6% 3 5% 5% 6% 9% 44%	1620
August	1st to 10th	Night	8% 6% 2 5% 6% 3 6% 7% 7% 8% 43%	1611
	11th to 20th	Night	10% 8% 3 7% 5% 3 5% 5% 6% 8% 40%	1765
	21st to end	Night	13% 5% 2 5% 5% 3 5% 5% 6% 9% 41%	1980
September	1st to 10th	Night	13% 6% 3 6% 5% 3 4 4 5% 7% 45%	1800
	11th to 20th	Night	10% 5% 2 4 3 3 2 4 5% 7% 55%	1831
	21st to end	Night	17% 6% 2 5% 5% 3 4 4 5% 7% 42%	1980
October	1st to 10th	Night	19% 7% 2 5% 4 3 3 3 4 6% 43%	2146
	11th to 20th	Night	16% 4 1 5% 4 2 3 3 5% 6% 50%	2160
	21st to end	Night	17% 7% 2 4 5% 2 4 3 4 6% 47%	2435
November	1st to 10th	Night	12% 5% 2 4 4 2 4 3 5% 6% 53%	2407
	11th to 20th	Night	17% 5% 2 5% 4 2 4 3 3 5% 49%	2470
	21st to end	Night	13% 5% 2 5% 5% 3 5% 5% 6% 7% 45%	2569
December	1st to 10th	Night	20% 7% 3 6% 3 2 4 5% 5% 6% 40%	2660
	11th to 20th	Night	16% 6% 3 5% 5% 3 4 4 5% 7% 43%	3288
	21st to end	Night	17% 7% 3 5% 5% 3 5% 5% 6% 8% 37%	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% 3 12% 27% 14% 4	2518
	11th to 20th	Day	48% 4 10% 22% 14% 3	2595
	21st to end	Day	48% 5% 13% 21% 10% 2	3124
February	1st to 10th	Day	43% 6% 13% 24% 12% 2	1710
	11th to 20th	Day	43% 6% 10% 24% 13% 3	1764
	21st to end	Day	48% 5% 8% 20% 13% 5%	1480
March	1st to 10th	Day	37% 5% 12% 28% 15% 3	1800
	11th to 20th	Day	41% 6% 11% 22% 16% 4	1975
	21st to end	Day	46% 5% 8% 20% 17% 4	2306
April	1st to 10th	Day	41% 6% 11% 20% 16% 6%	2160
	11th to 20th	Day	38% 6% 11% 23% 16% 5%	2134
	21st to end	Day	42% 6% 11% 18% 18% 4	2160
May	1st to 10th	Day	46% 6% 10% 19% 16% 3	2282
	11th to 20th	Day	46% 7% 12% 20% 14% 2	2482
	21st to end	Day	39% 8% 14% 24% 13% 2	2725
June	1st to 10th	Day	39% 8% 14% 23% 14% 2	2520
	11th to 20th	Day	39% 11% 13% 22% 13% 3	2520
	21st to end	Day	36% 9% 14% 23% 17% 1	2520
July	1st to 10th	Day	38% 10% 13% 21% 15% 3	2450
	11th to 20th	Day	32% 10% 16% 26% 15% 2	2445
	21st to end	Day	39% 9% 13% 21% 16% 2	2543
August	1st to 10th	Day	39% 9% 14% 23% 14% 1	2306
	11th to 20th	Day	39% 7% 16% 20% 16% 2	2126
	21st to end	Day	38% 8% 13% 20% 16% 4	2376
September	1st to 10th	Day	39% 7% 11% 20% 20% 3	2160
	11th to 20th	Day	33% 5% 11% 22% 25% 4	2128
	21st to end	Day	44% 5% 9% 18% 21% 2	1980
October	1st to 10th	Day	41% 6% 11% 22% 18% 1	1810
	11th to 20th	Day	37% 4 11% 24% 23% 3	1800
	21st to end	Day	41% 4 9% 25% 19% 2	1919
November	1st to 10th	Day	34% 4 12% 27% 20% 3	1671
	11th to 20th	Day	37% 6% 9% 23% 22% 3	1710
	21st to end	Day	37% 4 12% 31% 14% 3	1606
December	1st to 10th	Day	42% 5% 16% 22% 13% 1	1520
	11th to 20th	Day	43% 4 11% 28% 11% 3	1906
	21st to end	Day	43% 6% 14% 24% 13% 1	2772
January	1st to 10th	Night	40% 5% 9% 28% 14% 4	4429
	11th to 20th	Night	44% 4 10% 25% 14% 3	4362
	21st to end	Night	49% 4 8% 25% 12% 2	4532
February	1st to 10th	Night	43% 5% 13% 24% 13% 2	2470
	11th to 20th	Night	45% 4 9% 20% 17% 5%	2186
	21st to end	Night	43% 5% 9% 22% 16% 5%	1776
March	1st to 10th	Night	37% 5% 12% 24% 19% 4	2160
	11th to 20th	Night	42% 5% 10% 21% 18% 4	1980
	21st to end	Night	43% 4 9% 18% 19% 6%	2048
April	1st to 10th	Night	42% 5% 10% 20% 18% 5%	1800
	11th to 20th	Night	41% 5% 10% 20% 19% 5%	1775
	21st to end	Night	42% 5% 9% 19% 19% 5%	1800
May	1st to 10th	Night	47% 7% 10% 16% 18% 2	1691
	11th to 20th	Night	44% 7% 12% 16% 18% 3	1416
	21st to end	Night	43% 10% 14% 18% 14% 2	1551
June	1st to 10th	Night	38% 8% 11% 22% 20% 2	1440
	11th to 20th	Night	39% 9% 14% 24% 13% 2	1440
	21st to end	Night	33% 9% 15% 25% 15% 2	1440
July	1st to 10th	Night	41% 10% 15% 19% 14% 2	1400
	11th to 20th	Night	33% 11% 16% 23% 14% 2	1392
	21st to end	Night	34% 8% 16% 25% 15% 1	1530
August	1st to 10th	Night	36% 10% 17% 22% 15% 1	1600
	11th to 20th	Night	39% 9% 14% 20% 16% 2	1765
	21st to end	Night	38% 7% 14% 21% 17% 3	1980
September	1st to 10th	Night	39% 7% 13% 19% 18% 4	1800
	11th to 20th	Night	30% 6% 10% 23% 26% 5%	1831
	21st to end	Night	41% 7% 8% 21% 21% 2	1980
October	1st to 10th	Night	42% 6% 12% 21% 16% 3	2146
	11th to 20th	Night	35% 4 12% 28% 18% 3	2160
	21st to end	Night	39% 4 9% 25% 20% 3	2435
November	1st to 10th	Night	34% 5% 12% 25% 19% 5%	2407
	11th to 20th	Night	39% 5% 10% 21% 20% 5%	2470
	21st to end	Night	36% 5% 12% 27% 17% 2	2569
December	1st to 10th	Night	44% 5% 12% 23% 15% 1	2660
	11th to 20th	Night	41% 5% 12% 20% 18% 4	3288
	21st to end	Night	43% 7% 14% 24% 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	22% 27% 29% 17% 3 2	180
	11th to 20th	Day	25% 34% 26% 14% 1	204
	21st to end	Day	24% 27% 26% 18% 5% 1	297
February	1st to 10th	Day	25% 24% 32% 14% 4	270
	11th to 20th	Day	27% 25% 35% 11% 2	399
	21st to end	Day	28% 18% 36% 15% 2	346
March	1st to 10th	Day	20% 22% 33% 19% 5%	420
	11th to 20th	Day	20% 25% 33% 16% 5% 1	420
	21st to end	Day	25% 19% 30% 21% 5% 1	462
April	1st to 10th	Day	22% 20% 36% 15% 7% 1	420
	11th to 20th	Day	18% 17% 33% 21% 9% 2	412
	21st to end	Day	24% 18% 33% 20% 5% 1	420
May	1st to 10th	Day	27% 20% 27% 16% 9% 2	423
	11th to 20th	Day	20% 13% 30% 26% 10% 2	447
	21st to end	Day	17% 8% 21% 28% 20% 5%	485
June	1st to 10th	Day	13% 10% 26% 32% 14% 5%	450
	11th to 20th	Day	15% 10% 28% 30% 15% 3	450
	21st to end	Day	12% 8% 27% 31% 17% 5%	450
July	1st to 10th	Day	12% 4 21% 31% 24% 9%	445
	11th to 20th	Day	6% 2 21% 37% 26% 8%	444
	21st to end	Day	11% 5% 23% 34% 19% 7%	488
August	1st to 10th	Day	10% 4 24% 30% 23% 8%	446
	11th to 20th	Day	14% 3 16% 34% 24% 8%	439
	21st to end	Day	11% 5% 27% 28% 19% 10%	495
September	1st to 10th	Day	17% 9% 19% 27% 18% 10%	450
	11th to 20th	Day	13% 5% 27% 27% 17% 11%	450
	21st to end	Day	23% 10% 23% 26% 12% 5%	450
October	1st to 10th	Day	24% 6% 25% 24% 14% 7%	450
	11th to 20th	Day	17% 14% 27% 24% 16% 2	450
	21st to end	Day	21% 11% 37% 20% 9% 3	464
November	1st to 10th	Day	16% 10% 34% 25% 12% 3	365
	11th to 20th	Day	19% 17% 35% 21% 8%	370
	21st to end	Day	17% 16% 33% 27% 6% 1	266
December	1st to 10th	Day	23% 24% 35% 10% 8%	180
	11th to 20th	Day	28% 22% 32% 12% 6%	180
	21st to end	Day	26% 19% 30% 16% 8% 1	198
January	1st to 10th	Night	20% 15% 41% 21% 3	760
	11th to 20th	Night	23% 15% 34% 24% 3	760
	21st to end	Night	18% 15% 41% 24% 2	836
February	1st to 10th	Night	20% 13% 41% 24% 2	760
	11th to 20th	Night	25% 17% 39% 17% 1	722
	21st to end	Night	22% 17% 40% 19% 2	592
March	1st to 10th	Night	20% 15% 37% 24% 4	720
	11th to 20th	Night	22% 15% 38% 19% 6% 1	720
	21st to end	Night	20% 11% 42% 21% 5% 1	792
April	1st to 10th	Night	19% 19% 37% 19% 5%	720
	11th to 20th	Night	16% 13% 37% 29% 5%	711
	21st to end	Night	21% 12% 33% 29% 5%	720
May	1st to 10th	Night	20% 10% 37% 26% 6%	611
	11th to 20th	Night	18% 6% 38% 30% 7%	354
	21st to end	Night	19% 3 23% 40% 14% 2	389
June	1st to 10th	Night	16% 4 28% 40% 12%	360
	11th to 20th	Night	12% 4 26% 45% 12% 1	360
	21st to end	Night	9% 2 24% 53% 12%	360
July	1st to 10th	Night	11% 3 23% 45% 19% 1	350
	11th to 20th	Night	7% 3 17% 50% 21% 2	348
	21st to end	Night	8% 3 24% 43% 21% 1	440
August	1st to 10th	Night	11% 1 16% 45% 24% 2	537
	11th to 20th	Night	14% 3 16% 41% 23% 2	701
	21st to end	Night	15% 3 18% 38% 24% 3	792
September	1st to 10th	Night	15% 5% 22% 37% 19% 2	720
	11th to 20th	Night	13% 3 19% 36% 25% 4	720
	21st to end	Night	20% 6% 25% 30% 18% 1	720
October	1st to 10th	Night	21% 6% 27% 26% 16% 4	720
	11th to 20th	Night	18% 9% 27% 33% 12% 1	720
	21st to end	Night	21% 9% 34% 27% 9%	792
November	1st to 10th	Night	14% 7% 38% 29% 12% 1	740
	11th to 20th	Night	19% 12% 34% 27% 8% 1	760
	21st to end	Night	15% 13% 37% 26% 8% 1	760
December	1st to 10th	Night	23% 13% 34% 22% 7% 1	760
	11th to 20th	Night	18% 14% 37% 26% 5%	760
	21st to end	Night	20% 13% 36% 29% 2	836

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