Solebury Mountain Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Solebury Mountain Observatory clear sky chart from 2005-11-06 to 2024-04-03.

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	16% 6% 3 5% 5% 3 4 4 5% 7% 41%	78784
	Night	17% 6% 2 5% 5% 3 4 4 5% 6% 43%	81320
Transparency	Day	42% 6% 12% 22% 15% 3	78490
	Night	41% 6% 12% 23% 16% 3	81148
Seeing	Day	22% 14% 29% 21% 11% 3	14132
	Night	20% 12% 31% 27% 9% 1	23530

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% 8% 3 5% 4 3 4 4 5% 5% 46%	2517
	11th to 20th	Day	15% 10% 4 8% 5% 3 4 4 5% 6% 36%	2534
	21st to end	Day	22% 9% 3 6% 5% 3 4 3 4 5% 35%	3124
February	1st to 10th	Day	18% 7% 2 6% 5% 2 4 4 6% 7% 39%	1710
	11th to 20th	Day	16% 8% 3 6% 6% 3 4 3 4 6% 40%	1813
	21st to end	Day	20% 8% 3 6% 5% 2 4 4 4 5% 38%	1570
March	1st to 10th	Day	16% 6% 3 5% 5% 3 4 3 4 6% 45%	1897
	11th to 20th	Day	16% 6% 3 6% 7% 3 4 4 5% 6% 40%	2068
	21st to end	Day	20% 6% 3 5% 4 3 4 4 4 6% 40%	2444
April	1st to 10th	Day	18% 7% 3 6% 5% 2 4 4 5% 6% 41%	2184
	11th to 20th	Day	16% 6% 3 5% 4 3 4 4 5% 8% 42%	2134
	21st to end	Day	17% 6% 2 6% 6% 3 5% 4 6% 6% 39%	2160
May	1st to 10th	Day	20% 7% 2 6% 6% 3 5% 5% 5% 7% 35%	2320
	11th to 20th	Day	20% 6% 2 5% 5% 3 5% 5% 5% 7% 37%	2478
	21st to end	Day	15% 7% 3 5% 5% 4 4 4 6% 8% 40%	2725
June	1st to 10th	Day	14% 5% 2 5% 5% 4 5% 6% 7% 9% 38%	2520
	11th to 20th	Day	14% 6% 2 6% 6% 3 6% 5% 6% 8% 37%	2520
	21st to end	Day	13% 4 2 4 6% 4 5% 5% 6% 9% 41%	2520
July	1st to 10th	Day	13% 4 2 6% 6% 4 6% 6% 7% 8% 39%	2520
	11th to 20th	Day	9% 4 2 4 5% 3 5% 5% 8% 10% 43%	2520
	21st to end	Day	11% 6% 3 6% 6% 4 6% 6% 6% 9% 38%	2736
August	1st to 10th	Day	11% 5% 2 5% 6% 4 5% 7% 7% 8% 39%	2323
	11th to 20th	Day	12% 6% 2 5% 5% 4 5% 5% 6% 9% 40%	2126
	21st to end	Day	14% 6% 2 5% 4 4 5% 5% 6% 8% 42%	2376
September	1st to 10th	Day	15% 6% 2 5% 5% 3 4 4 6% 8% 43%	2160
	11th to 20th	Day	13% 4 2 4 4 3 3 4 5% 8% 50%	2120
	21st to end	Day	18% 6% 2 5% 6% 4 4 4 4 6% 41%	1980
October	1st to 10th	Day	19% 6% 2 3 4 3 4 4 5% 7% 42%	1819
	11th to 20th	Day	15% 5% 3 4 4 3 4 4 4 7% 45%	1800
	21st to end	Day	21% 5% 3 4 4 2 4 4 5% 6% 42%	1895
November	1st to 10th	Day	14% 6% 2 5% 4 2 3 3 3 6% 52%	1671
	11th to 20th	Day	17% 5% 2 4 4 3 4 5% 5% 5% 48%	1710
	21st to end	Day	16% 5% 2 5% 3 3 4 4 4 8% 46%	1592
December	1st to 10th	Day	19% 8% 2 5% 5% 3 4 4 4 8% 38%	1520
	11th to 20th	Day	21% 7% 2 4 4 3 4 3 4 6% 43%	1906
	21st to end	Day	17% 6% 4 6% 6% 4 6% 5% 5% 6% 35%	2772
January	1st to 10th	Night	16% 6% 2 5% 4 2 4 4 4 6% 46%	4429
	11th to 20th	Night	17% 8% 3 5% 5% 3 3 4 4 5% 43%	4411
	21st to end	Night	25% 9% 3 5% 4 2 3 4 3 5% 38%	4532
February	1st to 10th	Night	17% 8% 3 5% 4 3 3 4 4 6% 41%	2470
	11th to 20th	Night	18% 7% 3 5% 4 3 3 4 4 5% 41%	2252
	21st to end	Night	18% 8% 3 4 4 2 3 4 4 6% 43%	1884
March	1st to 10th	Night	17% 6% 2 4 4 3 4 4 6% 7% 45%	2270
	11th to 20th	Night	17% 6% 2 5% 5% 2 4 5% 4 5% 45%	2108
	21st to end	Night	19% 6% 2 5% 5% 3 3 4 4 6% 44%	2152
April	1st to 10th	Night	18% 6% 3 5% 5% 3 5% 4 5% 6% 40%	1821
	11th to 20th	Night	16% 6% 2 5% 6% 2 5% 5% 5% 6% 41%	1775
	21st to end	Night	20% 6% 2 3 4 2 3 4 5% 7% 44%	1800
May	1st to 10th	Night	20% 8% 3 5% 5% 3 4 4 6% 6% 36%	1655
	11th to 20th	Night	18% 6% 3 6% 5% 3 4 4 6% 6% 39%	1415
	21st to end	Night	15% 6% 3 6% 5% 3 4 4 6% 9% 41%	1550
June	1st to 10th	Night	17% 5% 2 5% 5% 3 5% 4 5% 6% 43%	1440
	11th to 20th	Night	14% 5% 2 5% 6% 4 5% 5% 6% 9% 40%	1440
	21st to end	Night	11% 4 2 4 5% 3 5% 4 6% 9% 45%	1440
July	1st to 10th	Night	11% 5% 3 5% 6% 4 6% 6% 6% 10% 38%	1440
	11th to 20th	Night	9% 4 2 5% 4 4 5% 6% 7% 10% 43%	1440
	21st to end	Night	9% 5% 2 5% 5% 3 6% 5% 7% 9% 44%	1578
August	1st to 10th	Night	10% 5% 3 5% 4 4 6% 6% 7% 9% 42%	1611
	11th to 20th	Night	11% 7% 3 6% 6% 3 5% 6% 6% 9% 38%	1760
	21st to end	Night	14% 6% 2 5% 5% 3 4 4 7% 9% 41%	1980
September	1st to 10th	Night	16% 6% 2 5% 4 3 3 5% 5% 5% 46%	1800
	11th to 20th	Night	12% 5% 2 4 4 3 4 3 4 6% 53%	1839
	21st to end	Night	17% 6% 2 4 5% 3 4 5% 4 7% 43%	1980
October	1st to 10th	Night	20% 6% 3 4 4 2 4 4 4 5% 44%	2137
	11th to 20th	Night	16% 4 2 4 4 2 3 4 5% 6% 49%	2160
	21st to end	Night	19% 7% 3 4 3 2 4 3 4 5% 46%	2458
November	1st to 10th	Night	12% 5% 2 5% 4 2 3 4 4 6% 53%	2407
	11th to 20th	Night	18% 6% 2 4 4 3 3 3 4 5% 48%	2470
	21st to end	Night	14% 6% 2 4 5% 3 5% 4 6% 8% 45%	2584
December	1st to 10th	Night	20% 6% 3 5% 4 3 4 4 5% 6% 40%	2660
	11th to 20th	Night	18% 5% 2 5% 5% 3 4 5% 5% 6% 41%	3288
	21st to end	Night	19% 7% 3 6% 5% 3 4 4 4 6% 38%	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% 4 12% 28% 13% 3	2518
	11th to 20th	Day	47% 6% 11% 20% 13% 2	2534
	21st to end	Day	52% 5% 10% 21% 10% 2	3124
February	1st to 10th	Day	44% 5% 14% 24% 11% 2	1710
	11th to 20th	Day	46% 3 9% 23% 16% 3	1822
	21st to end	Day	48% 5% 10% 21% 12% 4	1570
March	1st to 10th	Day	42% 4 12% 25% 14% 3	1900
	11th to 20th	Day	44% 4 10% 23% 15% 4	2068
	21st to end	Day	46% 5% 9% 19% 17% 5%	2444
April	1st to 10th	Day	44% 5% 10% 21% 15% 5%	2184
	11th to 20th	Day	39% 6% 11% 22% 17% 4	2134
	21st to end	Day	44% 5% 10% 19% 18% 5%	2160
May	1st to 10th	Day	48% 7% 9% 16% 17% 3	2320
	11th to 20th	Day	45% 6% 11% 21% 15% 2	2482
	21st to end	Day	42% 7% 14% 20% 15% 2	2725
June	1st to 10th	Day	40% 9% 14% 22% 14% 1	2520
	11th to 20th	Day	43% 8% 14% 21% 11% 2	2520
	21st to end	Day	39% 9% 14% 23% 15% 1	2520
July	1st to 10th	Day	42% 8% 13% 21% 14% 2	2450
	11th to 20th	Day	34% 8% 15% 25% 16% 3	2445
	21st to end	Day	41% 7% 12% 20% 17% 3	2583
August	1st to 10th	Day	39% 9% 14% 22% 16% 1	2310
	11th to 20th	Day	39% 8% 15% 21% 15% 2	2126
	21st to end	Day	40% 8% 11% 20% 18% 3	2376
September	1st to 10th	Day	39% 7% 12% 19% 20% 3	2160
	11th to 20th	Day	33% 5% 11% 24% 24% 3	2120
	21st to end	Day	44% 5% 9% 17% 21% 3	1980
October	1st to 10th	Day	42% 7% 11% 21% 17% 2	1819
	11th to 20th	Day	38% 5% 11% 24% 21% 2	1800
	21st to end	Day	42% 5% 10% 23% 18% 2	1895
November	1st to 10th	Day	35% 4 13% 25% 21% 3	1671
	11th to 20th	Day	38% 4 10% 24% 21% 3	1710
	21st to end	Day	38% 3 14% 30% 12% 3	1592
December	1st to 10th	Day	45% 5% 14% 22% 12% 1	1520
	11th to 20th	Day	44% 4 14% 25% 11% 2	1906
	21st to end	Day	47% 7% 13% 23% 10% 1	2772
January	1st to 10th	Night	39% 5% 10% 30% 12% 3	4429
	11th to 20th	Night	44% 4 13% 25% 12% 2	4411
	21st to end	Night	50% 4 9% 24% 12% 2	4532
February	1st to 10th	Night	43% 5% 13% 24% 12% 2	2470
	11th to 20th	Night	45% 5% 9% 19% 18% 4	2254
	21st to end	Night	43% 5% 8% 22% 18% 4	1884
March	1st to 10th	Night	39% 5% 12% 24% 16% 4	2280
	11th to 20th	Night	42% 5% 10% 21% 18% 3	2109
	21st to end	Night	43% 4 10% 17% 20% 6%	2152
April	1st to 10th	Night	43% 6% 11% 20% 17% 4	1821
	11th to 20th	Night	42% 6% 10% 20% 20% 3	1775
	21st to end	Night	40% 6% 11% 20% 19% 5%	1800
May	1st to 10th	Night	49% 5% 10% 17% 17% 2	1655
	11th to 20th	Night	46% 6% 12% 16% 18% 3	1416
	21st to end	Night	41% 8% 16% 19% 13% 3	1551
June	1st to 10th	Night	41% 6% 12% 21% 19% 1	1440
	11th to 20th	Night	40% 8% 14% 24% 13% 1	1440
	21st to end	Night	34% 9% 15% 26% 14% 2	1440
July	1st to 10th	Night	40% 11% 14% 19% 15% 2	1400
	11th to 20th	Night	35% 9% 14% 26% 14% 2	1392
	21st to end	Night	34% 9% 16% 23% 15% 3	1490
August	1st to 10th	Night	38% 9% 16% 21% 14% 2	1600
	11th to 20th	Night	42% 8% 15% 20% 13% 2	1760
	21st to end	Night	39% 7% 14% 19% 19% 2	1980
September	1st to 10th	Night	40% 7% 12% 20% 19% 2	1800
	11th to 20th	Night	33% 5% 11% 21% 25% 4	1839
	21st to end	Night	41% 5% 8% 22% 23% 2	1980
October	1st to 10th	Night	42% 5% 12% 23% 15% 2	2137
	11th to 20th	Night	36% 5% 12% 28% 17% 3	2160
	21st to end	Night	41% 4 9% 26% 17% 2	2458
November	1st to 10th	Night	34% 4 12% 24% 22% 4	2407
	11th to 20th	Night	39% 5% 9% 23% 19% 5%	2470
	21st to end	Night	38% 4 13% 27% 16% 2	2584
December	1st to 10th	Night	46% 4 12% 23% 14% 2	2660
	11th to 20th	Night	42% 6% 13% 20% 16% 3	3288
	21st to end	Night	47% 5% 12% 25% 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	29% 23% 29% 15% 2 1	180
	11th to 20th	Day	36% 25% 28% 9% 2	186
	21st to end	Day	25% 24% 34% 12% 5%	297
February	1st to 10th	Day	31% 24% 33% 9% 3	270
	11th to 20th	Day	30% 22% 35% 11% 2	421
	21st to end	Day	32% 20% 30% 14% 3	382
March	1st to 10th	Day	30% 20% 30% 17% 3	460
	11th to 20th	Day	27% 25% 31% 13% 3 1	460
	21st to end	Day	28% 23% 29% 13% 5% 1	506
April	1st to 10th	Day	29% 21% 29% 13% 5% 1	428
	11th to 20th	Day	24% 19% 32% 14% 9% 2	412
	21st to end	Day	30% 20% 30% 15% 4 2	420
May	1st to 10th	Day	30% 19% 28% 14% 6% 2	423
	11th to 20th	Day	23% 15% 33% 20% 8% 1	447
	21st to end	Day	20% 8% 25% 26% 18% 3	485
June	1st to 10th	Day	17% 10% 32% 24% 14% 3	450
	11th to 20th	Day	20% 12% 28% 26% 12% 3	450
	21st to end	Day	16% 9% 31% 27% 13% 3	450
July	1st to 10th	Day	12% 5% 23% 32% 21% 7%	445
	11th to 20th	Day	9% 4 25% 33% 24% 5%	444
	21st to end	Day	14% 7% 30% 31% 15% 3	488
August	1st to 10th	Day	11% 4 26% 35% 18% 7%	446
	11th to 20th	Day	14% 4 21% 34% 22% 6%	439
	21st to end	Day	14% 6% 27% 28% 15% 9%	495
September	1st to 10th	Day	16% 8% 24% 26% 17% 8%	450
	11th to 20th	Day	15% 7% 27% 27% 15% 10%	450
	21st to end	Day	22% 13% 24% 23% 12% 6%	450
October	1st to 10th	Day	24% 7% 29% 19% 14% 7%	450
	11th to 20th	Day	18% 14% 30% 26% 10% 2	450
	21st to end	Day	25% 15% 31% 17% 10% 2	453
November	1st to 10th	Day	21% 10% 31% 24% 12% 3	365
	11th to 20th	Day	25% 16% 32% 21% 5% 1	370
	21st to end	Day	21% 17% 40% 15% 6%	252
December	1st to 10th	Day	29% 24% 29% 10% 8%	180
	11th to 20th	Day	40% 17% 27% 10% 6%	180
	21st to end	Day	31% 17% 29% 16% 7% 1	198
January	1st to 10th	Night	21% 18% 38% 20% 3	760
	11th to 20th	Night	24% 16% 35% 22% 3	760
	21st to end	Night	20% 18% 39% 21% 1	836
February	1st to 10th	Night	23% 16% 34% 25% 2	760
	11th to 20th	Night	25% 20% 38% 15% 1	743
	21st to end	Night	26% 18% 36% 18% 2	628
March	1st to 10th	Night	23% 19% 33% 21% 3	760
	11th to 20th	Night	24% 18% 36% 18% 4	760
	21st to end	Night	21% 16% 39% 19% 5%	836
April	1st to 10th	Night	23% 18% 37% 17% 5%	729
	11th to 20th	Night	19% 13% 39% 23% 6%	711
	21st to end	Night	23% 13% 34% 26% 5%	720
May	1st to 10th	Night	25% 14% 30% 25% 6%	575
	11th to 20th	Night	21% 8% 37% 27% 7%	354
	21st to end	Night	16% 6% 24% 38% 13% 1	389
June	1st to 10th	Night	18% 6% 28% 36% 13% 1	360
	11th to 20th	Night	13% 4 30% 40% 12%	360
	21st to end	Night	11% 2 26% 48% 13% 1	360
July	1st to 10th	Night	11% 5% 23% 40% 20% 2	350
	11th to 20th	Night	11% 3 22% 43% 20% 1	348
	21st to end	Night	9% 4 25% 44% 18%	398
August	1st to 10th	Night	13% 1 17% 46% 21% 2	537
	11th to 20th	Night	14% 2 20% 37% 26% 2	696
	21st to end	Night	15% 4 17% 41% 21% 1	792
September	1st to 10th	Night	17% 3 24% 35% 18% 3	720
	11th to 20th	Night	15% 4 23% 34% 20% 4	720
	21st to end	Night	22% 5% 23% 31% 18% 1	720
October	1st to 10th	Night	23% 7% 25% 26% 16% 3	720
	11th to 20th	Night	17% 10% 29% 33% 12%	720
	21st to end	Night	22% 12% 33% 24% 8% 1	792
November	1st to 10th	Night	15% 10% 33% 30% 11% 1	740
	11th to 20th	Night	22% 15% 29% 27% 7%	760
	21st to end	Night	19% 15% 35% 25% 7%	760
December	1st to 10th	Night	25% 16% 31% 20% 6% 1	760
	11th to 20th	Night	21% 15% 35% 24% 5%	760
	21st to end	Night	23% 15% 33% 26% 2	836

Page generated at 2024-03-31 06:08:53. Version ac07

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