Sourland Mountain Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sourland Mountain Observatory clear sky chart from 2005-11-06 to 2024-11-08.

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% 40%	101372
	Night	17% 7% 2 6% 4 4 4 3 5% 6% 42%	97745
Transparency	Day	42% 6% 12% 22% 16% 3	104904
	Night	41% 5% 11% 23% 16% 3	102289
Seeing	Day	21% 14% 29% 22% 11% 3	15004
	Night	19% 11% 31% 28% 10% 1	24212

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	16% 7% 3 6% 4 4 3 3 5% 4 46%	2517
	11th to 20th	Day	15% 10% 3 9% 5% 4 4 3 5% 6% 36%	2520
	21st to end	Day	21% 10% 3 7% 5% 4 3 3 4 5% 35%	3122
February	1st to 10th	Day	17% 7% 3 6% 4 3 5% 3 5% 7% 39%	1710
	11th to 20th	Day	16% 8% 3 7% 5% 4 4 3 5% 5% 41%	1824
	21st to end	Day	20% 9% 3 6% 5% 3 4 4 5% 4 38%	1570
March	1st to 10th	Day	27% 8% 2 5% 4 3 3 2 4 5% 36%	3116
	11th to 20th	Day	9% 6% 2 6% 6% 5% 5% 4 6% 7% 45%	3432
	21st to end	Day	21% 6% 2 5% 4 4 3 3 4 5% 43%	4086
April	1st to 10th	Day	17% 7% 3 7% 4 4 4 4 5% 6% 39%	2280
	11th to 20th	Day	16% 6% 2 6% 4 4 4 4 6% 8% 41%	2254
	21st to end	Day	18% 6% 2 6% 4 5% 4 3 5% 7% 40%	2280
May	1st to 10th	Day	27% 8% 2 6% 5% 4 4 3 5% 7% 29%	4088
	11th to 20th	Day	25% 9% 3 6% 5% 4 4 4 4 6% 30%	4398
	21st to end	Day	13% 6% 2 6% 4 4 4 4 6% 9% 43%	4837
June	1st to 10th	Day	14% 6% 2 6% 5% 4 5% 5% 7% 9% 38%	2660
	11th to 20th	Day	14% 7% 2 7% 5% 4 5% 5% 7% 8% 37%	2660
	21st to end	Day	12% 6% 2 5% 5% 5% 4 4 6% 9% 41%	2660
July	1st to 10th	Day	9% 5% 2 7% 6% 7% 6% 6% 7% 10% 35%	4440
	11th to 20th	Day	11% 6% 2 6% 5% 5% 5% 5% 7% 9% 39%	4440
	21st to end	Day	14% 8% 3 7% 6% 5% 5% 5% 7% 8% 33%	4814
August	1st to 10th	Day	21% 6% 2 6% 5% 4 5% 4 6% 8% 33%	4089
	11th to 20th	Day	13% 6% 2 5% 4 4 5% 3 6% 9% 42%	3730
	21st to end	Day	12% 5% 3 5% 3 3 4 3 6% 8% 48%	4180
September	1st to 10th	Day	14% 6% 3 5% 4 4 4 3 6% 7% 45%	2280
	11th to 20th	Day	13% 4 2 5% 3 3 3 3 5% 8% 50%	2229
	21st to end	Day	20% 6% 2 6% 5% 5% 4 3 4 6% 40%	2090
October	1st to 10th	Day	19% 6% 2 5% 4 4 4 3 5% 6% 42%	1933
	11th to 20th	Day	15% 5% 2 5% 4 3 4 3 5% 6% 48%	1900
	21st to end	Day	19% 6% 2 4 3 3 4 3 5% 6% 45%	1988
November	1st to 10th	Day	13% 6% 2 5% 3 3 4 2 4 6% 52%	1734
	11th to 20th	Day	17% 6% 2 5% 3 3 3 4 6% 5% 47%	1710
	21st to end	Day	15% 6% 2 5% 4 3 4 2 6% 7% 45%	1603
December	1st to 10th	Day	18% 8% 3 6% 3 4 4 3 4 7% 38%	1520
	11th to 20th	Day	20% 7% 2 5% 4 4 4 3 4 6% 42%	1906
	21st to end	Day	17% 7% 3 7% 5% 5% 5% 5% 5% 7% 33%	2772
January	1st to 10th	Night	16% 6% 2 5% 4 3 4 3 5% 6% 46%	4429
	11th to 20th	Night	16% 9% 2 7% 4 4 4 3 4 5% 42%	4440
	21st to end	Night	25% 9% 2 5% 3 3 3 3 4 6% 37%	4532
February	1st to 10th	Night	17% 9% 3 5% 4 3 4 3 5% 5% 42%	2470
	11th to 20th	Night	18% 8% 3 6% 4 3 3 3 4 5% 41%	2242
	21st to end	Night	19% 8% 2 6% 3 3 4 3 5% 6% 42%	1884
March	1st to 10th	Night	24% 9% 2 5% 4 3 3 2 5% 5% 37%	3724
	11th to 20th	Night	12% 7% 2 5% 4 4 4 3 4 6% 48%	3525
	21st to end	Night	18% 8% 3 6% 3 3 3 3 3 4 44%	3544
April	1st to 10th	Night	17% 6% 2 7% 4 4 4 5% 5% 7% 39%	1900
	11th to 20th	Night	16% 7% 2 7% 5% 4 4 4 4 6% 40%	1875
	21st to end	Night	20% 6% 2 4 3 3 4 3 5% 7% 44%	1900
May	1st to 10th	Night	24% 10% 3 6% 4 4 3 4 5% 8% 29%	2880
	11th to 20th	Night	25% 10% 3 7% 4 3 4 3 4 6% 31%	2495
	21st to end	Night	14% 6% 3 5% 4 4 4 4 6% 10% 41%	2738
June	1st to 10th	Night	16% 7% 3 5% 4 4 3 4 6% 7% 43%	1520
	11th to 20th	Night	13% 6% 2 6% 4 5% 5% 4 5% 8% 42%	1520
	21st to end	Night	11% 4 2 6% 5% 5% 4 4 7% 9% 43%	1520
July	1st to 10th	Night	8% 6% 2 7% 6% 5% 6% 5% 8% 9% 38%	2520
	11th to 20th	Night	13% 6% 2 6% 5% 4 5% 5% 7% 10% 37%	2520
	21st to end	Night	16% 7% 3 6% 5% 4 6% 5% 6% 8% 35%	2739
August	1st to 10th	Night	23% 6% 2 6% 4 4 5% 4 6% 8% 31%	2811
	11th to 20th	Night	14% 7% 2 7% 4 4 5% 4 6% 7% 40%	3091
	21st to end	Night	11% 5% 2 5% 4 4 3 3 6% 8% 50%	3476
September	1st to 10th	Night	15% 6% 2 6% 4 3 4 4 5% 7% 44%	1900
	11th to 20th	Night	13% 6% 2 4 3 3 3 4 3 6% 53%	1949
	21st to end	Night	19% 6% 2 6% 3 4 3 3 4 7% 41%	2090
October	1st to 10th	Night	19% 6% 2 6% 3 3 4 3 5% 6% 43%	2242
	11th to 20th	Night	15% 4 2 5% 3 3 4 3 5% 6% 50%	2280
	21st to end	Night	19% 6% 2 5% 3 3 3 2 5% 5% 46%	2608
November	1st to 10th	Night	11% 5% 2 6% 3 3 3 3 4 6% 54%	2505
	11th to 20th	Night	18% 6% 2 5% 3 3 3 3 5% 4 48%	2470
	21st to end	Night	14% 6% 2 5% 4 4 4 3 6% 6% 45%	2574
December	1st to 10th	Night	20% 7% 2 5% 4 4 4 3 5% 6% 40%	2660
	11th to 20th	Night	18% 6% 2 5% 4 4 4 3 5% 6% 42%	3288
	21st to end	Night	19% 9% 3 7% 5% 4 4 3 4 5% 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% 3 12% 28% 13% 4	2518
	11th to 20th	Day	48% 5% 11% 21% 13% 2	2520
	21st to end	Day	52% 5% 10% 21% 11% 2	3122
February	1st to 10th	Day	45% 5% 13% 24% 12% 2	1710
	11th to 20th	Day	45% 4 9% 23% 16% 3	1833
	21st to end	Day	47% 5% 10% 21% 13% 4	1570
March	1st to 10th	Day	51% 3 9% 26% 9% 2	3119
	11th to 20th	Day	35% 5% 12% 29% 16% 3	3432
	21st to end	Day	45% 4 9% 17% 22% 5%	4086
April	1st to 10th	Day	44% 5% 10% 20% 16% 5%	2280
	11th to 20th	Day	39% 6% 12% 21% 18% 4	2254
	21st to end	Day	42% 6% 10% 20% 18% 5%	2280
May	1st to 10th	Day	54% 6% 11% 16% 11% 2	4102
	11th to 20th	Day	55% 6% 11% 18% 9% 1	4402
	21st to end	Day	37% 6% 12% 25% 17% 2	4837
June	1st to 10th	Day	39% 9% 13% 22% 15% 1	2660
	11th to 20th	Day	42% 8% 13% 23% 12% 2	2660
	21st to end	Day	38% 8% 14% 23% 16% 1	2660
July	1st to 10th	Day	42% 9% 14% 19% 14% 2	4370
	11th to 20th	Day	39% 8% 15% 22% 15% 1	4365
	21st to end	Day	47% 7% 11% 18% 16% 1	4661
August	1st to 10th	Day	48% 7% 12% 21% 10% 1	4075
	11th to 20th	Day	38% 6% 13% 28% 14% 1	3766
	21st to end	Day	33% 6% 10% 26% 22% 2	4180
September	1st to 10th	Day	39% 6% 11% 20% 21% 3	2280
	11th to 20th	Day	33% 4 11% 24% 25% 3	2229
	21st to end	Day	46% 5% 9% 17% 20% 3	2090
October	1st to 10th	Day	37% 5% 10% 18% 26% 5%	3206
	11th to 20th	Day	25% 4 11% 25% 30% 6%	3140
	21st to end	Day	26% 4 13% 24% 28% 5%	3252
November	1st to 10th	Day	34% 3 13% 25% 22% 3	1734
	11th to 20th	Day	38% 4 10% 23% 22% 3	1710
	21st to end	Day	37% 4 13% 30% 13% 3	1603
December	1st to 10th	Day	44% 5% 15% 22% 14% 1	1520
	11th to 20th	Day	44% 4 13% 25% 12% 2	1906
	21st to end	Day	47% 6% 13% 23% 11% 1	2772
January	1st to 10th	Night	39% 5% 10% 30% 12% 4	4429
	11th to 20th	Night	44% 4 13% 25% 12% 3	4440
	21st to end	Night	50% 4 9% 24% 13% 2	4532
February	1st to 10th	Night	43% 5% 12% 25% 12% 2	2470
	11th to 20th	Night	45% 4 8% 19% 19% 4	2244
	21st to end	Night	43% 5% 7% 23% 18% 4	1884
March	1st to 10th	Night	50% 4 8% 23% 12% 3	3734
	11th to 20th	Night	36% 5% 14% 26% 17% 3	3526
	21st to end	Night	44% 3 7% 16% 22% 6%	3544
April	1st to 10th	Night	43% 6% 11% 20% 17% 4	1900
	11th to 20th	Night	43% 5% 10% 19% 20% 3	1875
	21st to end	Night	39% 6% 9% 21% 20% 5%	1900
May	1st to 10th	Night	53% 6% 10% 19% 10% 1	2886
	11th to 20th	Night	54% 7% 14% 14% 10% 2	2496
	21st to end	Night	38% 8% 16% 21% 15% 3	2739
June	1st to 10th	Night	39% 7% 11% 22% 19% 2	1520
	11th to 20th	Night	39% 7% 13% 27% 13% 2	1520
	21st to end	Night	35% 8% 15% 26% 14% 2	1520
July	1st to 10th	Night	40% 10% 18% 17% 13% 2	2480
	11th to 20th	Night	40% 8% 15% 24% 12% 1	2472
	21st to end	Night	44% 8% 14% 17% 16% 2	2651
August	1st to 10th	Night	49% 8% 18% 16% 8% 1	2801
	11th to 20th	Night	42% 7% 11% 27% 13% 1	3121
	21st to end	Night	32% 5% 10% 29% 21% 1	3476
September	1st to 10th	Night	40% 6% 11% 20% 21% 2	1900
	11th to 20th	Night	33% 5% 10% 23% 26% 4	1949
	21st to end	Night	43% 5% 7% 22% 21% 2	2090
October	1st to 10th	Night	39% 5% 11% 22% 21% 2	3736
	11th to 20th	Night	24% 4 9% 29% 29% 5%	3779
	21st to end	Night	28% 4 11% 31% 23% 3	4294
November	1st to 10th	Night	34% 4 11% 25% 22% 5%	2505
	11th to 20th	Night	40% 4 9% 23% 20% 5%	2470
	21st to end	Night	38% 4 13% 27% 16% 2	2574
December	1st to 10th	Night	45% 4 12% 23% 14% 2	2660
	11th to 20th	Night	42% 6% 13% 20% 17% 4	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	26% 24% 27% 19% 2 1	180
	11th to 20th	Day	35% 27% 27% 9% 2	180
	21st to end	Day	24% 23% 35% 14% 4 1	297
February	1st to 10th	Day	30% 23% 33% 10% 3	270
	11th to 20th	Day	29% 21% 36% 12% 2	432
	21st to end	Day	31% 20% 29% 16% 3	382
March	1st to 10th	Day	29% 20% 29% 18% 3	460
	11th to 20th	Day	25% 26% 31% 13% 4 1	460
	21st to end	Day	28% 21% 29% 15% 5% 1	506
April	1st to 10th	Day	27% 20% 33% 12% 6% 1	460
	11th to 20th	Day	23% 21% 31% 14% 9% 2	452
	21st to end	Day	27% 20% 30% 16% 5% 3	460
May	1st to 10th	Day	30% 18% 29% 14% 7% 2	463
	11th to 20th	Day	23% 15% 32% 20% 9% 1	487
	21st to end	Day	19% 10% 25% 26% 17% 3	529
June	1st to 10th	Day	18% 10% 30% 26% 14% 3	490
	11th to 20th	Day	17% 11% 28% 28% 11% 3	490
	21st to end	Day	16% 10% 31% 28% 12% 3	490
July	1st to 10th	Day	12% 5% 23% 32% 22% 6%	485
	11th to 20th	Day	9% 5% 24% 35% 21% 6%	484
	21st to end	Day	14% 6% 32% 29% 15% 4	532
August	1st to 10th	Day	11% 5% 26% 33% 17% 7%	486
	11th to 20th	Day	14% 5% 21% 34% 20% 7%	479
	21st to end	Day	14% 5% 27% 29% 14% 10%	539
September	1st to 10th	Day	17% 9% 24% 26% 16% 8%	490
	11th to 20th	Day	16% 6% 25% 28% 16% 9%	490
	21st to end	Day	23% 13% 24% 23% 11% 6%	490
October	1st to 10th	Day	24% 8% 27% 21% 13% 7%	490
	11th to 20th	Day	18% 14% 29% 24% 11% 3	490
	21st to end	Day	21% 15% 29% 21% 11% 3	484
November	1st to 10th	Day	20% 10% 31% 24% 11% 3	386
	11th to 20th	Day	25% 15% 31% 20% 7% 1	370
	21st to end	Day	20% 17% 37% 19% 7% 1	263
December	1st to 10th	Day	26% 27% 29% 10% 8%	180
	11th to 20th	Day	39% 16% 27% 12% 6%	180
	21st to end	Day	30% 17% 29% 16% 7% 1	198
January	1st to 10th	Night	20% 18% 38% 21% 3	760
	11th to 20th	Night	24% 15% 36% 22% 3	760
	21st to end	Night	20% 18% 38% 23% 2	836
February	1st to 10th	Night	23% 15% 36% 25% 2	760
	11th to 20th	Night	25% 20% 37% 17% 1	743
	21st to end	Night	25% 17% 36% 20% 2	628
March	1st to 10th	Night	23% 18% 33% 22% 3	760
	11th to 20th	Night	24% 17% 35% 19% 4	760
	21st to end	Night	21% 14% 40% 20% 5%	836
April	1st to 10th	Night	21% 18% 38% 18% 5%	760
	11th to 20th	Night	19% 13% 37% 24% 5%	751
	21st to end	Night	21% 12% 35% 26% 6%	760
May	1st to 10th	Night	24% 15% 31% 24% 6%	603
	11th to 20th	Night	20% 9% 39% 25% 7%	374
	21st to end	Night	15% 6% 25% 39% 14% 1	411
June	1st to 10th	Night	17% 6% 28% 36% 14% 1	380
	11th to 20th	Night	13% 3 31% 41% 12%	380
	21st to end	Night	11% 4 25% 47% 13% 1	380
July	1st to 10th	Night	11% 4 25% 41% 18% 2	370
	11th to 20th	Night	11% 3 23% 42% 20% 1	368
	21st to end	Night	10% 5% 25% 43% 17%	416
August	1st to 10th	Night	13% 2 16% 46% 21% 2	553
	11th to 20th	Night	14% 3 19% 35% 26% 3	744
	21st to end	Night	15% 4 18% 40% 22% 2	836
September	1st to 10th	Night	16% 3 26% 34% 18% 3	760
	11th to 20th	Night	14% 4 23% 34% 21% 4	760
	21st to end	Night	23% 5% 22% 32% 17% 1	760
October	1st to 10th	Night	21% 7% 25% 26% 17% 3	760
	11th to 20th	Night	16% 10% 29% 32% 13%	760
	21st to end	Night	21% 11% 32% 27% 9%	836
November	1st to 10th	Night	15% 9% 35% 30% 11% 1	771
	11th to 20th	Night	20% 15% 29% 27% 8%	760
	21st to end	Night	18% 13% 34% 27% 7%	760
December	1st to 10th	Night	26% 15% 31% 21% 6% 1	760
	11th to 20th	Night	20% 14% 35% 25% 5%	760
	21st to end	Night	22% 15% 33% 28% 3	836

Page generated at 2024-11-05 08:15:51. Version ac07

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