Morris County Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Morris County Observatory clear sky chart from 2005-11-06 to 2025-07-06.

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	18% 6% 2 6% 4 4 4 4 5% 7% 40%	119926
	Night	17% 7% 2 6% 4 4 4 3 5% 6% 43%	118849
Transparency	Day	43% 5% 11% 22% 16% 3	123485
	Night	42% 5% 11% 22% 17% 3	123451
Seeing	Day	23% 17% 30% 20% 8% 2	15781
	Night	21% 15% 32% 24% 8% 1	24980

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	12% 6% 2 5% 4 4 4 3 6% 6% 48%	3597
	11th to 20th	Day	13% 9% 3 9% 6% 5% 4 3 4 6% 39%	3570
	21st to end	Day	17% 9% 4 7% 4 3 4 3 5% 4 40%	4392
February	1st to 10th	Day	16% 9% 2 7% 5% 4 4 3 5% 7% 38%	1800
	11th to 20th	Day	15% 7% 3 7% 5% 4 4 4 5% 6% 41%	1925
	21st to end	Day	19% 9% 3 5% 5% 4 4 3 5% 5% 38%	1650
March	1st to 10th	Day	21% 6% 2 5% 3 3 4 3 4 5% 43%	4476
	11th to 20th	Day	12% 6% 2 6% 4 4 5% 4 6% 7% 43%	4859
	21st to end	Day	18% 6% 2 5% 4 3 3 3 5% 7% 43%	5873
April	1st to 10th	Day	18% 8% 3 7% 4 4 4 3 5% 6% 37%	2400
	11th to 20th	Day	18% 6% 2 6% 4 3 5% 4 5% 7% 40%	2374
	21st to end	Day	18% 6% 2 6% 5% 4 4 4 6% 6% 40%	2400
May	1st to 10th	Day	30% 7% 2 6% 4 4 4 3 5% 7% 29%	5922
	11th to 20th	Day	24% 8% 3 7% 4 3 4 3 4 6% 34%	6318
	21st to end	Day	21% 6% 2 5% 4 4 4 4 6% 8% 36%	6949
June	1st to 10th	Day	16% 6% 2 5% 4 4 5% 5% 7% 9% 37%	2800
	11th to 20th	Day	17% 6% 2 6% 5% 5% 6% 4 6% 8% 36%	2800
	21st to end	Day	14% 5% 2 6% 5% 4 5% 4 5% 9% 40%	2800
July	1st to 10th	Day	10% 6% 3 7% 6% 6% 6% 4 7% 10% 36%	4510
	11th to 20th	Day	12% 5% 2 6% 4 5% 6% 4 7% 10% 39%	4440
	21st to end	Day	16% 7% 3 8% 6% 6% 5% 5% 6% 7% 32%	4814
August	1st to 10th	Day	23% 5% 2 6% 5% 4 6% 4 7% 7% 33%	4153
	11th to 20th	Day	15% 5% 2 6% 4 4 4 4 5% 8% 44%	3730
	21st to end	Day	13% 5% 2 5% 4 3 4 3 5% 8% 48%	4180
September	1st to 10th	Day	16% 6% 2 5% 4 5% 4 3 5% 7% 44%	2280
	11th to 20th	Day	14% 5% 2 5% 3 4 3 3 5% 8% 49%	2220
	21st to end	Day	20% 6% 3 6% 4 5% 4 3 5% 5% 40%	2090
October	1st to 10th	Day	20% 5% 2 6% 3 4 4 4 5% 6% 41%	1948
	11th to 20th	Day	15% 5% 2 5% 3 4 5% 3 5% 6% 48%	1900
	21st to end	Day	20% 5% 2 4 3 4 4 4 4 6% 44%	1967
November	1st to 10th	Day	14% 6% 3 4 3 2 3 3 4 5% 53%	1761
	11th to 20th	Day	18% 5% 2 4 3 3 3 4 6% 5% 47%	1800
	21st to end	Day	16% 7% 2 5% 4 4 5% 4 5% 7% 43%	1682
December	1st to 10th	Day	16% 7% 2 5% 4 3 3 3 5% 7% 45%	2600
	11th to 20th	Day	23% 7% 2 4 3 2 3 3 5% 6% 43%	2986
	21st to end	Day	17% 7% 3 7% 5% 4 5% 4 6% 7% 36%	3960
January	1st to 10th	Night	13% 6% 2 5% 4 4 4 4 5% 6% 49%	6349
	11th to 20th	Night	13% 8% 2 7% 4 4 4 3 4 6% 45%	6315
	21st to end	Night	18% 9% 2 5% 3 4 4 4 4 6% 41%	6561
February	1st to 10th	Night	16% 10% 3 6% 4 4 4 4 5% 5% 41%	2600
	11th to 20th	Night	17% 8% 4 6% 4 4 3 4 5% 5% 42%	2359
	21st to end	Night	18% 8% 2 6% 4 4 3 3 4 6% 42%	1980
March	1st to 10th	Night	19% 9% 2 5% 3 3 4 3 5% 6% 44%	5364
	11th to 20th	Night	13% 8% 3 5% 4 3 3 3 4 5% 48%	5084
	21st to end	Night	17% 9% 3 6% 3 4 4 3 4 5% 42%	5059
April	1st to 10th	Night	19% 8% 2 6% 4 5% 5% 4 6% 6% 36%	2000
	11th to 20th	Night	19% 6% 2 6% 4 4 4 4 4 7% 40%	1975
	21st to end	Night	20% 6% 2 5% 3 4 4 3 5% 6% 43%	2000
May	1st to 10th	Night	28% 8% 3 6% 4 4 4 3 5% 6% 28%	4044
	11th to 20th	Night	24% 9% 3 6% 4 4 3 3 5% 5% 34%	3575
	21st to end	Night	22% 7% 2 5% 4 4 4 3 5% 8% 36%	3926
June	1st to 10th	Night	16% 5% 2 5% 4 4 5% 3 6% 6% 44%	1600
	11th to 20th	Night	15% 7% 3 5% 5% 4 4 4 6% 7% 41%	1600
	21st to end	Night	13% 4 2 5% 4 4 5% 4 7% 10% 43%	1600
July	1st to 10th	Night	11% 5% 2 7% 5% 5% 5% 4 6% 9% 42%	2560
	11th to 20th	Night	13% 5% 2 6% 4 4 5% 4 7% 10% 38%	2520
	21st to end	Night	17% 7% 2 6% 4 4 5% 4 6% 8% 37%	2739
August	1st to 10th	Night	23% 5% 3 6% 4 4 4 4 6% 8% 33%	2747
	11th to 20th	Night	15% 6% 2 6% 5% 5% 5% 4 5% 7% 40%	3092
	21st to end	Night	11% 5% 2 5% 3 3 4 3 5% 7% 52%	3476
September	1st to 10th	Night	16% 6% 2 6% 5% 4 3 3 4 6% 45%	1900
	11th to 20th	Night	14% 5% 2 5% 3 2 3 3 4 7% 52%	1959
	21st to end	Night	19% 6% 2 5% 3 4 3 2 5% 7% 44%	2090
October	1st to 10th	Night	20% 7% 2 6% 4 3 3 2 5% 6% 42%	2228
	11th to 20th	Night	15% 5% 2 5% 3 3 3 3 5% 6% 50%	2280
	21st to end	Night	21% 6% 2 5% 3 3 3 3 4 6% 45%	2631
November	1st to 10th	Night	12% 5% 2 5% 4 3 3 3 5% 6% 52%	2537
	11th to 20th	Night	19% 6% 2 4 3 3 3 3 4 5% 48%	2600
	21st to end	Night	15% 6% 2 5% 4 4 4 4 5% 7% 44%	2715
December	1st to 10th	Night	13% 7% 2 6% 4 4 4 3 5% 6% 47%	4580
	11th to 20th	Night	24% 7% 2 5% 3 3 3 3 4 5% 42%	5208
	21st to end	Night	19% 10% 3 7% 4 3 3 3 4 4 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 8% 31% 19% 2	3598
	11th to 20th	Day	47% 4 10% 20% 14% 5%	3600
	21st to end	Day	48% 4 10% 21% 16% 1	4392
February	1st to 10th	Day	46% 6% 13% 21% 13% 2	1800
	11th to 20th	Day	44% 6% 9% 22% 16% 3	1934
	21st to end	Day	48% 5% 10% 21% 13% 3	1650
March	1st to 10th	Day	44% 4 9% 21% 14% 8%	4479
	11th to 20th	Day	39% 5% 13% 28% 11% 4	4859
	21st to end	Day	42% 3 11% 12% 25% 6%	5873
April	1st to 10th	Day	47% 5% 10% 19% 15% 5%	2400
	11th to 20th	Day	43% 5% 11% 20% 17% 3	2374
	21st to end	Day	43% 6% 10% 20% 17% 4	2400
May	1st to 10th	Day	54% 5% 14% 15% 10% 1	5933
	11th to 20th	Day	51% 5% 9% 20% 13% 1	6322
	21st to end	Day	45% 6% 11% 23% 14% 1	6949
June	1st to 10th	Day	42% 9% 13% 20% 15% 1	2800
	11th to 20th	Day	45% 8% 12% 22% 11% 2	2800
	21st to end	Day	41% 8% 13% 22% 15% 1	2800
July	1st to 10th	Day	44% 8% 12% 22% 14% 2	4440
	11th to 20th	Day	39% 6% 17% 23% 13% 1	4365
	21st to end	Day	50% 6% 10% 17% 16% 1	4661
August	1st to 10th	Day	49% 7% 14% 20% 10%	4139
	11th to 20th	Day	39% 5% 13% 29% 14% 1	3766
	21st to end	Day	36% 4 9% 29% 20% 2	4180
September	1st to 10th	Day	39% 8% 10% 21% 19% 3	2280
	11th to 20th	Day	34% 6% 10% 23% 25% 3	2220
	21st to end	Day	46% 5% 10% 17% 19% 3	2090
October	1st to 10th	Day	40% 4 8% 19% 24% 5%	3234
	11th to 20th	Day	28% 3 10% 25% 29% 5%	3140
	21st to end	Day	27% 3 15% 23% 27% 4	3218
November	1st to 10th	Day	34% 5% 12% 24% 22% 3	1761
	11th to 20th	Day	38% 5% 11% 22% 21% 3	1800
	21st to end	Day	41% 4 13% 28% 11% 2	1682
December	1st to 10th	Day	40% 4 15% 27% 12% 2	2600
	11th to 20th	Day	44% 4 14% 24% 13% 2	2986
	21st to end	Day	46% 6% 10% 21% 15% 2	3960
January	1st to 10th	Night	36% 4 9% 26% 22% 4	6349
	11th to 20th	Night	40% 4 14% 20% 15% 6%	6360
	21st to end	Night	46% 4 10% 19% 17% 5%	6561
February	1st to 10th	Night	45% 6% 12% 24% 12% 2	2600
	11th to 20th	Night	45% 5% 10% 18% 17% 4	2361
	21st to end	Night	44% 4 8% 24% 17% 3	1980
March	1st to 10th	Night	43% 4 9% 22% 13% 9%	5374
	11th to 20th	Night	38% 5% 15% 24% 14% 4	5085
	21st to end	Night	45% 4 6% 17% 22% 5%	5059
April	1st to 10th	Night	47% 6% 11% 19% 14% 4	2000
	11th to 20th	Night	44% 6% 10% 19% 20% 2	1975
	21st to end	Night	42% 6% 9% 21% 17% 4	2000
May	1st to 10th	Night	56% 6% 12% 15% 10% 1	4050
	11th to 20th	Night	52% 6% 12% 15% 14% 2	3576
	21st to end	Night	46% 6% 13% 23% 10% 2	3927
June	1st to 10th	Night	41% 5% 12% 22% 20% 1	1600
	11th to 20th	Night	41% 8% 14% 24% 12% 1	1600
	21st to end	Night	34% 9% 16% 24% 16% 1	1600
July	1st to 10th	Night	39% 8% 16% 19% 15% 2	2520
	11th to 20th	Night	40% 7% 15% 25% 13% 1	2472
	21st to end	Night	44% 6% 14% 16% 18% 2	2651
August	1st to 10th	Night	49% 7% 18% 16% 9% 1	2737
	11th to 20th	Night	44% 6% 11% 27% 11% 1	3122
	21st to end	Night	33% 5% 10% 32% 20% 1	3476
September	1st to 10th	Night	40% 6% 11% 23% 19% 1	1900
	11th to 20th	Night	34% 5% 10% 23% 25% 3	1959
	21st to end	Night	42% 5% 8% 22% 22% 1	2090
October	1st to 10th	Night	42% 3 10% 23% 21% 2	3722
	11th to 20th	Night	26% 4 10% 28% 28% 4	3779
	21st to end	Night	30% 3 12% 32% 20% 3	4330
November	1st to 10th	Night	33% 6% 12% 24% 22% 4	2537
	11th to 20th	Night	40% 4 9% 23% 20% 4	2600
	21st to end	Night	38% 5% 14% 27% 14% 1	2715
December	1st to 10th	Night	39% 4 12% 31% 11% 2	4580
	11th to 20th	Night	46% 4 10% 22% 15% 3	5208
	21st to end	Night	48% 4 10% 18% 16% 3	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	30% 26% 32% 11% 1 1	200
	11th to 20th	Day	37% 27% 29% 8% 1	200
	21st to end	Day	25% 30% 31% 9% 4	313
February	1st to 10th	Day	31% 27% 34% 7% 1	300
	11th to 20th	Day	31% 27% 33% 8%	473
	21st to end	Day	32% 25% 29% 12% 2	414
March	1st to 10th	Day	30% 24% 31% 12% 3	500
	11th to 20th	Day	27% 26% 31% 13% 3 1	500
	21st to end	Day	31% 23% 31% 11% 4 1	550
April	1st to 10th	Day	31% 24% 28% 10% 6%	500
	11th to 20th	Day	27% 24% 30% 13% 6% 1	492
	21st to end	Day	30% 19% 35% 12% 3 2	500
May	1st to 10th	Day	34% 19% 28% 13% 5% 1	503
	11th to 20th	Day	25% 17% 34% 17% 7% 1	527
	21st to end	Day	23% 10% 29% 27% 10% 1	573
June	1st to 10th	Day	19% 14% 31% 24% 11% 1	530
	11th to 20th	Day	21% 14% 30% 24% 9% 1	530
	21st to end	Day	18% 11% 33% 27% 10% 1	530
July	1st to 10th	Day	15% 6% 30% 29% 16% 4	505
	11th to 20th	Day	12% 4 28% 36% 17% 2	484
	21st to end	Day	16% 8% 32% 28% 13% 2	532
August	1st to 10th	Day	15% 8% 26% 31% 16% 5%	486
	11th to 20th	Day	15% 7% 27% 32% 14% 5%	479
	21st to end	Day	13% 9% 31% 27% 13% 6%	539
September	1st to 10th	Day	19% 12% 24% 25% 14% 5%	490
	11th to 20th	Day	15% 7% 29% 24% 15% 9%	490
	21st to end	Day	23% 14% 29% 20% 10% 4	490
October	1st to 10th	Day	25% 10% 29% 21% 12% 4	490
	11th to 20th	Day	18% 18% 32% 22% 9% 1	490
	21st to end	Day	24% 17% 30% 19% 8% 1	474
November	1st to 10th	Day	20% 15% 33% 21% 9% 2	395
	11th to 20th	Day	26% 20% 32% 19% 4	400
	21st to end	Day	26% 21% 34% 14% 4	282
December	1st to 10th	Day	31% 25% 28% 12% 6%	200
	11th to 20th	Day	36% 25% 25% 12% 3	200
	21st to end	Day	28% 20% 33% 14% 5%	220
January	1st to 10th	Night	22% 23% 37% 15% 3	800
	11th to 20th	Night	27% 19% 33% 18% 3	800
	21st to end	Night	21% 22% 39% 17% 2	880
February	1st to 10th	Night	23% 20% 37% 18% 2	800
	11th to 20th	Night	25% 26% 36% 12% 1	783
	21st to end	Night	27% 20% 35% 16% 2	660
March	1st to 10th	Night	24% 23% 32% 17% 3	800
	11th to 20th	Night	23% 23% 33% 18% 3 1	800
	21st to end	Night	22% 21% 38% 14% 5%	880
April	1st to 10th	Night	25% 21% 34% 16% 4	800
	11th to 20th	Night	23% 18% 36% 20% 4	791
	21st to end	Night	23% 16% 35% 23% 4	800
May	1st to 10th	Night	27% 16% 33% 20% 5%	603
	11th to 20th	Night	22% 13% 35% 22% 7%	394
	21st to end	Night	19% 7% 27% 35% 12%	433
June	1st to 10th	Night	19% 7% 30% 33% 11%	400
	11th to 20th	Night	16% 6% 32% 35% 11%	400
	21st to end	Night	13% 5% 28% 44% 10%	400
July	1st to 10th	Night	13% 6% 26% 38% 17% 2	380
	11th to 20th	Night	12% 4 24% 41% 17% 1	368
	21st to end	Night	15% 3 25% 43% 13% 1	416
August	1st to 10th	Night	14% 2 23% 39% 20% 2	515
	11th to 20th	Night	14% 4 22% 36% 22% 1	745
	21st to end	Night	15% 4 24% 38% 18% 1	836
September	1st to 10th	Night	18% 4 28% 33% 16% 2	760
	11th to 20th	Night	16% 5% 23% 32% 19% 3	760
	21st to end	Night	22% 7% 26% 31% 13% 1	760
October	1st to 10th	Night	22% 9% 29% 25% 13% 2	760
	11th to 20th	Night	17% 14% 30% 29% 9%	760
	21st to end	Night	24% 14% 33% 22% 7%	836
November	1st to 10th	Night	16% 14% 34% 26% 9% 1	780
	11th to 20th	Night	25% 15% 31% 23% 6%	800
	21st to end	Night	19% 20% 35% 21% 5% 1	800
December	1st to 10th	Night	25% 18% 32% 21% 4 1	800
	11th to 20th	Night	23% 19% 36% 20% 3	800
	21st to end	Night	24% 18% 35% 20% 3	880

Page generated at 2025-07-03 01:30:12. Version ac07

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