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 2026-10-29.

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% 6% 2 6% 4 4 4 4 6% 7% 40%	149699
	Night	17% 7% 2 6% 4 4 4 3 5% 6% 42%	142358
Transparency	Day	43% 5% 12% 23% 16% 2	153215
	Night	42% 4 11% 23% 16% 3	146931
Seeing	Day	23% 17% 30% 19% 8% 2	17529
	Night	21% 15% 32% 24% 8% 1	26650

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% 7% 2 6% 4 4 4 3 5% 6% 46%	4661
	11th to 20th	Day	14% 9% 3 7% 5% 4 4 3 4 5% 43%	4650
	21st to end	Day	15% 7% 3 6% 4 4 4 4 6% 5% 41%	5678
February	1st to 10th	Day	15% 9% 2 7% 5% 4 4 3 5% 6% 39%	1890
	11th to 20th	Day	16% 7% 3 7% 5% 4 4 4 5% 6% 40%	2024
	21st to end	Day	19% 10% 3 5% 5% 4 4 3 5% 5% 38%	1730
March	1st to 10th	Day	21% 6% 2 5% 3 3 4 3 5% 5% 43%	4576
	11th to 20th	Day	12% 6% 2 6% 4 4 5% 4 6% 7% 43%	4966
	21st to end	Day	18% 6% 2 5% 4 3 3 3 5% 7% 43%	6003
April	1st to 10th	Day	18% 8% 3 6% 4 4 4 3 5% 6% 38%	2520
	11th to 20th	Day	17% 6% 2 6% 4 3 4 4 5% 7% 41%	2494
	21st to end	Day	18% 6% 2 6% 5% 4 4 4 6% 6% 39%	2520
May	1st to 10th	Day	26% 6% 2 6% 4 4 4 3 5% 7% 34%	7688
	11th to 20th	Day	20% 7% 2 6% 4 4 4 3 5% 6% 39%	8221
	21st to end	Day	24% 6% 2 5% 4 4 4 4 5% 7% 34%	9060
June	1st to 10th	Day	16% 6% 2 5% 4 4 5% 5% 7% 9% 38%	2940
	11th to 20th	Day	16% 6% 2 6% 5% 5% 6% 4 6% 8% 37%	2940
	21st to end	Day	14% 5% 2 6% 5% 4 5% 4 5% 9% 39%	2940
July	1st to 10th	Day	14% 5% 2 6% 5% 5% 5% 4 6% 9% 38%	8280
	11th to 20th	Day	11% 5% 2 6% 4 5% 5% 5% 7% 11% 38%	8280
	21st to end	Day	14% 5% 2 6% 4 5% 4 4 5% 8% 41%	8993
August	1st to 10th	Day	18% 5% 2 7% 5% 5% 6% 5% 7% 9% 30%	6092
	11th to 20th	Day	13% 4 2 5% 4 4 4 4 6% 9% 45%	5488
	21st to end	Day	13% 5% 2 5% 4 4 4 3 6% 8% 45%	6080
September	1st to 10th	Day	15% 5% 2 5% 4 5% 4 3 5% 7% 44%	2520
	11th to 20th	Day	14% 5% 2 5% 4 4 3 3 5% 7% 49%	2454
	21st to end	Day	20% 6% 3 7% 4 5% 4 3 5% 5% 38%	2310
October	1st to 10th	Day	18% 5% 2 5% 3 4 4 4 5% 6% 44%	2153
	11th to 20th	Day	17% 5% 2 5% 3 4 5% 3 5% 6% 48%	2100
	21st to end	Day	19% 5% 2 4 3 4 4 3 5% 6% 45%	2147
November	1st to 10th	Day	13% 6% 2 4 3 3 3 3 4 5% 52%	1851
	11th to 20th	Day	17% 6% 2 4 4 3 4 4 6% 6% 46%	1890
	21st to end	Day	16% 7% 2 5% 4 4 5% 4 5% 7% 42%	1766
December	1st to 10th	Day	16% 7% 2 5% 4 3 3 3 5% 7% 44%	2680
	11th to 20th	Day	22% 7% 2 4 3 2 3 3 5% 6% 43%	3066
	21st to end	Day	17% 7% 3 7% 5% 4 5% 4 6% 7% 36%	4048
January	1st to 10th	Night	12% 8% 2 6% 4 4 4 3 5% 6% 45%	8234
	11th to 20th	Night	14% 8% 3 7% 4 4 4 3 4 6% 44%	8235
	21st to end	Night	15% 9% 2 5% 3 4 4 3 4 6% 45%	8486
February	1st to 10th	Night	16% 9% 3 6% 4 4 4 4 5% 5% 41%	2730
	11th to 20th	Night	17% 8% 4 6% 4 5% 4 4 5% 5% 41%	2480
	21st to end	Night	18% 8% 2 6% 4 4 3 3 4 6% 41%	2076
March	1st to 10th	Night	19% 9% 2 5% 3 3 3 3 4 5% 44%	5484
	11th to 20th	Night	13% 8% 3 5% 4 3 3 3 5% 6% 48%	5197
	21st to end	Night	17% 9% 3 6% 4 4 4 3 4 5% 42%	5171
April	1st to 10th	Night	19% 8% 2 6% 4 5% 4 4 6% 6% 36%	2100
	11th to 20th	Night	18% 6% 2 5% 4 4 4 4 4 7% 40%	2075
	21st to end	Night	19% 6% 2 5% 3 4 4 3 5% 5% 43%	2100
May	1st to 10th	Night	24% 8% 3 6% 4 4 4 3 5% 6% 31%	5249
	11th to 20th	Night	21% 8% 3 6% 4 4 3 3 5% 7% 38%	4639
	21st to end	Night	24% 7% 2 6% 4 4 4 3 5% 7% 34%	5114
June	1st to 10th	Night	16% 5% 2 5% 4 4 5% 3 5% 6% 45%	1680
	11th to 20th	Night	15% 7% 3 5% 5% 4 4 4 6% 8% 40%	1680
	21st to end	Night	13% 4 2 5% 4 4 5% 4 7% 10% 42%	1680
July	1st to 10th	Night	15% 5% 2 6% 4 4 4 4 6% 9% 41%	4680
	11th to 20th	Night	14% 7% 2 7% 4 4 5% 5% 7% 10% 36%	4680
	21st to end	Night	14% 6% 2 6% 4 4 4 4 6% 7% 44%	5084
August	1st to 10th	Night	20% 6% 3 7% 5% 5% 4 4 6% 8% 32%	4013
	11th to 20th	Night	15% 6% 2 6% 5% 4 5% 4 5% 7% 41%	4552
	21st to end	Night	14% 5% 2 5% 4 3 4 3 5% 6% 49%	5045
September	1st to 10th	Night	16% 6% 2 6% 5% 4 4 3 4 6% 44%	2100
	11th to 20th	Night	14% 5% 2 5% 4 3 3 3 4 7% 51%	2165
	21st to end	Night	20% 7% 2 6% 3 4 3 3 4 7% 41%	2310
October	1st to 10th	Night	18% 7% 2 6% 4 3 3 2 5% 6% 44%	2463
	11th to 20th	Night	16% 5% 2 5% 3 3 3 3 4 6% 50%	2520
	21st to end	Night	20% 6% 2 4 2 3 3 3 4 6% 47%	2870
November	1st to 10th	Night	12% 5% 2 5% 4 3 3 3 5% 6% 52%	2667
	11th to 20th	Night	19% 6% 2 4 3 3 3 3 4 5% 48%	2730
	21st to end	Night	14% 6% 2 5% 4 4 4 4 5% 7% 44%	2851
December	1st to 10th	Night	13% 7% 2 6% 4 4 4 3 5% 6% 47%	4720
	11th to 20th	Night	23% 7% 2 5% 3 3 3 3 4 5% 42%	5348
	21st to end	Night	19% 10% 3 7% 4 3 3 3 4 4 40%	7150

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 9% 29% 18% 2	4662
	11th to 20th	Day	44% 3 9% 21% 16% 7%	4680
	21st to end	Day	44% 3 11% 23% 17% 1	5678
February	1st to 10th	Day	45% 5% 13% 22% 13% 2	1890
	11th to 20th	Day	44% 6% 9% 23% 15% 3	2033
	21st to end	Day	47% 5% 10% 22% 13% 3	1730
March	1st to 10th	Day	44% 3 9% 21% 14% 8%	4579
	11th to 20th	Day	39% 5% 13% 28% 11% 4	4966
	21st to end	Day	42% 3 12% 13% 24% 6%	6003
April	1st to 10th	Day	47% 5% 10% 19% 15% 5%	2520
	11th to 20th	Day	42% 5% 12% 20% 17% 3	2494
	21st to end	Day	44% 5% 10% 21% 16% 4	2520
May	1st to 10th	Day	50% 4 12% 18% 14% 1	7700
	11th to 20th	Day	47% 4 9% 24% 14% 1	8225
	21st to end	Day	49% 5% 11% 21% 14% 1	9061
June	1st to 10th	Day	41% 8% 13% 20% 17% 1	2940
	11th to 20th	Day	44% 7% 12% 22% 12% 2	2940
	21st to end	Day	41% 7% 14% 22% 15% 1	2940
July	1st to 10th	Day	44% 6% 13% 20% 16% 1	8210
	11th to 20th	Day	41% 4 17% 26% 12% 1	8205
	21st to end	Day	42% 3 10% 23% 21% 1	8795
August	1st to 10th	Day	49% 6% 16% 18% 9% 1	6078
	11th to 20th	Day	37% 4 17% 31% 11%	5524
	21st to end	Day	38% 4 10% 30% 17% 2	6080
September	1st to 10th	Day	39% 7% 11% 21% 19% 3	2520
	11th to 20th	Day	35% 5% 10% 23% 24% 3	2454
	21st to end	Day	48% 5% 10% 16% 18% 3	2310
October	1st to 10th	Day	39% 4 8% 20% 25% 5%	3439
	11th to 20th	Day	28% 3 10% 25% 28% 5%	3340
	21st to end	Day	27% 3 15% 24% 27% 4	3398
November	1st to 10th	Day	34% 4 13% 23% 22% 3	1851
	11th to 20th	Day	38% 4 11% 22% 20% 4	1890
	21st to end	Day	42% 4 13% 28% 11% 2	1766
December	1st to 10th	Day	41% 4 14% 27% 12% 2	2680
	11th to 20th	Day	43% 4 14% 24% 13% 2	3066
	21st to end	Day	46% 6% 10% 21% 15% 2	4048
January	1st to 10th	Night	40% 4 11% 24% 18% 3	8234
	11th to 20th	Night	42% 4 12% 20% 17% 6%	8280
	21st to end	Night	41% 3 8% 22% 21% 5%	8486
February	1st to 10th	Night	44% 5% 12% 24% 12% 2	2730
	11th to 20th	Night	46% 4 10% 18% 17% 4	2482
	21st to end	Night	44% 4 7% 24% 17% 3	2076
March	1st to 10th	Night	43% 4 9% 21% 13% 9%	5494
	11th to 20th	Night	38% 5% 15% 24% 14% 4	5198
	21st to end	Night	45% 4 7% 17% 22% 5%	5171
April	1st to 10th	Night	47% 5% 11% 19% 14% 4	2100
	11th to 20th	Night	44% 6% 11% 19% 19% 2	2075
	21st to end	Night	42% 6% 9% 21% 17% 4	2100
May	1st to 10th	Night	53% 5% 11% 18% 12% 1	5255
	11th to 20th	Night	47% 5% 13% 22% 13% 1	4640
	21st to end	Night	51% 5% 11% 22% 10% 1	5115
June	1st to 10th	Night	40% 5% 11% 23% 20% 1	1680
	11th to 20th	Night	41% 7% 14% 24% 13% 1	1680
	21st to end	Night	35% 9% 16% 24% 15% 1	1680
July	1st to 10th	Night	42% 6% 13% 21% 16% 2	4640
	11th to 20th	Night	44% 5% 14% 25% 12% 1	4632
	21st to end	Night	39% 4 13% 24% 19% 1	4967
August	1st to 10th	Night	50% 6% 16% 18% 9% 1	4003
	11th to 20th	Night	43% 5% 15% 29% 8%	4582
	21st to end	Night	37% 4 11% 29% 18% 1	5045
September	1st to 10th	Night	41% 6% 11% 23% 18% 1	2100
	11th to 20th	Night	35% 4 10% 22% 25% 3	2165
	21st to end	Night	44% 5% 9% 21% 21% 1	2310
October	1st to 10th	Night	40% 3 9% 24% 21% 2	3957
	11th to 20th	Night	27% 4 9% 28% 27% 4	4019
	21st to end	Night	30% 3 12% 32% 20% 4	4569
November	1st to 10th	Night	33% 6% 12% 24% 22% 4	2667
	11th to 20th	Night	39% 4 8% 24% 20% 4	2730
	21st to end	Night	39% 5% 13% 27% 15% 1	2851
December	1st to 10th	Night	39% 4 12% 31% 12% 2	4720
	11th to 20th	Night	45% 4 10% 22% 15% 3	5348
	21st to end	Night	48% 4 10% 18% 16% 3	7150

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% 26% 33% 11% 1	220
	11th to 20th	Day	39% 27% 27% 7%	220
	21st to end	Day	28% 30% 30% 8% 4	344
February	1st to 10th	Day	30% 28% 33% 7% 2	330
	11th to 20th	Day	31% 27% 33% 8% 1	512
	21st to end	Day	31% 25% 30% 11% 2	446
March	1st to 10th	Day	31% 24% 31% 12% 3	540
	11th to 20th	Day	29% 25% 30% 13% 3 1	540
	21st to end	Day	31% 24% 29% 11% 4 1	594
April	1st to 10th	Day	33% 23% 28% 11% 6%	540
	11th to 20th	Day	26% 23% 31% 12% 6% 1	532
	21st to end	Day	29% 19% 35% 13% 3 1	540
May	1st to 10th	Day	34% 20% 29% 12% 4 1	543
	11th to 20th	Day	24% 16% 36% 17% 7% 1	567
	21st to end	Day	25% 12% 28% 25% 9% 1	617
June	1st to 10th	Day	18% 15% 31% 24% 11% 1	570
	11th to 20th	Day	22% 15% 30% 23% 9% 1	570
	21st to end	Day	18% 12% 33% 26% 10% 1	570
July	1st to 10th	Day	16% 6% 29% 30% 16% 4	565
	11th to 20th	Day	12% 4 30% 36% 16% 2	564
	21st to end	Day	15% 8% 33% 29% 12% 2	620
August	1st to 10th	Day	14% 8% 27% 30% 16% 5%	566
	11th to 20th	Day	16% 8% 27% 33% 13% 4	559
	21st to end	Day	13% 10% 33% 26% 12% 5%	627
September	1st to 10th	Day	18% 12% 28% 24% 13% 5%	570
	11th to 20th	Day	16% 7% 29% 26% 14% 8%	570
	21st to end	Day	23% 15% 28% 21% 10% 3	570
October	1st to 10th	Day	23% 11% 29% 21% 12% 4	570
	11th to 20th	Day	21% 18% 31% 21% 8% 1	570
	21st to end	Day	23% 16% 32% 19% 8% 1	540
November	1st to 10th	Day	21% 16% 32% 21% 8% 2	425
	11th to 20th	Day	26% 21% 31% 18% 3	430
	21st to end	Day	26% 23% 34% 13% 3	306
December	1st to 10th	Day	30% 26% 27% 11% 5%	220
	11th to 20th	Day	37% 24% 25% 11% 3	220
	21st to end	Day	30% 20% 32% 12% 5%	242
January	1st to 10th	Night	22% 22% 37% 16% 3	840
	11th to 20th	Night	28% 20% 33% 18% 3	840
	21st to end	Night	21% 22% 38% 17% 2	924
February	1st to 10th	Night	23% 20% 37% 18% 2	840
	11th to 20th	Night	26% 25% 36% 13% 1	823
	21st to end	Night	26% 19% 36% 17% 2	692
March	1st to 10th	Night	24% 23% 32% 18% 3	840
	11th to 20th	Night	23% 23% 34% 17% 3	840
	21st to end	Night	22% 22% 37% 14% 4	924
April	1st to 10th	Night	25% 21% 34% 16% 4	840
	11th to 20th	Night	22% 18% 36% 20% 4	831
	21st to end	Night	23% 15% 35% 24% 3	840
May	1st to 10th	Night	26% 16% 34% 19% 5%	633
	11th to 20th	Night	21% 13% 36% 23% 7%	414
	21st to end	Night	20% 7% 27% 34% 11%	455
June	1st to 10th	Night	19% 7% 31% 32% 11%	420
	11th to 20th	Night	16% 6% 33% 33% 11%	420
	21st to end	Night	13% 5% 28% 44% 10%	420
July	1st to 10th	Night	14% 6% 26% 38% 16% 2	410
	11th to 20th	Night	12% 4 25% 41% 17% 1	408
	21st to end	Night	15% 4 25% 42% 14% 1	460
August	1st to 10th	Night	14% 2 22% 40% 21% 2	570
	11th to 20th	Night	14% 4 22% 38% 21% 1	825
	21st to end	Night	15% 4 26% 37% 17% 1	924
September	1st to 10th	Night	18% 4 28% 33% 15% 2	840
	11th to 20th	Night	16% 5% 23% 33% 19% 3	840
	21st to end	Night	23% 7% 25% 31% 13% 1	840
October	1st to 10th	Night	21% 9% 30% 24% 14% 2	840
	11th to 20th	Night	18% 15% 29% 28% 9%	840
	21st to end	Night	22% 14% 33% 23% 7%	913
November	1st to 10th	Night	17% 13% 34% 26% 9% 1	820
	11th to 20th	Night	24% 17% 31% 22% 6%	840
	21st to end	Night	19% 20% 34% 22% 5% 1	840
December	1st to 10th	Night	25% 18% 32% 20% 4 1	840
	11th to 20th	Night	24% 19% 35% 20% 3	840
	21st to end	Night	24% 19% 34% 20% 3	924

Page generated at 2026-10-26 04:37:52. Version ac07

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