Holmdel
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Holmdel clear sky chart from 2005-11-06 to 2025-08-05.

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% 7% 2 6% 4 4 4 4 5% 7% 40%	125750
	Night	16% 8% 2 6% 4 4 4 3 5% 6% 42%	122283
Transparency	Day	41% 6% 12% 22% 16% 3	129277
	Night	41% 5% 11% 22% 17% 3	126830
Seeing	Day	19% 10% 29% 26% 13% 3	15983
	Night	19% 10% 32% 28% 10% 1	25116

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	13% 7% 2 5% 3 3 3 3 4 5% 52%	3597
	11th to 20th	Day	14% 8% 3 6% 4 4 4 3 4 5% 45%	3570
	21st to end	Day	19% 11% 4 6% 4 4 3 2 3 4 40%	4374
February	1st to 10th	Day	15% 10% 3 6% 5% 4 4 3 4 6% 41%	1816
	11th to 20th	Day	17% 8% 3 6% 4 4 4 3 4 5% 42%	1948
	21st to end	Day	17% 9% 3 7% 4 4 4 4 4 6% 39%	1650
March	1st to 10th	Day	22% 6% 2 5% 3 3 3 3 4 6% 45%	4476
	11th to 20th	Day	11% 8% 3 6% 5% 5% 4 3 6% 7% 43%	4793
	21st to end	Day	18% 6% 2 7% 4 4 4 3 4 6% 43%	5916
April	1st to 10th	Day	18% 9% 2 5% 5% 4 3 4 5% 6% 39%	2400
	11th to 20th	Day	15% 7% 3 6% 4 4 4 4 6% 8% 40%	2374
	21st to end	Day	17% 5% 2 5% 4 4 5% 4 6% 7% 41%	2400
May	1st to 10th	Day	25% 9% 2 6% 4 4 5% 4 5% 7% 28%	5886
	11th to 20th	Day	25% 9% 2 5% 4 3 3 3 4 6% 36%	6244
	21st to end	Day	21% 6% 2 6% 4 4 4 4 6% 8% 35%	6949
June	1st to 10th	Day	15% 6% 2 5% 5% 4 5% 5% 7% 10% 37%	2800
	11th to 20th	Day	15% 7% 2 6% 5% 4 5% 4 6% 9% 38%	2800
	21st to end	Day	10% 5% 2 6% 5% 5% 7% 4 7% 9% 40%	2800
July	1st to 10th	Day	9% 6% 2 7% 5% 5% 6% 5% 8% 11% 36%	6360
	11th to 20th	Day	11% 7% 3 7% 6% 6% 6% 5% 8% 10% 31%	6360
	21st to end	Day	11% 7% 2 7% 5% 5% 5% 4 7% 9% 38%	6926
August	1st to 10th	Day	19% 6% 2 7% 5% 4 5% 4 7% 8% 32%	4152
	11th to 20th	Day	12% 6% 2 7% 4 4 5% 4 6% 9% 40%	3730
	21st to end	Day	10% 5% 2 5% 4 4 5% 3 6% 10% 46%	4180
September	1st to 10th	Day	13% 6% 2 6% 4 4 5% 3 4 7% 46%	2280
	11th to 20th	Day	13% 5% 2 4 4 4 4 4 5% 7% 49%	2201
	21st to end	Day	19% 6% 3 7% 4 3 4 3 5% 6% 39%	2090
October	1st to 10th	Day	20% 7% 2 5% 3 3 4 3 5% 7% 43%	1981
	11th to 20th	Day	15% 5% 2 4 4 4 4 2 4 5% 50%	1900
	21st to end	Day	18% 6% 3 5% 3 3 4 4 4 6% 45%	1955
November	1st to 10th	Day	13% 7% 2 5% 3 3 3 2 4 5% 52%	1761
	11th to 20th	Day	16% 5% 3 5% 3 3 3 3 5% 5% 49%	1800
	21st to end	Day	16% 7% 2 5% 4 4 4 3 5% 6% 46%	1735
December	1st to 10th	Day	14% 7% 2 6% 3 3 4 3 5% 7% 46%	2600
	11th to 20th	Day	22% 9% 3 4 2 2 2 3 3 4 46%	2986
	21st to end	Day	16% 6% 2 6% 5% 5% 4 3 5% 7% 39%	3960
January	1st to 10th	Night	13% 7% 2 4 3 3 3 3 4 6% 52%	6349
	11th to 20th	Night	14% 8% 2 5% 4 3 3 3 4 5% 48%	6315
	21st to end	Night	18% 10% 2 5% 3 4 4 3 5% 6% 40%	6565
February	1st to 10th	Night	17% 10% 2 5% 3 3 3 3 5% 6% 41%	2582
	11th to 20th	Night	18% 8% 3 6% 4 3 3 3 5% 5% 42%	2338
	21st to end	Night	18% 8% 2 5% 3 3 3 3 5% 6% 42%	1980
March	1st to 10th	Night	18% 9% 2 5% 3 3 2 2 4 6% 45%	5364
	11th to 20th	Night	13% 11% 3 5% 4 3 3 3 4 5% 46%	5163
	21st to end	Night	18% 8% 3 6% 4 4 4 3 5% 5% 40%	5015
April	1st to 10th	Night	18% 9% 3 6% 4 4 4 4 5% 5% 39%	2000
	11th to 20th	Night	16% 8% 3 7% 3 4 3 3 5% 6% 41%	1975
	21st to end	Night	17% 6% 2 5% 3 3 4 3 5% 7% 43%	1997
May	1st to 10th	Night	23% 9% 4 8% 4 4 4 4 5% 8% 27%	4054
	11th to 20th	Night	24% 9% 2 6% 4 3 4 3 5% 6% 35%	3678
	21st to end	Night	22% 6% 3 6% 4 4 4 3 5% 9% 35%	3926
June	1st to 10th	Night	15% 7% 2 6% 4 3 4 4 5% 8% 41%	1600
	11th to 20th	Night	15% 7% 2 6% 5% 4 4 3 6% 9% 40%	1600
	21st to end	Night	8% 6% 2 5% 6% 5% 5% 5% 8% 9% 40%	1600
July	1st to 10th	Night	8% 6% 3 8% 6% 6% 6% 4 7% 10% 36%	3600
	11th to 20th	Night	12% 9% 3 8% 5% 4 5% 5% 6% 9% 32%	3600
	21st to end	Night	12% 7% 2 7% 4 4 4 4 6% 9% 41%	3926
August	1st to 10th	Night	22% 6% 2 6% 4 4 5% 4 6% 8% 31%	2818
	11th to 20th	Night	13% 7% 2 7% 5% 4 5% 4 6% 8% 40%	3097
	21st to end	Night	8% 5% 2 5% 4 3 4 3 6% 8% 52%	3476
September	1st to 10th	Night	13% 6% 2 6% 5% 5% 4 3 4 6% 45%	1900
	11th to 20th	Night	12% 5% 2 5% 3 4 3 3 5% 6% 52%	1977
	21st to end	Night	19% 7% 3 7% 4 3 4 2 4 6% 42%	2090
October	1st to 10th	Night	19% 6% 2 6% 3 3 4 4 5% 6% 43%	2195
	11th to 20th	Night	14% 4 1 5% 4 4 5% 2 4 6% 51%	2280
	21st to end	Night	19% 7% 2 5% 3 3 3 3 4 6% 45%	2641
November	1st to 10th	Night	13% 5% 1 5% 4 4 4 3 4 6% 53%	2537
	11th to 20th	Night	16% 8% 2 5% 4 3 3 3 3 5% 48%	2600
	21st to end	Night	14% 6% 1 5% 4 4 4 3 5% 6% 46%	2661
December	1st to 10th	Night	14% 8% 2 6% 3 3 4 3 4 5% 48%	4580
	11th to 20th	Night	23% 7% 2 5% 3 3 3 3 4 5% 42%	5208
	21st to end	Night	18% 9% 3 6% 4 3 4 3 5% 5% 41%	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	34% 4 8% 29% 22% 3	3598
	11th to 20th	Day	41% 4 9% 23% 17% 6%	3600
	21st to end	Day	49% 5% 9% 22% 15% 1	4374
February	1st to 10th	Day	45% 5% 14% 23% 13% 2	1816
	11th to 20th	Day	44% 5% 9% 24% 16% 3	1957
	21st to end	Day	45% 5% 11% 21% 13% 4	1650
March	1st to 10th	Day	40% 4 11% 21% 16% 8%	4479
	11th to 20th	Day	39% 5% 11% 27% 13% 5%	4793
	21st to end	Day	43% 5% 9% 15% 23% 6%	5916
April	1st to 10th	Day	44% 5% 11% 19% 16% 5%	2400
	11th to 20th	Day	40% 7% 12% 21% 16% 3	2374
	21st to end	Day	41% 7% 12% 19% 18% 4	2400
May	1st to 10th	Day	53% 8% 14% 15% 10% 1	5897
	11th to 20th	Day	50% 6% 10% 22% 12% 1	6248
	21st to end	Day	45% 7% 10% 22% 14% 1	6949
June	1st to 10th	Day	39% 10% 14% 21% 15% 2	2800
	11th to 20th	Day	41% 9% 14% 22% 12% 2	2800
	21st to end	Day	37% 10% 15% 22% 16% 1	2800
July	1st to 10th	Day	40% 10% 14% 21% 14% 1	6290
	11th to 20th	Day	45% 9% 18% 18% 9% 1	6285
	21st to end	Day	40% 7% 12% 21% 20% 1	6728
August	1st to 10th	Day	46% 8% 15% 21% 9% 1	4138
	11th to 20th	Day	39% 8% 13% 27% 12% 1	3766
	21st to end	Day	32% 7% 12% 28% 19% 2	4180
September	1st to 10th	Day	37% 7% 13% 20% 20% 2	2280
	11th to 20th	Day	35% 5% 13% 22% 24% 2	2201
	21st to end	Day	45% 6% 10% 17% 20% 2	2090
October	1st to 10th	Day	36% 5% 12% 19% 23% 5%	3293
	11th to 20th	Day	24% 4 11% 23% 32% 5%	3140
	21st to end	Day	27% 3 15% 25% 26% 4	3193
November	1st to 10th	Day	35% 3 14% 26% 20% 2	1761
	11th to 20th	Day	38% 5% 10% 22% 23% 3	1800
	21st to end	Day	39% 4 14% 29% 12% 2	1735
December	1st to 10th	Day	38% 4 15% 27% 14% 2	2600
	11th to 20th	Day	43% 4 10% 28% 13% 2	2986
	21st to end	Day	42% 7% 10% 23% 16% 2	3960
January	1st to 10th	Night	34% 3 9% 26% 22% 6%	6349
	11th to 20th	Night	39% 3 11% 24% 17% 7%	6360
	21st to end	Night	45% 4 9% 21% 18% 3	6565
February	1st to 10th	Night	44% 5% 14% 23% 13% 2	2582
	11th to 20th	Night	44% 4 9% 20% 18% 5%	2340
	21st to end	Night	41% 5% 8% 23% 18% 4	1980
March	1st to 10th	Night	42% 4 9% 23% 12% 10%	5374
	11th to 20th	Night	40% 5% 12% 25% 13% 4	5164
	21st to end	Night	46% 4 7% 15% 23% 5%	5015
April	1st to 10th	Night	46% 5% 10% 18% 17% 4	2000
	11th to 20th	Night	43% 6% 10% 18% 21% 3	1975
	21st to end	Night	40% 6% 10% 20% 20% 5%	1997
May	1st to 10th	Night	54% 8% 13% 14% 9% 2	4060
	11th to 20th	Night	51% 5% 12% 16% 14% 1	3679
	21st to end	Night	46% 8% 11% 22% 12% 2	3927
June	1st to 10th	Night	41% 8% 11% 20% 19% 1	1600
	11th to 20th	Night	40% 8% 14% 25% 12% 1	1600
	21st to end	Night	37% 10% 15% 22% 15% 2	1600
July	1st to 10th	Night	43% 8% 14% 20% 13% 1	3560
	11th to 20th	Night	46% 8% 16% 21% 9% 1	3552
	21st to end	Night	38% 7% 15% 21% 18% 1	3809
August	1st to 10th	Night	49% 9% 17% 16% 8% 1	2808
	11th to 20th	Night	40% 7% 12% 28% 12% 1	3127
	21st to end	Night	30% 6% 11% 30% 21% 1	3476
September	1st to 10th	Night	40% 7% 11% 22% 19% 2	1900
	11th to 20th	Night	33% 5% 12% 22% 24% 4	1977
	21st to end	Night	44% 6% 7% 22% 19% 2	2090
October	1st to 10th	Night	38% 6% 11% 22% 21% 2	3663
	11th to 20th	Night	24% 4 10% 26% 31% 5%	3779
	21st to end	Night	28% 4 11% 30% 24% 3	4340
November	1st to 10th	Night	34% 4 12% 24% 22% 4	2537
	11th to 20th	Night	40% 5% 8% 23% 20% 4	2600
	21st to end	Night	37% 5% 13% 27% 16% 1	2661
December	1st to 10th	Night	38% 4 11% 30% 14% 3	4580
	11th to 20th	Night	44% 4 10% 24% 14% 4	5208
	21st to end	Night	44% 5% 11% 19% 17% 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	21% 20% 37% 18% 5% 1	200
	11th to 20th	Day	23% 31% 31% 13% 3	200
	21st to end	Day	22% 20% 34% 18% 5% 1	310
February	1st to 10th	Day	26% 17% 36% 17% 3 1	316
	11th to 20th	Day	27% 19% 35% 18% 1	496
	21st to end	Day	22% 21% 34% 20% 4	414
March	1st to 10th	Day	21% 17% 39% 19% 4	500
	11th to 20th	Day	17% 17% 43% 17% 5% 1	500
	21st to end	Day	26% 17% 34% 18% 5%	550
April	1st to 10th	Day	24% 16% 35% 18% 5% 1	500
	11th to 20th	Day	21% 14% 35% 20% 9% 2	492
	21st to end	Day	23% 12% 36% 22% 6% 1	500
May	1st to 10th	Day	27% 9% 34% 20% 9% 2	503
	11th to 20th	Day	23% 6% 34% 26% 9% 1	527
	21st to end	Day	23% 5% 20% 27% 21% 3	573
June	1st to 10th	Day	15% 7% 26% 31% 17% 3	530
	11th to 20th	Day	16% 6% 29% 32% 14% 3	530
	21st to end	Day	12% 5% 25% 37% 18% 3	530
July	1st to 10th	Day	11% 5% 22% 34% 22% 6%	525
	11th to 20th	Day	10% 3 18% 36% 26% 7%	524
	21st to end	Day	12% 4 24% 37% 20% 3	576
August	1st to 10th	Day	12% 3 18% 38% 23% 7%	502
	11th to 20th	Day	13% 4 16% 34% 27% 6%	479
	21st to end	Day	12% 4 21% 35% 20% 9%	539
September	1st to 10th	Day	16% 6% 21% 29% 19% 9%	490
	11th to 20th	Day	13% 3 23% 34% 18% 9%	490
	21st to end	Day	26% 6% 24% 27% 14% 3	490
October	1st to 10th	Day	24% 6% 23% 23% 18% 6%	490
	11th to 20th	Day	16% 11% 29% 26% 14% 4	490
	21st to end	Day	20% 10% 33% 24% 11% 2	467
November	1st to 10th	Day	16% 10% 36% 23% 14% 2	395
	11th to 20th	Day	18% 18% 34% 21% 9%	400
	21st to end	Day	20% 15% 32% 24% 8% 1	335
December	1st to 10th	Day	20% 20% 40% 13% 7% 1	200
	11th to 20th	Day	29% 19% 28% 18% 7%	200
	21st to end	Day	22% 13% 38% 19% 8%	220
January	1st to 10th	Night	21% 15% 41% 19% 4	800
	11th to 20th	Night	24% 15% 36% 22% 3	800
	21st to end	Night	19% 16% 43% 21% 2	880
February	1st to 10th	Night	22% 14% 39% 23% 2	800
	11th to 20th	Night	24% 19% 41% 15% 1	783
	21st to end	Night	22% 18% 35% 22% 3	660
March	1st to 10th	Night	20% 15% 37% 23% 4	800
	11th to 20th	Night	22% 13% 40% 21% 5% 1	800
	21st to end	Night	20% 11% 40% 23% 5%	880
April	1st to 10th	Night	22% 12% 38% 23% 5%	800
	11th to 20th	Night	19% 11% 34% 30% 6%	791
	21st to end	Night	19% 8% 36% 30% 6% 1	797
May	1st to 10th	Night	23% 10% 31% 27% 8%	600
	11th to 20th	Night	23% 7% 34% 29% 7%	445
	21st to end	Night	18% 5% 21% 36% 18% 2	433
June	1st to 10th	Night	17% 6% 24% 36% 16% 1	400
	11th to 20th	Night	16% 4 22% 41% 17%	400
	21st to end	Night	9% 5% 19% 49% 18% 1	400
July	1st to 10th	Night	12% 4 20% 42% 21% 2	390
	11th to 20th	Night	11% 3 17% 42% 25% 2	388
	21st to end	Night	11% 2 19% 47% 20%	438
August	1st to 10th	Night	11% 3 16% 45% 22% 3	549
	11th to 20th	Night	12% 3 16% 39% 28% 2	750
	21st to end	Night	13% 3 14% 40% 26% 3	836
September	1st to 10th	Night	15% 3 22% 36% 19% 4	760
	11th to 20th	Night	15% 3 20% 35% 22% 6%	760
	21st to end	Night	21% 5% 23% 32% 16% 2	760
October	1st to 10th	Night	22% 7% 24% 26% 17% 3	760
	11th to 20th	Night	17% 9% 29% 34% 12% 1	760
	21st to end	Night	22% 7% 36% 25% 9% 1	836
November	1st to 10th	Night	15% 8% 37% 27% 12% 1	780
	11th to 20th	Night	19% 14% 34% 24% 8% 1	800
	21st to end	Night	17% 14% 38% 24% 7% 1	800
December	1st to 10th	Night	23% 16% 34% 20% 6% 1	800
	11th to 20th	Night	22% 11% 40% 23% 4	800
	21st to end	Night	21% 11% 40% 25% 3	880

Page generated at 2025-08-02 01:32:24. Version ac07

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