Monmouth
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Monmouth clear sky chart from 2005-11-06 to 2025-05-26.

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% 9% 3 8% 5% 4 4 3 5% 6% 37%	118269
	Night	18% 9% 3 8% 5% 4 4 3 5% 6% 36%	119826
Transparency	Day	48% 7% 12% 17% 13% 4	118014
	Night	49% 7% 12% 17% 11% 3	119670
Seeing	Day	17% 11% 22% 27% 19% 5%	15342
	Night	19% 7% 20% 34% 19% 2	24392

By Month

Percentage Cloud Cover SW (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	31% 16% 6% 14% 7% 5% 4 3 3 3 8%	3639
	11th to 20th	Day	25% 10% 4 10% 8% 5% 5% 3 5% 5% 20%	3640
	21st to end	Day	20% 10% 4 9% 6% 5% 5% 3 4 5% 28%	4510
February	1st to 10th	Day	24% 12% 4 12% 7% 6% 7% 3 5% 6% 14%	1800
	11th to 20th	Day	26% 13% 4 10% 6% 6% 5% 3 5% 4 18%	1755
	21st to end	Day	24% 15% 4 11% 6% 5% 5% 3 4 5% 18%	1550
March	1st to 10th	Day	16% 11% 4 11% 7% 7% 7% 5% 6% 7% 19%	4815
	11th to 20th	Day	23% 14% 4 8% 5% 5% 4 3 4 5% 25%	5000
	21st to end	Day	21% 12% 4 11% 8% 7% 6% 5% 6% 6% 14%	5559
April	1st to 10th	Day	22% 12% 4 12% 7% 5% 5% 4 5% 6% 18%	2400
	11th to 20th	Day	20% 11% 3 8% 5% 5% 6% 3 5% 5% 28%	2377
	21st to end	Day	18% 9% 3 7% 5% 6% 5% 4 6% 8% 28%	2600
May	1st to 10th	Day	18% 8% 3 8% 5% 5% 5% 4 5% 6% 35%	4418
	11th to 20th	Day	11% 6% 2 5% 3 3 3 3 5% 7% 52%	4517
	21st to end	Day	15% 7% 3 8% 6% 6% 6% 5% 7% 7% 30%	4886
June	1st to 10th	Day	18% 9% 3 8% 5% 4 4 3 5% 6% 35%	2660
	11th to 20th	Day	15% 8% 3 7% 6% 5% 5% 5% 6% 8% 32%	2660
	21st to end	Day	7% 5% 2 4 4 3 5% 3 5% 6% 56%	2660
July	1st to 10th	Day	3 2 1 2 2 2 2 2 3 5% 76%	4420
	11th to 20th	Day	3 2 1 2 2 2 2 2 3 4 77%	4420
	21st to end	Day	4 2 1 2 2 1 2 2 3 4 78%	4733
August	1st to 10th	Day	2 2 1 3 3 3 3 2 4 6% 71%	4091
	11th to 20th	Day	5% 3 2 5% 3 4 4 3 6% 7% 58%	4026
	21st to end	Day	6% 5% 2 4 3 3 4 3 5% 7% 58%	4315
September	1st to 10th	Day	6% 3 1 3 2 2 3 3 5% 6% 66%	2280
	11th to 20th	Day	9% 7% 2 7% 5% 4 5% 4 5% 7% 46%	2252
	21st to end	Day	14% 6% 2 6% 4 3 4 3 5% 6% 47%	2014
October	1st to 10th	Day	12% 6% 3 6% 4 4 4 4 5% 6% 47%	3180
	11th to 20th	Day	15% 8% 4 10% 6% 5% 6% 4 6% 7% 30%	3161
	21st to end	Day	21% 11% 3 10% 5% 6% 5% 3 6% 8% 21%	3431
November	1st to 10th	Day	23% 15% 5% 11% 6% 4 7% 3 5% 5% 15%	1648
	11th to 20th	Day	28% 12% 5% 9% 6% 5% 5% 4 4 5% 17%	1600
	21st to end	Day	24% 12% 4 12% 5% 5% 6% 3 5% 5% 20%	1600
December	1st to 10th	Day	19% 9% 4 10% 7% 5% 4 3 4 6% 28%	2620
	11th to 20th	Day	28% 14% 5% 13% 7% 6% 5% 5% 5% 5% 8%	3028
	21st to end	Day	32% 17% 6% 17% 7% 4 4 2 3 3 5%	4004
January	1st to 10th	Night	32% 16% 6% 10% 5% 5% 4 3 4 4 12%	6306
	11th to 20th	Night	23% 12% 4 8% 6% 5% 5% 3 5% 5% 24%	6304
	21st to end	Night	23% 11% 3 8% 5% 4 3 3 3 5% 32%	6468
February	1st to 10th	Night	20% 14% 4 10% 6% 6% 5% 4 5% 6% 18%	2600
	11th to 20th	Night	24% 12% 4 8% 5% 4 5% 4 5% 5% 25%	2532
	21st to end	Night	24% 12% 4 9% 5% 5% 4 4 5% 6% 23%	2079
March	1st to 10th	Night	14% 10% 4 11% 8% 7% 7% 5% 7% 7% 21%	5075
	11th to 20th	Night	21% 11% 4 8% 5% 4 4 3 5% 6% 29%	5000
	21st to end	Night	21% 11% 4 11% 7% 6% 6% 4 6% 7% 17%	5415
April	1st to 10th	Night	22% 11% 4 9% 6% 5% 4 3 5% 6% 26%	2000
	11th to 20th	Night	17% 9% 3 7% 5% 4 3 3 5% 7% 37%	1969
	21st to end	Night	15% 7% 3 8% 6% 4 4 4 5% 7% 35%	1800
May	1st to 10th	Night	17% 9% 3 7% 4 3 4 3 4 5% 42%	2763
	11th to 20th	Night	8% 5% 2 4 3 3 3 2 4 5% 59%	2596
	21st to end	Night	10% 6% 3 7% 5% 4 4 5% 7% 8% 42%	2805
June	1st to 10th	Night	15% 7% 2 6% 6% 4 4 3 5% 7% 42%	1520
	11th to 20th	Night	12% 6% 2 6% 4 4 3 4 6% 6% 48%	1520
	21st to end	Night	5% 5% 2 4 3 2 3 3 4 5% 64%	1520
July	1st to 10th	Night	2 2 1 2 2 1 1 1 2 3 83%	2540
	11th to 20th	Night	3 2 1 2 2 1 2 1 2 3 80%	2540
	21st to end	Night	3 2 1 2 1 1 2 1 3 3 82%	2817
August	1st to 10th	Night	1 2 1 2 1 2 2 2 4 5% 78%	2848
	11th to 20th	Night	5% 3 2 3 2 3 3 3 5% 7% 64%	2812
	21st to end	Night	7% 4 2 4 3 2 2 2 4 4 67%	3357
September	1st to 10th	Night	4 2 1 3 2 2 3 3 4 5% 70%	1900
	11th to 20th	Night	8% 5% 2 5% 4 4 4 3 6% 6% 53%	1924
	21st to end	Night	9% 5% 2 5% 3 4 4 2 6% 7% 54%	2166
October	1st to 10th	Night	9% 5% 2 5% 4 4 4 4 4 7% 52%	3800
	11th to 20th	Night	13% 6% 3 7% 5% 5% 5% 5% 6% 8% 37%	3777
	21st to end	Night	22% 10% 3 8% 5% 5% 5% 4 5% 6% 28%	4137
November	1st to 10th	Night	22% 8% 4 8% 6% 5% 5% 4 5% 7% 25%	2648
	11th to 20th	Night	28% 11% 3 9% 6% 5% 5% 4 5% 5% 21%	2800
	21st to end	Night	21% 8% 4 11% 6% 5% 5% 3 4 6% 27%	2800
December	1st to 10th	Night	17% 8% 3 7% 6% 5% 5% 4 6% 7% 32%	4560
	11th to 20th	Night	31% 14% 5% 12% 6% 5% 4 3 4 4 12%	5176
	21st to end	Night	29% 13% 5% 13% 7% 6% 4 3 4 5% 11%	6952

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	81% 5% 5% 6% 3	3639
	11th to 20th	Day	64% 7% 7% 15% 6% 1	3640
	21st to end	Day	57% 8% 6% 11% 15% 3	4510
February	1st to 10th	Day	69% 8% 8% 10% 4	1800
	11th to 20th	Day	68% 9% 8% 9% 4 2	1764
	21st to end	Day	69% 7% 8% 9% 6% 1	1550
March	1st to 10th	Day	61% 7% 15% 13% 4	4815
	11th to 20th	Day	60% 7% 7% 18% 8%	5000
	21st to end	Day	68% 10% 12% 7% 3	5559
April	1st to 10th	Day	66% 7% 11% 12% 3	2400
	11th to 20th	Day	57% 7% 11% 14% 8% 2	2380
	21st to end	Day	55% 9% 14% 14% 7% 1	2600
May	1st to 10th	Day	47% 8% 13% 19% 12%	4418
	11th to 20th	Day	32% 6% 17% 30% 13% 1	4520
	21st to end	Day	46% 14% 23% 14% 2	4887
June	1st to 10th	Day	50% 7% 17% 19% 6% 1	2660
	11th to 20th	Day	47% 9% 21% 17% 6%	2660
	21st to end	Day	29% 6% 19% 29% 12% 4	2660
July	1st to 10th	Day	14% 4 9% 18% 24% 32%	4351
	11th to 20th	Day	13% 3 6% 19% 38% 20%	4345
	21st to end	Day	12% 3 11% 28% 38% 7%	4583
August	1st to 10th	Day	16% 3 11% 31% 27% 12%	4076
	11th to 20th	Day	25% 7% 18% 32% 15% 3	4065
	21st to end	Day	26% 6% 13% 26% 23% 6%	4314
September	1st to 10th	Day	19% 5% 13% 30% 20% 12%	2280
	11th to 20th	Day	37% 8% 13% 20% 15% 6%	2252
	21st to end	Day	37% 7% 15% 21% 14% 6%	2014
October	1st to 10th	Day	37% 5% 8% 23% 24% 3	3180
	11th to 20th	Day	51% 8% 14% 15% 11% 1	3161
	21st to end	Day	60% 6% 8% 16% 10% 1	3431
November	1st to 10th	Day	69% 8% 9% 11% 4	1648
	11th to 20th	Day	69% 6% 10% 8% 5% 1	1600
	21st to end	Day	65% 8% 8% 8% 11% 1	1600
December	1st to 10th	Day	57% 5% 10% 16% 12%	2620
	11th to 20th	Day	76% 9% 8% 7% 1	3028
	21st to end	Day	83% 6% 6% 3 2	4004
January	1st to 10th	Night	76% 6% 7% 6% 4 1	6306
	11th to 20th	Night	60% 6% 8% 17% 7% 1	6304
	21st to end	Night	56% 5% 7% 13% 16% 4	6468
February	1st to 10th	Night	65% 8% 10% 12% 4	2600
	11th to 20th	Night	60% 7% 13% 12% 7% 2	2534
	21st to end	Night	62% 6% 12% 12% 6% 2	2079
March	1st to 10th	Night	58% 8% 14% 15% 6%	5075
	11th to 20th	Night	56% 7% 11% 18% 8% 1	5000
	21st to end	Night	65% 10% 14% 10% 1	5415
April	1st to 10th	Night	59% 8% 16% 12% 5%	2000
	11th to 20th	Night	48% 6% 19% 17% 7% 3	1969
	21st to end	Night	49% 7% 17% 18% 7% 2	1800
May	1st to 10th	Night	42% 8% 16% 23% 10% 1	2763
	11th to 20th	Night	28% 5% 16% 34% 14% 3	2596
	21st to end	Night	35% 13% 34% 15% 3	2805
June	1st to 10th	Night	43% 6% 18% 26% 5% 1	1520
	11th to 20th	Night	35% 8% 23% 26% 8%	1520
	21st to end	Night	23% 5% 21% 33% 13% 4	1520
July	1st to 10th	Night	10% 3 9% 20% 27% 31%	2500
	11th to 20th	Night	12% 2 8% 19% 31% 27%	2492
	21st to end	Night	9% 2 12% 30% 39% 8%	2729
August	1st to 10th	Night	11% 3 10% 36% 32% 9%	2839
	11th to 20th	Night	21% 5% 21% 35% 13% 4	2839
	21st to end	Night	23% 4 13% 30% 24% 6%	3357
September	1st to 10th	Night	17% 5% 14% 31% 22% 12%	1900
	11th to 20th	Night	30% 7% 16% 23% 15% 8%	1924
	21st to end	Night	29% 6% 17% 22% 17% 8%	2166
October	1st to 10th	Night	30% 6% 10% 30% 21% 2	3800
	11th to 20th	Night	42% 8% 20% 18% 10% 2	3777
	21st to end	Night	55% 7% 11% 16% 10% 1	4137
November	1st to 10th	Night	58% 9% 12% 15% 6%	2648
	11th to 20th	Night	65% 7% 10% 9% 7% 2	2800
	21st to end	Night	58% 7% 10% 10% 12% 2	2800
December	1st to 10th	Night	50% 6% 10% 19% 14% 1	4560
	11th to 20th	Night	76% 6% 7% 7% 3	5176
	21st to end	Night	73% 10% 9% 6% 2	6952

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	39% 13% 22% 18% 6% 3	200
	11th to 20th	Day	28% 14% 22% 21% 12% 4	200
	21st to end	Day	23% 15% 22% 21% 14% 5%	440
February	1st to 10th	Day	30% 15% 20% 21% 12% 4	400
	11th to 20th	Day	29% 14% 29% 16% 10% 2	395
	21st to end	Day	27% 20% 20% 21% 11% 1	364
March	1st to 10th	Day	26% 13% 30% 19% 10% 1	500
	11th to 20th	Day	26% 15% 22% 22% 12% 3	500
	21st to end	Day	26% 16% 25% 22% 10% 2	550
April	1st to 10th	Day	26% 17% 21% 21% 11% 4	500
	11th to 20th	Day	23% 16% 24% 22% 11% 4	492
	21st to end	Day	19% 15% 28% 20% 15% 4	500
May	1st to 10th	Day	16% 13% 24% 27% 15% 5%	503
	11th to 20th	Day	20% 12% 22% 24% 17% 6%	528
	21st to end	Day	11% 10% 22% 28% 21% 8%	550
June	1st to 10th	Day	16% 10% 23% 27% 21% 3	490
	11th to 20th	Day	15% 11% 25% 33% 14% 2	490
	21st to end	Day	6% 7% 19% 34% 28% 6%	490
July	1st to 10th	Day	5% 4 19% 39% 26% 8%	486
	11th to 20th	Day	2 4 21% 37% 27% 8%	484
	21st to end	Day	3 3 15% 36% 34% 8%	531
August	1st to 10th	Day	3 2 16% 33% 34% 11%	487
	11th to 20th	Day	2 3 11% 36% 36% 12%	477
	21st to end	Day	4 4 19% 36% 29% 8%	539
September	1st to 10th	Day	7% 3 23% 30% 28% 9%	490
	11th to 20th	Day	11% 7% 20% 30% 26% 7%	490
	21st to end	Day	12% 9% 22% 32% 19% 5%	490
October	1st to 10th	Day	15% 9% 22% 26% 22% 7%	490
	11th to 20th	Day	18% 10% 18% 27% 22% 6%	490
	21st to end	Day	24% 12% 25% 22% 13% 4	534
November	1st to 10th	Day	25% 14% 29% 19% 12% 3	242
	11th to 20th	Day	23% 17% 25% 17% 16% 3	200
	21st to end	Day	24% 19% 17% 19% 20% 3	200
December	1st to 10th	Day	28% 13% 13% 26% 17% 5%	200
	11th to 20th	Day	33% 13% 24% 22% 6% 3	200
	21st to end	Day	33% 17% 18% 22% 9% 2	220
January	1st to 10th	Night	34% 10% 21% 22% 11% 2	800
	11th to 20th	Night	29% 11% 18% 22% 17% 2	800
	21st to end	Night	26% 7% 17% 32% 16% 3	880
February	1st to 10th	Night	23% 11% 22% 28% 16% 1	800
	11th to 20th	Night	27% 10% 22% 26% 14%	784
	21st to end	Night	26% 12% 21% 28% 12%	660
March	1st to 10th	Night	22% 9% 23% 32% 13% 1	800
	11th to 20th	Night	21% 11% 19% 33% 15% 1	800
	21st to end	Night	23% 11% 25% 28% 12% 1	880
April	1st to 10th	Night	24% 9% 21% 29% 17% 1	800
	11th to 20th	Night	19% 8% 27% 31% 14% 1	781
	21st to end	Night	16% 6% 23% 37% 17% 1	600
May	1st to 10th	Night	12% 7% 24% 38% 17% 2	491
	11th to 20th	Night	14% 5% 20% 41% 19% 1	394
	21st to end	Night	14% 5% 20% 37% 22% 1	422
June	1st to 10th	Night	14% 5% 20% 41% 19%	380
	11th to 20th	Night	11% 2 31% 42% 12% 1	380
	21st to end	Night	7% 2 22% 52% 17%	380
July	1st to 10th	Night	4 2 13% 58% 23% 1	370
	11th to 20th	Night	5% 2 21% 51% 21%	368
	21st to end	Night	2 1 15% 52% 29% 1	448
August	1st to 10th	Night	3 1 8% 47% 37% 4	567
	11th to 20th	Night	4 1 8% 44% 40% 2	564
	21st to end	Night	6% 3 17% 45% 29% 2	747
September	1st to 10th	Night	5% 2 18% 44% 30% 1	760
	11th to 20th	Night	9% 3 14% 37% 32% 5%	760
	21st to end	Night	9% 4 18% 41% 25% 3	760
October	1st to 10th	Night	14% 2 24% 34% 24% 3	760
	11th to 20th	Night	17% 4 16% 36% 23% 4	760
	21st to end	Night	22% 7% 22% 28% 17% 3	836
November	1st to 10th	Night	23% 7% 21% 33% 16% 1	780
	11th to 20th	Night	30% 11% 19% 26% 14% 1	800
	21st to end	Night	24% 6% 20% 30% 19% 2	800
December	1st to 10th	Night	26% 7% 17% 30% 18% 3	800
	11th to 20th	Night	31% 11% 22% 23% 14% 1	800
	21st to end	Night	32% 13% 20% 24% 10% 1	880

Page generated at 2025-05-23 06:21:02. Version ac07

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