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 2026-09-29.

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	13% 7% 3 7% 5% 4 4 3 5% 6% 42%	158686
	Night	16% 8% 3 7% 5% 4 4 3 5% 6% 40%	150136
Transparency	Day	42% 6% 13% 21% 14% 4	153470
	Night	46% 6% 13% 20% 12% 3	146351
Seeing	Day	17% 10% 21% 27% 19% 6%	17112
	Night	19% 7% 20% 34% 19% 2	25986

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% 5% 3 3 3 7%	4722
	11th to 20th	Day	19% 8% 3 9% 7% 5% 5% 3 5% 6% 30%	4740
	21st to end	Day	19% 10% 4 10% 6% 5% 5% 4 5% 5% 27%	5843
February	1st to 10th	Day	24% 12% 4 12% 7% 6% 7% 3 5% 6% 15%	1890
	11th to 20th	Day	25% 13% 4 10% 6% 6% 5% 3 5% 4 18%	1845
	21st to end	Day	25% 15% 4 11% 6% 5% 5% 3 4 5% 18%	1625
March	1st to 10th	Day	16% 12% 4 11% 7% 7% 7% 5% 6% 7% 19%	4921
	11th to 20th	Day	23% 14% 4 8% 5% 5% 4 3 4 5% 25%	5110
	21st to end	Day	21% 12% 4 11% 8% 7% 6% 5% 6% 6% 15%	5681
April	1st to 10th	Day	21% 12% 4 12% 7% 5% 5% 4 6% 6% 19%	2520
	11th to 20th	Day	20% 11% 3 8% 5% 5% 6% 3 5% 5% 28%	2497
	21st to end	Day	18% 9% 3 7% 5% 6% 5% 4 6% 8% 28%	2730
May	1st to 10th	Day	10% 5% 2 6% 4 4 4 4 6% 8% 47%	7940
	11th to 20th	Day	10% 7% 2 7% 5% 5% 5% 4 6% 8% 41%	8160
	21st to end	Day	10% 6% 2 6% 5% 5% 5% 5% 7% 8% 42%	8992
June	1st to 10th	Day	17% 8% 3 8% 4 4 4 3 5% 6% 37%	2940
	11th to 20th	Day	13% 8% 3 6% 5% 5% 5% 4 6% 9% 35%	2940
	21st to end	Day	7% 5% 2 5% 4 4 5% 3 5% 6% 54%	2940
July	1st to 10th	Day	2 2 1 2 2 2 2 2 3 6% 77%	8219
	11th to 20th	Day	3 2 1 2 2 2 2 2 2 4 79%	8220
	21st to end	Day	3 2 1 2 2 2 2 2 3 5% 76%	8813
August	1st to 10th	Day	2 2 1 3 2 2 3 2 4 6% 74%	7547
	11th to 20th	Day	4 3 1 4 3 3 3 3 6% 8% 62%	7563
	21st to end	Day	5% 5% 2 4 3 3 4 3 5% 8% 58%	7998
September	1st to 10th	Day	6% 4 1 4 3 2 3 3 5% 7% 63%	2520
	11th to 20th	Day	9% 7% 2 7% 5% 4 5% 4 5% 7% 47%	2489
	21st to end	Day	13% 6% 2 6% 3 3 5% 4 5% 6% 47%	2207
October	1st to 10th	Day	12% 6% 3 6% 4 4 4 4 5% 6% 47%	3280
	11th to 20th	Day	15% 8% 4 10% 6% 5% 6% 4 6% 7% 30%	3261
	21st to end	Day	21% 11% 4 10% 5% 6% 5% 3 6% 8% 21%	3541
November	1st to 10th	Day	23% 15% 5% 11% 6% 4 7% 4 5% 5% 15%	1732
	11th to 20th	Day	28% 12% 6% 9% 7% 5% 5% 4 4 5% 16%	1680
	21st to end	Day	24% 12% 4 11% 5% 5% 6% 3 5% 5% 19%	1680
December	1st to 10th	Day	20% 9% 4 10% 7% 5% 4 3 4 6% 27%	2700
	11th to 20th	Day	27% 14% 5% 13% 7% 6% 5% 5% 5% 5% 8%	3108
	21st to end	Day	32% 16% 6% 17% 7% 4 4 2 3 3 6%	4092
January	1st to 10th	Night	31% 16% 6% 11% 6% 5% 4 3 4 4 11%	8172
	11th to 20th	Night	18% 10% 3 9% 6% 5% 5% 3 5% 5% 32%	8204
	21st to end	Night	21% 11% 4 9% 5% 4 4 3 4 5% 31%	8371
February	1st to 10th	Night	20% 14% 4 10% 6% 6% 5% 4 5% 6% 19%	2730
	11th to 20th	Night	24% 12% 4 8% 5% 4 5% 4 5% 5% 24%	2662
	21st to end	Night	24% 12% 4 9% 5% 5% 4 4 5% 6% 23%	2180
March	1st to 10th	Night	14% 10% 4 11% 8% 7% 7% 5% 7% 7% 21%	5188
	11th to 20th	Night	21% 11% 4 8% 5% 4 4 3 5% 6% 28%	5110
	21st to end	Night	21% 11% 4 11% 7% 6% 6% 4 6% 7% 17%	5535
April	1st to 10th	Night	21% 11% 4 9% 6% 5% 4 3 5% 6% 27%	2100
	11th to 20th	Night	17% 9% 3 7% 5% 4 4 3 6% 7% 35%	2068
	21st to end	Night	15% 7% 3 8% 5% 4 4 4 5% 7% 36%	1890
May	1st to 10th	Night	11% 6% 2 5% 3 3 3 3 5% 7% 52%	4988
	11th to 20th	Night	10% 7% 3 6% 4 4 4 3 5% 7% 47%	4700
	21st to end	Night	8% 6% 2 6% 4 4 4 4 7% 9% 46%	5181
June	1st to 10th	Night	15% 6% 2 6% 5% 4 4 3 5% 6% 45%	1680
	11th to 20th	Night	11% 5% 2 6% 4 4 3 3 5% 7% 50%	1680
	21st to end	Night	6% 5% 2 5% 3 2 3 3 4 5% 63%	1680
July	1st to 10th	Night	1 1 1 1 1 1 2 4 5% 81%	4740
	11th to 20th	Night	2 2 1 2 2 2 2 1 2 3 82%	4740
	21st to end	Night	2 2 1 3 1 1 2 2 3 4 79%	5265
August	1st to 10th	Night	2 2 1 3 2 2 3 2 4 5% 75%	5275
	11th to 20th	Night	6% 4 1 3 2 3 3 2 4 7% 64%	5292
	21st to end	Night	5% 3 1 4 2 2 3 2 4 6% 67%	6236
September	1st to 10th	Night	5% 3 1 4 2 3 3 3 4 5% 67%	2100
	11th to 20th	Night	8% 5% 2 5% 4 4 4 3 5% 6% 54%	2127
	21st to end	Night	9% 4 2 5% 3 3 4 2 6% 7% 55%	2370
October	1st to 10th	Night	9% 5% 2 5% 4 4 4 4 4 8% 52%	3920
	11th to 20th	Night	13% 6% 3 7% 5% 5% 5% 4 6% 8% 37%	3897
	21st to end	Night	21% 10% 3 8% 5% 5% 5% 4 5% 6% 28%	4269
November	1st to 10th	Night	22% 9% 4 9% 6% 5% 5% 4 5% 7% 24%	2784
	11th to 20th	Night	29% 11% 3 9% 6% 5% 5% 4 5% 5% 20%	2940
	21st to end	Night	21% 9% 4 11% 6% 5% 5% 3 4 6% 26%	2940
December	1st to 10th	Night	17% 9% 3 7% 6% 5% 5% 4 6% 7% 31%	4700
	11th to 20th	Night	31% 14% 5% 12% 6% 5% 4 3 4 4 12%	5316
	21st to end	Night	28% 13% 5% 13% 7% 6% 4 3 4 5% 12%	7106

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	82% 5% 5% 5% 2	4723
	11th to 20th	Day	53% 7% 7% 13% 14% 6%	4740
	21st to end	Day	58% 6% 6% 12% 15% 2	5843
February	1st to 10th	Day	69% 8% 8% 10% 4	1890
	11th to 20th	Day	69% 8% 8% 9% 4 2	1854
	21st to end	Day	69% 6% 8% 9% 6% 1	1625
March	1st to 10th	Day	61% 7% 15% 12% 4	4921
	11th to 20th	Day	61% 7% 7% 18% 8%	5110
	21st to end	Day	67% 10% 12% 7% 3	5681
April	1st to 10th	Day	65% 7% 12% 13% 3	2520
	11th to 20th	Day	57% 7% 11% 14% 8% 2	2500
	21st to end	Day	54% 8% 14% 15% 8% 1	2730
May	1st to 10th	Day	35% 6% 12% 31% 15%	7940
	11th to 20th	Day	38% 7% 19% 26% 8% 1	8163
	21st to end	Day	37% 9% 26% 23% 6%	8994
June	1st to 10th	Day	48% 7% 17% 21% 7% 1	2940
	11th to 20th	Day	44% 8% 20% 19% 8% 1	2940
	21st to end	Day	30% 6% 18% 29% 13% 4	2940
July	1st to 10th	Day	11% 3 14% 35% 19% 17%	8151
	11th to 20th	Day	12% 2 7% 19% 43% 17%	8145
	21st to end	Day	13% 3 15% 38% 27% 4	8615
August	1st to 10th	Day	12% 2 9% 28% 31% 17%	5976
	11th to 20th	Day	21% 5% 19% 37% 15% 3	5962
	21st to end	Day	23% 5% 16% 33% 19% 5%	6277
September	1st to 10th	Day	22% 5% 14% 29% 19% 11%	2520
	11th to 20th	Day	36% 8% 13% 22% 16% 5%	2489
	21st to end	Day	37% 6% 15% 22% 15% 5%	2207
October	1st to 10th	Day	38% 5% 9% 22% 23% 3	3280
	11th to 20th	Day	51% 8% 14% 15% 11% 1	3261
	21st to end	Day	60% 6% 8% 16% 10% 1	3541
November	1st to 10th	Day	69% 8% 9% 11% 3	1732
	11th to 20th	Day	70% 6% 10% 8% 5% 1	1680
	21st to end	Day	65% 8% 8% 8% 10% 1	1680
December	1st to 10th	Day	58% 5% 10% 16% 11%	2700
	11th to 20th	Day	75% 9% 8% 7% 1	3108
	21st to end	Day	82% 6% 6% 4 1	4092
January	1st to 10th	Night	77% 6% 7% 6% 3	8172
	11th to 20th	Night	52% 5% 7% 15% 14% 5%	8204
	21st to end	Night	56% 5% 6% 13% 17% 3	8371
February	1st to 10th	Night	65% 8% 10% 12% 5%	2730
	11th to 20th	Night	61% 7% 12% 12% 7% 2	2664
	21st to end	Night	62% 6% 12% 12% 6% 2	2180
March	1st to 10th	Night	58% 8% 13% 14% 5%	5188
	11th to 20th	Night	56% 7% 11% 18% 8% 1	5110
	21st to end	Night	65% 10% 14% 10% 2	5535
April	1st to 10th	Night	58% 8% 16% 13% 5%	2100
	11th to 20th	Night	49% 7% 19% 16% 7% 3	2068
	21st to end	Night	48% 7% 17% 19% 7% 2	1890
May	1st to 10th	Night	31% 6% 14% 36% 13% 1	4986
	11th to 20th	Night	36% 7% 18% 29% 8% 1	4700
	21st to end	Night	32% 9% 31% 24% 4	5182
June	1st to 10th	Night	41% 6% 17% 28% 7% 1	1680
	11th to 20th	Night	33% 7% 22% 28% 9% 1	1680
	21st to end	Night	24% 5% 20% 33% 14% 3	1680
July	1st to 10th	Night	8% 3 14% 34% 23% 17%	4700
	11th to 20th	Night	11% 2 9% 18% 40% 20%	4692
	21st to end	Night	12% 2 18% 37% 27% 4	5151
August	1st to 10th	Night	8% 2 7% 30% 36% 15%	4169
	11th to 20th	Night	19% 4 20% 41% 13% 3	4169
	21st to end	Night	19% 4 16% 38% 18% 5%	4881
September	1st to 10th	Night	20% 5% 14% 30% 20% 11%	2100
	11th to 20th	Night	29% 7% 16% 24% 16% 8%	2127
	21st to end	Night	29% 6% 17% 24% 17% 7%	2370
October	1st to 10th	Night	31% 6% 10% 30% 21% 2	3920
	11th to 20th	Night	42% 8% 20% 18% 10% 2	3897
	21st to end	Night	55% 7% 11% 16% 10% 1	4269
November	1st to 10th	Night	58% 9% 12% 14% 6%	2784
	11th to 20th	Night	66% 7% 10% 9% 7% 2	2940
	21st to end	Night	59% 7% 10% 10% 12% 2	2940
December	1st to 10th	Night	51% 6% 11% 19% 13% 1	4700
	11th to 20th	Night	76% 6% 7% 7% 3	5316
	21st to end	Night	73% 10% 9% 6% 2	7106

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% 15% 20% 18% 6% 2	220
	11th to 20th	Day	25% 12% 21% 25% 12% 4	220
	21st to end	Day	23% 14% 22% 22% 13% 5%	473
February	1st to 10th	Day	30% 14% 20% 21% 13% 3	430
	11th to 20th	Day	29% 13% 29% 16% 10% 2	425
	21st to end	Day	27% 19% 21% 21% 10% 1	391
March	1st to 10th	Day	27% 13% 29% 19% 10% 1	540
	11th to 20th	Day	27% 15% 23% 21% 11% 3	540
	21st to end	Day	26% 16% 25% 21% 10% 2	594
April	1st to 10th	Day	25% 16% 20% 21% 13% 5%	540
	11th to 20th	Day	22% 16% 24% 22% 11% 5%	532
	21st to end	Day	19% 14% 27% 20% 16% 4	540
May	1st to 10th	Day	15% 13% 23% 28% 15% 6%	543
	11th to 20th	Day	19% 13% 21% 24% 16% 5%	568
	21st to end	Day	11% 10% 22% 29% 21% 7%	617
June	1st to 10th	Day	15% 11% 23% 27% 21% 4	570
	11th to 20th	Day	13% 10% 25% 36% 14% 2	570
	21st to end	Day	7% 6% 19% 34% 28% 6%	570
July	1st to 10th	Day	5% 3 17% 39% 27% 9%	566
	11th to 20th	Day	3 4 23% 37% 26% 8%	564
	21st to end	Day	3 3 15% 34% 33% 11%	619
August	1st to 10th	Day	3 2 15% 33% 34% 12%	567
	11th to 20th	Day	3 3 10% 36% 35% 13%	557
	21st to end	Day	4 5% 18% 36% 29% 8%	627
September	1st to 10th	Day	8% 4 21% 30% 28% 10%	570
	11th to 20th	Day	10% 7% 20% 28% 26% 9%	570
	21st to end	Day	13% 9% 21% 32% 21% 5%	563
October	1st to 10th	Day	15% 9% 22% 27% 21% 7%	530
	11th to 20th	Day	18% 11% 18% 26% 22% 5%	530
	21st to end	Day	24% 11% 25% 22% 13% 4	578
November	1st to 10th	Day	25% 13% 29% 19% 11% 3	266
	11th to 20th	Day	23% 16% 25% 18% 15% 2	220
	21st to end	Day	24% 18% 17% 20% 19% 2	220
December	1st to 10th	Day	32% 12% 12% 25% 15% 4	220
	11th to 20th	Day	32% 15% 24% 20% 6% 2	220
	21st to end	Day	32% 17% 19% 22% 9% 2	242
January	1st to 10th	Night	34% 10% 22% 22% 10% 2	840
	11th to 20th	Night	28% 10% 19% 23% 18% 2	840
	21st to end	Night	25% 7% 17% 33% 15% 3	924
February	1st to 10th	Night	22% 10% 22% 29% 16% 1	840
	11th to 20th	Night	26% 11% 22% 26% 14%	824
	21st to end	Night	27% 12% 21% 28% 12%	692
March	1st to 10th	Night	22% 10% 23% 32% 13% 1	840
	11th to 20th	Night	22% 11% 20% 32% 14% 1	840
	21st to end	Night	23% 11% 25% 28% 12% 1	924
April	1st to 10th	Night	24% 8% 20% 30% 17% 1	840
	11th to 20th	Night	19% 8% 26% 31% 14% 1	820
	21st to end	Night	16% 6% 23% 38% 16%	630
May	1st to 10th	Night	12% 6% 24% 38% 19% 2	516
	11th to 20th	Night	14% 5% 21% 41% 19% 1	414
	21st to end	Night	14% 5% 20% 38% 22% 1	455
June	1st to 10th	Night	15% 5% 21% 41% 19%	420
	11th to 20th	Night	10% 2 31% 43% 13% 1	420
	21st to end	Night	8% 2 20% 52% 18%	420
July	1st to 10th	Night	3 2 12% 57% 25%	410
	11th to 20th	Night	4 2 21% 52% 20%	408
	21st to end	Night	2 1 15% 51% 30% 2	496
August	1st to 10th	Night	3 1 9% 47% 36% 4	627
	11th to 20th	Night	4 1 8% 44% 40% 3	624
	21st to end	Night	5% 3 16% 47% 28% 1	826
September	1st to 10th	Night	6% 2 18% 44% 30% 1	840
	11th to 20th	Night	8% 3 14% 38% 31% 5%	840
	21st to end	Night	9% 4 17% 42% 25% 3	832
October	1st to 10th	Night	14% 3 24% 34% 24% 3	800
	11th to 20th	Night	17% 5% 15% 36% 23% 4	800
	21st to end	Night	22% 7% 23% 28% 16% 3	880
November	1st to 10th	Night	24% 8% 20% 32% 15%	820
	11th to 20th	Night	30% 10% 20% 25% 13% 1	840
	21st to end	Night	24% 6% 20% 30% 18% 2	840
December	1st to 10th	Night	27% 7% 17% 30% 17% 2	840
	11th to 20th	Night	31% 10% 21% 22% 14% 1	840
	21st to end	Night	32% 13% 21% 24% 10% 1	924

Page generated at 2026-09-26 01:18:42. Version ac07

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