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 2024-11-02.

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	15% 8% 3 8% 5% 4 4 3 5% 6% 39%	101530
	Night	17% 9% 3 7% 5% 4 4 3 5% 5% 38%	97608
Transparency	Day	46% 7% 12% 18% 13% 5%	101275
	Night	47% 7% 13% 18% 11% 4	97452
Seeing	Day	17% 10% 22% 27% 19% 5%	14714
	Night	19% 7% 20% 34% 19% 2	23628

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	28% 17% 7% 16% 7% 5% 4 3 3 3 7%	2539
	11th to 20th	Day	35% 13% 5% 11% 6% 4 4 3 3 4 13%	2540
	21st to end	Day	26% 14% 6% 11% 7% 5% 5% 4 4 5% 13%	3146
February	1st to 10th	Day	25% 12% 4 11% 7% 6% 6% 3 5% 5% 15%	1710
	11th to 20th	Day	25% 13% 4 11% 6% 6% 5% 3 5% 4 18%	1665
	21st to end	Day	24% 16% 4 11% 6% 5% 5% 3 3 4 18%	1475
March	1st to 10th	Day	17% 13% 4 11% 7% 7% 6% 4 6% 6% 18%	3344
	11th to 20th	Day	16% 10% 3 7% 5% 5% 4 3 4 6% 36%	3490
	21st to end	Day	21% 13% 4 10% 8% 7% 6% 4 5% 5% 18%	3872
April	1st to 10th	Day	21% 12% 4 12% 7% 6% 5% 4 5% 5% 19%	2280
	11th to 20th	Day	21% 11% 3 8% 5% 5% 6% 3 5% 5% 26%	2256
	21st to end	Day	19% 10% 3 7% 6% 6% 5% 4 6% 8% 26%	2470
May	1st to 10th	Day	18% 8% 3 8% 5% 5% 4 4 5% 6% 34%	4282
	11th to 20th	Day	11% 5% 1 5% 3 3 3 3 5% 7% 54%	4377
	21st to end	Day	15% 7% 3 8% 7% 6% 6% 5% 7% 7% 30%	4813
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	15% 7% 3 7% 4 4 5% 4 5% 6% 40%	1900
	11th to 20th	Day	16% 9% 4 10% 6% 5% 4 4 5% 6% 31%	1900
	21st to end	Day	20% 13% 4 9% 5% 6% 3 3 4 6% 27%	2085
November	1st to 10th	Day	24% 15% 5% 11% 6% 4 7% 3 5% 5% 15%	1573
	11th to 20th	Day	27% 11% 5% 9% 6% 5% 5% 4 4 5% 18%	1520
	21st to end	Day	24% 12% 4 11% 5% 5% 6% 3 5% 5% 20%	1520
December	1st to 10th	Day	24% 13% 5% 10% 7% 4 4 3 4 5% 21%	1520
	11th to 20th	Day	24% 11% 5% 12% 7% 5% 5% 6% 6% 7% 10%	1928
	21st to end	Day	28% 16% 7% 19% 7% 5% 5% 2 4 3 6%	2794
January	1st to 10th	Night	29% 18% 7% 10% 6% 4 5% 3 3 4 11%	4406
	11th to 20th	Night	32% 16% 5% 9% 5% 4 3 2 4 4 16%	4417
	21st to end	Night	31% 14% 4 10% 6% 5% 4 3 3 5% 15%	4521
February	1st to 10th	Night	21% 15% 4 10% 6% 5% 5% 4 6% 6% 19%	2470
	11th to 20th	Night	23% 12% 4 8% 5% 4 5% 4 5% 5% 25%	2402
	21st to end	Night	23% 12% 4 9% 5% 5% 4 4 5% 6% 23%	1979
March	1st to 10th	Night	13% 12% 5% 12% 8% 7% 6% 4 6% 7% 22%	3526
	11th to 20th	Night	14% 8% 2 6% 5% 4 4 3 6% 7% 40%	3490
	21st to end	Night	19% 11% 4 12% 7% 6% 6% 4 6% 6% 20%	3780
April	1st to 10th	Night	22% 11% 4 9% 5% 5% 4 3 5% 6% 26%	1900
	11th to 20th	Night	17% 9% 3 7% 5% 4 3 3 5% 7% 35%	1870
	21st to end	Night	16% 8% 3 8% 6% 4 4 5% 5% 7% 34%	1710
May	1st to 10th	Night	17% 9% 3 7% 4 3 4 3 4 5% 42%	2679
	11th to 20th	Night	8% 5% 2 4 3 3 3 2 4 5% 60%	2516
	21st to end	Night	10% 6% 3 7% 5% 4 4 5% 7% 9% 42%	2762
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	12% 6% 2 6% 4 4 3 3 4 6% 49%	2280
	11th to 20th	Night	15% 6% 3 7% 4 3 4 4 6% 7% 41%	2280
	21st to end	Night	19% 9% 3 7% 5% 4 4 3 5% 5% 36%	2513
November	1st to 10th	Night	23% 8% 4 8% 6% 5% 5% 4 5% 7% 26%	2525
	11th to 20th	Night	27% 10% 3 9% 6% 5% 5% 4 5% 5% 22%	2660
	21st to end	Night	21% 8% 4 10% 6% 5% 5% 3 4 6% 28%	2660
December	1st to 10th	Night	24% 11% 4 8% 6% 5% 5% 3 5% 5% 25%	2660
	11th to 20th	Night	24% 11% 4 11% 7% 6% 5% 3 5% 6% 17%	3276
	21st to end	Night	24% 13% 5% 14% 7% 6% 4 3 5% 5% 13%	4862

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	83% 6% 6% 3 1 1	2539
	11th to 20th	Day	76% 5% 6% 8% 3 1	2540
	21st to end	Day	72% 9% 7% 7% 5%	3146
February	1st to 10th	Day	70% 8% 8% 10% 4	1710
	11th to 20th	Day	68% 9% 8% 9% 4 1	1674
	21st to end	Day	69% 7% 8% 9% 5% 1	1475
March	1st to 10th	Day	63% 8% 16% 10% 3	3344
	11th to 20th	Day	49% 8% 9% 24% 11%	3490
	21st to end	Day	65% 11% 12% 7% 4	3872
April	1st to 10th	Day	66% 7% 11% 12% 3	2280
	11th to 20th	Day	59% 7% 11% 13% 7% 2	2259
	21st to end	Day	56% 9% 14% 13% 7% 1	2470
May	1st to 10th	Day	48% 9% 13% 18% 12%	4282
	11th to 20th	Day	30% 6% 17% 31% 14% 1	4380
	21st to end	Day	47% 14% 23% 14% 2	4814
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	44% 7% 11% 19% 17% 4	1900
	11th to 20th	Day	53% 8% 12% 14% 12% 1	1900
	21st to end	Day	59% 7% 8% 13% 13% 1	2085
November	1st to 10th	Day	70% 8% 8% 10% 4	1573
	11th to 20th	Day	68% 6% 10% 8% 5% 1	1520
	21st to end	Day	64% 8% 8% 8% 11% 1	1520
December	1st to 10th	Day	66% 6% 8% 11% 9% 1	1520
	11th to 20th	Day	70% 11% 9% 8% 2	1928
	21st to end	Day	81% 7% 6% 3 2	2794
January	1st to 10th	Night	77% 7% 7% 4 3 1	4406
	11th to 20th	Night	73% 5% 7% 10% 4 1	4417
	21st to end	Night	72% 6% 8% 8% 6% 1	4521
February	1st to 10th	Night	65% 8% 10% 12% 4	2470
	11th to 20th	Night	60% 7% 13% 12% 6% 2	2404
	21st to end	Night	62% 7% 12% 11% 6% 2	1979
March	1st to 10th	Night	60% 8% 13% 14% 4	3526
	11th to 20th	Night	41% 9% 14% 24% 11% 1	3490
	21st to end	Night	63% 10% 13% 12% 1	3780
April	1st to 10th	Night	59% 8% 16% 11% 6%	1900
	11th to 20th	Night	49% 7% 19% 15% 6% 3	1870
	21st to end	Night	50% 7% 17% 18% 7% 2	1710
May	1st to 10th	Night	43% 8% 16% 22% 10% 1	2679
	11th to 20th	Night	27% 5% 16% 35% 15% 3	2516
	21st to end	Night	35% 13% 34% 15% 3	2762
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	36% 6% 11% 26% 18% 4	2280
	11th to 20th	Night	41% 8% 14% 19% 14% 3	2280
	21st to end	Night	48% 7% 12% 15% 16% 2	2513
November	1st to 10th	Night	58% 9% 12% 15% 6%	2525
	11th to 20th	Night	64% 7% 10% 9% 7% 2	2660
	21st to end	Night	57% 7% 10% 11% 13% 2	2660
December	1st to 10th	Night	60% 7% 11% 12% 10% 1	2660
	11th to 20th	Night	67% 9% 10% 10% 4	3276
	21st to end	Night	69% 10% 10% 7% 2	4862

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	38% 14% 21% 17% 7% 3	180
	11th to 20th	Day	31% 14% 22% 19% 11% 3	180
	21st to end	Day	25% 14% 22% 22% 13% 5%	407
February	1st to 10th	Day	30% 14% 19% 21% 12% 4	370
	11th to 20th	Day	29% 13% 29% 17% 10% 2	365
	21st to end	Day	26% 21% 22% 19% 10% 1	337
March	1st to 10th	Day	27% 13% 29% 19% 10% 1	460
	11th to 20th	Day	25% 14% 22% 23% 13% 3	460
	21st to end	Day	25% 17% 25% 21% 9% 2	506
April	1st to 10th	Day	25% 17% 22% 20% 12% 4	460
	11th to 20th	Day	24% 17% 25% 20% 10% 4	452
	21st to end	Day	20% 16% 29% 19% 14% 2	460
May	1st to 10th	Day	17% 14% 24% 26% 14% 5%	463
	11th to 20th	Day	20% 11% 21% 24% 18% 6%	488
	21st to end	Day	11% 10% 22% 29% 21% 7%	529
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% 24% 22% 13% 4	534
November	1st to 10th	Day	24% 14% 29% 19% 11% 2	221
	11th to 20th	Day	21% 15% 27% 17% 18% 3	180
	21st to end	Day	25% 17% 18% 17% 19% 3	180
December	1st to 10th	Day	29% 14% 14% 25% 14% 4	180
	11th to 20th	Day	33% 13% 23% 22% 6% 3	180
	21st to end	Day	30% 17% 18% 23% 10% 2	198
January	1st to 10th	Night	34% 10% 21% 22% 11% 2	760
	11th to 20th	Night	30% 11% 17% 22% 17% 2	760
	21st to end	Night	26% 7% 17% 32% 15% 3	836
February	1st to 10th	Night	23% 10% 21% 28% 16% 1	760
	11th to 20th	Night	25% 10% 21% 27% 15%	744
	21st to end	Night	26% 13% 22% 28% 12%	628
March	1st to 10th	Night	22% 10% 23% 31% 14% 1	760
	11th to 20th	Night	20% 11% 19% 33% 15% 1	760
	21st to end	Night	23% 11% 24% 28% 13% 1	836
April	1st to 10th	Night	25% 9% 21% 28% 17% 1	760
	11th to 20th	Night	19% 8% 26% 30% 15% 1	742
	21st to end	Night	17% 6% 24% 36% 16% 1	570
May	1st to 10th	Night	12% 7% 25% 38% 16% 2	467
	11th to 20th	Night	13% 4 20% 41% 20% 1	374
	21st to end	Night	14% 6% 20% 38% 21% 1	411
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	24% 7% 21% 32% 16% 1	744
	11th to 20th	Night	28% 11% 20% 26% 14% 1	760
	21st to end	Night	23% 6% 19% 31% 18% 2	760
December	1st to 10th	Night	27% 7% 18% 30% 16% 3	760
	11th to 20th	Night	30% 10% 22% 23% 14% 1	760
	21st to end	Night	31% 13% 20% 25% 10% 1	836

Page generated at 2024-10-29 22:22:57. Version ac07

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