Rehoboth
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Rehoboth clear sky chart from 2005-11-06 to 2025-07-06.

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	2 4 2 5% 4 4 5% 4 5% 7% 58%	123558
	Night	2 4 2 5% 4 4 4 4 5% 7% 60%	124179
Transparency	Day	23% 6% 8% 18% 26% 19%	123325
	Night	22% 6% 8% 18% 27% 19%	123999
Seeing	Day	6% 12% 25% 28% 20% 8%	15356
	Night	4 7% 24% 38% 24% 3	25852

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	1 5% 2 6% 3 3 4 3 4 6% 61%	4098
	11th to 20th	Day	2 4 2 4 3 3 3 2 3 5% 69%	4100
	21st to end	Day	2 8% 3 7% 3 4 4 3 4 5% 57%	4510
February	1st to 10th	Day	1 6% 3 6% 4 4 4 3 5% 6% 59%	1800
	11th to 20th	Day	2 6% 2 5% 5% 4 4 4 5% 8% 53%	1790
	21st to end	Day	2 6% 2 6% 3 3 5% 4 6% 7% 56%	1770
March	1st to 10th	Day	1 6% 2 5% 4 4 4 3 5% 8% 59%	4954
	11th to 20th	Day	2 8% 4 8% 5% 5% 6% 4 7% 8% 43%	5000
	21st to end	Day	1 4 2 5% 5% 4 4 4 5% 7% 57%	5486
April	1st to 10th	Day	2 5% 2 5% 3 4 4 3 5% 6% 61%	2335
	11th to 20th	Day	2 4 2 5% 4 4 4 4 6% 6% 60%	2371
	21st to end	Day	2 4 2 4 4 3 3 3 5% 6% 64%	2400
May	1st to 10th	Day	2 3 2 6% 4 5% 5% 3 4 6% 60%	5704
	11th to 20th	Day	1 3 1 4 4 4 5% 4 5% 6% 63%	5841
	21st to end	Day	1 2 1 3 3 3 4 3 5% 5% 71%	6423
June	1st to 10th	Day	1 2 1 3 4 3 4 3 5% 7% 67%	2600
	11th to 20th	Day	2 2 1 2 2 2 3 3 3 5% 75%	2600
	21st to end	Day	2 3 1 5% 4 4 5% 4 6% 7% 59%	2600
July	1st to 10th	Day	3 2 2 5% 5% 4 5% 4 5% 6% 59%	4176
	11th to 20th	Day	2 4 2 6% 6% 8% 9% 7% 9% 10% 37%	4110
	21st to end	Day	3 3 2 7% 6% 7% 7% 6% 9% 10% 39%	4454
August	1st to 10th	Day	4 5% 3 9% 8% 9% 7% 7% 8% 10% 30%	4092
	11th to 20th	Day	3 4 2 6% 6% 6% 6% 5% 8% 10% 45%	3891
	21st to end	Day	4 4 2 8% 7% 7% 8% 6% 8% 9% 39%	4180
September	1st to 10th	Day	5% 5% 2 5% 4 6% 6% 4 6% 7% 49%	2280
	11th to 20th	Day	4 3 2 5% 4 4 4 3 5% 6% 59%	2168
	21st to end	Day	4 3 1 4 2 3 4 2 4 5% 66%	2056
October	1st to 10th	Day	2 2 1 3 3 3 3 4 4 6% 69%	3170
	11th to 20th	Day	3 3 1 4 4 4 3 3 5% 5% 64%	3150
	21st to end	Day	2 2 1 2 2 2 3 2 3 5% 77%	3438
November	1st to 10th	Day	1 3 1 4 3 2 2 3 4 7% 70%	1959
	11th to 20th	Day	1 2 1 4 2 3 3 3 5% 5% 71%	2000
	21st to end	Day	3 7% 1 3 3 3 3 2 4 6% 64%	1695
December	1st to 10th	Day	1 3 1 3 3 2 2 2 3 5% 73%	2620
	11th to 20th	Day	2 5% 2 5% 4 4 3 3 4 8% 59%	3227
	21st to end	Day	1 5% 2 5% 4 4 4 3 5% 6% 61%	4510
January	1st to 10th	Night	1 7% 3 7% 3 4 4 4 5% 6% 55%	5867
	11th to 20th	Night	2 4 1 4 3 3 3 2 4 5% 70%	5880
	21st to end	Night	2 9% 3 6% 4 3 4 4 5% 6% 54%	6468
February	1st to 10th	Night	1 5% 2 5% 3 3 3 2 4 7% 64%	2600
	11th to 20th	Night	3 7% 2 5% 4 4 4 3 5% 7% 57%	2496
	21st to end	Night	3 5% 2 5% 3 4 4 3 5% 5% 62%	1855
March	1st to 10th	Night	1 6% 2 4 3 3 3 3 5% 6% 63%	4940
	11th to 20th	Night	2 9% 4 7% 4 4 4 4 6% 7% 50%	5000
	21st to end	Night	1 3 2 4 3 3 4 4 5% 7% 63%	5489
April	1st to 10th	Night	1 4 2 4 4 3 3 2 5% 7% 65%	2065
	11th to 20th	Night	3 4 1 5% 3 3 3 3 5% 6% 64%	1977
	21st to end	Night	3 3 1 3 3 2 2 3 5% 6% 68%	2000
May	1st to 10th	Night	3 4 1 4 3 4 5% 4 6% 7% 59%	4259
	11th to 20th	Night	2 2 2 4 3 4 4 3 4 6% 65%	4074
	21st to end	Night	1 2 1 2 2 2 3 3 5% 7% 72%	4474
June	1st to 10th	Night	3 4 1 4 4 4 4 3 5% 6% 64%	1800
	11th to 20th	Night	2 2 1 3 2 3 3 2 4 4 75%	1800
	21st to end	Night	2 3 2 5% 5% 4 6% 4 6% 5% 59%	1800
July	1st to 10th	Night	3 3 2 5% 4 4 4 4 5% 6% 59%	2905
	11th to 20th	Night	2 4 2 8% 7% 8% 8% 8% 9% 10% 34%	2860
	21st to end	Night	3 5% 2 7% 6% 6% 6% 7% 10% 12% 36%	3109
August	1st to 10th	Night	2 5% 2 11% 10% 9% 9% 7% 11% 9% 26%	2847
	11th to 20th	Night	3 4 2 8% 5% 6% 7% 6% 9% 11% 39%	2934
	21st to end	Night	3 4 2 6% 6% 7% 7% 7% 10% 12% 37%	3487
September	1st to 10th	Night	4 5% 2 6% 6% 6% 6% 5% 7% 10% 44%	1900
	11th to 20th	Night	3 3 1 4 4 4 4 3 5% 6% 64%	2007
	21st to end	Night	3 2 1 4 3 4 3 3 4 5% 68%	2123
October	1st to 10th	Night	2 2 1 3 3 3 3 3 4 6% 71%	3800
	11th to 20th	Night	4 4 1 5% 3 3 4 3 5% 6% 63%	3778
	21st to end	Night	1 2 1 2 2 2 3 2 4 6% 74%	4120
November	1st to 10th	Night	2 3 1 3 2 3 3 3 4 5% 70%	2340
	11th to 20th	Night	2 2 1 2 2 3 2 2 4 5% 76%	2400
	21st to end	Night	3 5% 1 3 3 3 3 3 5% 6% 65%	2674
December	1st to 10th	Night	2 3 1 2 2 2 2 2 4 7% 71%	4570
	11th to 20th	Night	2 4 2 4 3 3 3 3 5% 8% 63%	5013
	21st to end	Night	2 5% 2 5% 3 3 3 3 4 6% 64%	6468

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	23% 4 8% 30% 31% 5%	4099
	11th to 20th	Day	19% 4 9% 22% 21% 25%	4100
	21st to end	Day	28% 5% 6% 15% 22% 23%	4510
February	1st to 10th	Day	26% 5% 9% 21% 27% 13%	1800
	11th to 20th	Day	29% 5% 6% 23% 24% 13%	1799
	21st to end	Day	27% 5% 7% 15% 28% 18%	1770
March	1st to 10th	Day	21% 5% 6% 16% 34% 19%	4954
	11th to 20th	Day	30% 9% 9% 18% 24% 10%	5000
	21st to end	Day	23% 6% 7% 29% 26% 8%	5486
April	1st to 10th	Day	22% 4 6% 19% 32% 16%	2335
	11th to 20th	Day	23% 5% 5% 16% 33% 19%	2374
	21st to end	Day	20% 5% 6% 18% 34% 17%	2400
May	1st to 10th	Day	22% 7% 6% 16% 31% 19%	5704
	11th to 20th	Day	17% 6% 8% 11% 34% 25%	5844
	21st to end	Day	13% 4 5% 9% 27% 42%	6424
June	1st to 10th	Day	16% 5% 6% 12% 31% 31%	2600
	11th to 20th	Day	12% 2 4 10% 23% 49%	2600
	21st to end	Day	22% 6% 7% 12% 22% 31%	2600
July	1st to 10th	Day	23% 7% 7% 8% 9% 45%	4112
	11th to 20th	Day	30% 13% 14% 22% 13% 7%	4041
	21st to end	Day	31% 13% 15% 22% 14% 5%	4314
August	1st to 10th	Day	39% 15% 18% 13% 7% 7%	4078
	11th to 20th	Day	29% 10% 15% 18% 16% 13%	3930
	21st to end	Day	34% 10% 16% 16% 18% 6%	4179
September	1st to 10th	Day	31% 7% 11% 16% 17% 17%	2280
	11th to 20th	Day	25% 5% 9% 14% 25% 22%	2168
	21st to end	Day	19% 5% 6% 15% 30% 25%	2056
October	1st to 10th	Day	16% 4 7% 12% 23% 38%	3170
	11th to 20th	Day	19% 4 6% 12% 40% 19%	3150
	21st to end	Day	11% 3 4 16% 37% 28%	3438
November	1st to 10th	Day	15% 3 7% 24% 35% 16%	1959
	11th to 20th	Day	15% 3 6% 21% 37% 18%	2000
	21st to end	Day	22% 4 7% 18% 32% 17%	1695
December	1st to 10th	Day	15% 3 7% 27% 32% 17%	2620
	11th to 20th	Day	25% 4 6% 25% 35% 5%	3226
	21st to end	Day	23% 4 9% 24% 26% 12%	4510
January	1st to 10th	Night	27% 5% 7% 26% 28% 7%	5867
	11th to 20th	Night	17% 4 8% 23% 27% 22%	5880
	21st to end	Night	28% 6% 7% 14% 25% 21%	6468
February	1st to 10th	Night	22% 4 10% 22% 28% 14%	2600
	11th to 20th	Night	27% 4 7% 23% 25% 14%	2497
	21st to end	Night	24% 4 6% 16% 34% 16%	1855
March	1st to 10th	Night	19% 5% 5% 19% 34% 17%	4940
	11th to 20th	Night	29% 7% 8% 19% 27% 11%	5000
	21st to end	Night	17% 6% 9% 30% 32% 6%	5489
April	1st to 10th	Night	20% 4 5% 25% 31% 16%	2065
	11th to 20th	Night	19% 4 6% 17% 31% 22%	1977
	21st to end	Night	17% 4 7% 18% 37% 18%	2000
May	1st to 10th	Night	19% 7% 10% 20% 30% 15%	4256
	11th to 20th	Night	16% 6% 7% 12% 35% 24%	4075
	21st to end	Night	10% 4 5% 9% 32% 40%	4474
June	1st to 10th	Night	19% 4 7% 11% 26% 34%	1800
	11th to 20th	Night	13% 2 4 9% 21% 51%	1800
	21st to end	Night	23% 6% 8% 13% 19% 30%	1800
July	1st to 10th	Night	24% 6% 9% 9% 9% 43%	2860
	11th to 20th	Night	34% 12% 15% 22% 7% 10%	2806
	21st to end	Night	31% 13% 21% 21% 11% 2	3011
August	1st to 10th	Night	44% 14% 17% 11% 8% 7%	2838
	11th to 20th	Night	32% 11% 19% 14% 11% 14%	2961
	21st to end	Night	33% 12% 16% 17% 14% 8%	3487
September	1st to 10th	Night	33% 9% 11% 15% 15% 18%	1900
	11th to 20th	Night	19% 6% 11% 15% 24% 25%	2007
	21st to end	Night	18% 6% 6% 15% 27% 28%	2123
October	1st to 10th	Night	14% 5% 6% 12% 26% 38%	3800
	11th to 20th	Night	20% 4 5% 15% 33% 22%	3778
	21st to end	Night	11% 3 5% 17% 38% 26%	4120
November	1st to 10th	Night	16% 3 5% 21% 36% 18%	2340
	11th to 20th	Night	13% 3 7% 18% 39% 19%	2400
	21st to end	Night	21% 4 6% 19% 32% 19%	2674
December	1st to 10th	Night	13% 4 7% 26% 30% 20%	4570
	11th to 20th	Night	20% 4 8% 18% 38% 12%	5013
	21st to end	Night	21% 5% 9% 23% 29% 13%	6468

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	8% 10% 36% 29% 15% 2	300
	11th to 20th	Day	8% 16% 28% 28% 15% 4	300
	21st to end	Day	5% 11% 32% 32% 15% 5%	330
February	1st to 10th	Day	4 18% 31% 30% 16% 2	300
	11th to 20th	Day	8% 21% 30% 30% 10% 1	300
	21st to end	Day	9% 24% 33% 23% 10% 1	369
March	1st to 10th	Day	8% 23% 33% 25% 10% 2	500
	11th to 20th	Day	12% 19% 31% 23% 13% 2	500
	21st to end	Day	11% 27% 33% 19% 7% 2	550
April	1st to 10th	Day	8% 16% 36% 24% 11% 4	500
	11th to 20th	Day	8% 23% 36% 22% 8% 2	492
	21st to end	Day	8% 21% 31% 25% 12% 2	500
May	1st to 10th	Day	6% 17% 38% 28% 10% 2	503
	11th to 20th	Day	7% 15% 30% 29% 14% 5%	528
	21st to end	Day	5% 17% 33% 28% 14% 4	573
June	1st to 10th	Day	3 10% 25% 38% 19% 5%	530
	11th to 20th	Day	3 9% 32% 30% 18% 8%	530
	21st to end	Day	2 6% 28% 35% 21% 7%	530
July	1st to 10th	Day	4 2 15% 35% 34% 10%	507
	11th to 20th	Day	5% 2 8% 26% 36% 24%	484
	21st to end	Day	8% 1 7% 22% 40% 21%	531
August	1st to 10th	Day	5% 3 11% 28% 35% 18%	487
	11th to 20th	Day	6% 3 13% 31% 31% 16%	477
	21st to end	Day	6% 2 11% 30% 34% 17%	539
September	1st to 10th	Day	7% 3 12% 32% 35% 11%	490
	11th to 20th	Day	5% 4 23% 38% 23% 7%	490
	21st to end	Day	6% 8% 19% 32% 26% 9%	456
October	1st to 10th	Day	6% 10% 24% 22% 23% 16%	300
	11th to 20th	Day	6% 11% 23% 27% 21% 11%	300
	21st to end	Day	6% 9% 21% 28% 27% 9%	330
November	1st to 10th	Day	6% 12% 30% 28% 20% 4	300
	11th to 20th	Day	3 11% 20% 32% 26% 7%	300
	21st to end	Day	8% 14% 28% 25% 18% 7%	300
December	1st to 10th	Day	6% 12% 26% 29% 23% 4	300
	11th to 20th	Day	4 14% 31% 28% 19% 5%	300
	21st to end	Day	12% 18% 32% 23% 12% 4	330
January	1st to 10th	Night	6% 7% 27% 37% 21% 3	800
	11th to 20th	Night	5% 8% 28% 37% 19% 3	800
	21st to end	Night	5% 8% 28% 38% 18% 4	880
February	1st to 10th	Night	4 9% 30% 38% 16% 2	800
	11th to 20th	Night	5% 10% 32% 38% 13% 1	784
	21st to end	Night	7% 12% 34% 38% 8% 1	660
March	1st to 10th	Night	4 16% 29% 36% 14% 1	800
	11th to 20th	Night	6% 10% 30% 36% 18% 1	800
	21st to end	Night	4 12% 32% 37% 15%	880
April	1st to 10th	Night	3 13% 38% 34% 11% 1	665
	11th to 20th	Night	5% 17% 34% 35% 10% 1	593
	21st to end	Night	4 10% 39% 36% 10% 2	600
May	1st to 10th	Night	4 7% 35% 42% 12% 1	600
	11th to 20th	Night	4 9% 28% 40% 18% 1	591
	21st to end	Night	4 8% 31% 38% 18% 1	650
June	1st to 10th	Night	3 3 23% 51% 19% 1	600
	11th to 20th	Night	2 3 28% 46% 19% 2	600
	21st to end	Night	2 3 20% 44% 30% 1	600
July	1st to 10th	Night	6% 1 11% 43% 37% 3	570
	11th to 20th	Night	4 1 6% 34% 48% 7%	552
	21st to end	Night	6% 1 6% 26% 52% 9%	624
August	1st to 10th	Night	3 1 6% 30% 50% 9%	567
	11th to 20th	Night	4 1 9% 36% 43% 7%	564
	21st to end	Night	6% 1 5% 34% 49% 5%	627
September	1st to 10th	Night	5% 2 12% 41% 36% 4	570
	11th to 20th	Night	3 1 11% 44% 36% 5%	677
	21st to end	Night	3 4 17% 38% 33% 5%	760
October	1st to 10th	Night	4 5% 22% 41% 26% 3	760
	11th to 20th	Night	3 4 20% 42% 27% 4	760
	21st to end	Night	3 4 23% 36% 28% 6%	836
November	1st to 10th	Night	4 5% 21% 43% 24% 4	780
	11th to 20th	Night	3 5% 22% 41% 25% 5%	800
	21st to end	Night	7% 10% 24% 31% 24% 4	899
December	1st to 10th	Night	7% 9% 22% 40% 20% 3	1000
	11th to 20th	Night	7% 9% 28% 36% 19% 1	923
	21st to end	Night	6% 11% 28% 39% 14% 2	880

Page generated at 2025-07-02 23:30:18. Version ac07

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