Rehoboth Beach
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Rehoboth Beach clear sky chart from 2005-11-06 to 2024-11-08.

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% 6% 2 6% 4 4 5% 4 6% 8% 42%	101206
	Night	15% 7% 3 6% 4 4 4 3 5% 7% 42%	97840
Transparency	Day	38% 7% 13% 24% 15% 3	104810
	Night	40% 6% 12% 24% 16% 3	102375
Seeing	Day	15% 7% 22% 30% 20% 5%	15158
	Night	17% 8% 26% 31% 16% 2	24482

By Month

Percentage Cloud Cover SE (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	15% 7% 2 5% 3 3 3 4 4 6% 48%	2517
	11th to 20th	Day	15% 8% 3 7% 4 4 4 3 4 6% 41%	2680
	21st to end	Day	15% 9% 3 8% 5% 5% 3 4 5% 6% 37%	3124
February	1st to 10th	Day	14% 8% 2 7% 5% 4 5% 4 7% 8% 38%	1710
	11th to 20th	Day	17% 7% 2 5% 3 3 4 4 5% 7% 43%	1846
	21st to end	Day	17% 10% 3 6% 4 4 4 3 5% 6% 38%	1570
March	1st to 10th	Day	23% 6% 3 5% 3 3 4 3 4 6% 39%	3119
	11th to 20th	Day	10% 4 2 4 3 3 4 4 7% 8% 52%	3480
	21st to end	Day	18% 10% 2 6% 3 3 3 3 5% 5% 41%	4052
April	1st to 10th	Day	14% 7% 2 6% 4 3 3 3 6% 7% 44%	2280
	11th to 20th	Day	11% 6% 2 6% 3 4 3 3 6% 7% 49%	2254
	21st to end	Day	14% 6% 3 5% 4 4 4 3 6% 8% 44%	2280
May	1st to 10th	Day	18% 10% 4 8% 6% 4 5% 4 7% 7% 27%	3907
	11th to 20th	Day	22% 9% 3 6% 4 4 4 3 5% 6% 32%	4352
	21st to end	Day	9% 5% 2 6% 4 5% 5% 4 6% 11% 43%	4823
June	1st to 10th	Day	11% 5% 2 5% 4 4 5% 5% 7% 10% 42%	2660
	11th to 20th	Day	10% 5% 2 5% 4 5% 5% 4 8% 9% 43%	2660
	21st to end	Day	7% 5% 2 4 5% 4 5% 5% 7% 11% 45%	2660
July	1st to 10th	Day	6% 5% 2 7% 4 5% 6% 5% 8% 10% 42%	4440
	11th to 20th	Day	9% 5% 3 6% 4 5% 6% 5% 8% 11% 37%	4440
	21st to end	Day	9% 5% 3 7% 6% 6% 7% 6% 8% 11% 32%	4634
August	1st to 10th	Day	13% 6% 2 6% 4 4 6% 5% 8% 11% 34%	4024
	11th to 20th	Day	8% 6% 3 8% 4 6% 7% 4 6% 8% 41%	3730
	21st to end	Day	7% 4 3 5% 5% 5% 5% 4 6% 9% 48%	4180
September	1st to 10th	Day	13% 5% 2 4 3 4 5% 4 7% 7% 46%	2280
	11th to 20th	Day	11% 6% 3 6% 4 3 4 3 5% 7% 48%	2242
	21st to end	Day	18% 7% 3 7% 3 4 4 4 5% 7% 39%	2090
October	1st to 10th	Day	15% 5% 2 5% 3 3 4 3 5% 7% 46%	1920
	11th to 20th	Day	16% 6% 2 5% 3 3 3 2 5% 6% 50%	1900
	21st to end	Day	14% 6% 2 5% 4 3 4 3 5% 7% 47%	2048
November	1st to 10th	Day	14% 5% 2 4 3 3 3 3 5% 7% 50%	1734
	11th to 20th	Day	13% 7% 3 5% 5% 3 4 3 4 7% 45%	1710
	21st to end	Day	14% 4 2 5% 4 4 4 3 4 8% 48%	1658
December	1st to 10th	Day	15% 7% 2 6% 4 3 5% 4 6% 9% 38%	1520
	11th to 20th	Day	15% 9% 3 7% 3 3 3 3 4 5% 46%	1910
	21st to end	Day	15% 7% 3 5% 4 4 4 4 5% 7% 43%	2772
January	1st to 10th	Night	14% 7% 2 5% 3 4 4 4 5% 8% 43%	4429
	11th to 20th	Night	17% 8% 3 6% 4 3 3 3 4 5% 44%	4277
	21st to end	Night	19% 9% 3 6% 4 4 4 3 4 6% 37%	4532
February	1st to 10th	Night	17% 7% 2 7% 3 3 3 3 5% 7% 41%	2470
	11th to 20th	Night	18% 7% 3 6% 4 3 4 3 5% 6% 41%	2218
	21st to end	Night	19% 6% 3 6% 3 3 3 3 4 7% 44%	1884
March	1st to 10th	Night	21% 10% 3 6% 4 4 3 2 4 6% 36%	3716
	11th to 20th	Night	14% 6% 1 5% 4 3 4 3 6% 8% 46%	3480
	21st to end	Night	18% 10% 3 6% 3 3 3 3 4 4 42%	3578
April	1st to 10th	Night	17% 7% 2 6% 5% 4 3 3 5% 6% 41%	1900
	11th to 20th	Night	11% 7% 2 7% 4 4 4 3 4 7% 46%	1875
	21st to end	Night	17% 6% 2 6% 5% 4 5% 4 5% 7% 41%	1900
May	1st to 10th	Night	16% 11% 4 10% 5% 4 5% 3 5% 6% 31%	2984
	11th to 20th	Night	25% 9% 3 7% 4 4 4 4 5% 5% 29%	2569
	21st to end	Night	11% 8% 3 7% 5% 5% 6% 3 5% 8% 39%	2732
June	1st to 10th	Night	13% 7% 2 5% 5% 5% 4 4 6% 8% 41%	1520
	11th to 20th	Night	11% 5% 2 5% 4 6% 5% 6% 6% 10% 41%	1520
	21st to end	Night	8% 6% 1 6% 5% 5% 5% 5% 7% 12% 40%	1520
July	1st to 10th	Night	7% 6% 3 7% 5% 6% 6% 4 8% 10% 38%	2520
	11th to 20th	Night	9% 6% 2 7% 6% 4 6% 4 7% 10% 40%	2520
	21st to end	Night	11% 8% 4 7% 7% 5% 7% 4 7% 9% 31%	2916
August	1st to 10th	Night	15% 8% 3 8% 5% 5% 4 4 6% 9% 33%	2875
	11th to 20th	Night	10% 5% 2 7% 4 4 6% 4 6% 9% 42%	3097
	21st to end	Night	7% 5% 2 6% 4 3 4 3 6% 9% 52%	3476
September	1st to 10th	Night	14% 7% 2 6% 4 4 4 3 5% 8% 44%	1900
	11th to 20th	Night	10% 5% 2 5% 4 4 4 4 6% 9% 47%	1938
	21st to end	Night	20% 7% 2 6% 4 4 5% 3 4 7% 36%	2090
October	1st to 10th	Night	18% 5% 2 6% 4 3 4 3 4 6% 45%	2256
	11th to 20th	Night	16% 4 2 4 4 3 3 3 4 6% 51%	2280
	21st to end	Night	14% 7% 2 5% 3 3 4 3 5% 6% 47%	2547
November	1st to 10th	Night	13% 5% 2 6% 4 3 4 3 4 5% 50%	2505
	11th to 20th	Night	15% 7% 3 5% 3 4 3 3 4 6% 47%	2470
	21st to end	Night	12% 5% 2 5% 4 4 3 3 6% 7% 49%	2517
December	1st to 10th	Night	17% 8% 3 7% 4 3 4 3 4 7% 39%	2660
	11th to 20th	Night	18% 6% 2 6% 4 4 4 3 4 6% 43%	3285
	21st to end	Night	14% 8% 2 7% 4 3 4 4 5% 7% 41%	4884

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	36% 4 9% 33% 15% 3	2518
	11th to 20th	Day	44% 4 11% 20% 17% 4	2680
	21st to end	Day	47% 6% 12% 22% 12% 2	3124
February	1st to 10th	Day	42% 6% 14% 24% 12% 2	1710
	11th to 20th	Day	40% 5% 10% 25% 16% 3	1855
	21st to end	Day	46% 5% 11% 19% 14% 5%	1570
March	1st to 10th	Day	46% 5% 8% 24% 13% 4	3119
	11th to 20th	Day	27% 6% 10% 32% 20% 4	3480
	21st to end	Day	45% 5% 10% 19% 18% 4	4052
April	1st to 10th	Day	37% 6% 13% 21% 17% 5%	2280
	11th to 20th	Day	34% 6% 12% 24% 19% 6%	2254
	21st to end	Day	38% 7% 14% 20% 18% 4	2280
May	1st to 10th	Day	52% 10% 11% 18% 8% 2	3942
	11th to 20th	Day	50% 9% 14% 18% 7% 2	4356
	21st to end	Day	32% 10% 14% 25% 17% 1	4837
June	1st to 10th	Day	35% 10% 16% 23% 14% 2	2660
	11th to 20th	Day	34% 10% 16% 24% 14% 3	2660
	21st to end	Day	30% 10% 17% 25% 18% 1	2660
July	1st to 10th	Day	35% 11% 20% 19% 13% 2	4370
	11th to 20th	Day	37% 9% 21% 25% 8% 1	4365
	21st to end	Day	42% 10% 15% 20% 12% 1	4486
August	1st to 10th	Day	42% 8% 19% 25% 7%	4011
	11th to 20th	Day	38% 8% 12% 31% 10% 1	3766
	21st to end	Day	31% 7% 13% 30% 17% 2	4180
September	1st to 10th	Day	36% 8% 15% 20% 17% 3	2280
	11th to 20th	Day	36% 5% 11% 24% 21% 3	2242
	21st to end	Day	45% 7% 8% 20% 16% 3	2090
October	1st to 10th	Day	32% 5% 10% 23% 24% 6%	3193
	11th to 20th	Day	27% 3 6% 29% 27% 8%	3140
	21st to end	Day	25% 4 11% 30% 24% 7%	3350
November	1st to 10th	Day	34% 4 12% 30% 16% 4	1734
	11th to 20th	Day	39% 6% 9% 22% 20% 4	1710
	21st to end	Day	37% 5% 10% 30% 16% 3	1658
December	1st to 10th	Day	42% 5% 17% 22% 12% 3	1520
	11th to 20th	Day	41% 4 10% 30% 12% 3	1906
	21st to end	Day	39% 6% 19% 22% 14%	2772
January	1st to 10th	Night	39% 4 10% 27% 17% 3	4429
	11th to 20th	Night	42% 5% 10% 28% 14% 2	4277
	21st to end	Night	47% 5% 7% 29% 11% 2	4532
February	1st to 10th	Night	42% 4 13% 25% 14% 1	2470
	11th to 20th	Night	43% 4 9% 22% 17% 4	2220
	21st to end	Night	42% 4 10% 24% 18% 4	1884
March	1st to 10th	Night	49% 5% 9% 22% 13% 2	3716
	11th to 20th	Night	34% 6% 10% 27% 19% 4	3480
	21st to end	Night	46% 5% 6% 18% 20% 5%	3578
April	1st to 10th	Night	43% 5% 10% 19% 19% 5%	1900
	11th to 20th	Night	38% 5% 12% 19% 20% 6%	1875
	21st to end	Night	42% 5% 10% 21% 18% 4	1900
May	1st to 10th	Night	52% 7% 9% 21% 9% 1	3014
	11th to 20th	Night	55% 7% 11% 17% 9% 1	2570
	21st to end	Night	40% 10% 13% 20% 16% 1	2739
June	1st to 10th	Night	39% 9% 12% 21% 18% 1	1520
	11th to 20th	Night	36% 10% 13% 24% 15% 2	1520
	21st to end	Night	36% 9% 15% 24% 14% 3	1520
July	1st to 10th	Night	40% 10% 18% 20% 10% 1	2480
	11th to 20th	Night	37% 8% 21% 26% 7% 1	2472
	21st to end	Night	47% 8% 16% 17% 12%	2823
August	1st to 10th	Night	47% 8% 15% 21% 8%	2864
	11th to 20th	Night	37% 7% 15% 28% 12%	3127
	21st to end	Night	29% 6% 13% 27% 23% 2	3476
September	1st to 10th	Night	39% 6% 13% 22% 16% 4	1900
	11th to 20th	Night	33% 7% 12% 25% 21% 3	1938
	21st to end	Night	47% 7% 8% 19% 16% 2	2090
October	1st to 10th	Night	36% 4 10% 24% 23% 2	3763
	11th to 20th	Night	25% 3 13% 21% 32% 6%	3779
	21st to end	Night	24% 3 12% 29% 25% 7%	4195
November	1st to 10th	Night	36% 5% 10% 25% 19% 5%	2505
	11th to 20th	Night	41% 5% 9% 20% 21% 5%	2470
	21st to end	Night	34% 5% 12% 27% 20% 3	2517
December	1st to 10th	Night	45% 5% 13% 23% 12% 3	2660
	11th to 20th	Night	42% 5% 11% 22% 18% 3	3288
	21st to end	Night	41% 5% 17% 25% 10% 1	4884

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	15% 13% 37% 29% 6%	180
	11th to 20th	Day	17% 20% 38% 19% 7%	225
	21st to end	Day	19% 13% 33% 26% 9%	297
February	1st to 10th	Day	20% 10% 35% 27% 9%	270
	11th to 20th	Day	24% 13% 39% 19% 4	454
	21st to end	Day	24% 11% 37% 21% 7% 1	382
March	1st to 10th	Day	17% 13% 37% 26% 7%	460
	11th to 20th	Day	18% 10% 35% 28% 6% 2	460
	21st to end	Day	20% 10% 33% 30% 7%	506
April	1st to 10th	Day	17% 13% 32% 30% 7% 2	460
	11th to 20th	Day	12% 10% 25% 40% 12% 1	452
	21st to end	Day	18% 8% 26% 33% 13% 2	460
May	1st to 10th	Day	19% 8% 27% 30% 14% 2	463
	11th to 20th	Day	20% 4 23% 36% 15% 2	487
	21st to end	Day	15% 3 17% 31% 25% 9%	529
June	1st to 10th	Day	13% 3 16% 36% 27% 6%	490
	11th to 20th	Day	11% 2 13% 34% 31% 9%	490
	21st to end	Day	10% 1 13% 38% 30% 7%	490
July	1st to 10th	Day	10% 2 9% 27% 40% 12%	485
	11th to 20th	Day	3 2 6% 32% 45% 13%	484
	21st to end	Day	9% 2 9% 35% 36% 9%	532
August	1st to 10th	Day	10% 3 6% 37% 34% 9%	486
	11th to 20th	Day	10% 2 7% 33% 36% 13%	479
	21st to end	Day	9% 2 9% 31% 35% 13%	539
September	1st to 10th	Day	15% 2 14% 30% 24% 16%	490
	11th to 20th	Day	13% 3 12% 31% 32% 9%	490
	21st to end	Day	23% 6% 16% 33% 19% 3	490
October	1st to 10th	Day	19% 3 17% 29% 22% 9%	490
	11th to 20th	Day	16% 6% 23% 28% 22% 4	490
	21st to end	Day	16% 8% 27% 28% 19% 3	516
November	1st to 10th	Day	17% 9% 24% 26% 21% 4	386
	11th to 20th	Day	13% 14% 35% 24% 13% 1	370
	21st to end	Day	14% 14% 27% 29% 14% 2	318
December	1st to 10th	Day	20% 11% 37% 22% 9% 1	180
	11th to 20th	Day	21% 12% 33% 25% 9%	180
	21st to end	Day	19% 12% 27% 32% 11%	198
January	1st to 10th	Night	19% 16% 37% 24% 5%	760
	11th to 20th	Night	19% 14% 36% 26% 6%	760
	21st to end	Night	18% 14% 38% 26% 2	836
February	1st to 10th	Night	21% 10% 36% 28% 5%	760
	11th to 20th	Night	22% 14% 39% 23% 2	743
	21st to end	Night	21% 14% 35% 25% 5%	628
March	1st to 10th	Night	17% 13% 37% 26% 7%	760
	11th to 20th	Night	21% 10% 35% 26% 6% 2	760
	21st to end	Night	20% 9% 33% 31% 7% 1	836
April	1st to 10th	Night	19% 11% 35% 27% 8% 1	760
	11th to 20th	Night	14% 6% 30% 38% 12% 1	751
	21st to end	Night	20% 5% 28% 34% 11% 1	760
May	1st to 10th	Night	17% 6% 27% 37% 11% 2	679
	11th to 20th	Night	20% 6% 23% 36% 14% 1	422
	21st to end	Night	15% 3 12% 37% 27% 5%	411
June	1st to 10th	Night	15% 4 15% 40% 23% 2	380
	11th to 20th	Night	13% 1 13% 39% 31% 3	380
	21st to end	Night	9% 1 12% 45% 30% 3	380
July	1st to 10th	Night	8% 1 11% 39% 37% 4	370
	11th to 20th	Night	5% 1 10% 32% 46% 5%	368
	21st to end	Night	6% 2 10% 40% 38% 4	518
August	1st to 10th	Night	11% 1 6% 43% 35% 4	591
	11th to 20th	Night	10% 2 9% 36% 35% 7%	750
	21st to end	Night	10% 2 9% 35% 34% 9%	836
September	1st to 10th	Night	16% 2 14% 29% 31% 8%	760
	11th to 20th	Night	13% 2 13% 30% 35% 7%	760
	21st to end	Night	23% 4 18% 29% 24% 3	760
October	1st to 10th	Night	20% 4 18% 30% 22% 6%	760
	11th to 20th	Night	18% 7% 23% 32% 17% 2	760
	21st to end	Night	16% 9% 28% 29% 15% 2	836
November	1st to 10th	Night	15% 8% 28% 30% 15% 3	771
	11th to 20th	Night	19% 10% 31% 29% 11% 1	760
	21st to end	Night	13% 14% 31% 28% 12% 1	760
December	1st to 10th	Night	22% 12% 34% 21% 9% 2	760
	11th to 20th	Night	18% 12% 38% 26% 6%	760
	21st to end	Night	18% 10% 36% 31% 5%	836

Page generated at 2024-11-05 08:15:52. Version ac07

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