Rehoboth Beach
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Rehoboth Beach clear sky chart from 2005-11-05 to 2017-09-17.

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 TypeMinimum conditions for hour to be usableOut of hours
Clear of CloudsTransparencySeeingSky Brightness
Planetary:50%(no limit)Average(no limit)Nighttime Hours
Deep Sky:70%Average(no limit)5.9Nighttime Hours
CCD Imaging:70%Below AveragePoor(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

PlanetaryData
Pts
Deep Sky
Max 60%
Data
Pts
Both Planetary and Deep Sky
Max 60%
Data
Pts
Either Planetary or Deep SkyData
Pts
CCD ImagingData
Pts
Night
42%
15235
20%
46867
12%
15200
51%
15200
25%
29803

By Month

MonthDays of MonthPlanetaryData
Pts
Deep Sky
Max 60%
Data
Pts
Both Planetary and Deep Sky
Max 60%
Data
Pts
Either Planetary or Deep SkyData
Pts
CCD ImagingData
Pts
January1st to 15thNight
28%
719
21%
2504
9%
716
43%
716
20%
1539
January16th to endNight
22%
768
21%
2496
7%
768
39%
768
22%
1558
February1st to 15thNight
23%
703
19%
2231
9%
701
38%
701
23%
1399
February16th to endNight
24%
631
27%
1893
10%
631
45%
631
25%
1165
March1st to 15thNight
30%
720
20%
2097
11%
720
42%
720
25%
1341
March16th to endNight
33%
768
20%
2026
10%
768
41%
768
24%
1384
April1st to 15thNight
36%
718
19%
1796
6%
718
43%
718
32%
1179
April16th to endNight
47%
720
18%
1800
9%
720
49%
720
29%
1234
May1st to 15thNight
44%
579
16%
1659
9%
579
48%
579
23%
1149
May16th to endNight
58%
374
15%
1497
16%
374
62%
374
19%
955
June1st to 15thNight
60%
360
16%
1440
17%
360
64%
360
21%
878
June16th to endNight
63%
360
13%
1440
17%
360
65%
360
22%
857
July1st to 15thNight
65%
340
13%
1360
17%
340
66%
340
20%
842
July16th to endNight
68%
440
16%
1477
16%
413
72%
413
26%
880
August1st to 15thNight
70%
614
17%
1684
12%
611
70%
611
31%
1072
August16th to endNight
67%
764
18%
1910
11%
764
68%
764
33%
1266
September1st to 15thNight
60%
720
23%
1800
15%
720
62%
720
33%
1201
September16th to endNight
55%
665
19%
1802
16%
665
57%
665
26%
1228
October1st to 15thNight
50%
660
23%
1966
22%
660
55%
660
27%
1246
October16th to endNight
38%
704
25%
2134
16%
704
50%
704
28%
1300
November1st to 15thNight
36%
700
21%
2277
13%
700
50%
700
25%
1406
November16th to endNight
35%
720
21%
2370
13%
720
47%
720
22%
1475
December1st to 15thNight
28%
720
17%
2520
9%
720
39%
720
18%
1604
December16th to endNight
25%
768
22%
2688
9%
768
42%
768
21%
1645

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 ForecastData
Points
Cloud CoverDay
12%5%2442445%8%43%
47902
Night
14%5%2442445%7%42%
47043
Cloud CoverDay
12%5%2442445%8%43%
47911
Night
14%5%25%42445%7%42%
47049
TransparencyDay
38%6%13%23%15%2
47596
Night
40%5%11%22%16%2
46867
SeeingDay
16%5%20%29%22%6%
5824
Night
17%7%25%30%16%2
15238

By Month

Percentage Cloud Cover NE (2006-)
Color Meanings:
Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 15thDay
14%6%34425%5%5%6%41%
1432
16th to endDay
17%6%2442445%7%39%
1728
February1st to 15thDay
14%7%25%33346%7%39%
1628
16th to endDay
13%7%34425%5%47%42%
1580
March1st to 15thDay
16%42442445%6%43%
1850
16th to endDay
14%6%26%5%24446%43%
2197
April1st to 15thDay
13%5%2432435%7%46%
2152
16th to endDay
13%6%24423346%46%
2160
May1st to 15thDay
13%5%25%4244410%41%
2299
16th to endDay
12%4245%245%5%8%44%
2618
June1st to 15thDay
13%413425%46%9%43%
2520
16th to endDay
8%423335%7%6%11%43%
2520
July1st to 15thDay
8%425%425%46%10%44%
2520
16th to endDay
7%3145%36%6%8%12%39%
2589
August1st to 15thDay
9%5%15%5%35%5%6%9%43%
2253
16th to endDay
8%3145%35%6%6%8%46%
2292
September1st to 15thDay
11%4244235%5%7%47%
2160
16th to endDay
14%7%25%4245%46%41%
1864
October1st to 15thDay
15%5%235%33446%45%
1661
16th to endDay
15%5%2432435%6%47%
1735
November1st to 15thDay
17%5%2342235%7%44%
1581
16th to endDay
13%424424447%45%
1587
December1st to 15thDay
13%6%45%42445%8%39%
1440
16th to endDay
19%6%24423337%41%
1536
January1st to 15thNight
15%5%3343445%8%39%
2504
16th to endNight
16%6%3432445%6%41%
2496
February1st to 15thNight
15%6%35%424446%42%
2230
16th to endNight
15%5%2442445%6%45%
1893
March1st to 15thNight
16%6%24423346%45%
2084
16th to endNight
20%6%25%323345%42%
2026
April1st to 15thNight
15%5%245%33247%44%
1796
16th to endNight
17%5%24425%35%6%43%
1800
May1st to 15thNight
16%7%26%415%45%6%37%
1659
16th to endNight
12%7%245%35%46%7%40%
1495
June1st to 15thNight
14%5%23435%448%43%
1440
16th to endNight
8%425%5%36%5%7%10%40%
1440
July1st to 15thNight
7%5%35%6%45%5%6%9%41%
1440
16th to endNight
6%326%6%36%5%7%11%39%
1578
August1st to 15thNight
7%325%6%445%6%9%43%
1695
16th to endNight
9%5%15%5%245%5%9%44%
1910
September1st to 15thNight
13%5%15%424447%45%
1800
16th to endNight
15%6%244345%48%39%
1802
October1st to 15thNight
17%4245%2335%5%45%
1966
16th to endNight
16%414314446%46%
2134
November1st to 15thNight
15%6%24423435%46%
2277
16th to endNight
14%5%25%42445%6%43%
2370
December1st to 15thNight
16%7%26%42445%6%39%
2520
16th to endNight
17%5%24423446%44%
2688

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
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 15thDay
14%6%34335%5%5%6%42%
1432
16th to endDay
17%6%15%42435%7%40%
1728
February1st to 15thDay
14%7%25%42435%7%40%
1628
16th to endDay
13%7%35%32445%6%42%
1580
March1st to 15thDay
16%425%32445%6%44%
1860
16th to endDay
15%6%26%433445%43%
2196
April1st to 15thDay
13%425%32335%7%46%
2152
16th to endDay
13%5%34324347%46%
2160
May1st to 15thDay
14%6%25%5%2436%9%41%
2299
16th to endDay
12%4245%335%5%8%43%
2618
June1st to 15thDay
13%313425%5%7%10%41%
2520
16th to endDay
8%423435%6%6%11%42%
2520
July1st to 15thDay
8%325%4345%6%11%43%
2520
16th to endDay
7%3246%36%7%8%12%38%
2589
August1st to 15thDay
8%5%25%5%25%5%6%9%41%
2253
16th to endDay
8%3235%346%6%9%45%
2292
September1st to 15thDay
11%42432445%7%47%
2160
16th to endDay
15%6%35%4245%47%40%
1864
October1st to 15thDay
15%6%24424347%44%
1661
16th to endDay
14%5%24323346%48%
1735
November1st to 15thDay
18%5%2341335%7%43%
1581
16th to endDay
13%434424449%45%
1587
December1st to 15thDay
12%6%45%425%36%8%40%
1440
16th to endDay
19%7%24423337%41%
1536
January1st to 15thNight
16%5%2433436%7%41%
2504
16th to endNight
17%6%2442445%6%42%
2496
February1st to 15thNight
15%6%25%423446%43%
2223
16th to endNight
15%424423446%46%
1893
March1st to 15thNight
16%6%24423246%45%
2097
16th to endNight
19%6%25%423345%41%
2026
April1st to 15thNight
15%5%25%5%23347%44%
1796
16th to endNight
16%5%25%425%347%41%
1800
May1st to 15thNight
16%8%36%42446%6%38%
1659
16th to endNight
13%6%25%435%5%47%40%
1495
June1st to 15thNight
14%423435%5%310%42%
1440
16th to endNight
7%5%25%6%45%5%7%11%38%
1440
July1st to 15thNight
7%5%25%7%45%46%9%40%
1440
16th to endNight
5%3345%37%7%7%10%40%
1578
August1st to 15thNight
6%415%6%345%7%9%43%
1695
16th to endNight
10%5%25%5%245%6%9%44%
1910
September1st to 15thNight
13%6%24424448%44%
1800
16th to endNight
16%6%24435%5%5%7%39%
1802
October1st to 15thNight
17%424424446%44%
1966
16th to endNight
15%424324446%47%
2134
November1st to 15thNight
16%5%24423335%47%
2277
16th to endNight
14%6%25%42445%6%44%
2370
December1st to 15thNight
17%7%25%434447%39%
2520
16th to endNight
17%5%25%323345%44%
2688

Transparency (when cloud cover <= 30%)
Color Meanings:
Too cloudy to forecast Poor Below Average Average Above average Transparent
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 15thDay
41%414%23%13%3
1433
16th to endDay
42%411%25%14%2
1728
February1st to 15thDay
42%5%12%24%13%2
1631
16th to endDay
42%411%26%13%2
1580
March1st to 15thDay
40%5%13%23%15%2
1860
16th to endDay
42%5%9%23%16%2
2197
April1st to 15thDay
36%5%12%25%16%4
2152
16th to endDay
37%5%12%18%19%5%
2160
May1st to 15thDay
39%6%15%21%14%1
2299
16th to endDay
36%8%15%25%12%1
2622
June1st to 15thDay
36%9%15%24%13%1
2520
16th to endDay
32%9%17%21%16%1
2520
July1st to 15thDay
33%8%16%23%15%2
2371
16th to endDay
33%9%16%25%13%1
2427
August1st to 15thDay
37%8%13%25%14%1
2240
16th to endDay
33%8%14%22%17%3
2292
September1st to 15thDay
34%7%13%23%18%2
2160
16th to endDay
43%6%9%19%19%2
1864
October1st to 15thDay
39%5%11%26%12%4
1661
16th to endDay
35%5%9%27%19%2
1735
November1st to 15thDay
40%411%24%15%3
1581
16th to endDay
37%5%10%26%15%2
1587
December1st to 15thDay
40%5%17%21%11%3
1440
16th to endDay
44%412%25%12%1
1536
January1st to 15thNight
40%5%11%22%16%2
2504
16th to endNight
41%411%26%13%1
2496
February1st to 15thNight
41%311%26%14%2
2231
16th to endNight
38%39%26%19%2
1893
March1st to 15thNight
41%411%26%14%2
2097
16th to endNight
45%49%20%17%3
2026
April1st to 15thNight
39%411%21%19%4
1796
16th to endNight
42%5%9%17%20%5%
1800
May1st to 15thNight
45%6%10%21%13%2
1659
16th to endNight
42%9%13%19%14%1
1497
June1st to 15thNight
39%7%11%22%17%
1440
16th to endNight
37%8%14%21%15%2
1440
July1st to 15thNight
39%9%15%20%13%2
1360
16th to endNight
34%9%17%25%12%1
1477
August1st to 15thNight
34%8%16%21%18%
1684
16th to endNight
35%8%13%20%20%2
1910
September1st to 15thNight
38%6%12%24%15%3
1800
16th to endNight
41%8%8%20%18%2
1802
October1st to 15thNight
40%5%10%24%17%2
1966
16th to endNight
37%410%25%17%3
2134
November1st to 15thNight
40%410%20%18%5%
2277
16th to endNight
40%5%10%24%15%3
2370
December1st to 15thNight
44%5%13%22%12%2
2520
16th to endNight
41%414%23%13%2
2688

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
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 15thDay
15%10%38%30%6%
60
16th to endDay
22%12%31%23%9%
96
February1st to 15thDay
24%15%31%23%4
144
16th to endDay
17%12%35%30%4
239
March1st to 15thDay
21%10%28%29%10%
270
16th to endDay
19%6%32%31%5%3
288
April1st to 15thDay
17%8%25%32%12%2
270
16th to endDay
21%6%15%35%18%2
270
May1st to 15thDay
25%429%23%14%2
288
16th to endDay
15%218%25%26%11%
331
June1st to 15thDay
18%212%30%26%8%
315
16th to endDay
13%12%39%28%6%
315
July1st to 15thDay
11%19%29%40%7%
305
16th to endDay
6%17%32%38%13%
326
August1st to 15thDay
12%1436%32%11%
313
16th to endDay
8%6%29%40%13%
332
September1st to 15thDay
13%18%27%22%17%
315
16th to endDay
23%49%27%24%10%
259
October1st to 15thDay
20%216%32%21%6%
255
16th to endDay
13%8%31%23%20%2
267
November1st to 15thDay
18%6%29%23%17%3
235
16th to endDay
13%14%31%20%16%1
207
December1st to 15thDay
15%11%28%28%16%
60
16th to endDay
34%437%18%4
64
January1st to 15thNight
18%12%36%25%6%
720
16th to endNight
19%12%41%23%2
768
February1st to 15thNight
19%12%38%28%1
704
16th to endNight
17%15%38%24%3
631
March1st to 15thNight
20%9%34%27%7%
720
16th to endNight
22%8%29%28%8%2
768
April1st to 15thNight
17%5%35%33%8%
718
16th to endNight
20%422%36%14%1
720
May1st to 15thNight
18%5%25%34%12%2
579
16th to endNight
16%213%38%24%4
375
June1st to 15thNight
16%214%36%27%2
360
16th to endNight
10%111%42%32%2
360
July1st to 15thNight
7%12%39%37%2
340
16th to endNight
6%19%32%43%6%
440
August1st to 15thNight
9%6%42%35%4
614
16th to endNight
11%18%33%37%7%
764
September1st to 15thNight
16%113%30%32%5%
720
16th to endNight
18%215%28%28%5%
665
October1st to 15thNight
19%5%17%33%21%3
660
16th to endNight
17%8%30%25%16%1
704
November1st to 15thNight
19%8%29%25%14%3
700
16th to endNight
15%13%28%28%11%1
720
December1st to 15thNight
21%11%33%20%10%1
720
16th to endNight
19%10%40%25%3
768
Page generated at 2017-09-18 08:38:24. Version ac04

Copyright 2017 A. Danko


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