Arundel
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Arundel clear sky chart from 2005-11-05 to 2017-09-10.

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
27%
14577
12%
46773
7%
14545
33%
14545
15%
33975

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
13%
720
7%
2506
2%
716
19%
716
7%
2053
January16th to endNight
17%
768
10%
2688
5%
768
24%
768
9%
2028
February1st to 15thNight
15%
704
10%
2293
3%
701
24%
701
10%
1765
February16th to endNight
19%
631
12%
1922
5%
631
28%
631
11%
1482
March1st to 15thNight
17%
720
13%
2145
6%
720
25%
720
12%
1652
March16th to endNight
26%
768
19%
2004
7%
768
35%
768
21%
1400
April1st to 15thNight
23%
718
15%
1796
5%
718
28%
718
18%
1337
April16th to endNight
24%
633
16%
1713
6%
633
32%
633
19%
1214
May1st to 15thNight
28%
360
15%
1440
10%
360
40%
360
14%
988
May16th to endNight
29%
375
12%
1497
10%
374
41%
374
16%
990
June1st to 15thNight
29%
360
7%
1440
5%
360
36%
360
12%
1013
June16th to endNight
42%
360
8%
1440
11%
360
45%
360
17%
946
July1st to 15thNight
51%
340
11%
1360
15%
340
56%
340
25%
769
July16th to endNight
51%
376
12%
1418
15%
354
55%
354
23%
842
August1st to 15thNight
52%
380
13%
1451
12%
378
57%
378
20%
923
August16th to endNight
48%
735
19%
1881
10%
735
52%
735
34%
1203
September1st to 15thNight
42%
700
13%
1750
6%
700
45%
700
27%
1221
September16th to endNight
43%
657
19%
1785
11%
657
48%
657
29%
1167
October1st to 15thNight
28%
660
17%
1974
10%
660
37%
660
17%
1400
October16th to endNight
22%
704
11%
2238
6%
704
29%
704
13%
1703
November1st to 15thNight
25%
700
17%
2304
10%
700
35%
700
14%
1667
November16th to endNight
19%
720
10%
2520
6%
720
24%
720
9%
1970
December1st to 15thNight
13%
720
8%
2520
3%
720
19%
720
7%
2048
December16th to endNight
11%
768
10%
2688
3%
768
18%
768
6%
2194

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
20%10%46%5%34446%29%
47867
Night
18%11%46%5%24445%30%
46942
Cloud CoverDay
20%10%46%5%34446%29%
47876
Night
18%11%46%5%24445%31%
46948
TransparencyDay
55%5%10%18%8%1
47554
Night
54%5%10%18%8%
46773
SeeingDay
26%14%28%19%8%2
5487
Night
25%13%28%23%8%
14577

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
22%18%5%11%7%3422417%
1432
16th to endDay
12%17%7%8%7%35%45%6%21%
1536
February1st to 15thDay
13%16%5%12%8%34336%21%
1569
16th to endDay
14%18%5%8%7%34345%23%
1551
March1st to 15thDay
17%14%5%8%6%34445%26%
1805
16th to endDay
16%10%36%42345%7%35%
2220
April1st to 15thDay
23%12%35%323335%32%
2152
16th to endDay
22%9%35%5%2444434%
2257
May1st to 15thDay
23%8%36%5%24346%29%
2511
16th to endDay
22%7%36%5%24446%30%
2618
June1st to 15thDay
23%8%35%5%36%5%5%6%26%
2520
16th to endDay
21%6%35%5%35%5%5%8%27%
2520
July1st to 15thDay
17%5%25%6%35%5%5%8%34%
2520
16th to endDay
16%6%36%6%46%5%6%8%30%
2654
August1st to 15thDay
16%7%36%6%46%5%5%8%29%
2497
16th to endDay
15%425%5%35%46%7%39%
2308
September1st to 15thDay
22%6%245%24446%36%
2098
16th to endDay
21%7%23412346%43%
1845
October1st to 15thDay
24%9%34424446%31%
1653
16th to endDay
29%13%38%5%3333420%
1634
November1st to 15thDay
17%11%36%5%25%45%7%28%
1551
16th to endDay
27%13%6%5%42333325%
1440
December1st to 15thDay
25%18%5%8%5%3434417%
1440
16th to endDay
23%18%7%9%6%2432317%
1536
January1st to 15thNight
19%17%7%9%7%3334417%
2506
16th to endNight
12%16%6%9%7%35%45%5%22%
2688
February1st to 15thNight
11%15%8%10%8%3444423%
2291
16th to endNight
16%12%6%11%5%24346%24%
1922
March1st to 15thNight
20%11%5%7%6%34345%27%
2132
16th to endNight
15%9%35%5%33335%39%
2004
April1st to 15thNight
25%10%34423335%34%
1796
16th to endNight
20%9%25%423345%37%
1713
May1st to 15thNight
20%8%36%414435%35%
1440
16th to endNight
18%5%36%4246%5%5%37%
1495
June1st to 15thNight
20%9%27%5%35%46%6%29%
1440
16th to endNight
18%6%24425%6%5%7%36%
1440
July1st to 15thNight
11%425%42446%8%44%
1440
16th to endNight
11%4244345%6%9%42%
1514
August1st to 15thNight
12%426%435%5%7%7%40%
1461
16th to endNight
11%424423447%49%
1881
September1st to 15thNight
18%6%24424446%39%
1750
16th to endNight
19%5%23223346%46%
1785
October1st to 15thNight
19%8%36%5%3435%6%34%
1974
16th to endNight
28%11%36%414345%26%
2238
November1st to 15thNight
21%9%45%5%3445%5%30%
2304
16th to endNight
22%15%6%8%5%2443423%
2520
December1st to 15thNight
22%17%6%7%7%3334418%
2520
16th to endNight
23%19%5%8%6%2333418%
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
21%18%6%10%7%3423417%
1432
16th to endDay
13%15%7%9%7%345%45%22%
1536
February1st to 15thDay
13%16%5%11%8%34345%21%
1569
16th to endDay
15%17%6%9%6%44345%23%
1551
March1st to 15thDay
18%13%6%9%6%34345%25%
1815
16th to endDay
17%9%47%5%2335%6%35%
2219
April1st to 15thDay
23%12%45%423345%32%
2152
16th to endDay
22%9%45%42444433%
2257
May1st to 15thDay
23%9%36%5%24446%28%
2511
16th to endDay
22%7%36%5%3435%6%30%
2618
June1st to 15thDay
22%8%36%5%35%45%7%26%
2520
16th to endDay
22%6%35%6%25%6%5%7%26%
2520
July1st to 15thDay
16%5%36%5%35%45%7%34%
2520
16th to endDay
15%6%36%5%36%5%7%8%29%
2654
August1st to 15thDay
16%7%37%6%46%5%5%7%29%
2497
16th to endDay
14%5%25%5%345%5%8%38%
2308
September1st to 15thDay
21%6%25%5%34346%36%
2098
16th to endDay
21%5%24313347%42%
1845
October1st to 15thDay
24%9%25%423446%31%
1653
16th to endDay
28%14%47%5%3333421%
1634
November1st to 15thDay
18%11%36%5%25%447%29%
1551
16th to endDay
25%14%37%42334425%
1440
December1st to 15thDay
24%19%5%7%5%3334418%
1440
16th to endDay
22%19%7%8%5%2433318%
1536
January1st to 15thNight
19%17%7%8%7%3444417%
2506
16th to endNight
11%17%6%9%7%4445%5%23%
2688
February1st to 15thNight
11%14%7%10%8%4444423%
2284
16th to endNight
16%13%6%9%5%34445%25%
1922
March1st to 15thNight
20%11%5%7%6%44335%27%
2145
16th to endNight
15%10%45%5%23335%40%
2004
April1st to 15thNight
25%10%34323235%33%
1796
16th to endNight
21%8%34423445%36%
1713
May1st to 15thNight
20%9%36%5%23435%35%
1440
16th to endNight
19%6%35%43445%6%36%
1495
June1st to 15thNight
20%8%37%5%25%447%29%
1440
16th to endNight
18%6%25%427%45%7%35%
1440
July1st to 15thNight
12%6%244245%6%7%45%
1440
16th to endNight
12%4245%25%5%6%8%43%
1514
August1st to 15thNight
12%5%25%5%246%7%7%39%
1461
16th to endNight
12%5%1442435%7%48%
1881
September1st to 15thNight
18%6%25%43445%6%39%
1750
16th to endNight
19%5%23323345%46%
1785
October1st to 15thNight
19%7%36%5%2445%5%34%
1974
16th to endNight
28%11%36%5%13346%26%
2238
November1st to 15thNight
22%7%36%5%3345%6%31%
2304
16th to endNight
22%15%5%8%5%2433423%
2520
December1st to 15thNight
22%17%6%8%6%2433419%
2520
16th to endNight
23%18%5%8%5%2333419%
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
72%36%11%4
1433
16th to endDay
61%5%8%15%7%
1536
February1st to 15thDay
64%38%17%5%
1571
16th to endDay
63%37%14%9%1
1551
March1st to 15thDay
61%310%14%8%1
1815
16th to endDay
49%49%18%14%4
2220
April1st to 15thDay
55%38%18%11%2
2152
16th to endDay
53%46%18%12%3
2257
May1st to 15thDay
55%5%7%18%11%1
2511
16th to endDay
54%5%10%17%10%1
2622
June1st to 15thDay
57%6%9%16%9%
2520
16th to endDay
54%7%10%18%7%1
2520
July1st to 15thDay
45%7%15%23%9%
2371
16th to endDay
50%7%16%17%8%
2487
August1st to 15thDay
52%7%15%19%5%
2483
16th to endDay
42%5%16%25%9%
2308
September1st to 15thDay
48%5%12%22%10%
2098
16th to endDay
43%412%29%10%
1845
October1st to 15thDay
53%411%20%9%
1653
16th to endDay
67%49%13%4
1634
November1st to 15thDay
54%6%14%15%8%
1551
16th to endDay
63%411%14%5%
1440
December1st to 15thDay
70%411%11%2
1440
16th to endDay
70%47%10%6%
1536
January1st to 15thNight
70%48%11%3
2506
16th to endNight
61%49%14%7%1
2688
February1st to 15thNight
62%410%17%4
2293
16th to endNight
60%5%8%15%9%
1922
March1st to 15thNight
60%47%16%8%1
2145
16th to endNight
47%410%17%17%2
2004
April1st to 15thNight
54%36%20%13%1
1796
16th to endNight
48%5%9%18%15%2
1713
May1st to 15thNight
52%5%7%17%13%3
1440
16th to endNight
47%6%10%20%13%1
1497
June1st to 15thNight
53%7%10%19%7%
1440
16th to endNight
46%7%11%21%12%
1440
July1st to 15thNight
35%5%18%26%12%
1360
16th to endNight
36%8%16%26%11%
1418
August1st to 15thNight
40%9%18%24%7%
1451
16th to endNight
34%6%17%31%9%
1881
September1st to 15thNight
44%5%14%25%9%
1750
16th to endNight
40%412%31%9%
1785
October1st to 15thNight
50%5%10%21%10%
1974
16th to endNight
60%411%17%6%
2238
November1st to 15thNight
54%5%12%17%7%1
2304
16th to endNight
65%49%14%5%
2520
December1st to 15thNight
70%49%13%3
2520
16th to endNight
69%47%11%6%
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
35%16%28%16%3
60
16th to endDay
32%21%31%7%6%
64
February1st to 15thDay
39%23%30%5%1
89
16th to endDay
29%23%29%13%3
210
March1st to 15thDay
27%21%30%18%1
270
16th to endDay
26%15%30%16%8%2
288
April1st to 15thDay
31%20%25%14%5%1
270
16th to endDay
28%17%26%17%8%2
270
May1st to 15thDay
32%16%27%14%6%1
288
16th to endDay
27%14%33%17%6%
331
June1st to 15thDay
30%11%33%16%6%
315
16th to endDay
21%14%34%20%6%1
315
July1st to 15thDay
19%9%34%24%8%2
305
16th to endDay
17%6%34%29%10%2
326
August1st to 15thDay
18%8%26%30%11%4
313
16th to endDay
18%8%27%22%14%8%
332
September1st to 15thDay
24%8%24%20%15%6%
294
16th to endDay
23%11%23%20%12%7%
254
October1st to 15thDay
27%18%21%18%11%2
255
16th to endDay
38%13%26%14%7%
249
November1st to 15thDay
25%17%23%24%7%1
205
16th to endDay
40%18%26%15%
60
December1st to 15thDay
40%20%25%15%
60
16th to endDay
43%26%26%3
64
January1st to 15thNight
31%16%32%15%4
720
16th to endNight
21%18%33%19%6%1
768
February1st to 15thNight
20%20%34%19%4
704
16th to endNight
24%19%32%20%3
631
March1st to 15thNight
26%18%31%20%2
720
16th to endNight
23%14%31%22%6%1
768
April1st to 15thNight
30%15%27%23%3
718
16th to endNight
26%18%26%18%9%
633
May1st to 15thNight
26%9%31%23%8%1
360
16th to endNight
21%10%34%23%9%
375
June1st to 15thNight
25%9%29%28%6%
360
16th to endNight
21%5%22%35%14%1
360
July1st to 15thNight
13%8%24%35%17%1
340
16th to endNight
12%5%25%38%16%1
376
August1st to 15thNight
15%318%40%19%2
380
16th to endNight
14%5%23%32%20%2
735
September1st to 15thNight
21%5%25%32%15%
700
16th to endNight
22%7%23%27%17%1
657
October1st to 15thNight
23%14%25%25%9%
660
16th to endNight
34%13%24%20%6%
704
November1st to 15thNight
27%13%29%20%8%1
700
16th to endNight
31%19%24%15%7%1
720
December1st to 15thNight
32%20%27%16%3
720
16th to endNight
35%17%29%14%31
768
Page generated at 2017-09-11 19:35:30. Version ac04

Copyright 2017 A. Danko


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