Andover
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Andover clear sky chart from 2005-11-05 to 2018-03-11.

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%
15578
18%
49071
8%
15546
39%
15546
20%
32061

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
17%
780
19%
2716
5%
776
33%
776
16%
1723
January16th to endNight
15%
832
18%
2912
4%
832
33%
832
14%
1878
February1st to 15thNight
18%
764
17%
2387
5%
761
34%
761
16%
1625
February16th to endNight
18%
683
22%
2049
7%
683
37%
683
18%
1365
March1st to 15thNight
18%
764
17%
2282
6%
764
31%
764
17%
1579
March16th to endNight
22%
768
22%
2039
7%
768
34%
768
21%
1396
April1st to 15thNight
22%
718
18%
1796
4%
718
30%
718
21%
1270
April16th to endNight
24%
582
18%
1662
4%
582
34%
582
20%
1146
May1st to 15thNight
25%
540
15%
1620
7%
540
31%
540
17%
1126
May16th to endNight
26%
417
11%
1539
7%
416
33%
416
16%
1008
June1st to 15thNight
31%
360
12%
1440
9%
360
41%
360
15%
970
June16th to endNight
38%
360
12%
1440
12%
360
45%
360
21%
873
July1st to 15thNight
45%
340
12%
1360
14%
340
50%
340
22%
823
July16th to endNight
47%
376
15%
1418
14%
354
54%
354
21%
874
August1st to 15thNight
45%
509
17%
1580
12%
507
49%
507
27%
994
August16th to endNight
52%
708
21%
1854
11%
708
55%
708
32%
1202
September1st to 15thNight
40%
720
20%
1866
9%
720
47%
720
33%
1201
September16th to endNight
45%
717
27%
1980
18%
717
52%
717
33%
1218
October1st to 15thNight
36%
720
22%
2010
10%
720
46%
720
26%
1303
October16th to endNight
25%
768
19%
2496
7%
768
40%
768
19%
1608
November1st to 15thNight
31%
760
21%
2472
11%
760
44%
760
21%
1571
November16th to endNight
24%
780
22%
2535
8%
780
41%
780
19%
1608
December1st to 15thNight
19%
780
17%
2706
4%
780
35%
780
16%
1777
December16th to endNight
15%
832
19%
2912
4%
832
33%
832
15%
1923

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
17%6%2442445%6%39%
49566
Night
17%6%25%424446%40%
49241
Cloud CoverDay
17%6%25%42445%7%39%
49576
Night
17%6%25%424446%40%
49246
TransparencyDay
43%5%11%21%14%2
49254
Night
44%5%11%21%15%2
49071
SeeingDay
21%15%31%20%8%2
6420
Night
20%13%32%23%8%
15578

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
16%6%35%4245%46%41%
1552
16th to endDay
16%6%24425%345%43%
1664
February1st to 15thDay
17%6%35%5%25%5%6%6%34%
1800
16th to endDay
14%9%35%424445%40%
1710
March1st to 15thDay
20%9%35%42445%6%33%
1905
16th to endDay
18%7%35%413446%39%
2184
April1st to 15thDay
18%7%25%42335%6%38%
2152
16th to endDay
19%5%25%42435%7%39%
2298
May1st to 15thDay
24%7%35%433446%32%
2332
16th to endDay
17%5%25%43435%7%39%
2584
June1st to 15thDay
25%5%23425%5%5%7%32%
2520
16th to endDay
16%5%25%5%35%5%6%8%35%
2520
July1st to 15thDay
13%4245%25%6%7%9%38%
2520
16th to endDay
12%5%25%5%26%5%6%8%39%
2654
August1st to 15thDay
11%5%25%5%36%5%7%8%38%
2358
16th to endDay
10%423435%5%6%8%45%
2346
September1st to 15thDay
14%5%2442345%5%47%
2093
16th to endDay
16%5%23323345%49%
1980
October1st to 15thDay
19%5%1442435%6%41%
1948
16th to endDay
17%6%14423446%42%
1728
November1st to 15thDay
19%7%24414345%42%
1716
16th to endDay
17%5%35%432245%44%
1755
December1st to 15thDay
18%6%35%5%2435%5%39%
1583
16th to endDay
22%8%34424436%35%
1664
January1st to 15thNight
15%7%25%424445%41%
2716
16th to endNight
15%9%35%5%34435%39%
2912
February1st to 15thNight
15%9%25%5%345%46%36%
2386
16th to endNight
17%8%24423346%40%
2049
March1st to 15thNight
19%7%25%434445%37%
2269
16th to endNight
16%7%35%32433443%
2039
April1st to 15thNight
17%7%35%5%235%35%38%
1796
16th to endNight
22%5%2443443439%
1662
May1st to 15thNight
21%6%25%43445%6%35%
1620
16th to endNight
20%6%25%5%2446%8%34%
1537
June1st to 15thNight
23%7%24425%45%6%34%
1440
16th to endNight
16%5%2442445%8%40%
1440
July1st to 15thNight
12%6%25%5%245%5%8%40%
1440
16th to endNight
13%425%5%45%5%48%39%
1514
August1st to 15thNight
10%4245%35%5%6%7%43%
1590
16th to endNight
12%4145%3445%8%44%
1854
September1st to 15thNight
14%5%1442335%7%48%
1866
16th to endNight
14%5%13323336%52%
1980
October1st to 15thNight
18%5%14323445%45%
2010
16th to endNight
19%6%14424346%40%
2496
November1st to 15thNight
16%6%25%424446%43%
2472
16th to endNight
16%6%35%423346%43%
2535
December1st to 15thNight
19%7%35%42435%5%38%
2706
16th to endNight
19%7%25%43335%5%38%
2912

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
16%6%35%325%446%41%
1552
16th to endDay
17%5%25%423346%43%
1664
February1st to 15thDay
18%7%25%5%25%5%5%7%34%
1800
16th to endDay
15%8%35%425%346%39%
1710
March1st to 15thDay
20%8%35%334446%34%
1915
16th to endDay
18%7%34423446%39%
2184
April1st to 15thDay
18%7%25%5%3345%7%37%
2152
16th to endDay
19%5%245%2335%6%40%
2298
May1st to 15thDay
23%7%36%5%2445%5%32%
2332
16th to endDay
17%5%25%423448%40%
2584
June1st to 15thDay
25%5%23435%45%7%33%
2520
16th to endDay
15%5%15%5%36%5%6%9%34%
2520
July1st to 15thDay
12%4245%35%5%6%9%38%
2520
16th to endDay
12%425%5%35%5%7%8%38%
2654
August1st to 15thDay
11%426%5%36%5%7%8%37%
2358
16th to endDay
10%4244245%6%8%45%
2346
September1st to 15thDay
13%5%2443345%6%47%
2093
16th to endDay
15%5%23323345%49%
1980
October1st to 15thDay
19%424334346%41%
1948
16th to endDay
17%6%15%4235%45%42%
1728
November1st to 15thDay
20%7%2441334442%
1716
16th to endDay
17%434433436%44%
1755
December1st to 15thDay
18%6%35%433345%39%
1583
16th to endDay
22%7%34425%345%35%
1664
January1st to 15thNight
16%7%35%424445%41%
2716
16th to endNight
15%9%25%5%34435%39%
2912
February1st to 15thNight
16%8%35%4345%5%6%36%
2379
16th to endNight
18%8%34423445%40%
2049
March1st to 15thNight
19%7%35%425%346%36%
2282
16th to endNight
16%8%3433433443%
2038
April1st to 15thNight
18%7%35%5%24346%37%
1796
16th to endNight
22%5%15%434335%39%
1662
May1st to 15thNight
21%6%25%5%34446%35%
1620
16th to endNight
20%5%25%42345%8%34%
1537
June1st to 15thNight
23%7%25%325%437%34%
1440
16th to endNight
15%5%25%425%45%8%40%
1440
July1st to 15thNight
12%6%25%425%45%8%40%
1440
16th to endNight
13%5%26%436%5%5%8%39%
1514
August1st to 15thNight
10%4245%35%5%6%7%42%
1590
16th to endNight
12%4145%3445%8%44%
1854
September1st to 15thNight
13%424433446%48%
1866
16th to endNight
14%5%14422336%51%
1980
October1st to 15thNight
18%5%24423446%44%
2010
16th to endNight
19%5%24424447%40%
2496
November1st to 15thNight
16%6%25%424446%43%
2472
16th to endNight
16%6%25%424346%43%
2535
December1st to 15thNight
19%7%35%42345%5%38%
2706
16th to endNight
19%7%25%434346%38%
2912

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
43%5%11%24%13%2
1553
16th to endDay
42%412%26%13%1
1664
February1st to 15thDay
47%5%12%19%12%1
1803
16th to endDay
45%412%20%14%2
1710
March1st to 15thDay
50%411%18%11%3
1915
16th to endDay
44%38%21%15%5%
2184
April1st to 15thDay
46%410%19%15%3
2152
16th to endDay
43%47%21%18%3
2298
May1st to 15thDay
53%47%17%14%2
2332
16th to endDay
43%6%13%21%12%2
2588
June1st to 15thDay
50%6%12%19%10%1
2520
16th to endDay
44%7%12%19%14%
2520
July1st to 15thDay
40%8%11%23%15%1
2371
16th to endDay
40%6%15%22%12%2
2487
August1st to 15thDay
40%7%14%23%12%1
2344
16th to endDay
34%7%12%26%17%1
2346
September1st to 15thDay
36%5%11%22%22%1
2093
16th to endDay
36%47%24%24%2
1980
October1st to 15thDay
43%410%24%14%3
1948
16th to endDay
42%5%11%24%14%1
1728
November1st to 15thDay
44%311%23%14%1
1716
16th to endDay
42%312%21%17%1
1755
December1st to 15thDay
47%414%16%16%
1583
16th to endDay
51%411%19%11%1
1664
January1st to 15thNight
44%412%21%14%2
2716
16th to endNight
46%311%20%15%2
2912
February1st to 15thNight
47%412%20%12%2
2387
16th to endNight
45%49%22%14%3
2049
March1st to 15thNight
49%49%20%13%3
2282
16th to endNight
44%47%18%19%5%
2039
April1st to 15thNight
47%49%18%17%2
1796
16th to endNight
47%48%18%16%4
1662
May1st to 15thNight
48%5%9%16%15%3
1620
16th to endNight
46%6%15%18%10%1
1539
June1st to 15thNight
50%6%11%20%10%
1440
16th to endNight
40%6%13%22%15%1
1440
July1st to 15thNight
38%7%13%25%14%
1360
16th to endNight
41%6%12%26%10%1
1418
August1st to 15thNight
37%7%12%24%15%2
1580
16th to endNight
36%6%10%25%19%
1854
September1st to 15thNight
36%5%11%25%19%1
1866
16th to endNight
35%46%24%27%1
1980
October1st to 15thNight
40%411%24%15%3
2010
16th to endNight
43%412%24%13%
2496
November1st to 15thNight
41%5%10%22%16%2
2472
16th to endNight
43%411%23%15%2
2535
December1st to 15thNight
47%413%21%12%
2706
16th to endNight
47%411%21%14%
2912

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
16%33%26%20%3
90
16th to endDay
27%26%33%13%
96
February1st to 15thDay
26%22%35%14%1
276
16th to endDay
19%23%34%18%3
291
March1st to 15thDay
24%25%32%13%3
312
16th to endDay
21%23%31%14%6%1
288
April1st to 15thDay
24%18%31%15%9%
270
16th to endDay
22%17%33%18%5%2
270
May1st to 15thDay
34%17%25%14%5%2
288
16th to endDay
19%14%35%22%6%
331
June1st to 15thDay
24%12%36%16%9%
315
16th to endDay
18%14%38%21%32
315
July1st to 15thDay
17%8%32%26%13%1
305
16th to endDay
14%7%32%30%13%2
326
August1st to 15thDay
13%9%31%26%14%3
313
16th to endDay
12%6%28%31%15%5%
332
September1st to 15thDay
18%9%29%23%13%4
315
16th to endDay
20%8%28%16%13%13%
314
October1st to 15thDay
23%10%23%23%13%4
311
16th to endDay
21%17%29%22%8%
288
November1st to 15thDay
23%12%32%18%10%2
280
16th to endDay
22%19%30%16%10%1
285
December1st to 15thDay
23%26%32%9%7%
113
16th to endDay
27%31%32%9%
96
January1st to 15thNight
20%21%37%18%2
780
16th to endNight
23%18%36%18%2
832
February1st to 15thNight
21%18%37%20%1
764
16th to endNight
24%18%34%18%4
683
March1st to 15thNight
25%17%36%18%3
764
16th to endNight
21%18%34%18%7%
768
April1st to 15thNight
21%19%34%20%4
718
16th to endNight
23%15%32%22%5%
582
May1st to 15thNight
25%14%30%22%5%
540
16th to endNight
22%11%35%23%6%
417
June1st to 15thNight
24%8%31%25%8%1
360
16th to endNight
18%5%32%33%9%
360
July1st to 15thNight
13%329%40%12%1
340
16th to endNight
13%328%38%15%
376
August1st to 15thNight
13%429%38%14%
509
16th to endNight
14%423%37%18%1
708
September1st to 15thNight
16%5%31%29%14%1
720
16th to endNight
17%5%24%25%22%4
717
October1st to 15thNight
21%9%26%26%13%2
720
16th to endNight
22%15%32%20%8%
768
November1st to 15thNight
19%15%30%23%10%1
760
16th to endNight
20%18%30%21%7%
780
December1st to 15thNight
24%16%34%19%4
780
16th to endNight
23%20%35%18%2
832
Page generated at 2018-03-12 13:28:02. Version ac04

Copyright 2018 A. Danko


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