Fenwick Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Fenwick Observatory clear sky chart from 2005-11-06 to 2024-01-12.

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
38%
23718
21%
74650
12%
23670
48%
23670
25%
46610

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 10thNight
20%
757
25%
2488
7%
757
41%
757
22%
1511
January11th to 20thNight
24%
725
22%
2354
8%
725
41%
725
18%
1529
January21st to endNight
21%
792
26%
2574
11%
792
40%
792
23%
1552
February1st to 10thNight
23%
720
19%
2340
9%
720
37%
720
21%
1467
February11th to 20thNight
16%
700
20%
2217
6%
699
33%
699
18%
1418
February21st to endNight
19%
592
27%
1765
9%
592
39%
592
22%
1129
March1st to 10thNight
25%
720
26%
1980
10%
720
40%
720
28%
1214
March11th to 20thNight
22%
720
21%
1980
9%
720
34%
720
23%
1313
March21st to endNight
23%
792
21%
2170
7%
792
35%
792
23%
1458
April1st to 10thNight
23%
720
22%
1800
5%
720
35%
720
27%
1195
April11th to 20thNight
32%
711
24%
1775
7%
711
40%
711
35%
1122
April21st to endNight
31%
720
21%
1800
8%
720
37%
720
30%
1200
May1st to 10thNight
31%
621
17%
1701
7%
621
38%
621
26%
1123
May11th to 20thNight
39%
523
16%
1585
9%
523
44%
523
23%
1075
May21st to endNight
54%
388
18%
1550
17%
388
59%
388
21%
937
June1st to 10thNight
57%
360
17%
1440
18%
360
62%
360
23%
854
June11th to 20thNight
56%
360
15%
1440
17%
360
59%
360
22%
873
June21st to endNight
60%
360
20%
1440
19%
360
68%
360
26%
822
July1st to 10thNight
58%
377
17%
1427
19%
377
60%
377
23%
878
July11th to 20thNight
71%
522
15%
1566
13%
522
73%
522
32%
962
July21st to endNight
62%
591
17%
1672
13%
558
64%
558
28%
1099
August1st to 10thNight
62%
537
16%
1600
12%
534
63%
534
28%
1055
August11th to 20thNight
58%
619
16%
1683
10%
619
59%
619
25%
1163
August21st to endNight
61%
792
18%
1980
11%
792
63%
792
30%
1363
September1st to 10thNight
60%
720
21%
1800
14%
720
62%
720
32%
1209
September11th to 20thNight
60%
720
28%
1800
21%
720
63%
720
35%
1160
September21st to endNight
43%
720
18%
2074
14%
720
48%
720
23%
1418
October1st to 10thNight
50%
720
23%
2160
20%
720
57%
720
30%
1329
October11th to 20thNight
42%
720
27%
2160
20%
720
53%
720
28%
1319
October21st to endNight
39%
792
28%
2376
19%
792
53%
792
31%
1408
November1st to 10thNight
41%
740
26%
2233
17%
740
53%
740
30%
1335
November11th to 20thNight
35%
760
25%
2470
15%
760
48%
760
27%
1449
November21st to endNight
36%
760
25%
2644
16%
760
52%
760
27%
1473
December1st to 10thNight
26%
760
22%
2660
10%
760
42%
760
19%
1664
December11th to 20thNight
31%
759
23%
3185
12%
759
48%
759
20%
1855
December21st to endNight
30%
828
16%
4761
12%
817
46%
817
12%
2679

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
13%5%25%5%35%5%6%8%43%
74626
Night
14%6%25%5%3445%7%44%
75076
TransparencyDay
38%6%12%23%17%4
74343
Night
39%6%11%22%18%4
74878
SeeingDay
18%11%27%25%15%5%
13975
Night
17%10%29%30%13%2
23734

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
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 10thDay
14%7%35%5%24445%46%
1672
11th to 20thDay
17%7%36%5%34446%42%
1629
21st to endDay
16%6%25%5%2345%7%45%
1782
February1st to 10thDay
13%7%36%5%35%5%6%8%38%
1620
11th to 20thDay
21%6%33333446%44%
1628
21st to endDay
18%7%27%6%35%45%6%36%
1488
March1st to 10thDay
13%5%245%2335%7%51%
1980
11th to 20thDay
16%5%35%435%5%5%6%42%
1980
21st to endDay
17%8%36%5%25%45%6%40%
2186
April1st to 10thDay
10%5%2443445%7%52%
2160
11th to 20thDay
12%5%245%2445%7%48%
2134
21st to endDay
15%6%25%5%35%5%5%7%43%
2160
May1st to 10thDay
14%5%35%5%35%5%7%8%40%
2274
11th to 20thDay
17%6%35%6%445%6%7%38%
2305
21st to endDay
13%5%35%6%445%7%8%40%
2725
June1st to 10thDay
12%425%5%35%6%6%10%43%
2520
11th to 20thDay
11%325%6%35%6%8%9%41%
2520
21st to endDay
9%425%5%45%6%7%11%42%
2520
July1st to 10thDay
8%5%26%6%46%6%7%10%39%
2486
11th to 20thDay
6%326%7%46%5%8%13%40%
2340
21st to endDay
8%426%5%5%6%7%8%12%38%
2547
August1st to 10thDay
10%6%26%7%46%6%7%10%35%
2327
11th to 20thDay
10%6%28%7%46%6%7%9%35%
2198
21st to endDay
10%6%25%5%45%5%7%11%40%
2376
September1st to 10thDay
13%5%24335%5%6%9%44%
2160
11th to 20thDay
11%6%35%5%3435%8%48%
2160
21st to endDay
20%7%26%434446%39%
1879
October1st to 10thDay
16%5%25%5%34346%48%
1800
11th to 20thDay
17%5%2342345%5%51%
1800
21st to endDay
14%424433347%52%
1980
November1st to 10thDay
13%6%23324445%54%
1843
11th to 20thDay
14%6%2443345%6%50%
1710
21st to endDay
14%5%24423346%52%
1535
December1st to 10thDay
17%7%25%43446%9%41%
1520
11th to 20thDay
16%6%2432343453%
1910
21st to endDay
17%6%26%5%35%45%7%40%
2772
January1st to 10thNight
17%5%35%435%346%47%
2488
11th to 20thNight
17%6%35%5%35%5%5%6%40%
2354
21st to endNight
16%7%2442444449%
2574
February1st to 10thNight
16%6%25%5%3445%7%41%
2340
11th to 20thNight
19%7%36%434446%42%
2216
21st to endNight
17%6%25%5%23346%45%
1765
March1st to 10thNight
13%425%4335%5%6%50%
1980
11th to 20thNight
18%6%25%5%3446%7%40%
1980
21st to endNight
16%6%36%434445%44%
2170
April1st to 10thNight
13%6%36%6%35%347%46%
1800
11th to 20thNight
11%7%25%43345%7%50%
1775
21st to endNight
15%6%25%5%2445%7%45%
1800
May1st to 10thNight
13%6%25%5%3447%9%41%
1701
11th to 20thNight
16%6%35%5%35%5%5%7%39%
1584
21st to endNight
13%5%25%6%45%5%6%9%41%
1550
June1st to 10thNight
11%435%5%36%5%7%10%40%
1440
11th to 20thNight
10%5%25%5%46%5%7%10%40%
1440
21st to endNight
8%5%245%35%6%8%9%44%
1440
July1st to 10thNight
9%5%36%6%45%46%10%42%
1468
11th to 20thNight
5%335%5%47%6%8%10%44%
1620
21st to endNight
8%435%7%5%6%6%9%9%38%
1771
August1st to 10thNight
8%5%37%6%45%5%7%11%37%
1611
11th to 20thNight
12%6%26%6%46%6%8%9%35%
1683
21st to endNight
9%5%35%5%46%6%7%10%38%
1980
September1st to 10thNight
13%5%35%5%35%5%5%8%43%
1800
11th to 20thNight
11%6%35%5%345%46%48%
1800
21st to endNight
20%8%35%425%45%7%38%
2074
October1st to 10thNight
15%6%25%433446%48%
2160
11th to 20thNight
16%5%245%3335%6%48%
2160
21st to endNight
15%5%24423446%51%
2376
November1st to 10thNight
13%6%25%433345%52%
2233
11th to 20thNight
14%6%34424446%51%
2470
21st to endNight
13%4244245%5%7%50%
2644
December1st to 10thNight
17%7%245%3445%6%42%
2660
11th to 20thNight
18%6%34423446%47%
3285
21st to endNight
15%7%35%42445%7%42%
4884

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 10thDay
41%48%25%18%5%
1673
11th to 20thDay
44%5%9%22%18%3
1629
21st to endDay
40%410%23%19%5%
1782
February1st to 10thDay
42%6%11%25%14%3
1620
11th to 20thDay
42%5%6%22%20%5%
1637
21st to endDay
48%5%10%15%17%5%
1488
March1st to 10thDay
35%5%9%24%22%6%
1980
11th to 20thDay
41%5%10%20%16%8%
1980
21st to endDay
46%6%9%19%18%4
2186
April1st to 10thDay
31%5%12%23%20%9%
2160
11th to 20thDay
35%5%11%20%22%7%
2134
21st to endDay
41%6%11%22%15%6%
2160
May1st to 10thDay
40%8%15%19%15%3
2274
11th to 20thDay
44%7%12%23%11%2
2309
21st to endDay
40%7%15%25%12%1
2725
June1st to 10thDay
35%8%16%26%14%1
2520
11th to 20thDay
36%9%17%21%16%1
2520
21st to endDay
34%8%16%24%15%2
2520
July1st to 10thDay
37%9%14%21%16%3
2417
11th to 20thDay
33%8%21%25%12%2
2271
21st to endDay
36%10%14%23%15%1
2405
August1st to 10thDay
41%9%16%22%10%1
2314
11th to 20thDay
42%10%15%21%11%1
2198
21st to endDay
37%8%17%23%13%3
2376
September1st to 10thDay
37%7%15%17%20%3
2160
11th to 20thDay
36%5%9%26%19%4
2160
21st to endDay
46%5%9%20%16%3
1879
October1st to 10thDay
39%410%24%20%3
1800
11th to 20thDay
35%5%8%25%24%4
1800
21st to endDay
34%46%25%25%6%
1980
November1st to 10thDay
33%49%25%25%4
1843
11th to 20thDay
35%410%21%23%7%
1710
21st to endDay
34%47%25%24%5%
1535
December1st to 10thDay
40%6%11%25%14%5%
1520
11th to 20thDay
36%47%30%16%7%
1906
21st to endDay
42%6%10%27%14%1
2772
January1st to 10thNight
40%48%21%20%7%
2488
11th to 20thNight
44%5%9%21%16%4
2354
21st to endNight
38%5%7%24%21%5%
2574
February1st to 10thNight
42%410%24%17%3
2340
11th to 20thNight
44%37%21%18%7%
2218
21st to endNight
42%48%21%18%8%
1765
March1st to 10thNight
35%49%25%23%4
1980
11th to 20thNight
42%5%8%22%19%4
1980
21st to endNight
43%5%9%22%17%5%
2170
April1st to 10thNight
39%5%9%19%22%7%
1800
11th to 20thNight
34%5%10%22%22%7%
1775
21st to endNight
40%5%11%23%16%5%
1800
May1st to 10thNight
39%7%14%21%15%3
1701
11th to 20thNight
43%9%13%20%14%2
1585
21st to endNight
38%9%14%26%12%1
1551
June1st to 10thNight
37%8%14%25%15%1
1440
11th to 20thNight
37%10%18%18%16%1
1440
21st to endNight
32%10%15%22%18%3
1440
July1st to 10thNight
39%9%15%19%15%4
1427
11th to 20thNight
31%11%21%24%11%2
1566
21st to endNight
36%11%16%23%14%
1672
August1st to 10thNight
38%9%17%24%11%
1600
11th to 20thNight
41%11%16%19%12%1
1683
21st to endNight
38%10%14%24%12%2
1980
September1st to 10thNight
39%7%15%20%14%5%
1800
11th to 20thNight
35%6%10%25%21%3
1800
21st to endNight
46%5%10%18%16%4
2074
October1st to 10thNight
38%49%25%19%4
2160
11th to 20thNight
38%47%24%22%5%
2160
21st to endNight
35%49%24%23%6%
2376
November1st to 10thNight
36%49%22%24%5%
2233
11th to 20thNight
36%48%19%23%9%
2470
21st to endNight
33%5%9%25%22%6%
2644
December1st to 10thNight
43%5%8%23%17%4
2660
11th to 20thNight
39%49%21%21%6%
3288
21st to endNight
40%6%10%25%17%2
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
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 10thDay
26%24%32%14%4
254
11th to 20thDay
27%27%32%12%3
243
21st to endDay
24%24%38%13%2
264
February1st to 10thDay
23%25%38%11%3
240
11th to 20thDay
34%23%32%11%1
295
21st to endDay
29%19%31%18%3
346
March1st to 10thDay
20%22%35%18%5%
420
11th to 20thDay
22%24%35%15%41
420
21st to endDay
24%15%40%15%5%1
462
April1st to 10thDay
23%18%32%19%8%1
420
11th to 20thDay
18%12%34%21%9%4
412
21st to endDay
23%14%33%21%8%1
420
May1st to 10thDay
18%15%33%23%9%2
423
11th to 20thDay
21%9%28%28%12%2
447
21st to endDay
20%421%29%21%5%
485
June1st to 10thDay
12%6%24%30%22%5%
450
11th to 20thDay
13%5%24%35%16%6%
450
21st to endDay
11%5%22%35%21%6%
450
July1st to 10thDay
10%217%34%27%10%
445
11th to 20thDay
5%214%38%30%10%
444
21st to endDay
10%221%34%24%10%
488
August1st to 10thDay
14%317%31%26%9%
446
11th to 20thDay
11%416%30%29%10%
439
21st to endDay
12%315%31%24%15%
495
September1st to 10thDay
18%316%28%19%17%
450
11th to 20thDay
15%417%27%25%11%
450
21st to endDay
28%7%21%27%14%4
450
October1st to 10thDay
21%5%22%24%20%7%
450
11th to 20thDay
16%9%26%28%19%2
450
21st to endDay
16%11%33%27%9%4
495
November1st to 10thDay
18%9%31%24%13%4
449
11th to 20thDay
16%14%33%26%11%1
370
21st to endDay
19%14%31%24%10%2
195
December1st to 10thDay
23%18%36%15%7%1
180
11th to 20thDay
24%15%33%17%9%1
180
21st to endDay
23%17%30%21%9%1
198
January1st to 10thNight
22%17%39%19%3
760
11th to 20thNight
20%17%33%26%4
725
21st to endNight
21%16%38%24%2
792
February1st to 10thNight
20%14%39%23%3
720
11th to 20thNight
24%20%36%19%2
703
21st to endNight
22%17%38%20%3
592
March1st to 10thNight
19%16%37%25%3
720
11th to 20thNight
22%16%36%20%5%1
720
21st to endNight
19%14%39%23%4
792
April1st to 10thNight
17%18%39%22%4
720
11th to 20thNight
14%13%38%27%8%
711
21st to endNight
18%10%38%28%7%
720
May1st to 10thNight
17%10%37%28%9%
621
11th to 20thNight
17%5%31%34%12%1
523
21st to endNight
15%321%38%22%2
389
June1st to 10thNight
12%221%42%22%1
360
11th to 20thNight
12%419%40%22%3
360
21st to endNight
8%419%48%21%1
360
July1st to 10thNight
11%317%40%26%3
377
11th to 20thNight
5%13%42%35%5%
522
21st to endNight
7%217%45%25%4
591
August1st to 10thNight
11%212%45%28%3
537
11th to 20thNight
13%313%41%26%4
619
21st to endNight
12%214%36%29%6%
792
September1st to 10thNight
16%213%36%28%6%
720
11th to 20thNight
13%415%34%31%4
720
21st to endNight
24%321%34%17%1
720
October1st to 10thNight
17%5%21%32%21%4
720
11th to 20thNight
19%9%24%31%16%2
720
21st to endNight
16%10%30%29%13%1
792
November1st to 10thNight
18%8%27%31%13%2
740
11th to 20thNight
18%12%31%29%9%1
760
21st to endNight
14%14%32%30%9%1
760
December1st to 10thNight
21%14%34%24%8%
760
11th to 20thNight
19%12%34%30%6%
760
21st to endNight
21%14%29%32%5%
836
Page generated at 2024-01-08 22:31:29. Version ac07

Copyright 2024 Attilla Danko


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