Sewell
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sewell clear sky chart from 2005-11-06 to 2024-01-16.

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
32%
23294
20%
74652
10%
23248
44%
23248
22%
47065

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
18%
759
23%
2649
8%
757
38%
757
19%
1619
January11th to 20thNight
21%
744
20%
2552
6%
744
39%
744
16%
1661
January21st to endNight
20%
792
24%
2574
7%
792
40%
792
22%
1561
February1st to 10thNight
17%
720
16%
2340
5%
720
32%
720
18%
1510
February11th to 20thNight
12%
703
19%
2125
4%
699
33%
699
16%
1403
February21st to endNight
16%
592
25%
1776
8%
592
36%
592
17%
1155
March1st to 10thNight
22%
720
23%
2160
8%
720
40%
720
24%
1311
March11th to 20thNight
19%
720
22%
1983
8%
720
33%
720
21%
1310
March21st to endNight
18%
792
22%
2048
6%
792
30%
792
24%
1384
April1st to 10thNight
19%
720
19%
1800
3%
720
29%
720
22%
1237
April11th to 20thNight
26%
711
20%
1775
5%
711
34%
711
27%
1195
April21st to endNight
26%
720
20%
1800
5%
720
34%
720
25%
1216
May1st to 10thNight
24%
612
16%
1692
6%
612
31%
612
20%
1190
May11th to 20thNight
29%
354
18%
1416
10%
354
40%
354
16%
901
May21st to endNight
45%
388
14%
1551
14%
388
50%
388
17%
996
June1st to 10thNight
44%
360
19%
1440
17%
360
53%
360
21%
851
June11th to 20thNight
44%
360
16%
1440
15%
360
52%
360
21%
880
June21st to endNight
51%
360
17%
1440
16%
360
60%
360
26%
818
July1st to 10thNight
52%
350
14%
1400
15%
350
59%
350
19%
892
July11th to 20thNight
60%
348
15%
1392
17%
348
63%
348
24%
806
July21st to endNight
53%
438
18%
1528
15%
414
60%
414
26%
889
August1st to 10thNight
60%
537
17%
1600
12%
534
62%
534
28%
1017
August11th to 20thNight
54%
701
16%
1765
9%
701
56%
701
29%
1214
August21st to endNight
54%
792
17%
1980
8%
792
57%
792
31%
1333
September1st to 10thNight
47%
720
21%
1800
10%
720
52%
720
31%
1226
September11th to 20thNight
54%
720
30%
1832
19%
720
59%
720
41%
1109
September21st to endNight
41%
720
23%
1980
15%
720
49%
720
27%
1304
October1st to 10thNight
40%
720
17%
2146
12%
720
46%
720
24%
1396
October11th to 20thNight
38%
720
25%
2160
16%
720
51%
720
30%
1297
October21st to endNight
28%
792
25%
2437
13%
792
43%
792
25%
1510
November1st to 10thNight
34%
740
25%
2407
12%
740
50%
740
28%
1375
November11th to 20thNight
27%
760
25%
2470
12%
760
44%
760
22%
1501
November21st to endNight
27%
760
24%
2569
11%
760
45%
760
23%
1519
December1st to 10thNight
21%
760
19%
2660
7%
760
37%
760
17%
1687
December11th to 20thNight
21%
760
20%
3184
6%
759
38%
759
15%
1912
December21st to endNight
23%
829
14%
4781
8%
817
40%
817
11%
2880

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
14%6%25%5%35%5%6%8%42%
74761
Night
15%6%25%5%3445%7%43%
75035
TransparencyDay
40%7%12%23%16%3
74469
Night
40%6%11%22%17%3
74861
SeeingDay
19%16%29%21%11%3
13899
Night
18%13%32%27%9%1
23303

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 10thDay
13%7%35%5%35%45%7%43%
1517
11th to 20thDay
14%7%35%7%34447%42%
1525
21st to endDay
15%8%345%25%45%6%42%
1782
February1st to 10thDay
16%7%36%4445%6%6%39%
1620
11th to 20thDay
17%6%245%35%5%5%6%41%
1719
21st to endDay
18%10%46%5%35%445%38%
1480
March1st to 10thDay
13%6%25%434446%49%
1797
11th to 20thDay
17%5%35%436%46%7%40%
1975
21st to endDay
20%6%25%435%45%6%39%
2308
April1st to 10thDay
15%7%345%345%6%6%43%
2160
11th to 20thDay
14%6%25%5%25%45%8%44%
2134
21st to endDay
17%5%346%345%6%7%40%
2160
May1st to 10thDay
18%7%36%5%35%5%6%7%36%
2282
11th to 20thDay
17%6%36%5%45%5%5%7%37%
2478
21st to endDay
13%5%26%5%345%6%9%42%
2725
June1st to 10thDay
13%5%25%6%35%6%8%8%39%
2520
11th to 20thDay
12%5%26%5%36%6%7%9%38%
2520
21st to endDay
10%425%6%36%6%7%9%42%
2520
July1st to 10thDay
9%5%26%7%36%5%7%10%40%
2520
11th to 20thDay
6%425%6%36%6%7%11%43%
2520
21st to endDay
10%6%36%5%47%5%7%10%37%
2695
August1st to 10thDay
10%5%26%7%46%6%6%8%41%
2318
11th to 20thDay
11%5%35%6%35%6%5%9%41%
2126
21st to endDay
12%6%35%6%35%5%6%9%40%
2376
September1st to 10thDay
13%6%25%5%35%46%7%43%
2160
11th to 20thDay
13%42443445%7%51%
2126
21st to endDay
17%7%36%5%2445%7%40%
1980
October1st to 10thDay
19%6%2442445%6%44%
1812
11th to 20thDay
16%5%2332435%6%49%
1800
21st to endDay
18%6%25%424346%46%
1918
November1st to 10thDay
13%5%335%23347%52%
1671
11th to 20thDay
15%5%244345%5%7%47%
1710
21st to endDay
14%5%245%34447%48%
1609
December1st to 10thDay
19%7%25%33445%9%39%
1520
11th to 20thDay
19%8%345%23445%44%
1906
21st to endDay
16%7%25%5%36%6%6%8%36%
2772
January1st to 10thNight
17%6%2443445%5%45%
2649
11th to 20thNight
19%6%35%5%35%45%6%39%
2552
21st to endNight
14%6%35%435%447%44%
2574
February1st to 10thNight
17%8%35%5%2446%7%39%
2340
11th to 20thNight
19%8%35%5%33346%41%
2125
21st to endNight
18%7%35%42445%5%43%
1776
March1st to 10thNight
15%5%25%42445%8%47%
2150
11th to 20thNight
17%7%35%5%34445%44%
1982
21st to endNight
16%7%35%5%25%446%43%
2048
April1st to 10thNight
17%6%26%43446%7%41%
1800
11th to 20thNight
14%6%35%5%3445%7%43%
1775
21st to endNight
19%5%245%3435%7%43%
1800
May1st to 10thNight
18%7%36%5%35%5%5%7%35%
1692
11th to 20thNight
17%6%45%5%245%6%8%38%
1415
21st to endNight
15%6%26%5%35%6%5%7%39%
1550
June1st to 10thNight
14%5%25%5%35%46%9%43%
1440
11th to 20thNight
10%7%36%6%35%46%10%40%
1440
21st to endNight
9%6%24445%5%7%11%43%
1440
July1st to 10thNight
10%5%36%6%47%6%6%9%38%
1440
11th to 20thNight
7%4346%47%7%7%9%44%
1440
21st to endNight
9%5%26%6%35%5%6%9%44%
1618
August1st to 10thNight
8%6%25%6%36%7%7%8%43%
1611
11th to 20thNight
10%8%37%5%35%5%6%8%40%
1765
21st to endNight
13%5%25%5%35%5%6%9%41%
1980
September1st to 10thNight
13%6%36%5%3445%7%45%
1800
11th to 20thNight
10%5%2433245%7%55%
1832
21st to endNight
17%6%25%5%3445%7%42%
1980
October1st to 10thNight
19%7%25%433346%43%
2146
11th to 20thNight
16%415%42335%6%50%
2160
21st to endNight
17%7%245%24346%47%
2437
November1st to 10thNight
12%5%2442435%6%53%
2407
11th to 20thNight
17%5%25%424335%49%
2470
21st to endNight
13%5%25%5%35%5%6%7%45%
2569
December1st to 10thNight
20%7%36%3245%5%6%40%
2660
11th to 20thNight
16%6%35%5%3445%7%43%
3288
21st to endNight
17%7%35%5%35%5%6%8%37%
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
42%5%11%22%15%5%
1518
11th to 20thDay
42%6%12%23%14%3
1525
21st to endDay
42%410%24%15%3
1782
February1st to 10thDay
44%6%13%24%11%2
1620
11th to 20thDay
43%5%9%25%14%3
1728
21st to endDay
49%49%21%13%5%
1480
March1st to 10thDay
37%5%11%29%15%3
1800
11th to 20thDay
42%5%11%22%16%4
1975
21st to endDay
46%6%7%20%17%4
2308
April1st to 10thDay
41%6%10%20%16%6%
2160
11th to 20thDay
39%6%12%23%17%5%
2134
21st to endDay
42%6%11%19%18%5%
2160
May1st to 10thDay
46%7%9%19%16%3
2282
11th to 20thDay
45%7%12%20%13%2
2482
21st to endDay
38%9%14%24%13%2
2725
June1st to 10thDay
39%9%13%23%15%2
2520
11th to 20thDay
40%10%13%22%13%2
2520
21st to endDay
36%10%13%23%17%1
2520
July1st to 10thDay
39%10%13%21%15%2
2450
11th to 20thDay
31%10%16%26%14%3
2445
21st to endDay
39%10%13%22%16%1
2544
August1st to 10thDay
39%9%14%23%14%1
2305
11th to 20thDay
39%9%15%19%16%2
2126
21st to endDay
38%10%13%20%16%4
2376
September1st to 10thDay
40%6%11%19%20%3
2160
11th to 20thDay
33%6%9%23%25%4
2126
21st to endDay
45%5%8%18%21%2
1980
October1st to 10thDay
41%6%11%22%19%2
1812
11th to 20thDay
37%410%24%23%3
1800
21st to endDay
41%5%8%25%19%2
1918
November1st to 10thDay
34%411%27%20%3
1671
11th to 20thDay
37%6%9%23%22%3
1710
21st to endDay
37%411%31%14%3
1609
December1st to 10thDay
43%5%15%23%13%1
1520
11th to 20thDay
43%5%11%28%10%3
1906
21st to endDay
44%6%13%23%13%1
2772
January1st to 10thNight
41%5%9%24%18%4
2649
11th to 20thNight
45%6%12%22%13%2
2552
21st to endNight
39%410%26%18%3
2574
February1st to 10thNight
44%5%13%23%13%2
2340
11th to 20thNight
45%5%9%20%17%5%
2127
21st to endNight
43%5%9%22%16%5%
1776
March1st to 10thNight
37%412%25%19%3
2160
11th to 20thNight
42%410%21%18%4
1983
21st to endNight
44%49%19%18%6%
2048
April1st to 10thNight
43%5%9%20%19%5%
1800
11th to 20thNight
40%5%10%21%19%5%
1775
21st to endNight
42%49%20%20%5%
1800
May1st to 10thNight
47%6%9%17%18%2
1692
11th to 20thNight
44%8%12%15%18%3
1416
21st to endNight
44%9%14%18%13%2
1551
June1st to 10thNight
38%8%11%22%20%2
1440
11th to 20thNight
40%8%14%24%13%2
1440
21st to endNight
33%9%15%26%15%2
1440
July1st to 10thNight
41%11%14%20%13%2
1400
11th to 20thNight
33%10%17%24%14%2
1392
21st to endNight
34%9%15%25%16%2
1528
August1st to 10thNight
35%10%17%23%14%1
1600
11th to 20thNight
39%9%14%21%16%1
1765
21st to endNight
38%8%13%21%17%3
1980
September1st to 10thNight
38%8%12%20%18%4
1800
11th to 20thNight
30%5%11%24%26%4
1832
21st to endNight
41%6%9%21%21%2
1980
October1st to 10thNight
42%6%12%21%17%3
2146
11th to 20thNight
35%411%28%18%3
2160
21st to endNight
39%5%9%25%20%3
2437
November1st to 10thNight
33%6%11%25%19%5%
2407
11th to 20thNight
39%49%21%20%6%
2470
21st to endNight
36%6%11%27%18%2
2569
December1st to 10thNight
44%5%11%23%14%1
2660
11th to 20thNight
41%5%11%20%19%4
3288
21st to endNight
44%7%14%24%11%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
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 10thDay
25%27%31%12%41
180
11th to 20thDay
27%35%26%12%1
190
21st to endDay
24%34%27%11%31
264
February1st to 10thDay
28%31%29%10%2
240
11th to 20thDay
29%27%33%10%1
387
21st to endDay
29%24%33%12%1
346
March1st to 10thDay
23%26%31%17%3
420
11th to 20thDay
23%27%32%12%32
420
21st to endDay
26%23%32%14%41
462
April1st to 10thDay
22%26%35%10%5%1
420
11th to 20thDay
20%21%33%17%7%2
412
21st to endDay
24%24%32%15%5%
420
May1st to 10thDay
29%21%26%15%7%2
423
11th to 20thDay
21%17%33%20%7%2
447
21st to endDay
17%10%25%27%16%4
485
June1st to 10thDay
14%12%31%27%13%3
450
11th to 20thDay
16%12%30%27%12%3
450
21st to endDay
12%10%29%30%16%3
450
July1st to 10thDay
13%6%25%30%20%7%
445
11th to 20thDay
6%425%36%23%6%
444
21st to endDay
12%7%26%34%17%5%
488
August1st to 10thDay
10%6%26%33%18%7%
446
11th to 20thDay
15%420%33%22%7%
439
21st to endDay
11%8%28%27%18%8%
495
September1st to 10thDay
17%11%21%25%17%9%
450
11th to 20thDay
14%6%30%25%16%9%
450
21st to endDay
24%14%26%23%11%3
450
October1st to 10thDay
25%9%25%22%13%6%
450
11th to 20thDay
19%15%28%24%13%1
450
21st to endDay
20%17%35%17%8%2
464
November1st to 10thDay
16%15%33%22%12%2
365
11th to 20thDay
19%22%33%18%8%
370
21st to endDay
17%22%32%24%4
269
December1st to 10thDay
23%31%30%10%6%
180
11th to 20thDay
31%22%32%12%3
180
21st to endDay
27%22%29%17%6%1
198
January1st to 10thNight
20%20%38%19%3
760
11th to 20thNight
24%17%33%22%3
744
21st to endNight
18%19%39%21%2
792
February1st to 10thNight
22%19%38%20%1
720
11th to 20thNight
26%24%34%15%1
703
21st to endNight
24%22%36%17%2
592
March1st to 10thNight
20%20%35%21%4
720
11th to 20thNight
22%20%35%17%5%1
720
21st to endNight
20%17%42%16%5%
792
April1st to 10thNight
21%23%34%18%5%
720
11th to 20thNight
17%15%38%25%4
711
21st to endNight
22%16%33%25%5%
720
May1st to 10thNight
20%14%37%22%6%
612
11th to 20thNight
19%10%38%28%6%
354
21st to endNight
19%424%39%13%1
389
June1st to 10thNight
16%6%29%38%11%
360
11th to 20thNight
12%6%30%40%11%1
360
21st to endNight
9%331%46%11%
360
July1st to 10thNight
10%327%42%17%1
350
11th to 20thNight
8%5%19%48%18%2
348
21st to endNight
9%427%41%19%1
438
August1st to 10thNight
11%320%43%22%2
537
11th to 20thNight
14%319%42%21%2
701
21st to endNight
14%321%38%21%3
792
September1st to 10thNight
16%424%37%16%2
720
11th to 20thNight
13%422%35%21%4
720
21st to endNight
21%6%25%30%17%1
720
October1st to 10thNight
22%7%26%28%14%3
720
11th to 20thNight
19%11%28%29%12%1
720
21st to endNight
21%14%35%23%8%
792
November1st to 10thNight
14%12%36%26%12%1
740
11th to 20thNight
19%16%32%25%7%1
760
21st to endNight
16%18%36%23%8%1
760
December1st to 10thNight
24%16%34%18%7%1
760
11th to 20thNight
17%20%35%23%6%
760
21st to endNight
21%16%34%26%2
836
Page generated at 2024-01-13 09:37:54. Version ac07

Copyright 2024 Attilla Danko


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