Wetzel Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Wetzel Observatory clear sky chart from 2005-11-05 to 2017-12-02.

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
30%
15072
17%
47757
9%
15041
40%
15041
20%
31612

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
21%
720
19%
2506
8%
716
36%
716
18%
1614
January16th to endNight
18%
768
17%
2688
5%
768
34%
768
15%
1756
February1st to 15thNight
17%
703
15%
2253
5%
701
30%
701
15%
1577
February16th to endNight
23%
631
20%
1893
7%
631
39%
631
18%
1287
March1st to 15thNight
20%
720
17%
2136
6%
720
33%
720
17%
1510
March16th to endNight
25%
768
22%
2058
8%
768
35%
768
22%
1361
April1st to 15thNight
23%
718
17%
1796
4%
718
31%
718
22%
1293
April16th to endNight
25%
549
16%
1629
6%
549
34%
549
20%
1128
May1st to 15thNight
28%
540
14%
1620
7%
540
35%
540
18%
1133
May16th to endNight
32%
401
11%
1523
9%
400
39%
400
14%
1065
June1st to 15thNight
31%
360
10%
1440
8%
360
40%
360
13%
1012
June16th to endNight
46%
360
10%
1440
13%
360
51%
360
20%
905
July1st to 15thNight
52%
340
11%
1360
16%
340
56%
340
22%
840
July16th to endNight
52%
376
13%
1418
15%
354
57%
354
20%
873
August1st to 15thNight
46%
500
15%
1571
11%
498
49%
498
24%
1010
August16th to endNight
49%
657
21%
1803
13%
657
51%
657
32%
1133
September1st to 15thNight
44%
720
19%
1878
9%
720
50%
720
34%
1198
September16th to endNight
45%
717
27%
1980
16%
717
53%
717
36%
1169
October1st to 15thNight
38%
720
21%
2028
11%
720
47%
720
26%
1315
October16th to endNight
23%
768
17%
2496
7%
768
36%
768
18%
1664
November1st to 15thNight
30%
760
21%
2472
11%
760
44%
760
22%
1564
November16th to endNight
26%
780
21%
2535
9%
780
40%
780
19%
1632
December1st to 15thNight
19%
728
17%
2546
5%
728
34%
728
16%
1718
December16th to endNight
20%
768
17%
2688
7%
768
34%
768
14%
1855

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
18%6%245%2445%6%38%
48651
Night
17%7%25%434446%39%
47927
Cloud CoverDay
18%6%25%42445%6%38%
48661
Night
18%7%24424446%39%
47932
TransparencyDay
45%5%10%21%14%1
48339
Night
44%5%10%22%14%1
47757
SeeingDay
22%12%29%21%10%3
6109
Night
22%10%30%26%9%
15073

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%3443345%7%38%
1432
16th to endDay
14%8%35%5%2345%5%40%
1536
February1st to 15thDay
16%9%35%5%35%5%5%6%33%
1606
16th to endDay
13%9%36%5%25%5%5%5%36%
1580
March1st to 15thDay
18%9%26%5%34347%34%
1813
16th to endDay
16%6%345%24345%42%
2163
April1st to 15thDay
18%7%2442445%6%38%
2152
16th to endDay
20%5%345%23445%39%
2331
May1st to 15thDay
25%7%25%6%34446%30%
2332
16th to endDay
20%5%35%5%235%6%7%34%
2602
June1st to 15thDay
26%6%35%434446%31%
2520
16th to endDay
19%5%35%5%35%5%5%7%33%
2520
July1st to 15thDay
13%5%25%6%36%6%6%8%35%
2520
16th to endDay
14%5%25%5%36%6%6%9%34%
2654
August1st to 15thDay
14%6%25%6%35%45%7%37%
2367
16th to endDay
11%42442446%6%47%
2396
September1st to 15thDay
14%425%424446%47%
2082
16th to endDay
13%423323336%53%
1980
October1st to 15thDay
19%7%14423335%43%
1932
16th to endDay
19%6%24424346%41%
1728
November1st to 15thDay
20%42432346%7%40%
1716
16th to endDay
21%6%13423446%40%
1755
December1st to 15thDay
21%7%245%24447%34%
1398
16th to endDay
22%11%35%424345%32%
1536
January1st to 15thNight
14%9%3433435%6%40%
2506
16th to endNight
15%9%35%435%446%36%
2688
February1st to 15thNight
13%10%36%6%46%5%46%33%
2252
16th to endNight
15%8%36%5%24345%39%
1893
March1st to 15thNight
18%9%35%42445%5%35%
2123
16th to endNight
16%6%24424445%44%
2058
April1st to 15thNight
19%7%35%5%44345%36%
1796
16th to endNight
21%7%25%424446%37%
1629
May1st to 15thNight
20%7%35%43345%6%33%
1620
16th to endNight
22%6%36%425%45%7%30%
1521
June1st to 15thNight
25%7%245%34446%32%
1440
16th to endNight
18%5%3442445%8%39%
1440
July1st to 15thNight
14%4245%345%6%9%38%
1440
16th to endNight
13%32444446%10%40%
1514
August1st to 15thNight
13%5%15%5%345%6%8%40%
1581
16th to endNight
13%42342445%8%46%
1803
September1st to 15thNight
14%5%12423347%49%
1878
16th to endNight
13%413322336%53%
1980
October1st to 15thNight
17%5%14423446%42%
2028
16th to endNight
22%5%25%32235%6%37%
2496
November1st to 15thNight
17%6%24324446%42%
2472
16th to endNight
17%6%25%424345%42%
2535
December1st to 15thNight
21%8%35%423346%36%
2546
16th to endNight
21%10%2443434435%
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
16%7%3343435%7%38%
1432
16th to endDay
15%9%25%42445%6%39%
1536
February1st to 15thDay
16%9%25%435%5%5%5%34%
1606
16th to endDay
13%9%27%5%45%5%35%36%
1580
March1st to 15thDay
19%8%36%43435%6%34%
1823
16th to endDay
16%7%34424345%42%
2163
April1st to 15thDay
19%7%2442445%6%38%
2152
16th to endDay
20%5%245%33346%40%
2331
May1st to 15thDay
25%6%26%425%445%31%
2332
16th to endDay
21%5%35%4245%6%8%34%
2602
June1st to 15thDay
25%6%35%423446%32%
2520
16th to endDay
20%6%245%35%5%46%34%
2520
July1st to 15thDay
13%5%25%6%45%5%6%8%35%
2520
16th to endDay
13%5%26%435%6%6%7%36%
2654
August1st to 15thDay
14%5%25%6%35%5%5%7%39%
2367
16th to endDay
11%4234245%5%8%47%
2396
September1st to 15thDay
14%5%2442445%6%47%
2082
16th to endDay
13%413322346%54%
1980
October1st to 15thDay
20%6%24423335%43%
1932
16th to endDay
20%6%24424346%41%
1728
November1st to 15thDay
20%5%24313447%41%
1716
16th to endDay
21%6%23424435%41%
1755
December1st to 15thDay
22%8%245%2435%6%35%
1398
16th to endDay
22%11%35%33344432%
1536
January1st to 15thNight
15%8%24424446%40%
2506
16th to endNight
15%10%35%42445%6%37%
2688
February1st to 15thNight
13%9%35%6%36%446%33%
2245
16th to endNight
16%9%35%5%24345%39%
1893
March1st to 15thNight
19%8%35%42435%5%35%
2136
16th to endNight
17%7%24323345%44%
2057
April1st to 15thNight
19%7%25%5%34445%36%
1796
16th to endNight
22%6%25%423445%38%
1629
May1st to 15thNight
20%6%35%43346%7%34%
1620
16th to endNight
22%6%45%4345%5%6%30%
1521
June1st to 15thNight
24%8%25%34345%5%31%
1440
16th to endNight
19%5%13424448%39%
1440
July1st to 15thNight
15%4245%345%7%7%39%
1440
16th to endNight
13%415%4345%7%8%40%
1514
August1st to 15thNight
13%5%15%5%35%5%6%8%40%
1581
16th to endNight
14%31442445%8%46%
1803
September1st to 15thNight
14%5%13323346%49%
1878
16th to endNight
13%414313345%53%
1980
October1st to 15thNight
18%5%1442335%6%42%
2028
16th to endNight
22%6%2442245%6%37%
2496
November1st to 15thNight
18%6%23423445%42%
2472
16th to endNight
17%5%25%433445%42%
2535
December1st to 15thNight
22%8%34323445%37%
2546
16th to endNight
22%9%3443433436%
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
43%6%10%23%14%1
1433
16th to endDay
43%411%24%13%1
1536
February1st to 15thDay
49%5%12%19%12%
1609
16th to endDay
48%5%10%17%14%3
1580
March1st to 15thDay
50%311%18%13%3
1823
16th to endDay
43%48%18%19%5%
2163
April1st to 15thDay
45%5%7%20%16%3
2152
16th to endDay
45%5%9%18%16%3
2331
May1st to 15thDay
54%47%16%15%2
2332
16th to endDay
47%7%12%19%12%2
2606
June1st to 15thDay
53%5%10%18%10%
2520
16th to endDay
49%7%10%19%11%1
2520
July1st to 15thDay
41%9%11%24%11%
2371
16th to endDay
42%7%14%22%11%1
2487
August1st to 15thDay
42%7%15%24%9%
2353
16th to endDay
33%6%13%27%17%1
2396
September1st to 15thDay
36%6%10%26%18%1
2082
16th to endDay
32%48%29%23%1
1980
October1st to 15thDay
44%37%25%15%1
1932
16th to endDay
44%49%25%14%1
1728
November1st to 15thDay
42%5%13%23%14%1
1716
16th to endDay
44%413%19%16%1
1755
December1st to 15thDay
49%411%20%12%
1398
16th to endDay
53%410%17%11%1
1536
January1st to 15thNight
43%5%12%23%13%1
2506
16th to endNight
46%5%9%20%15%2
2688
February1st to 15thNight
50%5%10%19%12%1
2253
16th to endNight
46%5%9%21%13%2
1893
March1st to 15thNight
49%5%8%21%12%2
2136
16th to endNight
41%5%9%19%19%5%
2058
April1st to 15thNight
48%46%19%18%2
1796
16th to endNight
48%5%8%20%13%3
1629
May1st to 15thNight
48%6%9%17%14%2
1620
16th to endNight
52%6%12%17%9%1
1523
June1st to 15thNight
53%6%9%20%9%1
1440
16th to endNight
42%6%14%22%12%1
1440
July1st to 15thNight
39%8%14%24%12%
1360
16th to endNight
39%8%14%24%12%
1418
August1st to 15thNight
39%8%13%26%11%
1571
16th to endNight
34%7%12%27%16%
1803
September1st to 15thNight
35%6%10%30%15%1
1878
16th to endNight
32%49%31%20%1
1980
October1st to 15thNight
41%411%24%15%1
2028
16th to endNight
46%49%25%12%1
2496
November1st to 15thNight
42%412%24%14%1
2472
16th to endNight
43%5%12%22%15%1
2535
December1st to 15thNight
50%410%23%11%
2546
16th to endNight
52%49%20%12%
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
18%23%20%33%5%
60
16th to endDay
21%21%28%23%4
64
February1st to 15thDay
26%12%34%21%3
210
16th to endDay
17%16%34%24%5%
239
March1st to 15thDay
27%18%30%17%5%
270
16th to endDay
21%18%33%14%9%3
288
April1st to 15thDay
26%15%30%17%8%2
270
16th to endDay
25%16%31%14%7%3
270
May1st to 15thDay
35%12%24%15%9%2
288
16th to endDay
25%12%32%21%6%
331
June1st to 15thDay
25%13%31%20%8%1
315
16th to endDay
21%11%33%20%10%2
315
July1st to 15thDay
16%5%32%26%13%4
305
16th to endDay
14%332%30%13%5%
326
August1st to 15thDay
16%7%24%28%18%4
313
16th to endDay
13%8%21%29%18%9%
332
September1st to 15thDay
15%8%28%20%19%7%
315
16th to endDay
16%9%25%19%13%14%
314
October1st to 15thDay
23%9%22%23%16%5%
304
16th to endDay
23%14%30%20%10%
288
November1st to 15thDay
23%11%29%22%9%3
280
16th to endDay
28%12%26%23%7%1
285
December1st to 15thDay
23%17%28%20%9%
63
16th to endDay
40%17%28%12%1
64
January1st to 15thNight
21%15%36%23%4
720
16th to endNight
22%16%35%21%3
768
February1st to 15thNight
21%14%37%23%3
704
16th to endNight
21%14%33%25%5%
631
March1st to 15thNight
25%14%35%20%3
720
16th to endNight
22%16%32%21%7%1
768
April1st to 15thNight
23%13%34%24%4
718
16th to endNight
25%14%31%21%6%
549
May1st to 15thNight
25%10%30%26%7%
540
16th to endNight
26%7%23%31%8%
401
June1st to 15thNight
28%5%26%30%9%
360
16th to endNight
22%122%40%13%
360
July1st to 15thNight
14%124%38%20%
340
16th to endNight
14%322%36%22%
376
August1st to 15thNight
14%224%39%18%
500
16th to endNight
14%325%35%19%2
657
September1st to 15thNight
17%328%30%17%2
720
16th to endNight
16%5%27%26%19%3
717
October1st to 15thNight
20%9%25%27%15%1
720
16th to endNight
26%12%31%22%6%
768
November1st to 15thNight
22%10%30%27%7%1
760
16th to endNight
21%14%31%24%6%1
780
December1st to 15thNight
27%11%36%19%4
728
16th to endNight
28%13%31%23%2
768
Page generated at 2017-12-03 11:16:47. Version ac04

Copyright 2017 A. Danko


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