Spencer
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Spencer clear sky chart from 2005-11-05 to 2017-12-04.

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
40%
15956
18%
47874
12%
15917
45%
15917
21%
32746

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
18%
719
12%
2327
6%
716
25%
716
10%
1820
January16th to endNight
19%
768
14%
2496
7%
768
27%
768
13%
1854
February1st to 15thNight
23%
701
12%
2284
5%
701
31%
701
14%
1677
February16th to endNight
16%
631
13%
1893
6%
631
24%
631
13%
1442
March1st to 15thNight
25%
720
17%
1990
9%
720
31%
720
17%
1441
March16th to endNight
27%
768
15%
2112
8%
768
32%
768
18%
1536
April1st to 15thNight
27%
718
16%
1904
6%
718
35%
718
22%
1323
April16th to endNight
38%
553
21%
1633
11%
553
45%
553
25%
1073
May1st to 15thNight
35%
540
14%
1620
7%
540
41%
540
17%
1167
May16th to endNight
53%
561
16%
1684
12%
561
57%
561
28%
1089
June1st to 15thNight
62%
540
16%
1620
14%
540
65%
540
31%
1018
June16th to endNight
60%
540
16%
1620
14%
540
64%
540
31%
1000
July1st to 15thNight
58%
510
13%
1530
13%
510
59%
510
27%
999
July16th to endNight
65%
564
16%
1595
13%
531
68%
531
32%
975
August1st to 15thNight
66%
539
20%
1609
15%
536
67%
536
29%
1004
August16th to endNight
69%
615
25%
1761
20%
615
71%
615
37%
1041
September1st to 15thNight
62%
720
24%
1938
18%
720
65%
720
34%
1226
September16th to endNight
58%
717
27%
1980
22%
717
61%
717
32%
1245
October1st to 15thNight
52%
720
24%
2115
22%
720
57%
720
31%
1287
October16th to endNight
36%
768
24%
2304
18%
768
46%
768
24%
1517
November1st to 15thNight
41%
760
24%
2417
18%
760
50%
760
25%
1524
November16th to endNight
33%
780
20%
2535
14%
780
42%
780
18%
1710
December1st to 15thNight
24%
736
11%
2411
8%
736
29%
736
11%
1869
December16th to endNight
22%
768
14%
2496
6%
768
30%
768
12%
1909

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
16%8%35%5%3445%7%34%
48557
Night
16%8%35%5%34446%37%
48067
Cloud CoverDay
17%8%36%5%3445%6%34%
48567
Night
16%8%35%5%3445%6%37%
48071
TransparencyDay
49%5%10%20%12%1
48268
Night
47%410%20%14%2
47874
SeeingDay
21%8%21%22%16%8%
5755
Night
20%9%23%28%16%2
15962

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%12%6%10%7%3423422%
1611
16th to endDay
19%15%6%7%5%33435%24%
1728
February1st to 15thDay
21%13%5%7%5%24346%25%
1577
16th to endDay
19%15%5%7%5%24435%27%
1580
March1st to 15thDay
19%12%45%5%2333434%
1957
16th to endDay
20%9%46%433445%32%
2112
April1st to 15thDay
17%8%45%423447%37%
2044
16th to endDay
17%7%35%424447%38%
2337
May1st to 15thDay
20%7%36%5%345%47%29%
2331
16th to endDay
13%6%36%5%35%46%8%37%
2431
June1st to 15thDay
11%5%25%6%35%6%6%8%38%
2340
16th to endDay
11%5%35%6%45%6%6%11%33%
2340
July1st to 15thDay
14%5%35%6%46%5%6%8%32%
2340
16th to endDay
12%5%25%5%47%5%7%9%32%
2465
August1st to 15thDay
12%6%35%6%47%6%7%9%30%
2340
16th to endDay
10%5%25%6%35%5%7%8%39%
2429
September1st to 15thDay
15%434425%45%8%41%
2019
16th to endDay
17%6%24434445%43%
1980
October1st to 15thDay
17%6%25%423448%40%
1843
16th to endDay
21%6%24423235%43%
1920
November1st to 15thDay
15%7%24423345%44%
1770
16th to endDay
17%9%35%5%245%46%35%
1755
December1st to 15thDay
25%11%5%7%42333426%
1580
16th to endDay
23%13%5%7%6%23345%24%
1728
January1st to 15thNight
21%13%6%8%6%2443422%
2327
16th to endNight
20%13%5%7%5%24345%28%
2496
February1st to 15thNight
19%11%46%5%34346%29%
2282
16th to endNight
18%15%5%6%6%34345%26%
1893
March1st to 15thNight
19%9%36%5%25%45%5%32%
1978
16th to endNight
21%8%46%5%33436%33%
2112
April1st to 15thNight
17%7%35%5%3345%8%35%
1904
16th to endNight
13%5%26%5%2445%7%41%
1633
May1st to 15thNight
18%7%38%5%3445%7%31%
1620
16th to endNight
12%5%245%3446%10%40%
1682
June1st to 15thNight
8%323426%7%7%10%43%
1620
16th to endNight
9%4244245%6%10%44%
1620
July1st to 15thNight
12%6%26%4245%5%9%41%
1620
16th to endNight
8%4245%345%6%9%44%
1703
August1st to 15thNight
6%5%35%5%35%6%7%8%42%
1620
16th to endNight
9%31343435%9%49%
1761
September1st to 15thNight
10%424435%45%6%48%
1938
16th to endNight
13%415%424445%48%
1980
October1st to 15thNight
12%424434445%48%
2115
16th to endNight
20%425%423335%42%
2304
November1st to 15thNight
17%6%24423445%44%
2417
16th to endNight
18%9%25%434445%36%
2535
December1st to 15thNight
22%12%5%9%5%3443425%
2411
16th to endNight
21%13%5%6%6%3434425%
2496

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%13%5%10%7%3333422%
1611
16th to endDay
20%15%6%8%5%34335%24%
1728
February1st to 15thDay
20%14%5%8%423335%26%
1577
16th to endDay
19%16%47%5%2434427%
1580
March1st to 15thDay
19%11%46%5%2324433%
1968
16th to endDay
21%9%36%5%3335%5%32%
2111
April1st to 15thDay
17%8%34414447%37%
2044
16th to endDay
18%6%25%42335%7%38%
2337
May1st to 15thDay
22%7%36%5%35%46%6%29%
2331
16th to endDay
13%6%25%5%35%5%5%7%38%
2431
June1st to 15thDay
12%315%6%46%5%6%8%39%
2340
16th to endDay
11%5%25%6%45%7%6%9%34%
2340
July1st to 15thDay
14%6%26%6%46%6%5%8%32%
2340
16th to endDay
13%5%25%6%37%6%7%8%33%
2465
August1st to 15thDay
13%5%26%6%37%6%7%10%29%
2340
16th to endDay
10%425%6%35%5%6%8%39%
2429
September1st to 15thDay
15%4244345%6%7%41%
2019
16th to endDay
17%5%25%433445%42%
1980
October1st to 15thDay
18%6%2442245%7%41%
1843
16th to endDay
20%6%24423235%43%
1920
November1st to 15thDay
15%7%24413445%44%
1770
16th to endDay
17%10%35%424446%36%
1755
December1st to 15thDay
26%11%5%7%42433426%
1580
16th to endDay
23%13%5%6%5%23436%24%
1728
January1st to 15thNight
21%14%5%8%6%34435%22%
2327
16th to endNight
20%14%47%5%23345%28%
2496
February1st to 15thNight
20%11%47%434445%29%
2275
16th to endNight
19%13%48%6%34345%26%
1893
March1st to 15thNight
19%9%26%435%45%5%31%
1990
16th to endNight
22%8%445%33345%33%
2112
April1st to 15thNight
17%8%4443345%7%36%
1904
16th to endNight
14%6%25%43445%6%41%
1633
May1st to 15thNight
18%6%37%6%35%35%6%31%
1619
16th to endNight
12%5%15%43446%9%40%
1682
June1st to 15thNight
8%324436%6%6%10%43%
1620
16th to endNight
9%414435%5%6%9%44%
1620
July1st to 15thNight
13%5%25%5%335%5%8%41%
1620
16th to endNight
7%4245%345%6%10%44%
1703
August1st to 15thNight
7%5%25%5%45%6%6%8%41%
1620
16th to endNight
9%314425%36%8%49%
1761
September1st to 15thNight
10%5%1443445%6%48%
1938
16th to endNight
14%424423446%47%
1980
October1st to 15thNight
12%5%15%433446%48%
2115
16th to endNight
20%425%423345%41%
2304
November1st to 15thNight
17%6%24323445%44%
2417
16th to endNight
18%8%25%434435%37%
2535
December1st to 15thNight
23%12%48%5%3443325%
2411
16th to endNight
21%14%5%6%5%34345%25%
2496

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
66%29%14%6%
1612
16th to endDay
63%39%16%6%1
1728
February1st to 15thDay
60%310%15%7%
1579
16th to endDay
60%49%19%6%
1580
March1st to 15thDay
54%29%22%8%1
1968
16th to endDay
53%49%19%11%1
2112
April1st to 15thDay
45%49%21%15%2
2044
16th to endDay
45%411%19%13%5%
2337
May1st to 15thDay
54%5%10%18%9%1
2331
16th to endDay
43%6%13%22%12%1
2435
June1st to 15thDay
40%6%14%21%16%
2340
16th to endDay
43%7%14%18%14%1
2340
July1st to 15thDay
48%6%11%17%12%3
2201
16th to endDay
43%7%12%21%12%2
2310
August1st to 15thDay
46%7%13%20%10%1
2327
16th to endDay
39%6%12%25%13%2
2429
September1st to 15thDay
39%6%9%21%19%3
2019
16th to endDay
43%47%20%22%1
1980
October1st to 15thDay
42%411%23%17%1
1843
16th to endDay
45%28%26%15%1
1920
November1st to 15thDay
42%37%24%18%4
1770
16th to endDay
49%38%21%16%
1755
December1st to 15thDay
61%37%19%6%
1580
16th to endDay
62%410%16%6%
1728
January1st to 15thNight
65%38%13%8%1
2327
16th to endNight
59%310%18%7%1
2496
February1st to 15thNight
57%49%19%9%
2284
16th to endNight
61%29%17%8%
1893
March1st to 15thNight
52%410%21%10%1
1990
16th to endNight
53%49%19%13%
2112
April1st to 15thNight
47%48%20%16%3
1904
16th to endNight
43%410%18%17%6%
1633
May1st to 15thNight
52%5%8%18%12%2
1620
16th to endNight
39%6%14%23%13%2
1684
June1st to 15thNight
34%8%14%23%18%1
1620
16th to endNight
33%8%14%22%18%2
1620
July1st to 15thNight
41%5%12%20%16%2
1530
16th to endNight
31%9%15%23%17%2
1595
August1st to 15thNight
37%6%14%22%16%1
1609
16th to endNight
31%5%12%27%19%3
1761
September1st to 15thNight
34%5%11%20%21%5%
1938
16th to endNight
37%48%24%24%
1980
October1st to 15thNight
36%411%24%18%3
2115
16th to endNight
45%26%25%18%1
2304
November1st to 15thNight
42%38%19%20%5%
2417
16th to endNight
48%48%20%16%1
2535
December1st to 15thNight
64%37%15%8%1
2411
16th to endNight
62%410%17%5%
2496

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
32%26%26%7%33
90
16th to endDay
38%27%22%9%2
96
February1st to 15thDay
38%24%28%5%2
90
16th to endDay
37%17%37%8%
81
March1st to 15thDay
27%16%27%20%7%
258
16th to endDay
24%18%31%16%6%2
288
April1st to 15thDay
26%10%30%21%8%1
270
16th to endDay
26%5%28%20%12%7%
270
May1st to 15thDay
32%9%23%20%7%5%
288
16th to endDay
19%6%22%22%17%11%
331
June1st to 15thDay
12%422%29%22%8%
315
16th to endDay
14%9%26%23%17%8%
315
July1st to 15thDay
18%323%26%14%12%
305
16th to endDay
16%19%30%24%17%
326
August1st to 15thDay
16%111%31%21%15%
313
16th to endDay
10%311%28%30%15%
332
September1st to 15thDay
16%313%24%27%13%
315
16th to endDay
18%413%26%22%14%
314
October1st to 15thDay
18%422%23%26%4
315
16th to endDay
25%11%23%22%13%3
336
November1st to 15thDay
26%7%25%25%13%2
188
16th to endDay
27%17%22%22%8%1
135
December1st to 15thDay
34%19%21%12%11%1
88
16th to endDay
38%19%31%8%2
96
January1st to 15thNight
31%16%26%20%4
720
16th to endNight
29%16%30%20%2
768
February1st to 15thNight
27%13%31%26%
704
16th to endNight
27%18%31%19%2
631
March1st to 15thNight
26%13%28%24%6%
720
16th to endNight
25%12%30%22%8%1
768
April1st to 15thNight
23%14%32%21%8%
718
16th to endNight
16%9%29%28%14%1
553
May1st to 15thNight
21%8%27%29%12%1
540
16th to endNight
15%222%28%26%3
563
June1st to 15thNight
10%218%37%28%3
540
16th to endNight
11%217%43%22%2
540
July1st to 15thNight
14%214%35%28%3
510
16th to endNight
9%212%30%36%8%
564
August1st to 15thNight
9%29%39%35%4
539
16th to endNight
11%18%37%34%6%
615
September1st to 15thNight
13%214%30%33%5%
720
16th to endNight
16%314%29%29%5%
717
October1st to 15thNight
14%6%19%31%24%3
720
16th to endNight
22%9%25%25%14%2
768
November1st to 15thNight
20%9%24%28%16%
760
16th to endNight
24%12%24%28%9%1
780
December1st to 15thNight
31%12%24%24%7%
736
16th to endNight
29%15%27%25%2
768
Page generated at 2017-12-05 10:18:58. Version ac04

Copyright 2017 A. Danko


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