Spencer
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Spencer clear sky chart from 2005-11-06 to 2024-02-20.

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%
24214
17%
80073
12%
24107
44%
24107
19%
55691

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
17%
754
11%
4076
6%
737
26%
737
6%
3159
January11th to 20thNight
16%
760
11%
4067
6%
740
25%
740
6%
3154
January21st to endNight
18%
834
8%
4503
7%
814
27%
814
7%
3506
February1st to 10thNight
24%
760
14%
2470
7%
760
32%
760
14%
1833
February11th to 20thNight
14%
740
11%
2302
5%
739
21%
739
11%
1735
February21st to endNight
15%
592
16%
1776
6%
592
26%
592
13%
1357
March1st to 10thNight
24%
720
19%
1995
10%
720
33%
720
19%
1414
March11th to 20thNight
24%
720
17%
1980
8%
720
31%
720
18%
1426
March21st to endNight
25%
792
16%
2178
7%
792
32%
792
18%
1557
April1st to 10thNight
25%
720
17%
1962
6%
720
34%
720
22%
1357
April11th to 20thNight
33%
643
21%
1707
9%
643
41%
643
26%
1138
April21st to endNight
31%
540
19%
1620
9%
540
40%
540
22%
1099
May1st to 10thNight
34%
540
15%
1620
7%
540
40%
540
19%
1140
May11th to 20thNight
38%
531
15%
1593
8%
531
43%
531
19%
1131
May21st to endNight
55%
582
16%
1745
12%
582
60%
582
30%
1111
June1st to 10thNight
58%
540
17%
1620
15%
540
61%
540
31%
1014
June11th to 20thNight
56%
540
14%
1620
13%
540
59%
540
27%
1058
June21st to endNight
58%
540
17%
1620
15%
540
61%
540
31%
1002
July1st to 10thNight
59%
525
14%
1575
13%
525
60%
525
26%
1034
July11th to 20thNight
63%
522
17%
1566
14%
522
66%
522
31%
976
July21st to endNight
62%
591
18%
1672
15%
558
63%
558
28%
1069
August1st to 10thNight
65%
537
19%
1600
16%
534
65%
534
27%
1036
August11th to 20thNight
64%
534
21%
1598
16%
534
66%
534
29%
1007
August21st to endNight
65%
656
24%
1844
19%
656
67%
656
34%
1123
September1st to 10thNight
63%
720
22%
1916
16%
720
65%
720
34%
1212
September11th to 20thNight
62%
720
27%
1980
21%
720
66%
720
38%
1187
September21st to endNight
49%
720
26%
1980
18%
720
56%
720
30%
1278
October1st to 10thNight
52%
720
23%
2092
20%
720
57%
720
31%
1280
October11th to 20thNight
40%
720
23%
2160
17%
720
50%
720
27%
1367
October21st to endNight
37%
792
24%
2376
19%
792
45%
792
23%
1591
November1st to 10thNight
44%
740
26%
2324
21%
740
52%
740
28%
1405
November11th to 20thNight
31%
760
21%
2470
14%
760
42%
760
18%
1668
November21st to endNight
34%
760
20%
2470
14%
760
42%
760
18%
1682
December1st to 10thNight
21%
760
13%
2508
8%
760
28%
760
11%
1931
December11th to 20thNight
24%
759
13%
3002
10%
759
30%
759
11%
2224
December21st to endNight
23%
830
10%
4486
7%
817
32%
817
7%
3430

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%10%46%6%35%5%5%7%33%
78647
Night
17%10%47%5%3445%6%35%
80479
TransparencyDay
50%5%10%20%12%2
78369
Night
50%5%10%20%13%2
80276
SeeingDay
23%13%25%22%13%5%
13986
Night
21%11%24%28%14%2
24233

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
18%20%8%8%6%33445%20%
2836
11th to 20thDay
18%18%9%11%9%3433320%
2840
21st to endDay
23%21%5%9%6%32345%19%
3124
February1st to 10thDay
21%15%5%7%6%34346%28%
1710
11th to 20thDay
21%14%410%5%34445%26%
1750
21st to endDay
23%14%47%5%2445%5%28%
1480
March1st to 10thDay
17%11%47%5%3445%6%37%
1963
11th to 20thDay
21%10%47%5%4445%6%31%
1980
21st to endDay
21%11%37%5%3345%5%32%
2178
April1st to 10thDay
15%9%46%6%35%5%5%7%35%
1998
11th to 20thDay
17%8%35%5%3425%8%41%
2216
21st to endDay
21%8%36%5%3445%7%35%
2340
May1st to 10thDay
20%8%36%6%35%5%6%7%31%
2340
11th to 20thDay
21%7%36%5%35%5%6%7%32%
2301
21st to endDay
11%6%26%6%45%6%7%9%38%
2531
June1st to 10thDay
13%5%25%6%35%5%7%8%40%
2340
11th to 20thDay
11%5%26%7%5%6%6%6%9%37%
2340
21st to endDay
12%5%36%6%45%7%7%10%37%
2340
July1st to 10thDay
12%6%26%5%46%6%6%9%36%
2340
11th to 20thDay
10%5%36%7%47%6%6%8%37%
2340
21st to endDay
14%6%35%5%36%6%7%8%35%
2547
August1st to 10thDay
11%6%36%6%47%7%8%11%30%
2327
11th to 20thDay
13%6%36%7%46%6%8%9%33%
2303
21st to endDay
10%6%26%6%46%5%7%8%40%
2493
September1st to 10thDay
15%5%25%4345%6%7%44%
2040
11th to 20thDay
12%426%5%4446%9%45%
1980
21st to endDay
19%7%35%434446%41%
1980
October1st to 10thDay
16%6%344235%6%8%43%
1867
11th to 20thDay
17%7%35%5%3435%6%42%
1800
21st to endDay
21%7%35%5%34346%40%
1980
November1st to 10thDay
13%7%35%423446%50%
1751
11th to 20thDay
16%11%45%6%3345%6%37%
1710
21st to endDay
17%10%46%6%34446%35%
1710
December1st to 10thDay
26%13%6%8%435%445%24%
1595
11th to 20thDay
21%14%6%9%5%23335%28%
2153
21st to endDay
21%18%5%7%7%35%5%5%6%17%
3124
January1st to 10thNight
17%21%6%9%7%34445%20%
4109
11th to 20thNight
20%16%6%11%7%4434422%
4120
21st to endNight
26%16%6%8%7%3333422%
4532
February1st to 10thNight
21%12%5%8%5%34445%28%
2470
11th to 20thNight
23%11%48%6%45%445%28%
2300
21st to endNight
23%14%47%5%3435%5%27%
1776
March1st to 10thNight
18%10%37%435%445%37%
1995
11th to 20thNight
21%8%36%6%3446%7%32%
1980
21st to endNight
21%8%5%6%5%34345%35%
2178
April1st to 10thNight
16%9%445%3445%7%37%
1962
11th to 20thNight
15%6%36%5%345%6%8%40%
1707
21st to endNight
16%7%37%5%4445%6%38%
1620
May1st to 10thNight
19%7%36%6%46%45%6%34%
1620
11th to 20thNight
17%8%37%7%45%45%9%32%
1592
21st to endNight
12%5%25%445%5%6%10%42%
1744
June1st to 10thNight
10%5%25%5%35%6%6%10%44%
1620
11th to 20thNight
9%5%26%6%36%6%7%9%41%
1620
21st to endNight
11%425%5%45%5%7%10%44%
1620
July1st to 10thNight
11%5%27%6%445%6%9%41%
1620
11th to 20thNight
8%5%35%5%45%5%6%10%44%
1620
21st to endNight
10%5%35%6%35%6%7%9%41%
1771
August1st to 10thNight
8%6%36%6%46%7%7%8%39%
1611
11th to 20thNight
10%5%27%5%45%5%6%8%43%
1598
21st to endNight
11%425%5%25%46%10%48%
1844
September1st to 10thNight
11%6%25%5%345%5%8%47%
1916
11th to 20thNight
11%4245%3445%7%52%
1980
21st to endNight
16%5%26%4345%47%44%
1980
October1st to 10thNight
12%5%25%5%345%5%7%48%
2092
11th to 20thNight
16%6%26%434446%45%
2160
21st to endNight
22%5%26%5%34446%40%
2376
November1st to 10thNight
13%6%25%4235%5%5%49%
2324
11th to 20thNight
19%9%35%4345%47%36%
2470
21st to endNight
18%10%46%435%446%37%
2470
December1st to 10thNight
24%15%5%7%5%345%4426%
2508
11th to 20thNight
19%16%7%7%5%34445%27%
3042
21st to endNight
19%18%5%8%7%45%445%22%
4532

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
67%410%13%6%
2837
11th to 20thDay
72%36%14%5%
2840
21st to endDay
69%36%16%41
3124
February1st to 10thDay
60%310%18%9%1
1710
11th to 20thDay
62%48%16%9%1
1759
21st to endDay
58%48%18%10%1
1480
March1st to 10thDay
50%39%25%11%1
1963
11th to 20thDay
54%48%19%13%2
1980
21st to endDay
55%48%20%11%2
2178
April1st to 10thDay
48%5%10%19%14%4
1998
11th to 20thDay
44%410%20%18%4
2216
21st to endDay
49%5%12%20%11%3
2340
May1st to 10thDay
52%6%9%20%11%2
2340
11th to 20thDay
52%6%11%18%11%2
2305
21st to endDay
40%8%16%23%12%1
2531
June1st to 10thDay
41%6%13%23%16%1
2340
11th to 20thDay
42%7%14%21%14%2
2340
21st to endDay
40%8%14%23%14%2
2340
July1st to 10thDay
43%8%13%21%14%2
2275
11th to 20thDay
41%7%13%22%15%3
2271
21st to endDay
43%7%12%24%13%2
2405
August1st to 10thDay
43%9%15%22%10%
2314
11th to 20thDay
44%7%12%25%10%1
2303
21st to endDay
39%8%13%23%15%3
2493
September1st to 10thDay
38%6%10%22%20%5%
2040
11th to 20thDay
37%5%10%26%20%2
1980
21st to endDay
44%5%8%21%20%2
1980
October1st to 10thDay
39%413%22%19%3
1867
11th to 20thDay
44%48%25%18%1
1800
21st to endDay
47%48%23%16%2
1980
November1st to 10thDay
37%48%29%19%4
1751
11th to 20thDay
48%37%20%18%3
1710
21st to endDay
51%48%21%15%1
1710
December1st to 10thDay
64%47%20%5%1
1595
11th to 20thDay
60%39%18%10%
2150
21st to endDay
66%6%10%14%4
3124
January1st to 10thNight
67%48%14%6%1
4109
11th to 20thNight
67%48%15%5%
4120
21st to endNight
68%37%16%5%1
4532
February1st to 10thNight
58%49%19%10%1
2470
11th to 20thNight
62%37%17%12%1
2302
21st to endNight
61%38%15%9%3
1776
March1st to 10thNight
50%47%22%14%2
1995
11th to 20thNight
53%49%20%13%1
1980
21st to endNight
52%49%19%14%3
2178
April1st to 10thNight
48%49%20%16%3
1962
11th to 20thNight
42%5%11%19%17%6%
1707
21st to endNight
47%410%20%17%2
1620
May1st to 10thNight
50%6%10%19%13%3
1620
11th to 20thNight
50%7%10%20%11%3
1593
21st to endNight
36%8%16%26%13%1
1745
June1st to 10thNight
35%7%13%25%16%2
1620
11th to 20thNight
37%10%13%19%18%2
1620
21st to endNight
35%8%15%24%15%3
1620
July1st to 10thNight
40%8%13%21%15%3
1575
11th to 20thNight
34%9%14%23%17%3
1566
21st to endNight
36%10%14%23%17%1
1672
August1st to 10thNight
40%8%15%23%14%2
1600
11th to 20thNight
37%7%14%25%16%1
1598
21st to endNight
33%6%14%25%18%4
1844
September1st to 10thNight
35%6%13%20%18%7%
1916
11th to 20thNight
31%5%12%25%23%3
1980
21st to endNight
40%410%23%21%1
1980
October1st to 10thNight
35%6%12%25%19%3
2092
11th to 20thNight
42%39%23%21%2
2160
21st to endNight
47%46%24%17%3
2376
November1st to 10thNight
37%5%10%21%22%6%
2324
11th to 20thNight
48%5%7%19%18%4
2470
21st to endNight
51%39%21%15%2
2470
December1st to 10thNight
63%47%19%6%1
2508
11th to 20thNight
61%38%18%9%1
3044
21st to endNight
65%48%16%7%
4532

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
31%25%27%12%31
270
11th to 20thDay
36%27%30%7%1
270
21st to endDay
32%29%27%10%2
297
February1st to 10thDay
34%21%33%7%31
270
11th to 20thDay
45%25%24%41
267
21st to endDay
41%24%28%7%
198
March1st to 10thDay
30%21%28%17%4
403
11th to 20thDay
28%23%27%15%5%1
420
21st to endDay
33%16%32%14%5%
462
April1st to 10thDay
28%18%27%18%8%
420
11th to 20thDay
28%14%28%17%8%4
412
21st to endDay
33%15%28%16%6%2
420
May1st to 10thDay
29%16%25%18%8%4
423
11th to 20thDay
25%10%30%19%12%3
447
21st to endDay
14%9%22%28%18%8%
485
June1st to 10thDay
15%7%26%28%17%6%
450
11th to 20thDay
14%8%23%30%18%6%
450
21st to endDay
12%10%30%27%16%6%
450
July1st to 10thDay
15%6%20%23%19%18%
445
11th to 20thDay
8%422%35%20%10%
444
21st to endDay
17%5%18%30%20%10%
488
August1st to 10thDay
15%5%17%30%21%11%
446
11th to 20thDay
14%5%18%31%20%12%
439
21st to endDay
12%5%16%32%25%11%
495
September1st to 10thDay
15%5%17%27%26%10%
450
11th to 20thDay
11%314%32%28%12%
450
21st to endDay
22%10%22%25%16%5%
450
October1st to 10thDay
16%8%26%24%20%5%
450
11th to 20thDay
21%13%28%24%12%2
450
21st to endDay
28%14%26%23%8%2
495
November1st to 10thDay
21%13%30%23%10%2
349
11th to 20thDay
30%17%26%20%7%1
270
21st to endDay
24%21%31%19%31
270
December1st to 10thDay
36%18%25%15%5%
214
11th to 20thDay
28%21%33%13%5%
270
21st to endDay
35%22%26%12%4
297
January1st to 10thNight
29%19%29%19%4
760
11th to 20thNight
33%18%26%21%2
760
21st to endNight
28%17%30%21%3
836
February1st to 10thNight
28%15%29%27%2
760
11th to 20thNight
33%19%29%17%1
742
21st to endNight
33%16%32%17%2
592
March1st to 10thNight
25%17%29%24%4
720
11th to 20thNight
27%16%29%20%8%1
720
21st to endNight
25%16%30%23%6%
792
April1st to 10thNight
24%16%32%22%7%
720
11th to 20thNight
19%13%31%25%12%
643
21st to endNight
19%11%34%28%8%
540
May1st to 10thNight
20%10%31%27%12%
540
11th to 20thNight
20%8%27%30%14%1
531
21st to endNight
15%322%30%26%4
584
June1st to 10thNight
11%322%38%25%2
540
11th to 20thNight
12%419%35%27%3
540
21st to endNight
14%319%42%21%2
540
July1st to 10thNight
13%414%32%31%6%
525
11th to 20thNight
9%314%35%34%4
522
21st to endNight
12%314%34%31%6%
591
August1st to 10thNight
10%410%40%33%3
537
11th to 20thNight
10%412%37%32%5%
534
21st to endNight
13%214%34%31%6%
656
September1st to 10thNight
14%214%33%31%6%
720
11th to 20thNight
13%214%33%33%4
720
21st to endNight
16%6%21%31%22%3
720
October1st to 10thNight
14%6%23%31%24%3
720
11th to 20thNight
19%9%28%28%14%1
720
21st to endNight
25%10%22%30%11%1
792
November1st to 10thNight
16%10%26%32%16%1
740
11th to 20thNight
25%14%26%25%9%1
760
21st to endNight
25%11%24%31%8%1
760
December1st to 10thNight
33%15%26%22%5%
760
11th to 20thNight
25%17%29%24%5%
760
21st to endNight
29%15%27%27%2
836
Page generated at 2024-02-17 06:28:41. Version ac07

Copyright 2024 Attilla Danko


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