The Icebox
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the The Icebox clear sky chart from 2005-11-05 to 2017-09-16.

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%
15947
20%
46856
9%
15900
42%
15900
24%
28655

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%
900
16%
2506
6%
895
27%
895
16%
1660
January16th to endNight
16%
786
21%
2514
8%
786
32%
786
17%
1573
February1st to 15thNight
11%
701
12%
2275
3%
697
22%
697
12%
1547
February16th to endNight
10%
632
18%
1894
2%
632
27%
632
14%
1250
March1st to 15thNight
21%
720
20%
2085
6%
720
34%
720
19%
1290
March16th to endNight
21%
699
18%
2043
6%
699
33%
699
19%
1311
April1st to 15thNight
20%
539
17%
1798
6%
539
33%
539
19%
1094
April16th to endNight
25%
540
17%
1800
10%
540
37%
540
18%
1146
May1st to 15thNight
29%
540
15%
1590
6%
540
40%
540
21%
1059
May16th to endNight
42%
563
16%
1498
9%
561
48%
561
30%
923
June1st to 15thNight
46%
540
22%
1440
11%
540
54%
540
44%
765
June16th to endNight
62%
540
27%
1440
18%
540
69%
540
52%
745
July1st to 15thNight
67%
510
17%
1360
13%
510
70%
510
37%
820
July16th to endNight
71%
564
19%
1470
17%
531
73%
531
37%
860
August1st to 15thNight
68%
539
17%
1638
15%
536
70%
536
36%
922
August16th to endNight
66%
573
26%
1910
25%
573
71%
573
33%
1065
September1st to 15thNight
57%
540
26%
1800
20%
540
67%
540
34%
984
September16th to endNight
54%
514
31%
1776
24%
514
65%
514
39%
890
October1st to 15thNight
34%
660
25%
1980
12%
660
45%
660
27%
1157
October16th to endNight
28%
712
27%
2120
8%
712
44%
712
27%
1199
November1st to 15thNight
21%
875
25%
2275
7%
875
33%
875
26%
1381
November16th to endNight
21%
900
25%
2436
7%
900
35%
900
24%
1474
December1st to 15thNight
13%
900
13%
2520
2%
900
23%
900
15%
1673
December16th to endNight
14%
960
15%
2688
4%
960
23%
960
14%
1867

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
5%8%48%7%35%5%5%7%39%
47900
Night
26%37%6%35%45%7%45%
47033
TransparencyDay
42%7%12%19%13%3
47579
Night
32%8%16%23%15%3
46856
SeeingDay
14%24%30%18%10%2
5848
Night
9%24%28%22%12%1
15950

By Month

Percentage Cloud Cover SW (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
6%6%13%8%5%6%5%7%7%32%
1432
16th to endDay
8%6%12%7%4446%6%37%
1722
February1st to 15thDay
19%7%15%8%445%6%6%29%
1587
16th to endDay
5%6%14%12%46%5%5%6%32%
1580
March1st to 15thDay
110%5%9%7%4435%7%39%
1873
16th to endDay
210%7%10%8%4436%7%35%
2181
April1st to 15thDay
312%6%7%7%35%45%7%35%
2150
16th to endDay
6%15%5%9%8%35%45%7%28%
2160
May1st to 15thDay
8%13%38%6%5%5%5%5%7%30%
2358
16th to endDay
7%9%47%6%47%6%6%8%31%
2616
June1st to 15thDay
6%5%25%6%25%5%6%8%45%
2520
16th to endDay
33245%346%5%7%53%
2520
July1st to 15thDay
9%5%25%6%35%6%7%6%40%
2520
16th to endDay
8%6%36%7%47%6%6%6%36%
2595
August1st to 15thDay
11%6%37%6%45%46%7%36%
2311
16th to endDay
9%5%36%6%45%5%6%7%39%
2292
September1st to 15thDay
8%5%35%434445%50%
2160
16th to endDay
7%7%145%23435%54%
1852
October1st to 15thDay
6%8%27%8%33345%46%
1650
16th to endDay
48%46%5%2445%7%46%
1741
November1st to 15thDay
17%47%5%3446%7%47%
1583
16th to endDay
18%48%6%2245%8%48%
1521
December1st to 15thDay
9%6%13%10%5%45%7%6%30%
1440
16th to endDay
7%5%13%13%6%45%6%7%29%
1536
January1st to 15thNight
5%410%10%5%6%6%6%7%35%
2506
16th to endNight
7%49%8%6%5%5%5%6%40%
2514
February1st to 15thNight
17%5%12%10%5%7%46%7%31%
2264
16th to endNight
7%6%12%8%45%45%6%37%
1894
March1st to 15thNight
7%47%6%45%35%8%45%
2085
16th to endNight
29%6%6%5%24447%46%
2043
April1st to 15thNight
19%48%6%45%46%7%44%
1798
16th to endNight
410%5%7%6%3346%7%41%
1800
May1st to 15thNight
5%8%47%5%35%45%8%40%
1589
16th to endNight
5%6%25%5%2445%8%49%
1497
June1st to 15thNight
321222345%9%60%
1440
16th to endNight
2222235%6%7%64%
1440
July1st to 15thNight
3314435%5%8%10%48%
1440
16th to endNight
3325%5%25%5%6%10%49%
1571
August1st to 15thNight
5%324326%5%6%8%50%
1647
16th to endNight
44244346%5%7%51%
1910
September1st to 15thNight
5%3145%235%5%7%54%
1800
16th to endNight
4323424447%59%
1776
October1st to 15thNight
47%245%2445%7%51%
1980
16th to endNight
47%3442336%7%52%
2120
November1st to 15thNight
16%36%5%25%447%51%
2275
16th to endNight
17%37%6%3445%7%48%
2436
December1st to 15thNight
8%49%9%47%5%6%7%35%
2520
16th to endNight
5%5%12%11%5%6%5%7%7%32%
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
41%10%18%18%8%2
1433
16th to endDay
41%5%18%20%11%2
1722
February1st to 15thDay
48%9%16%15%7%1
1587
16th to endDay
46%6%13%19%11%1
1580
March1st to 15thDay
41%6%12%23%14%1
1873
16th to endDay
46%6%12%22%8%2
2181
April1st to 15thDay
47%5%14%17%11%3
2150
16th to endDay
54%7%11%18%6%1
2160
May1st to 15thDay
52%9%10%18%9%
2358
16th to endDay
48%10%12%18%9%1
2620
June1st to 15thDay
35%6%13%17%19%7%
2520
16th to endDay
27%8%7%22%25%8%
2520
July1st to 15thDay
40%9%11%15%15%7%
2371
16th to endDay
43%9%13%18%10%5%
2433
August1st to 15thDay
45%9%12%13%13%6%
2296
16th to endDay
42%7%10%19%16%3
2292
September1st to 15thDay
36%6%8%18%21%8%
2160
16th to endDay
32%5%10%26%22%2
1852
October1st to 15thDay
39%6%8%23%19%2
1650
16th to endDay
35%5%10%28%17%3
1741
November1st to 15thDay
32%7%15%20%20%4
1583
16th to endDay
31%6%15%28%14%3
1521
December1st to 15thDay
47%9%15%19%7%
1440
16th to endDay
48%10%11%18%8%2
1536
January1st to 15thNight
36%10%20%19%10%2
2506
16th to endNight
38%6%16%22%12%3
2514
February1st to 15thNight
43%9%15%20%9%1
2275
16th to endNight
40%6%15%21%12%3
1894
March1st to 15thNight
34%7%16%25%14%2
2085
16th to endNight
36%8%14%28%10%1
2043
April1st to 15thNight
35%8%14%24%13%3
1798
16th to endNight
40%7%15%23%12%
1800
May1st to 15thNight
40%8%15%23%11%
1590
16th to endNight
31%8%20%25%12%2
1498
June1st to 15thNight
19%6%17%25%22%7%
1440
16th to endNight
17%6%11%27%25%13%
1440
July1st to 15thNight
27%10%17%19%17%8%
1360
16th to endNight
27%8%21%22%13%6%
1470
August1st to 15thNight
28%7%20%20%16%7%
1638
16th to endNight
28%7%14%22%22%3
1910
September1st to 15thNight
26%7%14%19%21%9%
1800
16th to endNight
23%5%12%33%21%3
1776
October1st to 15thNight
29%6%12%27%19%4
1980
16th to endNight
27%7%13%29%19%2
2120
November1st to 15thNight
28%7%13%24%20%5%
2275
16th to endNight
30%6%13%28%17%3
2436
December1st to 15thNight
37%10%20%19%10%1
2520
16th to endNight
42%10%18%19%8%1
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
16%31%22%17%11%1
90
16th to endDay
9%44%28%14%3
96
February1st to 15thDay
23%46%22%5%2
90
16th to endDay
18%35%27%13%4
81
March1st to 15thDay
21%44%22%9%1
163
16th to endDay
20%47%25%6%
288
April1st to 15thDay
21%37%27%10%2
269
16th to endDay
24%47%18%7%1
270
May1st to 15thDay
18%27%31%14%6%1
399
16th to endDay
15%23%29%18%11%1
517
June1st to 15thDay
9%19%31%22%13%2
495
16th to endDay
5%15%35%22%16%4
495
July1st to 15thDay
10%9%28%25%19%6%
475
16th to endDay
8%7%32%24%19%7%
454
August1st to 15thDay
15%11%40%24%7%1
315
16th to endDay
13%11%33%28%10%2
332
September1st to 15thDay
13%19%36%19%8%1
315
16th to endDay
12%15%37%19%12%3
152
October1st to 15thDay
5%32%24%24%11%2
90
16th to endDay
23%27%22%19%5%1
96
November1st to 15thDay
6%27%24%20%17%3
90
16th to endDay
14%42%36%6%
90
December1st to 15thDay
14%51%28%5%
90
16th to endDay
10%56%21%8%3
96
January1st to 15thNight
15%33%28%14%6%1
900
16th to endNight
11%36%32%14%4
786
February1st to 15thNight
10%38%33%11%4
704
16th to endNight
10%39%32%14%3
632
March1st to 15thNight
7%36%29%17%8%
720
16th to endNight
8%34%33%20%2
699
April1st to 15thNight
7%29%38%19%4
539
16th to endNight
11%27%32%19%7%
540
May1st to 15thNight
10%17%36%23%10%1
540
16th to endNight
8%14%29%32%13%2
563
June1st to 15thNight
6%10%31%32%17%1
540
16th to endNight
35%25%38%25%1
540
July1st to 15thNight
5%314%37%35%3
510
16th to endNight
419%34%44%5%
564
August1st to 15thNight
6%213%43%31%3
539
16th to endNight
4315%37%32%6%
573
September1st to 15thNight
5%5%24%36%22%5%
540
16th to endNight
7%7%26%28%24%5%
514
October1st to 15thNight
10%23%28%23%12%2
660
16th to endNight
10%27%30%19%9%3
712
November1st to 15thNight
11%32%32%16%6%1
875
16th to endNight
9%34%31%19%3
900
December1st to 15thNight
11%41%32%11%3
900
16th to endNight
12%37%30%15%4
960
Page generated at 2017-09-16 15:07:02. Version ac04

Copyright 2017 A. Danko


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