Afterwood Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Afterwood Observatory clear sky chart from 2005-11-05 to 2018-01-12.

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
26%
15337
14%
48355
7%
15306
35%
15306
15%
33567

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
13%
765
12%
2662
5%
761
24%
761
10%
1881
January16th to endNight
12%
768
12%
2628
2%
768
24%
768
9%
1872
February1st to 15thNight
6%
704
9%
2261
1%
701
16%
701
7%
1724
February16th to endNight
14%
631
14%
1893
5%
631
25%
631
10%
1381
March1st to 15thNight
13%
720
12%
2148
5%
720
23%
720
11%
1602
March16th to endNight
21%
768
19%
1998
6%
768
31%
768
15%
1428
April1st to 15thNight
16%
718
12%
1796
2%
718
22%
718
14%
1365
April16th to endNight
25%
684
15%
1764
4%
684
32%
684
20%
1250
May1st to 15thNight
27%
446
16%
1526
9%
446
37%
446
16%
1047
May16th to endNight
34%
374
13%
1497
10%
374
44%
374
15%
983
June1st to 15thNight
34%
360
12%
1440
10%
360
45%
360
13%
953
June16th to endNight
45%
360
11%
1440
11%
360
54%
360
23%
830
July1st to 15thNight
51%
340
11%
1360
14%
340
57%
340
23%
801
July16th to endNight
56%
376
14%
1418
14%
354
62%
354
24%
829
August1st to 15thNight
46%
482
15%
1553
8%
480
53%
480
26%
969
August16th to endNight
51%
764
18%
1910
9%
764
55%
764
33%
1249
September1st to 15thNight
45%
720
18%
1800
8%
720
49%
720
29%
1209
September16th to endNight
48%
717
24%
1962
16%
717
53%
717
32%
1225
October1st to 15thNight
34%
720
17%
2124
11%
720
42%
720
20%
1447
October16th to endNight
21%
768
12%
2412
6%
768
31%
768
14%
1707
November1st to 15thNight
26%
760
16%
2472
9%
760
35%
760
15%
1691
November16th to endNight
22%
780
14%
2649
9%
780
31%
780
13%
1838
December1st to 15thNight
16%
780
9%
2730
2%
780
24%
780
8%
2049
December16th to endNight
10%
832
9%
2912
2%
832
20%
832
6%
2237

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%9%46%6%35%45%7%31%
48987
Night
14%8%36%5%35%45%7%34%
48525
Cloud CoverDay
14%8%47%6%35%5%5%7%31%
48996
Night
14%8%36%5%35%5%5%7%34%
48531
TransparencyDay
50%7%12%18%10%1
48675
Night
46%8%13%19%10%1
48355
SeeingDay
20%18%27%19%10%3
6020
Night
21%19%28%21%8%1
15338

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
11%9%47%9%46%5%6%7%27%
1520
16th to endDay
10%11%5%9%8%46%5%6%5%24%
1593
February1st to 15thDay
12%11%6%10%9%47%5%45%22%
1600
16th to endDay
13%11%48%8%25%46%6%27%
1580
March1st to 15thDay
15%13%47%6%3435%7%28%
1799
16th to endDay
15%10%5%6%5%34345%34%
2226
April1st to 15thDay
16%10%47%5%3434434%
2152
16th to endDay
15%9%36%5%35%45%6%35%
2196
May1st to 15thDay
20%8%37%6%345%45%31%
2436
16th to endDay
15%6%36%6%45%5%5%7%32%
2618
June1st to 15thDay
20%7%35%445%5%5%8%29%
2520
16th to endDay
14%6%37%7%47%5%5%8%28%
2520
July1st to 15thDay
11%7%36%6%46%5%6%9%31%
2520
16th to endDay
12%6%26%7%37%5%7%8%31%
2654
August1st to 15thDay
11%7%35%8%46%5%7%8%31%
2382
16th to endDay
13%6%345%36%6%7%8%35%
2292
September1st to 15thDay
14%7%36%5%34447%37%
2160
16th to endDay
12%6%2432445%6%45%
1998
October1st to 15thDay
15%10%36%5%2345%5%36%
1833
16th to endDay
18%11%36%6%3445%6%29%
1810
November1st to 15thDay
17%11%35%5%34346%34%
1716
16th to endDay
14%8%5%7%5%35%5%5%7%31%
1638
December1st to 15thDay
13%14%6%10%7%3445%5%23%
1560
16th to endDay
15%12%7%10%6%36%5%6%5%20%
1664
January1st to 15thNight
12%10%48%7%36%6%6%8%25%
2662
16th to endNight
11%10%5%8%8%45%46%7%28%
2628
February1st to 15thNight
12%11%6%9%8%45%5%5%6%24%
2260
16th to endNight
12%11%5%7%6%46%5%6%6%26%
1893
March1st to 15thNight
16%9%47%7%45%5%46%29%
2135
16th to endNight
15%8%37%5%2435%6%35%
1998
April1st to 15thNight
16%9%47%5%35%445%31%
1796
16th to endNight
18%8%35%424346%39%
1764
May1st to 15thNight
19%10%35%423347%35%
1526
16th to endNight
13%6%35%5%35%5%5%8%37%
1495
June1st to 15thNight
21%5%35%424447%35%
1440
16th to endNight
10%415%325%5%6%10%44%
1440
July1st to 15thNight
8%5%24435%5%6%8%43%
1440
16th to endNight
11%4234345%6%8%45%
1514
August1st to 15thNight
9%5%245%246%6%7%45%
1563
16th to endNight
12%5%2442335%8%46%
1910
September1st to 15thNight
14%5%1442445%5%46%
1800
16th to endNight
10%424434446%50%
1962
October1st to 15thNight
19%6%35%423346%40%
2124
16th to endNight
18%9%45%43445%7%32%
2412
November1st to 15thNight
15%9%36%5%3345%6%35%
2472
16th to endNight
13%9%5%7%6%35%5%46%33%
2649
December1st to 15thNight
16%12%48%6%35%5%5%6%25%
2730
16th to endNight
15%11%5%9%6%36%5%5%6%22%
2912

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
10%9%47%9%5%6%6%6%7%27%
1520
16th to endDay
10%10%5%9%8%46%5%6%6%25%
1593
February1st to 15thDay
12%11%6%9%9%5%6%5%5%5%22%
1600
16th to endDay
13%10%49%8%3445%6%27%
1580
March1st to 15thDay
15%11%5%7%6%35%45%6%28%
1809
16th to endDay
15%10%5%6%5%34445%35%
2225
April1st to 15thDay
16%10%47%6%3334434%
2152
16th to endDay
14%8%36%5%34446%36%
2196
May1st to 15thDay
19%8%37%6%345%45%31%
2436
16th to endDay
15%5%36%6%36%5%5%8%32%
2618
June1st to 15thDay
20%6%36%446%46%8%29%
2520
16th to endDay
13%6%37%7%37%6%6%8%28%
2520
July1st to 15thDay
10%7%36%7%46%6%6%9%31%
2520
16th to endDay
11%6%27%7%47%6%6%9%30%
2654
August1st to 15thDay
11%6%36%8%46%5%7%7%31%
2382
16th to endDay
13%6%245%36%6%8%8%35%
2292
September1st to 15thDay
13%7%26%5%25%5%47%37%
2160
16th to endDay
12%6%244245%5%6%45%
1998
October1st to 15thDay
15%9%36%5%3345%5%36%
1833
16th to endDay
18%9%38%5%3446%6%29%
1810
November1st to 15thDay
16%10%36%5%34447%34%
1716
16th to endDay
13%8%48%5%35%5%5%7%32%
1638
December1st to 15thDay
13%12%5%10%9%345%5%5%24%
1560
16th to endDay
15%12%6%10%7%37%5%5%5%20%
1664
January1st to 15thNight
11%9%47%7%36%6%7%8%25%
2662
16th to endNight
11%10%48%8%45%5%6%7%29%
2628
February1st to 15thNight
11%11%5%9%7%45%6%5%6%24%
2253
16th to endNight
11%11%47%7%5%6%5%6%7%26%
1893
March1st to 15thNight
15%8%47%6%5%5%5%5%6%29%
2148
16th to endNight
15%7%37%5%25%45%6%36%
1998
April1st to 15thNight
15%10%38%6%35%45%6%30%
1796
16th to endNight
16%8%36%5%14446%38%
1764
May1st to 15thNight
19%10%36%323346%36%
1526
16th to endNight
12%6%17%5%25%46%8%37%
1495
June1st to 15thNight
20%5%36%4245%5%7%35%
1440
16th to endNight
10%415%4245%7%10%44%
1440
July1st to 15thNight
8%5%24435%5%6%8%43%
1440
16th to endNight
10%4244245%6%7%45%
1514
August1st to 15thNight
9%4245%25%5%6%7%45%
1563
16th to endNight
13%5%1442445%8%46%
1910
September1st to 15thNight
13%5%244335%5%5%46%
1800
16th to endNight
10%42442435%7%49%
1962
October1st to 15thNight
18%7%35%423346%40%
2124
16th to endNight
17%9%36%5%3346%7%32%
2412
November1st to 15thNight
14%9%37%5%335%5%6%35%
2472
16th to endNight
12%8%48%6%35%5%5%5%34%
2649
December1st to 15thNight
15%10%48%7%35%5%5%6%25%
2730
16th to endNight
15%10%5%8%7%36%6%5%6%22%
2912

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
52%8%12%17%8%
1521
16th to endDay
56%8%14%14%6%1
1593
February1st to 15thDay
59%8%10%12%7%
1603
16th to endDay
54%7%11%16%9%
1580
March1st to 15thDay
54%6%13%15%8%1
1809
16th to endDay
50%5%9%16%14%3
2226
April1st to 15thDay
52%5%8%20%11%1
2152
16th to endDay
47%5%9%19%14%2
2196
May1st to 15thDay
54%6%7%18%10%1
2436
16th to endDay
47%9%13%18%9%1
2622
June1st to 15thDay
51%8%13%17%8%
2520
16th to endDay
50%8%14%15%9%
2520
July1st to 15thDay
46%9%13%19%9%
2371
16th to endDay
46%8%16%17%10%
2487
August1st to 15thDay
48%9%13%19%8%
2368
16th to endDay
41%9%14%23%11%
2292
September1st to 15thDay
45%7%11%21%13%1
2160
16th to endDay
36%6%10%25%18%1
1998
October1st to 15thDay
48%5%10%20%13%1
1833
16th to endDay
52%8%13%15%8%1
1810
November1st to 15thDay
49%6%12%19%10%1
1716
16th to endDay
48%7%15%16%10%
1638
December1st to 15thDay
59%7%13%13%5%
1560
16th to endDay
60%9%13%11%4
1664
January1st to 15thNight
50%8%14%15%9%1
2662
16th to endNight
50%8%14%16%8%1
2628
February1st to 15thNight
56%9%13%13%7%
2261
16th to endNight
51%8%15%15%7%1
1893
March1st to 15thNight
53%7%12%17%7%
2148
16th to endNight
46%6%11%18%13%2
1998
April1st to 15thNight
53%7%11%17%9%1
1796
16th to endNight
45%7%10%18%15%1
1764
May1st to 15thNight
49%5%9%18%15%1
1526
16th to endNight
43%10%13%20%10%1
1497
June1st to 15thNight
47%7%12%22%9%
1440
16th to endNight
32%10%18%26%10%
1440
July1st to 15thNight
34%9%16%25%12%1
1360
16th to endNight
35%8%18%24%11%1
1418
August1st to 15thNight
34%10%16%25%11%
1553
16th to endNight
36%6%14%29%12%
1910
September1st to 15thNight
37%8%13%24%15%
1800
16th to endNight
32%7%11%25%21%
1962
October1st to 15thNight
45%6%12%18%15%1
2124
16th to endNight
48%8%15%18%8%
2412
November1st to 15thNight
46%7%13%17%12%2
2472
16th to endNight
49%7%14%18%8%1
2649
December1st to 15thNight
55%9%15%13%6%
2730
16th to endNight
57%10%12%12%7%
2912

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
24%34%23%12%41
82
16th to endDay
36%27%21%13%
73
February1st to 15thDay
26%41%24%5%
117
16th to endDay
21%30%30%15%2
239
March1st to 15thDay
28%26%28%14%2
270
16th to endDay
26%26%26%12%6%2
288
April1st to 15thDay
27%25%24%14%7%1
270
16th to endDay
20%21%28%17%5%6%
270
May1st to 15thDay
29%18%25%14%8%4
288
16th to endDay
16%14%36%18%11%2
331
June1st to 15thDay
22%13%30%23%9%
315
16th to endDay
15%17%30%25%9%1
315
July1st to 15thDay
12%10%35%25%14%2
305
16th to endDay
12%7%33%29%12%3
326
August1st to 15thDay
9%10%30%26%16%7%
313
16th to endDay
13%8%20%28%17%12%
332
September1st to 15thDay
14%11%25%21%18%8%
315
16th to endDay
15%7%22%21%18%15%
314
October1st to 15thDay
19%13%22%23%16%3
315
16th to endDay
25%22%26%18%6%
308
November1st to 15thDay
25%18%25%19%10%1
280
16th to endDay
20%30%24%17%6%1
168
December1st to 15thDay
23%35%23%8%8%
90
16th to endDay
33%38%23%4
96
January1st to 15thNight
21%28%33%13%2
765
16th to endNight
22%29%30%16%1
768
February1st to 15thNight
21%28%37%11%1
704
16th to endNight
23%29%29%16%2
631
March1st to 15thNight
26%27%30%13%1
720
16th to endNight
24%26%25%18%5%
768
April1st to 15thNight
24%24%31%17%2
718
16th to endNight
22%19%29%16%10%
684
May1st to 15thNight
26%14%26%24%6%
446
16th to endNight
17%10%31%27%10%1
375
June1st to 15thNight
23%13%24%25%11%
360
16th to endNight
12%5%33%35%13%
360
July1st to 15thNight
10%5%26%40%15%
340
16th to endNight
13%421%42%17%1
376
August1st to 15thNight
11%5%30%32%18%1
482
16th to endNight
15%421%32%22%3
764
September1st to 15thNight
16%8%24%30%17%1
720
16th to endNight
14%8%23%26%19%6%
717
October1st to 15thNight
22%14%22%25%14%1
720
16th to endNight
24%21%28%21%4
768
November1st to 15thNight
21%21%25%22%8%1
760
16th to endNight
22%23%27%18%6%1
780
December1st to 15thNight
23%27%29%14%4
780
16th to endNight
26%30%28%12%2
832
Page generated at 2018-01-12 22:01:37. Version ac04

Copyright 2018 A. Danko


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