Andrew
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Andrew clear sky chart from 2005-11-05 to 2017-09-10.

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
42%
15194
10%
46689
7%
15169
45%
15169
18%
33415

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
33%
895
6%
2685
3%
895
36%
895
12%
2111
January16th to endNight
32%
941
13%
2861
7%
941
39%
941
16%
2066
February1st to 15thNight
37%
697
7%
2415
7%
696
40%
696
14%
1770
February16th to endNight
47%
632
12%
2052
13%
632
49%
632
16%
1499
March1st to 15thNight
41%
720
13%
2091
9%
720
44%
720
18%
1535
March16th to endNight
41%
767
10%
2112
7%
767
42%
767
17%
1614
April1st to 15thNight
43%
572
12%
1659
7%
572
46%
572
20%
1193
April16th to endNight
44%
540
13%
1610
11%
540
47%
540
20%
1124
May1st to 15thNight
49%
399
8%
1299
6%
399
51%
399
21%
850
May16th to endNight
44%
374
0%
1309
0%
374
44%
374
16%
922
June1st to 15thNight
45%
360
0%
1260
0%
360
45%
360
14%
892
June16th to endNight
52%
360
0%
1260
0%
360
52%
360
19%
861
July1st to 15thNight
56%
340
0%
1190
0%
340
56%
340
23%
747
July16th to endNight
61%
376
2%
1239
1%
354
62%
354
26%
738
August1st to 15thNight
65%
388
7%
1371
7%
386
67%
386
24%
831
August16th to endNight
56%
573
14%
1719
12%
573
59%
573
29%
1101
September1st to 15thNight
57%
572
14%
1704
11%
572
59%
572
30%
1054
September16th to endNight
50%
656
19%
1815
10%
656
57%
656
35%
1115
October1st to 15thNight
44%
660
15%
1972
10%
660
48%
660
22%
1361
October16th to endNight
40%
737
14%
2321
10%
737
45%
737
18%
1637
November1st to 15thNight
35%
875
14%
2465
9%
875
39%
875
17%
1852
November16th to endNight
31%
900
8%
2700
4%
900
35%
900
13%
2106
December1st to 15thNight
29%
900
7%
2700
4%
900
32%
900
11%
2177
December16th to endNight
35%
960
9%
2880
5%
960
39%
960
13%
2259

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
11%9%47%6%45%5%6%8%31%
47971
Night
9%9%48%7%45%5%6%7%31%
46843
TransparencyDay
49%9%18%18%4
47621
Night
49%8%16%19%6%
46697
SeeingDay
15%6%24%30%18%5%
6106
Night
13%425%35%17%2
15209

By Month

Percentage Cloud Cover NW (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
7%12%6%12%8%5%8%6%5%5%20%
1253
16th to endDay
5%13%5%11%9%36%45%6%27%
1374
February1st to 15thDay
8%11%6%10%9%45%5%6%7%24%
1440
16th to endDay
6%13%7%11%8%6%6%6%6%7%19%
1422
March1st to 15thDay
7%13%6%10%7%45%5%7%9%21%
1868
16th to endDay
12%13%6%8%7%35%45%7%25%
2111
April1st to 15thDay
12%12%46%6%3445%7%32%
2286
16th to endDay
14%11%47%5%35%45%7%28%
2349
May1st to 15thDay
11%7%36%6%36%5%6%7%35%
2649
16th to endDay
16%7%35%6%46%46%8%30%
2802
June1st to 15thDay
17%8%37%7%36%5%6%7%26%
2700
16th to endDay
15%7%35%7%46%5%7%9%27%
2700
July1st to 15thDay
11%425%5%35%6%7%9%38%
2700
16th to endDay
9%5%245%46%6%7%9%38%
2846
August1st to 15thDay
11%6%25%5%35%6%6%9%37%
2580
16th to endDay
8%5%26%6%45%47%9%40%
2483
September1st to 15thDay
11%6%26%5%36%45%7%40%
2141
16th to endDay
11%425%6%35%35%8%43%
1815
October1st to 15thDay
13%10%46%5%345%46%33%
1658
16th to endDay
10%10%37%5%35%5%5%8%35%
1539
November1st to 15thDay
9%12%47%6%46%6%6%8%28%
1391
16th to endDay
6%12%5%12%7%36%46%6%28%
1260
December1st to 15thDay
10%13%5%11%10%6%7%5%5%7%16%
1260
16th to endDay
6%10%6%12%10%48%6%7%9%18%
1344
January1st to 15thNight
8%11%6%10%10%5%7%5%6%7%22%
2685
16th to endNight
6%11%6%9%7%35%5%5%7%31%
2861
February1st to 15thNight
7%11%5%10%8%45%45%8%28%
2411
16th to endNight
6%10%6%9%7%5%6%6%6%7%28%
2052
March1st to 15thNight
7%9%5%8%8%46%5%6%6%30%
2091
16th to endNight
10%12%6%8%6%36%5%7%9%23%
2109
April1st to 15thNight
11%8%37%7%46%5%5%7%32%
1659
16th to endNight
13%10%5%6%435%45%6%34%
1610
May1st to 15thNight
12%6%25%7%45%5%6%6%38%
1299
16th to endNight
18%8%36%5%5%445%6%30%
1309
June1st to 15thNight
16%7%46%7%36%5%5%7%28%
1260
16th to endNight
13%5%25%6%35%6%6%8%34%
1260
July1st to 15thNight
9%435%6%35%47%11%38%
1260
16th to endNight
8%425%435%6%7%8%43%
1323
August1st to 15thNight
8%315%435%5%7%12%40%
1378
16th to endNight
8%5%15%6%346%7%9%41%
1719
September1st to 15thNight
11%415%5%34446%48%
1704
16th to endNight
10%41342345%8%50%
1815
October1st to 15thNight
12%10%46%4235%6%7%35%
1972
16th to endNight
10%9%47%7%35%5%6%7%32%
2321
November1st to 15thNight
12%11%5%8%6%45%5%5%7%28%
2465
16th to endNight
6%11%7%11%9%5%5%45%7%24%
2700
December1st to 15thNight
10%13%7%12%9%45%5%5%5%20%
2700
16th to endNight
5%11%5%12%9%5%8%7%6%7%20%
2880

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
61%8%14%10%4
1253
16th to endDay
55%7%12%15%6%1
1374
February1st to 15thDay
56%7%18%11%4
1440
16th to endDay
60%6%13%14%5%
1422
March1st to 15thDay
56%10%16%13%3
1868
16th to endDay
58%6%15%14%5%
2112
April1st to 15thDay
50%7%18%16%6%1
2286
16th to endDay
53%8%13%16%6%
2349
May1st to 15thDay
46%6%14%21%10%
2649
16th to endDay
49%7%14%17%9%
2807
June1st to 15thDay
54%9%15%16%4
2700
16th to endDay
50%10%18%15%4
2700
July1st to 15thDay
39%10%24%22%3
2541
16th to endDay
38%12%28%19%1
2667
August1st to 15thDay
40%12%27%17%2
2562
16th to endDay
37%10%26%20%3
2483
September1st to 15thDay
41%7%19%24%5%1
2141
16th to endDay
36%9%17%28%5%1
1815
October1st to 15thDay
48%7%17%21%3
1658
16th to endDay
45%10%14%25%3
1539
November1st to 15thDay
51%8%18%16%4
1391
16th to endDay
54%9%17%14%3
1260
December1st to 15thDay
65%9%10%12%2
1260
16th to endDay
59%8%13%13%4
1344
January1st to 15thNight
59%8%16%11%3
2685
16th to endNight
51%7%16%17%6%1
2861
February1st to 15thNight
53%8%16%14%6%
2422
16th to endNight
52%8%13%18%7%
2052
March1st to 15thNight
50%8%14%20%5%
2091
16th to endNight
54%8%13%16%7%
2112
April1st to 15thNight
48%7%14%19%8%1
1659
16th to endNight
48%6%13%17%11%2
1610
May1st to 15thNight
44%6%12%22%13%1
1300
16th to endNight
53%5%13%18%7%1
1309
June1st to 15thNight
52%8%15%18%6%
1260
16th to endNight
45%10%20%18%5%
1260
July1st to 15thNight
37%10%21%24%5%
1190
16th to endNight
33%10%26%26%3
1239
August1st to 15thNight
33%11%27%23%2
1371
16th to endNight
35%9%19%28%7%
1719
September1st to 15thNight
35%6%18%27%9%1
1704
16th to endNight
31%7%18%29%10%2
1815
October1st to 15thNight
45%7%15%23%7%
1972
16th to endNight
48%8%14%23%4
2321
November1st to 15thNight
53%7%12%20%5%
2465
16th to endNight
57%8%16%12%3
2700
December1st to 15thNight
63%7%13%11%3
2700
16th to endNight
57%9%15%13%4
2880

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
8%5%16%48%16%5%
60
16th to endDay
6%131%34%17%9%
64
February1st to 15thDay
11%428%34%17%2
67
16th to endDay
20%123%34%12%7%
81
March1st to 15thDay
13%5%38%30%10%2
270
16th to endDay
21%330%28%14%2
288
April1st to 15thDay
14%8%33%30%10%2
269
16th to endDay
25%10%20%31%11%2
279
May1st to 15thDay
12%8%22%32%17%6%
468
16th to endDay
19%5%19%29%20%5%
517
June1st to 15thDay
19%7%27%25%15%5%
495
16th to endDay
15%7%21%28%20%7%
495
July1st to 15thDay
11%416%34%27%6%
475
16th to endDay
12%322%29%26%5%
515
August1st to 15thDay
14%215%28%23%14%
403
16th to endDay
7%6%27%35%18%3
332
September1st to 15thDay
14%6%29%26%19%4
294
16th to endDay
14%10%28%29%14%2
255
October1st to 15thDay
27%7%23%24%15%2
112
16th to endDay
26%5%23%20%16%7%
96
November1st to 15thDay
18%321%44%10%1
87
16th to endDay
6%6%28%26%10%21%
60
December1st to 15thDay
13%335%28%15%5%
60
16th to endDay
6%425%29%21%12%
64
January1st to 15thNight
12%6%29%36%12%2
900
16th to endNight
10%8%31%35%12%1
941
February1st to 15thNight
11%427%34%18%2
704
16th to endNight
10%323%41%17%3
632
March1st to 15thNight
11%328%40%12%3
720
16th to endNight
14%5%25%32%19%2
768
April1st to 15thNight
13%425%36%17%2
572
16th to endNight
19%422%35%15%1
540
May1st to 15thNight
15%6%18%35%20%4
400
16th to endNight
22%418%30%21%2
375
June1st to 15thNight
18%5%19%35%18%3
360
16th to endNight
17%219%31%27%2
360
July1st to 15thNight
11%119%40%26%
340
16th to endNight
9%415%42%23%3
376
August1st to 15thNight
11%212%36%32%4
388
16th to endNight
10%123%37%25%1
573
September1st to 15thNight
13%317%37%26%1
572
16th to endNight
11%5%27%36%17%1
656
October1st to 15thNight
19%224%34%16%2
660
16th to endNight
16%427%35%13%1
737
November1st to 15thNight
17%5%30%33%11%2
875
16th to endNight
10%7%31%35%12%2
900
December1st to 15thNight
16%6%29%30%13%3
900
16th to endNight
10%329%35%17%4
960
Page generated at 2017-09-11 17:35:34. Version ac04

Copyright 2017 A. Danko


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