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 2018-03-11.

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%
16014
10%
49167
7%
15989
45%
15989
18%
35159

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
34%
970
6%
2910
4%
970
37%
970
13%
2275
January16th to endNight
32%
1019
13%
3099
7%
1019
38%
1019
16%
2261
February1st to 15thNight
37%
757
8%
2621
8%
756
41%
756
14%
1921
February16th to endNight
48%
684
12%
2221
12%
684
51%
684
16%
1613
March1st to 15thNight
42%
764
14%
2221
10%
764
45%
764
19%
1620
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
56%
591
14%
1758
11%
591
57%
591
29%
1098
September16th to endNight
50%
716
19%
1980
11%
716
57%
716
34%
1228
October1st to 15thNight
44%
720
14%
2151
10%
720
48%
720
23%
1472
October16th to endNight
39%
804
14%
2532
9%
804
45%
804
18%
1776
November1st to 15thNight
34%
950
13%
2676
8%
950
38%
950
16%
2048
November16th to endNight
31%
975
8%
2925
4%
975
35%
975
14%
2271
December1st to 15thNight
30%
975
8%
2925
4%
975
33%
975
12%
2293
December16th to endNight
35%
1040
11%
3120
5%
1040
41%
1040
14%
2410

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%
49492
Night
9%9%48%7%45%5%6%7%31%
49321
TransparencyDay
49%9%18%17%5%
49142
Night
49%8%16%19%6%
49175
SeeingDay
15%5%24%30%18%5%
6594
Night
13%426%35%17%2
16029

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%6%5%21%
1358
16th to endDay
5%13%6%12%9%36%45%6%27%
1489
February1st to 15thDay
7%11%6%9%9%45%5%7%8%24%
1564
16th to endDay
6%13%6%11%8%6%6%6%6%8%20%
1539
March1st to 15thDay
7%13%6%10%7%45%5%7%9%21%
1974
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%
2199
16th to endDay
11%425%6%35%45%7%43%
1980
October1st to 15thDay
14%10%46%5%335%47%33%
1809
16th to endDay
10%10%37%5%35%5%5%7%34%
1679
November1st to 15thDay
8%13%38%7%46%6%6%7%27%
1509
16th to endDay
5%12%412%7%36%5%6%6%29%
1365
December1st to 15thDay
9%12%5%10%10%6%7%5%5%7%18%
1365
16th to endDay
5%10%6%11%10%48%6%7%9%19%
1456
January1st to 15thNight
7%11%6%9%9%5%6%5%6%7%22%
2910
16th to endNight
6%11%6%9%7%35%5%5%7%30%
3099
February1st to 15thNight
6%10%5%10%8%46%45%8%28%
2617
16th to endNight
5%9%5%8%7%5%6%6%6%7%29%
2221
March1st to 15thNight
6%9%5%8%8%45%5%6%6%31%
2221
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
12%415%5%34446%47%
1758
16th to endNight
10%5%1342345%8%49%
1980
October1st to 15thNight
12%11%36%4235%5%7%36%
2151
16th to endNight
10%9%47%6%35%5%6%7%32%
2532
November1st to 15thNight
12%11%5%9%6%45%447%27%
2676
16th to endNight
6%11%7%11%9%5%5%46%7%24%
2925
December1st to 15thNight
9%12%6%12%9%45%45%5%23%
2925
16th to endNight
410%5%11%9%5%7%7%7%7%21%
3120

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
60%8%14%10%5%
1358
16th to endDay
56%7%12%15%7%1
1489
February1st to 15thDay
55%7%18%13%4
1564
16th to endDay
58%7%14%14%5%
1539
March1st to 15thDay
56%9%16%13%3
1974
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%23%5%1
2199
16th to endDay
37%9%17%27%6%1
1980
October1st to 15thDay
49%7%17%21%3
1809
16th to endDay
46%10%14%24%3
1679
November1st to 15thDay
53%8%17%15%4
1509
16th to endDay
53%10%17%15%3
1365
December1st to 15thDay
62%9%10%13%4
1365
16th to endDay
57%8%13%12%8%
1456
January1st to 15thNight
58%8%16%12%4
2910
16th to endNight
52%7%15%17%6%1
3099
February1st to 15thNight
53%8%15%15%6%
2628
16th to endNight
51%9%13%18%6%
2221
March1st to 15thNight
50%7%14%20%5%
2221
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
36%6%18%27%9%1
1758
16th to endNight
32%7%18%28%11%2
1980
October1st to 15thNight
44%7%15%23%8%
2151
16th to endNight
47%8%15%22%4
2532
November1st to 15thNight
56%6%12%19%4
2676
16th to endNight
57%8%17%12%3
2925
December1st to 15thNight
60%7%13%14%4
2925
16th to endNight
56%9%14%12%6%
3120

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%317%45%21%3
90
16th to endDay
6%231%36%15%8%
96
February1st to 15thDay
10%333%33%13%3
101
16th to endDay
14%25%35%18%5%
120
March1st to 15thDay
13%436%30%12%2
312
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
15%6%28%26%19%4
315
16th to endDay
15%9%25%30%16%3
315
October1st to 15thDay
28%7%23%20%17%2
159
16th to endDay
23%7%29%22%12%4
144
November1st to 15thDay
13%323%42%14%3
130
16th to endDay
6%7%33%31%6%14%
90
December1st to 15thDay
12%10%32%25%16%3
90
16th to endDay
5%328%32%21%9%
96
January1st to 15thNight
12%6%29%37%12%2
975
16th to endNight
11%8%31%34%12%1
1019
February1st to 15thNight
11%428%35%17%2
764
16th to endNight
9%223%41%18%3
684
March1st to 15thNight
10%328%40%13%2
764
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%318%37%26%1
591
16th to endNight
12%5%26%36%18%1
716
October1st to 15thNight
19%224%34%16%2
720
16th to endNight
16%5%28%35%13%
804
November1st to 15thNight
17%5%29%33%12%2
950
16th to endNight
10%7%32%34%12%2
975
December1st to 15thNight
15%6%30%30%13%3
975
16th to endNight
9%329%35%17%3
1040
Page generated at 2018-03-12 11:28:14. Version ac04

Copyright 2018 A. Danko


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