St. Andrews
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the St. Andrews clear sky chart from 2005-11-05 to 2017-12-02.

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%
15185
15%
47732
6%
15145
36%
15145
17%
33438

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
17%
735
15%
2594
3%
731
31%
731
13%
1792
January16th to endNight
14%
768
15%
2601
2%
768
28%
768
12%
1835
February1st to 15thNight
16%
704
11%
2286
3%
701
27%
701
12%
1655
February16th to endNight
19%
631
14%
1951
3%
631
32%
631
13%
1408
March1st to 15thNight
18%
720
15%
2048
5%
720
29%
720
15%
1530
March16th to endNight
23%
768
17%
2112
7%
768
32%
768
19%
1489
April1st to 15thNight
21%
623
15%
1776
5%
623
29%
623
16%
1308
April16th to endNight
24%
540
15%
1620
6%
540
32%
540
20%
1140
May1st to 15thNight
27%
540
13%
1620
6%
540
35%
540
17%
1205
May16th to endNight
30%
523
10%
1477
5%
522
37%
522
16%
1098
June1st to 15thNight
31%
360
8%
1260
6%
360
35%
360
14%
925
June16th to endNight
34%
360
8%
1260
8%
360
38%
360
15%
917
July1st to 15thNight
44%
340
9%
1190
10%
340
47%
340
18%
803
July16th to endNight
41%
451
9%
1485
8%
423
44%
423
15%
1075
August1st to 15thNight
47%
539
11%
1608
9%
535
49%
535
21%
1137
August16th to endNight
48%
573
18%
1719
12%
573
52%
573
26%
1107
September1st to 15thNight
39%
646
16%
1888
9%
646
44%
646
26%
1237
September16th to endNight
43%
717
26%
1980
15%
717
52%
717
34%
1195
October1st to 15thNight
35%
720
20%
2121
10%
720
43%
720
24%
1388
October16th to endNight
24%
768
16%
2387
5%
768
35%
768
18%
1634
November1st to 15thNight
28%
775
16%
2535
8%
775
37%
775
18%
1720
November16th to endNight
23%
825
17%
2730
5%
825
37%
825
15%
1850
December1st to 15thNight
13%
759
14%
2604
3%
759
27%
759
11%
1901
December16th to endNight
12%
800
14%
2880
2%
800
26%
800
10%
2089

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
19%6%25%42445%7%35%
48725
Night
20%7%35%424447%33%
47900
TransparencyDay
47%6%12%20%11%1
48411
Night
50%5%11%20%11%1
47732
SeeingDay
25%11%29%23%9%1
7008
Night
24%11%30%24%7%
15185

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
17%8%36%5%25%35%9%31%
1343
16th to endDay
16%10%35%5%25%5%5%9%29%
1623
February1st to 15thDay
16%8%36%6%45%45%10%26%
1575
16th to endDay
14%9%36%5%45%45%7%32%
1521
March1st to 15thDay
20%10%35%424437%33%
1900
16th to endDay
17%8%35%33445%6%38%
2112
April1st to 15thDay
20%7%35%6%24345%36%
2170
16th to endDay
22%7%244235%45%36%
2340
May1st to 15thDay
24%7%35%425%446%31%
2332
16th to endDay
25%6%245%2445%7%30%
2646
June1st to 15thDay
25%7%36%434347%29%
2700
16th to endDay
23%5%345%35%45%8%29%
2700
July1st to 15thDay
18%42443445%10%39%
2700
16th to endDay
16%7%34435%5%6%7%35%
2568
August1st to 15thDay
17%5%25%5%25%45%8%37%
2340
16th to endDay
12%41343445%9%45%
2483
September1st to 15thDay
14%423423347%48%
2070
16th to endDay
16%5%13312337%50%
1980
October1st to 15thDay
17%5%24324345%44%
1839
16th to endDay
21%5%25%424446%37%
1836
November1st to 15thDay
22%7%25%423346%37%
1651
16th to endDay
21%6%25%425%45%6%35%
1560
December1st to 15thDay
27%9%2431445%8%28%
1392
16th to endDay
24%8%36%4245%6%7%27%
1344
January1st to 15thNight
17%8%36%5%2445%8%32%
2594
16th to endNight
15%10%46%5%26%5%6%8%27%
2601
February1st to 15thNight
16%10%35%5%46%5%5%8%28%
2285
16th to endNight
17%10%37%6%23445%32%
1951
March1st to 15thNight
19%10%35%5%345%35%31%
2036
16th to endNight
18%8%35%42435%7%35%
2112
April1st to 15thNight
23%8%35%6%34435%31%
1776
16th to endNight
25%7%25%323446%35%
1620
May1st to 15thNight
24%6%36%5%34445%30%
1620
16th to endNight
25%7%25%5%3445%7%28%
1475
June1st to 15thNight
29%7%35%42345%7%26%
1260
16th to endNight
25%6%36%5%25%446%29%
1260
July1st to 15thNight
17%7%445%25%5%6%10%31%
1260
16th to endNight
22%8%25%5%35%45%6%29%
1586
August1st to 15thNight
18%8%25%435%45%8%33%
1620
16th to endNight
16%5%145%3345%7%42%
1719
September1st to 15thNight
18%6%23424347%42%
1888
16th to endNight
14%5%23213346%51%
1980
October1st to 15thNight
19%6%25%323345%42%
2121
16th to endNight
22%5%24423445%38%
2387
November1st to 15thNight
20%6%245%33447%36%
2535
16th to endNight
21%6%25%424447%36%
2730
December1st to 15thNight
26%9%26%424446%29%
2604
16th to endNight
24%9%35%5%24446%28%
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
50%6%14%18%8%1
1344
16th to endDay
51%7%10%19%10%1
1623
February1st to 15thDay
53%6%11%18%9%1
1578
16th to endDay
49%6%13%19%8%1
1521
March1st to 15thDay
52%5%10%19%10%1
1911
16th to endDay
45%5%10%20%14%3
2112
April1st to 15thDay
50%410%19%13%2
2170
16th to endDay
48%5%11%17%13%4
2340
May1st to 15thDay
53%5%10%17%10%1
2332
16th to endDay
52%7%11%20%6%1
2650
June1st to 15thDay
55%6%12%15%8%1
2700
16th to endDay
52%8%12%16%9%
2700
July1st to 15thDay
41%7%16%21%11%
2541
16th to endDay
44%8%16%21%8%
2407
August1st to 15thDay
43%7%15%22%9%
2327
16th to endDay
35%7%16%27%13%
2483
September1st to 15thDay
34%6%13%26%16%1
2070
16th to endDay
35%410%30%17%1
1980
October1st to 15thDay
42%412%28%12%
1839
16th to endDay
47%5%12%23%10%
1836
November1st to 15thDay
47%5%13%18%13%
1651
16th to endDay
50%5%14%17%10%1
1560
December1st to 15thDay
54%6%13%19%7%
1392
16th to endDay
55%6%10%17%9%
1344
January1st to 15thNight
50%6%12%20%9%1
2594
16th to endNight
52%6%11%20%9%
2601
February1st to 15thNight
52%7%12%16%9%1
2286
16th to endNight
53%5%10%16%11%1
1951
March1st to 15thNight
54%5%8%17%12%1
2048
16th to endNight
48%49%20%14%1
2112
April1st to 15thNight
54%49%14%14%2
1776
16th to endNight
51%410%17%15%2
1620
May1st to 15thNight
55%5%9%16%11%1
1620
16th to endNight
55%5%12%18%7%
1477
June1st to 15thNight
56%5%14%16%5%1
1260
16th to endNight
56%5%9%19%9%
1260
July1st to 15thNight
46%8%15%18%11%
1190
16th to endNight
54%6%11%18%7%
1485
August1st to 15thNight
47%7%14%19%10%
1608
16th to endNight
40%6%13%26%12%
1719
September1st to 15thNight
42%5%11%25%15%
1888
16th to endNight
34%311%29%19%1
1980
October1st to 15thNight
43%5%9%25%14%1
2121
16th to endNight
48%412%23%11%
2387
November1st to 15thNight
47%6%13%19%12%1
2535
16th to endNight
48%5%13%19%11%
2730
December1st to 15thNight
56%410%21%7%
2604
16th to endNight
56%5%10%18%9%
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
26%15%38%16%3
60
16th to endDay
24%17%39%15%3
151
February1st to 15thDay
19%19%39%16%3
236
16th to endDay
22%17%34%20%4
229
March1st to 15thDay
25%21%32%17%2
270
16th to endDay
24%18%31%15%7%2
288
April1st to 15thDay
28%16%31%17%41
270
16th to endDay
28%10%30%21%6%1
270
May1st to 15thDay
31%11%31%17%6%1
288
16th to endDay
31%9%28%21%8%1
499
June1st to 15thDay
27%9%30%24%7%1
495
16th to endDay
30%428%24%9%1
495
July1st to 15thDay
26%225%28%15%1
475
16th to endDay
20%429%32%12%
326
August1st to 15thDay
21%427%31%13%1
313
16th to endDay
16%5%24%31%20%1
332
September1st to 15thDay
16%6%28%35%10%1
315
16th to endDay
19%6%26%27%17%3
314
October1st to 15thDay
19%13%27%21%15%2
280
16th to endDay
25%15%31%21%5%
288
November1st to 15thDay
24%15%28%23%6%2
280
16th to endDay
26%17%28%19%7%
285
December1st to 15thDay
31%15%34%15%3
185
16th to endDay
31%26%32%7%1
64
January1st to 15thNight
22%18%34%21%2
735
16th to endNight
21%21%36%17%2
768
February1st to 15thNight
23%17%39%16%3
704
16th to endNight
24%18%31%20%3
631
March1st to 15thNight
25%15%34%21%3
720
16th to endNight
21%17%31%22%6%
768
April1st to 15thNight
28%10%35%20%5%
623
16th to endNight
27%7%35%22%6%
540
May1st to 15thNight
27%6%30%26%8%
540
16th to endNight
26%7%29%28%6%1
523
June1st to 15thNight
32%5%23%29%9%
360
16th to endNight
30%323%29%11%1
360
July1st to 15thNight
22%320%40%13%
340
16th to endNight
25%220%37%14%
451
August1st to 15thNight
22%218%40%15%
539
16th to endNight
19%123%38%16%1
573
September1st to 15thNight
22%229%30%13%1
646
16th to endNight
17%5%29%31%15%1
717
October1st to 15thNight
23%5%30%26%11%2
720
16th to endNight
25%13%33%19%8%
768
November1st to 15thNight
23%12%30%22%9%1
775
16th to endNight
25%17%30%19%6%
825
December1st to 15thNight
33%14%33%15%3
759
16th to endNight
31%18%33%13%2
800
Page generated at 2017-12-03 12:16:41. Version ac04

Copyright 2017 A. Danko


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