St. Louis
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the St. Louis clear sky chart from 2005-11-05 to 2018-02-22.

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
43%
16541
21%
48903
14%
16495
50%
16495
28%
30910

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
26%
974
18%
2706
7%
970
34%
970
23%
1846
January16th to endNight
26%
1040
19%
2704
7%
1040
35%
1040
25%
1863
February1st to 15thNight
26%
894
14%
2422
5%
891
32%
891
20%
1733
February16th to endNight
24%
659
20%
1977
7%
659
34%
659
23%
1295
March1st to 15thNight
27%
666
17%
2106
9%
666
35%
666
21%
1415
March16th to endNight
33%
576
14%
2028
10%
576
39%
576
18%
1375
April1st to 15thNight
33%
539
21%
1797
12%
539
46%
539
26%
1091
April16th to endNight
40%
540
22%
1800
17%
540
50%
540
26%
1109
May1st to 15thNight
44%
540
17%
1664
12%
539
50%
539
24%
1098
May16th to endNight
54%
563
20%
1497
14%
561
58%
561
30%
986
June1st to 15thNight
64%
540
21%
1440
15%
540
68%
540
41%
858
June16th to endNight
65%
540
23%
1440
15%
540
68%
540
43%
840
July1st to 15thNight
71%
510
19%
1360
16%
510
72%
510
40%
821
July16th to endNight
74%
564
23%
1482
21%
531
76%
531
42%
848
August1st to 15thNight
78%
539
23%
1685
25%
536
79%
536
38%
924
August16th to endNight
74%
573
24%
1910
28%
573
77%
573
37%
1034
September1st to 15thNight
65%
540
26%
1800
28%
540
68%
540
32%
1034
September16th to endNight
61%
668
33%
1931
26%
668
66%
668
37%
1105
October1st to 15thNight
52%
720
28%
2148
21%
720
58%
720
35%
1252
October16th to endNight
39%
768
28%
2325
19%
768
48%
768
32%
1365
November1st to 15thNight
40%
760
27%
2471
18%
760
52%
760
31%
1412
November16th to endNight
33%
813
24%
2568
15%
813
44%
813
27%
1571
December1st to 15thNight
31%
975
17%
2730
9%
975
38%
975
22%
1911
December16th to endNight
25%
1040
16%
2912
6%
1040
34%
1040
18%
2124

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
12%5%25%5%3445%7%41%
49355
Night
12%6%25%42345%6%45%
49085
TransparencyDay
39%6%12%23%14%2
49040
Night
38%5%11%23%17%3
48905
SeeingDay
13%6%22%27%21%8%
6352
Night
16%6%28%31%15%1
16542

By Month

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
14%8%37%6%445%45%33%
1559
16th to endDay
12%7%45%7%34446%39%
1872
February1st to 15thDay
15%7%5%8%4245%47%35%
1768
16th to endDay
12%8%47%5%36%346%37%
1643
March1st to 15thDay
16%8%46%424335%38%
1866
16th to endDay
17%8%46%6%35%5%5%7%30%
2194
April1st to 15thDay
13%5%25%5%25%46%6%42%
2151
16th to endDay
16%6%26%6%35%45%6%37%
2160
May1st to 15thDay
17%5%35%5%25%45%7%37%
2283
16th to endDay
11%5%36%5%35%5%6%8%39%
2617
June1st to 15thDay
7%3245%35%5%7%8%45%
2520
16th to endDay
5%3245%245%7%11%46%
2520
July1st to 15thDay
8%2145%45%5%7%10%43%
2520
16th to endDay
43135%26%6%7%11%46%
2581
August1st to 15thDay
6%3245%46%6%7%9%41%
2265
16th to endDay
7%5%246%35%5%6%9%43%
2292
September1st to 15thDay
12%5%2442345%7%47%
2160
16th to endDay
8%41442445%8%49%
2016
October1st to 15thDay
13%425%423335%49%
1809
16th to endDay
12%424423246%51%
1899
November1st to 15thDay
13%423424347%49%
1717
16th to endDay
16%6%24433336%43%
1719
December1st to 15thDay
16%8%36%5%24446%36%
1560
16th to endDay
17%10%46%5%33247%33%
1664
January1st to 15thNight
15%7%36%5%3435%6%38%
2706
16th to endNight
12%8%46%434446%39%
2704
February1st to 15thNight
14%9%36%6%43445%36%
2413
16th to endNight
13%8%36%5%33345%41%
1977
March1st to 15thNight
18%7%35%5%24345%39%
2106
16th to endNight
16%8%45%5%245%5%5%36%
2028
April1st to 15thNight
12%6%25%433447%46%
1797
16th to endNight
16%5%35%423347%44%
1800
May1st to 15thNight
16%6%2443345%6%41%
1664
16th to endNight
8%5%345%3446%7%45%
1496
June1st to 15thNight
6%3145%2445%9%52%
1440
16th to endNight
6%32341347%10%52%
1440
July1st to 15thNight
8%31443346%8%52%
1440
16th to endNight
32245%345%7%9%51%
1584
August1st to 15thNight
43144245%6%8%54%
1695
16th to endNight
43145%2446%8%53%
1910
September1st to 15thNight
10%5%15%42345%7%49%
1800
16th to endNight
9%412423447%54%
1931
October1st to 15thNight
10%5%24423346%52%
2148
16th to endNight
14%5%23423345%52%
2325
November1st to 15thNight
12%5%24323336%52%
2471
16th to endNight
16%7%24323345%46%
2568
December1st to 15thNight
20%9%35%42435%5%35%
2730
16th to endNight
18%10%46%5%34345%33%
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
49%6%10%20%11%1
1560
16th to endDay
43%5%15%24%10%1
1872
February1st to 15thDay
48%6%12%22%9%
1770
16th to endDay
47%6%11%21%11%1
1643
March1st to 15thDay
47%5%10%22%12%1
1866
16th to endDay
51%8%14%17%8%
2196
April1st to 15thDay
40%5%11%23%16%2
2151
16th to endDay
46%5%12%22%11%1
2160
May1st to 15thDay
44%8%13%23%10%
2283
16th to endDay
40%8%14%19%14%2
2621
June1st to 15thDay
32%8%14%23%18%2
2520
16th to endDay
28%8%17%23%18%3
2520
July1st to 15thDay
33%8%13%24%15%4
2371
16th to endDay
29%8%16%27%16%1
2420
August1st to 15thDay
34%8%12%25%17%
2251
16th to endDay
34%8%13%20%17%4
2292
September1st to 15thDay
36%6%9%23%20%4
2160
16th to endDay
32%5%9%28%20%3
2016
October1st to 15thDay
37%310%25%18%4
1809
16th to endDay
32%39%31%17%3
1899
November1st to 15thDay
34%311%24%19%6%
1717
16th to endDay
42%410%28%13%1
1719
December1st to 15thDay
47%5%13%21%11%
1560
16th to endDay
51%312%20%9%1
1664
January1st to 15thNight
45%5%10%23%14%1
2706
16th to endNight
44%414%22%12%
2704
February1st to 15thNight
49%5%10%19%13%1
2422
16th to endNight
44%313%23%13%1
1977
March1st to 15thNight
47%410%22%12%2
2106
16th to endNight
48%6%13%21%9%
2028
April1st to 15thNight
37%6%10%25%18%2
1797
16th to endNight
40%49%26%16%2
1800
May1st to 15thNight
41%7%12%21%16%1
1665
16th to endNight
36%9%12%21%16%3
1498
June1st to 15thNight
27%7%12%28%21%1
1440
16th to endNight
24%8%15%25%20%5%
1440
July1st to 15thNight
28%7%13%28%15%6%
1360
16th to endNight
25%7%15%30%17%2
1482
August1st to 15thNight
25%7%14%26%22%2
1685
16th to endNight
26%7%12%24%23%5%
1910
September1st to 15thNight
33%5%9%23%21%7%
1800
16th to endNight
29%5%8%25%26%4
1931
October1st to 15thNight
32%49%24%22%6%
2148
16th to endNight
34%38%26%21%4
2325
November1st to 15thNight
34%411%22%21%7%
2471
16th to endNight
39%39%26%19%1
2568
December1st to 15thNight
48%411%21%12%
2730
16th to endNight
52%5%11%18%9%1
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
25%12%37%17%7%
135
16th to endDay
7%23%42%22%4
144
February1st to 15thDay
19%16%37%20%5%
135
16th to endDay
23%19%31%23%4
100
March1st to 15thDay
30%12%38%12%42
90
16th to endDay
24%11%32%25%7%
180
April1st to 15thDay
15%11%30%25%16%
270
16th to endDay
22%6%29%22%16%2
270
May1st to 15thDay
16%11%27%26%12%5%
315
16th to endDay
15%429%29%12%7%
517
June1st to 15thDay
9%320%30%24%11%
495
16th to endDay
7%323%37%21%6%
495
July1st to 15thDay
11%113%35%28%9%
475
16th to endDay
5%12%31%34%16%
515
August1st to 15thDay
10%8%28%33%17%
418
16th to endDay
9%11%23%40%14%
332
September1st to 15thDay
13%213%21%33%15%
315
16th to endDay
11%310%28%30%16%
314
October1st to 15thDay
17%6%18%37%15%3
144
16th to endDay
9%14%29%29%15%1
144
November1st to 15thDay
14%429%24%20%7%
135
16th to endDay
24%14%30%20%8%1
135
December1st to 15thDay
10%21%34%19%10%3
135
16th to endDay
27%12%48%9%2
144
January1st to 15thNight
19%12%38%24%5%
975
16th to endNight
16%11%40%27%2
1040
February1st to 15thNight
19%11%37%28%2
894
16th to endNight
18%10%39%29%1
659
March1st to 15thNight
23%10%35%27%3
666
16th to endNight
19%8%31%31%8%
576
April1st to 15thNight
16%8%39%26%9%
539
16th to endNight
17%5%32%32%10%
540
May1st to 15thNight
17%427%36%13%
540
16th to endNight
10%224%41%18%2
563
June1st to 15thNight
7%118%46%24%1
540
16th to endNight
7%119%44%25%1
540
July1st to 15thNight
9%9%46%30%2
510
16th to endNight
411%35%43%4
564
August1st to 15thNight
6%7%37%43%4
539
16th to endNight
6%9%38%39%6%
573
September1st to 15thNight
13%211%33%33%5%
540
16th to endNight
11%416%28%33%6%
668
October1st to 15thNight
14%424%31%22%3
720
16th to endNight
17%7%33%30%10%
768
November1st to 15thNight
15%6%33%30%12%
760
16th to endNight
21%7%35%27%8%
813
December1st to 15thNight
24%10%30%28%5%
975
16th to endNight
23%10%35%27%3
1040
Page generated at 2018-02-23 10:21:32. Version ac04

Copyright 2018 A. Danko


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