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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 2017-05-24.

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%
15494
21%
45866
14%
15448
49%
15448
28%
29043

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%
899
18%
2497
7%
895
35%
895
23%
1691
January16th to endNight
25%
960
19%
2496
6%
960
34%
960
24%
1733
February1st to 15thNight
26%
824
15%
2232
5%
821
32%
821
20%
1591
February16th to endNight
25%
631
20%
1893
7%
631
35%
631
24%
1223
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%
542
18%
1441
13%
540
57%
540
29%
957
June1st to 15thNight
63%
495
22%
1320
15%
495
67%
495
38%
804
June16th to endNight
66%
495
20%
1320
14%
495
69%
495
42%
778
July1st to 15thNight
70%
465
21%
1240
17%
465
71%
465
39%
756
July16th to endNight
74%
522
21%
1364
19%
489
76%
489
41%
785
August1st to 15thNight
79%
494
25%
1544
27%
491
80%
491
40%
830
August16th to endNight
73%
525
23%
1750
26%
525
76%
525
36%
953
September1st to 15thNight
64%
495
27%
1650
29%
495
67%
495
31%
955
September16th to endNight
60%
612
31%
1770
24%
612
65%
612
36%
1022
October1st to 15thNight
53%
660
29%
1969
22%
660
59%
660
36%
1131
October16th to endNight
39%
704
26%
2131
17%
704
48%
704
32%
1258
November1st to 15thNight
41%
700
28%
2276
18%
700
54%
700
33%
1262
November16th to endNight
32%
750
22%
2370
14%
750
42%
750
26%
1473
December1st to 15thNight
30%
900
16%
2520
9%
900
37%
900
21%
1794
December16th to endNight
25%
960
16%
2688
7%
960
34%
960
18%
1959

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%35%5%35%45%7%41%
46413
Night
13%6%25%42345%6%44%
46048
TransparencyDay
40%6%12%23%14%2
46098
Night
39%5%11%23%16%3
45868
SeeingDay
14%6%22%27%21%8%
5334
Night
16%6%28%31%15%1
15495

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%7%37%6%445%45%34%
1438
16th to endDay
12%7%35%7%34446%39%
1728
February1st to 15thDay
15%7%47%434447%36%
1628
16th to endDay
11%8%47%6%36%346%38%
1580
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%38%
2516
June1st to 15thDay
7%4245%36%5%7%8%43%
2310
16th to endDay
6%3245%25%6%8%11%45%
2310
July1st to 15thDay
9%2145%46%5%7%10%42%
2310
16th to endDay
43135%36%6%7%11%45%
2391
August1st to 15thDay
6%4245%46%6%7%10%41%
2076
16th to endDay
7%5%246%35%5%6%9%42%
2100
September1st to 15thDay
13%5%3442345%7%44%
1980
16th to endDay
8%5%25%42445%8%49%
1848
October1st to 15thDay
13%424423336%51%
1658
16th to endDay
12%424423246%51%
1741
November1st to 15thDay
12%423424347%50%
1582
16th to endDay
17%6%34433336%42%
1587
December1st to 15thDay
18%9%36%5%34446%34%
1440
16th to endDay
18%10%46%5%23247%34%
1536
January1st to 15thNight
14%7%36%5%3435%6%39%
2497
16th to endNight
13%8%47%434446%38%
2496
February1st to 15thNight
14%10%36%6%33445%36%
2223
16th to endNight
12%8%46%5%33345%42%
1893
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%44%
1440
June1st to 15thNight
7%315%5%2446%9%50%
1320
16th to endNight
7%32341446%10%52%
1320
July1st to 15thNight
8%31443336%8%52%
1320
16th to endNight
32245%345%7%10%50%
1466
August1st to 15thNight
33134245%6%8%55%
1554
16th to endNight
5%3146%2445%8%52%
1750
September1st to 15thNight
11%5%15%41346%7%48%
1650
16th to endNight
10%412423447%53%
1770
October1st to 15thNight
10%414323347%53%
1969
16th to endNight
14%5%23312345%51%
2131
November1st to 15thNight
11%414323336%54%
2276
16th to endNight
17%7%34323345%45%
2370
December1st to 15thNight
21%9%35%42345%5%34%
2520
16th to endNight
18%10%46%5%34345%33%
2688

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
48%6%10%21%11%
1439
16th to endDay
44%5%15%24%9%1
1728
February1st to 15thDay
47%6%12%23%9%
1630
16th to endDay
46%6%12%22%12%1
1580
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%13%2
2520
June1st to 15thDay
34%9%15%23%16%1
2310
16th to endDay
29%8%17%22%17%3
2310
July1st to 15thDay
33%9%13%23%14%3
2161
16th to endDay
30%9%16%28%13%1
2230
August1st to 15thDay
33%9%13%24%18%
2062
16th to endDay
35%8%13%20%16%5%
2100
September1st to 15thDay
37%6%10%22%19%4
1980
16th to endDay
33%5%9%27%20%3
1848
October1st to 15thDay
34%310%26%20%4
1658
16th to endDay
32%310%31%17%4
1741
November1st to 15thDay
33%411%24%20%6%
1582
16th to endDay
43%411%27%12%1
1587
December1st to 15thDay
50%5%13%20%10%
1440
16th to endDay
51%312%21%9%1
1536
January1st to 15thNight
44%5%10%23%14%1
2497
16th to endNight
45%414%21%12%
2496
February1st to 15thNight
49%5%9%21%12%1
2232
16th to endNight
43%313%24%13%1
1893
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
37%9%13%20%15%3
1442
June1st to 15thNight
29%7%13%29%18%1
1320
16th to endNight
25%8%15%25%19%5%
1320
July1st to 15thNight
29%7%13%28%15%5%
1240
16th to endNight
26%7%16%31%16%2
1364
August1st to 15thNight
24%7%15%27%22%2
1544
16th to endNight
27%7%12%24%23%5%
1750
September1st to 15thNight
33%5%9%23%21%6%
1650
16th to endNight
30%5%7%24%26%4
1770
October1st to 15thNight
30%49%25%22%6%
1969
16th to endNight
35%39%25%21%4
2131
November1st to 15thNight
31%411%22%22%7%
2276
16th to endNight
40%49%26%18%1
2370
December1st to 15thNight
50%411%21%11%
2520
16th to endNight
52%5%11%19%10%2
2688

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
28%13%38%14%31
90
16th to endDay
10%23%45%17%2
96
February1st to 15thDay
16%17%40%20%5%
90
16th to endDay
14%17%34%28%4
81
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
16%428%29%12%7%
481
June1st to 15thDay
10%422%28%23%11%
420
16th to endDay
7%318%38%23%7%
420
July1st to 15thDay
12%113%34%26%11%
400
16th to endDay
5%12%31%33%16%
445
August1st to 15thDay
10%7%28%33%19%
349
16th to endDay
10%11%20%39%17%
268
September1st to 15thDay
14%212%21%34%13%
255
16th to endDay
13%412%26%27%15%
254
October1st to 15thDay
13%7%16%37%20%5%
98
16th to endDay
9%9%29%35%16%
96
November1st to 15thDay
5%5%27%22%27%11%
90
16th to endDay
35%16%27%10%8%1
90
December1st to 15thDay
14%15%35%20%10%4
90
16th to endDay
28%15%42%10%3
96
January1st to 15thNight
18%12%38%24%5%
900
16th to endNight
16%12%40%27%2
960
February1st to 15thNight
19%12%36%29%2
824
16th to endNight
17%11%39%29%1
631
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%40%19%2
542
June1st to 15thNight
7%118%46%23%1
495
16th to endNight
7%118%43%27%1
495
July1st to 15thNight
10%9%45%30%3
465
16th to endNight
410%35%44%4
522
August1st to 15thNight
5%7%38%44%4
494
16th to endNight
7%9%36%39%6%
525
September1st to 15thNight
13%211%34%32%5%
495
16th to endNight
12%416%27%32%6%
612
October1st to 15thNight
13%424%30%24%4
660
16th to endNight
18%7%32%31%10%
704
November1st to 15thNight
12%7%34%30%13%1
700
16th to endNight
22%8%34%26%8%
750
December1st to 15thNight
25%10%30%27%5%
900
16th to endNight
23%10%34%27%3
960
Page generated at 2017-05-25 12:27:33. Version ac04

Copyright 2017 A. Danko


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