Gretna City Park Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Gretna City Park Observatory clear sky chart from 2005-11-05 to

2017-09-12
.

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
60%
14889
23%
46902
19%
14847
65%
14847
31%
27828

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
43%
719
24%
2148
12%
716
53%
716
29%
1323
January16th to endNight
38%
768
26%
2304
13%
768
47%
768
27%
1459
February1st to 15thNight
42%
704
25%
2112
13%
701
51%
701
30%
1280
February16th to endNight
38%
631
23%
1893
11%
631
46%
631
27%
1194
March1st to 15thNight
43%
615
24%
2055
17%
615
51%
615
26%
1254
March16th to endNight
56%
576
24%
2039
20%
576
63%
576
31%
1094
April1st to 15thNight
52%
539
25%
1797
20%
539
61%
539
31%
1029
April16th to endNight
58%
540
27%
1800
25%
540
66%
540
35%
980
May1st to 15thNight
66%
539
21%
1799
22%
539
71%
539
34%
1003
May16th to endNight
71%
561
21%
1870
22%
561
74%
561
33%
1058
June1st to 15thNight
79%
540
13%
1800
16%
540
79%
540
31%
1048
June16th to endNight
75%
540
14%
1644
16%
540
76%
540
29%
1026
July1st to 15thNight
83%
510
13%
1540
15%
510
83%
510
31%
951
July16th to endNight
82%
564
10%
1772
14%
531
81%
531
24%
1141
August1st to 15thNight
86%
539
14%
1788
17%
536
86%
536
32%
1040
August16th to endNight
75%
573
13%
1910
15%
573
75%
573
25%
1228
September1st to 15thNight
73%
530
19%
1767
20%
530
74%
530
27%
1080
September16th to endNight
75%
629
27%
1787
23%
629
75%
629
34%
1112
October1st to 15thNight
74%
660
33%
1902
28%
660
76%
660
50%
974
October16th to endNight
61%
704
32%
2112
27%
704
67%
704
41%
1129
November1st to 15thNight
63%
700
33%
2100
29%
700
68%
700
38%
1184
November16th to endNight
53%
720
31%
2310
26%
720
61%
720
34%
1268
December1st to 15thNight
48%
720
25%
2340
21%
720
55%
720
27%
1414
December16th to endNight
41%
768
20%
2313
14%
768
46%
768
23%
1559

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
10%5%25%6%46%6%6%8%37%
47722
Night
9%4244245%6%9%47%
47114
TransparencyDay
40%8%13%17%14%5%
47438
Night
32%7%14%20%17%7%
46904
SeeingDay
11%313%23%28%19%
5165
Night
10%5%17%29%28%9%
14893

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
12%5%345%245%5%7%42%
1790
16th to endDay
18%6%245%2434443%
1920
February1st to 15thDay
12%6%2433335%8%46%
1750
16th to endDay
14%5%15%6%35%446%41%
1580
March1st to 15thDay
15%5%35%43445%7%41%
1914
16th to endDay
10%6%245%2335%8%45%
2182
April1st to 15thDay
11%5%25%435%5%6%9%41%
2151
16th to endDay
10%5%245%35%5%6%10%40%
2160
May1st to 15thDay
8%425%5%46%6%7%9%38%
2151
16th to endDay
8%5%25%6%47%6%6%9%39%
2244
June1st to 15thDay
8%5%37%8%48%7%8%11%26%
2160
16th to endDay
6%5%36%8%5%9%9%10%10%23%
2310
July1st to 15thDay
7%5%37%8%5%8%8%10%11%21%
2325
16th to endDay
8%5%37%8%6%10%9%7%10%21%
2276
August1st to 15thDay
9%5%27%8%5%9%8%9%10%23%
2160
16th to endDay
10%7%48%7%46%7%7%9%24%
2292
September1st to 15thDay
10%6%36%6%5%7%8%8%9%28%
2112
16th to endDay
8%5%15%7%5%5%6%6%7%38%
1832
October1st to 15thDay
6%3245%235%5%8%52%
1724
16th to endDay
7%31441345%7%54%
1760
November1st to 15thDay
8%42442445%7%52%
1758
16th to endDay
8%41342445%6%54%
1646
December1st to 15thDay
13%6%24435%45%7%42%
1620
16th to endDay
18%8%36%5%2335%7%34%
1905
January1st to 15thNight
13%5%2442345%7%46%
2148
16th to endNight
16%6%23423346%44%
2304
February1st to 15thNight
12%4245%1445%7%46%
2103
16th to endNight
16%5%34422446%46%
1893
March1st to 15thNight
12%5%2442445%8%44%
2055
16th to endNight
9%42332435%8%52%
2039
April1st to 15thNight
10%41442445%7%50%
1797
16th to endNight
6%42432445%9%52%
1800
May1st to 15thNight
5%323435%5%6%10%49%
1799
16th to endNight
5%324435%5%5%9%51%
1869
June1st to 15thNight
5%423436%5%7%12%44%
1800
16th to endNight
6%3245%36%6%6%11%44%
1644
July1st to 15thNight
3323326%6%8%13%44%
1630
16th to endNight
3325%5%37%8%9%13%38%
1892
August1st to 15thNight
3213435%7%9%14%44%
1800
16th to endNight
8%4245%45%5%8%11%39%
1910
September1st to 15thNight
7%4245%345%8%12%41%
1767
16th to endNight
7%4144345%6%10%46%
1787
October1st to 15thNight
4213322348%63%
1902
16th to endNight
9%213213446%58%
2112
November1st to 15thNight
8%314423445%56%
2100
16th to endNight
8%314334445%56%
2310
December1st to 15thNight
11%5%25%5%2445%7%46%
2340
16th to endNight
16%7%36%5%2445%6%38%
2313

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
40%5%8%16%19%8%
1791
16th to endDay
44%37%15%20%9%
1920
February1st to 15thDay
36%5%10%17%20%9%
1752
16th to endDay
43%5%8%16%19%6%
1580
March1st to 15thDay
40%6%9%20%16%5%
1914
16th to endDay
36%5%11%21%18%6%
2184
April1st to 15thDay
37%7%11%18%18%7%
2151
16th to endDay
35%7%13%21%16%5%
2160
May1st to 15thDay
36%8%14%18%13%7%
2151
16th to endDay
38%9%13%21%16%1
2248
June1st to 15thDay
45%10%17%17%9%
2160
16th to endDay
46%13%18%15%7%
2310
July1st to 15thDay
46%14%20%14%3
2187
16th to endDay
51%13%18%14%2
2133
August1st to 15thDay
47%14%20%13%3
2148
16th to endDay
50%13%16%11%5%1
2292
September1st to 15thDay
44%14%15%13%10%3
2112
16th to endDay
38%11%13%15%16%5%
1832
October1st to 15thDay
27%5%12%18%22%13%
1724
16th to endDay
27%47%17%26%15%
1760
November1st to 15thDay
30%5%8%22%24%8%
1758
16th to endDay
29%5%9%17%23%14%
1646
December1st to 15thDay
40%5%11%21%15%5%
1620
16th to endDay
48%5%9%17%13%4
1905
January1st to 15thNight
36%5%10%15%21%9%
2148
16th to endNight
40%47%14%20%12%
2304
February1st to 15thNight
36%48%19%20%10%
2112
16th to endNight
39%5%7%15%20%12%
1893
March1st to 15thNight
37%6%10%18%19%7%
2055
16th to endNight
30%414%20%21%7%
2039
April1st to 15thNight
32%6%12%21%16%10%
1797
16th to endNight
28%6%13%26%18%6%
1800
May1st to 15thNight
28%7%13%26%17%6%
1800
16th to endNight
28%8%15%26%18%1
1871
June1st to 15thNight
28%11%20%25%13%
1800
16th to endNight
31%12%24%20%10%
1644
July1st to 15thNight
25%16%30%23%3
1540
16th to endNight
31%16%28%19%3
1772
August1st to 15thNight
23%15%32%23%4
1788
16th to endNight
35%12%28%14%5%3
1910
September1st to 15thNight
33%11%21%16%14%3
1767
16th to endNight
30%10%15%20%16%6%
1787
October1st to 15thNight
20%413%22%22%16%
1902
16th to endNight
26%38%16%26%18%
2112
November1st to 15thNight
29%47%22%26%9%
2100
16th to endNight
29%5%6%18%23%16%
2310
December1st to 15thNight
37%5%10%23%17%5%
2340
16th to endNight
45%5%8%19%14%6%
2313

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
23%8%30%28%8%
90
16th to endDay
13%28%34%18%5%
96
February1st to 15thDay
7%20%30%32%7%2
90
16th to endDay
8%16%34%30%9%
81
March1st to 15thDay
24%10%35%28%1
90
16th to endDay
15%9%22%29%20%2
168
April1st to 15thDay
15%6%23%32%19%2
270
16th to endDay
12%5%21%31%23%5%
270
May1st to 15thDay
11%416%32%30%4
288
16th to endDay
11%113%26%26%19%
331
June1st to 15thDay
13%422%35%23%
315
16th to endDay
9%5%23%34%25%
465
July1st to 15thDay
6%419%35%34%
461
16th to endDay
9%110%34%43%
326
August1st to 15thDay
9%1110%32%43%
313
16th to endDay
10%6%13%33%35%
332
September1st to 15thDay
14%16%20%30%27%
299
16th to endDay
8%16%19%44%19%
254
October1st to 15thDay
3414%29%39%7%
164
16th to endDay
13%314%40%21%6%
96
November1st to 15thDay
20%5%17%33%20%3
90
16th to endDay
12%10%32%28%14%2
90
December1st to 15thDay
18%7%34%28%10%
90
16th to endDay
31%431%25%8%
96
January1st to 15thNight
15%8%27%38%8%1
720
16th to endNight
18%11%28%32%9%
768
February1st to 15thNight
14%9%29%33%12%
704
16th to endNight
18%10%29%32%8%
631
March1st to 15thNight
15%7%30%30%15%
615
16th to endNight
10%7%21%35%23%1
576
April1st to 15thNight
12%6%25%36%18%1
539
16th to endNight
9%423%37%22%2
540
May1st to 15thNight
6%316%43%28%
540
16th to endNight
5%113%30%39%9%
563
June1st to 15thNight
6%426%51%11%
540
16th to endNight
6%416%47%24%
540
July1st to 15thNight
4110%48%34%
510
16th to endNight
3210%47%35%
564
August1st to 15thNight
319%46%38%
539
16th to endNight
10%212%44%30%
573
September1st to 15thNight
9%1415%41%27%
530
16th to endNight
9%5%28%44%10%
629
October1st to 15thNight
5%111%35%38%6%
660
16th to endNight
9%5%19%29%28%6%
704
November1st to 15thNight
10%317%37%25%5%
700
16th to endNight
10%8%23%35%20%2
720
December1st to 15thNight
14%8%22%34%18%1
720
16th to endNight
21%8%23%31%13%1
768
Page generated at 2017-09-13 06:39:22. Version ac04

Copyright 2017 A. Danko


Gretna City Park Observatory Clear Sky Chart | Charts Home