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NEFAS Swamp Site
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the NEFAS Swamp Site clear sky chart from 2005-11-05 to 2019-05-11.

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
52%
18047
22%
53632
16%
18009
59%
18009
30%
33028

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
36%
836
24%
2717
15%
836
49%
836
26%
1627
January16th to endNight
35%
896
24%
2870
15%
896
47%
896
24%
1776
February1st to 15thNight
36%
821
22%
2468
13%
819
46%
819
27%
1518
February16th to endNight
39%
735
25%
2185
15%
735
50%
735
31%
1310
March1st to 15thNight
40%
840
29%
2310
14%
840
52%
840
35%
1363
March16th to endNight
42%
896
25%
2464
14%
896
50%
896
37%
1441
April1st to 15thNight
45%
838
25%
2306
15%
838
53%
838
37%
1370
April16th to endNight
51%
758
29%
2055
18%
758
58%
758
43%
1156
May1st to 15thNight
62%
616
27%
1851
18%
616
68%
616
41%
1016
May16th to endNight
66%
609
21%
1826
14%
609
70%
609
34%
1097
June1st to 15thNight
65%
585
13%
1755
10%
585
67%
585
25%
1161
June16th to endNight
74%
585
11%
1755
9%
585
75%
585
28%
1166
July1st to 15thNight
75%
555
11%
1665
10%
555
75%
555
29%
1068
July16th to endNight
73%
612
9%
1739
9%
579
74%
579
25%
1197
August1st to 15thNight
74%
575
9%
1715
9%
572
75%
572
25%
1179
August16th to endNight
66%
725
11%
2157
12%
725
66%
725
21%
1521
September1st to 15thNight
62%
780
13%
2145
12%
780
62%
780
22%
1535
September16th to endNight
60%
777
18%
2145
16%
777
62%
777
27%
1432
October1st to 15thNight
60%
780
29%
2206
26%
780
64%
780
35%
1327
October16th to endNight
55%
832
32%
2496
27%
832
65%
832
37%
1394
November1st to 15thNight
51%
820
29%
2461
22%
820
62%
820
37%
1381
November16th to endNight
43%
840
28%
2699
20%
840
57%
840
33%
1525
December1st to 15thNight
43%
840
26%
2730
19%
840
52%
840
27%
1659
December16th to endNight
45%
896
22%
2912
17%
896
53%
896
25%
1809

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%26%6%45%5%6%7%38%
54211
Night
9%5%25%5%3446%9%44%
53836
TransparencyDay
43%5%12%17%14%6%
53912
Night
35%6%14%20%15%7%
53639
SeeingDay
11%5%19%23%23%16%
7834
Night
11%5%21%31%24%5%
18057

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%6%35%5%2445%8%41%
1881
16th to endDay
13%6%25%425%446%45%
2055
February1st to 15thDay
15%7%25%424445%42%
2050
16th to endDay
12%6%25%5%33345%47%
1857
March1st to 15thDay
8%4133245%5%7%51%
2310
16th to endDay
9%425%5%34446%48%
2463
April1st to 15thDay
9%5%36%5%3445%5%46%
2302
16th to endDay
6%325%5%35%5%5%7%49%
2519
May1st to 15thDay
7%325%5%45%45%8%47%
2656
16th to endDay
10%5%26%7%45%6%6%7%35%
2639
June1st to 15thDay
9%5%27%8%5%7%7%7%9%27%
2535
16th to endDay
8%5%35%9%6%7%7%8%10%27%
2535
July1st to 15thDay
6%6%39%10%47%8%8%9%25%
2535
16th to endDay
8%6%48%9%6%9%7%7%10%22%
2673
August1st to 15thDay
11%6%38%10%5%8%7%8%10%19%
2487
16th to endDay
11%7%49%9%5%8%7%7%8%20%
2380
September1st to 15thDay
10%7%29%9%5%8%6%7%9%22%
2145
16th to endDay
13%8%38%7%46%5%47%29%
2145
October1st to 15thDay
9%7%35%5%45%5%45%42%
2083
16th to endDay
9%315%423445%52%
2080
November1st to 15thDay
8%425%42335%8%49%
2057
16th to endDay
9%42442435%6%50%
1918
December1st to 15thDay
13%7%15%5%2445%6%41%
1890
16th to endDay
11%6%36%5%35%45%7%40%
2016
January1st to 15thNight
12%5%2442445%7%45%
2717
16th to endNight
14%5%25%42435%6%44%
2870
February1st to 15thNight
13%6%35%423345%48%
2463
16th to endNight
11%5%24424348%48%
2185
March1st to 15thNight
7%5%145%23448%50%
2310
16th to endNight
10%414423435%55%
2464
April1st to 15thNight
8%42342335%7%52%
2306
16th to endNight
6%31332335%7%57%
2055
May1st to 15thNight
5%213435%5%6%9%52%
1851
16th to endNight
6%415%426%46%11%45%
1826
June1st to 15thNight
8%425%6%47%6%9%11%33%
1755
16th to endNight
6%3246%46%7%7%13%35%
1755
July1st to 15thNight
4425%5%36%7%8%13%37%
1755
16th to endNight
35%36%6%48%7%9%13%32%
1847
August1st to 15thNight
5%426%7%5%7%7%9%13%31%
1726
16th to endNight
8%6%36%5%46%7%8%11%30%
2157
September1st to 15thNight
8%5%37%7%46%6%8%12%29%
2145
16th to endNight
9%8%36%5%345%7%9%36%
2145
October1st to 15thNight
8%5%15%42336%7%49%
2206
16th to endNight
7%42443445%6%53%
2496
November1st to 15thNight
8%42432445%8%52%
2461
16th to endNight
9%5%24424447%50%
2699
December1st to 15thNight
13%6%245%24448%43%
2730
16th to endNight
11%5%25%5%3445%8%41%
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
41%37%18%19%9%
1882
16th to endDay
40%25%18%21%10%
2055
February1st to 15thDay
43%38%12%18%13%
2052
16th to endDay
39%28%14%22%12%
1857
March1st to 15thDay
30%310%21%22%11%
2310
16th to endDay
35%310%18%20%11%
2464
April1st to 15thDay
38%38%18%21%9%
2302
16th to endDay
33%49%21%20%11%
2519
May1st to 15thDay
34%410%21%20%8%
2656
16th to endDay
44%6%11%19%14%3
2643
June1st to 15thDay
50%7%16%15%8%
2535
16th to endDay
47%10%18%17%4
2535
July1st to 15thDay
49%8%23%15%2
2396
16th to endDay
52%9%21%13%2
2518
August1st to 15thDay
55%8%21%11%1
2474
16th to endDay
57%9%18%11%2
2380
September1st to 15thDay
55%8%15%12%5%1
2145
16th to endDay
52%6%13%15%9%3
2145
October1st to 15thDay
41%47%18%17%10%
2083
16th to endDay
33%36%15%24%15%
2080
November1st to 15thDay
32%48%23%20%10%
2057
16th to endDay
33%38%17%24%12%
1918
December1st to 15thDay
42%48%21%16%7%
1890
16th to endDay
41%410%21%13%7%
2016
January1st to 15thNight
38%39%20%18%9%
2717
16th to endNight
40%36%15%22%11%
2870
February1st to 15thNight
38%39%15%18%14%
2472
16th to endNight
36%39%19%19%11%
2185
March1st to 15thNight
31%311%22%18%11%
2310
16th to endNight
30%312%20%20%11%
2464
April1st to 15thNight
31%410%22%22%8%
2306
16th to endNight
26%412%24%21%10%
2055
May1st to 15thNight
25%5%15%25%19%7%
1852
16th to endNight
32%6%17%25%15%3
1828
June1st to 15thNight
39%9%22%21%6%
1755
16th to endNight
36%10%25%20%5%
1755
July1st to 15thNight
34%10%31%20%3
1665
16th to endNight
36%15%27%17%3
1739
August1st to 15thNight
37%13%31%15%2
1715
16th to endNight
43%12%24%15%3
2157
September1st to 15thNight
44%11%21%15%6%1
2145
16th to endNight
41%6%18%22%7%3
2145
October1st to 15thNight
33%5%11%21%18%9%
2206
16th to endNight
30%37%20%23%14%
2496
November1st to 15thNight
30%39%22%22%10%
2461
16th to endNight
33%38%19%21%13%
2699
December1st to 15thNight
39%311%22%16%7%
2730
16th to endNight
40%411%21%14%7%
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
15%13%43%15%8%3
180
16th to endDay
17%15%42%19%5%
192
February1st to 15thDay
23%13%31%18%11%1
180
16th to endDay
9%13%35%33%7%
176
March1st to 15thDay
11%12%34%28%11%1
390
16th to endDay
15%9%31%22%18%3
416
April1st to 15thDay
12%9%28%24%20%4
390
16th to endDay
7%6%24%30%19%12%
379
May1st to 15thDay
7%5%21%28%20%15%
388
16th to endDay
11%310%24%30%20%
395
June1st to 15thDay
12%18%19%31%25%
375
16th to endDay
9%413%36%35%
375
July1st to 15thDay
5%316%29%43%
365
16th to endDay
9%16%18%33%30%
390
August1st to 15thDay
12%16%15%29%32%
358
16th to endDay
10%1417%29%36%
396
September1st to 15thDay
13%18%23%25%26%
375
16th to endDay
18%15%20%32%22%
374
October1st to 15thDay
10%319%29%27%9%
375
16th to endDay
9%5%24%31%23%6%
400
November1st to 15thDay
11%326%30%23%4
385
16th to endDay
9%8%34%26%17%2
208
December1st to 15thDay
15%13%35%25%9%1
180
16th to endDay
16%8%31%32%8%2
192
January1st to 15thNight
16%10%30%29%11%1
840
16th to endNight
16%12%29%32%8%
896
February1st to 15thNight
16%10%29%31%10%
824
16th to endNight
13%9%32%37%7%
735
March1st to 15thNight
10%10%34%33%10%
840
16th to endNight
12%8%32%32%13%
896
April1st to 15thNight
10%8%30%35%13%
838
16th to endNight
9%5%28%37%18%1
758
May1st to 15thNight
5%222%45%20%2
617
16th to endNight
9%212%35%35%5%
611
June1st to 15thNight
9%110%32%36%9%
585
16th to endNight
8%5%24%45%15%
585
July1st to 15thNight
6%322%46%20%
555
16th to endNight
41323%49%16%
612
August1st to 15thNight
6%1319%53%16%
575
16th to endNight
11%15%21%41%17%
725
September1st to 15thNight
12%17%27%38%12%
780
16th to endNight
15%210%27%36%8%
777
October1st to 15thNight
11%217%35%29%2
780
16th to endNight
9%424%34%25%2
832
November1st to 15thNight
10%327%39%17%1
820
16th to endNight
10%5%33%30%17%1
840
December1st to 15thNight
14%7%29%32%16%
840
16th to endNight
14%8%24%35%15%
896
Page generated at 2019-05-12 00:31:06. Version ac04

Copyright 2019 A. Danko


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