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 2018-03-21.

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%
16538
22%
49177
16%
16500
59%
16500
30%
30220

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
34%
776
21%
2522
12%
776
47%
776
24%
1545
January16th to endNight
34%
832
24%
2665
15%
832
48%
832
24%
1648
February1st to 15thNight
35%
761
23%
2288
12%
759
46%
759
28%
1393
February16th to endNight
40%
683
26%
2030
16%
683
51%
683
31%
1215
March1st to 15thNight
40%
780
29%
2145
14%
780
52%
780
36%
1258
March16th to endNight
42%
792
25%
2178
15%
792
51%
792
38%
1263
April1st to 15thNight
44%
718
25%
1976
15%
718
52%
718
37%
1171
April16th to endNight
50%
657
29%
1782
18%
657
57%
657
41%
1023
May1st to 15thNight
60%
539
26%
1619
17%
539
66%
539
41%
892
May16th to endNight
69%
561
23%
1682
16%
561
73%
561
38%
964
June1st to 15thNight
65%
540
14%
1620
10%
540
67%
540
26%
1066
June16th to endNight
73%
540
11%
1620
10%
540
73%
540
28%
1074
July1st to 15thNight
73%
510
10%
1530
9%
510
73%
510
28%
996
July16th to endNight
74%
564
10%
1595
10%
531
75%
531
25%
1094
August1st to 15thNight
74%
539
8%
1609
8%
536
75%
536
25%
1101
August16th to endNight
66%
669
12%
1990
12%
669
66%
669
22%
1392
September1st to 15thNight
61%
720
13%
1980
12%
720
61%
720
21%
1420
September16th to endNight
58%
717
19%
1980
17%
717
60%
717
26%
1345
October1st to 15thNight
59%
720
27%
2036
24%
720
63%
720
34%
1230
October16th to endNight
56%
768
33%
2304
28%
768
65%
768
37%
1289
November1st to 15thNight
52%
760
30%
2281
23%
760
64%
760
40%
1242
November16th to endNight
44%
780
29%
2506
21%
780
57%
780
33%
1404
December1st to 15thNight
44%
780
25%
2535
20%
780
53%
780
28%
1516
December16th to endNight
44%
832
23%
2704
18%
832
53%
832
25%
1679

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%6%26%6%45%5%6%7%38%
49656
Night
9%5%25%5%3446%8%44%
49381
TransparencyDay
43%5%12%17%14%7%
49357
Night
35%5%14%20%15%8%
49184
SeeingDay
11%5%18%23%23%16%
6301
Night
11%5%21%31%24%4
16548

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
13%7%35%5%24448%40%
1746
16th to endDay
13%6%25%425%445%45%
1908
February1st to 15thDay
15%7%25%424345%44%
1900
16th to endDay
12%5%25%5%33345%48%
1726
March1st to 15thDay
8%42332445%7%52%
2145
16th to endDay
9%5%25%5%34446%47%
2173
April1st to 15thDay
9%5%36%5%3445%5%47%
1972
16th to endDay
6%425%5%36%5%5%7%46%
2185
May1st to 15thDay
6%325%5%35%5%5%8%47%
2331
16th to endDay
9%5%26%7%45%6%6%7%38%
2431
June1st to 15thDay
10%5%27%8%5%7%7%7%9%28%
2340
16th to endDay
8%5%35%8%6%7%7%8%10%26%
2340
July1st to 15thDay
6%6%49%10%47%7%8%10%24%
2340
16th to endDay
8%6%48%9%6%9%7%7%10%22%
2465
August1st to 15thDay
11%6%39%10%6%8%7%8%10%18%
2340
16th to endDay
12%8%49%9%5%7%7%7%8%20%
2196
September1st to 15thDay
11%7%39%8%5%8%6%7%9%22%
1980
16th to endDay
14%8%38%7%45%5%47%28%
1980
October1st to 15thDay
10%7%35%5%45%45%6%41%
1923
16th to endDay
9%415%423445%52%
1920
November1st to 15thDay
7%42432335%8%52%
1907
16th to endDay
9%42442335%6%52%
1781
December1st to 15thDay
13%6%15%5%2446%6%42%
1755
16th to endDay
10%6%36%5%35%45%8%40%
1872
January1st to 15thNight
13%5%245%2445%7%43%
2522
16th to endNight
14%5%25%42435%5%45%
2665
February1st to 15thNight
13%5%35%423345%49%
2283
16th to endNight
11%5%24423348%48%
2030
March1st to 15thNight
7%5%24423448%51%
2145
16th to endNight
9%414423336%55%
2178
April1st to 15thNight
8%42342335%7%52%
1976
16th to endNight
6%41342435%7%56%
1782
May1st to 15thNight
5%213435%5%6%9%52%
1619
16th to endNight
6%415%325%46%11%49%
1682
June1st to 15thNight
9%425%6%47%6%9%11%33%
1620
16th to endNight
7%3247%46%7%7%12%35%
1620
July1st to 15thNight
5%425%6%37%7%8%13%35%
1620
16th to endNight
35%26%6%48%7%9%13%32%
1703
August1st to 15thNight
5%425%7%47%7%9%13%31%
1620
16th to endNight
8%6%36%5%36%7%8%11%31%
1990
September1st to 15thNight
9%6%37%7%46%6%8%12%29%
1980
16th to endNight
10%8%36%5%345%7%9%34%
1980
October1st to 15thNight
9%5%25%42336%8%48%
2036
16th to endNight
7%42443445%6%53%
2304
November1st to 15thNight
7%32432445%8%54%
2281
16th to endNight
9%5%23424447%51%
2506
December1st to 15thNight
12%6%24424348%45%
2535
16th to endNight
11%5%35%5%3445%7%42%
2704

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
42%37%17%18%10%
1747
16th to endDay
40%25%18%21%11%
1908
February1st to 15thDay
42%37%12%19%14%
1902
16th to endDay
39%27%14%22%13%
1726
March1st to 15thDay
30%39%21%23%12%
2145
16th to endDay
35%310%18%20%10%
2174
April1st to 15thDay
37%37%17%23%10%
1972
16th to endDay
35%49%21%19%10%
2185
May1st to 15thDay
34%410%21%19%9%
2331
16th to endDay
41%5%11%21%15%4
2435
June1st to 15thDay
50%7%16%15%8%
2340
16th to endDay
48%10%18%17%5%
2340
July1st to 15thDay
50%8%23%15%1
2201
16th to endDay
52%9%21%13%3
2310
August1st to 15thDay
56%8%21%11%2
2327
16th to endDay
57%8%18%11%2
2196
September1st to 15thDay
55%8%15%13%5%1
1980
16th to endDay
54%6%11%14%10%3
1980
October1st to 15thDay
42%47%17%16%11%
1923
16th to endDay
34%36%15%23%16%
1920
November1st to 15thDay
31%37%24%21%11%
1907
16th to endDay
33%37%18%24%13%
1781
December1st to 15thDay
41%48%21%16%7%
1755
16th to endDay
41%410%21%14%7%
1872
January1st to 15thNight
40%39%18%17%10%
2522
16th to endNight
40%36%14%22%12%
2665
February1st to 15thNight
37%38%15%19%15%
2292
16th to endNight
36%38%18%20%11%
2030
March1st to 15thNight
31%310%23%19%11%
2145
16th to endNight
30%312%20%20%11%
2178
April1st to 15thNight
31%410%20%23%9%
1976
16th to endNight
27%413%23%21%9%
1782
May1st to 15thNight
26%5%14%26%19%8%
1620
16th to endNight
28%5%18%27%16%3
1684
June1st to 15thNight
39%8%21%22%7%
1620
16th to endNight
37%10%24%20%6%
1620
July1st to 15thNight
36%10%29%20%2
1530
16th to endNight
36%14%27%17%3
1595
August1st to 15thNight
37%13%32%14%2
1609
16th to endNight
42%11%25%15%4
1990
September1st to 15thNight
44%11%20%15%6%1
1980
16th to endNight
43%6%16%22%8%3
1980
October1st to 15thNight
33%5%11%20%18%9%
2036
16th to endNight
30%36%19%23%15%
2304
November1st to 15thNight
28%29%24%23%11%
2281
16th to endNight
32%38%19%21%14%
2506
December1st to 15thNight
38%311%23%16%7%
2535
16th to endNight
40%411%21%14%8%
2704

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
18%17%42%9%7%4
135
16th to endDay
18%17%36%21%6%
144
February1st to 15thDay
24%14%33%19%8%
135
16th to endDay
8%11%33%36%10%
136
March1st to 15thDay
11%13%31%29%11%2
330
16th to endDay
14%8%29%22%20%4
311
April1st to 15thDay
10%10%27%23%22%5%
270
16th to endDay
7%5%21%30%20%13%
270
May1st to 15thDay
7%6%23%25%20%16%
288
16th to endDay
8%29%25%31%22%
331
June1st to 15thDay
13%29%18%30%26%
315
16th to endDay
10%5%13%36%33%
315
July1st to 15thDay
5%316%30%42%
305
16th to endDay
8%417%35%32%
326
August1st to 15thDay
13%17%15%28%32%
313
16th to endDay
11%1416%29%35%
332
September1st to 15thDay
15%18%22%25%25%
315
16th to endDay
21%15%20%31%20%
314
October1st to 15thDay
12%418%30%25%9%
315
16th to endDay
10%5%22%32%24%4
336
November1st to 15thDay
10%324%31%25%5%
325
16th to endDay
9%8%32%27%18%3
161
December1st to 15thDay
11%13%34%27%10%2
135
16th to endDay
15%9%31%34%6%2
144
January1st to 15thNight
17%11%31%27%11%1
780
16th to endNight
17%12%29%31%8%
832
February1st to 15thNight
16%11%30%31%10%
764
16th to endNight
13%9%31%37%7%
683
March1st to 15thNight
10%10%34%32%10%
780
16th to endNight
11%7%33%32%14%
792
April1st to 15thNight
10%9%31%35%12%
718
16th to endNight
9%5%28%37%17%1
657
May1st to 15thNight
6%224%44%18%2
540
16th to endNight
8%212%36%34%5%
563
June1st to 15thNight
10%110%34%35%8%
540
16th to endNight
8%5%25%44%14%
540
July1st to 15thNight
7%323%46%19%
510
16th to endNight
41324%50%16%
564
August1st to 15thNight
6%1320%52%15%
539
16th to endNight
12%16%21%41%16%
669
September1st to 15thNight
13%17%27%38%11%
720
16th to endNight
16%210%28%35%6%
717
October1st to 15thNight
11%218%36%28%2
720
16th to endNight
9%423%35%24%1
768
November1st to 15thNight
9%328%39%18%1
760
16th to endNight
10%5%33%29%18%1
780
December1st to 15thNight
14%7%28%32%16%
780
16th to endNight
15%8%24%35%16%
832
Page generated at 2018-03-22 11:34:23. Version ac04

Copyright 2018 A. Danko


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