This page made possible by the sponsorship of: Southern Maryland Astronomical Society.

Nanjemoy Creek Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Nanjemoy Creek Observatory clear sky chart from 2005-11-06 to 2024-01-16.

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
36%
23555
21%
74692
11%
23508
47%
23508
24%
46807

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 10thNight
18%
757
24%
2574
7%
757
38%
757
20%
1545
January11th to 20thNight
22%
741
22%
2406
8%
741
40%
741
18%
1562
January21st to endNight
21%
792
25%
2574
10%
792
40%
792
22%
1555
February1st to 10thNight
22%
720
18%
2340
8%
720
36%
720
19%
1486
February11th to 20thNight
13%
701
20%
2209
4%
700
33%
700
18%
1422
February21st to endNight
17%
592
25%
1776
7%
592
38%
592
20%
1137
March1st to 10thNight
20%
720
25%
2012
8%
720
38%
720
26%
1259
March11th to 20thNight
21%
720
20%
1980
7%
720
34%
720
23%
1303
March21st to endNight
21%
792
21%
2143
7%
792
32%
792
23%
1430
April1st to 10thNight
22%
720
19%
1800
4%
720
33%
720
25%
1212
April11th to 20thNight
32%
711
22%
1775
7%
711
39%
711
32%
1153
April21st to endNight
32%
720
21%
1800
7%
720
38%
720
28%
1219
May1st to 10thNight
32%
622
17%
1702
8%
622
38%
622
25%
1161
May11th to 20thNight
38%
440
17%
1501
10%
440
45%
440
21%
978
May21st to endNight
51%
388
16%
1551
15%
388
56%
388
22%
937
June1st to 10thNight
53%
360
19%
1440
18%
360
61%
360
24%
841
June11th to 20thNight
53%
360
16%
1440
14%
360
59%
360
21%
866
June21st to endNight
55%
360
17%
1440
17%
360
61%
360
24%
835
July1st to 10thNight
59%
350
16%
1400
17%
350
63%
350
21%
857
July11th to 20thNight
69%
447
16%
1491
14%
447
70%
447
30%
867
July21st to endNight
63%
591
17%
1672
12%
558
67%
558
30%
1045
August1st to 10thNight
64%
537
15%
1600
11%
534
66%
534
27%
1049
August11th to 20thNight
58%
624
15%
1688
10%
624
59%
624
25%
1176
August21st to endNight
59%
792
18%
1980
10%
792
61%
792
32%
1337
September1st to 10thNight
55%
720
22%
1800
13%
720
59%
720
33%
1203
September11th to 20thNight
60%
720
28%
1800
19%
720
64%
720
38%
1143
September21st to endNight
43%
720
19%
2060
13%
720
50%
720
24%
1401
October1st to 10thNight
46%
720
20%
2160
17%
720
52%
720
28%
1362
October11th to 20thNight
39%
720
26%
2160
17%
720
51%
720
28%
1310
October21st to endNight
34%
792
27%
2376
16%
792
48%
792
28%
1445
November1st to 10thNight
35%
740
27%
2301
15%
740
51%
740
30%
1349
November11th to 20thNight
31%
760
25%
2470
13%
760
47%
760
25%
1454
November21st to endNight
34%
760
24%
2649
13%
760
50%
760
25%
1487
December1st to 10thNight
24%
760
20%
2660
6%
760
42%
760
18%
1659
December11th to 20thNight
24%
760
22%
3169
10%
759
40%
759
18%
1870
December21st to endNight
26%
826
14%
4793
10%
817
41%
817
12%
2892

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
13%5%25%5%35%5%6%8%44%
74697
Night
15%6%25%5%345%5%7%44%
75095
TransparencyDay
38%7%12%23%16%3
74408
Night
38%7%12%22%17%4
74903
SeeingDay
17%13%28%25%13%4
13915
Night
17%11%30%28%12%1
23571

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 10thDay
15%8%25%43445%6%44%
1588
11th to 20thDay
18%7%3442445%7%43%
1665
21st to endDay
16%6%35%5%3445%6%44%
1782
February1st to 10thDay
15%7%36%5%45%5%47%38%
1620
11th to 20thDay
19%6%25%434446%43%
1637
21st to endDay
19%8%35%5%35%447%37%
1480
March1st to 10thDay
13%6%3432435%6%51%
1946
11th to 20thDay
17%6%245%3445%5%44%
1980
21st to endDay
17%7%35%5%345%5%7%39%
2211
April1st to 10thDay
12%5%245%3446%7%47%
2160
11th to 20thDay
13%5%35%424446%49%
2134
21st to endDay
17%5%244345%5%7%43%
2160
May1st to 10thDay
15%6%24435%5%6%9%41%
2272
11th to 20thDay
17%5%25%4345%6%8%40%
2388
21st to endDay
13%425%5%35%5%7%9%42%
2725
June1st to 10thDay
12%325%5%35%5%5%9%46%
2520
11th to 20thDay
10%425%5%35%6%6%10%43%
2520
21st to endDay
8%4245%47%6%7%10%44%
2520
July1st to 10thDay
9%5%36%5%45%5%5%10%43%
2520
11th to 20thDay
5%3245%45%6%9%12%45%
2415
21st to endDay
9%5%25%6%46%7%8%11%38%
2547
August1st to 10thDay
9%5%26%6%5%6%6%7%11%38%
2327
11th to 20thDay
11%6%25%6%36%6%7%9%39%
2192
21st to endDay
10%5%25%5%446%6%10%43%
2376
September1st to 10thDay
14%4245%35%46%7%47%
2160
11th to 20thDay
10%5%3443346%8%50%
2160
21st to endDay
18%7%25%435%45%7%40%
1896
October1st to 10thDay
17%5%2432435%7%48%
1800
11th to 20thDay
17%5%24323346%52%
1800
21st to endDay
14%5%25%42435%6%49%
1980
November1st to 10thDay
13%42343345%7%53%
1775
11th to 20thDay
16%5%2332345%6%51%
1710
21st to endDay
16%5%2343445%5%51%
1529
December1st to 10thDay
17%6%25%42446%8%41%
1520
11th to 20thDay
16%7%24424446%49%
1910
21st to endDay
17%7%36%5%35%5%6%7%38%
2772
January1st to 10thNight
17%7%34423346%47%
2574
11th to 20thNight
16%8%36%5%3445%6%40%
2406
21st to endNight
16%7%25%424445%47%
2574
February1st to 10thNight
16%7%35%44445%6%42%
2340
11th to 20thNight
19%8%25%424335%45%
2207
21st to endNight
18%7%2442445%6%44%
1776
March1st to 10thNight
14%5%345%23446%50%
2012
11th to 20thNight
19%6%2433445%8%42%
1980
21st to endNight
15%6%36%5%245%5%7%42%
2143
April1st to 10thNight
15%6%35%5%2445%7%44%
1800
11th to 20thNight
12%6%26%424447%49%
1775
21st to endNight
19%4244245%6%8%44%
1800
May1st to 10thNight
15%7%35%435%5%5%8%40%
1702
11th to 20thNight
16%5%25%6%35%7%5%8%39%
1501
21st to endNight
14%425%5%4446%11%40%
1550
June1st to 10thNight
11%5%26%435%5%7%10%43%
1440
11th to 20thNight
12%5%35%5%35%6%5%10%41%
1440
21st to endNight
9%5%25%5%45%47%10%44%
1440
July1st to 10thNight
8%5%26%5%36%6%7%11%41%
1440
11th to 20thNight
6%335%5%45%7%8%11%44%
1540
21st to endNight
7%425%5%5%7%7%9%10%40%
1771
August1st to 10thNight
9%5%26%6%46%7%8%8%40%
1611
11th to 20thNight
11%6%36%6%46%6%8%9%36%
1688
21st to endNight
10%5%27%6%45%46%9%41%
1980
September1st to 10thNight
15%5%245%345%5%7%45%
1800
11th to 20thNight
9%6%245%33448%50%
1800
21st to endNight
19%7%25%4345%5%6%39%
2060
October1st to 10thNight
17%6%244245%46%45%
2160
11th to 20thNight
16%5%24423447%48%
2160
21st to endNight
15%5%2443345%7%47%
2376
November1st to 10thNight
13%5%34423345%54%
2301
11th to 20thNight
15%5%34324346%50%
2470
21st to endNight
12%4244345%5%7%50%
2649
December1st to 10thNight
17%7%35%43445%7%42%
2660
11th to 20thNight
18%5%25%424447%44%
3285
21st to endNight
16%6%35%5%35%46%8%38%
4884

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 10thDay
40%6%11%24%15%4
1589
11th to 20thDay
43%412%24%15%3
1665
21st to endDay
43%5%10%24%16%4
1782
February1st to 10thDay
46%6%11%24%11%2
1620
11th to 20thDay
42%49%24%18%3
1646
21st to endDay
47%5%12%16%16%4
1480
March1st to 10thDay
35%6%11%24%21%3
1946
11th to 20thDay
42%5%11%18%17%6%
1980
21st to endDay
45%6%9%19%17%4
2211
April1st to 10thDay
36%7%11%21%20%6%
2160
11th to 20thDay
36%6%10%21%21%6%
2134
21st to endDay
41%7%10%22%15%5%
2160
May1st to 10thDay
39%9%15%20%16%3
2272
11th to 20thDay
42%9%13%21%13%2
2392
21st to endDay
38%8%14%26%12%2
2725
June1st to 10thDay
34%9%14%27%15%1
2520
11th to 20thDay
35%10%14%23%16%2
2520
21st to endDay
33%10%15%24%16%2
2520
July1st to 10thDay
36%10%14%22%15%3
2450
11th to 20thDay
28%10%20%26%14%3
2341
21st to endDay
36%11%15%20%17%1
2405
August1st to 10thDay
39%10%15%24%11%1
2314
11th to 20thDay
38%11%15%22%13%1
2192
21st to endDay
35%9%15%23%14%4
2376
September1st to 10thDay
37%7%13%20%18%4
2160
11th to 20thDay
32%8%11%25%21%4
2160
21st to endDay
45%6%9%20%18%3
1896
October1st to 10thDay
37%6%11%25%18%3
1800
11th to 20thDay
35%49%26%22%4
1800
21st to endDay
36%5%9%24%22%4
1980
November1st to 10thDay
32%5%12%27%20%5%
1775
11th to 20thDay
33%5%10%24%21%6%
1710
21st to endDay
36%410%27%20%3
1529
December1st to 10thDay
41%7%12%25%12%4
1520
11th to 20thDay
37%5%10%31%13%4
1906
21st to endDay
41%9%12%26%11%1
2772
January1st to 10thNight
39%410%22%19%6%
2574
11th to 20thNight
44%5%12%21%16%2
2406
21st to endNight
39%49%25%20%2
2574
February1st to 10thNight
42%5%11%24%15%2
2340
11th to 20thNight
44%47%21%18%6%
2209
21st to endNight
42%411%22%16%5%
1776
March1st to 10thNight
37%5%10%25%20%3
2012
11th to 20thNight
41%6%11%22%17%3
1980
21st to endNight
42%6%10%21%16%6%
2143
April1st to 10thNight
40%6%10%19%21%5%
1800
11th to 20thNight
35%7%11%21%21%6%
1775
21st to endNight
39%8%11%24%13%5%
1800
May1st to 10thNight
41%8%13%20%14%4
1702
11th to 20thNight
42%9%14%18%16%2
1502
21st to endNight
38%9%17%22%13%2
1551
June1st to 10thNight
33%11%12%25%17%2
1440
11th to 20thNight
38%9%16%23%13%3
1440
21st to endNight
34%9%17%18%19%2
1440
July1st to 10thNight
37%12%17%18%14%4
1400
11th to 20thNight
30%10%18%25%15%2
1491
21st to endNight
33%11%16%26%14%1
1672
August1st to 10thNight
35%12%16%22%14%1
1600
11th to 20thNight
41%11%16%20%11%2
1688
21st to endNight
37%8%14%23%14%3
1980
September1st to 10thNight
37%7%13%21%16%6%
1800
11th to 20thNight
31%7%12%24%22%3
1800
21st to endNight
43%8%11%18%17%4
2060
October1st to 10thNight
39%5%11%23%18%3
2160
11th to 20thNight
36%5%8%26%21%3
2160
21st to endNight
36%6%9%23%22%4
2376
November1st to 10thNight
34%5%9%26%21%6%
2301
11th to 20thNight
37%410%21%22%6%
2470
21st to endNight
33%5%11%26%21%4
2649
December1st to 10thNight
42%6%11%24%14%3
2660
11th to 20thNight
40%5%10%23%18%4
3288
21st to endNight
41%10%14%23%11%1
4884

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 10thDay
25%23%32%15%4
213
11th to 20thDay
27%27%29%15%3
255
21st to endDay
23%25%37%11%4
264
February1st to 10thDay
23%26%35%11%4
240
11th to 20thDay
29%25%36%10%1
304
21st to endDay
30%22%30%16%2
346
March1st to 10thDay
21%25%33%20%2
420
11th to 20thDay
25%21%33%15%5%1
420
21st to endDay
21%19%35%19%5%1
462
April1st to 10thDay
20%21%31%22%5%1
420
11th to 20thDay
16%19%31%21%10%3
412
21st to endDay
23%16%32%22%6%1
420
May1st to 10thDay
23%17%30%19%10%2
423
11th to 20thDay
20%10%32%26%10%2
447
21st to endDay
17%8%25%26%19%5%
485
June1st to 10thDay
11%9%28%28%19%5%
450
11th to 20thDay
12%8%28%30%16%5%
450
21st to endDay
9%6%29%34%18%5%
450
July1st to 10thDay
12%419%33%24%9%
445
11th to 20thDay
5%116%40%27%10%
444
21st to endDay
9%323%35%23%8%
488
August1st to 10thDay
10%420%33%26%8%
446
11th to 20thDay
12%318%33%26%8%
439
21st to endDay
8%5%21%30%22%14%
495
September1st to 10thDay
14%5%21%27%18%16%
450
11th to 20thDay
11%7%20%34%17%11%
450
21st to endDay
21%11%25%27%11%5%
450
October1st to 10thDay
20%8%23%27%18%5%
450
11th to 20thDay
16%13%27%29%13%3
450
21st to endDay
17%12%36%24%9%3
495
November1st to 10thDay
17%11%33%25%12%3
415
11th to 20thDay
18%19%31%21%9%2
370
21st to endDay
21%20%29%19%11%1
189
December1st to 10thDay
18%22%39%14%6%1
180
11th to 20thDay
20%24%28%22%6%
180
21st to endDay
25%18%30%21%5%1
198
January1st to 10thNight
21%22%37%18%3
760
11th to 20thNight
22%18%33%23%4
741
21st to endNight
21%19%37%21%2
792
February1st to 10thNight
20%17%37%23%3
720
11th to 20thNight
25%22%38%14%2
703
21st to endNight
24%19%36%18%2
592
March1st to 10thNight
20%16%39%23%2
720
11th to 20thNight
22%16%37%19%6%
720
21st to endNight
19%16%40%21%41
792
April1st to 10thNight
18%20%37%21%4
720
11th to 20thNight
15%13%36%28%8%
711
21st to endNight
21%11%33%27%8%
720
May1st to 10thNight
18%11%34%26%11%
622
11th to 20thNight
17%7%33%33%10%
440
21st to endNight
15%423%37%20%1
389
June1st to 10thNight
12%226%38%21%1
360
11th to 20thNight
13%5%21%39%20%2
360
21st to endNight
8%423%46%16%2
360
July1st to 10thNight
9%320%39%27%3
350
11th to 20thNight
5%213%43%33%4
447
21st to endNight
7%220%39%29%3
591
August1st to 10thNight
9%214%43%29%3
537
11th to 20thNight
13%216%42%25%2
624
21st to endNight
12%217%35%28%6%
792
September1st to 10thNight
16%217%33%27%5%
720
11th to 20thNight
10%418%38%26%4
720
21st to endNight
21%6%23%31%18%1
720
October1st to 10thNight
19%6%22%30%18%5%
720
11th to 20thNight
17%11%27%28%16%1
720
21st to endNight
18%12%32%25%12%1
792
November1st to 10thNight
15%10%35%28%11%2
740
11th to 20thNight
19%16%31%26%8%
760
21st to endNight
16%16%32%27%9%1
760
December1st to 10thNight
21%16%33%20%9%1
760
11th to 20thNight
19%14%39%23%5%
760
21st to endNight
20%13%35%28%4
836
Page generated at 2024-01-13 01:38:08. Version ac07

Copyright 2024 Attilla Danko


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