Mason Neck State Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Mason Neck State Park clear sky chart from 2005-11-05 to 2017-08-12.

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
39%
15137
21%
46534
12%
15099
49%
15099
25%
29200

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
22%
717
23%
2404
9%
716
40%
716
20%
1494
January16th to endNight
21%
768
23%
2496
9%
768
39%
768
22%
1550
February1st to 15thNight
23%
702
21%
2287
7%
701
41%
701
23%
1385
February16th to endNight
20%
631
25%
1913
8%
631
41%
631
23%
1190
March1st to 15thNight
24%
720
22%
1999
9%
720
37%
720
25%
1290
March16th to endNight
27%
768
21%
2091
10%
768
37%
768
25%
1403
April1st to 15thNight
28%
718
19%
1796
5%
718
37%
718
30%
1192
April16th to endNight
41%
720
20%
1800
8%
720
46%
720
31%
1202
May1st to 15thNight
36%
579
16%
1659
7%
579
43%
579
23%
1126
May16th to endNight
54%
374
17%
1497
16%
374
59%
374
22%
900
June1st to 15thNight
62%
360
19%
1440
21%
360
69%
360
26%
817
June16th to endNight
58%
360
17%
1440
17%
360
63%
360
24%
835
July1st to 15thNight
58%
343
13%
1363
15%
343
61%
343
21%
857
July16th to endNight
69%
564
17%
1595
12%
531
74%
531
37%
923
August1st to 15thNight
65%
527
18%
1575
13%
524
65%
524
30%
998
August16th to endNight
62%
697
17%
1747
11%
697
63%
697
30%
1184
September1st to 15thNight
60%
660
26%
1650
15%
660
64%
660
34%
1092
September16th to endNight
53%
657
20%
1809
16%
657
56%
657
28%
1209
October1st to 15thNight
47%
660
24%
1980
20%
660
54%
660
26%
1260
October16th to endNight
39%
704
28%
2112
17%
704
54%
704
31%
1235
November1st to 15thNight
37%
700
25%
2213
15%
700
52%
700
28%
1314
November16th to endNight
33%
720
22%
2460
12%
720
47%
720
23%
1455
December1st to 15thNight
28%
720
20%
2520
9%
720
43%
720
18%
1597
December16th to endNight
24%
768
22%
2688
9%
768
41%
768
19%
1692

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%244345%5%7%43%
47425
Night
14%5%2442445%7%44%
46717
Cloud CoverDay
13%5%2442445%7%43%
47435
Night
14%5%2442445%7%44%
46721
TransparencyDay
38%6%11%23%16%3
47126
Night
38%5%11%22%17%3
46534
SeeingDay
17%7%23%25%18%7%
5547
Night
17%8%28%29%14%1
15143

By Month

Percentage Cloud Cover NE (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
17%5%2442345%7%42%
1531
16th to endDay
16%7%24424346%42%
1728
February1st to 15thDay
14%6%25%425%45%6%41%
1575
16th to endDay
14%6%345%3445%6%41%
1559
March1st to 15thDay
15%6%24424435%45%
1948
16th to endDay
16%6%345%24445%41%
2133
April1st to 15thDay
13%5%2443445%6%46%
2152
16th to endDay
16%424424345%45%
2160
May1st to 15thDay
16%5%244245%6%7%39%
2300
16th to endDay
13%424435%6%5%8%41%
2618
June1st to 15thDay
11%324425%5%5%9%44%
2520
16th to endDay
7%424436%6%6%10%44%
2520
July1st to 15thDay
9%415%5%35%6%7%10%39%
2514
16th to endDay
5%3145%47%6%8%11%40%
2465
August1st to 15thDay
9%5%26%6%45%6%7%7%37%
2280
16th to endDay
11%4245%35%5%6%9%41%
2100
September1st to 15thDay
12%423435%5%5%7%46%
1980
16th to endDay
16%6%24424447%41%
1816
October1st to 15thDay
18%414323445%46%
1650
16th to endDay
14%415%323345%49%
1760
November1st to 15thDay
14%5%13324347%50%
1643
16th to endDay
17%4132235%5%6%47%
1497
December1st to 15thDay
15%425%434447%44%
1440
16th to endDay
20%6%14324437%40%
1536
January1st to 15thNight
17%5%24324346%44%
2404
16th to endNight
17%7%24323346%43%
2496
February1st to 15thNight
14%6%245%23346%46%
2285
16th to endNight
14%7%24324446%45%
1913
March1st to 15thNight
16%5%24424447%44%
1987
16th to endNight
16%5%244235%46%42%
2091
April1st to 15thNight
13%425%424447%45%
1796
16th to endNight
16%4234245%46%44%
1800
May1st to 15thNight
16%6%25%42435%7%38%
1659
16th to endNight
12%5%235%35%47%9%41%
1495
June1st to 15thNight
9%413325%5%7%10%44%
1440
16th to endNight
8%425%5%25%6%7%8%43%
1440
July1st to 15thNight
8%5%26%6%25%6%7%9%38%
1443
16th to endNight
5%424425%6%8%12%43%
1703
August1st to 15thNight
8%415%5%346%6%9%42%
1586
16th to endNight
10%5%25%5%35%5%6%9%40%
1747
September1st to 15thNight
10%424425%5%5%8%45%
1650
16th to endNight
13%6%25%5%3445%8%39%
1809
October1st to 15thNight
17%5%25%323335%45%
1980
16th to endNight
14%313322446%51%
2112
November1st to 15thNight
14%5%3431333451%
2213
16th to endNight
15%424424447%46%
2460
December1st to 15thNight
16%5%25%4245%5%5%40%
2520
16th to endNight
18%5%245%2335%6%41%
2688

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
17%5%244235%46%42%
1531
16th to endDay
16%7%245%23336%42%
1728
February1st to 15thDay
15%6%25%435%447%41%
1575
16th to endDay
14%6%25%43445%6%41%
1559
March1st to 15thDay
15%6%24424446%45%
1959
16th to endDay
16%7%25%5%24346%41%
2132
April1st to 15thDay
13%5%2442435%7%46%
2152
16th to endDay
16%4245%23445%45%
2160
May1st to 15thDay
16%5%24425%5%6%8%39%
2300
16th to endDay
14%324435%5%6%8%41%
2618
June1st to 15thDay
11%324425%5%6%9%44%
2520
16th to endDay
7%314427%5%7%10%44%
2520
July1st to 15thDay
9%426%5%35%5%7%10%40%
2514
16th to endDay
6%2245%37%6%9%10%41%
2465
August1st to 15thDay
9%5%25%6%46%6%7%8%37%
2280
16th to endDay
11%3245%35%5%7%8%41%
2100
September1st to 15thDay
11%4234345%5%7%46%
1980
16th to endDay
15%6%25%5%24448%40%
1816
October1st to 15thDay
18%414323445%47%
1650
16th to endDay
14%415%323345%49%
1760
November1st to 15thDay
15%5%13223346%50%
1643
16th to endDay
16%4232235%45%47%
1497
December1st to 15thDay
16%325%424347%44%
1440
16th to endDay
20%6%24324437%40%
1536
January1st to 15thNight
17%5%24324347%43%
2404
16th to endNight
17%7%24423346%43%
2496
February1st to 15thNight
14%6%23423446%46%
2278
16th to endNight
15%7%2432435%5%45%
1913
March1st to 15thNight
16%5%2442335%6%44%
1999
16th to endNight
17%5%34423447%41%
2091
April1st to 15thNight
13%5%25%5%24447%45%
1796
16th to endNight
16%5%234245%46%45%
1800
May1st to 15thNight
16%6%25%5%2435%7%39%
1658
16th to endNight
12%423435%47%9%41%
1495
June1st to 15thNight
9%414335%5%8%9%45%
1440
16th to endNight
9%425%425%5%7%8%42%
1440
July1st to 15thNight
8%5%35%6%35%6%6%9%38%
1443
16th to endNight
6%423425%6%7%11%44%
1703
August1st to 15thNight
8%325%5%35%5%6%9%43%
1586
16th to endNight
10%425%5%35%6%5%9%40%
1747
September1st to 15thNight
11%5%24425%46%8%44%
1650
16th to endNight
13%6%25%5%3346%8%39%
1809
October1st to 15thNight
17%5%25%323346%45%
1980
16th to endNight
14%314313346%52%
2112
November1st to 15thNight
15%434313335%51%
2213
16th to endNight
15%424324447%46%
2460
December1st to 15thNight
16%6%25%43445%6%41%
2520
16th to endNight
18%5%15%423346%41%
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
41%5%12%22%14%3
1532
16th to endDay
42%49%23%15%3
1728
February1st to 15thDay
43%39%25%14%2
1577
16th to endDay
41%6%11%22%16%1
1559
March1st to 15thDay
40%5%10%23%16%4
1959
16th to endDay
44%5%10%18%17%3
2133
April1st to 15thDay
37%410%24%18%4
2152
16th to endDay
39%5%8%18%20%6%
2160
May1st to 15thDay
41%8%11%20%16%1
2300
16th to endDay
37%9%13%25%12%1
2622
June1st to 15thDay
34%7%14%26%14%1
2520
16th to endDay
32%9%15%23%16%2
2520
July1st to 15thDay
37%8%14%20%15%3
2365
16th to endDay
31%10%16%23%16%1
2310
August1st to 15thDay
41%7%12%22%15%1
2267
16th to endDay
37%7%13%23%15%3
2100
September1st to 15thDay
35%6%14%18%22%3
1980
16th to endDay
42%5%9%22%19%1
1816
October1st to 15thDay
38%5%9%26%16%3
1650
16th to endDay
36%38%26%21%3
1760
November1st to 15thDay
34%412%23%18%6%
1643
16th to endDay
37%5%10%24%18%3
1497
December1st to 15thDay
39%5%12%24%14%4
1440
16th to endDay
44%5%10%24%13%1
1536
January1st to 15thNight
41%410%19%18%4
2404
16th to endNight
41%39%25%17%1
2496
February1st to 15thNight
38%49%25%18%3
2287
16th to endNight
39%39%25%18%2
1913
March1st to 15thNight
40%5%11%26%14%2
1999
16th to endNight
42%5%9%22%17%3
2091
April1st to 15thNight
38%5%9%20%23%3
1796
16th to endNight
38%6%10%20%16%7%
1800
May1st to 15thNight
44%6%11%19%14%3
1659
16th to endNight
36%9%15%21%14%2
1497
June1st to 15thNight
32%8%13%27%15%1
1440
16th to endNight
34%8%15%19%18%2
1440
July1st to 15thNight
40%9%15%17%12%4
1363
16th to endNight
27%8%17%27%17%1
1595
August1st to 15thNight
34%9%13%21%18%1
1575
16th to endNight
38%8%10%23%15%2
1747
September1st to 15thNight
34%8%11%19%20%4
1650
16th to endNight
40%6%9%19%18%4
1809
October1st to 15thNight
41%48%23%18%3
1980
16th to endNight
33%48%26%22%4
2112
November1st to 15thNight
36%38%22%20%8%
2213
16th to endNight
37%49%24%19%4
2460
December1st to 15thNight
43%5%10%22%14%3
2520
16th to endNight
43%5%11%23%14%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
25%16%37%18%1
77
16th to endDay
19%23%31%20%4
96
February1st to 15thDay
27%16%42%11%2
90
16th to endDay
18%17%36%26%1
218
March1st to 15thDay
19%15%31%27%6%
270
16th to endDay
19%13%34%24%6%2
288
April1st to 15thDay
17%11%27%27%14%1
270
16th to endDay
20%7%25%27%13%5%
270
May1st to 15thDay
26%10%27%18%13%4
288
16th to endDay
20%221%24%23%7%
331
June1st to 15thDay
13%423%23%24%10%
315
16th to endDay
9%326%32%22%6%
315
July1st to 15thDay
14%114%36%23%10%
305
16th to endDay
6%110%30%34%16%
326
August1st to 15thDay
13%312%25%32%12%
297
16th to endDay
10%18%26%31%20%
268
September1st to 15thDay
10%415%23%21%24%
255
16th to endDay
26%116%26%18%11%
254
October1st to 15thDay
21%320%23%23%7%
255
16th to endDay
14%9%30%27%15%3
272
November1st to 15thDay
19%7%26%24%17%3
246
16th to endDay
20%9%32%23%11%2
117
December1st to 15thDay
16%10%35%21%10%6%
60
16th to endDay
39%431%23%1
64
January1st to 15thNight
21%15%35%22%5%
720
16th to endNight
23%13%38%22%2
768
February1st to 15thNight
20%12%38%25%2
704
16th to endNight
21%17%36%22%1
631
March1st to 15thNight
21%10%38%24%3
720
16th to endNight
19%11%37%23%6%1
768
April1st to 15thNight
16%13%38%27%4
718
16th to endNight
18%6%29%32%12%
720
May1st to 15thNight
19%7%30%28%13%1
579
16th to endNight
13%418%38%22%1
375
June1st to 15thNight
10%120%41%24%1
360
16th to endNight
9%220%45%21%1
360
July1st to 15thNight
9%119%38%28%1
343
16th to endNight
8%112%37%36%4
564
August1st to 15thNight
10%113%39%30%3
527
16th to endNight
13%212%35%32%4
697
September1st to 15thNight
12%117%30%34%2
660
16th to endNight
16%219%31%28%2
657
October1st to 15thNight
19%6%20%28%22%3
660
16th to endNight
16%9%31%25%15%
704
November1st to 15thNight
16%9%30%26%14%1
700
16th to endNight
17%14%29%26%10%
720
December1st to 15thNight
20%10%34%24%9%
720
16th to endNight
21%11%38%25%3
768
Page generated at 2017-08-13 14:16:40. Version ac04

Copyright 2017 A. Danko


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