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 2018-02-14.

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%
15881
21%
48834
12%
15843
49%
15843
26%
30581

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
23%
777
23%
2605
9%
776
41%
776
21%
1596
January16th to endNight
22%
832
24%
2704
10%
832
39%
832
22%
1673
February1st to 15thNight
22%
758
20%
2468
7%
757
40%
757
22%
1513
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
37%
579
16%
1659
7%
579
43%
579
23%
1126
May16th to endNight
53%
374
17%
1497
16%
374
58%
374
22%
900
June1st to 15thNight
61%
360
19%
1440
21%
360
68%
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
62%
343
21%
857
July16th to endNight
68%
564
17%
1595
12%
531
73%
531
37%
923
August1st to 15thNight
64%
539
17%
1609
13%
536
64%
536
29%
1024
August16th to endNight
63%
761
19%
1907
11%
761
64%
761
31%
1289
September1st to 15thNight
58%
720
25%
1800
14%
720
62%
720
34%
1199
September16th to endNight
55%
717
23%
1974
18%
717
59%
717
30%
1291
October1st to 15thNight
47%
720
23%
2160
19%
720
54%
720
26%
1380
October16th to endNight
40%
768
30%
2304
19%
768
54%
768
32%
1338
November1st to 15thNight
38%
760
25%
2403
14%
760
51%
760
28%
1438
November16th to endNight
34%
780
24%
2665
14%
780
49%
780
25%
1543
December1st to 15thNight
28%
780
19%
2730
8%
780
43%
780
18%
1739
December16th to endNight
24%
832
22%
2912
10%
832
41%
832
19%
1823

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%
49229
Night
14%5%2442445%7%44%
49017
Cloud CoverDay
13%5%2442445%7%43%
49239
Night
14%5%2442445%7%44%
49021
TransparencyDay
38%6%11%23%16%3
48930
Night
38%5%10%23%17%3
48834
SeeingDay
17%7%23%25%18%7%
6145
Night
17%8%28%29%14%1
15887

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
16%5%2442345%6%42%
1660
16th to endDay
16%7%24424346%43%
1872
February1st to 15thDay
15%6%35%5%24446%41%
1695
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
10%6%26%6%45%6%7%7%36%
2331
16th to endDay
11%4245%35%6%6%9%42%
2292
September1st to 15thDay
12%42343445%7%46%
2160
16th to endDay
14%6%24424447%43%
1981
October1st to 15thDay
18%41432345%5%46%
1800
16th to endDay
13%414423345%50%
1920
November1st to 15thDay
15%6%13324347%48%
1783
16th to endDay
15%414223445%50%
1622
December1st to 15thDay
15%425%434446%44%
1560
16th to endDay
19%6%25%323447%40%
1664
January1st to 15thNight
16%5%24324346%45%
2605
16th to endNight
16%6%25%323346%44%
2704
February1st to 15thNight
14%6%245%24346%45%
2466
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
9%415%5%346%6%9%42%
1620
16th to endNight
10%5%245%45%5%6%10%39%
1907
September1st to 15thNight
11%5%245%25%5%5%8%45%
1800
16th to endNight
12%6%25%5%3445%7%41%
1974
October1st to 15thNight
18%5%25%423335%45%
2160
16th to endNight
14%313322346%52%
2304
November1st to 15thNight
15%5%34313345%50%
2403
16th to endNight
14%413424447%48%
2665
December1st to 15thNight
16%5%25%4245%5%5%40%
2730
16th to endNight
17%5%245%2435%6%41%
2912

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
16%5%244235%5%6%42%
1660
16th to endDay
16%7%245%23346%43%
1872
February1st to 15thDay
16%6%25%5%24346%40%
1695
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
10%5%25%6%46%6%7%8%36%
2331
16th to endDay
11%3245%35%5%7%8%42%
2292
September1st to 15thDay
12%4234345%5%7%46%
2160
16th to endDay
14%6%245%24448%41%
1981
October1st to 15thDay
18%414323445%46%
1800
16th to endDay
14%414323345%51%
1920
November1st to 15thDay
15%5%13323346%49%
1783
16th to endDay
15%424223445%50%
1622
December1st to 15thDay
16%425%424346%44%
1560
16th to endDay
19%6%24324447%40%
1664
January1st to 15thNight
17%5%24324337%45%
2605
16th to endNight
16%7%24423346%44%
2704
February1st to 15thNight
15%6%24424446%45%
2459
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
9%425%5%35%5%6%9%43%
1620
16th to endNight
10%4245%35%6%5%9%40%
1907
September1st to 15thNight
11%5%24425%46%8%44%
1800
16th to endNight
12%6%25%5%3446%7%41%
1974
October1st to 15thNight
18%5%24333345%45%
2160
16th to endNight
14%314313345%52%
2304
November1st to 15thNight
15%424313335%50%
2403
16th to endNight
14%424324447%48%
2665
December1st to 15thNight
16%6%25%5%25%45%6%40%
2730
16th to endNight
18%5%25%5%24346%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
40%5%12%22%14%4
1661
16th to endDay
42%49%23%16%3
1872
February1st to 15thDay
44%39%25%14%3
1697
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%11%21%15%1
2318
16th to endDay
36%7%14%23%15%2
2292
September1st to 15thDay
35%6%13%20%21%3
2160
16th to endDay
40%49%23%19%2
1981
October1st to 15thDay
38%5%9%26%16%3
1800
16th to endDay
35%38%27%22%3
1920
November1st to 15thDay
36%412%23%17%6%
1783
16th to endDay
35%410%26%19%3
1622
December1st to 15thDay
39%5%11%25%13%3
1560
16th to endDay
43%5%10%25%13%1
1664
January1st to 15thNight
39%410%20%18%5%
2605
16th to endNight
41%39%25%18%1
2704
February1st to 15thNight
39%410%25%17%3
2468
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
35%9%13%21%18%1
1609
16th to endNight
38%8%11%24%15%2
1907
September1st to 15thNight
35%8%10%20%20%4
1800
16th to endNight
38%6%9%20%20%4
1974
October1st to 15thNight
41%48%22%19%3
2160
16th to endNight
32%48%27%22%4
2304
November1st to 15thNight
37%48%22%19%7%
2403
16th to endNight
35%49%24%21%4
2665
December1st to 15thNight
44%5%10%22%14%3
2730
16th to endNight
43%411%23%14%2
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
21%18%36%20%2
116
16th to endDay
19%22%29%21%7%
144
February1st to 15thDay
28%16%44%8%1
130
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
15%212%25%31%12%
313
16th to endDay
10%110%29%30%18%
332
September1st to 15thDay
12%320%24%18%21%
315
16th to endDay
21%215%26%20%12%
314
October1st to 15thDay
22%317%23%23%9%
315
16th to endDay
13%8%29%26%16%5%
336
November1st to 15thDay
20%7%24%27%17%3
296
16th to endDay
15%11%36%22%11%1
152
December1st to 15thDay
18%10%34%20%11%5%
90
16th to endDay
31%7%37%21%11
96
January1st to 15thNight
21%14%36%22%5%
780
16th to endNight
23%13%37%23%2
832
February1st to 15thNight
20%12%39%25%2
760
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
11%113%39%30%3
539
16th to endNight
13%211%35%33%4
761
September1st to 15thNight
13%118%31%32%2
720
16th to endNight
14%218%31%29%3
717
October1st to 15thNight
19%5%19%27%23%4
720
16th to endNight
16%9%31%25%16%1
768
November1st to 15thNight
17%8%30%27%14%1
760
16th to endNight
16%13%30%27%10%
780
December1st to 15thNight
20%10%33%25%9%
780
16th to endNight
21%10%38%26%3
832
Page generated at 2018-02-15 10:58:50. Version ac04

Copyright 2018 A. Danko


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