Martha’s Vineyard
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Martha’s Vineyard clear sky chart from 2005-11-05 to

2017-09-12
.

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
36%
14985
16%
46748
10%
14950
44%
14950
20%
31965

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
20%
720
15%
2506
6%
716
31%
716
14%
1724
January16th to endNight
17%
768
16%
2666
5%
768
30%
768
13%
1846
February1st to 15thNight
16%
704
14%
2156
4%
701
29%
701
14%
1547
February16th to endNight
23%
631
21%
1893
7%
631
40%
631
21%
1262
March1st to 15thNight
27%
720
16%
2137
8%
720
38%
720
19%
1478
March16th to endNight
30%
768
21%
2061
9%
768
40%
768
24%
1407
April1st to 15thNight
36%
718
18%
1796
7%
718
40%
718
25%
1282
April16th to endNight
39%
585
16%
1665
7%
585
44%
585
22%
1166
May1st to 15thNight
39%
540
14%
1620
8%
540
45%
540
19%
1165
May16th to endNight
44%
483
10%
1605
10%
482
46%
482
16%
1159
June1st to 15thNight
44%
360
12%
1440
15%
360
48%
360
15%
988
June16th to endNight
58%
360
10%
1440
17%
360
59%
360
19%
896
July1st to 15thNight
62%
340
11%
1360
16%
340
62%
340
19%
845
July16th to endNight
59%
399
13%
1440
18%
376
60%
376
18%
957
August1st to 15thNight
65%
539
16%
1608
13%
535
66%
535
28%
1028
August16th to endNight
65%
714
22%
1860
15%
714
66%
714
34%
1199
September1st to 15thNight
55%
707
20%
1848
13%
707
57%
707
31%
1210
September16th to endNight
53%
657
23%
1815
17%
657
58%
657
29%
1197
October1st to 15thNight
40%
660
20%
1829
13%
660
48%
660
23%
1263
October16th to endNight
32%
704
16%
2271
9%
704
42%
704
19%
1515
November1st to 15thNight
33%
700
15%
2277
11%
700
40%
700
17%
1568
November16th to endNight
29%
720
16%
2340
10%
720
37%
720
17%
1605
December1st to 15thNight
23%
720
13%
2427
5%
720
32%
720
12%
1746
December16th to endNight
17%
768
15%
2688
4%
768
30%
768
13%
1912

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
17%6%25%42445%7%40%
47910
Night
17%7%35%42445%6%36%
46921
Cloud CoverDay
16%6%25%42445%7%39%
47920
Night
17%8%35%5%2445%7%36%
46926
TransparencyDay
43%5%12%21%14%1
47602
Night
47%5%11%19%13%1
46748
SeeingDay
21%5%21%29%18%3
5999
Night
22%7%25%27%14%2
14985

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
19%7%24335%46%7%35%
1432
16th to endDay
15%7%35%5%23446%39%
1557
February1st to 15thDay
17%8%25%43446%6%34%
1702
16th to endDay
16%7%3443445%6%39%
1580
March1st to 15thDay
19%6%25%423348%38%
1812
16th to endDay
16%8%24423345%43%
2160
April1st to 15thDay
19%7%24314347%41%
2152
16th to endDay
18%7%2432345%6%41%
2295
May1st to 15thDay
24%9%36%323345%33%
2332
16th to endDay
16%7%25%5%3445%7%37%
2518
June1st to 15thDay
22%7%35%42345%7%34%
2520
16th to endDay
14%4244245%6%10%40%
2520
July1st to 15thDay
12%6%25%425%5%5%7%42%
2520
16th to endDay
13%6%35%425%5%7%9%38%
2618
August1st to 15thDay
11%5%25%42445%7%45%
2340
16th to endDay
11%5%25%32445%7%48%
2339
September1st to 15thDay
14%5%23324447%47%
2032
16th to endDay
15%5%2433445%6%46%
1815
October1st to 15thDay
19%6%24324245%42%
1801
16th to endDay
14%7%15%42335%6%43%
1598
November1st to 15thDay
21%6%35%413346%39%
1581
16th to endDay
17%7%345%25%448%35%
1620
December1st to 15thDay
20%8%36%424435%35%
1530
16th to endDay
23%9%25%5%23437%32%
1536
January1st to 15thNight
19%7%35%5%345%5%6%33%
2506
16th to endNight
19%11%345%2445%6%32%
2666
February1st to 15thNight
17%9%35%5%3445%6%32%
2155
16th to endNight
15%7%45%5%24446%39%
1893
March1st to 15thNight
18%7%35%42445%7%35%
2124
16th to endNight
17%7%23424446%41%
2061
April1st to 15thNight
18%9%25%424346%37%
1796
16th to endNight
21%6%35%5%24345%37%
1665
May1st to 15thNight
20%10%35%5%245%46%33%
1620
16th to endNight
19%10%35%5%25%45%7%30%
1603
June1st to 15thNight
24%9%24413447%32%
1440
16th to endNight
16%6%24425%5%5%7%39%
1440
July1st to 15thNight
14%7%25%425%5%5%8%37%
1440
16th to endNight
11%7%36%5%45%5%6%7%34%
1537
August1st to 15thNight
8%6%245%45%5%6%9%41%
1620
16th to endNight
12%4235%235%7%9%44%
1860
September1st to 15thNight
13%5%15%43246%8%44%
1848
16th to endNight
15%6%25%424435%46%
1815
October1st to 15thNight
19%6%25%424446%39%
1829
16th to endNight
18%6%245%34436%39%
2271
November1st to 15thNight
19%8%25%434335%37%
2277
16th to endNight
18%8%36%424447%35%
2340
December1st to 15thNight
21%8%35%424446%32%
2427
16th to endNight
21%9%36%424445%31%
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
19%8%33335%46%7%33%
1432
16th to endDay
16%6%46%424348%37%
1557
February1st to 15thDay
17%8%35%5%3446%7%33%
1702
16th to endDay
16%8%35%334448%38%
1580
March1st to 15thDay
19%6%25%43335%7%37%
1822
16th to endDay
16%8%34323436%42%
2160
April1st to 15thDay
19%5%24323347%41%
2152
16th to endDay
18%7%243245%5%5%41%
2295
May1st to 15thDay
23%10%35%423345%34%
2332
16th to endDay
16%7%25%43445%7%36%
2518
June1st to 15thDay
22%7%35%324447%34%
2520
16th to endDay
13%5%244245%6%9%40%
2520
July1st to 15thDay
12%6%25%5%3445%7%42%
2520
16th to endDay
12%6%25%5%35%5%5%9%38%
2618
August1st to 15thDay
11%5%25%5%2345%7%45%
2340
16th to endDay
11%5%2442445%7%47%
2339
September1st to 15thDay
13%5%14323446%48%
2032
16th to endDay
14%5%2442345%6%45%
1815
October1st to 15thDay
19%5%34323345%42%
1801
16th to endDay
14%6%25%424347%42%
1598
November1st to 15thDay
21%6%35%323345%38%
1581
16th to endDay
17%7%345%44448%35%
1620
December1st to 15thDay
20%7%47%5%24447%31%
1530
16th to endDay
22%9%26%424446%31%
1536
January1st to 15thNight
19%7%46%5%246%5%7%31%
2506
16th to endNight
19%11%45%42445%6%31%
2666
February1st to 15thNight
17%10%36%5%25%46%6%31%
2148
16th to endNight
14%7%35%5%34347%38%
1893
March1st to 15thNight
19%7%36%5%2445%7%35%
2137
16th to endNight
17%7%24434346%40%
2060
April1st to 15thNight
18%9%34424346%37%
1796
16th to endNight
21%6%25%5%33346%36%
1665
May1st to 15thNight
20%9%35%5%2435%6%32%
1620
16th to endNight
19%9%36%425%45%6%30%
1603
June1st to 15thNight
23%10%35%323348%32%
1440
16th to endNight
15%7%2343445%7%39%
1440
July1st to 15thNight
14%6%246%35%45%9%37%
1440
16th to endNight
12%6%46%6%46%6%6%7%34%
1537
August1st to 15thNight
8%5%25%5%35%5%6%8%42%
1620
16th to endNight
12%5%135%235%6%9%43%
1860
September1st to 15thNight
14%5%25%43346%8%43%
1848
16th to endNight
15%6%25%423346%45%
1815
October1st to 15thNight
19%7%24434436%38%
1829
16th to endNight
18%7%24425%345%39%
2271
November1st to 15thNight
19%8%35%5%24335%37%
2277
16th to endNight
18%9%36%42445%7%33%
2340
December1st to 15thNight
21%8%46%5%245%5%7%29%
2427
16th to endNight
21%9%36%42445%6%29%
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
48%6%14%19%9%1
1433
16th to endDay
46%313%22%11%1
1557
February1st to 15thDay
48%6%14%19%10%
1705
16th to endDay
44%5%11%22%13%2
1580
March1st to 15thDay
46%5%13%23%8%2
1822
16th to endDay
42%411%21%15%3
2160
April1st to 15thDay
42%5%9%21%18%2
2152
16th to endDay
42%5%10%22%15%3
2295
May1st to 15thDay
53%48%17%14%2
2332
16th to endDay
46%5%13%22%10%1
2522
June1st to 15thDay
50%5%11%20%11%
2520
16th to endDay
38%7%13%23%15%
2520
July1st to 15thDay
40%6%12%22%15%1
2371
16th to endDay
40%7%13%23%13%2
2454
August1st to 15thDay
38%6%13%25%15%1
2327
16th to endDay
34%7%10%26%18%1
2339
September1st to 15thDay
35%6%12%22%22%1
2032
16th to endDay
38%5%9%21%21%2
1815
October1st to 15thDay
43%410%22%16%2
1801
16th to endDay
40%416%21%15%2
1598
November1st to 15thDay
48%414%16%13%2
1581
16th to endDay
47%5%14%21%9%1
1620
December1st to 15thDay
50%7%15%15%10%
1530
16th to endDay
53%6%14%16%8%
1536
January1st to 15thNight
51%5%14%18%9%
2506
16th to endNight
52%411%18%11%1
2666
February1st to 15thNight
50%7%13%18%8%1
2156
16th to endNight
45%411%22%14%1
1893
March1st to 15thNight
47%5%12%19%11%3
2137
16th to endNight
44%49%18%18%4
2061
April1st to 15thNight
48%48%20%16%3
1796
16th to endNight
48%49%17%13%5%
1665
May1st to 15thNight
51%6%10%16%13%2
1620
16th to endNight
51%8%12%17%8%1
1605
June1st to 15thNight
52%5%9%17%14%
1440
16th to endNight
42%7%13%20%15%1
1440
July1st to 15thNight
42%7%13%21%14%
1360
16th to endNight
45%8%13%22%8%1
1440
August1st to 15thNight
37%8%12%25%14%1
1608
16th to endNight
35%6%11%27%17%1
1860
September1st to 15thNight
38%6%11%24%17%1
1848
16th to endNight
40%5%5%20%25%2
1815
October1st to 15thNight
46%49%21%14%2
1829
16th to endNight
46%5%14%19%13%1
2271
November1st to 15thNight
49%5%12%16%13%2
2277
16th to endNight
49%413%19%10%2
2340
December1st to 15thNight
52%7%14%15%9%
2427
16th to endNight
54%5%13%16%9%
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
23%11%36%25%3
60
16th to endDay
22%10%34%28%4
85
February1st to 15thDay
23%13%37%21%3
258
16th to endDay
16%10%37%26%8%
239
March1st to 15thDay
24%12%28%28%6%
270
16th to endDay
21%9%31%27%8%1
288
April1st to 15thDay
22%6%24%34%11%
270
16th to endDay
25%227%30%11%2
270
May1st to 15thDay
36%419%25%10%3
288
16th to endDay
23%17%33%21%3
331
June1st to 15thDay
26%115%30%24%1
315
16th to endDay
17%15%40%23%2
315
July1st to 15thDay
19%19%34%32%3
305
16th to endDay
14%10%35%33%5%
326
August1st to 15thDay
16%17%33%33%6%
313
16th to endDay
13%9%30%32%13%
332
September1st to 15thDay
18%117%28%25%9%
299
16th to endDay
20%314%26%24%11%
254
October1st to 15thDay
25%321%26%19%5%
252
16th to endDay
16%8%33%27%13%
240
November1st to 15thDay
27%5%30%18%15%2
235
16th to endDay
25%12%23%23%12%1
240
December1st to 15thDay
21%14%30%24%10%
150
16th to endDay
32%10%34%18%3
64
January1st to 15thNight
22%15%36%20%5%
720
16th to endNight
28%15%32%20%2
768
February1st to 15thNight
23%15%38%20%1
704
16th to endNight
17%13%41%22%4
631
March1st to 15thNight
23%9%31%27%7%
720
16th to endNight
22%7%32%26%9%1
768
April1st to 15thNight
23%330%33%8%
718
16th to endNight
23%225%31%14%1
585
May1st to 15thNight
25%123%30%15%2
540
16th to endNight
25%216%33%19%2
483
June1st to 15thNight
28%115%30%21%2
360
16th to endNight
19%110%40%27%1
360
July1st to 15thNight
16%10%40%28%2
340
16th to endNight
13%112%37%31%4
399
August1st to 15thNight
12%10%40%31%4
539
16th to endNight
16%7%32%32%9%
714
September1st to 15thNight
17%17%32%25%6%
707
16th to endNight
19%115%29%28%5%
657
October1st to 15thNight
24%5%22%27%16%3
660
16th to endNight
22%11%27%26%10%
704
November1st to 15thNight
24%9%25%25%13%2
700
16th to endNight
24%12%28%23%8%1
720
December1st to 15thNight
26%14%30%20%8%
720
16th to endNight
28%13%36%18%2
768
Page generated at 2017-09-13 07:39:17. Version ac04

Copyright 2017 A. Danko


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