Plum Island
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Plum Island clear sky chart from 2005-11-05 to 2017-10-31.

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
32%
15042
18%
47332
9%
15010
43%
15010
22%
30788

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
16%
720
19%
2506
6%
716
34%
716
17%
1609
January16th to endNight
14%
768
19%
2688
4%
768
33%
768
15%
1722
February1st to 15thNight
16%
704
16%
2204
4%
701
32%
701
17%
1494
February16th to endNight
20%
631
23%
1893
6%
631
41%
631
21%
1239
March1st to 15thNight
20%
720
18%
2142
7%
720
33%
720
19%
1459
March16th to endNight
23%
768
22%
2052
7%
768
35%
768
24%
1391
April1st to 15thNight
28%
718
19%
1796
5%
718
36%
718
25%
1268
April16th to endNight
30%
570
18%
1650
6%
570
39%
570
22%
1123
May1st to 15thNight
31%
540
15%
1620
7%
540
37%
540
21%
1117
May16th to endNight
36%
426
12%
1548
10%
425
43%
425
18%
1022
June1st to 15thNight
39%
360
12%
1440
12%
360
47%
360
15%
963
June16th to endNight
51%
360
11%
1440
13%
360
57%
360
22%
870
July1st to 15thNight
55%
340
12%
1360
17%
340
58%
340
22%
812
July16th to endNight
60%
376
15%
1418
20%
354
62%
354
22%
864
August1st to 15thNight
60%
518
17%
1589
13%
516
62%
516
29%
981
August16th to endNight
57%
690
21%
1836
13%
690
59%
690
33%
1186
September1st to 15thNight
48%
720
20%
1875
11%
720
53%
720
36%
1182
September16th to endNight
50%
717
27%
1980
18%
717
56%
717
36%
1213
October1st to 15thNight
40%
720
22%
2007
11%
720
49%
720
27%
1297
October16th to endNight
29%
768
18%
2494
9%
768
41%
768
21%
1600
November1st to 15thNight
32%
700
20%
2277
11%
700
45%
700
23%
1430
November16th to endNight
27%
720
20%
2340
8%
720
40%
720
20%
1501
December1st to 15thNight
19%
720
17%
2489
4%
720
35%
720
18%
1632
December16th to endNight
14%
768
18%
2688
4%
768
32%
768
15%
1813

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%5%2442445%7%41%
48424
Night
17%6%2442445%6%40%
47502
Cloud CoverDay
16%5%2442445%7%41%
48434
Night
17%6%25%424446%40%
47507
TransparencyDay
43%412%22%15%2
48112
Night
44%411%22%15%2
47332
SeeingDay
20%6%28%28%12%2
6071
Night
21%8%31%26%10%1
15042

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
18%5%2443335%7%41%
1432
16th to endDay
16%7%25%324347%43%
1536
February1st to 15thDay
17%8%25%5%3446%7%35%
1654
16th to endDay
13%8%35%5%25%45%5%39%
1580
March1st to 15thDay
21%7%35%424447%34%
1808
16th to endDay
17%7%24423346%42%
2170
April1st to 15thDay
17%5%24435%346%40%
2152
16th to endDay
18%423424446%43%
2310
May1st to 15thDay
24%6%35%5%24446%33%
2332
16th to endDay
17%5%24424448%40%
2576
June1st to 15thDay
24%5%24425%447%35%
2520
16th to endDay
15%4245%35%5%6%9%37%
2520
July1st to 15thDay
11%424435%46%10%40%
2520
16th to endDay
11%5%246%35%5%7%8%40%
2654
August1st to 15thDay
10%415%5%35%6%5%8%41%
2349
16th to endDay
11%3134246%6%8%48%
2363
September1st to 15thDay
13%413424347%48%
2085
16th to endDay
14%5%13323435%52%
1980
October1st to 15thDay
20%424424345%43%
1948
16th to endDay
17%5%15%434346%43%
1728
November1st to 15thDay
20%8%24313245%42%
1581
16th to endDay
18%5%25%423346%43%
1620
December1st to 15thDay
19%7%25%423445%39%
1470
16th to endDay
24%8%34413435%35%
1536
January1st to 15thNight
17%8%25%424346%40%
2506
16th to endNight
17%8%3443335%6%38%
2688
February1st to 15thNight
14%8%36%5%35%5%5%5%36%
2203
16th to endNight
16%8%2432435%442%
1893
March1st to 15thNight
19%7%25%424445%38%
2129
16th to endNight
17%6%35%42334443%
2052
April1st to 15thNight
18%8%245%235%45%39%
1796
16th to endNight
20%5%26%5%24445%38%
1650
May1st to 15thNight
21%6%25%5%2445%6%35%
1620
16th to endNight
21%6%25%5%24447%34%
1546
June1st to 15thNight
25%6%245%2345%6%33%
1440
16th to endNight
17%4245%2446%8%40%
1440
July1st to 15thNight
13%5%36%43445%9%39%
1440
16th to endNight
13%5%25%5%26%47%7%39%
1514
August1st to 15thNight
11%413435%6%5%8%43%
1599
16th to endNight
12%4245%3445%8%43%
1836
September1st to 15thNight
14%42432335%6%48%
1875
16th to endNight
14%423323246%51%
1980
October1st to 15thNight
18%42442245%5%44%
2007
16th to endNight
19%6%1443435%5%40%
2494
November1st to 15thNight
17%5%25%433446%43%
2277
16th to endNight
17%6%3433335%6%40%
2340
December1st to 15thNight
19%7%24424345%38%
2489
16th to endNight
20%9%2442335%5%36%
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
18%6%33323448%40%
1432
16th to endDay
16%6%34324347%42%
1536
February1st to 15thDay
19%7%25%5%24447%35%
1654
16th to endDay
13%7%35%425%446%39%
1580
March1st to 15thDay
21%7%35%42445%7%34%
1818
16th to endDay
17%7%235%23246%43%
2170
April1st to 15thDay
16%6%245%25%5%46%40%
2152
16th to endDay
17%424325%446%43%
2310
May1st to 15thDay
23%7%25%5%23336%34%
2332
16th to endDay
17%424435%45%7%40%
2576
June1st to 15thDay
24%5%24434447%35%
2520
16th to endDay
14%4245%35%5%6%8%38%
2520
July1st to 15thDay
11%42444447%9%42%
2520
16th to endDay
10%5%25%5%35%5%6%9%41%
2654
August1st to 15thDay
10%425%5%35%6%7%9%41%
2349
16th to endDay
11%3133235%6%8%49%
2363
September1st to 15thDay
13%424323347%49%
2085
16th to endDay
14%423333335%52%
1980
October1st to 15thDay
20%424423446%43%
1948
16th to endDay
17%4145%2435%5%44%
1728
November1st to 15thDay
21%8%24323246%42%
1581
16th to endDay
18%5%34423447%42%
1620
December1st to 15thDay
19%7%345%13445%39%
1470
16th to endDay
25%9%33323426%34%
1536
January1st to 15thNight
17%8%25%424347%38%
2506
16th to endNight
17%9%34434347%37%
2688
February1st to 15thNight
15%8%35%5%345%5%6%35%
2196
16th to endNight
17%8%24333347%40%
1893
March1st to 15thNight
20%8%25%424446%36%
2142
16th to endNight
17%6%35%43333443%
2051
April1st to 15thNight
18%8%25%3245%45%39%
1796
16th to endNight
20%6%25%5%24446%38%
1650
May1st to 15thNight
21%7%25%5%2445%6%34%
1620
16th to endNight
21%6%25%42435%7%34%
1546
June1st to 15thNight
24%7%24433346%33%
1440
16th to endNight
16%5%244245%5%8%41%
1440
July1st to 15thNight
12%5%36%435%45%8%39%
1440
16th to endNight
13%5%25%435%5%6%7%40%
1514
August1st to 15thNight
10%5%24436%6%5%8%42%
1599
16th to endNight
12%4245%245%5%7%44%
1836
September1st to 15thNight
13%5%2442345%6%48%
1875
16th to endNight
14%413323346%51%
1980
October1st to 15thNight
17%425%42345%6%43%
2007
16th to endNight
19%6%23424445%41%
2494
November1st to 15thNight
17%5%24434336%43%
2277
16th to endNight
16%7%35%42335%6%40%
2340
December1st to 15thNight
19%7%25%424446%38%
2489
16th to endNight
21%8%3442435%6%35%
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
43%311%24%13%3
1433
16th to endDay
42%312%26%13%1
1536
February1st to 15thDay
47%413%21%12%
1657
16th to endDay
45%311%22%14%2
1580
March1st to 15thDay
49%312%18%12%3
1818
16th to endDay
43%29%21%15%6%
2170
April1st to 15thDay
45%310%20%16%3
2152
16th to endDay
42%310%22%17%3
2310
May1st to 15thDay
52%38%18%15%2
2332
16th to endDay
42%6%14%21%13%1
2580
June1st to 15thDay
49%413%20%10%1
2520
16th to endDay
43%6%12%21%14%1
2520
July1st to 15thDay
37%6%13%24%15%1
2371
16th to endDay
40%5%15%24%12%2
2487
August1st to 15thDay
39%6%15%25%13%1
2335
16th to endDay
31%5%14%27%19%1
2363
September1st to 15thDay
35%312%23%22%1
2085
16th to endDay
35%38%26%24%2
1980
October1st to 15thDay
42%310%25%15%3
1948
16th to endDay
42%311%25%15%1
1728
November1st to 15thDay
44%311%23%14%1
1581
16th to endDay
42%413%20%17%1
1620
December1st to 15thDay
48%214%16%16%
1470
16th to endDay
52%5%11%19%11%
1536
January1st to 15thNight
46%312%22%13%1
2506
16th to endNight
46%310%20%16%2
2688
February1st to 15thNight
47%412%20%12%2
2204
16th to endNight
44%310%24%14%2
1893
March1st to 15thNight
48%310%20%14%3
2142
16th to endNight
44%38%17%20%5%
2052
April1st to 15thNight
46%38%20%17%3
1796
16th to endNight
48%38%18%17%3
1650
May1st to 15thNight
49%310%17%15%3
1620
16th to endNight
48%5%14%19%11%1
1548
June1st to 15thNight
51%411%20%10%1
1440
16th to endNight
41%5%14%20%16%1
1440
July1st to 15thNight
41%413%25%13%
1360
16th to endNight
40%6%14%26%10%1
1418
August1st to 15thNight
37%5%13%25%15%2
1589
16th to endNight
37%5%10%25%19%
1836
September1st to 15thNight
36%312%26%20%1
1875
16th to endNight
34%36%26%26%1
1980
October1st to 15thNight
41%310%25%14%3
2007
16th to endNight
44%411%25%14%
2494
November1st to 15thNight
42%312%22%15%3
2277
16th to endNight
44%312%22%14%2
2340
December1st to 15thNight
47%313%21%12%
2489
16th to endNight
48%5%11%21%12%
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
18%23%25%25%8%
60
16th to endDay
21%14%40%23%
64
February1st to 15thDay
26%14%36%19%3
231
16th to endDay
17%14%38%23%5%
239
March1st to 15thDay
24%13%35%20%4
270
16th to endDay
22%12%36%19%6%1
288
April1st to 15thDay
22%9%34%22%8%1
270
16th to endDay
20%7%35%25%8%1
270
May1st to 15thDay
33%6%27%19%11%1
288
16th to endDay
21%227%38%9%1
331
June1st to 15thDay
26%126%30%12%1
315
16th to endDay
17%231%36%9%2
315
July1st to 15thDay
18%218%36%21%2
305
16th to endDay
12%120%40%21%2
326
August1st to 15thDay
12%123%37%20%3
313
16th to endDay
14%117%37%21%7%
332
September1st to 15thDay
17%224%31%18%5%
315
16th to endDay
20%323%23%16%12%
314
October1st to 15thDay
23%6%22%26%16%5%
308
16th to endDay
20%9%32%24%12%
288
November1st to 15thDay
24%8%29%24%11%2
235
16th to endDay
25%14%26%21%10%2
240
December1st to 15thDay
21%13%40%16%8%
90
16th to endDay
26%14%35%23%
64
January1st to 15thNight
22%14%41%17%3
720
16th to endNight
23%16%38%17%3
768
February1st to 15thNight
21%15%41%19%1
704
16th to endNight
22%13%39%19%5%
631
March1st to 15thNight
25%12%37%23%2
720
16th to endNight
21%11%37%21%7%
768
April1st to 15thNight
23%7%36%26%5%
718
16th to endNight
24%6%32%27%9%
570
May1st to 15thNight
24%432%27%9%1
540
16th to endNight
24%427%31%12%
426
June1st to 15thNight
27%418%34%12%2
360
16th to endNight
17%221%44%13%
360
July1st to 15thNight
15%117%47%16%2
340
16th to endNight
16%14%46%20%1
376
August1st to 15thNight
13%117%44%22%
518
16th to endNight
16%215%38%24%3
690
September1st to 15thNight
16%125%34%19%2
720
16th to endNight
17%322%26%22%7%
717
October1st to 15thNight
20%6%25%28%15%2
720
16th to endNight
22%10%33%24%8%
768
November1st to 15thNight
18%8%35%26%10%1
700
16th to endNight
22%14%30%22%9%1
720
December1st to 15thNight
22%11%39%21%4
720
16th to endNight
26%14%39%16%1
768
Page generated at 2017-11-01 17:23:35. Version ac04

Copyright 2017 A. Danko


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