Block Island
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Block Island clear sky chart from 2005-11-06 to 2024-01-12.

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%
23101
17%
74519
10%
23057
45%
23057
20%
49607

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
20%
760
18%
2649
7%
757
33%
757
17%
1721
January11th to 20thNight
19%
727
15%
2541
5%
727
32%
727
13%
1803
January21st to endNight
18%
792
17%
2772
7%
792
33%
792
16%
1822
February1st to 10thNight
18%
720
15%
2196
4%
720
32%
720
16%
1566
February11th to 20thNight
15%
702
18%
2100
5%
700
31%
700
19%
1439
February21st to endNight
20%
592
22%
1776
9%
592
37%
592
19%
1208
March1st to 10thNight
25%
719
20%
2160
9%
719
40%
719
22%
1397
March11th to 20thNight
28%
720
20%
2071
9%
720
40%
720
21%
1402
March21st to endNight
29%
792
22%
2048
9%
792
39%
792
26%
1418
April1st to 10thNight
33%
720
20%
1800
7%
720
39%
720
25%
1281
April11th to 20thNight
40%
711
18%
1775
7%
711
46%
711
29%
1226
April21st to endNight
37%
563
19%
1643
10%
563
41%
563
22%
1128
May1st to 10thNight
39%
540
13%
1620
9%
540
43%
540
19%
1177
May11th to 20thNight
38%
532
17%
1594
11%
532
43%
532
22%
1111
May21st to endNight
49%
413
11%
1575
11%
412
52%
412
15%
1080
June1st to 10thNight
48%
360
14%
1440
16%
360
52%
360
17%
958
June11th to 20thNight
54%
360
15%
1440
20%
360
57%
360
20%
886
June21st to endNight
58%
360
14%
1440
19%
360
61%
360
20%
886
July1st to 10thNight
59%
350
12%
1400
18%
350
60%
350
19%
864
July11th to 20thNight
63%
348
15%
1392
21%
348
64%
348
20%
854
July21st to endNight
62%
394
18%
1486
22%
372
65%
372
22%
896
August1st to 10thNight
69%
521
17%
1584
14%
518
70%
518
31%
967
August11th to 20thNight
65%
612
17%
1676
12%
612
65%
612
30%
1113
August21st to endNight
64%
792
20%
1980
13%
792
65%
792
35%
1305
September1st to 10thNight
56%
720
20%
1800
12%
720
58%
720
30%
1234
September11th to 20thNight
55%
720
23%
1980
16%
720
59%
720
33%
1226
September21st to endNight
45%
720
22%
1980
15%
720
51%
720
25%
1374
October1st to 10thNight
40%
720
18%
1980
12%
720
45%
720
23%
1384
October11th to 20thNight
40%
720
22%
2166
14%
720
51%
720
26%
1367
October21st to endNight
31%
792
16%
2574
9%
792
41%
792
18%
1751
November1st to 10thNight
36%
740
20%
2407
14%
740
46%
740
23%
1514
November11th to 20thNight
26%
760
20%
2470
10%
760
40%
760
19%
1638
November21st to endNight
28%
760
19%
2470
8%
760
42%
760
20%
1571
December1st to 10thNight
23%
760
15%
2569
5%
760
35%
760
14%
1802
December11th to 20thNight
19%
760
16%
3182
4%
759
32%
759
11%
2087
December21st to endNight
18%
829
11%
4783
6%
817
32%
817
9%
3151

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
16%7%35%5%3445%7%41%
74807
Night
18%8%35%5%3445%7%38%
74898
TransparencyDay
42%5%13%23%15%2
74513
Night
46%5%12%21%14%2
74726
SeeingDay
19%6%23%30%18%4
14045
Night
21%9%26%27%14%2
23110

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 10thDay
16%8%345%35%47%7%38%
1517
11th to 20thDay
19%10%35%5%3346%6%36%
1448
21st to endDay
16%8%35%5%3445%8%40%
1584
February1st to 10thDay
20%7%36%5%25%5%6%7%33%
1760
11th to 20thDay
16%7%36%5%3446%7%40%
1748
21st to endDay
22%8%35%32445%7%36%
1480
March1st to 10thDay
15%6%25%4245%49%45%
1797
11th to 20thDay
17%5%35%4335%6%7%42%
1887
21st to endDay
18%8%36%333446%42%
2306
April1st to 10thDay
18%7%25%424446%43%
2160
11th to 20thDay
17%6%24424348%45%
2134
21st to endDay
20%5%345%35%5%6%7%39%
2317
May1st to 10thDay
22%9%46%424346%36%
2340
11th to 20thDay
18%8%35%5%2445%7%41%
2301
21st to endDay
15%9%34425%45%8%40%
2715
June1st to 10thDay
19%6%25%6%35%46%8%36%
2520
11th to 20thDay
14%6%36%5%345%5%9%39%
2520
21st to endDay
13%6%25%4345%6%9%43%
2520
July1st to 10thDay
11%6%25%5%3446%10%43%
2520
11th to 20thDay
11%6%35%5%35%46%9%43%
2520
21st to endDay
13%6%35%4345%6%8%43%
2740
August1st to 10thDay
10%426%5%345%6%9%45%
2327
11th to 20thDay
13%5%35%5%345%5%7%44%
2221
21st to endDay
12%5%35%4345%6%8%46%
2376
September1st to 10thDay
14%6%245%2446%7%46%
2160
11th to 20thDay
13%5%2441335%7%52%
1980
21st to endDay
18%7%25%5%2345%6%42%
1980
October1st to 10thDay
21%7%25%323436%42%
1980
11th to 20thDay
15%6%24324448%47%
1792
21st to endDay
19%6%245%3445%7%40%
1782
November1st to 10thDay
17%6%35%424345%46%
1671
11th to 20thDay
16%7%3442445%7%44%
1710
21st to endDay
16%7%46%6%2345%6%40%
1710
December1st to 10thDay
21%8%47%5%34346%35%
1606
11th to 20thDay
22%7%3442435%6%41%
1906
21st to endDay
20%12%37%5%2445%6%32%
2772
January1st to 10thNight
18%8%35%425%5%6%7%37%
2649
11th to 20thNight
23%9%36%4335%5%6%32%
2541
21st to endNight
16%10%37%5%3446%7%36%
2772
February1st to 10thNight
17%10%47%6%3445%6%34%
2196
11th to 20thNight
20%8%35%5%3346%7%36%
2098
21st to endNight
20%8%35%6%34446%37%
1776
March1st to 10thNight
18%7%25%4345%5%7%42%
2150
11th to 20thNight
17%8%36%5%3445%7%38%
2070
21st to endNight
18%8%35%434346%41%
2048
April1st to 10thNight
19%9%25%425%446%39%
1800
11th to 20thNight
17%7%345%25%45%5%42%
1775
21st to endNight
21%9%35%434446%38%
1643
May1st to 10thNight
22%9%45%6%3445%7%31%
1620
11th to 20thNight
19%9%36%43446%8%34%
1593
21st to endNight
19%10%26%5%25%6%5%6%33%
1574
June1st to 10thNight
19%9%45%5%35%5%5%7%35%
1440
11th to 20thNight
19%7%34425%46%9%38%
1440
21st to endNight
14%6%35%5%35%46%10%38%
1440
July1st to 10thNight
11%7%37%5%35%6%6%9%38%
1440
11th to 20thNight
12%7%36%5%36%5%6%9%37%
1440
21st to endNight
12%6%35%6%36%6%6%8%38%
1574
August1st to 10thNight
8%6%245%446%8%10%42%
1595
11th to 20thNight
10%6%35%5%45%5%7%8%42%
1676
21st to endNight
12%6%345%3446%8%45%
1980
September1st to 10thNight
14%6%36%6%35%46%7%40%
1800
11th to 20thNight
14%7%25%424346%50%
1980
21st to endNight
19%7%36%5%34445%41%
1980
October1st to 10thNight
22%7%35%434345%39%
1980
11th to 20thNight
16%6%25%43445%6%44%
2166
21st to endNight
20%7%35%5%35%45%6%37%
2574
November1st to 10thNight
16%7%25%5%2435%6%44%
2407
11th to 20thNight
18%8%35%5%245%5%6%40%
2470
21st to endNight
16%6%35%5%35%45%7%41%
2470
December1st to 10thNight
21%8%35%5%35%5%5%6%34%
2569
11th to 20thNight
21%8%35%434447%37%
3288
21st to endNight
20%11%47%424445%35%
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
45%413%25%12%1
1518
11th to 20thDay
49%6%15%18%10%2
1448
21st to endDay
45%413%22%14%1
1584
February1st to 10thDay
50%5%16%18%11%1
1760
11th to 20thDay
44%5%11%24%13%2
1757
21st to endDay
47%413%18%15%3
1480
March1st to 10thDay
38%5%14%25%14%4
1800
11th to 20thDay
40%412%25%15%2
1887
21st to endDay
45%49%21%17%4
2306
April1st to 10thDay
43%411%21%18%3
2160
11th to 20thDay
39%5%10%24%20%3
2134
21st to endDay
44%5%9%21%16%4
2317
May1st to 10thDay
50%410%21%12%3
2340
11th to 20thDay
44%5%10%21%18%3
2305
21st to endDay
43%6%15%22%12%2
2715
June1st to 10thDay
46%6%12%22%12%1
2520
11th to 20thDay
43%6%14%22%14%1
2520
21st to endDay
38%7%14%26%14%1
2520
July1st to 10thDay
38%8%14%22%16%2
2450
11th to 20thDay
37%7%14%29%12%1
2445
21st to endDay
37%7%13%23%17%3
2587
August1st to 10thDay
34%7%17%25%16%
2314
11th to 20thDay
38%9%13%26%12%1
2221
21st to endDay
37%7%12%23%19%2
2376
September1st to 10thDay
38%6%11%24%19%1
2160
11th to 20thDay
33%5%14%24%22%3
1980
21st to endDay
43%5%8%22%20%2
1980
October1st to 10thDay
44%5%11%22%16%3
1980
11th to 20thDay
37%414%27%16%1
1792
21st to endDay
44%5%13%22%13%3
1782
November1st to 10thDay
42%416%19%17%2
1671
11th to 20thDay
40%5%16%22%16%2
1710
21st to endDay
46%314%26%9%2
1710
December1st to 10thDay
52%313%17%13%1
1606
11th to 20thDay
47%316%15%14%4
1906
21st to endDay
53%5%11%21%9%
2772
January1st to 10thNight
47%414%22%12%2
2649
11th to 20thNight
54%5%12%20%8%1
2541
21st to endNight
48%411%20%15%1
2772
February1st to 10thNight
52%5%13%19%9%2
2196
11th to 20thNight
48%410%23%12%3
2100
21st to endNight
48%39%23%13%3
1776
March1st to 10thNight
42%5%12%22%15%4
2160
11th to 20thNight
46%49%21%15%4
2071
21st to endNight
45%48%18%19%6%
2048
April1st to 10thNight
47%5%8%21%17%3
1800
11th to 20thNight
44%49%21%19%3
1775
21st to endNight
48%49%20%15%4
1643
May1st to 10thNight
52%6%10%18%12%2
1620
11th to 20thNight
49%5%9%20%14%3
1594
21st to endNight
50%7%12%17%11%1
1575
June1st to 10thNight
49%6%11%18%15%1
1440
11th to 20thNight
43%6%13%24%14%1
1440
21st to endNight
41%8%12%25%14%1
1440
July1st to 10thNight
40%9%15%21%14%1
1400
11th to 20thNight
41%8%15%25%10%1
1392
21st to endNight
40%7%14%25%12%2
1486
August1st to 10thNight
34%8%18%25%13%2
1584
11th to 20thNight
38%8%16%26%11%1
1676
21st to endNight
36%6%13%24%19%2
1980
September1st to 10thNight
42%6%10%24%16%2
1800
11th to 20thNight
37%410%23%23%2
1980
21st to endNight
46%6%7%20%19%3
1980
October1st to 10thNight
49%49%21%14%3
1980
11th to 20thNight
40%5%13%28%13%1
2166
21st to endNight
49%5%12%19%14%2
2574
November1st to 10thNight
42%5%12%22%15%4
2407
11th to 20thNight
46%5%11%21%14%3
2470
21st to endNight
42%5%15%25%11%2
2470
December1st to 10thNight
52%5%14%17%11%1
2569
11th to 20thNight
49%5%13%18%15%2
3288
21st to endNight
52%5%11%22%10%
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
21%13%36%22%8%1
180
11th to 20thDay
19%19%35%21%6%
162
21st to endDay
19%10%39%23%8%1
176
February1st to 10thDay
27%11%36%21%5%
390
11th to 20thDay
21%12%40%24%3
416
21st to endDay
25%13%33%25%4
346
March1st to 10thDay
19%9%38%29%6%
420
11th to 20thDay
18%10%35%30%5%1
420
21st to endDay
22%8%34%25%9%2
462
April1st to 10thDay
22%9%30%27%11%1
420
11th to 20thDay
18%8%28%36%10%1
412
21st to endDay
24%6%22%36%11%1
420
May1st to 10thDay
26%5%27%30%12%
423
11th to 20thDay
17%428%33%15%2
447
21st to endDay
21%214%30%28%6%
485
June1st to 10thDay
18%217%33%26%3
450
11th to 20thDay
15%316%36%26%5%
450
21st to endDay
16%114%38%26%5%
450
July1st to 10thDay
16%39%32%33%8%
445
11th to 20thDay
9%25%34%40%9%
444
21st to endDay
13%49%39%32%3
488
August1st to 10thDay
12%29%36%33%7%
446
11th to 20thDay
16%38%31%33%8%
439
21st to endDay
13%211%35%28%11%
495
September1st to 10thDay
19%313%29%25%11%
450
11th to 20thDay
16%417%29%25%10%
450
21st to endDay
22%321%29%20%5%
450
October1st to 10thDay
24%5%19%28%18%6%
450
11th to 20thDay
17%7%23%32%19%2
414
21st to endDay
24%9%27%25%12%3
396
November1st to 10thDay
15%9%24%32%16%4
365
11th to 20thDay
23%13%29%26%9%
370
21st to endDay
20%12%30%26%10%1
370
December1st to 10thDay
21%11%33%25%9%
266
11th to 20thDay
25%14%36%21%41
180
21st to endDay
25%12%31%23%8%1
198
January1st to 10thNight
23%16%35%22%4
760
11th to 20thNight
29%14%33%20%4
727
21st to endNight
22%16%38%20%31
792
February1st to 10thNight
23%14%38%23%2
720
11th to 20thNight
24%13%43%16%3
703
21st to endNight
24%15%35%22%5%
592
March1st to 10thNight
22%13%35%24%6%
720
11th to 20thNight
21%10%36%27%6%2
720
21st to endNight
22%7%34%25%9%2
792
April1st to 10thNight
24%7%30%30%8%1
720
11th to 20thNight
20%6%27%34%12%1
711
21st to endNight
25%5%24%30%13%2
563
May1st to 10thNight
25%420%34%14%3
540
11th to 20thNight
22%424%37%11%2
532
21st to endNight
23%313%32%24%4
413
June1st to 10thNight
21%316%34%25%3
360
11th to 20thNight
21%313%34%27%1
360
21st to endNight
17%311%39%29%2
360
July1st to 10thNight
15%310%37%30%4
350
11th to 20thNight
17%18%36%33%5%
348
21st to endNight
14%39%37%33%4
394
August1st to 10thNight
10%29%38%35%6%
521
11th to 20thNight
12%210%35%33%8%
612
21st to endNight
15%38%31%34%9%
792
September1st to 10thNight
17%215%32%27%7%
720
11th to 20thNight
16%317%31%26%8%
720
21st to endNight
22%321%29%22%4
720
October1st to 10thNight
26%6%21%24%19%4
720
11th to 20thNight
19%9%25%31%15%2
720
21st to endNight
22%9%32%26%9%2
792
November1st to 10thNight
20%8%29%26%15%3
740
11th to 20thNight
23%13%32%23%8%1
760
21st to endNight
18%17%30%26%8%1
760
December1st to 10thNight
25%16%31%22%6%1
760
11th to 20thNight
25%19%32%18%5%1
760
21st to endNight
24%15%37%20%4
836
Page generated at 2024-01-09 07:14:45. Version ac07

Copyright 2024 Attilla Danko


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