Worcester
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Worcester 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
23%
15504
19%
48775
7%
15472
37%
15472
20%
31277

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
11%
780
20%
2716
4%
776
31%
776
15%
1695
January16th to endNight
12%
832
20%
2912
3%
832
33%
832
14%
1839
February1st to 15thNight
10%
760
18%
2359
4%
757
28%
757
15%
1579
February16th to endNight
13%
631
23%
1893
5%
631
34%
631
16%
1226
March1st to 15thNight
15%
720
17%
2160
6%
720
30%
720
15%
1483
March16th to endNight
20%
768
23%
2020
7%
768
33%
768
20%
1348
April1st to 15thNight
17%
718
18%
1796
3%
718
26%
718
19%
1282
April16th to endNight
19%
606
19%
1686
3%
606
30%
606
21%
1132
May1st to 15thNight
20%
540
16%
1620
6%
540
29%
540
17%
1105
May16th to endNight
24%
399
12%
1521
6%
398
33%
398
16%
1000
June1st to 15thNight
27%
360
13%
1440
7%
360
41%
360
15%
935
June16th to endNight
28%
360
12%
1440
10%
360
38%
360
22%
859
July1st to 15thNight
38%
340
13%
1360
11%
340
47%
340
23%
808
July16th to endNight
42%
376
15%
1418
14%
354
51%
354
23%
828
August1st to 15thNight
37%
491
17%
1562
9%
489
44%
489
29%
942
August16th to endNight
48%
746
22%
1892
10%
746
52%
746
36%
1198
September1st to 15thNight
35%
720
20%
1851
9%
720
42%
720
32%
1193
September16th to endNight
42%
717
27%
1980
17%
717
50%
717
35%
1198
October1st to 15thNight
31%
720
23%
2019
10%
720
44%
720
27%
1284
October16th to endNight
22%
768
18%
2487
6%
768
37%
768
19%
1605
November1st to 15thNight
25%
760
21%
2472
8%
760
41%
760
21%
1562
November16th to endNight
20%
780
23%
2535
8%
780
38%
780
19%
1566
December1st to 15thNight
17%
780
17%
2724
4%
780
32%
780
16%
1728
December16th to endNight
12%
832
20%
2912
4%
832
32%
832
14%
1882

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%6%25%43445%7%39%
49309
Night
16%6%25%42445%6%41%
48945
Cloud CoverDay
16%6%25%42445%6%39%
49319
Night
16%6%25%424446%41%
48950
TransparencyDay
44%411%22%15%2
48997
Night
43%311%23%15%2
48775
SeeingDay
22%14%32%19%8%2
6293
Night
21%15%34%21%6%
15504

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
14%6%35%436%446%40%
1552
16th to endDay
14%5%3442445%6%42%
1664
February1st to 15thDay
15%7%25%5%36%6%5%7%33%
1799
16th to endDay
14%8%35%5%25%347%39%
1580
March1st to 15thDay
19%8%25%324446%36%
1790
16th to endDay
16%6%25%5%25%346%41%
2202
April1st to 15thDay
16%7%26%5%35%346%37%
2152
16th to endDay
18%5%14434448%40%
2272
May1st to 15thDay
24%8%25%5%24446%31%
2332
16th to endDay
17%5%25%424448%38%
2603
June1st to 15thDay
24%5%34334447%33%
2520
16th to endDay
15%5%26%5%35%6%7%8%33%
2520
July1st to 15thDay
12%6%35%6%36%5%5%8%36%
2520
16th to endDay
12%5%26%5%35%5%6%8%37%
2654
August1st to 15thDay
12%6%25%6%45%5%6%7%37%
2376
16th to endDay
11%5%25%5%3446%8%42%
2309
September1st to 15thDay
13%5%24434446%44%
2109
16th to endDay
15%5%13323436%50%
1980
October1st to 15thDay
19%5%24424346%41%
1940
16th to endDay
15%6%25%5%24445%43%
1737
November1st to 15thDay
18%7%3442334443%
1716
16th to endDay
16%6%234245%5%5%43%
1755
December1st to 15thDay
17%7%25%5%2435%7%38%
1563
16th to endDay
20%8%244345%46%35%
1664
January1st to 15thNight
15%8%35%5%2335%5%42%
2716
16th to endNight
14%8%35%5%2435%6%39%
2912
February1st to 15thNight
14%7%36%5%25%446%38%
2358
16th to endNight
15%8%35%424346%41%
1893
March1st to 15thNight
16%8%25%5%445%46%36%
2147
16th to endNight
13%8%35%424345%43%
2020
April1st to 15thNight
15%8%36%5%345%46%35%
1796
16th to endNight
20%6%25%5%24335%40%
1686
May1st to 15thNight
22%6%25%42345%5%36%
1620
16th to endNight
18%5%35%435%35%8%35%
1519
June1st to 15thNight
22%5%245%24348%34%
1440
16th to endNight
15%5%24425%5%5%7%40%
1440
July1st to 15thNight
13%5%35%4345%6%9%39%
1440
16th to endNight
11%5%246%46%5%5%7%41%
1514
August1st to 15thNight
9%415%6%446%48%44%
1572
16th to endNight
12%41442446%8%45%
1892
September1st to 15thNight
13%5%2442445%5%45%
1851
16th to endNight
13%5%2432235%5%50%
1980
October1st to 15thNight
17%6%14423445%45%
2019
16th to endNight
18%6%34434346%40%
2487
November1st to 15thNight
15%7%2442334444%
2472
16th to endNight
17%6%24434346%42%
2535
December1st to 15thNight
18%7%25%42435%7%38%
2724
16th to endNight
17%7%35%32445%6%38%
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
14%7%34435%446%41%
1552
16th to endDay
14%6%25%4245%5%6%43%
1664
February1st to 15thDay
16%6%345%26%5%6%7%34%
1799
16th to endDay
14%8%35%6%25%346%40%
1580
March1st to 15thDay
19%8%25%42445%6%36%
1800
16th to endDay
16%6%245%24445%42%
2202
April1st to 15thDay
16%7%36%5%24445%38%
2152
16th to endDay
17%5%245%2445%7%40%
2272
May1st to 15thDay
24%8%25%5%24346%31%
2332
16th to endDay
17%5%25%42445%8%38%
2603
June1st to 15thDay
24%5%245%25%347%33%
2520
16th to endDay
15%425%5%46%5%7%7%35%
2520
July1st to 15thDay
12%5%35%6%46%5%5%7%37%
2520
16th to endDay
12%5%25%5%36%6%6%8%38%
2654
August1st to 15thDay
12%5%26%5%35%5%6%7%37%
2376
16th to endDay
11%5%245%3445%7%43%
2309
September1st to 15thDay
14%5%2443345%6%45%
2109
16th to endDay
15%5%13423436%49%
1980
October1st to 15thDay
19%5%24323346%42%
1940
16th to endDay
15%5%26%424445%43%
1737
November1st to 15thDay
19%6%34422345%42%
1716
16th to endDay
16%6%233245%6%5%43%
1755
December1st to 15thDay
17%6%345%23446%39%
1563
16th to endDay
20%7%24335%446%35%
1664
January1st to 15thNight
15%7%35%423446%41%
2716
16th to endNight
14%9%35%434435%41%
2912
February1st to 15thNight
14%8%36%6%2445%5%39%
2351
16th to endNight
15%8%34424345%41%
1893
March1st to 15thNight
16%8%25%6%3445%5%36%
2160
16th to endNight
14%7%36%424336%43%
2019
April1st to 15thNight
15%7%36%6%25%45%6%36%
1796
16th to endNight
20%5%25%433435%41%
1686
May1st to 15thNight
23%6%25%423445%36%
1620
16th to endNight
17%6%35%5%3445%8%35%
1519
June1st to 15thNight
22%425%5%2435%7%35%
1440
16th to endNight
14%5%345%235%7%7%40%
1440
July1st to 15thNight
12%5%25%5%2446%9%39%
1440
16th to endNight
11%5%25%5%25%5%6%7%40%
1514
August1st to 15thNight
10%4145%45%5%5%8%44%
1572
16th to endNight
12%32442345%8%46%
1892
September1st to 15thNight
14%424425%35%6%45%
1851
16th to endNight
14%5%24312346%50%
1980
October1st to 15thNight
18%6%14313435%46%
2019
16th to endNight
18%6%25%434445%40%
2487
November1st to 15thNight
15%7%24424345%44%
2472
16th to endNight
17%6%24423446%43%
2535
December1st to 15thNight
17%7%35%42335%6%39%
2724
16th to endNight
17%8%35%42345%5%39%
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
44%310%24%13%3
1553
16th to endDay
40%413%25%14%1
1664
February1st to 15thDay
47%412%20%12%1
1802
16th to endDay
46%39%23%14%3
1580
March1st to 15thDay
48%311%21%12%3
1800
16th to endDay
44%29%21%16%5%
2202
April1st to 15thDay
48%210%20%15%2
2152
16th to endDay
43%39%21%19%3
2272
May1st to 15thDay
54%36%19%13%2
2332
16th to endDay
44%413%22%12%2
2607
June1st to 15thDay
50%5%11%21%10%
2520
16th to endDay
44%6%12%21%13%
2520
July1st to 15thDay
44%5%10%22%15%1
2371
16th to endDay
41%5%14%22%13%3
2487
August1st to 15thDay
43%5%12%24%12%1
2362
16th to endDay
38%410%27%16%2
2309
September1st to 15thDay
38%411%23%19%2
2109
16th to endDay
35%37%26%25%2
1980
October1st to 15thDay
42%39%26%14%3
1940
16th to endDay
41%411%24%16%1
1737
November1st to 15thDay
44%311%23%14%1
1716
16th to endDay
39%411%24%18%1
1755
December1st to 15thDay
44%316%18%15%1
1563
16th to endDay
48%412%20%12%1
1664
January1st to 15thNight
43%311%23%14%2
2716
16th to endNight
45%212%21%15%2
2912
February1st to 15thNight
46%412%21%12%2
2359
16th to endNight
44%29%23%16%2
1893
March1st to 15thNight
48%49%21%13%2
2160
16th to endNight
43%28%20%19%5%
2020
April1st to 15thNight
47%49%19%17%1
1796
16th to endNight
46%28%21%16%4
1686
May1st to 15thNight
49%310%19%14%2
1620
16th to endNight
48%5%15%19%10%1
1521
June1st to 15thNight
47%5%12%22%10%1
1440
16th to endNight
40%5%14%23%15%
1440
July1st to 15thNight
39%5%13%27%13%
1360
16th to endNight
39%415%26%11%2
1418
August1st to 15thNight
37%415%24%16%1
1562
16th to endNight
35%312%29%18%
1892
September1st to 15thNight
38%311%25%18%1
1851
16th to endNight
35%27%25%26%2
1980
October1st to 15thNight
39%312%24%15%3
2019
16th to endNight
44%312%24%14%
2487
November1st to 15thNight
42%311%21%18%3
2472
16th to endNight
42%213%23%15%2
2535
December1st to 15thNight
45%314%23%12%
2724
16th to endNight
46%411%22%14%1
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
20%31%30%15%3
90
16th to endDay
30%18%39%11%
96
February1st to 15thDay
29%21%36%11%2
257
16th to endDay
23%22%34%15%3
239
March1st to 15thDay
32%19%32%12%3
270
16th to endDay
24%22%32%11%6%1
288
April1st to 15thDay
25%14%40%12%6%
270
16th to endDay
22%16%33%18%5%2
270
May1st to 15thDay
34%15%27%15%5%1
288
16th to endDay
20%12%38%18%9%
331
June1st to 15thDay
23%12%31%24%7%
315
16th to endDay
17%10%40%21%7%2
315
July1st to 15thDay
16%8%34%28%10%1
305
16th to endDay
13%7%31%31%11%3
326
August1st to 15thDay
12%7%32%30%13%2
313
16th to endDay
13%7%29%27%16%5%
332
September1st to 15thDay
17%8%30%24%13%4
315
16th to endDay
20%6%28%18%14%11%
314
October1st to 15thDay
22%8%27%22%13%5%
315
16th to endDay
23%17%32%19%8%
290
November1st to 15thDay
23%15%33%17%8%1
280
16th to endDay
27%18%27%18%5%1
285
December1st to 15thDay
25%22%35%9%6%
93
16th to endDay
39%23%30%5%1
96
January1st to 15thNight
22%22%39%13%1
780
16th to endNight
24%22%35%15%1
832
February1st to 15thNight
21%21%40%14%1
760
16th to endNight
26%23%32%15%1
631
March1st to 15thNight
25%22%34%16%2
720
16th to endNight
21%21%32%21%3
768
April1st to 15thNight
22%19%37%17%3
718
16th to endNight
23%16%34%18%5%
606
May1st to 15thNight
29%14%32%18%4
540
16th to endNight
23%9%37%24%4
399
June1st to 15thNight
25%7%30%28%7%
360
16th to endNight
15%5%44%28%6%
360
July1st to 15thNight
15%6%35%33%9%
340
16th to endNight
12%334%36%12%
376
August1st to 15thNight
11%437%34%10%
491
16th to endNight
13%326%37%16%1
746
September1st to 15thNight
17%5%34%29%11%1
720
16th to endNight
17%6%28%24%19%3
717
October1st to 15thNight
22%10%30%22%10%2
720
16th to endNight
24%17%30%18%7%
768
November1st to 15thNight
20%16%32%20%8%1
760
16th to endNight
24%18%31%16%7%1
780
December1st to 15thNight
26%17%34%16%4
780
16th to endNight
25%21%36%13%1
832
Page generated at 2018-02-15 10:58:52. Version ac04

Copyright 2018 A. Danko


Worcester Clear Sky Chart |Charts Home