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 2017-08-12.

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
23%
14762
19%
46458
7%
14730
37%
14730
20%
29859

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%
720
21%
2506
4%
716
32%
716
15%
1575
January16th to endNight
12%
768
20%
2688
4%
768
33%
768
15%
1689
February1st to 15thNight
11%
704
18%
2186
3%
701
28%
701
16%
1447
February16th to endNight
12%
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
31%
606
21%
1132
May1st to 15thNight
19%
540
16%
1620
6%
540
29%
540
17%
1105
May16th to endNight
24%
399
12%
1521
6%
398
34%
398
16%
1000
June1st to 15thNight
27%
360
12%
1440
7%
360
41%
360
15%
935
June16th to endNight
29%
360
12%
1440
10%
360
39%
360
22%
859
July1st to 15thNight
37%
340
13%
1360
11%
340
46%
340
23%
808
July16th to endNight
42%
376
15%
1418
14%
354
51%
354
23%
828
August1st to 15thNight
38%
480
17%
1529
9%
478
45%
478
29%
918
August16th to endNight
47%
683
19%
1733
9%
683
51%
683
35%
1104
September1st to 15thNight
36%
660
21%
1697
9%
660
43%
660
31%
1103
September16th to endNight
41%
657
26%
1815
16%
657
49%
657
35%
1094
October1st to 15thNight
29%
660
23%
1851
10%
660
42%
660
26%
1196
October16th to endNight
22%
704
17%
2280
5%
704
36%
704
18%
1480
November1st to 15thNight
25%
700
22%
2277
8%
700
42%
700
22%
1426
November16th to endNight
20%
720
20%
2340
7%
720
36%
720
18%
1477
December1st to 15thNight
17%
720
17%
2514
5%
720
32%
720
16%
1593
December16th to endNight
13%
768
20%
2688
4%
768
32%
768
14%
1751

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%38%
47523
Night
16%6%25%42445%6%40%
46628
Cloud CoverDay
16%6%25%42445%6%39%
47533
Night
16%6%25%424446%41%
46633
TransparencyDay
44%411%22%14%2
47211
Night
43%312%23%15%2
46458
SeeingDay
22%13%32%20%8%2
5722
Night
22%15%34%21%6%
14762

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%7%35%436%447%39%
1432
16th to endDay
14%5%245%2445%7%42%
1536
February1st to 15thDay
15%7%245%36%6%5%7%34%
1671
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%5%25%6%45%5%6%7%37%
2324
16th to endDay
11%6%25%5%35%45%8%40%
2116
September1st to 15thDay
13%6%2443445%6%44%
1933
16th to endDay
15%5%13322436%50%
1815
October1st to 15thDay
20%5%24424346%40%
1779
16th to endDay
15%6%25%5%245%5%6%42%
1592
November1st to 15thDay
19%7%2442334443%
1581
16th to endDay
16%6%244245%5%5%42%
1620
December1st to 15thDay
17%7%25%5%2435%7%39%
1443
16th to endDay
20%8%24435%5%46%35%
1536
January1st to 15thNight
15%8%35%5%2335%5%41%
2506
16th to endNight
14%8%35%5%2435%6%40%
2688
February1st to 15thNight
14%8%36%5%24447%38%
2185
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%45%
1539
16th to endNight
12%41442446%9%44%
1733
September1st to 15thNight
13%5%25%42445%5%44%
1697
16th to endNight
14%5%2431235%5%50%
1815
October1st to 15thNight
19%6%13423445%44%
1851
16th to endNight
18%6%34434346%40%
2280
November1st to 15thNight
16%7%2442334445%
2277
16th to endNight
18%6%2443435%6%40%
2340
December1st to 15thNight
18%6%25%424347%38%
2514
16th to endNight
17%8%35%42445%6%37%
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
14%7%34435%446%40%
1432
16th to endDay
13%5%25%5%245%5%6%42%
1536
February1st to 15thDay
16%6%245%36%5%6%7%35%
1671
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%
2324
16th to endDay
11%6%25%5%345%5%7%42%
2116
September1st to 15thDay
14%6%2443345%6%45%
1933
16th to endDay
15%5%13413436%50%
1815
October1st to 15thDay
20%5%2432335%6%41%
1779
16th to endDay
14%5%26%42445%6%43%
1592
November1st to 15thDay
20%5%24322345%43%
1581
16th to endDay
16%6%334245%6%5%42%
1620
December1st to 15thDay
17%6%345%23446%40%
1443
16th to endDay
21%7%24335%447%35%
1536
January1st to 15thNight
16%8%35%423446%41%
2506
16th to endNight
14%9%35%434435%41%
2688
February1st to 15thNight
13%8%36%5%15%45%6%40%
2178
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%
1539
16th to endNight
12%32442345%8%45%
1733
September1st to 15thNight
14%5%2442445%6%44%
1697
16th to endNight
14%5%24312346%50%
1815
October1st to 15thNight
19%6%14313435%44%
1851
16th to endNight
18%6%25%434446%40%
2280
November1st to 15thNight
16%7%2442425%5%45%
2277
16th to endNight
18%6%24423446%41%
2340
December1st to 15thNight
18%7%25%42335%6%40%
2514
16th to endNight
17%8%35%42345%5%38%
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
45%310%24%11%3
1433
16th to endDay
40%313%26%14%1
1536
February1st to 15thDay
47%413%21%12%
1674
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
2310
16th to endDay
40%410%27%15%2
2116
September1st to 15thDay
38%411%23%19%1
1933
16th to endDay
35%37%26%25%2
1815
October1st to 15thDay
43%39%25%14%3
1779
16th to endDay
41%412%23%15%2
1592
November1st to 15thDay
44%312%22%14%1
1581
16th to endDay
40%411%23%17%1
1620
December1st to 15thDay
44%316%19%15%
1443
16th to endDay
49%413%19%12%
1536
January1st to 15thNight
44%312%23%13%2
2506
16th to endNight
45%211%22%15%2
2688
February1st to 15thNight
45%413%22%12%2
2186
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
36%415%24%16%1
1529
16th to endNight
36%413%29%16%
1733
September1st to 15thNight
39%312%24%18%
1697
16th to endNight
34%37%25%27%2
1815
October1st to 15thNight
41%311%23%15%4
1851
16th to endNight
45%313%23%13%
2280
November1st to 15thNight
41%311%21%18%3
2277
16th to endNight
44%213%22%14%2
2340
December1st to 15thNight
45%314%23%12%
2514
16th to endNight
46%412%23%12%1
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
20%31%26%18%3
60
16th to endDay
31%15%40%12%
64
February1st to 15thDay
26%21%36%12%2
209
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
13%7%31%31%13%3
297
16th to endDay
14%6%25%29%17%6%
268
September1st to 15thDay
17%7%27%27%14%5%
255
16th to endDay
18%7%30%19%13%10%
254
October1st to 15thDay
23%9%26%21%11%5%
255
16th to endDay
21%18%34%19%7%
241
November1st to 15thDay
25%14%32%17%8%2
235
16th to endDay
26%18%27%18%6%2
240
December1st to 15thDay
26%23%36%9%3
63
16th to endDay
40%20%29%7%1
64
January1st to 15thNight
23%21%38%14%1
720
16th to endNight
24%22%35%15%1
768
February1st to 15thNight
21%21%40%14%2
704
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%438%35%10%
480
16th to endNight
13%427%36%16%1
683
September1st to 15thNight
18%5%32%30%11%1
660
16th to endNight
16%6%29%26%17%3
657
October1st to 15thNight
24%11%31%21%9%1
660
16th to endNight
25%17%30%19%6%
704
November1st to 15thNight
20%17%33%19%8%1
700
16th to endNight
25%18%30%16%7%1
720
December1st to 15thNight
26%18%34%16%4
720
16th to endNight
26%21%36%13%1
768
Page generated at 2017-08-13 14:16:14. Version ac04

Copyright 2017 A. Danko


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