Middlesex School Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Middlesex School Observatory clear sky chart from 2005-11-05 to 2017-10-06.

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
28%
14965
18%
47027
8%
14933
40%
14933
21%
30615

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
18%
720
19%
2506
7%
716
33%
716
17%
1607
January16th to endNight
16%
768
20%
2688
4%
768
35%
768
15%
1713
February1st to 15thNight
18%
704
17%
2193
5%
701
32%
701
17%
1469
February16th to endNight
18%
631
23%
1893
7%
631
38%
631
19%
1243
March1st to 15thNight
18%
720
17%
2157
6%
720
33%
720
17%
1484
March16th to endNight
22%
768
23%
2030
7%
768
35%
768
22%
1379
April1st to 15thNight
21%
718
18%
1796
4%
718
30%
718
22%
1270
April16th to endNight
23%
591
18%
1671
4%
591
32%
591
20%
1136
May1st to 15thNight
25%
540
15%
1620
7%
540
32%
540
18%
1124
May16th to endNight
26%
412
11%
1534
7%
411
34%
411
16%
1008
June1st to 15thNight
29%
360
12%
1440
9%
360
40%
360
15%
963
June16th to endNight
38%
360
12%
1440
11%
360
48%
360
21%
877
July1st to 15thNight
43%
340
12%
1360
14%
340
49%
340
23%
806
July16th to endNight
46%
376
16%
1418
14%
354
54%
354
21%
872
August1st to 15thNight
44%
503
17%
1574
11%
501
49%
501
27%
971
August16th to endNight
52%
721
21%
1867
11%
721
55%
721
35%
1198
September1st to 15thNight
39%
720
20%
1861
8%
720
46%
720
33%
1199
September16th to endNight
47%
717
26%
1980
17%
717
54%
717
34%
1222
October1st to 15thNight
34%
684
23%
1904
11%
684
45%
684
26%
1218
October16th to endNight
25%
704
16%
2288
6%
704
39%
704
21%
1487
November1st to 15thNight
30%
700
21%
2277
11%
700
44%
700
22%
1451
November16th to endNight
25%
720
20%
2340
8%
720
40%
720
19%
1504
December1st to 15thNight
22%
720
17%
2502
5%
720
37%
720
17%
1616
December16th to endNight
17%
768
19%
2688
6%
768
34%
768
15%
1798

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%6%39%
48175
Night
17%6%24424446%41%
47197
Cloud CoverDay
17%6%2442445%6%39%
48185
Night
17%6%24424346%41%
47202
TransparencyDay
44%5%11%21%15%2
47863
Night
43%5%11%21%15%2
47027
SeeingDay
22%12%31%20%9%2
5965
Night
21%12%33%25%7%
14965

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
16%7%25%424445%41%
1432
16th to endDay
15%5%2443445%5%43%
1536
February1st to 15thDay
17%7%36%426%45%7%34%
1663
16th to endDay
15%8%35%5%34435%40%
1580
March1st to 15thDay
21%7%34424446%36%
1793
16th to endDay
18%7%35%424346%40%
2193
April1st to 15thDay
18%8%25%5%24346%38%
2152
16th to endDay
18%4245%2445%7%40%
2289
May1st to 15thDay
24%7%25%424445%31%
2332
16th to endDay
17%5%25%444347%39%
2590
June1st to 15thDay
24%6%2433445%7%33%
2520
16th to endDay
16%425%5%35%6%6%8%34%
2520
July1st to 15thDay
12%435%6%35%6%6%9%36%
2520
16th to endDay
11%5%25%5%26%6%6%8%39%
2654
August1st to 15thDay
11%5%25%6%35%6%5%9%39%
2363
16th to endDay
11%424436%5%5%7%44%
2333
September1st to 15thDay
14%5%1442345%6%45%
2098
16th to endDay
15%5%24323345%50%
1980
October1st to 15thDay
19%5%15%423345%43%
1851
16th to endDay
17%5%25%4235%5%6%42%
1584
November1st to 15thDay
20%6%24323335%43%
1581
16th to endDay
16%6%35%42444443%
1620
December1st to 15thDay
18%6%25%5%24435%40%
1455
16th to endDay
23%8%24424435%35%
1536
January1st to 15thNight
16%8%25%42434441%
2506
16th to endNight
16%9%35%423345%40%
2688
February1st to 15thNight
14%8%36%5%3445%6%37%
2192
16th to endNight
16%9%34424346%41%
1893
March1st to 15thNight
18%7%345%24445%37%
2144
16th to endNight
15%8%3442343444%
2030
April1st to 15thNight
17%7%35%5%34346%38%
1796
16th to endNight
21%5%24424246%39%
1671
May1st to 15thNight
21%6%2443445%5%36%
1620
16th to endNight
19%5%25%4345%48%35%
1532
June1st to 15thNight
23%6%3442235%7%34%
1440
16th to endNight
15%5%245%2445%8%40%
1440
July1st to 15thNight
12%4345%25%5%6%8%41%
1440
16th to endNight
11%6%25%5%35%46%7%41%
1514
August1st to 15thNight
9%4145%25%5%6%7%45%
1584
16th to endNight
12%31443445%9%45%
1867
September1st to 15thNight
14%5%24423346%48%
1861
16th to endNight
14%5%23322345%52%
1980
October1st to 15thNight
19%5%1342235%5%46%
1904
16th to endNight
20%6%2442335%6%39%
2288
November1st to 15thNight
17%6%2442335%5%44%
2277
16th to endNight
18%6%34433346%41%
2340
December1st to 15thNight
19%7%24424346%39%
2502
16th to endNight
19%8%35%5%2445%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
17%6%35%3245%36%41%
1432
16th to endDay
15%5%24424447%42%
1536
February1st to 15thDay
17%7%35%426%45%6%34%
1663
16th to endDay
15%9%25%5%3443440%
1580
March1st to 15thDay
22%8%34423346%35%
1803
16th to endDay
19%6%25%423436%40%
2193
April1st to 15thDay
18%8%345%24445%38%
2152
16th to endDay
19%4245%2435%6%40%
2289
May1st to 15thDay
25%7%25%434445%32%
2332
16th to endDay
17%425%5%33447%39%
2590
June1st to 15thDay
25%5%2432446%6%33%
2520
16th to endDay
15%5%25%5%26%6%6%8%34%
2520
July1st to 15thDay
12%5%35%5%36%6%6%8%37%
2520
16th to endDay
11%5%25%436%5%6%8%39%
2654
August1st to 15thDay
12%4245%35%5%5%8%40%
2363
16th to endDay
12%424425%5%5%7%44%
2333
September1st to 15thDay
14%5%14424347%46%
2098
16th to endDay
15%423412345%51%
1980
October1st to 15thDay
19%425%42335%5%43%
1851
16th to endDay
16%5%25%42345%6%42%
1584
November1st to 15thDay
21%6%2332423444%
1581
16th to endDay
17%5%3442345%5%43%
1620
December1st to 15thDay
18%7%25%5%24345%40%
1455
16th to endDay
23%8%25%424436%35%
1536
January1st to 15thNight
16%9%25%5%33336%40%
2506
16th to endNight
16%9%26%5%23345%40%
2688
February1st to 15thNight
14%8%26%5%2445%6%37%
2185
16th to endNight
17%9%34324346%41%
1893
March1st to 15thNight
19%7%25%5%34446%36%
2157
16th to endNight
15%8%35%32433444%
2029
April1st to 15thNight
17%6%36%5%34446%38%
1796
16th to endNight
23%4245%2433440%
1671
May1st to 15thNight
22%5%24434446%35%
1620
16th to endNight
19%6%3443445%8%35%
1532
June1st to 15thNight
23%5%35%42345%8%34%
1440
16th to endNight
15%4245%35%45%7%40%
1440
July1st to 15thNight
12%5%245%25%5%6%8%41%
1440
16th to endNight
12%5%246%45%45%8%40%
1514
August1st to 15thNight
9%3236%445%5%9%44%
1584
16th to endNight
12%31443445%8%46%
1867
September1st to 15thNight
14%425%42335%6%47%
1861
16th to endNight
15%414313346%51%
1980
October1st to 15thNight
18%5%24314345%46%
1904
16th to endNight
19%6%2442435%5%40%
2288
November1st to 15thNight
17%6%25%323346%44%
2277
16th to endNight
18%6%34424346%41%
2340
December1st to 15thNight
19%6%245%24346%39%
2502
16th to endNight
18%9%35%5%23446%36%
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
44%5%10%24%12%3
1433
16th to endDay
41%312%27%14%1
1536
February1st to 15thDay
48%413%20%12%1
1666
16th to endDay
46%39%21%15%3
1580
March1st to 15thDay
49%311%20%11%3
1803
16th to endDay
45%48%20%14%6%
2193
April1st to 15thDay
47%49%19%15%3
2152
16th to endDay
43%5%8%20%18%3
2289
May1st to 15thDay
52%5%7%17%14%2
2332
16th to endDay
43%6%12%21%13%2
2594
June1st to 15thDay
50%6%11%20%10%1
2520
16th to endDay
44%7%12%18%15%
2520
July1st to 15thDay
41%7%11%21%15%2
2371
16th to endDay
41%6%14%22%12%3
2487
August1st to 15thDay
41%7%14%22%13%1
2349
16th to endDay
36%6%10%26%17%2
2333
September1st to 15thDay
37%5%11%22%20%2
2098
16th to endDay
36%38%24%24%2
1980
October1st to 15thDay
42%49%25%14%3
1851
16th to endDay
41%412%24%15%1
1584
November1st to 15thDay
45%310%23%15%1
1581
16th to endDay
41%412%22%16%1
1620
December1st to 15thDay
46%315%17%17%
1455
16th to endDay
51%5%12%19%11%
1536
January1st to 15thNight
46%312%21%13%2
2506
16th to endNight
45%410%20%15%2
2688
February1st to 15thNight
46%412%21%12%2
2193
16th to endNight
44%39%22%16%2
1893
March1st to 15thNight
48%49%19%13%3
2157
16th to endNight
44%38%18%19%5%
2030
April1st to 15thNight
47%39%18%18%2
1796
16th to endNight
47%39%18%16%4
1671
May1st to 15thNight
48%5%9%18%15%3
1620
16th to endNight
46%6%15%18%11%1
1534
June1st to 15thNight
49%6%12%20%10%1
1440
16th to endNight
40%6%13%22%15%1
1440
July1st to 15thNight
38%6%13%26%13%
1360
16th to endNight
40%6%12%26%10%2
1418
August1st to 15thNight
36%8%13%23%15%2
1574
16th to endNight
35%5%11%27%18%
1867
September1st to 15thNight
37%5%11%24%20%1
1861
16th to endNight
34%47%22%28%2
1980
October1st to 15thNight
40%410%24%16%3
1904
16th to endNight
44%413%23%13%
2288
November1st to 15thNight
42%5%11%21%17%3
2277
16th to endNight
44%412%21%15%2
2340
December1st to 15thNight
45%413%22%12%
2502
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
25%20%26%25%3
60
16th to endDay
26%20%39%14%
64
February1st to 15thDay
26%17%35%17%3
219
16th to endDay
20%19%34%19%5%
239
March1st to 15thDay
29%17%31%17%3
270
16th to endDay
24%20%32%10%10%1
288
April1st to 15thDay
26%15%34%14%8%1
270
16th to endDay
24%12%34%18%6%2
270
May1st to 15thDay
36%14%26%14%7%2
288
16th to endDay
21%11%38%21%6%1
331
June1st to 15thDay
25%11%34%19%6%1
315
16th to endDay
18%10%39%24%5%2
315
July1st to 15thDay
19%7%33%26%11%1
305
16th to endDay
15%5%31%32%12%3
326
August1st to 15thDay
14%8%31%28%13%3
313
16th to endDay
14%6%29%25%18%5%
332
September1st to 15thDay
20%6%32%20%15%5%
315
16th to endDay
20%7%25%18%14%13%
314
October1st to 15thDay
21%9%23%23%15%5%
277
16th to endDay
20%15%30%25%7%
240
November1st to 15thDay
29%8%30%18%10%2
235
16th to endDay
24%14%32%17%9%1
240
December1st to 15thDay
25%29%26%14%4
75
16th to endDay
29%26%26%17%
64
January1st to 15thNight
23%15%36%20%3
720
16th to endNight
24%15%36%19%3
768
February1st to 15thNight
20%17%38%21%1
704
16th to endNight
23%16%35%20%3
631
March1st to 15thNight
24%16%36%18%3
720
16th to endNight
21%17%35%19%6%
768
April1st to 15thNight
22%17%34%20%4
718
16th to endNight
24%16%33%18%7%
591
May1st to 15thNight
25%13%32%23%4
540
16th to endNight
23%8%37%25%5%
412
June1st to 15thNight
24%6%33%28%6%1
360
16th to endNight
16%337%34%6%
360
July1st to 15thNight
12%332%38%12%
340
16th to endNight
13%230%40%12%
376
August1st to 15thNight
12%331%40%11%
503
16th to endNight
14%224%41%15%1
721
September1st to 15thNight
17%5%32%29%13%
720
16th to endNight
17%5%25%28%20%3
717
October1st to 15thNight
22%9%27%26%11%2
684
16th to endNight
25%11%33%22%6%
704
November1st to 15thNight
20%12%31%24%10%
700
16th to endNight
22%16%30%22%7%1
720
December1st to 15thNight
25%14%34%21%4
720
16th to endNight
24%16%37%18%2
768
Page generated at 2017-10-07 14:07:48. Version ac04

Copyright 2017 A. Danko


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