Mill Pond Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Mill Pond Observatory clear sky chart from 2005-11-05 to

2017-09-12
.

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
27%
14634
13%
46792
7%
14602
34%
14602
16%
33538

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
13%
720
6%
2506
2%
716
18%
716
7%
2040
January16th to endNight
18%
768
10%
2679
5%
768
26%
768
10%
2034
February1st to 15thNight
15%
704
10%
2287
3%
701
23%
701
9%
1793
February16th to endNight
19%
631
14%
1913
6%
631
30%
631
12%
1442
March1st to 15thNight
16%
720
13%
2142
6%
720
26%
720
13%
1607
March16th to endNight
29%
768
20%
2004
9%
768
36%
768
21%
1416
April1st to 15thNight
22%
718
16%
1796
5%
718
28%
718
19%
1333
April16th to endNight
25%
653
17%
1733
5%
653
33%
653
20%
1227
May1st to 15thNight
28%
365
17%
1445
12%
365
40%
365
15%
959
May16th to endNight
32%
375
13%
1497
10%
374
44%
374
16%
959
June1st to 15thNight
31%
360
9%
1440
7%
360
39%
360
13%
990
June16th to endNight
38%
360
9%
1440
12%
360
44%
360
19%
909
July1st to 15thNight
50%
340
14%
1360
19%
340
57%
340
25%
764
July16th to endNight
48%
376
13%
1418
16%
354
53%
354
25%
826
August1st to 15thNight
48%
395
15%
1466
12%
393
55%
393
23%
890
August16th to endNight
47%
745
20%
1891
10%
745
52%
745
35%
1221
September1st to 15thNight
42%
707
15%
1768
7%
707
45%
707
27%
1235
September16th to endNight
43%
657
21%
1786
13%
657
48%
657
30%
1156
October1st to 15thNight
30%
660
18%
1974
10%
660
40%
660
20%
1364
October16th to endNight
23%
704
10%
2230
6%
704
30%
704
12%
1689
November1st to 15thNight
25%
700
17%
2289
9%
700
36%
700
15%
1624
November16th to endNight
20%
720
11%
2520
7%
720
28%
720
10%
1879
December1st to 15thNight
15%
720
7%
2520
2%
720
21%
720
7%
2012
December16th to endNight
10%
768
9%
2688
2%
768
18%
768
7%
2169

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
18%8%36%5%34446%32%
47879
Night
18%9%46%5%34446%31%
46961
Cloud CoverDay
18%8%36%5%34446%32%
47888
Night
18%9%46%5%34446%31%
46967
TransparencyDay
52%5%11%19%10%1
47566
Night
53%411%19%9%1
46792
SeeingDay
23%14%29%20%9%3
5520
Night
24%13%28%23%9%
14634

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
22%15%6%9%7%3334420%
1432
16th to endDay
14%16%5%8%6%35%45%5%23%
1545
February1st to 15thDay
15%14%410%7%35%445%22%
1575
16th to endDay
18%13%6%8%5%45%335%25%
1560
March1st to 15thDay
17%13%5%8%7%3432427%
1806
16th to endDay
19%8%36%423435%38%
2220
April1st to 15thDay
23%10%46%5%23325%33%
2152
16th to endDay
20%7%36%5%23445%35%
2232
May1st to 15thDay
21%7%35%5%34446%32%
2511
16th to endDay
19%6%25%5%34448%34%
2618
June1st to 15thDay
24%6%26%5%24447%30%
2520
16th to endDay
18%6%25%5%35%5%6%9%31%
2520
July1st to 15thDay
13%436%435%46%8%38%
2520
16th to endDay
12%5%25%6%36%5%7%9%35%
2654
August1st to 15thDay
12%6%26%6%345%6%8%35%
2481
16th to endDay
10%425%4346%5%8%43%
2298
September1st to 15thDay
16%5%25%42445%6%41%
2112
16th to endDay
15%6%24323247%45%
1843
October1st to 15thDay
20%8%25%5%24446%34%
1656
16th to endDay
25%11%37%6%3343425%
1641
November1st to 15thDay
16%8%36%6%45%447%31%
1567
16th to endDay
22%11%5%7%6%33335%26%
1440
December1st to 15thDay
25%13%48%6%35%5%4418%
1440
16th to endDay
25%16%5%8%5%2442320%
1536
January1st to 15thNight
19%15%6%10%7%3444418%
2506
16th to endNight
14%16%5%8%7%45%345%25%
2679
February1st to 15thNight
14%12%6%11%7%5%6%45%421%
2285
16th to endNight
16%13%5%8%5%35%5%5%427%
1913
March1st to 15thNight
19%11%5%7%6%3434428%
2129
16th to endNight
16%10%36%42333439%
2004
April1st to 15thNight
25%8%35%5%23346%32%
1796
16th to endNight
20%7%36%5%33346%36%
1733
May1st to 15thNight
22%8%35%324445%35%
1445
16th to endNight
18%6%25%5%25%448%36%
1495
June1st to 15thNight
24%6%25%5%345%5%7%30%
1440
16th to endNight
16%435%5%35%46%9%35%
1440
July1st to 15thNight
9%4245%26%5%7%10%41%
1440
16th to endNight
10%5%235%345%5%8%44%
1514
August1st to 15thNight
10%5%35%5%25%46%10%39%
1476
16th to endNight
11%414434448%47%
1891
September1st to 15thNight
15%5%35%6%34347%40%
1768
16th to endNight
17%423433345%47%
1786
October1st to 15thNight
20%7%344345%46%35%
1974
16th to endNight
25%9%37%5%33345%27%
2230
November1st to 15thNight
20%8%36%5%34446%32%
2289
16th to endNight
21%10%48%5%3445%5%25%
2520
December1st to 15thNight
22%16%5%8%6%34445%20%
2520
16th to endNight
25%16%5%6%6%3433420%
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
22%14%6%9%6%3434420%
1432
16th to endDay
14%17%5%7%6%45%5%5%5%23%
1545
February1st to 15thDay
16%14%5%9%8%35%45%5%22%
1575
16th to endDay
18%14%5%7%6%35%33426%
1560
March1st to 15thDay
17%13%5%9%8%3432327%
1816
16th to endDay
19%8%35%5%24335%38%
2219
April1st to 15thDay
23%9%46%5%2333432%
2152
16th to endDay
20%8%36%423445%35%
2232
May1st to 15thDay
21%7%35%5%34346%33%
2511
16th to endDay
18%6%25%5%3445%7%34%
2618
June1st to 15thDay
23%6%25%5%3445%7%30%
2520
16th to endDay
18%5%25%5%45%5%6%8%31%
2520
July1st to 15thDay
13%5%35%435%46%8%38%
2520
16th to endDay
12%5%25%5%36%5%7%9%35%
2654
August1st to 15thDay
12%5%25%6%45%5%6%8%36%
2481
16th to endDay
10%425%5%346%5%8%44%
2298
September1st to 15thDay
16%5%25%43345%6%41%
2112
16th to endDay
15%6%25%323346%45%
1843
October1st to 15thDay
20%8%25%5%34446%34%
1656
16th to endDay
25%10%38%5%2434425%
1641
November1st to 15thDay
15%8%37%5%45%5%47%32%
1567
16th to endDay
21%11%6%6%6%33345%25%
1440
December1st to 15thDay
24%14%48%6%45%435%17%
1440
16th to endDay
25%16%47%6%3443320%
1536
January1st to 15thNight
19%15%6%10%7%4444418%
2506
16th to endNight
13%16%5%9%6%35%44425%
2679
February1st to 15thNight
14%12%6%11%7%5%5%45%5%21%
2278
16th to endNight
16%12%5%8%5%25%5%5%427%
1913
March1st to 15thNight
20%11%47%7%3344428%
2142
16th to endNight
16%10%36%43334439%
2004
April1st to 15thNight
25%8%35%5%24345%32%
1796
16th to endNight
21%6%36%5%33345%36%
1733
May1st to 15thNight
22%7%35%433445%35%
1445
16th to endNight
18%6%25%4245%47%36%
1495
June1st to 15thNight
23%6%345%345%5%6%30%
1440
16th to endNight
15%5%15%5%35%5%6%9%35%
1440
July1st to 15thNight
10%4145%26%5%7%10%41%
1440
16th to endNight
11%414435%5%6%7%43%
1514
August1st to 15thNight
9%5%36%5%3446%10%39%
1476
16th to endNight
12%414424448%46%
1891
September1st to 15thNight
15%5%36%5%34447%40%
1768
16th to endNight
17%414334335%46%
1786
October1st to 15thNight
20%7%25%33445%6%36%
1974
16th to endNight
25%9%37%5%34445%27%
2230
November1st to 15thNight
20%8%36%5%34446%32%
2289
16th to endNight
20%11%48%5%34445%25%
2520
December1st to 15thNight
22%15%5%8%6%3444420%
2520
16th to endNight
25%16%47%6%3433420%
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
68%38%12%5%
1433
16th to endDay
61%412%13%7%
1545
February1st to 15thDay
64%48%18%2
1577
16th to endDay
61%310%13%9%
1560
March1st to 15thDay
62%311%13%7%1
1816
16th to endDay
49%38%17%15%4
2220
April1st to 15thDay
55%35%19%12%2
2152
16th to endDay
50%47%18%14%4
2232
May1st to 15thDay
51%48%19%13%1
2511
16th to endDay
48%5%11%20%12%1
2622
June1st to 15thDay
53%411%20%9%
2520
16th to endDay
49%6%13%20%10%
2520
July1st to 15thDay
40%7%13%27%11%
2371
16th to endDay
42%7%16%24%9%
2487
August1st to 15thDay
43%7%16%22%8%
2467
16th to endDay
37%6%16%27%12%
2298
September1st to 15thDay
41%5%12%26%12%
2112
16th to endDay
40%411%32%10%
1843
October1st to 15thDay
50%410%22%10%
1656
16th to endDay
62%5%10%14%6%
1641
November1st to 15thDay
52%5%13%18%9%
1567
16th to endDay
61%410%15%7%
1440
December1st to 15thDay
69%6%10%11%2
1440
16th to endDay
69%49%10%5%
1536
January1st to 15thNight
68%5%10%10%4
2506
16th to endNight
61%311%15%7%
2679
February1st to 15thNight
64%49%16%4
2287
16th to endNight
58%49%17%10%
1913
March1st to 15thNight
59%39%18%8%1
2142
16th to endNight
48%38%19%14%4
2004
April1st to 15thNight
54%37%19%14%1
1796
16th to endNight
49%47%18%16%3
1733
May1st to 15thNight
50%37%17%15%4
1445
16th to endNight
45%6%10%22%13%1
1497
June1st to 15thNight
52%6%12%18%9%
1440
16th to endNight
44%6%14%20%15%
1440
July1st to 15thNight
33%7%13%29%15%
1360
16th to endNight
36%6%16%24%14%
1418
August1st to 15thNight
39%6%19%23%11%
1466
16th to endNight
35%5%14%31%12%
1891
September1st to 15thNight
44%5%9%26%13%
1768
16th to endNight
39%410%32%12%
1786
October1st to 15thNight
48%410%24%11%
1974
16th to endNight
59%5%12%17%5%
2230
November1st to 15thNight
53%413%17%9%1
2289
16th to endNight
60%312%17%5%
2520
December1st to 15thNight
67%411%14%2
2520
16th to endNight
68%310%11%5%
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%25%20%21%8%
60
16th to endDay
35%21%24%15%3
65
February1st to 15thDay
36%30%27%5%
90
16th to endDay
32%14%33%17%2
219
March1st to 15thDay
25%22%29%17%4
270
16th to endDay
26%17%29%15%7%2
288
April1st to 15thDay
31%20%29%11%7%
270
16th to endDay
23%17%28%17%10%2
270
May1st to 15thDay
26%15%31%17%7%3
288
16th to endDay
19%20%33%15%9%1
331
June1st to 15thDay
30%12%29%19%5%1
315
16th to endDay
20%10%33%22%10%2
315
July1st to 15thDay
16%8%32%24%14%2
305
16th to endDay
15%7%28%31%12%3
326
August1st to 15thDay
15%6%28%31%13%5%
313
16th to endDay
12%6%30%25%15%9%
332
September1st to 15thDay
18%9%24%23%16%9%
299
16th to endDay
18%12%25%20%13%9%
254
October1st to 15thDay
25%13%23%20%13%2
255
16th to endDay
32%17%24%18%6%
250
November1st to 15thDay
19%17%29%23%8%1
221
16th to endDay
31%16%30%21%
60
December1st to 15thDay
25%23%36%13%1
60
16th to endDay
37%34%25%3
64
January1st to 15thNight
28%18%33%16%3
720
16th to endNight
23%18%31%20%5%
768
February1st to 15thNight
21%20%33%20%3
704
16th to endNight
24%16%33%22%3
631
March1st to 15thNight
26%18%32%17%3
720
16th to endNight
21%16%26%28%6%
768
April1st to 15thNight
27%16%28%23%3
718
16th to endNight
26%14%28%20%9%
653
May1st to 15thNight
26%11%28%23%8%2
365
16th to endNight
20%9%33%26%9%
375
June1st to 15thNight
24%10%25%30%8%
360
16th to endNight
15%8%30%30%13%1
360
July1st to 15thNight
11%6%27%36%17%
340
16th to endNight
14%228%38%15%1
376
August1st to 15thNight
14%422%34%22%1
395
16th to endNight
13%6%26%31%19%2
745
September1st to 15thNight
19%5%25%33%13%1
707
16th to endNight
20%7%25%24%19%1
657
October1st to 15thNight
24%10%29%23%12%
660
16th to endNight
31%14%24%22%6%
704
November1st to 15thNight
25%13%29%21%9%
700
16th to endNight
26%18%25%19%9%
720
December1st to 15thNight
32%17%26%18%3
720
16th to endNight
36%18%27%12%4
768
Page generated at 2017-09-13 07:39:03. Version ac04

Copyright 2017 A. Danko


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