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 2018-01-12.

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
27%
15120
13%
48366
7%
15088
34%
15088
16%
34628

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%
765
6%
2662
2%
761
19%
761
7%
2171
January16th to endNight
17%
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
32%
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
49%
376
13%
1418
16%
354
54%
354
25%
826
August1st to 15thNight
48%
395
15%
1466
12%
393
56%
393
23%
890
August16th to endNight
48%
745
20%
1891
10%
745
52%
745
35%
1221
September1st to 15thNight
43%
720
16%
1800
7%
720
45%
720
28%
1253
September16th to endNight
46%
717
23%
1949
15%
717
51%
717
31%
1239
October1st to 15thNight
31%
720
18%
2154
10%
720
41%
720
21%
1469
October16th to endNight
23%
768
11%
2433
6%
768
31%
768
13%
1830
November1st to 15thNight
24%
760
16%
2485
9%
760
35%
760
15%
1757
November16th to endNight
20%
780
11%
2730
7%
780
28%
780
10%
2035
December1st to 15thNight
15%
780
8%
2730
2%
780
22%
780
7%
2177
December16th to endNight
10%
832
9%
2912
3%
832
19%
832
7%
2327

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%
48983
Night
18%9%46%5%34446%31%
48535
Cloud CoverDay
18%8%36%5%34446%32%
48992
Night
18%9%36%5%34446%31%
48541
TransparencyDay
52%5%11%20%10%1
48670
Night
53%411%19%9%1
48366
SeeingDay
23%14%28%20%9%3
5867
Night
24%13%28%23%9%
15120

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%10%6%3334420%
1520
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%42%
2160
16th to endDay
14%5%24323247%47%
2010
October1st to 15thDay
20%8%25%5%24446%35%
1806
16th to endDay
24%11%37%5%33445%26%
1790
November1st to 15thDay
16%8%36%6%45%5%47%31%
1701
16th to endDay
22%11%5%7%6%33335%26%
1560
December1st to 15thDay
24%13%48%6%35%5%4418%
1560
16th to endDay
25%16%5%8%5%2442420%
1664
January1st to 15thNight
19%16%6%10%7%3444418%
2662
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%
1800
16th to endNight
16%423433346%47%
1949
October1st to 15thNight
20%7%34324446%37%
2154
16th to endNight
24%9%37%5%34445%28%
2433
November1st to 15thNight
21%8%36%424436%33%
2485
16th to endNight
21%11%48%5%3435%5%25%
2730
December1st to 15thNight
21%16%5%8%6%3444420%
2730
16th to endNight
24%15%5%7%6%3443421%
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
22%15%6%10%6%3334419%
1520
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%42%
2160
16th to endDay
13%6%25%323346%47%
2010
October1st to 15thDay
20%8%25%5%34446%35%
1806
16th to endDay
24%10%38%5%24345%26%
1790
November1st to 15thDay
16%8%37%5%45%5%46%31%
1701
16th to endDay
21%10%5%7%6%33346%25%
1560
December1st to 15thDay
23%14%48%7%45%435%18%
1560
16th to endDay
25%16%47%5%3443420%
1664
January1st to 15thNight
18%16%6%10%7%4444418%
2662
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%
1800
16th to endNight
16%414334336%47%
1949
October1st to 15thNight
19%7%25%33445%6%37%
2154
16th to endNight
24%9%36%5%34445%28%
2433
November1st to 15thNight
21%8%35%5%34436%33%
2485
16th to endNight
20%11%48%5%34445%25%
2730
December1st to 15thNight
21%15%5%8%6%3444420%
2730
16th to endNight
25%15%47%6%3433420%
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
68%48%12%5%
1521
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
40%5%12%27%12%
2160
16th to endDay
37%412%33%11%
2010
October1st to 15thDay
50%410%23%10%
1806
16th to endDay
60%5%11%15%6%
1790
November1st to 15thDay
52%5%13%18%9%
1701
16th to endDay
60%5%10%15%7%
1560
December1st to 15thDay
68%6%9%11%3
1560
16th to endDay
68%48%11%5%
1664
January1st to 15thNight
68%5%10%10%4
2662
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
43%5%9%27%12%
1800
16th to endNight
37%410%33%13%
1949
October1st to 15thNight
46%5%10%25%11%
2154
16th to endNight
58%5%12%17%5%
2433
November1st to 15thNight
53%413%18%8%1
2485
16th to endNight
60%312%17%5%
2730
December1st to 15thNight
67%410%14%3
2730
16th to endNight
67%39%12%6%
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
25%18%29%20%6%
82
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
17%8%24%22%17%9%
315
16th to endDay
15%12%21%22%18%9%
314
October1st to 15thDay
25%13%24%20%13%2
315
16th to endDay
31%17%25%18%6%
303
November1st to 15thDay
21%17%29%21%8%1
265
16th to endDay
27%26%28%16%
90
December1st to 15thDay
23%24%35%14%2
90
16th to endDay
36%35%19%8%
96
January1st to 15thNight
27%18%33%16%3
765
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%2
720
16th to endNight
19%7%23%24%21%2
717
October1st to 15thNight
23%9%29%23%13%
720
16th to endNight
30%15%24%22%6%
768
November1st to 15thNight
26%13%27%21%9%
760
16th to endNight
27%18%26%18%9%
780
December1st to 15thNight
32%18%27%17%3
780
16th to endNight
34%19%27%13%4
832
Page generated at 2018-01-12 22:01:34. Version ac04

Copyright 2018 A. Danko


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