Millbrook
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Millbrook clear sky chart from 2005-11-05 to 2017-05-01.

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
33%
14415
15%
45707
8%
14382
40%
14382
18%
31773

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
15%
719
10%
2506
3%
716
23%
716
9%
1938
January16th to endNight
20%
768
12%
2514
5%
768
29%
768
10%
1940
February1st to 15thNight
15%
702
11%
2287
3%
701
25%
701
10%
1767
February16th to endNight
22%
631
15%
2015
4%
631
35%
631
14%
1449
March1st to 15thNight
22%
720
14%
1995
5%
720
30%
720
18%
1455
March16th to endNight
30%
768
21%
2106
9%
768
40%
768
25%
1403
April1st to 15thNight
28%
718
16%
1796
6%
718
33%
718
22%
1309
April16th to endNight
36%
597
20%
1677
8%
597
42%
597
27%
1107
May1st to 15thNight
44%
407
16%
1403
13%
407
50%
407
21%
926
May16th to endNight
50%
342
17%
1369
17%
342
59%
342
25%
760
June1st to 15thNight
43%
330
12%
1320
12%
330
54%
330
18%
836
June16th to endNight
53%
330
11%
1320
13%
330
59%
330
23%
761
July1st to 15thNight
61%
310
17%
1240
25%
310
65%
310
32%
629
July16th to endNight
58%
396
15%
1350
15%
370
62%
370
30%
760
August1st to 15thNight
61%
494
18%
1474
13%
491
64%
491
34%
881
August16th to endNight
59%
594
21%
1644
11%
594
63%
594
35%
1002
September1st to 15thNight
50%
660
20%
1650
10%
660
54%
660
32%
1106
September16th to endNight
52%
657
21%
1832
14%
657
56%
657
30%
1174
October1st to 15thNight
37%
660
17%
1980
12%
660
43%
660
21%
1377
October16th to endNight
23%
704
12%
2112
6%
704
31%
704
14%
1608
November1st to 15thNight
31%
700
18%
2389
15%
700
39%
700
18%
1616
November16th to endNight
22%
720
11%
2520
6%
720
30%
720
11%
1883
December1st to 15thNight
15%
720
8%
2520
2%
720
22%
720
9%
1952
December16th to endNight
13%
768
8%
2688
2%
768
21%
768
8%
2134

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
15%8%36%6%3445%6%34%
46055
Night
15%8%36%5%3445%6%35%
45882
Cloud CoverDay
15%8%36%5%35%45%7%34%
46065
Night
14%8%36%5%3445%6%35%
45887
TransparencyDay
48%7%12%19%10%1
45748
Night
48%7%11%20%11%1
45707
SeeingDay
18%9%28%24%13%5%
4833
Night
19%10%30%26%11%1
14419

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%13%5%10%7%33336%26%
1432
16th to endDay
12%14%6%11%8%445%46%22%
1707
February1st to 15thDay
12%14%6%12%8%4443423%
1575
16th to endDay
16%13%5%8%7%3344427%
1458
March1st to 15thDay
15%10%47%8%3445%5%30%
1953
16th to endDay
16%8%45%423345%39%
2118
April1st to 15thDay
20%9%36%5%33346%32%
2152
16th to endDay
18%7%25%433345%39%
2294
May1st to 15thDay
15%6%36%5%36%46%5%37%
2226
16th to endDay
13%5%25%435%45%7%42%
2394
June1st to 15thDay
17%6%37%5%345%5%9%31%
2310
16th to endDay
15%5%24435%46%9%37%
2310
July1st to 15thDay
9%424436%5%7%9%42%
2310
16th to endDay
9%436%7%35%6%6%9%37%
2408
August1st to 15thDay
9%5%26%6%35%5%6%7%40%
2145
16th to endDay
13%5%24435%5%6%9%39%
2195
September1st to 15thDay
16%5%25%426%447%39%
1980
16th to endDay
14%6%25%4345%47%42%
1797
October1st to 15thDay
21%6%36%5%34446%33%
1650
16th to endDay
23%11%47%6%2335%5%26%
1760
November1st to 15thDay
16%9%35%6%35%46%6%33%
1465
16th to endDay
16%12%48%7%35%46%6%25%
1440
December1st to 15thDay
17%14%6%8%7%35%35%423%
1440
16th to endDay
19%14%7%7%7%345%46%20%
1536
January1st to 15thNight
18%13%5%8%7%34345%24%
2506
16th to endNight
13%13%6%9%6%35%45%426%
2514
February1st to 15thNight
12%13%5%9%6%46%5%5%5%25%
2285
16th to endNight
13%11%47%7%345%46%31%
2015
March1st to 15thNight
17%9%47%6%34345%33%
1983
16th to endNight
14%6%35%435%345%44%
2106
April1st to 15thNight
19%7%36%434347%35%
1796
16th to endNight
13%6%35%33445%5%43%
1677
May1st to 15thNight
14%5%25%5%45%5%5%7%38%
1403
16th to endNight
11%41442437%7%48%
1367
June1st to 15thNight
14%5%35%5%245%6%8%37%
1320
16th to endNight
9%5%25%5%35%46%8%43%
1320
July1st to 15thNight
431442445%9%54%
1320
16th to endNight
8%3144245%5%10%48%
1450
August1st to 15thNight
8%4145%3436%8%49%
1485
16th to endNight
7%425%4235%5%7%50%
1644
September1st to 15thNight
14%5%245%2445%7%44%
1650
16th to endNight
13%5%25%333346%47%
1832
October1st to 15thNight
19%5%25%6%33446%37%
1980
16th to endNight
21%7%37%5%35%5%46%28%
2112
November1st to 15thNight
15%8%35%6%3445%7%36%
2389
16th to endNight
21%9%47%5%25%5%5%6%26%
2520
December1st to 15thNight
18%12%5%8%6%34447%23%
2520
16th to endNight
20%12%5%7%7%345%5%7%19%
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
16%12%5%10%6%34236%26%
1432
16th to endDay
12%13%6%11%8%45%446%22%
1707
February1st to 15thDay
12%15%6%12%8%35%43422%
1575
16th to endDay
16%12%6%9%7%2335%428%
1458
March1st to 15thDay
15%10%28%7%44446%29%
1964
16th to endDay
15%8%45%433345%40%
2117
April1st to 15thDay
19%9%46%5%33347%32%
2152
16th to endDay
18%7%35%42435%5%39%
2294
May1st to 15thDay
14%6%26%5%35%5%6%6%36%
2226
16th to endDay
12%5%25%435%45%7%41%
2394
June1st to 15thDay
17%6%26%6%35%46%8%32%
2310
16th to endDay
13%6%24425%5%5%9%37%
2310
July1st to 15thDay
9%423436%5%6%10%42%
2310
16th to endDay
9%435%6%45%6%6%8%37%
2408
August1st to 15thDay
9%5%36%6%345%6%8%40%
2145
16th to endDay
13%5%23435%5%6%10%39%
2195
September1st to 15thDay
15%6%335%25%45%7%40%
1980
16th to endDay
13%6%35%434447%43%
1797
October1st to 15thDay
19%7%36%5%35%445%34%
1650
16th to endDay
22%10%47%5%3435%5%26%
1760
November1st to 15thDay
14%10%36%5%45%46%6%33%
1465
16th to endDay
16%13%38%6%35%45%6%25%
1440
December1st to 15thDay
16%13%6%8%7%4435%5%23%
1440
16th to endDay
18%13%7%7%7%245%46%20%
1536
January1st to 15thNight
17%14%5%8%7%34445%24%
2506
16th to endNight
12%13%5%10%7%35%445%26%
2514
February1st to 15thNight
12%12%6%9%6%46%446%26%
2278
16th to endNight
12%11%47%7%34446%31%
2015
March1st to 15thNight
18%9%36%5%34345%33%
1995
16th to endNight
15%6%35%425%345%44%
2106
April1st to 15thNight
18%7%46%5%3435%6%35%
1796
16th to endNight
13%6%35%42445%6%43%
1677
May1st to 15thNight
14%5%15%6%35%5%6%7%38%
1403
16th to endNight
11%41342436%7%49%
1367
June1st to 15thNight
14%5%35%4245%5%9%37%
1320
16th to endNight
9%5%25%5%25%5%5%9%43%
1320
July1st to 15thNight
432342445%9%54%
1320
16th to endNight
7%424425%46%9%49%
1450
August1st to 15thNight
7%4145%3346%8%49%
1485
16th to endNight
7%425%4245%5%7%50%
1644
September1st to 15thNight
14%5%235%2345%6%45%
1650
16th to endNight
14%5%24423346%48%
1832
October1st to 15thNight
18%6%25%6%24446%37%
1980
16th to endNight
21%7%37%5%36%446%28%
2112
November1st to 15thNight
15%7%36%6%3445%7%35%
2389
16th to endNight
21%8%46%5%25%5%5%6%26%
2520
December1st to 15thNight
18%13%49%5%3445%7%23%
2520
16th to endNight
19%13%5%8%6%4445%7%19%
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
60%5%12%14%7%
1433
16th to endDay
63%5%11%11%7%
1707
February1st to 15thDay
64%5%9%14%4
1577
16th to endDay
58%6%8%14%10%
1458
March1st to 15thDay
55%6%13%16%7%
1964
16th to endDay
46%5%8%20%16%2
2118
April1st to 15thDay
53%49%17%13%1
2152
16th to endDay
45%5%9%22%15%1
2294
May1st to 15thDay
45%8%10%20%14%1
2226
16th to endDay
40%7%13%22%14%1
2398
June1st to 15thDay
47%8%13%20%9%
2310
16th to endDay
41%8%14%21%13%
2310
July1st to 15thDay
32%8%13%27%16%
2161
16th to endDay
41%9%13%23%10%1
2245
August1st to 15thDay
39%9%13%21%13%1
2132
16th to endDay
36%9%14%26%10%1
2195
September1st to 15thDay
42%8%12%26%10%
1980
16th to endDay
40%9%11%28%10%
1797
October1st to 15thDay
51%6%9%21%10%1
1650
16th to endDay
59%6%14%13%5%
1760
November1st to 15thDay
49%7%14%17%9%1
1465
16th to endDay
58%6%13%13%7%
1440
December1st to 15thDay
62%7%13%13%2
1440
16th to endDay
64%8%9%14%3
1536
January1st to 15thNight
62%6%10%13%6%1
2506
16th to endNight
59%7%7%16%7%
2514
February1st to 15thNight
59%7%9%16%6%
2287
16th to endNight
53%6%11%19%8%
2015
March1st to 15thNight
53%412%20%8%
1995
16th to endNight
42%49%22%17%2
2106
April1st to 15thNight
48%5%9%18%15%1
1796
16th to endNight
40%6%10%19%20%2
1677
May1st to 15thNight
43%8%10%18%15%2
1403
16th to endNight
33%7%11%26%17%2
1369
June1st to 15thNight
42%8%10%21%15%1
1320
16th to endNight
37%6%15%23%16%1
1320
July1st to 15thNight
25%8%12%28%23%1
1240
16th to endNight
31%7%13%28%16%2
1350
August1st to 15thNight
30%8%17%26%15%1
1474
16th to endNight
31%7%12%31%15%1
1644
September1st to 15thNight
37%7%13%28%12%
1650
16th to endNight
37%6%9%31%14%
1832
October1st to 15thNight
47%7%11%20%12%
1980
16th to endNight
55%7%12%15%8%
2112
November1st to 15thNight
46%7%13%18%12%1
2389
16th to endNight
55%8%13%15%6%
2520
December1st to 15thNight
60%7%13%14%3
2520
16th to endNight
63%7%11%12%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
18%23%35%13%8%1
60
16th to endDay
32%13%34%15%4
93
February1st to 15thDay
22%28%42%6%
90
16th to endDay
29%18%34%15%1
117
March1st to 15thDay
25%13%34%21%4
270
16th to endDay
23%9%35%22%5%3
288
April1st to 15thDay
22%11%37%18%8%1
270
16th to endDay
21%12%29%22%10%4
270
May1st to 15thDay
17%6%29%22%13%8%
229
16th to endDay
13%7%29%28%15%5%
267
June1st to 15thDay
17%8%27%29%14%2
255
16th to endDay
16%325%31%18%6%
255
July1st to 15thDay
12%316%33%23%9%
245
16th to endDay
10%228%30%18%9%
270
August1st to 15thDay
7%321%33%22%11%
253
16th to endDay
15%118%24%25%14%
268
September1st to 15thDay
13%5%21%21%23%13%
255
16th to endDay
17%6%22%25%17%9%
254
October1st to 15thDay
18%7%30%23%13%6%
255
16th to endDay
25%16%27%25%5%
272
November1st to 15thDay
16%8%28%35%8%1
113
16th to endDay
21%18%23%23%13%
60
December1st to 15thDay
13%25%43%10%6%1
60
16th to endDay
32%20%40%6%
64
January1st to 15thNight
25%18%34%15%5%
720
16th to endNight
22%13%34%24%5%
768
February1st to 15thNight
19%17%39%20%3
704
16th to endNight
18%16%37%22%5%
631
March1st to 15thNight
23%14%34%23%3
720
16th to endNight
18%11%33%24%10%1
768
April1st to 15thNight
22%12%32%26%5%
718
16th to endNight
17%9%33%27%11%1
597
May1st to 15thNight
16%5%27%32%14%2
407
16th to endNight
13%326%36%18%
343
June1st to 15thNight
14%5%28%36%14%
330
16th to endNight
10%322%43%19%
330
July1st to 15thNight
5%322%46%20%1
310
16th to endNight
8%25%39%24%2
396
August1st to 15thNight
9%117%41%25%3
494
16th to endNight
10%120%34%28%3
594
September1st to 15thNight
16%222%31%21%4
660
16th to endNight
15%6%21%27%24%4
657
October1st to 15thNight
22%7%27%25%15%1
660
16th to endNight
25%11%32%23%6%
704
November1st to 15thNight
19%10%31%24%11%2
700
16th to endNight
23%13%32%20%8%
720
December1st to 15thNight
26%15%35%17%4
720
16th to endNight
28%12%36%19%2
768
Page generated at 2017-05-02 08:43:31. Version ac04

Copyright 2017 A. Danko


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