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 2017-12-04.

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%
15083
15%
47871
9%
15050
40%
15050
19%
33157

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
14%
702
11%
2287
3%
701
24%
701
10%
1767
February16th to endNight
21%
631
15%
2015
4%
631
34%
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
34%
718
22%
1309
April16th to endNight
35%
597
20%
1677
8%
597
42%
597
27%
1107
May1st to 15thNight
43%
441
15%
1521
12%
441
49%
441
19%
1016
May16th to endNight
47%
374
17%
1497
16%
374
57%
374
24%
848
June1st to 15thNight
45%
360
12%
1440
11%
360
54%
360
19%
899
June16th to endNight
52%
360
11%
1440
14%
360
57%
360
22%
844
July1st to 15thNight
60%
340
16%
1360
23%
340
65%
340
31%
703
July16th to endNight
59%
429
16%
1467
17%
403
63%
403
30%
832
August1st to 15thNight
63%
539
17%
1609
13%
536
66%
536
34%
961
August16th to endNight
59%
648
22%
1794
11%
648
64%
648
36%
1082
September1st to 15thNight
51%
720
20%
1800
10%
720
55%
720
33%
1193
September16th to endNight
53%
717
23%
1998
16%
717
57%
717
31%
1264
October1st to 15thNight
38%
720
16%
2160
12%
720
44%
720
21%
1493
October16th to endNight
24%
768
14%
2304
8%
768
33%
768
15%
1724
November1st to 15thNight
31%
760
17%
2593
14%
760
39%
760
18%
1771
November16th to endNight
22%
780
11%
2730
5%
780
30%
780
11%
2030
December1st to 15thNight
15%
736
8%
2574
2%
736
21%
736
9%
1995
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%7%34%
48622
Night
14%8%36%5%3445%6%35%
48046
Cloud CoverDay
15%8%36%5%35%45%7%34%
48632
Night
14%8%36%5%3445%6%36%
48051
TransparencyDay
48%7%12%20%10%1
48315
Night
47%7%11%20%11%1
47871
SeeingDay
18%9%28%24%13%5%
5632
Night
19%9%30%26%12%1
15087

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
16%6%36%5%36%46%5%35%
2427
16th to endDay
13%5%25%435%45%7%40%
2618
June1st to 15thDay
18%5%36%5%345%5%8%33%
2520
16th to endDay
15%5%25%436%46%9%36%
2520
July1st to 15thDay
9%4245%35%5%6%9%42%
2520
16th to endDay
9%436%7%36%6%6%9%36%
2599
August1st to 15thDay
9%5%26%6%35%5%6%8%39%
2340
16th to endDay
12%5%24435%5%6%9%39%
2395
September1st to 15thDay
15%5%25%425%45%7%41%
2160
16th to endDay
13%5%25%4345%47%44%
1960
October1st to 15thDay
21%6%36%6%34445%33%
1800
16th to endDay
22%10%47%6%3435%5%27%
1920
November1st to 15thDay
16%9%35%6%35%46%6%32%
1590
16th to endDay
16%12%48%6%3445%6%26%
1560
December1st to 15thDay
16%14%6%8%7%3435%5%23%
1468
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
15%5%25%5%45%5%5%7%37%
1521
16th to endNight
11%42442436%7%47%
1495
June1st to 15thNight
12%5%35%5%245%6%8%39%
1440
16th to endNight
10%5%25%5%35%46%8%42%
1440
July1st to 15thNight
5%31442445%9%53%
1440
16th to endNight
8%3144245%5%10%48%
1567
August1st to 15thNight
7%4145%3446%9%49%
1620
16th to endNight
7%4244235%5%7%51%
1794
September1st to 15thNight
13%5%245%2445%6%46%
1800
16th to endNight
12%5%25%333346%48%
1998
October1st to 15thNight
19%5%25%6%33446%37%
2160
16th to endNight
21%7%37%5%35%5%46%29%
2304
November1st to 15thNight
16%8%35%5%2445%7%35%
2593
16th to endNight
20%9%47%5%25%5%5%6%26%
2730
December1st to 15thNight
18%12%5%8%6%345%47%23%
2574
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
16%6%26%5%35%5%6%6%34%
2427
16th to endDay
13%5%25%435%5%5%7%40%
2618
June1st to 15thDay
17%6%26%5%2446%8%33%
2520
16th to endDay
14%6%24435%5%5%9%37%
2520
July1st to 15thDay
9%433436%5%6%10%41%
2520
16th to endDay
9%435%6%45%6%6%9%36%
2599
August1st to 15thDay
9%5%35%6%345%6%8%40%
2340
16th to endDay
12%5%24435%5%6%9%40%
2395
September1st to 15thDay
14%5%245%25%45%7%41%
2160
16th to endDay
13%5%25%434446%44%
1960
October1st to 15thDay
20%7%36%5%35%445%33%
1800
16th to endDay
22%10%47%5%2445%6%26%
1920
November1st to 15thDay
15%10%36%6%45%46%6%32%
1590
16th to endDay
16%12%38%6%45%5%5%6%26%
1560
December1st to 15thDay
16%13%6%8%7%4445%5%22%
1468
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
15%5%25%6%35%5%6%7%37%
1521
16th to endNight
12%41442435%7%47%
1495
June1st to 15thNight
13%5%35%4245%5%9%39%
1440
16th to endNight
10%5%25%5%25%5%5%9%42%
1440
July1st to 15thNight
5%42442445%9%53%
1440
16th to endNight
7%325%425%46%9%48%
1567
August1st to 15thNight
7%4145%3346%9%49%
1620
16th to endNight
7%4244245%5%7%51%
1794
September1st to 15thNight
13%4234235%5%6%47%
1800
16th to endNight
13%434423346%49%
1998
October1st to 15thNight
18%6%25%6%24446%38%
2160
16th to endNight
20%7%37%5%36%446%30%
2304
November1st to 15thNight
16%8%35%5%3445%7%35%
2593
16th to endNight
20%8%47%5%25%5%5%6%27%
2730
December1st to 15thNight
18%13%49%6%3445%7%23%
2574
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
47%7%10%19%14%1
2427
16th to endDay
41%7%13%22%13%1
2622
June1st to 15thDay
46%8%12%22%10%
2520
16th to endDay
42%8%14%20%12%
2520
July1st to 15thDay
33%8%13%26%16%
2371
16th to endDay
41%9%13%23%9%1
2436
August1st to 15thDay
39%10%13%21%13%1
2327
16th to endDay
36%9%14%26%11%1
2395
September1st to 15thDay
40%8%12%26%11%
2160
16th to endDay
38%9%11%29%11%
1960
October1st to 15thDay
52%6%9%21%9%1
1800
16th to endDay
57%6%15%14%5%
1920
November1st to 15thDay
50%7%14%17%9%1
1590
16th to endDay
57%7%14%13%7%
1560
December1st to 15thDay
62%7%13%13%2
1468
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
44%8%10%18%15%2
1521
16th to endNight
35%6%11%27%16%2
1497
June1st to 15thNight
41%7%11%22%15%1
1440
16th to endNight
37%6%14%23%15%1
1440
July1st to 15thNight
26%8%12%28%22%1
1360
16th to endNight
31%7%13%28%17%2
1467
August1st to 15thNight
30%8%18%27%14%1
1609
16th to endNight
30%7%12%31%16%1
1794
September1st to 15thNight
35%7%13%27%13%1
1800
16th to endNight
35%6%9%31%15%
1998
October1st to 15thNight
46%7%11%20%13%
2160
16th to endNight
54%7%12%16%8%
2304
November1st to 15thNight
47%7%13%18%12%1
2593
16th to endNight
55%8%13%15%6%
2730
December1st to 15thNight
60%7%13%13%3
2574
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
24%9%26%22%11%7%
288
16th to endDay
14%7%33%25%13%4
331
June1st to 15thDay
18%7%27%30%13%2
315
16th to endDay
18%5%26%28%15%5%
315
July1st to 15thDay
12%418%33%22%8%
305
16th to endDay
10%227%31%19%8%
326
August1st to 15thDay
7%223%32%21%12%
313
16th to endDay
14%320%25%23%13%
332
September1st to 15thDay
12%5%22%21%23%13%
315
16th to endDay
14%7%20%21%21%14%
314
October1st to 15thDay
20%7%28%22%13%6%
315
16th to endDay
25%18%25%24%6%
336
November1st to 15thDay
20%12%27%29%9%1
148
16th to endDay
20%22%30%17%10%
90
December1st to 15thDay
17%22%40%11%5%1
67
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
17%6%26%32%14%2
441
16th to endNight
14%427%35%17%
375
June1st to 15thNight
13%5%28%36%15%
360
16th to endNight
11%323%43%18%
360
July1st to 15thNight
5%322%45%20%1
340
16th to endNight
8%24%39%25%2
429
August1st to 15thNight
9%117%41%26%3
539
16th to endNight
10%120%34%28%3
648
September1st to 15thNight
16%221%32%21%4
720
16th to endNight
14%5%20%26%25%6%
717
October1st to 15thNight
22%7%26%25%15%2
720
16th to endNight
24%11%31%24%6%
768
November1st to 15thNight
20%10%30%24%11%1
760
16th to endNight
23%14%32%20%8%
780
December1st to 15thNight
26%15%34%18%4
736
16th to endNight
28%12%36%19%2
768
Page generated at 2017-12-05 10:19:01. Version ac04

Copyright 2017 A. Danko


Millbrook Clear Sky Chart |Charts Home