Mabee Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Mabee Observatory clear sky chart from 2005-11-05 to 2017-12-02.

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
45%
16177
25%
47844
15%
16131
54%
16131
37%
26945

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
35%
900
28%
2327
12%
895
46%
895
39%
1373
January16th to endNight
37%
960
32%
2496
13%
960
49%
960
43%
1424
February1st to 15thNight
32%
837
21%
2245
8%
833
40%
833
30%
1438
February16th to endNight
32%
632
28%
1894
10%
632
46%
632
35%
1052
March1st to 15thNight
33%
579
24%
2019
13%
579
46%
579
30%
1113
March16th to endNight
31%
576
19%
2112
12%
576
41%
576
24%
1245
April1st to 15thNight
33%
539
21%
1916
13%
539
48%
539
27%
1065
April16th to endNight
33%
540
21%
1620
15%
540
44%
540
29%
991
May1st to 15thNight
37%
540
21%
1620
16%
540
46%
540
31%
980
May16th to endNight
51%
562
18%
1684
16%
561
56%
561
35%
992
June1st to 15thNight
52%
540
18%
1620
11%
540
59%
540
41%
862
June16th to endNight
59%
540
22%
1620
14%
540
66%
540
49%
804
July1st to 15thNight
71%
510
19%
1530
18%
510
73%
510
44%
817
July16th to endNight
78%
564
24%
1594
24%
531
80%
531
46%
828
August1st to 15thNight
75%
539
22%
1610
27%
536
77%
536
40%
893
August16th to endNight
69%
573
26%
1760
28%
573
72%
573
40%
955
September1st to 15thNight
57%
540
22%
1980
22%
540
64%
540
33%
1048
September16th to endNight
57%
537
32%
1980
29%
537
66%
537
38%
964
October1st to 15thNight
46%
630
30%
2070
22%
630
53%
630
33%
1154
October16th to endNight
46%
768
35%
2304
18%
768
58%
768
50%
1131
November1st to 15thNight
42%
926
29%
2446
11%
926
53%
926
46%
1341
November16th to endNight
40%
975
30%
2535
12%
975
52%
975
42%
1455
December1st to 15thNight
36%
910
25%
2366
10%
910
46%
910
35%
1447
December16th to endNight
36%
960
27%
2496
12%
960
46%
960
33%
1573

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
9%5%2442445%7%50%
48607
Night
8%42332345%7%54%
48040
Cloud CoverDay
9%5%2442445%7%50%
48605
Night
8%42332345%7%54%
48040
TransparencyDay
32%5%13%27%17%3
48305
Night
29%413%26%20%5%
47845
SeeingDay
10%6%25%33%20%3
6086
Night
11%7%32%36%12%
16178

By Month

Percentage Cloud Cover SW (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
7%5%1343335%5%55%
1611
16th to endDay
7%6%2432345%7%52%
1728
February1st to 15thDay
6%7%36%434447%48%
1627
16th to endDay
8%6%2431335%7%52%
1580
March1st to 15thDay
9%6%15%5%2435%8%46%
1941
16th to endDay
17%6%3332335%6%43%
2112
April1st to 15thDay
12%5%25%423446%48%
2028
16th to endDay
14%7%3442435%6%42%
2340
May1st to 15thDay
12%6%25%42345%5%45%
2331
16th to endDay
12%6%25%5%4445%7%41%
2430
June1st to 15thDay
7%32442445%9%51%
2340
16th to endDay
5%2133245%5%10%55%
2340
July1st to 15thDay
7%3244445%6%10%47%
2340
16th to endDay
5%213425%46%10%51%
2466
August1st to 15thDay
5%3245%35%6%6%9%47%
2340
16th to endDay
6%214325%45%8%53%
2439
September1st to 15thDay
9%42442445%7%49%
1980
16th to endDay
8%414414446%55%
1980
October1st to 15thDay
12%423312347%54%
1878
16th to endDay
7%42332233461%
1920
November1st to 15thDay
5%423423445%58%
1742
16th to endDay
9%413212235%62%
1755
December1st to 15thDay
12%7%24323336%49%
1631
16th to endDay
12%7%35%413446%46%
1728
January1st to 15thNight
7%5%24423445%55%
2327
16th to endNight
7%423313445%60%
2496
February1st to 15thNight
9%7%36%423445%48%
2235
16th to endNight
8%5%23422447%54%
1894
March1st to 15thNight
8%6%24424347%50%
2019
16th to endNight
16%6%24423346%46%
2112
April1st to 15thNight
11%42442445%7%49%
1916
16th to endNight
14%6%13424446%47%
1620
May1st to 15thNight
13%6%2332345%7%46%
1619
16th to endNight
8%4133335%6%10%47%
1683
June1st to 15thNight
5%31332346%10%54%
1620
16th to endNight
31132435%9%61%
1620
July1st to 15thNight
5%2133145%7%10%53%
1620
16th to endNight
4322345%7%12%53%
1702
August1st to 15thNight
3214435%5%6%8%52%
1620
16th to endNight
5%42342345%7%56%
1760
September1st to 15thNight
7%324433446%54%
1980
16th to endNight
6%41331336%7%57%
1980
October1st to 15thNight
12%5%14322345%54%
2070
16th to endNight
7%312212236%65%
2304
November1st to 15thNight
7%313222337%61%
2446
16th to endNight
10%41321334460%
2535
December1st to 15thNight
9%6%3441335%7%50%
2366
16th to endNight
11%6%34424348%47%
2496

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
7%5%23433346%55%
1611
16th to endDay
7%5%25%32345%7%52%
1728
February1st to 15thDay
6%7%35%424446%49%
1627
16th to endDay
8%6%2431345%7%52%
1580
March1st to 15thDay
9%6%25%5%2445%7%46%
1941
16th to endDay
17%6%2432335%6%43%
2110
April1st to 15thDay
12%5%25%323446%48%
2028
16th to endDay
14%7%34424446%42%
2340
May1st to 15thDay
13%6%244235%5%6%45%
2331
16th to endDay
12%6%25%6%3445%7%41%
2430
June1st to 15thDay
7%324434449%52%
2340
16th to endDay
5%234245%5%9%56%
2340
July1st to 15thDay
7%3145%35%5%5%10%47%
2340
16th to endDay
5%2144345%6%9%52%
2466
August1st to 15thDay
5%3145%35%5%6%10%47%
2340
16th to endDay
6%213425%5%5%8%53%
2439
September1st to 15thDay
8%425%415%45%7%49%
1980
16th to endDay
8%414324446%54%
1980
October1st to 15thDay
12%5%23213247%54%
1878
16th to endDay
7%42332323461%
1920
November1st to 15thDay
5%424423445%58%
1742
16th to endDay
9%413212235%62%
1755
December1st to 15thDay
12%6%24323437%49%
1631
16th to endDay
12%7%35%313447%46%
1728
January1st to 15thNight
7%5%24414445%55%
2327
16th to endNight
7%423313345%60%
2496
February1st to 15thNight
9%7%35%424445%48%
2235
16th to endNight
7%5%24323447%53%
1894
March1st to 15thNight
8%6%24433446%51%
2019
16th to endNight
16%6%24423346%46%
2112
April1st to 15thNight
10%5%23424447%49%
1916
16th to endNight
14%6%23333346%47%
1620
May1st to 15thNight
13%6%1332346%7%46%
1619
16th to endNight
8%4143235%7%10%48%
1683
June1st to 15thNight
5%21322447%9%54%
1620
16th to endNight
31132445%9%61%
1620
July1st to 15thNight
5%2133245%6%10%53%
1620
16th to endNight
5%2123235%7%12%52%
1702
August1st to 15thNight
3213445%5%7%9%52%
1620
16th to endNight
5%32442435%7%56%
1760
September1st to 15thNight
7%3245%23447%53%
1980
16th to endNight
6%42331335%7%57%
1980
October1st to 15thNight
12%5%1432334454%
2070
16th to endNight
7%312212246%65%
2304
November1st to 15thNight
7%323213247%61%
2446
16th to endNight
10%422212345%60%
2535
December1st to 15thNight
10%6%25%314347%50%
2366
16th to endNight
11%6%24423347%47%
2496

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
29%413%31%18%2
1612
16th to endDay
29%317%30%15%3
1728
February1st to 15thDay
35%7%15%25%12%3
1628
16th to endDay
31%413%28%18%3
1580
March1st to 15thDay
37%410%24%19%3
1941
16th to endDay
40%5%12%24%13%3
2112
April1st to 15thDay
36%5%13%26%15%2
2028
16th to endDay
41%5%11%26%12%1
2340
May1st to 15thDay
38%5%11%23%18%1
2331
16th to endDay
40%6%14%24%12%1
2434
June1st to 15thDay
29%6%16%25%18%4
2340
16th to endDay
23%5%14%28%21%5%
2340
July1st to 15thDay
30%6%14%29%16%2
2201
16th to endDay
25%6%14%31%19%3
2311
August1st to 15thDay
30%7%17%25%15%4
2326
16th to endDay
27%6%13%28%17%6%
2439
September1st to 15thDay
32%5%14%24%15%7%
1980
16th to endDay
28%5%10%31%19%4
1980
October1st to 15thDay
30%411%23%24%5%
1878
16th to endDay
26%49%28%24%6%
1920
November1st to 15thDay
26%311%25%24%7%
1742
16th to endDay
25%29%32%24%4
1755
December1st to 15thDay
36%314%30%14%
1631
16th to endDay
39%312%26%15%3
1728
January1st to 15thNight
29%311%29%22%3
2327
16th to endNight
26%312%29%22%4
2496
February1st to 15thNight
37%5%13%24%14%4
2245
16th to endNight
30%314%27%18%6%
1894
March1st to 15thNight
33%311%24%19%7%
2019
16th to endNight
39%412%25%15%3
2112
April1st to 15thNight
33%411%24%22%2
1916
16th to endNight
37%314%20%18%4
1620
May1st to 15thNight
35%5%15%23%17%2
1620
16th to endNight
31%6%22%24%13%2
1685
June1st to 15thNight
24%5%18%29%18%3
1620
16th to endNight
18%6%15%31%22%5%
1620
July1st to 15thNight
23%6%13%29%22%4
1530
16th to endNight
22%6%16%30%22%2
1594
August1st to 15thNight
24%8%16%29%15%5%
1610
16th to endNight
26%6%12%25%22%6%
1760
September1st to 15thNight
29%5%12%25%17%9%
1980
16th to endNight
24%5%11%26%26%5%
1980
October1st to 15thNight
32%48%21%24%8%
2070
16th to endNight
20%39%27%31%7%
2304
November1st to 15thNight
23%410%26%26%8%
2446
16th to endNight
27%39%29%24%5%
2535
December1st to 15thNight
33%313%29%17%1
2366
16th to endNight
36%414%25%15%5%
2496

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
17%7%36%30%5%2
90
16th to endDay
15%10%47%23%11
96
February1st to 15thDay
5%18%46%22%6%
90
16th to endDay
312%49%24%7%2
81
March1st to 15thDay
12%13%48%24%1
90
16th to endDay
19%12%38%23%5%
96
April1st to 15thDay
14%12%36%26%10%
147
16th to endDay
20%12%37%21%7%1
450
May1st to 15thDay
13%11%32%29%10%2
468
16th to endDay
15%7%31%28%13%2
517
June1st to 15thDay
8%425%37%21%2
495
16th to endDay
5%323%43%21%2
495
July1st to 15thDay
8%215%44%25%4
475
16th to endDay
5%9%39%36%7%
515
August1st to 15thDay
6%110%39%38%4
493
16th to endDay
5%115%36%34%6%
479
September1st to 15thDay
5%212%42%34%3
135
16th to endDay
11%128%27%20%10%
135
October1st to 15thDay
11%6%33%26%13%8%
135
16th to endDay
5%10%36%27%15%4
144
November1st to 15thDay
11%5%31%34%13%2
135
16th to endDay
19%17%30%22%8%1
135
December1st to 15thDay
13%11%39%25%7%2
94
16th to endDay
20%10%39%23%5%
96
January1st to 15thNight
9%11%38%33%6%
900
16th to endNight
10%8%40%34%6%
960
February1st to 15thNight
14%9%38%32%4
837
16th to endNight
11%12%40%31%4
632
March1st to 15thNight
11%10%41%30%5%
579
16th to endNight
18%9%38%27%5%
576
April1st to 15thNight
13%10%39%28%7%
539
16th to endNight
18%9%36%28%7%
540
May1st to 15thNight
16%6%34%31%10%1
540
16th to endNight
11%429%36%15%2
563
June1st to 15thNight
6%430%38%19%
540
16th to endNight
3131%48%14%
540
July1st to 15thNight
6%13%52%24%1
510
16th to endNight
6%10%48%32%1
564
August1st to 15thNight
5%110%53%28%
539
16th to endNight
6%114%39%34%2
573
September1st to 15thNight
8%223%38%23%2
540
16th to endNight
8%326%38%21%1
537
October1st to 15thNight
16%6%27%30%17%1
630
16th to endNight
8%6%36%36%11%
768
November1st to 15thNight
8%7%36%33%12%
926
16th to endNight
13%9%34%33%9%
975
December1st to 15thNight
14%9%35%35%5%
910
16th to endNight
12%8%36%35%5%
960
Page generated at 2017-12-03 10:16:41. Version ac04

Copyright 2017 A. Danko


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