Allan & Kay Poage Memorial Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Allan & Kay Poage Memorial Observatory clear sky chart from 2005-11-05 to 2017-09-10.

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
48%
15560
29%
46841
19%
15516
58%
15516
38%
25612

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
37%
897
30%
2327
12%
895
48%
895
39%
1364
January16th to endNight
36%
960
33%
2496
12%
960
49%
960
39%
1459
February1st to 15thNight
33%
767
27%
2174
11%
763
44%
763
32%
1289
February16th to endNight
24%
611
30%
1873
10%
611
41%
611
32%
1046
March1st to 15thNight
32%
540
27%
1980
15%
540
47%
540
26%
1127
March16th to endNight
32%
576
25%
2112
14%
576
47%
576
28%
1161
April1st to 15thNight
31%
539
26%
1971
14%
539
50%
539
31%
1017
April16th to endNight
34%
540
27%
1719
16%
540
50%
540
34%
958
May1st to 15thNight
35%
540
23%
1620
14%
540
49%
540
31%
965
May16th to endNight
47%
563
26%
1684
21%
561
58%
561
39%
944
June1st to 15thNight
67%
540
25%
1620
24%
540
75%
540
53%
780
June16th to endNight
69%
540
26%
1620
27%
540
73%
540
46%
830
July1st to 15thNight
73%
510
25%
1530
26%
510
78%
510
48%
784
July16th to endNight
85%
564
31%
1594
36%
531
88%
531
57%
750
August1st to 15thNight
88%
539
37%
1610
44%
536
88%
536
61%
731
August16th to endNight
77%
573
28%
1883
32%
573
80%
573
40%
995
September1st to 15thNight
70%
525
23%
1925
27%
525
72%
525
34%
1007
September16th to endNight
72%
492
34%
1815
34%
492
77%
492
41%
878
October1st to 15thNight
57%
571
35%
1891
27%
571
66%
571
43%
947
October16th to endNight
51%
704
37%
2112
21%
704
63%
704
47%
1057
November1st to 15thNight
50%
709
32%
2109
18%
709
61%
709
42%
1134
November16th to endNight
40%
900
33%
2340
16%
900
51%
900
38%
1383
December1st to 15thNight
35%
900
31%
2340
12%
900
46%
900
35%
1442
December16th to endNight
36%
960
28%
2496
12%
960
45%
960
34%
1564

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
11%424324447%50%
47778
Night
10%313313347%56%
47038
TransparencyDay
33%49%23%21%7%
47478
Night
28%39%23%24%10%
46843
SeeingDay
10%6%19%30%25%7%
5559
Night
11%7%28%34%16%1
15563

By Month

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
14%6%13312225%55%
1611
16th to endDay
15%413213336%54%
1728
February1st to 15thDay
15%6%25%31322452%
1697
16th to endDay
17%5%13321235%53%
1599
March1st to 15thDay
19%5%24423435%45%
1980
16th to endDay
14%6%34333335%48%
2110
April1st to 15thDay
12%425%32335%7%48%
1977
16th to endDay
14%5%2332445%7%46%
2238
May1st to 15thDay
15%5%34424446%42%
2331
16th to endDay
11%5%345%35%5%6%8%40%
2430
June1st to 15thDay
5%3145%245%5%7%53%
2340
16th to endDay
7%3145%2445%8%51%
2340
July1st to 15thDay
6%324435%5%6%9%47%
2340
16th to endDay
3313436%6%6%11%50%
2466
August1st to 15thDay
31133245%7%8%59%
2340
16th to endDay
6%4145%36%7%7%10%41%
2313
September1st to 15thDay
11%31342446%6%49%
1922
16th to endDay
8%314323447%54%
1815
October1st to 15thDay
11%313224346%56%
1727
16th to endDay
10%3321222466%
1760
November1st to 15thDay
10%324313436%56%
1746
16th to endDay
13%42331223458%
1620
December1st to 15thDay
18%5%2431233449%
1620
16th to endDay
17%5%23312345%48%
1728
January1st to 15thNight
13%413312235%58%
2327
16th to endNight
13%42221324458%
2496
February1st to 15thNight
14%42331322456%
2165
16th to endNight
14%423212135%56%
1873
March1st to 15thNight
16%5%1321335%6%49%
1980
16th to endNight
11%414314346%54%
2112
April1st to 15thNight
9%323314448%54%
1971
16th to endNight
12%423223346%54%
1719
May1st to 15thNight
10%42441445%7%49%
1619
16th to endNight
7%414325%26%9%51%
1683
June1st to 15thNight
421132235%9%64%
1620
16th to endNight
321342445%10%57%
1620
July1st to 15thNight
421232445%11%56%
1620
16th to endNight
21222346%11%61%
1702
August1st to 15thNight
121222349%68%
1620
16th to endNight
5%3143245%6%11%50%
1883
September1st to 15thNight
11%41332345%7%53%
1925
16th to endNight
7%312323448%58%
1815
October1st to 15thNight
9%313312245%61%
1891
16th to endNight
9%31211323368%
2112
November1st to 15thNight
7%41432323462%
2109
16th to endNight
12%423212345%56%
2340
December1st to 15thNight
14%424313336%51%
2340
16th to endNight
14%5%24322346%50%
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
33%26%20%28%8%
1612
16th to endDay
33%25%19%29%9%
1728
February1st to 15thDay
37%2422%24%9%
1698
16th to endDay
36%26%21%21%12%
1599
March1st to 15thDay
42%26%17%21%9%
1980
16th to endDay
39%39%19%21%6%
2112
April1st to 15thDay
35%49%22%17%10%
1977
16th to endDay
37%48%19%24%6%
2238
May1st to 15thDay
41%48%17%20%7%
2331
16th to endDay
40%5%12%20%17%2
2434
June1st to 15thDay
28%5%13%29%19%3
2340
16th to endDay
30%411%28%20%4
2340
July1st to 15thDay
29%6%14%32%15%1
2201
16th to endDay
25%7%18%32%15%
2311
August1st to 15thDay
20%5%13%33%23%2
2326
16th to endDay
32%8%16%27%12%2
2313
September1st to 15thDay
32%411%25%18%7%
1922
16th to endDay
28%36%24%26%9%
1815
October1st to 15thDay
29%39%22%19%15%
1727
16th to endDay
24%26%19%31%16%
1760
November1st to 15thDay
30%29%24%22%9%
1746
16th to endDay
31%2418%31%12%
1620
December1st to 15thDay
39%25%21%25%5%
1620
16th to endDay
38%26%22%22%7%
1728
January1st to 15thNight
31%17%17%29%12%
2327
16th to endNight
30%25%19%28%13%
2496
February1st to 15thNight
34%36%17%24%14%
2175
16th to endNight
31%38%20%22%13%
1873
March1st to 15thNight
36%48%17%21%12%
1980
16th to endNight
32%410%20%25%6%
2112
April1st to 15thNight
28%410%23%18%14%
1971
16th to endNight
31%39%21%23%10%
1719
May1st to 15thNight
33%5%11%19%20%9%
1620
16th to endNight
28%417%26%18%4
1685
June1st to 15thNight
17%413%35%23%6%
1620
16th to endNight
22%413%28%25%6%
1620
July1st to 15thNight
21%414%37%18%4
1530
16th to endNight
14%5%19%37%20%2
1594
August1st to 15thNight
14%312%33%30%6%
1610
16th to endNight
25%5%14%31%18%4
1883
September1st to 15thNight
29%411%23%21%9%
1925
16th to endNight
24%47%23%27%12%
1815
October1st to 15thNight
24%39%24%21%17%
1891
16th to endNight
22%2418%29%23%
2112
November1st to 15thNight
27%26%24%25%13%
2109
16th to endNight
30%35%14%31%14%
2340
December1st to 15thNight
35%28%20%23%9%
2340
16th to endNight
36%37%22%21%9%
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
16%12%40%22%7%1
90
16th to endDay
11%11%47%18%9%1
96
February1st to 15thDay
10%20%44%21%4
90
16th to endDay
19%17%41%17%3
81
March1st to 15thDay
28%17%30%18%31
90
16th to endDay
10%17%37%22%10%1
96
April1st to 15thDay
12%17%30%27%12%
96
16th to endDay
18%14%31%26%8%
348
May1st to 15thDay
14%12%37%25%7%2
468
16th to endDay
15%6%32%26%16%2
517
June1st to 15thDay
6%214%43%24%8%
495
16th to endDay
6%213%37%28%10%
495
July1st to 15thDay
7%12%36%33%9%
475
16th to endDay
21325%50%15%
515
August1st to 15thDay
4335%44%12%
493
16th to endDay
11%17%32%34%12%
353
September1st to 15thDay
1224%50%21%
119
16th to endDay
6%222%45%23%
90
October1st to 15thDay
1220%38%31%6%
90
16th to endDay
15%6%11%43%20%2
96
November1st to 15thDay
25%325%30%13%2
90
16th to endDay
24%15%32%20%43
90
December1st to 15thDay
30%6%25%18%12%6%
90
16th to endDay
15%18%39%20%5%
96
January1st to 15thNight
15%10%32%32%8%
900
16th to endNight
15%11%34%31%6%
960
February1st to 15thNight
17%11%34%30%5%
767
16th to endNight
15%15%42%23%3
611
March1st to 15thNight
19%9%34%31%5%
540
16th to endNight
11%12%42%27%6%
576
April1st to 15thNight
9%13%42%28%5%
539
16th to endNight
14%8%39%28%8%
540
May1st to 15thNight
10%6%42%30%7%1
540
16th to endNight
8%5%32%36%16%1
563
June1st to 15thNight
5%120%46%24%2
540
16th to endNight
3117%45%28%3
540
July1st to 15thNight
414%45%31%3
510
16th to endNight
26%46%38%4
564
August1st to 15thNight
2447%39%6%
539
16th to endNight
7%6%38%39%6%
573
September1st to 15thNight
12%18%38%35%4
525
16th to endNight
8%111%36%37%4
492
October1st to 15thNight
11%125%31%26%3
571
16th to endNight
11%6%27%34%18%1
704
November1st to 15thNight
9%5%30%35%16%1
709
16th to endNight
15%9%30%31%11%1
900
December1st to 15thNight
17%8%35%31%7%
900
16th to endNight
18%9%32%32%7%
960
Page generated at 2017-09-11 18:35:29. Version ac04

Copyright 2017 A. Danko


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