Halloran Summit
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Halloran Summit clear sky chart from 2005-11-05 to 2017-10-31.

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
69%
16168
37%
47462
29%
16130
77%
16130
56%
22052

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
61%
717
32%
2327
26%
716
71%
716
45%
1124
January16th to endNight
57%
768
35%
2421
28%
768
69%
768
43%
1208
February1st to 15thNight
62%
697
35%
2112
29%
697
72%
697
48%
1040
February16th to endNight
57%
632
33%
1895
31%
632
66%
632
43%
979
March1st to 15thNight
58%
720
33%
2123
27%
720
70%
720
49%
1050
March16th to endNight
61%
768
35%
2100
24%
768
70%
768
51%
1064
April1st to 15thNight
53%
719
34%
1799
15%
719
64%
719
52%
940
April16th to endNight
60%
665
41%
1745
19%
665
72%
665
63%
808
May1st to 15thNight
63%
540
38%
1619
24%
539
71%
539
65%
680
May16th to endNight
64%
561
36%
1685
24%
561
72%
561
63%
698
June1st to 15thNight
71%
540
32%
1620
25%
540
76%
540
67%
665
June16th to endNight
78%
540
37%
1620
31%
540
83%
540
82%
606
July1st to 15thNight
87%
510
30%
1530
26%
510
89%
510
64%
666
July16th to endNight
82%
564
32%
1593
28%
531
84%
531
50%
791
August1st to 15thNight
87%
631
38%
1704
27%
628
89%
628
71%
760
August16th to endNight
88%
764
42%
1910
28%
764
89%
764
72%
907
September1st to 15thNight
86%
720
37%
1902
28%
720
89%
720
64%
928
September16th to endNight
81%
716
49%
1980
39%
716
88%
716
79%
817
October1st to 15thNight
76%
720
42%
1980
34%
720
83%
720
66%
901
October16th to endNight
75%
768
45%
2346
40%
768
84%
768
63%
995
November1st to 15thNight
71%
700
38%
2275
36%
700
79%
700
59%
959
November16th to endNight
70%
720
39%
2340
37%
720
77%
720
55%
1018
December1st to 15thNight
62%
720
34%
2340
29%
720
71%
720
43%
1153
December16th to endNight
57%
768
34%
2496
29%
768
67%
768
38%
1295

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
2212212335%71%
48289
Night
2212212335%71%
47657
TransparencyDay
15%35%14%26%34%
47984
Night
15%25%15%27%33%
47463
SeeingDay
410%25%38%17%3
5894
Night
35%16%34%31%8%
16180

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
4313212347%66%
1611
16th to endDay
5%413322346%61%
1803
February1st to 15thDay
4212324346%64%
1751
16th to endDay
5%423323336%59%
1579
March1st to 15thDay
231212348%68%
1836
16th to endDay
2212323447%66%
2121
April1st to 15thDay
3213312345%68%
2149
16th to endDay
21212225%76%
2214
May1st to 15thDay
11121223478%
2331
16th to endDay
122212235%75%
2429
June1st to 15thDay
1111225%81%
2340
16th to endDay
1112286%
2340
July1st to 15thDay
3212223335%68%
2340
16th to endDay
322332445%7%59%
2467
August1st to 15thDay
211212435%74%
2244
16th to endDay
211212345%72%
2292
September1st to 15thDay
112213335%75%
2058
16th to endDay
111212384%
1980
October1st to 15thDay
221221223475%
1980
16th to endDay
11121223477%
1872
November1st to 15thDay
22112223474%
1584
16th to endDay
2112222336%70%
1620
December1st to 15thDay
35%24323347%59%
1620
16th to endDay
7%323323347%58%
1728
January1st to 15thNight
321341335%6%63%
2327
16th to endNight
5%413222345%63%
2421
February1st to 15thNight
4413212336%65%
2101
16th to endNight
5%313313446%61%
1895
March1st to 15thNight
2212214446%64%
2123
16th to endNight
2212223347%65%
2100
April1st to 15thNight
2213313225%70%
1799
16th to endNight
11211335%77%
1745
May1st to 15thNight
11212336%76%
1619
16th to endNight
11212225%79%
1684
June1st to 15thNight
111223480%
1620
16th to endNight
1111289%
1620
July1st to 15thNight
112222347%71%
1620
16th to endNight
421332435%6%61%
1701
August1st to 15thNight
1111233477%
1713
16th to endNight
112112335%76%
1910
September1st to 15thNight
12313245%73%
1902
16th to endNight
111112286%
1980
October1st to 15thNight
21121233377%
1980
16th to endNight
11221223378%
2346
November1st to 15thNight
1312212235%74%
2275
16th to endNight
3212213236%71%
2340
December1st to 15thNight
431342435%7%60%
2340
16th to endNight
6%413323336%59%
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
18%26%23%34%14%
1612
16th to endDay
24%27%20%29%16%
1803
February1st to 15thDay
19%37%18%29%21%
1751
16th to endDay
26%46%17%29%15%
1579
March1st to 15thDay
15%37%19%33%21%
1836
16th to endDay
17%37%22%32%17%
2121
April1st to 15thDay
18%3419%32%22%
2149
16th to endDay
12%2419%30%31%
2214
May1st to 15thDay
10%2316%29%36%
2331
16th to endDay
13%2412%32%35%
2432
June1st to 15thDay
8%139%19%58%
2340
16th to endDay
7%12312%72%
2340
July1st to 15thDay
16%348%17%50%
2201
16th to endDay
20%47%11%20%35%
2312
August1st to 15thDay
11%347%23%48%
2229
16th to endDay
14%4410%22%44%
2292
September1st to 15thDay
12%35%10%21%45%
2058
16th to endDay
7%228%27%51%
1980
October1st to 15thDay
14%239%29%40%
1980
16th to endDay
11%2313%29%39%
1872
November1st to 15thDay
14%15%16%36%25%
1584
16th to endDay
15%37%17%31%25%
1620
December1st to 15thDay
24%39%20%25%15%
1620
16th to endDay
26%49%24%22%12%
1728
January1st to 15thNight
20%45%18%32%18%
2327
16th to endNight
23%37%21%21%23%
2421
February1st to 15thNight
21%26%19%25%23%
2112
16th to endNight
23%36%18%31%16%
1895
March1st to 15thNight
19%47%18%29%22%
2123
16th to endNight
18%37%21%30%18%
2100
April1st to 15thNight
18%15%19%33%21%
1799
16th to endNight
10%2420%29%32%
1745
May1st to 15thNight
9%25%17%33%31%
1620
16th to endNight
9%35%16%33%32%
1685
June1st to 15thNight
9%238%20%55%
1620
16th to endNight
5%16%15%70%
1620
July1st to 15thNight
11%3410%17%51%
1530
16th to endNight
19%45%11%22%35%
1593
August1st to 15thNight
9%3411%22%49%
1704
16th to endNight
10%2410%25%47%
1910
September1st to 15thNight
13%35%10%23%43%
1902
16th to endNight
6%128%28%53%
1980
October1st to 15thNight
12%1311%30%40%
1980
16th to endNight
11%2410%25%45%
2346
November1st to 15thNight
15%1315%35%28%
2275
16th to endNight
16%25%16%27%31%
2340
December1st to 15thNight
22%37%18%31%15%
2340
16th to endNight
26%39%21%24%14%
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%15%33%32%2
90
16th to endDay
8%13%28%32%14%2
171
February1st to 15thDay
6%10%32%35%12%2
266
16th to endDay
7%20%33%22%14%
238
March1st to 15thDay
417%27%33%17%1
270
16th to endDay
418%32%31%11%1
288
April1st to 15thDay
7%23%32%23%8%3
269
16th to endDay
428%29%23%12%1
270
May1st to 15thDay
313%31%34%15%1
288
16th to endDay
211%32%37%12%3
330
June1st to 15thDay
29%33%37%15%1
315
16th to endDay
224%45%20%6%
315
July1st to 15thDay
3116%52%19%6%
305
16th to endDay
38%55%25%7%
327
August1st to 15thDay
3118%45%24%6%
315
16th to endDay
4115%44%25%8%
332
September1st to 15thDay
1221%53%17%3
315
16th to endDay
16%22%44%21%2
315
October1st to 15thDay
210%29%40%14%1
315
16th to endDay
28%16%36%30%5%
194
November1st to 15thDay
112%14%36%22%13%
90
16th to endDay
5%12%31%33%17%
90
December1st to 15thDay
110%27%38%21%1
90
16th to endDay
10%12%28%32%15%1
96
January1st to 15thNight
45%21%37%22%8%
720
16th to endNight
8%7%20%34%22%6%
768
February1st to 15thNight
5%5%20%37%23%6%
704
16th to endNight
8%8%22%36%18%6%
632
March1st to 15thNight
36%25%33%23%7%
720
16th to endNight
210%20%36%23%6%
768
April1st to 15thNight
313%24%30%21%5%
719
16th to endNight
112%24%34%22%5%
665
May1st to 15thNight
7%26%32%30%3
540
16th to endNight
10%22%32%30%3
563
June1st to 15thNight
15%20%40%29%2
540
16th to endNight
116%40%37%2
540
July1st to 15thNight
27%32%51%5%
510
16th to endNight
5%1430%55%3
564
August1st to 15thNight
16%33%49%8%
631
16th to endNight
2424%51%16%
764
September1st to 15thNight
16%29%48%13%
720
16th to endNight
1212%29%36%17%
716
October1st to 15thNight
2413%41%30%6%
720
16th to endNight
1415%30%33%15%
768
November1st to 15thNight
2317%34%34%8%
700
16th to endNight
4416%34%30%10%
720
December1st to 15thNight
6%5%18%35%27%6%
720
16th to endNight
7%10%19%34%23%5%
768
Page generated at 2017-11-01 14:23:37. Version ac04

Copyright 2017 A. Danko


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