Helds Island Access
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Helds Island Access clear sky chart from 2005-11-05 to 2018-08-29.

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
36%
17117
21%
50633
12%
17069
45%
17069
27%
31834

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
19%
975
18%
2633
6%
970
29%
970
21%
1795
January16th to endNight
20%
1040
22%
2704
6%
1040
31%
1040
24%
1828
February1st to 15thNight
18%
952
15%
2480
3%
948
25%
948
19%
1775
February16th to endNight
17%
683
20%
2049
5%
683
29%
683
20%
1357
March1st to 15thNight
19%
647
19%
2207
8%
647
31%
647
19%
1433
March16th to endNight
19%
624
13%
2244
7%
624
28%
624
14%
1597
April1st to 15thNight
25%
584
21%
1947
10%
584
41%
584
23%
1181
April16th to endNight
30%
579
21%
1928
12%
579
44%
579
25%
1195
May1st to 15thNight
37%
585
18%
1800
12%
584
45%
584
26%
1153
May16th to endNight
44%
611
18%
1625
10%
609
50%
609
29%
1068
June1st to 15thNight
57%
585
20%
1560
14%
585
61%
585
42%
917
June16th to endNight
56%
585
22%
1560
12%
585
63%
585
44%
903
July1st to 15thNight
68%
555
20%
1480
16%
555
69%
555
41%
885
July16th to endNight
71%
612
22%
1704
21%
579
74%
579
42%
937
August1st to 15thNight
72%
575
24%
1740
27%
572
75%
572
40%
962
August16th to endNight
70%
615
23%
2050
28%
615
72%
615
37%
1105
September1st to 15thNight
60%
540
26%
1800
27%
540
64%
540
32%
1024
September16th to endNight
58%
626
32%
1951
23%
626
66%
626
34%
1101
October1st to 15thNight
44%
720
28%
2160
19%
720
51%
720
34%
1252
October16th to endNight
30%
768
27%
2304
14%
768
43%
768
30%
1350
November1st to 15thNight
32%
760
27%
2429
14%
760
47%
760
28%
1389
November16th to endNight
26%
881
24%
2636
11%
881
38%
881
25%
1640
December1st to 15thNight
22%
975
17%
2730
5%
975
32%
975
20%
1868
December16th to endNight
16%
1040
17%
2912
5%
1040
27%
1040
17%
2119

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
13%6%25%5%2445%7%42%
51618
Night
13%6%24423346%46%
50819
TransparencyDay
40%6%12%23%14%2
51307
Night
38%5%11%24%17%2
50635
SeeingDay
16%9%28%26%15%3
7145
Night
17%11%30%26%12%1
17117

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
12%9%46%413446%40%
1633
16th to endDay
11%10%35%5%24447%40%
1872
February1st to 15thDay
14%11%47%5%34336%35%
1713
16th to endDay
14%10%5%6%424346%37%
1710
March1st to 15thDay
15%9%45%425%346%37%
2093
16th to endDay
21%10%47%5%33345%30%
2329
April1st to 15thDay
16%7%25%5%34445%42%
2331
16th to endDay
19%7%26%5%24346%36%
2307
May1st to 15thDay
17%5%36%5%2445%7%36%
2475
16th to endDay
13%5%36%5%345%5%7%39%
2841
June1st to 15thDay
8%4245%35%5%6%8%44%
2730
16th to endDay
7%213435%5%8%10%46%
2730
July1st to 15thDay
9%313436%5%6%9%45%
2730
16th to endDay
6%3145%446%7%9%45%
2706
August1st to 15thDay
8%3146%25%6%7%9%43%
2463
16th to endDay
8%4246%3446%8%45%
2448
September1st to 15thDay
14%41343445%7%46%
2160
16th to endDay
9%5%245%2445%7%48%
1994
October1st to 15thDay
15%5%35%412335%48%
1800
16th to endDay
14%413423235%53%
1920
November1st to 15thDay
15%5%24412446%49%
1756
16th to endDay
16%7%35%313336%45%
1653
December1st to 15thDay
16%9%36%423437%39%
1560
16th to endDay
15%12%46%323336%36%
1664
January1st to 15thNight
14%6%36%6%33445%41%
2633
16th to endNight
12%9%35%424346%42%
2704
February1st to 15thNight
13%10%5%6%5%34446%36%
2470
16th to endNight
16%10%35%323235%42%
2049
March1st to 15thNight
16%8%345%24235%42%
2207
16th to endNight
20%9%45%5%245%5%6%30%
2244
April1st to 15thNight
14%6%24323346%46%
1947
16th to endNight
17%6%25%422347%44%
1928
May1st to 15thNight
14%5%2442435%8%44%
1800
16th to endNight
11%5%25%434449%45%
1624
June1st to 15thNight
7%31343345%9%52%
1560
16th to endNight
5%41332437%10%52%
1560
July1st to 15thNight
9%213324448%54%
1560
16th to endNight
43133245%5%10%53%
1811
August1st to 15thNight
5%31443346%8%55%
1750
16th to endNight
6%31442445%8%54%
2050
September1st to 15thNight
13%31342335%5%51%
1800
16th to endNight
7%424423347%54%
1951
October1st to 15thNight
11%414323346%53%
2160
16th to endNight
15%5%13322345%52%
2304
November1st to 15thNight
12%5%24322346%52%
2429
16th to endNight
15%7%2431334448%
2636
December1st to 15thNight
17%8%35%5%3345%6%37%
2730
16th to endNight
18%11%5%6%42333434%
2912

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
44%5%10%22%15%1
1634
16th to endDay
42%5%15%24%11%1
1872
February1st to 15thDay
50%5%11%21%9%
1714
16th to endDay
48%5%10%22%12%2
1710
March1st to 15thDay
47%5%9%20%13%2
2093
16th to endDay
56%5%10%18%8%
2331
April1st to 15thDay
42%5%10%22%16%1
2331
16th to endDay
49%5%10%20%12%1
2307
May1st to 15thDay
46%6%13%22%11%
2475
16th to endDay
42%8%13%19%13%2
2845
June1st to 15thDay
35%7%13%25%16%1
2730
16th to endDay
30%7%16%27%14%3
2730
July1st to 15thDay
33%8%14%27%11%3
2581
16th to endDay
31%9%16%28%12%1
2550
August1st to 15thDay
34%9%13%26%15%1
2449
16th to endDay
35%8%13%20%17%4
2448
September1st to 15thDay
36%6%9%23%20%3
2160
16th to endDay
34%6%8%29%17%2
1994
October1st to 15thDay
38%38%23%20%5%
1800
16th to endDay
34%39%28%20%3
1920
November1st to 15thDay
35%312%22%20%5%
1756
16th to endDay
41%39%27%16%
1653
December1st to 15thDay
46%313%23%11%
1560
16th to endDay
50%412%19%10%2
1664
January1st to 15thNight
44%411%22%15%1
2633
16th to endNight
42%5%12%24%14%
2704
February1st to 15thNight
49%410%20%13%1
2480
16th to endNight
45%311%21%15%1
2049
March1st to 15thNight
46%410%21%15%3
2207
16th to endNight
53%6%10%20%8%
2244
April1st to 15thNight
38%410%25%17%3
1947
16th to endNight
41%49%27%15%1
1928
May1st to 15thNight
38%7%13%22%16%
1801
16th to endNight
37%7%16%19%15%2
1626
June1st to 15thNight
27%5%15%28%20%2
1560
16th to endNight
25%6%15%28%19%4
1560
July1st to 15thNight
28%6%13%29%17%4
1480
16th to endNight
24%7%17%31%18%1
1704
August1st to 15thNight
25%7%13%30%21%2
1740
16th to endNight
26%7%13%24%22%5%
2050
September1st to 15thNight
33%5%9%22%23%5%
1800
16th to endNight
29%6%9%27%24%3
1951
October1st to 15thNight
31%5%10%24%22%6%
2160
16th to endNight
34%39%26%20%5%
2304
November1st to 15thNight
33%410%25%18%7%
2429
16th to endNight
39%39%27%18%1
2636
December1st to 15thNight
46%413%21%13%
2730
16th to endNight
53%410%18%10%2
2912

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
33%19%37%8%1
135
16th to endDay
13%30%38%15%
144
February1st to 15thDay
26%22%37%11%1
135
16th to endDay
36%20%26%13%2
120
March1st to 15thDay
28%24%37%8%
135
16th to endDay
35%20%31%10%1
187
April1st to 15thDay
23%15%36%18%6%
330
16th to endDay
25%13%30%21%8%
319
May1st to 15thDay
17%15%34%21%9%1
455
16th to endDay
16%9%33%25%10%4
597
June1st to 15thDay
8%430%34%17%4
570
16th to endDay
9%6%34%33%13%2
570
July1st to 15thDay
12%220%33%23%8%
550
16th to endDay
7%220%33%30%5%
595
August1st to 15thDay
10%116%36%28%5%
526
16th to endDay
10%124%33%23%7%
384
September1st to 15thDay
13%5%15%29%27%9%
315
16th to endDay
6%6%25%32%20%8%
250
October1st to 15thDay
24%9%30%23%10%1
135
16th to endDay
20%11%37%26%3
144
November1st to 15thDay
15%8%39%20%12%4
135
16th to endDay
30%18%28%17%4
135
December1st to 15thDay
21%23%34%12%5%2
135
16th to endDay
25%25%40%8%
144
January1st to 15thNight
21%19%36%17%4
975
16th to endNight
19%19%37%20%2
1040
February1st to 15thNight
21%19%37%19%1
952
16th to endNight
25%17%37%18%1
683
March1st to 15thNight
23%15%37%20%3
647
16th to endNight
25%11%40%17%5%
624
April1st to 15thNight
18%19%35%21%5%
584
16th to endNight
21%8%36%26%7%
579
May1st to 15thNight
16%7%34%30%10%
585
16th to endNight
15%430%29%18%2
611
June1st to 15thNight
8%225%37%24%1
585
16th to endNight
7%228%41%18%2
585
July1st to 15thNight
10%113%40%28%6%
555
16th to endNight
5%16%41%33%1
612
August1st to 15thNight
6%12%40%37%1
575
16th to endNight
7%116%38%32%4
615
September1st to 15thNight
15%215%35%26%5%
540
16th to endNight
10%5%19%31%28%4
626
October1st to 15thNight
14%6%30%25%18%3
720
16th to endNight
18%14%34%23%9%
768
November1st to 15thNight
16%16%32%25%9%
760
16th to endNight
21%15%34%21%6%
881
December1st to 15thNight
24%17%33%18%5%
975
16th to endNight
27%16%37%17%1
1040
Page generated at 2018-08-30 04:34:24. Version ac04

Copyright 2018 A. Danko


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