Port Hilford
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Port Hilford clear sky chart from 2005-11-05 to 2017-09-22.

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
22%
15282
11%
46915
5%
15238
29%
15238
12%
35310

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
14%
749
10%
2506
2%
746
24%
746
10%
1875
January16th to endNight
12%
785
10%
2601
1%
785
23%
785
10%
1923
February1st to 15thNight
10%
704
7%
2286
2%
701
17%
701
7%
1754
February16th to endNight
13%
631
8%
1976
3%
631
19%
631
9%
1546
March1st to 15thNight
17%
720
12%
2061
4%
720
24%
720
11%
1617
March16th to endNight
19%
717
13%
2061
6%
717
27%
717
13%
1549
April1st to 15thNight
21%
539
12%
1796
8%
539
28%
539
11%
1341
April16th to endNight
27%
540
12%
1712
7%
540
33%
540
14%
1263
May1st to 15thNight
24%
540
10%
1446
5%
540
28%
540
12%
1151
May16th to endNight
27%
561
10%
1496
4%
560
31%
560
15%
1155
June1st to 15thNight
25%
540
5%
1440
3%
540
26%
540
12%
1184
June16th to endNight
29%
540
5%
1440
3%
540
30%
540
12%
1156
July1st to 15thNight
37%
510
5%
1360
3%
510
38%
510
15%
1046
July16th to endNight
27%
565
6%
1419
5%
532
30%
532
11%
1167
August1st to 15thNight
38%
539
10%
1561
8%
535
40%
535
14%
1184
August16th to endNight
42%
573
14%
1842
9%
573
48%
573
18%
1254
September1st to 15thNight
37%
540
14%
1800
11%
540
43%
540
18%
1234
September16th to endNight
34%
585
19%
1875
13%
585
42%
585
20%
1239
October1st to 15thNight
28%
660
17%
1980
7%
660
36%
660
19%
1346
October16th to endNight
18%
714
11%
2167
4%
714
24%
714
13%
1629
November1st to 15thNight
25%
730
11%
2362
5%
730
31%
730
14%
1742
November16th to endNight
16%
750
10%
2520
3%
750
24%
750
10%
1872
December1st to 15thNight
12%
750
10%
2520
1%
750
23%
750
8%
1944
December16th to endNight
10%
800
7%
2688
1%
800
17%
800
7%
2139

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
23%9%36%5%3445%7%27%
47975
Night
23%9%35%424446%29%
47087
TransparencyDay
56%7%12%16%7%
47665
Night
56%6%12%16%7%
46915
SeeingDay
27%16%23%22%8%1
7693
Night
25%22%23%20%7%
15283

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
18%11%46%425%5%5%8%27%
1432
16th to endDay
17%10%46%5%3445%9%27%
1623
February1st to 15thDay
18%11%47%6%26%5%46%26%
1575
16th to endDay
14%12%5%7%7%36%45%6%26%
1496
March1st to 15thDay
20%9%5%8%5%24446%27%
1885
16th to endDay
17%11%47%5%345%5%5%27%
2163
April1st to 15thDay
25%9%35%424446%27%
2153
16th to endDay
27%10%34423445%29%
2247
May1st to 15thDay
29%10%46%42433424%
2506
16th to endDay
26%11%45%5%23346%24%
2618
June1st to 15thDay
32%9%36%5%24446%21%
2520
16th to endDay
30%9%35%5%34446%22%
2520
July1st to 15thDay
25%7%343345%5%9%26%
2520
16th to endDay
29%9%36%435%5%47%19%
2653
August1st to 15thDay
23%8%25%5%2445%8%28%
2386
16th to endDay
18%7%3442445%9%35%
2360
September1st to 15thDay
22%6%35%43245%6%33%
2160
16th to endDay
18%5%2444445%8%36%
1894
October1st to 15thDay
20%7%36%44445%6%32%
1650
16th to endDay
23%7%26%6%45%45%6%26%
1703
November1st to 15thDay
25%8%36%5%24445%28%
1495
16th to endDay
21%9%35%5%25%5%5%7%27%
1440
December1st to 15thDay
23%12%47%424447%23%
1440
16th to endDay
24%11%5%7%5%34445%22%
1536
January1st to 15thNight
19%10%35%5%25%46%7%28%
2506
16th to endNight
19%10%36%5%2445%7%29%
2601
February1st to 15thNight
19%11%5%7%5%44446%26%
2285
16th to endNight
15%12%6%8%6%35%446%25%
1976
March1st to 15thNight
21%10%47%5%35%347%26%
2049
16th to endNight
21%9%5%5%6%34436%30%
2061
April1st to 15thNight
28%10%35%423336%27%
1796
16th to endNight
27%8%35%424446%29%
1712
May1st to 15thNight
34%8%35%424335%24%
1446
16th to endNight
25%9%36%324447%27%
1494
June1st to 15thNight
32%10%36%423336%21%
1440
16th to endNight
32%9%36%323346%23%
1440
July1st to 15thNight
23%9%36%4245%5%8%25%
1440
16th to endNight
29%11%46%32445%6%19%
1515
August1st to 15thNight
24%8%25%5%2445%5%30%
1572
16th to endNight
20%6%25%324348%37%
1842
September1st to 15thNight
22%6%34434346%37%
1800
16th to endNight
21%7%34423245%41%
1875
October1st to 15thNight
22%5%24425%35%6%37%
1980
16th to endNight
24%7%25%5%345%5%6%29%
2167
November1st to 15thNight
24%9%24434446%30%
2362
16th to endNight
23%8%36%424446%30%
2520
December1st to 15thNight
26%10%45%424446%26%
2520
16th to endNight
26%11%45%5%34447%23%
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
54%9%13%17%5%
1433
16th to endDay
53%8%12%16%8%
1623
February1st to 15thDay
59%7%12%12%7%
1578
16th to endDay
57%6%10%15%8%1
1496
March1st to 15thDay
56%6%10%16%8%1
1896
16th to endDay
55%6%11%16%7%1
2163
April1st to 15thDay
55%7%8%15%11%1
2153
16th to endDay
56%6%10%14%10%
2247
May1st to 15thDay
62%5%10%14%6%
2506
16th to endDay
61%6%9%16%5%
2622
June1st to 15thDay
64%7%10%11%5%
2520
16th to endDay
63%7%8%13%6%
2520
July1st to 15thDay
53%8%16%14%7%
2372
16th to endDay
63%7%12%12%4
2486
August1st to 15thDay
52%9%13%17%6%
2372
16th to endDay
44%8%17%21%7%
2360
September1st to 15thDay
48%7%12%21%9%
2160
16th to endDay
44%7%11%24%11%
1894
October1st to 15thDay
49%7%12%21%8%
1650
16th to endDay
56%7%13%15%5%
1703
November1st to 15thDay
56%6%13%16%7%
1495
16th to endDay
56%7%14%15%5%
1440
December1st to 15thDay
61%7%13%15%3
1440
16th to endDay
64%5%12%11%5%
1536
January1st to 15thNight
54%8%15%14%5%
2506
16th to endNight
54%8%15%16%5%
2601
February1st to 15thNight
59%7%12%12%7%
2286
16th to endNight
59%7%12%14%5%
1976
March1st to 15thNight
60%6%9%14%8%
2061
16th to endNight
56%49%18%8%1
2061
April1st to 15thNight
58%5%9%16%9%1
1796
16th to endNight
55%6%9%15%12%1
1712
May1st to 15thNight
63%38%18%5%
1446
16th to endNight
57%5%10%18%5%
1496
June1st to 15thNight
65%5%9%13%5%
1440
16th to endNight
62%5%9%14%7%
1440
July1st to 15thNight
56%7%14%14%8%
1360
16th to endNight
64%6%11%11%4
1419
August1st to 15thNight
56%6%12%18%5%
1561
16th to endNight
46%7%15%22%7%
1842
September1st to 15thNight
47%6%12%22%9%
1800
16th to endNight
46%411%25%12%
1875
October1st to 15thNight
45%6%13%24%9%
1980
16th to endNight
55%7%13%16%6%
2167
November1st to 15thNight
54%7%14%16%7%
2362
16th to endNight
55%7%15%14%6%
2520
December1st to 15thNight
59%7%13%15%4
2520
16th to endNight
62%7%13%11%4
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
20%27%31%17%2
240
16th to endDay
23%25%32%14%3
256
February1st to 15thDay
23%27%30%17%
236
16th to endDay
21%22%31%19%5%
212
March1st to 15thDay
19%20%38%16%5%
256
16th to endDay
24%25%28%17%4
288
April1st to 15thDay
29%15%31%19%4
270
16th to endDay
24%14%25%25%8%1
270
May1st to 15thDay
36%15%19%18%6%3
462
16th to endDay
30%16%17%26%7%1
519
June1st to 15thDay
31%14%21%25%7%
495
16th to endDay
34%13%14%27%8%1
495
July1st to 15thDay
31%11%10%29%15%1
475
16th to endDay
33%14%15%25%10%
514
August1st to 15thDay
28%8%21%25%12%4
359
16th to endDay
22%8%18%29%17%2
332
September1st to 15thDay
22%8%25%28%13%1
315
16th to endDay
23%9%23%28%12%2
263
October1st to 15thDay
21%13%28%21%12%3
225
16th to endDay
27%15%32%17%6%
240
November1st to 15thDay
17%20%29%20%7%3
235
16th to endDay
27%22%30%14%5%
240
December1st to 15thDay
30%25%24%17%2
240
16th to endDay
28%26%29%13%1
256
January1st to 15thNight
20%30%30%16%2
750
16th to endNight
21%31%30%12%3
785
February1st to 15thNight
25%28%31%13%
704
16th to endNight
20%28%31%13%6%
631
March1st to 15thNight
23%25%27%16%6%
720
16th to endNight
22%27%23%20%5%
717
April1st to 15thNight
28%22%22%21%5%
539
16th to endNight
23%20%22%25%7%
540
May1st to 15thNight
34%18%17%18%10%1
540
16th to endNight
27%19%19%24%7%1
561
June1st to 15thNight
32%19%16%25%6%
540
16th to endNight
31%18%12%27%8%1
540
July1st to 15thNight
29%13%10%30%14%
510
16th to endNight
33%18%12%22%13%
565
August1st to 15thNight
29%10%11%27%17%2
539
16th to endNight
22%10%17%31%17%1
573
September1st to 15thNight
22%10%21%28%15%
540
16th to endNight
22%12%22%29%12%1
585
October1st to 15thNight
23%16%25%24%8%1
660
16th to endNight
26%19%30%17%5%
714
November1st to 15thNight
23%22%25%20%5%2
730
16th to endNight
24%28%26%15%5%
750
December1st to 15thNight
28%29%25%11%4
750
16th to endNight
29%29%25%11%2
800
Page generated at 2017-09-23 07:43:35. Version ac04

Copyright 2017 A. Danko


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