Harlan
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Harlan 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
46%
15828
19%
47847
15%
15785
51%
15785
22%
32049

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
23%
720
15%
2327
11%
716
30%
716
14%
1716
January16th to endNight
24%
768
17%
2496
10%
768
34%
768
14%
1784
February1st to 15thNight
22%
704
13%
2169
5%
701
30%
701
14%
1570
February16th to endNight
19%
631
16%
1893
9%
631
26%
631
12%
1429
March1st to 15thNight
30%
720
18%
2046
12%
720
34%
720
18%
1465
March16th to endNight
34%
768
14%
2112
10%
768
37%
768
18%
1547
April1st to 15thNight
36%
656
20%
1914
11%
656
45%
656
25%
1228
April16th to endNight
43%
540
20%
1632
12%
540
50%
540
23%
1094
May1st to 15thNight
43%
539
15%
1620
9%
539
47%
539
21%
1119
May16th to endNight
59%
561
16%
1683
13%
561
60%
561
24%
1120
June1st to 15thNight
67%
540
14%
1620
13%
540
69%
540
29%
1034
June16th to endNight
67%
540
17%
1620
15%
540
68%
540
27%
1022
July1st to 15thNight
65%
510
12%
1530
11%
510
66%
510
25%
1011
July16th to endNight
71%
564
15%
1595
14%
531
75%
531
29%
1013
August1st to 15thNight
74%
539
20%
1609
19%
536
74%
536
32%
983
August16th to endNight
73%
573
21%
1818
21%
573
74%
573
31%
1082
September1st to 15thNight
64%
714
21%
1974
18%
714
66%
714
29%
1277
September16th to endNight
62%
717
26%
1980
23%
717
64%
717
33%
1229
October1st to 15thNight
56%
720
31%
2042
28%
720
60%
720
35%
1221
October16th to endNight
45%
768
29%
2304
24%
768
54%
768
28%
1440
November1st to 15thNight
48%
760
27%
2467
25%
760
56%
760
28%
1486
November16th to endNight
42%
780
25%
2535
21%
780
51%
780
23%
1602
December1st to 15thNight
33%
728
15%
2365
13%
728
38%
728
14%
1730
December16th to endNight
29%
768
17%
2496
11%
768
37%
768
13%
1847

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
14%8%36%5%35%5%5%7%34%
48601
Night
13%7%35%5%3445%6%38%
48045
TransparencyDay
47%6%10%18%13%2
48302
Night
44%6%10%20%15%3
47848
SeeingDay
19%9%19%22%18%10%
5657
Night
18%10%18%29%20%3
15831

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
18%11%411%7%2334427%
1611
16th to endDay
15%12%6%6%42433434%
1728
February1st to 15thDay
16%11%5%8%6%23345%30%
1692
16th to endDay
17%11%410%5%2445%5%28%
1580
March1st to 15thDay
19%9%5%6%324345%35%
1914
16th to endDay
17%11%46%5%24446%31%
2111
April1st to 15thDay
13%7%25%5%25%45%7%38%
2043
16th to endDay
17%6%26%5%3345%6%36%
2328
May1st to 15thDay
18%8%37%7%35%5%5%5%28%
2331
16th to endDay
13%6%37%5%35%5%5%8%34%
2431
June1st to 15thDay
8%5%37%6%46%6%7%9%32%
2340
16th to endDay
9%6%35%6%47%5%7%10%33%
2340
July1st to 15thDay
13%6%37%6%46%7%6%9%28%
2340
16th to endDay
12%6%27%8%47%6%7%8%27%
2465
August1st to 15thDay
10%5%37%7%5%7%6%7%10%27%
2340
16th to endDay
11%5%26%6%5%6%6%6%9%33%
2375
September1st to 15thDay
15%5%26%6%45%5%6%6%34%
1980
16th to endDay
14%8%35%42345%5%42%
1980
October1st to 15thDay
12%5%15%423346%49%
1917
16th to endDay
17%7%24422235%45%
1920
November1st to 15thDay
13%7%243245%47%43%
1720
16th to endDay
14%9%25%324335%43%
1755
December1st to 15thDay
18%9%36%5%34445%32%
1632
16th to endDay
19%13%36%5%3345%7%27%
1728
January1st to 15thNight
18%9%5%9%8%3334430%
2327
16th to endNight
17%11%5%8%5%2323433%
2496
February1st to 15thNight
17%9%5%7%5%34446%30%
2160
16th to endNight
18%11%5%8%6%24445%27%
1893
March1st to 15thNight
17%12%45%5%23345%34%
2046
16th to endNight
14%10%46%5%35%45%5%33%
2112
April1st to 15thNight
14%6%3442445%7%42%
1914
16th to endNight
12%6%37%5%36%446%41%
1632
May1st to 15thNight
16%7%27%435%45%8%34%
1619
16th to endNight
9%6%26%5%45%5%6%8%39%
1682
June1st to 15thNight
7%414436%6%8%11%40%
1620
16th to endNight
7%5%25%5%36%5%6%10%41%
1620
July1st to 15thNight
10%5%25%5%45%6%5%10%38%
1620
16th to endNight
6%3236%46%6%9%10%37%
1703
August1st to 15thNight
6%5%24435%6%7%10%43%
1620
16th to endNight
8%313436%6%8%10%42%
1818
September1st to 15thNight
11%6%244346%5%7%43%
1974
16th to endNight
10%5%24434445%50%
1980
October1st to 15thNight
12%5%14312346%52%
2042
16th to endNight
14%7%24423345%46%
2304
November1st to 15thNight
14%6%24423336%48%
2467
16th to endNight
15%7%25%43335%444%
2535
December1st to 15thNight
19%10%5%7%5%3445%429%
2365
16th to endNight
20%11%46%6%245%35%28%
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
59%46%15%11%1
1612
16th to endDay
52%47%22%10%1
1728
February1st to 15thDay
56%45%19%11%1
1694
16th to endDay
55%5%10%16%10%1
1580
March1st to 15thDay
51%47%18%13%3
1914
16th to endDay
53%5%9%20%10%1
2112
April1st to 15thDay
42%5%11%21%15%3
2043
16th to endDay
47%5%8%20%13%3
2328
May1st to 15thDay
54%7%10%15%10%1
2331
16th to endDay
45%7%13%20%9%2
2435
June1st to 15thDay
43%10%14%19%10%1
2340
16th to endDay
43%9%12%16%16%1
2340
July1st to 15thDay
49%8%13%13%12%1
2201
16th to endDay
48%9%11%17%11%2
2310
August1st to 15thDay
48%9%13%16%10%
2327
16th to endDay
44%9%13%18%13%1
2375
September1st to 15thDay
46%7%11%17%12%3
1980
16th to endDay
41%5%8%21%20%1
1980
October1st to 15thDay
36%410%22%21%4
1917
16th to endDay
41%37%23%20%4
1920
November1st to 15thDay
40%47%19%23%5%
1720
16th to endDay
42%45%22%21%2
1755
December1st to 15thDay
52%5%8%19%11%2
1632
16th to endDay
55%5%11%15%10%1
1728
January1st to 15thNight
57%38%14%12%3
2327
16th to endNight
54%47%19%12%1
2496
February1st to 15thNight
53%5%9%18%10%1
2169
16th to endNight
57%6%8%17%9%1
1893
March1st to 15thNight
52%49%17%13%3
2046
16th to endNight
49%8%10%20%10%
2112
April1st to 15thNight
40%5%9%23%16%4
1914
16th to endNight
43%6%10%21%12%5%
1632
May1st to 15thNight
46%8%13%19%11%1
1620
16th to endNight
39%10%13%22%11%2
1684
June1st to 15thNight
34%10%19%21%13%1
1620
16th to endNight
36%9%14%22%14%3
1620
July1st to 15thNight
39%9%16%19%12%3
1530
16th to endNight
33%11%18%20%13%2
1595
August1st to 15thNight
31%9%19%21%16%1
1609
16th to endNight
31%9%18%24%14%1
1818
September1st to 15thNight
36%8%13%21%14%4
1974
16th to endNight
35%5%10%20%25%1
1980
October1st to 15thNight
32%5%7%24%24%5%
2042
16th to endNight
39%45%23%21%5%
2304
November1st to 15thNight
37%36%20%24%7%
2467
16th to endNight
42%45%23%21%3
2535
December1st to 15thNight
55%5%7%17%10%3
2365
16th to endNight
57%5%8%14%13%1
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
33%23%30%6%33
90
16th to endDay
31%26%32%8%2
96
February1st to 15thDay
37%22%32%6%1
90
16th to endDay
28%19%40%9%1
81
March1st to 15thDay
27%16%27%24%3
204
16th to endDay
18%18%30%20%11%1
288
April1st to 15thDay
21%14%21%24%15%2
270
16th to endDay
21%11%24%19%19%3
270
May1st to 15thDay
24%15%20%20%12%6%
288
16th to endDay
20%417%25%13%18%
331
June1st to 15thDay
12%411%28%26%17%
315
16th to endDay
13%7%21%22%21%14%
315
July1st to 15thDay
18%419%25%15%16%
305
16th to endDay
13%212%23%28%20%
326
August1st to 15thDay
15%213%25%24%18%
313
16th to endDay
12%111%26%26%20%
332
September1st to 15thDay
16%310%20%32%16%
315
16th to endDay
14%412%26%27%14%
314
October1st to 15thDay
15%6%16%26%26%7%
315
16th to endDay
19%12%17%22%23%3
336
November1st to 15thDay
24%7%33%15%14%3
138
16th to endDay
21%15%25%26%10%
135
December1st to 15thDay
23%22%31%19%21
94
16th to endDay
35%20%30%10%3
96
January1st to 15thNight
24%18%27%24%4
720
16th to endNight
24%18%26%27%2
768
February1st to 15thNight
24%18%29%24%2
704
16th to endNight
26%22%27%20%2
631
March1st to 15thNight
24%17%22%28%7%
720
16th to endNight
19%15%24%29%10%
768
April1st to 15thNight
19%14%25%27%11%
656
16th to endNight
14%9%25%33%15%
540
May1st to 15thNight
19%7%21%33%15%1
540
16th to endNight
10%315%31%30%7%
563
June1st to 15thNight
7%311%35%34%7%
540
16th to endNight
8%10%37%38%5%
540
July1st to 15thNight
15%18%30%40%4
510
16th to endNight
7%17%26%45%10%
564
August1st to 15thNight
9%6%31%44%6%
539
16th to endNight
10%16%27%44%9%
573
September1st to 15thNight
14%29%28%38%7%
714
16th to endNight
13%312%29%35%5%
717
October1st to 15thNight
14%7%15%29%25%7%
720
16th to endNight
18%10%19%28%19%3
768
November1st to 15thNight
18%11%16%31%18%3
760
16th to endNight
19%15%19%32%13%
780
December1st to 15thNight
24%16%19%29%9%
728
16th to endNight
27%14%23%28%6%
768
Page generated at 2017-12-03 11:16:46. Version ac04

Copyright 2017 A. Danko


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