Harrison
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Harrison clear sky chart from 2005-11-05 to 2017-09-23.

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
33%
15910
15%
47023
8%
15868
39%
15868
20%
32587

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
15%
900
8%
2506
2%
895
21%
895
9%
2056
January16th to endNight
17%
960
8%
2688
2%
960
22%
960
11%
2159
February1st to 15thNight
17%
710
11%
2250
3%
710
24%
710
11%
1716
February16th to endNight
19%
631
12%
1893
4%
631
27%
631
13%
1438
March1st to 15thNight
27%
720
15%
2118
8%
720
33%
720
18%
1475
March16th to endNight
29%
756
18%
2100
9%
756
37%
756
23%
1419
April1st to 15thNight
26%
539
16%
1785
9%
539
35%
539
18%
1208
April16th to endNight
34%
540
20%
1620
9%
540
44%
540
25%
1056
May1st to 15thNight
34%
540
15%
1620
7%
540
43%
540
24%
1077
May16th to endNight
40%
562
16%
1554
8%
561
49%
561
30%
983
June1st to 15thNight
44%
464
14%
1364
10%
464
49%
464
28%
850
June16th to endNight
50%
478
15%
1378
8%
478
56%
478
33%
844
July1st to 15thNight
63%
510
17%
1360
13%
510
67%
510
46%
760
July16th to endNight
57%
564
18%
1417
11%
531
61%
531
40%
829
August1st to 15thNight
61%
539
21%
1598
15%
536
67%
536
42%
871
August16th to endNight
60%
573
22%
1773
17%
573
66%
573
37%
1004
September1st to 15thNight
54%
624
23%
1884
17%
624
61%
624
38%
1042
September16th to endNight
50%
689
23%
1903
16%
689
56%
689
34%
1177
October1st to 15thNight
39%
660
20%
1873
14%
660
46%
660
26%
1250
October16th to endNight
24%
704
12%
2269
6%
704
31%
704
15%
1622
November1st to 15thNight
30%
700
18%
2276
14%
700
38%
700
19%
1533
November16th to endNight
22%
720
10%
2376
5%
720
28%
720
11%
1817
December1st to 15thNight
15%
867
6%
2667
2%
867
19%
867
9%
2147
December16th to endNight
15%
960
8%
2751
2%
960
21%
960
9%
2254

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%9%47%6%35%45%7%31%
47871
Night
14%9%46%5%35%45%7%33%
47192
Cloud CoverDay
14%9%47%6%35%45%7%31%
47880
Night
14%8%46%5%35%45%7%34%
47197
TransparencyDay
51%412%20%10%1
47558
Night
49%413%21%10%
47023
SeeingDay
17%11%29%22%12%5%
5984
Night
18%10%29%27%11%1
15914

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
16%14%7%12%7%5%7%345%13%
1432
16th to endDay
13%17%10%14%8%5%5%43312%
1536
February1st to 15thDay
13%14%6%10%10%5%6%445%18%
1612
16th to endDay
11%15%7%10%11%46%5%45%17%
1580
March1st to 15thDay
15%10%37%7%35%5%5%6%29%
1832
16th to endDay
15%10%48%6%34445%31%
2136
April1st to 15thDay
20%12%45%423345%32%
2163
16th to endDay
16%9%25%6%35%447%34%
2340
May1st to 15thDay
19%7%25%5%35%45%6%33%
2331
16th to endDay
12%5%25%6%25%45%8%40%
2559
June1st to 15thDay
12%5%26%5%35%5%5%8%37%
2589
16th to endDay
11%5%35%5%36%6%6%8%37%
2572
July1st to 15thDay
6%325%6%36%6%5%10%42%
2520
16th to endDay
9%415%6%37%5%6%9%38%
2655
August1st to 15thDay
8%426%6%5%6%5%6%9%38%
2349
16th to endDay
13%6%244345%5%8%41%
2427
September1st to 15thDay
14%4245%3445%8%42%
2063
16th to endDay
11%5%35%5%4446%8%39%
1894
October1st to 15thDay
18%10%36%6%2335%434%
1757
16th to endDay
22%12%38%7%2445%6%21%
1603
November1st to 15thDay
15%10%46%6%3435%7%32%
1582
16th to endDay
21%16%6%8%6%4434417%
1581
December1st to 15thDay
17%15%8%12%8%4434416%
1290
16th to endDay
22%17%9%8%7%34445%13%
1468
January1st to 15thNight
19%12%6%10%7%45%445%18%
2506
16th to endNight
12%14%7%10%8%47%6%6%6%15%
2688
February1st to 15thNight
12%12%6%8%8%46%5%5%5%23%
2248
16th to endNight
15%11%5%10%7%45%45%6%22%
1893
March1st to 15thNight
14%8%46%6%345%45%34%
2105
16th to endNight
14%7%46%42446%7%37%
2100
April1st to 15thNight
19%8%36%424347%32%
1785
16th to endNight
16%8%24433347%40%
1620
May1st to 15thNight
14%5%35%5%45%46%7%37%
1620
16th to endNight
11%5%245%2446%8%42%
1552
June1st to 15thNight
13%5%34325%46%8%42%
1364
16th to endNight
8%5%34435%35%9%44%
1378
July1st to 15thNight
5%3144245%5%10%53%
1440
16th to endNight
6%423425%46%9%50%
1513
August1st to 15thNight
6%2234245%7%9%52%
1608
16th to endNight
10%41432345%7%51%
1773
September1st to 15thNight
10%42332335%7%53%
1884
16th to endNight
10%5%25%42445%7%46%
1903
October1st to 15thNight
16%8%35%424345%41%
1873
16th to endNight
21%9%36%5%3445%6%29%
2269
November1st to 15thNight
13%10%36%5%2445%7%34%
2276
16th to endNight
19%15%47%6%35%5%6%420%
2376
December1st to 15thNight
19%14%7%9%6%35%446%17%
2667
16th to endNight
21%15%6%9%6%35%5%5%5%15%
2751

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
16%14%6%13%7%6%7%345%14%
1432
16th to endDay
13%16%11%13%8%5%6%43412%
1536
February1st to 15thDay
13%14%5%10%10%5%6%35%5%18%
1612
16th to endDay
11%13%7%10%11%45%5%5%5%18%
1580
March1st to 15thDay
14%10%38%6%45%5%5%6%29%
1842
16th to endDay
15%9%47%7%34445%32%
2135
April1st to 15thDay
20%12%45%5%23346%32%
2163
16th to endDay
16%9%26%6%35%35%6%34%
2340
May1st to 15thDay
19%7%35%5%35%45%6%33%
2331
16th to endDay
11%6%35%5%345%5%8%40%
2559
June1st to 15thDay
12%6%26%5%35%46%8%37%
2589
16th to endDay
11%5%35%5%36%6%7%8%37%
2572
July1st to 15thDay
6%425%6%36%6%5%10%42%
2520
16th to endDay
8%425%6%36%6%6%8%39%
2655
August1st to 15thDay
7%5%25%7%47%5%6%9%38%
2349
16th to endDay
12%6%246%345%5%8%41%
2427
September1st to 15thDay
13%335%43445%9%42%
2063
16th to endDay
11%5%26%5%445%5%9%38%
1894
October1st to 15thDay
16%9%47%6%23345%35%
1757
16th to endDay
21%12%49%5%3445%6%21%
1603
November1st to 15thDay
15%9%47%7%3435%7%32%
1582
16th to endDay
20%16%5%8%7%35%435%18%
1581
December1st to 15thDay
17%15%7%12%8%45%33417%
1290
16th to endDay
21%17%8%9%6%44345%14%
1468
January1st to 15thNight
20%12%6%9%8%45%45%419%
2506
16th to endNight
12%13%7%10%7%47%6%6%7%16%
2688
February1st to 15thNight
12%11%7%8%8%46%6%5%6%23%
2241
16th to endNight
15%11%5%9%7%45%45%6%23%
1893
March1st to 15thNight
15%8%46%6%35%446%34%
2118
16th to endNight
14%7%45%43445%7%37%
2100
April1st to 15thNight
18%8%46%42436%7%33%
1785
16th to endNight
17%8%24424347%40%
1620
May1st to 15thNight
14%5%35%6%35%5%6%7%37%
1619
16th to endNight
11%5%245%35%45%9%42%
1552
June1st to 15thNight
13%5%3442446%8%42%
1364
16th to endNight
8%5%34435%45%10%44%
1378
July1st to 15thNight
5%21442345%10%53%
1440
16th to endNight
5%424425%46%9%50%
1513
August1st to 15thNight
5%31342447%9%52%
1608
16th to endNight
10%32432345%8%52%
1773
September1st to 15thNight
10%313314447%54%
1884
16th to endNight
9%5%25%424447%47%
1903
October1st to 15thNight
16%7%25%5%2435%5%41%
1873
16th to endNight
21%8%36%6%24445%30%
2269
November1st to 15thNight
13%9%37%6%245%5%7%34%
2276
16th to endNight
19%14%46%7%35%46%5%21%
2376
December1st to 15thNight
19%13%6%9%6%45%446%18%
2667
16th to endNight
21%14%6%9%7%35%5%5%6%15%
2751

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
72%39%11%2
1433
16th to endDay
77%28%8%3
1536
February1st to 15thDay
66%310%14%4
1614
16th to endDay
67%210%13%5%
1580
March1st to 15thDay
53%412%20%8%
1842
16th to endDay
53%312%20%7%1
2136
April1st to 15thDay
54%39%19%12%
2163
16th to endDay
49%313%16%14%2
2340
May1st to 15thDay
49%410%21%10%2
2331
16th to endDay
40%5%13%26%12%
2563
June1st to 15thDay
43%413%25%13%
2589
16th to endDay
41%6%14%22%13%
2572
July1st to 15thDay
34%5%12%28%17%1
2371
16th to endDay
38%6%12%23%15%2
2488
August1st to 15thDay
39%6%12%27%13%1
2335
16th to endDay
40%5%12%25%14%2
2427
September1st to 15thDay
39%312%31%12%1
2063
16th to endDay
41%416%26%11%
1894
October1st to 15thDay
50%49%24%10%
1757
16th to endDay
61%413%14%4
1603
November1st to 15thDay
52%313%21%7%
1582
16th to endDay
68%310%12%4
1581
December1st to 15thDay
71%311%11%2
1290
16th to endDay
73%310%9%2
1468
January1st to 15thNight
67%49%13%5%
2506
16th to endNight
64%5%14%12%3
2688
February1st to 15thNight
60%5%9%18%6%
2250
16th to endNight
60%313%14%7%
1893
March1st to 15thNight
49%5%12%20%10%1
2118
16th to endNight
45%315%21%12%1
2100
April1st to 15thNight
50%210%21%14%
1785
16th to endNight
44%310%22%16%3
1620
May1st to 15thNight
44%413%21%13%2
1620
16th to endNight
37%413%27%14%2
1554
June1st to 15thNight
38%5%13%25%17%
1364
16th to endNight
35%415%25%17%
1378
July1st to 15thNight
25%314%32%21%2
1360
16th to endNight
29%5%17%30%16%1
1417
August1st to 15thNight
26%417%33%16%
1598
16th to endNight
30%414%29%19%1
1773
September1st to 15thNight
29%412%34%18%1
1884
16th to endNight
35%414%35%9%
1903
October1st to 15thNight
43%411%27%12%
1873
16th to endNight
54%413%20%6%
2269
November1st to 15thNight
47%414%20%10%
2276
16th to endNight
62%314%14%3
2376
December1st to 15thNight
66%311%13%3
2667
16th to endNight
68%311%12%3
2751

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
23%21%42%12%1
90
16th to endDay
34%10%37%12%5%
96
February1st to 15thDay
23%34%34%5%2
90
16th to endDay
25%23%35%11%3
81
March1st to 15thDay
28%18%37%11%5%
132
16th to endDay
27%8%31%19%9%3
288
April1st to 15thDay
28%12%27%20%10%
270
16th to endDay
22%11%30%21%9%4
270
May1st to 15thDay
22%14%31%19%7%4
288
16th to endDay
15%13%33%22%10%3
459
June1st to 15thDay
14%12%33%27%8%3
495
16th to endDay
14%11%34%23%11%3
495
July1st to 15thDay
6%9%30%27%18%8%
475
16th to endDay
10%7%29%28%14%8%
515
August1st to 15thDay
8%222%32%19%14%
322
16th to endDay
17%5%20%26%18%12%
332
September1st to 15thDay
14%423%24%20%12%
315
16th to endDay
15%7%20%28%22%7%
283
October1st to 15thDay
21%11%23%27%13%1
255
16th to endDay
25%21%36%13%2
115
November1st to 15thDay
12%16%44%15%10%1
90
16th to endDay
33%24%28%8%4
83
December1st to 15thDay
31%35%25%8%
60
16th to endDay
36%34%27%2
85
January1st to 15thNight
26%17%30%18%6%
900
16th to endNight
18%13%37%24%5%
960
February1st to 15thNight
19%17%35%23%4
713
16th to endNight
22%13%32%25%5%
631
March1st to 15thNight
19%15%31%24%7%
720
16th to endNight
18%12%33%26%7%
756
April1st to 15thNight
22%11%33%26%5%
539
16th to endNight
22%8%32%27%7%1
540
May1st to 15thNight
17%8%33%29%9%1
540
16th to endNight
13%9%29%31%14%1
563
June1st to 15thNight
15%7%26%35%14%1
464
16th to endNight
10%427%38%16%1
478
July1st to 15thNight
8%318%43%22%3
510
16th to endNight
7%124%41%23%1
564
August1st to 15thNight
7%120%41%26%2
539
16th to endNight
11%219%37%26%2
573
September1st to 15thNight
12%5%24%29%22%5%
624
16th to endNight
13%5%23%30%22%4
689
October1st to 15thNight
19%7%27%32%11%1
660
16th to endNight
27%13%30%21%6%
704
November1st to 15thNight
18%14%31%24%10%1
700
16th to endNight
25%16%30%21%6%
720
December1st to 15thNight
25%17%33%19%3
867
16th to endNight
27%14%32%20%3
960
Page generated at 2017-09-24 09:15:55. Version ac04

Copyright 2017 A. Danko


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