Strawberry Hill Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Strawberry Hill Observatory clear sky chart from 2005-11-05 to 2017-04-24.

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
30%
15441
11%
45690
7%
15399
34%
15399
16%
34178

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
13%
900
4%
2506
2%
895
14%
895
6%
2232
January16th to endNight
15%
960
5%
2688
2%
960
18%
960
8%
2340
February1st to 15thNight
16%
737
6%
2273
3%
737
19%
737
7%
1912
February16th to endNight
20%
631
8%
1893
4%
631
24%
631
9%
1565
March1st to 15thNight
27%
720
14%
2128
7%
720
32%
720
17%
1546
March16th to endNight
31%
738
17%
2082
10%
738
37%
738
21%
1470
April1st to 15thNight
27%
539
14%
1789
9%
539
34%
539
17%
1272
April16th to endNight
32%
522
19%
1566
9%
522
41%
522
25%
1036
May1st to 15thNight
32%
495
15%
1485
9%
495
39%
495
20%
1044
May16th to endNight
42%
514
14%
1391
6%
513
50%
513
29%
908
June1st to 15thNight
41%
402
14%
1227
11%
402
46%
402
25%
792
June16th to endNight
50%
412
12%
1237
8%
412
54%
412
30%
766
July1st to 15thNight
58%
465
16%
1240
11%
465
61%
465
41%
730
July16th to endNight
54%
522
14%
1305
9%
489
57%
489
34%
817
August1st to 15thNight
60%
494
19%
1440
14%
491
65%
491
37%
829
August16th to endNight
58%
525
18%
1630
16%
525
61%
525
29%
994
September1st to 15thNight
51%
561
18%
1716
14%
561
56%
561
30%
1044
September16th to endNight
46%
657
18%
1815
12%
657
50%
657
27%
1206
October1st to 15thNight
35%
660
17%
1867
11%
660
42%
660
21%
1342
October16th to endNight
23%
704
9%
2286
6%
704
27%
704
12%
1766
November1st to 15thNight
26%
700
14%
2276
11%
700
31%
700
14%
1676
November16th to endNight
17%
723
6%
2385
4%
723
21%
723
8%
1988
December1st to 15thNight
10%
900
2%
2700
1%
900
12%
900
5%
2450
December16th to endNight
11%
960
4%
2765
1%
960
14%
960
6%
2453

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%11%47%6%35%45%6%29%
45909
Night
14%11%5%8%6%34445%29%
45858
Cloud CoverDay
15%11%47%6%3445%6%29%
45918
Night
15%11%5%8%6%34445%29%
45863
TransparencyDay
54%5%11%18%9%
45595
Night
56%5%11%17%8%
45690
SeeingDay
20%11%28%23%11%4
5340
Night
20%11%30%27%9%1
15445

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
15%16%10%16%8%6%433310%
1432
16th to endDay
11%18%11%14%11%46%4339%
1536
February1st to 15thDay
11%15%9%13%14%45%43413%
1587
16th to endDay
11%17%9%13%10%46%5%3313%
1580
March1st to 15thDay
12%12%5%11%9%35%5%46%25%
1821
16th to endDay
15%12%5%7%6%34445%30%
2152
April1st to 15thDay
19%14%35%423446%30%
2158
16th to endDay
16%11%26%42435%6%34%
2253
May1st to 15thDay
17%10%36%5%35%446%32%
2136
16th to endDay
10%7%25%5%25%46%8%42%
2371
June1st to 15thDay
14%7%25%5%35%5%5%8%36%
2398
16th to endDay
12%6%35%5%345%6%9%36%
2387
July1st to 15thDay
10%425%5%36%5%6%9%40%
2310
16th to endDay
10%5%25%5%35%6%7%8%38%
2459
August1st to 15thDay
9%6%25%6%45%5%7%9%38%
2181
16th to endDay
14%6%25%5%3446%6%40%
2217
September1st to 15thDay
17%5%25%5%25%447%39%
1903
16th to endDay
15%7%245%35%45%7%37%
1815
October1st to 15thDay
21%9%36%5%34446%31%
1763
16th to endDay
24%16%37%7%3445%6%16%
1584
November1st to 15thDay
16%15%46%5%34348%26%
1582
16th to endDay
17%21%10%11%5%3333413%
1569
December1st to 15thDay
16%19%9%16%10%2323310%
1260
16th to endDay
18%22%11%12%8%3323310%
1455
January1st to 15thNight
17%15%7%14%11%5%5%33311%
2506
16th to endNight
11%15%7%12%11%5%7%445%12%
2688
February1st to 15thNight
11%13%8%13%10%5%6%5%2316%
2271
16th to endNight
13%15%6%13%9%45%435%17%
1893
March1st to 15thNight
12%11%5%9%5%245%45%33%
2115
16th to endNight
14%9%6%6%5%245%46%35%
2082
April1st to 15thNight
19%12%46%42335%6%30%
1789
16th to endNight
15%9%35%423346%41%
1566
May1st to 15thNight
15%8%36%5%46%5%5%7%32%
1485
16th to endNight
10%6%345%25%46%8%42%
1389
June1st to 15thNight
12%6%25%5%25%45%8%40%
1227
16th to endNight
8%435%4245%6%9%43%
1237
July1st to 15thNight
9%32442435%9%51%
1320
16th to endNight
7%5%245%245%7%8%46%
1401
August1st to 15thNight
6%3144345%6%9%49%
1449
16th to endNight
12%4246%34347%47%
1630
September1st to 15thNight
14%6%24222445%49%
1716
16th to endNight
14%5%25%43345%7%41%
1815
October1st to 15thNight
19%9%36%42434436%
1867
16th to endNight
23%12%5%6%5%34446%23%
2286
November1st to 15thNight
14%13%47%5%45%5%46%28%
2276
16th to endNight
16%22%7%9%7%3444416%
2385
December1st to 15thNight
17%17%10%15%8%45%33310%
2700
16th to endNight
16%20%9%14%8%4433410%
2765

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
15%17%11%14%9%5%5%33210%
1432
16th to endDay
11%18%10%16%9%46%3339%
1536
February1st to 15thDay
12%15%9%13%12%45%33413%
1587
16th to endDay
11%18%9%12%10%35%5%4314%
1580
March1st to 15thDay
13%10%5%9%9%445%45%26%
1831
16th to endDay
15%12%5%7%5%35%345%30%
2151
April1st to 15thDay
20%13%45%424335%31%
2158
16th to endDay
17%10%36%5%2335%6%35%
2253
May1st to 15thDay
18%9%36%5%34445%33%
2136
16th to endDay
10%6%25%5%245%5%8%42%
2371
June1st to 15thDay
15%7%25%5%245%5%8%36%
2398
16th to endDay
13%5%35%435%6%6%8%37%
2387
July1st to 15thDay
10%5%25%5%345%6%9%40%
2310
16th to endDay
11%5%35%5%35%5%7%9%38%
2459
August1st to 15thDay
10%5%26%5%35%5%6%9%38%
2181
16th to endDay
15%6%245%3445%7%40%
2217
September1st to 15thDay
18%5%25%424448%39%
1903
16th to endDay
15%7%25%5%3445%7%37%
1815
October1st to 15thDay
21%9%36%5%34346%31%
1763
16th to endDay
25%16%47%6%345%45%16%
1584
November1st to 15thDay
16%15%37%43435%7%26%
1582
16th to endDay
18%21%8%11%6%3323414%
1569
December1st to 15thDay
16%19%10%14%10%4324210%
1260
16th to endDay
19%21%12%12%7%3333211%
1455
January1st to 15thNight
17%15%7%15%10%45%33312%
2506
16th to endNight
12%15%8%13%10%5%6%445%13%
2688
February1st to 15thNight
12%14%9%12%10%46%43416%
2264
16th to endNight
14%15%7%13%9%35%43418%
1893
March1st to 15thNight
13%11%5%7%6%24445%33%
2128
16th to endNight
14%9%6%6%425%446%36%
2082
April1st to 15thNight
19%11%5%6%42335%5%31%
1789
16th to endNight
15%9%35%423346%41%
1566
May1st to 15thNight
15%8%35%6%346%6%6%33%
1484
16th to endNight
10%6%44435%46%8%42%
1389
June1st to 15thNight
13%5%35%6%3445%8%40%
1227
16th to endNight
8%5%35%4345%6%8%44%
1237
July1st to 15thNight
9%32441445%8%51%
1320
16th to endNight
7%4245%245%6%8%46%
1401
August1st to 15thNight
7%4143345%6%9%49%
1449
16th to endNight
12%5%14334447%47%
1630
September1st to 15thNight
15%5%24313435%49%
1716
16th to endNight
15%5%25%5%2345%7%40%
1815
October1st to 15thNight
20%8%36%5%32345%36%
1867
16th to endNight
23%13%46%5%34445%24%
2286
November1st to 15thNight
14%13%36%6%35%5%47%28%
2276
16th to endNight
18%21%8%9%5%33345%16%
2385
December1st to 15thNight
18%18%9%12%9%45%34310%
2700
16th to endNight
17%19%10%13%6%4433312%
2765

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
79%6%5%6%2
1433
16th to endDay
78%5%6%7%1
1536
February1st to 15thDay
74%5%9%8%1
1589
16th to endDay
73%48%10%2
1580
March1st to 15thDay
59%6%10%16%6%
1831
16th to endDay
55%5%12%19%6%1
2152
April1st to 15thDay
54%410%20%9%
2158
16th to endDay
48%5%11%15%16%2
2253
May1st to 15thDay
51%5%9%22%8%1
2136
16th to endDay
39%5%12%27%14%1
2375
June1st to 15thDay
44%6%12%23%13%
2398
16th to endDay
42%6%16%21%12%1
2387
July1st to 15thDay
36%7%11%26%16%1
2161
16th to endDay
40%7%13%23%13%1
2292
August1st to 15thDay
39%7%13%26%12%
2166
16th to endDay
41%6%11%23%13%2
2217
September1st to 15thDay
43%5%12%25%12%
1903
16th to endDay
44%5%16%23%10%
1815
October1st to 15thDay
53%5%9%23%7%
1763
16th to endDay
67%6%12%10%2
1584
November1st to 15thDay
57%412%17%7%
1582
16th to endDay
73%5%10%8%2
1569
December1st to 15thDay
80%47%5%
1260
16th to endDay
80%47%5%1
1455
January1st to 15thNight
77%5%8%6%2
2506
16th to endNight
72%7%10%8%2
2688
February1st to 15thNight
72%48%12%2
2273
16th to endNight
68%411%11%3
1893
March1st to 15thNight
52%6%12%17%10%
2128
16th to endNight
49%5%11%22%10%1
2082
April1st to 15thNight
53%49%20%11%
1789
16th to endNight
44%412%19%16%2
1566
May1st to 15thNight
48%6%12%22%9%1
1485
16th to endNight
39%6%12%25%13%2
1391
June1st to 15thNight
41%6%12%23%15%
1227
16th to endNight
35%7%16%23%16%
1237
July1st to 15thNight
29%412%30%20%1
1240
16th to endNight
34%6%15%28%14%1
1305
August1st to 15thNight
30%5%17%31%13%
1440
16th to endNight
36%5%14%26%15%1
1630
September1st to 15thNight
37%414%28%14%
1716
16th to endNight
41%5%14%28%8%
1815
October1st to 15thNight
51%49%23%10%
1867
16th to endNight
60%5%14%15%4
2286
November1st to 15thNight
55%6%13%15%8%
2276
16th to endNight
70%5%11%9%1
2385
December1st to 15thNight
80%5%7%5%1
2700
16th to endNight
77%49%6%1
2765

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
22%13%44%20%
90
16th to endDay
32%6%36%21%3
96
February1st to 15thDay
20%27%43%5%3
90
16th to endDay
17%28%34%14%4
81
March1st to 15thDay
28%21%29%14%5%
121
16th to endDay
30%9%22%24%11%2
288
April1st to 15thDay
27%13%29%19%8%1
270
16th to endDay
23%11%31%18%11%3
243
May1st to 15thDay
27%11%27%20%7%4
228
16th to endDay
14%14%30%25%10%3
415
June1st to 15thDay
16%15%30%24%10%2
420
16th to endDay
13%9%32%29%9%4
420
July1st to 15thDay
16%9%24%28%16%5%
400
16th to endDay
14%8%29%25%16%5%
445
August1st to 15thDay
13%425%23%19%12%
289
16th to endDay
22%5%16%25%21%8%
268
September1st to 15thDay
18%222%25%19%11%
255
16th to endDay
18%8%21%27%16%7%
254
October1st to 15thDay
24%9%29%25%9%1
255
16th to endDay
32%17%36%11%2
96
November1st to 15thDay
17%12%36%24%7%1
90
16th to endDay
22%32%25%15%3
83
December1st to 15thDay
36%31%21%6%3
60
16th to endDay
28%37%30%3
83
January1st to 15thNight
25%16%33%19%4
900
16th to endNight
18%15%37%23%4
960
February1st to 15thNight
18%17%35%23%5%
740
16th to endNight
23%15%30%25%4
631
March1st to 15thNight
19%15%32%23%8%
720
16th to endNight
18%13%31%26%8%1
738
April1st to 15thNight
25%12%30%25%5%
539
16th to endNight
21%10%31%27%8%1
522
May1st to 15thNight
16%10%34%30%6%
495
16th to endNight
13%8%28%36%11%
515
June1st to 15thNight
17%9%26%35%10%
402
16th to endNight
9%6%27%38%16%1
412
July1st to 15thNight
10%221%40%23%1
465
16th to endNight
10%227%36%21%1
522
August1st to 15thNight
8%122%41%23%2
494
16th to endNight
15%416%40%22%1
525
September1st to 15thNight
20%321%30%19%4
561
16th to endNight
18%6%25%29%17%3
657
October1st to 15thNight
25%6%26%31%9%
660
16th to endNight
31%14%26%21%5%
704
November1st to 15thNight
23%13%32%22%7%
700
16th to endNight
27%14%33%21%2
723
December1st to 15thNight
25%18%37%16%2
900
16th to endNight
24%16%35%19%3
960
Page generated at 2017-04-25 07:48:27. Version ac04

Copyright 2017 A. Danko


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