Blackrock Ranger Station
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Blackrock Ranger Station clear sky chart from 2005-11-05 to 2017-09-16.

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
60%
15544
33%
46831
25%
15510
69%
15510
53%
21620

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
53%
716
27%
2506
21%
716
64%
716
42%
1180
January16th to endNight
50%
768
31%
2469
24%
768
63%
768
39%
1232
February1st to 15thNight
50%
700
30%
2108
24%
699
60%
699
42%
1084
February16th to endNight
46%
632
27%
1895
23%
632
55%
632
39%
1011
March1st to 15thNight
46%
720
25%
2160
18%
720
58%
720
40%
1125
March16th to endNight
45%
768
27%
2004
15%
768
54%
768
44%
1093
April1st to 15thNight
41%
719
29%
1799
11%
719
51%
719
43%
994
April16th to endNight
49%
720
34%
1800
13%
720
58%
720
61%
860
May1st to 15thNight
48%
581
32%
1661
18%
581
56%
581
59%
744
May16th to endNight
50%
550
31%
1674
19%
550
59%
550
52%
721
June1st to 15thNight
64%
360
34%
1440
32%
360
77%
360
58%
504
June16th to endNight
73%
360
41%
1440
40%
360
85%
360
79%
423
July1st to 15thNight
88%
340
34%
1360
40%
340
92%
340
62%
477
July16th to endNight
86%
477
37%
1510
37%
448
87%
448
61%
612
August1st to 15thNight
83%
717
37%
1790
24%
713
84%
713
78%
810
August16th to endNight
87%
764
44%
1910
28%
764
88%
764
79%
872
September1st to 15thNight
85%
720
42%
1818
29%
720
89%
720
76%
829
September16th to endNight
79%
660
45%
1826
36%
660
86%
660
77%
753
October1st to 15thNight
65%
660
38%
1856
29%
660
76%
660
59%
872
October16th to endNight
66%
704
41%
2159
35%
704
77%
704
60%
915
November1st to 15thNight
65%
700
34%
2275
30%
700
76%
700
54%
983
November16th to endNight
62%
720
33%
2340
31%
720
70%
720
50%
1037
December1st to 15thNight
52%
720
30%
2343
21%
720
66%
720
40%
1143
December16th to endNight
44%
768
27%
2688
20%
768
56%
768
33%
1346

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
2212323446%65%
47929
Night
1212323446%66%
47016
TransparencyDay
16%48%17%27%25%
47610
Night
14%5%9%20%28%21%
46836
SeeingDay
7%20%37%24%6%2
5816
Night
38%23%31%25%7%
15555

By Month

Percentage Cloud Cover SW (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
323326%45%8%59%
1432
16th to endDay
5%5%24425%5%5%6%53%
1750
February1st to 15thDay
15%2242446%8%56%
1751
16th to endDay
35%235%345%6%6%52%
1579
March1st to 15thDay
3135%35%6%6%7%56%
1800
16th to endDay
13135%35%5%6%8%54%
2217
April1st to 15thDay
3334324347%59%
2149
16th to endDay
111232335%8%66%
2160
May1st to 15thDay
12332335%6%65%
2289
16th to endDay
4312412345%63%
2436
June1st to 15thDay
111221235%7%69%
2520
16th to endDay
111223381%
2520
July1st to 15thDay
3212314445%68%
2520
16th to endDay
3212423445%65%
2551
August1st to 15thDay
11111321379%
2160
16th to endDay
11121323476%
2292
September1st to 15thDay
111332222373%
2142
16th to endDay
11121123378%
1823
October1st to 15thDay
3212223436%67%
1771
16th to endDay
1213323345%68%
1713
November1st to 15thDay
1312313346%69%
1584
16th to endDay
3125%23346%65%
1620
December1st to 15thDay
1313315%5%5%9%58%
1614
16th to endDay
2323426%6%48%54%
1536
January1st to 15thNight
13144245%5%7%60%
2506
16th to endNight
45%133245%5%7%56%
2469
February1st to 15thNight
4233236%8%9%54%
2101
16th to endNight
4313435%6%6%7%54%
1895
March1st to 15thNight
3235%35%47%7%55%
2160
16th to endNight
2135%35%6%6%9%53%
2004
April1st to 15thNight
12135%35%6%47%57%
1799
16th to endNight
112135%46%73%
1800
May1st to 15thNight
1131245%8%67%
1661
16th to endNight
1112212335%73%
1673
June1st to 15thNight
11212347%74%
1440
16th to endNight
112387%
1440
July1st to 15thNight
111113245%76%
1440
16th to endNight
221111222477%
1613
August1st to 15thNight
1111122384%
1800
16th to endNight
111112384%
1910
September1st to 15thNight
111222382%
1818
16th to endNight
111123382%
1826
October1st to 15thNight
3112212335%72%
1856
16th to endNight
112213345%72%
2159
November1st to 15thNight
11123235%5%6%67%
2275
16th to endNight
1133245%5%8%64%
2340
December1st to 15thNight
1313325%5%5%9%57%
2343
16th to endNight
1213436%7%7%9%51%
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
18%7%12%22%28%11%
1432
16th to endDay
27%5%13%17%21%14%
1750
February1st to 15thDay
20%6%13%22%24%12%
1751
16th to endDay
24%8%13%21%24%7%
1579
March1st to 15thDay
19%8%13%24%21%12%
1800
16th to endDay
20%9%14%26%21%8%
2217
April1st to 15thDay
22%5%12%24%25%10%
2149
16th to endDay
13%5%14%27%30%9%
2160
May1st to 15thDay
15%49%21%34%14%
2289
16th to endDay
19%37%23%35%9%
2439
June1st to 15thDay
12%28%13%32%31%
2520
16th to endDay
8%137%24%55%
2520
July1st to 15thDay
15%348%15%52%
2371
16th to endDay
18%35%11%20%40%
2392
August1st to 15thDay
10%127%24%53%
2146
16th to endDay
11%148%30%43%
2292
September1st to 15thDay
13%1410%23%45%
2142
16th to endDay
9%316%34%35%
1823
October1st to 15thDay
15%47%15%35%22%
1771
16th to endDay
15%26%16%36%21%
1713
November1st to 15thDay
15%210%24%30%16%
1584
16th to endDay
17%49%21%29%17%
1620
December1st to 15thDay
17%8%14%22%25%12%
1614
16th to endDay
23%8%12%24%18%12%
1536
January1st to 15thNight
18%7%10%22%27%12%
2506
16th to endNight
22%412%19%24%16%
2469
February1st to 15thNight
19%8%13%22%23%12%
2112
16th to endNight
21%8%13%21%26%8%
1895
March1st to 15thNight
19%8%12%23%22%13%
2160
16th to endNight
18%7%18%27%22%6%
2004
April1st to 15thNight
18%6%13%27%25%8%
1799
16th to endNight
9%412%34%30%9%
1800
May1st to 15thNight
10%5%12%26%36%9%
1662
16th to endNight
11%411%25%35%10%
1674
June1st to 15thNight
10%28%19%34%25%
1440
16th to endNight
5%39%30%50%
1440
July1st to 15thNight
10%2310%18%54%
1360
16th to endNight
12%35%11%24%43%
1510
August1st to 15thNight
8%129%28%50%
1790
16th to endNight
7%1210%37%41%
1910
September1st to 15thNight
8%1410%32%42%
1818
16th to endNight
6%1316%36%35%
1826
October1st to 15thNight
14%2419%37%20%
1856
16th to endNight
11%37%18%38%21%
2159
November1st to 15thNight
13%411%19%33%16%
2275
16th to endNight
14%5%12%21%29%17%
2340
December1st to 15thNight
19%7%12%24%26%9%
2343
16th to endNight
20%9%15%22%18%13%
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
21%33%30%6%5%3
60
16th to endDay
14%28%30%20%5%
242
February1st to 15thDay
7%27%31%24%7%1
266
16th to endDay
12%34%33%15%3
238
March1st to 15thDay
11%27%37%14%8%1
270
16th to endDay
9%35%35%16%3
288
April1st to 15thDay
19%33%28%13%31
269
16th to endDay
11%38%35%11%2
270
May1st to 15thDay
9%26%38%20%41
288
16th to endDay
11%25%34%21%5%1
330
June1st to 15thDay
5%19%45%23%41
315
16th to endDay
217%42%24%10%2
315
July1st to 15thDay
27%38%38%8%3
305
16th to endDay
4341%37%8%5%
327
August1st to 15thDay
410%43%30%8%3
315
16th to endDay
25%40%36%9%6%
332
September1st to 15thDay
311%44%32%7%
315
16th to endDay
312%40%34%8%
258
October1st to 15thDay
7%22%40%24%5%
255
16th to endDay
7%17%45%24%4
225
November1st to 15thDay
7%11%16%31%25%7%
90
16th to endDay
7%22%31%34%4
90
December1st to 15thDay
5%20%41%25%6%
89
16th to endDay
14%18%26%25%12%3
64
January1st to 15thNight
48%28%29%21%8%
720
16th to endNight
7%12%24%31%18%5%
768
February1st to 15thNight
37%31%29%19%7%
704
16th to endNight
7%12%30%27%16%5%
632
March1st to 15thNight
313%31%28%15%6%
720
16th to endNight
316%30%27%17%4
768
April1st to 15thNight
418%31%27%15%3
719
16th to endNight
311%33%26%18%5%
720
May1st to 15thNight
39%35%30%17%3
582
16th to endNight
414%26%32%20%1
552
June1st to 15thNight
2426%41%22%2
360
16th to endNight
124%44%26%2
360
July1st to 15thNight
25%43%41%6%
340
16th to endNight
16%37%46%6%
477
August1st to 15thNight
110%39%38%8%
717
16th to endNight
18%31%45%12%
764
September1st to 15thNight
119%29%46%11%
720
16th to endNight
413%28%39%13%
660
October1st to 15thNight
35%23%31%26%9%
660
16th to endNight
26%19%28%29%12%
704
November1st to 15thNight
18%20%34%26%9%
700
16th to endNight
38%21%37%22%7%
720
December1st to 15thNight
5%10%26%33%18%6%
720
16th to endNight
414%31%28%16%4
768
Page generated at 2017-09-17 09:05:40. Version ac04

Copyright 2017 A. Danko


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