Horsetail Fall
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Horsetail Fall clear sky chart from 2005-11-05 to 2018-02-13.

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
65%
15929
29%
48762
25%
15895
70%
15895
43%
25393

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
54%
776
23%
2716
21%
776
61%
776
32%
1491
January16th to endNight
50%
832
26%
2707
20%
832
61%
832
30%
1568
February1st to 15thNight
55%
748
28%
2329
25%
745
63%
745
33%
1349
February16th to endNight
50%
632
22%
1895
21%
632
55%
632
29%
1194
March1st to 15thNight
52%
720
20%
2127
18%
720
57%
720
30%
1322
March16th to endNight
53%
768
21%
2010
14%
768
58%
768
36%
1243
April1st to 15thNight
54%
719
21%
1799
10%
719
58%
719
35%
1153
April16th to endNight
56%
720
23%
1800
11%
720
60%
720
43%
1054
May1st to 15thNight
65%
608
27%
1688
18%
608
69%
608
50%
869
May16th to endNight
70%
402
26%
1525
28%
402
73%
402
40%
710
June1st to 15thNight
77%
360
28%
1440
33%
360
83%
360
46%
594
June16th to endNight
88%
360
38%
1440
48%
360
93%
360
70%
460
July1st to 15thNight
94%
340
33%
1360
44%
340
95%
340
70%
440
July16th to endNight
87%
447
37%
1481
39%
419
88%
419
58%
595
August1st to 15thNight
87%
657
36%
1731
26%
654
87%
654
72%
789
August16th to endNight
92%
764
43%
1910
27%
764
92%
764
78%
877
September1st to 15thNight
89%
720
42%
1800
30%
720
90%
720
75%
837
September16th to endNight
80%
716
43%
1950
38%
716
84%
716
70%
874
October1st to 15thNight
66%
720
31%
2114
28%
720
72%
720
52%
1033
October16th to endNight
73%
768
38%
2322
37%
768
80%
768
55%
1083
November1st to 15thNight
69%
760
30%
2470
32%
760
73%
760
42%
1250
November16th to endNight
59%
780
30%
2535
29%
780
65%
780
38%
1363
December1st to 15thNight
53%
780
23%
2701
19%
780
62%
780
30%
1514
December16th to endNight
42%
832
25%
2912
19%
832
54%
832
25%
1731

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
7%6%23212335%60%
49282
Night
7%5%12212335%62%
48951
TransparencyDay
27%38%21%24%14%
48960
Night
25%38%22%25%14%
48773
SeeingDay
13%14%35%24%9%3
6272
Night
10%415%32%29%8%
15939

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
12%8%13323246%50%
1552
16th to endDay
11%12%33323246%46%
1868
February1st to 15thDay
9%9%23213447%50%
1788
16th to endDay
11%14%6%4323325%43%
1579
March1st to 15thDay
8%13%45%42345%7%40%
1830
16th to endDay
9%14%45%323346%41%
2214
April1st to 15thDay
9%13%45%323345%43%
2149
16th to endDay
11%8%23322336%52%
2160
May1st to 15thDay
7%6%13312337%58%
2262
16th to endDay
9%9%23323345%52%
2586
June1st to 15thDay
6%313313335%63%
2520
16th to endDay
21111112481%
2520
July1st to 15thDay
112233477%
2520
16th to endDay
211221223475%
2583
August1st to 15thDay
11111212381%
2220
16th to endDay
11121222478%
2292
September1st to 15thDay
211221233476%
2160
16th to endDay
311222225%472%
2010
October1st to 15thDay
6%41221135%5%64%
1844
16th to endDay
6%3222233466%
1901
November1st to 15thDay
8%423314335%59%
1719
16th to endDay
9%6%22323346%55%
1755
December1st to 15thDay
13%7%24323335%49%
1586
16th to endDay
13%7%4432345%6%42%
1664
January1st to 15thNight
10%7%1332345%6%51%
2716
16th to endNight
9%9%23323446%50%
2707
February1st to 15thNight
10%7%2341335%7%50%
2328
16th to endNight
9%12%44323336%45%
1895
March1st to 15thNight
9%10%43412336%48%
2127
16th to endNight
8%10%33213247%50%
2010
April1st to 15thNight
7%10%34423346%49%
1799
16th to endNight
7%6%23313335%60%
1800
May1st to 15thNight
4312213336%67%
1688
16th to endNight
5%5%12212345%63%
1524
June1st to 15thNight
422212346%68%
1440
16th to endNight
1121385%
1440
July1st to 15thNight
121223381%
1440
16th to endNight
221221213375%
1583
August1st to 15thNight
11212212381%
1740
16th to endNight
111212383%
1910
September1st to 15thNight
11121111284%
1800
16th to endNight
21211212379%
1950
October1st to 15thNight
4312212235%69%
2114
16th to endNight
5%2112223471%
2322
November1st to 15thNight
7%5%12212247%61%
2470
16th to endNight
7%6%2332335%5%56%
2535
December1st to 15thNight
11%7%13313346%52%
2701
16th to endNight
15%9%24313346%45%
2912

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
35%410%21%19%8%
1552
16th to endDay
38%5%9%17%16%11%
1868
February1st to 15thDay
35%49%25%16%8%
1788
16th to endDay
46%47%23%15%2
1579
March1st to 15thDay
44%412%15%15%6%
1830
16th to endDay
44%5%15%19%13%2
2214
April1st to 15thDay
42%5%13%21%15%2
2149
16th to endDay
34%5%13%27%15%3
2160
May1st to 15thDay
26%313%33%20%3
2262
16th to endDay
33%413%27%18%3
2590
June1st to 15thDay
24%410%24%25%10%
2520
16th to endDay
10%1319%42%22%
2520
July1st to 15thDay
10%2411%31%39%
2371
16th to endDay
13%27%13%24%38%
2422
August1st to 15thDay
10%1315%31%37%
2204
16th to endDay
11%2414%41%25%
2292
September1st to 15thDay
12%25%19%35%25%
2160
16th to endDay
14%27%29%31%14%
2010
October1st to 15thDay
22%28%21%29%15%
1844
16th to endDay
22%36%25%27%15%
1901
November1st to 15thDay
29%310%25%21%8%
1719
16th to endDay
30%47%20%29%6%
1755
December1st to 15thDay
38%49%20%18%10%
1586
16th to endDay
41%48%17%16%11%
1664
January1st to 15thNight
32%48%22%23%9%
2716
16th to endNight
33%5%8%18%19%14%
2707
February1st to 15thNight
33%47%26%19%9%
2339
16th to endNight
40%311%21%18%3
1895
March1st to 15thNight
37%411%19%18%8%
2127
16th to endNight
34%416%23%18%3
2010
April1st to 15thNight
35%5%14%25%15%4
1799
16th to endNight
27%414%30%18%3
1800
May1st to 15thNight
19%5%12%34%24%4
1689
16th to endNight
22%413%30%23%5%
1525
June1st to 15thNight
17%312%24%31%9%
1440
16th to endNight
7%2318%44%23%
1440
July1st to 15thNight
7%15%12%32%39%
1360
16th to endNight
14%2413%26%38%
1481
August1st to 15thNight
10%1316%28%38%
1731
16th to endNight
8%1317%45%23%
1910
September1st to 15thNight
9%1318%42%24%
1800
16th to endNight
11%15%32%32%15%
1950
October1st to 15thNight
18%37%25%29%15%
2114
16th to endNight
17%37%22%34%15%
2322
November1st to 15thNight
24%38%25%25%12%
2470
16th to endNight
28%39%21%27%9%
2535
December1st to 15thNight
33%410%20%19%11%
2701
16th to endNight
39%39%15%18%13%
2912

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
40%7%23%18%5%4
90
16th to endDay
20%13%26%25%12%2
300
February1st to 15thDay
18%14%26%21%14%4
296
16th to endDay
26%19%29%19%41
238
March1st to 15thDay
18%22%28%16%11%1
270
16th to endDay
18%25%31%17%6%
288
April1st to 15thDay
24%20%31%18%4
269
16th to endDay
20%22%35%18%2
270
May1st to 15thDay
21%17%35%18%5%2
288
16th to endDay
22%16%23%25%7%4
330
June1st to 15thDay
11%18%42%16%7%4
315
16th to endDay
312%37%30%9%6%
315
July1st to 15thDay
3246%32%9%5%
305
16th to endDay
38%42%32%6%6%
327
August1st to 15thDay
212%53%17%9%4
315
16th to endDay
36%43%30%9%6%
332
September1st to 15thDay
48%48%26%9%1
315
16th to endDay
8%12%41%27%8%1
315
October1st to 15thDay
9%21%32%27%7%1
315
16th to endDay
10%12%32%32%10%1
317
November1st to 15thDay
14%8%17%25%25%8%
135
16th to endDay
15%11%23%30%14%3
135
December1st to 15thDay
13%10%33%21%15%5%
96
16th to endDay
13%7%28%21%22%6%
96
January1st to 15thNight
14%420%30%21%8%
780
16th to endNight
15%7%21%29%18%7%
832
February1st to 15thNight
13%5%19%33%20%7%
752
16th to endNight
18%7%19%28%20%5%
632
March1st to 15thNight
15%8%18%30%20%6%
720
16th to endNight
14%8%17%30%23%4
768
April1st to 15thNight
12%7%20%34%20%5%
719
16th to endNight
11%5%20%30%23%8%
720
May1st to 15thNight
5%419%37%25%6%
609
16th to endNight
9%213%30%35%7%
403
June1st to 15thNight
6%39%33%42%5%
360
16th to endNight
27%41%43%4
360
July1st to 15thNight
232%60%4
340
16th to endNight
3325%53%13%
447
August1st to 15thNight
16%38%43%9%
657
16th to endNight
1432%52%9%
764
September1st to 15thNight
2436%43%12%
720
16th to endNight
3112%32%36%13%
716
October1st to 15thNight
6%418%30%29%10%
720
16th to endNight
7%212%29%32%14%
768
November1st to 15thNight
9%5%12%36%26%9%
760
16th to endNight
11%420%34%22%7%
780
December1st to 15thNight
17%418%35%17%6%
780
16th to endNight
21%8%21%28%16%3
832
Page generated at 2018-02-13 17:46:05. Version ac04

Copyright 2018 A. Danko


Horsetail Fall Clear Sky Chart |Charts Home