Twentymile Rock
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Twentymile Rock clear sky chart from 2005-11-06 to 2024-01-13.

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
53%
23769
19%
74693
16%
23728
57%
23728
27%
46729

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 10thNight
40%
780
8%
2670
7%
780
42%
780
12%
2041
January11th to 20thNight
47%
732
12%
2562
12%
732
50%
732
15%
1845
January21st to endNight
42%
792
10%
2575
10%
792
44%
792
13%
1952
February1st to 10thNight
38%
720
10%
2340
6%
720
44%
720
16%
1695
February11th to 20thNight
43%
704
13%
2235
11%
700
49%
700
19%
1539
February21st to endNight
41%
592
13%
1776
10%
592
46%
592
18%
1279
March1st to 10thNight
48%
720
14%
2084
11%
720
53%
720
22%
1455
March11th to 20thNight
53%
720
20%
1980
14%
720
59%
720
30%
1285
March21st to endNight
46%
792
12%
2178
8%
792
49%
792
23%
1519
April1st to 10thNight
47%
698
18%
1904
11%
698
51%
698
27%
1274
April11th to 20thNight
41%
533
20%
1601
13%
533
47%
533
27%
1029
April21st to endNight
52%
540
22%
1620
14%
540
57%
540
32%
972
May1st to 10thNight
51%
540
19%
1620
15%
540
54%
540
34%
947
May11th to 20thNight
55%
531
19%
1595
16%
531
58%
531
33%
948
May21st to endNight
53%
582
15%
1618
13%
582
56%
582
29%
1047
June1st to 10thNight
60%
375
18%
1275
18%
375
66%
375
32%
699
June11th to 20thNight
55%
360
23%
1260
22%
360
65%
360
35%
671
June21st to endNight
71%
360
30%
1260
35%
360
79%
360
54%
532
July1st to 10thNight
76%
350
26%
1282
34%
350
81%
350
51%
537
July11th to 20thNight
79%
348
31%
1392
40%
348
86%
348
59%
498
July21st to endNight
75%
562
29%
1647
29%
531
78%
531
54%
765
August1st to 10thNight
70%
537
27%
1602
23%
534
72%
534
47%
821
August11th to 20thNight
76%
534
35%
1602
28%
534
78%
534
58%
747
August21st to endNight
69%
594
37%
1782
29%
594
73%
594
54%
852
September1st to 10thNight
70%
658
32%
1874
24%
658
76%
658
55%
924
September11th to 20thNight
72%
720
32%
1980
26%
720
75%
720
49%
1054
September21st to endNight
67%
720
33%
1980
25%
720
72%
720
49%
1050
October1st to 10thNight
61%
720
24%
2060
19%
720
65%
720
39%
1174
October11th to 20thNight
59%
720
29%
2160
23%
720
65%
720
40%
1187
October21st to endNight
57%
792
24%
2488
19%
792
63%
792
33%
1431
November1st to 10thNight
53%
740
21%
2405
20%
740
56%
740
26%
1480
November11th to 20thNight
48%
826
17%
2536
12%
826
54%
826
24%
1645
November21st to endNight
52%
950
15%
2660
11%
950
55%
950
27%
1779
December1st to 10thNight
44%
950
10%
2660
7%
950
46%
950
18%
1972
December11th to 20thNight
41%
948
9%
3338
6%
948
43%
948
12%
2558
December21st to endNight
34%
1029
5%
5092
4%
1026
37%
1026
8%
3526

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
6%7%36%5%345%5%7%49%
74654
Night
7%8%36%6%35%5%5%7%45%
75082
TransparencyDay
33%7%12%21%18%9%
74363
Night
37%7%14%19%15%8%
74893
SeeingDay
8%8%22%29%23%9%
14053
Night
10%5%22%40%21%2
23793

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 10thDay
9%12%6%11%8%445%6%8%26%
1509
11th to 20thDay
10%8%410%10%5%6%5%46%31%
1459
21st to endDay
9%15%6%11%9%45%45%6%27%
1778
February1st to 10thDay
5%9%6%13%8%46%7%6%6%31%
1620
11th to 20thDay
7%10%5%10%8%48%6%7%8%28%
1611
21st to endDay
6%10%5%10%7%45%47%7%36%
1480
March1st to 10thDay
5%10%48%7%35%6%5%8%36%
1874
11th to 20thDay
6%9%48%6%46%6%5%8%39%
1980
21st to endDay
8%11%5%8%6%45%5%5%7%35%
2178
April1st to 10thDay
8%9%37%5%46%5%5%8%40%
2052
11th to 20thDay
5%9%45%5%45%5%6%6%47%
2307
21st to endDay
7%8%36%6%35%45%9%44%
2340
May1st to 10thDay
6%7%35%5%35%46%8%49%
2340
11th to 20thDay
6%7%25%6%36%6%5%8%46%
2301
21st to endDay
10%7%36%5%35%6%6%9%41%
2658
June1st to 10thDay
6%425%6%35%6%6%9%49%
2681
11th to 20thDay
6%5%25%43445%8%53%
2700
21st to endDay
2212313447%71%
2700
July1st to 10thDay
321232345%9%66%
2636
11th to 20thDay
2212223346%73%
2520
21st to endDay
321442445%6%65%
2573
August1st to 10thDay
5%324423447%62%
2328
11th to 20thDay
2212313346%73%
2299
21st to endDay
431333345%6%67%
2574
September1st to 10thDay
4213312335%72%
2080
11th to 20thDay
5%41332345%7%64%
1980
21st to endDay
7%41332335%6%63%
1980
October1st to 10thDay
11%5%245%335%5%5%52%
1900
11th to 20thDay
5%6%25%5%25%5%46%56%
1800
21st to endDay
7%5%25%5%35%5%6%8%50%
1864
November1st to 10thDay
9%7%47%6%24448%44%
1674
11th to 20thDay
6%8%36%6%45%6%6%8%42%
1624
21st to endDay
7%10%49%6%2445%7%42%
1520
December1st to 10thDay
8%11%5%11%9%35%5%46%32%
1520
11th to 20thDay
10%13%5%11%10%5%5%6%5%9%22%
1772
21st to endDay
6%12%6%10%7%45%45%7%35%
2442
January1st to 10thNight
8%13%6%11%8%45%5%5%7%27%
2670
11th to 20thNight
9%11%6%8%7%45%45%8%32%
2562
21st to endNight
10%12%5%12%7%45%447%29%
2575
February1st to 10thNight
7%10%5%9%8%5%6%6%6%6%32%
2340
11th to 20thNight
9%10%47%6%45%5%5%8%37%
2234
21st to endNight
410%6%9%8%5%6%6%5%7%34%
1776
March1st to 10thNight
5%11%48%7%46%5%6%7%36%
2084
11th to 20thNight
5%7%36%6%46%6%6%10%42%
1980
21st to endNight
8%10%48%7%46%5%7%7%35%
2178
April1st to 10thNight
8%8%47%6%345%6%7%42%
1904
11th to 20thNight
7%9%36%435%5%5%7%44%
1601
21st to endNight
7%7%46%5%345%6%6%48%
1620
May1st to 10thNight
6%6%36%436%6%5%6%50%
1620
11th to 20thNight
5%6%26%5%45%6%6%9%45%
1594
21st to endNight
11%7%35%6%35%5%6%10%40%
1618
June1st to 10thNight
6%326%5%45%6%7%8%48%
1275
11th to 20thNight
8%425%43445%8%53%
1260
21st to endNight
22133235%5%6%67%
1260
July1st to 10thNight
331332445%8%64%
1320
11th to 20thNight
221232245%6%72%
1440
21st to endNight
23133335%46%65%
1744
August1st to 10thNight
5%3144245%6%8%58%
1611
11th to 20thNight
22123145%47%67%
1602
21st to endNight
432332445%6%66%
1782
September1st to 10thNight
4313223335%70%
1874
11th to 20thNight
7%31333345%7%61%
1980
21st to endNight
7%41332335%6%62%
1980
October1st to 10thNight
8%5%24433445%57%
2060
11th to 20thNight
7%6%2442435%6%58%
2160
21st to endNight
6%5%25%5%35%5%6%7%51%
2488
November1st to 10thNight
10%8%35%5%35%5%6%6%45%
2405
11th to 20thNight
7%8%36%6%45%6%6%7%42%
2536
21st to endNight
7%8%47%7%346%5%7%43%
2660
December1st to 10thNight
8%12%6%9%7%45%45%7%33%
2660
11th to 20thNight
9%14%5%8%8%36%5%6%7%28%
3415
21st to endNight
7%12%5%10%8%45%5%5%6%32%
5214

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 10thDay
55%12%15%12%41
1509
11th to 20thDay
53%9%17%16%41
1459
21st to endDay
59%8%13%15%41
1778
February1st to 10thDay
51%12%16%16%5%1
1620
11th to 20thDay
50%10%17%18%5%1
1620
21st to endDay
45%11%17%18%8%2
1480
March1st to 10thDay
44%9%17%20%9%1
1874
11th to 20thDay
41%9%16%23%10%2
1980
21st to endDay
47%9%16%19%7%1
2178
April1st to 10thDay
40%9%16%19%13%2
2052
11th to 20thDay
36%6%14%26%15%2
2310
21st to endDay
36%7%12%28%17%1
2340
May1st to 10thDay
31%7%12%25%22%3
2340
11th to 20thDay
33%7%11%29%16%3
2304
21st to endDay
37%8%14%27%11%2
2658
June1st to 10thDay
30%6%14%29%19%2
2681
11th to 20thDay
28%6%11%21%22%13%
2700
21st to endDay
13%37%22%34%20%
2700
July1st to 10thDay
14%46%18%33%26%
2565
11th to 20thDay
13%25%14%27%39%
2445
21st to endDay
19%37%14%25%33%
2430
August1st to 10thDay
21%48%18%27%22%
2313
11th to 20thDay
13%35%19%35%25%
2299
21st to endDay
17%47%18%33%21%
2574
September1st to 10thDay
16%37%17%32%25%
2080
11th to 20thDay
20%5%9%25%28%14%
1980
21st to endDay
22%38%28%29%9%
1980
October1st to 10thDay
33%6%12%26%17%6%
1900
11th to 20thDay
28%6%17%31%15%3
1800
21st to endDay
31%8%18%24%17%1
1864
November1st to 10thDay
40%6%19%22%12%1
1674
11th to 20thDay
39%9%20%23%7%2
1624
21st to endDay
42%8%20%20%8%1
1520
December1st to 10thDay
53%9%14%16%7%1
1520
11th to 20thDay
59%10%13%14%3
1770
21st to endDay
48%9%17%19%6%1
2442
January1st to 10thNight
55%11%16%13%41
2670
11th to 20thNight
51%10%16%18%5%1
2562
21st to endNight
57%8%15%13%6%1
2575
February1st to 10thNight
50%10%16%17%5%1
2340
11th to 20thNight
46%9%17%21%7%1
2235
21st to endNight
48%10%17%16%7%2
1776
March1st to 10thNight
45%9%16%22%7%1
2084
11th to 20thNight
35%10%17%24%13%2
1980
21st to endNight
44%9%18%20%7%1
2178
April1st to 10thNight
41%7%15%20%15%3
1904
11th to 20thNight
38%8%13%23%15%2
1601
21st to endNight
34%5%14%26%20%
1620
May1st to 10thNight
31%7%11%28%21%3
1620
11th to 20thNight
31%8%14%22%21%4
1595
21st to endNight
37%8%15%25%12%2
1618
June1st to 10thNight
29%7%16%21%23%4
1275
11th to 20thNight
28%6%11%18%25%12%
1260
21st to endNight
15%47%17%30%26%
1260
July1st to 10thNight
15%5%7%15%28%29%
1282
11th to 20thNight
12%35%13%25%43%
1392
21st to endNight
18%36%14%22%38%
1647
August1st to 10thNight
22%5%9%17%19%28%
1602
11th to 20thNight
16%35%15%32%29%
1602
21st to endNight
18%37%14%28%30%
1782
September1st to 10thNight
18%46%12%30%30%
1874
11th to 20thNight
22%5%8%21%25%19%
1980
21st to endNight
22%47%23%32%11%
1980
October1st to 10thNight
29%5%12%26%20%7%
2060
11th to 20thNight
27%5%12%33%19%4
2160
21st to endNight
29%8%16%24%21%2
2488
November1st to 10thNight
38%7%16%24%13%2
2405
11th to 20thNight
40%8%18%24%8%2
2536
21st to endNight
40%8%20%20%10%1
2660
December1st to 10thNight
50%10%18%14%7%2
2660
11th to 20thNight
54%11%16%16%3
3416
21st to endNight
51%10%14%14%9%1
5214

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 10thDay
13%9%20%26%23%9%
180
11th to 20thDay
14%6%12%38%22%8%
165
21st to endDay
13%5%22%34%19%6%
262
February1st to 10thDay
9%10%28%31%19%2
240
11th to 20thDay
11%9%26%35%16%3
276
21st to endDay
9%12%27%34%16%3
346
March1st to 10thDay
8%9%32%35%15%2
420
11th to 20thDay
9%11%21%36%21%2
420
21st to endDay
10%14%30%29%15%1
462
April1st to 10thDay
12%15%24%27%17%5%
420
11th to 20thDay
9%19%33%22%13%4
412
21st to endDay
8%12%27%28%18%8%
420
May1st to 10thDay
8%11%26%26%22%7%
423
11th to 20thDay
12%10%21%26%22%10%
448
21st to endDay
11%7%20%27%23%12%
613
June1st to 10thDay
7%9%21%25%26%12%
630
11th to 20thDay
11%11%24%29%19%5%
630
21st to endDay
4423%33%26%10%
630
July1st to 10thDay
3319%35%29%11%
560
11th to 20thDay
25%21%35%31%5%
444
21st to endDay
3317%32%29%16%
487
August1st to 10thDay
5%5%18%30%30%12%
447
11th to 20thDay
4319%23%31%21%
437
21st to endDay
5%5%17%29%28%17%
495
September1st to 10thDay
4418%27%30%17%
450
11th to 20thDay
5%7%21%27%25%15%
450
21st to endDay
9%7%16%24%29%15%
450
October1st to 10thDay
12%6%18%25%22%17%
370
11th to 20thDay
5%9%23%21%23%18%
270
21st to endDay
13%12%22%23%25%6%
297
November1st to 10thDay
13%13%21%24%23%7%
270
11th to 20thDay
7%7%16%38%26%5%
270
21st to endDay
15%418%36%23%4
270
December1st to 10thDay
12%9%19%35%19%7%
270
11th to 20thDay
19%8%16%35%21%2
221
21st to endDay
15%12%15%31%19%8%
198
January1st to 10thNight
14%7%20%38%20%2
784
11th to 20thNight
13%7%18%39%20%4
732
21st to endNight
15%420%40%17%4
792
February1st to 10thNight
12%5%29%38%14%1
720
11th to 20thNight
14%5%27%37%15%3
704
21st to endNight
7%9%28%40%14%2
592
March1st to 10thNight
8%7%25%44%15%1
720
11th to 20thNight
8%5%26%43%18%1
720
21st to endNight
11%8%26%39%15%1
792
April1st to 10thNight
11%8%26%39%16%1
698
11th to 20thNight
11%7%36%35%11%1
533
21st to endNight
9%6%26%39%18%2
540
May1st to 10thNight
8%7%30%37%18%1
540
11th to 20thNight
8%5%25%35%25%2
531
21st to endNight
13%5%21%37%21%3
584
June1st to 10thNight
7%6%19%39%27%3
375
11th to 20thNight
7%5%26%44%18%1
360
21st to endNight
4318%48%24%4
360
July1st to 10thNight
3114%48%32%2
350
11th to 20thNight
212%59%26%1
348
21st to endNight
3114%46%32%3
562
August1st to 10thNight
4316%44%32%1
537
11th to 20thNight
2216%43%36%2
534
21st to endNight
4220%41%31%2
594
September1st to 10thNight
6%217%40%31%4
658
11th to 20thNight
7%313%40%30%7%
720
21st to endNight
8%317%36%29%6%
720
October1st to 10thNight
9%319%38%29%2
720
11th to 20thNight
9%5%21%37%25%4
720
21st to endNight
8%6%22%41%19%3
792
November1st to 10thNight
12%6%23%38%19%2
740
11th to 20thNight
11%7%26%39%17%2
826
21st to endNight
11%5%21%39%21%2
950
December1st to 10thNight
13%7%20%44%14%2
950
11th to 20thNight
15%8%20%40%15%2
950
21st to endNight
18%7%24%37%13%1
1045
Page generated at 2024-01-10 17:35:26. Version ac07

Copyright 2024 Attilla Danko


Twentymile Rock Clear Sky Chart |Charts Home