Helmer Observatory
Clear Sky Chart
History

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

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
28%
24242
11%
74955
7%
24184
34%
24184
15%
55873

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
14%
950
6%
2648
2%
946
18%
946
8%
2258
January11th to 20thNight
15%
905
5%
2533
1%
905
17%
905
6%
2213
January21st to endNight
13%
990
6%
2772
2%
990
17%
990
7%
2379
February1st to 10thNight
17%
858
9%
2478
3%
858
23%
858
11%
2003
February11th to 20thNight
19%
703
11%
2121
5%
700
26%
700
11%
1687
February21st to endNight
16%
592
11%
1776
4%
592
23%
592
10%
1414
March1st to 10thNight
25%
720
15%
2160
8%
720
31%
720
18%
1506
March11th to 20thNight
23%
720
17%
2049
8%
720
32%
720
18%
1450
March21st to endNight
30%
707
18%
2093
10%
707
37%
707
19%
1471
April1st to 10thNight
26%
540
10%
1800
6%
540
31%
540
13%
1325
April11th to 20thNight
32%
533
18%
1674
10%
533
40%
533
20%
1157
April21st to endNight
30%
540
16%
1620
7%
540
38%
540
20%
1122
May1st to 10thNight
32%
540
15%
1620
9%
540
39%
540
20%
1118
May11th to 20thNight
35%
531
15%
1433
8%
531
41%
531
22%
1025
May21st to endNight
42%
547
14%
1516
8%
546
47%
546
27%
1000
June1st to 10thNight
40%
360
13%
1260
9%
360
46%
360
25%
759
June11th to 20thNight
41%
360
14%
1260
10%
360
46%
360
24%
768
June21st to endNight
41%
360
14%
1260
10%
360
46%
360
26%
752
July1st to 10thNight
51%
484
15%
1359
8%
484
55%
484
37%
799
July11th to 20thNight
50%
522
16%
1392
9%
522
54%
522
34%
867
July21st to endNight
54%
591
17%
1487
12%
558
57%
558
35%
928
August1st to 10thNight
57%
537
18%
1458
12%
534
62%
534
34%
901
August11th to 20thNight
58%
534
19%
1598
13%
534
65%
534
36%
923
August21st to endNight
46%
594
18%
1867
13%
594
52%
594
30%
1141
September1st to 10thNight
51%
540
18%
1800
15%
540
55%
540
26%
1093
September11th to 20thNight
42%
706
17%
1966
12%
706
46%
706
27%
1312
September21st to endNight
41%
720
16%
1980
11%
720
44%
720
25%
1361
October1st to 10thNight
33%
720
14%
1980
8%
720
39%
720
21%
1403
October11th to 20thNight
27%
720
9%
2293
5%
720
33%
720
13%
1721
October21st to endNight
24%
792
10%
2574
7%
792
29%
792
10%
2058
November1st to 10thNight
21%
740
13%
2406
7%
740
29%
740
13%
1811
November11th to 20thNight
18%
760
10%
2470
6%
760
24%
760
8%
1987
November21st to endNight
18%
888
5%
2762
3%
888
20%
888
8%
2287
December1st to 10thNight
15%
950
6%
2850
2%
950
20%
950
8%
2349
December11th to 20thNight
13%
949
5%
3520
1%
948
18%
948
5%
2853
December21st to endNight
10%
1039
3%
5120
1%
1026
14%
1026
3%
4672

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
15%10%48%7%45%5%5%7%31%
74544
Night
15%12%5%9%7%45%5%5%6%29%
75149
TransparencyDay
52%7%12%19%9%1
74250
Night
55%7%12%18%8%1
74978
SeeingDay
20%15%33%21%8%3
14518
Night
20%12%31%26%10%1
24250

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 10thDay
12%13%9%14%12%5%6%46%6%13%
1517
11th to 20thDay
16%13%8%13%12%6%5%5%5%6%12%
1440
21st to endDay
14%15%6%14%12%6%8%5%4413%
1584
February1st to 10thDay
8%13%5%11%12%7%7%6%7%7%17%
1480
11th to 20thDay
12%14%7%13%11%5%6%6%5%5%17%
1724
21st to endDay
12%13%9%14%10%5%5%445%19%
1480
March1st to 10thDay
12%14%5%9%9%45%5%45%28%
1798
11th to 20thDay
13%11%6%8%7%45%45%6%31%
1910
21st to endDay
17%11%5%9%7%4445%7%29%
2278
April1st to 10thDay
18%14%5%9%6%35%446%27%
2160
11th to 20thDay
19%12%6%7%5%3445%5%31%
2235
21st to endDay
16%12%47%6%3445%7%32%
2340
May1st to 10thDay
17%9%36%5%25%446%37%
2340
11th to 20thDay
17%8%36%5%345%5%7%40%
2460
21st to endDay
12%6%36%5%35%5%6%9%42%
2756
June1st to 10thDay
13%5%35%5%35%5%6%8%41%
2700
11th to 20thDay
14%7%26%5%35%5%6%9%39%
2700
21st to endDay
15%7%25%5%35%46%8%40%
2700
July1st to 10thDay
8%4245%345%6%9%50%
2556
11th to 20thDay
10%6%35%435%5%5%9%44%
2520
21st to endDay
9%6%35%5%35%6%6%9%43%
2743
August1st to 10thDay
10%435%5%35%6%6%9%43%
2471
11th to 20thDay
13%6%35%4345%5%8%44%
2303
21st to endDay
15%7%25%4345%6%8%42%
2485
September1st to 10thDay
17%7%25%6%35%45%8%39%
2156
11th to 20thDay
13%6%36%6%35%5%6%9%40%
1980
21st to endDay
17%9%36%6%35%5%6%8%33%
1980
October1st to 10thDay
20%8%48%6%35%5%5%7%31%
1980
11th to 20thDay
23%15%48%7%35%5%5%7%18%
1663
21st to endDay
24%17%38%8%45%45%6%15%
1782
November1st to 10thDay
19%14%6%7%6%35%5%5%5%25%
1672
11th to 20thDay
16%17%8%11%7%45%5%5%6%17%
1710
21st to endDay
18%18%8%11%9%45%5%4412%
1413
December1st to 10thDay
13%16%8%16%9%35%445%17%
1330
11th to 20thDay
16%20%7%14%8%5%5%345%13%
1671
21st to endDay
25%21%9%12%7%343449%
2527
January1st to 10thNight
13%15%7%14%10%5%6%5%5%5%16%
2648
11th to 20thNight
13%16%6%14%11%6%6%5%45%14%
2533
21st to endNight
13%13%7%13%13%5%7%5%45%14%
2772
February1st to 10thNight
9%15%6%9%12%5%7%6%5%6%21%
2478
11th to 20thNight
11%13%7%12%10%5%5%5%5%6%22%
2120
21st to endNight
12%16%6%13%8%45%46%6%21%
1776
March1st to 10thNight
10%11%48%7%35%5%7%7%33%
2149
11th to 20thNight
13%10%6%7%5%36%447%34%
2048
21st to endNight
13%11%48%6%345%6%6%34%
2093
April1st to 10thNight
18%13%5%6%6%45%5%7%6%27%
1800
11th to 20thNight
19%9%47%5%2445%6%35%
1674
21st to endNight
16%10%36%6%35%445%38%
1620
May1st to 10thNight
14%10%46%6%45%5%6%6%35%
1620
11th to 20thNight
17%8%36%7%45%6%5%7%33%
1433
21st to endNight
13%7%25%5%346%6%9%41%
1515
June1st to 10thNight
13%5%34435%5%7%8%42%
1260
11th to 20thNight
14%6%25%5%35%47%8%42%
1260
21st to endNight
15%7%3432445%8%46%
1260
July1st to 10thNight
10%4245%245%6%8%52%
1399
11th to 20thNight
11%6%245%35%5%6%7%47%
1440
21st to endNight
8%6%26%43445%8%51%
1575
August1st to 10thNight
7%6%25%5%4446%8%48%
1467
11th to 20thNight
8%425%5%345%5%7%53%
1598
21st to endNight
13%7%25%42445%7%46%
1867
September1st to 10thNight
12%7%35%4345%5%6%46%
1800
11th to 20thNight
15%7%25%5%2445%8%43%
1966
21st to endNight
17%7%35%5%3446%8%38%
1980
October1st to 10thNight
18%9%26%6%345%5%7%36%
1980
11th to 20thNight
20%13%36%6%35%5%6%6%26%
2293
21st to endNight
23%14%47%5%46%5%5%6%21%
2574
November1st to 10thNight
16%15%48%7%45%5%45%28%
2406
11th to 20thNight
18%14%6%11%6%36%5%6%5%20%
2470
21st to endNight
16%16%7%10%7%46%5%5%6%18%
2762
December1st to 10thNight
13%15%8%13%7%45%45%7%17%
2850
11th to 20thNight
15%14%6%15%8%45%5%6%5%18%
3526
21st to endNight
22%22%11%14%7%343238%
5137

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
72%8%8%10%2
1518
11th to 20thDay
73%8%8%10%2
1440
21st to endDay
75%6%8%7%31
1584
February1st to 10thDay
64%8%11%11%4
1480
11th to 20thDay
67%7%10%10%6%
1734
21st to endDay
68%6%7%12%6%
1480
March1st to 10thDay
57%6%10%17%8%1
1800
11th to 20thDay
55%5%12%20%7%2
1910
21st to endDay
56%6%11%18%9%1
2278
April1st to 10thDay
58%6%9%19%8%
2160
11th to 20thDay
54%5%10%19%11%1
2235
21st to endDay
52%5%9%18%12%4
2340
May1st to 10thDay
48%6%9%19%14%3
2340
11th to 20thDay
44%6%9%25%14%1
2464
21st to endDay
38%8%15%24%12%2
2756
June1st to 10thDay
39%7%12%24%15%2
2700
11th to 20thDay
41%7%12%22%16%1
2700
21st to endDay
42%7%14%24%12%2
2700
July1st to 10thDay
29%7%14%31%18%1
2487
11th to 20thDay
35%8%12%28%15%2
2445
21st to endDay
36%8%14%26%15%1
2591
August1st to 10thDay
36%8%16%29%12%1
2456
11th to 20thDay
37%8%14%29%13%1
2303
21st to endDay
40%7%16%24%12%1
2485
September1st to 10thDay
44%6%12%25%13%1
2156
11th to 20thDay
40%9%19%27%5%
1980
21st to endDay
48%8%16%21%7%
1980
October1st to 10thDay
52%8%13%20%7%
1980
11th to 20thDay
64%7%11%15%3
1663
21st to endDay
69%6%10%10%4
1782
November1st to 10thDay
60%6%13%17%5%
1672
11th to 20thDay
66%7%13%10%4
1710
21st to endDay
74%8%10%6%1
1413
December1st to 10thDay
70%6%11%9%4
1330
11th to 20thDay
74%7%8%9%3
1671
21st to endDay
81%5%5%5%3
2527
January1st to 10thNight
69%7%11%10%3
2648
11th to 20thNight
72%9%8%8%2
2533
21st to endNight
72%6%8%11%3
2772
February1st to 10thNight
63%7%10%13%6%1
2478
11th to 20thNight
64%5%11%15%5%
2121
21st to endNight
64%6%8%15%6%
1776
March1st to 10thNight
49%6%14%22%9%1
2160
11th to 20thNight
51%5%11%21%11%1
2049
21st to endNight
49%6%12%20%12%1
2093
April1st to 10thNight
55%7%10%16%11%1
1800
11th to 20thNight
49%5%9%23%11%2
1674
21st to endNight
49%6%10%19%14%3
1620
May1st to 10thNight
48%6%10%19%14%3
1620
11th to 20thNight
49%6%8%23%12%2
1434
21st to endNight
39%8%11%25%14%3
1516
June1st to 10thNight
37%7%14%23%17%2
1260
11th to 20thNight
39%6%13%23%15%3
1260
21st to endNight
37%6%11%29%14%2
1260
July1st to 10thNight
29%7%15%29%18%2
1359
11th to 20thNight
34%6%12%29%16%2
1392
21st to endNight
33%7%13%27%18%1
1487
August1st to 10thNight
33%7%16%30%13%2
1458
11th to 20thNight
30%6%16%33%13%1
1598
21st to endNight
36%6%15%28%14%1
1867
September1st to 10thNight
37%7%14%28%13%1
1800
11th to 20thNight
39%8%17%27%8%1
1966
21st to endNight
43%8%18%26%6%
1980
October1st to 10thNight
48%7%14%23%8%1
1980
11th to 20thNight
56%7%15%16%5%
2293
21st to endNight
64%7%11%14%4
2574
November1st to 10thNight
58%6%12%17%7%
2406
11th to 20thNight
64%8%10%11%6%
2470
21st to endNight
66%8%14%9%2
2762
December1st to 10thNight
67%7%12%12%2
2850
11th to 20thNight
67%7%12%9%4
3525
21st to endNight
83%46%5%2
5137

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
20%14%43%19%3
270
11th to 20thDay
23%15%41%17%31
240
21st to endDay
22%18%36%19%5%
264
February1st to 10thDay
19%24%42%12%3
240
11th to 20thDay
20%25%40%10%41
240
21st to endDay
27%29%33%11%
198
March1st to 10thDay
22%23%38%13%4
240
11th to 20thDay
23%17%35%17%9%1
350
21st to endDay
27%19%28%18%6%2
462
April1st to 10thDay
27%16%32%21%31
420
11th to 20thDay
26%20%25%19%8%1
412
21st to endDay
24%15%32%18%10%2
420
May1st to 10thDay
26%16%30%15%7%4
423
11th to 20thDay
19%17%37%17%8%2
606
21st to endDay
16%17%34%21%9%3
679
June1st to 10thDay
15%16%38%21%9%1
630
11th to 20thDay
18%16%33%24%6%3
630
21st to endDay
20%11%33%25%8%3
630
July1st to 10thDay
9%11%38%28%11%3
621
11th to 20thDay
12%12%34%26%11%5%
618
21st to endDay
12%9%35%26%13%5%
684
August1st to 10thDay
12%10%33%27%12%6%
590
11th to 20thDay
16%5%21%31%20%8%
439
21st to endDay
21%10%28%25%12%4
495
September1st to 10thDay
21%12%26%22%14%5%
450
11th to 20thDay
14%12%33%26%10%5%
450
21st to endDay
23%13%23%28%11%2
450
October1st to 10thDay
23%16%29%19%9%3
450
11th to 20thDay
31%18%33%16%21
303
21st to endDay
36%19%32%11%2
297
November1st to 10thDay
23%22%33%19%3
270
11th to 20thDay
24%26%31%14%5%
270
21st to endDay
28%28%32%10%11
192
December1st to 10thDay
24%19%31%18%7%2
180
11th to 20thDay
23%20%40%11%23
180
21st to endDay
33%20%30%12%5%
225
January1st to 10thNight
18%18%35%22%7%
950
11th to 20thNight
21%17%33%20%8%1
905
21st to endNight
20%13%37%22%6%1
990
February1st to 10thNight
16%16%39%23%6%
858
11th to 20thNight
21%17%33%23%6%1
703
21st to endNight
20%16%39%21%5%
592
March1st to 10thNight
16%15%35%25%8%1
720
11th to 20thNight
21%17%33%22%6%1
720
21st to endNight
19%11%33%27%8%1
707
April1st to 10thNight
25%12%30%26%6%1
540
11th to 20thNight
23%10%30%28%8%1
533
21st to endNight
20%10%33%28%8%1
540
May1st to 10thNight
18%11%32%31%8%1
540
11th to 20thNight
20%8%32%30%8%1
531
21st to endNight
16%8%29%32%14%
548
June1st to 10thNight
15%8%32%35%9%
360
11th to 20thNight
17%8%28%35%12%
360
21st to endNight
16%7%31%36%10%1
360
July1st to 10thNight
11%431%40%14%1
484
11th to 20thNight
13%427%34%21%2
522
21st to endNight
11%424%39%20%2
591
August1st to 10thNight
10%323%44%20%
537
11th to 20thNight
11%419%37%27%2
534
21st to endNight
15%427%34%17%2
594
September1st to 10thNight
16%423%34%19%3
540
11th to 20thNight
18%10%26%27%17%3
706
21st to endNight
20%8%25%31%14%2
720
October1st to 10thNight
23%9%28%26%12%2
720
11th to 20thNight
26%13%29%23%9%
720
21st to endNight
32%12%26%24%5%1
792
November1st to 10thNight
24%15%32%22%6%1
740
11th to 20thNight
26%18%30%20%7%
760
21st to endNight
26%17%32%19%5%
888
December1st to 10thNight
23%20%31%20%5%1
950
11th to 20thNight
23%19%33%17%6%2
950
21st to endNight
29%15%33%20%4
1045
Page generated at 2024-01-08 11:14:19. Version ac07

Copyright 2024 Attilla Danko


Helmer Observatory Clear Sky Chart |Charts Home