Armstrong
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Armstrong clear sky chart from 2005-11-06 to 2024-02-05.

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
27%
24438
9%
80405
5%
24337
32%
24337
13%
61066

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
19%
946
6%
4584
4%
926
26%
926
6%
3661
January11th to 20thNight
21%
940
5%
4422
2%
930
25%
930
6%
3638
January21st to endNight
20%
1037
5%
4878
3%
1023
26%
1023
6%
3951
February1st to 10thNight
25%
923
11%
2561
5%
923
30%
923
15%
1965
February11th to 20thNight
30%
879
13%
2274
5%
875
35%
875
18%
1727
February21st to endNight
26%
599
15%
1783
6%
599
34%
599
17%
1316
March1st to 10thNight
28%
718
14%
2160
8%
718
33%
718
16%
1567
March11th to 20thNight
24%
664
14%
2104
7%
664
32%
664
15%
1506
March21st to endNight
34%
594
20%
1990
15%
594
44%
594
19%
1338
April1st to 10thNight
30%
540
13%
1800
9%
540
38%
540
16%
1273
April11th to 20thNight
31%
533
12%
1733
8%
533
37%
533
17%
1248
April21st to endNight
35%
540
15%
1508
8%
540
40%
540
24%
1052
May1st to 10thNight
32%
540
11%
1440
5%
540
35%
540
20%
1065
May11th to 20thNight
32%
531
12%
1416
5%
531
37%
531
24%
1000
May21st to endNight
32%
487
8%
1455
4%
485
35%
485
17%
1063
June1st to 10thNight
34%
360
5%
1238
5%
360
38%
360
18%
830
June11th to 20thNight
34%
360
4%
1080
3%
360
37%
360
24%
711
June21st to endNight
37%
360
4%
1080
4%
360
38%
360
23%
733
July1st to 10thNight
39%
389
7%
1089
4%
389
44%
389
29%
694
July11th to 20thNight
42%
522
7%
1363
3%
522
44%
522
30%
902
July21st to endNight
51%
591
11%
1487
5%
558
52%
558
32%
963
August1st to 10thNight
45%
537
12%
1423
6%
534
49%
534
28%
974
August11th to 20thNight
47%
534
16%
1422
8%
534
53%
534
29%
933
August21st to endNight
41%
594
15%
1926
10%
594
49%
594
24%
1229
September1st to 10thNight
45%
540
17%
1800
13%
540
52%
540
26%
1098
September11th to 20thNight
30%
572
13%
1832
8%
572
38%
572
18%
1289
September21st to endNight
32%
720
12%
1980
7%
720
36%
720
19%
1468
October1st to 10thNight
28%
720
11%
2150
6%
720
33%
720
16%
1592
October11th to 20thNight
23%
720
9%
2254
5%
720
28%
720
11%
1774
October21st to endNight
20%
792
7%
2574
4%
792
24%
792
8%
2108
November1st to 10thNight
17%
816
8%
2482
4%
816
22%
816
8%
2049
November11th to 20thNight
14%
950
6%
2660
2%
950
17%
950
7%
2298
November21st to endNight
12%
950
4%
2847
1%
950
14%
950
5%
2503
December1st to 10thNight
14%
950
5%
2850
1%
950
18%
950
7%
2410
December11th to 20thNight
18%
950
9%
3459
3%
949
23%
949
6%
2781
December21st to endNight
18%
1040
4%
5301
4%
1026
21%
1026
3%
4357

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%11%5%9%7%45%5%5%6%27%
78083
Night
13%12%5%9%8%46%5%5%6%25%
80769
TransparencyDay
55%7%11%18%8%1
77778
Night
58%7%11%17%7%1
80608
SeeingDay
21%15%33%21%8%2
14757
Night
20%11%32%26%9%1
24467

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
9%11%6%14%13%10%11%7%6%5%9%
2344
11th to 20thDay
6%8%6%13%15%9%10%7%46%16%
2530
21st to endDay
13%17%8%17%10%46%5%6%410%
2783
February1st to 10thDay
6%12%412%9%6%7%10%7%5%22%
1492
11th to 20thDay
7%12%6%10%8%5%8%7%8%6%23%
1574
21st to endDay
411%7%11%10%47%6%6%8%26%
1472
March1st to 10thDay
10%10%5%11%9%46%5%45%31%
1798
11th to 20thDay
11%13%5%10%7%35%5%5%6%31%
1872
21st to endDay
14%10%48%7%45%45%6%33%
2366
April1st to 10thDay
13%11%5%9%7%345%46%34%
2160
11th to 20thDay
17%11%5%7%5%3445%6%33%
2175
21st to endDay
15%12%46%6%3445%6%35%
2451
May1st to 10thDay
20%11%5%8%7%3445%6%26%
2520
11th to 20thDay
19%9%46%5%35%5%5%7%31%
2479
21st to endDay
20%6%35%5%35%45%7%35%
2819
June1st to 10thDay
21%7%46%6%35%5%5%6%31%
2718
11th to 20thDay
15%6%36%6%46%5%6%7%35%
2880
21st to endDay
16%6%36%6%45%6%5%8%34%
2880
July1st to 10thDay
15%6%35%6%46%6%5%7%38%
2836
11th to 20thDay
14%6%26%7%46%6%6%9%34%
2548
21st to endDay
14%6%36%6%46%6%6%8%35%
2743
August1st to 10thDay
12%6%35%7%5%6%6%7%9%34%
2507
11th to 20thDay
13%6%25%6%445%6%9%40%
2479
21st to endDay
16%9%47%5%345%6%7%33%
2428
September1st to 10thDay
18%7%37%6%345%5%6%36%
2160
11th to 20thDay
24%9%46%5%2445%6%30%
2109
21st to endDay
23%11%37%5%245%46%30%
1980
October1st to 10thDay
19%18%5%8%5%34445%25%
1807
11th to 20thDay
21%20%5%8%7%34445%19%
1706
21st to endDay
19%22%6%11%7%34435%16%
1782
November1st to 10thDay
17%17%8%13%8%44445%18%
1593
11th to 20thDay
17%21%8%13%10%4433411%
1520
21st to endDay
17%19%9%15%9%5%5%43311%
1330
December1st to 10thDay
10%14%7%14%10%6%7%6%5%5%15%
1330
11th to 20thDay
11%15%6%11%8%6%6%7%6%7%17%
1671
21st to endDay
17%21%8%10%9%5%5%5%6%411%
2241
January1st to 10thNight
6%14%7%12%11%8%8%6%7%7%13%
4597
11th to 20thNight
7%8%5%14%14%8%11%8%7%6%12%
4440
21st to endNight
9%15%8%13%10%5%7%7%6%6%13%
4884
February1st to 10thNight
6%11%6%10%8%5%9%9%7%8%22%
2561
11th to 20thNight
7%13%47%9%5%9%8%8%7%24%
2273
21st to endNight
6%10%7%11%8%5%6%7%7%7%27%
1783
March1st to 10thNight
7%9%5%10%10%5%7%5%6%6%28%
2149
11th to 20thNight
12%11%5%8%8%45%446%32%
2103
21st to endNight
12%10%47%7%45%45%6%36%
1990
April1st to 10thNight
14%11%5%9%7%4445%6%32%
1800
11th to 20thNight
16%13%47%5%36%45%6%32%
1733
21st to endNight
14%10%5%7%5%3445%6%37%
1508
May1st to 10thNight
17%10%38%5%45%5%5%5%32%
1440
11th to 20thNight
18%7%36%5%35%45%7%37%
1416
21st to endNight
22%8%36%5%345%5%5%33%
1454
June1st to 10thNight
18%5%247%35%5%7%7%35%
1238
11th to 20thNight
14%8%25%6%346%5%5%43%
1080
21st to endNight
16%7%35%435%5%5%9%36%
1080
July1st to 10thNight
10%6%36%6%25%5%5%8%43%
1121
11th to 20thNight
11%6%36%4445%6%8%43%
1409
21st to endNight
10%6%25%435%6%6%8%45%
1575
August1st to 10thNight
11%5%36%6%35%5%6%8%41%
1432
11th to 20thNight
12%6%25%6%25%5%5%9%44%
1422
21st to endNight
13%6%25%6%35%5%6%9%40%
1926
September1st to 10thNight
14%6%25%4335%5%7%47%
1800
11th to 20thNight
19%9%46%5%3445%6%35%
1832
21st to endNight
25%9%46%424446%34%
1980
October1st to 10thNight
19%14%47%5%34346%32%
2150
11th to 20thNight
18%18%5%8%6%44446%24%
2254
21st to endNight
20%17%5%9%8%45%5%5%6%17%
2574
November1st to 10thNight
19%16%7%11%8%45%44420%
2482
11th to 20thNight
18%16%7%13%10%5%5%44415%
2660
21st to endNight
16%18%7%13%11%47%43312%
2847
December1st to 10thNight
10%14%7%14%12%6%6%6%5%5%14%
2850
11th to 20thNight
11%14%6%14%9%5%6%6%6%6%17%
3526
21st to endNight
15%18%7%11%10%5%5%6%5%5%14%
5400

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
73%7%8%9%2
2345
11th to 20thDay
68%5%9%15%3
2530
21st to endDay
74%6%7%8%5%
2783
February1st to 10thDay
58%7%10%18%6%1
1492
11th to 20thDay
56%6%10%18%9%
1583
21st to endDay
54%5%11%16%14%1
1472
March1st to 10thDay
55%410%18%11%1
1800
11th to 20thDay
53%6%11%16%12%2
1872
21st to endDay
50%6%10%19%14%1
2366
April1st to 10thDay
52%411%19%13%2
2160
11th to 20thDay
52%5%9%22%11%1
2175
21st to endDay
48%6%10%18%15%2
2451
May1st to 10thDay
58%6%9%18%8%
2520
11th to 20thDay
51%6%11%21%10%1
2483
21st to endDay
48%7%12%19%13%1
2819
June1st to 10thDay
51%7%11%17%14%
2718
11th to 20thDay
45%8%10%21%13%1
2880
21st to endDay
45%9%16%21%9%
2880
July1st to 10thDay
41%9%13%26%11%1
2759
11th to 20thDay
41%10%15%24%9%1
2471
21st to endDay
44%9%13%25%8%
2591
August1st to 10thDay
42%10%19%24%5%
2492
11th to 20thDay
40%9%17%26%9%
2479
21st to endDay
47%9%14%21%8%1
2428
September1st to 10thDay
47%7%12%26%8%
2160
11th to 20thDay
54%8%15%18%5%
2109
21st to endDay
54%6%14%20%6%
1980
October1st to 10thDay
60%7%11%18%3
1807
11th to 20thDay
67%5%12%13%2
1706
21st to endDay
70%7%9%11%3
1782
November1st to 10thDay
70%6%11%10%4
1593
11th to 20thDay
77%7%8%6%2
1520
21st to endDay
77%6%8%5%3
1330
December1st to 10thDay
67%9%9%12%3
1330
11th to 20thDay
64%6%11%13%5%
1671
21st to endDay
74%6%7%10%4
2241
January1st to 10thNight
67%6%11%12%3
4597
11th to 20thNight
69%7%10%11%2
4440
21st to endNight
69%6%11%9%4
4884
February1st to 10thNight
56%8%10%18%8%
2561
11th to 20thNight
55%6%12%20%7%
2274
21st to endNight
54%7%11%20%9%1
1783
March1st to 10thNight
53%6%11%19%10%1
2160
11th to 20thNight
54%5%11%20%9%1
2104
21st to endNight
48%5%9%19%15%3
1990
April1st to 10thNight
53%5%8%20%12%2
1800
11th to 20thNight
53%6%8%20%11%2
1733
21st to endNight
47%5%10%20%13%4
1508
May1st to 10thNight
52%6%10%20%11%1
1440
11th to 20thNight
46%6%10%23%13%2
1417
21st to endNight
51%8%9%17%14%2
1455
June1st to 10thNight
45%9%12%21%12%1
1238
11th to 20thNight
42%6%10%25%15%1
1080
21st to endNight
44%8%14%24%10%1
1080
July1st to 10thNight
36%7%14%29%13%
1089
11th to 20thNight
35%10%14%32%9%
1363
21st to endNight
34%9%17%31%9%1
1487
August1st to 10thNight
39%10%18%27%6%1
1423
11th to 20thNight
36%9%15%29%11%
1422
21st to endNight
38%10%19%24%9%1
1926
September1st to 10thNight
37%7%16%29%11%1
1800
11th to 20thNight
49%8%16%23%4
1832
21st to endNight
52%7%13%22%6%
1980
October1st to 10thNight
54%7%15%19%5%
2150
11th to 20thNight
61%7%13%15%3
2254
21st to endNight
65%9%11%12%2
2574
November1st to 10thNight
67%7%11%11%31
2482
11th to 20thNight
74%6%8%10%3
2660
21st to endNight
75%7%8%7%2
2847
December1st to 10thNight
68%9%9%10%4
2850
11th to 20thNight
65%7%9%15%4
3525
21st to endNight
70%7%7%14%2
5400

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
18%13%37%27%5%
256
11th to 20thDay
13%12%39%24%9%3
270
21st to endDay
16%11%38%23%10%1
297
February1st to 10thDay
13%15%44%23%4
252
11th to 20thDay
16%17%48%11%7%2
240
21st to endDay
13%25%39%18%5%1
198
March1st to 10thDay
15%16%44%16%6%2
240
11th to 20thDay
21%22%33%19%41
240
21st to endDay
19%12%34%23%10%2
452
April1st to 10thDay
20%18%32%22%6%2
420
11th to 20thDay
25%15%28%21%10%1
412
21st to endDay
21%17%30%22%8%3
531
May1st to 10thDay
24%16%31%20%7%2
603
11th to 20thDay
21%18%32%19%7%3
625
21st to endDay
25%15%32%21%7%1
679
June1st to 10thDay
23%16%30%20%9%2
630
11th to 20thDay
18%15%38%19%7%3
630
21st to endDay
18%13%33%24%9%3
630
July1st to 10thDay
16%14%34%23%10%3
621
11th to 20thDay
16%15%32%24%10%3
618
21st to endDay
13%13%30%28%11%5%
684
August1st to 10thDay
16%12%33%25%11%3
626
11th to 20thDay
18%10%30%26%11%4
615
21st to endDay
22%13%29%21%12%3
516
September1st to 10thDay
23%14%28%23%10%2
450
11th to 20thDay
28%11%30%21%8%1
450
21st to endDay
30%12%25%22%9%2
450
October1st to 10thDay
29%13%31%19%6%1
277
11th to 20thDay
26%17%34%16%6%1
270
21st to endDay
36%20%32%9%4
297
November1st to 10thDay
24%17%37%18%4
270
11th to 20thDay
29%20%33%13%41
270
21st to endDay
34%21%26%16%3
180
December1st to 10thDay
17%18%36%22%43
180
11th to 20thDay
21%19%35%19%7%
180
21st to endDay
21%18%30%20%7%4
198
January1st to 10thNight
15%14%40%25%5%
950
11th to 20thNight
18%11%35%27%8%1
950
21st to endNight
14%10%38%26%10%1
1045
February1st to 10thNight
13%10%41%27%8%1
923
11th to 20thNight
13%14%35%27%10%1
879
21st to endNight
11%12%38%28%11%2
599
March1st to 10thNight
13%14%33%26%13%1
720
11th to 20thNight
20%14%34%22%7%2
664
21st to endNight
18%11%29%28%11%3
594
April1st to 10thNight
19%13%28%32%7%1
540
11th to 20thNight
24%9%29%30%8%
533
21st to endNight
19%7%31%28%13%2
540
May1st to 10thNight
22%12%29%28%9%
540
11th to 20thNight
21%10%31%29%8%1
531
21st to endNight
25%10%29%28%9%
487
June1st to 10thNight
21%7%31%30%11%1
360
11th to 20thNight
18%9%34%27%11%
360
21st to endNight
19%8%31%29%12%1
360
July1st to 10thNight
13%8%32%34%13%1
389
11th to 20thNight
12%8%31%34%14%1
522
21st to endNight
13%6%25%34%19%2
591
August1st to 10thNight
13%9%28%36%14%
537
11th to 20thNight
15%7%25%31%19%3
534
21st to endNight
15%8%31%31%14%1
594
September1st to 10thNight
18%8%25%35%13%1
540
11th to 20thNight
25%10%30%24%10%
572
21st to endNight
30%7%26%26%9%1
720
October1st to 10thNight
29%14%25%24%8%1
720
11th to 20thNight
28%11%28%25%7%1
720
21st to endNight
28%13%30%21%7%1
792
November1st to 10thNight
27%14%34%19%6%1
816
11th to 20thNight
27%13%32%21%6%1
950
21st to endNight
27%17%31%19%5%
950
December1st to 10thNight
17%16%40%19%7%2
950
11th to 20thNight
20%15%34%21%8%1
950
21st to endNight
24%12%28%26%8%2
1045
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