Four Corners Algonquin Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Four Corners Algonquin Observatory clear sky chart from 2005-11-05 to 2019-06-02.

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
24%
16845
12%
53607
6%
16812
31%
16812
14%
39486

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
11%
840
6%
2926
2%
836
16%
836
5%
2443
January16th to endNight
15%
896
9%
2989
4%
896
22%
896
8%
2382
February1st to 15thNight
11%
824
9%
2677
3%
821
18%
821
8%
2145
February16th to endNight
14%
735
10%
2353
4%
735
22%
735
11%
1799
March1st to 15thNight
14%
840
12%
2349
4%
840
22%
840
13%
1804
March16th to endNight
27%
896
19%
2444
8%
896
36%
896
23%
1660
April1st to 15thNight
17%
838
15%
2096
4%
838
23%
838
17%
1589
April16th to endNight
29%
673
16%
1919
8%
673
35%
673
20%
1385
May1st to 15thNight
34%
470
17%
1730
14%
470
43%
470
17%
1133
May16th to endNight
29%
439
13%
1753
7%
438
43%
438
19%
1071
June1st to 15thNight
32%
392
10%
1569
8%
392
41%
392
16%
1018
June16th to endNight
38%
390
10%
1386
10%
390
45%
390
20%
894
July1st to 15thNight
43%
370
16%
1403
18%
370
51%
370
29%
773
July16th to endNight
45%
408
13%
1546
13%
386
52%
386
24%
910
August1st to 15thNight
49%
575
14%
1715
9%
572
54%
572
27%
1106
August16th to endNight
45%
694
16%
1936
8%
694
50%
694
32%
1219
September1st to 15thNight
41%
780
17%
1950
7%
780
44%
780
30%
1319
September16th to endNight
42%
777
19%
2158
13%
777
46%
777
27%
1420
October1st to 15thNight
25%
780
14%
2340
8%
780
34%
780
18%
1687
October16th to endNight
16%
832
10%
2522
4%
832
24%
832
10%
2024
November1st to 15thNight
23%
820
13%
2830
9%
820
30%
820
11%
2129
November16th to endNight
16%
840
8%
2940
5%
840
21%
840
7%
2418
December1st to 15thNight
11%
840
6%
2940
1%
840
17%
840
5%
2514
December16th to endNight
10%
896
7%
3136
3%
896
15%
896
5%
2644

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
17%11%47%6%34446%28%
54729
Night
15%12%5%8%6%34446%29%
53777
Cloud CoverDay
17%11%47%6%34446%28%
54739
Night
15%11%48%6%34446%29%
53782
TransparencyDay
56%6%10%17%9%1
54417
Night
55%6%11%17%9%
53607
SeeingDay
25%16%31%17%6%2
7657
Night
22%15%31%20%7%
16845

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 15thDay
16%16%7%12%8%24345%17%
1672
16th to endDay
13%14%6%12%9%35%5%45%19%
1938
February1st to 15thDay
10%16%7%12%11%35%5%3418%
1845
16th to endDay
15%17%5%10%8%35%435%20%
1691
March1st to 15thDay
14%15%6%9%8%4443425%
2257
16th to endDay
12%10%5%7%6%34345%35%
2483
April1st to 15thDay
22%14%5%6%5%24345%27%
2512
16th to endDay
21%10%25%42233436%
2658
May1st to 15thDay
20%11%46%5%24345%32%
2879
16th to endDay
16%7%36%6%34447%34%
3066
June1st to 15thDay
22%8%46%5%34447%28%
2744
16th to endDay
17%7%35%5%35%5%5%8%31%
2898
July1st to 15thDay
14%6%25%5%26%5%5%6%38%
2805
16th to endDay
13%6%36%7%46%5%5%8%32%
2876
August1st to 15thDay
15%7%27%7%45%5%5%6%30%
2487
16th to endDay
16%6%26%5%46%5%6%8%32%
2604
September1st to 15thDay
19%7%35%42435%6%35%
2340
16th to endDay
18%6%35%5%33347%38%
2130
October1st to 15thDay
22%11%46%6%34336%28%
1950
16th to endDay
28%16%5%7%5%23335%18%
2054
November1st to 15thDay
19%14%48%5%24346%24%
1688
16th to endDay
21%17%8%10%6%3423416%
1680
December1st to 15thDay
16%21%8%12%7%3434412%
1680
16th to endDay
17%19%8%12%6%33345%14%
1792
January1st to 15thNight
16%17%7%11%9%46%44414%
2926
16th to endNight
12%14%6%12%8%46%5%45%19%
2989
February1st to 15thNight
11%15%8%11%9%45%445%19%
2675
16th to endNight
11%16%5%9%7%44445%24%
2353
March1st to 15thNight
15%12%5%11%6%3434428%
2337
16th to endNight
10%10%47%6%2335%6%39%
2444
April1st to 15thNight
19%12%5%7%5%23345%31%
2096
16th to endNight
20%9%36%5%24345%35%
1919
May1st to 15thNight
20%8%25%42435%7%35%
1730
16th to endNight
13%6%25%42445%7%41%
1751
June1st to 15thNight
17%7%26%43446%7%36%
1569
16th to endNight
12%7%36%6%25%5%5%7%37%
1386
July1st to 15thNight
10%424423447%50%
1482
16th to endNight
10%5%235%25%46%8%44%
1642
August1st to 15thNight
10%6%245%3445%8%44%
1726
16th to endNight
10%5%25%42446%8%45%
1936
September1st to 15thNight
13%6%245%3345%8%42%
1950
16th to endNight
14%8%34423346%44%
2158
October1st to 15thNight
19%9%35%5%24345%34%
2340
16th to endNight
24%14%47%6%24445%21%
2522
November1st to 15thNight
17%13%5%6%6%3445%5%27%
2830
16th to endNight
19%17%6%9%7%3443418%
2940
December1st to 15thNight
16%19%9%12%6%3444414%
2940
16th to endNight
18%17%7%12%7%3433414%
3136

Percentage Cloud Cover SE (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
16%16%7%12%8%33345%17%
1672
16th to endDay
12%14%6%12%9%35%5%45%19%
1938
February1st to 15thDay
11%15%8%12%10%35%43418%
1845
16th to endDay
15%17%5%9%8%35%43421%
1691
March1st to 15thDay
14%15%5%9%7%4443424%
2268
16th to endDay
12%9%5%7%6%34246%35%
2482
April1st to 15thDay
22%13%5%6%5%23335%27%
2512
16th to endDay
22%10%26%42223436%
2658
May1st to 15thDay
19%10%47%434345%32%
2879
16th to endDay
16%7%36%6%3445%7%34%
3066
June1st to 15thDay
22%8%46%5%34447%28%
2744
16th to endDay
17%6%35%6%45%5%5%7%31%
2898
July1st to 15thDay
14%5%25%5%36%5%5%7%37%
2805
16th to endDay
13%5%36%7%36%5%5%8%32%
2876
August1st to 15thDay
14%7%37%7%46%6%6%6%30%
2487
16th to endDay
15%6%26%5%45%6%5%8%32%
2604
September1st to 15thDay
20%7%25%42445%7%35%
2340
16th to endDay
18%6%345%33346%39%
2130
October1st to 15thDay
21%10%47%5%34345%28%
1950
16th to endDay
29%15%47%5%23335%18%
2054
November1st to 15thDay
19%14%47%6%23446%25%
1688
16th to endDay
21%16%9%9%7%3433416%
1680
December1st to 15thDay
15%22%7%13%7%3443412%
1680
16th to endDay
17%19%7%12%6%23345%15%
1792
January1st to 15thNight
15%17%6%11%9%46%5%4414%
2926
16th to endNight
12%13%6%11%9%46%5%5%419%
2989
February1st to 15thNight
11%15%7%11%9%5%4445%19%
2668
16th to endNight
12%15%5%9%7%35%445%24%
2353
March1st to 15thNight
16%12%5%10%6%4444428%
2349
16th to endNight
10%10%47%6%2335%6%39%
2444
April1st to 15thNight
19%12%5%7%423345%31%
2096
16th to endNight
19%10%35%5%23346%35%
1919
May1st to 15thNight
19%8%25%32335%7%36%
1730
16th to endNight
13%6%245%2446%7%41%
1751
June1st to 15thNight
17%7%35%43446%7%36%
1569
16th to endNight
12%6%26%6%26%5%5%8%37%
1386
July1st to 15thNight
9%42442335%7%50%
1482
16th to endNight
10%5%245%35%5%5%8%45%
1642
August1st to 15thNight
10%5%25%43445%9%43%
1726
16th to endNight
10%42442446%8%45%
1936
September1st to 15thNight
14%6%24434448%43%
1950
16th to endNight
14%8%1441335%5%44%
2158
October1st to 15thNight
19%10%35%424446%34%
2340
16th to endNight
23%15%46%6%34445%21%
2522
November1st to 15thNight
17%12%5%7%6%3445%5%27%
2830
16th to endNight
19%17%5%9%7%34435%18%
2940
December1st to 15thNight
16%19%9%11%7%3334414%
2940
16th to endNight
18%17%8%12%7%35%33415%
3136

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
69%47%11%6%
1673
16th to endDay
65%6%8%10%7%1
1938
February1st to 15thDay
68%5%7%12%5%
1847
16th to endDay
66%47%12%9%
1691
March1st to 15thDay
64%49%14%5%1
2268
16th to endDay
50%47%19%14%4
2483
April1st to 15thDay
59%47%15%10%2
2512
16th to endDay
51%37%20%13%2
2658
May1st to 15thDay
54%48%18%11%1
2879
16th to endDay
48%6%12%18%12%1
3070
June1st to 15thDay
54%6%9%17%9%
2744
16th to endDay
49%7%11%18%11%1
2898
July1st to 15thDay
42%7%10%26%11%1
2655
16th to endDay
48%7%13%21%8%
2709
August1st to 15thDay
51%8%14%17%7%
2474
16th to endDay
46%8%13%22%7%
2604
September1st to 15thDay
47%6%12%21%10%
2340
16th to endDay
45%7%11%27%8%
2130
October1st to 15thDay
57%5%10%15%8%
1950
16th to endDay
69%5%9%10%4
2054
November1st to 15thDay
60%7%11%13%6%
1688
16th to endDay
73%47%9%31
1680
December1st to 15thDay
75%48%8%3
1680
16th to endDay
71%5%6%10%5%
1792
January1st to 15thNight
71%6%8%8%4
2926
16th to endNight
65%5%8%11%7%
2989
February1st to 15thNight
67%5%10%12%5%
2677
16th to endNight
60%5%9%16%7%
2353
March1st to 15thNight
59%410%16%8%1
2349
16th to endNight
44%410%20%16%2
2444
April1st to 15thNight
56%38%18%12%1
2096
16th to endNight
51%47%18%16%1
1919
May1st to 15thNight
47%5%11%18%15%1
1730
16th to endNight
39%7%14%21%14%1
1753
June1st to 15thNight
46%6%12%20%12%1
1569
16th to endNight
43%6%13%23%11%
1386
July1st to 15thNight
31%7%13%26%20%1
1403
16th to endNight
36%7%16%27%11%
1546
August1st to 15thNight
36%9%17%25%10%
1715
16th to endNight
34%7%19%27%9%
1936
September1st to 15thNight
39%7%16%24%12%
1950
16th to endNight
40%5%14%30%7%
2158
October1st to 15thNight
51%6%11%18%11%
2340
16th to endNight
64%6%10%13%4
2522
November1st to 15thNight
57%7%12%14%7%
2830
16th to endNight
68%6%9%10%3
2940
December1st to 15thNight
73%5%7%9%3
2940
16th to endNight
73%46%8%5%
3136

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
30%25%30%10%3
120
16th to endDay
28%24%34%11%1
170
February1st to 15thDay
31%32%32%4
180
16th to endDay
36%24%30%7%2
194
March1st to 15thDay
28%21%31%16%1
390
16th to endDay
22%19%34%16%7%
416
April1st to 15thDay
30%20%31%12%4
390
16th to endDay
29%16%27%14%9%2
379
May1st to 15thDay
32%14%29%15%5%2
408
16th to endDay
21%19%34%16%5%1
459
June1st to 15thDay
25%13%34%20%6%
379
16th to endDay
19%12%37%21%6%2
543
July1st to 15thDay
14%10%34%30%8%2
439
16th to endDay
14%10%34%27%11%2
390
August1st to 15thDay
18%6%31%27%8%6%
358
16th to endDay
20%9%25%26%11%6%
396
September1st to 15thDay
18%10%26%20%14%8%
375
16th to endDay
20%12%29%18%13%5%
374
October1st to 15thDay
28%20%28%14%6%2
375
16th to endDay
39%20%26%10%3
392
November1st to 15thDay
37%17%28%13%1
162
16th to endDay
35%25%30%7%
120
December1st to 15thDay
28%23%29%19%
120
16th to endDay
25%35%25%10%3
128
January1st to 15thNight
26%23%32%14%3
840
16th to endNight
22%18%34%18%41
896
February1st to 15thNight
19%21%40%13%4
824
16th to endNight
21%20%37%17%2
735
March1st to 15thNight
23%21%34%16%3
840
16th to endNight
16%18%34%21%8%1
896
April1st to 15thNight
26%19%31%18%4
838
16th to endNight
25%14%27%20%10%
673
May1st to 15thNight
24%10%28%26%10%
470
16th to endNight
17%10%39%23%9%
439
June1st to 15thNight
21%9%32%29%7%
392
16th to endNight
15%9%31%32%11%
390
July1st to 15thNight
12%433%34%14%1
370
16th to endNight
10%7%34%33%13%
408
August1st to 15thNight
11%5%26%33%18%3
575
16th to endNight
11%6%31%30%17%1
694
September1st to 15thNight
16%7%29%26%15%3
780
16th to endNight
20%9%24%27%16%2
777
October1st to 15thNight
26%13%30%19%8%1
780
16th to endNight
33%17%28%15%4
832
November1st to 15thNight
26%19%26%19%7%
820
16th to endNight
30%18%29%16%4
840
December1st to 15thNight
27%22%33%13%2
840
16th to endNight
30%19%31%15%3
896
Page generated at 2019-06-02 19:43:06. Version ac04

Copyright 2019 A. Danko


Four Corners Algonquin Observatory Clear Sky Chart |Charts Home