St. Anthony
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the St. Anthony 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
22%
23895
8%
74913
3%
23824
27%
23824
11%
59199

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%
850
9%
2839
2%
847
22%
847
7%
2305
January11th to 20thNight
16%
814
6%
2656
1%
814
22%
814
6%
2197
January21st to endNight
17%
880
11%
2772
4%
880
26%
880
11%
2153
February1st to 10thNight
22%
800
10%
2520
3%
800
30%
800
12%
1886
February11th to 20thNight
16%
766
9%
2319
2%
763
22%
763
12%
1765
February21st to endNight
24%
592
13%
1776
3%
592
32%
592
15%
1302
March1st to 10thNight
22%
717
11%
2160
3%
717
29%
717
11%
1667
March11th to 20thNight
26%
622
12%
2062
7%
622
32%
622
12%
1571
March21st to endNight
19%
594
10%
2058
5%
594
27%
594
10%
1621
April1st to 10thNight
17%
540
9%
1800
5%
540
24%
540
8%
1451
April11th to 20thNight
25%
534
12%
1602
9%
534
29%
534
13%
1247
April21st to endNight
23%
540
10%
1616
5%
540
27%
540
13%
1257
May1st to 10thNight
21%
540
4%
1440
1%
540
22%
540
9%
1231
May11th to 20thNight
23%
532
5%
1266
1%
532
25%
532
13%
1051
May21st to endNight
21%
583
3%
1356
1%
582
23%
582
12%
1149
June1st to 10thNight
24%
540
0%
1260
0%
540
24%
540
10%
1102
June11th to 20thNight
26%
540
0%
1260
0%
540
26%
540
12%
1080
June21st to endNight
28%
540
0%
1260
0%
540
28%
540
12%
1078
July1st to 10thNight
28%
526
1%
1226
1%
526
29%
526
14%
1009
July11th to 20thNight
32%
522
3%
1218
2%
522
32%
522
20%
967
July21st to endNight
33%
590
4%
1420
2%
558
35%
558
14%
1157
August1st to 10thNight
32%
538
4%
1422
1%
534
33%
534
14%
1153
August11th to 20thNight
37%
532
7%
1514
4%
532
38%
532
14%
1173
August21st to endNight
32%
594
8%
1782
5%
594
35%
594
13%
1398
September1st to 10thNight
29%
540
10%
1778
6%
540
36%
540
16%
1280
September11th to 20thNight
21%
540
10%
1954
5%
540
30%
540
12%
1440
September21st to endNight
24%
540
11%
1980
6%
540
32%
540
13%
1413
October1st to 10thNight
22%
584
12%
2044
4%
584
31%
584
13%
1507
October11th to 20thNight
29%
810
13%
2340
5%
810
35%
810
15%
1786
October21st to endNight
21%
891
9%
2574
3%
891
24%
891
11%
2067
November1st to 10thNight
16%
830
10%
2462
2%
830
22%
830
11%
1904
November11th to 20thNight
22%
850
9%
2812
3%
850
28%
850
11%
2153
November21st to endNight
13%
850
8%
2850
1%
850
20%
850
6%
2331
December1st to 10thNight
14%
850
7%
2850
2%
850
21%
850
7%
2361
December11th to 20thNight
14%
850
5%
3511
2%
849
18%
849
5%
2917
December21st to endNight
18%
934
3%
5154
2%
907
22%
907
4%
4070

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
23%13%5%7%6%3445%6%24%
74585
Night
22%13%5%8%6%35%45%6%24%
75159
TransparencyDay
60%7%12%14%6%
74272
Night
62%7%11%13%6%1
75007
SeeingDay
29%11%27%23%9%2
16980
Night
28%11%28%24%8%1
23900

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
18%14%6%9%7%46%5%7%5%20%
1326
11th to 20thDay
12%16%6%9%8%47%6%7%7%18%
1356
21st to endDay
13%15%5%11%9%5%4347%23%
1584
February1st to 10thDay
14%13%5%8%7%36%6%5%5%27%
1440
11th to 20thDay
14%15%5%9%7%45%45%6%27%
1529
21st to endDay
13%15%5%7%6%3445%6%31%
1480
March1st to 10thDay
18%12%6%9%7%445%5%5%26%
1796
11th to 20thDay
14%16%6%10%8%44445%24%
1898
21st to endDay
22%16%6%7%7%34335%23%
2294
April1st to 10thDay
23%16%6%9%6%3435%5%20%
2160
11th to 20thDay
19%13%6%7%6%4445%6%26%
2306
21st to endDay
23%14%7%9%6%33445%22%
2343
May1st to 10thDay
26%19%6%7%5%33435%18%
2520
11th to 20thDay
24%14%5%8%5%44346%23%
2627
21st to endDay
28%14%5%7%6%34445%21%
2918
June1st to 10thDay
33%15%47%5%34445%17%
2700
11th to 20thDay
30%14%5%7%424346%21%
2700
21st to endDay
25%13%47%5%345%47%22%
2700
July1st to 10thDay
26%11%48%5%3445%6%23%
2700
11th to 20thDay
20%11%47%5%345%5%6%31%
2700
21st to endDay
23%10%47%6%45%5%6%7%24%
2812
August1st to 10thDay
26%11%36%5%3445%6%27%
2506
11th to 20thDay
22%10%46%6%35%5%5%7%27%
2385
21st to endDay
25%9%47%5%35%5%5%6%26%
2574
September1st to 10thDay
26%8%35%434446%32%
2178
11th to 20thDay
27%10%46%5%45%45%5%26%
2005
21st to endDay
23%9%36%5%35%45%7%29%
1980
October1st to 10thDay
25%12%36%5%3444430%
1914
11th to 20thDay
25%13%46%6%3445%5%25%
1620
21st to endDay
23%17%5%8%6%3433424%
1782
November1st to 10thDay
23%14%48%6%2444427%
1614
11th to 20thDay
20%14%5%6%7%44335%29%
1368
21st to endDay
25%14%6%6%5%25%435%24%
1330
December1st to 10thDay
18%19%7%9%7%336%5%5%18%
1330
11th to 20thDay
24%13%6%8%8%5%6%5%5%416%
1668
21st to endDay
22%12%46%7%35%45%6%25%
2442
January1st to 10thNight
17%15%6%9%6%35%5%6%6%21%
2839
11th to 20thNight
14%13%6%10%8%5%7%7%5%7%18%
2656
21st to endNight
17%13%5%8%8%45%45%6%24%
2772
February1st to 10thNight
15%11%5%8%8%46%6%46%28%
2520
11th to 20thNight
15%15%6%9%7%445%45%27%
2315
21st to endNight
13%11%6%8%8%35%45%6%31%
1776
March1st to 10thNight
16%15%5%9%7%45%5%4426%
2151
11th to 20thNight
15%13%5%9%8%5%6%5%5%6%24%
2061
21st to endNight
21%15%6%9%7%35%44422%
2058
April1st to 10thNight
24%14%7%9%6%4444420%
1800
11th to 20thNight
21%15%5%7%6%35%447%24%
1602
21st to endNight
25%14%7%7%433445%25%
1616
May1st to 10thNight
27%18%6%8%6%3444318%
1440
11th to 20thNight
24%18%5%9%435%445%20%
1265
21st to endNight
31%14%5%8%5%2434420%
1356
June1st to 10thNight
35%12%46%6%35%44416%
1260
11th to 20thNight
31%11%47%5%45%446%19%
1260
21st to endNight
27%14%5%7%6%35%5%5%6%17%
1260
July1st to 10thNight
27%12%37%5%35%45%5%24%
1260
11th to 20thNight
19%11%5%7%7%35%46%7%27%
1260
21st to endNight
23%12%48%5%345%6%6%21%
1503
August1st to 10thNight
25%12%47%6%345%5%6%24%
1433
11th to 20thNight
23%9%46%6%45%48%8%25%
1514
21st to endNight
21%12%48%6%35%46%6%24%
1782
September1st to 10thNight
25%8%25%5%34446%32%
1778
11th to 20thNight
24%10%46%6%245%5%5%29%
1954
21st to endNight
23%10%36%5%3445%6%29%
1980
October1st to 10thNight
26%11%36%5%335%46%28%
2044
11th to 20thNight
22%13%37%6%34446%28%
2340
21st to endNight
28%13%47%5%35%446%22%
2574
November1st to 10thNight
23%12%47%6%44447%25%
2462
11th to 20thNight
23%14%46%5%3445%6%26%
2812
21st to endNight
22%17%5%8%7%3444421%
2850
December1st to 10thNight
18%18%6%10%6%45%44421%
2850
11th to 20thNight
23%15%6%8%6%45%45%6%18%
3531
21st to endNight
23%13%5%8%7%35%45%6%22%
5225

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
67%7%12%11%3
1327
11th to 20thDay
65%10%12%10%3
1356
21st to endDay
63%6%10%13%8%1
1584
February1st to 10thDay
56%6%11%19%7%1
1440
11th to 20thDay
57%7%9%16%10%1
1536
21st to endDay
53%5%8%16%17%1
1480
March1st to 10thDay
59%6%9%15%10%1
1800
11th to 20thDay
62%5%9%15%9%1
1898
21st to endDay
63%6%8%12%10%1
2294
April1st to 10thDay
65%6%8%13%8%1
2160
11th to 20thDay
57%8%10%14%10%
2306
21st to endDay
63%6%9%14%7%
2343
May1st to 10thDay
68%8%9%10%5%1
2520
11th to 20thDay
61%7%11%14%6%
2631
21st to endDay
63%6%12%13%5%
2918
June1st to 10thDay
69%6%10%10%5%
2700
11th to 20thDay
65%7%12%14%2
2700
21st to endDay
62%9%12%14%41
2700
July1st to 10thDay
59%9%14%14%3
2625
11th to 20thDay
51%9%17%18%5%
2618
21st to endDay
57%9%18%13%3
2655
August1st to 10thDay
58%8%16%15%3
2492
11th to 20thDay
54%10%16%17%3
2385
21st to endDay
56%9%16%16%3
2574
September1st to 10thDay
51%7%14%19%7%1
2178
11th to 20thDay
58%8%13%15%6%
2005
21st to endDay
53%9%15%17%6%
1980
October1st to 10thDay
56%8%12%18%7%
1914
11th to 20thDay
60%8%13%13%6%
1620
21st to endDay
63%6%11%14%41
1782
November1st to 10thDay
61%6%11%13%7%1
1614
11th to 20thDay
58%7%12%16%6%1
1368
21st to endDay
64%7%9%13%7%
1330
December1st to 10thDay
67%8%10%11%4
1330
11th to 20thDay
71%7%9%9%31
1667
21st to endDay
60%8%12%14%6%
2442
January1st to 10thNight
65%7%11%11%41
2839
11th to 20thNight
67%9%11%11%3
2656
21st to endNight
61%6%11%15%7%
2772
February1st to 10thNight
58%6%10%16%9%1
2520
11th to 20thNight
58%6%12%15%8%1
2319
21st to endNight
54%7%10%17%12%1
1776
March1st to 10thNight
60%6%10%14%9%1
2160
11th to 20thNight
59%7%9%14%10%1
2062
21st to endNight
63%6%7%13%8%1
2058
April1st to 10thNight
67%5%8%11%7%1
1800
11th to 20thNight
59%7%10%17%7%
1602
21st to endNight
63%410%14%9%1
1616
May1st to 10thNight
71%6%8%11%4
1440
11th to 20thNight
65%6%9%15%4
1266
21st to endNight
68%6%8%13%5%
1357
June1st to 10thNight
71%7%7%11%41
1260
11th to 20thNight
65%10%13%10%3
1260
21st to endNight
67%8%9%12%4
1260
July1st to 10thNight
61%8%12%15%3
1226
11th to 20thNight
55%8%18%15%4
1218
21st to endNight
59%11%15%13%3
1420
August1st to 10thNight
59%10%14%14%2
1422
11th to 20thNight
55%11%16%15%3
1514
21st to endNight
58%10%15%14%4
1782
September1st to 10thNight
53%7%16%19%6%
1778
11th to 20thNight
56%7%13%17%6%
1954
21st to endNight
53%7%16%16%7%1
1980
October1st to 10thNight
57%7%12%16%8%
2044
11th to 20thNight
56%7%13%17%6%
2340
21st to endNight
63%7%11%12%5%2
2574
November1st to 10thNight
58%7%13%14%6%1
2462
11th to 20thNight
60%6%13%16%4
2812
21st to endNight
67%7%10%10%5%
2850
December1st to 10thNight
67%8%10%11%4
2850
11th to 20thNight
69%7%11%9%3
3533
21st to endNight
64%9%9%11%6%
5225

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
23%17%29%21%8%2
370
11th to 20thDay
22%18%34%16%9%1
347
21st to endDay
21%17%34%22%6%
374
February1st to 10thDay
22%13%35%22%6%2
340
11th to 20thDay
21%16%37%20%5%1
336
21st to endDay
19%16%36%18%8%2
280
March1st to 10thDay
20%15%34%22%9%1
340
11th to 20thDay
22%13%27%22%14%2
340
21st to endDay
27%13%30%23%5%2
426
April1st to 10thDay
28%16%29%18%6%2
420
11th to 20thDay
26%9%28%24%10%4
584
21st to endDay
28%10%27%26%8%2
600
May1st to 10thDay
36%10%23%19%10%2
603
11th to 20thDay
29%9%26%20%13%3
624
21st to endDay
34%9%27%23%7%1
680
June1st to 10thDay
41%8%19%21%8%2
630
11th to 20thDay
36%6%23%23%10%2
630
21st to endDay
29%6%25%25%12%4
630
July1st to 10thDay
32%5%25%24%11%3
620
11th to 20thDay
24%6%24%33%11%2
618
21st to endDay
27%5%24%32%12%2
685
August1st to 10thDay
31%422%27%13%2
625
11th to 20thDay
27%422%32%13%2
617
21st to endDay
27%7%23%27%12%3
693
September1st to 10thDay
30%9%28%24%8%1
468
11th to 20thDay
35%9%27%22%6%1
372
21st to endDay
26%12%34%22%5%1
360
October1st to 10thDay
27%14%33%20%41
360
11th to 20thDay
31%10%24%22%12%1
360
21st to endDay
29%14%29%20%8%1
396
November1st to 10thDay
32%18%32%16%21
365
11th to 20thDay
26%17%27%21%8%1
370
21st to endDay
33%16%30%17%3
370
December1st to 10thDay
29%14%29%19%8%1
370
11th to 20thDay
25%19%33%18%41
370
21st to endDay
28%14%31%19%5%2
407
January1st to 10thNight
27%18%30%16%7%1
850
11th to 20thNight
21%16%35%21%6%1
814
21st to endNight
24%16%34%23%3
880
February1st to 10thNight
21%15%32%25%5%2
800
11th to 20thNight
22%16%36%20%5%1
767
21st to endNight
19%10%34%27%8%2
592
March1st to 10thNight
20%17%32%23%7%1
720
11th to 20thNight
22%10%29%31%7%1
622
21st to endNight
28%14%31%20%6%1
594
April1st to 10thNight
29%9%32%20%8%2
540
11th to 20thNight
28%9%29%23%10%1
534
21st to endNight
32%6%28%24%8%1
540
May1st to 10thNight
36%7%21%24%10%3
540
11th to 20thNight
33%7%25%20%13%1
532
21st to endNight
35%8%25%22%9%
583
June1st to 10thNight
41%420%24%9%1
540
11th to 20thNight
37%5%21%25%12%1
540
21st to endNight
31%6%22%27%13%1
540
July1st to 10thNight
31%424%29%10%1
526
11th to 20thNight
24%428%33%11%1
522
21st to endNight
27%5%21%32%14%1
590
August1st to 10thNight
31%6%19%31%14%1
538
11th to 20thNight
27%420%34%13%2
532
21st to endNight
25%5%24%31%14%1
594
September1st to 10thNight
29%8%28%26%9%
540
11th to 20thNight
28%10%33%24%5%1
540
21st to endNight
29%9%33%23%6%
540
October1st to 10thNight
32%7%31%25%41
584
11th to 20thNight
30%9%23%27%10%
810
21st to endNight
34%13%25%21%5%1
891
November1st to 10thNight
30%16%31%18%41
830
11th to 20thNight
29%15%28%20%7%1
850
21st to endNight
29%19%31%18%3
850
December1st to 10thNight
28%14%31%20%6%
850
11th to 20thNight
29%20%29%18%4
850
21st to endNight
23%15%33%22%7%1
935
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