Stephen C. Foster State Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Stephen C. Foster State Park clear sky chart from 2005-11-06 to 2024-03-18.

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
50%
24514
21%
79967
14%
24413
57%
24413
26%
49415

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
30%
753
23%
3995
10%
737
47%
737
15%
2270
January11th to 20thNight
39%
753
25%
3978
17%
740
53%
740
17%
2299
January21st to endNight
24%
832
15%
4384
10%
814
40%
814
13%
2590
February1st to 10thNight
35%
760
22%
2280
11%
760
46%
760
25%
1445
February11th to 20thNight
32%
742
23%
2218
9%
739
46%
739
26%
1359
February21st to endNight
34%
628
24%
1866
14%
628
44%
628
30%
1110
March1st to 10thNight
37%
760
28%
2090
14%
760
49%
760
35%
1246
March11th to 20thNight
36%
752
25%
2068
13%
752
47%
752
31%
1267
March21st to endNight
38%
792
26%
2178
11%
792
50%
792
34%
1270
April1st to 10thNight
41%
720
23%
1980
13%
720
48%
720
33%
1202
April11th to 20thNight
40%
711
24%
1927
14%
711
48%
711
33%
1168
April21st to endNight
53%
603
33%
1683
20%
603
62%
603
43%
933
May1st to 10thNight
56%
540
28%
1620
17%
540
63%
540
43%
844
May11th to 20thNight
63%
531
19%
1592
13%
531
67%
531
33%
977
May21st to endNight
70%
582
22%
1744
16%
582
73%
582
33%
1065
June1st to 10thNight
62%
540
14%
1620
10%
540
63%
540
23%
1105
June11th to 20thNight
70%
540
15%
1620
11%
540
72%
540
29%
1054
June21st to endNight
71%
540
12%
1620
9%
540
72%
540
26%
1087
July1st to 10thNight
73%
525
9%
1575
8%
525
73%
525
24%
1094
July11th to 20thNight
67%
522
9%
1566
9%
522
68%
522
22%
1100
July21st to endNight
75%
591
12%
1672
12%
558
76%
558
29%
1099
August1st to 10thNight
72%
537
10%
1600
9%
534
73%
534
24%
1110
August11th to 20thNight
73%
534
9%
1650
9%
534
73%
534
24%
1139
August21st to endNight
60%
724
12%
2110
12%
724
61%
724
19%
1548
September1st to 10thNight
59%
720
13%
1980
12%
720
60%
720
22%
1400
September11th to 20thNight
55%
720
9%
1980
9%
720
55%
720
19%
1482
September21st to endNight
61%
720
22%
1980
19%
720
65%
720
31%
1276
October1st to 10thNight
55%
720
26%
1980
22%
720
60%
720
33%
1233
October11th to 20thNight
57%
720
32%
2155
26%
720
66%
720
38%
1203
October21st to endNight
52%
792
29%
2376
24%
792
61%
792
32%
1386
November1st to 10thNight
49%
740
27%
2221
21%
740
58%
740
35%
1271
November11th to 20thNight
41%
760
28%
2360
19%
760
54%
760
31%
1383
November21st to endNight
41%
760
25%
2470
18%
760
52%
760
28%
1473
December1st to 10thNight
43%
760
25%
2470
16%
760
55%
760
28%
1471
December11th to 20thNight
40%
759
23%
2932
16%
758
49%
758
21%
1753
December21st to endNight
39%
831
15%
4427
15%
817
50%
817
14%
2703

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
11%6%36%6%46%5%6%8%40%
79066
Night
10%6%35%5%35%5%6%8%44%
80727
TransparencyDay
41%6%12%17%16%7%
78789
Night
37%7%13%18%16%8%
80523
SeeingDay
14%8%22%25%21%10%
14386
Night
12%7%23%33%22%4
24541

By Month

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 10thDay
12%8%25%42445%7%48%
2836
11th to 20thDay
14%7%36%5%34447%42%
2840
21st to endDay
13%6%35%4345%6%7%44%
3188
February1st to 10thDay
15%7%35%6%2445%7%42%
1900
11th to 20thDay
14%6%344345%45%48%
1848
21st to endDay
14%5%35%6%33445%47%
1585
March1st to 10thDay
10%425%4335%47%52%
2090
11th to 20thDay
10%5%25%6%45%5%6%7%45%
2058
21st to endDay
11%5%25%43445%8%49%
2178
April1st to 10thDay
9%5%26%435%5%6%8%47%
1980
11th to 20thDay
11%5%36%7%36%5%5%6%43%
1981
21st to endDay
6%4245%35%5%5%7%53%
2290
May1st to 10thDay
7%2245%45%5%6%8%53%
2340
11th to 20thDay
8%5%26%7%46%6%8%10%38%
2301
21st to endDay
8%6%37%7%46%8%7%9%36%
2531
June1st to 10thDay
11%5%38%8%47%8%8%10%29%
2340
11th to 20thDay
7%5%36%8%5%10%8%8%10%30%
2340
21st to endDay
8%5%38%10%5%7%7%8%10%29%
2340
July1st to 10thDay
7%6%48%9%6%9%8%8%11%26%
2340
11th to 20thDay
8%6%39%10%6%9%7%8%11%23%
2340
21st to endDay
7%6%48%9%6%8%7%7%10%28%
2547
August1st to 10thDay
10%6%48%10%6%7%8%8%10%22%
2327
11th to 20thDay
9%7%310%8%6%8%8%8%10%22%
2246
21st to endDay
14%8%39%8%47%6%8%9%24%
2225
September1st to 10thDay
11%6%39%8%5%7%7%8%9%27%
1980
11th to 20thDay
13%9%38%7%5%6%6%7%8%28%
1980
21st to endDay
13%6%36%6%5%6%6%5%7%38%
1980
October1st to 10thDay
11%6%37%6%35%45%8%42%
1980
11th to 20thDay
8%42433445%7%54%
1804
21st to endDay
10%4245%345%6%7%50%
1980
November1st to 10thDay
9%6%25%42435%6%52%
1857
11th to 20thDay
10%6%25%433447%53%
1817
21st to endDay
12%7%25%435%5%5%7%47%
1710
December1st to 10thDay
10%6%25%6%45%5%6%8%44%
1710
11th to 20thDay
17%6%345%3435%6%45%
2153
21st to endDay
16%9%46%6%34335%42%
3124
January1st to 10thNight
13%7%46%43445%6%43%
4109
11th to 20thNight
10%7%35%5%35%6%6%8%42%
4120
21st to endNight
13%8%36%6%3445%7%41%
4464
February1st to 10thNight
15%6%25%6%3345%7%44%
2280
11th to 20thNight
13%6%36%423446%48%
2218
21st to endNight
12%6%25%5%2345%8%49%
1866
March1st to 10thNight
11%6%25%42435%7%52%
2090
11th to 20thNight
10%7%345%2435%8%49%
2068
21st to endNight
9%424434447%54%
2178
April1st to 10thNight
11%5%234345%6%8%49%
1980
11th to 20thNight
8%6%36%5%3445%7%51%
1927
21st to endNight
6%42343445%9%57%
1683
May1st to 10thNight
5%32433445%8%59%
1620
11th to 20thNight
7%4245%37%6%6%9%47%
1592
21st to endNight
7%5%25%435%6%7%10%46%
1744
June1st to 10thNight
9%5%37%8%46%8%8%10%33%
1620
11th to 20thNight
5%426%6%46%6%9%12%38%
1620
21st to endNight
7%5%25%7%47%6%7%15%35%
1620
July1st to 10thNight
6%5%25%7%5%7%9%11%13%31%
1620
11th to 20thNight
7%7%47%8%36%9%10%10%30%
1620
21st to endNight
4336%7%46%6%10%13%38%
1771
August1st to 10thNight
7%436%7%47%8%8%13%34%
1611
11th to 20thNight
5%5%36%6%5%6%8%9%14%33%
1650
21st to endNight
10%7%38%7%47%7%7%10%30%
2110
September1st to 10thNight
10%7%27%7%45%6%9%12%30%
1980
11th to 20thNight
11%7%38%8%5%7%6%7%7%31%
1980
21st to endNight
8%7%36%6%345%6%9%42%
1980
October1st to 10thNight
10%5%35%5%3445%8%49%
1980
11th to 20thNight
7%5%2442445%7%56%
2155
21st to endNight
7%5%26%6%3445%7%51%
2376
November1st to 10thNight
11%5%24435%45%7%51%
2221
11th to 20thNight
12%6%34424336%52%
2360
21st to endNight
12%7%35%43445%7%46%
2470
December1st to 10thNight
13%6%3443446%8%45%
2470
11th to 20thNight
17%6%3442335%6%47%
3042
21st to endNight
16%8%36%6%3445%5%40%
4532

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
38%37%16%23%12%
2837
11th to 20thDay
42%46%15%18%15%
2840
21st to endDay
38%410%14%22%12%
3188
February1st to 10thDay
43%310%15%19%10%
1900
11th to 20thDay
39%46%15%23%13%
1858
21st to endDay
39%37%17%19%14%
1585
March1st to 10thDay
33%38%21%24%11%
2090
11th to 20thDay
37%412%18%18%10%
2058
21st to endDay
35%412%20%20%10%
2178
April1st to 10thDay
35%6%10%18%19%12%
1980
11th to 20thDay
41%5%7%17%20%10%
1981
21st to endDay
29%6%9%25%23%9%
2290
May1st to 10thDay
29%5%10%23%24%9%
2340
11th to 20thDay
39%7%15%20%15%4
2305
21st to endDay
42%8%11%21%16%3
2531
June1st to 10thDay
47%9%16%17%10%1
2340
11th to 20thDay
44%11%17%21%7%
2340
21st to endDay
47%11%21%15%6%1
2340
July1st to 10thDay
49%12%23%14%2
2275
11th to 20thDay
51%10%23%10%5%
2271
21st to endDay
47%10%21%18%3
2405
August1st to 10thDay
52%12%19%15%2
2314
11th to 20thDay
52%12%22%12%2
2246
21st to endDay
54%11%19%12%31
2225
September1st to 10thDay
51%10%16%14%8%2
1980
11th to 20thDay
52%9%14%15%8%2
1980
21st to endDay
45%7%12%16%16%4
1980
October1st to 10thDay
41%5%10%17%16%11%
1980
11th to 20thDay
30%5%6%23%30%8%
1804
21st to endDay
33%5%7%18%21%16%
1980
November1st to 10thDay
33%48%18%22%14%
1857
11th to 20thDay
33%47%18%25%12%
1817
21st to endDay
38%49%19%22%9%
1710
December1st to 10thDay
39%5%11%20%16%8%
1710
11th to 20thDay
42%39%17%21%8%
2150
21st to endDay
48%35%17%20%7%
3124
January1st to 10thNight
41%46%13%22%14%
4109
11th to 20thNight
40%5%6%15%23%11%
4120
21st to endNight
43%5%9%13%19%10%
4464
February1st to 10thNight
41%48%16%19%11%
2280
11th to 20thNight
39%38%17%18%14%
2219
21st to endNight
34%5%10%20%17%14%
1866
March1st to 10thNight
32%411%21%19%13%
2090
11th to 20thNight
35%414%19%17%11%
2068
21st to endNight
31%412%23%19%10%
2178
April1st to 10thNight
33%6%14%17%19%12%
1980
11th to 20thNight
33%5%9%22%21%10%
1927
21st to endNight
26%5%12%28%21%8%
1683
May1st to 10thNight
24%5%13%27%22%10%
1620
11th to 20thNight
32%9%19%21%14%5%
1593
21st to endNight
32%9%14%26%16%3
1745
June1st to 10thNight
42%10%19%18%10%1
1620
11th to 20thNight
34%12%23%24%7%
1620
21st to endNight
37%13%27%17%6%1
1620
July1st to 10thNight
38%15%27%17%31
1575
11th to 20thNight
42%12%28%13%5%
1566
21st to endNight
33%14%29%21%3
1672
August1st to 10thNight
38%15%29%16%3
1600
11th to 20thNight
37%15%31%14%3
1650
21st to endNight
47%12%21%16%31
2110
September1st to 10thNight
43%12%22%15%7%2
1980
11th to 20thNight
49%12%15%16%8%1
1980
21st to endNight
37%7%18%20%14%4
1980
October1st to 10thNight
36%6%12%19%16%11%
1980
11th to 20thNight
28%6%7%24%28%7%
2155
21st to endNight
32%6%8%18%21%15%
2376
November1st to 10thNight
31%5%9%21%20%14%
2221
11th to 20thNight
36%38%17%25%12%
2360
21st to endNight
38%49%21%19%9%
2470
December1st to 10thNight
37%414%21%17%7%
2470
11th to 20thNight
39%5%8%17%21%9%
3044
21st to endNight
46%410%17%19%5%
4532

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
16%20%41%18%5%
270
11th to 20thDay
16%15%40%17%9%3
270
21st to endDay
24%16%44%13%2
297
February1st to 10thDay
24%11%41%19%5%1
270
11th to 20thDay
19%21%38%17%5%
270
21st to endDay
17%17%41%22%4
240
March1st to 10thDay
17%15%31%25%11%
460
11th to 20thDay
17%15%32%22%10%2
449
21st to endDay
16%12%36%23%11%2
462
April1st to 10thDay
19%13%28%24%15%1
420
11th to 20thDay
16%10%31%25%13%5%
412
21st to endDay
9%8%31%27%19%7%
420
May1st to 10thDay
9%10%28%26%19%8%
423
11th to 20thDay
7%422%32%23%13%
447
21st to endDay
11%413%26%33%13%
485
June1st to 10thDay
15%313%28%25%16%
450
11th to 20thDay
10%5%12%22%31%20%
450
21st to endDay
10%28%28%32%21%
450
July1st to 10thDay
7%25%24%36%27%
445
11th to 20thDay
8%1420%39%29%
444
21st to endDay
10%36%27%37%17%
488
August1st to 10thDay
13%39%18%33%24%
446
11th to 20thDay
10%2321%37%27%
439
21st to endDay
14%38%22%33%20%
495
September1st to 10thDay
12%48%26%29%22%
450
11th to 20thDay
15%5%11%32%26%11%
450
21st to endDay
14%212%29%30%12%
450
October1st to 10thDay
14%6%27%28%19%7%
450
11th to 20thDay
8%6%24%36%20%6%
450
21st to endDay
14%7%27%30%18%4
495
November1st to 10thDay
16%6%28%29%17%5%
455
11th to 20thDay
19%8%37%24%8%3
377
21st to endDay
17%11%35%27%8%1
270
December1st to 10thDay
16%16%33%21%12%2
270
11th to 20thDay
23%13%33%25%6%1
270
21st to endDay
19%7%38%28%7%2
297
January1st to 10thNight
16%13%35%29%6%1
760
11th to 20thNight
13%12%30%33%11%1
760
21st to endNight
19%14%37%25%4
836
February1st to 10thNight
19%11%30%31%8%
760
11th to 20thNight
18%13%31%32%5%
743
21st to endNight
16%12%34%35%3
628
March1st to 10thNight
14%12%33%34%7%
760
11th to 20thNight
14%10%36%27%12%1
752
21st to endNight
12%12%34%31%11%
792
April1st to 10thNight
15%11%29%34%10%1
720
11th to 20thNight
11%9%33%35%11%1
711
21st to endNight
8%6%28%41%16%
603
May1st to 10thNight
5%5%28%45%16%1
540
11th to 20thNight
9%418%43%23%3
531
21st to endNight
9%310%41%34%4
584
June1st to 10thNight
11%311%39%34%3
540
11th to 20thNight
6%39%34%34%13%
540
21st to endNight
8%18%34%39%11%
540
July1st to 10thNight
7%25%30%42%14%
525
11th to 20thNight
9%2324%45%17%
522
21st to endNight
325%32%48%10%
591
August1st to 10thNight
8%1428%47%12%
537
11th to 20thNight
6%1323%50%17%
534
21st to endNight
14%36%24%39%13%
724
September1st to 10thNight
12%38%28%39%11%
720
11th to 20thNight
14%411%31%35%5%
720
21st to endNight
12%313%34%34%5%
720
October1st to 10thNight
13%222%36%25%3
720
11th to 20thNight
10%5%23%36%24%3
720
21st to endNight
9%6%25%34%24%1
792
November1st to 10thNight
12%6%27%36%18%1
740
11th to 20thNight
15%9%29%33%14%1
760
21st to endNight
16%6%31%32%14%1
760
December1st to 10thNight
16%9%27%33%15%1
760
11th to 20thNight
18%9%28%30%15%1
760
21st to endNight
17%11%27%32%12%
836
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