Forestville
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Forestville clear sky chart from 2005-11-06 to 2024-01-16.

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
32%
22814
13%
74847
7%
22769
39%
22769
16%
53977

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
21%
850
11%
2838
4%
847
29%
847
11%
2197
January11th to 20thNight
21%
761
12%
2639
5%
761
29%
761
12%
1986
January21st to endNight
29%
792
18%
2772
8%
792
42%
792
16%
1903
February1st to 10thNight
24%
720
15%
2471
5%
720
38%
720
15%
1771
February11th to 20thNight
22%
702
10%
2249
3%
700
32%
700
12%
1724
February21st to endNight
29%
592
15%
1776
8%
592
40%
592
17%
1307
March1st to 10thNight
27%
720
14%
2160
7%
720
36%
720
16%
1593
March11th to 20thNight
27%
720
16%
2000
8%
720
35%
720
19%
1471
March21st to endNight
29%
792
17%
2142
7%
792
36%
792
20%
1568
April1st to 10thNight
22%
702
13%
1782
5%
702
27%
702
16%
1408
April11th to 20thNight
33%
534
17%
1598
7%
534
41%
534
20%
1114
April21st to endNight
36%
540
15%
1620
10%
540
42%
540
19%
1136
May1st to 10thNight
35%
540
10%
1620
6%
540
40%
540
16%
1217
May11th to 20thNight
40%
357
15%
1310
12%
357
51%
357
18%
860
May21st to endNight
34%
389
11%
1357
7%
388
42%
388
16%
955
June1st to 10thNight
45%
360
5%
1260
4%
360
46%
360
15%
899
June11th to 20thNight
49%
360
7%
1260
5%
360
51%
360
21%
833
June21st to endNight
42%
360
5%
1260
3%
360
43%
360
14%
917
July1st to 10thNight
44%
350
7%
1225
6%
350
47%
350
14%
884
July11th to 20thNight
52%
348
9%
1218
11%
348
54%
348
19%
826
July21st to endNight
52%
394
7%
1482
9%
372
54%
372
14%
1049
August1st to 10thNight
58%
391
9%
1455
13%
389
59%
389
17%
1004
August11th to 20thNight
53%
532
10%
1596
8%
532
55%
532
20%
1147
August21st to endNight
56%
594
16%
1782
11%
594
58%
594
23%
1216
September1st to 10thNight
43%
670
14%
1794
7%
670
47%
670
25%
1249
September11th to 20thNight
41%
720
12%
1980
7%
720
45%
720
24%
1386
September21st to endNight
42%
720
19%
1980
13%
720
47%
720
28%
1324
October1st to 10thNight
39%
720
18%
2051
10%
720
47%
720
23%
1415
October11th to 20thNight
34%
720
13%
2258
7%
720
40%
720
18%
1633
October21st to endNight
29%
792
11%
2574
6%
792
36%
792
15%
1903
November1st to 10thNight
27%
753
13%
2435
6%
753
35%
753
14%
1757
November11th to 20thNight
26%
850
13%
2660
6%
850
33%
850
14%
1949
November21st to endNight
24%
850
10%
2816
4%
850
32%
850
11%
2151
December1st to 10thNight
24%
850
12%
2850
5%
850
32%
850
12%
2150
December11th to 20thNight
21%
850
12%
3459
4%
848
30%
848
10%
2536
December21st to endNight
20%
919
9%
5118
3%
906
30%
906
6%
3539

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%9%47%6%35%5%5%7%32%
74615
Night
17%10%47%6%3445%6%33%
75195
TransparencyDay
50%8%13%18%10%1
74307
Night
52%7%11%18%10%1
75038
SeeingDay
21%7%28%29%12%2
14661
Night
22%7%28%30%11%1
22831

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
15%17%6%8%6%3445%6%26%
1327
11th to 20thDay
15%14%6%7%6%45%445%29%
1442
21st to endDay
10%11%5%8%6%46%45%7%33%
1584
February1st to 10thDay
7%11%6%10%8%5%5%5%6%7%32%
1487
11th to 20thDay
12%12%6%13%9%5%345%5%26%
1598
21st to endDay
12%11%5%8%6%45%5%6%8%32%
1480
March1st to 10thDay
15%13%5%6%5%46%5%5%7%29%
1797
11th to 20thDay
15%11%5%8%6%45%45%7%31%
1959
21st to endDay
15%14%47%6%34447%32%
2211
April1st to 10thDay
20%11%47%6%45%5%5%6%28%
2177
11th to 20thDay
16%9%36%5%345%5%7%37%
2312
21st to endDay
21%9%36%6%3445%5%32%
2340
May1st to 10thDay
23%9%37%6%33446%32%
2352
11th to 20thDay
19%8%35%5%35%45%6%36%
2587
21st to endDay
19%7%36%4345%6%8%36%
2919
June1st to 10thDay
21%8%37%5%45%5%6%7%30%
2700
11th to 20thDay
18%6%36%6%35%6%5%8%34%
2700
21st to endDay
23%7%37%5%445%6%7%30%
2700
July1st to 10thDay
16%7%37%6%46%6%6%10%29%
2700
11th to 20thDay
14%5%28%7%47%7%6%8%33%
2700
21st to endDay
12%6%37%8%5%6%7%7%8%31%
2746
August1st to 10thDay
16%5%36%7%47%8%9%9%27%
2455
11th to 20thDay
14%6%36%6%45%47%9%36%
2304
21st to endDay
13%6%36%7%46%7%6%8%36%
2574
September1st to 10thDay
16%6%26%5%35%5%5%7%39%
2165
11th to 20thDay
19%6%25%5%3345%6%42%
1980
21st to endDay
19%6%35%5%3445%7%40%
1980
October1st to 10thDay
17%6%27%6%35%5%5%8%36%
1908
11th to 20thDay
24%6%36%5%36%5%6%7%29%
1697
21st to endDay
26%9%37%6%34445%29%
1782
November1st to 10thDay
17%9%48%6%36%5%6%6%29%
1643
11th to 20thDay
20%10%46%6%35%5%6%5%29%
1520
21st to endDay
22%13%47%5%35%346%28%
1360
December1st to 10thDay
19%12%5%7%6%245%6%6%28%
1330
11th to 20thDay
18%15%5%6%5%2333435%
1668
21st to endDay
18%14%48%42223438%
2431
January1st to 10thNight
15%15%6%9%7%35%44426%
2838
11th to 20thNight
14%15%6%9%6%45%445%29%
2639
21st to endNight
9%12%410%6%35%45%7%34%
2772
February1st to 10thNight
10%11%5%9%7%46%45%6%32%
2471
11th to 20thNight
11%15%6%10%6%46%5%45%28%
2246
21st to endNight
12%13%6%7%7%45%5%45%32%
1776
March1st to 10thNight
14%13%6%8%6%3445%6%31%
2150
11th to 20thNight
15%13%47%6%44445%34%
1999
21st to endNight
13%14%5%6%5%4445%6%34%
2142
April1st to 10thNight
23%12%5%7%7%3343428%
1782
11th to 20thNight
21%9%244446%5%5%36%
1598
21st to endNight
24%10%35%423346%35%
1620
May1st to 10thNight
25%10%36%5%44445%30%
1620
11th to 20thNight
19%8%37%5%2435%7%38%
1309
21st to endNight
18%8%47%5%25%46%8%32%
1356
June1st to 10thNight
20%6%27%7%47%5%6%8%30%
1260
11th to 20thNight
18%6%26%5%45%45%8%38%
1260
21st to endNight
25%8%46%5%345%45%31%
1260
July1st to 10thNight
16%7%38%6%5%6%6%6%6%30%
1260
11th to 20thNight
13%7%35%7%45%7%6%10%32%
1260
21st to endNight
16%7%36%6%36%7%6%9%31%
1569
August1st to 10thNight
15%6%37%5%45%6%7%8%34%
1465
11th to 20thNight
17%7%36%6%45%7%6%9%31%
1596
21st to endNight
13%6%26%6%45%5%6%7%39%
1782
September1st to 10thNight
16%6%26%6%335%6%8%39%
1794
11th to 20thNight
20%6%25%5%345%45%41%
1980
21st to endNight
19%6%245%33445%46%
1980
October1st to 10thNight
16%6%27%5%35%5%5%6%41%
2051
11th to 20thNight
25%7%36%43345%5%33%
2258
21st to endNight
24%7%36%5%345%5%6%31%
2574
November1st to 10thNight
19%11%47%6%345%5%6%32%
2435
11th to 20thNight
19%11%47%5%345%5%5%32%
2660
21st to endNight
19%14%48%6%3445%6%27%
2816
December1st to 10thNight
19%12%5%8%6%34345%30%
2850
11th to 20thNight
19%13%5%7%6%34445%30%
3531
21st to endNight
15%13%5%8%6%44446%31%
5236

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
59%7%11%16%6%
1328
11th to 20thDay
58%7%8%18%7%2
1442
21st to endDay
50%7%10%18%13%1
1584
February1st to 10thDay
51%8%12%16%12%2
1487
11th to 20thDay
62%6%10%15%8%
1606
21st to endDay
48%8%9%21%13%2
1480
March1st to 10thDay
53%7%12%13%13%2
1800
11th to 20thDay
53%6%11%17%13%1
1959
21st to endDay
53%6%10%16%13%2
2211
April1st to 10thDay
55%6%10%14%12%2
2177
11th to 20thDay
46%7%12%23%11%2
2312
21st to endDay
52%6%9%19%11%2
2340
May1st to 10thDay
53%6%12%18%10%2
2352
11th to 20thDay
46%8%13%19%14%1
2591
21st to endDay
46%8%11%22%12%1
2919
June1st to 10thDay
52%8%10%17%11%2
2700
11th to 20thDay
48%7%13%18%12%2
2700
21st to endDay
53%8%13%16%9%1
2700
July1st to 10thDay
48%12%15%18%8%
2625
11th to 20thDay
45%10%15%21%9%1
2619
21st to endDay
48%12%14%20%6%
2592
August1st to 10thDay
46%16%16%17%5%
2441
11th to 20thDay
43%11%19%20%6%
2304
21st to endDay
43%11%16%22%7%
2574
September1st to 10thDay
42%9%16%21%12%
2165
11th to 20thDay
43%7%15%24%10%
1980
21st to endDay
43%8%16%23%10%
1980
October1st to 10thDay
46%8%15%17%12%1
1908
11th to 20thDay
53%9%16%18%4
1697
21st to endDay
57%8%10%16%9%
1782
November1st to 10thDay
53%9%16%15%7%1
1643
11th to 20thDay
55%8%13%18%7%
1520
21st to endDay
60%6%12%14%7%
1360
December1st to 10thDay
56%9%13%16%6%
1330
11th to 20thDay
55%6%9%20%11%
1668
21st to endDay
52%5%14%19%6%4
2431
January1st to 10thNight
62%6%10%15%7%
2838
11th to 20thNight
58%7%10%17%7%1
2639
21st to endNight
49%7%9%20%14%1
2772
February1st to 10thNight
54%6%9%18%12%2
2471
11th to 20thNight
58%8%9%16%9%
2249
21st to endNight
54%6%10%20%9%1
1776
March1st to 10thNight
54%7%10%18%11%1
2160
11th to 20thNight
54%5%10%18%12%2
2000
21st to endNight
51%6%9%18%14%1
2142
April1st to 10thNight
61%47%12%13%3
1782
11th to 20thNight
48%6%9%19%16%2
1598
21st to endNight
52%49%19%14%3
1620
May1st to 10thNight
57%5%7%16%13%1
1620
11th to 20thNight
47%6%11%20%14%2
1310
21st to endNight
50%9%8%18%14%2
1357
June1st to 10thNight
52%8%10%18%11%2
1260
11th to 20thNight
46%6%12%19%13%3
1260
21st to endNight
55%7%9%17%12%1
1260
July1st to 10thNight
50%12%12%19%8%
1225
11th to 20thNight
44%11%15%21%9%
1218
21st to endNight
49%11%15%17%7%
1482
August1st to 10thNight
44%13%17%19%7%
1455
11th to 20thNight
46%11%16%19%7%1
1596
21st to endNight
42%10%14%26%8%
1782
September1st to 10thNight
42%10%15%23%10%1
1794
11th to 20thNight
45%8%15%22%10%1
1980
21st to endNight
41%6%12%26%14%1
1980
October1st to 10thNight
44%9%13%22%12%2
2051
11th to 20thNight
51%8%13%21%7%
2258
21st to endNight
53%9%13%17%8%
2574
November1st to 10thNight
53%7%13%17%9%1
2435
11th to 20thNight
53%7%13%18%7%
2660
21st to endNight
59%8%11%13%9%
2816
December1st to 10thNight
58%6%12%17%6%
2850
11th to 20thNight
56%7%10%17%9%
3532
21st to endNight
54%8%12%14%10%2
5236

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
29%7%26%30%8%
180
11th to 20thDay
21%11%29%29%8%1
170
21st to endDay
16%8%32%26%15%3
176
February1st to 10thDay
13%14%32%31%8%2
207
11th to 20thDay
16%11%37%26%9%1
348
21st to endDay
18%9%37%26%10%1
346
March1st to 10thDay
24%8%30%26%10%1
420
11th to 20thDay
21%11%30%25%11%3
420
21st to endDay
22%9%34%26%7%1
462
April1st to 10thDay
24%14%30%21%9%2
420
11th to 20thDay
21%10%30%27%11%2
412
21st to endDay
25%6%29%30%9%1
420
May1st to 10thDay
27%7%27%27%10%2
423
11th to 20thDay
22%5%30%28%12%3
556
21st to endDay
24%8%31%25%10%2
680
June1st to 10thDay
26%331%31%8%1
630
11th to 20thDay
21%6%26%28%16%3
630
21st to endDay
24%324%35%12%2
630
July1st to 10thDay
20%323%37%16%2
620
11th to 20thDay
16%420%40%18%2
618
21st to endDay
14%6%20%38%19%2
490
August1st to 10thDay
17%417%39%20%2
446
11th to 20thDay
19%320%36%20%3
439
21st to endDay
15%7%22%32%19%3
495
September1st to 10thDay
17%5%28%30%17%4
450
11th to 20thDay
22%8%26%32%10%3
450
21st to endDay
20%5%30%29%14%3
450
October1st to 10thDay
18%5%34%26%14%4
414
11th to 20thDay
29%9%25%24%11%3
360
21st to endDay
31%11%27%22%8%2
396
November1st to 10thDay
21%15%34%25%41
365
11th to 20thDay
26%9%29%25%11%1
370
21st to endDay
30%10%30%25%41
210
December1st to 10thDay
23%7%29%23%14%4
180
11th to 20thDay
24%13%34%22%6%2
180
21st to endDay
25%12%30%24%8%1
198
January1st to 10thNight
23%8%33%30%6%
850
11th to 20thNight
23%11%34%26%7%
761
21st to endNight
15%7%34%33%10%1
792
February1st to 10thNight
14%8%39%29%9%1
720
11th to 20thNight
18%11%34%26%9%1
703
21st to endNight
18%7%31%32%10%1
592
March1st to 10thNight
21%8%32%30%8%1
720
11th to 20thNight
21%10%33%26%9%1
720
21st to endNight
20%8%32%30%8%1
792
April1st to 10thNight
29%7%31%25%8%
702
11th to 20thNight
25%7%29%26%11%2
534
21st to endNight
30%6%22%31%10%1
540
May1st to 10thNight
29%5%20%35%10%1
540
11th to 20thNight
24%224%34%15%1
357
21st to endNight
23%431%29%13%1
389
June1st to 10thNight
21%322%40%14%
360
11th to 20thNight
19%419%32%24%3
360
21st to endNight
28%416%35%16%1
360
July1st to 10thNight
18%5%22%37%16%3
350
11th to 20thNight
14%417%43%21%1
348
21st to endNight
19%316%38%23%2
394
August1st to 10thNight
16%212%43%24%2
391
11th to 20thNight
18%216%39%21%2
532
21st to endNight
13%416%43%19%4
594
September1st to 10thNight
19%326%35%16%1
670
11th to 20thNight
24%424%30%15%3
720
21st to endNight
20%426%33%16%2
720
October1st to 10thNight
19%5%30%32%12%2
720
11th to 20thNight
27%5%27%25%14%2
720
21st to endNight
28%6%30%26%10%1
792
November1st to 10thNight
25%10%30%27%6%1
753
11th to 20thNight
23%11%31%24%9%1
850
21st to endNight
27%9%29%29%6%
850
December1st to 10thNight
25%7%31%27%8%2
850
11th to 20thNight
24%12%33%22%8%1
850
21st to endNight
25%11%31%24%7%1
935
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