Forestville
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Forestville clear sky chart from 2005-11-05 to 2017-09-23.

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
60%
15342
25%
46987
22%
15305
65%
15305
34%
26896

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
58%
716
17%
2372
16%
716
62%
716
25%
1475
January16th to endNight
56%
768
25%
2496
25%
768
60%
768
28%
1531
February1st to 15thNight
53%
699
22%
2288
21%
698
58%
698
23%
1465
February16th to endNight
46%
632
20%
1936
16%
632
54%
632
25%
1248
March1st to 15thNight
50%
720
15%
1980
12%
720
53%
720
24%
1367
March16th to endNight
45%
768
21%
2111
15%
768
50%
768
29%
1370
April1st to 15thNight
43%
719
23%
1799
11%
719
49%
719
30%
1176
April16th to endNight
51%
720
26%
1800
12%
720
57%
720
40%
1068
May1st to 15thNight
59%
552
27%
1632
17%
552
65%
552
44%
849
May16th to endNight
61%
411
26%
1534
23%
411
69%
411
37%
732
June1st to 15thNight
61%
360
25%
1440
25%
360
70%
360
34%
678
June16th to endNight
76%
360
34%
1440
42%
360
81%
360
54%
540
July1st to 15thNight
85%
395
28%
1415
32%
395
86%
395
53%
581
July16th to endNight
77%
564
30%
1593
28%
531
77%
531
43%
809
August1st to 15thNight
74%
538
29%
1611
25%
535
74%
535
44%
810
August16th to endNight
75%
740
33%
1886
21%
740
77%
740
52%
1030
September1st to 15thNight
79%
720
35%
1800
23%
720
81%
720
57%
953
September16th to endNight
74%
688
38%
1902
32%
688
79%
688
55%
952
October1st to 15thNight
65%
660
29%
1980
28%
660
72%
660
42%
1055
October16th to endNight
68%
704
30%
2112
31%
704
72%
704
38%
1202
November1st to 15thNight
65%
700
25%
2163
24%
700
69%
700
36%
1226
November16th to endNight
58%
720
22%
2489
24%
720
62%
720
28%
1436
December1st to 15thNight
51%
720
19%
2520
18%
720
56%
720
20%
1640
December16th to endNight
47%
768
21%
2688
19%
768
53%
768
22%
1703

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
9%5%23313346%58%
47919
Night
10%423323347%54%
47176
TransparencyDay
29%49%20%22%13%
47608
Night
32%49%19%21%13%
46988
SeeingDay
12%11%24%30%16%4
6055
Night
13%413%29%31%7%
15353

By Month

Percentage Cloud Cover SW (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
18%424422346%45%
1564
16th to endDay
16%7%33424336%44%
1728
February1st to 15thDay
18%5%2432434444%
1576
16th to endDay
19%6%34324447%40%
1536
March1st to 15thDay
18%6%35%43435%7%36%
1980
16th to endDay
17%424434347%41%
2112
April1st to 15thDay
14%6%245%25%347%43%
2149
16th to endDay
8%423213338%57%
2160
May1st to 15thDay
6%412212247%64%
2316
16th to endDay
6%5%13312246%60%
2575
June1st to 15thDay
6%5%13213236%63%
2520
16th to endDay
2211111235%75%
2520
July1st to 15thDay
131212235%74%
2457
16th to endDay
15%1222135%73%
2468
August1st to 15thDay
15%13212235%71%
2340
16th to endDay
15%22212136%69%
2315
September1st to 15thDay
1413211235%71%
2160
16th to endDay
421212237%70%
1892
October1st to 15thDay
9%311223345%61%
1650
16th to endDay
11%413212346%57%
1760
November1st to 15thDay
9%31343335%7%53%
1695
16th to endDay
14%6%2443243449%
1470
December1st to 15thDay
21%7%2442333442%
1440
16th to endDay
22%5%24324336%40%
1536
January1st to 15thNight
17%5%2342345%8%42%
2372
16th to endNight
19%5%23213336%48%
2496
February1st to 15thNight
17%5%3442435%6%42%
2276
16th to endNight
17%6%2432345%7%43%
1936
March1st to 15thNight
16%5%34425%5%5%6%40%
1980
16th to endNight
15%6%24313345%47%
2111
April1st to 15thNight
11%5%2442435%6%49%
1799
16th to endNight
7%323323336%60%
1800
May1st to 15thNight
4424313247%62%
1632
16th to endNight
4313222436%63%
1533
June1st to 15thNight
3423314348%60%
1440
16th to endNight
32111223476%
1440
July1st to 15thNight
1212213237%71%
1500
16th to endNight
16%1321235%10%59%
1701
August1st to 15thNight
16%24313347%61%
1620
16th to endNight
16%24212348%61%
1886
September1st to 15thNight
15%13213238%66%
1800
16th to endNight
341212235%70%
1902
October1st to 15thNight
6%42331335%5%60%
1980
16th to endNight
9%424223347%54%
2112
November1st to 15thNight
10%42332325%9%53%
2163
16th to endNight
14%414422336%51%
2489
December1st to 15thNight
23%5%23423346%41%
2520
16th to endNight
21%423323346%44%
2688

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
42%412%17%13%9%
1564
16th to endDay
44%47%13%19%11%
1728
February1st to 15thDay
43%48%20%18%4
1576
16th to endDay
45%5%11%23%11%3
1536
March1st to 15thDay
48%6%11%16%12%4
1980
16th to endDay
43%6%12%20%14%2
2112
April1st to 15thDay
42%5%13%20%15%2
2149
16th to endDay
27%5%15%26%20%5%
2160
May1st to 15thDay
21%410%30%25%7%
2316
16th to endDay
26%415%27%20%4
2579
June1st to 15thDay
24%411%23%23%11%
2520
16th to endDay
14%35%17%37%21%
2520
July1st to 15thDay
15%1412%31%34%
2313
16th to endDay
18%2412%27%35%
2313
August1st to 15thDay
18%15%17%31%25%
2324
16th to endDay
19%15%17%33%21%
2315
September1st to 15thDay
17%25%17%30%26%
2160
16th to endDay
17%27%25%28%17%
1892
October1st to 15thDay
25%48%20%26%14%
1650
16th to endDay
29%5%10%23%21%9%
1760
November1st to 15thDay
31%6%12%30%12%7%
1695
16th to endDay
40%5%9%19%17%7%
1470
December1st to 15thDay
46%410%15%18%4
1440
16th to endDay
47%49%17%13%7%
1536
January1st to 15thNight
39%6%13%18%13%8%
2372
16th to endNight
39%48%15%17%14%
2496
February1st to 15thNight
43%49%18%16%7%
2288
16th to endNight
40%5%13%21%15%3
1936
March1st to 15thNight
44%6%13%15%15%4
1980
16th to endNight
39%5%11%21%17%4
2111
April1st to 15thNight
35%6%14%20%18%3
1799
16th to endNight
27%49%27%22%8%
1800
May1st to 15thNight
23%48%23%29%11%
1633
16th to endNight
23%412%28%22%7%
1534
June1st to 15thNight
24%5%9%22%23%14%
1440
16th to endNight
14%25%17%34%26%
1440
July1st to 15thNight
17%138%33%35%
1415
16th to endNight
27%16%11%21%31%
1593
August1st to 15thNight
26%15%15%24%26%
1611
16th to endNight
24%15%16%27%24%
1886
September1st to 15thNight
20%2414%30%27%
1800
16th to endNight
19%1424%28%20%
1902
October1st to 15thNight
26%37%20%24%17%
1980
16th to endNight
31%37%20%23%12%
2112
November1st to 15thNight
30%414%28%14%7%
2163
16th to endNight
35%49%22%19%8%
2489
December1st to 15thNight
46%47%16%19%5%
2520
16th to endNight
42%5%9%16%18%7%
2688

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
28%10%26%15%16%2
192
16th to endDay
19%12%22%26%16%1
256
February1st to 15thDay
23%10%23%24%15%2
236
16th to endDay
20%15%25%23%12%
231
March1st to 15thDay
25%16%25%18%9%4
270
16th to endDay
18%19%36%18%6%1
288
April1st to 15thDay
18%28%25%19%6%1
269
16th to endDay
14%26%27%21%7%2
270
May1st to 15thDay
11%19%32%27%7%1
288
16th to endDay
13%13%21%29%18%3
330
June1st to 15thDay
9%15%30%32%10%2
315
16th to endDay
36%27%38%20%4
315
July1st to 15thDay
5%217%45%23%5%
305
16th to endDay
2116%51%22%6%
327
August1st to 15thDay
4321%45%18%5%
315
16th to endDay
3123%40%23%6%
332
September1st to 15thDay
5%322%39%21%7%
315
16th to endDay
5%9%21%30%23%8%
284
October1st to 15thDay
9%11%26%29%16%7%
255
16th to endDay
16%11%22%27%20%2
272
November1st to 15thDay
9%9%19%25%28%6%
201
16th to endDay
10%15%36%15%18%3
65
December1st to 15thDay
35%16%21%15%11%
60
16th to endDay
20%17%14%26%15%6%
64
January1st to 15thNight
18%311%33%26%6%
720
16th to endNight
21%412%28%25%6%
768
February1st to 15thNight
20%5%12%31%26%3
704
16th to endNight
20%6%19%29%18%5%
632
March1st to 15thNight
19%7%15%27%25%4
720
16th to endNight
18%6%23%28%19%3
768
April1st to 15thNight
13%11%22%29%20%3
719
16th to endNight
10%12%21%25%24%6%
720
May1st to 15thNight
7%320%32%31%4
553
16th to endNight
6%6%19%31%31%5%
412
June1st to 15thNight
7%5%19%37%28%1
360
16th to endNight
5%114%38%38%2
360
July1st to 15thNight
3429%53%8%
395
16th to endNight
6%328%47%13%
564
August1st to 15thNight
46%29%47%11%
538
16th to endNight
46%33%48%7%
740
September1st to 15thNight
316%27%49%12%
720
16th to endNight
5%210%29%38%13%
688
October1st to 15thNight
9%213%29%32%11%
660
16th to endNight
11%211%26%35%12%
704
November1st to 15thNight
12%213%31%31%9%
700
16th to endNight
14%5%13%29%28%8%
720
December1st to 15thNight
25%5%11%27%22%6%
720
16th to endNight
24%6%16%32%18%2
768
Page generated at 2017-09-24 06:15:54. Version ac04

Copyright 2017 A. Danko


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