North Bay
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the North Bay clear sky chart from 2005-11-05 to 2017-08-12.

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
29%
14830
11%
46353
7%
14800
34%
14800
15%
34801

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
16%
897
5%
2685
3%
895
18%
895
7%
2315
January16th to endNight
24%
774
9%
2547
7%
774
28%
774
10%
2042
February1st to 15thNight
22%
702
7%
2287
4%
701
25%
701
9%
1831
February16th to endNight
22%
631
9%
2051
5%
631
27%
631
9%
1655
March1st to 15thNight
21%
720
11%
1986
6%
720
27%
720
14%
1552
March16th to endNight
33%
768
19%
2112
10%
768
39%
768
23%
1475
April1st to 15thNight
28%
706
14%
1793
6%
706
32%
706
20%
1352
April16th to endNight
32%
540
17%
1620
10%
540
39%
540
20%
1148
May1st to 15thNight
35%
426
16%
1506
14%
426
42%
426
20%
999
May16th to endNight
41%
374
12%
1497
12%
374
50%
374
19%
952
June1st to 15thNight
41%
360
9%
1302
10%
360
46%
360
18%
880
June16th to endNight
43%
360
9%
1260
7%
360
47%
360
18%
840
July1st to 15thNight
53%
340
14%
1190
16%
340
56%
340
28%
685
July16th to endNight
53%
401
13%
1403
14%
377
55%
377
24%
854
August1st to 15thNight
49%
527
12%
1575
10%
524
51%
524
23%
1087
August16th to endNight
49%
550
16%
1600
8%
550
54%
550
26%
1048
September1st to 15thNight
43%
660
14%
1650
7%
660
45%
660
30%
1128
September16th to endNight
43%
657
17%
1839
11%
657
47%
657
26%
1237
October1st to 15thNight
30%
660
14%
1980
10%
660
36%
660
16%
1458
October16th to endNight
20%
704
9%
2126
6%
704
24%
704
10%
1739
November1st to 15thNight
24%
700
12%
2451
10%
700
29%
700
12%
1829
November16th to endNight
19%
720
7%
2520
6%
720
21%
720
8%
2084
December1st to 15thNight
14%
720
5%
2520
2%
720
18%
720
6%
2148
December16th to endNight
14%
933
6%
2853
3%
933
17%
933
6%
2463

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%37%5%3445%7%30%
47625
Night
18%11%47%6%34445%28%
46515
TransparencyDay
54%6%11%18%8%
47305
Night
57%5%10%17%7%
46353
SeeingDay
22%8%27%26%10%3
5644
Night
24%8%28%26%10%1
14836

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
20%19%6%8%7%43235%18%
1253
16th to endDay
14%15%6%11%8%35%446%20%
1671
February1st to 15thDay
10%16%6%12%8%45%5%46%19%
1575
16th to endDay
16%16%6%9%6%34345%23%
1422
March1st to 15thDay
17%11%48%6%33446%28%
1961
16th to endDay
13%7%38%5%2445%5%38%
2112
April1st to 15thDay
21%8%46%43345%6%31%
2163
16th to endDay
20%8%25%323236%39%
2340
May1st to 15thDay
20%9%36%434446%31%
2445
16th to endDay
15%5%26%6%3445%7%38%
2618
June1st to 15thDay
16%7%27%6%35%46%8%30%
2656
16th to endDay
15%6%36%5%45%5%6%9%32%
2700
July1st to 15thDay
13%425%5%35%5%5%8%40%
2700
16th to endDay
13%4145%35%5%7%10%38%
2666
August1st to 15thDay
13%5%25%5%25%6%6%7%37%
2288
16th to endDay
13%6%25%5%3346%8%39%
2239
September1st to 15thDay
16%8%35%5%345%47%35%
1980
16th to endDay
20%5%46%424446%37%
1788
October1st to 15thDay
22%9%37%43345%6%29%
1650
16th to endDay
31%12%47%6%3323420%
1744
November1st to 15thDay
22%11%46%6%2435%7%25%
1406
16th to endDay
29%15%7%10%6%2223414%
1440
December1st to 15thDay
21%21%6%10%7%2443412%
1440
16th to endDay
20%20%9%12%6%2333313%
1368
January1st to 15thNight
21%18%6%10%7%3444316%
2685
16th to endNight
16%17%6%10%6%34346%20%
2547
February1st to 15thNight
12%14%7%11%9%45%46%419%
2285
16th to endNight
16%19%6%9%6%4431322%
2051
March1st to 15thNight
18%14%5%8%6%4333426%
1974
16th to endNight
15%10%35%6%23336%38%
2112
April1st to 15thNight
21%12%45%423335%32%
1793
16th to endNight
20%8%35%433436%34%
1620
May1st to 15thNight
18%7%26%5%33447%35%
1506
16th to endNight
16%6%35%424348%38%
1495
June1st to 15thNight
15%8%36%5%35%45%7%33%
1302
16th to endNight
14%5%35%5%45%45%9%36%
1260
July1st to 15thNight
11%41432447%9%44%
1260
16th to endNight
12%4245%345%6%8%42%
1500
August1st to 15thNight
14%6%25%5%36%6%5%5%39%
1586
16th to endNight
13%6%26%43445%6%42%
1600
September1st to 15thNight
16%6%25%423337%42%
1650
16th to endNight
16%6%36%42335%6%42%
1839
October1st to 15thNight
23%8%37%5%2344431%
1980
16th to endNight
29%12%37%6%3334421%
2126
November1st to 15thNight
20%12%46%5%24445%27%
2451
16th to endNight
27%14%5%8%7%4433318%
2520
December1st to 15thNight
23%19%7%9%6%2443315%
2520
16th to endNight
22%18%7%12%7%2332314%
2853

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
70%48%11%4
1254
16th to endDay
66%5%8%13%5%
1671
February1st to 15thDay
67%6%8%13%4
1577
16th to endDay
65%47%14%8%
1422
March1st to 15thDay
57%5%11%16%7%
1972
16th to endDay
47%5%10%18%15%2
2112
April1st to 15thDay
54%410%16%11%1
2163
16th to endDay
48%48%23%13%2
2340
May1st to 15thDay
53%48%18%12%2
2445
16th to endDay
46%6%13%18%12%1
2622
June1st to 15thDay
52%7%10%20%9%
2656
16th to endDay
48%8%14%18%9%1
2700
July1st to 15thDay
40%6%13%28%10%
2541
16th to endDay
42%7%14%24%9%
2500
August1st to 15thDay
44%8%15%23%8%
2275
16th to endDay
43%8%15%25%7%
2239
September1st to 15thDay
49%6%13%22%7%
1980
16th to endDay
48%7%13%25%5%
1788
October1st to 15thDay
55%6%13%16%8%
1650
16th to endDay
69%5%10%10%4
1744
November1st to 15thDay
58%7%12%14%6%
1406
16th to endDay
73%49%8%3
1440
December1st to 15thDay
76%5%7%9%1
1440
16th to endDay
76%45%9%2
1368
January1st to 15thNight
73%5%8%8%3
2685
16th to endNight
66%5%8%14%5%
2547
February1st to 15thNight
66%5%11%12%3
2287
16th to endNight
68%36%14%6%
2051
March1st to 15thNight
61%310%15%7%
1986
16th to endNight
48%49%20%15%2
2112
April1st to 15thNight
56%37%18%12%2
1793
16th to endNight
51%46%19%14%2
1620
May1st to 15thNight
48%49%21%14%1
1506
16th to endNight
44%6%12%21%13%2
1497
June1st to 15thNight
49%411%22%9%1
1302
16th to endNight
45%8%12%21%10%1
1260
July1st to 15thNight
33%7%15%28%12%2
1190
16th to endNight
37%8%16%26%10%
1403
August1st to 15thNight
43%9%15%22%9%
1575
16th to endNight
40%7%15%24%10%
1600
September1st to 15thNight
41%5%17%25%8%
1650
16th to endNight
44%5%14%29%6%
1839
October1st to 15thNight
55%5%11%19%9%
1980
16th to endNight
66%5%9%11%5%
2126
November1st to 15thNight
57%6%12%16%5%
2451
16th to endNight
69%5%10%9%3
2520
December1st to 15thNight
74%48%10%2
2520
16th to endNight
75%46%8%5%
2853

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
25%20%40%10%5%
60
16th to endDay
29%437%19%7%1
88
February1st to 15thDay
28%14%38%15%2
90
16th to endDay
39%13%30%16%
81
March1st to 15thDay
25%12%31%24%5%
264
16th to endDay
19%9%33%26%9%2
288
April1st to 15thDay
27%9%29%23%7%2
270
16th to endDay
26%11%28%18%10%5%
270
May1st to 15thDay
32%7%16%24%14%4
288
16th to endDay
18%9%32%22%12%3
331
June1st to 15thDay
23%8%28%28%10%1
451
16th to endDay
16%7%29%30%12%2
495
July1st to 15thDay
14%6%25%36%14%2
475
16th to endDay
15%226%35%15%5%
364
August1st to 15thDay
19%318%34%15%9%
297
16th to endDay
22%418%33%13%7%
268
September1st to 15thDay
17%5%28%23%16%8%
255
16th to endDay
24%6%24%25%13%5%
254
October1st to 15thDay
24%9%30%24%9%1
255
16th to endDay
38%12%23%19%4
256
November1st to 15thDay
23%11%35%21%8%
60
16th to endDay
38%15%30%15%1
60
December1st to 15thDay
25%15%43%15%1
60
16th to endDay
34%20%39%6%
64
January1st to 15thNight
30%9%30%22%6%
900
16th to endNight
24%6%32%25%9%1
774
February1st to 15thNight
17%10%37%26%7%
704
16th to endNight
24%8%32%27%6%
631
March1st to 15thNight
25%12%31%23%5%
720
16th to endNight
19%8%30%29%10%
768
April1st to 15thNight
27%9%29%27%5%
706
16th to endNight
24%9%28%25%10%1
540
May1st to 15thNight
24%5%29%27%12%1
426
16th to endNight
19%6%29%32%12%
375
June1st to 15thNight
19%5%25%36%12%
360
16th to endNight
16%326%36%16%
360
July1st to 15thNight
12%225%43%15%
340
16th to endNight
13%223%39%18%1
401
August1st to 15thNight
17%321%32%22%3
527
16th to endNight
16%225%36%16%2
550
September1st to 15thNight
20%5%25%26%19%2
660
16th to endNight
19%6%26%27%17%2
657
October1st to 15thNight
28%8%27%25%9%
660
16th to endNight
36%9%27%21%4
704
November1st to 15thNight
25%12%29%22%8%1
700
16th to endNight
34%11%26%20%7%
720
December1st to 15thNight
30%15%30%18%4
720
16th to endNight
33%10%28%21%5%1
933
Page generated at 2017-08-13 14:16:26. Version ac04

Copyright 2017 A. Danko


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