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 2018-02-22.

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
33%
15625
11%
48815
8%
15595
37%
15595
15%
36486

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
21%
972
5%
2910
3%
970
23%
970
8%
2455
January16th to endNight
27%
840
9%
2761
8%
840
31%
840
10%
2198
February1st to 15thNight
26%
762
8%
2482
5%
761
30%
761
10%
1967
February16th to endNight
26%
659
9%
2141
6%
659
30%
659
10%
1715
March1st to 15thNight
26%
720
12%
1986
6%
720
30%
720
16%
1545
March16th to endNight
38%
768
19%
2112
11%
768
43%
768
24%
1471
April1st to 15thNight
32%
706
14%
1794
6%
706
35%
706
21%
1352
April16th to endNight
36%
540
17%
1620
11%
540
41%
540
21%
1150
May1st to 15thNight
40%
426
15%
1506
15%
426
45%
426
20%
1001
May16th to endNight
46%
374
12%
1497
14%
374
53%
374
19%
941
June1st to 15thNight
43%
360
9%
1300
10%
360
47%
360
18%
889
June16th to endNight
48%
360
9%
1260
8%
360
51%
360
20%
835
July1st to 15thNight
58%
340
14%
1190
16%
340
61%
340
29%
691
July16th to endNight
59%
401
13%
1401
17%
377
60%
377
23%
864
August1st to 15thNight
51%
539
12%
1609
10%
536
52%
536
23%
1108
August16th to endNight
53%
600
17%
1746
9%
600
57%
600
26%
1142
September1st to 15thNight
48%
720
15%
1800
8%
720
50%
720
30%
1225
September16th to endNight
48%
717
19%
2007
13%
717
51%
717
29%
1309
October1st to 15thNight
35%
720
14%
2160
11%
720
39%
720
18%
1588
October16th to endNight
21%
768
10%
2319
6%
768
26%
768
11%
1865
November1st to 15thNight
25%
760
11%
2661
10%
760
29%
760
12%
2007
November16th to endNight
21%
780
8%
2730
5%
780
24%
780
8%
2249
December1st to 15thNight
17%
780
6%
2730
2%
780
22%
780
6%
2299
December16th to endNight
18%
1013
7%
3093
4%
1013
21%
1013
7%
2620

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
18%10%47%5%34446%30%
49442
Night
18%12%47%6%34445%28%
48977
TransparencyDay
53%6%12%18%8%
49122
Night
57%5%11%17%7%
48815
SeeingDay
22%5%24%29%13%3
6227
Night
24%5%26%30%11%1
15631

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%7%7%7%3433417%
1358
16th to endDay
16%16%6%11%7%35%346%18%
1810
February1st to 15thDay
10%16%7%12%9%35%446%19%
1710
16th to endDay
16%16%6%10%6%45%33422%
1479
March1st to 15thDay
17%11%47%6%24446%28%
1961
16th to endDay
13%7%47%6%34446%38%
2112
April1st to 15thDay
21%10%46%43335%5%30%
2164
16th to endDay
20%9%35%413245%38%
2340
May1st to 15thDay
21%9%35%5%34446%31%
2445
16th to endDay
16%6%35%5%3445%7%36%
2618
June1st to 15thDay
16%8%37%5%35%46%7%30%
2658
16th to endDay
15%6%37%6%35%5%6%8%30%
2700
July1st to 15thDay
13%425%5%35%45%9%38%
2700
16th to endDay
13%426%5%345%7%9%37%
2666
August1st to 15thDay
14%6%25%6%35%5%7%7%36%
2340
16th to endDay
15%6%26%5%3345%8%37%
2444
September1st to 15thDay
17%6%26%6%3435%7%36%
2160
16th to endDay
21%6%24424446%37%
1950
October1st to 15thDay
21%9%26%5%33446%31%
1800
16th to endDay
30%11%38%5%3333421%
1902
November1st to 15thDay
23%12%36%6%235%47%24%
1526
16th to endDay
29%16%5%9%5%3223415%
1560
December1st to 15thDay
20%22%6%11%6%24435%13%
1560
16th to endDay
20%19%9%10%6%3433415%
1479
January1st to 15thNight
20%17%7%10%7%3344415%
2910
16th to endNight
16%17%6%9%7%43445%19%
2761
February1st to 15thNight
11%14%7%11%9%45%5%5%420%
2480
16th to endNight
16%18%7%8%8%4432322%
2141
March1st to 15thNight
18%13%5%8%6%33345%26%
1974
16th to endNight
14%11%35%5%23436%38%
2112
April1st to 15thNight
21%12%45%424335%32%
1794
16th to endNight
20%8%25%434346%34%
1620
May1st to 15thNight
18%8%25%5%34446%36%
1506
16th to endNight
17%6%35%433449%37%
1495
June1st to 15thNight
16%8%36%6%3445%8%33%
1300
16th to endNight
15%427%5%35%5%6%8%35%
1260
July1st to 15thNight
11%4243335%6%9%44%
1260
16th to endNight
11%5%245%245%6%8%42%
1498
August1st to 15thNight
13%7%246%26%5%5%5%39%
1620
16th to endNight
14%5%245%345%5%7%42%
1746
September1st to 15thNight
16%5%24423347%44%
1800
16th to endNight
16%6%3442335%6%43%
2007
October1st to 15thNight
23%8%36%5%2444432%
2160
16th to endNight
28%12%36%6%2434423%
2319
November1st to 15thNight
21%11%47%6%34445%27%
2661
16th to endNight
27%14%47%5%34435%19%
2730
December1st to 15thNight
21%19%7%9%5%2443416%
2730
16th to endNight
20%18%8%11%7%2433415%
3093

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
69%49%11%4
1359
16th to endDay
66%5%9%13%5%
1810
February1st to 15thDay
65%5%10%13%4
1712
16th to endDay
65%38%14%8%
1479
March1st to 15thDay
56%412%17%7%
1972
16th to endDay
46%410%19%15%2
2112
April1st to 15thDay
53%5%10%17%11%1
2164
16th to endDay
47%48%23%13%2
2340
May1st to 15thDay
53%48%18%12%2
2445
16th to endDay
45%7%14%18%12%1
2622
June1st to 15thDay
50%7%11%20%9%
2658
16th to endDay
47%8%14%19%9%1
2700
July1st to 15thDay
39%6%14%27%11%1
2541
16th to endDay
42%7%16%24%9%
2500
August1st to 15thDay
42%9%16%22%8%
2327
16th to endDay
43%7%17%25%6%
2444
September1st to 15thDay
46%7%14%22%8%
2160
16th to endDay
47%6%15%26%4
1950
October1st to 15thDay
54%6%12%17%8%
1800
16th to endDay
67%5%10%11%4
1902
November1st to 15thDay
60%7%12%13%5%
1526
16th to endDay
72%5%9%8%3
1560
December1st to 15thDay
75%6%7%9%1
1560
16th to endDay
73%46%11%3
1479
January1st to 15thNight
71%49%9%3
2910
16th to endNight
66%49%14%5%
2761
February1st to 15thNight
64%6%11%13%4
2482
16th to endNight
67%37%14%6%
2141
March1st to 15thNight
61%311%15%7%
1986
16th to endNight
47%49%20%14%2
2112
April1st to 15thNight
55%37%18%12%2
1794
16th to endNight
51%47%19%14%2
1620
May1st to 15thNight
48%410%20%13%2
1506
16th to endNight
43%6%13%21%12%2
1497
June1st to 15thNight
48%7%10%22%9%2
1300
16th to endNight
44%8%13%21%11%1
1260
July1st to 15thNight
32%8%15%27%12%2
1190
16th to endNight
38%8%15%26%10%
1401
August1st to 15thNight
43%9%15%21%9%
1609
16th to endNight
39%8%16%25%9%
1746
September1st to 15thNight
40%6%16%25%9%1
1800
16th to endNight
41%416%30%7%
2007
October1st to 15thNight
54%410%20%8%
2160
16th to endNight
65%5%11%12%5%
2319
November1st to 15thNight
59%6%12%15%5%
2661
16th to endNight
69%5%10%9%3
2730
December1st to 15thNight
72%5%8%10%2
2730
16th to endNight
73%46%9%5%
3093

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%15%28%20%6%
90
16th to endDay
34%6%22%25%10%
132
February1st to 15thDay
26%8%37%24%2
135
16th to endDay
42%11%25%22%
100
March1st to 15thDay
25%8%29%28%7%
263
16th to endDay
17%5%30%33%9%3
288
April1st to 15thDay
25%429%26%11%2
270
16th to endDay
25%5%27%25%10%5%
270
May1st to 15thDay
32%316%25%18%4
288
16th to endDay
19%425%29%16%3
331
June1st to 15thDay
22%326%30%13%2
453
16th to endDay
15%422%38%14%4
495
July1st to 15thDay
13%321%38%18%4
475
16th to endDay
15%218%37%21%5%
364
August1st to 15thDay
19%13%34%23%8%
313
16th to endDay
21%415%28%19%9%
332
September1st to 15thDay
19%419%26%21%8%
315
16th to endDay
22%419%28%20%4
314
October1st to 15thDay
23%6%29%29%9%1
315
16th to endDay
33%12%25%22%5%1
318
November1st to 15thDay
25%14%32%21%5%1
90
16th to endDay
41%11%28%16%2
90
December1st to 15thDay
26%12%37%20%3
90
16th to endDay
27%9%39%19%31
96
January1st to 15thNight
30%6%28%27%7%
975
16th to endNight
23%6%26%31%10%1
840
February1st to 15thNight
17%6%35%33%7%
764
16th to endNight
24%6%28%33%6%
659
March1st to 15thNight
26%6%32%29%5%
720
16th to endNight
19%428%33%11%1
768
April1st to 15thNight
27%6%27%31%7%
706
16th to endNight
25%5%27%29%11%1
540
May1st to 15thNight
23%325%32%12%2
426
16th to endNight
20%326%34%15%
375
June1st to 15thNight
18%324%36%15%1
360
16th to endNight
15%321%39%19%1
360
July1st to 15thNight
11%120%47%17%
340
16th to endNight
11%217%44%21%1
401
August1st to 15thNight
17%219%33%23%3
539
16th to endNight
18%220%35%19%3
600
September1st to 15thNight
20%321%29%21%3
720
16th to endNight
18%422%30%20%2
717
October1st to 15thNight
27%6%24%30%9%1
720
16th to endNight
36%8%28%21%4
768
November1st to 15thNight
27%9%30%23%8%1
760
16th to endNight
35%9%25%22%7%
780
December1st to 15thNight
29%10%32%22%4
780
16th to endNight
31%6%29%25%6%1
1013
Page generated at 2018-02-23 11:21:32. Version ac04

Copyright 2018 A. Danko


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