Bellingham
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Bellingham clear sky chart from 2005-11-05 to 2017-04-26.

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
35%
14146
9%
45551
7%
14118
37%
14118
12%
34481

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
27%
750
9%
2686
8%
746
30%
746
8%
2218
January16th to endNight
28%
771
8%
2697
8%
771
31%
771
9%
2133
February1st to 15thNight
26%
700
6%
2288
5%
700
28%
700
7%
1888
February16th to endNight
28%
632
12%
2027
9%
632
33%
632
10%
1579
March1st to 15thNight
22%
720
4%
2072
3%
720
23%
720
8%
1746
March16th to endNight
22%
768
5%
2064
3%
768
23%
768
8%
1777
April1st to 15thNight
31%
719
6%
1799
4%
719
31%
719
11%
1514
April16th to endNight
33%
510
8%
1566
5%
510
34%
510
10%
1234
May1st to 15thNight
46%
329
13%
1319
20%
329
48%
329
16%
847
May16th to endNight
42%
342
4%
1368
6%
342
44%
342
10%
972
June1st to 15thNight
41%
330
2%
1164
2%
330
41%
330
15%
812
June16th to endNight
44%
330
5%
1155
2%
330
46%
330
14%
803
July1st to 15thNight
59%
310
11%
1085
10%
310
61%
310
30%
586
July16th to endNight
63%
348
14%
1255
17%
326
74%
326
35%
588
August1st to 15thNight
70%
390
17%
1372
21%
388
72%
388
34%
689
August16th to endNight
61%
574
19%
1624
15%
574
64%
574
33%
950
September1st to 15thNight
66%
660
20%
1650
12%
660
67%
660
38%
1000
September16th to endNight
44%
656
17%
1806
11%
656
47%
656
20%
1288
October1st to 15thNight
41%
660
11%
1980
11%
660
42%
660
18%
1407
October16th to endNight
33%
704
6%
2187
5%
704
35%
704
9%
1755
November1st to 15thNight
22%
700
5%
2449
5%
700
23%
700
6%
2091
November16th to endNight
21%
720
5%
2520
4%
720
23%
720
7%
2061
December1st to 15thNight
25%
723
7%
2538
6%
723
27%
723
8%
2070
December16th to endNight
15%
800
5%
2880
3%
800
18%
800
5%
2473

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
22%8%36%5%24446%30%
46138
Night
26%8%35%5%24345%29%
45708
Cloud CoverDay
24%8%36%5%3445%5%28%
46138
Night
27%9%35%5%24345%28%
45711
TransparencyDay
56%8%12%15%6%
45798
Night
58%6%12%14%6%1
45552
SeeingDay
21%15%18%25%15%2
5437
Night
27%19%11%20%17%4
14152

By Month

Percentage Cloud Cover NW (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
39%9%26%5%35%33317%
1253
16th to endDay
34%12%36%5%235%4418%
1522
February1st to 15thDay
30%12%47%6%34345%16%
1576
16th to endDay
26%11%37%6%25%36%6%22%
1446
March1st to 15thDay
35%12%5%8%5%2333415%
1887
16th to endDay
28%11%48%6%4444417%
2160
April1st to 15thDay
23%10%36%6%35%5%5%7%20%
2149
16th to endDay
22%9%47%6%35%46%7%21%
2304
May1st to 15thDay
18%6%26%5%35%5%5%6%35%
2301
16th to endDay
20%8%46%6%35%5%5%7%27%
2391
June1st to 15thDay
19%6%35%5%345%5%7%31%
2464
16th to endDay
17%6%36%6%345%5%8%33%
2475
July1st to 15thDay
9%424323346%53%
2475
16th to endDay
9%313214346%58%
2511
August1st to 15thDay
8%5%23424346%53%
2250
16th to endDay
12%424424447%47%
2226
September1st to 15thDay
10%5%24413326%53%
1980
16th to endDay
22%6%36%5%33446%33%
1821
October1st to 15thDay
23%8%35%5%2446%7%28%
1650
16th to endDay
31%8%36%6%2336%7%19%
1684
November1st to 15thDay
41%9%45%42433315%
1408
16th to endDay
33%11%47%6%2333417%
1440
December1st to 15thDay
31%14%47%42432320%
1421
16th to endDay
38%14%36%425%34413%
1344
January1st to 15thNight
40%10%3442333320%
2686
16th to endNight
33%11%35%423346%22%
2697
February1st to 15thNight
32%11%46%5%23345%20%
2276
16th to endNight
27%12%36%5%3333426%
2027
March1st to 15thNight
34%10%36%6%24435%17%
2072
16th to endNight
31%11%48%6%25%345%16%
2060
April1st to 15thNight
24%11%47%6%3436%5%22%
1799
16th to endNight
28%10%45%5%34445%23%
1566
May1st to 15thNight
17%5%24425%46%6%40%
1319
16th to endNight
15%7%26%6%35%6%8%8%28%
1368
June1st to 15thNight
17%7%37%7%34445%34%
1164
16th to endNight
17%5%35%6%35%46%8%31%
1155
July1st to 15thNight
6%325%424225%60%
1155
16th to endNight
8%212213336%64%
1350
August1st to 15thNight
6%2133335%5%7%57%
1380
16th to endNight
7%4145%2345%7%52%
1624
September1st to 15thNight
8%214423336%59%
1650
16th to endNight
21%6%26%423446%37%
1806
October1st to 15thNight
21%6%25%5%25%435%37%
1980
16th to endNight
31%8%26%4345%47%20%
2187
November1st to 15thNight
40%8%25%5%3343416%
2449
16th to endNight
34%9%47%5%3332420%
2520
December1st to 15thNight
33%10%36%5%2334421%
2538
16th to endNight
37%13%36%42322318%
2880

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
38%11%35%6%2343416%
1253
16th to endDay
36%11%36%5%23435%18%
1522
February1st to 15thDay
32%12%5%6%5%35%336%15%
1576
16th to endDay
27%12%37%5%34345%21%
1446
March1st to 15thDay
35%12%5%7%5%3433414%
1887
16th to endDay
30%13%5%7%7%4444314%
2160
April1st to 15thDay
24%12%5%7%7%36%45%5%16%
2149
16th to endDay
25%10%37%6%35%46%6%18%
2304
May1st to 15thDay
20%6%35%6%35%5%5%5%32%
2301
16th to endDay
22%9%46%6%345%5%6%24%
2391
June1st to 15thDay
22%7%46%6%3446%6%28%
2464
16th to endDay
19%7%35%6%35%5%6%7%29%
2475
July1st to 15thDay
10%5%2432435%6%51%
2475
16th to endDay
9%324413346%55%
2511
August1st to 15thDay
9%5%2442345%7%51%
2250
16th to endDay
13%42442445%7%46%
2226
September1st to 15thDay
10%5%24423246%51%
1980
16th to endDay
23%6%25%42345%7%32%
1821
October1st to 15thDay
24%9%26%4345%6%7%27%
1650
16th to endDay
32%8%35%6%3335%6%20%
1684
November1st to 15thDay
43%9%46%42333313%
1408
16th to endDay
33%11%5%7%5%23345%16%
1440
December1st to 15thDay
31%14%47%5%2433320%
1421
16th to endDay
39%12%36%5%3443412%
1344
January1st to 15thNight
40%11%36%32323320%
2685
16th to endNight
33%11%35%423246%21%
2697
February1st to 15thNight
32%11%46%424345%19%
2276
16th to endNight
27%14%45%5%2333425%
2027
March1st to 15thNight
34%11%36%5%3434418%
2072
16th to endNight
32%12%5%8%5%1344416%
2064
April1st to 15thNight
24%12%5%7%6%3445%6%20%
1799
16th to endNight
29%10%36%5%34345%22%
1566
May1st to 15thNight
18%5%24425%45%7%38%
1319
16th to endNight
16%8%27%6%35%5%8%7%27%
1368
June1st to 15thNight
19%6%37%6%245%5%5%33%
1164
16th to endNight
17%7%45%435%48%8%30%
1155
July1st to 15thNight
6%423414336%58%
1155
16th to endNight
9%212212236%64%
1350
August1st to 15thNight
7%21332445%7%57%
1380
16th to endNight
7%4145%2345%8%52%
1624
September1st to 15thNight
8%313423345%58%
1650
16th to endNight
22%6%245%2445%6%36%
1806
October1st to 15thNight
22%8%25%5%2443437%
1980
16th to endNight
32%8%36%5%34445%20%
2187
November1st to 15thNight
42%8%36%5%2433316%
2449
16th to endNight
35%10%46%5%2434319%
2520
December1st to 15thNight
33%11%36%32444421%
2538
16th to endNight
37%15%46%5%2323316%
2880

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
72%5%6%9%5%
1253
16th to endDay
69%5%10%10%3
1522
February1st to 15thDay
71%5%8%6%5%2
1576
16th to endDay
64%7%9%11%5%1
1446
March1st to 15thDay
74%5%8%9%1
1887
16th to endDay
73%7%9%9%
2160
April1st to 15thDay
66%11%10%10%1
2149
16th to endDay
62%10%11%10%3
2304
May1st to 15thDay
50%10%13%17%8%
2301
16th to endDay
58%12%14%11%2
2395
June1st to 15thDay
54%10%16%12%4
2464
16th to endDay
51%10%16%17%3
2475
July1st to 15thDay
33%8%16%26%12%2
2316
16th to endDay
27%9%17%30%13%1
2343
August1st to 15thDay
31%9%20%29%7%1
2233
16th to endDay
35%8%19%27%7%1
2226
September1st to 15thDay
34%7%16%21%17%2
1980
16th to endDay
52%8%11%16%8%1
1821
October1st to 15thDay
53%9%16%13%6%
1650
16th to endDay
63%8%14%10%2
1684
November1st to 15thDay
75%5%8%7%21
1408
16th to endDay
70%5%7%9%5%1
1440
December1st to 15thDay
70%6%48%8%
1421
16th to endDay
74%8%6%6%31
1344
January1st to 15thNight
70%46%12%41
2686
16th to endNight
65%5%10%13%41
2697
February1st to 15thNight
67%6%10%8%42
2288
16th to endNight
62%5%9%15%5%1
2027
March1st to 15thNight
69%6%11%9%3
2072
16th to endNight
70%7%9%11%1
2064
April1st to 15thNight
63%10%10%12%2
1799
16th to endNight
63%5%11%14%4
1566
May1st to 15thNight
43%8%18%18%10%1
1320
16th to endNight
50%11%21%12%3
1368
June1st to 15thNight
50%6%20%15%42
1164
16th to endNight
48%9%18%19%22
1155
July1st to 15thNight
30%414%29%15%4
1085
16th to endNight
22%5%17%31%18%4
1255
August1st to 15thNight
24%6%22%31%11%3
1372
16th to endNight
29%6%19%29%11%2
1624
September1st to 15thNight
27%6%16%24%20%3
1650
16th to endNight
48%7%11%21%9%2
1806
October1st to 15thNight
50%5%14%19%8%
1980
16th to endNight
63%7%14%10%3
2187
November1st to 15thNight
73%5%9%6%22
2449
16th to endNight
68%6%10%7%6%
2520
December1st to 15thNight
67%6%10%9%5%
2538
16th to endNight
74%5%7%7%4
2880

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
13%5%8%28%26%18%
60
16th to endDay
50%8%16%8%15%1
73
February1st to 15thDay
38%19%16%15%8%2
236
16th to endDay
31%18%18%21%10%
216
March1st to 15thDay
43%23%18%11%2
270
16th to endDay
32%23%20%14%7%1
288
April1st to 15thDay
21%20%22%20%13%2
269
16th to endDay
20%20%22%25%10%1
254
May1st to 15thDay
17%16%22%24%16%1
228
16th to endDay
18%17%21%21%19%1
266
June1st to 15thDay
13%17%20%29%17%1
409
16th to endDay
13%17%20%31%16%
420
July1st to 15thDay
10%13%15%34%23%3
400
16th to endDay
5%14%15%33%27%4
320
August1st to 15thDay
11%7%14%37%23%5%
255
16th to endDay
10%11%17%40%16%3
268
September1st to 15thDay
9%9%29%24%23%3
255
16th to endDay
25%7%20%28%13%5%
255
October1st to 15thDay
32%11%20%20%13%1
255
16th to endDay
35%11%13%22%12%3
196
November1st to 15thDay
55%10%25%8%1
60
16th to endDay
28%8%13%23%13%13%
60
December1st to 15thDay
46%11%11%13%16%
60
16th to endDay
39%12%12%21%6%7%
64
January1st to 15thNight
36%21%8%13%15%3
750
16th to endNight
31%21%11%18%13%3
771
February1st to 15thNight
33%20%12%19%12%2
704
16th to endNight
30%21%13%19%11%3
632
March1st to 15thNight
37%23%11%14%10%2
720
16th to endNight
30%24%12%17%10%3
768
April1st to 15thNight
25%22%11%23%14%3
719
16th to endNight
29%20%7%25%13%3
510
May1st to 15thNight
17%20%9%20%26%5%
330
16th to endNight
16%20%8%23%26%4
343
June1st to 15thNight
14%22%10%23%23%4
330
16th to endNight
16%21%10%27%19%4
330
July1st to 15thNight
6%16%10%26%33%6%
310
16th to endNight
6%18%427%32%10%
348
August1st to 15thNight
8%10%6%22%40%12%
390
16th to endNight
10%11%9%23%37%8%
574
September1st to 15thNight
10%10%7%28%28%14%
660
16th to endNight
23%12%10%21%24%7%
656
October1st to 15thNight
24%13%12%25%19%5%
660
16th to endNight
35%13%10%21%13%5%
704
November1st to 15thNight
39%20%13%19%7%1
700
16th to endNight
34%22%12%15%10%4
720
December1st to 15thNight
34%21%11%19%10%2
723
16th to endNight
38%24%15%14%6%1
800
Page generated at 2017-04-27 14:48:47. Version ac04

Copyright 2017 A. Danko


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