Everett Astro SP
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Everett Astro SP clear sky chart from 2005-11-06 to 2024-01-12.

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
38%
22450
9%
74514
9%
22397
40%
22397
13%
56590

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
22%
837
7%
2811
6%
833
23%
833
7%
2402
January11th to 20thNight
30%
724
8%
2534
9%
724
31%
724
9%
2050
January21st to endNight
31%
792
9%
2749
10%
792
32%
792
10%
2192
February1st to 10thNight
28%
720
7%
2340
6%
720
31%
720
9%
1943
February11th to 20thNight
29%
702
7%
2274
8%
700
31%
700
10%
1866
February21st to endNight
29%
592
10%
1857
8%
592
31%
592
10%
1498
March1st to 10thNight
32%
720
8%
2134
7%
720
33%
720
12%
1693
March11th to 20thNight
29%
720
9%
1980
6%
720
31%
720
11%
1620
March21st to endNight
25%
792
4%
2094
2%
792
26%
792
9%
1788
April1st to 10thNight
31%
720
6%
1800
3%
720
32%
720
12%
1528
April11th to 20thNight
34%
693
9%
1761
5%
693
35%
693
15%
1422
April21st to endNight
30%
478
7%
1558
6%
478
32%
478
11%
1252
May1st to 10thNight
46%
360
10%
1440
13%
360
48%
360
15%
965
May11th to 20thNight
50%
354
9%
1416
15%
354
50%
354
14%
991
May21st to endNight
43%
388
4%
1552
7%
388
45%
388
11%
1156
June1st to 10thNight
41%
360
4%
1390
5%
360
42%
360
13%
998
June11th to 20thNight
36%
360
3%
1260
4%
360
37%
360
11%
990
June21st to endNight
56%
360
8%
1260
8%
360
58%
360
21%
819
July1st to 10thNight
62%
350
10%
1225
12%
350
62%
350
26%
737
July11th to 20thNight
66%
348
15%
1325
22%
348
68%
348
31%
713
July21st to endNight
72%
394
19%
1488
30%
372
76%
372
37%
694
August1st to 10thNight
76%
367
19%
1433
28%
365
77%
365
33%
715
August11th to 20thNight
76%
534
23%
1602
22%
534
77%
534
40%
884
August21st to endNight
62%
706
20%
1894
16%
706
63%
706
33%
1197
September1st to 10thNight
63%
720
19%
1800
11%
720
63%
720
37%
1147
September11th to 20thNight
54%
720
17%
1800
12%
720
54%
720
27%
1283
September21st to endNight
50%
720
16%
2046
13%
720
51%
720
23%
1442
October1st to 10thNight
48%
720
10%
2160
11%
720
48%
720
19%
1558
October11th to 20thNight
40%
720
11%
2160
12%
720
42%
720
16%
1616
October21st to endNight
34%
792
11%
2502
10%
792
37%
792
14%
1913
November1st to 10thNight
25%
740
5%
2544
5%
740
27%
740
9%
2094
November11th to 20thNight
24%
760
8%
2660
7%
760
26%
760
9%
2137
November21st to endNight
27%
760
5%
2660
5%
760
28%
760
9%
2143
December1st to 10thNight
32%
760
9%
2660
10%
760
34%
760
10%
2099
December11th to 20thNight
22%
760
6%
3237
4%
759
23%
759
5%
2724
December21st to endNight
19%
907
3%
5108
5%
885
21%
885
3%
4321

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
25%9%36%5%34446%30%
74946
Night
28%9%36%5%34445%29%
74748
TransparencyDay
57%6%13%15%7%1
74640
Night
59%6%12%15%7%1
74572
SeeingDay
29%8%20%25%14%3
13925
Night
35%5%14%26%17%2
22458

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 10thDay
44%11%36%6%2323316%
1349
11th to 20thDay
33%11%47%5%33446%20%
1448
21st to endDay
36%10%36%5%35%445%19%
1606
February1st to 10thDay
37%11%36%6%34445%17%
1620
11th to 20thDay
31%14%47%6%2344421%
1575
21st to endDay
32%13%47%6%3443421%
1399
March1st to 10thDay
30%11%47%7%445%46%19%
1824
11th to 20thDay
32%12%46%6%34435%21%
1980
21st to endDay
32%13%48%7%44445%15%
2261
April1st to 10thDay
27%12%49%6%45%46%6%17%
2160
11th to 20thDay
29%10%38%6%46%445%21%
2146
21st to endDay
25%10%39%7%46%5%6%5%20%
2400
May1st to 10thDay
20%8%37%7%45%46%6%30%
2520
11th to 20thDay
21%8%27%6%45%5%6%7%27%
2477
21st to endDay
28%9%46%6%34446%25%
2723
June1st to 10thDay
26%8%36%6%4445%7%27%
2565
11th to 20thDay
27%9%47%7%45%5%5%6%22%
2700
21st to endDay
15%6%37%5%3446%7%38%
2700
July1st to 10thDay
13%6%25%5%235%47%47%
2700
11th to 20thDay
12%5%24424447%51%
2588
21st to endDay
10%323323346%61%
2741
August1st to 10thDay
12%5%24424446%54%
2495
11th to 20thDay
9%42443345%8%55%
2298
21st to endDay
14%6%35%5%345%5%7%43%
2462
September1st to 10thDay
13%5%36%5%33346%48%
2160
11th to 20thDay
17%8%37%5%4345%6%40%
2160
21st to endDay
21%7%246%33446%38%
1910
October1st to 10thDay
23%9%37%6%35%45%7%30%
1800
11th to 20thDay
30%9%36%5%34347%26%
1800
21st to endDay
34%8%36%5%43445%22%
1854
November1st to 10thDay
39%10%35%5%245%45%16%
1534
11th to 20thDay
38%9%36%5%3434323%
1520
21st to endDay
38%11%45%5%23345%20%
1520
December1st to 10thDay
33%11%46%5%2433424%
1520
11th to 20thDay
36%12%47%5%24436%17%
1925
21st to endDay
31%14%5%11%7%24445%14%
2506
January1st to 10thNight
44%10%36%43343316%
2811
11th to 20thNight
36%10%36%6%34445%20%
2534
21st to endNight
34%10%36%6%34445%21%
2749
February1st to 10thNight
36%12%36%5%34445%19%
2340
11th to 20thNight
32%14%36%5%2433422%
2272
21st to endNight
30%13%36%5%25%445%22%
1857
March1st to 10thNight
30%13%35%43445%5%23%
2134
11th to 20thNight
33%10%36%434346%22%
1979
21st to endNight
32%13%46%6%3445%5%18%
2094
April1st to 10thNight
29%12%47%5%36%45%7%18%
1800
11th to 20thNight
26%10%46%6%35%5%5%6%26%
1761
21st to endNight
27%9%47%8%345%46%22%
1558
May1st to 10thNight
21%8%46%5%2445%5%37%
1440
11th to 20thNight
21%6%46%6%345%5%6%34%
1416
21st to endNight
22%9%5%7%6%45%45%5%30%
1552
June1st to 10thNight
24%7%46%5%45%45%6%31%
1390
11th to 20thNight
30%9%46%7%4435%5%24%
1260
21st to endNight
15%7%245%36%45%7%43%
1260
July1st to 10thNight
13%5%25%43445%451%
1260
11th to 20thNight
10%32442345%7%56%
1369
21st to endNight
10%423323345%62%
1576
August1st to 10thNight
9%31332335%6%61%
1441
11th to 20thNight
9%313322446%62%
1602
21st to endNight
14%5%25%434445%52%
1894
September1st to 10thNight
12%6%24433445%54%
1800
11th to 20thNight
19%7%36%5%33345%42%
1800
21st to endNight
20%9%25%5%23435%41%
2046
October1st to 10thNight
21%8%36%7%34445%35%
2160
11th to 20thNight
28%8%35%42345%5%32%
2160
21st to endNight
32%8%35%5%33347%27%
2502
November1st to 10thNight
39%9%26%5%24445%19%
2544
11th to 20thNight
39%8%35%5%2334423%
2660
21st to endNight
38%10%35%5%34445%21%
2660
December1st to 10thNight
33%10%35%5%2445%425%
2660
11th to 20thNight
34%14%48%5%33445%16%
3280
21st to endNight
31%14%5%9%6%45%5%4413%
5127

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
76%45%11%31
1349
11th to 20thDay
66%7%10%8%6%2
1448
21st to endDay
67%6%10%12%5%
1606
February1st to 10thDay
71%7%9%8%31
1620
11th to 20thDay
70%49%8%8%
1584
21st to endDay
69%5%10%10%5%
1399
March1st to 10thDay
68%5%12%11%4
1824
11th to 20thDay
70%5%9%11%31
1980
21st to endDay
75%6%10%8%1
2261
April1st to 10thDay
70%7%15%8%1
2160
11th to 20thDay
67%5%11%11%5%
2146
21st to endDay
68%7%11%9%5%1
2400
May1st to 10thDay
56%7%17%14%5%
2520
11th to 20thDay
57%7%18%13%4
2480
21st to endDay
64%7%15%13%1
2724
June1st to 10thDay
60%7%17%11%5%1
2565
11th to 20thDay
65%8%15%10%2
2700
21st to endDay
47%9%19%18%6%1
2700
July1st to 10thDay
39%7%15%25%12%1
2626
11th to 20thDay
35%7%14%29%14%1
2509
21st to endDay
27%5%15%34%15%3
2589
August1st to 10thDay
34%7%18%26%14%1
2478
11th to 20thDay
29%7%20%29%12%3
2298
21st to endDay
41%6%17%27%8%1
2462
September1st to 10thDay
38%6%16%24%12%4
2160
11th to 20thDay
48%7%12%17%15%2
2160
21st to endDay
49%7%17%15%10%3
1910
October1st to 10thDay
52%10%13%18%7%1
1800
11th to 20thDay
58%6%12%18%5%1
1800
21st to endDay
65%410%12%9%
1854
November1st to 10thDay
71%5%12%8%4
1534
11th to 20thDay
70%5%8%8%7%2
1520
21st to endDay
70%46%10%8%1
1520
December1st to 10thDay
67%5%7%12%9%1
1520
11th to 20thDay
71%6%10%11%11
1928
21st to endDay
72%8%9%8%2
2506
January1st to 10thNight
74%5%7%9%31
2811
11th to 20thNight
68%5%10%9%6%2
2534
21st to endNight
67%5%9%13%6%1
2749
February1st to 10thNight
70%5%9%10%41
2340
11th to 20thNight
68%6%10%9%7%1
2274
21st to endNight
66%6%10%13%41
1857
March1st to 10thNight
63%6%13%13%5%
2134
11th to 20thNight
66%5%10%14%41
1980
21st to endNight
70%7%13%9%1
2094
April1st to 10thNight
67%7%13%12%1
1800
11th to 20thNight
62%6%13%11%7%1
1761
21st to endNight
65%7%11%11%5%1
1558
May1st to 10thNight
51%5%20%17%6%1
1440
11th to 20thNight
52%8%19%14%6%1
1416
21st to endNight
57%9%18%15%1
1552
June1st to 10thNight
56%6%17%15%5%
1390
11th to 20thNight
62%7%16%12%3
1260
21st to endNight
41%10%20%20%5%3
1260
July1st to 10thNight
37%7%15%25%13%4
1225
11th to 20thNight
32%6%17%29%15%1
1325
21st to endNight
24%5%14%33%20%4
1488
August1st to 10thNight
26%7%15%32%16%3
1433
11th to 20thNight
24%9%17%31%15%3
1602
21st to endNight
36%5%16%31%10%1
1894
September1st to 10thNight
34%6%15%28%14%4
1800
11th to 20thNight
47%5%11%19%15%4
1800
21st to endNight
48%6%13%20%10%2
2046
October1st to 10thNight
51%7%13%21%8%1
2160
11th to 20thNight
56%6%13%17%7%1
2160
21st to endNight
59%6%11%15%8%
2502
November1st to 10thNight
70%5%13%9%31
2544
11th to 20thNight
69%410%10%5%2
2660
21st to endNight
69%48%10%9%1
2660
December1st to 10thNight
65%5%10%11%8%1
2660
11th to 20thNight
71%7%8%9%31
3276
21st to endNight
74%8%9%8%3
5127

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
43%8%16%16%11%6%
180
11th to 20thDay
41%12%14%15%15%2
162
21st to endDay
48%7%12%17%12%4
198
February1st to 10thDay
49%9%19%16%7%
340
11th to 20thDay
45%10%21%16%7%1
335
21st to endDay
39%10%19%24%8%
310
March1st to 10thDay
36%12%26%16%9%1
420
11th to 20thDay
37%12%17%21%10%2
420
21st to endDay
42%13%22%13%9%1
462
April1st to 10thDay
36%12%24%17%9%2
420
11th to 20thDay
33%15%24%16%10%3
412
21st to endDay
30%13%26%20%10%1
420
May1st to 10thDay
22%11%26%27%12%1
423
11th to 20thDay
29%9%19%25%14%4
448
21st to endDay
31%8%16%28%13%3
485
June1st to 10thDay
26%9%26%24%13%3
495
11th to 20thDay
26%8%26%26%11%2
630
21st to endDay
17%6%22%33%19%3
630
July1st to 10thDay
15%323%37%19%2
621
11th to 20thDay
12%6%21%37%20%4
508
21st to endDay
10%317%39%24%6%
487
August1st to 10thDay
13%5%15%37%22%9%
447
11th to 20thDay
11%216%37%25%8%
437
21st to endDay
15%7%23%33%16%7%
495
September1st to 10thDay
18%6%23%34%14%4
450
11th to 20thDay
21%8%18%28%21%3
450
21st to endDay
23%9%21%29%15%4
450
October1st to 10thDay
29%7%19%22%18%4
450
11th to 20thDay
37%416%21%18%4
450
21st to endDay
38%12%15%20%11%4
369
November1st to 10thDay
44%10%18%16%10%1
203
11th to 20thDay
46%8%10%15%15%6%
180
21st to endDay
42%8%17%13%9%11%
180
December1st to 10thDay
52%6%11%11%13%8%
180
11th to 20thDay
46%8%19%16%10%1
180
21st to endDay
43%8%18%21%9%2
198
January1st to 10thNight
51%7%13%17%11%1
837
11th to 20thNight
44%7%12%23%13%1
724
21st to endNight
43%413%26%13%1
792
February1st to 10thNight
43%7%14%27%8%1
720
11th to 20thNight
42%6%13%28%10%1
704
21st to endNight
39%7%16%27%11%1
592
March1st to 10thNight
38%9%16%24%12%1
720
11th to 20thNight
42%8%15%22%12%1
720
21st to endNight
43%8%17%22%9%1
792
April1st to 10thNight
37%7%16%27%12%1
720
11th to 20thNight
34%6%18%27%13%1
693
21st to endNight
35%6%20%25%13%2
478
May1st to 10thNight
26%5%15%34%20%
360
11th to 20thNight
27%411%34%23%2
354
21st to endNight
28%5%13%29%22%3
389
June1st to 10thNight
27%5%18%32%14%3
360
11th to 20thNight
35%6%13%29%16%1
360
21st to endNight
20%412%35%26%4
360
July1st to 10thNight
15%49%34%34%3
350
11th to 20thNight
13%114%35%34%3
348
21st to endNight
11%39%31%41%5%
394
August1st to 10thNight
10%26%30%44%8%
367
11th to 20thNight
11%25%30%41%11%
534
21st to endNight
18%211%31%33%4
706
September1st to 10thNight
17%211%36%30%4
720
11th to 20thNight
24%311%25%31%7%
720
21st to endNight
28%5%10%28%25%4
720
October1st to 10thNight
26%412%28%26%4
720
11th to 20thNight
35%415%25%18%3
720
21st to endNight
40%6%16%25%12%2
792
November1st to 10thNight
46%7%17%22%8%
740
11th to 20thNight
46%420%19%9%2
760
21st to endNight
44%5%16%20%13%1
760
December1st to 10thNight
38%6%17%25%12%2
760
11th to 20thNight
49%7%13%24%6%1
760
21st to endNight
50%7%16%20%7%
912
Page generated at 2024-01-08 19:31:29. Version ac07

Copyright 2024 Attilla Danko


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