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Everett
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Everett clear sky chart from 2005-11-06 to 2024-01-16.

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
40%
22501
10%
74619
10%
22448
42%
22448
15%
55015

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
25%
850
7%
2836
7%
846
26%
846
7%
2388
January11th to 20thNight
31%
745
9%
2601
9%
745
33%
745
10%
2059
January21st to endNight
33%
792
9%
2740
9%
792
34%
792
11%
2144
February1st to 10thNight
30%
720
9%
2340
8%
720
32%
720
10%
1898
February11th to 20thNight
31%
701
8%
2274
8%
700
32%
700
11%
1820
February21st to endNight
31%
592
11%
1865
10%
592
34%
592
12%
1455
March1st to 10thNight
34%
720
9%
2124
9%
720
36%
720
14%
1660
March11th to 20thNight
31%
720
10%
1980
7%
720
33%
720
13%
1577
March21st to endNight
28%
792
5%
2102
2%
792
29%
792
11%
1742
April1st to 10thNight
33%
720
7%
1800
3%
720
34%
720
13%
1486
April11th to 20thNight
36%
685
10%
1753
6%
685
38%
685
17%
1369
April21st to endNight
34%
486
8%
1566
6%
486
35%
486
13%
1207
May1st to 10thNight
47%
360
12%
1440
16%
360
49%
360
17%
940
May11th to 20thNight
51%
354
10%
1416
16%
354
53%
354
16%
928
May21st to endNight
43%
388
6%
1552
10%
388
45%
388
12%
1101
June1st to 10thNight
42%
360
4%
1368
5%
360
43%
360
15%
952
June11th to 20thNight
40%
360
4%
1260
4%
360
40%
360
12%
962
June21st to endNight
60%
360
10%
1260
9%
360
62%
360
24%
769
July1st to 10thNight
66%
350
11%
1225
14%
350
67%
350
28%
708
July11th to 20thNight
69%
348
17%
1307
25%
348
71%
348
34%
676
July21st to endNight
74%
394
20%
1488
33%
372
77%
372
40%
678
August1st to 10thNight
76%
377
20%
1443
28%
375
77%
375
36%
704
August11th to 20thNight
78%
534
24%
1602
23%
534
79%
534
45%
836
August21st to endNight
63%
697
21%
1885
17%
697
64%
697
35%
1159
September1st to 10thNight
67%
720
20%
1800
12%
720
67%
720
39%
1118
September11th to 20thNight
54%
720
19%
1800
12%
720
55%
720
29%
1258
September21st to endNight
50%
720
17%
2051
14%
720
52%
720
25%
1418
October1st to 10thNight
49%
720
10%
2160
11%
720
49%
720
22%
1508
October11th to 20thNight
43%
720
12%
2160
12%
720
45%
720
19%
1549
October21st to endNight
35%
792
11%
2495
11%
792
39%
792
16%
1847
November1st to 10thNight
28%
740
8%
2554
7%
740
31%
740
10%
2040
November11th to 20thNight
29%
760
9%
2660
8%
760
31%
760
10%
2081
November21st to endNight
30%
760
6%
2660
6%
760
31%
760
10%
2101
December1st to 10thNight
35%
760
11%
2660
12%
760
37%
760
12%
2037
December11th to 20thNight
24%
759
5%
3234
4%
759
25%
759
5%
2635
December21st to endNight
20%
925
3%
5158
5%
901
23%
901
4%
4205

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
21%9%47%6%3445%6%30%
74930
Night
24%10%37%6%3445%6%29%
74869
TransparencyDay
57%314%18%7%1
74623
Night
59%312%17%7%1
74694
SeeingDay
23%9%20%25%17%5%
13976
Night
28%9%15%24%20%4
22511

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
39%11%5%8%5%2344415%
1329
11th to 20thDay
29%11%39%6%35%45%6%19%
1465
21st to endDay
31%11%48%8%45%45%5%15%
1613
February1st to 10thDay
33%12%5%7%6%35%446%15%
1620
11th to 20thDay
27%13%49%6%3345%5%20%
1575
21st to endDay
27%14%48%7%34445%20%
1390
March1st to 10thDay
26%12%5%7%5%46%5%5%7%18%
1833
11th to 20thDay
28%12%46%6%4445%5%22%
1980
21st to endDay
27%13%5%9%7%45%45%6%15%
2254
April1st to 10thDay
23%13%5%7%7%45%6%6%7%17%
2160
11th to 20thDay
24%9%5%8%7%46%5%46%22%
2156
21st to endDay
20%10%48%8%5%6%5%6%6%23%
2394
May1st to 10thDay
17%7%48%8%445%7%6%32%
2520
11th to 20thDay
18%8%36%6%45%6%6%8%30%
2477
21st to endDay
23%10%48%6%345%5%7%27%
2723
June1st to 10thDay
22%8%37%6%3445%8%29%
2587
11th to 20thDay
23%9%47%6%45%5%6%7%24%
2700
21st to endDay
13%6%46%5%345%6%8%39%
2700
July1st to 10thDay
11%6%245%345%5%7%48%
2700
11th to 20thDay
10%5%25%424447%53%
2607
21st to endDay
9%322323345%63%
2741
August1st to 10thDay
9%5%2442345%7%55%
2486
11th to 20thDay
8%32442346%9%55%
2298
21st to endDay
11%6%36%5%3445%7%44%
2470
September1st to 10thDay
10%7%36%42445%7%48%
2160
11th to 20thDay
14%7%47%6%3446%6%40%
2160
21st to endDay
19%7%36%5%4445%7%37%
1904
October1st to 10thDay
20%8%47%6%45%5%6%7%29%
1800
11th to 20thDay
27%10%36%6%345%5%8%24%
1800
21st to endDay
29%10%47%6%345%5%6%21%
1860
November1st to 10thDay
34%11%47%5%35%5%46%16%
1523
11th to 20thDay
34%11%36%5%25%35%5%22%
1520
21st to endDay
34%11%46%5%43445%19%
1520
December1st to 10thDay
28%12%5%8%6%3444423%
1520
11th to 20thDay
32%12%5%7%6%35%45%5%15%
1925
21st to endDay
26%15%5%11%7%4445%5%14%
2460
January1st to 10thNight
38%12%47%6%3444415%
2836
11th to 20thNight
32%11%47%5%345%45%20%
2601
21st to endNight
31%11%48%6%33446%20%
2740
February1st to 10thNight
32%12%47%5%34445%20%
2340
11th to 20thNight
29%14%47%6%2444422%
2272
21st to endNight
27%13%36%6%345%5%6%21%
1865
March1st to 10thNight
26%12%46%5%35%46%6%23%
2124
11th to 20thNight
29%11%5%6%5%35%446%22%
1979
21st to endNight
27%14%47%5%35%6%5%6%17%
2102
April1st to 10thNight
24%11%48%7%36%6%6%7%19%
1800
11th to 20thNight
22%11%36%7%35%5%6%5%27%
1753
21st to endNight
23%10%37%8%45%45%6%23%
1566
May1st to 10thNight
19%8%46%6%3445%6%37%
1440
11th to 20thNight
19%7%46%5%345%6%6%35%
1416
21st to endNight
20%9%49%6%345%5%5%31%
1552
June1st to 10thNight
20%8%47%5%35%5%5%5%31%
1368
11th to 20thNight
26%10%39%6%3445%5%25%
1260
21st to endNight
14%5%25%435%5%7%9%41%
1260
July1st to 10thNight
12%5%2444445%5%51%
1260
11th to 20thNight
8%42342345%8%56%
1350
21st to endNight
8%5%24223335%63%
1576
August1st to 10thNight
7%5%14324347%60%
1451
11th to 20thNight
6%5%13313437%62%
1602
21st to endNight
10%6%35%5%34446%51%
1885
September1st to 10thNight
10%5%25%42445%5%54%
1800
11th to 20thNight
16%9%35%7%24445%42%
1800
21st to endNight
17%8%36%6%33346%39%
2051
October1st to 10thNight
18%9%38%6%34446%35%
2160
11th to 20thNight
25%9%245%3445%6%32%
2160
21st to endNight
28%9%36%6%2345%7%28%
2495
November1st to 10thNight
34%11%36%5%34445%20%
2554
11th to 20thNight
34%10%46%5%3444422%
2660
21st to endNight
33%11%47%5%34445%20%
2660
December1st to 10thNight
30%11%37%5%3445%6%23%
2660
11th to 20thNight
29%14%5%8%7%45%445%16%
3280
21st to endNight
27%14%5%9%7%45%5%45%14%
5191

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%25%12%41
1329
11th to 20thDay
66%411%10%7%2
1465
21st to endDay
69%210%15%3
1613
February1st to 10thDay
71%410%10%41
1620
11th to 20thDay
69%210%11%8%
1584
21st to endDay
71%19%12%6%1
1390
March1st to 10thDay
68%212%14%5%
1833
11th to 20thDay
69%210%15%31
1980
21st to endDay
73%311%12%1
2254
April1st to 10thDay
69%315%12%1
2160
11th to 20thDay
66%210%15%6%1
2156
21st to endDay
65%411%14%6%1
2394
May1st to 10thDay
56%317%18%6%
2520
11th to 20thDay
56%419%17%5%
2480
21st to endDay
63%317%16%2
2724
June1st to 10thDay
58%317%16%5%1
2587
11th to 20thDay
63%316%14%3
2700
21st to endDay
46%421%21%7%1
2700
July1st to 10thDay
39%413%28%13%2
2626
11th to 20thDay
35%314%32%15%1
2527
21st to endDay
27%214%37%17%3
2589
August1st to 10thDay
33%318%31%14%1
2469
11th to 20thDay
29%321%32%12%3
2298
21st to endDay
41%315%31%9%1
2470
September1st to 10thDay
39%215%28%12%4
2160
11th to 20thDay
48%214%20%15%2
2160
21st to endDay
48%317%19%10%2
1904
October1st to 10thDay
55%313%21%7%
1800
11th to 20thDay
60%213%19%5%1
1800
21st to endDay
65%210%14%9%
1860
November1st to 10thDay
71%312%10%4
1523
11th to 20thDay
68%310%11%7%2
1520
21st to endDay
69%36%13%9%1
1520
December1st to 10thDay
67%38%12%9%1
1520
11th to 20thDay
72%211%12%21
1928
21st to endDay
75%111%10%2
2460
January1st to 10thNight
75%37%10%41
2836
11th to 20thNight
68%310%12%6%1
2601
21st to endNight
67%210%15%5%1
2740
February1st to 10thNight
70%39%12%5%1
2340
11th to 20thNight
68%311%11%7%1
2274
21st to endNight
66%211%15%5%1
1865
March1st to 10thNight
64%212%17%5%
2124
11th to 20thNight
65%310%16%41
1980
21st to endNight
70%314%11%1
2102
April1st to 10thNight
66%5%13%14%2
1800
11th to 20thNight
61%314%15%7%1
1753
21st to endNight
64%312%15%6%1
1566
May1st to 10thNight
51%316%22%8%1
1440
11th to 20thNight
51%321%18%7%1
1416
21st to endNight
57%5%19%17%2
1552
June1st to 10thNight
55%416%19%5%1
1368
11th to 20thNight
63%315%15%2
1260
21st to endNight
43%322%24%5%3
1260
July1st to 10thNight
39%215%27%13%4
1225
11th to 20thNight
31%315%34%16%2
1307
21st to endNight
25%212%36%21%4
1488
August1st to 10thNight
27%415%33%18%3
1443
11th to 20thNight
25%419%34%15%3
1602
21st to endNight
37%316%34%10%1
1885
September1st to 10thNight
35%315%31%13%4
1800
11th to 20thNight
47%311%22%14%4
1800
21st to endNight
48%313%24%10%2
2051
October1st to 10thNight
52%214%24%7%1
2160
11th to 20thNight
55%317%19%7%1
2160
21st to endNight
59%312%17%8%
2495
November1st to 10thNight
68%311%13%31
2554
11th to 20thNight
68%211%13%5%2
2660
21st to endNight
68%28%12%9%1
2660
December1st to 10thNight
64%311%14%8%1
2660
11th to 20thNight
73%311%10%31
3276
21st to endNight
76%110%10%3
5191

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
38%10%16%16%12%8%
180
11th to 20thDay
34%14%18%14%14%5%
170
21st to endDay
40%11%14%18%13%4
205
February1st to 10thDay
42%11%21%15%9%1
340
11th to 20thDay
38%13%24%16%9%1
335
21st to endDay
31%17%18%24%9%2
306
March1st to 10thDay
30%15%26%16%11%2
420
11th to 20thDay
28%16%19%19%15%4
420
21st to endDay
33%13%25%18%10%1
462
April1st to 10thDay
27%16%22%20%12%3
420
11th to 20thDay
25%14%28%17%9%6%
412
21st to endDay
21%15%27%24%11%2
420
May1st to 10thDay
13%12%26%33%14%3
423
11th to 20thDay
22%8%19%26%19%6%
448
21st to endDay
20%11%18%27%18%7%
485
June1st to 10thDay
21%8%24%26%17%3
517
11th to 20thDay
20%9%25%29%14%3
630
21st to endDay
13%421%35%22%5%
630
July1st to 10thDay
12%319%35%26%4
621
11th to 20thDay
9%5%19%32%28%7%
526
21st to endDay
8%115%37%30%8%
487
August1st to 10thDay
10%412%36%27%12%
447
11th to 20thDay
6%312%38%30%12%
437
21st to endDay
13%423%31%21%9%
495
September1st to 10thDay
16%5%22%34%17%6%
450
11th to 20thDay
16%8%18%26%26%5%
450
21st to endDay
22%9%20%27%16%6%
450
October1st to 10thDay
24%9%20%22%18%7%
450
11th to 20thDay
31%9%18%20%16%6%
450
21st to endDay
33%13%18%17%14%5%
375
November1st to 10thDay
44%11%17%16%10%2
197
11th to 20thDay
41%11%12%14%12%11%
180
21st to endDay
35%14%17%13%9%12%
180
December1st to 10thDay
42%11%12%11%13%11%
180
11th to 20thDay
40%13%19%15%12%1
180
21st to endDay
41%9%17%24%7%3
198
January1st to 10thNight
41%13%14%16%14%2
850
11th to 20thNight
36%12%14%17%18%3
745
21st to endNight
35%9%14%23%15%3
792
February1st to 10thNight
37%10%16%24%11%2
720
11th to 20thNight
33%12%15%22%16%2
704
21st to endNight
32%9%20%24%12%3
592
March1st to 10thNight
32%11%17%24%15%2
720
11th to 20thNight
32%15%16%21%14%2
720
21st to endNight
30%15%20%24%9%1
792
April1st to 10thNight
28%11%19%25%14%2
720
11th to 20thNight
26%10%20%25%15%4
685
21st to endNight
27%9%21%27%14%2
486
May1st to 10thNight
19%9%16%32%22%2
360
11th to 20thNight
21%6%12%29%29%3
354
21st to endNight
22%6%17%26%23%5%
389
June1st to 10thNight
23%8%18%29%18%4
360
11th to 20thNight
27%8%15%30%18%3
360
21st to endNight
18%312%34%29%4
360
July1st to 10thNight
14%311%31%37%4
350
11th to 20thNight
9%412%36%34%5%
348
21st to endNight
8%410%29%43%6%
394
August1st to 10thNight
9%27%28%44%10%
377
11th to 20thNight
8%17%25%43%15%
534
21st to endNight
12%5%12%30%35%6%
697
September1st to 10thNight
13%211%35%33%6%
720
11th to 20thNight
19%412%22%31%11%
720
21st to endNight
22%6%15%26%26%6%
720
October1st to 10thNight
21%7%12%26%26%8%
720
11th to 20thNight
29%9%14%22%22%5%
720
21st to endNight
32%10%16%22%15%4
792
November1st to 10thNight
39%11%15%22%12%1
740
11th to 20thNight
38%8%19%19%13%3
760
21st to endNight
37%9%15%19%15%5%
760
December1st to 10thNight
33%8%15%25%16%3
760
11th to 20thNight
40%12%16%19%11%1
760
21st to endNight
40%13%17%19%10%1
930
Page generated at 2024-01-12 22:38:08. Version ac07

Copyright 2024 Attilla Danko


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