Everett
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Everett clear sky chart from 2005-11-05 to 2017-04-24.

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
41%
14163
9%
45484
9%
14134
42%
14134
15%
33849

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
31%
741
9%
2633
10%
737
32%
737
9%
2114
January16th to endNight
35%
768
9%
2667
10%
768
36%
768
11%
2062
February1st to 15thNight
33%
700
7%
2288
6%
699
35%
699
11%
1831
February16th to endNight
34%
632
10%
2014
11%
632
35%
632
13%
1550
March1st to 15thNight
27%
720
5%
2076
4%
720
29%
720
11%
1701
March16th to endNight
27%
768
5%
2061
3%
768
28%
768
10%
1724
April1st to 15thNight
35%
719
6%
1799
4%
719
35%
719
14%
1491
April16th to endNight
36%
531
8%
1575
6%
531
38%
531
15%
1221
May1st to 15thNight
50%
329
13%
1319
18%
329
52%
329
19%
825
May16th to endNight
43%
342
3%
1368
5%
342
44%
342
10%
1019
June1st to 15thNight
41%
330
4%
1221
4%
330
42%
330
14%
868
June16th to endNight
47%
330
6%
1155
6%
330
48%
330
16%
820
July1st to 15thNight
66%
310
13%
1085
16%
310
67%
310
32%
595
July16th to endNight
69%
348
15%
1304
23%
326
73%
326
32%
659
August1st to 15thNight
76%
398
19%
1380
24%
396
77%
396
37%
699
August16th to endNight
65%
588
19%
1638
16%
588
66%
588
38%
968
September1st to 15thNight
69%
660
21%
1650
13%
660
70%
660
42%
1005
September16th to endNight
50%
656
19%
1804
15%
656
52%
656
25%
1255
October1st to 15thNight
49%
660
12%
1980
13%
660
49%
660
22%
1377
October16th to endNight
37%
704
8%
2185
8%
704
39%
704
13%
1692
November1st to 15thNight
28%
700
6%
2428
7%
700
29%
700
9%
1991
November16th to endNight
31%
720
6%
2520
6%
720
32%
720
10%
2000
December1st to 15thNight
35%
720
8%
2520
9%
720
36%
720
10%
1997
December16th to endNight
23%
789
5%
2814
5%
789
24%
789
6%
2385

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%34446%29%
46146
Night
25%9%36%5%24445%28%
45642
Cloud CoverDay
25%8%36%5%24445%28%
46146
Night
27%8%35%5%24445%27%
45645
TransparencyDay
58%313%17%6%
45807
Night
59%312%16%6%1
45485
SeeingDay
29%5%19%25%15%4
5333
Night
34%411%24%21%4
14169

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
36%10%47%42323320%
1304
16th to endDay
32%9%37%7%34345%17%
1554
February1st to 15thDay
29%11%48%6%35%445%16%
1576
16th to endDay
27%13%37%6%33445%21%
1460
March1st to 15thDay
33%12%46%5%35%44414%
1881
16th to endDay
30%13%5%8%6%34345%14%
2163
April1st to 15thDay
25%11%5%6%7%35%5%5%6%16%
2149
16th to endDay
21%10%48%7%45%5%5%5%20%
2244
May1st to 15thDay
19%6%35%6%345%5%6%33%
2301
16th to endDay
23%9%47%6%345%46%24%
2391
June1st to 15thDay
22%7%36%6%24447%30%
2406
16th to endDay
17%7%5%7%6%345%5%6%29%
2475
July1st to 15thDay
10%424423346%52%
2472
16th to endDay
11%423323345%55%
2461
August1st to 15thDay
9%42442345%7%51%
2241
16th to endDay
10%5%25%5%2445%7%47%
2212
September1st to 15thDay
9%5%25%323246%53%
1980
16th to endDay
18%7%36%4435%46%35%
1823
October1st to 15thDay
22%9%35%5%345%5%8%27%
1650
16th to endDay
31%10%37%6%245%46%16%
1686
November1st to 15thDay
38%9%36%5%25%445%15%
1430
16th to endDay
36%11%45%43333418%
1440
December1st to 15thDay
28%13%5%7%6%2434319%
1440
16th to endDay
35%12%47%5%3433315%
1407
January1st to 15thNight
35%10%36%5%2333421%
2633
16th to endNight
32%9%35%5%24445%20%
2667
February1st to 15thNight
29%11%38%5%34445%19%
2276
16th to endNight
28%10%36%5%24435%23%
2014
March1st to 15thNight
31%10%46%5%35%446%18%
2076
16th to endNight
30%13%46%5%345%5%5%15%
2057
April1st to 15thNight
22%10%38%7%35%6%5%6%19%
1799
16th to endNight
23%9%36%7%35%5%45%24%
1575
May1st to 15thNight
17%6%45%42445%5%39%
1319
16th to endNight
20%8%48%6%35%5%6%5%24%
1368
June1st to 15thNight
22%9%36%434346%30%
1221
16th to endNight
18%7%38%5%35%5%5%7%28%
1155
July1st to 15thNight
8%325%333345%55%
1155
16th to endNight
9%5%23213446%55%
1400
August1st to 15thNight
7%413313347%59%
1388
16th to endNight
8%5%24424426%53%
1638
September1st to 15thNight
7%425%32334456%
1650
16th to endNight
18%8%35%5%23346%37%
1804
October1st to 15thNight
19%8%37%5%23446%35%
1980
16th to endNight
30%9%25%6%3345%6%22%
2185
November1st to 15thNight
37%9%36%43434318%
2428
16th to endNight
33%10%36%5%24435%20%
2520
December1st to 15thNight
31%10%46%5%24345%21%
2520
16th to endNight
33%14%5%7%5%3433414%
2814

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
39%11%3442322320%
1304
16th to endDay
35%8%46%424345%18%
1554
February1st to 15thDay
31%11%46%5%34346%17%
1576
16th to endDay
31%10%47%5%2423422%
1460
March1st to 15thDay
37%12%36%5%25%33414%
1881
16th to endDay
33%12%6%6%6%3434414%
2163
April1st to 15thDay
27%11%48%5%46%45%5%15%
2149
16th to endDay
25%9%48%7%35%5%5%5%18%
2244
May1st to 15thDay
20%7%35%5%35%45%6%31%
2301
16th to endDay
26%10%47%5%34446%22%
2391
June1st to 15thDay
24%9%36%5%24446%28%
2406
16th to endDay
19%8%47%6%25%5%5%6%27%
2475
July1st to 15thDay
12%42332335%5%51%
2472
16th to endDay
12%423313346%53%
2461
August1st to 15thDay
10%5%2333345%6%51%
2241
16th to endDay
12%5%245%2345%7%46%
2212
September1st to 15thDay
12%5%25%322245%53%
1980
16th to endDay
21%7%26%42345%6%35%
1823
October1st to 15thDay
24%8%25%434348%28%
1650
16th to endDay
35%8%36%6%34445%18%
1686
November1st to 15thDay
42%8%35%3345%3414%
1430
16th to endDay
37%11%45%422335%19%
1440
December1st to 15thDay
32%13%46%5%2333420%
1440
16th to endDay
39%11%5%8%5%2323215%
1407
January1st to 15thNight
37%9%36%42333321%
2632
16th to endNight
35%9%35%5%24345%21%
2667
February1st to 15thNight
31%12%36%434346%19%
2276
16th to endNight
30%11%36%433435%23%
2014
March1st to 15thNight
34%10%5%5%43444418%
2076
16th to endNight
34%12%35%5%25%45%415%
2061
April1st to 15thNight
25%9%38%6%45%5%5%5%18%
1799
16th to endNight
25%8%38%5%45%446%22%
1575
May1st to 15thNight
18%6%35%41435%5%39%
1319
16th to endNight
22%7%48%7%35%5%5%5%23%
1368
June1st to 15thNight
24%7%36%6%24335%30%
1221
16th to endNight
20%7%35%6%35%5%5%6%29%
1155
July1st to 15thNight
9%425%333345%54%
1155
16th to endNight
11%42331245%6%54%
1400
August1st to 15thNight
7%412322346%60%
1388
16th to endNight
9%5%23424435%53%
1638
September1st to 15thNight
9%5%2442334456%
1650
16th to endNight
21%7%25%422346%38%
1804
October1st to 15thNight
21%7%35%6%33345%35%
1980
16th to endNight
33%8%25%433446%21%
2185
November1st to 15thNight
40%9%35%43333417%
2428
16th to endNight
37%8%36%5%23345%20%
2520
December1st to 15thNight
34%10%35%5%2344420%
2520
16th to endNight
37%14%46%5%3333413%
2814

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%37%11%7%
1304
16th to endDay
67%211%12%41
1554
February1st to 15thDay
69%311%9%41
1576
16th to endDay
67%110%14%6%
1460
March1st to 15thDay
75%111%9%2
1881
16th to endDay
75%39%11%
2163
April1st to 15thDay
70%313%10%1
2149
16th to endDay
67%312%12%3
2244
May1st to 15thDay
53%215%19%7%
2301
16th to endDay
64%417%11%2
2395
June1st to 15thDay
59%316%14%5%
2406
16th to endDay
56%219%17%3
2475
July1st to 15thDay
36%414%29%14%2
2313
16th to endDay
32%215%30%16%1
2294
August1st to 15thDay
34%320%30%9%1
2224
16th to endDay
37%216%31%8%2
2212
September1st to 15thDay
34%214%27%17%2
1980
16th to endDay
50%316%19%8%2
1823
October1st to 15thDay
54%216%18%7%
1650
16th to endDay
67%211%14%4
1686
November1st to 15thDay
73%310%7%22
1430
16th to endDay
69%37%11%7%
1440
December1st to 15thDay
69%47%12%6%
1440
16th to endDay
75%27%9%4
1407
January1st to 15thNight
68%37%13%6%
2633
16th to endNight
65%210%12%6%1
2667
February1st to 15thNight
67%311%11%41
2288
16th to endNight
64%112%15%5%
2014
March1st to 15thNight
69%211%14%2
2076
16th to endNight
70%311%12%
2061
April1st to 15thNight
65%5%13%13%2
1799
16th to endNight
62%214%15%4
1575
May1st to 15thNight
47%217%21%10%
1320
16th to endNight
60%6%18%12%2
1368
June1st to 15thNight
57%217%15%4
1221
16th to endNight
56%317%20%11
1155
July1st to 15thNight
34%213%32%13%4
1085
16th to endNight
30%313%29%19%3
1304
August1st to 15thNight
27%418%33%13%2
1380
16th to endNight
33%218%33%10%1
1638
September1st to 15thNight
32%214%28%17%4
1650
16th to endNight
47%311%24%10%2
1804
October1st to 15thNight
51%215%21%7%
1980
16th to endNight
63%214%14%4
2185
November1st to 15thNight
71%210%10%22
2428
16th to endNight
68%29%10%8%
2520
December1st to 15thNight
66%412%12%5%
2520
16th to endNight
76%28%8%3
2814

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
20%15%21%25%26%
60
16th to endDay
51%6%9%15%12%4
82
February1st to 15thDay
44%5%17%19%9%2
236
16th to endDay
42%5%20%21%8%1
218
March1st to 15thDay
50%10%21%12%4
270
16th to endDay
49%9%20%10%9%
288
April1st to 15thDay
31%8%26%18%11%3
269
16th to endDay
32%7%24%20%11%4
243
May1st to 15thDay
28%7%18%29%14%2
228
16th to endDay
32%412%24%19%6%
266
June1st to 15thDay
23%5%21%26%19%3
351
16th to endDay
19%7%21%32%16%2
420
July1st to 15thDay
13%119%35%25%4
397
16th to endDay
13%115%38%23%7%
271
August1st to 15thDay
13%115%38%24%7%
255
16th to endDay
13%219%37%19%6%
268
September1st to 15thDay
18%320%31%20%6%
255
16th to endDay
23%5%18%29%18%4
255
October1st to 15thDay
32%5%21%23%14%2
255
16th to endDay
42%414%19%15%3
198
November1st to 15thDay
56%9%17%14%3
64
16th to endDay
41%6%8%15%11%16%
60
December1st to 15thDay
55%6%11%10%15%1
60
16th to endDay
43%10%10%15%12%6%
64
January1st to 15thNight
45%5%9%15%19%4
741
16th to endNight
41%410%20%19%3
768
February1st to 15thNight
39%5%9%25%15%3
704
16th to endNight
38%5%11%24%17%3
632
March1st to 15thNight
42%7%15%19%12%2
720
16th to endNight
43%6%14%23%11%1
768
April1st to 15thNight
32%5%13%27%18%2
719
16th to endNight
30%415%27%18%2
531
May1st to 15thNight
22%5%11%26%30%3
330
16th to endNight
25%5%10%29%23%5%
343
June1st to 15thNight
29%312%28%22%3
330
16th to endNight
23%313%35%20%3
330
July1st to 15thNight
13%110%32%36%6%
310
16th to endNight
13%19%29%38%7%
348
August1st to 15thNight
12%425%43%13%
398
16th to endNight
14%29%27%34%11%
588
September1st to 15thNight
13%17%25%37%13%
660
16th to endNight
26%39%23%28%7%
656
October1st to 15thNight
27%39%29%25%4
660
16th to endNight
39%410%23%16%4
704
November1st to 15thNight
47%412%25%9%1
700
16th to endNight
43%411%19%14%5%
720
December1st to 15thNight
41%5%7%25%18%1
720
16th to endNight
48%313%20%11%1
789
Page generated at 2017-04-25 04:48:27. Version ac04

Copyright 2017 A. Danko


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