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 2005-11-05 to 2018-08-29.

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
39%
15659
9%
50361
9%
15629
40%
15629
14%
38188

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%
805
8%
2829
9%
801
33%
801
9%
2308
January16th to endNight
30%
832
8%
2896
9%
832
31%
832
10%
2308
February1st to 15thNight
31%
761
7%
2483
6%
759
34%
759
9%
2033
February16th to endNight
32%
684
10%
2173
9%
684
34%
684
11%
1745
March1st to 15thNight
28%
780
6%
2256
5%
780
29%
780
10%
1866
March16th to endNight
25%
832
5%
2226
3%
832
26%
832
9%
1894
April1st to 15thNight
32%
779
5%
1949
3%
779
32%
779
11%
1682
April16th to endNight
35%
584
6%
1742
5%
584
36%
584
13%
1390
May1st to 15thNight
50%
389
10%
1559
15%
389
51%
389
17%
1014
May16th to endNight
45%
406
5%
1624
8%
406
46%
406
10%
1224
June1st to 15thNight
41%
390
3%
1459
4%
390
41%
390
12%
1077
June16th to endNight
49%
390
7%
1365
6%
390
50%
390
16%
973
July1st to 15thNight
67%
370
12%
1309
16%
370
67%
370
31%
723
July16th to endNight
71%
408
16%
1544
25%
386
73%
386
33%
771
August1st to 15thNight
79%
454
19%
1598
25%
452
79%
452
37%
816
August16th to endNight
67%
693
20%
1923
17%
693
67%
693
37%
1136
September1st to 15thNight
68%
720
20%
1800
12%
720
68%
720
41%
1109
September16th to endNight
50%
716
17%
1965
14%
716
51%
716
23%
1397
October1st to 15thNight
47%
720
10%
2160
11%
720
48%
720
20%
1545
October16th to endNight
36%
768
9%
2388
9%
768
37%
768
12%
1889
November1st to 15thNight
21%
760
3%
2630
3%
760
22%
760
7%
2240
November16th to endNight
25%
780
4%
2730
4%
780
27%
780
8%
2241
December1st to 15thNight
34%
780
8%
2730
8%
780
35%
780
10%
2181
December16th to endNight
19%
858
5%
3023
5%
858
20%
858
5%
2626

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
26%8%35%5%23345%30%
51908
Night
29%8%35%423345%29%
50520
Cloud CoverDay
28%8%35%423345%29%
51908
Night
30%8%25%423335%28%
50523
TransparencyDay
58%5%13%14%6%
51570
Night
59%5%12%14%6%1
50362
SeeingDay
31%6%19%25%13%3
7098
Night
35%413%25%18%2
15664

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
41%10%3442233320%
1436
16th to endDay
39%9%36%424335%19%
1680
February1st to 15thDay
34%11%35%5%3434418%
1711
16th to endDay
32%11%36%5%2333422%
1587
March1st to 15thDay
38%11%36%5%3333416%
2032
16th to endDay
35%12%47%5%3443414%
2349
April1st to 15thDay
31%10%38%6%45%35%5%14%
2329
16th to endDay
28%9%38%6%35%5%5%5%19%
2490
May1st to 15thDay
21%7%36%6%3445%6%30%
2721
16th to endDay
26%9%37%5%34446%24%
2839
June1st to 15thDay
27%8%36%6%34445%26%
2828
16th to endDay
21%7%47%6%3445%5%29%
2925
July1st to 15thDay
12%423423336%52%
2909
16th to endDay
12%423323235%56%
2881
August1st to 15thDay
11%413423346%53%
2604
16th to endDay
12%5%24423446%48%
2576
September1st to 15thDay
12%425%422245%53%
2160
16th to endDay
22%6%25%433445%36%
1991
October1st to 15thDay
25%8%25%434447%30%
1800
16th to endDay
37%7%36%433345%20%
1835
November1st to 15thDay
45%7%245%2443414%
1558
16th to endDay
41%9%345%1224418%
1560
December1st to 15thDay
33%11%45%5%2333421%
1560
16th to endDay
41%12%47%42223315%
1547
January1st to 15thNight
41%8%35%42343320%
2829
16th to endNight
37%9%25%433335%20%
2896
February1st to 15thNight
34%11%36%424335%20%
2471
16th to endNight
31%11%35%5%2323424%
2173
March1st to 15thNight
35%10%35%43344420%
2256
16th to endNight
35%10%35%5%34345%17%
2222
April1st to 15thNight
29%10%37%6%35%5%5%6%17%
1949
16th to endNight
28%7%46%7%24445%23%
1742
May1st to 15thNight
19%6%35%424345%39%
1559
16th to endNight
21%7%47%6%45%45%5%27%
1624
June1st to 15thNight
26%6%35%6%34345%29%
1459
16th to endNight
20%7%346%35%446%32%
1365
July1st to 15thNight
10%32432234456%
1380
16th to endNight
9%422312346%58%
1640
August1st to 15thNight
8%212212336%63%
1606
16th to endNight
11%314324335%56%
1923
September1st to 15thNight
10%5%1432234457%
1800
16th to endNight
21%7%25%422336%38%
1965
October1st to 15thNight
23%7%245%3334437%
2160
16th to endNight
34%7%25%433337%23%
2388
November1st to 15thNight
43%8%26%5%2333416%
2630
16th to endNight
40%9%2442333420%
2730
December1st to 15thNight
34%9%25%42334423%
2730
16th to endNight
40%12%46%42233314%
3023

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
43%10%2432222320%
1436
16th to endDay
41%9%34323335%19%
1680
February1st to 15thDay
36%10%35%6%2334418%
1711
16th to endDay
33%13%36%5%3333322%
1587
March1st to 15thDay
40%11%35%42423316%
2032
16th to endDay
37%12%46%6%35%33313%
2349
April1st to 15thDay
33%11%37%6%35%345%13%
2329
16th to endDay
30%11%36%6%35%5%4417%
2490
May1st to 15thDay
23%8%35%6%33446%29%
2721
16th to endDay
29%9%36%5%34445%23%
2839
June1st to 15thDay
30%8%35%5%34435%25%
2828
16th to endDay
23%8%36%5%35%5%45%27%
2925
July1st to 15thDay
13%414422335%51%
2909
16th to endDay
13%424322335%54%
2881
August1st to 15thDay
13%413323346%52%
2604
16th to endDay
14%5%2442435%6%47%
2576
September1st to 15thDay
14%5%14423335%52%
2160
16th to endDay
24%6%25%423346%36%
1991
October1st to 15thDay
26%7%25%5%24446%30%
1800
16th to endDay
39%8%24423345%21%
1835
November1st to 15thDay
47%8%245%2343314%
1558
16th to endDay
42%10%36%313335%17%
1560
December1st to 15thDay
35%10%46%41433421%
1560
16th to endDay
42%13%47%31232315%
1547
January1st to 15thNight
42%9%2431333320%
2828
16th to endNight
39%9%25%42333421%
2896
February1st to 15thNight
36%10%36%423335%20%
2471
16th to endNight
32%12%25%423335%22%
2173
March1st to 15thNight
37%11%24323435%19%
2256
16th to endNight
37%10%35%5%33345%16%
2226
April1st to 15thNight
32%10%36%5%345%5%6%16%
1949
16th to endNight
28%10%36%5%34445%22%
1742
May1st to 15thNight
21%5%26%424346%38%
1559
16th to endNight
24%7%37%5%25%5%45%27%
1624
June1st to 15thNight
28%6%26%5%32345%29%
1459
16th to endNight
23%6%35%43445%5%32%
1365
July1st to 15thNight
11%414323335%55%
1380
16th to endNight
10%5%13213335%58%
1640
August1st to 15thNight
8%32212346%63%
1606
16th to endNight
12%413323345%55%
1923
September1st to 15thNight
12%5%23312235%57%
1800
16th to endNight
22%6%26%423236%38%
1965
October1st to 15thNight
24%6%25%43323437%
2160
16th to endNight
35%8%24434336%22%
2388
November1st to 15thNight
44%9%25%5%2433415%
2630
16th to endNight
42%8%35%423335%19%
2730
December1st to 15thNight
35%9%35%33344423%
2730
16th to endNight
43%12%35%42422313%
3023

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
70%36%11%6%
1436
16th to endDay
67%5%10%9%5%1
1680
February1st to 15thDay
70%6%9%8%31
1711
16th to endDay
68%39%12%5%
1587
March1st to 15thDay
74%39%9%2
2032
16th to endDay
77%48%8%
2349
April1st to 15thDay
73%6%12%6%
2329
16th to endDay
69%5%12%7%4
2490
May1st to 15thDay
56%5%17%14%5%
2721
16th to endDay
63%7%16%11%1
2843
June1st to 15thDay
62%6%16%9%4
2828
16th to endDay
56%7%16%15%3
2925
July1st to 15thDay
36%6%14%26%14%1
2751
16th to endDay
32%5%14%30%15%2
2714
August1st to 15thDay
33%6%18%26%12%1
2587
16th to endDay
37%5%17%27%9%2
2576
September1st to 15thDay
35%414%22%18%3
2160
16th to endDay
51%6%16%14%8%2
1991
October1st to 15thDay
54%7%14%16%7%
1800
16th to endDay
65%5%9%12%5%
1835
November1st to 15thDay
75%5%9%5%21
1558
16th to endDay
71%5%7%7%6%
1560
December1st to 15thDay
67%5%7%12%6%1
1560
16th to endDay
76%46%8%3
1547
January1st to 15thNight
68%5%8%10%5%1
2829
16th to endNight
67%49%10%6%2
2896
February1st to 15thNight
68%5%10%9%42
2483
16th to endNight
65%5%10%13%5%
2173
March1st to 15thNight
68%5%11%12%2
2256
16th to endNight
70%6%12%10%
2226
April1st to 15thNight
68%7%11%10%1
1949
16th to endNight
64%414%11%4
1742
May1st to 15thNight
47%5%21%17%7%
1560
16th to endNight
58%8%16%13%1
1624
June1st to 15thNight
58%5%18%12%4
1459
16th to endNight
52%6%17%18%31
1365
July1st to 15thNight
33%414%29%14%3
1309
16th to endNight
28%415%28%19%3
1544
August1st to 15thNight
24%7%17%33%14%3
1598
16th to endNight
31%5%18%31%10%2
1923
September1st to 15thNight
31%415%24%19%4
1800
16th to endNight
48%5%12%19%10%2
1965
October1st to 15thNight
52%5%14%18%8%
2160
16th to endNight
62%6%11%14%5%
2388
November1st to 15thNight
74%411%5%12
2630
16th to endNight
70%48%8%7%
2730
December1st to 15thNight
65%6%10%10%6%
2730
16th to endNight
77%46%7%4
3023

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%46%17%28%13%
90
16th to endDay
63%9%8%9%6%2
112
February1st to 15thDay
47%6%18%19%7%
281
16th to endDay
44%6%21%19%6%
262
March1st to 15thDay
49%10%20%13%4
330
16th to endDay
52%9%17%9%8%1
352
April1st to 15thDay
41%10%23%14%6%2
329
16th to endDay
34%11%24%17%10%1
318
May1st to 15thDay
28%9%23%25%10%2
348
16th to endDay
31%6%17%24%15%4
394
June1st to 15thDay
27%8%23%25%13%2
473
16th to endDay
21%8%25%29%13%2
570
July1st to 15thDay
14%322%40%18%1
535
16th to endDay
12%118%38%23%5%
391
August1st to 15thDay
14%115%36%23%9%
359
16th to endDay
12%418%35%20%7%
385
September1st to 15thDay
18%420%33%17%4
315
16th to endDay
24%6%21%29%15%2
315
October1st to 15thDay
33%5%23%19%15%2
315
16th to endDay
46%5%10%21%13%2
251
November1st to 15thDay
59%11%17%7%4
97
16th to endDay
56%5%10%12%411%
90
December1st to 15thDay
47%48%12%18%7%
90
16th to endDay
51%8%11%19%6%3
96
January1st to 15thNight
46%5%11%20%15%
805
16th to endNight
46%5%11%22%12%1
832
February1st to 15thNight
42%5%12%29%9%1
764
16th to endNight
41%5%13%26%11%
684
March1st to 15thNight
45%8%13%18%11%1
780
16th to endNight
45%6%16%21%8%1
832
April1st to 15thNight
38%6%14%26%12%1
779
16th to endNight
35%317%28%13%2
584
May1st to 15thNight
24%315%31%23%1
390
16th to endNight
28%212%29%23%3
407
June1st to 15thNight
31%315%28%18%2
390
16th to endNight
25%311%35%20%3
390
July1st to 15thNight
13%210%33%34%4
370
16th to endNight
12%19%29%42%5%
408
August1st to 15thNight
10%426%47%10%
454
16th to endNight
15%19%27%37%8%
693
September1st to 15thNight
15%18%28%36%9%
720
16th to endNight
28%211%25%27%4
716
October1st to 15thNight
27%413%29%23%2
720
16th to endNight
41%313%24%14%2
768
November1st to 15thNight
50%418%20%5%
760
16th to endNight
46%417%17%11%1
780
December1st to 15thNight
41%5%11%27%11%2
780
16th to endNight
50%5%16%20%6%
858
Page generated at 2018-08-30 02:34:17. Version ac04

Copyright 2018 A. Danko


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