The University of Puget Sound Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the The University of Puget Sound Observatory clear sky chart from 2005-11-05 to 2017-04-25.

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
42%
14189
10%
45433
9%
14160
44%
14160
16%
32938

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%
733
10%
2581
9%
729
34%
729
10%
2053
January16th to endNight
36%
768
9%
2643
10%
768
38%
768
12%
2020
February1st to 15thNight
32%
697
6%
2288
4%
697
34%
697
10%
1821
February16th to endNight
31%
632
10%
2014
7%
632
36%
632
12%
1542
March1st to 15thNight
28%
720
5%
2064
4%
720
30%
720
11%
1685
March16th to endNight
26%
768
6%
2070
3%
768
27%
768
10%
1716
April1st to 15thNight
37%
719
8%
1799
3%
719
39%
719
15%
1444
April16th to endNight
43%
553
9%
1603
7%
553
44%
553
18%
1179
May1st to 15thNight
47%
329
13%
1319
18%
329
49%
329
17%
849
May16th to endNight
50%
343
4%
1368
5%
342
52%
342
12%
982
June1st to 15thNight
47%
330
6%
1250
6%
330
50%
330
18%
840
June16th to endNight
47%
330
6%
1155
7%
330
48%
330
18%
762
July1st to 15thNight
73%
310
14%
1108
17%
310
75%
310
37%
568
July16th to endNight
75%
348
17%
1304
29%
326
78%
326
40%
590
August1st to 15thNight
79%
421
20%
1405
22%
419
81%
419
41%
710
August16th to endNight
70%
589
21%
1639
16%
589
72%
589
43%
904
September1st to 15thNight
73%
660
24%
1650
15%
660
74%
660
49%
946
September16th to endNight
51%
656
20%
1807
16%
656
53%
656
27%
1209
October1st to 15thNight
47%
660
12%
1980
11%
660
50%
660
21%
1378
October16th to endNight
37%
704
9%
2170
9%
704
40%
704
14%
1655
November1st to 15thNight
29%
700
7%
2422
7%
700
32%
700
10%
1938
November16th to endNight
29%
720
8%
2520
7%
720
31%
720
10%
1926
December1st to 15thNight
34%
720
8%
2520
8%
720
36%
720
12%
1937
December16th to endNight
24%
779
6%
2754
4%
779
26%
779
7%
2284

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%8%36%5%3445%6%29%
46216
Night
22%7%35%5%34446%31%
45593
Cloud CoverDay
22%8%36%5%34446%30%
46216
Night
24%7%25%5%34446%31%
45596
TransparencyDay
54%6%15%16%6%
45879
Night
53%6%14%17%6%1
45434
SeeingDay
22%9%19%24%17%6%
5333
Night
25%7%16%26%20%3
14197

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%8%46%5%3433418%
1352
16th to endDay
28%11%5%6%5%35%5%46%17%
1581
February1st to 15thDay
31%10%5%8%5%34446%16%
1576
16th to endDay
28%10%37%7%245%46%19%
1460
March1st to 15thDay
34%9%48%6%35%34413%
1896
16th to endDay
29%10%47%8%46%5%5%5%13%
2154
April1st to 15thDay
24%10%48%7%45%5%6%6%17%
2149
16th to endDay
20%8%47%6%46%5%6%7%23%
2242
May1st to 15thDay
17%7%45%5%25%5%5%7%32%
2301
16th to endDay
20%8%5%8%6%46%5%6%7%21%
2391
June1st to 15thDay
17%8%37%6%35%5%5%8%27%
2377
16th to endDay
16%7%36%6%45%6%6%8%28%
2475
July1st to 15thDay
10%424324345%55%
2448
16th to endDay
10%414324447%52%
2461
August1st to 15thDay
7%425%423447%52%
2216
16th to endDay
10%415%5%2345%7%48%
2210
September1st to 15thDay
9%425%423336%53%
1980
16th to endDay
18%7%25%5%33447%35%
1821
October1st to 15thDay
22%8%47%5%2435%7%28%
1650
16th to endDay
31%9%46%5%3445%6%17%
1702
November1st to 15thDay
33%8%37%6%35%5%45%16%
1433
16th to endDay
31%10%47%5%24445%19%
1440
December1st to 15thDay
26%9%5%7%7%45%35%5%19%
1440
16th to endDay
31%13%5%6%7%2444414%
1461
January1st to 15thNight
37%8%35%42333421%
2581
16th to endNight
28%9%35%425%447%22%
2643
February1st to 15thNight
29%10%37%6%34446%20%
2276
16th to endNight
26%9%36%43445%5%26%
2014
March1st to 15thNight
33%10%36%5%35%345%18%
2064
16th to endNight
28%11%37%6%35%5%5%5%16%
2066
April1st to 15thNight
20%8%36%6%46%5%5%7%24%
1799
16th to endNight
18%7%25%7%25%5%5%9%30%
1603
May1st to 15thNight
16%7%25%5%45%45%7%36%
1319
16th to endNight
13%6%37%6%47%5%7%7%29%
1368
June1st to 15thNight
12%6%26%5%345%49%37%
1250
16th to endNight
12%7%36%6%35%5%5%6%38%
1155
July1st to 15thNight
4323224346%62%
1180
16th to endNight
5%222213236%67%
1400
August1st to 15thNight
4312213349%63%
1413
16th to endNight
7%41331245%6%59%
1639
September1st to 15thNight
6%312213345%64%
1650
16th to endNight
16%6%34423348%42%
1807
October1st to 15thNight
21%6%26%5%34445%35%
1980
16th to endNight
28%8%25%5%3445%6%26%
2170
November1st to 15thNight
34%7%25%6%35%44421%
2422
16th to endNight
27%9%37%5%35%446%22%
2520
December1st to 15thNight
26%8%47%6%34445%24%
2520
16th to endNight
33%11%48%5%2343418%
2754

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
37%8%36%5%2444319%
1352
16th to endDay
30%11%37%33445%6%18%
1581
February1st to 15thDay
32%9%48%6%33346%17%
1576
16th to endDay
29%10%47%6%33445%21%
1460
March1st to 15thDay
35%11%46%6%35%335%14%
1896
16th to endDay
29%11%5%6%7%35%45%6%14%
2154
April1st to 15thDay
24%10%47%7%346%5%7%17%
2149
16th to endDay
21%7%47%6%46%5%5%7%24%
2242
May1st to 15thDay
18%7%36%5%35%45%6%33%
2301
16th to endDay
21%9%48%5%35%5%5%7%22%
2391
June1st to 15thDay
19%8%46%6%35%45%7%29%
2377
16th to endDay
17%7%36%7%45%45%7%30%
2475
July1st to 15thDay
10%414413345%55%
2448
16th to endDay
11%414323347%53%
2461
August1st to 15thDay
7%424333446%54%
2216
16th to endDay
10%5%24423447%50%
2210
September1st to 15thDay
9%5%24422346%53%
1980
16th to endDay
19%7%25%42336%7%36%
1821
October1st to 15thDay
22%9%36%434447%30%
1650
16th to endDay
32%8%37%5%34446%18%
1702
November1st to 15thDay
35%8%37%5%335%46%17%
1433
16th to endDay
33%9%46%5%34345%20%
1440
December1st to 15thDay
28%8%5%7%6%45%45%5%19%
1440
16th to endDay
33%13%36%5%34335%15%
1461
January1st to 15thNight
38%9%3442333423%
2580
16th to endNight
30%9%25%5%23347%23%
2643
February1st to 15thNight
31%9%36%6%33446%20%
2276
16th to endNight
28%8%26%5%245%45%25%
2014
March1st to 15thNight
34%10%35%43445%5%19%
2064
16th to endNight
29%10%36%7%44445%17%
2070
April1st to 15thNight
20%7%46%6%46%5%6%6%25%
1799
16th to endNight
18%8%35%5%35%47%8%29%
1603
May1st to 15thNight
16%7%27%5%245%5%7%35%
1319
16th to endNight
15%6%37%6%47%6%5%8%27%
1368
June1st to 15thNight
14%6%36%6%345%48%35%
1250
16th to endNight
12%7%46%5%5%4446%37%
1155
July1st to 15thNight
4313324435%62%
1180
16th to endNight
6%312213346%65%
1400
August1st to 15thNight
421331345%6%63%
1413
16th to endNight
8%41232245%6%59%
1639
September1st to 15thNight
7%212223345%64%
1650
16th to endNight
17%6%25%43235%6%42%
1807
October1st to 15thNight
22%5%25%6%23445%36%
1980
16th to endNight
29%6%25%5%33446%26%
2170
November1st to 15thNight
36%7%25%5%3443421%
2422
16th to endNight
29%9%36%5%34336%23%
2520
December1st to 15thNight
28%9%25%5%34445%25%
2520
16th to endNight
35%10%46%5%2433419%
2754

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%5%7%11%41
1352
16th to endDay
64%413%11%41
1581
February1st to 15thDay
68%6%12%8%4
1576
16th to endDay
66%5%10%12%4
1460
March1st to 15thDay
72%5%11%9%1
1896
16th to endDay
70%7%10%11%
2154
April1st to 15thDay
63%8%14%12%1
2149
16th to endDay
58%8%14%14%3
2242
May1st to 15thDay
50%5%17%18%8%
2301
16th to endDay
58%7%20%10%2
2395
June1st to 15thDay
54%6%21%12%5%
2377
16th to endDay
51%6%21%16%3
2475
July1st to 15thDay
31%6%15%27%17%2
2291
16th to endDay
29%6%15%28%17%2
2294
August1st to 15thDay
30%5%20%31%10%1
2199
16th to endDay
34%5%15%32%9%2
2210
September1st to 15thDay
31%5%15%26%16%4
1980
16th to endDay
46%5%18%19%8%1
1821
October1st to 15thDay
53%5%16%17%6%
1650
16th to endDay
66%5%12%12%2
1702
November1st to 15thDay
68%5%11%10%31
1433
16th to endDay
66%5%10%12%5%
1440
December1st to 15thDay
65%6%11%12%4
1440
16th to endDay
73%48%8%4
1461
January1st to 15thNight
65%5%9%13%41
2581
16th to endNight
60%6%11%13%6%2
2643
February1st to 15thNight
64%5%13%9%5%
2288
16th to endNight
59%6%13%14%6%
2014
March1st to 15thNight
65%5%13%13%1
2064
16th to endNight
65%7%13%12%1
2070
April1st to 15thNight
56%10%14%16%1
1799
16th to endNight
51%8%19%16%4
1603
May1st to 15thNight
47%5%16%18%10%
1320
16th to endNight
52%10%22%12%2
1368
June1st to 15thNight
47%7%20%18%5%
1250
16th to endNight
47%422%19%31
1155
July1st to 15thNight
26%5%18%31%13%5%
1108
16th to endNight
20%6%16%32%20%4
1304
August1st to 15thNight
22%7%20%32%15%2
1405
16th to endNight
25%5%20%34%12%2
1639
September1st to 15thNight
23%5%17%29%18%6%
1650
16th to endNight
42%5%14%23%11%2
1807
October1st to 15thNight
49%414%22%7%1
1980
16th to endNight
59%5%14%14%5%
2170
November1st to 15thNight
65%6%11%12%22
2422
16th to endNight
62%413%11%7%
2520
December1st to 15thNight
61%6%13%14%4
2520
16th to endNight
70%5%10%8%3
2754

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
23%313%18%25%16%
60
16th to endDay
38%9%18%11%20%1
109
February1st to 15thDay
39%11%14%19%10%4
236
16th to endDay
35%15%16%20%11%1
218
March1st to 15thDay
40%17%23%12%5%
270
16th to endDay
34%15%25%15%5%2
288
April1st to 15thDay
26%14%26%18%10%4
269
16th to endDay
23%11%27%20%12%4
250
May1st to 15thDay
21%13%21%24%14%4
228
16th to endDay
18%6%21%25%19%9%
266
June1st to 15thDay
14%10%21%24%20%7%
322
16th to endDay
14%7%20%35%18%4
420
July1st to 15thDay
8%413%33%28%10%
375
16th to endDay
8%413%30%31%12%
271
August1st to 15thDay
9%210%31%34%11%
255
16th to endDay
12%5%14%32%23%11%
268
September1st to 15thDay
12%5%19%28%24%9%
255
16th to endDay
17%7%21%30%18%5%
255
October1st to 15thDay
27%9%20%21%17%3
255
16th to endDay
33%8%18%21%12%5%
214
November1st to 15thDay
43%13%24%13%31
65
16th to endDay
33%6%25%10%11%13%
60
December1st to 15thDay
40%18%23%16%1
60
16th to endDay
28%14%18%18%14%6%
64
January1st to 15thNight
38%9%14%17%17%2
733
16th to endNight
32%7%13%23%18%3
768
February1st to 15thNight
32%8%16%22%17%2
704
16th to endNight
31%9%19%22%14%2
632
March1st to 15thNight
36%10%18%20%12%1
720
16th to endNight
31%11%18%26%9%1
768
April1st to 15thNight
22%7%21%29%15%2
719
16th to endNight
22%5%19%33%15%2
553
May1st to 15thNight
17%8%17%32%22%2
330
16th to endNight
13%5%16%32%28%3
343
June1st to 15thNight
13%6%24%28%26%1
330
16th to endNight
15%7%18%33%24%
330
July1st to 15thNight
5%212%37%37%3
310
16th to endNight
7%37%39%37%4
348
August1st to 15thNight
5%18%32%44%7%
421
16th to endNight
10%111%28%41%5%
589
September1st to 15thNight
9%110%31%38%8%
660
16th to endNight
19%413%32%25%4
656
October1st to 15thNight
24%414%28%23%4
660
16th to endNight
31%6%15%26%18%2
704
November1st to 15thNight
34%8%19%26%10%
700
16th to endNight
31%10%19%19%15%3
720
December1st to 15thNight
31%8%16%27%15%1
720
16th to endNight
39%8%18%21%12%
779
Page generated at 2017-04-26 14:21:40. Version ac04

Copyright 2017 A. Danko


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