Fishtrap
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Fishtrap clear sky chart from 2005-11-06 to 2024-01-13.

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
48%
22797
16%
74912
14%
22754
53%
22754
22%
49078

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%
759
7%
2646
4%
756
29%
756
8%
2168
January11th to 20thNight
32%
728
7%
2548
5%
728
35%
728
10%
2007
January21st to endNight
36%
792
8%
2772
6%
792
40%
792
11%
2126
February1st to 10thNight
35%
720
10%
2485
7%
720
40%
720
14%
1803
February11th to 20thNight
38%
704
11%
2178
8%
700
43%
700
18%
1528
February21st to endNight
40%
592
17%
1776
13%
592
47%
592
20%
1247
March1st to 10thNight
43%
720
14%
2160
12%
720
47%
720
20%
1525
March11th to 20thNight
43%
720
17%
2125
13%
720
48%
720
21%
1460
March21st to endNight
39%
792
12%
1980
5%
792
42%
792
20%
1505
April1st to 10thNight
47%
720
16%
1800
7%
720
50%
720
27%
1256
April11th to 20thNight
42%
675
20%
1743
10%
675
48%
675
29%
1170
April21st to endNight
50%
540
18%
1620
13%
540
55%
540
26%
1040
May1st to 10thNight
54%
396
21%
1476
21%
396
62%
396
29%
813
May11th to 20thNight
56%
354
17%
1416
26%
354
59%
354
23%
800
May21st to endNight
60%
388
13%
1552
20%
388
64%
388
24%
885
June1st to 10thNight
54%
360
11%
1378
14%
360
59%
360
25%
788
June11th to 20thNight
47%
360
14%
1260
12%
360
53%
360
28%
735
June21st to endNight
66%
360
16%
1370
22%
360
70%
360
35%
674
July1st to 10thNight
79%
350
19%
1400
27%
350
84%
350
51%
549
July11th to 20thNight
77%
348
25%
1392
38%
348
83%
348
55%
519
July21st to endNight
84%
394
32%
1488
47%
372
90%
372
67%
494
August1st to 10thNight
81%
358
33%
1424
43%
356
86%
356
57%
529
August11th to 20thNight
82%
446
34%
1514
35%
446
84%
446
58%
636
August21st to endNight
72%
775
32%
1963
20%
775
76%
775
58%
1021
September1st to 10thNight
75%
720
32%
1800
18%
720
78%
720
60%
938
September11th to 20thNight
68%
720
30%
1885
20%
720
70%
720
45%
1080
September21st to endNight
61%
720
27%
1980
22%
720
65%
720
40%
1148
October1st to 10thNight
58%
720
22%
2070
20%
720
62%
720
35%
1233
October11th to 20thNight
54%
720
22%
2241
20%
720
59%
720
30%
1348
October21st to endNight
47%
792
21%
2574
18%
792
54%
792
25%
1631
November1st to 10thNight
40%
740
13%
2405
12%
740
44%
740
18%
1692
November11th to 20thNight
36%
760
11%
2572
9%
760
40%
760
14%
1849
November21st to endNight
41%
774
9%
2674
7%
774
44%
774
14%
1943
December1st to 10thNight
40%
950
10%
2850
7%
950
44%
950
14%
2188
December11th to 20thNight
28%
949
4%
3485
2%
949
29%
949
7%
2957
December21st to endNight
24%
881
5%
4910
4%
869
29%
869
4%
3793

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
10%8%36%5%35%5%5%7%44%
74566
Night
12%8%47%6%35%45%7%41%
75161
TransparencyDay
39%7%13%21%15%5%
74268
Night
43%7%12%19%13%5%
74977
SeeingDay
12%8%23%27%22%8%
13447
Night
15%6%21%34%21%3
22807

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
20%16%5%9%6%45%5%5%6%20%
1519
11th to 20thDay
19%14%8%12%8%46%5%5%416%
1456
21st to endDay
14%16%5%12%6%3445%8%22%
1584
February1st to 10thDay
14%11%5%8%7%5%6%5%5%6%27%
1472
11th to 20thDay
13%12%48%7%36%5%5%6%31%
1671
21st to endDay
12%13%6%8%5%35%5%5%7%31%
1480
March1st to 10thDay
13%11%47%6%5%7%5%6%8%28%
1800
11th to 20thDay
11%10%47%7%47%6%6%7%32%
1831
21st to endDay
13%11%48%7%47%6%6%7%27%
2376
April1st to 10thDay
10%10%48%7%5%6%5%6%9%30%
2160
11th to 20thDay
9%8%37%6%45%47%8%40%
2167
21st to endDay
10%7%36%5%346%5%7%43%
2340
May1st to 10thDay
5%5%26%435%5%6%9%48%
2483
11th to 20thDay
10%5%36%7%45%6%7%8%39%
2477
21st to endDay
10%7%46%6%36%5%7%8%40%
2723
June1st to 10thDay
12%7%45%5%345%5%7%43%
2578
11th to 20thDay
10%6%35%5%25%5%6%8%46%
2700
21st to endDay
5%32432445%7%60%
2582
July1st to 10thDay
331332235%5%70%
2520
11th to 20thDay
3212222346%73%
2520
21st to endDay
111121222482%
2741
August1st to 10thDay
3213222345%73%
2507
11th to 20thDay
3213212347%72%
2384
21st to endDay
431443345%7%61%
2390
September1st to 10thDay
4313312347%70%
2160
11th to 20thDay
5%4244345%5%7%56%
2075
21st to endDay
6%5%25%5%245%6%7%52%
1980
October1st to 10thDay
8%6%26%5%3436%6%50%
1886
11th to 20thDay
11%6%24435%5%5%6%49%
1718
21st to endDay
14%8%45%6%35%5%47%40%
1782
November1st to 10thDay
16%8%38%6%35%5%5%8%33%
1674
11th to 20thDay
17%11%5%8%5%35%6%5%430%
1606
21st to endDay
14%12%6%9%7%25%6%6%7%25%
1482
December1st to 10thDay
16%14%6%10%7%5%6%45%6%21%
1330
11th to 20thDay
19%16%7%13%9%45%5%45%15%
1682
21st to endDay
15%16%7%11%7%35%6%5%5%19%
2730
January1st to 10thNight
22%15%7%9%6%34445%20%
2646
11th to 20thNight
20%12%5%10%7%45%446%24%
2548
21st to endNight
15%14%5%8%7%36%45%7%26%
2772
February1st to 10thNight
15%13%5%7%6%35%46%6%30%
2485
11th to 20thNight
13%10%5%7%6%345%6%6%35%
2176
21st to endNight
10%12%37%6%45%5%6%9%33%
1776
March1st to 10thNight
14%8%37%6%46%5%47%34%
2160
11th to 20thNight
13%7%37%7%35%5%5%8%36%
2124
21st to endNight
12%9%48%8%5%7%6%6%8%28%
1980
April1st to 10thNight
10%9%36%6%36%5%6%8%36%
1800
11th to 20thNight
9%9%47%5%3445%6%44%
1743
21st to endNight
7%7%47%6%36%6%6%7%42%
1620
May1st to 10thNight
6%5%35%5%5%46%7%7%48%
1476
11th to 20thNight
9%6%36%7%345%6%9%42%
1416
21st to endNight
7%6%35%6%35%5%6%9%45%
1552
June1st to 10thNight
10%6%25%5%445%47%47%
1378
11th to 20thNight
9%5%25%6%35%5%47%49%
1260
21st to endNight
6%324435%5%6%6%57%
1370
July1st to 10thNight
313215%45%7%69%
1440
11th to 20thNight
3112323346%73%
1440
21st to endNight
111221234480%
1576
August1st to 10thNight
3213212336%74%
1432
11th to 20thNight
1222213446%72%
1514
21st to endNight
321332345%7%67%
1963
September1st to 10thNight
3312323346%70%
1800
11th to 20thNight
4325%43445%6%59%
1885
21st to endNight
8%5%2443436%7%54%
1980
October1st to 10thNight
10%5%35%5%2435%7%52%
2070
11th to 20thNight
11%5%244345%5%8%48%
2241
21st to endNight
14%7%25%5%3445%6%44%
2574
November1st to 10thNight
17%9%36%6%345%6%7%34%
2405
11th to 20thNight
16%8%47%6%46%5%5%7%32%
2572
21st to endNight
16%10%5%7%7%45%45%6%30%
2674
December1st to 10thNight
14%11%5%9%6%46%5%5%8%29%
2850
11th to 20thNight
20%14%6%12%8%36%5%5%6%15%
3510
21st to endNight
18%13%5%11%7%46%5%5%6%21%
4953

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
65%11%11%11%21
1519
11th to 20thDay
70%9%11%8%2
1456
21st to endDay
60%9%16%11%31
1584
February1st to 10thDay
58%9%15%12%5%1
1472
11th to 20thDay
54%9%15%16%6%
1680
21st to endDay
52%9%12%18%9%1
1480
March1st to 10thDay
52%9%14%18%5%1
1800
11th to 20thDay
51%8%14%20%7%
1831
21st to endDay
55%8%18%15%4
2376
April1st to 10thDay
50%8%13%20%8%1
2160
11th to 20thDay
42%5%16%22%12%2
2167
21st to endDay
39%8%14%24%12%2
2340
May1st to 10thDay
30%8%15%30%16%1
2483
11th to 20thDay
39%8%15%24%13%1
2480
21st to endDay
39%9%15%26%11%1
2724
June1st to 10thDay
41%6%11%23%16%3
2578
11th to 20thDay
34%7%14%26%14%3
2700
21st to endDay
23%5%12%29%24%7%
2582
July1st to 10thDay
17%48%25%28%17%
2451
11th to 20thDay
14%39%18%37%19%
2445
21st to endDay
9%25%17%45%22%
2589
August1st to 10thDay
15%38%22%34%18%
2490
11th to 20thDay
13%48%26%36%12%
2384
21st to endDay
22%5%9%27%31%7%
2390
September1st to 10thDay
16%411%29%27%13%
2160
11th to 20thDay
26%5%14%24%24%7%
2075
21st to endDay
30%8%17%27%14%4
1980
October1st to 10thDay
35%6%13%30%15%1
1886
11th to 20thDay
35%6%17%30%10%1
1718
21st to endDay
44%8%15%22%11%
1782
November1st to 10thDay
48%9%16%20%6%1
1674
11th to 20thDay
56%9%16%14%42
1606
21st to endDay
55%12%16%12%41
1482
December1st to 10thDay
64%9%11%11%5%
1330
11th to 20thDay
72%9%10%7%1
1684
21st to endDay
63%10%13%10%4
2730
January1st to 10thNight
66%9%11%11%21
2646
11th to 20thNight
61%9%16%12%2
2548
21st to endNight
58%9%15%13%31
2772
February1st to 10thNight
54%7%16%16%6%1
2485
11th to 20thNight
49%8%19%15%8%
2178
21st to endNight
48%7%14%20%9%1
1776
March1st to 10thNight
48%7%14%20%9%1
2160
11th to 20thNight
46%7%12%23%11%1
2125
21st to endNight
51%9%14%20%6%
1980
April1st to 10thNight
43%7%13%25%11%1
1800
11th to 20thNight
40%6%10%24%16%2
1743
21st to endNight
39%8%12%22%16%3
1620
May1st to 10thNight
31%7%11%31%16%3
1476
11th to 20thNight
37%6%14%23%17%3
1416
21st to endNight
35%8%14%29%13%2
1552
June1st to 10thNight
37%6%9%22%23%4
1378
11th to 20thNight
35%6%8%26%20%5%
1260
21st to endNight
25%7%9%25%25%9%
1370
July1st to 10thNight
15%46%20%32%23%
1400
11th to 20thNight
13%36%18%32%28%
1392
21st to endNight
9%2414%35%36%
1488
August1st to 10thNight
14%27%15%36%27%
1424
11th to 20thNight
13%46%22%35%20%
1514
21st to endNight
16%5%9%23%31%16%
1963
September1st to 10thNight
16%47%26%29%17%
1800
11th to 20thNight
26%5%10%24%25%11%
1885
21st to endNight
28%6%13%28%17%8%
1980
October1st to 10thNight
33%5%10%29%21%2
2070
11th to 20thNight
35%6%13%27%17%2
2241
21st to endNight
39%7%13%25%14%2
2574
November1st to 10thNight
48%8%16%20%7%1
2405
11th to 20thNight
52%9%16%16%6%1
2572
21st to endNight
54%8%15%17%6%
2674
December1st to 10thNight
55%10%14%17%5%
2850
11th to 20thNight
69%9%12%8%2
3507
21st to endNight
61%11%13%11%4
4953

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
24%7%31%21%13%3
180
11th to 20thDay
26%7%20%25%18%5%
164
21st to endDay
27%9%24%23%16%1
176
February1st to 10thDay
21%8%36%24%9%2
192
11th to 20thDay
22%12%28%23%13%2
379
21st to endDay
16%14%28%25%14%3
346
March1st to 10thDay
18%10%36%20%13%4
420
11th to 20thDay
16%10%24%27%18%5%
420
21st to endDay
17%15%29%24%13%3
462
April1st to 10thDay
16%11%26%28%14%5%
420
11th to 20thDay
12%17%29%22%14%6%
412
21st to endDay
11%11%26%28%18%5%
420
May1st to 10thDay
9%7%22%32%23%6%
423
11th to 20thDay
15%6%18%27%21%13%
448
21st to endDay
9%7%16%28%25%14%
485
June1st to 10thDay
12%7%21%25%23%11%
508
11th to 20thDay
13%7%28%30%15%7%
630
21st to endDay
4421%27%32%12%
512
July1st to 10thDay
3417%36%35%5%
446
11th to 20thDay
35%19%34%30%10%
444
21st to endDay
2215%29%37%16%
487
August1st to 10thDay
5%412%29%32%18%
447
11th to 20thDay
3214%26%34%22%
437
21st to endDay
7%420%26%29%14%
495
September1st to 10thDay
6%5%19%29%29%12%
450
11th to 20thDay
8%5%24%21%29%13%
450
21st to endDay
8%8%24%28%24%7%
450
October1st to 10thDay
12%7%25%26%23%8%
450
11th to 20thDay
15%8%20%24%26%8%
368
21st to endDay
20%10%23%30%11%5%
297
November1st to 10thDay
20%9%22%33%14%2
270
11th to 20thDay
25%10%20%24%15%5%
221
21st to endDay
19%11%19%28%18%4
180
December1st to 10thDay
19%11%22%26%16%7%
180
11th to 20thDay
28%10%23%24%13%1
180
21st to endDay
26%7%28%25%11%4
198
January1st to 10thNight
28%10%22%26%11%2
760
11th to 20thNight
25%7%20%28%19%2
728
21st to endNight
22%421%33%18%2
792
February1st to 10thNight
22%9%24%30%13%1
720
11th to 20thNight
20%7%23%30%18%2
704
21st to endNight
16%10%22%33%16%3
592
March1st to 10thNight
18%7%24%33%15%3
720
11th to 20thNight
16%8%24%32%19%2
720
21st to endNight
17%7%28%34%12%2
792
April1st to 10thNight
16%5%25%33%19%3
720
11th to 20thNight
12%5%34%32%15%2
675
21st to endNight
9%8%25%35%22%2
540
May1st to 10thNight
7%5%28%33%24%4
396
11th to 20thNight
12%6%15%32%28%7%
354
21st to endNight
8%5%20%37%26%3
389
June1st to 10thNight
13%322%35%24%3
360
11th to 20thNight
12%5%29%33%18%3
360
21st to endNight
8%416%39%30%3
360
July1st to 10thNight
4113%43%36%4
350
11th to 20thNight
3315%49%29%2
348
21st to endNight
1211%45%37%5%
394
August1st to 10thNight
339%37%41%7%
358
11th to 20thNight
229%40%36%11%
446
21st to endNight
3317%38%33%5%
775
September1st to 10thNight
4214%44%29%6%
720
11th to 20thNight
5%417%32%33%9%
720
21st to endNight
10%5%20%32%28%6%
720
October1st to 10thNight
13%417%37%26%3
720
11th to 20thNight
13%5%20%34%24%4
720
21st to endNight
16%6%24%34%15%4
792
November1st to 10thNight
22%7%20%38%13%1
740
11th to 20thNight
21%8%26%29%13%2
760
21st to endNight
21%6%20%32%19%2
774
December1st to 10thNight
19%7%21%36%15%2
950
11th to 20thNight
26%7%22%33%12%1
950
21st to endNight
31%10%19%30%10%1
888
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