Colville Flats
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Colville Flats clear sky chart from 2005-11-06 to 2024-01-17.

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
47%
22908
14%
75032
12%
22867
52%
22867
20%
50837

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
23%
760
7%
2646
5%
756
27%
756
7%
2210
January11th to 20thNight
27%
746
8%
2610
5%
746
31%
746
8%
2140
January21st to endNight
31%
792
6%
2772
4%
792
34%
792
9%
2247
February1st to 10thNight
35%
720
10%
2507
8%
720
40%
720
13%
1842
February11th to 20thNight
38%
702
12%
2211
8%
700
44%
700
17%
1595
February21st to endNight
46%
592
16%
1776
12%
592
53%
592
21%
1220
March1st to 10thNight
43%
720
13%
2160
9%
720
48%
720
20%
1521
March11th to 20thNight
44%
720
15%
2121
11%
720
48%
720
21%
1480
March21st to endNight
39%
792
12%
1980
4%
792
43%
792
20%
1479
April1st to 10thNight
51%
720
14%
1800
5%
720
55%
720
26%
1256
April11th to 20thNight
43%
664
16%
1732
9%
664
47%
664
24%
1198
April21st to endNight
49%
522
16%
1602
11%
522
54%
522
24%
1018
May1st to 10thNight
53%
360
18%
1440
20%
360
60%
360
24%
809
May11th to 20thNight
59%
354
16%
1416
25%
354
63%
354
24%
803
May21st to endNight
51%
389
10%
1530
14%
388
55%
388
20%
960
June1st to 10thNight
55%
360
9%
1260
9%
360
57%
360
24%
780
June11th to 20thNight
55%
360
8%
1260
6%
360
57%
360
25%
766
June21st to endNight
66%
360
14%
1260
9%
360
69%
360
38%
636
July1st to 10thNight
73%
350
14%
1356
15%
350
76%
350
45%
577
July11th to 20thNight
72%
348
19%
1392
26%
348
81%
348
50%
543
July21st to endNight
82%
394
28%
1488
42%
372
91%
372
66%
493
August1st to 10thNight
77%
358
27%
1424
37%
356
83%
356
50%
568
August11th to 20thNight
79%
409
33%
1477
36%
409
83%
409
54%
609
August21st to endNight
73%
756
32%
1944
21%
756
77%
756
58%
994
September1st to 10thNight
70%
720
30%
1800
15%
720
75%
720
56%
964
September11th to 20thNight
70%
720
27%
1872
18%
720
72%
720
40%
1127
September21st to endNight
66%
720
26%
1980
20%
720
69%
720
41%
1133
October1st to 10thNight
59%
720
19%
2094
17%
720
62%
720
32%
1278
October11th to 20thNight
55%
720
20%
2250
16%
720
61%
720
27%
1397
October21st to endNight
49%
792
17%
2574
13%
792
56%
792
22%
1697
November1st to 10thNight
43%
740
9%
2405
8%
740
45%
740
14%
1794
November11th to 20thNight
34%
760
10%
2631
7%
760
38%
760
12%
1962
November21st to endNight
33%
874
7%
2774
5%
874
36%
874
12%
2163
December1st to 10thNight
35%
950
9%
2850
5%
950
38%
950
13%
2229
December11th to 20thNight
26%
950
3%
3507
2%
949
27%
949
5%
3094
December21st to endNight
25%
994
5%
5131
4%
985
30%
985
5%
4255

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%9%36%6%45%5%6%7%39%
74595
Night
11%11%47%6%35%5%6%7%38%
75233
TransparencyDay
43%8%13%19%13%3
74297
Night
45%8%13%19%12%3
75049
SeeingDay
14%13%29%28%14%3
13676
Night
16%5%21%34%21%3
22920

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
18%21%6%11%9%45%445%14%
1519
11th to 20thDay
15%15%8%11%10%45%446%17%
1488
21st to endDay
14%16%6%13%7%45%5%6%7%18%
1584
February1st to 10thDay
11%13%6%9%8%46%5%5%7%26%
1449
11th to 20thDay
11%12%5%7%5%36%5%7%8%29%
1637
21st to endDay
10%12%47%7%5%5%6%6%7%30%
1480
March1st to 10thDay
11%12%48%7%36%6%7%9%26%
1800
11th to 20thDay
13%10%36%7%346%6%9%31%
1835
21st to endDay
13%11%6%8%8%5%6%5%7%7%25%
2376
April1st to 10thDay
11%9%38%8%5%7%6%5%9%27%
2160
11th to 20thDay
10%7%37%8%47%6%7%7%32%
2179
21st to endDay
10%7%37%7%46%6%6%8%35%
2356
May1st to 10thDay
7%7%37%6%45%6%6%9%41%
2520
11th to 20thDay
9%6%37%6%46%6%7%9%36%
2477
21st to endDay
11%8%46%7%46%6%8%8%32%
2741
June1st to 10thDay
14%8%36%6%45%46%7%36%
2700
11th to 20thDay
10%7%47%8%47%6%6%9%33%
2700
21st to endDay
5%425%6%45%5%6%8%50%
2700
July1st to 10thDay
3314435%6%5%7%59%
2559
11th to 20thDay
322343445%8%63%
2520
21st to endDay
2112323346%72%
2741
August1st to 10thDay
33134345%5%8%62%
2507
11th to 20thDay
3213324447%66%
2421
21st to endDay
4424425%46%7%59%
2408
September1st to 10thDay
431332445%6%64%
2160
11th to 20thDay
6%426%5%45%6%7%8%49%
2088
21st to endDay
8%426%5%35%5%6%7%49%
1980
October1st to 10thDay
10%6%26%6%45%45%8%45%
1864
11th to 20thDay
9%7%36%6%36%5%7%7%42%
1710
21st to endDay
16%9%47%5%35%46%6%34%
1782
November1st to 10thDay
17%11%48%7%45%45%7%29%
1674
11th to 20thDay
14%13%5%7%8%36%45%5%30%
1544
21st to endDay
15%17%5%9%10%345%6%6%21%
1386
December1st to 10thDay
12%13%6%12%8%35%6%6%6%22%
1330
11th to 20thDay
18%23%7%10%7%34445%15%
1682
21st to endDay
14%21%8%10%7%45%5%5%6%14%
2538
January1st to 10thNight
20%19%7%10%7%34445%17%
2646
11th to 20thNight
17%16%8%11%7%3435%6%20%
2610
21st to endNight
12%20%7%11%8%35%5%45%21%
2772
February1st to 10thNight
11%15%5%8%6%35%5%6%7%28%
2507
11th to 20thNight
10%11%5%7%6%45%5%6%7%33%
2209
21st to endNight
7%9%5%7%7%45%5%7%6%38%
1776
March1st to 10thNight
11%11%36%7%45%6%7%8%33%
2160
11th to 20thNight
12%8%46%6%36%5%5%7%38%
2121
21st to endNight
11%9%47%6%47%6%7%9%31%
1980
April1st to 10thNight
10%7%45%6%36%7%8%8%37%
1800
11th to 20thNight
8%7%48%8%46%5%47%38%
1732
21st to endNight
6%7%46%6%45%6%7%8%41%
1602
May1st to 10thNight
8%5%36%6%36%5%6%8%44%
1440
11th to 20thNight
7%5%25%5%36%5%7%9%46%
1416
21st to endNight
11%7%46%8%345%7%7%38%
1530
June1st to 10thNight
10%6%36%5%36%7%8%8%40%
1260
11th to 20thNight
7%5%37%5%36%6%7%9%41%
1260
21st to endNight
4324425%5%7%8%56%
1260
July1st to 10thNight
22124345%5%9%63%
1396
11th to 20thNight
221232446%8%68%
1440
21st to endNight
11212347%78%
1576
August1st to 10thNight
333212347%71%
1432
11th to 20thNight
2212323447%70%
1477
21st to endNight
421222346%8%66%
1944
September1st to 10thNight
321233446%7%65%
1800
11th to 20thNight
6%325%4246%6%9%53%
1872
21st to endNight
7%42432447%7%56%
1980
October1st to 10thNight
10%5%26%5%24447%50%
2094
11th to 20thNight
9%6%35%6%4446%8%46%
2250
21st to endNight
14%9%25%4345%5%7%42%
2574
November1st to 10thNight
17%12%45%5%35%6%6%8%29%
2405
11th to 20thNight
14%13%5%7%5%35%6%6%5%30%
2631
21st to endNight
16%15%7%9%6%3445%6%25%
2774
December1st to 10thNight
13%16%5%10%7%35%5%5%6%26%
2850
11th to 20thNight
16%24%8%10%7%3444416%
3510
21st to endNight
16%23%5%9%7%35%5%6%5%16%
5147

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
72%9%7%7%4
1519
11th to 20thDay
69%7%11%9%21
1488
21st to endDay
65%8%11%12%4
1584
February1st to 10thDay
57%10%15%12%6%1
1449
11th to 20thDay
51%11%16%14%8%
1646
21st to endDay
54%9%13%15%9%1
1480
March1st to 10thDay
53%10%18%12%7%1
1800
11th to 20thDay
50%10%14%19%7%
1835
21st to endDay
57%10%17%11%41
2376
April1st to 10thDay
53%9%14%17%6%1
2160
11th to 20thDay
48%10%15%18%9%1
2179
21st to endDay
45%10%14%20%8%3
2356
May1st to 10thDay
38%8%14%26%12%2
2520
11th to 20thDay
42%9%15%23%10%1
2480
21st to endDay
46%10%15%20%8%
2742
June1st to 10thDay
46%6%11%20%13%4
2700
11th to 20thDay
46%10%13%18%11%2
2700
21st to endDay
30%7%13%26%19%4
2700
July1st to 10thDay
23%7%12%23%24%12%
2490
11th to 20thDay
20%5%10%20%30%15%
2445
21st to endDay
14%47%24%35%16%
2589
August1st to 10thDay
19%7%11%23%27%12%
2490
11th to 20thDay
18%5%10%28%33%6%
2421
21st to endDay
23%6%12%30%25%4
2408
September1st to 10thDay
20%7%11%31%25%6%
2160
11th to 20thDay
31%9%12%23%20%4
2088
21st to endDay
34%8%17%26%12%3
1980
October1st to 10thDay
39%7%16%28%10%
1864
11th to 20thDay
39%9%17%25%10%
1710
21st to endDay
50%9%15%18%7%1
1782
November1st to 10thDay
56%10%14%14%5%1
1674
11th to 20thDay
58%8%14%14%5%2
1544
21st to endDay
63%10%12%11%31
1386
December1st to 10thDay
63%7%12%12%5%
1330
11th to 20thDay
72%8%11%6%3
1684
21st to endDay
67%11%10%7%4
2538
January1st to 10thNight
69%8%9%8%5%
2646
11th to 20thNight
67%7%11%12%3
2610
21st to endNight
65%8%13%10%31
2772
February1st to 10thNight
54%9%16%13%7%2
2507
11th to 20thNight
49%9%15%18%8%
2211
21st to endNight
44%9%17%17%12%1
1776
March1st to 10thNight
47%9%19%17%7%1
2160
11th to 20thNight
46%8%14%22%10%
2122
21st to endNight
48%10%15%18%8%
1980
April1st to 10thNight
42%8%16%24%9%1
1800
11th to 20thNight
45%6%14%21%13%2
1732
21st to endNight
39%8%14%24%14%2
1602
May1st to 10thNight
35%7%13%27%16%2
1440
11th to 20thNight
33%10%15%27%13%3
1416
21st to endNight
42%8%15%24%10%1
1530
June1st to 10thNight
38%9%11%21%16%5%
1260
11th to 20thNight
36%8%16%22%14%3
1260
21st to endNight
23%7%13%28%23%6%
1260
July1st to 10thNight
17%5%10%26%27%16%
1356
11th to 20thNight
14%5%12%24%26%20%
1392
21st to endNight
8%36%23%35%25%
1488
August1st to 10thNight
15%49%20%33%18%
1424
11th to 20thNight
14%49%28%36%8%
1477
21st to endNight
15%5%12%28%33%7%
1944
September1st to 10thNight
17%6%9%30%28%11%
1800
11th to 20thNight
28%7%11%24%23%6%
1872
21st to endNight
26%7%16%31%14%5%
1980
October1st to 10thNight
35%6%15%31%13%1
2094
11th to 20thNight
38%6%17%26%13%1
2250
21st to endNight
42%9%15%25%9%1
2574
November1st to 10thNight
53%10%17%13%6%1
2405
11th to 20thNight
55%10%15%14%5%2
2631
21st to endNight
61%7%13%13%6%
2774
December1st to 10thNight
60%7%14%16%3
2850
11th to 20thNight
73%10%8%6%3
3507
21st to endNight
68%10%9%8%5%
5147

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
29%9%22%26%12%2
180
11th to 20thDay
29%6%26%23%12%3
172
21st to endDay
29%6%27%29%9%1
176
February1st to 10thDay
18%15%39%22%6%
169
11th to 20thDay
19%14%30%29%7%1
363
21st to endDay
15%14%32%25%12%1
346
March1st to 10thDay
20%22%30%18%9%1
420
11th to 20thDay
19%16%24%26%16%
420
21st to endDay
18%21%29%22%9%1
462
April1st to 10thDay
22%13%33%21%9%2
420
11th to 20thDay
17%24%29%17%9%3
412
21st to endDay
15%19%28%27%9%2
420
May1st to 10thDay
12%17%32%26%10%3
423
11th to 20thDay
17%13%29%26%13%2
448
21st to endDay
13%12%27%29%15%4
503
June1st to 10thDay
17%13%24%29%14%3
630
11th to 20thDay
13%17%28%27%12%3
630
21st to endDay
5%9%26%33%23%3
630
July1st to 10thDay
5%12%30%36%15%2
485
11th to 20thDay
5%12%36%32%13%2
444
21st to endDay
312%30%34%16%5%
487
August1st to 10thDay
6%8%25%37%19%5%
447
11th to 20thDay
48%28%33%21%6%
437
21st to endDay
5%12%29%30%18%6%
495
September1st to 10thDay
8%11%28%28%20%4
450
11th to 20thDay
10%13%26%31%17%4
450
21st to endDay
12%18%26%26%15%3
450
October1st to 10thDay
12%12%31%27%16%2
450
11th to 20thDay
17%9%30%28%13%3
360
21st to endDay
25%10%29%28%5%3
297
November1st to 10thDay
24%7%27%31%10%1
270
11th to 20thDay
23%11%29%25%11%1
192
21st to endDay
28%8%28%21%14%1
180
December1st to 10thDay
23%9%26%22%16%4
180
11th to 20thDay
23%7%29%30%10%1
180
21st to endDay
23%6%26%34%11%1
198
January1st to 10thNight
30%7%26%26%10%2
760
11th to 20thNight
26%5%23%30%14%3
746
21st to endNight
25%319%35%16%2
792
February1st to 10thNight
21%5%26%32%13%3
720
11th to 20thNight
17%5%26%34%16%1
704
21st to endNight
13%8%23%35%17%4
592
March1st to 10thNight
17%5%26%33%18%2
720
11th to 20thNight
16%7%24%35%17%1
720
21st to endNight
17%7%26%32%15%2
792
April1st to 10thNight
13%7%20%34%24%3
720
11th to 20thNight
11%8%26%36%16%3
664
21st to endNight
8%11%24%36%19%2
522
May1st to 10thNight
10%8%20%36%25%2
360
11th to 20thNight
11%5%16%34%29%5%
354
21st to endNight
12%6%19%32%26%5%
389
June1st to 10thNight
10%6%22%36%23%4
360
11th to 20thNight
10%5%23%38%21%3
360
21st to endNight
5%318%41%30%3
360
July1st to 10thNight
3314%40%35%4
350
11th to 20thNight
2320%44%30%2
348
21st to endNight
1213%43%38%4
394
August1st to 10thNight
5%312%28%44%9%
358
11th to 20thNight
2312%33%41%8%
409
21st to endNight
4415%36%36%4
756
September1st to 10thNight
3319%38%31%6%
720
11th to 20thNight
7%412%33%36%8%
720
21st to endNight
10%416%36%27%7%
720
October1st to 10thNight
13%416%37%28%2
720
11th to 20thNight
12%8%19%34%25%2
720
21st to endNight
19%5%21%36%15%4
792
November1st to 10thNight
25%6%18%39%11%1
740
11th to 20thNight
24%7%24%29%14%1
760
21st to endNight
25%5%22%30%17%2
874
December1st to 10thNight
23%6%21%34%15%3
950
11th to 20thNight
28%5%21%35%10%1
950
21st to endNight
29%6%23%32%10%1
1004
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