Umatilla
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Umatilla 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
49%
22492
16%
74755
15%
22461
54%
22461
23%
48530

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
28%
757
6%
2646
3%
756
31%
756
8%
2200
January11th to 20thNight
37%
732
6%
2560
5%
732
40%
732
10%
2021
January21st to endNight
40%
792
8%
2772
6%
792
43%
792
12%
2126
February1st to 10thNight
40%
720
8%
2376
7%
720
43%
720
14%
1751
February11th to 20thNight
43%
701
13%
2210
13%
700
46%
700
17%
1579
February21st to endNight
38%
592
14%
1776
11%
592
44%
592
17%
1272
March1st to 10thNight
43%
720
13%
2160
11%
720
47%
720
21%
1501
March11th to 20thNight
47%
720
15%
2080
13%
720
51%
720
23%
1445
March21st to endNight
36%
792
14%
2001
6%
792
39%
792
20%
1497
April1st to 10thNight
42%
720
14%
1800
6%
720
44%
720
26%
1268
April11th to 20thNight
44%
711
20%
1779
10%
711
48%
711
31%
1181
April21st to endNight
47%
590
17%
1670
11%
590
52%
590
30%
1053
May1st to 10thNight
53%
365
22%
1445
22%
365
61%
365
30%
739
May11th to 20thNight
57%
354
20%
1416
25%
354
62%
354
26%
767
May21st to endNight
57%
388
14%
1552
19%
388
62%
388
24%
876
June1st to 10thNight
51%
360
13%
1440
15%
360
59%
360
25%
789
June11th to 20thNight
41%
360
15%
1440
16%
360
52%
360
27%
756
June21st to endNight
61%
360
20%
1440
28%
360
71%
360
42%
639
July1st to 10thNight
70%
350
22%
1400
34%
350
79%
350
55%
521
July11th to 20thNight
66%
348
27%
1392
38%
348
76%
348
60%
496
July21st to endNight
73%
394
35%
1488
42%
372
86%
372
69%
482
August1st to 10thNight
75%
358
34%
1424
43%
356
81%
356
55%
536
August11th to 20thNight
80%
524
35%
1592
29%
524
83%
524
62%
688
August21st to endNight
72%
792
35%
1980
21%
792
76%
792
63%
1000
September1st to 10thNight
74%
720
34%
1800
18%
720
77%
720
65%
904
September11th to 20thNight
71%
720
33%
1836
22%
720
73%
720
51%
1014
September21st to endNight
65%
720
30%
1980
25%
720
68%
720
44%
1095
October1st to 10thNight
61%
720
22%
2136
21%
720
65%
720
37%
1235
October11th to 20thNight
56%
720
24%
2164
23%
720
61%
720
31%
1306
October21st to endNight
50%
792
21%
2574
19%
792
56%
792
25%
1623
November1st to 10thNight
41%
740
17%
2405
15%
740
46%
740
19%
1653
November11th to 20thNight
38%
760
10%
2592
9%
760
42%
760
14%
1898
November21st to endNight
46%
760
10%
2660
8%
760
51%
760
16%
1883
December1st to 10thNight
38%
760
8%
2660
6%
760
41%
760
10%
2088
December11th to 20thNight
33%
758
3%
3276
3%
758
35%
758
5%
2842
December21st to endNight
30%
822
5%
4833
6%
817
34%
817
6%
3806

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
8%7%36%5%3445%7%47%
74792
Night
10%8%46%6%35%5%5%7%42%
74966
TransparencyDay
36%6%12%21%17%7%
74495
Night
42%7%12%20%13%5%
74784
SeeingDay
11%9%20%26%23%12%
13307
Night
13%6%22%34%21%3
22515

By Month

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 10thDay
20%17%6%12%7%45%5%46%15%
1519
11th to 20thDay
18%15%6%10%8%5%6%45%420%
1456
21st to endDay
15%15%7%11%10%46%5%45%19%
1584
February1st to 10thDay
14%13%5%10%8%445%6%6%24%
1580
11th to 20thDay
12%12%5%9%6%45%45%6%31%
1638
21st to endDay
10%9%47%9%46%7%6%8%30%
1480
March1st to 10thDay
12%10%5%7%5%36%6%8%8%31%
1800
11th to 20thDay
10%9%47%7%5%5%6%5%8%33%
1876
21st to endDay
10%7%48%8%47%6%7%9%31%
2354
April1st to 10thDay
8%7%36%6%46%6%7%8%39%
2160
11th to 20thDay
8%6%35%5%35%5%5%8%47%
2129
21st to endDay
7%5%25%5%345%5%7%51%
2290
May1st to 10thDay
6%425%435%5%7%9%53%
2513
11th to 20thDay
8%5%36%6%35%5%6%9%45%
2477
21st to endDay
8%5%25%5%35%5%6%8%48%
2723
June1st to 10thDay
9%5%35%4345%6%6%50%
2520
11th to 20thDay
8%4233345%5%7%57%
2520
21st to endDay
331332335%6%68%
2520
July1st to 10thDay
2112213345%77%
2520
11th to 20thDay
2113212345%76%
2520
21st to endDay
111111223484%
2741
August1st to 10thDay
2212222245%76%
2507
11th to 20thDay
2112212236%78%
2305
21st to endDay
3213322346%71%
2376
September1st to 10thDay
2211312346%75%
2160
11th to 20thDay
342443445%7%60%
2122
21st to endDay
7%5%25%5%23447%56%
1980
October1st to 10thDay
8%6%25%5%3445%7%52%
1822
11th to 20thDay
6%5%25%6%35%5%7%9%47%
1795
21st to endDay
12%8%45%6%45%46%8%37%
1782
November1st to 10thDay
13%9%48%8%36%6%5%7%32%
1674
11th to 20thDay
15%13%6%9%6%47%45%6%25%
1587
21st to endDay
12%13%6%11%7%46%6%6%7%22%
1520
December1st to 10thDay
12%11%7%11%11%47%5%6%5%22%
1520
11th to 20thDay
15%16%10%15%9%45%45%412%
1928
21st to endDay
15%15%6%13%11%5%7%5%46%14%
2794
January1st to 10thNight
19%14%6%11%7%45%5%6%6%18%
2646
11th to 20thNight
16%13%5%9%8%36%45%6%22%
2560
21st to endNight
15%11%6%9%7%35%5%6%7%24%
2772
February1st to 10thNight
14%11%47%7%35%5%5%8%31%
2376
11th to 20thNight
11%10%5%8%7%35%5%6%7%34%
2208
21st to endNight
11%9%48%6%46%5%5%6%35%
1776
March1st to 10thNight
13%9%47%6%45%6%6%8%34%
2160
11th to 20thNight
10%7%36%6%5%6%7%7%8%35%
2080
21st to endNight
10%9%47%7%46%6%7%7%32%
2001
April1st to 10thNight
11%10%46%6%35%6%48%37%
1800
11th to 20thNight
9%7%37%6%3435%7%46%
1779
21st to endNight
7%6%36%5%45%5%5%8%45%
1670
May1st to 10thNight
6%425%5%35%5%5%7%53%
1445
11th to 20thNight
9%6%24436%6%7%10%44%
1416
21st to endNight
5%5%35%6%46%6%8%9%44%
1552
June1st to 10thNight
10%4245%45%5%7%9%47%
1440
11th to 20thNight
7%7%244345%47%54%
1440
21st to endNight
431432445%5%64%
1440
July1st to 10thNight
3212212347%72%
1440
11th to 20thNight
3111223345%77%
1440
21st to endNight
111221223481%
1576
August1st to 10thNight
3212313336%72%
1432
11th to 20thNight
3112222335%76%
1592
21st to endNight
221332235%5%72%
1980
September1st to 10thNight
321232334475%
1800
11th to 20thNight
342432445%7%62%
1836
21st to endNight
6%42442445%7%59%
1980
October1st to 10thNight
8%5%345%2435%6%54%
2136
11th to 20thNight
8%6%25%5%345%5%6%50%
2164
21st to endNight
10%7%36%5%35%45%7%44%
2574
November1st to 10thNight
15%8%37%6%45%5%5%7%35%
2405
11th to 20thNight
16%10%47%7%35%6%6%7%30%
2592
21st to endNight
13%10%48%6%47%6%6%7%30%
2660
December1st to 10thNight
14%12%7%11%8%46%45%6%24%
2660
11th to 20thNight
17%16%7%11%8%5%5%6%5%6%14%
3276
21st to endNight
14%15%6%9%8%46%6%5%6%20%
4862

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
71%8%11%8%2
1519
11th to 20thDay
65%9%13%11%2
1456
21st to endDay
65%8%13%11%3
1584
February1st to 10thDay
59%9%17%11%4
1580
11th to 20thDay
51%9%16%17%7%
1647
21st to endDay
49%10%16%16%8%1
1480
March1st to 10thDay
48%9%15%20%9%
1800
11th to 20thDay
48%7%15%22%7%
1876
21st to endDay
48%10%16%20%6%
2354
April1st to 10thDay
40%8%15%23%13%1
2160
11th to 20thDay
34%6%16%24%16%4
2132
21st to endDay
30%7%14%28%18%3
2290
May1st to 10thDay
25%5%13%33%21%3
2513
11th to 20thDay
34%7%12%26%18%3
2480
21st to endDay
33%7%14%27%17%3
2724
June1st to 10thDay
33%6%11%27%19%4
2520
11th to 20thDay
26%5%12%28%23%5%
2520
21st to endDay
16%49%30%29%12%
2520
July1st to 10thDay
12%37%21%34%23%
2451
11th to 20thDay
11%46%14%34%31%
2445
21st to endDay
7%2414%41%32%
2589
August1st to 10thDay
12%28%22%36%20%
2490
11th to 20thDay
10%36%26%35%20%
2305
21st to endDay
16%37%28%36%11%
2376
September1st to 10thDay
12%38%29%31%16%
2160
11th to 20thDay
23%6%11%25%25%10%
2122
21st to endDay
28%5%13%32%17%4
1980
October1st to 10thDay
31%5%13%29%18%3
1822
11th to 20thDay
32%8%18%28%12%2
1795
21st to endDay
43%8%16%23%9%1
1782
November1st to 10thDay
50%9%15%19%6%1
1674
11th to 20thDay
60%9%13%15%3
1587
21st to endDay
58%10%16%11%4
1520
December1st to 10thDay
62%9%13%13%3
1520
11th to 20thDay
75%7%10%7%2
1928
21st to endDay
71%9%10%9%1
2794
January1st to 10thNight
66%10%13%10%2
2646
11th to 20thNight
62%9%14%13%3
2560
21st to endNight
58%9%17%14%21
2772
February1st to 10thNight
53%9%19%16%3
2376
11th to 20thNight
49%10%15%20%6%
2210
21st to endNight
49%8%15%18%8%1
1776
March1st to 10thNight
46%8%15%21%9%1
2160
11th to 20thNight
44%9%15%25%7%
2080
21st to endNight
47%11%14%22%6%
2001
April1st to 10thNight
44%7%15%22%12%
1800
11th to 20thNight
39%6%12%26%14%4
1779
21st to endNight
34%8%14%22%16%5%
1670
May1st to 10thNight
28%7%11%29%21%5%
1445
11th to 20thNight
32%7%13%24%19%4
1416
21st to endNight
33%9%14%25%16%3
1552
June1st to 10thNight
33%7%12%27%17%4
1440
11th to 20thNight
30%7%10%30%19%4
1440
21st to endNight
20%5%8%28%26%13%
1440
July1st to 10thNight
13%38%21%29%26%
1400
11th to 20thNight
10%49%17%29%31%
1392
21st to endNight
9%1414%37%35%
1488
August1st to 10thNight
14%26%18%36%22%
1424
11th to 20thNight
12%46%21%33%24%
1592
21st to endNight
13%49%22%37%16%
1980
September1st to 10thNight
14%39%25%30%19%
1800
11th to 20thNight
21%5%10%24%24%16%
1836
21st to endNight
24%6%11%27%25%7%
1980
October1st to 10thNight
30%6%10%28%24%2
2136
11th to 20thNight
34%7%11%29%16%3
2164
21st to endNight
40%6%12%26%14%2
2574
November1st to 10thNight
48%6%13%25%7%
2405
11th to 20thNight
53%9%15%19%4
2592
21st to endNight
50%9%18%17%5%
2660
December1st to 10thNight
61%9%13%14%3
2660
11th to 20thNight
71%10%11%7%1
3276
21st to endNight
64%9%13%10%4
4862

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
23%18%21%19%14%4
180
11th to 20thDay
29%10%12%28%16%4
164
21st to endDay
25%6%19%29%20%1
176
February1st to 10thDay
22%14%19%26%14%5%
300
11th to 20thDay
21%13%22%23%16%5%
363
21st to endDay
14%14%25%25%16%5%
346
March1st to 10thDay
19%13%27%21%16%4
420
11th to 20thDay
15%11%21%30%16%7%
420
21st to endDay
13%13%27%29%15%2
462
April1st to 10thDay
14%16%25%24%14%8%
420
11th to 20thDay
11%17%30%21%13%8%
412
21st to endDay
7%14%28%24%18%8%
420
May1st to 10thDay
9%8%24%25%26%8%
423
11th to 20thDay
12%7%24%22%21%14%
448
21st to endDay
10%5%21%24%26%14%
485
June1st to 10thDay
10%8%20%23%22%17%
450
11th to 20thDay
8%12%26%28%18%8%
450
21st to endDay
37%18%26%29%17%
450
July1st to 10thDay
2315%30%40%10%
446
11th to 20thDay
25%15%33%30%15%
444
21st to endDay
1314%22%34%26%
487
August1st to 10thDay
4411%24%32%25%
447
11th to 20thDay
229%24%28%35%
437
21st to endDay
5%5%16%26%28%19%
495
September1st to 10thDay
3413%30%32%19%
450
11th to 20thDay
5%6%16%25%29%18%
450
21st to endDay
8%8%16%28%28%12%
450
October1st to 10thDay
12%8%18%24%26%13%
450
11th to 20thDay
10%11%15%25%26%13%
445
21st to endDay
16%10%21%32%12%9%
297
November1st to 10thDay
18%11%23%30%15%4
270
11th to 20thDay
20%12%25%22%16%6%
212
21st to endDay
12%8%22%31%21%8%
180
December1st to 10thDay
12%8%28%27%12%13%
180
11th to 20thDay
21%9%24%34%10%3
180
21st to endDay
23%7%22%30%15%4
198
January1st to 10thNight
25%10%22%26%15%2
760
11th to 20thNight
21%7%18%34%19%2
732
21st to endNight
18%6%18%35%20%2
792
February1st to 10thNight
19%9%21%33%15%3
720
11th to 20thNight
14%10%21%33%19%3
704
21st to endNight
16%13%24%31%15%1
592
March1st to 10thNight
16%8%24%33%17%2
720
11th to 20thNight
11%8%24%36%19%1
720
21st to endNight
14%10%31%31%13%1
792
April1st to 10thNight
16%8%25%33%17%2
720
11th to 20thNight
11%11%29%27%18%4
711
21st to endNight
8%10%30%33%17%2
590
May1st to 10thNight
7%6%28%34%21%3
365
11th to 20thNight
11%6%20%34%25%4
354
21st to endNight
7%424%42%20%3
389
June1st to 10thNight
10%5%28%35%19%2
360
11th to 20thNight
10%7%36%31%14%1
360
21st to endNight
45%25%39%26%1
360
July1st to 10thNight
3320%46%26%1
350
11th to 20thNight
4226%46%21%1
348
21st to endNight
1220%46%28%2
394
August1st to 10thNight
3216%46%29%4
358
11th to 20thNight
4110%37%37%10%
524
21st to endNight
3317%40%32%6%
792
September1st to 10thNight
3218%39%33%4
720
11th to 20thNight
5%315%34%36%8%
720
21st to endNight
7%419%31%34%6%
720
October1st to 10thNight
11%417%37%27%4
720
11th to 20thNight
12%6%18%32%24%7%
720
21st to endNight
13%6%24%32%19%5%
792
November1st to 10thNight
19%6%23%35%17%1
740
11th to 20thNight
20%9%23%31%15%3
760
21st to endNight
16%7%19%35%19%3
760
December1st to 10thNight
18%6%19%34%18%4
760
11th to 20thNight
22%7%19%35%15%2
760
21st to endNight
25%8%22%31%13%1
836
Page generated at 2024-01-10 07:16:11. Version ac07

Copyright 2024 Attilla Danko


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