Spray
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Spray clear sky chart from 2005-11-05 to 2018-02-13.

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
52%
15273
16%
48798
15%
15248
54%
15248
23%
32168

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
38%
776
8%
2716
9%
776
40%
776
12%
2074
January16th to endNight
45%
832
12%
2896
13%
832
47%
832
15%
2079
February1st to 15thNight
42%
748
7%
2444
8%
747
44%
747
13%
1869
February16th to endNight
37%
632
13%
1912
12%
632
40%
632
15%
1453
March1st to 15thNight
39%
720
7%
2145
7%
720
41%
720
14%
1648
March16th to endNight
36%
768
9%
2007
5%
768
38%
768
16%
1550
April1st to 15thNight
41%
719
11%
1799
6%
719
42%
719
19%
1368
April16th to endNight
46%
663
15%
1743
9%
663
48%
663
24%
1216
May1st to 15thNight
56%
365
19%
1445
21%
365
61%
365
27%
800
May16th to endNight
55%
374
11%
1496
16%
374
59%
374
19%
954
June1st to 15thNight
59%
360
12%
1440
18%
360
62%
360
24%
839
June16th to endNight
65%
360
18%
1440
28%
360
70%
360
32%
712
July1st to 15thNight
81%
340
20%
1360
31%
340
86%
340
48%
555
July16th to endNight
84%
376
32%
1416
46%
354
88%
354
61%
494
August1st to 15thNight
86%
415
32%
1487
36%
413
88%
413
54%
605
August16th to endNight
79%
749
37%
1895
25%
749
81%
749
68%
908
September1st to 15thNight
78%
720
35%
1800
22%
720
80%
720
68%
887
September16th to endNight
67%
716
29%
1935
24%
716
69%
716
40%
1130
October1st to 15thNight
59%
720
19%
2159
19%
720
62%
720
31%
1323
October16th to endNight
55%
768
18%
2413
20%
768
56%
768
23%
1599
November1st to 15thNight
43%
760
12%
2478
12%
760
45%
760
15%
1842
November16th to endNight
42%
780
8%
2730
9%
780
43%
780
14%
1999
December1st to 15thNight
45%
780
9%
2730
9%
780
46%
780
14%
2010
December16th to endNight
34%
832
9%
2912
8%
832
36%
832
10%
2254

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%8%36%5%3445%7%43%
49260
Night
9%8%36%5%3445%6%41%
48966
Cloud CoverDay
8%8%36%5%3445%6%43%
49260
Night
9%8%36%5%3445%7%41%
48970
TransparencyDay
41%7%11%18%15%5%
48931
Night
42%7%13%18%13%4
48799
SeeingDay
13%16%29%24%12%3
5910
Night
13%8%19%34%21%2
15283

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
14%9%5%7%7%46%5%6%8%23%
1552
16th to endDay
12%11%47%5%45%5%6%8%28%
1677
February1st to 15thDay
9%12%48%7%36%5%7%8%25%
1685
16th to endDay
10%12%49%7%36%5%6%8%25%
1561
March1st to 15thDay
11%14%6%10%8%45%5%5%7%19%
1812
16th to endDay
10%13%5%10%8%45%5%5%7%21%
2217
April1st to 15thDay
10%13%5%7%6%46%5%6%7%26%
2149
16th to endDay
10%10%37%4345%5%6%37%
2217
May1st to 15thDay
8%7%45%5%3345%7%43%
2502
16th to endDay
13%9%36%5%45%5%46%35%
2615
June1st to 15thDay
11%6%27%5%3445%7%40%
2520
16th to endDay
7%41432335%6%56%
2520
July1st to 15thDay
2112313345%70%
2520
16th to endDay
112112235%76%
2657
August1st to 15thDay
1112213346%71%
2463
16th to endDay
212112235%74%
2306
September1st to 15thDay
2212212225%74%
2160
16th to endDay
6%5%2442345%6%52%
2025
October1st to 15thDay
11%7%35%5%3345%7%41%
1800
16th to endDay
11%7%27%6%45%45%8%37%
1809
November1st to 15thDay
14%11%38%7%35%5%6%7%26%
1709
16th to endDay
12%13%5%8%5%35%5%7%7%24%
1560
December1st to 15thDay
10%12%49%6%45%5%5%8%27%
1560
16th to endDay
15%15%6%10%6%36%45%6%19%
1664
January1st to 15thNight
12%12%5%8%7%35%5%5%8%24%
2716
16th to endNight
12%12%48%6%245%6%7%30%
2896
February1st to 15thNight
11%11%5%8%7%45%46%6%27%
2432
16th to endNight
9%11%5%8%8%36%446%29%
1912
March1st to 15thNight
12%10%5%8%6%46%5%7%7%25%
2145
16th to endNight
9%11%48%7%46%6%6%8%27%
2003
April1st to 15thNight
11%11%47%5%446%5%7%31%
1799
16th to endNight
9%9%35%43445%6%42%
1743
May1st to 15thNight
7%5%24423447%52%
1445
16th to endNight
10%7%35%4246%5%8%41%
1496
June1st to 15thNight
10%5%35%324348%49%
1440
16th to endNight
5%314423345%60%
1440
July1st to 15thNight
112214345%71%
1440
16th to endNight
11212225%79%
1512
August1st to 15thNight
21222325%5%71%
1495
16th to endNight
112212225%78%
1895
September1st to 15thNight
221121223476%
1800
16th to endNight
5%414434345%58%
1935
October1st to 15thNight
8%6%3442335%7%49%
2159
16th to endNight
10%7%36%6%44446%42%
2413
November1st to 15thNight
14%9%47%7%36%5%6%7%27%
2478
16th to endNight
13%10%47%7%45%5%5%7%29%
2730
December1st to 15thNight
10%11%48%6%35%5%5%8%29%
2730
16th to endNight
13%15%5%8%7%35%46%6%22%
2912

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
13%10%5%7%7%5%6%5%5%9%22%
1552
16th to endDay
12%11%47%6%45%46%9%26%
1677
February1st to 15thDay
10%11%5%8%7%46%5%5%8%25%
1685
16th to endDay
10%11%49%7%36%5%6%7%26%
1561
March1st to 15thDay
10%15%7%9%8%46%5%5%6%19%
1812
16th to endDay
11%14%6%9%8%5%5%6%5%7%21%
2217
April1st to 15thDay
10%12%5%7%7%46%5%6%7%26%
2149
16th to endDay
10%10%37%5%3445%6%37%
2217
May1st to 15thDay
8%8%46%5%34446%43%
2502
16th to endDay
13%9%37%6%35%5%5%5%35%
2615
June1st to 15thDay
11%6%36%5%25%36%7%40%
2520
16th to endDay
7%414323446%56%
2520
July1st to 15thDay
2112312445%70%
2520
16th to endDay
1111212235%76%
2657
August1st to 15thDay
1112213345%71%
2463
16th to endDay
221112345%74%
2306
September1st to 15thDay
212312225%74%
2160
16th to endDay
7%425%5%2435%7%51%
2025
October1st to 15thDay
11%8%345%3445%7%42%
1800
16th to endDay
12%7%27%6%35%45%6%37%
1809
November1st to 15thDay
13%11%47%7%45%6%5%7%26%
1709
16th to endDay
12%12%6%9%5%346%5%8%24%
1560
December1st to 15thDay
10%12%5%8%7%36%6%5%7%25%
1560
16th to endDay
15%16%5%9%7%36%45%5%19%
1664
January1st to 15thNight
13%11%5%8%7%45%5%5%8%24%
2716
16th to endNight
12%13%47%6%345%5%7%30%
2896
February1st to 15thNight
11%11%48%7%46%46%6%27%
2432
16th to endNight
9%12%5%7%7%35%45%6%29%
1912
March1st to 15thNight
11%10%48%7%46%5%7%7%25%
2145
16th to endNight
9%10%38%7%36%6%5%9%27%
2007
April1st to 15thNight
11%9%5%7%5%36%5%6%8%31%
1799
16th to endNight
9%9%35%6%2445%6%42%
1743
May1st to 15thNight
7%5%2443445%6%52%
1445
16th to endNight
10%7%25%435%5%5%7%41%
1496
June1st to 15thNight
10%5%245%2435%6%49%
1440
16th to endNight
5%323324346%59%
1440
July1st to 15thNight
112214446%70%
1440
16th to endNight
1121133479%
1512
August1st to 15thNight
2111212347%70%
1495
16th to endNight
11221114477%
1895
September1st to 15thNight
211121223475%
1800
16th to endNight
5%41343345%5%57%
1935
October1st to 15thNight
8%6%35%334347%49%
2159
16th to endNight
11%6%26%7%44446%42%
2413
November1st to 15thNight
14%9%38%6%46%5%6%7%27%
2478
16th to endNight
13%10%46%7%36%5%5%6%30%
2730
December1st to 15thNight
10%13%5%7%6%35%5%5%8%28%
2730
16th to endNight
13%15%5%9%6%45%45%6%22%
2912

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
58%10%11%12%5%
1552
16th to endDay
53%9%15%12%5%3
1677
February1st to 15thDay
54%10%16%12%5%
1685
16th to endDay
57%10%12%15%3
1561
March1st to 15thDay
64%7%11%11%4
1812
16th to endDay
62%9%12%13%3
2217
April1st to 15thDay
56%8%13%15%5%
2149
16th to endDay
46%8%14%20%9%
2217
May1st to 15thDay
40%6%13%26%12%
2502
16th to endDay
50%8%12%20%7%
2619
June1st to 15thDay
43%8%10%22%13%2
2520
16th to endDay
28%411%28%21%5%
2520
July1st to 15thDay
16%48%19%32%19%
2371
16th to endDay
11%36%13%35%29%
2490
August1st to 15thDay
15%36%21%34%17%
2446
16th to endDay
13%37%26%35%13%
2306
September1st to 15thDay
14%27%25%34%14%
2160
16th to endDay
32%7%10%23%20%5%
2025
October1st to 15thDay
40%7%12%20%15%3
1800
16th to endDay
46%6%11%21%12%
1809
November1st to 15thDay
55%8%12%15%6%
1709
16th to endDay
56%9%14%11%8%
1560
December1st to 15thDay
56%8%14%13%5%
1560
16th to endDay
65%7%13%10%2
1664
January1st to 15thNight
57%9%14%12%6%
2716
16th to endNight
53%6%13%14%8%3
2896
February1st to 15thNight
56%9%15%11%6%
2444
16th to endNight
55%9%11%17%6%
1912
March1st to 15thNight
55%9%14%14%41
2145
16th to endNight
53%10%17%16%2
2007
April1st to 15thNight
51%9%15%18%5%
1799
16th to endNight
43%8%16%20%9%1
1743
May1st to 15thNight
33%6%15%28%15%
1446
16th to endNight
42%8%17%22%8%
1496
June1st to 15thNight
35%7%14%25%14%2
1440
16th to endNight
27%5%13%32%17%5%
1440
July1st to 15thNight
15%5%10%23%26%18%
1360
16th to endNight
10%36%18%35%25%
1416
August1st to 15thNight
14%49%24%31%16%
1487
16th to endNight
11%27%27%36%14%
1895
September1st to 15thNight
12%27%28%32%15%
1800
16th to endNight
28%6%10%24%21%8%
1935
October1st to 15thNight
35%6%12%25%17%3
2159
16th to endNight
43%6%12%18%16%2
2413
November1st to 15thNight
54%8%12%16%8%
2478
16th to endNight
53%8%14%12%10%
2730
December1st to 15thNight
52%9%15%15%5%
2730
16th to endNight
60%7%14%13%4
2912

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
14%6%23%22%30%3
90
16th to endDay
24%12%33%22%6%
109
February1st to 15thDay
20%20%24%24%8%1
273
16th to endDay
22%22%31%16%6%
235
March1st to 15thDay
22%31%26%15%4
270
16th to endDay
21%29%28%17%3
288
April1st to 15thDay
16%25%29%17%8%3
269
16th to endDay
15%25%32%13%8%2
270
May1st to 15thDay
15%22%28%21%10%1
288
16th to endDay
17%13%22%26%14%5%
330
June1st to 15thDay
10%18%27%24%14%4
315
16th to endDay
7%16%31%26%12%5%
315
July1st to 15thDay
6%9%36%28%16%3
305
16th to endDay
214%36%26%15%5%
327
August1st to 15thDay
29%33%30%17%6%
315
16th to endDay
49%24%30%24%6%
332
September1st to 15thDay
5%8%28%29%20%6%
315
16th to endDay
10%10%27%29%18%2
315
October1st to 15thDay
17%14%26%26%11%3
315
16th to endDay
16%13%24%25%13%5%
225
November1st to 15thDay
12%18%32%28%7%
133
16th to endDay
21%17%27%26%6%
90
December1st to 15thDay
15%18%28%18%8%8%
90
16th to endDay
20%16%30%23%8%
96
January1st to 15thNight
20%10%21%30%15%1
780
16th to endNight
19%8%18%35%17%1
832
February1st to 15thNight
18%8%22%35%14%
752
16th to endNight
15%12%26%30%13%1
632
March1st to 15thNight
16%9%26%31%13%1
720
16th to endNight
15%14%26%29%13%
768
April1st to 15thNight
15%10%25%28%18%1
719
16th to endNight
15%12%20%28%20%2
663
May1st to 15thNight
11%6%21%31%28%1
366
16th to endNight
11%6%19%30%28%4
375
June1st to 15thNight
10%6%18%39%22%3
360
16th to endNight
8%6%16%40%26%1
360
July1st to 15thNight
2112%42%39%2
340
16th to endNight
111%46%37%2
376
August1st to 15thNight
26%39%45%6%
415
16th to endNight
2211%37%38%7%
749
September1st to 15thNight
3112%33%40%7%
720
16th to endNight
8%5%14%34%31%6%
716
October1st to 15thNight
13%417%37%25%2
720
16th to endNight
14%6%16%35%23%3
768
November1st to 15thNight
19%9%20%38%11%
760
16th to endNight
20%12%19%31%15%2
780
December1st to 15thNight
18%10%19%34%15%1
780
16th to endNight
21%14%24%31%8%
832
Page generated at 2018-02-13 17:45:57. Version ac04

Copyright 2018 A. Danko


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