Willow Slough Fish and Wildlife Area
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Willow Slough Fish and Wildlife Area clear sky chart from 2005-11-05 to 2018-03-21.

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
38%
16721
18%
49192
11%
16679
44%
16679
23%
33116

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
19%
975
13%
2716
5%
970
27%
970
17%
2019
January16th to endNight
21%
1040
13%
2883
5%
1040
27%
1040
16%
2174
February1st to 15thNight
21%
816
13%
2347
4%
816
28%
816
17%
1690
February16th to endNight
24%
683
16%
2049
7%
683
33%
683
16%
1489
March1st to 15thNight
25%
780
14%
2340
8%
780
30%
780
18%
1652
March16th to endNight
28%
675
16%
2090
8%
675
37%
675
20%
1456
April1st to 15thNight
27%
539
15%
1797
10%
539
37%
539
21%
1181
April16th to endNight
33%
540
19%
1725
12%
540
42%
540
22%
1167
May1st to 15thNight
37%
540
15%
1620
9%
540
42%
540
21%
1131
May16th to endNight
53%
562
17%
1529
10%
561
58%
561
30%
1016
June1st to 15thNight
54%
540
18%
1440
12%
540
58%
540
38%
889
June16th to endNight
53%
540
17%
1440
10%
540
58%
540
32%
927
July1st to 15thNight
63%
510
17%
1360
13%
510
65%
510
38%
823
July16th to endNight
71%
564
23%
1417
17%
531
74%
531
43%
834
August1st to 15thNight
74%
539
21%
1607
20%
536
75%
536
39%
926
August16th to endNight
68%
573
21%
1910
22%
573
72%
573
32%
1098
September1st to 15thNight
65%
564
28%
1824
28%
564
69%
564
35%
1026
September16th to endNight
63%
717
30%
1980
23%
717
67%
717
38%
1161
October1st to 15thNight
50%
720
26%
2035
20%
720
56%
720
33%
1242
October16th to endNight
30%
768
20%
2454
13%
768
39%
768
21%
1588
November1st to 15thNight
33%
760
23%
2471
16%
760
44%
760
24%
1528
November16th to endNight
28%
780
19%
2535
12%
780
37%
780
20%
1699
December1st to 15thNight
21%
956
12%
2711
5%
956
28%
956
16%
2027
December16th to endNight
17%
1040
11%
2912
3%
1040
24%
1040
11%
2373

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
14%7%36%5%3445%7%36%
49667
Night
14%8%36%5%24446%39%
49360
Cloud CoverDay
14%8%36%5%345%5%7%36%
49676
Night
14%8%36%5%24446%39%
49365
TransparencyDay
46%6%11%20%12%1
49353
Night
45%5%11%21%14%2
49192
SeeingDay
16%7%26%24%17%7%
6512
Night
18%8%28%29%13%1
16725

By Month

Percentage Cloud Cover NE (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
18%14%5%7%6%4434425%
1552
16th to endDay
14%15%7%8%434436%26%
1692
February1st to 15thDay
17%11%5%7%6%35%446%27%
1844
16th to endDay
17%11%47%6%34345%30%
1710
March1st to 15thDay
18%12%47%5%24446%29%
1940
16th to endDay
17%9%47%5%25%5%47%29%
2271
April1st to 15thDay
18%9%35%5%24346%35%
2151
16th to endDay
19%7%245%3445%6%35%
2234
May1st to 15thDay
19%9%35%5%33446%31%
2331
16th to endDay
12%6%36%5%35%5%6%8%37%
2584
June1st to 15thDay
10%425%5%345%5%8%43%
2520
16th to endDay
9%335%6%35%6%6%11%37%
2520
July1st to 15thDay
8%5%15%5%36%5%6%8%42%
2520
16th to endDay
6%3245%45%6%7%10%42%
2655
August1st to 15thDay
6%425%6%35%5%6%9%45%
2342
16th to endDay
8%5%25%6%245%6%8%43%
2292
September1st to 15thDay
12%5%245%2445%7%45%
2124
16th to endDay
9%5%24425%45%8%47%
1980
October1st to 15thDay
16%6%25%43345%6%41%
1923
16th to endDay
17%7%36%5%3445%6%34%
1770
November1st to 15thDay
16%6%33423347%44%
1717
16th to endDay
17%8%46%5%24346%37%
1755
December1st to 15thDay
18%11%49%5%35%435%27%
1576
16th to endDay
20%15%6%6%5%23436%22%
1664
January1st to 15thNight
19%11%47%5%2435%431%
2716
16th to endNight
14%13%6%8%6%34436%28%
2883
February1st to 15thNight
17%11%5%7%5%23335%33%
2345
16th to endNight
17%11%47%5%24445%31%
2049
March1st to 15thNight
17%10%45%5%23446%34%
2327
16th to endNight
15%8%36%5%35%5%5%7%34%
2090
April1st to 15thNight
16%7%36%5%24436%38%
1797
16th to endNight
17%7%36%434346%38%
1725
May1st to 15thNight
19%6%25%5%25%45%7%35%
1620
16th to endNight
9%426%5%35%46%8%43%
1527
June1st to 15thNight
10%5%2442345%8%49%
1440
16th to endNight
7%5%25%5%3446%9%43%
1440
July1st to 15thNight
7%314425%45%9%51%
1440
16th to endNight
43145%25%45%9%52%
1513
August1st to 15thNight
43145%25%5%6%11%50%
1616
16th to endNight
8%4244245%5%7%50%
1910
September1st to 15thNight
11%413323346%53%
1824
16th to endNight
7%32433445%9%50%
1980
October1st to 15thNight
13%5%25%323336%50%
2035
16th to endNight
17%8%36%413245%41%
2454
November1st to 15thNight
13%7%2443335%6%43%
2471
16th to endNight
18%8%35%42335%6%37%
2535
December1st to 15thNight
19%12%48%42433431%
2711
16th to endNight
21%15%5%9%6%35%43422%
2912

Percentage Cloud Cover SE (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
18%15%47%7%3434425%
1552
16th to endDay
14%15%7%8%5%24446%26%
1692
February1st to 15thDay
17%11%5%8%5%35%45%6%26%
1844
16th to endDay
17%12%47%6%34345%30%
1710
March1st to 15thDay
18%12%48%424446%29%
1950
16th to endDay
17%9%47%5%25%5%47%29%
2270
April1st to 15thDay
18%9%35%5%24446%35%
2151
16th to endDay
19%7%35%6%2445%6%34%
2234
May1st to 15thDay
20%9%36%43445%6%31%
2331
16th to endDay
11%6%36%5%35%5%6%8%37%
2584
June1st to 15thDay
10%4246%345%5%8%43%
2520
16th to endDay
9%426%5%46%6%7%10%37%
2520
July1st to 15thDay
8%425%5%36%5%6%8%42%
2520
16th to endDay
6%3245%45%7%7%10%41%
2655
August1st to 15thDay
6%4246%35%5%6%8%45%
2342
16th to endDay
8%5%246%35%5%6%8%43%
2292
September1st to 15thDay
11%5%244245%6%6%45%
2124
16th to endDay
8%425%435%45%8%47%
1980
October1st to 15thDay
15%7%25%42445%6%41%
1923
16th to endDay
17%7%26%6%2445%6%34%
1770
November1st to 15thDay
16%6%245%22346%44%
1717
16th to endDay
17%8%46%433337%37%
1755
December1st to 15thDay
17%12%5%8%6%34445%27%
1576
16th to endDay
20%15%6%7%6%23446%23%
1664
January1st to 15thNight
19%11%47%5%3335%431%
2716
16th to endNight
14%13%6%8%6%34446%28%
2883
February1st to 15thNight
17%11%5%7%5%23335%33%
2338
16th to endNight
17%12%47%5%2445%5%31%
2049
March1st to 15thNight
17%11%46%423445%34%
2340
16th to endNight
15%8%46%5%2446%7%34%
2090
April1st to 15thNight
15%7%36%5%25%446%37%
1797
16th to endNight
17%7%36%5%3435%5%38%
1725
May1st to 15thNight
19%6%35%5%3445%7%34%
1619
16th to endNight
9%426%6%35%45%8%43%
1527
June1st to 15thNight
9%5%2342335%8%50%
1440
16th to endNight
7%435%6%445%5%10%43%
1440
July1st to 15thNight
7%32442435%9%51%
1440
16th to endNight
43145%25%45%8%53%
1513
August1st to 15thNight
33144445%6%11%49%
1616
16th to endNight
8%325%4245%5%7%50%
1910
September1st to 15thNight
10%414423347%53%
1824
16th to endNight
7%42442445%8%51%
1980
October1st to 15thNight
13%5%24323336%50%
2035
16th to endNight
18%7%36%423335%41%
2454
November1st to 15thNight
13%7%2443445%7%43%
2471
16th to endNight
18%8%34424346%36%
2535
December1st to 15thNight
19%11%5%8%424335%30%
2711
16th to endNight
21%15%5%8%6%3443422%
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
62%310%13%9%
1553
16th to endDay
58%412%16%6%
1692
February1st to 15thDay
58%5%11%16%7%1
1846
16th to endDay
56%5%10%21%5%1
1710
March1st to 15thDay
55%5%11%19%7%
1950
16th to endDay
54%5%13%21%5%
2271
April1st to 15thDay
48%5%10%20%13%
2151
16th to endDay
48%6%11%17%11%4
2234
May1st to 15thDay
52%6%11%21%8%
2331
16th to endDay
42%7%11%19%15%2
2588
June1st to 15thDay
36%7%11%23%18%1
2520
16th to endDay
38%8%13%19%17%2
2520
July1st to 15thDay
39%7%11%21%17%3
2371
16th to endDay
34%9%16%23%13%2
2488
August1st to 15thDay
34%8%13%25%17%1
2327
16th to endDay
36%7%13%21%16%4
2292
September1st to 15thDay
36%7%10%23%16%5%
2124
16th to endDay
34%5%9%25%22%2
1980
October1st to 15thDay
42%5%10%23%15%2
1923
16th to endDay
49%412%21%11%
1770
November1st to 15thDay
40%412%22%16%3
1717
16th to endDay
48%412%23%10%
1755
December1st to 15thDay
58%5%10%18%6%
1576
16th to endDay
63%5%12%12%5%
1664
January1st to 15thNight
55%410%17%11%1
2716
16th to endNight
57%413%16%8%
2883
February1st to 15thNight
54%312%19%9%1
2347
16th to endNight
54%5%11%19%9%1
2049
March1st to 15thNight
51%411%19%10%2
2340
16th to endNight
47%7%14%20%9%1
2090
April1st to 15thNight
46%311%21%14%1
1797
16th to endNight
46%5%8%19%13%4
1725
May1st to 15thNight
47%6%11%21%11%
1620
16th to endNight
38%8%12%18%18%3
1529
June1st to 15thNight
32%5%12%24%22%2
1440
16th to endNight
35%7%13%22%17%3
1440
July1st to 15thNight
31%5%13%26%19%3
1360
16th to endNight
27%5%15%27%19%3
1417
August1st to 15thNight
26%8%15%25%20%2
1607
16th to endNight
31%7%10%24%20%5%
1910
September1st to 15thNight
31%49%25%21%6%
1824
16th to endNight
29%5%8%27%24%3
1980
October1st to 15thNight
35%38%27%22%1
2035
16th to endNight
44%39%26%14%1
2454
November1st to 15thNight
40%49%24%16%4
2471
16th to endNight
47%412%23%10%
2535
December1st to 15thNight
57%39%17%10%
2711
16th to endNight
66%48%13%6%
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
29%10%31%22%6%
135
16th to endDay
21%14%37%23%2
144
February1st to 15thDay
23%19%40%16%
135
16th to endDay
29%14%30%17%7%1
120
March1st to 15thDay
26%17%29%25%1
135
16th to endDay
26%9%28%25%8%1
282
April1st to 15thDay
23%10%30%21%11%2
270
16th to endDay
23%7%28%22%12%4
270
May1st to 15thDay
24%9%29%20%12%3
288
16th to endDay
16%6%31%24%15%5%
484
June1st to 15thDay
11%428%30%18%6%
495
16th to endDay
12%6%32%27%16%5%
495
July1st to 15thDay
10%326%28%17%13%
475
16th to endDay
6%118%32%26%13%
515
August1st to 15thDay
8%115%26%28%19%
357
16th to endDay
11%119%24%28%15%
332
September1st to 15thDay
13%414%25%30%10%
315
16th to endDay
8%5%14%27%31%12%
314
October1st to 15thDay
17%5%25%24%22%4
258
16th to endDay
22%13%30%27%5%
144
November1st to 15thDay
18%6%30%20%17%7%
135
16th to endDay
25%13%40%14%5%
135
December1st to 15thDay
16%21%38%16%5%1
135
16th to endDay
26%23%40%6%2
144
January1st to 15thNight
25%13%35%20%4
975
16th to endNight
20%13%34%27%3
1040
February1st to 15thNight
24%10%36%23%4
819
16th to endNight
23%11%34%25%4
683
March1st to 15thNight
23%10%36%23%5%
780
16th to endNight
18%9%38%24%8%
675
April1st to 15thNight
18%11%36%25%6%
539
16th to endNight
20%7%34%27%9%
540
May1st to 15thNight
21%430%32%9%
540
16th to endNight
9%326%39%19%1
563
June1st to 15thNight
10%323%45%15%
540
16th to endNight
9%325%40%19%1
540
July1st to 15thNight
9%218%40%27%1
510
16th to endNight
5%114%40%34%3
564
August1st to 15thNight
5%10%47%30%5%
539
16th to endNight
9%112%36%35%4
573
September1st to 15thNight
12%412%36%30%3
564
16th to endNight
9%317%32%33%3
717
October1st to 15thNight
16%5%22%34%18%1
720
16th to endNight
21%11%32%24%9%
768
November1st to 15thNight
17%9%34%25%10%1
760
16th to endNight
22%12%32%24%8%
780
December1st to 15thNight
25%12%32%22%5%
956
16th to endNight
30%11%32%22%3
1040
Page generated at 2018-03-22 10:34:26. Version ac04

Copyright 2018 A. Danko


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