Wilkinson Memorial Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Wilkinson Memorial Observatory clear sky chart from 2005-11-05 to 2017-09-17.

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
41%
15541
16%
46740
10%
15510
47%
15510
26%
29467

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
28%
895
13%
2685
7%
895
34%
895
18%
1870
January16th to endNight
28%
927
17%
2772
7%
927
39%
927
20%
1850
February1st to 15thNight
39%
696
14%
2288
12%
696
45%
696
22%
1479
February16th to endNight
37%
632
15%
2052
10%
632
43%
632
19%
1385
March1st to 15thNight
36%
720
14%
2048
7%
720
43%
720
26%
1370
March16th to endNight
34%
750
13%
2094
7%
750
39%
750
20%
1489
April1st to 15thNight
40%
539
15%
1765
10%
539
46%
539
24%
1122
April16th to endNight
39%
540
16%
1603
12%
540
43%
540
23%
1093
May1st to 15thNight
51%
539
15%
1440
10%
539
54%
539
34%
906
May16th to endNight
39%
480
9%
1415
7%
478
41%
478
22%
963
June1st to 15thNight
46%
360
5%
1260
4%
360
48%
360
25%
745
June16th to endNight
52%
360
7%
1260
6%
360
55%
360
34%
664
July1st to 15thNight
60%
340
8%
1190
6%
340
64%
340
40%
571
July16th to endNight
66%
429
20%
1288
16%
403
72%
403
53%
576
August1st to 15thNight
63%
539
18%
1525
14%
536
68%
536
43%
845
August16th to endNight
64%
573
27%
1734
22%
573
67%
573
42%
913
September1st to 15thNight
56%
540
20%
1800
19%
540
61%
540
34%
992
September16th to endNight
53%
632
25%
1841
18%
632
62%
632
38%
1034
October1st to 15thNight
41%
660
22%
1980
11%
660
50%
660
29%
1204
October16th to endNight
40%
755
20%
2210
10%
755
48%
755
28%
1388
November1st to 15thNight
33%
875
20%
2450
8%
875
42%
875
28%
1531
November16th to endNight
30%
900
15%
2520
6%
900
37%
900
23%
1706
December1st to 15thNight
31%
900
11%
2640
6%
900
36%
900
20%
1858
December16th to endNight
32%
960
16%
2880
6%
960
41%
960
22%
1913

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%35%5%6%8%39%
48069
Night
6%6%36%5%35%5%6%8%40%
46891
Cloud CoverDay
8%7%36%6%35%5%6%8%39%
48070
Night
6%6%36%5%35%5%6%8%40%
46893
TransparencyDay
40%5%17%25%10%1
47724
Night
39%5%17%24%11%1
46740
SeeingDay
12%7%27%30%17%4
6096
Night
10%8%30%33%14%1
15555

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
5%10%49%6%5%6%6%7%8%29%
1253
16th to endDay
17%49%8%47%6%8%9%30%
1463
February1st to 15thDay
6%8%5%8%8%45%5%5%8%32%
1575
16th to endDay
5%10%5%12%12%45%6%7%8%22%
1422
March1st to 15thDay
35%49%8%5%6%5%7%10%33%
1910
16th to endDay
8%10%5%10%8%35%46%8%27%
2129
April1st to 15thDay
9%9%35%6%35%5%7%10%32%
2180
16th to endDay
14%9%36%43445%8%35%
2355
May1st to 15thDay
10%8%35%5%36%5%5%7%37%
2511
16th to endDay
20%8%37%5%35%5%5%6%29%
2697
June1st to 15thDay
14%7%35%5%35%6%5%8%33%
2700
16th to endDay
9%415%435%5%6%9%43%
2700
July1st to 15thDay
43144245%6%8%52%
2700
16th to endDay
421342445%8%58%
2792
August1st to 15thDay
6%424425%5%6%8%49%
2424
16th to endDay
6%313323338%58%
2468
September1st to 15thDay
11%5%14424345%51%
2160
16th to endDay
12%423323447%51%
1823
October1st to 15thDay
9%9%36%43445%7%42%
1650
16th to endDay
6%9%36%5%3447%9%39%
1648
November1st to 15thDay
5%8%35%435%6%7%9%40%
1408
16th to endDay
6%7%47%6%45%5%6%9%35%
1440
December1st to 15thDay
6%8%411%9%6%6%7%7%6%24%
1317
16th to endDay
5%10%39%9%36%6%6%8%30%
1344
January1st to 15thNight
47%5%8%6%5%6%7%7%8%31%
2685
16th to endNight
36%38%7%46%5%7%10%34%
2772
February1st to 15thNight
5%6%47%5%5%7%6%6%8%36%
2277
16th to endNight
48%6%8%8%46%5%6%9%31%
2052
March1st to 15thNight
46%37%7%36%6%7%10%35%
2048
16th to endNight
8%9%5%9%6%25%5%8%9%28%
2091
April1st to 15thNight
8%7%45%5%345%6%9%38%
1765
16th to endNight
12%8%46%5%3446%7%35%
1603
May1st to 15thNight
8%6%25%435%46%8%44%
1439
16th to endNight
17%6%37%5%2336%6%35%
1415
June1st to 15thNight
12%6%25%4335%6%7%42%
1260
16th to endNight
5%32343446%9%51%
1260
July1st to 15thNight
3215%42336%7%58%
1260
16th to endNight
311231435%9%62%
1376
August1st to 15thNight
6%413414447%56%
1533
16th to endNight
7%312324347%57%
1734
September1st to 15thNight
8%5%15%423446%53%
1800
16th to endNight
7%42242445%7%53%
1841
October1st to 15thNight
8%6%245%25%5%5%7%45%
1980
16th to endNight
6%8%26%43446%9%42%
2210
November1st to 15thNight
7%5%25%5%35%5%5%8%45%
2450
16th to endNight
5%9%37%6%45%5%6%7%37%
2520
December1st to 15thNight
48%5%9%8%46%6%6%10%28%
2640
16th to endNight
5%9%37%6%46%5%7%10%32%
2880

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
410%49%6%47%6%6%8%30%
1253
16th to endDay
17%49%8%48%7%8%8%30%
1463
February1st to 15thDay
5%8%5%9%7%5%6%5%6%8%32%
1575
16th to endDay
5%10%5%11%12%45%6%6%8%23%
1422
March1st to 15thDay
35%49%8%5%6%5%7%10%33%
1910
16th to endDay
8%9%5%11%8%35%5%6%8%27%
2130
April1st to 15thDay
9%9%36%6%45%5%7%10%32%
2180
16th to endDay
14%9%36%5%2446%7%35%
2355
May1st to 15thDay
10%8%35%5%45%5%5%7%37%
2511
16th to endDay
20%9%36%5%35%5%5%6%29%
2697
June1st to 15thDay
14%7%36%5%36%6%5%7%33%
2700
16th to endDay
9%415%5%35%6%7%9%43%
2700
July1st to 15thDay
4315%4245%6%9%52%
2700
16th to endDay
331332446%8%57%
2792
August1st to 15thDay
6%424425%5%6%8%48%
2424
16th to endDay
5%313423347%58%
2468
September1st to 15thDay
10%5%15%5%23345%50%
2160
16th to endDay
12%423322447%51%
1823
October1st to 15thDay
9%8%36%4235%5%8%42%
1650
16th to endDay
6%9%36%5%345%7%9%39%
1648
November1st to 15thDay
5%8%35%445%5%6%9%41%
1408
16th to endDay
6%7%47%5%45%6%6%9%34%
1440
December1st to 15thDay
6%8%411%9%5%8%8%6%6%24%
1317
16th to endDay
5%10%48%9%46%6%6%8%30%
1344
January1st to 15thNight
47%48%7%46%7%8%8%32%
2685
16th to endNight
36%38%7%46%6%7%10%34%
2772
February1st to 15thNight
5%6%47%5%47%6%6%8%36%
2277
16th to endNight
47%5%9%8%45%6%6%9%30%
2052
March1st to 15thNight
46%37%7%46%6%6%10%35%
2048
16th to endNight
7%9%5%9%6%35%5%7%9%28%
2094
April1st to 15thNight
8%7%46%5%35%5%6%8%38%
1765
16th to endNight
12%9%45%6%35%5%5%6%35%
1603
May1st to 15thNight
8%6%25%435%46%9%43%
1439
16th to endNight
17%6%46%6%3345%7%35%
1414
June1st to 15thNight
12%6%25%4335%6%6%42%
1260
16th to endNight
5%234435%46%9%51%
1260
July1st to 15thNight
321443335%8%57%
1260
16th to endNight
311222345%10%62%
1376
August1st to 15thNight
6%3135%2345%7%56%
1533
16th to endNight
7%31232445%7%57%
1734
September1st to 15thNight
8%5%245%24346%53%
1800
16th to endNight
7%42333445%7%53%
1841
October1st to 15thNight
8%7%245%25%5%5%7%45%
1980
16th to endNight
6%8%36%4245%5%9%42%
2210
November1st to 15thNight
7%5%25%5%25%5%5%8%45%
2450
16th to endNight
5%9%37%6%45%5%6%7%37%
2520
December1st to 15thNight
48%5%9%7%47%7%7%10%27%
2640
16th to endNight
49%37%7%36%5%8%10%32%
2880

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
50%6%15%21%5%
1253
16th to endDay
46%7%18%20%5%1
1463
February1st to 15thDay
49%417%21%6%
1575
16th to endDay
56%5%16%13%7%
1422
March1st to 15thDay
43%7%23%19%5%
1910
16th to endDay
52%5%18%20%3
2130
April1st to 15thDay
44%6%18%23%6%
2180
16th to endDay
46%316%23%7%1
2355
May1st to 15thDay
44%415%27%8%
2511
16th to endDay
54%414%19%6%
2701
June1st to 15thDay
46%6%15%21%8%
2700
16th to endDay
34%5%20%29%9%
2700
July1st to 15thDay
27%418%31%14%2
2541
16th to endDay
22%413%34%20%4
2617
August1st to 15thDay
30%5%17%28%15%2
2408
16th to endDay
25%312%33%20%4
2468
September1st to 15thDay
34%312%28%17%3
2160
16th to endDay
32%412%31%17%2
1823
October1st to 15thDay
39%320%27%8%
1650
16th to endDay
39%5%21%25%7%
1648
November1st to 15thDay
38%5%21%27%6%
1408
16th to endDay
44%6%18%19%10%1
1440
December1st to 15thDay
55%6%18%17%1
1317
16th to endDay
49%5%19%19%5%
1344
January1st to 15thNight
45%8%18%21%41
2685
16th to endNight
42%6%17%22%8%1
2772
February1st to 15thNight
43%5%18%23%8%1
2288
16th to endNight
48%416%21%9%
2052
March1st to 15thNight
41%6%21%19%9%
2048
16th to endNight
48%6%15%21%7%
2094
April1st to 15thNight
40%6%15%25%10%1
1765
16th to endNight
47%313%22%11%2
1603
May1st to 15thNight
35%5%13%31%13%
1440
16th to endNight
48%416%20%10%
1415
June1st to 15thNight
38%419%23%12%
1260
16th to endNight
29%420%32%12%
1260
July1st to 15thNight
24%316%30%21%4
1190
16th to endNight
15%315%35%23%5%
1288
August1st to 15thNight
26%414%35%15%3
1525
16th to endNight
25%39%30%23%6%
1734
September1st to 15thNight
31%310%26%18%8%
1800
16th to endNight
28%414%29%18%3
1841
October1st to 15thNight
36%417%28%12%1
1980
16th to endNight
37%5%17%26%12%
2210
November1st to 15thNight
35%6%19%25%11%1
2450
16th to endNight
43%5%23%18%8%
2520
December1st to 15thNight
49%5%21%19%4
2640
16th to endNight
44%5%18%24%7%
2880

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
8%5%20%23%31%11%
60
16th to endDay
6%7%31%23%25%5%
77
February1st to 15thDay
13%12%33%31%10%
90
16th to endDay
14%228%37%17%
81
March1st to 15thDay
6%15%44%25%6%1
213
16th to endDay
10%9%40%26%10%2
288
April1st to 15thDay
11%14%36%27%8%1
269
16th to endDay
23%10%25%26%13%1
285
May1st to 15thDay
15%5%25%30%17%5%
468
16th to endDay
21%7%22%24%18%5%
517
June1st to 15thDay
13%9%26%30%17%2
495
16th to endDay
11%8%26%32%17%4
495
July1st to 15thDay
6%423%37%24%4
475
16th to endDay
5%427%36%22%3
515
August1st to 15thDay
9%5%23%33%21%6%
398
16th to endDay
7%7%19%38%22%4
332
September1st to 15thDay
13%5%27%33%14%4
315
16th to endDay
18%8%24%25%17%5%
224
October1st to 15thDay
27%6%26%25%11%2
90
16th to endDay
13%5%26%28%21%5%
96
November1st to 15thDay
6%7%41%31%13%
90
16th to endDay
5%15%33%23%14%7%
90
December1st to 15thDay
5%8%44%27%8%4
69
16th to endDay
10%10%39%31%43
64
January1st to 15thNight
8%14%37%27%10%2
900
16th to endNight
7%17%36%26%9%1
927
February1st to 15thNight
8%9%30%32%16%2
704
16th to endNight
7%9%28%36%14%3
632
March1st to 15thNight
7%8%38%29%13%2
720
16th to endNight
12%8%32%32%12%2
750
April1st to 15thNight
12%7%33%34%10%1
539
16th to endNight
17%7%24%34%14%1
540
May1st to 15thNight
11%6%23%39%17%2
540
16th to endNight
18%7%21%31%17%3
480
June1st to 15thNight
16%5%25%34%16%1
360
16th to endNight
7%5%29%40%17%
360
July1st to 15thNight
6%422%46%18%1
340
16th to endNight
45%20%44%22%2
429
August1st to 15thNight
8%220%41%23%2
539
16th to endNight
9%417%41%25%1
573
September1st to 15thNight
12%223%34%22%3
540
16th to endNight
9%426%39%17%2
632
October1st to 15thNight
12%7%31%31%15%2
660
16th to endNight
10%9%29%37%12%1
755
November1st to 15thNight
10%13%37%28%9%1
875
16th to endNight
10%11%37%31%8%
900
December1st to 15thNight
9%9%36%29%13%1
900
16th to endNight
10%11%33%31%11%1
960
Page generated at 2017-09-18 06:38:24. Version ac04

Copyright 2017 A. Danko


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