Meyer-Womble Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Meyer-Womble Observatory clear sky chart from 2005-11-05 to 2017-08-12.

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
31%
15823
26%
46506
9%
15776
48%
15776
28%
25510

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%
900
29%
2506
7%
895
40%
895
23%
1312
January16th to endNight
15%
780
33%
2508
8%
780
44%
780
26%
1220
February1st to 15thNight
15%
700
24%
2264
4%
696
38%
696
17%
1177
February16th to endNight
12%
632
31%
1894
3%
632
41%
632
22%
1011
March1st to 15thNight
20%
720
27%
2088
5%
720
39%
720
23%
1148
March16th to endNight
20%
696
25%
2040
6%
696
38%
696
22%
1157
April1st to 15thNight
20%
539
24%
1798
7%
539
41%
539
24%
949
April16th to endNight
24%
540
22%
1800
9%
540
42%
540
22%
1018
May1st to 15thNight
29%
540
18%
1611
5%
540
43%
540
23%
1013
May16th to endNight
40%
563
18%
1498
8%
561
50%
561
31%
912
June1st to 15thNight
48%
540
23%
1440
12%
540
57%
540
45%
759
June16th to endNight
60%
540
26%
1440
17%
540
67%
540
49%
751
July1st to 15thNight
65%
510
17%
1360
13%
510
69%
510
32%
854
July16th to endNight
69%
564
19%
1475
16%
531
71%
531
36%
877
August1st to 15thNight
61%
527
16%
1611
15%
524
64%
524
30%
966
August16th to endNight
62%
525
23%
1750
21%
525
68%
525
31%
1016
September1st to 15thNight
55%
495
28%
1650
21%
495
67%
495
32%
913
September16th to endNight
53%
506
33%
1771
23%
506
68%
506
38%
875
October1st to 15thNight
33%
660
30%
1980
12%
660
48%
660
33%
1042
October16th to endNight
30%
711
32%
2119
10%
711
48%
711
31%
1115
November1st to 15thNight
25%
875
32%
2275
8%
875
43%
875
33%
1224
November16th to endNight
20%
900
33%
2420
7%
900
41%
900
30%
1275
December1st to 15thNight
14%
900
23%
2520
2%
900
33%
900
21%
1364
December16th to endNight
16%
960
24%
2688
5%
960
34%
960
19%
1562

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
5%7%36%6%35%5%5%7%42%
47478
Night
242442445%9%55%
46684
TransparencyDay
38%7%11%22%16%4
47158
Night
24%6%15%28%19%5%
46506
SeeingDay
15%25%27%20%9%2
5694
Night
7%26%28%23%12%1
15827

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 15thDay
346%345%5%6%9%51%
1432
16th to endDay
336%6%3445%8%53%
1725
February1st to 15thDay
337%6%25%5%6%12%45%
1596
16th to endDay
348%6%35%5%5%8%50%
1580
March1st to 15thDay
16%35%6%45%35%8%46%
1869
16th to endDay
29%47%5%36%47%9%38%
2184
April1st to 15thDay
310%36%6%36%46%7%41%
2150
16th to endDay
6%16%5%8%6%345%45%33%
2160
May1st to 15thDay
8%14%5%7%6%35%5%5%7%31%
2337
16th to endDay
10%11%47%6%45%45%6%32%
2616
June1st to 15thDay
7%5%36%5%45%5%5%7%42%
2520
16th to endDay
5%435%5%36%6%6%7%46%
2520
July1st to 15thDay
11%6%38%7%46%6%5%6%33%
2520
16th to endDay
11%7%48%7%46%6%6%7%28%
2591
August1st to 15thDay
14%8%48%7%45%5%5%5%28%
2252
16th to endDay
11%7%48%6%36%45%6%35%
2100
September1st to 15thDay
11%7%26%434345%45%
1980
16th to endDay
5%6%25%5%245%45%51%
1857
October1st to 15thDay
7%6%36%5%24345%50%
1650
16th to endDay
46%25%3235%47%52%
1741
November1st to 15thDay
142332446%9%57%
1583
16th to endDay
315%42336%8%59%
1539
December1st to 15thDay
327%6%4445%9%51%
1440
16th to endDay
336%6%35%46%10%49%
1536
January1st to 15thNight
2134345%6%10%59%
2506
16th to endNight
22442235%9%61%
2508
February1st to 15thNight
23432446%10%56%
2254
16th to endNight
3245%2445%10%56%
1894
March1st to 15thNight
4244245%6%8%55%
2088
16th to endNight
35%3431435%8%54%
2040
April1st to 15thNight
16%1432446%9%56%
1798
16th to endNight
49%35%323448%49%
1800
May1st to 15thNight
7%9%25%3345%6%8%43%
1610
16th to endNight
6%5%24435%46%9%47%
1497
June1st to 15thNight
32112235%5%10%59%
1440
16th to endNight
2233235%6%8%61%
1440
July1st to 15thNight
45%245%37%5%6%10%43%
1440
16th to endNight
5%4245%35%47%10%45%
1576
August1st to 15thNight
6%6%245%25%5%5%8%46%
1620
16th to endNight
7%425%5%345%6%8%47%
1750
September1st to 15thNight
7%5%15%325%46%8%50%
1650
16th to endNight
3313323445%61%
1771
October1st to 15thNight
4313314447%60%
1980
16th to endNight
25%24313346%60%
2119
November1st to 15thNight
41232335%10%62%
2275
16th to endNight
32332445%9%60%
2420
December1st to 15thNight
41442335%9%58%
2520
16th to endNight
325%5%345%5%9%54%
2688

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
27%6%20%25%15%3
1433
16th to endDay
27%6%14%28%16%5%
1725
February1st to 15thDay
30%8%18%26%12%3
1597
16th to endDay
30%7%11%28%18%3
1580
March1st to 15thDay
34%5%12%28%16%2
1869
16th to endDay
38%7%10%28%11%3
2184
April1st to 15thDay
39%6%11%21%14%4
2150
16th to endDay
50%5%8%21%11%2
2160
May1st to 15thDay
50%6%10%20%11%
2337
16th to endDay
50%6%9%20%10%2
2620
June1st to 15thDay
38%7%10%15%20%7%
2520
16th to endDay
33%6%7%22%22%7%
2520
July1st to 15thDay
47%8%9%14%13%6%
2371
16th to endDay
48%10%11%16%8%3
2429
August1st to 15thDay
52%9%8%11%12%5%
2237
16th to endDay
45%8%8%20%14%3
2100
September1st to 15thDay
39%6%6%17%20%9%
1980
16th to endDay
30%7%7%23%26%3
1857
October1st to 15thDay
35%5%6%23%25%3
1650
16th to endDay
27%7%8%25%25%5%
1741
November1st to 15thDay
23%6%14%23%24%8%
1583
16th to endDay
21%5%12%30%21%6%
1539
December1st to 15thDay
28%8%17%29%14%1
1440
16th to endDay
28%9%16%24%15%4
1536
January1st to 15thNight
18%6%20%31%18%4
2506
16th to endNight
20%415%32%20%7%
2508
February1st to 15thNight
22%7%16%34%15%3
2264
16th to endNight
22%5%12%33%20%5%
1894
March1st to 15thNight
23%6%13%32%20%4
2088
16th to endNight
26%7%13%32%16%3
2040
April1st to 15thNight
24%7%12%31%18%4
1798
16th to endNight
32%5%15%29%15%1
1800
May1st to 15thNight
37%6%15%24%14%1
1611
16th to endNight
31%6%18%27%13%2
1498
June1st to 15thNight
17%8%16%26%21%9%
1440
16th to endNight
18%6%11%27%24%11%
1440
July1st to 15thNight
33%9%14%20%15%7%
1360
16th to endNight
30%7%20%24%12%4
1475
August1st to 15thNight
33%8%16%19%15%6%
1611
16th to endNight
32%7%13%25%17%3
1750
September1st to 15thNight
30%5%12%21%19%10%
1650
16th to endNight
22%6%9%33%25%3
1771
October1st to 15thNight
22%5%12%29%24%5%
1980
16th to endNight
23%411%28%27%4
2119
November1st to 15thNight
18%6%13%27%24%10%
2275
16th to endNight
19%5%12%30%24%6%
2420
December1st to 15thNight
22%6%22%28%16%3
2520
16th to endNight
25%9%18%26%16%3
2688

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%42%16%16%14%1
90
16th to endDay
7%40%29%21%1
96
February1st to 15thDay
15%60%17%6%
90
16th to endDay
11%46%23%14%3
81
March1st to 15thDay
15%44%24%13%1
159
16th to endDay
16%46%27%9%
288
April1st to 15thDay
20%36%28%11%2
269
16th to endDay
26%41%21%8%1
270
May1st to 15thDay
17%26%31%17%5%
396
16th to endDay
19%20%28%18%10%2
517
June1st to 15thDay
9%21%29%24%12%2
495
16th to endDay
5%12%35%26%17%3
495
July1st to 15thDay
15%8%22%26%19%6%
475
16th to endDay
13%9%20%29%19%8%
450
August1st to 15thDay
20%13%30%26%9%1
300
16th to endDay
20%11%28%29%8%1
268
September1st to 15thDay
17%28%34%16%3
255
16th to endDay
8%18%35%22%10%4
148
October1st to 15thDay
6%33%25%17%14%2
90
16th to endDay
20%27%26%18%6%1
96
November1st to 15thDay
6%30%20%23%15%4
90
16th to endDay
14%42%33%7%2
90
December1st to 15thDay
16%54%21%6%1
90
16th to endDay
456%26%11%11
96
January1st to 15thNight
10%40%26%14%7%1
900
16th to endNight
9%35%35%14%5%
780
February1st to 15thNight
8%41%31%14%4
704
16th to endNight
5%42%33%14%3
632
March1st to 15thNight
5%37%31%16%7%
720
16th to endNight
8%34%34%19%3
696
April1st to 15thNight
8%27%39%18%4
539
16th to endNight
10%28%32%22%6%
540
May1st to 15thNight
13%16%35%24%9%1
540
16th to endNight
10%13%28%29%16%1
563
June1st to 15thNight
7%10%32%34%14%1
540
16th to endNight
35%24%40%23%2
540
July1st to 15thNight
8%213%36%35%4
510
16th to endNight
7%28%35%39%6%
564
August1st to 15thNight
9%212%42%30%3
527
16th to endNight
7%415%38%28%6%
525
September1st to 15thNight
8%424%37%18%5%
495
16th to endNight
6%10%24%32%23%3
506
October1st to 15thNight
6%24%32%20%13%1
660
16th to endNight
7%29%28%21%10%3
711
November1st to 15thNight
6%33%30%18%8%1
875
16th to endNight
5%36%34%17%5%
900
December1st to 15thNight
9%41%31%13%3
900
16th to endNight
6%41%30%16%5%
960
Page generated at 2017-08-13 12:16:32. Version ac04

Copyright 2017 A. Danko


Meyer-Womble Observatory Clear Sky Chart | Charts Home