Walter F. Barber, Jr. Memorial Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Walter F. Barber, Jr. Memorial Observatory clear sky chart from 2005-11-05 to 2017-09-19.

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
46%
15437
23%
46966
15%
15394
55%
15394
28%
28652

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
25%
720
24%
2327
9%
716
42%
716
20%
1441
January16th to endNight
24%
768
25%
2409
11%
768
40%
768
20%
1560
February1st to 15thNight
25%
704
24%
2111
9%
701
40%
701
24%
1319
February16th to endNight
22%
631
24%
1893
8%
631
36%
631
23%
1190
March1st to 15thNight
28%
720
23%
2088
10%
720
40%
720
25%
1307
March16th to endNight
37%
768
22%
2112
11%
768
45%
768
30%
1305
April1st to 15thNight
39%
593
25%
1851
16%
593
51%
593
31%
1062
April16th to endNight
46%
540
26%
1734
17%
540
56%
540
32%
975
May1st to 15thNight
50%
540
23%
1620
12%
540
60%
540
33%
978
May16th to endNight
61%
561
22%
1682
16%
561
66%
561
34%
1003
June1st to 15thNight
71%
540
17%
1620
14%
540
72%
540
33%
988
June16th to endNight
76%
540
18%
1620
15%
540
77%
540
36%
955
July1st to 15thNight
72%
510
15%
1530
13%
510
73%
510
31%
965
July16th to endNight
70%
564
16%
1595
14%
531
72%
531
29%
1018
August1st to 15thNight
74%
539
19%
1690
21%
536
74%
536
31%
1037
August16th to endNight
65%
573
20%
1910
22%
573
67%
573
23%
1251
September1st to 15thNight
64%
681
20%
1941
19%
681
65%
681
30%
1248
September16th to endNight
58%
673
25%
1858
19%
673
63%
673
32%
1168
October1st to 15thNight
53%
660
34%
1815
25%
660
61%
660
40%
1048
October16th to endNight
49%
704
33%
2108
24%
704
61%
704
36%
1165
November1st to 15thNight
46%
700
30%
2276
23%
700
59%
700
35%
1217
November16th to endNight
38%
720
27%
2340
17%
720
52%
720
27%
1339
December1st to 15thNight
31%
720
23%
2340
13%
720
45%
720
23%
1447
December16th to endNight
27%
768
20%
2496
12%
768
39%
768
19%
1666

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
12%5%25%5%35%5%5%7%39%
47842
Night
11%5%2443445%7%45%
47166
TransparencyDay
41%6%11%19%17%4
47543
Night
36%5%11%20%20%6%
46969
SeeingDay
15%7%20%22%21%13%
5326
Night
14%9%23%26%21%4
15439

By Month

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
16%7%35%424245%42%
1611
16th to endDay
15%7%34324445%43%
1812
February1st to 15thDay
14%7%345%34436%42%
1750
16th to endDay
17%6%25%4235%3442%
1580
March1st to 15thDay
15%7%27%5%33345%40%
1871
16th to endDay
14%7%35%5%3445%6%39%
2111
April1st to 15thDay
12%6%25%5%34445%44%
2106
16th to endDay
11%4235%33448%47%
2226
May1st to 15thDay
10%6%346%36%446%42%
2331
16th to endDay
9%5%26%5%45%6%6%9%39%
2431
June1st to 15thDay
9%6%27%7%46%7%7%10%30%
2340
16th to endDay
4325%6%46%7%7%10%40%
2340
July1st to 15thDay
9%5%37%8%6%8%7%7%9%26%
2340
16th to endDay
7%426%7%49%8%9%10%28%
2465
August1st to 15thDay
7%416%7%48%8%9%10%30%
2256
16th to endDay
13%6%37%7%5%7%6%7%8%25%
2292
September1st to 15thDay
13%6%25%5%46%6%6%8%34%
2007
16th to endDay
16%6%25%5%24445%41%
1848
October1st to 15thDay
14%415%323345%51%
1815
16th to endDay
13%31341333457%
1760
November1st to 15thDay
13%6%23312345%53%
1582
16th to endDay
14%5%24324345%49%
1620
December1st to 15thDay
16%6%26%5%3335%6%40%
1620
16th to endDay
22%8%35%5%33335%34%
1728
January1st to 15thNight
15%7%24324445%43%
2327
16th to endNight
16%7%345%23345%41%
2409
February1st to 15thNight
14%5%25%5%34346%44%
2103
16th to endNight
16%5%25%424346%44%
1893
March1st to 15thNight
14%5%235%24447%45%
2088
16th to endNight
10%6%25%424447%48%
2112
April1st to 15thNight
10%42432445%7%49%
1851
16th to endNight
9%42442345%7%51%
1734
May1st to 15thNight
8%323445%47%6%47%
1619
16th to endNight
6%4245%345%6%10%46%
1682
June1st to 15thNight
43245%47%5%7%12%43%
1620
16th to endNight
3215%5%35%5%7%14%43%
1620
July1st to 15thNight
6%3246%46%6%7%12%38%
1620
16th to endNight
5%326%6%46%6%7%13%36%
1703
August1st to 15thNight
5%5%145%45%6%7%12%39%
1701
16th to endNight
12%6%35%5%445%7%9%36%
1910
September1st to 15thNight
9%5%25%5%35%5%5%9%42%
1941
16th to endNight
12%6%2442335%7%47%
1858
October1st to 15thNight
11%5%13213347%54%
1815
16th to endNight
9%42442332459%
2108
November1st to 15thNight
10%413423245%56%
2276
16th to endNight
11%5%24423445%50%
2340
December1st to 15thNight
13%8%26%42335%5%43%
2340
16th to endNight
20%7%36%42435%6%36%
2496

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
42%39%15%24%4
1612
16th to endDay
41%36%19%20%7%
1812
February1st to 15thDay
42%37%20%23%3
1752
16th to endDay
43%45%18%21%6%
1580
March1st to 15thDay
45%48%16%19%5%
1871
16th to endDay
42%410%21%16%3
2112
April1st to 15thDay
40%49%20%19%6%
2106
16th to endDay
34%5%9%22%22%4
2226
May1st to 15thDay
40%5%11%19%19%3
2331
16th to endDay
39%6%13%24%14%2
2435
June1st to 15thDay
44%8%15%21%9%1
2340
16th to endDay
34%8%16%24%14%2
2340
July1st to 15thDay
46%9%18%16%7%1
2201
16th to endDay
42%13%17%16%8%1
2310
August1st to 15thDay
41%10%17%20%9%1
2243
16th to endDay
51%9%12%14%9%1
2292
September1st to 15thDay
43%7%14%16%13%3
2007
16th to endDay
43%48%19%19%3
1848
October1st to 15thDay
34%47%18%26%8%
1815
16th to endDay
30%35%17%31%11%
1760
November1st to 15thDay
33%25%16%31%10%
1582
16th to endDay
36%45%17%28%8%
1620
December1st to 15thDay
44%38%20%16%7%
1620
16th to endDay
53%27%16%14%5%
1728
January1st to 15thNight
41%37%18%23%5%
2327
16th to endNight
43%35%18%21%7%
2409
February1st to 15thNight
40%36%20%19%9%
2112
16th to endNight
40%35%20%23%5%
1893
March1st to 15thNight
38%49%21%18%7%
2088
16th to endNight
36%410%25%19%4
2112
April1st to 15thNight
33%38%23%22%7%
1851
16th to endNight
32%410%24%20%7%
1734
May1st to 15thNight
32%6%13%20%23%2
1620
16th to endNight
31%7%13%28%15%3
1684
June1st to 15thNight
30%10%20%26%11%
1620
16th to endNight
28%8%21%20%17%2
1620
July1st to 15thNight
33%9%20%23%10%2
1530
16th to endNight
35%9%21%20%11%1
1595
August1st to 15thNight
33%8%18%24%12%2
1690
16th to endNight
41%8%16%18%13%1
1910
September1st to 15thNight
37%7%15%19%15%4
1941
16th to endNight
36%5%10%22%18%5%
1858
October1st to 15thNight
30%38%21%26%9%
1815
16th to endNight
29%2416%32%14%
2108
November1st to 15thNight
29%36%16%31%12%
2276
16th to endNight
34%47%17%26%10%
2340
December1st to 15thNight
41%38%20%18%7%
2340
16th to endNight
48%37%17%17%5%
2496

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
18%21%35%20%22
90
16th to endDay
17%26%48%43
96
February1st to 15thDay
12%31%43%10%3
90
16th to endDay
22%18%43%16%
81
March1st to 15thDay
18%20%37%16%5%1
161
16th to endDay
18%13%31%22%12%2
288
April1st to 15thDay
15%15%29%20%17%1
270
16th to endDay
13%7%26%27%19%5%
270
May1st to 15thDay
13%11%27%20%18%9%
288
16th to endDay
12%5%20%26%19%14%
331
June1st to 15thDay
13%210%20%26%26%
315
16th to endDay
7%12%26%26%26%
315
July1st to 15thDay
8%8%24%28%29%
305
16th to endDay
7%17%21%33%28%
326
August1st to 15thDay
12%7%26%31%20%
313
16th to endDay
18%27%25%28%18%
332
September1st to 15thDay
15%410%20%29%19%
315
16th to endDay
21%116%26%23%10%
266
October1st to 15thDay
18%223%25%22%7%
255
16th to endDay
16%5%20%23%27%5%
253
November1st to 15thDay
30%18%16%20%13%1
90
16th to endDay
11%12%40%23%12%1
90
December1st to 15thDay
24%20%33%17%4
90
16th to endDay
26%17%36%14%41
96
January1st to 15thNight
21%17%30%22%6%
720
16th to endNight
19%18%34%24%3
768
February1st to 15thNight
17%17%35%25%3
704
16th to endNight
18%19%34%23%3
631
March1st to 15thNight
16%16%35%22%7%
720
16th to endNight
14%14%30%27%13%
768
April1st to 15thNight
14%13%30%26%13%1
593
16th to endNight
14%8%26%31%17%1
540
May1st to 15thNight
10%5%27%30%22%3
540
16th to endNight
10%216%30%34%6%
563
June1st to 15thNight
5%112%31%35%14%
540
16th to endNight
310%30%44%10%
540
July1st to 15thNight
7%17%26%44%12%
510
16th to endNight
7%16%24%46%13%
564
August1st to 15thNight
8%5%27%44%12%
539
16th to endNight
15%16%26%37%12%
573
September1st to 15thNight
13%18%24%39%12%
681
16th to endNight
16%214%33%29%4
673
October1st to 15thNight
13%324%28%23%5%
660
16th to endNight
11%10%23%27%21%4
704
November1st to 15thNight
13%9%26%26%21%2
700
16th to endNight
16%15%26%27%13%
720
December1st to 15thNight
18%14%30%25%10%
720
16th to endNight
25%14%30%22%7%
768
Page generated at 2017-09-20 04:49:47. Version ac04

Copyright 2017 A. Danko


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