John H. Witte Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the John H. Witte Observatory clear sky chart from 2005-11-05 to

2017-09-12
.

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
39%
15941
19%
46823
11%
15897
46%
15897
26%
30373

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%
900
15%
2506
6%
895
32%
895
21%
1749
January16th to endNight
21%
960
15%
2514
4%
960
29%
960
21%
1809
February1st to 15thNight
24%
877
12%
2288
3%
876
31%
876
21%
1652
February16th to endNight
28%
646
21%
1908
8%
646
39%
646
25%
1229
March1st to 15thNight
30%
633
18%
2073
12%
633
38%
633
21%
1333
March16th to endNight
28%
576
12%
2054
7%
576
34%
576
15%
1432
April1st to 15thNight
30%
539
17%
1797
12%
539
40%
539
22%
1168
April16th to endNight
35%
540
18%
1800
14%
540
45%
540
21%
1206
May1st to 15thNight
36%
540
17%
1540
9%
540
44%
540
22%
1063
May16th to endNight
46%
563
20%
1497
9%
561
53%
561
31%
980
June1st to 15thNight
55%
540
16%
1440
9%
540
58%
540
35%
901
June16th to endNight
52%
540
16%
1440
8%
540
55%
540
34%
906
July1st to 15thNight
63%
510
17%
1360
10%
510
66%
510
40%
813
July16th to endNight
71%
564
22%
1461
17%
531
74%
531
44%
824
August1st to 15thNight
73%
539
22%
1610
24%
536
74%
536
41%
885
August16th to endNight
69%
573
22%
1904
25%
573
73%
573
34%
1088
September1st to 15thNight
65%
530
27%
1767
29%
530
69%
530
36%
949
September16th to endNight
60%
583
27%
1785
20%
583
67%
583
38%
998
October1st to 15thNight
45%
660
26%
1980
18%
660
52%
660
33%
1172
October16th to endNight
34%
704
20%
2131
10%
704
44%
704
27%
1324
November1st to 15thNight
34%
700
25%
2276
14%
700
47%
700
29%
1317
November16th to endNight
26%
864
18%
2484
8%
864
36%
864
23%
1655
December1st to 15thNight
23%
900
14%
2520
5%
900
30%
900
18%
1854
December16th to endNight
21%
960
14%
2688
5%
960
29%
960
15%
2066

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%7%36%5%3445%7%39%
47843
Night
12%7%35%424446%43%
46996
Cloud CoverDay
13%7%36%5%3445%7%39%
47852
Night
12%7%35%424446%43%
47000
TransparencyDay
43%6%13%22%12%1
47534
Night
40%5%13%23%14%2
46824
SeeingDay
13%7%26%28%18%5%
5956
Night
16%8%30%30%13%1
15944

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
12%11%5%8%6%5%5%446%29%
1432
16th to endDay
14%14%5%9%5%3445%5%27%
1710
February1st to 15thDay
14%10%48%6%345%46%30%
1575
16th to endDay
12%9%37%6%35%446%36%
1563
March1st to 15thDay
13%9%46%6%25%346%36%
1887
16th to endDay
18%10%37%5%24446%31%
2169
April1st to 15thDay
15%9%48%5%23345%36%
2151
16th to endDay
21%7%36%5%23446%33%
2160
May1st to 15thDay
18%8%36%5%35%347%31%
2407
16th to endDay
14%6%36%5%35%5%6%7%36%
2617
June1st to 15thDay
10%6%26%6%345%5%8%40%
2520
16th to endDay
8%435%5%35%5%7%9%42%
2520
July1st to 15thDay
7%4245%35%5%6%9%46%
2520
16th to endDay
5%4145%35%6%6%10%46%
2606
August1st to 15thDay
5%425%5%36%6%7%9%41%
2340
16th to endDay
10%425%5%35%36%8%45%
2296
September1st to 15thDay
11%31442345%7%51%
2112
16th to endDay
8%414436%5%48%48%
1833
October1st to 15thDay
14%5%2433334450%
1650
16th to endDay
15%6%36%333345%44%
1741
November1st to 15thDay
12%7%245%2446%7%43%
1582
16th to endDay
17%10%44424447%37%
1476
December1st to 15thDay
19%11%5%8%5%34446%27%
1440
16th to endDay
17%14%6%9%6%22345%27%
1536
January1st to 15thNight
12%8%47%5%35%347%36%
2506
16th to endNight
11%10%5%7%6%2445%5%35%
2514
February1st to 15thNight
13%9%47%5%3435%6%34%
2285
16th to endNight
13%7%37%423345%44%
1908
March1st to 15thNight
14%7%35%424345%42%
2061
16th to endNight
15%9%47%6%35%45%6%32%
2054
April1st to 15thNight
14%8%35%424445%41%
1797
16th to endNight
18%8%25%6%23346%38%
1800
May1st to 15thNight
16%5%35%5%25%446%39%
1540
16th to endNight
8%5%25%435%5%7%7%43%
1496
June1st to 15thNight
9%5%135%2445%8%48%
1440
16th to endNight
7%325%5%36%5%5%9%45%
1440
July1st to 15thNight
6%31442446%9%52%
1440
16th to endNight
5%31333447%11%50%
1560
August1st to 15thNight
332442445%9%54%
1620
16th to endNight
8%414324446%54%
1904
September1st to 15thNight
11%412323347%55%
1767
16th to endNight
6%3135%3345%9%52%
1785
October1st to 15thNight
12%5%14413336%52%
1980
16th to endNight
14%6%25%423346%45%
2131
November1st to 15thNight
12%7%23313346%51%
2276
16th to endNight
16%7%35%5%23346%41%
2484
December1st to 15thNight
17%10%48%5%33345%34%
2520
16th to endNight
19%13%5%7%5%2434428%
2688

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
12%11%5%8%7%46%446%29%
1432
16th to endDay
15%13%5%9%6%24445%27%
1710
February1st to 15thDay
14%10%5%7%6%345%5%5%31%
1575
16th to endDay
12%10%37%6%345%36%36%
1563
March1st to 15thDay
14%9%46%5%35%346%36%
1898
16th to endDay
18%10%47%5%23445%32%
2167
April1st to 15thDay
15%9%47%6%23445%36%
2151
16th to endDay
22%6%26%5%24446%33%
2160
May1st to 15thDay
19%7%46%5%34347%31%
2407
16th to endDay
14%6%26%5%35%5%5%7%36%
2617
June1st to 15thDay
10%5%36%5%3445%8%41%
2520
16th to endDay
8%425%5%36%5%6%9%42%
2520
July1st to 15thDay
7%4235%35%5%6%8%46%
2520
16th to endDay
5%414435%6%6%9%47%
2606
August1st to 15thDay
6%425%5%36%6%7%10%41%
2340
16th to endDay
10%4245%25%35%8%46%
2296
September1st to 15thDay
11%31342445%7%51%
2112
16th to endDay
8%423435%5%5%8%48%
1833
October1st to 15thDay
14%5%2432334450%
1650
16th to endDay
16%6%36%333345%44%
1741
November1st to 15thDay
12%7%335%2445%6%43%
1582
16th to endDay
17%9%34423447%38%
1476
December1st to 15thDay
20%11%48%5%35%446%27%
1440
16th to endDay
18%14%5%9%6%22245%27%
1536
January1st to 15thNight
12%8%47%6%35%347%36%
2506
16th to endNight
11%10%5%7%5%3445%6%35%
2514
February1st to 15thNight
13%9%47%5%3445%6%34%
2278
16th to endNight
13%8%36%422435%44%
1908
March1st to 15thNight
15%6%45%424345%42%
2073
16th to endNight
16%9%37%6%35%45%6%31%
2054
April1st to 15thNight
15%8%35%5%24345%41%
1797
16th to endNight
19%7%16%433346%38%
1800
May1st to 15thNight
17%5%25%5%245%46%39%
1539
16th to endNight
8%5%26%426%5%6%8%43%
1496
June1st to 15thNight
9%42442445%9%47%
1440
16th to endNight
7%3245%35%5%5%9%45%
1440
July1st to 15thNight
6%31342446%9%52%
1440
16th to endNight
5%21343446%12%50%
1560
August1st to 15thNight
432342345%9%54%
1620
16th to endNight
8%424324446%55%
1904
September1st to 15thNight
11%312323346%56%
1767
16th to endNight
7%3135%2445%9%52%
1785
October1st to 15thNight
12%414423335%52%
1980
16th to endNight
14%6%25%423346%45%
2131
November1st to 15thNight
12%7%23312346%51%
2276
16th to endNight
16%7%25%5%23346%41%
2484
December1st to 15thNight
17%10%47%5%23345%34%
2520
16th to endNight
19%13%5%7%5%3334429%
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
55%6%11%16%10%
1433
16th to endDay
57%6%12%15%7%
1710
February1st to 15thDay
53%5%15%19%5%
1576
16th to endDay
48%5%15%20%9%
1563
March1st to 15thDay
48%6%15%21%8%
1898
16th to endDay
53%5%13%19%7%1
2169
April1st to 15thDay
50%411%22%10%
2151
16th to endDay
51%6%10%19%11%1
2160
May1st to 15thDay
52%5%11%21%8%
2407
16th to endDay
44%8%14%17%13%1
2621
June1st to 15thDay
40%7%12%23%14%1
2520
16th to endDay
35%8%13%22%16%2
2520
July1st to 15thDay
33%8%15%26%13%3
2371
16th to endDay
30%8%17%26%15%1
2443
August1st to 15thDay
34%9%14%25%15%
2326
16th to endDay
35%6%13%26%15%3
2296
September1st to 15thDay
31%5%11%26%20%4
2112
16th to endDay
33%6%12%29%17%1
1833
October1st to 15thDay
37%39%24%22%1
1650
16th to endDay
42%413%24%13%2
1741
November1st to 15thDay
39%5%12%23%16%2
1582
16th to endDay
46%416%22%8%
1476
December1st to 15thDay
58%5%13%16%6%
1440
16th to endDay
60%410%13%8%1
1536
January1st to 15thNight
48%414%18%12%
2506
16th to endNight
49%5%16%18%9%
2514
February1st to 15thNight
49%414%19%10%
2288
16th to endNight
42%413%26%12%1
1908
March1st to 15thNight
43%5%12%26%10%1
2073
16th to endNight
52%5%14%18%8%
2054
April1st to 15thNight
44%49%24%14%2
1797
16th to endNight
46%5%11%18%14%3
1800
May1st to 15thNight
43%8%12%20%13%
1540
16th to endNight
35%8%13%20%18%2
1498
June1st to 15thNight
32%7%13%24%18%3
1440
16th to endNight
33%7%14%18%20%4
1440
July1st to 15thNight
28%7%15%29%16%4
1360
16th to endNight
24%6%18%28%20%1
1461
August1st to 15thNight
25%6%15%30%18%3
1610
16th to endNight
29%7%10%25%20%6%
1904
September1st to 15thNight
29%410%26%23%5%
1767
16th to endNight
27%6%12%28%21%2
1785
October1st to 15thNight
33%410%23%23%4
1980
16th to endNight
38%5%12%24%16%2
2131
November1st to 15thNight
34%412%24%19%4
2276
16th to endNight
44%412%25%12%
2484
December1st to 15thNight
53%5%12%20%7%
2520
16th to endNight
58%410%16%8%
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
26%12%36%18%5%
90
16th to endDay
22%14%30%23%7%1
96
February1st to 15thDay
11%23%38%16%8%1
90
16th to endDay
16%17%35%17%7%6%
81
March1st to 15thDay
18%22%37%17%3
90
16th to endDay
36%11%23%20%7%1
153
April1st to 15thDay
17%14%32%24%12%
270
16th to endDay
24%7%30%23%11%2
270
May1st to 15thDay
19%12%30%26%10%1
430
16th to endDay
17%9%31%24%12%4
517
June1st to 15thDay
9%5%26%33%20%4
495
16th to endDay
9%8%30%30%17%4
495
July1st to 15thDay
10%223%34%20%8%
475
16th to endDay
6%115%38%30%8%
515
August1st to 15thDay
7%117%34%30%8%
493
16th to endDay
8%315%30%32%9%
336
September1st to 15thDay
9%318%31%28%9%
299
16th to endDay
9%6%19%29%27%7%
209
October1st to 15thDay
5%10%32%23%14%14%
90
16th to endDay
18%10%33%28%9%
96
November1st to 15thDay
47%33%28%18%6%
90
16th to endDay
40%17%23%15%3
90
December1st to 15thDay
21%20%34%13%10%1
90
16th to endDay
26%25%39%6%3
96
January1st to 15thNight
15%14%39%22%7%
900
16th to endNight
17%12%39%25%4
960
February1st to 15thNight
19%11%37%26%5%
880
16th to endNight
16%10%40%27%4
646
March1st to 15thNight
19%10%35%27%7%
633
16th to endNight
19%11%34%25%7%
576
April1st to 15thNight
18%12%35%28%5%
539
16th to endNight
21%7%30%30%9%
540
May1st to 15thNight
19%6%32%30%9%1
540
16th to endNight
9%433%36%14%
563
June1st to 15thNight
11%323%43%17%
540
16th to endNight
7%231%37%19%1
540
July1st to 15thNight
7%217%43%27%2
510
16th to endNight
7%12%45%32%2
564
August1st to 15thNight
5%110%45%32%3
539
16th to endNight
11%111%42%29%4
573
September1st to 15thNight
13%215%35%29%4
530
16th to endNight
7%422%33%26%4
583
October1st to 15thNight
15%5%28%29%19%1
660
16th to endNight
18%9%34%28%8%
704
November1st to 15thNight
17%10%35%25%10%
700
16th to endNight
19%12%37%22%7%
864
December1st to 15thNight
22%13%35%24%4
900
16th to endNight
24%13%33%23%3
960
Page generated at 2017-09-13 06:39:15. Version ac04

Copyright 2017 A. Danko


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