Lawrence Hall of Science
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lawrence Hall of Science 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
61%
15219
24%
46543
21%
15183
65%
15183
32%
27363

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
61%
716
18%
2383
17%
716
65%
716
27%
1445
January16th to endNight
56%
768
24%
2496
25%
768
59%
768
26%
1551
February1st to 15thNight
54%
698
22%
2288
21%
698
59%
698
24%
1441
February16th to endNight
51%
632
21%
1906
17%
632
58%
632
26%
1231
March1st to 15thNight
51%
720
17%
2001
14%
720
54%
720
25%
1340
March16th to endNight
50%
768
20%
2093
14%
768
54%
768
29%
1362
April1st to 15thNight
47%
719
22%
1799
11%
719
52%
719
31%
1177
April16th to endNight
53%
720
25%
1800
11%
720
58%
720
41%
1071
May1st to 15thNight
64%
601
24%
1681
16%
601
67%
601
44%
924
May16th to endNight
59%
393
23%
1516
21%
393
66%
393
30%
789
June1st to 15thNight
65%
360
21%
1440
22%
360
71%
360
30%
739
June16th to endNight
77%
360
31%
1440
39%
360
81%
360
45%
608
July1st to 15thNight
83%
379
26%
1399
30%
379
85%
379
41%
653
July16th to endNight
67%
564
24%
1593
23%
531
69%
531
29%
947
August1st to 15thNight
66%
533
24%
1582
19%
530
68%
530
29%
948
August16th to endNight
70%
700
27%
1750
16%
700
70%
700
41%
1081
September1st to 15thNight
77%
660
33%
1650
23%
660
78%
660
48%
955
September16th to endNight
75%
656
34%
1802
31%
656
78%
656
51%
942
October1st to 15thNight
67%
660
28%
1980
27%
660
73%
660
41%
1067
October16th to endNight
68%
704
30%
2112
30%
704
72%
704
36%
1202
November1st to 15thNight
66%
700
27%
2181
27%
700
71%
700
37%
1215
November16th to endNight
60%
720
24%
2443
26%
720
63%
720
31%
1376
December1st to 15thNight
54%
720
20%
2520
18%
720
59%
720
22%
1603
December16th to endNight
47%
768
20%
2688
18%
768
54%
768
22%
1696

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
7%424323346%56%
47426
Night
8%424424447%50%
46730
TransparencyDay
29%49%19%23%14%
47113
Night
34%49%18%20%12%
46544
SeeingDay
10%10%28%33%14%3
5869
Night
11%414%33%29%5%
15231

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
15%5%25%42435%7%42%
1552
16th to endDay
15%6%246%34335%43%
1728
February1st to 15thDay
17%6%25%5%23445%42%
1576
16th to endDay
16%7%3442445%7%37%
1568
March1st to 15thDay
13%8%26%43445%9%37%
1956
16th to endDay
11%6%36%5%3445%6%40%
2130
April1st to 15thDay
13%6%25%434447%42%
2149
16th to endDay
6%31332325%7%58%
2160
May1st to 15thDay
331322335%7%63%
2267
16th to endDay
5%42432335%7%58%
2593
June1st to 15thDay
4323323447%60%
2520
16th to endDay
112312337%72%
2520
July1st to 15thDay
113222346%71%
2474
16th to endDay
213312238%70%
2468
August1st to 15thDay
1213412337%67%
2283
16th to endDay
213312235%71%
2100
September1st to 15thDay
1213312336%70%
1980
16th to endDay
2212312235%70%
1825
October1st to 15thDay
5%323313346%62%
1650
16th to endDay
8%5%13323345%58%
1760
November1st to 15thDay
8%5%24424446%52%
1676
16th to endDay
11%7%35%42325%6%46%
1515
December1st to 15thDay
16%9%35%4145%4441%
1440
16th to endDay
18%7%25%324346%40%
1536
January1st to 15thNight
14%5%2432445%8%43%
2383
16th to endNight
15%7%34314337%46%
2496
February1st to 15thNight
14%7%35%424436%43%
2276
16th to endNight
14%5%2442445%7%42%
1906
March1st to 15thNight
14%7%35%424346%41%
2001
16th to endNight
12%6%35%5%23346%46%
2093
April1st to 15thNight
10%5%344245%6%7%45%
1799
16th to endNight
5%323413346%59%
1800
May1st to 15thNight
332442445%7%58%
1681
16th to endNight
43245%3435%7%55%
1515
June1st to 15thNight
2315%42446%9%53%
1440
16th to endNight
23323338%66%
1440
July1st to 15thNight
123435%45%10%57%
1482
16th to endNight
1327%9%46%6%7%9%40%
1701
August1st to 15thNight
2327%8%5%6%6%6%10%40%
1591
16th to endNight
227%8%445%5%10%47%
1750
September1st to 15thNight
12145%3435%9%58%
1650
16th to endNight
1213422248%63%
1802
October1st to 15thNight
6%414313436%59%
1980
16th to endNight
6%4244245%5%6%54%
2112
November1st to 15thNight
7%5%23313348%54%
2181
16th to endNight
9%6%245%12345%52%
2443
December1st to 15thNight
16%7%24433337%42%
2520
16th to endNight
17%6%25%413346%43%
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
40%5%13%16%16%7%
1552
16th to endDay
44%49%11%18%11%
1728
February1st to 15thDay
43%49%18%20%3
1576
16th to endDay
44%5%10%23%12%3
1568
March1st to 15thDay
43%5%12%19%13%5%
1956
16th to endDay
42%6%13%19%15%3
2130
April1st to 15thDay
40%5%14%18%18%2
2149
16th to endDay
26%413%26%22%6%
2160
May1st to 15thDay
21%39%30%26%8%
2267
16th to endDay
27%5%12%27%21%6%
2597
June1st to 15thDay
25%5%9%22%23%13%
2520
16th to endDay
14%25%18%34%24%
2520
July1st to 15thDay
17%2411%24%39%
2328
16th to endDay
17%2411%25%38%
2313
August1st to 15thDay
20%2411%32%28%
2267
16th to endDay
17%1317%38%21%
2100
September1st to 15thDay
17%2414%32%29%
1980
16th to endDay
18%25%24%29%19%
1825
October1st to 15thDay
25%28%20%27%15%
1650
16th to endDay
28%38%24%22%12%
1760
November1st to 15thDay
32%412%29%14%7%
1676
16th to endDay
38%49%18%22%5%
1515
December1st to 15thDay
44%5%9%18%18%4
1440
16th to endDay
44%5%11%17%15%5%
1536
January1st to 15thNight
38%5%12%19%15%8%
2383
16th to endNight
40%48%14%16%15%
2496
February1st to 15thNight
42%410%18%17%7%
2288
16th to endNight
41%5%12%23%14%2
1906
March1st to 15thNight
43%411%19%14%5%
2001
16th to endNight
40%5%11%19%18%4
2093
April1st to 15thNight
36%5%14%19%19%3
1799
16th to endNight
27%412%25%21%8%
1800
May1st to 15thNight
26%49%23%25%11%
1682
16th to endNight
30%5%12%24%21%6%
1516
June1st to 15thNight
28%6%10%18%22%13%
1440
16th to endNight
20%2315%33%24%
1440
July1st to 15thNight
24%338%25%35%
1399
16th to endNight
39%25%8%16%27%
1593
August1st to 15thNight
39%2310%22%21%
1582
16th to endNight
33%2310%28%21%
1750
September1st to 15thNight
27%248%27%29%
1650
16th to endNight
21%35%22%27%20%
1802
October1st to 15thNight
26%37%21%22%17%
1980
16th to endNight
30%46%22%20%14%
2112
November1st to 15thNight
30%412%28%16%7%
2181
16th to endNight
33%49%23%21%8%
2443
December1st to 15thNight
43%5%8%16%18%6%
2520
16th to endNight
42%5%11%15%17%7%
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
25%7%26%22%17%
180
16th to endDay
18%9%22%31%14%2
256
February1st to 15thDay
21%11%22%26%16%1
236
16th to endDay
21%13%25%23%14%1
236
March1st to 15thDay
19%17%28%16%13%4
270
16th to endDay
16%19%30%23%8%1
288
April1st to 15thDay
18%22%30%20%7%1
269
16th to endDay
13%25%25%26%6%2
270
May1st to 15thDay
6%17%36%31%7%
288
16th to endDay
10%14%26%33%11%2
330
June1st to 15thDay
8%13%36%31%6%2
315
16th to endDay
2431%43%14%2
315
July1st to 15thDay
2225%50%17%
305
16th to endDay
1126%48%14%5%
327
August1st to 15thDay
3329%46%14%3
300
16th to endDay
228%50%14%3
268
September1st to 15thDay
1323%46%18%7%
255
16th to endDay
39%25%29%23%7%
255
October1st to 15thDay
8%8%27%33%14%6%
255
16th to endDay
13%9%29%26%19%2
272
November1st to 15thDay
9%7%22%23%31%4
182
16th to endDay
15%12%26%31%15%
73
December1st to 15thDay
23%15%36%13%10%1
60
16th to endDay
10%20%23%25%18%1
64
January1st to 15thNight
16%311%35%26%7%
720
16th to endNight
19%412%30%26%6%
768
February1st to 15thNight
17%6%11%33%25%4
704
16th to endNight
17%6%19%29%22%4
632
March1st to 15thNight
18%7%14%27%27%4
720
16th to endNight
15%7%19%32%21%2
768
April1st to 15thNight
13%10%22%32%18%2
719
16th to endNight
9%9%23%30%23%4
720
May1st to 15thNight
6%218%42%27%3
602
16th to endNight
6%5%22%38%23%4
394
June1st to 15thNight
4320%46%22%2
360
16th to endNight
213%48%32%1
360
July1st to 15thNight
38%40%43%3
379
16th to endNight
436%34%43%8%
564
August1st to 15thNight
6%111%34%39%6%
533
16th to endNight
5%9%40%37%6%
700
September1st to 15thNight
48%31%43%10%
660
16th to endNight
4110%35%38%9%
656
October1st to 15thNight
9%412%31%34%7%
660
16th to endNight
10%311%28%33%12%
704
November1st to 15thNight
9%313%31%33%8%
700
16th to endNight
12%5%12%31%28%8%
720
December1st to 15thNight
20%5%12%32%22%5%
720
16th to endNight
19%7%17%32%21%1
768
Page generated at 2017-08-13 11:16:35. Version ac04

Copyright 2017 A. Danko


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