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Monrovia
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Monrovia clear sky chart from 2005-11-05 to 2017-09-10.

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
73%
15836
33%
46710
28%
15790
78%
15790
52%
23100

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
62%
716
28%
2479
25%
716
71%
716
41%
1217
January16th to endNight
57%
768
34%
2323
26%
768
68%
768
40%
1262
February1st to 15thNight
67%
697
34%
2105
32%
696
73%
696
46%
1078
February16th to endNight
59%
632
26%
1895
25%
632
64%
632
36%
1089
March1st to 15thNight
64%
720
29%
2160
25%
720
73%
720
46%
1104
March16th to endNight
68%
768
28%
2010
22%
768
72%
768
48%
1114
April1st to 15thNight
63%
719
28%
1799
16%
719
68%
719
47%
1041
April16th to endNight
67%
720
30%
1800
15%
720
71%
720
55%
962
May1st to 15thNight
67%
611
28%
1691
19%
611
70%
611
47%
927
May16th to endNight
71%
561
29%
1685
23%
561
73%
561
51%
846
June1st to 15thNight
82%
482
29%
1562
27%
482
84%
482
55%
714
June16th to endNight
94%
360
38%
1440
46%
360
94%
360
65%
491
July1st to 15thNight
93%
340
34%
1360
41%
340
93%
340
60%
487
July16th to endNight
90%
633
31%
1654
25%
592
91%
592
60%
798
August1st to 15thNight
92%
717
35%
1790
23%
713
92%
713
74%
844
August16th to endNight
93%
764
42%
1910
29%
764
93%
764
76%
882
September1st to 15thNight
91%
700
39%
1780
31%
700
91%
700
69%
855
September16th to endNight
88%
656
43%
1815
41%
656
90%
656
75%
774
October1st to 15thNight
76%
660
36%
1820
33%
660
80%
660
56%
915
October16th to endNight
77%
704
38%
2142
39%
704
81%
704
52%
1035
November1st to 15thNight
75%
700
36%
2275
35%
700
82%
700
56%
1006
November16th to endNight
72%
720
36%
2340
36%
720
77%
720
49%
1105
December1st to 15thNight
64%
720
32%
2340
28%
720
73%
720
39%
1227
December16th to endNight
55%
768
32%
2535
27%
768
65%
768
37%
1327

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
4212213335%68%
47894
Night
4212213335%67%
46910
TransparencyDay
18%37%16%26%26%
47586
Night
19%37%16%25%26%
46718
SeeingDay
6%9%32%37%10%3
5901
Night
6%114%35%34%7%
15850

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
7%33412326%63%
1456
16th to endDay
11%314213345%57%
1896
February1st to 15thDay
8%223212346%62%
1751
16th to endDay
12%5%24323236%51%
1579
March1st to 15thDay
5%313224448%58%
1800
16th to endDay
5%21342446%8%56%
2211
April1st to 15thDay
6%31332435%8%58%
2149
16th to endDay
5%212213235%69%
2160
May1st to 15thDay
3313213346%65%
2258
16th to endDay
423224336%64%
2429
June1st to 15thDay
422214246%66%
2394
16th to endDay
111222284%
2520
July1st to 15thDay
111213335%74%
2520
16th to endDay
1111113346%73%
2393
August1st to 15thDay
111222383%
2160
16th to endDay
11233481%
2292
September1st to 15thDay
1111123381%
2067
16th to endDay
11111133381%
1815
October1st to 15thDay
5%212212235%69%
1807
16th to endDay
321321233471%
1730
November1st to 15thDay
321331333470%
1584
16th to endDay
5%312323235%65%
1620
December1st to 15thDay
7%31332345%9%56%
1620
16th to endDay
12%313213347%57%
1683
January1st to 15thNight
6%313223346%62%
2479
16th to endNight
10%323213235%60%
2323
February1st to 15thNight
6%323313235%64%
2101
16th to endNight
12%423324335%54%
1895
March1st to 15thNight
5%312214448%61%
2160
16th to endNight
421332435%7%61%
2010
April1st to 15thNight
6%412325%336%62%
1799
16th to endNight
3211124435%68%
1800
May1st to 15thNight
3212225%347%63%
1691
16th to endNight
2212225%336%67%
1684
June1st to 15thNight
111225%347%69%
1562
16th to endNight
11412482%
1440
July1st to 15thNight
11223235%76%
1440
16th to endNight
21111345%7%69%
1769
August1st to 15thNight
1112235%78%
1800
16th to endNight
1111123382%
1910
September1st to 15thNight
1112223478%
1780
16th to endNight
11223382%
1815
October1st to 15thNight
321332213471%
1820
16th to endNight
321221333470%
2142
November1st to 15thNight
3212212235%73%
2275
16th to endNight
5%21221335%6%65%
2340
December1st to 15thNight
7%214423337%58%
2340
16th to endNight
11%312212236%60%
2535

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
24%46%12%24%27%
1456
16th to endDay
28%47%14%18%26%
1896
February1st to 15thDay
23%36%15%24%25%
1751
16th to endDay
32%38%17%27%10%
1579
March1st to 15thDay
22%411%20%20%20%
1800
16th to endDay
22%6%13%22%20%14%
2211
April1st to 15thDay
23%412%24%23%11%
2149
16th to endDay
17%311%21%28%17%
2160
May1st to 15thDay
20%410%19%27%16%
2258
16th to endDay
21%49%25%28%10%
2432
June1st to 15thDay
21%38%14%30%21%
2394
16th to endDay
9%148%31%44%
2520
July1st to 15thDay
12%35%12%24%41%
2371
16th to endDay
12%48%21%30%23%
2245
August1st to 15thDay
7%2413%34%37%
2146
16th to endDay
8%25%12%38%33%
2292
September1st to 15thDay
9%25%12%32%38%
2067
16th to endDay
7%25%13%33%37%
1815
October1st to 15thDay
17%46%18%27%26%
1807
16th to endDay
16%4411%21%40%
1730
November1st to 15thDay
17%36%15%23%32%
1584
16th to endDay
21%46%13%22%32%
1620
December1st to 15thDay
24%6%9%18%18%22%
1620
16th to endDay
27%5%8%17%19%20%
1683
January1st to 15thNight
24%36%13%23%27%
2479
16th to endNight
27%47%14%16%29%
2323
February1st to 15thNight
22%37%16%23%26%
2112
16th to endNight
31%5%9%14%24%14%
1895
March1st to 15thNight
21%5%10%19%23%19%
2160
16th to endNight
22%5%11%22%22%15%
2010
April1st to 15thNight
25%39%24%21%14%
1799
16th to endNight
19%311%22%27%16%
1800
May1st to 15thNight
23%5%9%19%26%15%
1692
16th to endNight
19%410%26%28%11%
1685
June1st to 15thNight
16%311%16%30%20%
1562
16th to endNight
9%26%11%27%42%
1440
July1st to 15thNight
11%25%13%25%41%
1360
16th to endNight
14%39%21%26%23%
1654
August1st to 15thNight
9%2413%37%32%
1790
16th to endNight
7%26%12%36%33%
1910
September1st to 15thNight
11%35%10%31%37%
1780
16th to endNight
9%15%14%32%37%
1815
October1st to 15thNight
18%35%15%31%25%
1820
16th to endNight
18%4410%23%39%
2142
November1st to 15thNight
16%26%14%25%35%
2275
16th to endNight
19%37%15%18%33%
2340
December1st to 15thNight
26%48%15%19%24%
2340
16th to endNight
27%48%14%24%20%
2535

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
17%8%39%26%8%
84
16th to endDay
15%12%34%28%8%
284
February1st to 15thDay
11%11%30%34%9%1
266
16th to endDay
17%16%34%23%7%
238
March1st to 15thDay
8%15%33%23%16%1
270
16th to endDay
7%15%39%27%8%1
288
April1st to 15thDay
10%20%39%22%5%2
269
16th to endDay
421%44%23%32
270
May1st to 15thDay
10%15%36%27%6%2
288
16th to endDay
11%10%39%28%9%
330
June1st to 15thDay
6%9%33%38%8%2
315
16th to endDay
2229%47%10%7%
315
July1st to 15thDay
1122%51%16%5%
305
16th to endDay
218%54%14%9%
327
August1st to 15thDay
2123%57%8%5%
315
16th to endDay
22%55%14%6%
332
September1st to 15thDay
2234%48%8%3
294
16th to endDay
15%38%41%8%4
255
October1st to 15thDay
6%12%38%33%7%1
255
16th to endDay
5%7%34%37%13%1
242
November1st to 15thDay
37%15%32%33%7%
90
16th to endDay
48%36%35%13%1
90
December1st to 15thDay
45%23%45%21%
90
16th to endDay
16%8%30%33%10%
89
January1st to 15thNight
9%221%43%20%3
720
16th to endNight
12%222%35%23%3
768
February1st to 15thNight
8%216%42%25%3
704
16th to endNight
15%219%36%22%3
632
March1st to 15thNight
5%224%39%23%4
720
16th to endNight
5%219%39%28%3
768
April1st to 15thNight
8%220%42%22%3
719
16th to endNight
4323%37%25%5%
720
May1st to 15thNight
6%320%36%28%4
612
16th to endNight
5%217%39%30%4
563
June1st to 15thNight
2112%44%36%3
482
16th to endNight
1235%55%5%
360
July1st to 15thNight
312%70%12%
340
16th to endNight
21223%56%13%
633
August1st to 15thNight
1325%54%14%
717
16th to endNight
1120%57%18%
764
September1st to 15thNight
2426%50%16%
700
16th to endNight
17%31%47%12%
656
October1st to 15thNight
413%38%36%5%
660
16th to endNight
5%112%33%34%11%
704
November1st to 15thNight
414%39%32%8%
700
16th to endNight
6%116%38%29%8%
720
December1st to 15thNight
9%218%41%25%3
720
16th to endNight
11%5%22%39%17%2
768
Page generated at 2017-09-11 16:35:24. Version ac04

Copyright 2017 A. Danko


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