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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 2020-06-03.

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
72%
19542
33%
57681
28%
19496
77%
19496
50%
28839

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%
896
28%
3103
25%
896
70%
896
39%
1550
January16th to endNight
58%
960
35%
2904
27%
960
69%
960
41%
1569
February1st to 15thNight
65%
877
34%
2645
31%
876
72%
876
46%
1353
February16th to endNight
57%
792
29%
2375
27%
792
65%
792
38%
1332
March1st to 15thNight
59%
900
25%
2700
22%
900
67%
900
38%
1503
March16th to endNight
65%
960
28%
2511
21%
960
69%
960
44%
1436
April1st to 15thNight
62%
899
28%
2249
16%
899
67%
899
43%
1350
April16th to endNight
67%
892
31%
2230
16%
892
72%
892
54%
1206
May1st to 15thNight
67%
764
27%
2114
18%
764
69%
764
45%
1180
May16th to endNight
68%
705
30%
2117
24%
705
70%
705
49%
1088
June1st to 15thNight
83%
569
31%
1843
28%
569
85%
569
56%
833
June16th to endNight
93%
420
36%
1680
44%
420
93%
420
61%
599
July1st to 15thNight
93%
400
36%
1600
43%
400
93%
400
59%
583
July16th to endNight
90%
739
30%
1952
24%
698
91%
698
61%
934
August1st to 15thNight
92%
825
37%
2060
24%
821
92%
821
75%
963
August16th to endNight
93%
892
40%
2230
28%
892
93%
892
75%
1037
September1st to 15thNight
89%
840
40%
2138
33%
840
90%
840
70%
1022
September16th to endNight
86%
836
43%
2310
40%
836
89%
836
73%
997
October1st to 15thNight
77%
840
36%
2316
33%
840
81%
840
57%
1152
October16th to endNight
77%
896
41%
2726
40%
896
82%
896
56%
1262
November1st to 15thNight
76%
880
37%
2860
38%
880
83%
880
56%
1265
November16th to endNight
69%
900
34%
2925
33%
900
75%
900
46%
1439
December1st to 15thNight
61%
900
31%
2925
27%
900
69%
900
38%
1557
December16th to endNight
55%
960
33%
3168
27%
960
66%
960
39%
1629

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
4212213345%67%
58702
Night
4212213346%66%
57881
TransparencyDay
18%37%16%26%25%
58394
Night
20%38%16%25%25%
57689
SeeingDay
7%8%30%36%12%3
9567
Night
6%115%36%32%6%
19556

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%313413336%60%
1822
16th to endDay
10%314313345%58%
2370
February1st to 15thDay
9%223212346%62%
2201
16th to endDay
10%5%24323236%54%
1979
March1st to 15thDay
7%424324447%53%
2250
16th to endDay
6%21443446%8%54%
2764
April1st to 15thDay
7%31332335%8%56%
2689
16th to endDay
4212213345%67%
2665
May1st to 15thDay
4314213346%62%
2825
16th to endDay
5%214324346%61%
3053
June1st to 15thDay
422224336%67%
2820
16th to endDay
111222381%
2940
July1st to 15thDay
111213345%73%
2940
16th to endDay
1111113346%73%
2798
August1st to 15thDay
111222383%
2473
16th to endDay
11233480%
2676
September1st to 15thDay
1111223481%
2482
16th to endDay
11111223379%
2310
October1st to 15thDay
5%212212235%70%
2300
16th to endDay
311221123474%
2202
November1st to 15thDay
2212213335%70%
1989
16th to endDay
6%212323346%62%
2025
December1st to 15thDay
7%31332345%9%56%
2025
16th to endDay
10%313223347%57%
2104
January1st to 15thNight
7%313223346%60%
3103
16th to endNight
9%323213345%60%
2904
February1st to 15thNight
7%323313245%64%
2641
16th to endNight
10%423323335%56%
2375
March1st to 15thNight
7%313324448%54%
2700
16th to endNight
5%31332445%7%57%
2511
April1st to 15thNight
6%423325%346%57%
2249
16th to endNight
3212224446%66%
2230
May1st to 15thNight
3323325%347%60%
2114
16th to endNight
2313225%336%66%
2116
June1st to 15thNight
111225%447%69%
1843
16th to endNight
111423478%
1680
July1st to 15thNight
11223335%75%
1680
16th to endNight
21111345%8%68%
2067
August1st to 15thNight
1112245%78%
2070
16th to endNight
11134480%
2230
September1st to 15thNight
1112233478%
2138
16th to endNight
1111213481%
2310
October1st to 15thNight
311231223471%
2316
16th to endNight
32221323473%
2726
November1st to 15thNight
2212212235%71%
2860
16th to endNight
6%21231335%6%61%
2925
December1st to 15thNight
7%314423346%56%
2925
16th to endNight
10%323212236%61%
3168

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
26%46%14%23%24%
1822
16th to endDay
27%47%15%20%24%
2370
February1st to 15thDay
23%35%14%24%26%
2201
16th to endDay
30%38%17%26%13%
1979
March1st to 15thDay
28%5%10%18%18%18%
2250
16th to endDay
25%6%12%20%20%13%
2764
April1st to 15thDay
26%5%12%23%21%11%
2689
16th to endDay
18%310%21%30%15%
2665
May1st to 15thDay
23%410%19%27%14%
2825
16th to endDay
22%310%25%27%9%
3056
June1st to 15thDay
19%39%15%31%20%
2820
16th to endDay
10%1410%30%42%
2940
July1st to 15thDay
11%36%13%24%39%
2791
16th to endDay
11%410%22%29%21%
2650
August1st to 15thDay
7%2413%34%38%
2459
16th to endDay
8%25%13%39%31%
2676
September1st to 15thDay
9%25%12%33%37%
2482
16th to endDay
9%15%14%34%34%
2310
October1st to 15thDay
17%35%16%24%31%
2300
16th to endDay
13%3411%23%43%
2202
November1st to 15thDay
16%37%15%23%33%
1989
16th to endDay
22%47%13%21%29%
2025
December1st to 15thDay
24%6%8%18%18%23%
2025
16th to endDay
27%5%8%17%21%20%
2104
January1st to 15thNight
25%47%15%22%24%
3103
16th to endNight
26%47%15%18%27%
2904
February1st to 15thNight
23%37%16%22%26%
2652
16th to endNight
29%48%15%24%17%
2375
March1st to 15thNight
28%5%10%17%20%16%
2700
16th to endNight
25%5%10%22%22%13%
2511
April1st to 15thNight
28%49%23%19%14%
2249
16th to endNight
20%310%21%30%13%
2230
May1st to 15thNight
24%5%9%20%25%14%
2115
16th to endNight
21%39%27%27%10%
2117
June1st to 15thNight
16%312%17%30%20%
1843
16th to endNight
11%16%13%27%39%
1680
July1st to 15thNight
12%25%13%25%39%
1600
16th to endNight
14%311%21%26%22%
1952
August1st to 15thNight
8%2413%36%33%
2060
16th to endNight
8%26%13%37%31%
2230
September1st to 15thNight
11%26%10%31%37%
2138
16th to endNight
9%15%14%33%35%
2310
October1st to 15thNight
18%25%15%28%28%
2316
16th to endNight
16%3410%22%43%
2726
November1st to 15thNight
16%36%15%23%34%
2860
16th to endNight
22%38%16%18%30%
2925
December1st to 15thNight
28%49%15%18%24%
2925
16th to endNight
26%48%14%26%20%
3168

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
13%7%34%28%15%1
180
16th to endDay
11%10%31%32%11%1
470
February1st to 15thDay
13%11%28%30%10%4
446
16th to endDay
12%15%37%26%8%
398
March1st to 15thDay
15%16%34%20%11%1
450
16th to endDay
10%15%37%26%8%1
480
April1st to 15thDay
12%15%36%25%8%2
449
16th to endDay
6%18%39%24%8%2
438
May1st to 15thDay
12%11%33%30%8%3
468
16th to endDay
12%12%36%27%9%1
522
June1st to 15thDay
5%7%29%40%12%4
444
16th to endDay
3227%48%11%7%
435
July1st to 15thDay
119%49%20%7%
425
16th to endDay
216%52%17%10%
455
August1st to 15thDay
2122%53%13%7%
419
16th to endDay
19%52%19%7%
460
September1st to 15thDay
1231%46%13%4
435
16th to endDay
45%33%39%11%4
435
October1st to 15thDay
5%11%36%35%9%1
435
16th to endDay
46%29%36%18%4
426
November1st to 15thDay
3419%43%25%3
225
16th to endDay
9%5%30%32%17%4
225
December1st to 15thDay
8%5%27%40%15%2
225
16th to endDay
11%9%27%33%15%2
222
January1st to 15thNight
9%221%43%20%2
900
16th to endNight
12%222%37%22%2
960
February1st to 15thNight
9%218%40%24%4
884
16th to endNight
13%222%37%20%3
792
March1st to 15thNight
9%324%38%20%3
900
16th to endNight
7%220%40%25%3
960
April1st to 15thNight
9%320%40%22%2
899
16th to endNight
4321%39%25%5%
892
May1st to 15thNight
7%219%37%28%4
765
16th to endNight
6%219%39%27%3
707
June1st to 15thNight
112%42%39%3
569
16th to endNight
2233%54%6%
420
July1st to 15thNight
313%69%13%
400
16th to endNight
2225%56%12%
739
August1st to 15thNight
1327%52%14%
825
16th to endNight
1123%56%17%
892
September1st to 15thNight
25%29%47%14%
840
16th to endNight
28%33%44%11%
836
October1st to 15thNight
413%42%34%4
840
16th to endNight
4113%35%33%11%
896
November1st to 15thNight
313%45%29%7%
880
16th to endNight
7%117%36%28%7%
900
December1st to 15thNight
10%219%40%23%3
900
16th to endNight
11%424%38%18%3
960
Page generated at 2020-06-04 00:18:54. Version ac04

Copyright 2020 A. Danko


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