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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 2022-11-11.

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%
22592
34%
66728
28%
22539
77%
22539
51%
33237

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%
1009
30%
3489
27%
1009
72%
1009
41%
1708
January16th to endNight
59%
1077
35%
3261
28%
1077
70%
1077
41%
1755
February1st to 15thNight
63%
980
36%
2968
30%
979
72%
979
47%
1494
February16th to endNight
57%
888
29%
2663
26%
887
66%
887
40%
1453
March1st to 15thNight
59%
1015
27%
3046
23%
1015
67%
1015
39%
1676
March16th to endNight
64%
1083
27%
2834
20%
1083
69%
1083
45%
1598
April1st to 15thNight
63%
1016
30%
2539
18%
1016
68%
1016
44%
1504
April16th to endNight
66%
994
31%
2488
16%
994
70%
994
53%
1354
May1st to 15thNight
68%
860
28%
2371
19%
860
69%
860
46%
1322
May16th to endNight
66%
778
29%
2328
23%
778
69%
778
48%
1213
June1st to 15thNight
80%
678
31%
2204
28%
676
81%
676
54%
1004
June16th to endNight
90%
497
36%
2024
45%
497
90%
497
57%
743
July1st to 15thNight
91%
488
37%
1951
45%
488
91%
488
59%
713
July16th to endNight
90%
890
30%
2349
24%
846
91%
846
60%
1136
August1st to 15thNight
91%
985
35%
2485
23%
981
91%
981
73%
1178
August16th to endNight
91%
1078
40%
2696
28%
1078
91%
1078
73%
1277
September1st to 15thNight
88%
1016
41%
2588
33%
1016
89%
1016
70%
1236
September16th to endNight
86%
1007
43%
2785
41%
1007
89%
1007
73%
1201
October1st to 15thNight
76%
1016
36%
2802
32%
1016
80%
1016
55%
1407
October16th to endNight
76%
1084
40%
3303
39%
1083
82%
1083
56%
1534
November1st to 15thNight
73%
1041
36%
3383
36%
1041
80%
1041
53%
1525
November16th to endNight
70%
1014
33%
3290
33%
1014
75%
1014
45%
1612
December1st to 15thNight
62%
1015
32%
3305
28%
1015
70%
1015
39%
1737
December16th to endNight
54%
1083
32%
3576
25%
1083
65%
1083
38%
1857

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%68%
68122
Night
4212213345%66%
66972
TransparencyDay
17%47%16%26%27%
67821
Night
19%48%16%24%26%
66776
SeeingDay
6%8%28%36%15%4
12828
Night
5%215%37%32%6%
22613

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%313412346%61%
2057
16th to endDay
10%414323245%58%
2634
February1st to 15thDay
8%223212335%64%
2453
16th to endDay
9%413323236%58%
2230
March1st to 15thDay
7%424324447%54%
2541
16th to endDay
5%21342446%7%56%
3091
April1st to 15thDay
6%313323347%58%
3027
16th to endDay
4312213345%67%
3010
May1st to 15thDay
4314213346%62%
3157
16th to endDay
5%313324346%62%
3375
June1st to 15thDay
322214346%68%
3391
16th to endDay
1111223379%
3553
July1st to 15thDay
111212245%75%
3551
16th to endDay
1111112346%73%
3362
August1st to 15thDay
111212482%
2941
16th to endDay
112335%80%
3233
September1st to 15thDay
1111123480%
2997
16th to endDay
11111123480%
2793
October1st to 15thDay
422212345%70%
2765
16th to endDay
31221223474%
2654
November1st to 15thDay
3212212335%70%
2354
16th to endDay
5%212323346%64%
2274
December1st to 15thDay
7%31332335%8%56%
2295
16th to endDay
11%413223347%57%
2384
January1st to 15thNight
6%313223346%61%
3488
16th to endNight
9%323213345%60%
3261
February1st to 15thNight
6%31321223466%
2963
16th to endNight
10%412323335%59%
2664
March1st to 15thNight
7%413324447%55%
3047
16th to endNight
5%31332445%7%58%
2834
April1st to 15thNight
6%413325%346%58%
2540
16th to endNight
3312214445%65%
2495
May1st to 15thNight
2323325%35%6%61%
2372
16th to endNight
3413225%335%64%
2327
June1st to 15thNight
111215%45%6%68%
2213
16th to endNight
111434476%
2024
July1st to 15thNight
121235%5%75%
2039
16th to endNight
21111345%7%69%
2475
August1st to 15thNight
11112245%77%
2495
16th to endNight
11145%379%
2696
September1st to 15thNight
1111234378%
2588
16th to endNight
111113382%
2786
October1st to 15thNight
22231325%470%
2801
16th to endNight
32221323472%
3305
November1st to 15thNight
3212212235%71%
3383
16th to endNight
5%21231335%7%62%
3290
December1st to 15thNight
7%31442335%7%57%
3305
16th to endNight
10%312212336%59%
3581

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%14%25%24%
2058
16th to endDay
28%46%15%19%25%
2633
February1st to 15thDay
22%35%14%23%29%
2455
16th to endDay
27%37%16%26%18%
2230
March1st to 15thDay
26%5%9%17%19%20%
2541
16th to endDay
23%6%12%20%22%14%
3104
April1st to 15thDay
24%5%11%24%21%12%
3025
16th to endDay
17%310%21%30%16%
3011
May1st to 15thDay
21%5%9%19%28%14%
3163
16th to endDay
21%5%9%25%28%9%
3376
June1st to 15thDay
17%48%16%31%21%
3388
16th to endDay
11%2411%29%41%
3555
July1st to 15thDay
10%35%13%26%39%
3396
16th to endDay
11%49%22%28%23%
3200
August1st to 15thDay
7%2313%32%40%
2926
16th to endDay
7%35%13%37%32%
3236
September1st to 15thDay
8%25%12%31%40%
3001
16th to endDay
8%25%14%33%36%
2792
October1st to 15thDay
16%45%16%24%32%
2767
16th to endDay
13%4411%24%41%
2653
November1st to 15thDay
16%37%16%24%32%
2354
16th to endDay
20%47%13%21%32%
2278
December1st to 15thDay
25%6%8%17%17%24%
2295
16th to endDay
27%48%16%22%20%
2384
January1st to 15thNight
23%47%14%24%24%
3493
16th to endNight
26%47%14%18%28%
3264
February1st to 15thNight
22%37%15%21%29%
2972
16th to endNight
27%47%14%24%21%
2665
March1st to 15thNight
27%5%10%17%21%18%
3047
16th to endNight
23%6%10%21%22%15%
2847
April1st to 15thNight
25%6%9%23%19%14%
2539
16th to endNight
19%5%10%22%28%14%
2493
May1st to 15thNight
22%7%9%21%25%14%
2375
16th to endNight
20%5%10%26%27%9%
2328
June1st to 15thNight
14%5%11%17%29%20%
2204
16th to endNight
11%36%13%26%37%
2024
July1st to 15thNight
10%35%14%27%37%
1952
16th to endNight
13%5%10%22%24%23%
2351
August1st to 15thNight
9%35%13%33%35%
2488
16th to endNight
8%46%14%35%30%
2700
September1st to 15thNight
10%35%10%29%39%
2588
16th to endNight
8%25%14%32%36%
2785
October1st to 15thNight
17%46%15%25%30%
2802
16th to endNight
16%4411%22%41%
3304
November1st to 15thNight
17%36%15%23%33%
3383
16th to endNight
21%48%16%17%31%
3291
December1st to 15thNight
26%48%15%18%25%
3305
16th to endNight
26%48%14%25%20%
3576

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
11%5%31%35%14%2
244
16th to endDay
11%14%28%32%11%1
587
February1st to 15thDay
11%11%30%32%10%3
559
16th to endDay
10%17%34%28%8%
501
March1st to 15thDay
13%17%34%22%11%1
569
16th to endDay
9%17%35%27%8%
605
April1st to 15thDay
9%17%35%25%10%1
566
16th to endDay
320%38%26%8%2
555
May1st to 15thDay
10%11%33%30%10%3
584
16th to endDay
9%12%37%28%10%1
625
June1st to 15thDay
48%28%39%15%4
615
16th to endDay
2326%45%13%8%
615
July1st to 15thDay
116%47%24%8%
601
16th to endDay
114%50%21%12%
640
August1st to 15thDay
1119%48%20%8%
581
16th to endDay
118%50%23%6%
649
September1st to 15thDay
2127%43%18%5%
614
16th to endDay
25%31%40%15%5%
612
October1st to 15thDay
411%30%36%15%1
613
16th to endDay
37%28%36%19%4
606
November1st to 15thDay
5%419%41%23%4
347
16th to endDay
6%6%29%35%16%5%
315
December1st to 15thDay
8%5%27%40%14%3
315
16th to endDay
13%7%27%33%14%2
310
January1st to 15thNight
7%222%45%19%3
1010
16th to endNight
12%220%38%22%2
1078
February1st to 15thNight
8%320%39%23%4
987
16th to endNight
11%422%38%20%2
889
March1st to 15thNight
8%422%39%20%3
1015
16th to endNight
6%320%41%23%3
1084
April1st to 15thNight
8%417%42%23%2
1016
16th to endNight
35%21%39%25%4
997
May1st to 15thNight
5%319%39%28%4
860
16th to endNight
5%320%39%27%3
779
June1st to 15thNight
2113%39%39%3
678
16th to endNight
25%35%51%6%
497
July1st to 15thNight
2313%68%11%
488
16th to endNight
21228%52%13%
892
August1st to 15thNight
1428%49%14%
987
16th to endNight
1422%54%17%
1080
September1st to 15thNight
27%29%47%13%
1016
16th to endNight
19%34%43%10%
1007
October1st to 15thNight
3212%41%35%4
1016
16th to endNight
5%114%37%32%10%
1084
November1st to 15thNight
5%114%44%28%6%
1041
16th to endNight
7%216%40%27%6%
1014
December1st to 15thNight
9%320%41%22%3
1015
16th to endNight
12%5%23%38%17%3
1083
Page generated at 2022-11-12 11:12:28. Version ac05

Copyright 2022 A. Danko


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