Montebello
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Montebello 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
64%
15289
26%
46550
23%
15253
68%
15253
39%
25477

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
59%
716
19%
2366
18%
716
63%
716
28%
1426
January16th to endNight
57%
768
24%
2496
25%
768
60%
768
26%
1560
February1st to 15thNight
53%
700
23%
2288
23%
700
59%
700
26%
1416
February16th to endNight
47%
632
21%
1896
16%
632
54%
632
26%
1215
March1st to 15thNight
53%
720
19%
1998
16%
720
56%
720
28%
1316
March16th to endNight
50%
768
20%
2093
14%
768
55%
768
29%
1364
April1st to 15thNight
45%
719
20%
1799
10%
719
50%
719
31%
1183
April16th to endNight
54%
720
25%
1800
11%
720
59%
720
42%
1049
May1st to 15thNight
63%
619
25%
1699
16%
619
67%
619
53%
863
May16th to endNight
65%
411
23%
1534
20%
411
72%
411
40%
715
June1st to 15thNight
69%
360
26%
1440
26%
360
78%
360
45%
601
June16th to endNight
84%
360
36%
1440
45%
360
88%
360
64%
487
July1st to 15thNight
89%
401
34%
1421
37%
401
92%
401
75%
485
July16th to endNight
87%
564
36%
1593
33%
531
88%
531
65%
678
August1st to 15thNight
84%
543
34%
1592
26%
540
85%
540
61%
707
August16th to endNight
84%
700
36%
1750
23%
700
86%
700
69%
843
September1st to 15thNight
87%
660
42%
1650
30%
660
88%
660
73%
774
September16th to endNight
79%
656
38%
1801
34%
656
82%
656
61%
862
October1st to 15thNight
71%
660
28%
1980
28%
660
76%
660
46%
1011
October16th to endNight
69%
704
32%
2112
33%
704
73%
704
41%
1133
November1st to 15thNight
66%
700
28%
2170
28%
700
70%
700
39%
1184
November16th to endNight
63%
720
24%
2424
26%
720
67%
720
33%
1348
December1st to 15thNight
55%
720
21%
2520
19%
720
62%
720
24%
1539
December16th to endNight
45%
768
19%
2688
16%
768
52%
768
20%
1718

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%423323347%56%
47414
Night
7%42442345%8%53%
46739
TransparencyDay
27%39%20%23%15%
47103
Night
28%310%20%21%14%
46551
SeeingDay
8%12%26%33%15%4
5901
Night
8%5%13%33%31%7%
15299

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
14%5%24425%35%7%44%
1569
16th to endDay
15%6%35%424346%42%
1728
February1st to 15thDay
14%7%35%43345%5%40%
1576
16th to endDay
16%8%37%42335%6%38%
1576
March1st to 15thDay
12%7%46%5%245%6%10%33%
1959
16th to endDay
11%6%36%6%3445%6%40%
2130
April1st to 15thDay
14%6%35%42345%7%41%
2149
16th to endDay
8%424323348%55%
2160
May1st to 15thDay
4313223349%61%
2249
16th to endDay
6%5%24422447%54%
2576
June1st to 15thDay
6%31221345%7%60%
2520
16th to endDay
111112235%76%
2520
July1st to 15thDay
111212346%75%
2450
16th to endDay
1111112245%76%
2468
August1st to 15thDay
122212348%71%
2272
16th to endDay
11212349%72%
2100
September1st to 15thDay
12111237%75%
1980
16th to endDay
332212236%70%
1826
October1st to 15thDay
6%322313447%60%
1650
16th to endDay
6%413424346%57%
1760
November1st to 15thDay
9%425%435%447%49%
1687
16th to endDay
9%6%35%5%34346%47%
1533
December1st to 15thDay
13%7%46%6%25%5%46%38%
1440
16th to endDay
16%8%36%5%23347%37%
1536
January1st to 15thNight
12%6%25%42446%7%42%
2366
16th to endNight
14%5%25%424346%44%
2496
February1st to 15thNight
10%7%45%6%35%45%7%40%
2276
16th to endNight
14%7%244235%5%7%40%
1896
March1st to 15thNight
12%6%26%5%34446%43%
1998
16th to endNight
10%6%35%5%34437%44%
2093
April1st to 15thNight
11%5%344346%6%7%43%
1799
16th to endNight
6%32232445%7%57%
1800
May1st to 15thNight
232332337%10%57%
1699
16th to endNight
3324325%6%6%9%52%
1533
June1st to 15thNight
22142346%9%61%
1440
16th to endNight
12221247%74%
1440
July1st to 15thNight
111325%8%73%
1506
16th to endNight
1122125%7%10%63%
1701
August1st to 15thNight
12123225%6%13%60%
1601
16th to endNight
2121337%11%65%
1750
September1st to 15thNight
12211235%9%70%
1650
16th to endNight
2112212347%68%
1801
October1st to 15thNight
421342445%6%60%
1980
16th to endNight
5%424422347%57%
2112
November1st to 15thNight
7%42432435%8%54%
2170
16th to endNight
7%5%34334447%51%
2424
December1st to 15thNight
11%6%25%5%345%47%42%
2520
16th to endNight
15%7%25%5%3435%5%41%
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
38%412%18%15%10%
1569
16th to endDay
42%5%7%12%18%13%
1728
February1st to 15thDay
44%38%18%20%5%
1576
16th to endDay
47%39%23%12%4
1576
March1st to 15thDay
45%411%19%14%5%
1959
16th to endDay
43%6%13%18%15%2
2130
April1st to 15thDay
41%313%20%18%2
2149
16th to endDay
28%413%24%22%6%
2160
May1st to 15thDay
20%313%27%27%7%
2249
16th to endDay
28%315%24%21%5%
2580
June1st to 15thDay
22%5%13%22%22%14%
2520
16th to endDay
10%17%19%33%26%
2520
July1st to 15thDay
9%1415%24%43%
2306
16th to endDay
9%2415%31%36%
2313
August1st to 15thDay
12%15%18%32%29%
2256
16th to endDay
9%15%22%36%23%
2100
September1st to 15thDay
10%15%20%30%32%
1980
16th to endDay
17%26%25%29%20%
1826
October1st to 15thDay
24%48%20%24%16%
1650
16th to endDay
27%211%22%23%12%
1760
November1st to 15thDay
33%49%25%19%6%
1687
16th to endDay
37%49%16%25%5%
1533
December1st to 15thDay
46%310%15%18%5%
1440
16th to endDay
46%412%15%16%5%
1536
January1st to 15thNight
38%411%19%16%9%
2366
16th to endNight
39%5%8%13%16%16%
2496
February1st to 15thNight
41%39%19%17%8%
2288
16th to endNight
41%413%24%12%3
1896
March1st to 15thNight
41%411%20%14%6%
1998
16th to endNight
40%413%18%16%5%
2093
April1st to 15thNight
37%5%16%21%16%3
1799
16th to endNight
25%414%25%20%8%
1800
May1st to 15thNight
19%314%23%27%11%
1700
16th to endNight
22%320%24%21%6%
1534
June1st to 15thNight
16%5%14%25%21%16%
1440
16th to endNight
9%16%17%31%32%
1440
July1st to 15thNight
7%1316%29%41%
1421
16th to endNight
11%27%22%23%31%
1593
August1st to 15thNight
15%1423%28%26%
1592
16th to endNight
12%25%22%30%27%
1750
September1st to 15thNight
10%15%17%27%37%
1650
16th to endNight
14%36%20%30%23%
1801
October1st to 15thNight
23%310%21%22%19%
1980
16th to endNight
26%47%22%24%15%
2112
November1st to 15thNight
28%411%26%20%8%
2170
16th to endNight
32%49%22%21%9%
2424
December1st to 15thNight
40%5%9%16%20%8%
2520
16th to endNight
44%411%15%16%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
21%15%24%24%13%1
198
16th to endDay
17%11%30%24%13%2
256
February1st to 15thDay
17%18%25%25%11%2
236
16th to endDay
18%16%32%21%8%1
237
March1st to 15thDay
18%20%28%20%10%3
270
16th to endDay
11%22%35%22%6%1
288
April1st to 15thDay
15%26%30%18%7%1
269
16th to endDay
7%28%31%23%6%1
270
May1st to 15thDay
6%18%34%29%9%2
288
16th to endDay
6%16%26%33%13%3
330
June1st to 15thDay
5%13%33%33%11%2
315
16th to endDay
15%26%42%19%5%
315
July1st to 15thDay
2118%48%24%4
305
16th to endDay
118%49%22%7%
327
August1st to 15thDay
1124%40%24%7%
300
16th to endDay
122%52%16%7%
268
September1st to 15thDay
1319%45%20%9%
255
16th to endDay
47%22%36%22%6%
255
October1st to 15thDay
7%10%23%37%18%3
255
16th to endDay
10%9%28%33%15%2
272
November1st to 15thDay
9%10%18%25%29%6%
193
16th to endDay
420%30%24%16%5%
75
December1st to 15thDay
16%16%33%20%13%
60
16th to endDay
14%18%14%23%21%7%
64
January1st to 15thNight
15%411%33%27%7%
720
16th to endNight
16%413%30%24%10%
768
February1st to 15thNight
12%8%14%32%24%7%
704
16th to endNight
18%8%19%29%19%5%
632
March1st to 15thNight
13%8%16%28%27%5%
720
16th to endNight
12%8%19%36%20%3
768
April1st to 15thNight
12%11%22%31%19%2
719
16th to endNight
6%10%23%29%22%6%
720
May1st to 15thNight
3322%37%28%5%
620
16th to endNight
3418%38%30%4
412
June1st to 15thNight
3318%45%28%2
360
16th to endNight
19%48%36%2
360
July1st to 15thNight
5%35%51%6%
401
16th to endNight
131%52%12%
564
August1st to 15thNight
25%33%50%7%
543
16th to endNight
7%34%48%8%
700
September1st to 15thNight
16%30%46%13%
660
16th to endNight
328%31%39%13%
656
October1st to 15thNight
4312%31%35%11%
660
16th to endNight
7%5%8%29%33%15%
704
November1st to 15thNight
7%314%31%33%9%
700
16th to endNight
8%5%12%35%28%9%
720
December1st to 15thNight
12%6%15%33%25%6%
720
16th to endNight
16%9%18%29%20%4
768
Page generated at 2017-08-13 11:16:28. Version ac04

Copyright 2017 A. Danko


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