Mont Hereford
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Mont Hereford clear sky chart from 2005-11-05 to 2017-10-16.

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
25%
14790
10%
47153
6%
14758
29%
14758
11%
36569

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
11%
720
6%
2506
3%
716
14%
716
4%
2158
January16th to endNight
13%
768
6%
2688
3%
768
17%
768
5%
2285
February1st to 15thNight
11%
704
5%
2298
2%
701
15%
701
5%
1995
February16th to endNight
13%
631
8%
1893
3%
631
20%
631
8%
1576
March1st to 15thNight
17%
720
11%
2160
6%
720
23%
720
9%
1725
March16th to endNight
23%
768
15%
2019
7%
768
30%
768
14%
1557
April1st to 15thNight
20%
718
12%
1796
3%
718
25%
718
14%
1456
April16th to endNight
22%
567
14%
1647
5%
567
30%
567
16%
1188
May1st to 15thNight
23%
489
13%
1569
8%
489
32%
489
15%
1130
May16th to endNight
30%
375
10%
1497
9%
374
38%
374
12%
1066
June1st to 15thNight
31%
360
8%
1440
7%
360
37%
360
10%
1084
June16th to endNight
43%
360
7%
1440
10%
360
47%
360
15%
991
July1st to 15thNight
47%
340
10%
1360
16%
340
51%
340
17%
892
July16th to endNight
50%
376
11%
1418
13%
354
51%
354
17%
932
August1st to 15thNight
48%
437
11%
1508
10%
435
50%
435
18%
1029
August16th to endNight
48%
684
18%
1830
10%
684
51%
684
30%
1191
September1st to 15thNight
42%
720
11%
1845
6%
720
44%
720
25%
1316
September16th to endNight
44%
717
21%
1980
15%
717
48%
717
29%
1276
October1st to 15thNight
31%
720
14%
2058
8%
720
37%
720
16%
1539
October16th to endNight
18%
708
7%
2299
3%
708
23%
708
8%
1857
November1st to 15thNight
20%
700
12%
2277
9%
700
25%
700
11%
1784
November16th to endNight
19%
720
11%
2417
9%
720
23%
720
8%
1940
December1st to 15thNight
10%
720
3%
2520
0%
720
14%
720
4%
2213
December16th to endNight
8%
768
5%
2688
2%
768
12%
768
3%
2389

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
20%12%5%7%6%34445%24%
48274
Night
18%12%5%8%6%34445%25%
47323
TransparencyDay
60%5%10%15%6%
47962
Night
61%5%9%15%7%
47153
SeeingDay
30%15%25%17%8%2
5838
Night
27%16%25%21%8%
14790

By Month

Percentage Cloud Cover NE (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
16%14%8%14%11%46%5%3311%
1432
16th to endDay
10%15%9%11%11%36%5%3417%
1536
February1st to 15thDay
13%16%10%14%11%46%33312%
1561
16th to endDay
11%16%9%15%9%5%5%23217%
1580
March1st to 15thDay
15%15%8%10%7%35%5%3422%
1790
16th to endDay
17%15%6%9%6%3322328%
2201
April1st to 15thDay
19%17%5%7%42333427%
2152
16th to endDay
19%14%25%5%2444431%
2312
May1st to 15thDay
25%10%35%5%3434428%
2391
16th to endDay
23%7%36%5%36%45%7%24%
2618
June1st to 15thDay
32%8%25%5%2445%5%22%
2520
16th to endDay
22%8%36%5%36%45%7%26%
2520
July1st to 15thDay
18%6%36%5%35%5%6%9%26%
2520
16th to endDay
20%6%36%6%45%5%6%7%24%
2654
August1st to 15thDay
21%7%37%5%46%5%5%7%24%
2429
16th to endDay
18%7%25%5%245%6%7%33%
2370
September1st to 15thDay
23%7%24423436%37%
2115
16th to endDay
18%7%24323448%39%
1980
October1st to 15thDay
21%12%35%4235%5%6%27%
1901
16th to endDay
23%22%46%42333420%
1593
November1st to 15thDay
21%17%6%6%424345%24%
1581
16th to endDay
17%15%7%9%6%2434423%
1542
December1st to 15thDay
19%21%8%12%5%4433313%
1440
16th to endDay
21%20%10%12%7%2432211%
1536
January1st to 15thNight
14%16%8%14%10%46%43313%
2506
16th to endNight
11%17%9%12%9%5%7%43314%
2688
February1st to 15thNight
11%14%8%15%13%6%7%33313%
2297
16th to endNight
13%16%8%13%8%36%32419%
1893
March1st to 15thNight
17%15%6%8%7%35%43324%
2147
16th to endNight
15%14%6%9%5%3333331%
2019
April1st to 15thNight
21%13%5%8%6%3444424%
1796
16th to endNight
21%12%24423345%33%
1647
May1st to 15thNight
22%9%36%5%24446%30%
1569
16th to endNight
22%8%25%5%44446%29%
1495
June1st to 15thNight
30%6%35%325%5%46%25%
1440
16th to endNight
19%6%35%4345%5%7%34%
1440
July1st to 15thNight
14%6%35%5%36%5%6%9%33%
1440
16th to endNight
15%6%25%436%5%5%8%35%
1514
August1st to 15thNight
17%6%35%5%345%6%8%33%
1518
16th to endNight
15%4245%2345%6%44%
1830
September1st to 15thNight
19%7%26%5%24345%39%
1845
16th to endNight
19%5%1332335%6%45%
1980
October1st to 15thNight
20%10%37%5%33435%32%
2058
16th to endNight
27%16%36%43344420%
2299
November1st to 15thNight
20%16%5%6%5%33345%23%
2277
16th to endNight
18%15%8%10%8%2333323%
2417
December1st to 15thNight
20%21%8%11%8%3433213%
2520
16th to endNight
19%20%9%12%9%3422310%
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
76%5%6%8%2
1433
16th to endDay
70%48%12%3
1536
February1st to 15thDay
78%349%2
1564
16th to endDay
73%36%8%6%1
1580
March1st to 15thDay
67%49%11%6%1
1800
16th to endDay
63%37%14%10%1
2201
April1st to 15thDay
61%37%16%9%1
2152
16th to endDay
54%5%9%16%10%3
2312
May1st to 15thDay
59%48%17%8%
2391
16th to endDay
56%8%11%15%7%
2622
June1st to 15thDay
62%6%10%14%4
2520
16th to endDay
56%6%11%18%6%
2520
July1st to 15thDay
51%7%15%19%6%
2371
16th to endDay
56%7%13%18%4
2487
August1st to 15thDay
55%8%16%15%3
2415
16th to endDay
47%5%15%20%9%
2370
September1st to 15thDay
48%6%12%22%9%
2115
16th to endDay
43%5%12%24%12%
1980
October1st to 15thDay
55%5%12%18%7%
1901
16th to endDay
68%410%11%5%
1593
November1st to 15thDay
62%48%13%7%1
1581
16th to endDay
65%410%12%6%
1542
December1st to 15thDay
76%47%8%3
1440
16th to endDay
80%445%5%
1536
January1st to 15thNight
76%47%9%2
2506
16th to endNight
73%5%6%10%3
2688
February1st to 15thNight
76%46%9%3
2298
16th to endNight
71%36%10%7%
1893
March1st to 15thNight
65%46%15%6%1
2160
16th to endNight
59%37%15%11%2
2019
April1st to 15thNight
61%5%5%15%10%
1796
16th to endNight
51%5%10%17%13%2
1647
May1st to 15thNight
54%5%9%18%11%1
1569
16th to endNight
54%7%12%18%6%
1497
June1st to 15thNight
60%6%8%18%5%
1440
16th to endNight
48%8%12%21%7%
1440
July1st to 15thNight
43%10%14%23%7%
1360
16th to endNight
44%10%15%20%9%
1418
August1st to 15thNight
45%9%17%22%5%
1508
16th to endNight
38%5%17%26%10%
1830
September1st to 15thNight
48%414%24%7%
1845
16th to endNight
39%5%12%28%12%1
1980
October1st to 15thNight
55%5%10%19%9%
2058
16th to endNight
65%6%9%12%5%
2299
November1st to 15thNight
63%410%13%6%1
2277
16th to endNight
66%47%14%5%
2417
December1st to 15thNight
77%46%8%2
2520
16th to endNight
80%45%5%4
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%25%36%15%1
60
16th to endDay
32%21%31%10%3
64
February1st to 15thDay
33%22%24%15%3
149
16th to endDay
27%26%26%15%3
239
March1st to 15thDay
32%18%28%16%3
270
16th to endDay
26%23%25%14%9%1
288
April1st to 15thDay
37%16%25%13%5%1
270
16th to endDay
31%21%23%11%8%3
270
May1st to 15thDay
42%11%25%11%6%3
288
16th to endDay
29%17%27%19%5%1
331
June1st to 15thDay
40%13%22%16%7%
315
16th to endDay
26%15%33%16%6%2
315
July1st to 15thDay
23%11%32%21%9%1
305
16th to endDay
22%9%32%25%8%2
326
August1st to 15thDay
26%8%28%19%14%2
313
16th to endDay
23%11%19%20%18%6%
332
September1st to 15thDay
26%10%18%23%14%6%
315
16th to endDay
18%13%18%23%16%9%
314
October1st to 15thDay
29%17%21%18%10%3
310
16th to endDay
39%17%23%12%7%
243
November1st to 15thDay
34%15%25%15%6%1
235
16th to endDay
37%17%18%17%6%1
162
December1st to 15thDay
40%20%30%8%1
60
16th to endDay
43%25%28%11
64
January1st to 15thNight
25%25%30%14%2
720
16th to endNight
23%25%29%17%3
768
February1st to 15thNight
22%24%33%16%3
704
16th to endNight
25%21%32%16%3
631
March1st to 15thNight
31%18%28%18%2
720
16th to endNight
27%20%24%17%8%
768
April1st to 15thNight
32%20%23%18%4
718
16th to endNight
30%17%26%17%7%
567
May1st to 15thNight
27%14%31%19%6%
489
16th to endNight
27%10%25%28%7%
375
June1st to 15thNight
35%6%20%27%10%
360
16th to endNight
18%8%25%36%10%
360
July1st to 15thNight
17%5%24%35%16%
340
16th to endNight
16%5%21%37%19%
376
August1st to 15thNight
19%418%36%19%1
437
16th to endNight
19%5%21%32%19%2
684
September1st to 15thNight
23%7%20%32%14%1
720
16th to endNight
21%8%21%25%19%2
717
October1st to 15thNight
30%11%23%22%11%1
720
16th to endNight
39%17%21%16%4
708
November1st to 15thNight
29%18%26%16%7%1
700
16th to endNight
29%23%22%15%7%1
720
December1st to 15thNight
35%24%25%11%3
720
16th to endNight
34%22%25%13%2
768
Page generated at 2017-10-17 16:35:27. Version ac04

Copyright 2017 A. Danko


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