This page made possible by the sponsorship of: Bob Pitt.

Hoover
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Hoover clear sky chart from 2005-11-05 to 2017-12-04.

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
51%
15555
24%
47917
18%
15512
58%
15512
31%
28688

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
29%
720
25%
2327
12%
716
45%
716
24%
1427
January16th to endNight
27%
768
26%
2304
11%
768
41%
768
23%
1502
February1st to 15thNight
32%
704
26%
2112
11%
701
45%
701
28%
1292
February16th to endNight
29%
631
25%
1893
12%
631
41%
631
27%
1178
March1st to 15thNight
32%
720
21%
2157
13%
720
40%
720
27%
1350
March16th to endNight
40%
702
25%
2046
14%
702
49%
702
31%
1230
April1st to 15thNight
41%
539
25%
1797
17%
539
54%
539
31%
1016
April16th to endNight
47%
540
28%
1800
20%
540
59%
540
34%
970
May1st to 15thNight
52%
540
23%
1650
15%
540
60%
540
31%
1009
May16th to endNight
69%
561
24%
1682
19%
561
74%
561
38%
950
June1st to 15thNight
74%
540
17%
1620
15%
540
75%
540
34%
953
June16th to endNight
77%
540
19%
1620
18%
540
78%
540
36%
947
July1st to 15thNight
74%
510
14%
1530
13%
510
75%
510
30%
965
July16th to endNight
75%
564
17%
1637
17%
531
78%
531
32%
1013
August1st to 15thNight
76%
539
18%
1788
21%
536
77%
536
32%
1049
August16th to endNight
71%
573
21%
1910
25%
573
71%
573
26%
1220
September1st to 15thNight
64%
615
20%
1875
21%
615
65%
615
28%
1186
September16th to endNight
68%
717
29%
1980
24%
717
71%
717
39%
1145
October1st to 15thNight
60%
720
34%
1980
26%
720
66%
720
42%
1119
October16th to endNight
54%
768
35%
2316
29%
768
62%
768
38%
1282
November1st to 15thNight
53%
760
29%
2471
25%
760
63%
760
36%
1322
November16th to endNight
44%
780
30%
2535
22%
780
56%
780
32%
1417
December1st to 15thNight
38%
736
23%
2391
17%
736
47%
736
26%
1463
December16th to endNight
31%
768
20%
2496
15%
768
39%
768
19%
1683

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
12%5%25%5%35%5%5%7%41%
48565
Night
11%42442445%7%47%
48120
TransparencyDay
40%5%10%19%18%4
48271
Night
35%5%10%20%20%7%
47919
SeeingDay
14%5%18%24%23%14%
5427
Night
13%6%22%29%23%4
15557

By Month

Percentage Cloud Cover SE (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
20%6%2442333443%
1611
16th to endDay
18%6%24323335%45%
1917
February1st to 15thDay
16%7%35%424336%42%
1750
16th to endDay
19%6%24434435%41%
1580
March1st to 15thDay
15%8%26%5%23335%41%
1803
16th to endDay
13%7%245%245%47%41%
2186
April1st to 15thDay
12%435%434447%44%
2151
16th to endDay
8%335%5%345%5%7%46%
2160
May1st to 15thDay
12%5%244345%5%7%43%
2298
16th to endDay
8%425%6%3446%9%42%
2431
June1st to 15thDay
7%5%35%6%46%7%7%10%35%
2340
16th to endDay
5%3245%37%5%7%11%43%
2340
July1st to 15thDay
8%427%7%48%7%9%11%28%
2340
16th to endDay
7%426%7%48%8%8%10%29%
2417
August1st to 15thDay
8%4247%48%8%8%10%32%
2160
16th to endDay
12%5%27%8%5%7%7%7%9%27%
2292
September1st to 15thDay
12%5%26%5%36%6%48%37%
2073
16th to endDay
12%5%145%245%5%6%46%
1980
October1st to 15thDay
9%42433435%6%51%
1980
16th to endDay
10%42441323458%
1905
November1st to 15thDay
12%5%23323235%53%
1717
16th to endDay
13%5%23324336%50%
1755
December1st to 15thDay
18%7%34424346%40%
1651
16th to endDay
21%10%45%432335%35%
1728
January1st to 15thNight
15%6%3343344446%
2327
16th to endNight
17%7%3442444441%
2304
February1st to 15thNight
16%5%14323346%46%
2103
16th to endNight
17%5%24423445%46%
1893
March1st to 15thNight
15%6%24423447%44%
2157
16th to endNight
12%42432445%7%48%
2046
April1st to 15thNight
10%32442446%7%49%
1797
16th to endNight
8%415%32435%7%53%
1800
May1st to 15thNight
9%4145%345%5%8%46%
1649
16th to endNight
43145%35%5%6%10%49%
1682
June1st to 15thNight
4323437%7%8%11%43%
1620
16th to endNight
4314435%5%8%12%45%
1620
July1st to 15thNight
7%425%5%36%5%7%9%41%
1620
16th to endNight
5%335%6%45%6%6%12%41%
1748
August1st to 15thNight
5%315%435%7%8%12%42%
1800
16th to endNight
8%5%15%6%36%5%7%9%39%
1910
September1st to 15thNight
9%425%7%35%46%9%40%
1875
16th to endNight
7%3145%2345%7%53%
1980
October1st to 15thNight
8%423323346%58%
1980
16th to endNight
11%42422233359%
2316
November1st to 15thNight
10%323313345%56%
2471
16th to endNight
10%5%14423345%53%
2535
December1st to 15thNight
15%6%25%424347%43%
2391
16th to endNight
20%8%35%5%24345%37%
2496

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
44%26%15%25%5%
1612
16th to endDay
41%35%20%22%7%
1917
February1st to 15thDay
44%26%24%18%4
1752
16th to endDay
45%35%15%23%6%
1580
March1st to 15thDay
45%29%16%20%5%
1803
16th to endDay
41%410%21%19%2
2187
April1st to 15thDay
38%49%20%19%7%
2151
16th to endDay
35%5%8%22%24%2
2160
May1st to 15thDay
39%411%18%21%4
2298
16th to endDay
38%6%13%24%14%3
2435
June1st to 15thDay
39%9%15%21%12%1
2340
16th to endDay
32%7%15%25%15%3
2340
July1st to 15thDay
41%11%17%18%8%1
2201
16th to endDay
42%11%18%17%9%
2266
August1st to 15thDay
39%11%17%18%9%3
2148
16th to endDay
48%9%13%16%9%2
2292
September1st to 15thDay
43%8%12%18%13%4
2073
16th to endDay
36%5%9%22%19%5%
1980
October1st to 15thDay
32%48%21%22%10%
1980
16th to endDay
30%2317%34%10%
1905
November1st to 15thDay
34%35%17%29%9%
1717
16th to endDay
36%35%18%26%10%
1755
December1st to 15thDay
46%38%19%16%6%
1651
16th to endDay
52%36%18%13%4
1728
January1st to 15thNight
40%36%18%25%5%
2327
16th to endNight
44%3418%21%8%
2304
February1st to 15thNight
39%26%22%20%9%
2112
16th to endNight
39%35%20%24%6%
1893
March1st to 15thNight
40%39%19%20%7%
2157
16th to endNight
34%49%25%22%4
2046
April1st to 15thNight
33%410%23%20%8%
1797
16th to endNight
29%49%25%23%7%
1800
May1st to 15thNight
34%6%11%18%23%5%
1650
16th to endNight
27%6%16%27%15%5%
1684
June1st to 15thNight
28%9%18%25%16%1
1620
16th to endNight
28%9%17%23%18%3
1620
July1st to 15thNight
34%9%21%21%9%3
1530
16th to endNight
31%10%22%22%11%
1637
August1st to 15thNight
30%9%19%23%13%3
1788
16th to endNight
38%8%16%20%13%3
1910
September1st to 15thNight
38%6%15%19%14%5%
1875
16th to endNight
30%411%24%22%7%
1980
October1st to 15thNight
28%37%22%23%13%
1980
16th to endNight
30%2313%32%16%
2316
November1st to 15thNight
29%37%17%27%14%
2471
16th to endNight
33%26%18%25%13%
2535
December1st to 15thNight
40%310%19%20%5%
2391
16th to endNight
49%36%17%16%6%
2496

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
20%15%35%24%31
90
16th to endDay
21%19%48%6%12
96
February1st to 15thDay
20%25%36%16%1
90
16th to endDay
25%8%43%22%
81
March1st to 15thDay
27%18%36%10%5%1
93
16th to endDay
21%5%32%23%16%1
288
April1st to 15thDay
17%8%28%25%17%1
270
16th to endDay
10%6%28%28%21%5%
270
May1st to 15thDay
12%7%23%26%19%10%
288
16th to endDay
12%414%27%23%16%
331
June1st to 15thDay
12%11%21%29%25%
315
16th to endDay
8%28%21%28%30%
315
July1st to 15thDay
6%5%22%31%31%
305
16th to endDay
8%16%15%31%37%
326
August1st to 15thDay
11%5%24%32%25%
313
16th to endDay
14%16%22%31%23%
332
September1st to 15thDay
14%29%23%30%20%
315
16th to endDay
9%111%31%34%11%
314
October1st to 15thDay
12%420%29%28%4
315
16th to endDay
14%8%20%29%23%3
214
November1st to 15thDay
22%9%27%31%8%
135
16th to endDay
14%11%31%27%13%1
135
December1st to 15thDay
23%11%32%27%5%2
100
16th to endDay
30%12%36%14%6%
96
January1st to 15thNight
19%13%35%23%7%
720
16th to endNight
20%13%34%26%5%
768
February1st to 15thNight
19%10%34%30%5%
704
16th to endNight
19%12%35%28%3
631
March1st to 15thNight
19%11%32%28%7%
720
16th to endNight
14%10%31%28%15%
702
April1st to 15thNight
10%9%34%27%16%
539
16th to endNight
11%7%27%34%17%2
540
May1st to 15thNight
10%5%25%31%22%4
540
16th to endNight
7%114%35%35%6%
563
June1st to 15thNight
8%7%33%40%9%
540
16th to endNight
416%24%46%17%
540
July1st to 15thNight
8%425%44%15%
510
16th to endNight
7%5%20%47%18%
564
August1st to 15thNight
6%326%49%13%
539
16th to endNight
10%15%26%43%12%
573
September1st to 15thNight
12%19%27%38%10%
615
16th to endNight
10%11%32%37%6%
717
October1st to 15thNight
11%320%30%30%3
720
16th to endNight
13%5%21%30%25%3
768
November1st to 15thNight
13%5%23%33%20%4
760
16th to endNight
13%11%27%31%15%1
780
December1st to 15thNight
20%9%26%32%11%
736
16th to endNight
25%10%28%26%9%
768
Page generated at 2017-12-05 09:19:02. Version ac04

Copyright 2017 A. Danko


Hoover Clear Sky Chart |Charts Home