West Mountain
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the West Mountain clear sky chart from 2005-11-05 to 2018-02-13.

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%
16341
24%
49040
21%
16305
67%
16305
36%
28247

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
56%
776
15%
2522
15%
776
58%
776
22%
1675
January16th to endNight
56%
832
19%
2704
20%
832
57%
832
23%
1763
February1st to 15thNight
58%
748
15%
2444
17%
748
60%
748
25%
1564
February16th to endNight
53%
632
21%
1902
21%
632
56%
632
29%
1202
March1st to 15thNight
62%
720
22%
2013
19%
720
66%
720
36%
1205
March16th to endNight
57%
768
22%
2112
17%
768
61%
768
33%
1316
April1st to 15thNight
52%
650
19%
1879
15%
650
55%
650
32%
1128
April16th to endNight
56%
540
26%
1620
19%
540
60%
540
35%
929
May1st to 15thNight
61%
539
25%
1620
20%
539
64%
539
38%
890
May16th to endNight
66%
561
21%
1685
18%
561
68%
561
39%
925
June1st to 15thNight
67%
540
23%
1620
21%
540
71%
540
47%
792
June16th to endNight
70%
540
29%
1620
26%
540
78%
540
65%
692
July1st to 15thNight
76%
510
19%
1530
18%
510
79%
510
43%
810
July16th to endNight
77%
564
23%
1593
22%
531
77%
531
40%
864
August1st to 15thNight
74%
539
29%
1611
22%
536
79%
536
47%
810
August16th to endNight
78%
573
37%
1737
32%
573
81%
573
51%
847
September1st to 15thNight
80%
690
31%
1950
25%
690
85%
690
57%
950
September16th to endNight
76%
716
39%
1980
32%
716
79%
716
55%
990
October1st to 15thNight
70%
720
31%
2096
24%
720
75%
720
47%
1108
October16th to endNight
70%
768
35%
2304
31%
768
74%
768
44%
1208
November1st to 15thNight
65%
760
27%
2461
27%
760
67%
760
37%
1343
November16th to endNight
63%
809
27%
2564
27%
809
66%
809
35%
1455
December1st to 15thNight
58%
975
16%
2730
14%
975
59%
975
30%
1776
December16th to endNight
46%
871
15%
2743
15%
871
47%
871
17%
2005

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
5%5%2442445%8%51%
48992
Night
6%6%2442445%7%51%
49234
TransparencyDay
31%310%20%20%13%
48687
Night
32%311%23%18%10%
49040
SeeingDay
8%10%23%32%18%5%
5780
Night
9%5%13%39%27%4
16352

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
10%10%35%6%25%46%8%35%
1746
16th to endDay
9%11%46%5%25%45%8%35%
1872
February1st to 15thDay
11%10%36%5%3445%8%35%
1683
16th to endDay
6%10%46%5%3446%8%39%
1571
March1st to 15thDay
37%35%5%245%48%48%
1947
16th to endDay
7%8%25%5%35%5%5%8%41%
2112
April1st to 15thDay
6%7%35%436%5%46%46%
2064
16th to endDay
6%6%2443445%7%49%
2340
May1st to 15thDay
5%4234245%6%7%52%
2331
16th to endDay
5%3134345%8%9%50%
2429
June1st to 15thDay
3213334448%60%
2340
16th to endDay
212113235%75%
2340
July1st to 15thDay
2112425%6%5%9%59%
2340
16th to endDay
2222325%5%6%8%57%
2467
August1st to 15thDay
12134245%7%9%57%
2340
16th to endDay
22232346%7%63%
2465
September1st to 15thDay
211222435%6%66%
2009
16th to endDay
5%11222346%67%
1980
October1st to 15thDay
5%413234446%58%
1863
16th to endDay
5%423313347%59%
1920
November1st to 15thDay
10%5%24424346%50%
1725
16th to endDay
6%7%25%4245%5%9%45%
1707
December1st to 15thDay
9%10%47%5%24448%38%
1560
16th to endDay
12%14%47%5%3445%9%27%
1841
January1st to 15thNight
10%10%37%5%3446%9%33%
2522
16th to endNight
10%10%47%5%2446%9%34%
2704
February1st to 15thNight
9%10%36%42445%8%40%
2433
16th to endNight
6%8%45%5%25%45%9%41%
1902
March1st to 15thNight
6%7%3443345%7%48%
2013
16th to endNight
6%7%25%5%345%6%8%45%
2112
April1st to 15thNight
8%6%25%4235%46%50%
1879
16th to endNight
7%5%25%32345%7%52%
1620
May1st to 15thNight
5%41433445%8%53%
1619
16th to endNight
5%4144245%6%7%52%
1684
June1st to 15thNight
3213224447%63%
1620
16th to endNight
111212346%74%
1620
July1st to 15thNight
2123326%6%7%9%54%
1620
16th to endNight
22145%36%5%6%7%53%
1701
August1st to 15thNight
22135%3445%8%59%
1620
16th to endNight
11332446%8%62%
1737
September1st to 15thNight
2112223446%68%
1950
16th to endNight
5%213222245%68%
1980
October1st to 15thNight
5%413313346%61%
2096
16th to endNight
5%413323346%61%
2304
November1st to 15thNight
7%424323347%55%
2461
16th to endNight
6%7%45%324346%52%
2564
December1st to 15thNight
11%10%34324346%44%
2730
16th to endNight
16%13%5%7%5%24447%27%
2743

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%6%21%21%6%
1747
16th to endDay
45%5%19%19%9%1
1872
February1st to 15thDay
46%417%21%8%1
1683
16th to endDay
43%414%25%12%
1571
March1st to 15thDay
35%315%27%14%3
1947
16th to endDay
41%312%25%12%3
2112
April1st to 15thDay
39%312%22%17%4
2064
16th to endDay
35%29%24%22%5%
2340
May1st to 15thDay
29%39%23%26%8%
2331
16th to endDay
29%410%23%25%6%
2432
June1st to 15thDay
22%36%15%33%19%
2340
16th to endDay
13%228%27%46%
2340
July1st to 15thDay
21%5%413%21%34%
2201
16th to endDay
23%37%14%21%29%
2312
August1st to 15thDay
22%4418%20%28%
2325
16th to endDay
19%2417%31%24%
2465
September1st to 15thDay
19%36%15%28%27%
2009
16th to endDay
18%3422%31%19%
1980
October1st to 15thDay
28%37%23%30%6%
1863
16th to endDay
25%29%30%26%4
1920
November1st to 15thDay
35%39%26%20%4
1725
16th to endDay
33%416%29%13%2
1707
December1st to 15thDay
43%319%24%8%
1560
16th to endDay
52%5%16%17%6%
1841
January1st to 15thNight
45%5%19%21%6%1
2522
16th to endNight
44%417%22%8%2
2704
February1st to 15thNight
41%6%17%23%10%
2444
16th to endNight
41%313%29%11%
1902
March1st to 15thNight
33%314%31%14%2
2013
16th to endNight
35%411%28%15%4
2112
April1st to 15thNight
36%212%23%19%5%
1879
16th to endNight
32%310%27%21%3
1620
May1st to 15thNight
29%39%24%25%8%
1620
16th to endNight
29%310%27%22%6%
1685
June1st to 15thNight
20%36%18%33%17%
1620
16th to endNight
12%1311%26%45%
1620
July1st to 15thNight
23%5%5%13%18%33%
1530
16th to endNight
27%47%14%18%27%
1593
August1st to 15thNight
22%38%20%17%27%
1611
16th to endNight
19%36%15%29%25%
1737
September1st to 15thNight
17%27%16%26%29%
1950
16th to endNight
19%2420%29%24%
1980
October1st to 15thNight
24%28%24%28%10%
2096
16th to endNight
25%36%28%30%5%
2304
November1st to 15thNight
29%310%27%21%6%
2461
16th to endNight
32%312%30%17%3
2564
December1st to 15thNight
41%316%27%9%
2730
16th to endNight
56%313%18%6%
2743

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
27%6%5%25%28%6%
135
16th to endDay
13%11%12%29%25%6%
144
February1st to 15thDay
15%11%9%37%22%3
126
16th to endDay
10%15%28%31%12%1
230
March1st to 15thDay
7%13%27%32%15%1
270
16th to endDay
16%17%32%25%7%1
288
April1st to 15thDay
10%23%26%17%15%5%
269
16th to endDay
13%24%25%25%8%2
270
May1st to 15thDay
7%12%38%26%11%3
288
16th to endDay
8%9%24%29%21%6%
330
June1st to 15thDay
316%27%33%15%3
315
16th to endDay
110%26%35%20%5%
315
July1st to 15thDay
15%24%38%21%8%
305
16th to endDay
3323%45%20%3
327
August1st to 15thDay
3424%39%20%6%
315
16th to endDay
3321%37%23%9%
332
September1st to 15thDay
46%27%31%20%8%
315
16th to endDay
7%8%18%31%25%8%
315
October1st to 15thDay
5%9%30%26%18%10%
198
16th to endDay
7%8%16%34%25%7%
144
November1st to 15thDay
7%11%14%32%20%13%
135
16th to endDay
14%12%10%35%22%3
135
December1st to 15thDay
17%312%40%17%8%
135
16th to endDay
15%5%9%43%25%
144
January1st to 15thNight
14%5%10%36%27%5%
780
16th to endNight
12%7%11%35%27%5%
832
February1st to 15thNight
12%5%12%45%19%4
752
16th to endNight
11%5%19%43%17%2
632
March1st to 15thNight
9%7%13%45%21%1
720
16th to endNight
10%7%19%41%18%2
768
April1st to 15thNight
12%10%18%37%18%2
650
16th to endNight
10%8%17%37%23%2
540
May1st to 15thNight
6%5%18%41%24%2
540
16th to endNight
6%5%14%38%30%4
563
June1st to 15thNight
47%15%41%29%2
540
16th to endNight
2220%38%32%2
540
July1st to 15thNight
328%34%45%5%
510
16th to endNight
317%37%46%3
564
August1st to 15thNight
412%44%35%2
539
16th to endNight
1210%36%42%5%
573
September1st to 15thNight
3110%38%37%9%
690
16th to endNight
6%38%30%38%11%
716
October1st to 15thNight
7%314%40%28%5%
720
16th to endNight
6%5%11%38%31%6%
768
November1st to 15thNight
9%5%13%37%29%5%
760
16th to endNight
9%5%14%39%23%6%
809
December1st to 15thNight
15%5%12%43%20%3
975
16th to endNight
21%7%10%38%18%2
871
Page generated at 2018-02-13 18:46:04. Version ac04

Copyright 2018 A. Danko


West Mountain Clear Sky Chart |Charts Home