Dowdy Ranch Visitor Center
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Dowdy Ranch Visitor Center clear sky chart from 2005-11-05 to 2017-09-21.

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
70%
15451
28%
46950
25%
15414
73%
15414
39%
25693

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
66%
716
19%
2403
19%
716
68%
716
30%
1382
January16th to endNight
65%
768
24%
2496
26%
768
66%
768
28%
1509
February1st to 15thNight
64%
697
26%
2256
28%
697
68%
697
29%
1351
February16th to endNight
60%
632
23%
1895
22%
632
65%
632
30%
1166
March1st to 15thNight
60%
720
19%
2037
18%
720
63%
720
29%
1314
March16th to endNight
56%
768
21%
2067
16%
768
60%
768
31%
1325
April1st to 15thNight
55%
719
23%
1799
14%
719
58%
719
34%
1157
April16th to endNight
60%
720
27%
1800
12%
720
65%
720
47%
1021
May1st to 15thNight
68%
665
25%
1745
15%
665
71%
665
47%
960
May16th to endNight
69%
375
26%
1496
26%
374
75%
374
36%
702
June1st to 15thNight
72%
360
27%
1440
26%
360
81%
360
38%
671
June16th to endNight
83%
360
36%
1440
44%
360
88%
360
56%
537
July1st to 15thNight
89%
356
31%
1376
37%
356
91%
356
53%
540
July16th to endNight
89%
564
33%
1593
30%
531
90%
531
49%
776
August1st to 15thNight
85%
595
30%
1668
23%
592
85%
592
51%
850
August16th to endNight
89%
764
40%
1910
26%
764
90%
764
66%
961
September1st to 15thNight
87%
720
40%
1800
28%
720
88%
720
64%
913
September16th to endNight
82%
680
41%
1842
37%
680
85%
680
57%
921
October1st to 15thNight
74%
660
30%
1980
32%
660
78%
660
45%
1031
October16th to endNight
76%
704
35%
2112
38%
704
79%
704
46%
1084
November1st to 15thNight
74%
700
32%
2208
33%
700
78%
700
45%
1113
November16th to endNight
70%
720
26%
2379
26%
720
73%
720
36%
1282
December1st to 15thNight
62%
720
22%
2520
23%
720
66%
720
26%
1505
December16th to endNight
56%
768
21%
2688
20%
768
60%
768
25%
1622

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%213323446%61%
47914
Night
6%3133245%5%7%56%
47137
TransparencyDay
25%38%19%24%18%
47599
Night
28%38%18%23%16%
46951
SeeingDay
8%8%24%32%20%5%
6003
Night
8%312%35%31%9%
15463

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%5%25%43435%8%46%
1534
16th to endDay
13%6%35%434445%44%
1728
February1st to 15thDay
13%6%25%424336%46%
1608
16th to endDay
14%6%26%5%36%5%46%39%
1579
March1st to 15thDay
9%5%35%5%36%5%6%8%39%
1920
16th to endDay
9%436%5%35%5%5%7%43%
2157
April1st to 15thDay
10%5%35%5%245%48%44%
2149
16th to endDay
6%213324347%61%
2160
May1st to 15thDay
11231445%9%64%
2200
16th to endDay
321232445%8%61%
2615
June1st to 15thDay
2212313448%66%
2520
16th to endDay
1111236%79%
2520
July1st to 15thDay
1112335%79%
2501
16th to endDay
1112335%79%
2468
August1st to 15thDay
1112336%78%
2283
16th to endDay
1112236%80%
2292
September1st to 15thDay
112225%81%
2160
16th to endDay
111112346%73%
1906
October1st to 15thDay
311231245%8%66%
1650
16th to endDay
4213424436%62%
1760
November1st to 15thDay
7%224324447%55%
1650
16th to endDay
8%41443345%6%51%
1578
December1st to 15thDay
12%6%45%6%24445%43%
1440
16th to endDay
13%5%36%5%34447%41%
1536
January1st to 15thNight
10%4244345%5%7%47%
2403
16th to endNight
12%425%424446%49%
2496
February1st to 15thNight
12%424425%45%7%46%
2245
16th to endNight
11%4244345%47%48%
1895
March1st to 15thNight
9%425%5%35%5%5%7%46%
2037
16th to endNight
8%5%24435%45%7%47%
2067
April1st to 15thNight
8%2245%26%6%5%6%49%
1799
16th to endNight
421232345%8%61%
1800
May1st to 15thNight
1212425%5%6%10%57%
1745
16th to endNight
122226%7%6%9%59%
1496
June1st to 15thNight
113325%6%7%8%60%
1440
16th to endNight
21445%7%72%
1440
July1st to 15thNight
11115%6%6%9%66%
1457
16th to endNight
112246%9%11%58%
1701
August1st to 15thNight
11325%7%9%10%58%
1677
16th to endNight
11125%8%10%67%
1910
September1st to 15thNight
1112245%7%71%
1800
16th to endNight
2212445%6%69%
1842
October1st to 15thNight
4212423448%61%
1980
16th to endNight
321241445%6%63%
2112
November1st to 15thNight
5%213213348%61%
2208
16th to endNight
6%3234245%48%54%
2379
December1st to 15thNight
10%6%35%425%447%45%
2520
16th to endNight
15%424423445%47%
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
37%5%10%21%16%8%
1534
16th to endDay
41%5%7%14%19%11%
1728
February1st to 15thDay
40%48%20%19%6%
1608
16th to endDay
46%5%8%22%14%3
1579
March1st to 15thDay
40%6%11%18%18%4
1920
16th to endDay
39%7%13%18%17%3
2157
April1st to 15thDay
38%411%21%18%4
2149
16th to endDay
25%413%24%23%8%
2160
May1st to 15thDay
18%410%28%29%8%
2200
16th to endDay
23%313%26%24%7%
2619
June1st to 15thDay
20%310%22%24%18%
2520
16th to endDay
10%317%34%32%
2520
July1st to 15thDay
10%128%24%53%
2353
16th to endDay
10%238%26%48%
2313
August1st to 15thDay
13%113%29%41%
2267
16th to endDay
9%1113%36%37%
2292
September1st to 15thDay
10%1314%33%37%
2160
16th to endDay
13%15%25%33%20%
1906
October1st to 15thDay
18%49%22%25%19%
1650
16th to endDay
24%38%21%24%17%
1760
November1st to 15thDay
29%5%10%23%23%8%
1650
16th to endDay
33%49%19%28%4
1578
December1st to 15thDay
42%411%14%20%5%
1440
16th to endDay
41%6%12%16%16%5%
1536
January1st to 15thNight
34%5%12%20%19%7%
2403
16th to endNight
37%5%10%13%18%14%
2496
February1st to 15thNight
37%39%22%17%8%
2256
16th to endNight
37%412%25%15%4
1895
March1st to 15thNight
39%5%12%18%17%7%
2037
16th to endNight
38%412%19%17%7%
2067
April1st to 15thNight
35%5%13%24%17%4
1799
16th to endNight
23%413%27%22%9%
1800
May1st to 15thNight
24%38%23%26%12%
1746
16th to endNight
25%311%25%26%7%
1496
June1st to 15thNight
25%38%18%23%20%
1440
16th to endNight
15%213%32%35%
1440
July1st to 15thNight
16%125%27%46%
1376
16th to endNight
22%239%23%38%
1593
August1st to 15thNight
23%1211%27%33%
1668
16th to endNight
16%212%32%35%
1910
September1st to 15thNight
16%129%29%39%
1800
16th to endNight
19%1218%34%23%
1842
October1st to 15thNight
23%36%23%21%20%
1980
16th to endNight
24%26%23%24%18%
2112
November1st to 15thNight
24%311%23%27%10%
2208
16th to endNight
29%410%20%25%9%
2379
December1st to 15thNight
39%410%17%20%7%
2520
16th to endNight
39%413%16%18%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
20%6%26%28%13%3
162
16th to endDay
20%6%20%26%22%3
256
February1st to 15thDay
19%7%21%26%21%3
242
16th to endDay
17%13%21%27%17%2
238
March1st to 15thDay
16%15%24%20%19%4
270
16th to endDay
14%17%28%25%12%1
288
April1st to 15thDay
17%18%26%23%11%1
269
16th to endDay
12%18%34%22%9%2
270
May1st to 15thDay
5%13%42%25%10%2
288
16th to endDay
7%11%33%30%12%4
330
June1st to 15thDay
313%38%30%11%2
315
16th to endDay
15%24%40%22%5%
315
July1st to 15thDay
22%47%23%4
305
16th to endDay
1116%45%23%10%
327
August1st to 15thDay
3323%41%22%6%
315
16th to endDay
116%40%30%11%
332
September1st to 15thDay
1218%40%26%9%
315
16th to endDay
36%20%30%28%9%
276
October1st to 15thDay
5%10%24%30%22%6%
255
16th to endDay
9%5%22%31%26%4
272
November1st to 15thDay
8%5%15%22%37%10%
156
16th to endDay
8%8%19%39%24%
83
December1st to 15thDay
23%6%25%33%11%
60
16th to endDay
15%10%10%31%25%6%
64
January1st to 15thNight
13%28%34%29%11%
720
16th to endNight
14%39%32%28%11%
768
February1st to 15thNight
14%48%33%28%9%
704
16th to endNight
15%5%13%37%21%6%
632
March1st to 15thNight
12%415%32%27%7%
720
16th to endNight
11%8%16%35%23%5%
768
April1st to 15thNight
11%7%19%35%21%4
719
16th to endNight
7%6%22%32%24%7%
720
May1st to 15thNight
3221%42%25%5%
666
16th to endNight
4319%40%28%3
375
June1st to 15thNight
2120%46%26%2
360
16th to endNight
1112%44%37%3
360
July1st to 15thNight
25%37%48%5%
356
16th to endNight
1434%46%12%
564
August1st to 15thNight
18%40%42%7%
595
16th to endNight
7%35%46%10%
764
September1st to 15thNight
27%33%44%11%
720
16th to endNight
39%33%38%13%
680
October1st to 15thNight
6%210%33%32%14%
660
16th to endNight
6%29%32%29%20%
704
November1st to 15thNight
7%29%33%34%13%
700
16th to endNight
9%310%32%32%12%
720
December1st to 15thNight
15%48%36%26%8%
720
16th to endNight
17%5%13%33%25%4
768
Page generated at 2017-09-22 04:35:31. Version ac04

Copyright 2017 A. Danko


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