Phelan
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Phelan clear sky chart from 2005-11-05 to 2017-09-24.

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
73%
15873
36%
46806
29%
15829
79%
15829
59%
21480

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
62%
716
29%
2466
26%
716
71%
716
42%
1180
January16th to endNight
59%
768
35%
2310
27%
768
70%
768
44%
1209
February1st to 15thNight
64%
700
34%
2105
31%
697
72%
697
46%
1079
February16th to endNight
56%
632
31%
1895
29%
632
64%
632
42%
1011
March1st to 15thNight
63%
720
31%
2160
27%
720
73%
720
49%
1065
March16th to endNight
63%
768
33%
2020
23%
768
71%
768
54%
1042
April1st to 15thNight
57%
719
33%
1799
15%
719
66%
719
55%
961
April16th to endNight
62%
720
36%
1800
17%
720
70%
720
66%
887
May1st to 15thNight
70%
581
36%
1661
22%
581
75%
581
73%
690
May16th to endNight
65%
561
35%
1685
24%
561
71%
561
69%
700
June1st to 15thNight
77%
508
35%
1588
30%
508
82%
508
75%
599
June16th to endNight
91%
360
42%
1440
49%
360
94%
360
84%
410
July1st to 15thNight
93%
340
36%
1360
43%
340
94%
340
70%
438
July16th to endNight
89%
615
33%
1640
27%
578
90%
578
65%
746
August1st to 15thNight
93%
717
38%
1790
25%
713
93%
713
82%
799
August16th to endNight
94%
764
45%
1910
30%
764
94%
764
81%
861
September1st to 15thNight
93%
720
41%
1847
33%
720
94%
720
78%
824
September16th to endNight
87%
692
48%
1914
43%
692
91%
692
82%
775
October1st to 15thNight
75%
660
40%
1815
34%
660
81%
660
63%
855
October16th to endNight
78%
704
41%
2150
39%
704
84%
704
63%
922
November1st to 15thNight
76%
700
36%
2275
36%
700
84%
700
62%
939
November16th to endNight
73%
720
38%
2340
38%
720
80%
720
54%
1048
December1st to 15thNight
65%
720
33%
2340
29%
720
75%
720
44%
1137
December16th to endNight
55%
768
32%
2496
26%
768
66%
768
38%
1303

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
111112336%74%
48090
Night
111112336%75%
47002
TransparencyDay
12%46%15%27%33%
47780
Night
13%5%7%16%28%29%
46814
SeeingDay
29%25%35%20%5%
5914
Night
2318%35%33%7%
15884

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
21332345%7%66%
1455
16th to endDay
2313224448%61%
1911
February1st to 15thDay
1312213249%66%
1751
16th to endDay
2213324448%61%
1579
March1st to 15thDay
12221246%11%64%
1800
16th to endDay
1111346%10%65%
2199
April1st to 15thDay
1112213247%71%
2149
16th to endDay
11111138%78%
2160
May1st to 15thDay
112246%78%
2289
16th to endDay
111112225%79%
2429
June1st to 15thDay
11136%82%
2367
16th to endDay
1111288%
2520
July1st to 15thDay
111212235%77%
2520
16th to endDay
112212346%73%
2408
August1st to 15thDay
1222383%
2160
16th to endDay
11112335%79%
2292
September1st to 15thDay
1112235%80%
2112
16th to endDay
11112385%
1904
October1st to 15thDay
11212347%74%
1815
16th to endDay
11112235%78%
1718
November1st to 15thDay
111112336%75%
1584
16th to endDay
2112213348%69%
1620
December1st to 15thDay
221131335%10%65%
1620
16th to endDay
22133243410%60%
1728
January1st to 15thNight
221232345%9%63%
2466
16th to endNight
3213313348%65%
2310
February1st to 15thNight
2212213339%66%
2101
16th to endNight
12122245%6%9%61%
1895
March1st to 15thNight
122134310%67%
2160
16th to endNight
11221235%10%68%
2020
April1st to 15thNight
112213338%71%
1799
16th to endNight
1111238%79%
1800
May1st to 15thNight
11236%82%
1661
16th to endNight
111113484%
1684
June1st to 15thNight
1125%86%
1588
16th to endNight
111291%
1440
July1st to 15thNight
121122383%
1440
16th to endNight
11212335%76%
1751
August1st to 15thNight
11112386%
1800
16th to endNight
1113385%
1910
September1st to 15thNight
11123384%
1847
16th to endNight
12488%
1914
October1st to 15thNight
1112337%76%
1815
16th to endNight
11111122481%
2150
November1st to 15thNight
11212335%77%
2275
16th to endNight
21212348%72%
2340
December1st to 15thNight
232223448%64%
2340
16th to endNight
321322345%8%62%
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
20%5%8%19%28%18%
1455
16th to endDay
24%5%7%19%23%19%
1911
February1st to 15thDay
18%6%5%19%26%22%
1751
16th to endDay
24%6%7%19%28%12%
1579
March1st to 15thDay
15%7%7%23%25%20%
1800
16th to endDay
15%6%10%24%27%16%
2199
April1st to 15thDay
17%46%22%32%17%
2149
16th to endDay
9%47%23%30%24%
2160
May1st to 15thDay
8%37%20%32%27%
2289
16th to endDay
10%35%17%40%22%
2432
June1st to 15thDay
5%4311%28%46%
2367
16th to endDay
5%12317%69%
2520
July1st to 15thDay
9%246%19%56%
2371
16th to endDay
11%36%14%24%39%
2258
August1st to 15thDay
6%137%20%60%
2146
16th to endDay
8%228%25%51%
2292
September1st to 15thDay
7%25%8%27%48%
2112
16th to endDay
7%127%32%48%
1904
October1st to 15thDay
13%4413%31%32%
1815
16th to endDay
10%45%12%27%39%
1718
November1st to 15thDay
13%37%16%33%25%
1584
16th to endDay
16%5%6%16%28%26%
1620
December1st to 15thDay
16%7%10%22%26%16%
1620
16th to endDay
24%7%9%22%21%13%
1728
January1st to 15thNight
20%6%7%17%28%19%
2466
16th to endNight
22%5%9%17%22%22%
2310
February1st to 15thNight
19%7%7%17%25%22%
2112
16th to endNight
22%7%9%19%26%13%
1895
March1st to 15thNight
16%7%8%21%24%21%
2160
16th to endNight
15%6%10%23%29%14%
2020
April1st to 15thNight
17%5%8%27%24%16%
1799
16th to endNight
9%5%8%24%32%19%
1800
May1st to 15thNight
6%410%22%33%22%
1662
16th to endNight
7%48%21%38%18%
1685
June1st to 15thNight
435%15%31%39%
1588
16th to endNight
2135%22%64%
1440
July1st to 15thNight
7%148%18%59%
1360
16th to endNight
11%36%12%25%39%
1640
August1st to 15thNight
5%227%27%55%
1790
16th to endNight
5%238%33%46%
1910
September1st to 15thNight
6%35%8%30%45%
1847
16th to endNight
43210%35%44%
1914
October1st to 15thNight
11%4413%34%30%
1815
16th to endNight
9%5%5%9%29%39%
2150
November1st to 15thNight
12%36%16%33%27%
2275
16th to endNight
14%6%7%19%25%27%
2340
December1st to 15thNight
19%6%10%17%27%18%
2340
16th to endNight
23%7%10%18%24%15%
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
410%32%40%10%
64
16th to endDay
5%17%30%28%15%1
279
February1st to 15thDay
413%27%34%16%3
266
16th to endDay
7%15%31%32%13%
238
March1st to 15thDay
318%25%29%19%2
270
16th to endDay
316%31%28%17%2
288
April1st to 15thDay
5%21%30%23%14%4
269
16th to endDay
123%35%23%12%3
270
May1st to 15thDay
115%27%33%17%4
288
16th to endDay
210%33%31%17%4
330
June1st to 15thDay
17%27%39%18%5%
315
16th to endDay
1325%40%21%8%
315
July1st to 15thDay
216%43%23%13%
305
16th to endDay
211%47%24%12%
327
August1st to 15thDay
315%49%20%10%
315
16th to endDay
111%43%30%12%
332
September1st to 15thDay
222%40%29%4
315
16th to endDay
1421%39%28%4
288
October1st to 15thDay
110%30%37%18%1
255
16th to endDay
25%28%29%31%2
219
November1st to 15thDay
6%14%30%32%16%
90
16th to endDay
112%33%33%20%
90
December1st to 15thDay
110%25%33%25%4
90
16th to endDay
8%15%26%33%14%2
96
January1st to 15thNight
4324%40%21%6%
720
16th to endNight
4426%35%24%4
768
February1st to 15thNight
3423%37%26%4
704
16th to endNight
36%31%34%19%4
632
March1st to 15thNight
1427%38%22%5%
720
16th to endNight
15%26%37%25%4
768
April1st to 15thNight
27%29%33%23%3
719
16th to endNight
15%29%35%23%5%
720
May1st to 15thNight
224%39%28%3
582
16th to endNight
328%37%27%3
563
June1st to 15thNight
118%48%28%1
508
16th to endNight
6%48%40%3
360
July1st to 15thNight
127%61%8%
340
16th to endNight
1329%56%7%
615
August1st to 15thNight
1231%52%12%
717
16th to endNight
125%55%17%
764
September1st to 15thNight
1330%50%14%
720
16th to endNight
10%31%44%12%
692
October1st to 15thNight
1218%36%33%7%
660
16th to endNight
2115%34%32%14%
704
November1st to 15thNight
1117%37%33%9%
700
16th to endNight
1218%35%31%9%
720
December1st to 15thNight
4421%37%25%5%
720
16th to endNight
5%6%28%35%20%3
768
Page generated at 2017-09-25 06:02:18. Version ac04

Copyright 2017 A. Danko


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