Boyce Thompson Arboretum
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Boyce Thompson Arboretum clear sky chart from 2005-11-05 to 2018-08-29.

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
74%
16806
35%
50636
31%
16767
79%
16767
50%
24803

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%
779
30%
2522
29%
776
72%
776
42%
1279
January16th to endNight
62%
832
35%
2704
32%
832
71%
832
39%
1418
February1st to 15thNight
67%
760
34%
2401
31%
760
76%
760
47%
1160
February16th to endNight
61%
684
35%
2006
33%
684
67%
684
41%
1101
March1st to 15thNight
67%
780
38%
2145
30%
780
74%
780
53%
1075
March16th to endNight
75%
832
37%
2288
29%
832
80%
832
57%
1125
April1st to 15thNight
69%
740
34%
2104
25%
740
76%
740
53%
1038
April16th to endNight
70%
579
42%
1871
35%
579
79%
579
63%
756
May1st to 15thNight
75%
584
39%
1754
33%
584
80%
584
61%
773
May16th to endNight
79%
609
39%
1828
33%
609
83%
609
70%
745
June1st to 15thNight
85%
585
36%
1755
31%
585
86%
585
67%
750
June16th to endNight
89%
585
32%
1755
29%
585
90%
585
68%
745
July1st to 15thNight
81%
555
21%
1665
18%
555
81%
555
41%
911
July16th to endNight
78%
612
20%
1737
16%
579
78%
579
33%
1047
August1st to 15thNight
85%
575
27%
1719
25%
572
84%
572
43%
914
August16th to endNight
82%
639
29%
1987
28%
639
82%
639
39%
1099
September1st to 15thNight
80%
720
30%
1980
27%
720
81%
720
46%
1111
September16th to endNight
82%
716
44%
1980
34%
716
85%
716
65%
912
October1st to 15thNight
76%
720
38%
2088
30%
720
81%
720
62%
951
October16th to endNight
82%
768
46%
2304
40%
768
87%
768
67%
980
November1st to 15thNight
77%
760
39%
2280
33%
760
82%
760
58%
1053
November16th to endNight
73%
780
40%
2524
39%
780
78%
780
52%
1151
December1st to 15thNight
66%
780
36%
2535
35%
780
72%
780
43%
1267
December16th to endNight
66%
832
35%
2704
36%
832
70%
832
38%
1442

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
4212223346%65%
51617
Night
5%212323346%65%
50832
TransparencyDay
19%45%12%26%32%
51312
Night
19%3412%25%33%
50638
SeeingDay
5%8%23%34%21%5%
6636
Night
5%210%37%36%6%
16814

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
7%313323235%61%
1746
16th to endDay
9%312212335%63%
1872
February1st to 15thDay
5%423212335%63%
1791
16th to endDay
10%423223326%57%
1753
March1st to 15thDay
6%21231335%5%62%
2145
16th to endDay
3323313235%67%
2288
April1st to 15thDay
2212223236%69%
2171
16th to endDay
211112235%77%
2361
May1st to 15thDay
1111112325%75%
2526
16th to endDay
21111122381%
2637
June1st to 15thDay
1211222478%
2535
16th to endDay
11111223379%
2535
July1st to 15thDay
3413335%5%6%9%52%
2535
16th to endDay
5%2146%46%7%8%11%40%
2675
August1st to 15thDay
33245%25%5%6%8%51%
2485
16th to endDay
43134345%7%8%54%
2509
September1st to 15thDay
421332336%7%59%
1980
16th to endDay
311222135%75%
1980
October1st to 15thDay
31121323474%
1872
16th to endDay
12221123477%
1920
November1st to 15thDay
221223246%70%
1909
16th to endDay
5%2321323470%
1765
December1st to 15thDay
8%313323246%59%
1755
16th to endDay
8%5%2431325%5%57%
1872
January1st to 15thNight
7%313323345%60%
2522
16th to endNight
10%31232333460%
2704
February1st to 15thNight
5%313313235%65%
2390
16th to endNight
8%323323445%57%
2006
March1st to 15thNight
6%212113346%66%
2145
16th to endNight
3212212346%68%
2288
April1st to 15thNight
5%21232323469%
2104
16th to endNight
21121223378%
1871
May1st to 15thNight
112213245%74%
1754
16th to endNight
211112481%
1828
June1st to 15thNight
22111222478%
1755
16th to endNight
1111224478%
1755
July1st to 15thNight
22244246%7%9%50%
1755
16th to endNight
43145%46%7%9%13%38%
1845
August1st to 15thNight
2213435%7%7%10%51%
1728
16th to endNight
23135%346%7%9%49%
1987
September1st to 15thNight
33133245%6%7%56%
1980
16th to endNight
21221232475%
1980
October1st to 15thNight
311121123475%
2088
16th to endNight
121111122478%
2304
November1st to 15thNight
3213213235%70%
2280
16th to endNight
5%21321223469%
2524
December1st to 15thNight
9%313312347%60%
2535
16th to endNight
10%31332334457%
2704

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
25%35%11%31%22%
1747
16th to endDay
23%3314%29%25%
1872
February1st to 15thDay
22%36%13%25%28%
1791
16th to endDay
27%3214%27%22%
1753
March1st to 15thDay
21%327%33%31%
2145
16th to endDay
20%229%35%29%
2288
April1st to 15thDay
15%2211%35%32%
2171
16th to endDay
11%229%29%46%
2361
May1st to 15thDay
11%228%27%46%
2526
16th to endDay
10%116%28%50%
2640
June1st to 15thDay
11%11319%61%
2535
16th to endDay
10%235%16%61%
2535
July1st to 15thDay
24%6%12%14%17%24%
2396
16th to endDay
31%11%17%23%13%3
2520
August1st to 15thDay
27%6%9%18%19%18%
2470
16th to endDay
24%8%8%19%24%14%
2509
September1st to 15thDay
22%5%8%16%25%22%
1980
16th to endDay
12%228%32%41%
1980
October1st to 15thDay
14%2310%27%41%
1872
16th to endDay
11%339%28%43%
1920
November1st to 15thDay
14%2313%34%32%
1909
16th to endDay
18%3211%27%37%
1765
December1st to 15thDay
24%35%15%28%22%
1755
16th to endDay
27%4418%30%14%
1872
January1st to 15thNight
25%2410%29%26%
2522
16th to endNight
27%4212%26%25%
2704
February1st to 15thNight
21%2414%26%30%
2401
16th to endNight
27%3314%26%24%
2006
March1st to 15thNight
19%2210%28%35%
2145
16th to endNight
16%3213%35%28%
2288
April1st to 15thNight
19%228%34%31%
2104
16th to endNight
11%228%27%48%
1871
May1st to 15thNight
12%328%29%43%
1755
16th to endNight
9%218%21%57%
1829
June1st to 15thNight
11%21415%64%
1755
16th to endNight
10%22316%63%
1755
July1st to 15thNight
24%7%12%15%16%24%
1665
16th to endNight
31%8%18%20%16%4
1737
August1st to 15thNight
23%7%12%20%15%21%
1719
16th to endNight
26%7%10%18%21%16%
1987
September1st to 15thNight
23%6%8%21%20%20%
1980
16th to endNight
13%239%29%41%
1980
October1st to 15thNight
14%2311%23%44%
2088
16th to endNight
11%2310%25%46%
2304
November1st to 15thNight
16%2312%31%33%
2280
16th to endNight
19%2310%24%40%
2524
December1st to 15thNight
24%2314%28%25%
2535
16th to endNight
27%4416%28%18%
2704

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
18%5%20%35%19%
135
16th to endDay
12%7%20%35%20%3
144
February1st to 15thDay
8%7%26%29%24%3
216
16th to endDay
12%18%34%24%10%
290
March1st to 15thDay
6%15%33%26%16%1
330
16th to endDay
417%35%26%14%1
352
April1st to 15thDay
419%34%25%10%6%
329
16th to endDay
424%34%25%7%3
318
May1st to 15thDay
318%33%29%12%2
348
16th to endDay
411%36%34%12%1
394
June1st to 15thDay
45%36%34%16%2
375
16th to endDay
2118%48%21%6%
375
July1st to 15thDay
6%112%43%29%7%
365
16th to endDay
417%36%35%15%
391
August1st to 15thDay
316%37%38%11%
359
16th to endDay
117%35%38%15%
385
September1st to 15thDay
8%217%38%26%6%
315
16th to endDay
6%7%24%39%20%2
315
October1st to 15thDay
47%20%38%23%5%
207
16th to endDay
3313%40%30%9%
144
November1st to 15thDay
38%24%35%25%1
135
16th to endDay
7%8%23%33%22%3
135
December1st to 15thDay
7%5%25%35%23%1
135
16th to endDay
15%9%13%40%16%5%
144
January1st to 15thNight
9%313%43%25%4
780
16th to endNight
11%315%39%24%5%
832
February1st to 15thNight
7%413%43%27%4
764
16th to endNight
10%315%46%21%1
684
March1st to 15thNight
6%5%16%41%25%4
780
16th to endNight
3311%43%33%4
832
April1st to 15thNight
46%12%45%27%2
740
16th to endNight
15%18%41%27%4
579
May1st to 15thNight
2413%43%31%5%
585
16th to endNight
3212%41%35%4
611
June1st to 15thNight
216%42%43%4
585
16th to endNight
11332%54%5%
585
July1st to 15thNight
31321%60%9%
555
16th to endNight
31216%58%17%
612
August1st to 15thNight
22116%61%16%
575
16th to endNight
4117%61%14%
639
September1st to 15thNight
4426%50%12%
720
16th to endNight
226%39%36%11%
716
October1st to 15thNight
3212%39%35%5%
720
16th to endNight
218%37%40%9%
768
November1st to 15thNight
4111%42%33%6%
760
16th to endNight
5%312%40%34%4
780
December1st to 15thNight
10%312%38%32%2
780
16th to endNight
11%39%45%24%4
832
Page generated at 2018-08-30 02:34:17. Version ac04

Copyright 2018 A. Danko


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