Smithsferry Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Smithsferry Observatory clear sky chart from 2005-11-05 to 2017-09-19.

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
54%
14737
18%
46843
17%
14710
57%
14710
25%
29976

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
40%
716
10%
2506
9%
716
44%
716
13%
1896
January16th to endNight
48%
768
14%
2688
15%
768
49%
768
18%
1858
February1st to 15thNight
39%
699
8%
2276
6%
696
43%
696
15%
1704
February16th to endNight
38%
632
10%
1895
9%
632
41%
632
14%
1465
March1st to 15thNight
40%
720
8%
2151
7%
720
43%
720
15%
1632
March16th to endNight
41%
768
11%
2046
7%
768
43%
768
20%
1519
April1st to 15thNight
46%
719
15%
1799
8%
719
48%
719
25%
1281
April16th to endNight
50%
559
22%
1639
15%
559
54%
559
30%
1007
May1st to 15thNight
61%
533
19%
1613
15%
533
65%
533
34%
928
May16th to endNight
61%
374
15%
1496
22%
374
63%
374
23%
881
June1st to 15thNight
62%
360
14%
1440
20%
360
66%
360
25%
827
June16th to endNight
75%
360
22%
1440
36%
360
79%
360
40%
651
July1st to 15thNight
87%
340
22%
1360
36%
340
90%
340
52%
524
July16th to endNight
85%
376
33%
1416
48%
354
87%
354
59%
511
August1st to 15thNight
81%
473
31%
1546
31%
471
82%
471
53%
692
August16th to endNight
83%
677
36%
1823
27%
677
83%
677
63%
871
September1st to 15thNight
81%
720
33%
1851
22%
720
83%
720
59%
960
September16th to endNight
69%
671
32%
1856
27%
671
71%
671
43%
1050
October1st to 15thNight
62%
660
24%
1858
21%
660
65%
660
36%
1109
October16th to endNight
57%
704
20%
2288
20%
704
60%
704
26%
1450
November1st to 15thNight
50%
700
18%
2275
18%
700
51%
700
21%
1540
November16th to endNight
42%
720
12%
2373
10%
720
45%
720
17%
1680
December1st to 15thNight
40%
720
8%
2520
5%
720
43%
720
13%
1884
December16th to endNight
33%
768
10%
2688
9%
768
37%
768
12%
2056

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
11%9%35%424445%43%
47987
Night
13%9%35%423446%43%
47013
Cloud CoverDay
10%9%35%424445%43%
47988
Night
11%10%35%424446%43%
47016
TransparencyDay
41%5%10%18%15%8%
47659
Night
41%5%12%19%14%6%
46844
SeeingDay
15%13%32%26%10%1
5355
Night
16%416%34%24%3
14748

By Month

Percentage Cloud Cover NW (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
15%14%47%5%245%5%6%27%
1432
16th to endDay
17%15%5%6%324346%30%
1536
February1st to 15thDay
16%15%5%7%5%3344427%
1583
16th to endDay
13%19%8%8%6%33445%21%
1579
March1st to 15thDay
19%17%5%7%436%435%21%
1809
16th to endDay
19%17%5%7%5%25%35%5%22%
2174
April1st to 15thDay
13%16%5%7%5%35%445%28%
2149
16th to endDay
12%12%36%424346%39%
2319
May1st to 15thDay
8%8%26%5%3445%7%42%
2336
16th to endDay
11%10%37%7%345%5%6%33%
2615
June1st to 15thDay
14%7%26%6%35%5%5%7%34%
2520
16th to endDay
7%324323345%59%
2520
July1st to 15thDay
3212323345%66%
2520
16th to endDay
2112212335%72%
2657
August1st to 15thDay
3213323345%66%
2405
16th to endDay
231221333470%
2378
September1st to 15thDay
421322223469%
2109
16th to endDay
9%413414336%56%
1849
October1st to 15thDay
12%5%25%5%34445%47%
1769
16th to endDay
14%9%37%5%34335%37%
1584
November1st to 15thDay
17%13%36%5%2435%6%31%
1584
16th to endDay
17%13%46%6%3334431%
1584
December1st to 15thDay
19%17%45%424246%28%
1440
16th to endDay
22%15%48%323245%26%
1536
January1st to 15thNight
19%15%46%5%23335%29%
2506
16th to endNight
14%15%35%423437%34%
2688
February1st to 15thNight
17%15%37%5%24445%29%
2265
16th to endNight
15%16%47%5%34446%26%
1895
March1st to 15thNight
18%14%5%6%6%3443429%
2151
16th to endNight
18%12%35%42445%7%30%
2043
April1st to 15thNight
12%9%45%5%35%45%6%37%
1799
16th to endNight
13%6%23424345%48%
1639
May1st to 15thNight
7%5%1442445%6%52%
1613
16th to endNight
9%7%345%245%5%10%40%
1496
June1st to 15thNight
13%5%2432435%8%45%
1440
16th to endNight
6%21232435%5%61%
1440
July1st to 15thNight
1122145%47%67%
1440
16th to endNight
22121233474%
1512
August1st to 15thNight
32222245%6%65%
1554
16th to endNight
222212245%72%
1823
September1st to 15thNight
221232233470%
1851
16th to endNight
9%41332323459%
1856
October1st to 15thNight
10%42442345%5%51%
1858
16th to endNight
14%7%2443445%7%40%
2288
November1st to 15thNight
20%8%245%23447%35%
2275
16th to endNight
18%12%35%5%24335%34%
2373
December1st to 15thNight
16%13%46%6%35%445%28%
2520
16th to endNight
20%17%47%43333426%
2688

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
14%14%5%8%5%335%46%29%
1432
16th to endDay
15%16%47%423337%31%
1536
February1st to 15thDay
14%16%5%8%6%4444426%
1583
16th to endDay
11%20%8%9%6%3335%5%21%
1579
March1st to 15thDay
16%18%5%7%5%345%4421%
1809
16th to endDay
17%18%5%8%6%24446%22%
2175
April1st to 15thDay
12%15%48%6%35%346%27%
2149
16th to endDay
11%12%36%424346%38%
2319
May1st to 15thDay
7%8%35%6%35%45%7%42%
2336
16th to endDay
11%9%47%7%36%45%6%32%
2615
June1st to 15thDay
13%7%37%6%35%5%5%6%34%
2520
16th to endDay
6%423324345%58%
2520
July1st to 15thDay
3212223446%66%
2520
16th to endDay
2112313345%71%
2657
August1st to 15thDay
2213324445%65%
2405
16th to endDay
221221234470%
2378
September1st to 15thDay
321322234468%
2109
16th to endDay
9%413324436%56%
1849
October1st to 15thDay
11%5%25%434445%47%
1769
16th to endDay
12%9%47%6%24445%37%
1584
November1st to 15thDay
17%12%46%5%2335%6%31%
1584
16th to endDay
16%14%47%5%34335%31%
1584
December1st to 15thDay
18%17%5%6%323246%28%
1440
16th to endDay
20%16%48%42325%5%26%
1536
January1st to 15thNight
16%16%5%6%5%23445%29%
2506
16th to endNight
13%16%35%323336%36%
2688
February1st to 15thNight
15%15%37%6%24345%29%
2265
16th to endNight
14%16%5%7%5%35%445%26%
1895
March1st to 15thNight
15%15%46%7%24445%28%
2151
16th to endNight
16%13%35%425%5%5%8%30%
2046
April1st to 15thNight
11%10%36%5%35%5%46%37%
1799
16th to endNight
12%5%335%24346%48%
1639
May1st to 15thNight
6%5%24435%45%6%51%
1613
16th to endNight
8%6%35%6%345%5%10%40%
1496
June1st to 15thNight
12%5%2442445%9%45%
1440
16th to endNight
5%31332345%5%61%
1440
July1st to 15thNight
11121446%7%67%
1440
16th to endNight
121222133474%
1512
August1st to 15thNight
321232245%5%66%
1554
16th to endNight
1212212345%71%
1823
September1st to 15thNight
2312223245%69%
1851
16th to endNight
9%41341323460%
1856
October1st to 15thNight
9%5%15%42445%5%51%
1858
16th to endNight
13%8%2443445%7%40%
2288
November1st to 15thNight
18%10%35%42335%6%35%
2275
16th to endNight
16%12%35%5%24445%34%
2373
December1st to 15thNight
15%15%46%6%35%445%27%
2520
16th to endNight
18%18%6%7%5%2333426%
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
56%9%15%14%3
1432
16th to endDay
54%7%14%16%5%
1536
February1st to 15thDay
58%8%13%15%3
1583
16th to endDay
63%8%10%14%2
1579
March1st to 15thDay
62%8%10%13%5%
1809
16th to endDay
63%6%10%15%4
2175
April1st to 15thDay
56%6%14%16%5%
2149
16th to endDay
46%5%11%23%11%1
2319
May1st to 15thDay
38%6%12%30%11%1
2336
16th to endDay
49%7%12%17%10%1
2619
June1st to 15thDay
46%6%10%19%13%3
2520
16th to endDay
25%37%22%30%11%
2520
July1st to 15thDay
18%36%15%30%26%
2371
16th to endDay
13%349%28%40%
2490
August1st to 15thDay
19%37%15%29%24%
2388
16th to endDay
16%35%18%35%20%
2378
September1st to 15thDay
18%36%19%32%19%
2109
16th to endDay
28%47%28%22%7%
1849
October1st to 15thDay
36%6%12%22%17%3
1769
16th to endDay
46%6%11%19%15%
1584
November1st to 15thDay
52%5%14%18%8%
1584
16th to endDay
55%5%13%16%7%1
1584
December1st to 15thDay
57%6%18%14%2
1440
16th to endDay
61%5%12%15%4
1536
January1st to 15thNight
57%8%14%14%41
2506
16th to endNight
49%7%14%18%9%
2688
February1st to 15thNight
56%7%14%16%5%
2276
16th to endNight
58%7%13%15%41
1895
March1st to 15thNight
56%6%12%17%5%1
2151
16th to endNight
51%7%16%18%6%
2046
April1st to 15thNight
45%6%15%22%9%
1799
16th to endNight
37%413%27%15%1
1639
May1st to 15thNight
30%6%13%30%18%
1614
16th to endNight
38%6%13%29%10%1
1496
June1st to 15thNight
35%7%12%27%13%4
1440
16th to endNight
22%48%23%27%13%
1440
July1st to 15thNight
14%38%14%33%25%
1360
16th to endNight
13%1412%29%39%
1416
August1st to 15thNight
17%26%17%30%24%
1546
16th to endNight
14%36%17%33%25%
1823
September1st to 15thNight
17%36%18%33%20%
1851
16th to endNight
28%37%24%25%11%
1856
October1st to 15thNight
32%5%13%26%19%3
1858
16th to endNight
40%6%13%20%18%
2288
November1st to 15thNight
47%5%13%21%10%
2275
16th to endNight
51%6%13%18%7%2
2373
December1st to 15thNight
56%7%15%14%5%
2520
16th to endNight
62%412%15%4
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
16%5%18%33%20%6%
60
16th to endDay
34%323%21%15%1
64
February1st to 15thDay
26%10%24%17%17%3
153
16th to endDay
24%21%32%14%6%
238
March1st to 15thDay
31%15%31%18%3
270
16th to endDay
29%21%28%18%3
288
April1st to 15thDay
18%22%28%17%8%3
269
16th to endDay
23%22%30%17%5%
270
May1st to 15thDay
13%18%36%24%7%
288
16th to endDay
16%11%25%28%14%3
330
June1st to 15thDay
12%17%33%26%6%2
315
16th to endDay
8%13%37%26%11%1
315
July1st to 15thDay
5%8%35%35%13%1
305
16th to endDay
113%40%33%10%1
327
August1st to 15thDay
5%10%40%33%9%1
315
16th to endDay
37%34%37%13%3
332
September1st to 15thDay
8%9%27%38%13%2
315
16th to endDay
11%8%36%30%11%
268
October1st to 15thDay
11%13%34%30%8%1
239
16th to endDay
21%13%20%30%11%2
96
November1st to 15thDay
20%6%18%31%23%
90
16th to endDay
16%19%35%17%8%2
84
December1st to 15thDay
51%10%26%8%3
60
16th to endDay
28%421%32%12%
64
January1st to 15thNight
25%417%29%19%2
720
16th to endNight
23%216%29%23%4
768
February1st to 15thNight
24%5%19%31%17%2
704
16th to endNight
22%6%22%30%15%2
632
March1st to 15thNight
23%7%21%30%15%2
720
16th to endNight
22%7%22%32%13%
768
April1st to 15thNight
16%6%23%29%21%2
719
16th to endNight
15%6%22%35%17%2
559
May1st to 15thNight
9%5%17%42%23%2
534
16th to endNight
12%313%34%33%3
375
June1st to 15thNight
14%214%39%26%3
360
16th to endNight
7%9%46%34%1
360
July1st to 15thNight
27%49%37%4
340
16th to endNight
35%46%40%2
376
August1st to 15thNight
6%15%42%40%3
473
16th to endNight
39%40%40%5%
677
September1st to 15thNight
47%40%42%5%
720
16th to endNight
10%311%30%33%10%
671
October1st to 15thNight
12%314%38%25%5%
660
16th to endNight
18%213%35%24%4
704
November1st to 15thNight
24%216%33%21%1
700
16th to endNight
22%6%21%26%18%4
720
December1st to 15thNight
23%5%20%30%17%1
720
16th to endNight
27%6%23%27%13%1
768
Page generated at 2017-09-20 02:49:56. Version ac04

Copyright 2017 A. Danko


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