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Sanford
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sanford clear sky chart from 2005-11-05 to 2018-03-11.

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
61%
16693
21%
49049
17%
16651
65%
16651
30%
30716

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
44%
779
20%
2522
14%
776
53%
776
25%
1567
January16th to endNight
44%
832
24%
2691
19%
832
54%
832
28%
1628
February1st to 15thNight
45%
761
23%
2283
15%
758
55%
758
32%
1363
February16th to endNight
49%
683
28%
1960
18%
683
58%
683
36%
1145
March1st to 15thNight
53%
764
29%
2101
19%
764
62%
764
44%
1167
March16th to endNight
55%
768
25%
2112
19%
768
60%
768
41%
1215
April1st to 15thNight
58%
718
24%
1976
17%
718
62%
718
41%
1123
April16th to endNight
64%
720
27%
1815
18%
720
67%
720
42%
1084
May1st to 15thNight
69%
599
26%
1679
19%
599
72%
599
42%
938
May16th to endNight
74%
561
21%
1682
17%
561
75%
561
31%
1041
June1st to 15thNight
68%
540
13%
1620
11%
540
68%
540
23%
1121
June16th to endNight
69%
540
8%
1620
8%
540
69%
540
23%
1151
July1st to 15thNight
71%
510
8%
1530
6%
510
71%
510
21%
1093
July16th to endNight
74%
564
9%
1595
8%
531
75%
531
22%
1118
August1st to 15thNight
82%
539
8%
1609
8%
536
82%
536
27%
1083
August16th to endNight
66%
738
9%
2008
9%
738
66%
738
22%
1449
September1st to 15thNight
68%
720
9%
1980
9%
720
68%
720
19%
1461
September16th to endNight
62%
717
13%
1980
13%
717
62%
717
19%
1466
October1st to 15thNight
68%
720
25%
2070
26%
720
70%
720
31%
1297
October16th to endNight
64%
768
28%
2304
28%
768
68%
768
34%
1377
November1st to 15thNight
63%
760
27%
2281
23%
760
70%
760
36%
1324
November16th to endNight
56%
780
30%
2392
24%
780
66%
780
34%
1408
December1st to 15thNight
56%
780
26%
2535
23%
780
64%
780
29%
1496
December16th to endNight
56%
832
24%
2704
22%
832
62%
832
30%
1601

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
8%5%36%7%46%6%6%8%36%
49557
Night
8%425%5%35%5%6%9%44%
49258
TransparencyDay
43%7%13%16%13%5%
49258
Night
35%7%15%20%14%6%
49061
SeeingDay
9%313%22%25%26%
6446
Night
9%215%32%30%8%
16700

By Month

Percentage Cloud Cover SE (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
11%6%45%5%45%448%39%
1746
16th to endDay
10%5%26%43445%8%45%
1882
February1st to 15thDay
10%6%25%5%36%45%7%43%
1900
16th to endDay
8%425%5%35%45%7%46%
1798
March1st to 15thDay
6%3245%35%45%8%49%
2096
16th to endDay
8%425%5%35%447%47%
2111
April1st to 15thDay
7%315%5%36%5%6%9%44%
1972
16th to endDay
6%425%5%36%6%6%8%44%
2143
May1st to 15thDay
6%324436%6%6%8%47%
2280
16th to endDay
8%426%7%46%6%8%9%35%
2431
June1st to 15thDay
10%5%37%9%47%7%6%9%25%
2340
16th to endDay
9%6%37%8%5%8%7%7%9%24%
2340
July1st to 15thDay
9%7%38%8%6%9%8%7%9%21%
2340
16th to endDay
9%7%38%9%5%9%7%7%9%21%
2465
August1st to 15thDay
6%5%39%11%5%9%7%8%11%22%
2340
16th to endDay
10%6%410%8%6%7%6%7%9%22%
2176
September1st to 15thDay
9%6%38%10%6%8%7%8%8%22%
1980
16th to endDay
12%8%48%8%5%7%6%7%9%21%
1980
October1st to 15thDay
10%5%37%7%46%6%6%8%33%
1888
16th to endDay
10%5%25%5%36%5%5%6%44%
1920
November1st to 15thDay
6%425%5%35%5%6%8%45%
1907
16th to endDay
10%6%25%6%36%5%46%43%
1895
December1st to 15thDay
10%5%45%6%4445%7%40%
1755
16th to endDay
7%6%246%35%5%6%8%44%
1872
January1st to 15thNight
10%6%36%5%2446%8%41%
2522
16th to endNight
12%5%25%4245%5%6%45%
2691
February1st to 15thNight
10%5%24324446%50%
2283
16th to endNight
8%3145%24447%52%
1960
March1st to 15thNight
6%21332345%8%56%
2101
16th to endNight
5%324423446%57%
2112
April1st to 15thNight
6%3234235%6%8%54%
1976
16th to endNight
6%3234335%5%7%53%
1815
May1st to 15thNight
5%21343445%9%56%
1679
16th to endNight
6%3245%35%6%7%9%45%
1682
June1st to 15thNight
7%6%26%7%36%6%8%11%33%
1620
16th to endNight
7%437%7%46%7%7%11%31%
1620
July1st to 15thNight
7%6%26%6%46%9%8%10%32%
1620
16th to endNight
5%5%36%7%48%7%8%10%32%
1703
August1st to 15thNight
4415%6%47%7%8%14%35%
1620
16th to endNight
9%6%36%6%36%5%7%11%31%
2008
September1st to 15thNight
7%435%6%5%8%8%7%10%31%
1980
16th to endNight
9%7%37%7%46%8%6%10%27%
1980
October1st to 15thNight
7%5%15%435%5%6%9%44%
2070
16th to endNight
9%5%25%5%24448%48%
2304
November1st to 15thNight
6%3245%445%6%8%48%
2281
16th to endNight
8%42442445%8%48%
2392
December1st to 15thNight
9%424435%45%8%46%
2535
16th to endNight
8%424435%46%9%44%
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
43%5%7%19%17%6%
1747
16th to endDay
36%48%18%21%10%
1882
February1st to 15thDay
40%5%9%14%19%12%
1902
16th to endDay
36%410%15%22%9%
1798
March1st to 15thDay
32%49%25%18%8%
2096
16th to endDay
36%5%10%18%20%8%
2112
April1st to 15thDay
34%5%11%19%22%6%
1972
16th to endDay
35%6%10%20%19%8%
2143
May1st to 15thDay
32%6%11%22%19%7%
2280
16th to endDay
41%8%15%17%13%2
2435
June1st to 15thDay
50%9%16%19%3
2340
16th to endDay
51%10%21%12%3
2340
July1st to 15thDay
52%14%19%12%1
2201
16th to endDay
54%11%19%12%1
2310
August1st to 15thDay
50%13%23%10%1
2327
16th to endDay
56%12%18%11%1
2176
September1st to 15thDay
54%11%18%11%4
1980
16th to endDay
54%10%15%12%5%1
1980
October1st to 15thDay
46%7%9%15%13%7%
1888
16th to endDay
39%5%6%15%22%11%
1920
November1st to 15thDay
33%5%7%22%22%7%
1907
16th to endDay
40%5%8%17%17%9%
1895
December1st to 15thDay
40%5%12%20%14%6%
1755
16th to endDay
37%415%20%15%7%
1872
January1st to 15thNight
40%410%20%15%7%
2522
16th to endNight
38%48%19%20%9%
2691
February1st to 15thNight
34%410%17%17%14%
2292
16th to endNight
30%5%12%19%23%8%
1960
March1st to 15thNight
25%5%13%27%20%7%
2101
16th to endNight
27%5%13%23%20%9%
2112
April1st to 15thNight
26%6%14%23%19%8%
1976
16th to endNight
28%412%25%20%7%
1815
May1st to 15thNight
26%5%16%25%18%8%
1680
16th to endNight
31%10%15%23%17%1
1684
June1st to 15thNight
41%11%19%23%3
1620
16th to endNight
43%11%23%17%3
1620
July1st to 15thNight
42%14%26%14%2
1530
16th to endNight
40%14%27%16%2
1595
August1st to 15thNight
33%14%36%12%1
1609
16th to endNight
43%12%26%16%1
2008
September1st to 15thNight
42%16%20%15%4
1980
16th to endNight
47%11%18%16%41
1980
October1st to 15thNight
35%7%11%21%17%6%
2070
16th to endNight
34%49%16%24%10%
2304
November1st to 15thNight
31%5%12%21%21%7%
2281
16th to endNight
32%6%8%22%19%10%
2392
December1st to 15thNight
35%5%12%25%13%7%
2535
16th to endNight
34%6%13%25%12%7%
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
20%8%38%21%6%5%
135
16th to endDay
10%12%38%25%11%2
144
February1st to 15thDay
5%11%25%34%16%7%
135
16th to endDay
9%7%24%30%24%3
208
March1st to 15thDay
6%6%30%33%19%3
312
16th to endDay
9%322%28%28%6%
288
April1st to 15thDay
5%423%29%27%11%
270
16th to endDay
5%215%26%28%20%
270
May1st to 15thDay
5%314%23%31%22%
288
16th to endDay
6%25%18%34%33%
331
June1st to 15thDay
13%16%17%24%36%
315
16th to endDay
8%313%23%52%
315
July1st to 15thDay
5%16%22%63%
305
16th to endDay
10%128%24%52%
326
August1st to 15thDay
31313%21%55%
313
16th to endDay
13%37%21%53%
332
September1st to 15thDay
13%139%26%45%
315
16th to endDay
11%1116%29%38%
314
October1st to 15thDay
12%49%25%35%12%
315
16th to endDay
10%318%30%26%10%
336
November1st to 15thDay
6%213%32%34%9%
325
16th to endDay
10%219%38%23%5%
275
December1st to 15thDay
8%6%34%31%15%2
135
16th to endDay
6%120%37%28%5%
144
January1st to 15thNight
12%5%27%34%18%1
780
16th to endNight
14%5%27%38%13%
832
February1st to 15thNight
13%330%35%15%1
764
16th to endNight
8%431%42%12%
683
March1st to 15thNight
6%430%42%14%1
764
16th to endNight
6%326%41%20%1
768
April1st to 15thNight
6%325%40%23%1
718
16th to endNight
6%319%46%23%1
720
May1st to 15thNight
7%112%45%29%3
600
16th to endNight
7%6%31%43%9%
563
June1st to 15thNight
10%1424%45%13%
540
16th to endNight
8%1213%47%25%
540
July1st to 15thNight
9%1110%48%29%
510
16th to endNight
5%112%51%28%
564
August1st to 15thNight
412%51%30%
539
16th to endNight
12%2314%42%25%
738
September1st to 15thNight
11%1217%46%21%
720
16th to endNight
13%2220%46%14%
717
October1st to 15thNight
10%26%32%40%7%
720
16th to endNight
10%212%35%32%5%
768
November1st to 15thNight
6%118%40%30%3
760
16th to endNight
9%322%40%22%2
780
December1st to 15thNight
10%321%37%24%2
780
16th to endNight
9%421%36%25%1
832
Page generated at 2018-03-12 13:28:12. Version ac04

Copyright 2018 A. Danko


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