Craig's Observing Site
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Craig's Observing Site clear sky chart from 2005-11-05 to 2017-09-23.

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
44%
15919
26%
46707
15%
15873
54%
15873
38%
26160

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
38%
900
29%
2327
13%
895
48%
895
40%
1370
January16th to endNight
40%
960
32%
2496
14%
960
51%
960
42%
1440
February1st to 15thNight
35%
776
21%
2187
9%
772
44%
772
30%
1390
February16th to endNight
34%
632
29%
1894
12%
632
48%
632
34%
1068
March1st to 15thNight
38%
639
26%
2079
14%
639
49%
639
34%
1115
March16th to endNight
30%
576
20%
2112
11%
576
42%
576
25%
1203
April1st to 15thNight
29%
539
21%
1852
12%
539
44%
539
29%
1031
April16th to endNight
32%
540
22%
1636
13%
540
45%
540
28%
1001
May1st to 15thNight
37%
540
20%
1620
14%
540
48%
540
28%
998
May16th to endNight
41%
562
18%
1684
11%
561
48%
561
33%
986
June1st to 15thNight
43%
540
18%
1620
9%
540
51%
540
40%
880
June16th to endNight
54%
540
25%
1444
12%
540
61%
540
54%
749
July1st to 15thNight
61%
510
20%
1413
13%
510
65%
510
45%
787
July16th to endNight
66%
564
24%
1594
22%
531
69%
531
42%
861
August1st to 15thNight
67%
539
22%
1610
22%
536
72%
536
38%
908
August16th to endNight
64%
573
27%
1824
26%
573
71%
573
42%
950
September1st to 15thNight
53%
540
25%
1935
20%
540
65%
540
35%
1006
September16th to endNight
54%
516
33%
1903
27%
516
65%
516
41%
886
October1st to 15thNight
44%
531
32%
1851
24%
531
55%
531
32%
984
October16th to endNight
47%
767
31%
2175
15%
767
57%
767
49%
1115
November1st to 15thNight
48%
875
34%
2275
14%
875
59%
875
54%
1183
November16th to endNight
43%
900
31%
2340
14%
900
53%
900
45%
1312
December1st to 15thNight
38%
900
25%
2340
11%
900
46%
900
39%
1381
December16th to endNight
40%
960
29%
2496
14%
960
50%
960
35%
1556

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%42332345%7%53%
48197
Night
8%42332335%7%55%
46897
Cloud CoverDay
8%423323447%53%
48195
Night
8%42332335%7%55%
46897
TransparencyDay
30%5%13%27%18%4
47890
Night
28%413%26%21%5%
46708
SeeingDay
10%7%29%33%16%2
5904
Night
10%7%33%36%11%
15923

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
5%5%2432345%7%56%
1611
16th to endDay
5%5%15%5%23446%54%
1728
February1st to 15thDay
7%7%445%24447%47%
1684
16th to endDay
6%5%143245%5%7%54%
1580
March1st to 15thDay
8%5%23323447%53%
1881
16th to endDay
14%7%34423345%47%
2112
April1st to 15thDay
11%5%24433346%49%
2093
16th to endDay
15%6%35%42345%5%42%
2322
May1st to 15thDay
11%41342445%7%49%
2331
16th to endDay
11%4234235%5%8%47%
2430
June1st to 15thDay
7%2134235%5%7%56%
2340
16th to endDay
311332346%7%61%
2511
July1st to 15thDay
5%3143245%6%9%51%
2460
16th to endDay
6%21332445%10%54%
2466
August1st to 15thDay
8%5%244245%6%9%47%
2340
16th to endDay
6%31332345%7%56%
2376
September1st to 15thDay
11%5%24423445%53%
2025
16th to endDay
5%313413447%59%
1893
October1st to 15thDay
14%412212245%57%
1768
16th to endDay
8%41221232464%
1695
November1st to 15thDay
5%312323347%62%
1583
16th to endDay
8%6%12212225%64%
1620
December1st to 15thDay
8%8%3442335%6%50%
1620
16th to endDay
8%7%35%434336%47%
1728
January1st to 15thNight
5%5%36%313335%57%
2327
16th to endNight
6%414323345%60%
2496
February1st to 15thNight
7%5%45%5%34435%48%
2177
16th to endNight
6%5%2442435%6%54%
1894
March1st to 15thNight
8%424323347%54%
2079
16th to endNight
13%6%33324335%50%
2112
April1st to 15thNight
12%5%1332335%7%49%
1852
16th to endNight
14%42432345%6%47%
1636
May1st to 15thNight
11%5%244235%5%6%48%
1619
16th to endNight
10%31432447%10%48%
1683
June1st to 15thNight
6%31333436%10%53%
1620
16th to endNight
311221446%11%59%
1444
July1st to 15thNight
42134345%7%10%52%
1497
16th to endNight
6%2233235%6%11%52%
1702
August1st to 15thNight
5%2145%25%5%6%10%50%
1620
16th to endNight
5%314323347%59%
1824
September1st to 15thNight
8%41332335%6%57%
1935
16th to endNight
5%3232335%6%62%
1903
October1st to 15thNight
11%413322335%58%
1851
16th to endNight
8%31221224465%
2175
November1st to 15thNight
6%311212346%66%
2275
16th to endNight
7%413322335%61%
2340
December1st to 15thNight
8%424313447%54%
2340
16th to endNight
9%7%35%423346%50%
2496

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
5%5%2332335%7%57%
1611
16th to endDay
5%5%245%3345%6%54%
1728
February1st to 15thDay
7%7%345%34446%47%
1684
16th to endDay
6%5%143235%5%7%54%
1580
March1st to 15thDay
8%5%233245%47%53%
1881
16th to endDay
14%7%33422346%46%
2110
April1st to 15thDay
11%5%25%424346%49%
2093
16th to endDay
16%6%35%42345%6%42%
2322
May1st to 15thDay
12%413424447%49%
2331
16th to endDay
11%42442445%8%47%
2430
June1st to 15thDay
7%31332445%7%56%
2340
16th to endDay
311332345%8%61%
2511
July1st to 15thDay
5%3143245%6%10%51%
2460
16th to endDay
6%31342445%10%54%
2466
August1st to 15thDay
8%4233245%6%8%48%
2340
16th to endDay
7%31332345%7%56%
2376
September1st to 15thDay
11%5%14323435%53%
2025
16th to endDay
5%3134235%47%59%
1893
October1st to 15thDay
14%312212335%57%
1768
16th to endDay
8%5%1221232464%
1695
November1st to 15thDay
5%313323346%62%
1583
16th to endDay
8%6%12212225%64%
1620
December1st to 15thDay
8%8%3342335%6%50%
1620
16th to endDay
9%7%35%424347%47%
1728
January1st to 15thNight
46%35%323335%57%
2327
16th to endNight
5%414413345%60%
2496
February1st to 15thNight
7%5%45%5%25%436%48%
2177
16th to endNight
6%5%2442435%7%54%
1894
March1st to 15thNight
8%5%23313347%54%
2079
16th to endNight
13%6%23324336%50%
2112
April1st to 15thNight
12%5%1323335%8%49%
1852
16th to endNight
14%42431345%7%47%
1636
May1st to 15thNight
11%5%234235%5%6%48%
1619
16th to endNight
10%31332447%10%48%
1683
June1st to 15thNight
6%21332436%10%54%
1620
16th to endNight
32221437%11%59%
1444
July1st to 15thNight
4213435%5%6%10%52%
1497
16th to endNight
6%2133235%6%11%52%
1702
August1st to 15thNight
5%214435%46%10%51%
1620
16th to endNight
5%213313447%59%
1824
September1st to 15thNight
8%41432235%6%57%
1935
16th to endNight
5%2332335%6%62%
1903
October1st to 15thNight
11%413322335%58%
1851
16th to endNight
8%31221224465%
2175
November1st to 15thNight
6%31212346%66%
2275
16th to endNight
7%413323345%61%
2340
December1st to 15thNight
8%5%24313347%54%
2340
16th to endNight
9%6%35%323346%50%
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
26%416%33%16%3
1612
16th to endDay
31%5%14%29%14%4
1728
February1st to 15thDay
37%5%18%23%10%4
1685
16th to endDay
28%5%16%24%19%6%
1580
March1st to 15thDay
29%411%27%20%5%
1881
16th to endDay
39%5%12%23%15%3
2112
April1st to 15thDay
36%411%26%16%3
2093
16th to endDay
42%411%27%13%1
2322
May1st to 15thDay
33%6%13%27%18%1
2331
16th to endDay
34%7%15%26%12%2
2434
June1st to 15thDay
26%5%17%28%15%5%
2340
16th to endDay
20%5%12%31%23%7%
2511
July1st to 15thDay
27%7%11%27%22%4
2316
16th to endDay
24%6%13%30%20%4
2311
August1st to 15thDay
31%7%18%25%12%5%
2326
16th to endDay
26%6%12%27%22%5%
2376
September1st to 15thDay
32%410%24%20%8%
2025
16th to endDay
23%5%12%29%24%3
1893
October1st to 15thDay
29%310%26%24%5%
1768
16th to endDay
24%29%29%27%6%
1695
November1st to 15thDay
22%310%26%29%6%
1583
16th to endDay
25%19%31%26%5%
1620
December1st to 15thDay
34%5%16%26%16%1
1620
16th to endDay
37%412%26%16%1
1728
January1st to 15thNight
29%312%29%22%2
2327
16th to endNight
27%412%29%22%4
2496
February1st to 15thNight
37%5%13%25%13%4
2187
16th to endNight
30%412%26%18%8%
1894
March1st to 15thNight
29%410%24%22%8%
2079
16th to endNight
36%413%23%17%4
2112
April1st to 15thNight
32%413%25%21%2
1852
16th to endNight
36%5%14%22%18%2
1636
May1st to 15thNight
36%6%12%21%18%4
1620
16th to endNight
29%8%20%25%13%2
1685
June1st to 15thNight
24%7%17%26%19%4
1620
16th to endNight
18%416%27%27%5%
1444
July1st to 15thNight
23%6%15%25%22%5%
1413
16th to endNight
24%6%13%29%19%5%
1594
August1st to 15thNight
26%7%16%29%13%5%
1610
16th to endNight
24%5%12%28%22%6%
1824
September1st to 15thNight
27%6%11%25%20%9%
1935
16th to endNight
22%410%24%31%6%
1903
October1st to 15thNight
29%5%8%23%25%8%
1851
16th to endNight
21%29%27%29%8%
2175
November1st to 15thNight
18%310%25%31%11%
2275
16th to endNight
25%210%27%24%9%
2340
December1st to 15thNight
29%315%29%19%1
2340
16th to endNight
35%314%23%20%3
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
11%10%38%32%7%
90
16th to endDay
10%9%42%25%12%
96
February1st to 15thDay
12%10%41%30%5%1
90
16th to endDay
128%38%13%17%1
81
March1st to 15thDay
11%17%40%23%6%1
90
16th to endDay
18%10%38%25%7%
96
April1st to 15thDay
10%17%38%25%6%
212
16th to endDay
22%12%35%21%6%1
432
May1st to 15thDay
11%13%33%28%12%1
468
16th to endDay
17%9%34%26%11%1
517
June1st to 15thDay
5%7%31%38%13%4
495
16th to endDay
3431%36%21%1
495
July1st to 15thDay
6%322%41%23%3
475
16th to endDay
7%115%42%27%4
515
August1st to 15thDay
9%214%45%26%1
493
16th to endDay
8%224%38%23%2
416
September1st to 15thDay
6%329%42%16%2
180
16th to endDay
7%9%23%35%20%4
111
October1st to 15thDay
7%328%40%15%4
90
16th to endDay
9%240%28%16%3
96
November1st to 15thDay
6%5%37%30%17%2
90
16th to endDay
20%11%37%22%8%
90
December1st to 15thDay
11%17%43%21%6%
90
16th to endDay
18%8%46%21%4
96
January1st to 15thNight
7%9%38%34%8%
900
16th to endNight
8%8%38%37%6%
960
February1st to 15thNight
10%8%38%35%7%
779
16th to endNight
9%12%40%30%6%
632
March1st to 15thNight
10%12%36%33%7%
639
16th to endNight
17%12%37%26%5%
576
April1st to 15thNight
16%12%40%26%4
539
16th to endNight
15%12%35%29%5%
540
May1st to 15thNight
13%7%35%33%7%
540
16th to endNight
11%6%36%31%12%
563
June1st to 15thNight
7%5%40%32%12%
540
16th to endNight
3435%45%11%
540
July1st to 15thNight
4127%46%18%
510
16th to endNight
6%120%48%23%1
564
August1st to 15thNight
7%117%52%20%
539
16th to endNight
5%23%44%24%1
573
September1st to 15thNight
9%229%40%16%1
540
16th to endNight
7%430%37%18%1
516
October1st to 15thNight
14%8%29%32%13%
531
16th to endNight
10%5%33%35%14%
767
November1st to 15thNight
8%9%32%37%12%
875
16th to endNight
10%9%35%34%9%1
900
December1st to 15thNight
11%9%37%35%6%
900
16th to endNight
12%8%34%35%8%
960
Page generated at 2017-09-24 08:15:54. Version ac04

Copyright 2017 A. Danko


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