Isabella
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Isabella clear sky chart from 2005-11-05 to 2017-12-02.

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
28%
16545
12%
47539
6%
16498
34%
16498
17%
34519

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
17%
900
10%
2506
4%
895
24%
895
11%
1946
January16th to endNight
11%
960
11%
2673
1%
960
19%
960
12%
2101
February1st to 15thNight
18%
879
12%
2285
1%
875
25%
875
13%
1709
February16th to endNight
23%
726
13%
1988
4%
726
29%
726
14%
1495
March1st to 15thNight
24%
663
14%
2103
8%
663
31%
663
15%
1502
March16th to endNight
32%
576
17%
2043
12%
576
41%
576
16%
1373
April1st to 15thNight
28%
539
13%
1797
8%
539
36%
539
16%
1260
April16th to endNight
28%
540
12%
1643
7%
540
34%
540
16%
1219
May1st to 15thNight
29%
540
11%
1440
4%
540
33%
540
17%
1090
May16th to endNight
38%
563
9%
1498
3%
561
42%
561
22%
1069
June1st to 15thNight
42%
540
7%
1426
4%
540
44%
540
23%
1005
June16th to endNight
39%
540
8%
1260
3%
540
41%
540
26%
913
July1st to 15thNight
45%
510
10%
1270
5%
510
47%
510
35%
837
July16th to endNight
52%
564
15%
1417
7%
531
53%
531
36%
882
August1st to 15thNight
50%
539
19%
1482
11%
536
55%
536
36%
897
August16th to endNight
45%
573
19%
1813
16%
573
51%
573
28%
1084
September1st to 15thNight
51%
540
18%
1800
15%
540
59%
540
29%
1047
September16th to endNight
38%
630
13%
1956
10%
630
42%
630
21%
1309
October1st to 15thNight
29%
720
17%
2160
9%
720
36%
720
19%
1488
October16th to endNight
21%
768
11%
2413
4%
768
29%
768
12%
1833
November1st to 15thNight
20%
890
11%
2601
5%
890
26%
890
12%
1959
November16th to endNight
20%
975
11%
2730
4%
975
26%
975
11%
2151
December1st to 15thNight
15%
910
7%
2547
2%
910
20%
910
8%
2079
December16th to endNight
12%
960
10%
2688
2%
960
19%
960
7%
2271

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
15%10%47%6%35%45%7%30%
48912
Night
13%10%47%5%35%5%5%7%31%
47706
Cloud CoverDay
14%10%47%6%35%45%7%30%
48922
Night
12%9%47%5%35%5%5%7%32%
47711
Cloud CoverDay
14%10%47%6%35%45%7%30%
48920
Night
12%10%47%6%35%5%5%7%31%
47711
TransparencyDay
51%7%12%19%8%
48594
Night
49%8%12%20%8%
47542
SeeingDay
21%15%33%19%7%2
6443
Night
19%15%31%24%8%1
16546

By Month

Percentage Cloud Cover NE (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
12%11%5%8%7%35%5%6%10%23%
1432
16th to endDay
10%12%5%14%7%445%7%8%19%
1548
February1st to 15thDay
10%9%5%6%6%36%5%6%8%29%
1575
16th to endDay
11%12%7%8%9%345%46%26%
1485
March1st to 15thDay
10%11%6%8%6%3345%6%34%
1857
16th to endDay
16%13%5%7%6%34336%27%
2181
April1st to 15thDay
13%12%46%5%35%445%33%
2151
16th to endDay
22%12%46%5%23346%29%
2316
May1st to 15thDay
22%11%47%5%35%435%26%
2511
16th to endDay
19%7%36%5%35%45%7%32%
2617
June1st to 15thDay
17%7%26%4245%5%8%34%
2529
16th to endDay
18%7%36%5%36%5%6%7%29%
2700
July1st to 15thDay
12%5%25%4345%6%9%40%
2610
16th to endDay
10%5%25%5%36%5%6%9%39%
2655
August1st to 15thDay
11%5%25%6%35%47%8%38%
2468
16th to endDay
14%6%14435%46%9%38%
2388
September1st to 15thDay
10%7%36%5%335%5%8%38%
2160
16th to endDay
17%8%37%5%23346%35%
1990
October1st to 15thDay
16%11%37%6%25%5%6%6%29%
1800
16th to endDay
21%16%47%6%3333326%
1809
November1st to 15thDay
14%16%6%8%5%34345%25%
1584
16th to endDay
14%12%6%10%7%35%5%6%6%20%
1560
December1st to 15thDay
11%14%6%9%7%36%47%8%18%
1450
16th to endDay
16%18%7%11%7%34445%14%
1536
January1st to 15thNight
12%10%5%8%8%46%6%6%10%19%
2506
16th to endNight
10%13%5%10%7%46%46%9%19%
2673
February1st to 15thNight
8%10%47%7%47%6%7%7%28%
2285
16th to endNight
9%11%49%7%46%6%6%7%27%
1988
March1st to 15thNight
12%9%5%9%5%35%446%34%
2090
16th to endNight
13%10%46%5%24446%36%
2043
April1st to 15thNight
15%10%46%435%5%5%433%
1797
16th to endNight
20%11%36%5%25%45%5%29%
1643
May1st to 15thNight
22%8%35%5%245%5%6%30%
1440
16th to endNight
14%6%36%435%5%45%39%
1496
June1st to 15thNight
15%5%35%5%45%46%6%38%
1426
16th to endNight
12%5%35%5%26%5%7%7%38%
1260
July1st to 15thNight
8%5%343235%5%9%47%
1347
16th to endNight
6%314425%5%5%9%50%
1513
August1st to 15thNight
9%4243235%47%52%
1491
16th to endNight
11%5%2443345%6%49%
1813
September1st to 15thNight
8%425%32446%6%50%
1800
16th to endNight
14%6%37%5%3345%7%40%
1956
October1st to 15thNight
13%10%35%5%24446%37%
2160
16th to endNight
18%11%48%6%345%45%28%
2413
November1st to 15thNight
14%13%5%7%6%35%5%5%6%25%
2601
16th to endNight
15%10%48%7%46%5%6%7%22%
2730
December1st to 15thNight
12%15%6%8%7%36%6%6%8%17%
2547
16th to endNight
14%17%8%11%6%46%5%46%14%
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
12%11%6%6%6%45%5%7%10%24%
1432
16th to endDay
10%12%5%12%8%45%5%6%8%20%
1548
February1st to 15thDay
10%9%5%6%5%36%5%6%9%30%
1575
16th to endDay
11%12%6%9%8%4345%6%26%
1485
March1st to 15thDay
10%11%6%7%6%3435%6%34%
1867
16th to endDay
16%13%5%8%6%35%336%27%
2181
April1st to 15thDay
13%12%46%6%25%445%33%
2151
16th to endDay
22%12%46%5%23346%29%
2316
May1st to 15thDay
22%11%37%5%345%45%26%
2511
16th to endDay
19%7%36%5%35%45%7%32%
2617
June1st to 15thDay
16%6%37%4345%48%34%
2529
16th to endDay
18%7%27%5%35%5%6%7%29%
2700
July1st to 15thDay
11%5%25%425%5%5%9%40%
2610
16th to endDay
9%5%25%5%36%5%6%9%39%
2655
August1st to 15thDay
11%5%25%6%35%6%7%7%38%
2468
16th to endDay
13%6%24435%46%8%39%
2388
September1st to 15thDay
10%8%37%5%345%6%8%38%
2160
16th to endDay
17%7%46%6%24346%35%
1990
October1st to 15thDay
16%11%36%6%35%5%6%7%28%
1800
16th to endDay
20%15%48%6%3323426%
1809
November1st to 15thDay
14%16%5%8%5%35%346%25%
1584
16th to endDay
14%13%5%9%7%46%47%6%20%
1560
December1st to 15thDay
12%14%6%8%7%45%5%7%8%19%
1450
16th to endDay
16%18%7%10%7%3435%5%15%
1536
January1st to 15thNight
12%10%5%8%7%47%6%6%11%21%
2506
16th to endNight
10%12%5%10%7%46%5%6%10%20%
2673
February1st to 15thNight
8%10%47%5%47%6%7%8%28%
2278
16th to endNight
8%10%5%9%7%36%5%6%7%27%
1988
March1st to 15thNight
11%10%5%8%5%35%445%35%
2103
16th to endNight
13%11%36%5%34446%36%
2043
April1st to 15thNight
15%10%47%435%5%5%433%
1797
16th to endNight
19%10%46%5%25%5%5%6%28%
1643
May1st to 15thNight
21%8%35%6%245%5%6%30%
1439
16th to endNight
14%6%36%5%35%5%45%39%
1496
June1st to 15thNight
14%5%25%5%35%5%5%6%38%
1426
16th to endNight
12%5%35%425%6%6%7%39%
1260
July1st to 15thNight
8%5%2442446%9%48%
1347
16th to endNight
5%314425%6%410%50%
1513
August1st to 15thNight
9%42432345%7%52%
1491
16th to endNight
11%42442346%7%49%
1813
September1st to 15thNight
9%425%42446%6%50%
1800
16th to endNight
13%6%36%5%2445%7%39%
1956
October1st to 15thNight
13%9%35%5%3445%6%37%
2160
16th to endNight
18%10%47%5%45%445%28%
2413
November1st to 15thNight
14%12%47%6%45%5%5%7%25%
2601
16th to endNight
15%10%48%6%37%6%6%7%22%
2730
December1st to 15thNight
11%15%5%8%6%35%6%7%9%18%
2547
16th to endNight
15%17%8%10%6%35%6%5%6%15%
2688

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%12%5%7%6%36%5%7%10%23%
1432
16th to endDay
10%11%6%13%8%45%5%7%9%18%
1548
February1st to 15thDay
10%9%6%7%5%36%5%7%8%29%
1575
16th to endDay
11%12%6%9%9%3445%5%25%
1485
March1st to 15thDay
9%11%6%8%6%3435%7%33%
1867
16th to endDay
16%13%5%8%6%34436%27%
2179
April1st to 15thDay
13%12%46%6%35%5%45%33%
2151
16th to endDay
21%12%46%5%23346%28%
2316
May1st to 15thDay
21%11%48%5%34445%26%
2511
16th to endDay
18%7%36%5%35%45%7%31%
2617
June1st to 15thDay
16%7%46%5%245%5%8%33%
2529
16th to endDay
17%7%37%5%36%5%6%8%29%
2700
July1st to 15thDay
10%6%25%5%345%6%8%40%
2610
16th to endDay
9%436%5%46%6%6%9%38%
2655
August1st to 15thDay
10%6%25%6%45%6%6%8%38%
2468
16th to endDay
12%6%245%35%5%6%9%38%
2388
September1st to 15thDay
9%8%37%5%3445%8%38%
2160
16th to endDay
17%8%37%6%33346%34%
1990
October1st to 15thDay
16%9%47%6%346%6%6%29%
1800
16th to endDay
20%16%5%8%5%3422426%
1809
November1st to 15thDay
14%16%6%8%5%3445%6%24%
1584
16th to endDay
13%12%6%10%8%45%5%6%6%19%
1560
December1st to 15thDay
11%14%5%10%7%45%6%7%8%17%
1450
16th to endDay
16%17%7%11%7%36%5%45%13%
1536
January1st to 15thNight
12%10%48%7%5%7%6%6%12%19%
2506
16th to endNight
10%13%5%10%7%46%5%6%9%19%
2673
February1st to 15thNight
8%10%47%6%47%7%7%8%27%
2278
16th to endNight
8%10%6%9%7%46%6%5%7%26%
1988
March1st to 15thNight
11%10%5%8%5%35%446%34%
2103
16th to endNight
13%11%46%6%34446%35%
2043
April1st to 15thNight
15%10%47%5%345%45%33%
1797
16th to endNight
19%11%35%5%245%5%6%28%
1643
May1st to 15thNight
20%9%36%5%34446%30%
1439
16th to endNight
13%7%36%435%5%45%38%
1496
June1st to 15thNight
14%6%35%5%35%46%6%38%
1426
16th to endNight
11%6%36%435%6%7%6%38%
1260
July1st to 15thNight
8%5%25%41446%9%47%
1347
16th to endNight
5%314435%5%5%9%50%
1513
August1st to 15thNight
9%425%42335%7%52%
1491
16th to endNight
10%42443345%7%48%
1813
September1st to 15thNight
9%4244245%6%6%49%
1800
16th to endNight
13%6%36%6%24447%40%
1956
October1st to 15thNight
13%9%35%5%3445%6%37%
2160
16th to endNight
18%10%47%6%4445%5%27%
2413
November1st to 15thNight
13%12%47%7%46%5%5%6%24%
2601
16th to endNight
15%11%48%7%47%6%6%8%21%
2730
December1st to 15thNight
11%15%5%8%7%46%6%7%9%16%
2547
16th to endNight
14%17%8%10%6%36%5%5%6%14%
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
51%10%11%17%8%
1433
16th to endDay
59%7%11%14%6%
1548
February1st to 15thDay
48%8%12%17%11%
1576
16th to endDay
58%5%9%18%8%
1485
March1st to 15thDay
50%5%14%16%11%
1867
16th to endDay
58%5%11%16%6%1
2181
April1st to 15thDay
51%5%11%17%12%1
2151
16th to endDay
56%49%17%9%1
2316
May1st to 15thDay
58%7%8%16%7%
2511
16th to endDay
50%6%11%19%10%
2621
June1st to 15thDay
46%8%13%22%8%
2529
16th to endDay
50%9%14%18%6%
2700
July1st to 15thDay
37%8%13%28%12%
2458
16th to endDay
39%9%13%25%11%1
2488
August1st to 15thDay
39%9%13%26%8%1
2453
16th to endDay
39%8%17%21%12%
2388
September1st to 15thDay
41%8%14%27%7%
2160
16th to endDay
49%6%17%20%4
1990
October1st to 15thDay
51%7%13%20%7%
1800
16th to endDay
62%5%9%15%6%
1809
November1st to 15thDay
59%6%10%15%6%
1584
16th to endDay
61%10%8%11%7%
1560
December1st to 15thDay
59%10%11%14%4
1450
16th to endDay
70%8%6%9%3
1536
January1st to 15thNight
54%11%9%17%7%
2506
16th to endNight
57%8%10%15%7%
2673
February1st to 15thNight
49%9%12%16%10%1
2288
16th to endNight
52%8%10%19%8%
1988
March1st to 15thNight
50%7%10%18%12%1
2103
16th to endNight
46%7%12%21%9%2
2043
April1st to 15thNight
50%6%11%17%13%1
1797
16th to endNight
54%7%8%19%10%
1643
May1st to 15thNight
52%8%10%20%9%
1440
16th to endNight
44%9%10%21%13%
1498
June1st to 15thNight
44%8%10%24%10%1
1426
16th to endNight
41%11%15%22%7%1
1260
July1st to 15thNight
32%8%11%32%12%
1270
16th to endNight
27%11%16%28%14%1
1417
August1st to 15thNight
31%6%16%31%12%2
1482
16th to endNight
33%8%15%26%15%
1813
September1st to 15thNight
31%8%16%35%7%
1800
16th to endNight
43%8%18%24%5%
1956
October1st to 15thNight
45%7%12%25%8%
2160
16th to endNight
56%7%11%17%6%
2413
November1st to 15thNight
55%7%13%16%6%
2601
16th to endNight
55%11%12%13%6%1
2730
December1st to 15thNight
58%12%12%12%3
2547
16th to endNight
66%8%7%11%5%
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
24%24%28%20%2
90
16th to endDay
26%17%33%18%4
96
February1st to 15thDay
22%32%36%7%1
90
16th to endDay
33%19%30%12%3
81
March1st to 15thDay
16%24%37%14%6%
90
16th to endDay
29%18%25%13%6%6%
165
April1st to 15thDay
21%14%33%22%7%
270
16th to endDay
32%17%27%15%6%
372
May1st to 15thDay
27%17%32%16%32
468
16th to endDay
21%15%37%16%5%3
517
June1st to 15thDay
20%18%32%18%7%2
495
16th to endDay
20%15%34%19%8%1
495
July1st to 15thDay
15%10%35%23%10%3
475
16th to endDay
11%12%35%26%9%5%
515
August1st to 15thDay
15%11%29%29%12%2
493
16th to endDay
17%11%31%23%12%3
428
September1st to 15thDay
13%11%30%27%13%3
315
16th to endDay
23%16%33%16%8%
249
October1st to 15thDay
20%18%42%10%6%1
135
16th to endDay
34%22%31%9%1
144
November1st to 15thDay
27%23%36%7%5%
135
16th to endDay
33%19%31%10%4
135
December1st to 15thDay
31%13%39%10%4
94
16th to endDay
22%22%39%11%12
96
January1st to 15thNight
19%22%34%18%4
900
16th to endNight
19%20%42%14%3
960
February1st to 15thNight
16%20%36%19%5%
880
16th to endNight
16%18%34%22%7%1
726
March1st to 15thNight
18%18%30%23%6%1
663
16th to endNight
19%13%30%25%9%3
576
April1st to 15thNight
20%13%32%27%5%
539
16th to endNight
25%10%30%24%7%2
540
May1st to 15thNight
26%14%25%25%6%1
540
16th to endNight
15%10%30%33%9%1
563
June1st to 15thNight
18%9%24%35%11%1
540
16th to endNight
15%8%31%31%13%
540
July1st to 15thNight
11%7%31%33%14%
510
16th to endNight
8%6%29%37%16%1
564
August1st to 15thNight
10%6%27%33%20%2
539
16th to endNight
13%9%27%31%15%1
573
September1st to 15thNight
12%7%26%31%20%2
540
16th to endNight
18%12%27%27%12%1
630
October1st to 15thNight
22%16%28%23%8%
720
16th to endNight
26%14%30%21%5%
768
November1st to 15thNight
21%20%30%21%5%1
890
16th to endNight
24%20%30%19%5%
975
December1st to 15thNight
20%21%35%17%5%
910
16th to endNight
25%18%32%16%5%1
960
Page generated at 2017-12-03 10:16:42. Version ac04

Copyright 2017 A. Danko


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