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 2017-04-25.

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
27%
15790
12%
45391
6%
15743
33%
15743
17%
33011

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
26%
875
13%
1709
February16th to endNight
23%
726
12%
1988
4%
726
29%
726
14%
1495
March1st to 15thNight
23%
663
14%
2103
8%
663
31%
663
15%
1502
March16th to endNight
31%
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%
525
12%
1603
7%
525
35%
525
16%
1184
May1st to 15thNight
27%
495
12%
1320
4%
495
32%
495
16%
1014
May16th to endNight
38%
515
9%
1370
3%
513
42%
513
23%
967
June1st to 15thNight
40%
495
7%
1307
4%
495
42%
495
22%
941
June16th to endNight
40%
495
8%
1155
4%
495
42%
495
26%
833
July1st to 15thNight
43%
465
11%
1158
5%
465
45%
465
34%
773
July16th to endNight
51%
522
13%
1305
6%
489
53%
489
35%
820
August1st to 15thNight
50%
494
20%
1358
12%
491
54%
491
36%
820
August16th to endNight
44%
525
19%
1661
16%
525
50%
525
28%
987
September1st to 15thNight
51%
495
19%
1650
15%
495
59%
495
29%
964
September16th to endNight
39%
577
13%
1793
10%
577
43%
577
22%
1182
October1st to 15thNight
29%
660
17%
1980
10%
660
37%
660
19%
1374
October16th to endNight
23%
704
10%
2212
4%
704
30%
704
12%
1678
November1st to 15thNight
21%
820
12%
2396
5%
820
27%
820
13%
1785
November16th to endNight
21%
900
12%
2520
5%
900
27%
900
12%
1977
December1st to 15thNight
15%
900
7%
2520
2%
900
20%
900
9%
2055
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%3445%7%30%
46251
Night
13%10%47%5%35%5%5%7%31%
45558
Cloud CoverDay
14%10%47%6%35%45%7%30%
46261
Night
13%9%47%5%35%5%5%7%31%
45563
Cloud CoverDay
14%10%47%6%35%45%7%30%
46259
Night
12%10%47%6%35%5%5%7%31%
45563
TransparencyDay
51%7%12%19%8%
45933
Night
49%8%12%20%8%
45394
SeeingDay
21%16%32%19%8%2
5520
Night
19%15%31%24%8%1
15791

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%
2244
May1st to 15thDay
23%12%47%5%24435%26%
2301
16th to endDay
17%6%36%5%35%45%7%33%
2393
June1st to 15thDay
18%7%26%4245%5%8%32%
2318
16th to endDay
18%7%35%5%36%5%5%7%31%
2475
July1st to 15thDay
12%5%25%4345%6%9%40%
2393
16th to endDay
11%5%25%5%36%5%6%9%38%
2459
August1st to 15thDay
11%5%25%6%35%47%8%38%
2263
16th to endDay
12%6%14435%47%9%39%
2188
September1st to 15thDay
10%8%36%5%336%5%8%38%
1980
16th to endDay
18%8%37%5%23346%36%
1825
October1st to 15thDay
17%10%37%6%25%5%6%6%29%
1650
16th to endDay
21%16%47%6%3333325%
1658
November1st to 15thDay
15%15%5%8%5%25%45%5%26%
1459
16th to endDay
14%12%7%11%7%35%5%6%5%20%
1440
December1st to 15thDay
11%14%6%9%7%37%47%8%18%
1440
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
19%11%36%5%25%45%5%29%
1603
May1st to 15thNight
22%9%45%5%245%5%6%29%
1320
16th to endNight
14%6%36%435%6%45%40%
1368
June1st to 15thNight
16%5%35%5%45%46%6%35%
1307
16th to endNight
11%5%35%5%26%5%7%7%39%
1155
July1st to 15thNight
8%5%344235%5%9%47%
1235
16th to endNight
6%314426%5%5%9%50%
1401
August1st to 15thNight
9%4243235%47%52%
1367
16th to endNight
10%5%2443345%6%49%
1661
September1st to 15thNight
8%5%2442447%6%49%
1650
16th to endNight
14%6%37%433446%41%
1793
October1st to 15thNight
13%10%36%5%24446%36%
1980
16th to endNight
18%10%48%6%345%45%29%
2212
November1st to 15thNight
13%13%5%7%6%35%5%5%6%27%
2396
16th to endNight
16%11%47%7%36%5%6%7%22%
2520
December1st to 15thNight
12%15%6%8%7%36%6%6%8%17%
2520
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%11%46%5%23346%29%
2244
May1st to 15thDay
23%11%37%5%2443426%
2301
16th to endDay
17%6%36%5%35%45%7%33%
2393
June1st to 15thDay
18%7%47%43445%8%32%
2318
16th to endDay
17%7%27%5%35%5%6%7%31%
2475
July1st to 15thDay
11%5%25%425%5%5%9%40%
2393
16th to endDay
10%5%25%5%36%5%6%10%38%
2459
August1st to 15thDay
11%5%25%6%35%6%7%7%39%
2263
16th to endDay
12%6%24435%46%8%39%
2188
September1st to 15thDay
10%8%37%5%345%6%8%37%
1980
16th to endDay
17%7%46%6%24346%35%
1825
October1st to 15thDay
16%11%36%6%345%6%7%28%
1650
16th to endDay
21%16%47%6%3333425%
1658
November1st to 15thDay
14%15%5%8%5%35%446%26%
1459
16th to endDay
14%13%6%10%7%45%47%5%20%
1440
December1st to 15thDay
11%14%6%9%7%45%5%7%8%19%
1440
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%29%
1603
May1st to 15thNight
22%8%35%6%245%46%29%
1319
16th to endNight
14%6%36%5%35%5%5%5%40%
1368
June1st to 15thNight
16%6%35%6%35%45%6%36%
1307
16th to endNight
12%5%25%425%5%6%7%40%
1155
July1st to 15thNight
8%5%25%5%2446%8%47%
1235
16th to endNight
5%314425%6%410%50%
1401
August1st to 15thNight
8%424324447%52%
1367
16th to endNight
10%4245%2346%7%49%
1661
September1st to 15thNight
9%4244245%6%6%49%
1650
16th to endNight
13%6%36%5%23347%41%
1793
October1st to 15thNight
13%9%35%5%3445%6%36%
1980
16th to endNight
18%10%47%5%46%445%28%
2212
November1st to 15thNight
13%12%47%6%45%5%5%7%27%
2396
16th to endNight
16%11%47%6%37%5%6%7%23%
2520
December1st to 15thNight
12%15%5%8%6%35%6%7%9%18%
2520
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%
2244
May1st to 15thDay
22%11%48%5%3444425%
2301
16th to endDay
16%7%36%5%35%45%7%33%
2393
June1st to 15thDay
17%8%46%5%245%5%8%31%
2318
16th to endDay
16%7%37%5%36%5%6%8%30%
2475
July1st to 15thDay
10%6%25%5%35%5%6%9%39%
2393
16th to endDay
9%5%36%5%36%6%6%10%37%
2459
August1st to 15thDay
10%6%25%6%45%6%6%8%38%
2263
16th to endDay
11%6%245%35%5%6%9%39%
2188
September1st to 15thDay
9%8%37%5%3445%8%37%
1980
16th to endDay
17%7%36%6%23447%35%
1825
October1st to 15thDay
16%10%47%6%346%6%7%28%
1650
16th to endDay
20%16%5%8%6%3422425%
1658
November1st to 15thDay
14%15%6%8%5%35%45%6%24%
1459
16th to endDay
14%12%7%10%8%45%5%6%6%19%
1440
December1st to 15thDay
11%14%5%10%7%45%6%7%8%17%
1440
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
18%11%35%5%245%5%6%28%
1603
May1st to 15thNight
21%10%36%5%34446%29%
1319
16th to endNight
13%6%36%435%5%45%39%
1368
June1st to 15thNight
15%7%35%5%35%45%6%36%
1307
16th to endNight
11%6%26%435%5%7%6%39%
1155
July1st to 15thNight
7%5%25%5%2446%9%46%
1235
16th to endNight
5%324435%5%5%9%50%
1401
August1st to 15thNight
8%425%42345%7%51%
1367
16th to endNight
9%425%43345%8%48%
1661
September1st to 15thNight
9%42442446%6%48%
1650
16th to endNight
13%6%36%5%24446%42%
1793
October1st to 15thNight
13%10%35%6%2445%6%36%
1980
16th to endNight
18%10%47%6%4445%5%28%
2212
November1st to 15thNight
12%12%47%7%46%5%5%6%26%
2396
16th to endNight
16%11%47%6%37%5%6%8%21%
2520
December1st to 15thNight
12%15%5%8%7%36%6%7%9%16%
2520
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%410%17%9%1
2244
May1st to 15thDay
60%7%8%15%6%
2301
16th to endDay
49%6%12%20%10%
2397
June1st to 15thDay
48%7%13%22%7%
2318
16th to endDay
49%9%14%19%7%
2475
July1st to 15thDay
37%8%13%27%12%
2241
16th to endDay
39%10%13%24%10%1
2292
August1st to 15thDay
39%8%14%26%9%1
2248
16th to endDay
38%8%17%22%12%
2188
September1st to 15thDay
42%7%15%28%6%
1980
16th to endDay
48%6%18%20%5%
1825
October1st to 15thDay
51%7%13%19%6%
1650
16th to endDay
62%5%8%15%6%
1658
November1st to 15thDay
58%6%10%16%6%
1459
16th to endDay
62%9%8%11%7%
1440
December1st to 15thDay
59%10%11%14%4
1440
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
53%7%8%19%10%
1603
May1st to 15thNight
54%8%10%19%7%
1320
16th to endNight
43%8%10%23%13%
1370
June1st to 15thNight
47%8%10%24%9%
1307
16th to endNight
40%11%14%23%8%1
1155
July1st to 15thNight
33%9%10%32%13%
1158
16th to endNight
27%11%17%28%13%1
1305
August1st to 15thNight
31%6%16%30%13%2
1358
16th to endNight
33%8%15%26%15%
1661
September1st to 15thNight
32%8%16%35%7%
1650
16th to endNight
42%7%18%25%5%
1793
October1st to 15thNight
45%7%13%25%7%
1980
16th to endNight
56%8%12%17%5%
2212
November1st to 15thNight
54%7%13%16%7%
2396
16th to endNight
55%11%11%13%6%1
2520
December1st to 15thNight
58%12%12%12%3
2520
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
30%17%28%16%6%
347
May1st to 15thDay
29%18%29%15%32
393
16th to endDay
18%16%37%18%6%3
437
June1st to 15thDay
22%19%29%17%7%2
420
16th to endDay
19%15%33%20%9%2
420
July1st to 15thDay
15%12%35%22%11%3
400
16th to endDay
12%12%35%25%8%5%
445
August1st to 15thDay
15%13%30%27%11%2
418
16th to endDay
16%12%31%24%12%3
356
September1st to 15thDay
13%10%29%28%14%3
255
16th to endDay
24%15%31%16%10%1
195
October1st to 15thDay
23%12%42%10%10%2
90
16th to endDay
37%19%30%10%2
96
November1st to 15thDay
22%25%38%8%4
90
16th to endDay
36%13%30%13%5%1
90
December1st to 15thDay
30%14%41%11%3
90
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%8%2
525
May1st to 15thNight
27%14%25%23%6%1
495
16th to endNight
14%10%30%33%9%
515
June1st to 15thNight
20%8%25%34%10%1
495
16th to endNight
14%8%31%31%13%
495
July1st to 15thNight
11%7%33%33%12%
465
16th to endNight
8%5%29%37%15%1
522
August1st to 15thNight
9%6%28%32%20%2
494
16th to endNight
12%10%28%31%15%1
525
September1st to 15thNight
12%7%26%31%20%1
495
16th to endNight
18%12%26%27%13%1
577
October1st to 15thNight
22%16%28%23%9%
660
16th to endNight
25%14%30%21%6%
704
November1st to 15thNight
20%20%30%21%5%
820
16th to endNight
24%18%30%20%5%
900
December1st to 15thNight
20%21%35%17%4
900
16th to endNight
25%18%32%16%5%1
960
Page generated at 2017-04-26 16:21:40. Version ac04

Copyright 2017 A. Danko


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