Grand Island
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Grand Island clear sky chart from 2005-11-06 to 2024-02-25.

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
38%
24812
23%
79658
12%
24711
49%
24711
30%
46820

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 10thNight
32%
939
20%
4369
9%
926
44%
926
17%
2769
January11th to 20thNight
30%
948
25%
4092
10%
930
40%
930
20%
2329
January21st to endNight
29%
1037
16%
4383
8%
1023
39%
1023
18%
2883
February1st to 10thNight
25%
950
17%
2470
6%
950
32%
950
26%
1685
February11th to 20thNight
31%
778
19%
2252
8%
774
40%
774
28%
1410
February21st to endNight
27%
610
25%
1830
6%
610
43%
610
30%
1078
March1st to 10thNight
27%
666
23%
2106
8%
666
40%
666
29%
1218
March11th to 20thNight
31%
540
25%
1980
17%
540
44%
540
27%
1130
March21st to endNight
24%
594
16%
2178
9%
594
35%
594
19%
1386
April1st to 10thNight
25%
540
18%
1908
8%
540
40%
540
24%
1118
April11th to 20thNight
25%
533
21%
1649
10%
533
40%
533
26%
1008
April21st to endNight
36%
540
22%
1620
16%
540
47%
540
28%
993
May1st to 10thNight
35%
540
17%
1620
10%
540
45%
540
27%
1025
May11th to 20thNight
36%
531
17%
1593
11%
531
43%
531
28%
997
May21st to endNight
39%
583
14%
1746
6%
582
45%
582
27%
1127
June1st to 10thNight
56%
540
19%
1590
11%
540
59%
540
40%
881
June11th to 20thNight
43%
540
22%
1440
8%
540
50%
540
41%
844
June21st to endNight
54%
540
22%
1440
11%
540
59%
540
47%
803
July1st to 10thNight
62%
525
18%
1400
11%
525
64%
525
42%
817
July11th to 20thNight
68%
522
22%
1464
16%
522
71%
522
49%
772
July21st to endNight
67%
591
23%
1673
19%
558
71%
558
44%
890
August1st to 10thNight
62%
537
19%
1601
19%
534
66%
534
36%
921
August11th to 20thNight
59%
534
28%
1600
25%
534
68%
534
41%
861
August21st to endNight
59%
594
28%
1831
25%
594
67%
594
43%
953
September1st to 10thNight
54%
540
27%
1926
24%
540
65%
540
41%
928
September11th to 20thNight
47%
540
31%
1980
24%
540
62%
540
36%
989
September21st to endNight
45%
540
30%
1980
21%
540
60%
540
36%
992
October1st to 10thNight
40%
561
30%
2001
21%
561
51%
561
29%
1103
October11th to 20thNight
35%
720
29%
2160
13%
720
46%
720
37%
1174
October21st to endNight
38%
895
29%
2479
12%
895
48%
895
38%
1429
November1st to 10thNight
42%
925
32%
2405
12%
925
54%
925
47%
1301
November11th to 20thNight
33%
950
31%
2470
10%
950
47%
950
39%
1431
November21st to endNight
37%
950
28%
2470
12%
950
47%
950
40%
1438
December1st to 10thNight
29%
950
25%
2470
8%
950
42%
950
36%
1509
December11th to 20thNight
30%
949
28%
2852
9%
948
42%
948
31%
1610
December21st to endNight
28%
1040
17%
4630
8%
1026
42%
1026
16%
3018

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
10%6%35%5%3445%7%48%
78900
Night
9%6%35%43445%7%50%
80437
TransparencyDay
35%6%14%26%16%3
78617
Night
33%6%13%27%18%3
80243
SeeingDay
14%10%31%30%13%2
14729
Night
12%9%36%33%10%
24840

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 10thDay
7%13%47%7%35%446%39%
2538
11th to 20thDay
6%11%5%8%6%35%6%5%7%40%
2758
21st to endDay
7%8%5%12%6%33345%44%
3135
February1st to 10thDay
9%9%46%6%45%5%6%7%38%
1710
11th to 20thDay
6%7%37%4345%6%7%47%
1831
21st to endDay
9%8%25%5%35%45%6%48%
1520
March1st to 10thDay
9%6%35%424447%52%
1854
11th to 20thDay
14%7%35%42446%7%44%
1980
21st to endDay
15%11%47%5%345%5%6%36%
2178
April1st to 10thDay
12%6%25%434447%47%
2050
11th to 20thDay
15%8%25%5%3435%6%44%
2259
21st to endDay
18%6%24435%45%7%41%
2340
May1st to 10thDay
14%6%35%5%35%5%6%7%41%
2340
11th to 20thDay
17%7%245%3445%8%43%
2302
21st to endDay
13%6%26%6%345%7%8%38%
2531
June1st to 10thDay
7%4134245%5%8%55%
2364
11th to 20thDay
9%5%235%35%5%6%7%52%
2520
21st to endDay
7%3243245%7%10%53%
2520
July1st to 10thDay
7%42443446%9%51%
2520
11th to 20thDay
5%3244345%5%8%57%
2444
21st to endDay
7%424435%5%6%10%51%
2546
August1st to 10thDay
7%426%5%446%7%10%44%
2328
11th to 20thDay
7%4243245%5%9%54%
2301
21st to endDay
8%5%245%2445%6%55%
2520
September1st to 10thDay
12%425%423346%55%
2034
11th to 20thDay
9%42443345%7%56%
1980
21st to endDay
9%423323447%60%
1980
October1st to 10thDay
14%6%34322445%54%
1940
11th to 20thDay
11%424323346%59%
1800
21st to endDay
13%7%34323345%54%
1873
November1st to 10thDay
7%5%144345%5%8%55%
1673
11th to 20thDay
8%5%245%33337%57%
1710
21st to endDay
10%8%2442445%8%50%
1710
December1st to 10thDay
7%6%46%5%3445%7%50%
1710
11th to 20thDay
7%8%36%5%3445%6%48%
2161
21st to endDay
13%10%311%6%345%5%5%36%
2940
January1st to 10thNight
6%12%49%7%345%6%6%38%
4417
11th to 20thNight
6%8%36%5%36%45%5%48%
4206
21st to endNight
7%10%5%12%5%3345%6%41%
4532
February1st to 10thNight
9%9%47%6%35%446%43%
2470
11th to 20thNight
5%7%36%6%35%6%5%6%47%
2252
21st to endNight
7%7%35%5%3445%7%52%
1830
March1st to 10thNight
10%6%35%444345%52%
2106
11th to 20thNight
13%7%3432345%7%49%
1980
21st to endNight
15%9%36%5%345%5%7%40%
2178
April1st to 10thNight
11%7%25%425%45%7%47%
1908
11th to 20thNight
12%6%25%43446%9%44%
1649
21st to endNight
14%42443435%7%49%
1620
May1st to 10thNight
14%6%24435%5%6%6%45%
1620
11th to 20thNight
12%7%26%5%3446%7%46%
1593
21st to endNight
14%425%4245%7%10%41%
1745
June1st to 10thNight
6%4143345%7%10%53%
1590
11th to 20thNight
8%42343445%8%55%
1440
21st to endNight
43144235%6%10%57%
1440
July1st to 10thNight
6%4245%25%5%7%9%53%
1440
11th to 20thNight
322332446%9%62%
1512
21st to endNight
4323435%46%11%54%
1772
August1st to 10thNight
5%425%435%6%7%9%50%
1611
11th to 20thNight
5%3145%3446%8%56%
1600
21st to endNight
6%424324347%62%
1831
September1st to 10thNight
8%31332335%6%63%
1926
11th to 20thNight
7%42342345%6%59%
1980
21st to endNight
7%41342445%6%60%
1980
October1st to 10thNight
15%414323447%53%
2001
11th to 20thNight
10%5%14323346%59%
2160
21st to endNight
12%5%13323346%57%
2479
November1st to 10thNight
5%4133235%47%63%
2405
11th to 20thNight
8%5%24424347%57%
2470
21st to endNight
9%6%2432335%7%56%
2470
December1st to 10thNight
6%7%35%43445%7%52%
2470
11th to 20thNight
7%5%35%5%2345%8%53%
3036
21st to endNight
15%11%38%5%24345%40%
4718

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 10thDay
46%5%15%23%9%1
2539
11th to 20thDay
43%6%18%18%13%2
2758
21st to endDay
44%5%14%23%13%1
3135
February1st to 10thDay
44%6%15%21%11%2
1710
11th to 20thDay
37%5%15%24%15%4
1841
21st to endDay
37%6%12%26%15%5%
1520
March1st to 10thDay
33%5%14%26%19%3
1854
11th to 20thDay
39%5%12%26%15%2
1980
21st to endDay
49%5%15%21%9%1
2178
April1st to 10thDay
36%6%15%26%15%2
2050
11th to 20thDay
41%414%23%14%3
2262
21st to endDay
43%6%12%26%13%1
2340
May1st to 10thDay
41%7%15%21%14%1
2340
11th to 20thDay
41%6%17%23%13%
2306
21st to endDay
42%8%17%21%10%1
2531
June1st to 10thDay
26%8%17%32%15%2
2364
11th to 20thDay
31%7%14%28%18%3
2520
21st to endDay
25%8%15%31%17%4
2520
July1st to 10thDay
28%6%16%30%18%2
2451
11th to 20thDay
25%8%13%29%21%5%
2369
21st to endDay
27%8%17%31%15%1
2405
August1st to 10thDay
32%9%18%27%12%1
2314
11th to 20thDay
26%7%15%33%18%2
2301
21st to endDay
29%7%13%23%24%5%
2520
September1st to 10thDay
32%5%11%25%21%6%
2034
11th to 20thDay
28%6%12%31%22%3
1980
21st to endDay
25%49%34%26%1
1980
October1st to 10thDay
34%49%27%25%2
1940
11th to 20thDay
29%410%29%21%8%
1800
21st to endDay
35%312%24%22%5%
1873
November1st to 10thDay
27%6%14%29%22%3
1673
11th to 20thDay
31%312%27%24%4
1710
21st to endDay
35%412%27%19%4
1710
December1st to 10thDay
34%5%15%29%14%3
1710
11th to 20thDay
37%5%14%31%13%
2159
21st to endDay
50%5%10%22%11%1
2940
January1st to 10thNight
45%5%12%23%13%1
4417
11th to 20thNight
37%5%15%27%15%1
4206
21st to endNight
45%6%12%21%15%1
4532
February1st to 10thNight
43%6%13%23%13%3
2470
11th to 20thNight
36%7%13%26%15%3
2252
21st to endNight
33%5%12%23%22%6%
1830
March1st to 10thNight
35%411%28%18%4
2106
11th to 20thNight
36%410%26%21%4
1980
21st to endNight
44%6%14%23%12%1
2178
April1st to 10thNight
36%6%14%24%18%2
1908
11th to 20thNight
36%6%14%27%14%2
1649
21st to endNight
35%7%12%26%18%2
1620
May1st to 10thNight
38%6%15%25%15%1
1620
11th to 20thNight
38%6%17%25%14%
1594
21st to endNight
37%10%17%22%12%2
1746
June1st to 10thNight
23%9%19%30%16%2
1590
11th to 20thNight
27%7%15%28%18%5%
1440
21st to endNight
22%7%15%32%20%4
1440
July1st to 10thNight
26%7%16%28%19%4
1400
11th to 20thNight
19%8%17%28%24%5%
1464
21st to endNight
22%7%17%33%17%3
1673
August1st to 10thNight
27%9%20%29%13%2
1601
11th to 20thNight
24%7%14%34%18%2
1600
21st to endNight
24%6%13%25%24%8%
1831
September1st to 10thNight
24%410%27%24%10%
1926
11th to 20thNight
26%5%9%32%24%4
1980
21st to endNight
26%5%9%29%28%3
1980
October1st to 10thNight
32%5%10%25%24%3
2001
11th to 20thNight
28%48%25%26%8%
2160
21st to endNight
30%312%26%23%6%
2479
November1st to 10thNight
21%5%13%29%26%6%
2405
11th to 20thNight
29%410%29%24%5%
2470
21st to endNight
29%313%27%23%4
2470
December1st to 10thNight
32%5%14%30%17%2
2470
11th to 20thNight
30%413%36%16%1
3037
21st to endNight
46%6%11%25%11%1
4718

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 10thDay
17%15%35%23%7%2
270
11th to 20thDay
17%17%34%23%7%1
270
21st to endDay
16%10%44%22%7%1
297
February1st to 10thDay
14%16%45%20%6%
270
11th to 20thDay
13%12%47%21%6%1
270
21st to endDay
17%16%45%17%4
210
March1st to 10thDay
15%13%44%23%5%1
240
11th to 20thDay
24%10%37%20%9%
240
21st to endDay
28%16%36%16%5%
264
April1st to 10thDay
17%22%39%17%5%
310
11th to 20thDay
20%16%35%24%4
540
21st to endDay
22%17%30%20%9%2
600
May1st to 10thDay
17%12%33%27%10%1
603
11th to 20thDay
20%11%31%24%12%3
625
21st to endDay
15%10%31%30%11%2
679
June1st to 10thDay
6%7%27%36%20%5%
630
11th to 20thDay
10%6%33%33%15%3
630
21st to endDay
8%7%30%34%19%2
630
July1st to 10thDay
9%319%38%26%4
621
11th to 20thDay
6%320%44%22%5%
618
21st to endDay
7%320%42%24%4
684
August1st to 10thDay
8%318%46%22%3
626
11th to 20thDay
7%421%42%24%2
615
21st to endDay
10%324%38%20%5%
639
September1st to 10thDay
15%5%27%35%15%3
324
11th to 20thDay
7%7%31%36%14%5%
270
21st to endDay
14%11%30%31%11%3
270
October1st to 10thDay
22%11%25%31%7%4
270
11th to 20thDay
15%14%37%24%8%2
270
21st to endDay
18%18%33%23%7%1
297
November1st to 10thDay
14%16%39%21%8%2
270
11th to 20thDay
11%14%46%22%6%
270
21st to endDay
22%14%34%18%10%2
270
December1st to 10thDay
10%13%43%30%41
270
11th to 20thDay
16%10%43%26%5%
270
21st to endDay
21%13%45%20%1
297
January1st to 10thNight
12%11%37%32%7%1
950
11th to 20thNight
11%13%40%29%6%1
950
21st to endNight
11%9%42%30%7%
1045
February1st to 10thNight
14%11%43%27%5%
950
11th to 20thNight
11%11%41%31%5%
778
21st to endNight
11%13%45%26%5%
610
March1st to 10thNight
13%12%44%26%41
666
11th to 20thNight
17%10%40%27%5%1
540
21st to endNight
21%11%39%24%5%
594
April1st to 10thNight
16%14%43%24%3
540
11th to 20thNight
17%13%42%25%31
533
21st to endNight
18%12%30%31%7%1
540
May1st to 10thNight
16%10%36%31%7%
540
11th to 20thNight
16%8%34%34%8%1
531
21st to endNight
16%8%33%31%12%1
584
June1st to 10thNight
8%5%26%43%15%2
540
11th to 20thNight
9%6%38%37%11%
540
21st to endNight
6%433%44%14%
540
July1st to 10thNight
6%321%45%24%1
525
11th to 20thNight
3222%50%21%1
522
21st to endNight
5%219%53%21%1
591
August1st to 10thNight
5%320%48%22%2
537
11th to 20thNight
7%225%47%19%
534
21st to endNight
7%425%44%19%2
594
September1st to 10thNight
10%329%42%15%1
540
11th to 20thNight
9%6%32%37%14%1
540
21st to endNight
8%7%36%34%14%1
540
October1st to 10thNight
17%10%30%30%12%
561
11th to 20thNight
13%12%37%30%8%
720
21st to endNight
16%12%31%31%10%
895
November1st to 10thNight
7%12%36%38%7%1
925
11th to 20thNight
12%11%41%30%7%
950
21st to endNight
11%10%38%30%10%
950
December1st to 10thNight
10%11%45%29%5%
950
11th to 20thNight
13%9%41%30%6%
950
21st to endNight
16%13%36%29%5%
1045
Page generated at 2024-02-22 05:05:48. Version ac07

Copyright 2024 Attilla Danko


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