Grand Forks
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Grand Forks 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
37%
14853
12%
46914
8%
14823
42%
14823
16%
32952

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
20%
720
6%
2506
4%
716
24%
716
6%
2101
January16th to endNight
24%
768
6%
2688
5%
768
27%
768
7%
2206
February1st to 15thNight
28%
702
7%
2399
5%
700
33%
700
11%
1790
February16th to endNight
34%
632
11%
1928
8%
632
40%
632
16%
1387
March1st to 15thNight
28%
720
7%
2160
5%
720
31%
720
12%
1675
March16th to endNight
28%
768
8%
2012
2%
768
32%
768
14%
1567
April1st to 15thNight
39%
719
11%
1799
5%
719
42%
719
19%
1333
April16th to endNight
38%
536
12%
1616
9%
536
42%
536
18%
1105
May1st to 15thNight
45%
359
15%
1440
16%
359
53%
359
18%
838
May16th to endNight
41%
374
7%
1472
10%
374
44%
374
12%
1014
June1st to 15thNight
44%
360
5%
1260
3%
360
46%
360
18%
833
June16th to endNight
44%
360
8%
1260
2%
360
47%
360
19%
787
July1st to 15thNight
61%
340
11%
1318
8%
340
65%
340
33%
608
July16th to endNight
62%
376
19%
1416
23%
354
78%
354
40%
593
August1st to 15thNight
70%
360
23%
1432
30%
358
76%
358
37%
645
August16th to endNight
65%
646
29%
1792
19%
646
71%
646
49%
903
September1st to 15thNight
60%
720
26%
1800
12%
720
64%
720
46%
997
September16th to endNight
55%
688
24%
1882
16%
688
60%
688
32%
1161
October1st to 15thNight
45%
660
16%
1952
13%
660
49%
660
25%
1261
October16th to endNight
39%
704
12%
2282
7%
704
45%
704
16%
1623
November1st to 15thNight
31%
700
9%
2339
8%
700
34%
700
11%
1813
November16th to endNight
22%
796
6%
2596
3%
796
26%
796
9%
2087
December1st to 15thNight
23%
900
7%
2700
4%
900
26%
900
9%
2218
December16th to endNight
17%
945
7%
2865
2%
945
21%
945
7%
2407

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
12%9%47%6%35%45%6%34%
48010
Night
14%10%46%5%3445%6%34%
47081
Cloud CoverDay
12%9%36%6%35%45%6%34%
48010
Night
14%10%46%5%3445%6%34%
47085
TransparencyDay
49%7%12%17%9%2
47681
Night
49%6%13%18%9%1
46914
SeeingDay
17%19%25%24%10%2
5747
Night
17%18%18%26%16%1
14857

By Month

Percentage Cloud Cover NW (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
19%17%8%8%6%35%43419%
1432
16th to endDay
16%17%5%9%6%345%5%5%20%
1536
February1st to 15thDay
17%15%5%8%5%345%45%23%
1465
16th to endDay
14%13%38%7%36%5%6%7%22%
1545
March1st to 15thDay
18%15%5%7%5%3445%6%21%
1800
16th to endDay
17%13%5%10%8%45%5%5%6%17%
2211
April1st to 15thDay
13%11%5%9%8%47%5%6%6%21%
2149
16th to endDay
11%11%48%7%45%46%7%27%
2343
May1st to 15thDay
11%7%47%7%46%5%5%8%32%
2511
16th to endDay
13%8%48%7%45%5%6%8%26%
2639
June1st to 15thDay
19%7%46%7%45%5%5%5%28%
2700
16th to endDay
13%6%37%6%45%45%6%35%
2700
July1st to 15thDay
43144345%5%7%53%
2559
16th to endDay
331342445%6%59%
2657
August1st to 15thDay
331443445%7%56%
2520
16th to endDay
5%213425%45%8%55%
2409
September1st to 15thDay
4314423347%59%
2160
16th to endDay
10%5%25%5%3445%7%45%
1914
October1st to 15thDay
13%7%45%5%3445%7%37%
1675
16th to endDay
20%12%36%5%3445%5%27%
1589
November1st to 15thDay
23%10%46%5%345%5%7%23%
1518
16th to endDay
18%14%5%8%6%35%5%5%422%
1350
December1st to 15thDay
15%15%6%10%8%2334426%
1260
16th to endDay
19%18%6%10%433345%20%
1368
January1st to 15thNight
24%16%7%10%5%3333417%
2506
16th to endNight
17%18%6%10%6%33446%17%
2688
February1st to 15thNight
18%15%46%5%34346%28%
2387
16th to endNight
13%12%37%5%3446%8%31%
1928
March1st to 15thNight
17%12%5%6%6%35%5%5%7%25%
2160
16th to endNight
14%10%46%6%37%5%47%27%
2008
April1st to 15thNight
13%8%35%6%35%5%6%7%33%
1799
16th to endNight
8%8%36%6%35%6%7%8%35%
1616
May1st to 15thNight
9%5%25%436%6%7%7%43%
1439
16th to endNight
12%8%36%6%35%6%7%8%31%
1472
June1st to 15thNight
14%5%35%5%36%6%6%9%34%
1260
16th to endNight
9%336%6%35%5%6%7%41%
1260
July1st to 15thNight
3234245%47%62%
1398
16th to endNight
21232445%6%66%
1512
August1st to 15thNight
32232345%6%64%
1440
16th to endNight
221232345%7%64%
1792
September1st to 15thNight
3212323446%64%
1800
16th to endNight
8%5%2432445%8%50%
1882
October1st to 15thNight
13%6%35%42445%7%43%
1952
16th to endNight
18%8%37%5%3445%7%31%
2282
November1st to 15thNight
22%13%35%5%25%5%46%24%
2339
16th to endNight
22%15%7%7%5%23445%22%
2596
December1st to 15thNight
19%15%7%9%5%3433421%
2700
16th to endNight
22%19%6%9%5%2333419%
2865

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
20%17%7%9%6%35%43418%
1432
16th to endDay
15%18%5%9%6%34445%19%
1536
February1st to 15thDay
18%16%5%7%6%245%45%23%
1465
16th to endDay
13%14%49%6%35%6%6%7%22%
1545
March1st to 15thDay
19%15%5%7%5%35%446%21%
1800
16th to endDay
17%14%5%10%7%46%446%17%
2211
April1st to 15thDay
13%11%5%9%8%46%5%5%6%21%
2149
16th to endDay
11%11%48%7%45%5%5%7%27%
2343
May1st to 15thDay
10%8%47%7%46%45%7%33%
2511
16th to endDay
13%8%48%8%46%5%7%8%25%
2639
June1st to 15thDay
18%7%46%7%45%5%5%5%28%
2700
16th to endDay
12%6%47%7%35%5%5%6%35%
2700
July1st to 15thDay
44235%35%5%5%6%54%
2559
16th to endDay
3313424446%59%
2657
August1st to 15thDay
33135%2445%8%55%
2520
16th to endDay
422442445%8%56%
2409
September1st to 15thDay
4314323347%59%
2160
16th to endDay
10%5%25%5%24447%45%
1914
October1st to 15thDay
14%7%26%6%2445%6%38%
1675
16th to endDay
21%12%35%6%34446%27%
1589
November1st to 15thDay
22%13%36%5%3445%7%24%
1518
16th to endDay
18%13%6%6%7%26%45%421%
1350
December1st to 15thDay
17%14%6%9%8%3324425%
1260
16th to endDay
18%19%6%9%5%23345%20%
1368
January1st to 15thNight
25%17%6%9%6%2333416%
2506
16th to endNight
17%18%7%11%6%3435%6%16%
2688
February1st to 15thNight
17%16%46%5%2335%7%26%
2387
16th to endNight
13%12%36%5%4336%7%31%
1928
March1st to 15thNight
18%12%47%6%3446%6%24%
2160
16th to endNight
15%11%36%7%45%5%5%6%27%
2012
April1st to 15thNight
12%8%35%5%46%5%7%8%32%
1799
16th to endNight
8%8%36%6%35%6%7%7%35%
1616
May1st to 15thNight
8%5%25%425%6%7%7%43%
1439
16th to endNight
12%8%37%6%36%6%6%8%30%
1472
June1st to 15thNight
13%5%35%5%35%5%8%8%33%
1260
16th to endNight
9%316%7%35%6%6%7%41%
1260
July1st to 15thNight
321332445%7%62%
1398
16th to endNight
21232435%7%66%
1512
August1st to 15thNight
32231445%7%63%
1440
16th to endNight
121232336%8%64%
1792
September1st to 15thNight
3213423446%64%
1800
16th to endNight
8%6%1443435%8%50%
1882
October1st to 15thNight
13%5%25%5%2345%8%43%
1952
16th to endNight
17%8%36%5%345%46%32%
2282
November1st to 15thNight
24%12%45%5%2445%6%23%
2339
16th to endNight
22%16%7%7%5%24335%21%
2596
December1st to 15thNight
19%16%7%9%6%3343420%
2700
16th to endNight
22%20%7%8%42333319%
2865

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
68%8%10%8%3
1432
16th to endDay
64%7%12%11%21
1536
February1st to 15thDay
61%9%14%11%21
1465
16th to endDay
59%8%14%11%6%
1545
March1st to 15thDay
63%9%16%9%1
1800
16th to endDay
66%9%12%8%3
2211
April1st to 15thDay
61%7%14%12%3
2149
16th to endDay
55%8%13%18%31
2343
May1st to 15thDay
49%7%13%19%9%1
2511
16th to endDay
55%9%16%14%4
2643
June1st to 15thDay
55%8%9%15%8%2
2700
16th to endDay
47%8%11%18%13%
2700
July1st to 15thDay
29%7%10%23%20%8%
2410
16th to endDay
25%6%10%21%26%8%
2490
August1st to 15thDay
25%6%13%27%21%5%
2503
16th to endDay
26%6%13%30%19%3
2409
September1st to 15thDay
25%6%11%28%24%3
2160
16th to endDay
38%7%13%24%13%2
1914
October1st to 15thDay
44%7%14%25%7%
1675
16th to endDay
57%8%13%16%4
1589
November1st to 15thDay
59%9%14%11%31
1518
16th to endDay
62%9%12%12%3
1350
December1st to 15thDay
63%6%11%15%3
1260
16th to endDay
66%5%12%11%4
1368
January1st to 15thNight
71%5%10%8%3
2506
16th to endNight
68%6%11%9%3
2688
February1st to 15thNight
57%6%16%13%4
2399
16th to endNight
51%6%18%17%6%
1928
March1st to 15thNight
57%8%16%13%3
2160
16th to endNight
56%8%13%16%4
2012
April1st to 15thNight
47%9%17%18%6%
1799
16th to endNight
45%7%16%23%5%
1616
May1st to 15thNight
36%8%16%22%15%1
1440
16th to endNight
48%9%16%18%5%
1472
June1st to 15thNight
43%7%12%21%11%2
1260
16th to endNight
38%8%13%19%18%1
1260
July1st to 15thNight
21%5%11%23%26%10%
1318
16th to endNight
17%410%26%28%12%
1416
August1st to 15thNight
18%7%11%29%25%7%
1432
16th to endNight
17%414%32%26%5%
1792
September1st to 15thNight
21%410%30%28%5%
1800
16th to endNight
33%6%13%26%15%4
1882
October1st to 15thNight
38%7%18%25%9%
1952
16th to endNight
51%6%15%22%4
2282
November1st to 15thNight
59%8%13%12%41
2339
16th to endNight
65%5%12%11%4
2596
December1st to 15thNight
65%7%11%12%2
2700
16th to endNight
70%5%8%11%4
2865

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%115%28%30%5%
60
16th to endDay
39%7%23%18%9%1
64
February1st to 15thDay
21%16%29%21%8%2
125
16th to endDay
24%21%22%21%9%
233
March1st to 15thDay
30%29%28%11%
270
16th to endDay
27%30%24%14%2
288
April1st to 15thDay
23%26%25%17%5%1
269
16th to endDay
18%29%27%16%5%2
270
May1st to 15thDay
17%26%26%23%31
288
16th to endDay
18%16%23%23%14%3
354
June1st to 15thDay
16%21%20%24%13%2
495
16th to endDay
14%18%26%23%13%2
495
July1st to 15thDay
9%15%26%31%13%2
344
16th to endDay
7%19%29%28%12%3
327
August1st to 15thDay
6%12%23%35%17%4
315
16th to endDay
7%16%25%31%15%3
332
September1st to 15thDay
9%18%25%25%18%2
315
16th to endDay
11%17%30%26%11%2
284
October1st to 15thDay
19%20%32%20%7%
255
16th to endDay
44%417%22%5%3
101
November1st to 15thDay
36%10%16%32%3
79
16th to endDay
28%11%26%15%13%5%
60
December1st to 15thDay
36%320%35%31
60
16th to endDay
23%7%34%25%7%1
64
January1st to 15thNight
28%19%19%21%9%
720
16th to endNight
23%18%19%26%12%
768
February1st to 15thNight
21%20%19%25%12%1
704
16th to endNight
17%18%20%25%16%
632
March1st to 15thNight
21%22%18%25%10%1
720
16th to endNight
18%21%23%23%11%1
768
April1st to 15thNight
13%20%18%28%17%1
719
16th to endNight
11%24%19%27%13%2
536
May1st to 15thNight
11%20%17%31%17%1
360
16th to endNight
13%20%14%24%22%3
375
June1st to 15thNight
13%20%15%29%20%1
360
16th to endNight
10%20%16%30%20%1
360
July1st to 15thNight
6%16%11%33%29%3
340
16th to endNight
218%12%29%34%2
376
August1st to 15thNight
5%11%8%28%41%4
360
16th to endNight
411%16%31%32%4
646
September1st to 15thNight
412%16%28%32%5%
720
16th to endNight
10%13%16%31%24%3
688
October1st to 15thNight
16%12%18%31%18%1
660
16th to endNight
21%12%18%29%14%2
704
November1st to 15thNight
26%18%18%29%6%
700
16th to endNight
28%22%17%19%11%1
796
December1st to 15thNight
25%20%19%26%7%
900
16th to endNight
28%20%24%22%4
945
Page generated at 2017-09-24 06:15:46. Version ac04

Copyright 2017 A. Danko


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