Thompson
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Thompson clear sky chart from 2005-11-05 to 2017-10-31.

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
31%
15739
8%
47111
5%
15696
34%
15696
15%
35626

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
25%
900
8%
2817
5%
895
31%
895
12%
2212
January16th to endNight
23%
960
8%
2880
3%
960
27%
960
10%
2317
February1st to 15thNight
29%
875
12%
2463
5%
875
35%
875
19%
1799
February16th to endNight
33%
789
11%
2051
5%
789
36%
789
16%
1587
March1st to 15thNight
39%
675
14%
2115
11%
675
44%
675
19%
1511
March16th to endNight
35%
576
17%
2096
15%
576
44%
576
19%
1394
April1st to 15thNight
37%
539
16%
1651
12%
539
42%
539
21%
1126
April16th to endNight
34%
540
14%
1571
5%
540
38%
540
25%
1019
May1st to 15thNight
25%
540
2%
1260
1%
540
25%
540
19%
986
May16th to endNight
30%
563
0%
1311
0%
561
30%
561
26%
952
June1st to 15thNight
41%
221
0%
941
0%
221
41%
221
18%
581
June16th to endNight
43%
180
0%
900
0%
180
43%
180
13%
579
July1st to 15thNight
44%
301
0%
981
0%
301
44%
301
22%
650
July16th to endNight
55%
558
0%
1233
0%
525
56%
525
27%
883
August1st to 15thNight
50%
539
7%
1310
5%
536
51%
536
31%
899
August16th to endNight
39%
573
8%
1702
4%
573
41%
573
18%
1244
September1st to 15thNight
35%
540
11%
1740
9%
540
41%
540
22%
1155
September16th to endNight
30%
537
10%
1980
8%
537
35%
537
13%
1469
October1st to 15thNight
27%
738
8%
2178
5%
738
30%
738
13%
1726
October16th to endNight
16%
960
5%
2561
1%
960
18%
960
7%
2255
November1st to 15thNight
20%
875
9%
2526
4%
875
24%
875
9%
2113
November16th to endNight
22%
900
6%
2717
2%
900
25%
900
10%
2215
December1st to 15thNight
26%
900
5%
2896
3%
900
29%
900
9%
2361
December16th to endNight
31%
960
9%
3231
8%
960
36%
960
10%
2593

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%5%5%7%28%
48680
Night
13%11%5%8%7%35%5%5%6%25%
47243
Cloud CoverDay
15%10%47%6%35%5%5%7%28%
48688
Night
13%11%5%8%7%45%5%5%6%25%
47247
TransparencyDay
54%6%13%18%6%
48328
Night
57%6%12%18%5%
47111
SeeingDay
22%10%29%23%11%3
6442
Night
20%7%29%27%12%1
15744

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
9%11%6%12%9%47%6%7%9%15%
1119
16th to endDay
13%15%6%8%8%36%7%8%7%15%
1344
February1st to 15thDay
6%9%47%6%49%8%7%9%26%
1400
16th to endDay
6%10%48%9%5%9%9%8%7%20%
1428
March1st to 15thDay
12%11%6%8%5%445%5%6%28%
1841
16th to endDay
10%11%47%6%36%447%32%
2127
April1st to 15thDay
10%7%38%8%35%45%7%34%
2297
16th to endDay
8%9%46%6%245%6%6%39%
2388
May1st to 15thDay
16%12%5%7%6%34445%30%
2691
16th to endDay
18%8%36%5%34446%34%
2803
June1st to 15thDay
18%7%36%5%3445%6%34%
3017
16th to endDay
14%6%37%7%5%5%5%6%7%30%
3060
July1st to 15thDay
17%6%36%6%35%47%8%31%
2916
16th to endDay
14%6%36%6%35%5%5%8%33%
2851
August1st to 15thDay
15%6%36%6%45%5%6%7%32%
2642
16th to endDay
21%8%26%6%35%447%28%
2500
September1st to 15thDay
18%9%36%5%43447%31%
2220
16th to endDay
23%12%36%5%2446%8%23%
1980
October1st to 15thDay
25%17%5%7%5%33345%19%
1767
16th to endDay
24%22%7%10%6%2333413%
1662
November1st to 15thDay
19%19%6%9%8%2433417%
1332
16th to endDay
9%15%7%13%11%45%5%5%7%13%
1242
December1st to 15thDay
9%12%6%10%9%46%8%6%8%17%
1062
16th to endDay
10%15%6%10%9%6%5%6%6%5%15%
991
January1st to 15thNight
8%11%5%10%9%5%8%8%6%7%16%
2817
16th to endNight
12%15%6%8%8%47%8%6%7%14%
2880
February1st to 15thNight
5%10%47%8%48%8%7%7%25%
2459
16th to endNight
7%12%6%8%9%48%6%5%8%22%
2051
March1st to 15thNight
10%10%5%7%5%35%6%45%34%
2102
16th to endNight
11%10%46%5%35%5%5%6%34%
2096
April1st to 15thNight
9%10%45%6%35%5%5%7%35%
1651
16th to endNight
7%9%36%5%35%45%7%42%
1571
May1st to 15thNight
19%12%5%6%5%35%5%45%27%
1260
16th to endNight
16%7%36%424446%39%
1310
June1st to 15thNight
16%6%26%5%2345%7%38%
941
16th to endNight
14%6%36%6%36%6%6%7%33%
900
July1st to 15thNight
13%5%25%5%25%5%6%9%35%
1041
16th to endNight
10%5%24436%6%9%9%36%
1316
August1st to 15thNight
13%5%24425%46%6%43%
1317
16th to endNight
17%7%26%6%345%5%7%32%
1702
September1st to 15thNight
19%7%24424345%42%
1740
16th to endNight
21%11%27%5%3345%7%26%
1980
October1st to 15thNight
24%13%46%43435%6%22%
2178
16th to endNight
25%20%6%9%5%2333414%
2561
November1st to 15thNight
19%16%6%10%8%3433418%
2526
16th to endNight
11%13%6%13%9%45%5%5%7%16%
2717
December1st to 15thNight
8%15%8%11%9%5%7%6%5%6%14%
2896
16th to endNight
11%14%6%12%9%5%7%5%5%5%17%
3231

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
9%11%6%13%8%36%5%7%9%16%
1119
16th to endDay
13%15%6%7%8%36%7%7%8%14%
1344
February1st to 15thDay
6%9%38%6%310%9%7%9%25%
1400
16th to endDay
7%9%48%9%5%9%8%8%7%20%
1428
March1st to 15thDay
12%11%7%8%6%345%5%6%28%
1851
16th to endDay
10%11%47%5%46%447%32%
2125
April1st to 15thDay
10%7%38%8%36%5%5%7%34%
2297
16th to endDay
8%9%47%5%3446%5%39%
2388
May1st to 15thDay
16%12%47%7%34445%30%
2691
16th to endDay
18%8%36%434446%34%
2803
June1st to 15thDay
18%8%35%5%3445%6%34%
3017
16th to endDay
14%6%37%7%46%5%6%7%30%
3060
July1st to 15thDay
18%5%35%6%35%5%6%8%30%
2916
16th to endDay
15%6%36%5%45%5%6%8%33%
2851
August1st to 15thDay
15%6%35%6%35%6%6%8%32%
2642
16th to endDay
21%7%36%5%35%45%7%28%
2500
September1st to 15thDay
18%9%36%5%435%47%31%
2220
16th to endDay
22%12%36%5%3346%8%23%
1980
October1st to 15thDay
25%17%5%7%5%23435%19%
1767
16th to endDay
24%21%8%9%6%2333413%
1662
November1st to 15thDay
18%19%6%8%9%3443318%
1332
16th to endDay
9%15%7%13%11%45%5%5%6%14%
1242
December1st to 15thDay
9%12%5%10%9%46%8%6%8%17%
1062
16th to endDay
11%15%6%11%9%5%6%6%6%6%15%
991
January1st to 15thNight
8%11%6%10%9%5%8%8%6%7%17%
2817
16th to endNight
12%15%6%8%8%5%6%7%6%7%14%
2880
February1st to 15thNight
5%10%47%8%47%9%8%7%25%
2452
16th to endNight
7%12%6%8%8%5%7%6%6%8%22%
2051
March1st to 15thNight
10%11%5%7%6%45%6%45%33%
2115
16th to endNight
11%10%46%5%35%5%6%6%34%
2094
April1st to 15thNight
9%10%46%6%45%45%6%35%
1651
16th to endNight
7%9%36%5%3445%7%42%
1571
May1st to 15thNight
19%13%47%5%45%445%27%
1259
16th to endNight
16%7%26%42435%6%39%
1311
June1st to 15thNight
16%6%36%5%2435%7%38%
941
16th to endNight
14%6%37%7%26%6%7%6%33%
900
July1st to 15thNight
13%5%26%4445%7%9%36%
1041
16th to endNight
10%5%24445%6%9%10%36%
1316
August1st to 15thNight
13%5%24425%46%6%44%
1317
16th to endNight
18%7%26%6%345%5%7%32%
1702
September1st to 15thNight
19%8%14323445%42%
1740
16th to endNight
21%11%27%5%235%5%7%26%
1980
October1st to 15thNight
23%13%46%42435%6%23%
2178
16th to endNight
25%20%6%9%6%2333315%
2561
November1st to 15thNight
19%15%6%10%8%3443418%
2526
16th to endNight
11%14%6%12%9%5%5%45%7%16%
2717
December1st to 15thNight
8%16%8%11%9%5%7%6%5%7%14%
2896
16th to endNight
11%14%6%11%9%5%7%5%5%6%17%
3231

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
62%5%12%16%2
1119
16th to endDay
63%5%11%14%5%
1344
February1st to 15thDay
50%5%13%21%9%
1400
16th to endDay
56%6%12%15%8%
1428
March1st to 15thDay
55%412%19%7%
1851
16th to endDay
51%5%10%20%9%2
2127
April1st to 15thDay
49%412%22%10%
2297
16th to endDay
43%5%11%25%13%
2388
May1st to 15thDay
56%49%20%7%
2691
16th to endDay
49%5%10%21%12%
2807
June1st to 15thDay
49%5%9%22%12%
3017
16th to endDay
50%7%12%22%7%
3060
July1st to 15thDay
48%8%14%21%6%
2747
16th to endDay
48%8%17%22%3
2671
August1st to 15thDay
46%10%19%20%2
2625
16th to endDay
54%8%19%14%3
2500
September1st to 15thDay
52%7%20%16%2
2220
16th to endDay
58%5%17%15%2
1980
October1st to 15thDay
68%5%11%11%1
1767
16th to endDay
77%47%8%1
1662
November1st to 15thDay
71%49%13%1
1332
16th to endDay
68%6%13%10%
1242
December1st to 15thDay
61%6%14%15%1
1062
16th to endDay
67%5%8%15%2
991
January1st to 15thNight
62%6%13%16%2
2817
16th to endNight
64%5%10%13%5%
2880
February1st to 15thNight
51%6%12%21%7%
2463
16th to endNight
58%410%18%7%
2051
March1st to 15thNight
51%5%13%20%8%
2115
16th to endNight
47%5%11%22%10%2
2096
April1st to 15thNight
47%410%24%12%
1651
16th to endNight
41%5%9%28%12%2
1571
May1st to 15thNight
57%5%9%17%8%1
1260
16th to endNight
46%5%9%23%14%
1311
June1st to 15thNight
43%5%12%20%16%1
941
16th to endNight
47%7%10%26%8%
900
July1st to 15thNight
44%6%15%26%6%
981
16th to endNight
38%12%18%25%4
1233
August1st to 15thNight
37%8%20%28%4
1310
16th to endNight
50%8%20%17%3
1702
September1st to 15thNight
43%6%19%24%5%
1740
16th to endNight
56%7%13%18%3
1980
October1st to 15thNight
60%7%14%14%2
2178
16th to endNight
74%5%8%9%1
2561
November1st to 15thNight
70%48%13%2
2526
16th to endNight
66%5%12%13%
2717
December1st to 15thNight
67%5%13%12%1
2896
16th to endNight
66%5%9%15%2
3231

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
410%38%38%7%
67
16th to endDay
41%10%23%14%7%2
96
February1st to 15thDay
12%8%38%25%8%5%
90
16th to endDay
14%9%33%22%16%3
81
March1st to 15thDay
25%13%27%21%7%4
90
16th to endDay
18%10%30%24%11%3
111
April1st to 15thDay
13%14%35%26%8%1
416
16th to endDay
11%14%32%25%13%2
450
May1st to 15thDay
25%15%32%17%6%2
468
16th to endDay
22%11%30%24%9%1
517
June1st to 15thDay
24%9%29%22%9%4
495
16th to endDay
21%9%30%23%11%4
495
July1st to 15thDay
19%8%33%24%9%4
475
16th to endDay
19%10%24%23%16%6%
515
August1st to 15thDay
20%7%23%26%16%4
493
16th to endDay
22%8%26%29%10%2
523
September1st to 15thDay
25%10%31%21%11%
375
16th to endDay
35%11%14%23%13%1
135
October1st to 15thDay
45%12%29%8%4
135
16th to endDay
39%13%23%16%6%
144
November1st to 15thDay
22%12%30%22%13%
90
16th to endDay
24%432%20%16%2
87
December1st to 15thDay
26%5%28%31%8%
57
16th to endDay
10%5%43%27%13%
37
January1st to 15thNight
13%8%34%29%11%2
900
16th to endNight
19%10%33%29%6%
960
February1st to 15thNight
10%6%39%27%12%3
880
16th to endNight
12%8%30%31%14%2
789
March1st to 15thNight
15%7%27%33%13%1
675
16th to endNight
17%6%32%25%14%2
576
April1st to 15thNight
14%7%32%32%10%1
539
16th to endNight
12%10%33%25%15%2
540
May1st to 15thNight
27%10%31%18%10%1
540
16th to endNight
22%10%33%24%9%
563
June1st to 15thNight
19%6%24%33%14%1
221
16th to endNight
15%8%26%33%15%1
180
July1st to 15thNight
15%5%29%29%17%1
301
16th to endNight
15%420%30%26%3
558
August1st to 15thNight
16%324%32%21%2
539
16th to endNight
22%426%33%12%
573
September1st to 15thNight
24%8%26%25%13%1
540
16th to endNight
29%7%27%23%10%1
537
October1st to 15thNight
33%5%27%24%8%1
738
16th to endNight
38%8%23%19%8%1
960
November1st to 15thNight
26%9%29%21%11%1
875
16th to endNight
18%9%32%28%8%2
900
December1st to 15thNight
15%8%31%31%10%1
900
16th to endNight
18%6%25%31%15%3
960
Page generated at 2017-11-01 16:23:38. Version ac04

Copyright 2017 A. Danko


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