Merritt
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Merritt clear sky chart from 2005-11-05 to 2018-11-30.

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
43%
16238
10%
51586
8%
16212
45%
16212
18%
36022

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
26%
823
4%
2911
3%
821
29%
821
7%
2455
January16th to endNight
30%
832
5%
2912
4%
832
32%
832
9%
2369
February1st to 15thNight
33%
757
7%
2554
6%
757
35%
757
11%
2001
February16th to endNight
42%
684
12%
2163
10%
684
46%
684
18%
1514
March1st to 15thNight
32%
780
9%
2308
6%
780
35%
780
15%
1709
March16th to endNight
36%
832
10%
2191
4%
832
38%
832
18%
1605
April1st to 15thNight
41%
779
9%
1949
4%
779
43%
779
20%
1435
April16th to endNight
44%
522
11%
1680
8%
522
48%
522
20%
1119
May1st to 15thNight
50%
389
12%
1559
17%
389
55%
389
23%
923
May16th to endNight
54%
406
6%
1624
9%
406
55%
406
19%
1016
June1st to 15thNight
51%
390
3%
1255
0%
390
51%
390
23%
810
June16th to endNight
51%
390
4%
1213
0%
390
51%
390
30%
718
July1st to 15thNight
63%
370
8%
1295
4%
370
64%
370
38%
648
July16th to endNight
70%
408
14%
1503
19%
386
75%
386
48%
627
August1st to 15thNight
77%
384
19%
1528
26%
382
79%
382
44%
651
August16th to endNight
65%
687
21%
1929
17%
687
68%
687
42%
1071
September1st to 15thNight
65%
780
20%
1950
11%
780
67%
780
43%
1144
September16th to endNight
53%
776
19%
2116
12%
776
56%
776
31%
1350
October1st to 15thNight
51%
780
13%
2340
12%
780
54%
780
22%
1561
October16th to endNight
39%
832
11%
2649
8%
832
44%
832
18%
1865
November1st to 15thNight
30%
820
8%
2842
7%
820
32%
820
11%
2189
November16th to endNight
30%
840
7%
2940
5%
840
34%
840
10%
2312
December1st to 15thNight
36%
977
8%
2935
5%
977
37%
977
13%
2315
December16th to endNight
26%
1000
7%
3240
4%
1000
30%
1000
10%
2615

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
7%8%37%7%46%6%6%8%34%
52731
Night
6%8%47%6%45%5%6%7%35%
51743
Cloud CoverDay
9%8%37%6%35%5%6%7%35%
52731
Night
8%9%47%6%35%5%6%7%35%
51746
TransparencyDay
46%9%16%18%8%1
52391
Night
46%9%18%17%7%1
51587
SeeingDay
15%15%27%22%13%4
7662
Night
13%7%25%32%18%2
16249

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
7%13%5%10%8%6%8%6%7%7%17%
1358
16th to endDay
7%11%49%11%48%6%8%8%20%
1661
February1st to 15thDay
7%16%5%9%8%5%6%5%6%8%20%
1639
16th to endDay
311%5%8%9%5%7%7%7%8%26%
1596
March1st to 15thDay
7%11%5%10%8%47%7%6%8%23%
1982
16th to endDay
6%9%5%9%7%48%7%8%10%22%
2384
April1st to 15thDay
9%11%5%8%7%5%7%7%7%7%22%
2329
16th to endDay
8%10%48%7%36%5%7%9%28%
2555
May1st to 15thDay
6%8%36%6%45%6%6%9%35%
2721
16th to endDay
11%7%38%7%46%5%6%8%29%
2839
June1st to 15thDay
12%6%36%7%46%5%6%7%32%
3029
16th to endDay
8%6%25%6%45%6%6%8%39%
3072
July1st to 15thDay
4313435%5%5%7%56%
2925
16th to endDay
421333445%7%58%
2923
August1st to 15thDay
331433445%7%57%
2676
16th to endDay
5%414425%5%6%7%50%
2624
September1st to 15thDay
7%425%5%345%46%49%
2340
16th to endDay
11%7%36%5%36%6%6%8%35%
2170
October1st to 15thDay
9%9%37%7%45%5%46%34%
1950
16th to endDay
9%10%38%6%5%6%6%5%8%28%
1927
November1st to 15thDay
13%10%5%8%8%45%5%5%7%26%
1674
16th to endDay
6%12%5%8%9%47%6%7%8%22%
1659
December1st to 15thDay
6%11%5%10%10%5%7%6%6%8%20%
1352
16th to endDay
6%11%5%8%9%5%8%7%6%8%22%
1346
January1st to 15thNight
8%14%7%11%9%48%6%6%6%15%
2911
16th to endNight
7%13%5%11%10%5%7%6%5%7%18%
2912
February1st to 15thNight
8%14%6%10%7%46%5%6%7%23%
2542
16th to endNight
28%5%9%8%45%6%6%9%32%
2163
March1st to 15thNight
5%9%5%7%6%46%6%6%8%31%
2308
16th to endNight
37%47%7%5%6%7%8%9%32%
2187
April1st to 15thNight
5%8%37%8%46%6%5%7%35%
1949
16th to endNight
48%36%6%36%48%10%38%
1680
May1st to 15thNight
5%6%35%4345%5%7%46%
1559
16th to endNight
7%426%6%35%6%6%8%41%
1624
June1st to 15thNight
9%325%5%45%6%8%10%37%
1255
16th to endNight
4325%5%35%6%7%8%47%
1213
July1st to 15thNight
321232446%8%60%
1365
16th to endNight
31121345%6%67%
1598
August1st to 15thNight
311231435%8%66%
1536
16th to endNight
333425%5%6%7%56%
1929
September1st to 15thNight
6%31332445%7%58%
1950
16th to endNight
8%425%43445%10%46%
2116
October1st to 15thNight
8%6%26%5%445%5%5%43%
2340
16th to endNight
8%8%37%6%446%6%8%34%
2649
November1st to 15thNight
10%11%5%8%6%47%5%6%8%25%
2842
16th to endNight
8%13%6%10%8%46%6%5%6%22%
2940
December1st to 15thNight
7%12%6%11%8%45%5%6%6%23%
2935
16th to endNight
6%14%6%10%8%5%7%5%7%7%20%
3240

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
9%14%410%8%5%8%6%6%6%18%
1358
16th to endDay
7%13%410%10%46%6%7%8%21%
1661
February1st to 15thDay
8%16%6%8%9%35%5%6%7%21%
1639
16th to endDay
412%5%8%9%47%6%7%6%27%
1596
March1st to 15thDay
8%14%5%9%8%46%5%6%7%23%
1982
16th to endDay
7%10%5%8%7%48%7%7%9%23%
2384
April1st to 15thDay
10%12%48%6%47%7%7%7%22%
2329
16th to endDay
9%11%5%7%7%35%5%6%9%28%
2555
May1st to 15thDay
7%9%35%7%46%5%6%8%36%
2721
16th to endDay
13%7%37%7%45%5%6%7%30%
2839
June1st to 15thDay
14%7%36%6%46%46%7%31%
3029
16th to endDay
10%6%26%6%35%5%5%7%39%
3072
July1st to 15thDay
5%3135%245%47%56%
2925
16th to endDay
5%31332445%6%59%
2923
August1st to 15thDay
431342445%7%57%
2676
16th to endDay
6%4144245%6%7%50%
2624
September1st to 15thDay
9%426%5%33446%49%
2340
16th to endDay
12%7%36%5%35%6%6%8%35%
2170
October1st to 15thDay
11%9%38%6%35%45%6%34%
1950
16th to endDay
11%9%48%7%35%6%5%8%28%
1927
November1st to 15thDay
15%12%47%7%4445%7%25%
1674
16th to endDay
8%13%6%8%8%46%6%6%8%22%
1659
December1st to 15thDay
8%12%5%9%9%5%6%7%6%7%22%
1352
16th to endDay
7%12%6%9%8%5%6%6%6%6%23%
1346
January1st to 15thNight
10%15%6%11%9%5%6%5%5%6%15%
2910
16th to endNight
8%14%6%10%9%46%5%5%8%19%
2912
February1st to 15thNight
10%16%5%9%7%35%5%5%7%23%
2542
16th to endNight
38%49%9%46%5%6%8%32%
2163
March1st to 15thNight
8%11%46%7%36%5%5%8%31%
2308
16th to endNight
410%5%7%6%46%6%7%10%32%
2191
April1st to 15thNight
6%9%46%8%45%7%6%7%34%
1949
16th to endNight
5%8%37%5%35%5%7%10%37%
1680
May1st to 15thNight
6%7%344245%5%8%46%
1559
16th to endNight
8%7%36%5%345%6%9%39%
1624
June1st to 15thNight
8%5%26%6%36%6%7%9%37%
1255
16th to endNight
4326%5%25%6%7%8%46%
1213
July1st to 15thNight
42123245%6%7%59%
1365
16th to endNight
41221336%6%66%
1598
August1st to 15thNight
311331335%8%64%
1536
16th to endNight
42134346%6%7%55%
1929
September1st to 15thNight
7%31342436%6%57%
1950
16th to endNight
10%5%244245%5%8%45%
2116
October1st to 15thNight
9%7%35%5%35%5%45%43%
2340
16th to endNight
10%9%27%6%35%5%6%7%34%
2649
November1st to 15thNight
12%13%5%8%7%35%6%6%6%25%
2842
16th to endNight
10%14%6%8%8%46%5%5%6%23%
2940
December1st to 15thNight
8%13%6%10%8%5%5%45%6%23%
2935
16th to endNight
7%15%5%11%8%46%5%6%7%21%
3240

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%13%14%7%1
1358
16th to endDay
56%12%14%12%2
1661
February1st to 15thDay
60%12%12%10%3
1639
16th to endDay
52%10%17%14%5%
1596
March1st to 15thDay
58%8%15%12%3
1982
16th to endDay
54%10%19%12%2
2384
April1st to 15thDay
57%11%15%13%2
2329
16th to endDay
52%8%17%14%6%
2555
May1st to 15thDay
44%8%16%19%10%1
2721
16th to endDay
50%9%17%17%4
2843
June1st to 15thDay
49%8%16%16%7%1
3029
16th to endDay
41%8%17%20%10%1
3072
July1st to 15thDay
27%6%15%25%20%5%
2766
16th to endDay
23%6%15%27%22%4
2755
August1st to 15thDay
24%7%18%28%16%4
2659
16th to endDay
29%8%17%28%13%2
2624
September1st to 15thDay
34%6%15%24%15%2
2340
16th to endDay
44%9%17%18%7%2
2170
October1st to 15thDay
49%7%15%20%6%
1950
16th to endDay
50%12%16%17%3
1927
November1st to 15thDay
57%9%14%14%3
1674
16th to endDay
56%12%14%12%3
1659
December1st to 15thDay
57%11%15%11%2
1352
16th to endDay
57%13%14%11%3
1346
January1st to 15thNight
65%11%13%7%1
2911
16th to endNight
60%12%13%10%2
2912
February1st to 15thNight
58%10%14%12%3
2554
16th to endNight
47%8%19%19%5%
2163
March1st to 15thNight
49%11%20%15%3
2308
16th to endNight
46%11%22%17%2
2191
April1st to 15thNight
46%10%19%19%4
1949
16th to endNight
40%11%23%18%5%
1680
May1st to 15thNight
35%9%21%20%11%1
1560
16th to endNight
39%10%22%21%6%
1624
June1st to 15thNight
40%7%21%22%6%1
1255
16th to endNight
32%7%27%19%11%
1213
July1st to 15thNight
22%7%18%29%17%4
1295
16th to endNight
15%6%18%31%23%5%
1503
August1st to 15thNight
17%6%23%30%18%3
1528
16th to endNight
24%7%21%27%15%3
1929
September1st to 15thNight
25%6%19%28%16%3
1950
16th to endNight
34%8%21%22%10%3
2116
October1st to 15thNight
41%8%17%22%9%
2340
16th to endNight
47%9%18%20%4
2649
November1st to 15thNight
55%11%15%11%4
2842
16th to endNight
58%10%14%11%3
2940
December1st to 15thNight
58%9%15%13%2
2935
16th to endNight
60%11%13%11%3
3240

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
7%117%28%25%18%
90
16th to endDay
22%5%26%32%10%3
96
February1st to 15thDay
20%12%24%31%10%1
209
16th to endDay
10%20%29%24%13%1
264
March1st to 15thDay
23%23%25%20%5%2
330
16th to endDay
21%25%29%15%6%1
352
April1st to 15thDay
24%23%27%15%6%2
329
16th to endDay
22%22%26%14%10%3
318
May1st to 15thDay
16%20%31%17%9%4
348
16th to endDay
15%13%23%23%15%6%
394
June1st to 15thDay
16%18%29%20%14%2
674
16th to endDay
14%16%30%21%14%2
717
July1st to 15thDay
8%18%32%26%12%1
550
16th to endDay
7%12%29%28%14%7%
432
August1st to 15thDay
5%6%25%27%24%11%
359
16th to endDay
10%13%30%21%16%6%
396
September1st to 15thDay
12%14%22%25%19%5%
375
16th to endDay
16%13%24%25%15%5%
375
October1st to 15thDay
21%14%23%20%15%5%
375
16th to endDay
19%9%20%25%15%8%
247
November1st to 15thDay
23%14%29%19%11%1
128
16th to endDay
13%5%27%26%16%9%
118
December1st to 15thDay
14%317%25%24%14%
90
16th to endDay
18%428%32%13%3
96
January1st to 15thNight
19%7%28%28%14%2
825
16th to endNight
16%6%30%31%12%2
832
February1st to 15thNight
19%5%25%33%12%2
764
16th to endNight
7%7%29%36%18%1
684
March1st to 15thNight
15%13%29%27%12%1
780
16th to endNight
9%16%27%29%13%2
832
April1st to 15thNight
13%11%22%34%15%1
779
16th to endNight
10%11%25%36%14%2
522
May1st to 15thNight
10%6%26%33%20%2
390
16th to endNight
12%222%32%27%1
407
June1st to 15thNight
10%7%24%38%16%1
390
16th to endNight
6%5%29%37%18%1
390
July1st to 15thNight
5%5%22%41%24%1
370
16th to endNight
4218%42%26%4
408
August1st to 15thNight
3111%34%41%6%
384
16th to endNight
7%318%36%31%2
687
September1st to 15thNight
8%5%16%29%32%7%
780
16th to endNight
13%6%21%29%24%4
776
October1st to 15thNight
13%7%19%35%21%2
780
16th to endNight
15%8%28%28%16%3
832
November1st to 15thNight
20%10%28%31%7%
820
16th to endNight
19%8%30%27%12%2
840
December1st to 15thNight
14%6%25%35%15%1
977
16th to endNight
14%8%32%35%8%
1000
Page generated at 2018-12-01 08:35:35. Version ac04

Copyright 2018 A. Danko


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