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 2017-04-30.

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
41%
14351
9%
45618
7%
14325
44%
14325
17%
32285

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%
748
4%
2686
3%
746
28%
746
7%
2257
January16th to endNight
30%
768
5%
2688
4%
768
32%
768
8%
2196
February1st to 15thNight
33%
697
6%
2354
5%
697
35%
697
10%
1858
February16th to endNight
43%
632
12%
1999
10%
632
47%
632
18%
1396
March1st to 15thNight
31%
720
8%
2130
5%
720
34%
720
15%
1581
March16th to endNight
34%
768
9%
2022
4%
768
37%
768
17%
1497
April1st to 15thNight
42%
719
9%
1799
4%
719
44%
719
20%
1318
April16th to endNight
44%
487
11%
1561
8%
487
49%
487
21%
1039
May1st to 15thNight
47%
329
11%
1319
15%
329
52%
329
22%
793
May16th to endNight
50%
342
4%
1368
5%
342
51%
342
17%
901
June1st to 15thNight
49%
330
2%
1062
0%
330
49%
330
22%
701
June16th to endNight
48%
330
4%
1026
0%
330
48%
330
29%
617
July1st to 15thNight
61%
310
7%
1085
3%
310
63%
310
36%
558
July16th to endNight
68%
348
12%
1269
15%
326
72%
326
45%
553
August1st to 15thNight
75%
330
18%
1312
25%
328
77%
328
41%
582
August16th to endNight
62%
581
18%
1631
14%
581
65%
581
38%
942
September1st to 15thNight
65%
660
20%
1650
11%
660
67%
660
43%
967
September16th to endNight
51%
656
18%
1790
12%
656
55%
656
30%
1152
October1st to 15thNight
51%
660
12%
1980
12%
660
54%
660
22%
1312
October16th to endNight
36%
704
9%
2241
6%
704
42%
704
16%
1632
November1st to 15thNight
27%
700
8%
2426
7%
700
30%
700
11%
1867
November16th to endNight
29%
720
7%
2520
5%
720
33%
720
10%
2001
December1st to 15thNight
33%
901
8%
2709
5%
901
35%
901
12%
2160
December16th to endNight
26%
911
7%
2991
4%
911
30%
911
10%
2405

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%33%
46128
Night
6%9%47%7%46%5%6%7%34%
45775
Cloud CoverDay
9%9%37%6%45%5%6%7%33%
46128
Night
8%9%47%6%35%5%6%7%34%
45778
TransparencyDay
47%9%16%17%7%1
45788
Night
47%10%18%17%6%
45619
SeeingDay
15%17%28%22%11%3
5540
Night
13%8%26%32%17%2
14362

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
8%11%5%10%8%6%8%6%7%8%18%
1253
16th to endDay
7%11%5%9%11%5%7%6%7%8%19%
1533
February1st to 15thDay
7%17%6%10%8%46%5%7%8%19%
1509
16th to endDay
311%5%8%9%5%6%7%6%8%25%
1475
March1st to 15thDay
7%11%5%9%8%47%7%6%9%22%
1830
16th to endDay
5%9%5%9%7%5%8%7%7%9%23%
2201
April1st to 15thDay
9%10%5%8%7%5%7%8%6%7%23%
2149
16th to endDay
7%10%48%7%46%5%7%10%27%
2379
May1st to 15thDay
6%8%37%7%46%6%6%9%32%
2301
16th to endDay
12%8%39%8%46%5%6%8%25%
2391
June1st to 15thDay
13%7%36%7%36%5%5%8%31%
2563
16th to endDay
8%6%35%7%45%6%6%8%37%
2600
July1st to 15thDay
4314435%5%5%7%54%
2475
16th to endDay
5%21343445%8%55%
2497
August1st to 15thDay
43143445%6%8%52%
2310
16th to endDay
5%4245%35%6%7%8%46%
2219
September1st to 15thDay
7%425%5%34446%50%
1980
16th to endDay
11%7%25%5%36%6%6%9%35%
1836
October1st to 15thDay
9%9%37%7%46%5%47%33%
1650
16th to endDay
10%11%48%7%5%7%6%5%8%25%
1631
November1st to 15thDay
13%10%5%8%7%45%5%5%8%25%
1430
16th to endDay
6%13%6%8%9%47%5%8%7%21%
1426
December1st to 15thDay
6%12%5%9%9%5%6%6%6%9%21%
1248
16th to endDay
5%11%6%7%9%5%8%6%6%8%22%
1242
January1st to 15thNight
8%13%7%11%9%5%8%6%6%6%15%
2686
16th to endNight
7%13%6%11%10%5%6%6%5%7%18%
2688
February1st to 15thNight
7%14%7%10%7%46%5%6%7%22%
2342
16th to endNight
28%5%9%8%5%5%6%6%9%32%
1999
March1st to 15thNight
5%9%5%7%6%46%6%6%9%31%
2130
16th to endNight
47%5%7%7%5%6%7%8%8%31%
2018
April1st to 15thNight
5%7%38%8%46%6%5%8%35%
1799
16th to endNight
37%36%6%36%48%10%38%
1561
May1st to 15thNight
5%7%34435%5%5%6%47%
1319
16th to endNight
8%5%27%6%35%6%7%9%36%
1368
June1st to 15thNight
10%435%5%45%6%7%10%36%
1062
16th to endNight
4425%5%35%6%7%8%46%
1026
July1st to 15thNight
32123245%6%8%59%
1155
16th to endNight
41221346%7%64%
1364
August1st to 15thNight
311231435%8%63%
1320
16th to endNight
3313426%6%7%8%53%
1631
September1st to 15thNight
6%31332345%7%58%
1650
16th to endNight
7%425%5%344410%46%
1790
October1st to 15thNight
7%6%26%5%45%5%5%5%43%
1980
16th to endNight
9%9%38%7%45%6%6%8%30%
2241
November1st to 15thNight
10%11%6%9%7%47%5%6%7%25%
2426
16th to endNight
8%14%7%10%8%46%5%5%6%22%
2520
December1st to 15thNight
7%13%6%11%8%45%5%6%6%22%
2709
16th to endNight
5%13%6%9%9%5%7%6%7%7%20%
2991

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%12%49%7%5%8%7%6%6%19%
1253
16th to endDay
7%13%410%10%36%6%7%8%20%
1533
February1st to 15thDay
8%17%7%8%8%35%5%6%7%20%
1509
16th to endDay
412%5%8%9%47%6%7%6%27%
1475
March1st to 15thDay
8%14%5%9%8%46%5%6%7%22%
1830
16th to endDay
7%10%5%8%7%48%7%7%8%23%
2201
April1st to 15thDay
10%12%48%7%47%7%7%7%22%
2149
16th to endDay
9%11%48%7%36%5%6%9%27%
2379
May1st to 15thDay
8%9%35%7%46%5%6%8%33%
2301
16th to endDay
14%8%37%8%46%5%6%7%26%
2391
June1st to 15thDay
15%8%36%6%36%46%7%30%
2563
16th to endDay
10%6%26%6%46%5%6%7%37%
2600
July1st to 15thDay
5%3135%245%5%7%54%
2475
16th to endDay
6%31342445%6%55%
2497
August1st to 15thDay
5%41343446%7%53%
2310
16th to endDay
6%415%435%6%6%7%47%
2219
September1st to 15thDay
9%426%5%33436%50%
1980
16th to endDay
12%7%36%5%35%5%5%8%36%
1836
October1st to 15thDay
11%9%38%6%36%45%6%33%
1650
16th to endDay
13%10%48%7%35%7%5%7%25%
1631
November1st to 15thDay
16%12%47%6%4445%8%25%
1430
16th to endDay
7%13%6%8%8%46%6%6%8%21%
1426
December1st to 15thDay
8%12%5%9%8%45%7%6%7%23%
1248
16th to endDay
7%12%6%9%8%46%6%6%6%24%
1242
January1st to 15thNight
10%15%7%10%8%5%7%6%5%6%16%
2685
16th to endNight
9%14%6%10%9%46%5%5%8%19%
2688
February1st to 15thNight
10%16%6%9%7%35%5%5%7%22%
2342
16th to endNight
38%410%8%46%5%6%8%32%
1999
March1st to 15thNight
8%11%46%7%36%5%6%8%31%
2130
16th to endNight
5%9%5%7%6%46%6%7%9%31%
2022
April1st to 15thNight
6%8%37%8%45%7%6%7%35%
1799
16th to endNight
48%37%5%35%5%7%10%37%
1561
May1st to 15thNight
6%7%344245%47%47%
1319
16th to endNight
9%7%36%5%345%7%10%35%
1368
June1st to 15thNight
9%5%26%5%36%6%6%9%36%
1062
16th to endNight
5%327%6%35%6%6%8%46%
1026
July1st to 15thNight
42133245%7%7%58%
1155
16th to endNight
411221336%7%63%
1364
August1st to 15thNight
311331336%8%62%
1320
16th to endNight
42134346%7%7%52%
1631
September1st to 15thNight
8%21342336%6%58%
1650
16th to endNight
9%5%245%3445%8%46%
1790
October1st to 15thNight
9%7%35%5%35%5%5%5%43%
1980
16th to endNight
11%10%37%6%35%5%6%7%30%
2241
November1st to 15thNight
12%13%5%7%7%35%5%6%6%25%
2426
16th to endNight
10%15%7%9%8%35%5%5%6%22%
2520
December1st to 15thNight
9%13%6%11%8%45%45%6%22%
2709
16th to endNight
7%14%5%10%9%47%5%6%7%21%
2991

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
61%13%15%8%1
1253
16th to endDay
57%12%14%12%2
1533
February1st to 15thDay
60%13%12%9%2
1509
16th to endDay
52%10%17%13%6%
1475
March1st to 15thDay
58%9%16%12%3
1830
16th to endDay
54%10%19%11%2
2201
April1st to 15thDay
56%11%15%13%2
2149
16th to endDay
52%8%18%14%4
2379
May1st to 15thDay
46%8%15%18%9%1
2301
16th to endDay
54%10%16%14%3
2395
June1st to 15thDay
50%8%16%15%6%1
2563
16th to endDay
43%8%18%19%9%
2600
July1st to 15thDay
28%7%16%25%18%3
2316
16th to endDay
25%7%17%28%17%3
2329
August1st to 15thDay
27%7%20%28%12%2
2293
16th to endDay
32%9%17%24%13%2
2219
September1st to 15thDay
34%6%15%25%15%2
1980
16th to endDay
43%9%16%19%8%3
1836
October1st to 15thDay
49%8%16%19%6%
1650
16th to endDay
54%12%16%14%2
1631
November1st to 15thDay
57%10%14%13%3
1430
16th to endDay
56%12%14%12%3
1426
December1st to 15thDay
57%12%15%11%3
1248
16th to endDay
56%13%14%11%2
1242
January1st to 15thNight
65%12%13%7%1
2686
16th to endNight
61%12%13%10%1
2688
February1st to 15thNight
58%10%14%11%3
2354
16th to endNight
46%8%19%18%6%
1999
March1st to 15thNight
49%11%20%14%3
2130
16th to endNight
47%11%21%17%2
2022
April1st to 15thNight
45%10%19%19%4
1799
16th to endNight
39%11%25%19%3
1561
May1st to 15thNight
36%9%22%19%11%1
1320
16th to endNight
42%11%24%16%4
1368
June1st to 15thNight
42%8%21%19%6%1
1062
16th to endNight
34%7%28%19%10%
1026
July1st to 15thNight
23%8%19%28%16%3
1085
16th to endNight
16%6%20%32%18%4
1269
August1st to 15thNight
18%7%26%31%14%2
1312
16th to endNight
26%8%21%26%14%2
1631
September1st to 15thNight
26%6%19%28%16%3
1650
16th to endNight
35%8%19%22%10%3
1790
October1st to 15thNight
41%8%17%22%9%
1980
16th to endNight
50%9%18%18%2
2241
November1st to 15thNight
56%10%15%12%4
2426
16th to endNight
59%11%14%11%3
2520
December1st to 15thNight
60%9%14%14%2
2709
16th to endNight
59%12%14%11%2
2991

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
3113%33%31%16%
60
16th to endDay
23%120%37%12%4
64
February1st to 15thDay
19%14%21%30%12%1
169
16th to endDay
10%20%27%24%14%2
221
March1st to 15thDay
25%27%26%17%2
270
16th to endDay
20%29%30%14%4
288
April1st to 15thDay
23%23%27%15%6%2
269
16th to endDay
20%25%29%14%7%1
267
May1st to 15thDay
15%22%31%16%9%3
228
16th to endDay
18%15%26%22%12%5%
266
June1st to 15thDay
16%16%28%21%14%1
508
16th to endDay
13%16%31%21%14%2
545
July1st to 15thDay
7%20%32%28%10%1
400
16th to endDay
8%13%35%28%9%4
306
August1st to 15thDay
7%7%30%30%18%6%
255
16th to endDay
11%15%35%21%12%3
268
September1st to 15thDay
12%15%23%23%18%6%
255
16th to endDay
14%16%28%21%13%4
255
October1st to 15thDay
20%16%25%19%12%5%
255
16th to endDay
23%7%20%28%13%5%
143
November1st to 15thDay
21%20%29%20%7%
64
16th to endDay
6%6%28%25%20%13%
60
December1st to 15thDay
18%5%23%25%20%8%
60
16th to endDay
15%6%29%29%14%4
64
January1st to 15thNight
19%7%30%27%13%1
750
16th to endNight
16%6%30%30%13%2
768
February1st to 15thNight
18%5%24%34%13%2
704
16th to endNight
7%7%29%36%18%1
632
March1st to 15thNight
14%14%31%26%11%1
720
16th to endNight
9%17%28%29%12%1
768
April1st to 15thNight
13%11%22%33%16%1
719
16th to endNight
9%12%26%36%14%1
487
May1st to 15thNight
10%7%29%30%20%2
330
16th to endNight
13%225%31%25%1
343
June1st to 15thNight
10%8%26%36%16%1
330
16th to endNight
6%6%31%38%15%1
330
July1st to 15thNight
5%5%24%39%24%
310
16th to endNight
4319%44%25%1
348
August1st to 15thNight
4212%37%38%4
330
16th to endNight
7%320%37%28%2
581
September1st to 15thNight
8%416%28%32%8%
660
16th to endNight
11%7%23%28%24%4
656
October1st to 15thNight
11%8%20%35%21%1
660
16th to endNight
16%8%28%27%16%2
704
November1st to 15thNight
20%11%30%29%6%
700
16th to endNight
18%9%30%27%11%2
720
December1st to 15thNight
15%7%27%35%13%
901
16th to endNight
13%8%33%34%8%
911
Page generated at 2017-04-30 17:40:13. Version ac04

Copyright 2017 A. Danko


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