Colliers Mills WMA
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Colliers Mills WMA clear sky chart from 2005-11-05 to 2017-09-19.

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
36%
15101
20%
46878
11%
15070
47%
15070
24%
29576

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%
720
21%
2506
10%
716
42%
716
19%
1560
January16th to endNight
21%
768
21%
2559
7%
768
39%
768
21%
1577
February1st to 15thNight
20%
704
18%
2231
5%
701
36%
701
20%
1406
February16th to endNight
18%
631
26%
1893
8%
631
41%
631
22%
1171
March1st to 15thNight
24%
720
21%
2131
9%
720
38%
720
23%
1361
March16th to endNight
26%
768
22%
2007
9%
768
36%
768
27%
1330
April1st to 15thNight
25%
718
18%
1796
5%
718
32%
718
27%
1200
April16th to endNight
33%
720
19%
1800
6%
720
38%
720
29%
1207
May1st to 15thNight
31%
516
17%
1596
8%
516
38%
516
21%
1079
May16th to endNight
46%
374
16%
1497
14%
374
53%
374
19%
942
June1st to 15thNight
45%
360
14%
1440
13%
360
53%
360
18%
904
June16th to endNight
56%
360
15%
1440
18%
360
61%
360
26%
806
July1st to 15thNight
55%
340
12%
1360
15%
340
58%
340
21%
829
July16th to endNight
65%
376
17%
1418
18%
354
71%
354
27%
796
August1st to 15thNight
63%
597
18%
1668
13%
595
65%
595
34%
1031
August16th to endNight
61%
764
18%
1910
10%
764
62%
764
32%
1278
September1st to 15thNight
53%
720
23%
1800
13%
720
57%
720
34%
1182
September16th to endNight
57%
673
26%
1837
21%
673
60%
673
34%
1141
October1st to 15thNight
44%
660
23%
1944
17%
660
52%
660
30%
1215
October16th to endNight
35%
704
25%
2175
14%
704
49%
704
29%
1309
November1st to 15thNight
35%
700
24%
2277
14%
700
49%
700
26%
1378
November16th to endNight
33%
720
20%
2385
12%
720
44%
720
21%
1523
December1st to 15thNight
25%
720
17%
2520
7%
720
37%
720
18%
1629
December16th to endNight
20%
768
21%
2688
6%
768
38%
768
18%
1722

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
14%5%25%5%3445%7%41%
47941
Night
15%5%2442445%6%43%
47048
Cloud CoverDay
14%6%25%43445%7%40%
47950
Night
15%6%2442445%7%43%
47054
TransparencyDay
41%5%11%22%15%2
47629
Night
40%5%11%22%17%2
46878
SeeingDay
18%8%26%25%15%5%
5801
Night
18%9%30%30%11%1
15102

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
14%6%245%3445%5%42%
1432
16th to endDay
16%6%1441445%6%43%
1662
February1st to 15thDay
15%6%26%5%24346%41%
1630
16th to endDay
13%7%36%5%3346%5%40%
1580
March1st to 15thDay
16%7%25%5%24447%39%
1817
16th to endDay
18%7%24414335%43%
2217
April1st to 15thDay
18%6%24424346%42%
2152
16th to endDay
14%415%435%45%6%43%
2160
May1st to 15thDay
18%6%25%42445%7%37%
2363
16th to endDay
16%6%245%35%45%7%38%
2618
June1st to 15thDay
14%5%25%5%36%5%5%9%37%
2520
16th to endDay
12%425%5%36%5%6%8%39%
2520
July1st to 15thDay
10%5%35%5%46%6%6%9%35%
2520
16th to endDay
9%5%35%6%46%5%7%9%36%
2654
August1st to 15thDay
12%426%5%345%7%8%38%
2268
16th to endDay
13%5%25%5%35%5%6%8%39%
2292
September1st to 15thDay
12%5%25%334446%46%
2160
16th to endDay
14%6%24425%5%5%7%41%
1867
October1st to 15thDay
15%7%24423346%45%
1683
16th to endDay
18%424313445%47%
1696
November1st to 15thDay
17%6%24413335%46%
1581
16th to endDay
15%4245%33446%45%
1573
December1st to 15thDay
15%6%3442445%6%42%
1440
16th to endDay
19%7%2442335%6%39%
1536
January1st to 15thNight
17%5%2442445%6%42%
2506
16th to endNight
17%7%23323446%43%
2559
February1st to 15thNight
14%7%25%42435%6%41%
2230
16th to endNight
15%6%25%323346%46%
1893
March1st to 15thNight
17%6%24323346%44%
2118
16th to endNight
17%6%25%32324445%
2007
April1st to 15thNight
16%6%3431445%7%43%
1796
16th to endNight
17%5%2442446%7%42%
1800
May1st to 15thNight
17%6%37%5%2345%6%38%
1596
16th to endNight
15%6%245%245%48%39%
1495
June1st to 15thNight
16%5%24435%45%7%40%
1440
16th to endNight
7%5%245%35%5%5%9%44%
1440
July1st to 15thNight
9%5%25%5%35%5%6%10%38%
1440
16th to endNight
7%435%436%5%8%9%43%
1514
August1st to 15thNight
9%425%3345%7%8%45%
1678
16th to endNight
11%4345%345%6%7%42%
1910
September1st to 15thNight
12%5%13435%446%46%
1800
16th to endNight
12%5%25%323347%48%
1837
October1st to 15thNight
16%5%24325%346%46%
1944
16th to endNight
16%5%13413345%49%
2175
November1st to 15thNight
16%5%25%313245%48%
2277
16th to endNight
16%6%25%5%34446%40%
2385
December1st to 15thNight
19%7%2443345%5%37%
2520
16th to endNight
18%6%3442445%6%39%
2688

Percentage Cloud Cover SE (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
14%6%245%34446%41%
1432
16th to endDay
16%7%2442346%6%43%
1662
February1st to 15thDay
15%5%36%5%24445%42%
1630
16th to endDay
13%7%36%5%3445%6%40%
1580
March1st to 15thDay
16%6%25%424447%40%
1827
16th to endDay
17%7%25%423435%43%
2216
April1st to 15thDay
18%5%24424346%42%
2152
16th to endDay
15%425%435%46%6%43%
2160
May1st to 15thDay
17%7%3443445%7%37%
2363
16th to endDay
16%6%25%435%45%7%38%
2618
June1st to 15thDay
14%5%25%5%35%5%5%9%37%
2520
16th to endDay
11%425%5%35%5%6%8%39%
2520
July1st to 15thDay
10%5%25%6%46%7%7%9%35%
2520
16th to endDay
9%5%25%6%36%5%8%9%35%
2654
August1st to 15thDay
11%5%26%5%35%5%6%8%38%
2268
16th to endDay
13%5%25%435%5%6%8%39%
2292
September1st to 15thDay
13%5%2444345%6%45%
2160
16th to endDay
14%6%25%5%34447%42%
1867
October1st to 15thDay
14%8%25%413346%45%
1683
16th to endDay
17%424323345%47%
1696
November1st to 15thDay
17%5%23423335%45%
1581
16th to endDay
15%5%245%24346%45%
1573
December1st to 15thDay
16%5%3442445%7%41%
1440
16th to endDay
19%7%24423346%39%
1536
January1st to 15thNight
17%5%24424447%41%
2506
16th to endNight
17%7%23324447%43%
2559
February1st to 15thNight
13%8%25%43435%6%42%
2223
16th to endNight
15%7%24313346%46%
1893
March1st to 15thNight
17%5%24423446%44%
2131
16th to endNight
17%6%35%32333445%
2007
April1st to 15thNight
15%7%24323447%43%
1796
16th to endNight
17%5%243245%5%7%42%
1800
May1st to 15thNight
17%6%36%424446%37%
1596
16th to endNight
14%6%25%5%34447%39%
1495
June1st to 15thNight
16%4245%44447%40%
1440
16th to endNight
7%425%5%246%6%9%43%
1440
July1st to 15thNight
9%5%25%5%36%5%7%10%38%
1440
16th to endNight
6%435%436%6%7%9%42%
1514
August1st to 15thNight
9%425%43446%8%45%
1678
16th to endNight
11%5%25%5%35%5%6%6%43%
1910
September1st to 15thNight
13%4145%34447%46%
1800
16th to endNight
13%5%2442235%7%48%
1837
October1st to 15thNight
16%5%24314347%46%
1944
16th to endNight
16%5%14422436%49%
2175
November1st to 15thNight
15%5%34313235%48%
2277
16th to endNight
16%5%25%5%245%5%6%40%
2385
December1st to 15thNight
19%7%245%3435%6%37%
2520
16th to endNight
17%7%25%42445%6%39%
2688

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
42%414%21%13%3
1433
16th to endDay
40%412%25%14%3
1662
February1st to 15thDay
44%411%23%13%2
1633
16th to endDay
43%410%25%13%2
1580
March1st to 15thDay
44%5%13%22%11%2
1827
16th to endDay
43%48%22%17%3
2217
April1st to 15thDay
42%49%23%14%4
2152
16th to endDay
39%411%19%22%2
2160
May1st to 15thDay
46%5%10%19%15%2
2363
16th to endDay
45%5%13%21%12%2
2622
June1st to 15thDay
43%7%12%24%11%
2520
16th to endDay
39%8%12%22%14%1
2520
July1st to 15thDay
41%8%11%20%15%1
2371
16th to endDay
40%7%12%24%12%2
2487
August1st to 15thDay
39%7%13%21%16%1
2254
16th to endDay
39%6%11%20%18%3
2292
September1st to 15thDay
37%5%10%21%22%2
2160
16th to endDay
41%5%9%19%22%2
1867
October1st to 15thDay
40%412%22%18%1
1683
16th to endDay
38%310%26%19%2
1696
November1st to 15thDay
41%311%23%17%2
1581
16th to endDay
39%411%25%16%2
1573
December1st to 15thDay
41%417%22%13%1
1440
16th to endDay
45%414%20%13%
1536
January1st to 15thNight
41%5%11%22%15%3
2506
16th to endNight
41%411%25%15%1
2559
February1st to 15thNight
42%313%22%15%2
2231
16th to endNight
39%38%24%19%3
1893
March1st to 15thNight
41%311%23%16%3
2131
16th to endNight
43%210%21%17%4
2007
April1st to 15thNight
41%410%22%17%3
1796
16th to endNight
40%5%10%17%23%3
1800
May1st to 15thNight
46%5%9%18%18%2
1596
16th to endNight
43%7%13%18%15%2
1497
June1st to 15thNight
44%6%12%19%16%
1440
16th to endNight
33%7%16%24%16%2
1440
July1st to 15thNight
38%8%16%19%13%2
1360
16th to endNight
33%7%18%26%11%2
1418
August1st to 15thNight
34%6%14%23%19%1
1668
16th to endNight
38%7%12%19%20%2
1910
September1st to 15thNight
36%6%10%23%21%1
1800
16th to endNight
35%48%24%24%2
1837
October1st to 15thNight
38%411%25%17%2
1944
16th to endNight
37%310%26%19%2
2175
November1st to 15thNight
38%49%22%19%5%
2277
16th to endNight
43%411%23%14%2
2385
December1st to 15thNight
46%414%20%12%1
2520
16th to endNight
44%412%22%13%1
2688

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%30%31%13%31
60
16th to endDay
25%17%32%21%2
85
February1st to 15thDay
21%25%32%18%2
146
16th to endDay
15%19%41%20%2
239
March1st to 15thDay
18%20%30%24%6%
270
16th to endDay
18%18%36%18%6%2
288
April1st to 15thDay
21%13%35%17%10%2
270
16th to endDay
20%7%31%24%10%5%
270
May1st to 15thDay
28%12%26%18%10%4
288
16th to endDay
24%419%27%18%4
331
June1st to 15thDay
17%6%27%27%16%4
315
16th to endDay
16%226%33%17%4
315
July1st to 15thDay
14%220%30%25%6%
305
16th to endDay
12%418%30%25%8%
326
August1st to 15thDay
15%118%30%24%9%
313
16th to endDay
12%15%31%24%15%
332
September1st to 15thDay
14%5%26%20%20%11%
315
16th to endDay
20%315%28%16%15%
266
October1st to 15thDay
21%320%29%16%8%
255
16th to endDay
15%11%31%27%13%1
260
November1st to 15thDay
20%7%27%27%15%1
235
16th to endDay
18%12%35%19%11%1
193
December1st to 15thDay
21%25%20%16%15%1
60
16th to endDay
37%9%35%14%3
64
January1st to 15thNight
19%14%35%25%5%
720
16th to endNight
21%13%40%22%2
768
February1st to 15thNight
18%15%41%24%
704
16th to endNight
19%19%38%20%2
631
March1st to 15thNight
20%14%37%23%4
720
16th to endNight
19%10%37%24%7%
768
April1st to 15thNight
19%13%37%24%4
718
16th to endNight
19%7%35%30%6%
720
May1st to 15thNight
20%9%32%30%6%
516
16th to endNight
17%421%40%14%
375
June1st to 15thNight
19%323%40%12%
360
16th to endNight
7%223%49%16%
360
July1st to 15thNight
11%220%45%19%
340
16th to endNight
7%116%49%23%1
376
August1st to 15thNight
12%114%44%24%2
597
16th to endNight
12%213%40%27%3
764
September1st to 15thNight
15%221%36%20%2
720
16th to endNight
16%315%35%25%4
673
October1st to 15thNight
20%424%31%16%2
660
16th to endNight
19%8%31%30%9%
704
November1st to 15thNight
17%8%32%26%13%1
700
16th to endNight
17%12%30%28%10%
720
December1st to 15thNight
23%12%32%21%8%1
720
16th to endNight
20%13%38%23%3
768
Page generated at 2017-09-20 04:49:53. Version ac04

Copyright 2017 A. Danko


Colliers Mills WMA Clear Sky Chart | Charts Home