Dawson
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Dawson clear sky chart from 2005-11-05 to 2017-09-24.

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
50%
13705
5%
46468
5%
13691
50%
13691
11%
36749

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
47%
945
4%
3354
5%
945
47%
945
9%
2743
January16th to endNight
47%
800
7%
3264
9%
800
47%
800
7%
2639
February1st to 15thNight
53%
731
9%
2680
9%
729
54%
729
13%
1991
February16th to endNight
55%
659
9%
2168
9%
659
55%
659
16%
1628
March1st to 15thNight
60%
687
14%
2217
15%
687
61%
687
23%
1458
March16th to endNight
57%
575
9%
2051
10%
575
58%
575
17%
1404
April1st to 15thNight
57%
539
2%
1583
1%
539
57%
539
16%
1192
April16th to endNight
60%
533
0%
1313
0%
533
60%
533
23%
975
May1st to 15thNight
53%
290
0%
1011
0%
290
53%
290
14%
743
May16th to endNight
60%
187
0%
763
0%
187
60%
187
17%
491
June1st to 15thNight
60%
180
0%
540
0%
180
60%
180
16%
408
June16th to endNight
60%
180
0%
540
0%
180
60%
180
18%
398
July1st to 15thNight
52%
170
0%
510
0%
170
52%
170
15%
386
July16th to endNight
56%
188
0%
808
0%
177
55%
177
9%
608
August1st to 15thNight
54%
370
0%
1085
0%
369
53%
369
15%
821
August16th to endNight
48%
573
0%
1456
0%
573
48%
573
12%
1216
September1st to 15thNight
54%
540
4%
1692
4%
540
54%
540
12%
1328
September16th to endNight
47%
564
5%
1907
6%
564
47%
564
11%
1462
October1st to 15thNight
51%
671
7%
2059
7%
671
52%
671
14%
1596
October16th to endNight
47%
736
4%
2489
4%
736
47%
736
9%
2046
November1st to 15thNight
41%
730
3%
2802
4%
730
41%
730
6%
2391
November16th to endNight
45%
885
3%
3180
4%
885
46%
885
6%
2715
December1st to 15thNight
37%
948
4%
3348
4%
948
38%
948
6%
2936
December16th to endNight
39%
1024
3%
3648
3%
1024
39%
1024
5%
3174

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
9%10%49%8%5%7%6%7%8%22%
48572
Night
7%13%6%10%8%5%7%6%7%8%18%
46542
TransparencyDay
55%11%16%13%3
48151
Night
59%10%13%12%3
46468
SeeingDay
13%414%24%28%14%
8479
Night
13%110%30%33%10%
13716

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%15%10%10%9%47%47%11%9%
597
16th to endDay
412%6%14%12%6%8%5%8%8%12%
960
February1st to 15thDay
29%7%13%11%6%7%9%8%11%12%
1184
16th to endDay
212%5%9%9%6%10%7%12%12%12%
1306
March1st to 15thDay
29%6%10%8%45%6%8%10%26%
1742
16th to endDay
39%411%9%36%7%7%7%30%
2173
April1st to 15thDay
5%13%5%10%7%5%6%6%6%6%27%
2363
16th to endDay
46%5%8%8%47%7%7%7%31%
2645
May1st to 15thDay
9%9%5%8%8%5%6%6%6%7%27%
2937
16th to endDay
6%7%48%8%47%7%8%10%27%
3348
June1st to 15thDay
8%7%48%8%5%7%8%8%10%21%
3420
16th to endDay
11%6%37%8%5%7%7%7%8%24%
3420
July1st to 15thDay
14%8%49%7%5%8%6%7%7%21%
3420
16th to endDay
12%9%48%9%6%7%7%6%7%20%
3302
August1st to 15thDay
11%8%38%8%5%6%7%7%8%24%
2869
16th to endDay
15%11%410%8%36%6%6%7%17%
2745
September1st to 15thDay
14%10%38%7%46%6%6%7%24%
2268
16th to endDay
15%10%48%7%45%5%6%7%23%
1910
October1st to 15thDay
11%13%5%10%9%45%5%46%22%
1570
16th to endDay
11%14%6%11%11%5%8%5%5%7%10%
1381
November1st to 15thDay
7%19%6%13%10%5%5%7%6%6%10%
1056
16th to endDay
6%13%7%16%11%6%7%6%8%10%4
768
December1st to 15thDay
7%16%11%11%9%47%9%6%7%6%
612
16th to endDay
312%5%18%12%5%11%6%7%10%5%
576
January1st to 15thNight
7%16%7%11%9%5%7%6%7%9%11%
3354
16th to endNight
5%14%8%13%9%5%8%6%9%7%11%
3264
February1st to 15thNight
311%5%11%10%5%7%8%8%9%18%
2668
16th to endNight
211%6%11%9%5%7%7%7%11%20%
2168
March1st to 15thNight
28%5%8%8%45%5%6%9%35%
2217
16th to endNight
210%6%10%8%45%5%5%7%33%
2046
April1st to 15thNight
5%14%5%6%7%37%8%6%8%25%
1583
16th to endNight
47%48%8%46%7%7%8%31%
1313
May1st to 15thNight
8%9%48%9%5%7%5%6%8%27%
1010
16th to endNight
45%36%7%5%7%7%9%9%32%
763
June1st to 15thNight
7%6%39%7%6%8%7%10%9%24%
540
16th to endNight
8%5%38%8%27%7%9%10%27%
540
July1st to 15thNight
9%10%5%7%7%37%8%6%10%22%
540
16th to endNight
10%7%5%7%8%47%7%7%9%23%
865
August1st to 15thNight
11%7%38%6%5%7%6%7%8%27%
1090
16th to endNight
17%10%48%7%45%6%7%8%18%
1456
September1st to 15thNight
13%9%47%7%46%6%6%7%25%
1692
16th to endNight
15%11%47%6%45%6%6%7%23%
1907
October1st to 15thNight
11%10%48%6%5%6%6%5%7%27%
2059
16th to endNight
11%16%5%9%8%47%6%6%8%15%
2489
November1st to 15thNight
7%18%9%12%9%5%8%6%6%410%
2802
16th to endNight
7%14%8%12%10%6%7%9%10%7%4
3180
December1st to 15thNight
10%18%8%13%9%47%6%7%6%7%
3348
16th to endNight
415%8%16%10%6%8%7%8%8%4
3648

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
66%9%9%9%5%
597
16th to endDay
65%8%9%12%3
960
February1st to 15thDay
59%9%10%13%5%1
1184
16th to endDay
55%8%13%16%5%
1306
March1st to 15thDay
47%8%10%20%11%1
1742
16th to endDay
47%9%15%18%8%
2173
April1st to 15thDay
55%9%18%14%2
2363
16th to endDay
46%11%20%15%5%
2645
May1st to 15thDay
53%8%15%18%4
2937
16th to endDay
46%10%16%22%4
3352
June1st to 15thDay
51%12%17%14%2
3420
16th to endDay
52%12%15%15%3
3420
July1st to 15thDay
56%12%17%11%1
3221
16th to endDay
60%12%19%6%
3096
August1st to 15thDay
52%14%21%10%
2849
16th to endDay
62%13%16%7%
2745
September1st to 15thDay
56%11%19%11%
2268
16th to endDay
57%10%19%11%
1910
October1st to 15thDay
60%9%18%9%1
1570
16th to endDay
69%8%14%7%
1381
November1st to 15thDay
70%8%13%7%
1056
16th to endDay
71%8%13%6%
768
December1st to 15thDay
71%11%7%8%1
612
16th to endDay
68%12%11%42
576
January1st to 15thNight
64%9%10%9%41
3354
16th to endNight
66%7%9%10%4
3264
February1st to 15thNight
55%8%11%17%6%
2680
16th to endNight
54%8%14%14%8%
2168
March1st to 15thNight
43%6%14%23%10%1
2217
16th to endNight
48%7%13%20%9%
2051
April1st to 15thNight
51%11%19%13%3
1583
16th to endNight
45%11%19%17%5%
1313
May1st to 15thNight
52%10%15%18%3
1011
16th to endNight
44%8%15%25%5%
763
June1st to 15thNight
50%12%17%15%3
540
16th to endNight
47%12%18%19%2
540
July1st to 15thNight
53%10%22%11%2
510
16th to endNight
53%14%22%8%1
808
August1st to 15thNight
51%12%21%13%
1085
16th to endNight
60%12%18%7%
1456
September1st to 15thNight
54%13%14%15%1
1692
16th to endNight
56%11%17%13%1
1907
October1st to 15thNight
55%10%19%11%3
2059
16th to endNight
63%10%15%9%
2489
November1st to 15thNight
70%9%12%7%
2802
16th to endNight
68%10%12%7%
3180
December1st to 15thNight
72%10%7%7%2
3348
16th to endNight
71%10%10%5%2
3648

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
13%36%40%36%
30
16th to endDay
12%312%21%43%6%
32
February1st to 15thDay
9%27%20%32%26%
212
16th to endDay
7%19%30%31%19%
211
March1st to 15thDay
8%315%23%25%23%
240
16th to endDay
10%111%21%27%26%
267
April1st to 15thDay
10%316%26%30%12%
448
16th to endDay
8%6%18%26%30%10%
450
May1st to 15thDay
16%8%18%24%22%10%
468
16th to endDay
10%7%22%26%24%9%
688
June1st to 15thDay
10%416%27%31%10%
855
16th to endDay
12%411%24%32%15%
855
July1st to 15thDay
16%213%24%29%14%
815
16th to endDay
18%212%22%31%12%
591
August1st to 15thDay
14%412%25%29%13%
494
16th to endDay
22%414%21%26%11%
523
September1st to 15thDay
20%413%21%21%18%
423
16th to endDay
13%8%17%22%24%13%
262
October1st to 15thDay
20%413%20%22%20%
225
16th to endDay
18%29%21%25%22%
235
November1st to 15thDay
10%310%31%28%16%
60
16th to endDay
6%6%36%15%36%
33
December1st to 15thDay
13%36%10%43%23%
30
16th to endDay
6%6%15%37%15%18%
32
January1st to 15thNight
14%28%38%26%10%
950
16th to endNight
12%110%40%28%7%
800
February1st to 15thNight
8%111%34%33%10%
734
16th to endNight
5%110%39%33%9%
659
March1st to 15thNight
5%210%32%40%8%
687
16th to endNight
7%19%26%42%12%
576
April1st to 15thNight
12%28%29%34%11%
539
16th to endNight
7%112%30%36%11%
533
May1st to 15thNight
14%315%21%37%7%
291
16th to endNight
7%118%29%37%5%
188
June1st to 15thNight
10%111%28%44%3
180
16th to endNight
11%27%27%44%7%
180
July1st to 15thNight
12%113%28%33%10%
170
16th to endNight
11%12%21%38%14%
188
August1st to 15thNight
16%111%22%37%10%
370
16th to endNight
21%18%20%35%12%
573
September1st to 15thNight
19%19%27%31%11%
540
16th to endNight
22%312%21%29%9%
564
October1st to 15thNight
17%211%26%33%8%
671
16th to endNight
19%27%26%31%11%
736
November1st to 15thNight
17%27%28%32%11%
730
16th to endNight
13%18%28%30%17%
885
December1st to 15thNight
16%211%30%27%11%
948
16th to endNight
10%19%34%31%12%
1024
Page generated at 2017-09-25 06:02:23. Version ac04

Copyright 2017 A. Danko


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