Glennallen
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Glennallen clear sky chart from 2005-11-05 to 2017-09-20.

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%
13071
5%
46435
5%
13053
44%
13053
10%
36383

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
41%
769
4%
3184
3%
769
43%
769
7%
2595
January16th to endNight
35%
800
5%
3126
5%
800
36%
800
6%
2627
February1st to 15thNight
47%
727
6%
2634
5%
727
48%
727
11%
2046
February16th to endNight
50%
659
11%
2176
8%
659
53%
659
16%
1594
March1st to 15thNight
53%
582
17%
2172
16%
582
59%
582
21%
1358
March16th to endNight
58%
575
11%
2023
14%
575
59%
575
20%
1347
April1st to 15thNight
48%
539
6%
1646
3%
539
49%
539
15%
1228
April16th to endNight
56%
540
1%
1341
1%
540
56%
540
24%
959
May1st to 15thNight
42%
400
0%
1121
0%
400
42%
400
15%
878
May16th to endNight
50%
187
0%
920
0%
187
50%
187
14%
585
June1st to 15thNight
41%
180
0%
720
0%
180
41%
180
11%
536
June16th to endNight
46%
180
0%
650
0%
180
46%
180
11%
497
July1st to 15thNight
41%
170
0%
680
0%
170
41%
170
8%
531
July16th to endNight
45%
250
0%
925
0%
234
43%
234
7%
763
August1st to 15thNight
39%
436
0%
1152
0%
434
39%
434
12%
939
August16th to endNight
37%
573
1%
1537
1%
573
38%
573
10%
1283
September1st to 15thNight
35%
540
4%
1688
3%
540
35%
540
11%
1360
September16th to endNight
36%
506
5%
1864
6%
506
37%
506
9%
1470
October1st to 15thNight
42%
645
8%
2077
8%
645
43%
645
13%
1612
October16th to endNight
47%
736
6%
2455
5%
736
47%
736
12%
1929
November1st to 15thNight
35%
730
3%
2677
3%
730
36%
730
7%
2227
November16th to endNight
42%
750
5%
3060
7%
750
43%
750
7%
2459
December1st to 15thNight
36%
765
5%
3151
6%
765
36%
765
6%
2654
December16th to endNight
34%
832
4%
3456
4%
832
35%
832
5%
2906

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
10%10%5%9%8%46%6%6%7%23%
48483
Night
9%12%5%11%8%46%6%6%7%20%
46527
TransparencyDay
55%10%16%13%3
48080
Night
59%10%13%13%3
46435
SeeingDay
13%6%16%23%21%17%
8192
Night
14%5%16%29%27%7%
13085

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
10%16%8%13%10%35%7%5%7%11%
754
16th to endDay
8%14%9%15%11%6%9%6%5%48%
1097
February1st to 15thDay
5%15%6%14%10%48%8%6%7%13%
1230
16th to endDay
311%6%11%11%5%7%6%8%8%18%
1298
March1st to 15thDay
26%410%10%47%7%9%9%26%
1785
16th to endDay
310%5%8%7%5%8%6%6%8%27%
2201
April1st to 15thDay
39%6%10%7%5%8%6%7%7%27%
2299
16th to endDay
46%47%7%46%7%6%7%36%
2619
May1st to 15thDay
10%12%6%9%7%36%5%5%6%27%
2829
16th to endDay
7%7%36%5%45%5%6%8%38%
3191
June1st to 15thDay
12%9%47%8%46%6%7%8%24%
3240
16th to endDay
12%7%47%7%47%6%6%8%27%
3297
July1st to 15thDay
15%8%47%7%47%7%6%8%22%
3240
16th to endDay
14%6%37%7%47%7%6%9%23%
3180
August1st to 15thDay
16%8%38%8%46%5%5%7%25%
2802
16th to endDay
19%10%5%9%7%45%45%6%21%
2663
September1st to 15thDay
16%11%49%8%45%5%5%5%23%
2271
16th to endDay
14%13%48%6%446%6%6%23%
1865
October1st to 15thDay
11%11%6%11%9%5%6%5%6%6%20%
1550
16th to endDay
9%15%5%13%9%5%7%5%7%6%15%
1417
November1st to 15thDay
8%16%7%13%12%6%7%5%5%412%
1180
16th to endDay
5%14%6%11%11%5%8%8%6%10%13%
900
December1st to 15thDay
12%15%5%12%13%46%5%8%5%10%
807
16th to endDay
312%7%15%10%6%10%8%9%8%7%
768
January1st to 15thNight
8%15%6%11%9%6%7%5%6%7%14%
3184
16th to endNight
9%13%7%15%11%5%6%6%6%7%10%
3126
February1st to 15thNight
49%6%12%11%6%7%7%6%7%20%
2622
16th to endNight
410%5%11%7%36%7%7%8%26%
2176
March1st to 15thNight
36%5%6%6%47%5%7%9%36%
2172
16th to endNight
39%5%8%7%45%6%7%10%31%
2018
April1st to 15thNight
39%5%9%8%48%7%8%8%25%
1646
16th to endNight
49%37%7%45%5%7%9%33%
1341
May1st to 15thNight
12%13%6%9%6%47%5%45%26%
1120
16th to endNight
9%7%26%8%45%5%5%7%36%
920
June1st to 15thNight
12%8%5%8%8%346%6%8%25%
720
16th to endNight
17%8%5%7%6%46%5%46%27%
650
July1st to 15thNight
18%6%5%6%8%45%8%7%8%20%
720
16th to endNight
17%9%49%7%5%9%5%5%8%17%
989
August1st to 15thNight
16%9%39%7%46%5%6%8%21%
1158
16th to endNight
20%11%39%7%445%5%5%21%
1537
September1st to 15thNight
18%11%39%7%46%5%5%6%22%
1688
16th to endNight
18%11%49%7%45%5%46%22%
1864
October1st to 15thNight
10%13%5%9%6%45%6%6%7%26%
2077
16th to endNight
9%14%49%8%45%5%7%7%22%
2455
November1st to 15thNight
7%17%8%13%9%45%46%5%16%
2677
16th to endNight
6%12%6%13%10%5%7%8%7%9%13%
3060
December1st to 15thNight
12%17%7%11%8%36%5%7%7%11%
3151
16th to endNight
6%15%8%14%11%5%7%6%6%7%10%
3456

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
68%7%9%9%31
754
16th to endDay
74%8%6%6%3
1097
February1st to 15thDay
63%11%8%12%3
1230
16th to endDay
58%9%10%15%7%
1298
March1st to 15thDay
47%9%12%17%13%
1785
16th to endDay
48%11%16%17%5%
2201
April1st to 15thDay
52%11%20%14%1
2299
16th to endDay
43%9%19%22%4
2619
May1st to 15thDay
56%8%13%16%5%
2829
16th to endDay
41%8%16%24%8%1
3195
June1st to 15thDay
55%11%14%15%3
3240
16th to endDay
51%12%18%14%3
3297
July1st to 15thDay
57%12%18%10%
3051
16th to endDay
54%14%22%8%
2981
August1st to 15thDay
56%11%20%10%1
2783
16th to endDay
61%10%17%9%1
2663
September1st to 15thDay
60%10%18%10%
2271
16th to endDay
58%11%19%9%
1865
October1st to 15thDay
61%11%16%9%
1550
16th to endDay
63%13%13%7%
1417
November1st to 15thDay
71%11%8%7%
1180
16th to endDay
59%12%15%10%2
900
December1st to 15thDay
70%9%6%11%1
807
16th to endDay
67%10%11%9%1
768
January1st to 15thNight
66%8%10%9%41
3184
16th to endNight
68%9%10%8%3
3126
February1st to 15thNight
58%10%11%14%41
2634
16th to endNight
50%10%13%16%9%
2176
March1st to 15thNight
39%8%11%21%18%
2172
16th to endNight
44%8%15%21%9%
2023
April1st to 15thNight
52%10%16%17%3
1646
16th to endNight
43%9%20%20%5%
1341
May1st to 15thNight
57%8%12%17%4
1121
16th to endNight
44%10%13%23%8%
920
June1st to 15thNight
52%13%16%15%2
720
16th to endNight
56%10%12%16%3
650
July1st to 15thNight
59%11%18%9%
680
16th to endNight
62%13%16%7%
925
August1st to 15thNight
57%13%16%11%
1152
16th to endNight
62%11%12%11%1
1537
September1st to 15thNight
60%10%17%11%
1688
16th to endNight
60%11%15%11%1
1864
October1st to 15thNight
56%10%15%16%1
2077
16th to endNight
57%10%18%11%1
2455
November1st to 15thNight
67%9%13%9%
2677
16th to endNight
61%12%13%10%1
3060
December1st to 15thNight
68%10%9%10%1
3151
16th to endNight
68%10%10%8%1
3456

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
10%6%10%36%30%6%
30
16th to endDay
11%38%26%30%18%
169
February1st to 15thDay
10%6%9%24%30%18%
225
16th to endDay
7%112%37%24%16%
211
March1st to 15thDay
35%13%31%21%24%
240
16th to endDay
7%411%19%27%29%
352
April1st to 15thDay
46%22%25%24%15%
443
16th to endDay
6%6%16%30%26%14%
450
May1st to 15thDay
13%8%23%21%16%16%
468
16th to endDay
12%8%22%21%21%13%
531
June1st to 15thDay
16%8%20%26%19%8%
675
16th to endDay
13%316%27%21%16%
732
July1st to 15thDay
17%414%23%18%21%
645
16th to endDay
16%415%23%20%20%
532
August1st to 15thDay
16%7%19%18%19%19%
494
16th to endDay
23%9%16%18%18%13%
523
September1st to 15thDay
20%12%21%16%15%13%
478
16th to endDay
19%12%11%17%18%21%
241
October1st to 15thDay
14%5%16%16%20%26%
225
16th to endDay
17%411%16%27%22%
240
November1st to 15thDay
16%18%33%25%15%
196
16th to endDay
6%13%6%20%16%36%
30
December1st to 15thDay
326%46%23%
30
16th to endDay
39%15%37%21%12%
32
January1st to 15thNight
14%314%32%26%8%
773
16th to endNight
13%314%33%26%8%
800
February1st to 15thNight
7%5%12%38%28%7%
734
16th to endNight
7%316%41%23%6%
659
March1st to 15thNight
5%421%33%28%6%
582
16th to endNight
6%312%25%38%14%
576
April1st to 15thNight
7%323%30%30%5%
539
16th to endNight
7%415%34%32%5%
540
May1st to 15thNight
16%5%20%27%26%1
401
16th to endNight
11%420%33%29%
188
June1st to 15thNight
17%324%36%17%
180
16th to endNight
20%316%30%25%3
180
July1st to 15thNight
20%420%24%27%4
170
16th to endNight
20%316%28%27%4
250
August1st to 15thNight
22%5%21%21%23%6%
436
16th to endNight
23%8%17%24%22%3
573
September1st to 15thNight
25%7%23%22%16%4
540
16th to endNight
20%9%19%21%22%6%
506
October1st to 15thNight
15%6%20%24%27%5%
645
16th to endNight
15%412%26%33%6%
736
November1st to 15thNight
15%215%34%26%5%
730
16th to endNight
9%6%15%28%25%14%
750
December1st to 15thNight
19%5%10%23%27%13%
765
16th to endNight
11%5%14%30%26%11%
832
Page generated at 2017-09-21 03:18:12. Version ac04

Copyright 2017 A. Danko


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