This page made possible by the sponsorship of: Cary MacWilliams.

Ghost Lake
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Ghost Lake clear sky chart from 2005-11-06 to 2024-11-05.

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
32%
24192
14%
98942
7%
23976
41%
23976
17%
60440

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 10thNight
19%
945
14%
4687
4%
926
29%
926
11%
3056
January11th to 20thNight
22%
902
21%
4532
6%
888
34%
888
13%
2800
January21st to endNight
22%
833
13%
4835
7%
814
39%
814
11%
2845
February1st to 10thNight
25%
760
14%
2660
8%
760
35%
760
15%
1761
February11th to 20thNight
23%
743
13%
2449
6%
740
35%
740
17%
1646
February21st to endNight
26%
628
18%
1894
7%
628
39%
628
20%
1268
March1st to 10thNight
28%
758
18%
3590
8%
744
38%
744
13%
2351
March11th to 20thNight
30%
754
18%
3406
7%
740
41%
740
20%
1775
March21st to endNight
33%
827
7%
3659
4%
814
38%
814
11%
2782
April1st to 10thNight
27%
733
14%
1873
4%
733
33%
733
19%
1359
April11th to 20thNight
27%
563
14%
1691
7%
563
33%
563
18%
1184
April21st to endNight
28%
570
10%
1710
6%
570
33%
570
17%
1178
May1st to 10thNight
38%
433
8%
2514
7%
427
43%
427
9%
1769
May11th to 20thNight
47%
369
10%
2158
14%
364
50%
364
14%
1332
May21st to endNight
41%
404
3%
2403
3%
399
43%
399
10%
1592
June1st to 10thNight
39%
380
2%
1330
0%
380
39%
380
17%
899
June11th to 20thNight
36%
380
0%
1330
0%
380
36%
380
14%
924
June21st to endNight
57%
380
0%
1330
0%
380
57%
380
24%
793
July1st to 10thNight
60%
364
1%
1962
0%
360
61%
360
18%
1123
July11th to 20thNight
53%
359
4%
1955
3%
359
55%
359
22%
935
July21st to endNight
66%
409
10%
2249
16%
383
71%
383
25%
999
August1st to 10thNight
61%
369
13%
2364
18%
366
66%
366
16%
1313
August11th to 20thNight
63%
486
10%
2609
18%
481
66%
481
22%
1389
August21st to endNight
56%
617
16%
2915
16%
605
61%
605
25%
1447
September1st to 10thNight
50%
703
19%
1843
12%
703
52%
703
36%
1133
September11th to 20thNight
48%
760
17%
2076
9%
760
53%
760
30%
1320
September21st to endNight
38%
760
22%
2090
10%
760
47%
760
31%
1281
October1st to 10thNight
39%
753
26%
3320
10%
740
48%
740
20%
1754
October11th to 20thNight
33%
750
14%
3768
8%
740
45%
740
19%
1876
October21st to endNight
25%
827
22%
4224
7%
813
41%
813
16%
2223
November1st to 10thNight
22%
831
17%
2540
5%
831
36%
831
19%
1712
November11th to 20thNight
18%
950
19%
2770
3%
950
33%
950
21%
1744
November21st to endNight
21%
950
15%
2850
4%
950
31%
950
20%
1840
December1st to 10thNight
23%
950
17%
2850
6%
950
34%
950
20%
1887
December11th to 20thNight
24%
950
14%
3486
6%
949
33%
949
16%
2355
December21st to endNight
22%
1042
11%
5020
4%
1026
34%
1026
13%
2795

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
8%9%38%5%5%5%47%8%38%
105637
Night
6%9%38%5%5%5%46%8%41%
101981
TransparencyDay
39%10%16%22%11%2
105386
Night
37%10%17%23%11%2
101878
SeeingDay
15%16%32%25%10%2
15323
Night
11%13%35%29%11%1
24322

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 10thDay
15%5%12%7%5%447%9%39%
2219
11th to 20thDay
28%310%6%5%6%5%7%9%38%
2295
21st to endDay
18%38%5%5%5%48%9%42%
2794
February1st to 10thDay
28%39%8%6%6%5%7%10%35%
1520
11th to 20thDay
19%5%10%6%7%6%6%7%9%34%
1618
21st to endDay
210%5%14%7%6%5%35%8%34%
1558
March1st to 10thDay
17%412%6%5%6%5%7%10%36%
3138
11th to 20thDay
5%9%36%5%4436%8%47%
3412
21st to endDay
421%8%14%5%4435%6%26%
3942
April1st to 10thDay
6%14%411%7%5%6%47%8%28%
2306
11th to 20thDay
8%17%6%10%5%4446%7%29%
2440
21st to endDay
12%14%48%6%45%45%7%31%
2470
May1st to 10thDay
16%17%48%5%5%5%45%5%26%
4348
11th to 20thDay
10%10%49%5%5%5%5%8%9%30%
4694
21st to endDay
18%11%311%6%6%5%45%7%24%
5161
June1st to 10thDay
17%10%38%5%5%5%5%7%7%26%
2850
11th to 20thDay
22%10%37%6%6%5%5%6%7%23%
2850
21st to endDay
10%5%27%6%6%5%5%7%9%38%
2850
July1st to 10thDay
9%5%26%5%5%5%5%6%7%45%
4740
11th to 20thDay
7%42445%6%6%8%9%45%
4740
21st to endDay
5%415%44447%9%52%
4959
August1st to 10thDay
10%5%26%5%5%6%5%7%8%41%
4401
11th to 20thDay
9%426%5%6%6%5%8%10%40%
4125
21st to endDay
9%5%25%44446%8%50%
4521
September1st to 10thDay
11%5%26%43446%6%47%
2334
11th to 20thDay
13%7%35%345%35%7%45%
2103
21st to endDay
8%8%25%4445%7%7%45%
2090
October1st to 10thDay
6%8%25%435%46%9%47%
3396
11th to 20thDay
5%8%37%45%5%5%8%10%41%
2852
21st to endDay
5%8%35%5%5%5%36%8%47%
3101
November1st to 10thDay
414%47%6%45%6%6%8%36%
1620
11th to 20thDay
310%36%5%5%5%5%6%7%45%
1406
21st to endDay
210%410%6%4446%8%41%
1330
December1st to 10thDay
38%312%7%5%5%46%8%39%
1330
11th to 20thDay
29%5%12%7%7%6%6%7%7%33%
1682
21st to endDay
39%48%5%4446%7%46%
2442
January1st to 10thNight
210%6%12%6%6%6%5%7%9%30%
4726
11th to 20thNight
28%411%7%6%5%5%7%8%36%
4631
21st to endNight
310%410%6%5%5%5%7%9%38%
4862
February1st to 10thNight
38%410%7%6%6%5%7%8%35%
2660
11th to 20thNight
211%411%6%6%6%47%8%34%
2448
21st to endNight
18%6%11%9%7%5%45%9%37%
1894
March1st to 10thNight
17%313%8%7%8%6%7%9%32%
3736
11th to 20thNight
48%35%44447%9%49%
3566
21st to endNight
7%20%7%12%5%4445%7%25%
3710
April1st to 10thNight
6%15%5%10%6%45%46%7%34%
1873
11th to 20thNight
8%14%5%9%6%5%446%7%34%
1691
21st to endNight
9%13%48%5%45%46%8%35%
1710
May1st to 10thNight
17%17%38%43435%6%30%
2600
11th to 20thNight
11%10%39%6%5%436%8%35%
2199
21st to endNight
15%9%49%6%5%5%45%8%30%
2414
June1st to 10thNight
17%8%35%44447%8%35%
1330
11th to 20thNight
21%8%26%45%5%5%6%8%30%
1330
21st to endNight
8%5%27%5%6%447%9%44%
1330
July1st to 10thNight
9%6%27%345%36%6%49%
2220
11th to 20thNight
6%3133445%6%9%55%
2220
21st to endNight
4425%33335%7%61%
2590
August1st to 10thNight
13%6%26%44447%9%43%
2529
11th to 20thNight
10%415%3445%7%11%45%
2710
21st to endNight
9%5%1433436%8%53%
3146
September1st to 10thNight
11%7%25%33435%7%51%
1843
11th to 20thNight
14%8%2433335%6%48%
2076
21st to endNight
9%7%35%33436%7%49%
2090
October1st to 10thNight
6%8%25%34435%8%51%
3580
11th to 20thNight
5%7%25%34447%9%50%
4076
21st to endNight
5%10%36%44446%8%47%
4457
November1st to 10thNight
412%5%8%5%45%5%7%8%37%
2540
11th to 20thNight
38%38%445%47%9%44%
2770
21st to endNight
210%410%6%45%37%9%40%
2850
December1st to 10thNight
210%49%6%6%6%46%9%37%
2850
11th to 20thNight
19%411%7%6%6%5%8%8%34%
3510
21st to endNight
29%49%5%6%5%5%6%8%42%
5214

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 10thDay
39%8%15%24%12%2
2219
11th to 20thDay
40%8%12%19%18%4
2316
21st to endDay
31%12%19%28%8%1
2794
February1st to 10thDay
41%9%18%19%10%3
1520
11th to 20thDay
42%9%17%20%10%1
1627
21st to endDay
47%7%13%19%12%2
1558
March1st to 10thDay
37%11%18%18%15%1
3138
11th to 20thDay
31%9%21%25%12%1
3413
21st to endDay
55%11%14%13%6%
3942
April1st to 10thDay
49%11%18%15%7%
2306
11th to 20thDay
51%10%13%18%8%1
2440
21st to endDay
51%8%14%18%6%1
2470
May1st to 10thDay
56%9%12%19%4
4348
11th to 20thDay
42%13%15%22%7%
4698
21st to endDay
54%12%12%14%8%
5162
June1st to 10thDay
52%11%14%14%8%1
2850
11th to 20thDay
57%10%12%13%7%1
2850
21st to endDay
39%11%17%22%9%2
2850
July1st to 10thDay
32%10%13%21%21%4
4666
11th to 20thDay
28%11%17%29%12%2
4659
21st to endDay
24%8%12%26%23%6%
4802
August1st to 10thDay
34%12%15%30%7%1
4384
11th to 20thDay
34%11%23%24%7%1
4166
21st to endDay
29%8%20%31%10%2
4520
September1st to 10thDay
34%8%16%24%14%4
2334
11th to 20thDay
38%9%16%24%12%2
2103
21st to endDay
34%9%17%25%12%3
2090
October1st to 10thDay
32%7%19%32%8%1
3396
11th to 20thDay
34%10%21%20%12%3
2852
21st to endDay
34%7%14%32%11%1
3101
November1st to 10thDay
43%11%14%20%11%1
1620
11th to 20thDay
36%8%19%24%11%1
1406
21st to endDay
37%10%19%22%9%3
1330
December1st to 10thDay
41%8%17%18%14%2
1330
11th to 20thDay
42%12%16%19%10%1
1684
21st to endDay
33%8%12%24%18%5%
2442
January1st to 10thNight
43%12%17%18%8%2
4726
11th to 20thNight
42%8%13%17%13%7%
4672
21st to endNight
38%12%18%21%11%1
4862
February1st to 10thNight
42%11%13%20%11%3
2660
11th to 20thNight
44%9%17%17%12%2
2449
21st to endNight
43%7%12%23%12%2
1894
March1st to 10thNight
39%14%14%19%13%1
3736
11th to 20thNight
27%11%22%25%14%1
3566
21st to endNight
54%11%14%15%5%1
3710
April1st to 10thNight
48%7%15%19%10%1
1873
11th to 20thNight
48%8%14%20%9%1
1691
21st to endNight
45%10%16%20%7%2
1710
May1st to 10thNight
54%7%12%21%6%
2600
11th to 20thNight
39%13%14%29%5%1
2199
21st to endNight
46%13%14%19%7%1
2414
June1st to 10thNight
44%11%16%21%8%1
1330
11th to 20thNight
48%10%16%15%10%2
1330
21st to endNight
34%10%20%25%10%1
1330
July1st to 10thNight
32%9%13%24%17%4
2185
11th to 20thNight
24%10%24%29%9%4
2178
21st to endNight
22%7%12%32%22%4
2508
August1st to 10thNight
34%9%16%28%12%1
2521
11th to 20thNight
27%12%30%23%8%
2735
21st to endNight
25%9%23%31%11%1
3146
September1st to 10thNight
32%6%20%26%13%3
1843
11th to 20thNight
36%7%16%25%12%4
2076
21st to endNight
32%7%19%25%14%3
2090
October1st to 10thNight
31%7%17%27%17%1
3580
11th to 20thNight
28%8%22%29%12%1
4076
21st to endNight
32%8%15%35%10%
4457
November1st to 10thNight
42%9%15%20%11%2
2540
11th to 20thNight
35%9%18%22%14%1
2770
21st to endNight
38%9%18%21%10%4
2850
December1st to 10thNight
41%8%16%22%10%4
2850
11th to 20thNight
40%14%19%19%8%1
3507
21st to endNight
35%10%15%23%13%5%
5214

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 10thDay
7%14%38%27%10%4
180
11th to 20thDay
7%11%43%29%7%2
180
21st to endDay
10%17%44%19%8%3
198
February1st to 10thDay
15%19%36%19%7%4
180
11th to 20thDay
8%21%37%25%8%
248
21st to endDay
8%21%34%27%9%1
370
March1st to 10thDay
10%22%36%25%5%2
460
11th to 20thDay
10%25%34%22%6%3
460
21st to endDay
13%24%36%18%8%2
506
April1st to 10thDay
17%23%37%18%5%1
460
11th to 20thDay
17%22%31%20%8%1
452
21st to endDay
22%25%27%20%7%
460
May1st to 10thDay
21%18%27%21%10%2
472
11th to 20thDay
18%13%29%27%12%1
675
21st to endDay
22%10%24%28%13%2
734
June1st to 10thDay
20%17%31%22%9%1
680
11th to 20thDay
26%15%29%19%9%2
680
21st to endDay
13%13%30%26%15%3
680
July1st to 10thDay
14%7%29%28%18%3
671
11th to 20thDay
14%12%27%30%14%3
668
21st to endDay
9%11%31%32%14%3
635
August1st to 10thDay
11%9%33%31%11%4
487
11th to 20thDay
10%8%33%32%14%3
477
21st to endDay
12%13%33%26%12%3
539
September1st to 10thDay
14%16%34%24%11%3
490
11th to 20thDay
17%13%34%25%8%2
490
21st to endDay
16%23%30%23%6%1
490
October1st to 10thDay
15%18%32%22%11%2
435
11th to 20thDay
13%18%32%27%9%1
300
21st to endDay
17%19%35%21%7%1
330
November1st to 10thDay
17%17%39%22%41
282
11th to 20thDay
15%20%42%20%3
216
21st to endDay
9%23%34%19%11%4
180
December1st to 10thDay
5%18%42%27%7%1
180
11th to 20thDay
7%19%41%27%6%1
180
21st to endDay
6%14%43%26%8%3
198
January1st to 10thNight
10%18%46%21%5%1
950
11th to 20thNight
8%16%46%24%5%1
908
21st to endNight
8%22%41%22%6%
836
February1st to 10thNight
8%14%41%23%13%1
760
11th to 20thNight
8%14%40%28%8%1
744
21st to endNight
6%12%39%27%14%1
628
March1st to 10thNight
6%13%44%27%9%1
760
11th to 20thNight
8%15%39%29%7%1
760
21st to endNight
10%12%32%35%10%1
836
April1st to 10thNight
12%13%35%30%9%1
733
11th to 20thNight
16%11%36%28%9%
563
21st to endNight
16%15%32%27%9%
570
May1st to 10thNight
18%10%25%36%10%1
436
11th to 20thNight
13%6%26%38%16%1
374
21st to endNight
22%8%21%30%18%1
411
June1st to 10thNight
21%9%26%31%13%1
380
11th to 20thNight
22%9%26%26%16%1
380
21st to endNight
10%6%20%36%26%2
380
July1st to 10thNight
12%5%16%40%26%1
370
11th to 20thNight
13%223%42%18%1
368
21st to endNight
5%7%16%45%25%2
416
August1st to 10thNight
13%315%37%30%2
378
11th to 20thNight
11%317%41%25%2
499
21st to endNight
11%6%21%44%17%1
627
September1st to 10thNight
16%6%22%36%17%2
703
11th to 20thNight
19%7%20%35%18%2
760
21st to endNight
14%12%32%30%12%1
760
October1st to 10thNight
13%10%29%35%11%1
760
11th to 20thNight
13%10%37%31%8%1
760
21st to endNight
10%18%38%27%6%1
836
November1st to 10thNight
14%14%44%21%6%
831
11th to 20thNight
9%23%46%19%21
950
21st to endNight
8%19%43%23%6%1
950
December1st to 10thNight
7%18%44%23%8%
950
11th to 20thNight
5%18%44%26%7%
950
21st to endNight
6%17%44%23%9%1
1045
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