Ashcroft
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Ashcroft clear sky chart from 2005-11-06 to 2024-03-18.

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
42%
23150
10%
81417
7%
23051
45%
23051
15%
58857

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
25%
838
4%
4709
2%
816
28%
816
4%
3982
January11th to 20thNight
26%
834
10%
4661
2%
817
29%
817
5%
3453
January21st to endNight
29%
827
4%
4862
4%
814
34%
814
5%
4138
February1st to 10thNight
29%
760
9%
2571
6%
760
34%
760
10%
2042
February11th to 20thNight
40%
740
12%
2404
8%
740
46%
740
17%
1707
February21st to endNight
37%
628
9%
1979
8%
628
41%
628
14%
1491
March1st to 10thNight
38%
760
12%
2280
9%
760
43%
760
19%
1595
March11th to 20thNight
40%
752
14%
2095
7%
752
46%
752
23%
1436
March21st to endNight
41%
792
11%
2061
6%
792
43%
792
20%
1532
April1st to 10thNight
46%
720
10%
1800
5%
720
48%
720
23%
1295
April11th to 20thNight
41%
668
12%
1736
6%
668
45%
668
21%
1248
April21st to endNight
43%
388
14%
1468
14%
388
49%
388
18%
950
May1st to 10thNight
44%
360
10%
1440
12%
360
48%
360
16%
980
May11th to 20thNight
57%
354
10%
1416
17%
354
59%
354
19%
907
May21st to endNight
53%
388
5%
1503
6%
388
54%
388
17%
1008
June1st to 10thNight
43%
360
3%
1139
0%
360
43%
360
20%
790
June11th to 20thNight
46%
360
1%
1080
0%
360
46%
360
20%
774
June21st to endNight
56%
360
2%
1103
0%
360
56%
360
29%
680
July1st to 10thNight
58%
350
3%
1225
0%
350
58%
350
27%
737
July11th to 20thNight
60%
348
9%
1218
7%
348
61%
348
29%
691
July21st to endNight
73%
394
13%
1452
21%
372
77%
372
36%
715
August1st to 10thNight
72%
358
16%
1424
25%
356
74%
356
35%
691
August11th to 20thNight
71%
418
23%
1486
26%
418
75%
418
35%
778
August21st to endNight
61%
687
17%
1875
12%
687
63%
687
32%
1182
September1st to 10thNight
61%
720
19%
1800
11%
720
64%
720
39%
1110
September11th to 20thNight
61%
720
21%
1800
11%
720
63%
720
33%
1167
September21st to endNight
48%
720
17%
2040
11%
720
52%
720
27%
1311
October1st to 10thNight
52%
720
13%
2160
12%
720
55%
720
23%
1442
October11th to 20thNight
45%
720
13%
2164
10%
720
49%
720
21%
1487
October21st to endNight
36%
792
12%
2574
9%
792
42%
792
18%
1774
November1st to 10thNight
31%
740
9%
2590
6%
740
36%
740
12%
1951
November11th to 20thNight
34%
760
10%
2660
6%
760
39%
760
12%
1991
November21st to endNight
31%
779
7%
2679
4%
779
35%
779
10%
2114
December1st to 10thNight
35%
959
9%
2869
6%
959
38%
959
13%
2273
December11th to 20thNight
27%
1039
3%
3747
2%
1039
28%
1039
7%
3262
December21st to endNight
25%
1037
5%
5347
4%
1014
29%
1014
6%
4173

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%48%8%46%6%7%8%33%
78032
Night
6%10%49%8%46%6%7%8%31%
81692
TransparencyDay
47%10%16%18%8%1
77741
Night
48%12%16%16%7%1
81563
SeeingDay
11%15%31%26%14%3
14668
Night
11%8%29%33%18%2
23197

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
7%13%7%16%11%6%7%7%6%7%14%
2219
11th to 20thDay
10%9%6%9%9%5%6%6%7%10%24%
2203
21st to endDay
5%19%7%12%9%5%6%6%6%7%16%
2794
February1st to 10thDay
7%13%6%9%7%5%8%7%7%9%24%
1605
11th to 20thDay
5%11%5%8%7%47%7%8%9%31%
1665
21st to endDay
311%5%9%11%7%8%7%8%8%24%
1474
March1st to 10thDay
29%49%8%6%8%7%8%9%31%
1900
11th to 20thDay
37%37%8%5%7%8%9%10%33%
2028
21st to endDay
310%48%10%6%8%7%7%10%26%
2295
April1st to 10thDay
49%6%9%9%5%8%8%7%9%26%
2160
11th to 20thDay
6%10%6%8%9%5%6%7%8%8%27%
2173
21st to endDay
6%11%5%8%9%5%6%6%7%9%29%
2492
May1st to 10thDay
8%10%5%9%7%5%7%6%6%8%30%
2520
11th to 20thDay
7%8%37%8%47%5%8%10%33%
2477
21st to endDay
12%9%5%8%8%47%6%5%7%28%
2767
June1st to 10thDay
12%8%48%8%5%6%6%7%7%29%
2816
11th to 20thDay
15%8%48%10%5%7%6%7%7%23%
2880
21st to endDay
7%6%38%8%5%7%6%6%8%37%
2852
July1st to 10thDay
6%425%6%46%7%7%9%44%
2700
11th to 20thDay
6%4245%36%5%7%10%48%
2700
21st to endDay
43245%35%5%6%7%56%
2778
August1st to 10thDay
6%4244345%6%8%52%
2507
11th to 20thDay
4325%5%35%5%7%8%54%
2411
21st to endDay
7%5%37%6%46%6%7%8%41%
2480
September1st to 10thDay
6%5%25%5%45%46%7%51%
2160
11th to 20thDay
10%6%37%5%35%6%6%7%43%
2160
21st to endDay
9%6%37%6%46%5%5%9%40%
1918
October1st to 10thDay
8%8%47%6%45%5%7%6%42%
1800
11th to 20thDay
7%6%36%6%5%6%7%8%9%37%
1795
21st to endDay
8%11%37%8%46%5%8%9%31%
1782
November1st to 10thDay
7%11%5%9%8%47%6%6%8%28%
1488
11th to 20thDay
49%48%7%5%7%6%6%9%36%
1520
21st to endDay
5%10%6%9%9%5%7%7%8%10%25%
1479
December1st to 10thDay
5%12%7%10%10%5%7%8%6%9%22%
1309
11th to 20thDay
6%17%10%13%10%5%6%6%5%5%18%
1442
21st to endDay
411%5%12%10%6%8%8%8%8%20%
2283
January1st to 10thNight
8%17%7%13%9%5%7%6%7%7%14%
4726
11th to 20thNight
9%13%6%11%9%45%5%9%7%21%
4694
21st to endNight
6%15%6%12%10%6%8%7%6%7%16%
4862
February1st to 10thNight
9%12%5%11%11%5%6%6%6%7%22%
2571
11th to 20thNight
5%12%37%8%5%7%6%6%8%33%
2402
21st to endNight
313%6%10%8%5%7%6%7%8%27%
1979
March1st to 10thNight
311%5%9%7%47%6%7%11%30%
2280
11th to 20thNight
27%37%6%46%8%9%10%39%
2095
21st to endNight
38%47%7%5%7%7%9%10%33%
2061
April1st to 10thNight
38%39%7%47%7%7%9%37%
1800
11th to 20thNight
37%47%9%5%7%7%8%9%35%
1736
21st to endNight
5%9%47%7%35%6%7%10%37%
1468
May1st to 10thNight
8%8%5%9%8%35%46%8%36%
1440
11th to 20thNight
6%6%46%7%45%7%8%11%36%
1416
21st to endNight
12%8%36%6%46%5%8%10%32%
1503
June1st to 10thNight
13%5%37%7%45%6%7%9%34%
1139
11th to 20thNight
10%7%37%8%5%7%7%6%10%31%
1080
21st to endNight
5%6%26%5%5%5%6%7%7%45%
1103
July1st to 10thNight
6%7%35%6%36%6%7%8%46%
1260
11th to 20thNight
6%4345%36%5%7%8%49%
1260
21st to endNight
44135%36%5%5%10%55%
1537
August1st to 10thNight
4315%4335%7%9%55%
1432
11th to 20thNight
5%414435%5%6%7%56%
1486
21st to endNight
7%426%5%46%6%7%8%45%
1875
September1st to 10thNight
4425%5%35%5%5%8%54%
1800
11th to 20thNight
8%6%245%35%5%6%8%47%
1800
21st to endNight
7%7%35%5%35%5%6%9%45%
2040
October1st to 10thNight
7%7%36%6%46%6%6%8%42%
2160
11th to 20thNight
8%8%37%6%35%6%6%8%40%
2164
21st to endNight
6%10%48%8%45%6%6%7%36%
2574
November1st to 10thNight
9%11%49%8%46%6%6%8%28%
2590
11th to 20thNight
5%9%410%8%46%7%7%8%32%
2660
21st to endNight
7%12%7%9%8%5%6%6%7%9%23%
2679
December1st to 10thNight
5%12%7%11%9%46%6%7%8%25%
2869
11th to 20thNight
10%17%8%14%9%45%5%6%7%16%
3750
21st to endNight
6%13%5%10%10%6%9%8%7%7%19%
5401

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
63%18%10%8%1
2219
11th to 20thDay
53%12%18%8%26%
2224
21st to endDay
66%12%11%9%2
2794
February1st to 10thDay
57%11%13%11%6%1
1605
11th to 20thDay
48%11%17%16%9%
1674
21st to endDay
56%10%14%14%5%1
1474
March1st to 10thDay
48%11%18%15%7%1
1900
11th to 20thDay
45%11%21%18%5%
2028
21st to endDay
54%10%19%14%2
2295
April1st to 10thDay
54%11%17%13%4
2160
11th to 20thDay
53%10%12%15%8%1
2173
21st to endDay
52%8%16%17%7%
2492
May1st to 10thDay
51%8%17%15%9%
2520
11th to 20thDay
46%9%19%18%8%
2480
21st to endDay
54%7%14%17%6%1
2768
June1st to 10thDay
54%8%13%14%8%3
2816
11th to 20thDay
58%8%15%13%5%
2880
21st to endDay
42%7%19%18%11%2
2852
July1st to 10thDay
35%7%17%21%17%3
2626
11th to 20thDay
31%8%18%27%14%3
2619
21st to endDay
24%7%16%29%21%4
2623
August1st to 10thDay
28%8%17%27%18%2
2490
11th to 20thDay
26%7%19%28%17%3
2411
21st to endDay
37%8%18%26%9%2
2480
September1st to 10thDay
32%8%18%28%12%3
2160
11th to 20thDay
41%8%14%23%13%2
2160
21st to endDay
43%9%20%18%9%2
1918
October1st to 10thDay
42%10%16%25%7%
1800
11th to 20thDay
43%12%20%20%6%
1795
21st to endDay
49%11%16%19%4
1782
November1st to 10thDay
56%10%13%17%41
1488
11th to 20thDay
46%16%15%17%6%
1520
21st to endDay
51%15%17%12%41
1479
December1st to 10thDay
58%13%14%12%2
1309
11th to 20thDay
65%13%10%9%3
1444
21st to endDay
57%16%14%10%2
2283
January1st to 10thNight
63%17%12%6%2
4726
11th to 20thNight
58%11%14%9%35%
4735
21st to endNight
65%15%11%7%3
4862
February1st to 10thNight
58%12%11%13%5%1
2571
11th to 20thNight
49%9%17%17%8%1
2404
21st to endNight
53%10%17%14%5%
1979
March1st to 10thNight
45%11%20%16%8%
2280
11th to 20thNight
38%13%20%22%6%1
2096
21st to endNight
45%13%21%17%4
2061
April1st to 10thNight
43%11%20%19%6%
1800
11th to 20thNight
44%12%16%18%10%
1736
21st to endNight
41%11%16%20%11%
1468
May1st to 10thNight
46%11%15%18%9%1
1440
11th to 20thNight
39%13%18%22%8%1
1416
21st to endNight
45%10%19%18%7%
1503
June1st to 10thNight
47%8%14%19%9%3
1139
11th to 20thNight
47%10%17%16%10%
1080
21st to endNight
35%8%21%21%11%4
1103
July1st to 10thNight
34%9%16%22%15%3
1225
11th to 20thNight
28%11%18%26%15%3
1218
21st to endNight
23%8%15%29%20%5%
1452
August1st to 10thNight
23%8%18%27%20%4
1424
11th to 20thNight
26%8%17%28%18%3
1486
21st to endNight
33%9%20%25%11%1
1875
September1st to 10thNight
29%8%17%30%14%3
1800
11th to 20thNight
35%7%16%24%15%3
1800
21st to endNight
36%10%22%20%11%2
2040
October1st to 10thNight
42%9%16%25%8%
2160
11th to 20thNight
44%9%19%21%7%
2164
21st to endNight
46%9%19%20%6%
2574
November1st to 10thNight
54%11%16%14%41
2590
11th to 20thNight
49%16%15%13%6%1
2660
21st to endNight
55%14%15%10%4
2679
December1st to 10thNight
55%13%14%13%4
2869
11th to 20thNight
65%15%10%7%3
3747
21st to endNight
58%15%14%10%3
5401

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
6%16%38%25%9%6%
180
11th to 20thDay
7%14%32%30%14%3
180
21st to endDay
15%10%37%25%11%1
198
February1st to 10thDay
10%16%48%20%5%1
265
11th to 20thDay
10%12%39%27%10%2
365
21st to endDay
8%17%39%23%10%2
337
March1st to 10thDay
10%20%35%21%12%1
460
11th to 20thDay
9%22%35%18%13%2
449
21st to endDay
13%24%31%20%9%2
462
April1st to 10thDay
15%22%30%25%7%1
420
11th to 20thDay
17%22%28%18%12%3
412
21st to endDay
13%22%30%22%10%2
420
May1st to 10thDay
12%20%32%25%10%2
423
11th to 20thDay
13%10%30%28%14%5%
448
21st to endDay
13%12%29%29%13%3
529
June1st to 10thDay
15%19%30%25%10%1
746
11th to 20thDay
17%13%27%27%14%1
810
21st to endDay
10%10%28%30%20%2
782
July1st to 10thDay
8%12%31%30%17%2
621
11th to 20thDay
6%14%29%30%17%4
618
21st to endDay
47%24%35%26%4
524
August1st to 10thDay
7%8%23%30%28%5%
447
11th to 20thDay
5%10%23%35%22%5%
437
21st to endDay
7%13%28%32%15%6%
495
September1st to 10thDay
9%16%30%30%12%3
450
11th to 20thDay
15%13%26%27%16%4
450
21st to endDay
14%19%32%23%10%2
450
October1st to 10thDay
15%14%30%22%14%4
450
11th to 20thDay
13%22%28%22%14%1
445
21st to endDay
17%12%34%26%11%1
297
November1st to 10thDay
14%19%35%17%13%1
180
11th to 20thDay
11%10%42%22%12%4
180
21st to endDay
11%12%36%28%8%7%
180
December1st to 10thDay
9%7%32%27%20%5%
180
11th to 20thDay
8%11%33%28%13%7%
180
21st to endDay
11%10%35%33%10%2
198
January1st to 10thNight
15%10%36%28%10%2
850
11th to 20thNight
13%7%35%32%12%1
847
21st to endNight
10%6%36%31%14%2
836
February1st to 10thNight
14%7%34%32%12%1
760
11th to 20thNight
10%6%32%36%14%1
744
21st to endNight
8%10%35%29%17%2
628
March1st to 10thNight
10%9%33%31%16%1
760
11th to 20thNight
5%13%35%30%16%2
752
21st to endNight
8%9%32%32%17%2
792
April1st to 10thNight
8%10%25%34%21%2
720
11th to 20thNight
5%9%34%34%17%1
668
21st to endNight
6%9%34%32%18%1
388
May1st to 10thNight
9%8%29%33%20%2
360
11th to 20thNight
9%5%22%39%23%3
354
21st to endNight
16%321%35%23%2
389
June1st to 10thNight
13%8%26%33%19%1
360
11th to 20thNight
14%6%22%39%17%2
360
21st to endNight
6%6%25%36%26%2
360
July1st to 10thNight
7%422%41%24%3
350
11th to 20thNight
7%5%19%38%27%3
348
21st to endNight
5%313%42%35%3
394
August1st to 10thNight
5%313%33%40%6%
358
11th to 20thNight
5%416%36%35%5%
418
21st to endNight
8%5%20%37%30%2
687
September1st to 10thNight
7%5%20%41%25%2
720
11th to 20thNight
11%5%17%29%31%7%
720
21st to endNight
12%10%24%30%20%4
720
October1st to 10thNight
11%9%22%33%23%2
720
11th to 20thNight
14%9%27%30%18%3
720
21st to endNight
14%9%32%32%11%3
792
November1st to 10thNight
16%9%33%31%10%1
740
11th to 20thNight
12%10%34%31%12%2
760
21st to endNight
14%11%31%31%10%3
779
December1st to 10thNight
10%7%31%36%14%2
959
11th to 20thNight
14%9%35%32%9%1
1040
21st to endNight
13%10%36%31%10%1
1044
Page generated at 2024-03-15 11:01:42. Version ac07

Copyright © 2024 Attilla Danko.


Ashcroft Clear Sky Chart |Charts Home