Ashcroft
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Ashcroft clear sky chart from 2005-11-05 to 2018-02-22.

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
44%
15400
9%
48902
7%
15373
47%
15373
17%
35306

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
28%
823
3%
2911
2%
821
30%
821
6%
2495
January16th to endNight
30%
846
5%
2974
3%
846
33%
846
8%
2463
February1st to 15thNight
35%
758
8%
2552
7%
758
39%
758
11%
1999
February16th to endNight
47%
660
10%
2105
9%
660
50%
660
19%
1481
March1st to 15thNight
36%
720
10%
2118
5%
720
41%
720
17%
1513
March16th to endNight
39%
768
10%
2029
4%
767
43%
767
19%
1490
April1st to 15thNight
45%
719
9%
1799
4%
719
48%
719
21%
1287
April16th to endNight
45%
468
12%
1548
11%
468
49%
468
17%
1080
May1st to 15thNight
51%
359
11%
1439
15%
359
55%
359
17%
959
May16th to endNight
53%
374
4%
1463
5%
374
54%
374
15%
1030
June1st to 15thNight
51%
360
2%
1119
0%
360
51%
360
20%
781
June16th to endNight
48%
360
2%
1096
0%
360
48%
360
24%
730
July1st to 15thNight
66%
340
3%
1190
1%
340
66%
340
31%
670
July16th to endNight
67%
376
10%
1335
14%
354
70%
354
32%
713
August1st to 15thNight
77%
360
16%
1432
24%
358
79%
358
34%
705
August16th to endNight
65%
619
18%
1765
15%
619
67%
619
34%
1059
September1st to 15thNight
68%
720
19%
1800
11%
720
70%
720
40%
1095
September16th to endNight
57%
716
19%
1961
12%
716
60%
716
30%
1247
October1st to 15thNight
51%
720
12%
2160
11%
720
53%
720
22%
1458
October16th to endNight
42%
768
10%
2440
7%
768
47%
768
18%
1713
November1st to 15thNight
31%
760
8%
2660
6%
760
35%
760
12%
2035
November16th to endNight
32%
793
7%
2743
4%
793
35%
793
9%
2194
December1st to 15thNight
36%
993
7%
3003
5%
993
38%
993
11%
2421
December16th to endNight
30%
1020
8%
3260
4%
1020
34%
1020
10%
2688

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
6%8%47%7%46%6%6%8%31%
49369
Night
6%9%48%7%46%6%7%8%31%
49060
TransparencyDay
49%9%16%17%7%
49027
Night
48%11%16%17%6%
48907
SeeingDay
12%14%29%27%12%2
6707
Night
10%7%26%34%18%2
15410

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
5%10%7%12%12%6%7%7%7%7%13%
1358
16th to endDay
5%12%6%11%9%47%7%8%8%18%
1602
February1st to 15thDay
8%11%6%9%7%47%6%6%8%23%
1640
16th to endDay
39%47%9%5%7%7%7%9%27%
1514
March1st to 15thDay
27%49%8%5%7%7%8%9%27%
1841
16th to endDay
28%47%9%5%8%7%8%9%26%
2190
April1st to 15thDay
5%9%6%10%9%5%7%6%7%8%23%
2149
16th to endDay
6%9%6%8%9%46%6%7%8%24%
2412
May1st to 15thDay
6%9%48%7%47%5%6%7%30%
2511
16th to endDay
11%9%48%8%5%8%5%6%7%23%
2645
June1st to 15thDay
14%7%5%7%8%5%6%5%6%6%25%
2838
16th to endDay
8%7%38%9%47%6%6%7%28%
2861
July1st to 15thDay
5%4245%36%5%6%9%45%
2700
16th to endDay
5%3245%36%5%6%8%47%
2739
August1st to 15thDay
4425%435%5%7%9%48%
2520
16th to endDay
4426%6%45%6%7%7%43%
2436
September1st to 15thDay
6%415%5%3445%7%51%
2160
16th to endDay
9%6%26%5%36%5%6%9%38%
1998
October1st to 15thDay
6%6%36%5%45%5%7%8%39%
1800
16th to endDay
8%9%36%7%46%6%8%9%29%
1783
November1st to 15thDay
7%10%38%8%47%6%5%10%28%
1528
16th to endDay
310%7%9%8%5%6%6%7%9%24%
1532
December1st to 15thDay
411%8%10%9%46%6%5%7%24%
1286
16th to endDay
5%12%6%12%10%5%6%6%5%7%20%
1326
January1st to 15thNight
6%16%6%10%10%5%9%7%7%6%12%
2911
16th to endNight
6%13%6%12%10%5%8%7%6%6%16%
2974
February1st to 15thNight
10%12%49%9%45%5%5%6%23%
2540
16th to endNight
39%48%6%47%5%7%9%31%
2105
March1st to 15thNight
39%38%6%47%6%8%10%32%
2118
16th to endNight
27%36%5%47%8%9%10%33%
2029
April1st to 15thNight
37%27%7%46%6%8%9%35%
1799
16th to endNight
39%47%7%46%6%7%10%32%
1548
May1st to 15thNight
6%7%38%6%35%5%7%8%37%
1439
16th to endNight
12%7%36%6%36%6%8%9%28%
1463
June1st to 15thNight
11%5%26%7%36%7%6%9%33%
1119
16th to endNight
6%6%36%7%5%6%5%6%8%37%
1096
July1st to 15thNight
4422426%5%7%8%50%
1260
16th to endNight
5%313425%5%6%10%51%
1427
August1st to 15thNight
335%33447%9%54%
1440
16th to endNight
4415%5%35%6%7%7%48%
1765
September1st to 15thNight
5%324424446%55%
1800
16th to endNight
7%5%24435%5%5%8%47%
1961
October1st to 15thNight
6%7%37%6%35%5%5%6%41%
2160
16th to endNight
6%7%38%7%46%6%6%8%33%
2440
November1st to 15thNight
8%10%48%8%46%6%6%9%27%
2660
16th to endNight
6%11%6%10%7%5%6%5%8%8%22%
2743
December1st to 15thNight
5%12%7%11%9%46%5%7%8%22%
3003
16th to endNight
5%15%6%11%9%5%6%6%7%8%18%
3260

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%11%11%8%1
1358
16th to endDay
57%13%15%11%2
1602
February1st to 15thDay
58%11%13%12%3
1640
16th to endDay
50%10%16%16%6%
1514
March1st to 15thDay
51%11%19%12%3
1841
16th to endDay
54%9%20%13%2
2190
April1st to 15thDay
58%9%14%13%3
2149
16th to endDay
56%9%15%13%4
2412
May1st to 15thDay
50%7%16%15%9%
2511
16th to endDay
59%8%15%13%3
2649
June1st to 15thDay
58%7%13%13%6%1
2838
16th to endDay
50%7%16%15%8%
2861
July1st to 15thDay
34%6%15%23%16%3
2541
16th to endDay
31%7%17%29%12%1
2569
August1st to 15thDay
31%8%17%27%13%1
2503
16th to endDay
36%7%19%24%10%1
2436
September1st to 15thDay
32%7%15%27%14%1
2160
16th to endDay
43%9%18%17%8%2
1998
October1st to 15thDay
42%10%18%22%7%
1800
16th to endDay
51%12%16%16%3
1783
November1st to 15thDay
54%13%10%16%5%
1528
16th to endDay
52%13%15%13%3
1532
December1st to 15thDay
57%12%14%13%1
1286
16th to endDay
60%12%11%12%3
1326
January1st to 15thNight
65%13%11%7%1
2911
16th to endNight
61%13%12%8%2
2974
February1st to 15thNight
58%10%12%14%3
2552
16th to endNight
47%8%20%17%5%
2105
March1st to 15thNight
44%11%20%16%5%
2118
16th to endNight
43%13%21%17%3
2033
April1st to 15thNight
45%9%19%19%6%
1799
16th to endNight
45%12%17%18%6%
1548
May1st to 15thNight
44%10%13%20%10%
1440
16th to endNight
47%11%20%15%4
1463
June1st to 15thNight
45%9%15%19%8%1
1119
16th to endNight
42%7%19%20%8%1
1096
July1st to 15thNight
30%8%15%24%17%3
1190
16th to endNight
28%8%18%28%14%2
1335
August1st to 15thNight
24%7%19%28%16%3
1432
16th to endNight
31%7%19%26%11%3
1765
September1st to 15thNight
28%6%15%30%17%1
1800
16th to endNight
35%8%19%22%11%3
1961
October1st to 15thNight
43%8%17%22%8%
2160
16th to endNight
46%9%21%18%3
2440
November1st to 15thNight
53%12%14%13%5%
2660
16th to endNight
56%14%13%10%3
2743
December1st to 15thNight
56%14%14%12%3
3003
16th to endNight
61%11%10%11%4
3260

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
3221%31%26%15%
90
16th to endDay
13%11%37%25%10%2
96
February1st to 15thDay
15%11%34%30%7%1
210
16th to endDay
9%13%33%30%10%2
237
March1st to 15thDay
15%26%33%21%3
270
16th to endDay
13%28%38%14%4
288
April1st to 15thDay
18%16%31%24%9%
269
16th to endDay
16%27%28%21%5%1
270
May1st to 15thDay
13%17%33%25%7%2
288
16th to endDay
18%11%24%25%16%3
360
June1st to 15thDay
18%13%24%27%13%1
633
16th to endDay
13%13%28%28%15%1
656
July1st to 15thDay
9%15%27%32%13%2
475
16th to endDay
6%11%29%35%14%2
408
August1st to 15thDay
5%8%23%32%23%5%
315
16th to endDay
7%12%32%30%14%3
332
September1st to 15thDay
9%16%28%27%14%3
315
16th to endDay
16%11%31%26%9%4
315
October1st to 15thDay
14%20%31%20%9%3
315
16th to endDay
14%10%29%31%14%
199
November1st to 15thDay
13%20%36%15%12%2
90
16th to endDay
13%7%34%25%10%8%
90
December1st to 15thDay
27%24%28%24%12%
90
16th to endDay
10%230%38%16%2
96
January1st to 15thNight
13%9%32%27%15%2
825
16th to endNight
11%6%34%32%13%2
846
February1st to 15thNight
15%7%25%35%13%1
764
16th to endNight
6%5%28%37%19%1
660
March1st to 15thNight
9%13%32%32%9%2
720
16th to endNight
5%12%32%32%15%2
768
April1st to 15thNight
8%9%23%34%21%2
719
16th to endNight
8%5%31%37%15%1
468
May1st to 15thNight
10%6%23%38%19%2
360
16th to endNight
17%315%35%25%2
375
June1st to 15thNight
12%6%20%36%20%2
360
16th to endNight
9%5%25%39%19%1
360
July1st to 15thNight
6%417%39%30%2
340
16th to endNight
7%414%39%32%2
376
August1st to 15thNight
5%11%32%43%7%
360
16th to endNight
8%315%36%33%2
619
September1st to 15thNight
8%412%35%31%6%
720
16th to endNight
11%6%19%32%26%4
716
October1st to 15thNight
12%5%23%34%20%2
720
16th to endNight
12%7%28%32%15%2
768
November1st to 15thNight
13%10%34%30%9%1
760
16th to endNight
13%10%30%31%10%3
793
December1st to 15thNight
12%6%26%37%13%2
993
16th to endNight
10%6%36%35%9%
1020
Page generated at 2018-02-23 08:21:33. Version ac04

Copyright 2018 A. Danko


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