Maycroft
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Maycroft clear sky chart from 2005-11-06 to 2024-01-13.

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%
23437
16%
74747
8%
23389
41%
23389
21%
46020

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
21%
950
15%
2836
5%
946
30%
946
16%
1841
January11th to 20thNight
22%
834
17%
2664
7%
834
33%
834
18%
1729
January21st to endNight
26%
792
21%
2772
9%
792
44%
792
20%
1588
February1st to 10thNight
28%
720
14%
2506
9%
720
37%
720
15%
1631
February11th to 20thNight
24%
704
15%
2273
7%
700
36%
700
16%
1481
February21st to endNight
29%
592
18%
1780
11%
592
40%
592
18%
1203
March1st to 10thNight
24%
720
15%
2160
7%
720
34%
720
18%
1415
March11th to 20thNight
30%
720
19%
2008
7%
720
41%
720
21%
1280
March21st to endNight
29%
792
13%
2142
3%
792
35%
792
19%
1478
April1st to 10thNight
26%
694
14%
1774
4%
694
33%
694
19%
1255
April11th to 20thNight
29%
533
16%
1601
8%
533
35%
533
18%
1063
April21st to endNight
28%
540
13%
1620
8%
540
34%
540
18%
1100
May1st to 10thNight
37%
490
10%
1570
9%
490
41%
490
19%
1024
May11th to 20thNight
49%
354
15%
1262
17%
354
53%
354
23%
751
May21st to endNight
39%
388
8%
1358
7%
388
41%
388
17%
922
June1st to 10thNight
40%
360
6%
1260
2%
360
44%
360
20%
777
June11th to 20thNight
32%
360
4%
1260
0%
360
34%
360
16%
841
June21st to endNight
51%
360
6%
1260
1%
360
54%
360
30%
668
July1st to 10thNight
58%
350
8%
1225
4%
350
60%
350
36%
623
July11th to 20thNight
57%
348
14%
1218
13%
348
62%
348
38%
601
July21st to endNight
62%
394
20%
1436
21%
372
73%
372
40%
627
August1st to 10thNight
63%
358
21%
1424
24%
356
72%
356
34%
687
August11th to 20thNight
61%
530
22%
1598
19%
530
65%
530
43%
835
August21st to endNight
48%
594
28%
1782
19%
594
54%
594
38%
959
September1st to 10thNight
49%
661
22%
1755
12%
661
52%
661
38%
1010
September11th to 20thNight
48%
720
22%
1980
13%
720
55%
720
35%
1167
September21st to endNight
37%
720
21%
1980
11%
720
45%
720
29%
1192
October1st to 10thNight
42%
720
20%
2038
11%
720
50%
720
26%
1285
October11th to 20thNight
35%
720
21%
2286
10%
720
49%
720
24%
1313
October21st to endNight
25%
792
17%
2574
6%
792
38%
792
17%
1638
November1st to 10thNight
21%
786
16%
2451
7%
786
32%
786
14%
1628
November11th to 20thNight
17%
950
19%
2686
4%
950
32%
950
17%
1680
November21st to endNight
21%
950
14%
2850
5%
950
30%
950
18%
1825
December1st to 10thNight
26%
950
17%
2850
9%
950
34%
950
18%
1824
December11th to 20thNight
21%
950
12%
3482
4%
949
30%
949
13%
2302
December21st to endNight
21%
1041
10%
5026
5%
1026
31%
1026
11%
2777

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%8%36%6%35%5%6%9%40%
74620
Night
5%7%37%6%35%5%6%9%44%
75131
TransparencyDay
40%7%16%23%12%2
74310
Night
36%8%18%24%12%2
74960
SeeingDay
18%22%28%20%10%2
14147
Night
14%19%28%26%12%2
23442

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
26%48%10%35%5%9%12%37%
1329
11th to 20thDay
16%37%6%5%7%6%9%12%38%
1375
21st to endDay
29%5%8%9%45%5%6%10%36%
1584
February1st to 10thDay
28%38%10%5%6%6%5%10%36%
1454
11th to 20thDay
210%5%9%7%46%5%7%10%33%
1575
21st to endDay
29%5%11%7%46%6%6%9%35%
1476
March1st to 10thDay
28%6%8%7%45%6%6%11%39%
1800
11th to 20thDay
48%5%7%5%35%7%7%10%38%
1951
21st to endDay
6%14%5%9%6%45%5%6%9%31%
2210
April1st to 10thDay
6%11%5%9%6%5%6%6%7%9%29%
2186
11th to 20thDay
8%14%6%9%6%35%5%7%7%31%
2310
21st to endDay
9%13%5%8%6%445%6%8%33%
2340
May1st to 10thDay
12%12%49%7%46%46%8%28%
2387
11th to 20thDay
14%10%36%5%35%5%6%8%33%
2629
21st to endDay
23%10%47%5%45%5%5%7%26%
2917
June1st to 10thDay
15%10%46%7%46%6%6%8%30%
2700
11th to 20thDay
19%9%37%6%46%5%6%7%28%
2700
21st to endDay
9%425%5%46%6%7%9%44%
2700
July1st to 10thDay
7%5%245%46%6%7%9%47%
2700
11th to 20thDay
8%3245%35%6%5%8%52%
2700
21st to endDay
43234345%6%7%60%
2794
August1st to 10thDay
9%424435%5%6%8%50%
2507
11th to 20thDay
7%3244345%6%8%54%
2302
21st to endDay
9%4145%345%6%7%51%
2574
September1st to 10thDay
12%6%234245%5%7%50%
2200
11th to 20thDay
11%6%2443446%7%48%
1980
21st to endDay
9%7%2443446%8%49%
1980
October1st to 10thDay
10%10%45%5%45%5%5%6%40%
1922
11th to 20thDay
5%8%47%6%4446%8%43%
1672
21st to endDay
411%46%5%446%6%10%40%
1782
November1st to 10thDay
6%12%46%5%26%5%8%9%38%
1608
11th to 20thDay
28%46%425%5%8%10%46%
1492
21st to endDay
39%5%9%6%35%5%5%8%43%
1330
December1st to 10thDay
26%48%6%36%6%9%9%43%
1330
11th to 20thDay
28%410%6%36%6%7%12%37%
1682
21st to endDay
16%46%7%35%5%7%10%45%
2442
January1st to 10thNight
26%5%7%8%35%6%8%12%40%
2836
11th to 20thNight
26%37%8%47%6%8%11%37%
2664
21st to endNight
17%36%445%6%7%11%44%
2772
February1st to 10thNight
38%410%8%46%6%7%10%36%
2506
11th to 20thNight
211%5%8%6%46%6%7%11%36%
2272
21st to endNight
26%5%10%7%47%6%6%7%38%
1780
March1st to 10thNight
18%5%8%8%5%45%7%11%38%
2160
11th to 20thNight
47%47%5%35%5%7%10%44%
2008
21st to endNight
48%5%9%5%35%6%8%10%36%
2142
April1st to 10thNight
6%9%5%9%6%35%47%7%38%
1774
11th to 20thNight
7%12%38%6%345%6%8%37%
1601
21st to endNight
7%11%5%8%6%45%6%5%7%37%
1620
May1st to 10thNight
11%10%45%5%36%46%8%37%
1570
11th to 20thNight
11%7%26%6%245%5%9%43%
1262
21st to endNight
21%8%35%5%35%5%47%35%
1358
June1st to 10thNight
12%7%26%6%35%6%6%8%40%
1260
11th to 20thNight
16%8%26%5%37%5%6%9%34%
1260
21st to endNight
5%5%23436%6%6%8%52%
1260
July1st to 10thNight
6%42443446%10%53%
1260
11th to 20thNight
5%4234235%5%8%60%
1260
21st to endNight
5%21332445%5%66%
1520
August1st to 10thNight
7%32442436%7%57%
1432
11th to 20thNight
7%3233235%6%9%57%
1598
21st to endNight
8%5%2432335%8%57%
1782
September1st to 10thNight
10%5%14323447%57%
1755
11th to 20thNight
11%7%2232346%8%52%
1980
21st to endNight
10%6%3342445%9%50%
1980
October1st to 10thNight
8%9%35%5%2345%7%47%
2038
11th to 20thNight
5%6%35%5%345%6%11%47%
2286
21st to endNight
5%8%47%6%35%6%7%10%40%
2574
November1st to 10thNight
5%11%47%6%35%5%6%8%40%
2451
11th to 20thNight
26%36%5%346%8%10%48%
2686
21st to endNight
27%5%7%5%45%5%6%10%43%
2850
December1st to 10thNight
26%48%7%35%6%7%10%42%
2850
11th to 20thNight
27%49%7%47%7%8%9%35%
3510
21st to endNight
17%48%7%45%6%6%9%44%
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%10%20%21%7%4
1329
11th to 20thDay
36%11%24%19%7%2
1375
21st to endDay
43%6%18%22%10%1
1584
February1st to 10thDay
43%8%19%20%8%2
1454
11th to 20thDay
44%9%18%21%8%1
1584
21st to endDay
45%7%15%22%9%2
1476
March1st to 10thDay
40%9%19%22%10%1
1800
11th to 20thDay
38%10%18%22%10%1
1952
21st to endDay
49%8%18%19%6%
2210
April1st to 10thDay
47%9%17%20%7%
2186
11th to 20thDay
51%7%14%19%8%1
2310
21st to endDay
49%6%16%21%7%1
2340
May1st to 10thDay
53%6%15%18%7%
2387
11th to 20thDay
47%7%14%22%8%1
2633
21st to endDay
56%6%15%15%7%
2918
June1st to 10thDay
50%8%14%19%8%1
2700
11th to 20thDay
53%7%11%18%10%1
2700
21st to endDay
34%7%17%26%14%2
2700
July1st to 10thDay
31%7%15%28%15%4
2626
11th to 20thDay
30%5%14%25%21%5%
2619
21st to endDay
22%6%12%29%26%6%
2639
August1st to 10thDay
30%6%15%26%18%6%
2490
11th to 20thDay
26%6%17%33%16%3
2302
21st to endDay
30%6%13%27%21%4
2574
September1st to 10thDay
33%5%12%27%17%5%
2200
11th to 20thDay
33%5%14%29%17%3
1980
21st to endDay
33%6%17%31%11%2
1980
October1st to 10thDay
42%7%16%23%10%1
1922
11th to 20thDay
38%7%17%25%12%1
1672
21st to endDay
39%9%19%21%10%2
1782
November1st to 10thDay
41%11%17%20%10%1
1608
11th to 20thDay
32%11%21%24%10%1
1492
21st to endDay
39%8%23%19%8%3
1330
December1st to 10thDay
35%9%24%19%10%3
1330
11th to 20thDay
38%10%24%21%7%
1684
21st to endDay
31%8%16%25%16%4
2442
January1st to 10thNight
37%10%21%20%9%3
2836
11th to 20thNight
38%10%20%21%8%2
2664
21st to endNight
32%8%19%26%13%1
2772
February1st to 10thNight
43%8%16%20%11%3
2506
11th to 20thNight
41%8%20%22%8%
2273
21st to endNight
45%7%13%23%11%2
1780
March1st to 10thNight
40%8%22%21%8%
2160
11th to 20thNight
35%8%22%22%12%1
2008
21st to endNight
41%9%20%20%8%1
2142
April1st to 10thNight
44%8%16%22%10%1
1774
11th to 20thNight
43%7%15%26%8%
1601
21st to endNight
45%7%14%25%8%1
1620
May1st to 10thNight
42%7%18%24%9%
1570
11th to 20thNight
37%7%16%30%10%1
1262
21st to endNight
50%5%17%20%8%
1358
June1st to 10thNight
41%5%18%25%9%1
1260
11th to 20thNight
46%7%16%20%10%1
1260
21st to endNight
26%8%21%28%15%2
1260
July1st to 10thNight
25%5%19%34%13%3
1225
11th to 20thNight
23%5%16%27%23%5%
1218
21st to endNight
19%5%13%29%26%7%
1436
August1st to 10thNight
26%5%15%29%20%5%
1424
11th to 20thNight
23%5%19%32%18%2
1598
21st to endNight
26%411%33%23%2
1782
September1st to 10thNight
28%414%32%15%5%
1755
11th to 20thNight
30%6%15%30%16%3
1980
21st to endNight
32%6%18%27%14%3
1980
October1st to 10thNight
36%7%16%26%15%1
2038
11th to 20thNight
31%7%17%29%13%3
2286
21st to endNight
39%9%17%24%11%
2574
November1st to 10thNight
42%9%18%20%9%1
2451
11th to 20thNight
30%12%21%23%13%1
2686
21st to endNight
36%9%22%19%11%3
2850
December1st to 10thNight
37%9%21%19%11%3
2850
11th to 20thNight
41%11%22%19%6%
3507
21st to endNight
36%8%18%20%14%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
15%26%29%18%5%7%
180
11th to 20thDay
18%21%30%23%7%2
165
21st to endDay
12%33%37%9%6%3
176
February1st to 10thDay
21%26%37%11%41
166
11th to 20thDay
18%24%32%19%6%1
240
21st to endDay
17%25%35%17%6%
342
March1st to 10thDay
18%31%32%12%6%2
420
11th to 20thDay
18%29%28%15%8%2
420
21st to endDay
22%34%24%13%5%2
462
April1st to 10thDay
20%27%34%15%4
420
11th to 20thDay
21%29%28%15%6%1
412
21st to endDay
25%26%25%16%6%1
420
May1st to 10thDay
20%20%28%19%10%2
423
11th to 20thDay
24%17%22%20%14%4
600
21st to endDay
25%14%20%24%14%2
679
June1st to 10thDay
20%23%25%20%11%2
630
11th to 20thDay
24%24%22%19%8%2
630
21st to endDay
11%16%29%25%16%4
630
July1st to 10thDay
10%15%26%28%18%3
621
11th to 20thDay
11%18%28%25%16%2
618
21st to endDay
6%16%35%27%14%2
540
August1st to 10thDay
13%17%30%28%10%2
447
11th to 20thDay
8%15%35%26%12%4
437
21st to endDay
13%19%33%22%10%3
495
September1st to 10thDay
19%23%28%20%8%2
450
11th to 20thDay
16%19%34%21%9%2
450
21st to endDay
22%26%28%15%6%2
450
October1st to 10thDay
19%23%26%21%9%2
392
11th to 20thDay
17%27%25%19%11%1
270
21st to endDay
24%24%29%13%7%2
297
November1st to 10thDay
26%29%24%18%41
270
11th to 20thDay
21%33%31%11%4
257
21st to endDay
21%27%25%13%8%5%
180
December1st to 10thDay
16%32%23%19%9%2
180
11th to 20thDay
21%27%31%16%42
180
21st to endDay
14%23%32%19%9%3
198
January1st to 10thNight
18%24%31%20%6%1
950
11th to 20thNight
11%24%36%22%6%1
834
21st to endNight
10%27%31%23%8%2
792
February1st to 10thNight
11%20%33%23%9%3
720
11th to 20thNight
14%19%32%27%6%1
704
21st to endNight
12%16%33%24%14%1
592
March1st to 10thNight
9%23%34%21%11%1
720
11th to 20thNight
13%23%27%27%9%2
720
21st to endNight
13%21%26%29%9%2
792
April1st to 10thNight
14%20%29%25%10%2
694
11th to 20thNight
15%24%25%25%10%1
533
21st to endNight
16%18%30%25%9%1
540
May1st to 10thNight
18%16%23%25%17%1
490
11th to 20thNight
19%10%16%29%25%2
354
21st to endNight
24%11%18%26%20%1
389
June1st to 10thNight
16%16%21%31%14%3
360
11th to 20thNight
23%14%24%24%14%1
360
21st to endNight
9%11%22%36%22%1
360
July1st to 10thNight
7%8%20%38%26%1
350
11th to 20thNight
7%7%23%43%17%2
348
21st to endNight
7%7%19%41%24%2
394
August1st to 10thNight
10%5%14%40%30%1
358
11th to 20thNight
8%7%21%38%24%2
530
21st to endNight
10%12%24%34%18%2
594
September1st to 10thNight
13%11%22%30%20%4
661
11th to 20thNight
19%9%20%29%18%5%
720
21st to endNight
14%17%27%24%14%3
720
October1st to 10thNight
16%17%20%32%15%2
720
11th to 20thNight
13%23%23%27%13%2
720
21st to endNight
15%25%27%23%9%1
792
November1st to 10thNight
20%27%26%21%6%1
786
11th to 20thNight
18%29%31%16%41
950
21st to endNight
14%25%34%18%7%1
950
December1st to 10thNight
12%24%31%23%9%2
950
11th to 20thNight
13%24%34%24%5%
950
21st to endNight
13%23%34%20%8%1
1045
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