Martz Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Martz Observatory clear sky chart from 2005-11-05 to 2018-03-21.

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
25%
15714
11%
49264
7%
15675
30%
15675
12%
37332

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
8%
777
6%
2638
3%
776
12%
776
4%
2304
January16th to endNight
9%
832
5%
2704
2%
832
13%
832
4%
2341
February1st to 15thNight
8%
763
5%
2482
2%
761
12%
761
5%
2163
February16th to endNight
10%
683
8%
2150
2%
683
17%
683
7%
1801
March1st to 15thNight
13%
780
11%
2145
5%
780
18%
780
8%
1766
March16th to endNight
18%
792
15%
2178
6%
792
26%
792
12%
1656
April1st to 15thNight
18%
718
11%
1815
4%
718
23%
718
15%
1402
April16th to endNight
26%
608
17%
1688
4%
608
35%
608
20%
1161
May1st to 15thNight
27%
522
14%
1602
7%
522
35%
522
14%
1150
May16th to endNight
35%
374
17%
1497
15%
374
43%
374
16%
928
June1st to 15thNight
32%
360
12%
1440
9%
360
42%
360
16%
924
June16th to endNight
34%
360
13%
1440
11%
360
45%
360
16%
903
July1st to 15thNight
50%
340
14%
1360
18%
340
54%
340
21%
801
July16th to endNight
46%
535
14%
1566
9%
502
55%
502
25%
959
August1st to 15thNight
55%
539
16%
1609
12%
536
58%
536
27%
1020
August16th to endNight
55%
654
19%
1800
12%
654
58%
654
31%
1137
September1st to 15thNight
43%
720
19%
1800
12%
720
46%
720
27%
1244
September16th to endNight
46%
717
20%
2011
16%
717
48%
717
24%
1350
October1st to 15thNight
35%
720
15%
2160
13%
720
39%
720
19%
1515
October16th to endNight
19%
768
12%
2304
7%
768
26%
768
12%
1780
November1st to 15thNight
27%
760
16%
2503
12%
760
33%
760
14%
1792
November16th to endNight
14%
780
9%
2730
5%
780
21%
780
7%
2196
December1st to 15thNight
10%
780
4%
2730
2%
780
12%
780
3%
2391
December16th to endNight
6%
832
2%
2912
0%
832
8%
832
3%
2648

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
18%11%5%7%6%34446%27%
49578
Night
17%12%5%8%6%34445%27%
49446
Cloud CoverDay
18%11%5%7%6%34446%26%
49588
Night
17%12%5%8%6%34445%27%
49450
TransparencyDay
57%5%10%15%8%
49278
Night
58%5%10%15%8%1
49264
SeeingDay
24%20%24%17%9%4
5998
Night
21%26%22%18%9%1
15719

By Month

Percentage Cloud Cover NE (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
17%17%9%13%10%2433313%
1630
16th to endDay
13%16%11%16%10%4433411%
1872
February1st to 15thDay
17%19%10%13%9%4332312%
1710
16th to endDay
17%16%6%11%9%2432419%
1607
March1st to 15thDay
17%18%7%10%5%2433421%
2134
16th to endDay
17%12%7%7%5%23346%28%
2174
April1st to 15thDay
20%15%5%5%423445%28%
2131
16th to endDay
20%9%24433336%37%
2283
May1st to 15thDay
19%10%47%6%24446%30%
2346
16th to endDay
17%5%35%435%5%5%7%36%
2618
June1st to 15thDay
19%6%36%5%245%5%6%32%
2520
16th to endDay
18%6%25%435%5%6%9%32%
2520
July1st to 15thDay
12%5%36%7%46%5%6%7%34%
2520
16th to endDay
14%6%35%6%36%6%7%10%30%
2493
August1st to 15thDay
14%7%26%6%446%7%8%31%
2340
16th to endDay
15%6%25%6%35%5%7%9%32%
2389
September1st to 15thDay
22%7%36%5%2345%6%32%
2159
16th to endDay
17%6%35%5%35%5%5%7%35%
1947
October1st to 15thDay
22%8%36%6%24446%30%
1800
16th to endDay
27%13%47%5%34335%21%
1920
November1st to 15thDay
15%16%36%5%2435%7%28%
1681
16th to endDay
21%21%6%7%5%23435%18%
1560
December1st to 15thDay
18%23%11%11%5%2333313%
1560
16th to endDay
19%22%12%15%7%333227%
1664
January1st to 15thNight
18%18%8%14%9%3433312%
2638
16th to endNight
14%18%10%13%10%4433313%
2704
February1st to 15thNight
16%18%8%13%11%45%23213%
2480
16th to endNight
15%13%7%15%10%3433318%
2150
March1st to 15thNight
17%15%7%11%6%3433420%
2133
16th to endNight
14%12%7%8%5%34345%29%
2178
April1st to 15thNight
22%13%44424345%30%
1815
16th to endNight
14%11%245%34347%38%
1688
May1st to 15thNight
18%7%26%6%245%46%34%
1602
16th to endNight
12%6%25%435%447%42%
1495
June1st to 15thNight
14%7%25%5%245%5%7%38%
1440
16th to endNight
14%6%25%425%5%6%8%38%
1440
July1st to 15thNight
9%5%246%3346%7%46%
1440
16th to endNight
11%4245%245%6%9%43%
1673
August1st to 15thNight
9%4245%346%7%9%42%
1620
16th to endNight
11%5%235%2446%8%45%
1800
September1st to 15thNight
16%6%24434446%42%
1800
16th to endNight
17%6%25%423447%40%
2011
October1st to 15thNight
20%7%25%434346%36%
2160
16th to endNight
29%9%25%434345%25%
2304
November1st to 15thNight
18%13%45%423445%32%
2503
16th to endNight
18%21%6%7%43443420%
2730
December1st to 15thNight
20%21%10%11%6%3343312%
2730
16th to endNight
18%20%10%16%7%343338%
2912

Percentage Cloud Cover SE (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
18%16%8%12%10%2434413%
1630
16th to endDay
13%17%10%16%10%4434311%
1872
February1st to 15thDay
17%20%9%12%9%4421213%
1710
16th to endDay
18%15%6%12%8%2432419%
1607
March1st to 15thDay
18%17%8%11%5%2333421%
2145
16th to endDay
17%14%7%7%5%23345%28%
2173
April1st to 15thDay
21%13%6%4424445%27%
2131
16th to endDay
20%9%24423445%37%
2283
May1st to 15thDay
20%10%37%5%23447%29%
2346
16th to endDay
17%6%25%5%35%45%7%36%
2618
June1st to 15thDay
19%7%36%5%35%5%5%7%31%
2520
16th to endDay
18%6%15%435%5%6%9%31%
2520
July1st to 15thDay
12%6%27%6%36%6%5%8%34%
2520
16th to endDay
13%6%45%6%46%6%6%8%31%
2493
August1st to 15thDay
14%7%27%6%46%5%6%8%30%
2340
16th to endDay
15%6%16%5%45%6%7%9%31%
2389
September1st to 15thDay
21%8%35%6%33446%32%
2159
16th to endDay
16%6%36%5%34448%35%
1947
October1st to 15thDay
23%8%36%5%24446%31%
1800
16th to endDay
26%14%37%6%34335%22%
1920
November1st to 15thDay
16%16%35%43435%7%28%
1681
16th to endDay
22%21%6%7%413445%18%
1560
December1st to 15thDay
18%23%11%11%5%1333313%
1560
16th to endDay
20%21%12%16%6%233237%
1664
January1st to 15thNight
19%18%7%14%9%35%23312%
2638
16th to endNight
14%18%9%13%10%5%333313%
2704
February1st to 15thNight
15%18%8%13%11%45%33313%
2473
16th to endNight
15%13%7%14%10%45%33318%
2150
March1st to 15thNight
18%15%8%10%6%33335%20%
2145
16th to endNight
14%12%6%8%6%34345%29%
2178
April1st to 15thNight
22%13%44424446%29%
1815
16th to endNight
13%11%145%34448%37%
1688
May1st to 15thNight
19%6%35%5%3445%6%34%
1601
16th to endNight
13%7%3343445%7%42%
1495
June1st to 15thNight
15%5%35%5%245%5%7%37%
1440
16th to endNight
15%6%25%4345%5%8%38%
1440
July1st to 15thNight
9%5%25%5%345%5%8%45%
1440
16th to endNight
11%3244345%6%8%43%
1673
August1st to 15thNight
9%424435%6%6%10%41%
1620
16th to endNight
11%5%2343346%9%45%
1800
September1st to 15thNight
16%6%25%5%2445%5%41%
1800
16th to endNight
16%6%35%42335%7%40%
2011
October1st to 15thNight
19%7%36%434346%36%
2160
16th to endNight
28%11%34424445%25%
2304
November1st to 15thNight
18%13%35%423446%32%
2503
16th to endNight
19%20%6%8%5%24335%20%
2730
December1st to 15thNight
21%20%10%11%6%2443212%
2730
16th to endNight
19%19%10%15%8%343238%
2912

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
75%47%8%3
1631
16th to endDay
78%48%6%1
1872
February1st to 15thDay
79%45%7%3
1712
16th to endDay
69%39%12%4
1607
March1st to 15thDay
66%49%13%5%
2145
16th to endDay
57%48%19%8%1
2174
April1st to 15thDay
57%411%17%9%
2131
16th to endDay
49%5%9%18%15%2
2283
May1st to 15thDay
55%5%10%19%8%
2346
16th to endDay
46%6%14%18%11%1
2622
June1st to 15thDay
50%7%11%19%9%1
2520
16th to endDay
47%6%15%18%11%
2520
July1st to 15thDay
47%7%9%20%14%
2371
16th to endDay
47%8%15%17%10%
2337
August1st to 15thDay
48%8%13%18%10%
2327
16th to endDay
45%7%13%20%11%1
2389
September1st to 15thDay
52%6%10%19%11%
2159
16th to endDay
47%6%9%22%12%
1947
October1st to 15thDay
54%6%10%15%12%1
1800
16th to endDay
65%5%11%12%4
1920
November1st to 15thDay
54%5%11%14%10%2
1681
16th to endDay
68%5%9%11%41
1560
December1st to 15thDay
76%39%8%1
1560
16th to endDay
83%46%41
1664
January1st to 15thNight
77%46%6%4
2638
16th to endNight
76%48%7%2
2704
February1st to 15thNight
77%37%8%2
2482
16th to endNight
71%38%11%4
2150
March1st to 15thNight
67%5%6%14%5%
2145
16th to endNight
57%5%9%15%10%1
2178
April1st to 15thNight
56%5%10%17%10%
1815
16th to endNight
45%5%10%20%13%4
1688
May1st to 15thNight
49%8%10%20%10%1
1602
16th to endNight
40%8%12%22%13%2
1497
June1st to 15thNight
43%7%13%22%12%
1440
16th to endNight
41%8%12%24%11%1
1440
July1st to 15thNight
36%8%12%23%17%1
1360
16th to endNight
36%7%15%22%15%2
1566
August1st to 15thNight
35%8%16%28%10%1
1609
16th to endNight
34%7%15%26%13%1
1800
September1st to 15thNight
42%6%12%22%14%1
1800
16th to endNight
43%412%22%15%1
2011
October1st to 15thNight
49%5%11%17%16%
2160
16th to endNight
60%5%13%15%5%
2304
November1st to 15thNight
53%5%11%16%8%3
2503
16th to endNight
67%49%13%4
2730
December1st to 15thNight
78%48%6%2
2730
16th to endNight
82%47%4
2912

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
29%37%24%5%3
108
16th to endDay
26%36%29%6%
144
February1st to 15thDay
34%37%25%1
135
16th to endDay
33%27%33%5%
160
March1st to 15thDay
30%29%23%12%4
330
16th to endDay
27%28%24%13%41
311
April1st to 15thDay
29%28%19%14%6%1
270
16th to endDay
23%22%24%15%8%3
270
May1st to 15thDay
32%23%17%16%7%1
288
16th to endDay
18%21%25%19%9%4
331
June1st to 15thDay
20%20%26%21%8%2
315
16th to endDay
23%20%26%20%7%2
315
July1st to 15thDay
15%15%24%25%12%7%
305
16th to endDay
12%14%26%26%12%7%
326
August1st to 15thDay
15%11%22%23%15%10%
313
16th to endDay
17%10%20%22%14%14%
332
September1st to 15thDay
18%10%19%19%21%10%
315
16th to endDay
14%13%19%16%22%13%
314
October1st to 15thDay
22%12%25%21%12%5%
315
16th to endDay
34%20%25%13%5%
336
November1st to 15thDay
27%15%25%22%6%2
189
16th to endDay
34%23%31%8%2
90
December1st to 15thDay
36%26%23%6%5%1
90
16th to endDay
46%25%27%1
96
January1st to 15thNight
23%37%27%9%3
780
16th to endNight
23%39%23%11%1
832
February1st to 15thNight
25%36%25%11%1
764
16th to endNight
23%32%29%12%1
683
March1st to 15thNight
26%32%23%14%3
780
16th to endNight
21%31%24%17%4
792
April1st to 15thNight
26%29%23%16%4
718
16th to endNight
17%26%25%22%6%1
608
May1st to 15thNight
19%25%18%27%8%
522
16th to endNight
12%21%26%26%12%
375
June1st to 15thNight
15%20%26%26%10%
360
16th to endNight
13%21%24%29%10%
360
July1st to 15thNight
11%14%16%36%19%1
340
16th to endNight
12%18%15%28%22%1
535
August1st to 15thNight
10%12%16%32%25%1
539
16th to endNight
11%10%16%28%28%3
654
September1st to 15thNight
17%13%18%24%23%2
720
16th to endNight
16%15%15%20%23%7%
717
October1st to 15thNight
22%16%22%23%13%1
720
16th to endNight
33%19%25%17%4
768
November1st to 15thNight
22%24%22%22%6%1
760
16th to endNight
28%32%20%11%5%
780
December1st to 15thNight
31%36%18%10%3
780
16th to endNight
28%37%22%9%1
832
Page generated at 2018-03-22 11:34:19. Version ac04

Copyright 2018 A. Danko


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