Marfa
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Marfa clear sky chart from 2005-11-05 to 2017-12-02.

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
64%
15672
32%
47986
24%
15630
72%
15630
45%
24401

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
57%
716
35%
2148
23%
716
69%
716
45%
1110
January16th to endNight
54%
768
38%
2304
24%
768
67%
768
46%
1155
February1st to 15thNight
56%
702
37%
2106
22%
696
71%
696
54%
981
February16th to endNight
47%
632
34%
1894
18%
632
61%
632
50%
919
March1st to 15thNight
52%
720
36%
2133
20%
720
65%
720
49%
1057
March16th to endNight
50%
654
37%
1998
22%
654
65%
654
50%
955
April1st to 15thNight
46%
539
35%
1798
21%
539
64%
539
43%
857
April16th to endNight
50%
540
36%
1800
24%
540
70%
540
51%
793
May1st to 15thNight
50%
539
29%
1799
21%
539
66%
539
46%
849
May16th to endNight
60%
561
26%
1784
25%
561
67%
561
40%
937
June1st to 15thNight
73%
540
24%
1620
23%
540
77%
540
49%
818
June16th to endNight
78%
540
24%
1638
25%
540
80%
540
40%
888
July1st to 15thNight
80%
510
19%
1700
22%
510
81%
510
37%
923
July16th to endNight
81%
564
22%
1771
25%
531
82%
531
34%
995
August1st to 15thNight
84%
539
23%
1789
28%
536
85%
536
39%
933
August16th to endNight
78%
573
20%
1910
24%
573
79%
573
28%
1145
September1st to 15thNight
78%
540
20%
1808
23%
540
78%
540
32%
1032
September16th to endNight
74%
537
26%
1980
28%
537
77%
537
30%
1120
October1st to 15thNight
71%
561
32%
2001
31%
561
74%
561
43%
949
October16th to endNight
72%
768
39%
2304
28%
768
78%
768
58%
1064
November1st to 15thNight
71%
835
37%
2355
25%
835
77%
835
62%
1096
November16th to endNight
65%
975
41%
2535
23%
975
74%
975
58%
1271
December1st to 15thNight
60%
910
38%
2366
22%
910
68%
910
51%
1285
December16th to endNight
54%
909
38%
2445
21%
909
65%
909
50%
1269

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
431332445%7%59%
48418
Night
321332445%8%60%
48212
Cloud CoverDay
431332445%7%59%
48416
Night
321332445%8%60%
48212
TransparencyDay
23%5%8%18%25%19%
48138
Night
21%5%9%18%24%20%
47994
SeeingDay
5%5%19%29%28%11%
5422
Night
4322%41%24%2
15681

By Month

Percentage Cloud Cover SW (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
6%322324335%62%
1790
16th to endDay
4412213445%64%
1920
February1st to 15thDay
2112213445%68%
1750
16th to endDay
222213346%70%
1580
March1st to 15thDay
132432345%7%61%
1824
16th to endDay
2212213346%67%
2226
April1st to 15thDay
3212323446%66%
2150
16th to endDay
2112222235%72%
2160
May1st to 15thDay
2212323335%69%
2151
16th to endDay
321222346%7%64%
2324
June1st to 15thDay
1122135%5%8%66%
2340
16th to endDay
3213336%5%8%9%51%
2316
July1st to 15thDay
6%4146%36%7%8%8%41%
2160
16th to endDay
6%335%5%47%7%8%10%37%
2277
August1st to 15thDay
6%3146%47%6%7%10%40%
2160
16th to endDay
7%426%7%47%6%9%8%35%
2292
September1st to 15thDay
9%435%6%36%6%6%7%40%
2151
16th to endDay
6%5%24435%5%5%7%48%
1980
October1st to 15thDay
421221335%5%65%
1956
16th to endDay
321221122474%
1920
November1st to 15thDay
321222246%71%
1818
16th to endDay
422212235%71%
1755
December1st to 15thDay
331321345%6%63%
1631
16th to endDay
321332335%7%63%
1787
January1st to 15thNight
441332335%5%60%
2148
16th to endNight
5%21332336%7%61%
2304
February1st to 15thNight
2212323346%67%
2102
16th to endNight
3212224346%65%
1894
March1st to 15thNight
332222335%8%62%
2133
16th to endNight
3312313436%66%
1998
April1st to 15thNight
3213313446%63%
1798
16th to endNight
221221433470%
1800
May1st to 15thNight
321242345%6%64%
1799
16th to endNight
3213425%5%6%8%57%
1783
June1st to 15thNight
1112325%7%7%10%55%
1620
16th to endNight
3213326%7%8%10%51%
1638
July1st to 15thNight
3213435%8%6%11%49%
1800
16th to endNight
33135%35%5%8%12%46%
1891
August1st to 15thNight
32133346%10%15%45%
1800
16th to endNight
3215%5%47%7%8%11%41%
1910
September1st to 15thNight
5%3135%245%8%10%46%
1808
16th to endNight
5%2145%35%7%7%10%44%
1980
October1st to 15thNight
421332345%8%61%
2001
16th to endNight
2212212335%72%
2304
November1st to 15thNight
321113236%71%
2355
16th to endNight
2212213235%71%
2535
December1st to 15thNight
4313324446%61%
2366
16th to endNight
3313323335%66%
2445

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
5%423323436%61%
1790
16th to endDay
4412312447%63%
1920
February1st to 15thDay
2112323445%68%
1750
16th to endDay
2211213237%69%
1580
March1st to 15thDay
13243235%5%7%61%
1824
16th to endDay
2312213347%67%
2224
April1st to 15thDay
3212324446%66%
2150
16th to endDay
212223235%73%
2160
May1st to 15thDay
1212313345%68%
2151
16th to endDay
321122345%8%64%
2324
June1st to 15thDay
11131345%8%66%
2340
16th to endDay
4213426%5%8%9%51%
2316
July1st to 15thDay
6%4145%36%7%8%8%41%
2160
16th to endDay
6%325%5%5%7%7%9%9%37%
2277
August1st to 15thDay
6%315%5%47%7%8%10%40%
2160
16th to endDay
7%426%7%47%6%8%9%35%
2292
September1st to 15thDay
10%5%25%5%37%5%6%7%39%
2151
16th to endDay
7%5%245%35%5%5%7%48%
1980
October1st to 15thDay
43321435%5%65%
1956
16th to endDay
3212211225%74%
1920
November1st to 15thDay
321222246%70%
1818
16th to endDay
4212211245%71%
1755
December1st to 15thDay
4313313446%63%
1631
16th to endDay
3312323346%63%
1787
January1st to 15thNight
432432345%5%61%
2148
16th to endNight
5%21242336%7%61%
2304
February1st to 15thNight
1212223347%67%
2102
16th to endNight
3112224346%65%
1894
March1st to 15thNight
331221335%8%62%
2133
16th to endNight
3312223336%66%
1998
April1st to 15thNight
3222314446%63%
1798
16th to endNight
2112214335%70%
1800
May1st to 15thNight
321332335%6%64%
1799
16th to endNight
321332446%8%58%
1783
June1st to 15thNight
2112325%6%8%10%56%
1620
16th to endNight
3213325%7%8%10%50%
1638
July1st to 15thNight
3213335%7%7%11%49%
1800
16th to endNight
33135%35%5%7%13%46%
1891
August1st to 15thNight
3213325%5%9%16%45%
1800
16th to endNight
3315%5%46%6%8%11%42%
1910
September1st to 15thNight
6%3135%245%7%11%47%
1808
16th to endNight
5%2246%26%7%7%9%45%
1980
October1st to 15thNight
421332436%8%61%
2001
16th to endNight
22221234471%
2304
November1st to 15thNight
222212237%71%
2355
16th to endNight
3112212335%71%
2535
December1st to 15thNight
431242335%7%61%
2366
16th to endNight
3313222336%66%
2445

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
24%3417%31%17%
1791
16th to endDay
21%35%14%35%19%
1920
February1st to 15thDay
16%35%14%25%33%
1751
16th to endDay
15%2313%36%27%
1580
March1st to 15thDay
21%3415%27%27%
1824
16th to endDay
17%25%11%28%33%
2226
April1st to 15thDay
18%37%9%28%32%
2150
16th to endDay
14%249%29%39%
2160
May1st to 15thDay
18%35%13%26%34%
2151
16th to endDay
16%48%17%26%26%
2327
June1st to 15thDay
13%410%19%29%21%
2340
16th to endDay
25%7%12%20%22%12%
2316
July1st to 15thDay
35%9%13%23%16%2
2031
16th to endDay
34%10%17%24%10%1
2134
August1st to 15thDay
34%9%15%25%14%1
2147
16th to endDay
39%10%17%17%12%2
2292
September1st to 15thDay
39%7%14%20%13%4
2151
16th to endDay
32%7%10%20%21%7%
1980
October1st to 15thDay
19%410%25%21%18%
1956
16th to endDay
16%1416%30%30%
1920
November1st to 15thDay
14%37%23%29%22%
1818
16th to endDay
16%25%16%33%25%
1755
December1st to 15thDay
21%35%19%32%17%
1631
16th to endDay
19%35%21%33%14%
1787
January1st to 15thNight
24%36%16%29%20%
2148
16th to endNight
22%35%15%35%17%
2304
February1st to 15thNight
17%26%12%26%33%
2112
16th to endNight
19%36%9%32%30%
1894
March1st to 15thNight
20%2416%26%29%
2133
16th to endNight
18%36%14%27%30%
1998
April1st to 15thNight
20%47%10%25%30%
1798
16th to endNight
17%26%11%24%37%
1800
May1st to 15thNight
19%47%15%21%30%
1800
16th to endNight
23%7%9%18%18%22%
1785
June1st to 15thNight
19%6%13%23%23%13%
1620
16th to endNight
23%8%14%20%20%13%
1638
July1st to 15thNight
25%8%18%30%15%2
1700
16th to endNight
26%10%19%28%13%1
1771
August1st to 15thNight
22%8%21%29%15%1
1789
16th to endNight
31%11%17%23%13%3
1910
September1st to 15thNight
29%9%20%23%11%5%
1808
16th to endNight
30%9%15%20%16%7%
1980
October1st to 15thNight
20%5%13%24%18%17%
2001
16th to endNight
15%35%15%28%31%
2304
November1st to 15thNight
14%26%20%33%21%
2355
16th to endNight
16%2413%32%30%
2535
December1st to 15thNight
22%35%19%28%20%
2366
16th to endNight
20%25%19%35%16%
2445

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
12%5%30%35%15%1
90
16th to endDay
6%18%32%21%13%7%
96
February1st to 15thDay
18%23%22%36%7%
90
16th to endDay
8%14%20%33%18%3
81
March1st to 15thDay
433%40%13%7%
114
16th to endDay
313%42%23%11%4
288
April1st to 15thDay
5%12%45%21%12%2
269
16th to endDay
216%39%29%8%3
270
May1st to 15thDay
210%41%32%11%1
288
16th to endDay
4326%41%22%1
411
June1st to 15thDay
111%41%36%9%
495
16th to endDay
38%29%46%11%
471
July1st to 15thDay
6%5%26%33%25%
305
16th to endDay
4424%41%23%
327
August1st to 15thDay
8%416%41%27%
315
16th to endDay
9%1325%37%21%
332
September1st to 15thDay
7%17%30%36%16%
306
16th to endDay
11%14%27%33%12%
135
October1st to 15thDay
11%11%24%34%17%
135
16th to endDay
2215%23%33%22%
144
November1st to 15thDay
7%421%30%26%9%
135
16th to endDay
8%9%21%28%22%8%
135
December1st to 15thDay
7%5%15%44%22%4
94
16th to endDay
7%12%34%30%14%1
96
January1st to 15thNight
6%327%42%18%2
720
16th to endNight
5%5%29%40%16%1
768
February1st to 15thNight
36%30%38%19%1
704
16th to endNight
46%38%41%9%
632
March1st to 15thNight
5%7%31%39%14%1
720
16th to endNight
37%34%36%15%2
654
April1st to 15thNight
38%37%43%6%
539
16th to endNight
27%37%42%9%
540
May1st to 15thNight
45%37%42%10%
540
16th to endNight
3327%48%16%
563
June1st to 15thNight
216%57%22%
540
16th to endNight
410%54%29%
540
July1st to 15thNight
36%47%40%1
510
16th to endNight
3444%43%3
564
August1st to 15thNight
3130%57%7%
539
16th to endNight
45%32%52%5%
573
September1st to 15thNight
5%6%38%43%5%
540
16th to endNight
5%9%45%35%2
537
October1st to 15thNight
5%17%45%28%2
561
16th to endNight
4217%37%29%8%
768
November1st to 15thNight
3219%41%28%5%
835
16th to endNight
3421%39%26%4
975
December1st to 15thNight
6%325%41%20%2
910
16th to endNight
5%7%28%41%14%2
909
Page generated at 2017-12-03 10:16:48. Version ac04

Copyright 2017 A. Danko


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