Fort Griffin State Historic Site
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Fort Griffin State Historic Site 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
52%
16287
32%
48904
21%
16244
63%
16244
44%
25412

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
46%
973
34%
2522
16%
970
57%
970
46%
1393
January16th to endNight
46%
975
38%
2639
17%
975
60%
975
48%
1382
February1st to 15thNight
42%
764
31%
2292
15%
760
54%
760
40%
1222
February16th to endNight
30%
660
32%
1978
11%
660
47%
660
38%
1066
March1st to 15thNight
35%
618
30%
2058
15%
618
50%
618
35%
1108
March16th to endNight
37%
576
29%
2112
19%
576
52%
576
36%
1024
April1st to 15thNight
28%
539
27%
1909
11%
539
50%
539
37%
945
April16th to endNight
33%
540
31%
1716
16%
540
54%
540
43%
861
May1st to 15thNight
36%
540
26%
1620
15%
540
53%
540
37%
906
May16th to endNight
52%
561
29%
1684
22%
561
66%
561
46%
883
June1st to 15thNight
61%
540
23%
1620
20%
540
70%
540
49%
821
June16th to endNight
71%
540
27%
1620
28%
540
75%
540
50%
811
July1st to 15thNight
80%
510
26%
1530
29%
510
81%
510
47%
791
July16th to endNight
87%
564
35%
1594
41%
531
89%
531
60%
738
August1st to 15thNight
86%
539
35%
1668
43%
536
86%
536
54%
796
August16th to endNight
79%
573
31%
1910
35%
573
82%
573
43%
967
September1st to 15thNight
71%
540
25%
1974
28%
540
74%
540
34%
1047
September16th to endNight
68%
537
33%
1980
31%
537
75%
537
36%
1004
October1st to 15thNight
63%
540
37%
1980
32%
540
71%
540
46%
897
October16th to endNight
57%
754
41%
2290
24%
754
67%
754
55%
1059
November1st to 15thNight
53%
914
31%
2434
14%
914
61%
914
51%
1281
November16th to endNight
46%
975
38%
2535
17%
975
57%
975
48%
1390
December1st to 15thNight
46%
975
35%
2535
17%
975
56%
975
45%
1425
December16th to endNight
40%
1040
32%
2704
14%
1040
52%
1040
41%
1595

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%313323446%58%
49351
Night
7%313323346%61%
49100
Cloud CoverDay
8%313323346%58%
49349
Night
7%313313346%61%
49100
TransparencyDay
26%49%22%26%10%
49049
Night
23%38%21%26%14%
48905
SeeingDay
8%420%31%25%8%
6042
Night
8%5%29%38%16%1
16291

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
8%5%23312135%60%
1746
16th to endDay
8%323213335%60%
1950
February1st to 15thDay
9%413212246%60%
1900
16th to endDay
12%42221223460%
1642
March1st to 15thDay
12%413313347%54%
1902
16th to endDay
9%413323435%57%
2112
April1st to 15thDay
7%31321345%6%58%
2036
16th to endDay
8%42331333461%
2244
May1st to 15thDay
11%324423435%53%
2331
16th to endDay
9%3135%245%6%6%50%
2430
June1st to 15thDay
42134245%47%59%
2340
16th to endDay
6%11332445%7%58%
2340
July1st to 15thDay
6%213425%5%5%11%51%
2340
16th to endDay
2112325%46%10%59%
2466
August1st to 15thDay
2235%2445%6%60%
2279
16th to endDay
6%3133246%6%9%51%
2292
September1st to 15thDay
11%424424447%50%
1986
16th to endDay
10%41332235%7%54%
1980
October1st to 15thDay
8%212313445%63%
1980
16th to endDay
5%21121133372%
1920
November1st to 15thDay
5%412313345%64%
1753
16th to endDay
8%212312225%65%
1755
December1st to 15thDay
11%5%23313325%56%
1755
16th to endDay
11%5%23413345%54%
1872
January1st to 15thNight
8%312312235%63%
2522
16th to endNight
7%212212235%65%
2639
February1st to 15thNight
9%413313345%60%
2282
16th to endNight
11%312212345%60%
1978
March1st to 15thNight
11%313323345%57%
2058
16th to endNight
8%313223346%61%
2112
April1st to 15thNight
6%313313346%60%
1909
16th to endNight
8%313212246%62%
1716
May1st to 15thNight
8%313323347%56%
1619
16th to endNight
5%11132447%8%59%
1683
June1st to 15thNight
32133245%6%8%59%
1620
16th to endNight
311233335%8%63%
1620
July1st to 15thNight
5%21222335%10%58%
1620
16th to endNight
211121336%11%63%
1702
August1st to 15thNight
11123134410%62%
1678
16th to endNight
421342345%8%58%
1910
September1st to 15thNight
10%412424446%53%
1974
16th to endNight
9%31432345%7%54%
1980
October1st to 15thNight
8%212212335%65%
1980
16th to endNight
421221122473%
2290
November1st to 15thNight
5%212223345%66%
2434
16th to endNight
8%313212235%64%
2535
December1st to 15thNight
10%412212336%60%
2535
16th to endNight
9%5%23323445%56%
2704

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
8%5%23312135%60%
1746
16th to endDay
8%323213335%60%
1950
February1st to 15thDay
9%413212246%61%
1900
16th to endDay
12%42221223460%
1642
March1st to 15thDay
13%413323246%54%
1902
16th to endDay
9%423423435%57%
2110
April1st to 15thDay
8%313223446%58%
2036
16th to endDay
8%42332324461%
2244
May1st to 15thDay
11%423423436%53%
2331
16th to endDay
8%4234245%5%7%51%
2430
June1st to 15thDay
421342445%7%59%
2340
16th to endDay
6%2242445%8%58%
2340
July1st to 15thDay
6%313425%5%5%10%51%
2340
16th to endDay
2123245%5%10%58%
2466
August1st to 15thDay
2213435%5%5%7%60%
2279
16th to endDay
6%3134246%7%9%51%
2292
September1st to 15thDay
11%42342345%7%50%
1986
16th to endDay
10%42332225%7%54%
1980
October1st to 15thDay
8%212312345%63%
1980
16th to endDay
5%21121223372%
1920
November1st to 15thDay
6%31331334464%
1753
16th to endDay
8%212222225%65%
1755
December1st to 15thDay
11%5%23213335%56%
1755
16th to endDay
11%5%23423345%54%
1872
January1st to 15thNight
8%412312335%63%
2522
16th to endNight
7%212212236%65%
2639
February1st to 15thNight
9%413313335%61%
2282
16th to endNight
10%313212345%60%
1978
March1st to 15thNight
11%313313335%57%
2058
16th to endNight
8%312223345%61%
2112
April1st to 15thNight
6%313323336%61%
1909
16th to endNight
8%31322246%63%
1716
May1st to 15thNight
8%323323447%56%
1619
16th to endNight
421232446%8%59%
1683
June1st to 15thNight
3133145%6%9%59%
1620
16th to endNight
311233335%8%63%
1620
July1st to 15thNight
5%21222336%10%58%
1620
16th to endNight
211121336%11%64%
1702
August1st to 15thNight
121232345%9%63%
1678
16th to endNight
421342435%8%58%
1910
September1st to 15thNight
10%413424446%54%
1974
16th to endNight
8%31432336%7%54%
1980
October1st to 15thNight
8%212212335%65%
1980
16th to endNight
421221222473%
2290
November1st to 15thNight
5%213223345%66%
2434
16th to endNight
8%313212335%64%
2535
December1st to 15thNight
10%412212336%60%
2535
16th to endNight
9%414323445%56%
2704

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
28%26%22%29%11%
1747
16th to endDay
26%25%16%34%13%
1950
February1st to 15thDay
26%36%21%29%14%
1901
16th to endDay
28%2418%27%17%
1642
March1st to 15thDay
31%38%17%28%11%
1902
16th to endDay
29%48%20%24%12%
2112
April1st to 15thDay
25%410%21%21%17%
2036
16th to endDay
27%36%17%29%14%
2244
May1st to 15thDay
33%49%18%22%12%
2331
16th to endDay
31%5%11%23%22%5%
2434
June1st to 15thDay
22%6%11%25%27%6%
2340
16th to endDay
23%5%12%27%23%8%
2340
July1st to 15thDay
25%5%15%28%20%3
2201
16th to endDay
17%6%13%32%25%3
2311
August1st to 15thDay
21%5%13%25%26%6%
2265
16th to endDay
27%7%12%26%21%4
2292
September1st to 15thDay
32%6%9%21%23%6%
1986
16th to endDay
30%48%20%24%12%
1980
October1st to 15thDay
24%39%24%25%12%
1980
16th to endDay
17%2419%33%21%
1920
November1st to 15thDay
22%37%24%27%13%
1753
16th to endDay
23%2321%31%17%
1755
December1st to 15thDay
31%25%20%27%11%
1755
16th to endDay
33%26%22%26%8%
1872
January1st to 15thNight
24%26%18%31%16%
2522
16th to endNight
22%25%15%33%20%
2639
February1st to 15thNight
27%37%16%26%18%
2292
16th to endNight
26%36%18%25%18%
1978
March1st to 15thNight
30%36%18%23%18%
2058
16th to endNight
25%39%23%26%11%
2112
April1st to 15thNight
24%410%19%21%20%
1909
16th to endNight
23%311%19%25%15%
1716
May1st to 15thNight
28%5%10%18%22%15%
1620
16th to endNight
21%6%15%24%24%7%
1685
June1st to 15thNight
18%6%13%27%27%6%
1620
16th to endNight
19%5%12%26%25%10%
1620
July1st to 15thNight
21%5%8%33%24%6%
1530
16th to endNight
13%414%31%29%7%
1594
August1st to 15thNight
17%49%26%32%9%
1668
16th to endNight
23%5%11%25%26%8%
1910
September1st to 15thNight
29%5%10%21%23%9%
1974
16th to endNight
27%48%20%24%14%
1980
October1st to 15thNight
21%211%22%26%15%
1980
16th to endNight
17%2418%31%25%
2290
November1st to 15thNight
20%38%25%24%18%
2434
16th to endNight
23%2316%33%19%
2535
December1st to 15thNight
26%26%21%27%14%
2535
16th to endNight
29%36%20%24%14%
2704

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
14%9%22%41%9%1
135
16th to endDay
9%6%35%31%15%2
144
February1st to 15thDay
8%11%34%30%15%
135
16th to endDay
18%7%38%28%8%1
100
March1st to 15thDay
15%7%35%30%11%
90
16th to endDay
8%10%31%31%15%3
96
April1st to 15thDay
9%15%40%25%10%
155
16th to endDay
12%13%38%24%9%
354
May1st to 15thDay
12%7%39%28%9%1
468
16th to endDay
12%5%29%33%15%4
517
June1st to 15thDay
6%119%43%24%5%
495
16th to endDay
4111%38%32%11%
495
July1st to 15thDay
5%7%38%40%7%
475
16th to endDay
2326%45%22%
515
August1st to 15thDay
2128%49%17%
432
16th to endDay
6%8%30%37%15%
332
September1st to 15thDay
321%46%28%
141
16th to endDay
16%227%39%14%
135
October1st to 15thDay
412%37%35%10%
135
16th to endDay
6%227%34%21%6%
144
November1st to 15thDay
20%326%28%15%5%
135
16th to endDay
14%11%28%24%15%5%
135
December1st to 15thDay
14%434%36%8%2
135
16th to endDay
17%10%38%25%8%
144
January1st to 15thNight
11%8%32%37%11%
975
16th to endNight
8%8%33%40%8%
975
February1st to 15thNight
10%7%35%38%7%
764
16th to endNight
14%10%43%27%4
660
March1st to 15thNight
12%7%41%31%6%
618
16th to endNight
8%11%41%32%6%
576
April1st to 15thNight
7%10%51%28%2
539
16th to endNight
8%7%48%30%5%
540
May1st to 15thNight
8%7%44%31%7%
540
16th to endNight
5%236%38%15%1
563
June1st to 15thNight
3128%46%18%1
540
16th to endNight
4116%56%18%2
540
July1st to 15thNight
47%47%37%1
510
16th to endNight
2350%39%3
564
August1st to 15thNight
2341%50%2
539
16th to endNight
47%36%46%3
573
September1st to 15thNight
11%9%39%37%2
540
16th to endNight
10%13%42%30%2
537
October1st to 15thNight
10%123%42%21%1
540
16th to endNight
7%429%38%19%1
754
November1st to 15thNight
7%430%39%15%1
914
16th to endNight
10%6%33%34%13%
975
December1st to 15thNight
13%5%32%39%9%
975
16th to endNight
13%5%36%36%7%
1040
Page generated at 2018-02-23 10:21:41. Version ac04

Copyright 2018 A. Danko


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