Grayson Lake State Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Grayson Lake State Park clear sky chart from 2005-11-05 to 2017-10-31.

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
41%
15699
19%
47430
13%
15658
47%
15658
23%
31531

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
17%
719
14%
2327
7%
716
26%
716
11%
1781
January16th to endNight
19%
768
16%
2496
7%
768
29%
768
13%
1797
February1st to 15thNight
21%
703
14%
2208
6%
701
30%
701
15%
1591
February16th to endNight
15%
631
14%
1893
6%
631
22%
631
13%
1427
March1st to 15thNight
25%
720
18%
2042
10%
720
32%
720
18%
1444
March16th to endNight
30%
768
15%
2112
8%
768
35%
768
21%
1506
April1st to 15thNight
33%
656
20%
1902
10%
656
42%
656
25%
1227
April16th to endNight
36%
540
21%
1620
11%
540
45%
540
25%
1062
May1st to 15thNight
36%
540
14%
1620
8%
540
42%
540
21%
1145
May16th to endNight
56%
561
18%
1684
13%
561
61%
561
28%
1076
June1st to 15thNight
63%
540
17%
1620
15%
540
67%
540
33%
972
June16th to endNight
64%
540
17%
1620
14%
540
67%
540
35%
961
July1st to 15thNight
58%
510
13%
1530
12%
510
60%
510
29%
987
July16th to endNight
69%
564
18%
1595
15%
531
71%
531
32%
975
August1st to 15thNight
72%
539
23%
1609
20%
536
74%
536
34%
960
August16th to endNight
69%
573
25%
1776
23%
573
70%
573
35%
1010
September1st to 15thNight
61%
714
24%
1974
18%
714
64%
714
33%
1251
September16th to endNight
57%
717
27%
1980
22%
717
61%
717
33%
1222
October1st to 15thNight
54%
720
28%
2061
24%
720
60%
720
35%
1225
October16th to endNight
39%
768
26%
2309
20%
768
49%
768
25%
1484
November1st to 15thNight
46%
700
27%
2276
21%
700
56%
700
29%
1335
November16th to endNight
32%
720
21%
2340
14%
720
43%
720
21%
1516
December1st to 15thNight
26%
720
14%
2340
9%
720
32%
720
14%
1716
December16th to endNight
21%
768
15%
2496
6%
768
32%
768
13%
1861

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
15%7%35%5%3445%7%37%
48308
Night
14%7%35%5%3445%7%39%
47623
Cloud CoverDay
15%7%36%5%3445%7%36%
48318
Night
14%7%35%5%2445%7%39%
47627
TransparencyDay
46%6%11%20%13%2
48019
Night
43%5%10%21%15%2
47430
SeeingDay
18%9%23%22%16%9%
5554
Night
18%9%24%27%17%2
15703

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
19%12%6%10%6%33335%26%
1611
16th to endDay
18%13%47%434336%30%
1728
February1st to 15thDay
16%12%6%8%5%23335%29%
1652
16th to endDay
16%13%45%436%45%6%29%
1580
March1st to 15thDay
22%10%25%423435%33%
1906
16th to endDay
19%8%36%5%34436%34%
2112
April1st to 15thDay
16%6%346%34347%40%
2055
16th to endDay
16%7%25%43345%7%39%
2340
May1st to 15thDay
19%7%36%6%35%35%6%31%
2331
16th to endDay
10%5%26%7%46%6%5%8%36%
2431
June1st to 15thDay
10%4246%35%6%6%8%41%
2340
16th to endDay
8%425%6%47%6%7%8%38%
2340
July1st to 15thDay
14%6%26%6%35%5%7%8%33%
2340
16th to endDay
12%5%25%5%37%5%6%10%33%
2465
August1st to 15thDay
10%5%26%6%46%6%6%10%34%
2340
16th to endDay
8%5%245%35%5%7%9%41%
2417
September1st to 15thDay
12%5%25%5%245%48%42%
1980
16th to endDay
16%5%14423345%46%
1980
October1st to 15thDay
13%5%23333346%49%
1899
16th to endDay
19%6%24312235%45%
1911
November1st to 15thDay
12%5%26%334335%48%
1582
16th to endDay
16%8%35%424345%39%
1620
December1st to 15thDay
24%9%46%424445%28%
1620
16th to endDay
20%13%46%6%13435%29%
1728
January1st to 15thNight
18%10%5%9%6%35%345%26%
2327
16th to endNight
18%10%48%5%3444431%
2496
February1st to 15thNight
17%11%5%7%5%24445%31%
2206
16th to endNight
19%11%47%6%34346%27%
1893
March1st to 15thNight
17%8%36%5%34435%35%
2030
16th to endNight
14%8%36%6%34447%35%
2112
April1st to 15thNight
14%6%25%42445%7%42%
1902
16th to endNight
14%5%245%34447%41%
1620
May1st to 15thNight
18%6%36%43445%8%34%
1620
16th to endNight
9%4145%45%5%5%10%42%
1682
June1st to 15thNight
7%213435%6%6%11%46%
1620
16th to endNight
8%4133245%8%13%44%
1620
July1st to 15thNight
11%5%244345%5%7%44%
1620
16th to endNight
6%3245%36%48%11%43%
1703
August1st to 15thNight
7%3135%345%7%10%47%
1620
16th to endNight
7%32443347%8%50%
1776
September1st to 15thNight
12%424434448%47%
1974
16th to endNight
10%5%245%23446%49%
1980
October1st to 15thNight
11%414423347%51%
2061
16th to endNight
16%6%25%423336%44%
2309
November1st to 15thNight
13%6%13413335%50%
2276
16th to endNight
18%8%36%423246%40%
2340
December1st to 15thNight
21%11%46%5%24346%29%
2340
16th to endNight
20%12%5%6%5%34446%26%
2496

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%12%5%11%6%2324426%
1611
16th to endDay
18%13%47%424346%30%
1728
February1st to 15thDay
17%11%7%9%5%23335%29%
1652
16th to endDay
16%13%45%435%5%5%5%29%
1580
March1st to 15thDay
22%10%35%423345%33%
1917
16th to endDay
19%8%36%5%34446%34%
2111
April1st to 15thDay
15%6%345%34337%40%
2055
16th to endDay
15%7%35%5%2345%6%39%
2340
May1st to 15thDay
19%7%46%6%35%45%6%30%
2331
16th to endDay
10%5%26%7%46%5%6%8%36%
2431
June1st to 15thDay
9%5%25%5%35%6%6%8%40%
2340
16th to endDay
8%5%25%7%47%6%6%9%38%
2340
July1st to 15thDay
14%5%26%5%35%6%7%9%32%
2340
16th to endDay
11%5%25%6%38%5%7%10%32%
2465
August1st to 15thDay
9%6%25%6%46%6%7%10%33%
2340
16th to endDay
8%5%246%35%5%7%9%40%
2417
September1st to 15thDay
12%6%26%5%2345%7%42%
1980
16th to endDay
16%5%24424435%46%
1980
October1st to 15thDay
12%5%1433345%6%49%
1899
16th to endDay
19%5%34312335%45%
1911
November1st to 15thDay
12%6%24424335%48%
1582
16th to endDay
16%8%35%423436%39%
1620
December1st to 15thDay
24%10%36%424445%28%
1620
16th to endDay
21%12%46%5%22445%29%
1728
January1st to 15thNight
18%11%5%9%7%2444426%
2327
16th to endNight
18%10%47%5%2444431%
2496
February1st to 15thNight
16%11%47%5%24445%31%
2199
16th to endNight
18%12%48%6%35%346%27%
1893
March1st to 15thNight
17%9%46%5%34445%35%
2042
16th to endNight
14%8%36%6%35%447%35%
2112
April1st to 15thNight
14%6%3442445%6%42%
1902
16th to endNight
14%5%345%345%5%7%41%
1620
May1st to 15thNight
17%7%26%5%3446%8%34%
1619
16th to endNight
9%4245%45%5%5%10%41%
1682
June1st to 15thNight
7%2235%35%6%6%11%45%
1620
16th to endNight
8%3134245%9%11%45%
1620
July1st to 15thNight
11%6%2443445%8%44%
1620
16th to endNight
6%315%5%35%5%7%12%43%
1703
August1st to 15thNight
6%3145%345%7%10%47%
1620
16th to endNight
7%3244235%6%8%50%
1776
September1st to 15thNight
11%5%23425%45%7%47%
1974
16th to endNight
10%5%25%423446%49%
1980
October1st to 15thNight
11%424423447%51%
2061
16th to endNight
16%6%25%423336%44%
2309
November1st to 15thNight
14%6%24323335%51%
2276
16th to endNight
18%8%26%5%23345%40%
2340
December1st to 15thNight
21%12%5%6%5%24445%29%
2340
16th to endNight
20%13%5%6%42435%6%26%
2496

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
61%48%16%8%1
1612
16th to endDay
55%410%21%6%1
1728
February1st to 15thDay
57%5%8%18%8%1
1654
16th to endDay
55%410%20%8%
1580
March1st to 15thDay
53%310%20%9%1
1917
16th to endDay
51%6%9%22%9%
2112
April1st to 15thDay
45%39%22%15%3
2055
16th to endDay
44%5%10%20%13%5%
2340
May1st to 15thDay
52%6%12%18%8%2
2331
16th to endDay
44%8%12%21%12%1
2435
June1st to 15thDay
37%10%12%22%15%1
2340
16th to endDay
40%9%12%17%17%2
2340
July1st to 15thDay
45%8%13%15%14%2
2201
16th to endDay
42%9%13%21%11%2
2310
August1st to 15thDay
41%9%16%18%12%1
2327
16th to endDay
36%7%14%23%14%2
2417
September1st to 15thDay
39%6%12%20%16%4
1980
16th to endDay
40%5%7%21%22%2
1980
October1st to 15thDay
35%412%25%19%3
1899
16th to endDay
42%29%26%16%1
1911
November1st to 15thDay
39%38%23%21%4
1582
16th to endDay
46%39%21%18%
1620
December1st to 15thDay
57%5%9%18%8%1
1620
16th to endDay
56%412%18%6%
1728
January1st to 15thNight
60%5%7%13%11%1
2327
16th to endNight
55%48%21%8%1
2496
February1st to 15thNight
54%49%20%10%1
2208
16th to endNight
58%410%18%8%
1893
March1st to 15thNight
50%49%20%12%1
2042
16th to endNight
49%5%12%20%11%
2112
April1st to 15thNight
40%5%10%21%19%3
1902
16th to endNight
41%6%10%20%14%6%
1620
May1st to 15thNight
48%7%12%18%10%3
1620
16th to endNight
36%8%14%21%16%2
1684
June1st to 15thNight
30%9%15%23%17%3
1620
16th to endNight
29%8%17%22%18%4
1620
July1st to 15thNight
37%7%13%20%16%4
1530
16th to endNight
31%9%16%24%14%3
1595
August1st to 15thNight
30%8%14%24%18%2
1609
16th to endNight
29%6%12%27%19%4
1776
September1st to 15thNight
34%7%11%19%19%7%
1974
16th to endNight
35%5%9%20%27%1
1980
October1st to 15thNight
32%411%27%18%5%
2061
16th to endNight
42%47%23%20%2
2309
November1st to 15thNight
36%37%20%24%7%
2276
16th to endNight
46%38%23%15%1
2340
December1st to 15thNight
56%49%18%9%1
2340
16th to endNight
58%410%17%7%1
2496

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
33%18%34%7%32
90
16th to endDay
37%29%17%14%1
96
February1st to 15thDay
25%30%33%7%3
90
16th to endDay
32%13%39%13%1
81
March1st to 15thDay
32%12%31%16%6%
207
16th to endDay
21%14%35%18%8%1
288
April1st to 15thDay
22%12%31%21%10%1
270
16th to endDay
19%10%33%20%9%7%
270
May1st to 15thDay
23%13%30%15%10%5%
288
16th to endDay
15%8%26%21%14%13%
331
June1st to 15thDay
12%419%29%23%11%
315
16th to endDay
13%7%27%20%18%11%
315
July1st to 15thDay
21%319%27%12%15%
305
16th to endDay
11%215%23%23%24%
326
August1st to 15thDay
14%111%29%28%15%
313
16th to endDay
11%211%30%28%16%
332
September1st to 15thDay
14%315%22%29%13%
315
16th to endDay
18%313%23%24%16%
314
October1st to 15thDay
13%6%22%26%22%8%
315
16th to endDay
18%11%28%22%16%2
327
November1st to 15thDay
17%11%28%18%18%4
90
16th to endDay
32%16%27%15%6%1
90
December1st to 15thDay
28%22%28%12%5%2
90
16th to endDay
32%26%29%10%2
96
January1st to 15thNight
28%18%29%18%4
720
16th to endNight
25%18%33%20%2
768
February1st to 15thNight
28%14%33%23%
704
16th to endNight
26%20%32%18%2
631
March1st to 15thNight
24%15%29%25%5%
720
16th to endNight
19%12%31%25%10%
768
April1st to 15thNight
18%13%32%23%10%
656
16th to endNight
16%9%33%27%12%1
540
May1st to 15thNight
20%8%27%27%13%2
540
16th to endNight
11%321%33%26%4
563
June1st to 15thNight
8%219%40%25%4
540
16th to endNight
8%317%38%29%2
540
July1st to 15thNight
14%216%35%26%5%
510
16th to endNight
8%110%32%38%7%
564
August1st to 15thNight
8%9%37%38%5%
539
16th to endNight
8%110%34%35%9%
573
September1st to 15thNight
13%114%28%35%6%
714
16th to endNight
13%316%25%35%5%
717
October1st to 15thNight
14%5%19%28%26%4
720
16th to endNight
21%9%25%23%17%1
768
November1st to 15thNight
18%8%24%28%18%2
700
16th to endNight
22%13%26%25%10%
720
December1st to 15thNight
29%13%24%26%6%
720
16th to endNight
29%14%29%22%3
768
Page generated at 2017-11-01 17:23:41. Version ac04

Copyright 2017 A. Danko


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