Horsethief Lake State Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Horsethief Lake State Park clear sky chart from 2005-11-05 to 2017-09-22.

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
39%
14646
15%
46911
10%
14621
46%
14621
21%
29857

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
23%
716
6%
2506
3%
716
27%
716
6%
2031
January16th to endNight
29%
768
7%
2649
6%
768
33%
768
10%
2072
February1st to 15thNight
35%
700
8%
2288
7%
700
38%
700
13%
1677
February16th to endNight
32%
632
13%
1961
9%
632
37%
632
16%
1369
March1st to 15thNight
32%
720
8%
2100
6%
720
35%
720
15%
1546
March16th to endNight
32%
768
11%
2040
4%
768
37%
768
18%
1429
April1st to 15thNight
32%
719
13%
1799
5%
719
36%
719
23%
1253
April16th to endNight
34%
630
17%
1710
7%
630
41%
630
26%
1058
May1st to 15thNight
40%
359
21%
1439
17%
359
53%
359
25%
696
May16th to endNight
39%
375
12%
1496
12%
374
47%
374
23%
797
June1st to 15thNight
35%
360
12%
1440
10%
360
46%
360
23%
768
June16th to endNight
35%
360
18%
1440
12%
360
55%
360
28%
638
July1st to 15thNight
54%
340
20%
1360
20%
340
69%
340
55%
462
July16th to endNight
51%
376
31%
1416
29%
354
76%
354
59%
460
August1st to 15thNight
64%
449
32%
1522
24%
447
77%
447
58%
583
August16th to endNight
59%
699
36%
1845
18%
699
68%
699
57%
873
September1st to 15thNight
61%
720
33%
1800
16%
720
67%
720
64%
854
September16th to endNight
55%
683
30%
1859
19%
683
62%
683
42%
1007
October1st to 15thNight
47%
660
19%
1980
15%
660
53%
660
28%
1205
October16th to endNight
43%
704
14%
2186
11%
704
49%
704
20%
1446
November1st to 15thNight
39%
700
11%
2347
9%
700
44%
700
15%
1675
November16th to endNight
33%
720
9%
2520
5%
720
39%
720
11%
1853
December1st to 15thNight
30%
720
9%
2520
7%
720
33%
720
9%
1971
December16th to endNight
26%
768
7%
2688
4%
768
30%
768
9%
2134

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
7%6%35%5%35%5%5%7%45%
47995
Night
8%7%35%5%3445%7%43%
47079
Cloud CoverDay
8%6%35%5%345%5%7%46%
47995
Night
9%7%35%5%3445%7%43%
47083
TransparencyDay
38%5%15%22%14%4
47666
Night
39%6%16%21%11%3
46912
SeeingDay
13%22%27%19%12%4
5559
Night
13%20%19%27%16%1
14655

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 15thDay
14%14%7%11%8%5%6%6%5%5%12%
1432
16th to endDay
15%13%7%9%8%46%46%6%14%
1575
February1st to 15thDay
12%12%5%8%7%5%7%6%5%7%20%
1576
16th to endDay
9%8%36%7%46%8%7%7%29%
1512
March1st to 15thDay
12%9%48%7%5%6%6%7%9%23%
1857
16th to endDay
9%7%48%7%5%8%7%7%8%25%
2184
April1st to 15thDay
7%6%36%5%46%7%8%9%33%
2149
16th to endDay
5%5%245%36%5%7%9%43%
2247
May1st to 15thDay
5%3246%35%5%6%8%48%
2511
16th to endDay
7%4344346%6%7%47%
2615
June1st to 15thDay
5%3244345%6%7%51%
2520
16th to endDay
3213325%45%7%58%
2520
July1st to 15thDay
2112236%77%
2520
16th to endDay
211111122380%
2657
August1st to 15thDay
1122245%76%
2430
16th to endDay
22322335%73%
2357
September1st to 15thDay
211212236%75%
2160
16th to endDay
4324425%5%5%6%55%
1911
October1st to 15thDay
9%5%36%6%346%5%6%41%
1650
16th to endDay
10%7%37%7%45%6%7%7%33%
1686
November1st to 15thDay
12%7%47%9%46%6%9%8%23%
1510
16th to endDay
14%12%6%9%8%6%6%6%46%18%
1440
December1st to 15thDay
13%15%8%9%7%45%345%21%
1440
16th to endDay
17%15%5%8%7%46%5%6%6%16%
1536
January1st to 15thNight
16%13%7%10%7%36%45%6%18%
2506
16th to endNight
13%12%6%9%8%35%5%5%7%22%
2649
February1st to 15thNight
12%9%5%7%5%45%6%6%7%29%
2276
16th to endNight
8%8%36%7%35%5%7%8%35%
1961
March1st to 15thNight
12%8%46%6%35%6%6%8%30%
2100
16th to endNight
8%5%37%6%46%6%7%8%34%
2036
April1st to 15thNight
8%6%35%6%35%6%7%8%39%
1799
16th to endNight
6%3234245%7%11%47%
1710
May1st to 15thNight
5%2235%1445%8%56%
1439
16th to endNight
4313436%5%7%10%48%
1496
June1st to 15thNight
6%423335%5%6%7%51%
1440
16th to endNight
233324447%62%
1440
July1st to 15thNight
1112245%79%
1440
16th to endNight
111122383%
1512
August1st to 15thNight
122233478%
1530
16th to endNight
111211235%77%
1845
September1st to 15thNight
1111133479%
1800
16th to endNight
431332335%7%60%
1859
October1st to 15thNight
8%5%25%43435%5%50%
1980
16th to endNight
10%5%26%5%35%6%6%9%38%
2186
November1st to 15thNight
12%8%37%6%45%5%7%7%30%
2347
16th to endNight
11%12%47%5%46%5%6%7%27%
2520
December1st to 15thNight
15%13%6%8%7%35%5%45%24%
2520
16th to endNight
17%13%6%8%7%35%5%5%7%20%
2688

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
17%15%6%10%7%46%6%47%13%
1432
16th to endDay
16%14%8%9%7%35%6%5%6%15%
1575
February1st to 15thDay
14%12%49%7%46%6%5%7%20%
1576
16th to endDay
11%8%36%7%5%6%6%7%7%29%
1512
March1st to 15thDay
14%8%47%9%36%6%7%8%22%
1857
16th to endDay
10%8%38%8%46%7%6%9%26%
2184
April1st to 15thDay
8%6%35%6%36%7%8%9%34%
2149
16th to endDay
6%6%24435%5%7%9%43%
2247
May1st to 15thDay
5%325%5%345%6%8%48%
2511
16th to endDay
8%4244345%6%8%47%
2615
June1st to 15thDay
6%3245%25%45%8%51%
2520
16th to endDay
3213324448%59%
2520
July1st to 15thDay
111112335%78%
2520
16th to endDay
21111223479%
2657
August1st to 15thDay
1112335%76%
2430
16th to endDay
212223335%74%
2357
September1st to 15thDay
211113225%76%
2160
16th to endDay
5%324425%45%6%55%
1911
October1st to 15thDay
9%6%26%7%4446%5%42%
1650
16th to endDay
11%6%27%6%46%47%7%34%
1686
November1st to 15thDay
13%8%48%7%5%5%5%7%9%24%
1510
16th to endDay
16%11%5%9%7%5%7%6%5%6%18%
1440
December1st to 15thDay
15%14%7%9%6%45%445%21%
1440
16th to endDay
18%14%5%8%5%5%5%5%5%6%17%
1536
January1st to 15thNight
18%14%6%9%6%45%45%5%18%
2506
16th to endNight
15%11%6%8%6%45%45%7%23%
2649
February1st to 15thNight
13%10%46%5%45%5%5%8%30%
2276
16th to endNight
9%9%37%6%346%5%8%35%
1961
March1st to 15thNight
13%9%37%5%36%5%7%8%29%
2100
16th to endNight
8%6%37%6%45%6%8%9%33%
2040
April1st to 15thNight
8%6%36%5%35%6%8%8%39%
1799
16th to endNight
7%3144345%7%10%47%
1710
May1st to 15thNight
5%3134245%5%6%57%
1439
16th to endNight
43244445%5%10%48%
1496
June1st to 15thNight
6%313446%46%7%51%
1440
16th to endNight
231332435%6%63%
1440
July1st to 15thNight
1112235%79%
1440
16th to endNight
111222482%
1512
August1st to 15thNight
1112223478%
1530
16th to endNight
112212235%77%
1845
September1st to 15thNight
11111234478%
1800
16th to endNight
5%31242335%7%61%
1859
October1st to 15thNight
9%6%25%424345%50%
1980
16th to endNight
10%6%25%6%35%5%6%8%38%
2186
November1st to 15thNight
14%8%36%6%45%6%6%7%30%
2347
16th to endNight
14%11%46%5%36%5%5%7%28%
2520
December1st to 15thNight
16%12%6%7%7%35%45%6%23%
2520
16th to endNight
18%12%5%8%7%35%45%7%20%
2688

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
72%6%10%8%1
1432
16th to endDay
69%6%12%8%2
1575
February1st to 15thDay
62%8%17%10%
1576
16th to endDay
50%9%20%14%5%
1512
March1st to 15thDay
56%8%14%15%4
1857
16th to endDay
52%9%19%15%3
2184
April1st to 15thDay
43%8%21%20%6%
2149
16th to endDay
34%8%22%21%10%1
2247
May1st to 15thDay
31%6%15%29%15%1
2511
16th to endDay
34%5%21%27%9%
2619
June1st to 15thDay
30%5%16%31%13%1
2520
16th to endDay
23%317%34%16%4
2520
July1st to 15thDay
9%211%29%32%14%
2371
16th to endDay
10%27%23%35%20%
2490
August1st to 15thDay
10%210%30%31%13%
2413
16th to endDay
14%310%33%30%8%
2357
September1st to 15thDay
13%110%31%30%11%
2160
16th to endDay
28%417%26%17%4
1911
October1st to 15thDay
41%5%15%21%13%1
1650
16th to endDay
48%7%16%18%7%
1686
November1st to 15thDay
55%9%14%16%2
1510
16th to endDay
65%7%13%9%2
1440
December1st to 15thDay
66%6%11%12%4
1440
16th to endDay
70%412%10%2
1536
January1st to 15thNight
65%7%12%11%2
2506
16th to endNight
60%8%14%13%3
2649
February1st to 15thNight
52%8%22%14%2
2288
16th to endNight
45%9%19%21%3
1961
March1st to 15thNight
50%9%18%17%4
2100
16th to endNight
44%7%23%19%4
2040
April1st to 15thNight
40%8%20%23%7%
1799
16th to endNight
30%9%22%26%9%1
1710
May1st to 15thNight
25%420%31%15%1
1440
16th to endNight
29%8%27%25%8%
1496
June1st to 15thNight
30%6%17%33%11%
1440
16th to endNight
22%415%37%17%3
1440
July1st to 15thNight
9%215%28%29%14%
1360
16th to endNight
7%29%22%38%19%
1416
August1st to 15thNight
10%210%33%30%12%
1522
16th to endNight
12%310%33%31%9%
1845
September1st to 15thNight
10%211%33%27%15%
1800
16th to endNight
23%415%30%19%7%
1859
October1st to 15thNight
36%414%24%18%2
1980
16th to endNight
41%8%17%19%11%
2186
November1st to 15thNight
50%8%17%19%4
2347
16th to endNight
54%7%16%17%4
2520
December1st to 15thNight
61%7%13%14%3
2520
16th to endNight
62%7%14%11%3
2688

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
26%5%23%25%15%5%
60
16th to endDay
31%13%22%13%16%2
103
February1st to 15thDay
25%21%22%17%11%2
236
16th to endDay
18%27%25%18%6%2
227
March1st to 15thDay
25%25%26%17%4
270
16th to endDay
27%30%21%14%5%
288
April1st to 15thDay
13%33%28%13%8%2
269
16th to endDay
18%37%21%13%5%4
270
May1st to 15thDay
15%28%25%17%11%2
288
16th to endDay
12%21%28%19%14%3
330
June1st to 15thDay
7%30%30%13%13%3
315
16th to endDay
9%27%30%20%8%3
315
July1st to 15thDay
316%38%22%15%2
305
16th to endDay
120%38%18%13%6%
327
August1st to 15thDay
414%29%20%19%11%
315
16th to endDay
315%22%25%22%9%
332
September1st to 15thDay
5%20%23%20%20%9%
315
16th to endDay
8%17%30%25%17%2
280
October1st to 15thDay
17%21%24%22%10%3
255
16th to endDay
25%13%23%21%11%4
198
November1st to 15thDay
19%10%18%33%16%1
77
16th to endDay
31%5%15%31%13%3
60
December1st to 15thDay
46%6%28%18%
60
16th to endDay
20%9%12%40%15%1
64
January1st to 15thNight
24%21%14%24%12%1
720
16th to endNight
21%20%13%26%15%3
768
February1st to 15thNight
18%22%14%27%15%1
704
16th to endNight
14%25%19%26%14%
632
March1st to 15thNight
17%23%19%28%10%
720
16th to endNight
14%27%20%26%9%1
768
April1st to 15thNight
12%27%23%22%12%
719
16th to endNight
9%29%23%22%12%2
630
May1st to 15thNight
8%26%21%27%15%
360
16th to endNight
5%23%26%28%14%1
375
June1st to 15thNight
8%25%28%25%11%
360
16th to endNight
5%27%28%24%12%
360
July1st to 15thNight
115%26%34%20%
340
16th to endNight
121%24%34%17%1
376
August1st to 15thNight
112%18%38%24%5%
449
16th to endNight
313%21%28%28%4
699
September1st to 15thNight
112%21%25%31%6%
720
16th to endNight
7%14%17%29%27%2
683
October1st to 15thNight
13%15%19%30%17%3
660
16th to endNight
16%12%19%29%19%2
704
November1st to 15thNight
16%20%17%34%11%1
700
16th to endNight
20%22%16%26%12%1
720
December1st to 15thNight
23%20%16%28%10%
720
16th to endNight
22%23%17%25%10%
768
Page generated at 2017-09-23 03:43:43. Version ac04

Copyright 2017 A. Danko


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