Arrowhead Beach
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Arrowhead Beach clear sky chart from 2005-11-05 to 2018-01-12.

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
43%
16032
21%
48404
13%
15996
51%
15996
26%
30662

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
31%
761
21%
2485
11%
761
43%
761
21%
1562
January16th to endNight
22%
768
22%
2496
8%
768
40%
768
23%
1576
February1st to 15thNight
25%
701
20%
2258
9%
701
41%
701
23%
1399
February16th to endNight
23%
631
27%
1893
12%
631
41%
631
28%
1134
March1st to 15thNight
30%
720
23%
2001
11%
720
43%
720
30%
1259
March16th to endNight
31%
768
21%
2082
11%
768
39%
768
27%
1386
April1st to 15thNight
33%
718
21%
1796
8%
718
42%
718
32%
1180
April16th to endNight
37%
720
20%
1800
9%
720
42%
720
32%
1197
May1st to 15thNight
39%
679
15%
1759
6%
679
44%
679
28%
1205
May16th to endNight
60%
425
17%
1548
16%
425
62%
425
26%
906
June1st to 15thNight
63%
360
15%
1440
17%
360
66%
360
22%
858
June16th to endNight
61%
360
16%
1440
17%
360
66%
360
24%
855
July1st to 15thNight
66%
420
12%
1440
13%
420
67%
420
22%
937
July16th to endNight
72%
564
14%
1595
11%
531
75%
531
29%
1029
August1st to 15thNight
62%
596
15%
1666
10%
593
62%
593
28%
1109
August16th to endNight
61%
764
16%
1910
10%
764
62%
764
26%
1361
September1st to 15thNight
62%
720
23%
1800
15%
720
65%
720
31%
1208
September16th to endNight
52%
717
18%
1960
14%
717
56%
717
24%
1373
October1st to 15thNight
50%
720
24%
2160
21%
720
57%
720
28%
1379
October16th to endNight
44%
768
34%
2304
23%
768
60%
768
35%
1299
November1st to 15thNight
42%
760
23%
2365
16%
760
52%
760
29%
1428
November16th to endNight
41%
780
26%
2564
19%
780
52%
780
28%
1503
December1st to 15thNight
34%
780
19%
2730
12%
780
46%
780
21%
1717
December16th to endNight
31%
832
23%
2912
13%
832
45%
832
22%
1802

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
12%5%25%5%345%5%7%41%
48915
Night
13%5%2442445%7%44%
48595
Cloud CoverDay
12%5%25%5%345%5%7%41%
48925
Night
12%5%2442445%7%44%
48599
TransparencyDay
39%7%11%20%16%3
48624
Night
38%6%11%20%17%4
48404
SeeingDay
17%7%24%25%19%7%
6220
Night
15%7%27%31%15%1
16040

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
15%5%25%32335%6%46%
1694
16th to endDay
17%5%1332445%5%46%
1728
February1st to 15thDay
15%6%24424445%45%
1603
16th to endDay
13%5%2443435%6%46%
1580
March1st to 15thDay
13%5%24413335%50%
1945
16th to endDay
17%5%25%333435%43%
2142
April1st to 15thDay
11%5%14323348%51%
2152
16th to endDay
10%435%5%35%5%5%6%46%
2160
May1st to 15thDay
12%5%26%5%35%5%5%8%38%
2202
16th to endDay
11%5%25%5%345%6%9%41%
2567
June1st to 15thDay
9%4246%35%6%7%9%38%
2520
16th to endDay
7%426%5%36%6%8%11%36%
2520
July1st to 15thDay
7%425%5%47%6%8%11%36%
2429
16th to endDay
6%5%26%6%47%6%9%10%33%
2465
August1st to 15thDay
11%6%25%7%36%6%6%9%33%
2271
16th to endDay
11%5%37%7%36%6%6%9%31%
2292
September1st to 15thDay
13%5%25%5%35%6%5%8%38%
2160
16th to endDay
19%8%36%6%35%45%6%30%
1997
October1st to 15thDay
15%7%25%5%2235%6%42%
1800
16th to endDay
10%425%32333455%
1920
November1st to 15thDay
17%5%14313445%48%
1822
16th to endDay
12%424423346%51%
1722
December1st to 15thDay
15%5%24323446%45%
1560
16th to endDay
19%5%245%24335%42%
1664
January1st to 15thNight
14%6%24434446%43%
2485
16th to endNight
15%6%35%424345%44%
2496
February1st to 15thNight
17%6%2441335%6%44%
2257
16th to endNight
12%6%24423436%50%
1893
March1st to 15thNight
13%423424447%48%
1989
16th to endNight
16%424434445%44%
2082
April1st to 15thNight
10%6%25%424447%47%
1796
16th to endNight
14%5%24423447%46%
1800
May1st to 15thNight
12%5%25%5%245%6%10%39%
1759
16th to endNight
10%31442446%10%45%
1546
June1st to 15thNight
9%5%345%246%7%8%42%
1440
16th to endNight
6%425%5%35%6%8%11%41%
1440
July1st to 15thNight
6%5%246%36%7%6%11%37%
1527
16th to endNight
7%323437%6%9%13%36%
1703
August1st to 15thNight
9%7%36%5%3446%9%39%
1677
16th to endNight
9%5%35%7%45%5%6%10%35%
1910
September1st to 15thNight
12%424425%45%8%44%
1800
16th to endNight
18%6%144345%5%8%36%
1960
October1st to 15thNight
15%5%23434335%47%
2160
16th to endNight
11%424323345%56%
2304
November1st to 15thNight
16%5%23313336%49%
2365
16th to endNight
13%5%14423346%49%
2564
December1st to 15thNight
14%7%25%5%34446%41%
2730
16th to endNight
16%7%24423346%43%
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
15%6%2442335%6%46%
1694
16th to endDay
17%5%23324445%45%
1728
February1st to 15thDay
14%6%24424445%45%
1603
16th to endDay
13%6%14434446%46%
1580
March1st to 15thDay
13%425%423335%50%
1956
16th to endDay
18%435%324436%43%
2141
April1st to 15thDay
11%413423447%51%
2152
16th to endDay
10%5%245%35%5%5%6%46%
2160
May1st to 15thDay
12%5%27%5%35%45%8%38%
2202
16th to endDay
10%5%25%5%35%5%6%8%41%
2567
June1st to 15thDay
8%5%245%36%7%7%9%38%
2520
16th to endDay
7%426%5%36%6%8%11%36%
2520
July1st to 15thDay
7%425%5%46%6%8%11%36%
2429
16th to endDay
6%5%26%7%36%7%8%11%33%
2465
August1st to 15thDay
11%5%26%5%46%7%6%9%33%
2271
16th to endDay
11%6%26%7%45%7%6%9%30%
2292
September1st to 15thDay
12%5%25%5%45%5%6%8%38%
2160
16th to endDay
18%8%46%5%34448%30%
1997
October1st to 15thDay
16%6%25%5%2335%6%42%
1800
16th to endDay
10%415%42333455%
1920
November1st to 15thDay
17%6%14313345%48%
1822
16th to endDay
12%413423447%51%
1722
December1st to 15thDay
16%5%25%423446%45%
1560
16th to endDay
18%6%25%434336%41%
1664
January1st to 15thNight
14%6%2443345%6%43%
2485
16th to endNight
15%6%35%423345%44%
2496
February1st to 15thNight
16%6%2431335%6%44%
2250
16th to endNight
12%6%24423446%50%
1893
March1st to 15thNight
14%423423446%49%
2001
16th to endNight
16%424434435%45%
2082
April1st to 15thNight
10%6%26%424447%47%
1796
16th to endNight
14%5%24423347%46%
1800
May1st to 15thNight
11%5%25%5%345%6%10%39%
1758
16th to endNight
10%31442447%9%46%
1546
June1st to 15thNight
9%6%245%245%6%10%41%
1440
16th to endNight
6%425%5%26%5%10%10%41%
1440
July1st to 15thNight
6%5%26%6%37%6%8%10%37%
1527
16th to endNight
7%3235%37%5%9%13%37%
1703
August1st to 15thNight
8%7%35%5%2446%10%39%
1677
16th to endNight
9%5%36%7%35%5%7%10%35%
1910
September1st to 15thNight
12%4244345%6%8%43%
1800
16th to endNight
17%6%24435%46%7%36%
1960
October1st to 15thNight
15%6%24434335%46%
2160
16th to endNight
11%423323245%56%
2304
November1st to 15thNight
16%5%23312337%48%
2365
16th to endNight
12%5%24424346%49%
2564
December1st to 15thNight
14%7%25%5%35%446%42%
2730
16th to endNight
16%7%24423346%43%
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
39%49%19%21%6%
1695
16th to endDay
39%48%21%20%5%
1728
February1st to 15thDay
40%46%22%21%5%
1606
16th to endDay
37%5%9%23%20%3
1580
March1st to 15thDay
37%5%9%22%19%5%
1956
16th to endDay
42%5%8%20%18%4
2142
April1st to 15thDay
32%49%25%21%5%
2152
16th to endDay
37%7%10%19%19%6%
2160
May1st to 15thDay
42%7%13%20%13%2
2202
16th to endDay
38%9%13%24%12%1
2571
June1st to 15thDay
38%9%14%22%14%1
2520
16th to endDay
37%10%16%19%13%2
2520
July1st to 15thDay
37%11%18%20%9%2
2287
16th to endDay
38%10%18%20%10%1
2310
August1st to 15thDay
45%10%14%18%10%1
2258
16th to endDay
46%9%14%17%10%1
2292
September1st to 15thDay
40%8%13%17%16%2
2160
16th to endDay
52%5%9%16%14%
1997
October1st to 15thDay
42%5%6%20%21%2
1800
16th to endDay
32%36%22%30%4
1920
November1st to 15thDay
38%410%19%21%5%
1822
16th to endDay
33%5%9%22%23%6%
1722
December1st to 15thDay
39%5%10%22%16%5%
1560
16th to endDay
45%38%22%16%4
1664
January1st to 15thNight
41%5%8%17%20%6%
2485
16th to endNight
42%49%19%18%6%
2496
February1st to 15thNight
41%47%19%21%5%
2258
16th to endNight
35%49%24%19%6%
1893
March1st to 15thNight
35%6%11%23%17%5%
2001
16th to endNight
40%5%9%21%18%3
2082
April1st to 15thNight
37%410%19%21%6%
1796
16th to endNight
37%6%10%20%18%6%
1800
May1st to 15thNight
40%8%14%22%12%2
1759
16th to endNight
32%10%17%25%12%1
1548
June1st to 15thNight
36%9%15%24%12%1
1440
16th to endNight
33%11%17%21%13%2
1440
July1st to 15thNight
37%12%18%19%11%1
1440
16th to endNight
32%12%18%24%9%2
1595
August1st to 15thNight
38%9%19%19%12%
1666
16th to endNight
41%10%15%21%9%1
1910
September1st to 15thNight
36%8%16%17%15%3
1800
16th to endNight
45%7%11%16%17%1
1960
October1st to 15thNight
40%48%19%22%3
2160
16th to endNight
30%47%22%28%6%
2304
November1st to 15thNight
37%410%17%24%6%
2365
16th to endNight
35%47%20%22%8%
2564
December1st to 15thNight
42%5%11%19%17%4
2730
16th to endNight
42%410%21%16%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
23%17%41%15%1
119
16th to endDay
30%23%35%8%2
96
February1st to 15thDay
22%25%35%15%1
120
16th to endDay
17%11%45%22%2
239
March1st to 15thDay
16%15%34%23%8%1
270
16th to endDay
18%10%35%22%9%3
288
April1st to 15thDay
19%10%30%21%13%4
270
16th to endDay
12%5%31%31%13%4
270
May1st to 15thDay
19%9%31%23%13%3
288
16th to endDay
19%318%23%26%9%
331
June1st to 15thDay
14%5%17%26%28%7%
315
16th to endDay
11%317%34%25%6%
315
July1st to 15thDay
9%114%33%30%10%
305
16th to endDay
9%29%29%36%13%
326
August1st to 15thDay
14%215%23%29%14%
313
16th to endDay
16%9%24%31%17%
332
September1st to 15thDay
15%417%25%20%16%
315
16th to endDay
25%318%22%21%8%
314
October1st to 15thDay
23%321%26%18%6%
315
16th to endDay
10%7%30%23%19%8%
336
November1st to 15thDay
22%6%26%24%16%2
305
16th to endDay
15%12%24%27%16%2
252
December1st to 15thDay
28%14%30%16%8%1
90
16th to endDay
25%17%32%19%5%
96
January1st to 15thNight
17%15%31%27%8%
765
16th to endNight
18%11%42%23%3
768
February1st to 15thNight
21%12%36%26%1
704
16th to endNight
15%14%43%21%3
631
March1st to 15thNight
17%10%39%26%6%
720
16th to endNight
18%9%37%25%8%
768
April1st to 15thNight
14%11%37%29%7%
718
16th to endNight
16%6%34%32%8%
720
May1st to 15thNight
13%7%33%35%9%
679
16th to endNight
12%20%42%22%
426
June1st to 15thNight
11%215%45%23%1
360
16th to endNight
7%118%48%23%1
360
July1st to 15thNight
9%113%44%28%2
420
16th to endNight
7%110%42%32%5%
564
August1st to 15thNight
12%113%38%30%4
596
16th to endNight
11%211%34%35%4
764
September1st to 15thNight
14%212%37%29%4
720
16th to endNight
20%314%34%24%2
717
October1st to 15thNight
20%321%30%22%2
720
16th to endNight
15%6%30%26%18%2
768
November1st to 15thNight
18%5%26%31%14%3
760
16th to endNight
15%9%29%27%16%1
780
December1st to 15thNight
18%7%33%29%10%
780
16th to endNight
20%9%34%30%5%
832
Page generated at 2018-01-12 22:01:35. Version ac04

Copyright 2018 A. Danko


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