Hillsboro
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Hillsboro clear sky chart from 2005-11-05 to 2017-09-18.

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%
15875
24%
46928
14%
15829
52%
15829
35%
27002

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
33%
900
27%
2327
11%
895
45%
895
37%
1393
January16th to endNight
34%
960
30%
2496
11%
960
46%
960
40%
1448
February1st to 15thNight
30%
848
19%
2256
7%
844
38%
844
29%
1479
February16th to endNight
29%
632
27%
1894
10%
632
43%
632
32%
1081
March1st to 15thNight
32%
575
23%
2015
11%
575
45%
575
28%
1140
March16th to endNight
26%
576
18%
2112
11%
576
37%
576
22%
1297
April1st to 15thNight
30%
539
20%
1911
11%
539
45%
539
27%
1072
April16th to endNight
31%
540
21%
1620
14%
540
43%
540
27%
1009
May1st to 15thNight
37%
539
20%
1620
16%
539
46%
539
27%
1014
May16th to endNight
49%
562
18%
1684
14%
561
54%
561
34%
996
June1st to 15thNight
50%
540
18%
1620
9%
540
57%
540
39%
892
June16th to endNight
56%
540
23%
1620
14%
540
63%
540
48%
814
July1st to 15thNight
67%
510
19%
1530
15%
510
70%
510
44%
818
July16th to endNight
71%
564
23%
1594
23%
531
75%
531
43%
864
August1st to 15thNight
74%
539
21%
1610
24%
536
76%
536
38%
905
August16th to endNight
66%
573
28%
1750
28%
573
70%
573
40%
951
September1st to 15thNight
57%
540
22%
1980
23%
540
64%
540
31%
1074
September16th to endNight
56%
501
31%
1848
28%
501
64%
501
36%
933
October1st to 15thNight
45%
583
30%
1903
22%
583
52%
583
31%
1078
October16th to endNight
43%
704
32%
2112
15%
704
55%
704
46%
1066
November1st to 15thNight
44%
850
31%
2250
12%
850
55%
850
45%
1226
November16th to endNight
36%
900
28%
2340
10%
900
48%
900
41%
1345
December1st to 15thNight
32%
900
24%
2340
9%
900
42%
900
32%
1483
December16th to endNight
33%
960
26%
2496
11%
960
43%
960
31%
1624

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
9%5%2442445%7%50%
47866
Night
8%424323447%53%
47124
Cloud CoverDay
9%5%2442445%7%50%
47864
Night
8%424323447%53%
47124
TransparencyDay
33%6%13%26%17%3
47564
Night
30%5%13%26%19%4
46929
SeeingDay
10%7%27%33%17%3
5876
Night
10%8%33%34%11%
15877

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%413434345%54%
1611
16th to endDay
7%6%25%423346%52%
1728
February1st to 15thDay
7%6%36%5%35%345%47%
1615
16th to endDay
8%6%2342345%7%51%
1580
March1st to 15thDay
10%5%25%5%2445%6%46%
1944
16th to endDay
16%8%34323346%43%
2112
April1st to 15thDay
13%6%24324446%47%
2034
16th to endDay
16%7%24423347%41%
2340
May1st to 15thDay
11%7%35%5%2445%7%44%
2331
16th to endDay
12%7%25%5%345%6%7%41%
2430
June1st to 15thDay
7%4135%3345%7%52%
2340
16th to endDay
5%11332446%8%57%
2340
July1st to 15thDay
8%313425%5%8%9%47%
2340
16th to endDay
5%314425%5%6%9%51%
2466
August1st to 15thDay
6%325%425%5%6%8%48%
2340
16th to endDay
7%41433446%7%53%
2449
September1st to 15thDay
9%425%42435%7%49%
1980
16th to endDay
7%424324447%54%
1837
October1st to 15thDay
12%312322446%54%
1716
16th to endDay
7%5%13213345%61%
1760
November1st to 15thDay
5%41332335%5%61%
1605
16th to endDay
9%5%13212135%60%
1620
December1st to 15thDay
12%6%25%42345%5%48%
1620
16th to endDay
12%7%35%323337%45%
1728
January1st to 15thNight
7%5%24324435%55%
2327
16th to endNight
6%5%13323345%59%
2496
February1st to 15thNight
9%8%35%423445%47%
2246
16th to endNight
8%6%23424346%52%
1894
March1st to 15thNight
8%5%2442435%6%50%
2015
16th to endNight
16%6%34423346%45%
2112
April1st to 15thNight
10%5%2442435%7%50%
1911
16th to endNight
13%6%2432335%7%46%
1620
May1st to 15thNight
13%5%2432345%7%45%
1619
16th to endNight
9%31332347%11%48%
1683
June1st to 15thNight
5%21232447%11%52%
1620
16th to endNight
311131445%10%61%
1620
July1st to 15thNight
5%31332445%10%55%
1620
16th to endNight
5%21342446%10%53%
1702
August1st to 15thNight
4215%4345%6%10%50%
1620
16th to endNight
7%314324346%57%
1750
September1st to 15thNight
7%41443335%6%53%
1980
16th to endNight
5%414323346%58%
1848
October1st to 15thNight
13%413323345%54%
1903
16th to endNight
7%32212335%64%
2112
November1st to 15thNight
7%212223347%61%
2250
16th to endNight
10%413213236%59%
2340
December1st to 15thNight
10%6%34423347%49%
2340
16th to endNight
10%7%35%324447%46%
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
8%423434336%54%
1611
16th to endDay
7%6%25%324346%52%
1728
February1st to 15thDay
6%7%25%6%35%446%46%
1615
16th to endDay
8%6%3342335%7%51%
1580
March1st to 15thDay
10%5%25%5%2435%7%46%
1944
16th to endDay
16%8%34322337%43%
2110
April1st to 15thDay
13%6%15%324437%47%
2034
16th to endDay
16%7%25%423347%41%
2340
May1st to 15thDay
10%7%35%5%24347%44%
2331
16th to endDay
12%6%25%5%3446%8%40%
2430
June1st to 15thDay
7%3245%2445%7%52%
2340
16th to endDay
5%21332445%9%57%
2340
July1st to 15thDay
8%3134345%7%9%47%
2340
16th to endDay
5%214425%47%9%52%
2466
August1st to 15thDay
5%325%435%46%9%48%
2340
16th to endDay
7%41443345%7%54%
2449
September1st to 15thDay
10%42442435%6%49%
1980
16th to endDay
6%425%324446%54%
1837
October1st to 15thDay
12%423323445%55%
1716
16th to endDay
7%6%13213345%61%
1760
November1st to 15thDay
6%413323346%61%
1605
16th to endDay
9%6%2322236%60%
1620
December1st to 15thDay
12%5%25%42335%5%48%
1620
16th to endDay
12%6%45%423337%45%
1728
January1st to 15thNight
7%5%24324435%55%
2327
16th to endNight
6%423323345%59%
2496
February1st to 15thNight
8%9%35%42345%5%47%
2246
16th to endNight
8%6%14424446%53%
1894
March1st to 15thNight
8%5%2442445%7%50%
2015
16th to endNight
15%7%24423345%45%
2112
April1st to 15thNight
10%415%423348%49%
1911
16th to endNight
14%5%34323446%46%
1620
May1st to 15thNight
13%435%42445%7%45%
1619
16th to endNight
9%3134245%6%10%48%
1683
June1st to 15thNight
5%2342446%12%52%
1620
16th to endNight
311232445%10%61%
1620
July1st to 15thNight
5%31232446%10%55%
1620
16th to endNight
421332446%10%53%
1702
August1st to 15thNight
42145%345%6%9%51%
1620
16th to endNight
7%314324347%57%
1750
September1st to 15thNight
7%42443435%6%52%
1980
16th to endNight
5%424413347%58%
1848
October1st to 15thNight
12%413323336%53%
1903
16th to endNight
7%33312336%64%
2112
November1st to 15thNight
7%312213347%61%
2250
16th to endNight
10%5%22213236%58%
2340
December1st to 15thNight
11%6%34423347%48%
2340
16th to endNight
11%7%35%424446%46%
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
31%413%30%17%2
1612
16th to endDay
32%417%27%14%2
1728
February1st to 15thDay
38%5%15%25%11%3
1616
16th to endDay
32%5%13%27%17%3
1580
March1st to 15thDay
36%6%10%24%18%3
1944
16th to endDay
42%5%13%23%12%2
2112
April1st to 15thDay
37%6%13%25%15%1
2034
16th to endDay
41%6%12%24%12%1
2340
May1st to 15thDay
40%5%12%24%15%1
2331
16th to endDay
40%8%13%23%11%1
2434
June1st to 15thDay
31%6%15%25%17%4
2340
16th to endDay
22%7%15%27%23%4
2340
July1st to 15thDay
30%7%14%28%15%3
2201
16th to endDay
25%7%14%30%18%3
2311
August1st to 15thDay
31%7%16%24%16%3
2326
16th to endDay
28%7%12%28%16%7%
2449
September1st to 15thDay
33%7%14%22%15%7%
1980
16th to endDay
28%6%11%28%21%4
1837
October1st to 15thDay
30%5%11%23%24%4
1716
16th to endDay
26%311%28%24%5%
1760
November1st to 15thDay
24%412%26%24%7%
1605
16th to endDay
27%39%33%22%3
1620
December1st to 15thDay
37%414%27%14%
1620
16th to endDay
39%411%26%14%2
1728
January1st to 15thNight
30%412%28%21%2
2327
16th to endNight
27%414%28%20%4
2496
February1st to 15thNight
38%6%13%24%14%3
2256
16th to endNight
31%413%26%18%5%
1894
March1st to 15thNight
33%5%11%23%19%6%
2015
16th to endNight
41%5%12%24%14%3
2112
April1st to 15thNight
33%5%12%24%22%2
1911
16th to endNight
37%5%13%21%18%3
1620
May1st to 15thNight
37%6%13%22%16%2
1620
16th to endNight
30%8%22%24%13%1
1685
June1st to 15thNight
24%7%18%29%16%3
1620
16th to endNight
18%6%13%34%20%5%
1620
July1st to 15thNight
23%6%15%29%21%4
1530
16th to endNight
24%6%15%30%20%2
1594
August1st to 15thNight
26%8%17%27%14%5%
1610
16th to endNight
26%5%11%26%22%7%
1750
September1st to 15thNight
30%6%12%24%16%8%
1980
16th to endNight
26%5%10%24%27%5%
1848
October1st to 15thNight
32%5%9%21%24%7%
1903
16th to endNight
22%39%29%30%5%
2112
November1st to 15thNight
22%410%25%26%10%
2250
16th to endNight
27%311%29%22%5%
2340
December1st to 15thNight
35%413%27%16%1
2340
16th to endNight
37%5%13%23%15%4
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
17%12%34%30%5%
90
16th to endDay
16%9%48%23%1
96
February1st to 15thDay
7%21%45%20%5%
90
16th to endDay
319%44%20%8%2
81
March1st to 15thDay
13%21%48%15%1
90
16th to endDay
20%15%40%20%2
96
April1st to 15thDay
16%15%33%25%8%
153
16th to endDay
17%15%39%19%7%
450
May1st to 15thDay
14%12%34%25%10%2
468
16th to endDay
16%10%30%29%10%2
517
June1st to 15thDay
7%428%37%19%1
495
16th to endDay
5%5%30%38%16%2
495
July1st to 15thDay
10%118%44%21%3
475
16th to endDay
5%12%42%32%6%
515
August1st to 15thDay
6%114%41%32%3
493
16th to endDay
8%118%37%26%6%
489
September1st to 15thDay
4422%40%25%2
135
16th to endDay
5%8%22%33%19%10%
96
October1st to 15thDay
5%7%33%28%16%7%
90
16th to endDay
35%47%23%16%3
96
November1st to 15thDay
6%328%42%15%3
90
16th to endDay
25%18%33%17%22
90
December1st to 15thDay
11%20%37%23%43
90
16th to endDay
19%17%34%25%3
96
January1st to 15thNight
10%12%39%30%6%
900
16th to endNight
10%10%41%32%4
960
February1st to 15thNight
13%10%40%31%3
848
16th to endNight
10%15%41%28%3
632
March1st to 15thNight
10%12%40%28%7%
575
16th to endNight
18%11%41%22%5%
576
April1st to 15thNight
12%13%39%26%6%
539
16th to endNight
17%11%36%27%6%
540
May1st to 15thNight
16%7%34%31%8%1
540
16th to endNight
10%6%31%35%14%2
563
June1st to 15thNight
6%5%34%36%17%
540
16th to endNight
3234%45%13%
540
July1st to 15thNight
5%19%50%21%1
510
16th to endNight
6%14%47%29%1
564
August1st to 15thNight
5%9%57%24%1
539
16th to endNight
8%116%39%30%3
573
September1st to 15thNight
9%323%39%21%2
540
16th to endNight
7%427%36%22%
501
October1st to 15thNight
14%6%28%29%18%1
583
16th to endNight
8%7%38%33%10%
704
November1st to 15thNight
8%11%33%33%12%
850
16th to endNight
12%13%36%30%7%
900
December1st to 15thNight
14%12%36%30%5%
900
16th to endNight
13%9%38%31%6%
960
Page generated at 2017-09-19 06:32:31. Version ac04

Copyright 2017 A. Danko


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