PFO Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the PFO Observatory clear sky chart from 2005-11-05 to 2017-09-23.

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
22%
14906
14%
46810
5%
14863
31%
14863
13%
33628

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
13%
743
14%
2640
2%
739
28%
739
10%
1837
January16th to endNight
12%
768
16%
2556
1%
768
29%
768
11%
1772
February1st to 15thNight
12%
704
12%
2286
3%
701
23%
701
11%
1615
February16th to endNight
16%
631
12%
1985
2%
631
28%
631
10%
1477
March1st to 15thNight
15%
720
15%
2025
4%
720
27%
720
14%
1499
March16th to endNight
20%
768
17%
2112
6%
768
29%
768
15%
1525
April1st to 15thNight
19%
596
14%
1782
6%
596
26%
596
13%
1331
April16th to endNight
20%
540
14%
1620
4%
540
29%
540
15%
1168
May1st to 15thNight
23%
540
10%
1593
5%
540
28%
540
12%
1213
May16th to endNight
23%
561
9%
1496
3%
560
29%
560
14%
1174
June1st to 15thNight
24%
361
7%
1261
4%
361
28%
361
10%
975
June16th to endNight
30%
360
7%
1260
6%
360
33%
360
11%
950
July1st to 15thNight
37%
340
8%
1190
8%
340
39%
340
13%
851
July16th to endNight
30%
486
7%
1460
6%
455
35%
455
12%
1121
August1st to 15thNight
39%
539
10%
1608
7%
535
41%
535
15%
1204
August16th to endNight
41%
573
17%
1725
10%
573
46%
573
21%
1172
September1st to 15thNight
33%
606
15%
1866
9%
606
40%
606
21%
1259
September16th to endNight
36%
689
23%
1902
12%
689
45%
689
26%
1232
October1st to 15thNight
28%
660
19%
1966
9%
660
37%
660
19%
1330
October16th to endNight
20%
704
15%
2161
4%
704
31%
704
16%
1524
November1st to 15thNight
24%
717
15%
2378
8%
717
33%
717
16%
1638
November16th to endNight
19%
750
15%
2520
5%
750
30%
750
11%
1777
December1st to 15thNight
10%
750
13%
2538
2%
750
23%
750
8%
1890
December16th to endNight
8%
800
12%
2880
2%
800
21%
800
8%
2094

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
20%7%35%5%2445%6%33%
48092
Night
21%8%35%424446%32%
46981
TransparencyDay
51%6%11%19%10%1
47781
Night
52%5%10%19%10%
46810
SeeingDay
25%18%25%20%7%1
6957
Night
24%23%24%19%6%
14906

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%10%36%435%346%35%
1295
16th to endDay
16%11%345%2445%7%34%
1665
February1st to 15thDay
13%11%35%7%36%46%7%31%
1575
16th to endDay
13%11%47%5%35%5%5%6%32%
1485
March1st to 15thDay
19%10%46%5%24346%31%
1924
16th to endDay
15%9%36%5%34446%36%
2112
April1st to 15thDay
20%10%46%5%33335%32%
2165
16th to endDay
23%5%25%5%23447%34%
2340
May1st to 15thDay
25%8%35%5%24346%28%
2357
16th to endDay
25%7%25%42445%7%28%
2627
June1st to 15thDay
25%9%46%5%345%45%26%
2700
16th to endDay
26%6%25%5%2445%8%28%
2700
July1st to 15thDay
19%6%25%435%5%5%9%33%
2700
16th to endDay
20%8%245%25%45%7%31%
2589
August1st to 15thDay
18%7%35%5%245%5%7%35%
2340
16th to endDay
15%5%25%43447%7%40%
2477
September1st to 15thDay
18%5%23423447%42%
2091
16th to endDay
18%413323346%47%
1895
October1st to 15thDay
19%6%14433436%41%
1663
16th to endDay
20%7%35%5%24445%34%
1710
November1st to 15thDay
23%6%25%5%2335%6%35%
1479
16th to endDay
22%7%345%34447%32%
1440
December1st to 15thDay
27%8%24323446%30%
1419
16th to endDay
25%8%36%5%34246%29%
1344
January1st to 15thNight
17%8%35%425%5%5%7%33%
2640
16th to endNight
16%10%35%5%3445%9%32%
2556
February1st to 15thNight
17%9%25%5%35%45%7%31%
2285
16th to endNight
16%11%47%5%345%45%29%
1985
March1st to 15thNight
18%9%36%5%3445%5%32%
2013
16th to endNight
18%9%34434447%34%
2112
April1st to 15thNight
24%7%36%5%3444430%
1782
16th to endNight
24%7%25%424445%32%
1620
May1st to 15thNight
26%7%35%5%34447%26%
1593
16th to endNight
24%7%35%5%35%5%47%26%
1494
June1st to 15thNight
30%9%27%5%23447%22%
1261
16th to endNight
27%9%35%5%24345%27%
1260
July1st to 15thNight
22%8%36%425%45%7%29%
1260
16th to endNight
24%8%35%6%26%46%6%24%
1564
August1st to 15thNight
21%8%25%4335%6%7%30%
1620
16th to endNight
16%7%235%2446%7%39%
1725
September1st to 15thNight
21%7%24423347%38%
1866
16th to endNight
17%5%14313346%46%
1902
October1st to 15thNight
21%6%24423345%39%
1966
16th to endNight
22%8%24423345%36%
2161
November1st to 15thNight
22%5%25%5%33446%36%
2378
16th to endNight
21%7%35%434446%34%
2520
December1st to 15thNight
27%9%34324346%30%
2538
16th to endNight
26%10%35%424346%28%
2880

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
50%6%14%17%8%1
1296
16th to endDay
48%6%9%21%12%
1665
February1st to 15thDay
52%6%12%18%7%1
1578
16th to endDay
51%5%13%18%8%1
1485
March1st to 15thDay
54%49%18%10%1
1935
16th to endDay
48%5%10%19%14%2
2112
April1st to 15thDay
55%38%16%13%2
2165
16th to endDay
49%411%17%14%2
2340
May1st to 15thDay
56%5%8%18%9%1
2357
16th to endDay
55%7%11%20%4
2631
June1st to 15thDay
61%5%9%15%6%1
2700
16th to endDay
54%8%10%17%8%
2700
July1st to 15thDay
48%8%14%18%9%
2541
16th to endDay
49%10%13%19%5%
2431
August1st to 15thDay
48%10%12%20%8%
2327
16th to endDay
42%8%14%24%10%
2477
September1st to 15thDay
42%7%13%23%12%1
2091
16th to endDay
39%5%9%27%17%1
1895
October1st to 15thDay
44%5%10%27%11%
1663
16th to endDay
51%5%10%21%10%
1710
November1st to 15thDay
50%5%13%16%12%
1479
16th to endDay
52%6%12%17%10%
1440
December1st to 15thDay
55%5%11%19%6%
1419
16th to endDay
57%5%10%15%10%
1344
January1st to 15thNight
49%7%12%19%9%1
2640
16th to endNight
50%6%11%22%10%
2556
February1st to 15thNight
50%6%12%18%10%
2286
16th to endNight
55%6%9%16%10%1
1985
March1st to 15thNight
53%5%8%17%12%1
2025
16th to endNight
50%5%8%18%14%1
2112
April1st to 15thNight
56%48%13%12%3
1782
16th to endNight
52%5%9%17%13%1
1620
May1st to 15thNight
58%5%9%16%8%1
1593
16th to endNight
57%7%10%16%7%
1496
June1st to 15thNight
63%49%16%31
1261
16th to endNight
60%5%8%16%8%
1260
July1st to 15thNight
54%5%12%18%8%
1190
16th to endNight
57%8%11%16%5%
1460
August1st to 15thNight
53%8%11%18%8%
1608
16th to endNight
45%6%12%25%9%
1725
September1st to 15thNight
47%410%23%13%
1866
16th to endNight
40%410%27%16%
1902
October1st to 15thNight
46%49%25%12%1
1966
16th to endNight
50%5%10%21%11%
2161
November1st to 15thNight
49%5%14%19%11%
2378
16th to endNight
51%6%12%18%10%
2520
December1st to 15thNight
58%5%8%20%7%
2538
16th to endNight
57%5%11%17%8%
2880

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%26%21%28%
60
16th to endDay
19%27%37%14%1
193
February1st to 15thDay
19%30%28%16%3
236
16th to endDay
19%26%30%19%4
223
March1st to 15thDay
22%30%28%15%3
270
16th to endDay
24%24%29%15%5%
288
April1st to 15thDay
30%23%27%13%4
270
16th to endDay
24%18%29%18%6%2
270
May1st to 15thDay
32%17%27%14%6%
313
16th to endDay
29%20%25%16%6%
519
June1st to 15thDay
26%17%26%21%7%
495
16th to endDay
29%16%23%20%9%1
495
July1st to 15thDay
28%13%19%25%11%1
475
16th to endDay
26%14%21%25%9%1
382
August1st to 15thDay
25%9%20%30%12%1
313
16th to endDay
21%9%22%29%14%1
332
September1st to 15thDay
25%8%23%29%11%1
315
16th to endDay
21%9%26%27%12%2
283
October1st to 15thDay
24%15%24%20%11%3
227
16th to endDay
24%21%31%17%41
240
November1st to 15thDay
21%21%26%20%7%2
235
16th to endDay
25%29%26%12%5%
240
December1st to 15thDay
30%22%29%13%4
219
16th to endDay
35%20%34%7%1
64
January1st to 15thNight
20%33%27%15%3
743
16th to endNight
19%32%31%13%3
768
February1st to 15thNight
21%30%32%13%1
704
16th to endNight
23%29%25%17%3
631
March1st to 15thNight
22%28%28%17%2
720
16th to endNight
20%28%27%18%5%
768
April1st to 15thNight
24%24%27%19%4
596
16th to endNight
23%22%28%20%4
540
May1st to 15thNight
27%20%22%20%6%1
540
16th to endNight
24%23%23%21%5%
561
June1st to 15thNight
31%19%17%24%6%
361
16th to endNight
30%18%13%26%10%
360
July1st to 15thNight
30%14%12%30%12%1
340
16th to endNight
25%19%16%24%13%
486
August1st to 15thNight
25%11%15%29%16%1
539
16th to endNight
22%10%20%30%14%1
573
September1st to 15thNight
26%11%23%25%11%
606
16th to endNight
21%13%24%25%13%2
689
October1st to 15thNight
22%17%26%22%9%2
660
16th to endNight
26%20%30%17%4
704
November1st to 15thNight
19%23%25%20%9%1
717
16th to endNight
21%31%25%15%6%
750
December1st to 15thNight
29%30%25%11%3
750
16th to endNight
30%30%26%10%2
800
Page generated at 2017-09-24 10:15:46. Version ac04

Copyright 2017 A. Danko


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