Birdton
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Birdton 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
24%
14959
14%
47287
5%
14921
34%
14921
16%
33004

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
16%
743
14%
2640
2%
739
30%
739
10%
1833
January16th to endNight
16%
768
15%
2627
2%
768
32%
768
13%
1796
February1st to 15thNight
18%
704
13%
2286
3%
701
30%
701
15%
1582
February16th to endNight
17%
631
12%
1971
2%
631
28%
631
11%
1469
March1st to 15thNight
17%
720
16%
2047
5%
720
28%
720
15%
1491
March16th to endNight
19%
768
17%
2112
5%
768
29%
768
18%
1501
April1st to 15thNight
16%
611
15%
1761
4%
611
25%
611
14%
1294
April16th to endNight
22%
540
16%
1620
6%
540
31%
540
18%
1124
May1st to 15thNight
25%
540
11%
1599
5%
540
31%
540
15%
1166
May16th to endNight
20%
489
10%
1424
3%
488
28%
488
14%
1083
June1st to 15thNight
29%
360
7%
1260
5%
360
33%
360
13%
941
June16th to endNight
34%
360
7%
1260
6%
360
37%
360
16%
874
July1st to 15thNight
37%
340
11%
1190
8%
340
45%
340
22%
784
July16th to endNight
38%
424
9%
1405
8%
398
43%
398
16%
973
August1st to 15thNight
42%
539
11%
1608
8%
535
45%
535
22%
1087
August16th to endNight
41%
573
19%
1719
10%
573
47%
573
28%
1058
September1st to 15thNight
32%
629
15%
1869
7%
629
39%
629
24%
1224
September16th to endNight
38%
717
24%
1980
13%
717
47%
717
31%
1200
October1st to 15thNight
30%
720
19%
2130
8%
720
40%
720
24%
1394
October16th to endNight
21%
768
16%
2392
4%
768
33%
768
15%
1681
November1st to 15thNight
23%
715
16%
2370
8%
715
34%
715
16%
1636
November16th to endNight
24%
750
15%
2520
6%
750
35%
750
13%
1789
December1st to 15thNight
15%
750
13%
2617
3%
750
27%
750
10%
1893
December16th to endNight
12%
800
12%
2880
3%
800
24%
800
9%
2131

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
21%8%35%5%34446%32%
48467
Night
20%8%35%5%2445%6%34%
47453
TransparencyDay
52%5%11%20%9%1
48151
Night
50%5%11%21%10%
47287
SeeingDay
28%13%29%18%8%1
6937
Night
25%13%31%22%6%
14959

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
16%11%47%5%25%45%5%31%
1295
16th to endDay
16%10%47%6%34446%31%
1596
February1st to 15thDay
12%10%46%8%45%5%5%6%30%
1575
16th to endDay
16%14%5%7%7%34446%26%
1500
March1st to 15thDay
20%13%35%5%33336%29%
1901
16th to endDay
17%9%5%8%6%24345%32%
2112
April1st to 15thDay
23%11%35%42435%5%30%
2185
16th to endDay
26%8%15%423335%33%
2340
May1st to 15thDay
26%8%36%423445%29%
2353
16th to endDay
26%8%26%6%23346%28%
2699
June1st to 15thDay
27%8%47%5%34445%24%
2700
16th to endDay
27%6%36%5%25%5%46%26%
2700
July1st to 15thDay
17%5%25%5%35%5%5%8%34%
2700
16th to endDay
19%7%345%45%5%6%8%29%
2650
August1st to 15thDay
21%6%35%5%35%45%6%32%
2340
16th to endDay
14%425%5%45%5%5%6%39%
2483
September1st to 15thDay
18%5%245%2445%7%39%
2089
16th to endDay
18%414323336%47%
1980
October1st to 15thDay
20%7%24423346%39%
1830
16th to endDay
24%9%26%5%23345%32%
1827
November1st to 15thDay
22%9%25%43336%6%32%
1487
16th to endDay
22%10%26%4235%35%31%
1440
December1st to 15thDay
25%8%445%34445%28%
1341
16th to endDay
22%13%5%5%5%2444426%
1344
January1st to 15thNight
15%9%46%5%35%5%6%6%31%
2640
16th to endNight
14%10%36%6%345%6%7%30%
2627
February1st to 15thNight
12%11%37%5%36%45%6%32%
2285
16th to endNight
16%14%47%5%25%5%4429%
1971
March1st to 15thNight
19%9%36%5%24445%33%
2035
16th to endNight
16%10%46%43345%435%
2112
April1st to 15thNight
24%8%25%5%34445%31%
1761
16th to endNight
25%6%24323346%36%
1620
May1st to 15thNight
24%6%35%6%34446%30%
1599
16th to endNight
23%7%35%6%35%445%28%
1422
June1st to 15thNight
26%5%35%6%35%5%5%6%27%
1260
16th to endNight
22%5%25%5%25%45%8%31%
1260
July1st to 15thNight
15%5%24445%5%5%9%36%
1260
16th to endNight
20%5%25%5%345%6%7%33%
1504
August1st to 15thNight
16%6%35%5%3345%7%38%
1620
16th to endNight
15%42432345%8%45%
1719
September1st to 15thNight
19%5%2442435%6%41%
1869
16th to endNight
15%313323346%50%
1980
October1st to 15thNight
18%6%24423447%41%
2130
16th to endNight
23%7%25%423445%34%
2392
November1st to 15thNight
23%6%3443435%5%34%
2370
16th to endNight
21%8%36%42445%6%33%
2520
December1st to 15thNight
26%8%35%5%24445%30%
2617
16th to endNight
24%10%46%5%3345%6%26%
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
52%6%13%17%8%1
1296
16th to endDay
53%39%21%11%
1596
February1st to 15thDay
52%5%12%20%7%1
1578
16th to endDay
58%411%17%7%1
1500
March1st to 15thDay
57%39%16%11%2
1912
16th to endDay
54%39%19%11%2
2112
April1st to 15thDay
56%29%16%12%2
2185
16th to endDay
52%310%17%12%3
2340
May1st to 15thDay
56%48%19%9%1
2353
16th to endDay
56%5%11%18%6%
2703
June1st to 15thDay
60%5%11%13%8%
2700
16th to endDay
57%5%10%17%8%
2700
July1st to 15thDay
43%7%15%21%11%
2541
16th to endDay
50%7%16%18%6%
2487
August1st to 15thDay
51%5%13%23%5%
2327
16th to endDay
42%6%15%25%8%
2483
September1st to 15thDay
43%6%13%25%10%
2089
16th to endDay
38%410%29%15%1
1980
October1st to 15thDay
45%413%27%9%
1830
16th to endDay
53%311%21%8%
1827
November1st to 15thDay
51%5%13%15%12%
1487
16th to endDay
53%414%17%8%
1440
December1st to 15thDay
57%412%18%6%
1341
16th to endDay
59%48%17%8%
1344
January1st to 15thNight
50%6%13%19%9%
2640
16th to endNight
48%6%11%21%10%
2627
February1st to 15thNight
50%413%20%9%
2286
16th to endNight
56%5%9%15%10%1
1971
March1st to 15thNight
53%49%18%12%2
2047
16th to endNight
50%39%20%13%1
2112
April1st to 15thNight
54%5%8%16%12%3
1761
16th to endNight
49%49%18%14%2
1620
May1st to 15thNight
54%5%10%19%9%1
1599
16th to endNight
57%6%11%15%7%
1424
June1st to 15thNight
56%7%10%17%5%1
1260
16th to endNight
50%6%13%20%8%
1260
July1st to 15thNight
42%7%14%25%8%
1190
16th to endNight
48%8%14%18%9%
1405
August1st to 15thNight
45%6%15%24%8%
1608
16th to endNight
36%6%17%29%9%
1719
September1st to 15thNight
42%5%11%26%12%1
1869
16th to endNight
34%414%29%16%1
1980
October1st to 15thNight
43%411%27%12%
2130
16th to endNight
50%5%11%22%10%
2392
November1st to 15thNight
49%5%13%20%9%1
2370
16th to endNight
51%5%12%20%8%
2520
December1st to 15thNight
56%410%22%5%
2617
16th to endNight
58%5%10%18%7%
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
26%20%40%11%1
60
16th to endDay
25%20%33%16%4
124
February1st to 15thDay
20%15%36%22%5%
236
16th to endDay
26%19%27%18%7%
226
March1st to 15thDay
31%19%31%12%31
270
16th to endDay
26%18%28%15%8%2
288
April1st to 15thDay
35%17%27%12%5%
270
16th to endDay
32%15%30%10%7%2
270
May1st to 15thDay
35%16%25%15%32
309
16th to endDay
33%14%30%14%7%
519
June1st to 15thDay
36%12%24%20%6%
495
16th to endDay
30%9%31%18%9%1
495
July1st to 15thDay
24%8%30%23%12%1
475
16th to endDay
23%7%30%25%12%1
381
August1st to 15thDay
23%5%31%23%13%2
313
16th to endDay
19%9%27%24%14%4
332
September1st to 15thDay
19%9%33%25%9%1
315
16th to endDay
18%13%29%21%12%4
314
October1st to 15thDay
25%15%23%20%10%3
277
16th to endDay
32%17%30%11%7%
288
November1st to 15thDay
26%12%31%17%10%
235
16th to endDay
32%17%24%19%6%
240
December1st to 15thDay
36%19%21%19%2
141
16th to endDay
37%20%29%12%
64
January1st to 15thNight
23%20%32%20%3
743
16th to endNight
22%19%34%19%4
768
February1st to 15thNight
21%17%36%19%5%
704
16th to endNight
27%18%31%17%4
631
March1st to 15thNight
26%17%32%20%3
720
16th to endNight
23%16%34%20%5%
768
April1st to 15thNight
30%16%30%17%4
611
16th to endNight
31%13%31%18%5%
540
May1st to 15thNight
28%12%29%24%4
540
16th to endNight
27%12%33%22%4
489
June1st to 15thNight
28%7%31%26%5%
360
16th to endNight
26%6%29%30%6%1
360
July1st to 15thNight
16%435%32%10%
340
16th to endNight
21%428%33%11%
424
August1st to 15thNight
18%424%37%14%
539
16th to endNight
16%5%32%29%16%
573
September1st to 15thNight
21%9%31%27%9%
629
16th to endNight
18%10%28%30%11%1
717
October1st to 15thNight
22%11%31%23%10%1
720
16th to endNight
27%16%31%18%5%
768
November1st to 15thNight
27%13%31%19%7%
715
16th to endNight
27%17%25%21%7%
750
December1st to 15thNight
33%16%29%17%3
750
16th to endNight
34%18%28%15%2
800
Page generated at 2017-11-01 18:23:32. Version ac04

Copyright 2017 A. Danko


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