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 2017-03-19.

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%
14276
14%
45214
5%
14238
33%
14238
16%
31617

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
20%
720
16%
1979
5%
720
29%
720
18%
1407
April1st to 15thNight
16%
560
16%
1614
4%
560
26%
560
14%
1183
April16th to endNight
23%
495
16%
1485
6%
495
32%
495
19%
1017
May1st to 15thNight
26%
495
12%
1466
6%
495
32%
495
16%
1050
May16th to endNight
21%
447
9%
1302
3%
446
28%
446
13%
996
June1st to 15thNight
28%
330
7%
1155
5%
330
32%
330
12%
875
June16th to endNight
34%
330
6%
1155
6%
330
37%
330
15%
804
July1st to 15thNight
38%
310
12%
1085
9%
310
46%
310
22%
716
July16th to endNight
36%
392
8%
1294
7%
366
40%
366
15%
911
August1st to 15thNight
42%
494
11%
1473
9%
490
44%
490
21%
1001
August16th to endNight
41%
525
17%
1575
9%
525
47%
525
28%
973
September1st to 15thNight
31%
576
15%
1712
7%
576
39%
576
24%
1125
September16th to endNight
38%
657
22%
1815
12%
657
47%
657
31%
1103
October1st to 15thNight
29%
660
20%
1952
9%
660
40%
660
23%
1290
October16th to endNight
20%
704
15%
2194
4%
704
32%
704
15%
1546
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%36%5%34446%31%
45610
Night
20%8%35%5%2445%6%34%
45380
TransparencyDay
52%5%11%19%9%1
45294
Night
50%5%11%21%10%
45214
SeeingDay
28%13%29%19%8%1
6001
Night
25%14%30%22%6%
14276

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%31%
1976
April1st to 15thDay
23%10%35%42435%5%31%
2002
16th to endDay
24%8%25%423336%35%
2145
May1st to 15thDay
24%8%36%433446%30%
2156
16th to endDay
27%7%26%5%23346%28%
2468
June1st to 15thDay
28%9%47%5%24445%24%
2475
16th to endDay
26%6%35%5%25%5%46%26%
2475
July1st to 15thDay
17%5%25%435%5%5%8%34%
2475
16th to endDay
20%7%35%5%35%5%6%7%27%
2455
August1st to 15thDay
22%6%35%5%35%45%6%31%
2145
16th to endDay
14%425%5%35%5%5%7%39%
2275
September1st to 15thDay
18%5%245%2445%7%39%
1916
16th to endDay
19%414323335%47%
1815
October1st to 15thDay
20%7%25%5%23346%38%
1678
16th to endDay
24%9%27%5%23346%30%
1675
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%
1979
April1st to 15thNight
23%8%25%5%34445%32%
1614
16th to endNight
24%6%24323346%37%
1485
May1st to 15thNight
22%6%35%6%34446%32%
1466
16th to endNight
25%8%35%6%35%5%45%28%
1300
June1st to 15thNight
27%6%35%6%35%5%45%26%
1155
16th to endNight
22%5%25%6%25%45%8%30%
1155
July1st to 15thNight
16%5%33445%5%5%8%37%
1155
16th to endNight
21%5%35%5%35%5%6%7%32%
1393
August1st to 15thNight
17%5%35%5%3345%6%38%
1485
16th to endNight
15%4243235%5%8%44%
1575
September1st to 15thNight
18%5%2442435%6%41%
1712
16th to endNight
15%313323346%50%
1815
October1st to 15thNight
19%6%24423447%40%
1952
16th to endNight
23%8%25%42345%5%34%
2194
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%18%11%2
1976
April1st to 15thDay
55%28%17%12%2
2002
16th to endDay
50%39%18%13%4
2145
May1st to 15thDay
54%5%8%19%9%1
2156
16th to endDay
56%5%11%19%5%
2472
June1st to 15thDay
61%5%10%12%8%1
2475
16th to endDay
57%5%10%17%8%
2475
July1st to 15thDay
43%7%15%21%10%
2316
16th to endDay
52%7%16%17%6%
2292
August1st to 15thDay
52%6%12%23%5%
2132
16th to endDay
42%7%16%25%8%
2275
September1st to 15thDay
44%6%13%24%11%
1916
16th to endDay
39%49%29%15%1
1815
October1st to 15thDay
46%413%25%9%
1678
16th to endDay
55%411%20%7%
1675
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
1979
April1st to 15thNight
53%48%16%13%3
1614
16th to endNight
48%49%18%15%3
1485
May1st to 15thNight
52%5%10%19%9%1
1466
16th to endNight
58%6%11%15%7%
1302
June1st to 15thNight
58%7%10%16%5%1
1155
16th to endNight
51%6%13%20%8%
1155
July1st to 15thNight
42%7%13%26%9%
1085
16th to endNight
50%8%14%18%7%
1294
August1st to 15thNight
46%6%15%24%7%
1473
16th to endNight
36%6%17%29%8%
1575
September1st to 15thNight
42%5%11%26%12%1
1712
16th to endNight
34%414%30%15%
1815
October1st to 15thNight
44%411%25%13%
1952
16th to endNight
50%5%10%21%10%
2194
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
23%17%27%17%10%3
238
April1st to 15thDay
34%17%26%13%6%
210
16th to endDay
26%16%31%10%10%3
210
May1st to 15thDay
29%16%30%17%32
247
16th to endDay
33%12%31%14%8%
439
June1st to 15thDay
38%11%22%20%6%
420
16th to endDay
29%7%30%20%10%1
420
July1st to 15thDay
25%8%28%23%13%1
400
16th to endDay
26%7%29%24%11%
321
August1st to 15thDay
25%330%24%13%2
253
16th to endDay
19%6%29%25%14%4
268
September1st to 15thDay
19%8%31%28%10%1
255
16th to endDay
18%14%30%18%11%5%
254
October1st to 15thDay
26%15%20%20%12%4
230
16th to endDay
32%17%30%11%7%
240
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%17%33%20%5%
720
April1st to 15thNight
30%17%30%17%4
560
16th to endNight
28%13%32%19%6%
495
May1st to 15thNight
26%12%30%25%4
495
16th to endNight
28%11%33%22%4
447
June1st to 15thNight
30%7%30%26%5%
330
16th to endNight
25%6%29%31%6%1
330
July1st to 15thNight
17%435%32%10%
310
16th to endNight
22%428%32%11%
392
August1st to 15thNight
19%424%36%13%
494
16th to endNight
16%431%30%16%
525
September1st to 15thNight
21%8%32%26%9%
576
16th to endNight
18%10%28%31%10%1
657
October1st to 15thNight
23%11%30%23%9%1
660
16th to endNight
27%16%30%18%5%
704
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 2017-03-20 09:18:33. Version ac04

Copyright 2017 A. Danko


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