Whiteway
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Whiteway clear sky chart from 2005-11-05 to 2017-09-22.

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
16%
14910
7%
46848
2%
14865
20%
14865
8%
38365

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
6%
750
5%
2634
1%
746
12%
746
4%
2296
January16th to endNight
9%
800
7%
2688
1%
800
15%
800
5%
2272
February1st to 15thNight
8%
734
5%
2330
1%
731
13%
731
6%
1965
February16th to endNight
8%
639
5%
1940
0%
639
12%
639
5%
1669
March1st to 15thNight
14%
655
8%
2095
3%
655
19%
655
7%
1736
March16th to endNight
12%
576
6%
2112
3%
576
17%
576
5%
1818
April1st to 15thNight
15%
539
8%
1721
4%
539
22%
539
8%
1405
April16th to endNight
15%
540
9%
1620
4%
540
21%
540
9%
1322
May1st to 15thNight
22%
540
5%
1599
2%
540
24%
540
9%
1324
May16th to endNight
18%
561
6%
1309
1%
560
21%
560
10%
1125
June1st to 15thNight
18%
540
3%
1260
0%
540
20%
540
11%
1075
June16th to endNight
18%
540
4%
1260
1%
540
20%
540
14%
1028
July1st to 15thNight
24%
510
5%
1190
3%
510
26%
510
17%
952
July16th to endNight
20%
565
5%
1372
2%
532
21%
532
11%
1155
August1st to 15thNight
26%
539
7%
1567
3%
535
29%
535
13%
1226
August16th to endNight
27%
573
9%
1719
4%
573
33%
573
15%
1292
September1st to 15thNight
26%
540
9%
1864
6%
540
32%
540
14%
1362
September16th to endNight
25%
514
13%
1890
8%
514
32%
514
15%
1299
October1st to 15thNight
21%
514
12%
1922
6%
514
30%
514
10%
1435
October16th to endNight
14%
711
7%
2263
2%
711
19%
711
7%
1890
November1st to 15thNight
17%
730
7%
2350
2%
730
22%
730
9%
1879
November16th to endNight
10%
750
8%
2563
1%
750
17%
750
7%
2109
December1st to 15thNight
12%
750
7%
2700
2%
750
17%
750
6%
2221
December16th to endNight
8%
800
4%
2880
1%
800
11%
800
4%
2510

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
22%13%5%8%6%34345%20%
48045
Night
23%15%5%8%6%34335%18%
47009
TransparencyDay
65%5%10%12%5%
47724
Night
67%5%10%11%4
46848
SeeingDay
33%16%26%16%5%1
8227
Night
31%17%28%17%4
14910

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
21%20%7%11%7%3343411%
1302
16th to endDay
22%19%7%11%7%35%235%11%
1536
February1st to 15thDay
21%15%6%10%9%45%445%12%
1528
16th to endDay
19%19%9%14%6%3334312%
1533
March1st to 15thDay
18%15%8%10%8%44345%16%
1854
16th to endDay
24%19%7%9%7%2333313%
2112
April1st to 15thDay
20%14%5%9%8%3434420%
2224
16th to endDay
25%14%47%43433423%
2340
May1st to 15thDay
24%14%47%42445%6%20%
2352
16th to endDay
22%12%5%7%6%34347%20%
2805
June1st to 15thDay
27%14%5%8%6%34345%17%
2700
16th to endDay
25%11%46%6%34246%24%
2700
July1st to 15thDay
18%9%47%5%35%45%7%29%
2700
16th to endDay
21%9%47%7%36%5%46%23%
2699
August1st to 15thDay
25%9%37%5%35%45%6%23%
2382
16th to endDay
20%10%47%6%345%5%8%23%
2483
September1st to 15thDay
21%9%46%435%45%5%30%
2093
16th to endDay
17%8%35%6%3445%6%35%
1882
October1st to 15thDay
27%10%35%433335%27%
1708
16th to endDay
26%17%47%6%3334418%
1606
November1st to 15thDay
20%15%47%5%33446%22%
1507
16th to endDay
26%19%6%7%6%2233416%
1395
December1st to 15thDay
23%16%6%9%5%34346%16%
1260
16th to endDay
23%20%8%10%5%3433412%
1344
January1st to 15thNight
23%18%8%10%8%3433312%
2634
16th to endNight
20%15%7%13%8%35%335%13%
2688
February1st to 15thNight
20%15%7%11%8%34345%13%
2330
16th to endNight
20%20%7%13%6%22335%13%
1940
March1st to 15thNight
15%13%8%11%9%36%44417%
2082
16th to endNight
23%19%6%11%7%2442214%
2112
April1st to 15thNight
23%17%6%8%5%23345%18%
1721
16th to endNight
25%19%5%8%32333321%
1620
May1st to 15thNight
27%16%46%434346%17%
1599
16th to endNight
29%13%37%6%3445%5%16%
1307
June1st to 15thNight
27%14%5%7%5%345%36%17%
1260
16th to endNight
28%12%46%5%23346%21%
1260
July1st to 15thNight
21%10%46%6%36%35%7%24%
1260
16th to endNight
25%11%5%8%5%35%45%5%19%
1467
August1st to 15thNight
25%11%46%5%24446%24%
1578
16th to endNight
20%9%47%5%3346%7%26%
1719
September1st to 15thNight
24%10%36%424346%29%
1864
16th to endNight
19%9%27%5%34347%32%
1890
October1st to 15thNight
27%11%37%423345%25%
1922
16th to endNight
29%16%46%5%3443417%
2263
November1st to 15thNight
24%16%46%5%23345%22%
2350
16th to endNight
22%18%5%7%5%34345%17%
2563
December1st to 15thNight
23%15%6%10%6%3432418%
2700
16th to endNight
24%20%8%9%7%3432411%
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
78%5%6%7%3
1303
16th to endDay
76%5%5%8%4
1536
February1st to 15thDay
72%5%10%6%4
1532
16th to endDay
77%48%5%3
1533
March1st to 15thDay
72%48%10%3
1864
16th to endDay
76%47%8%2
2112
April1st to 15thDay
68%49%12%4
2224
16th to endDay
66%47%12%8%
2340
May1st to 15thDay
64%5%13%11%4
2352
16th to endDay
65%6%9%12%5%
2809
June1st to 15thDay
71%5%10%9%2
2700
16th to endDay
62%5%9%14%8%
2700
July1st to 15thDay
53%8%12%18%6%
2542
16th to endDay
61%8%13%12%4
2531
August1st to 15thDay
62%6%12%14%4
2368
16th to endDay
59%7%14%15%3
2483
September1st to 15thDay
55%6%12%18%7%
2093
16th to endDay
48%6%15%19%9%
1882
October1st to 15thDay
60%5%12%13%6%
1708
16th to endDay
69%5%8%11%4
1606
November1st to 15thDay
63%7%13%12%3
1507
16th to endDay
72%5%9%8%3
1395
December1st to 15thDay
69%5%9%10%5%
1260
16th to endDay
75%5%6%8%3
1344
January1st to 15thNight
75%6%7%7%3
2634
16th to endNight
72%5%9%8%4
2688
February1st to 15thNight
72%410%9%3
2330
16th to endNight
73%6%8%9%2
1940
March1st to 15thNight
69%5%9%10%4
2095
16th to endNight
74%5%8%7%3
2112
April1st to 15thNight
68%49%12%4
1721
16th to endNight
68%37%11%7%1
1620
May1st to 15thNight
68%5%9%11%3
1599
16th to endNight
69%6%9%10%4
1309
June1st to 15thNight
67%6%11%10%4
1260
16th to endNight
63%5%12%13%5%
1260
July1st to 15thNight
56%8%12%18%3
1190
16th to endNight
65%8%9%13%2
1372
August1st to 15thNight
61%5%15%13%4
1567
16th to endNight
54%7%15%17%4
1719
September1st to 15thNight
55%6%13%17%6%
1864
16th to endNight
50%6%14%19%8%
1890
October1st to 15thNight
60%5%12%15%5%
1922
16th to endNight
69%6%9%11%3
2263
November1st to 15thNight
63%7%13%10%4
2350
16th to endNight
68%6%11%10%3
2563
December1st to 15thNight
70%5%7%12%5%
2700
16th to endNight
77%46%7%3
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
28%29%30%10%1
240
16th to endDay
31%26%25%12%21
256
February1st to 15thDay
28%23%26%17%2
236
16th to endDay
31%29%26%9%2
212
March1st to 15thDay
27%25%29%12%3
240
16th to endDay
32%23%29%8%5%
256
April1st to 15thDay
33%17%25%17%6%
347
16th to endDay
40%16%21%16%4
450
May1st to 15thDay
33%14%24%18%7%2
468
16th to endDay
38%13%27%15%31
519
June1st to 15thDay
40%11%23%16%5%1
495
16th to endDay
36%12%29%13%6%1
495
July1st to 15thDay
29%10%30%20%8%1
475
16th to endDay
34%8%26%20%9%
514
August1st to 15thDay
35%7%26%19%7%2
493
16th to endDay
31%9%22%25%9%
523
September1st to 15thDay
34%10%24%23%6%1
330
16th to endDay
24%14%30%21%8%
242
October1st to 15thDay
33%15%24%16%8%
225
16th to endDay
35%22%22%15%3
240
November1st to 15thDay
34%17%25%14%6%1
235
16th to endDay
37%21%26%12%2
240
December1st to 15thDay
30%27%25%9%7%
240
16th to endDay
33%25%26%10%3
256
January1st to 15thNight
32%24%28%10%2
750
16th to endNight
28%28%26%14%2
800
February1st to 15thNight
29%25%30%13%2
734
16th to endNight
31%26%25%12%3
639
March1st to 15thNight
21%26%29%16%4
655
16th to endNight
31%21%27%15%3
576
April1st to 15thNight
30%19%27%16%5%
539
16th to endNight
35%14%29%16%3
540
May1st to 15thNight
35%10%25%23%5%
540
16th to endNight
35%14%25%18%4
561
June1st to 15thNight
34%11%28%19%5%
540
16th to endNight
35%9%30%18%6%
540
July1st to 15thNight
26%10%33%23%5%
510
16th to endNight
29%9%35%20%5%
565
August1st to 15thNight
34%6%27%23%7%
539
16th to endNight
25%9%32%26%6%
573
September1st to 15thNight
31%6%32%23%5%
540
16th to endNight
24%10%33%23%7%
514
October1st to 15thNight
32%13%25%20%6%
514
16th to endNight
37%17%25%14%3
711
November1st to 15thNight
32%17%27%16%5%
730
16th to endNight
32%20%29%13%3
750
December1st to 15thNight
31%26%24%13%4
750
16th to endNight
33%23%28%11%21
800
Page generated at 2017-09-23 08:13:35. Version ac04

Copyright 2017 A. Danko


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