Westfield
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Westfield clear sky chart from 2005-11-05 to 2017-09-24.

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%
14897
14%
46827
5%
14855
33%
14855
15%
33570

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%
742
14%
2637
2%
738
31%
738
12%
1824
January16th to endNight
14%
768
16%
2568
2%
768
29%
768
13%
1789
February1st to 15thNight
15%
704
12%
2286
3%
701
27%
701
13%
1624
February16th to endNight
18%
631
12%
1982
2%
631
29%
631
12%
1473
March1st to 15thNight
17%
720
15%
2028
4%
720
29%
720
16%
1510
March16th to endNight
21%
768
17%
2112
6%
768
30%
768
17%
1527
April1st to 15thNight
20%
599
14%
1779
5%
599
28%
599
15%
1334
April16th to endNight
22%
540
14%
1620
6%
540
29%
540
17%
1175
May1st to 15thNight
25%
540
10%
1597
6%
540
30%
540
14%
1224
May16th to endNight
26%
552
9%
1487
3%
551
32%
551
14%
1161
June1st to 15thNight
26%
360
7%
1260
5%
360
30%
360
11%
968
June16th to endNight
33%
360
7%
1260
6%
360
36%
360
12%
946
July1st to 15thNight
40%
340
8%
1190
8%
340
44%
340
15%
846
July16th to endNight
35%
476
7%
1456
7%
446
37%
446
13%
1108
August1st to 15thNight
41%
539
9%
1608
8%
535
42%
535
17%
1170
August16th to endNight
41%
573
17%
1719
10%
573
45%
573
23%
1141
September1st to 15thNight
33%
612
14%
1872
9%
612
39%
612
22%
1261
September16th to endNight
38%
693
24%
1913
13%
693
47%
693
30%
1220
October1st to 15thNight
30%
660
19%
1963
9%
660
39%
660
22%
1322
October16th to endNight
21%
704
15%
2167
3%
704
32%
704
16%
1528
November1st to 15thNight
26%
716
15%
2373
7%
716
36%
716
17%
1637
November16th to endNight
23%
750
15%
2520
5%
750
35%
750
13%
1773
December1st to 15thNight
12%
750
13%
2550
2%
750
25%
750
10%
1884
December16th to endNight
10%
800
12%
2880
2%
800
23%
800
9%
2125

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%8%35%434446%34%
48099
Night
20%8%35%424446%33%
46997
TransparencyDay
50%7%12%18%9%1
47787
Night
51%6%11%19%10%
46827
SeeingDay
26%13%29%21%7%1
6932
Night
25%13%31%22%6%
14897

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%11%46%43445%5%36%
1299
16th to endDay
16%11%35%5%24345%36%
1653
February1st to 15thDay
13%11%36%6%45%5%47%31%
1575
16th to endDay
13%11%49%5%25%446%31%
1490
March1st to 15thDay
19%11%47%5%24345%31%
1921
16th to endDay
16%8%46%5%34346%35%
2112
April1st to 15thDay
20%11%46%433345%31%
2167
16th to endDay
24%7%35%423346%34%
2340
May1st to 15thDay
25%9%35%5%24445%28%
2353
16th to endDay
25%7%35%43445%7%28%
2637
June1st to 15thDay
26%10%46%5%34335%26%
2700
16th to endDay
26%6%36%5%2445%7%28%
2700
July1st to 15thDay
19%6%2443446%9%34%
2700
16th to endDay
20%7%25%5%35%45%6%33%
2595
August1st to 15thDay
19%6%25%4345%5%7%35%
2340
16th to endDay
15%5%25%5%3445%8%40%
2482
September1st to 15thDay
17%5%2432445%6%43%
2085
16th to endDay
17%414223345%49%
1906
October1st to 15thDay
20%5%24424336%41%
1667
16th to endDay
21%7%35%5%25%435%34%
1704
November1st to 15thDay
23%6%35%433346%35%
1482
16th to endDay
20%8%345%24446%34%
1440
December1st to 15thDay
27%9%34323445%31%
1407
16th to endDay
24%9%36%433346%30%
1344
January1st to 15thNight
16%8%25%5%35%45%7%36%
2637
16th to endNight
16%9%36%5%2346%7%34%
2568
February1st to 15thNight
16%9%35%435%45%8%32%
2285
16th to endNight
16%11%48%6%34445%30%
1982
March1st to 15thNight
19%9%36%5%34445%33%
2016
16th to endNight
17%10%35%5%2445%6%34%
2112
April1st to 15thNight
22%8%36%6%24345%30%
1779
16th to endNight
23%7%36%4235%36%32%
1620
May1st to 15thNight
25%7%35%5%3445%6%27%
1597
16th to endNight
23%7%36%5%45%5%47%26%
1485
June1st to 15thNight
28%10%36%6%23437%23%
1260
16th to endNight
26%8%35%6%33346%28%
1260
July1st to 15thNight
18%8%36%5%2446%8%31%
1260
16th to endNight
21%7%46%6%25%46%6%27%
1559
August1st to 15thNight
20%6%35%3345%6%7%33%
1620
16th to endNight
15%7%2432346%6%42%
1719
September1st to 15thNight
20%7%24324447%38%
1872
16th to endNight
15%42432325%6%48%
1913
October1st to 15thNight
20%6%25%5%22446%40%
1963
16th to endNight
22%8%25%424345%36%
2167
November1st to 15thNight
22%5%25%424346%36%
2373
16th to endNight
21%7%35%424437%35%
2520
December1st to 15thNight
26%9%35%42334432%
2550
16th to endNight
26%10%34324445%30%
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
49%7%15%17%8%1
1300
16th to endDay
48%6%10%20%12%
1653
February1st to 15thDay
52%7%13%18%7%1
1578
16th to endDay
52%6%13%18%7%1
1490
March1st to 15thDay
54%49%18%10%1
1932
16th to endDay
48%5%10%19%13%2
2112
April1st to 15thDay
55%48%16%13%2
2167
16th to endDay
50%5%9%18%13%2
2340
May1st to 15thDay
57%6%8%17%9%1
2353
16th to endDay
54%8%12%18%4
2641
June1st to 15thDay
60%6%10%14%7%1
2700
16th to endDay
54%9%11%16%8%
2700
July1st to 15thDay
45%11%17%15%9%
2541
16th to endDay
49%11%15%17%5%
2436
August1st to 15thDay
47%10%13%19%7%
2327
16th to endDay
40%10%16%23%9%
2482
September1st to 15thDay
41%7%14%23%12%1
2085
16th to endDay
37%5%10%27%17%1
1906
October1st to 15thDay
45%5%11%26%11%
1667
16th to endDay
50%6%11%20%10%
1704
November1st to 15thDay
49%6%13%16%13%
1482
16th to endDay
51%7%12%17%10%
1440
December1st to 15thDay
54%6%12%20%6%
1407
16th to endDay
57%411%15%10%
1344
January1st to 15thNight
48%7%13%18%9%1
2637
16th to endNight
49%6%12%21%9%
2568
February1st to 15thNight
50%7%12%18%9%
2286
16th to endNight
55%6%9%16%9%1
1982
March1st to 15thNight
53%6%8%17%11%1
2028
16th to endNight
49%6%8%19%13%1
2112
April1st to 15thNight
55%5%8%14%12%3
1779
16th to endNight
52%6%9%17%12%1
1620
May1st to 15thNight
57%7%8%16%8%1
1597
16th to endNight
57%7%11%15%7%
1487
June1st to 15thNight
61%6%11%15%41
1260
16th to endNight
60%5%9%16%8%
1260
July1st to 15thNight
51%8%13%18%8%
1190
16th to endNight
56%8%12%14%6%
1456
August1st to 15thNight
50%8%14%17%8%
1608
16th to endNight
42%8%14%24%10%
1719
September1st to 15thNight
46%5%11%23%12%
1872
16th to endNight
38%5%11%27%16%
1913
October1st to 15thNight
46%410%25%12%1
1963
16th to endNight
50%5%11%21%11%
2167
November1st to 15thNight
48%6%14%18%10%
2373
16th to endNight
50%6%12%19%9%
2520
December1st to 15thNight
56%6%9%21%6%
2550
16th to endNight
57%6%10%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
21%31%31%15%
60
16th to endDay
19%19%44%13%2
181
February1st to 15thDay
20%23%33%18%3
236
16th to endDay
21%20%33%20%3
224
March1st to 15thDay
25%20%34%15%3
270
16th to endDay
25%21%28%15%7%1
288
April1st to 15thDay
31%18%30%14%4
270
16th to endDay
27%15%29%20%7%1
270
May1st to 15thDay
33%11%34%11%7%
309
16th to endDay
30%14%26%20%6%1
519
June1st to 15thDay
29%12%29%22%6%
495
16th to endDay
30%8%27%22%8%1
495
July1st to 15thDay
28%6%25%25%12%1
475
16th to endDay
26%5%29%27%9%1
379
August1st to 15thDay
24%7%25%31%9%1
313
16th to endDay
17%11%25%31%13%1
332
September1st to 15thDay
24%7%28%29%8%1
315
16th to endDay
21%6%29%26%12%2
287
October1st to 15thDay
24%11%26%22%10%3
228
16th to endDay
25%20%30%16%5%
240
November1st to 15thDay
24%14%30%20%6%2
235
16th to endDay
26%21%31%14%5%
240
December1st to 15thDay
33%16%29%16%3
207
16th to endDay
32%28%29%7%1
64
January1st to 15thNight
22%21%33%18%3
742
16th to endNight
22%22%36%15%3
768
February1st to 15thNight
23%18%38%16%2
704
16th to endNight
23%19%32%19%3
631
March1st to 15thNight
24%16%37%20%2
720
16th to endNight
22%15%34%20%6%
768
April1st to 15thNight
28%12%33%20%5%
599
16th to endNight
27%11%35%20%5%
540
May1st to 15thNight
29%7%30%25%5%1
540
16th to endNight
27%10%29%27%4
552
June1st to 15thNight
34%8%24%26%5%
360
16th to endNight
28%6%23%31%8%
360
July1st to 15thNight
27%5%20%35%12%
340
16th to endNight
26%5%25%31%11%
476
August1st to 15thNight
25%223%32%15%
539
16th to endNight
20%428%33%11%
573
September1st to 15thNight
26%6%29%26%10%
612
16th to endNight
18%8%30%28%12%1
693
October1st to 15thNight
23%9%30%24%10%1
660
16th to endNight
27%16%30%19%4
704
November1st to 15thNight
24%11%30%22%9%1
716
16th to endNight
26%17%29%19%7%
750
December1st to 15thNight
31%18%32%13%2
750
16th to endNight
32%20%31%13%2
800
Page generated at 2017-09-25 10:02:17. Version ac04

Copyright 2017 A. Danko


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