Lancaster
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lancaster clear sky chart from 2005-11-05 to 2017-04-08.

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
72%
15241
37%
45332
30%
15196
79%
15196
61%
20364

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
58%
716
29%
2491
26%
716
68%
716
43%
1188
January16th to endNight
57%
768
36%
2378
27%
768
71%
768
45%
1185
February1st to 15thNight
63%
700
34%
2106
29%
698
72%
698
49%
1049
February16th to endNight
59%
632
32%
1895
29%
632
67%
632
45%
987
March1st to 15thNight
64%
720
30%
2160
27%
720
72%
720
53%
1032
March16th to endNight
65%
768
35%
2004
23%
768
73%
768
59%
1019
April1st to 15thNight
57%
691
35%
1729
17%
691
67%
691
59%
900
April16th to endNight
65%
660
35%
1650
17%
660
71%
660
70%
789
May1st to 15thNight
71%
555
38%
1545
24%
555
77%
555
74%
649
May16th to endNight
62%
513
34%
1541
22%
513
70%
513
71%
616
June1st to 15thNight
77%
397
39%
1387
35%
397
84%
397
79%
459
June16th to endNight
90%
330
40%
1320
46%
330
93%
330
84%
372
July1st to 15thNight
94%
310
38%
1240
46%
310
95%
310
68%
404
July16th to endNight
90%
536
36%
1475
31%
497
90%
497
68%
636
August1st to 15thNight
93%
657
41%
1640
27%
653
94%
653
84%
719
August16th to endNight
94%
700
44%
1750
29%
700
95%
700
83%
778
September1st to 15thNight
92%
660
46%
1675
36%
660
93%
660
83%
731
September16th to endNight
87%
656
47%
1815
41%
656
92%
656
83%
730
October1st to 15thNight
77%
660
41%
1834
35%
660
84%
660
66%
836
October16th to endNight
78%
704
44%
2144
42%
704
86%
704
68%
887
November1st to 15thNight
77%
700
37%
2275
37%
700
84%
700
61%
943
November16th to endNight
74%
720
39%
2340
38%
720
81%
720
58%
1005
December1st to 15thNight
64%
720
34%
2340
28%
720
75%
720
46%
1127
December16th to endNight
55%
768
31%
2598
26%
768
66%
768
39%
1323

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
111212236%75%
45910
Night
111212236%75%
45529
TransparencyDay
12%36%17%28%32%
45600
Night
12%46%18%29%28%
45339
SeeingDay
210%29%34%17%5%
5257
Night
2318%39%30%5%
15252

By Month

Percentage Cloud Cover SW (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
3312424448%60%
1447
16th to endDay
45%1432335%7%58%
1842
February1st to 15thDay
2112324348%63%
1751
16th to endDay
3213444447%59%
1579
March1st to 15thDay
111121346%10%64%
1800
16th to endDay
111121345%8%66%
2216
April1st to 15thDay
1112312246%70%
2058
16th to endDay
1111247%78%
1980
May1st to 15thDay
111226%80%
2074
16th to endDay
12111225%80%
2221
June1st to 15thDay
1123484%
2238
16th to endDay
1289%
2310
July1st to 15thDay
1111122481%
2310
16th to endDay
111111125%79%
2267
August1st to 15thDay
11111387%
1980
16th to endDay
11212485%
2100
September1st to 15thDay
11122385%
1955
16th to endDay
1221386%
1815
October1st to 15thDay
11212245%76%
1793
16th to endDay
1121133479%
1727
November1st to 15thDay
111212336%74%
1584
16th to endDay
112324338%66%
1620
December1st to 15thDay
221342446%9%59%
1620
16th to endDay
4313423438%58%
1623
January1st to 15thNight
221441235%7%63%
2491
16th to endNight
3213312247%64%
2378
February1st to 15thNight
1313213247%67%
2101
16th to endNight
321232445%6%63%
1895
March1st to 15thNight
111222335%8%67%
2160
16th to endNight
12213348%70%
2004
April1st to 15thNight
112213247%71%
1729
16th to endNight
11112135%81%
1650
May1st to 15thNight
1146%82%
1545
16th to endNight
1245%82%
1540
June1st to 15thNight
1116%86%
1387
16th to endNight
1292%
1320
July1st to 15thNight
111122483%
1320
16th to endNight
11212225%78%
1588
August1st to 15thNight
122388%
1650
16th to endNight
1122286%
1750
September1st to 15thNight
11388%
1675
16th to endNight
1112388%
1815
October1st to 15thNight
1112345%77%
1834
16th to endNight
11121235%80%
2144
November1st to 15thNight
1111212335%76%
2275
16th to endNight
22213347%71%
2340
December1st to 15thNight
3112323347%65%
2340
16th to endNight
4214314448%61%
2598

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
21%48%21%26%16%
1447
16th to endDay
24%5%9%19%21%18%
1842
February1st to 15thDay
18%5%5%23%28%18%
1751
16th to endDay
24%5%7%21%30%10%
1579
March1st to 15thDay
14%6%11%24%25%18%
1800
16th to endDay
16%5%10%27%25%14%
2216
April1st to 15thDay
15%48%26%28%15%
2058
16th to endDay
8%310%24%33%20%
1980
May1st to 15thDay
8%37%20%31%28%
2074
16th to endDay
9%35%20%41%18%
2224
June1st to 15thDay
5%3412%28%45%
2238
16th to endDay
413419%66%
2310
July1st to 15thDay
8%227%18%59%
2161
16th to endDay
10%2413%26%42%
2117
August1st to 15thDay
5%117%24%60%
1966
16th to endDay
5%127%29%53%
2100
September1st to 15thDay
6%138%26%53%
1955
16th to endDay
5%117%35%47%
1815
October1st to 15thDay
10%4316%32%32%
1793
16th to endDay
8%45%13%31%36%
1727
November1st to 15thDay
12%46%17%37%21%
1584
16th to endDay
15%5%7%20%28%22%
1620
December1st to 15thDay
19%6%10%22%26%13%
1620
16th to endDay
24%6%10%25%19%11%
1623
January1st to 15thNight
20%6%7%19%29%17%
2491
16th to endNight
20%6%8%19%23%21%
2378
February1st to 15thNight
18%6%7%19%26%21%
2112
16th to endNight
20%6%9%21%29%11%
1895
March1st to 15thNight
15%5%11%23%24%19%
2160
16th to endNight
13%6%10%27%28%13%
2004
April1st to 15thNight
15%49%32%22%14%
1729
16th to endNight
9%38%27%35%16%
1650
May1st to 15thNight
5%48%26%34%21%
1546
16th to endNight
6%37%25%42%14%
1541
June1st to 15thNight
327%15%32%38%
1387
16th to endNight
337%26%58%
1320
July1st to 15thNight
7%329%19%59%
1240
16th to endNight
10%3412%29%40%
1475
August1st to 15thNight
426%29%56%
1640
16th to endNight
5%129%31%49%
1750
September1st to 15thNight
4237%29%51%
1675
16th to endNight
5%119%39%43%
1815
October1st to 15thNight
10%4314%35%31%
1834
16th to endNight
8%3412%31%38%
2144
November1st to 15thNight
12%35%18%33%26%
2275
16th to endNight
13%48%20%27%26%
2340
December1st to 15thNight
19%5%9%18%28%17%
2340
16th to endNight
23%6%10%23%22%13%
2598

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
9%21%24%29%13%2
75
16th to endDay
6%17%29%23%17%6%
275
February1st to 15thDay
216%29%28%16%6%
266
16th to endDay
6%19%32%21%15%4
238
March1st to 15thDay
420%28%23%20%3
270
16th to endDay
316%35%25%15%3
288
April1st to 15thDay
322%36%24%10%2
239
16th to endDay
222%40%23%8%2
210
May1st to 15thDay
114%39%28%11%3
228
16th to endDay
111%42%29%9%5%
266
June1st to 15thDay
19%38%36%10%3
255
16th to endDay
1334%41%11%7%
255
July1st to 15thDay
228%47%14%5%
245
16th to endDay
220%49%18%7%
271
August1st to 15thDay
1127%45%17%6%
255
16th to endDay
19%55%16%8%
268
September1st to 15thDay
223%45%21%6%
255
16th to endDay
15%23%37%25%6%
255
October1st to 15thDay
111%29%30%22%3
255
16th to endDay
25%29%25%29%7%
239
November1st to 15thDay
15%13%32%25%22%
90
16th to endDay
28%30%37%20%1
90
December1st to 15thDay
27%22%33%32%2
90
16th to endDay
8%16%18%36%16%2
79
January1st to 15thNight
45%24%39%21%5%
720
16th to endNight
45%27%37%21%3
768
February1st to 15thNight
3325%38%24%4
704
16th to endNight
46%27%39%17%3
632
March1st to 15thNight
1425%43%21%3
720
16th to endNight
15%25%42%22%2
768
April1st to 15thNight
26%30%38%20%2
691
16th to endNight
15%27%39%21%4
660
May1st to 15thNight
323%49%21%2
556
16th to endNight
6%28%38%24%1
515
June1st to 15thNight
318%53%23%
397
16th to endNight
7%55%35%1
330
July1st to 15thNight
1237%55%3
310
16th to endNight
1336%51%6%
536
August1st to 15thNight
438%47%9%
657
16th to endNight
1231%53%11%
700
September1st to 15thNight
5%33%50%10%
660
16th to endNight
10%36%42%9%
656
October1st to 15thNight
1116%43%30%5%
660
16th to endNight
2114%36%36%8%
704
November1st to 15thNight
1215%41%30%7%
700
16th to endNight
2117%39%31%6%
720
December1st to 15thNight
4422%40%26%3
720
16th to endNight
5%6%28%36%20%2
768
Page generated at 2017-04-09 03:54:17. Version ac04

Copyright 2017 A. Danko


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