Lowry Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lowry Observatory clear sky chart from 2005-11-05 to 2017-10-06.

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
44%
16053
24%
47030
14%
16009
53%
16009
36%
27147

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
39%
900
25%
2506
12%
895
50%
895
39%
1404
January16th to endNight
34%
960
27%
2688
10%
960
47%
960
38%
1518
February1st to 15thNight
30%
714
20%
2145
7%
711
42%
711
30%
1309
February16th to endNight
33%
632
25%
1894
10%
632
47%
632
34%
1117
March1st to 15thNight
40%
720
25%
2160
13%
720
50%
720
37%
1218
March16th to endNight
36%
579
21%
2032
14%
579
47%
579
28%
1187
April1st to 15thNight
31%
539
17%
1798
10%
539
44%
539
26%
1084
April16th to endNight
32%
540
17%
1698
12%
540
43%
540
24%
1094
May1st to 15thNight
41%
540
18%
1620
12%
540
49%
540
29%
1007
May16th to endNight
39%
561
17%
1562
9%
561
44%
561
27%
1050
June1st to 15thNight
42%
540
14%
1440
5%
540
47%
540
33%
915
June16th to endNight
59%
540
19%
1440
10%
540
63%
540
43%
843
July1st to 15thNight
57%
510
17%
1360
8%
510
61%
510
38%
813
July16th to endNight
68%
564
23%
1416
16%
531
71%
531
46%
793
August1st to 15thNight
63%
539
19%
1598
17%
536
66%
536
35%
940
August16th to endNight
63%
573
25%
1910
25%
573
71%
573
43%
961
September1st to 15thNight
55%
540
26%
1845
21%
540
65%
540
37%
960
September16th to endNight
56%
537
31%
1980
28%
537
67%
537
38%
969
October1st to 15thNight
46%
535
30%
1903
24%
535
55%
535
31%
1038
October16th to endNight
52%
855
31%
2263
17%
855
58%
855
46%
1247
November1st to 15thNight
49%
875
33%
2275
17%
875
56%
875
49%
1248
November16th to endNight
47%
900
33%
2340
16%
900
58%
900
45%
1333
December1st to 15thNight
35%
900
23%
2469
10%
900
45%
900
36%
1477
December16th to endNight
37%
960
25%
2688
10%
960
50%
960
34%
1622

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
8%42332345%7%53%
48182
Night
7%42442445%7%52%
47202
Cloud CoverDay
8%42332345%7%54%
48180
Night
7%5%2442445%7%52%
47202
TransparencyDay
29%5%14%28%18%4
47856
Night
30%5%14%27%18%4
47030
SeeingDay
10%5%27%33%19%3
6024
Night
9%6%34%39%10%
16060

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
5%6%24323346%56%
1432
16th to endDay
5%6%2442435%8%53%
1536
February1st to 15thDay
6%7%445%3336%7%45%
1724
16th to endDay
6%5%35%334446%55%
1580
March1st to 15thDay
7%31322345%8%57%
1800
16th to endDay
10%6%3442435%8%47%
2189
April1st to 15thDay
12%5%24313347%50%
2150
16th to endDay
15%6%34424346%43%
2262
May1st to 15thDay
12%5%2442445%7%47%
2331
16th to endDay
12%425%32345%7%48%
2549
June1st to 15thDay
9%313324448%53%
2520
16th to endDay
311231345%8%64%
2520
July1st to 15thDay
6%21342446%8%54%
2520
16th to endDay
42133245%6%11%55%
2656
August1st to 15thDay
6%3244246%7%10%47%
2350
16th to endDay
5%314423445%60%
2292
September1st to 15thDay
8%313323347%58%
2113
16th to endDay
7%313223346%62%
1980
October1st to 15thDay
13%42231334454%
1853
16th to endDay
7%5%22213336%60%
1598
November1st to 15thDay
4424324347%58%
1583
16th to endDay
6%5%23222447%57%
1620
December1st to 15thDay
6%7%345%2336%5%52%
1488
16th to endDay
6%6%15%424446%50%
1536
January1st to 15thNight
35%2442445%8%54%
2506
16th to endNight
45%2442436%7%55%
2688
February1st to 15thNight
5%9%3443445%7%46%
2135
16th to endNight
5%6%25%43446%6%50%
1894
March1st to 15thNight
45%3442335%6%55%
2160
16th to endNight
10%6%34323347%48%
2032
April1st to 15thNight
12%6%245%24347%46%
1798
16th to endNight
16%6%15%424347%41%
1698
May1st to 15thNight
11%5%143345%5%7%45%
1619
16th to endNight
14%414435%45%8%42%
1561
June1st to 15thNight
10%4245%25%5%5%9%45%
1440
16th to endNight
33135%346%6%9%52%
1440
July1st to 15thNight
5%323425%5%8%9%47%
1440
16th to endNight
2213335%5%6%10%54%
1512
August1st to 15thNight
5%414435%5%7%9%47%
1606
16th to endNight
3213323348%61%
1910
September1st to 15thNight
8%312433447%55%
1845
16th to endNight
6%313233346%61%
1980
October1st to 15thNight
12%6%1232225%6%53%
1903
16th to endNight
8%313323336%61%
2263
November1st to 15thNight
4422323447%60%
2275
16th to endNight
5%323434337%58%
2340
December1st to 15thNight
6%6%25%433347%51%
2469
16th to endNight
6%6%35%424347%50%
2688

Percentage Cloud Cover SE (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
5%6%25%323346%56%
1432
16th to endDay
5%5%3431345%8%53%
1536
February1st to 15thDay
7%8%345%2345%7%46%
1724
16th to endDay
6%6%24424346%55%
1580
March1st to 15thDay
7%41232345%7%57%
1800
16th to endDay
10%5%2442335%7%48%
2187
April1st to 15thDay
13%5%24323346%51%
2150
16th to endDay
16%6%24423346%44%
2262
May1st to 15thDay
13%42442445%7%48%
2331
16th to endDay
13%424424447%48%
2549
June1st to 15thDay
9%32331445%8%53%
2520
16th to endDay
4112223448%65%
2520
July1st to 15thDay
7%21332446%8%55%
2520
16th to endDay
41133245%6%10%56%
2656
August1st to 15thDay
6%4134246%7%10%47%
2350
16th to endDay
5%323413446%60%
2292
September1st to 15thDay
8%312322346%59%
2113
16th to endDay
7%213223346%63%
1980
October1st to 15thDay
14%5%1232334454%
1853
16th to endDay
8%5%13323335%61%
1598
November1st to 15thDay
4414424347%58%
1583
16th to endDay
6%5%14223447%57%
1620
December1st to 15thDay
6%6%345%2335%6%52%
1488
16th to endDay
7%6%25%415%447%50%
1536
January1st to 15thNight
35%2442445%7%55%
2506
16th to endNight
442432445%7%55%
2688
February1st to 15thNight
6%9%3443345%7%46%
2135
16th to endNight
5%6%345%2445%6%50%
1894
March1st to 15thNight
5%5%2443435%6%55%
2160
16th to endNight
10%7%33424346%49%
2032
April1st to 15thNight
12%6%245%23346%47%
1798
16th to endNight
17%6%2442435%6%42%
1698
May1st to 15thNight
11%5%144345%5%7%46%
1619
16th to endNight
15%424435%448%42%
1561
June1st to 15thNight
11%323425%5%6%8%45%
1440
16th to endNight
42135%345%6%9%53%
1440
July1st to 15thNight
6%3134345%7%10%48%
1440
16th to endNight
2213325%5%7%8%56%
1512
August1st to 15thNight
5%314435%5%8%8%47%
1606
16th to endNight
431342335%7%61%
1910
September1st to 15thNight
8%31243435%6%56%
1845
16th to endNight
7%313323346%61%
1980
October1st to 15thNight
12%5%13312346%53%
1903
16th to endNight
8%312313345%61%
2263
November1st to 15thNight
4413323348%60%
2275
16th to endNight
5%422434348%58%
2340
December1st to 15thNight
6%6%26%423347%51%
2469
16th to endNight
7%6%35%424347%51%
2688

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
29%317%31%15%1
1433
16th to endDay
28%416%31%16%2
1536
February1st to 15thDay
36%417%27%9%3
1725
16th to endDay
29%6%13%30%17%3
1580
March1st to 15thDay
25%415%28%22%4
1800
16th to endDay
34%6%16%23%15%2
2189
April1st to 15thDay
32%6%11%32%13%3
2150
16th to endDay
40%414%22%15%1
2262
May1st to 15thDay
36%414%26%16%1
2331
16th to endDay
34%6%18%24%12%3
2553
June1st to 15thDay
28%5%17%28%15%4
2520
16th to endDay
17%412%32%25%7%
2520
July1st to 15thDay
25%5%12%27%20%7%
2371
16th to endDay
20%6%15%29%22%5%
2489
August1st to 15thDay
28%8%18%24%15%5%
2334
16th to endDay
24%410%28%23%8%
2292
September1st to 15thDay
26%39%27%21%11%
2113
16th to endDay
22%48%29%31%3
1980
October1st to 15thDay
32%410%25%21%5%
1853
16th to endDay
25%49%33%22%5%
1598
November1st to 15thDay
26%312%28%22%6%
1583
16th to endDay
27%312%30%23%3
1620
December1st to 15thDay
32%316%33%11%2
1488
16th to endDay
32%5%16%27%16%2
1536
January1st to 15thNight
25%6%17%30%17%2
2506
16th to endNight
27%5%15%30%18%2
2688
February1st to 15thNight
35%6%16%27%11%2
2145
16th to endNight
32%5%13%28%15%5%
1894
March1st to 15thNight
29%411%26%22%5%
2160
16th to endNight
36%412%24%17%3
2032
April1st to 15thNight
37%413%24%15%3
1798
16th to endNight
41%5%12%22%15%1
1698
May1st to 15thNight
36%6%16%24%15%1
1620
16th to endNight
38%9%16%21%10%3
1562
June1st to 15thNight
34%7%18%24%10%4
1440
16th to endNight
25%7%16%24%21%4
1440
July1st to 15thNight
28%7%15%26%14%6%
1360
16th to endNight
22%7%18%29%19%2
1416
August1st to 15thNight
29%8%19%25%12%5%
1598
16th to endNight
22%5%12%27%23%8%
1910
September1st to 15thNight
26%5%11%23%22%10%
1845
16th to endNight
25%48%29%26%6%
1980
October1st to 15thNight
31%5%10%24%23%5%
1903
16th to endNight
24%411%27%24%7%
2263
November1st to 15thNight
22%311%29%23%8%
2275
16th to endNight
26%312%28%23%5%
2340
December1st to 15thNight
32%416%31%13%1
2469
16th to endNight
34%317%27%15%1
2688

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
15%337%20%18%4
90
16th to endDay
11%447%27%8%1
96
February1st to 15thDay
12%12%46%26%2
90
16th to endDay
6%9%39%30%12%1
81
March1st to 15thDay
8%5%34%33%16%1
90
16th to endDay
13%10%31%30%12%1
177
April1st to 15thDay
9%14%38%28%8%
269
16th to endDay
23%9%31%24%11%
372
May1st to 15thDay
12%10%27%30%16%2
468
16th to endDay
17%6%28%30%13%2
517
June1st to 15thDay
8%430%27%21%7%
495
16th to endDay
3426%42%20%2
495
July1st to 15thDay
10%217%41%26%2
475
16th to endDay
5%19%40%29%4
515
August1st to 15thDay
9%319%35%28%3
490
16th to endDay
6%126%42%17%5%
332
September1st to 15thDay
3422%35%23%10%
268
16th to endDay
14%220%29%27%5%
135
October1st to 15thDay
13%127%34%18%4
107
16th to endDay
10%420%32%23%8%
96
November1st to 15thDay
7%13%38%24%15%
90
16th to endDay
17%8%27%32%10%3
90
December1st to 15thDay
16%450%15%12%1
90
16th to endDay
10%10%47%21%7%2
96
January1st to 15thNight
6%9%39%35%9%
900
16th to endNight
6%8%45%32%7%
960
February1st to 15thNight
8%6%46%32%5%
719
16th to endNight
8%7%44%33%5%
632
March1st to 15thNight
7%7%40%37%6%
720
16th to endNight
13%7%37%34%6%
579
April1st to 15thNight
15%9%39%33%2
539
16th to endNight
20%10%32%29%7%
540
May1st to 15thNight
13%7%32%38%7%1
540
16th to endNight
17%5%33%32%10%
563
June1st to 15thNight
12%6%33%35%11%1
540
16th to endNight
5%228%49%13%
540
July1st to 15thNight
7%125%49%15%
510
16th to endNight
3120%54%19%1
564
August1st to 15thNight
6%121%52%17%
539
16th to endNight
2223%52%17%
573
September1st to 15thNight
8%229%43%15%
540
16th to endNight
8%5%26%40%17%1
537
October1st to 15thNight
15%7%27%36%13%
535
16th to endNight
10%5%27%41%14%
855
November1st to 15thNight
6%6%32%42%10%1
875
16th to endNight
7%5%35%40%10%
900
December1st to 15thNight
9%7%40%33%7%
900
16th to endNight
9%8%36%37%7%
960
Page generated at 2017-10-07 12:07:48. Version ac04

Copyright 2017 A. Danko


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