Maury Lewin Astronomical Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Maury Lewin Astronomical Observatory clear sky chart from 2005-11-05 to 2018-01-12.

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%
16341
34%
48216
28%
16295
77%
16295
51%
23786

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%
761
27%
2639
24%
760
67%
760
38%
1326
January16th to endNight
55%
768
34%
2304
25%
768
67%
768
39%
1266
February1st to 15thNight
63%
697
34%
2104
30%
696
71%
696
46%
1080
February16th to endNight
56%
632
28%
1895
26%
632
62%
632
35%
1096
March1st to 15thNight
62%
720
29%
2160
25%
720
71%
720
47%
1093
March16th to endNight
66%
768
29%
2010
22%
768
71%
768
48%
1118
April1st to 15thNight
60%
719
28%
1799
16%
719
65%
719
47%
1038
April16th to endNight
64%
720
32%
1800
16%
720
68%
720
54%
962
May1st to 15thNight
65%
605
29%
1685
19%
605
68%
605
47%
910
May16th to endNight
70%
561
29%
1685
23%
561
73%
561
51%
839
June1st to 15thNight
79%
497
29%
1577
27%
497
81%
497
56%
728
June16th to endNight
95%
360
40%
1440
48%
360
95%
360
66%
488
July1st to 15thNight
93%
340
34%
1360
42%
340
93%
340
62%
477
July16th to endNight
89%
636
31%
1658
24%
596
89%
596
61%
796
August1st to 15thNight
91%
717
36%
1790
24%
713
91%
713
75%
835
August16th to endNight
93%
764
43%
1910
29%
764
93%
764
77%
877
September1st to 15thNight
90%
720
39%
1837
31%
720
90%
720
70%
875
September16th to endNight
87%
716
46%
1980
43%
716
90%
716
74%
847
October1st to 15thNight
77%
720
36%
1980
32%
720
82%
720
58%
976
October16th to endNight
75%
768
40%
2343
41%
768
80%
768
53%
1112
November1st to 15thNight
72%
760
35%
2470
33%
760
80%
760
52%
1128
November16th to endNight
70%
780
37%
2535
36%
780
76%
780
49%
1200
December1st to 15thNight
61%
780
32%
2535
27%
780
70%
780
41%
1302
December16th to endNight
56%
832
34%
2720
28%
832
67%
832
38%
1417

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
5%212212335%68%
49098
Night
5%212312335%68%
48416
TransparencyDay
18%37%16%27%27%
48789
Night
19%37%16%26%27%
48225
SeeingDay
6%9%32%36%11%3
6301
Night
5%215%35%33%6%
16354

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
8%413412335%62%
1538
16th to endDay
11%42321343457%
1917
February1st to 15thDay
8%312313335%62%
1751
16th to endDay
13%5%23332336%51%
1579
March1st to 15thDay
5%21431445%8%58%
1800
16th to endDay
5%2135%2445%9%56%
2211
April1st to 15thDay
6%3123245%36%59%
2149
16th to endDay
5%212212235%69%
2160
May1st to 15thDay
4312312336%66%
2265
16th to endDay
5%312313346%64%
2429
June1st to 15thDay
5%22312336%68%
2379
16th to endDay
111111385%
2520
July1st to 15thDay
111212335%74%
2520
16th to endDay
212212245%74%
2390
August1st to 15thDay
111125%83%
2160
16th to endDay
111133481%
2292
September1st to 15thDay
1111123481%
2121
16th to endDay
21111122381%
1980
October1st to 15thDay
5%211212225%71%
1978
16th to endDay
321221224472%
1881
November1st to 15thDay
3212313245%68%
1719
16th to endDay
5%312222336%64%
1755
December1st to 15thDay
6%21321335%8%59%
1755
16th to endDay
11%312312337%58%
1849
January1st to 15thNight
7%313323336%60%
2639
16th to endNight
11%313213335%60%
2304
February1st to 15thNight
7%313313236%63%
2101
16th to endNight
13%4133235%35%53%
1895
March1st to 15thNight
432321245%6%62%
2160
16th to endNight
5%31241345%8%60%
2010
April1st to 15thNight
6%422423335%61%
1799
16th to endNight
4211322235%69%
1800
May1st to 15thNight
3312433335%64%
1685
16th to endNight
231423236%67%
1684
June1st to 15thNight
2111423336%70%
1577
16th to endNight
1111112483%
1440
July1st to 15thNight
2111122235%76%
1440
16th to endNight
211213346%69%
1772
August1st to 15thNight
11211235%79%
1800
16th to endNight
111123481%
1910
September1st to 15thNight
11121231379%
1837
16th to endNight
121112383%
1980
October1st to 15thNight
321221232472%
1980
16th to endNight
42231223471%
2343
November1st to 15thNight
321321233470%
2470
16th to endNight
5%2222325%6%64%
2535
December1st to 15thNight
6%313413345%61%
2535
16th to endNight
10%312212245%61%
2720

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
26%37%14%23%25%
1538
16th to endDay
29%28%13%19%26%
1917
February1st to 15thDay
24%26%16%24%25%
1751
16th to endDay
33%37%16%27%10%
1579
March1st to 15thDay
23%410%21%20%21%
1800
16th to endDay
23%5%12%22%20%14%
2211
April1st to 15thDay
25%410%24%23%11%
2149
16th to endDay
18%39%22%28%17%
2160
May1st to 15thDay
21%310%18%28%16%
2265
16th to endDay
21%39%24%29%10%
2432
June1st to 15thDay
20%29%14%31%22%
2379
16th to endDay
8%236%32%45%
2520
July1st to 15thDay
11%35%10%25%42%
2371
16th to endDay
12%46%22%29%24%
2241
August1st to 15thDay
7%2313%35%38%
2146
16th to endDay
7%2411%39%33%
2292
September1st to 15thDay
8%25%11%33%37%
2121
16th to endDay
8%2413%33%37%
1980
October1st to 15thDay
17%35%16%27%29%
1978
16th to endDay
16%3411%21%41%
1881
November1st to 15thDay
18%37%16%24%30%
1719
16th to endDay
22%36%13%22%32%
1755
December1st to 15thDay
22%5%9%18%18%26%
1755
16th to endDay
27%47%17%20%22%
1849
January1st to 15thNight
26%46%14%22%26%
2639
16th to endNight
28%47%14%16%29%
2304
February1st to 15thNight
23%37%16%23%26%
2112
16th to endNight
32%47%16%24%14%
1895
March1st to 15thNight
22%410%20%23%19%
2160
16th to endNight
22%6%10%22%23%15%
2010
April1st to 15thNight
25%39%24%21%14%
1799
16th to endNight
19%49%23%27%16%
1800
May1st to 15thNight
23%48%19%28%16%
1686
16th to endNight
20%310%25%28%11%
1685
June1st to 15thNight
16%310%16%31%21%
1577
16th to endNight
8%239%30%45%
1440
July1st to 15thNight
10%25%11%26%43%
1360
16th to endNight
14%47%21%26%25%
1658
August1st to 15thNight
8%2312%38%34%
1790
16th to endNight
6%3411%38%34%
1910
September1st to 15thNight
11%2410%33%37%
1837
16th to endNight
9%1313%34%37%
1980
October1st to 15thNight
17%25%15%31%26%
1980
16th to endNight
18%349%23%40%
2343
November1st to 15thNight
18%36%14%25%31%
2470
16th to endNight
21%26%15%20%33%
2535
December1st to 15thNight
25%38%15%19%27%
2535
16th to endNight
26%48%13%25%21%
2720

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
22%6%35%28%9%
100
16th to endDay
15%12%37%27%5%1
287
February1st to 15thDay
11%13%31%32%9%1
266
16th to endDay
18%15%34%23%7%
238
March1st to 15thDay
8%17%32%24%15%1
270
16th to endDay
8%14%42%25%7%1
288
April1st to 15thDay
11%19%40%21%42
269
16th to endDay
422%44%21%32
270
May1st to 15thDay
10%15%37%28%6%2
288
16th to endDay
9%10%40%27%10%
330
June1st to 15thDay
5%10%37%35%9%2
315
16th to endDay
2331%46%10%6%
315
July1st to 15thDay
125%50%15%5%
305
16th to endDay
1118%54%14%8%
327
August1st to 15thDay
1227%52%10%5%
315
16th to endDay
122%54%13%6%
332
September1st to 15thDay
1235%45%10%3
315
16th to endDay
36%36%37%10%4
315
October1st to 15thDay
5%11%38%31%11%1
315
16th to endDay
7%7%29%35%16%4
297
November1st to 15thDay
5%7%20%36%27%2
135
16th to endDay
6%7%29%31%21%2
135
December1st to 15thDay
27%27%36%22%3
135
16th to endDay
9%10%23%32%18%5%
139
January1st to 15thNight
9%323%40%19%3
764
16th to endNight
13%322%35%21%3
768
February1st to 15thNight
8%218%41%24%4
704
16th to endNight
15%321%35%20%3
632
March1st to 15thNight
5%224%41%22%4
720
16th to endNight
5%320%38%28%3
768
April1st to 15thNight
8%422%39%21%3
719
16th to endNight
4424%36%25%5%
720
May1st to 15thNight
4321%35%29%4
606
16th to endNight
4317%38%30%4
563
June1st to 15thNight
2114%41%36%3
497
16th to endNight
237%54%5%
360
July1st to 15thNight
2113%71%11%
340
16th to endNight
21225%56%11%
636
August1st to 15thNight
326%55%13%
717
16th to endNight
1221%57%16%
764
September1st to 15thNight
15%28%49%15%
720
16th to endNight
18%31%44%12%
716
October1st to 15thNight
413%40%35%4
720
16th to endNight
6%112%34%34%11%
768
November1st to 15thNight
416%40%30%7%
760
16th to endNight
6%117%37%29%7%
780
December1st to 15thNight
8%220%39%24%3
780
16th to endNight
10%424%37%19%3
832
Page generated at 2018-01-12 19:01:33. Version ac04

Copyright 2018 A. Danko


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