Salem
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Salem clear sky chart from 2005-11-05 to 2017-04-26.

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
46%
14315
12%
45667
12%
14288
48%
14288
18%
32553

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
31%
717
8%
2506
7%
716
33%
716
9%
2055
January16th to endNight
39%
768
11%
2571
11%
768
40%
768
13%
1959
February1st to 15thNight
37%
696
7%
2288
6%
696
38%
696
10%
1857
February16th to endNight
32%
632
10%
2009
7%
632
37%
632
12%
1549
March1st to 15thNight
33%
720
5%
2031
4%
720
34%
720
11%
1672
March16th to endNight
33%
768
6%
2088
4%
768
34%
768
12%
1731
April1st to 15thNight
36%
719
7%
1799
4%
719
36%
719
15%
1464
April16th to endNight
45%
586
10%
1642
7%
586
47%
586
18%
1223
May1st to 15thNight
52%
367
14%
1357
15%
367
56%
367
22%
852
May16th to endNight
50%
343
6%
1368
10%
342
50%
342
13%
986
June1st to 15thNight
53%
330
9%
1320
13%
330
55%
330
17%
860
June16th to endNight
56%
330
10%
1320
15%
330
58%
330
22%
782
July1st to 15thNight
80%
310
20%
1240
30%
310
83%
310
46%
510
July16th to endNight
82%
349
25%
1305
37%
327
86%
327
54%
498
August1st to 15thNight
85%
493
27%
1476
26%
490
87%
490
56%
681
August16th to endNight
75%
599
30%
1649
22%
599
77%
599
52%
850
September1st to 15thNight
79%
660
29%
1650
19%
660
80%
660
59%
870
September16th to endNight
67%
656
25%
1814
21%
656
68%
656
36%
1090
October1st to 15thNight
52%
660
17%
1980
16%
660
55%
660
25%
1314
October16th to endNight
43%
704
12%
2126
12%
704
45%
704
17%
1575
November1st to 15thNight
34%
700
8%
2400
9%
700
36%
700
10%
1936
November16th to endNight
37%
720
6%
2520
7%
720
38%
720
11%
1949
December1st to 15thNight
33%
720
8%
2520
8%
720
35%
720
10%
1995
December16th to endNight
26%
768
5%
2688
6%
768
27%
768
7%
2295

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
19%8%47%5%34446%32%
46012
Night
19%7%36%5%24445%35%
45836
Cloud CoverDay
19%8%47%5%34446%31%
46012
Night
20%7%36%5%24445%35%
45840
TransparencyDay
53%6%12%15%9%2
45684
Night
51%6%12%16%10%2
45668
SeeingDay
22%7%18%24%20%6%
5094
Night
24%415%30%22%2
14327

By Month

Percentage Cloud Cover NW (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
33%11%6%10%6%3432313%
1432
16th to endDay
25%9%5%8%9%35%235%20%
1651
February1st to 15thDay
30%12%5%8%6%34335%14%
1576
16th to endDay
26%12%49%7%34345%17%
1463
March1st to 15thDay
30%11%48%7%45%43413%
1926
16th to endDay
27%11%48%7%45%5%45%14%
2136
April1st to 15thDay
22%12%5%7%8%35%45%6%17%
2149
16th to endDay
20%10%46%7%446%5%6%23%
2227
May1st to 15thDay
16%8%37%425%347%36%
2262
16th to endDay
20%8%36%6%45%46%7%25%
2391
June1st to 15thDay
17%9%47%5%345%46%31%
2310
16th to endDay
11%7%37%5%35%5%5%6%39%
2310
July1st to 15thDay
5%323323446%60%
2310
16th to endDay
7%212212336%63%
2458
August1st to 15thDay
331332345%8%59%
2145
16th to endDay
5%424412348%58%
2201
September1st to 15thDay
6%412213346%61%
1980
16th to endDay
16%6%36%43445%6%40%
1815
October1st to 15thDay
17%11%47%5%34446%28%
1650
16th to endDay
23%10%47%7%35%445%22%
1746
November1st to 15thDay
29%12%6%10%6%35%445%11%
1458
16th to endDay
26%12%49%7%4443418%
1440
December1st to 15thDay
26%12%5%10%7%35%345%16%
1440
16th to endDay
31%13%6%10%7%3342411%
1536
January1st to 15thNight
30%11%47%6%24445%19%
2506
16th to endNight
26%8%47%5%24445%26%
2571
February1st to 15thNight
25%10%5%8%5%35%446%21%
2276
16th to endNight
22%10%47%6%34445%26%
2009
March1st to 15thNight
27%10%37%6%345%4422%
2031
16th to endNight
25%9%37%6%445%5%5%20%
2084
April1st to 15thNight
24%10%47%6%2435%6%25%
1799
16th to endNight
18%7%35%5%35%447%33%
1642
May1st to 15thNight
12%5%35%4445%5%7%42%
1357
16th to endNight
17%7%36%435%5%5%9%30%
1368
June1st to 15thNight
14%6%45%5%25%5%46%40%
1320
16th to endNight
9%6%25%42435%8%45%
1320
July1st to 15thNight
3212113335%71%
1320
16th to endNight
31111225%77%
1401
August1st to 15thNight
322222347%69%
1485
16th to endNight
5%312312325%67%
1649
September1st to 15thNight
42221123472%
1650
16th to endNight
11%313323347%53%
1814
October1st to 15thNight
15%5%25%5%33345%44%
1980
16th to endNight
22%7%35%5%24445%33%
2126
November1st to 15thNight
29%7%36%6%45%5%45%20%
2400
16th to endNight
26%9%36%6%24445%26%
2520
December1st to 15thNight
27%10%47%6%33335%22%
2520
16th to endNight
28%12%5%7%7%35%34416%
2688

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
35%9%5%12%6%3423213%
1432
16th to endDay
27%10%5%9%9%2433419%
1651
February1st to 15thDay
29%13%5%10%6%24425%14%
1576
16th to endDay
28%9%6%8%6%34435%17%
1463
March1st to 15thDay
31%10%5%9%7%4444413%
1926
16th to endDay
27%11%5%8%7%45%5%4414%
2136
April1st to 15thDay
22%11%49%7%45%45%6%17%
2149
16th to endDay
20%9%47%8%345%5%6%23%
2227
May1st to 15thDay
15%7%37%5%34346%36%
2262
16th to endDay
21%7%36%5%46%5%6%8%25%
2391
June1st to 15thDay
16%8%5%6%5%35%5%47%30%
2310
16th to endDay
11%7%37%5%35%5%46%39%
2310
July1st to 15thDay
5%313323447%60%
2310
16th to endDay
6%313212346%63%
2458
August1st to 15thDay
231342446%8%59%
2145
16th to endDay
6%314423347%58%
2201
September1st to 15thDay
5%5%13223346%61%
1980
16th to endDay
15%8%36%42345%6%39%
1815
October1st to 15thDay
19%10%47%5%3435%6%28%
1650
16th to endDay
23%10%49%7%34435%22%
1746
November1st to 15thDay
30%12%6%10%6%345%3411%
1458
16th to endDay
27%11%5%9%6%4443318%
1440
December1st to 15thDay
26%12%6%10%7%3434416%
1440
16th to endDay
34%12%410%7%2343312%
1536
January1st to 15thNight
30%10%47%6%34435%19%
2506
16th to endNight
26%9%47%5%24346%26%
2571
February1st to 15thNight
26%9%48%5%35%45%5%21%
2276
16th to endNight
23%9%46%6%34445%25%
2009
March1st to 15thNight
27%10%47%6%35%44421%
2031
16th to endNight
26%8%48%6%4445%5%20%
2088
April1st to 15thNight
24%10%47%6%3435%5%24%
1799
16th to endNight
18%7%37%6%25%447%31%
1642
May1st to 15thNight
13%5%35%43446%7%41%
1357
16th to endNight
19%7%35%425%6%6%7%29%
1368
June1st to 15thNight
14%6%45%5%3445%5%38%
1320
16th to endNight
9%7%26%5%35%446%45%
1320
July1st to 15thNight
4211113335%70%
1320
16th to endNight
3112111235%75%
1401
August1st to 15thNight
32222225%7%69%
1485
16th to endNight
5%213212235%68%
1649
September1st to 15thNight
4311112325%71%
1650
16th to endNight
11%413423346%52%
1814
October1st to 15thNight
16%5%25%433345%43%
1980
16th to endNight
22%6%37%5%24445%33%
2126
November1st to 15thNight
30%8%36%7%3445%420%
2400
16th to endNight
27%9%36%6%2444426%
2520
December1st to 15thNight
29%9%47%6%34245%22%
2520
16th to endNight
30%12%5%8%6%3443415%
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
77%448%41
1432
16th to endDay
69%47%9%6%2
1651
February1st to 15thDay
70%9%7%8%3
1576
16th to endDay
69%6%7%8%6%
1463
March1st to 15thDay
73%7%8%7%3
1926
16th to endDay
72%7%9%8%2
2136
April1st to 15thDay
67%7%13%10%2
2149
16th to endDay
60%7%13%11%5%1
2227
May1st to 15thDay
49%413%20%10%1
2262
16th to endDay
57%9%15%13%3
2395
June1st to 15thDay
53%7%17%15%5%
2310
16th to endDay
44%7%19%21%6%1
2310
July1st to 15thDay
23%6%14%27%21%6%
2161
16th to endDay
20%411%25%30%7%
2291
August1st to 15thDay
20%7%18%31%18%3
2129
16th to endDay
24%5%14%28%21%4
2201
September1st to 15thDay
23%412%26%20%11%
1980
16th to endDay
45%6%13%18%12%3
1815
October1st to 15thDay
53%6%10%15%9%3
1650
16th to endDay
61%9%10%9%7%
1746
November1st to 15thDay
74%7%8%8%1
1458
16th to endDay
70%6%7%7%8%
1440
December1st to 15thDay
70%5%8%10%5%
1440
16th to endDay
76%6%7%6%3
1536
January1st to 15thNight
68%6%8%9%6%1
2506
16th to endNight
60%5%9%11%9%3
2571
February1st to 15thNight
65%6%10%11%4
2288
16th to endNight
61%5%12%11%7%1
2009
March1st to 15thNight
65%7%10%12%4
2031
16th to endNight
65%7%13%11%2
2088
April1st to 15thNight
62%6%14%11%5%
1799
16th to endNight
53%6%15%16%5%1
1642
May1st to 15thNight
43%5%17%21%9%3
1358
16th to endNight
53%9%17%14%31
1368
June1st to 15thNight
47%6%19%19%7%
1320
16th to endNight
40%420%23%8%1
1320
July1st to 15thNight
17%416%30%23%7%
1240
16th to endNight
13%312%27%32%10%
1305
August1st to 15thNight
15%417%39%18%4
1476
16th to endNight
19%5%12%37%19%6%
1649
September1st to 15thNight
17%314%29%20%13%
1650
16th to endNight
32%5%15%23%15%7%
1814
October1st to 15thNight
43%6%10%20%14%4
1980
16th to endNight
52%8%11%13%12%1
2126
November1st to 15thNight
65%6%10%12%5%
2400
16th to endNight
61%6%9%8%11%2
2520
December1st to 15thNight
65%5%9%12%7%
2520
16th to endNight
73%6%8%7%3
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
38%13%26%16%5%
60
16th to endDay
29%7%13%20%21%8%
179
February1st to 15thDay
37%8%16%16%16%3
236
16th to endDay
31%11%18%24%9%3
219
March1st to 15thDay
43%15%18%15%5%1
270
16th to endDay
32%11%26%19%7%2
288
April1st to 15thDay
28%12%19%20%10%7%
269
16th to endDay
28%12%22%18%11%5%
254
May1st to 15thDay
22%10%23%24%17%1
228
16th to endDay
20%7%14%22%22%12%
266
June1st to 15thDay
16%8%19%25%22%7%
255
16th to endDay
15%7%18%29%25%3
255
July1st to 15thDay
5%316%30%31%13%
245
16th to endDay
6%413%35%32%8%
271
August1st to 15thDay
3212%35%37%8%
255
16th to endDay
5%5%14%30%29%13%
268
September1st to 15thDay
9%223%23%29%10%
255
16th to endDay
16%5%16%29%29%3
255
October1st to 15thDay
28%5%18%21%18%6%
255
16th to endDay
29%5%23%22%13%5%
258
November1st to 15thDay
33%7%26%21%8%2
69
16th to endDay
40%8%15%13%15%8%
60
December1st to 15thDay
43%8%33%13%1
60
16th to endDay
35%7%18%14%20%3
64
January1st to 15thNight
34%7%14%23%17%2
720
16th to endNight
30%5%13%25%22%3
768
February1st to 15thNight
30%6%16%26%18%1
704
16th to endNight
28%8%22%25%15%
632
March1st to 15thNight
32%8%19%26%12%
720
16th to endNight
29%6%20%28%13%
768
April1st to 15thNight
28%6%17%28%17%1
719
16th to endNight
25%219%30%20%1
586
May1st to 15thNight
16%219%38%20%1
368
16th to endNight
26%111%32%26%1
343
June1st to 15thNight
18%315%40%20%1
330
16th to endNight
15%119%41%22%
330
July1st to 15thNight
7%17%47%35%
310
16th to endNight
418%48%34%2
349
August1st to 15thNight
4436%49%5%
493
16th to endNight
6%19%38%40%2
599
September1st to 15thNight
6%9%38%38%5%
660
16th to endNight
13%110%36%33%2
656
October1st to 15thNight
18%318%32%24%3
660
16th to endNight
26%415%27%21%4
704
November1st to 15thNight
34%5%16%29%13%
700
16th to endNight
30%8%16%24%17%2
720
December1st to 15thNight
33%6%16%26%14%1
720
16th to endNight
35%6%21%20%14%1
768
Page generated at 2017-04-27 14:48:54. Version ac04

Copyright 2017 A. Danko


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