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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 2017-08-12.

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
47%
14543
12%
46525
12%
14516
49%
14516
18%
32965

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%
598
10%
1678
7%
598
47%
598
18%
1247
May1st to 15thNight
52%
400
13%
1480
14%
400
55%
400
23%
925
May16th to endNight
52%
375
9%
1496
13%
374
53%
374
14%
1047
June1st to 15thNight
52%
360
8%
1440
12%
360
54%
360
17%
951
June16th to endNight
57%
360
12%
1440
17%
360
60%
360
23%
836
July1st to 15thNight
81%
340
18%
1360
29%
340
83%
340
47%
549
July16th to endNight
83%
377
28%
1417
40%
355
87%
355
56%
528
August1st to 15thNight
85%
526
26%
1575
25%
523
87%
523
57%
721
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
18%8%46%5%34446%32%
47468
Night
19%7%35%5%24445%36%
46694
Cloud CoverDay
19%8%37%5%34446%32%
47468
Night
20%7%36%5%24345%35%
46698
TransparencyDay
52%6%12%16%9%2
47140
Night
51%5%12%17%10%2
46526
SeeingDay
21%7%18%24%21%7%
5515
Night
23%415%30%22%2
14555

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%47%7%45%6%5%6%23%
2280
May1st to 15thDay
17%8%37%425%347%35%
2469
16th to endDay
20%7%36%6%35%45%7%28%
2615
June1st to 15thDay
17%9%47%5%35%5%46%30%
2520
16th to endDay
11%6%36%435%5%5%6%41%
2520
July1st to 15thDay
5%323323446%62%
2520
16th to endDay
7%212212336%66%
2654
August1st to 15thDay
331332345%8%61%
2291
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%
1678
May1st to 15thNight
12%5%35%4435%5%7%42%
1480
16th to endNight
16%7%36%435%5%5%9%33%
1496
June1st to 15thNight
14%6%45%5%25%5%46%38%
1440
16th to endNight
9%6%25%42435%8%47%
1440
July1st to 15thNight
3212112335%72%
1440
16th to endNight
21111225%78%
1513
August1st to 15thNight
322212237%70%
1584
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%346%5%6%23%
2280
May1st to 15thDay
16%7%37%5%3435%6%35%
2469
16th to endDay
20%7%36%5%45%5%6%7%27%
2615
June1st to 15thDay
17%9%47%5%35%5%47%29%
2520
16th to endDay
11%6%37%5%35%5%46%41%
2520
July1st to 15thDay
4313323347%62%
2520
16th to endDay
6%213212335%65%
2654
August1st to 15thDay
231342445%8%60%
2291
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
19%7%36%6%25%447%32%
1678
May1st to 15thNight
12%6%35%43446%7%41%
1480
16th to endNight
18%7%35%5%246%6%8%31%
1496
June1st to 15thNight
15%6%45%6%3445%6%37%
1440
16th to endNight
9%7%25%434446%47%
1440
July1st to 15thNight
3211112335%71%
1440
16th to endNight
312111235%76%
1513
August1st to 15thNight
222222247%70%
1584
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
2280
May1st to 15thDay
49%5%14%20%9%
2469
16th to endDay
55%9%15%15%4
2619
June1st to 15thDay
54%7%17%15%5%
2520
16th to endDay
42%7%18%22%6%2
2520
July1st to 15thDay
22%5%14%28%23%6%
2371
16th to endDay
19%410%27%30%6%
2487
August1st to 15thDay
20%6%18%30%18%5%
2275
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%16%16%5%1
1678
May1st to 15thNight
42%5%17%22%8%3
1481
16th to endNight
51%8%17%16%5%1
1496
June1st to 15thNight
47%6%18%19%6%
1440
16th to endNight
39%419%24%8%2
1440
July1st to 15thNight
17%315%30%25%7%
1360
16th to endNight
12%311%30%31%10%
1417
August1st to 15thNight
15%416%38%19%7%
1575
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
27%12%23%18%12%5%
270
May1st to 15thDay
25%9%22%22%18%2
288
16th to endDay
19%6%13%22%23%14%
330
June1st to 15thDay
18%9%18%23%22%7%
315
16th to endDay
14%5%17%30%27%4
315
July1st to 15thDay
4214%28%36%11%
305
16th to endDay
5%312%36%33%9%
327
August1st to 15thDay
3211%32%35%16%
300
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
598
May1st to 15thNight
16%319%38%20%1
401
16th to endNight
24%111%33%27%1
375
June1st to 15thNight
19%314%41%20%1
360
16th to endNight
14%119%42%22%
360
July1st to 15thNight
6%17%49%34%
340
16th to endNight
317%49%35%2
377
August1st to 15thNight
3334%49%6%
526
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 2017-08-13 11:16:33. Version ac04

Copyright 2017 A. Danko


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