Congress
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Congress clear sky chart from 2005-11-05 to 2018-01-20.

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
76%
16233
37%
48484
33%
16195
81%
16195
56%
22627

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
71%
778
34%
2522
34%
776
75%
776
45%
1236
January16th to endNight
67%
788
37%
2561
37%
788
74%
788
44%
1271
February1st to 15thNight
70%
698
37%
2145
35%
698
78%
698
52%
1019
February16th to endNight
67%
632
35%
1895
35%
632
72%
632
46%
977
March1st to 15thNight
68%
720
39%
2012
32%
720
77%
720
57%
974
March16th to endNight
74%
768
38%
2112
30%
768
80%
768
58%
1037
April1st to 15thNight
65%
719
31%
1978
20%
719
72%
719
56%
983
April16th to endNight
68%
562
45%
1645
31%
562
78%
562
73%
669
May1st to 15thNight
76%
539
40%
1619
32%
539
80%
539
67%
674
May16th to endNight
80%
561
39%
1684
31%
561
83%
561
71%
690
June1st to 15thNight
83%
540
35%
1620
31%
540
84%
540
73%
649
June16th to endNight
90%
540
36%
1620
33%
540
91%
540
79%
626
July1st to 15thNight
88%
510
27%
1530
23%
510
88%
510
55%
719
July16th to endNight
84%
564
27%
1593
22%
531
86%
531
43%
849
August1st to 15thNight
86%
539
33%
1611
28%
536
87%
536
55%
764
August16th to endNight
83%
699
35%
1881
28%
699
84%
699
53%
989
September1st to 15thNight
84%
720
32%
1980
28%
720
86%
720
53%
1021
September16th to endNight
85%
716
46%
1980
38%
716
89%
716
73%
860
October1st to 15thNight
79%
720
40%
2031
33%
720
84%
720
66%
910
October16th to endNight
82%
768
45%
2304
40%
768
87%
768
66%
986
November1st to 15thNight
80%
760
38%
2387
37%
760
84%
760
58%
1069
November16th to endNight
78%
780
42%
2535
43%
780
82%
780
56%
1113
December1st to 15thNight
73%
780
36%
2535
36%
780
77%
780
48%
1196
December16th to endNight
66%
832
37%
2704
36%
832
72%
832
43%
1346

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
4212213345%67%
49044
Night
3212213346%68%
48681
TransparencyDay
17%2412%25%36%
48739
Night
17%2412%25%37%
48487
SeeingDay
45%21%36%24%6%
5923
Night
4110%34%38%10%
16244

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
7%313212335%64%
1746
16th to endDay
9%33223335%62%
1766
February1st to 15thDay
4413322345%63%
1715
16th to endDay
9%31331345%6%57%
1579
March1st to 15thDay
431222225%5%66%
1947
16th to endDay
4223323235%67%
2112
April1st to 15thDay
4212213347%65%
1970
16th to endDay
12112235%76%
2311
May1st to 15thDay
1112112245%73%
2331
16th to endDay
22111212479%
2429
June1st to 15thDay
1111112482%
2340
16th to endDay
1111213383%
2340
July1st to 15thDay
22134345%5%7%59%
2340
16th to endDay
44245%36%7%8%8%42%
2467
August1st to 15thDay
43134245%5%6%57%
2340
16th to endDay
421342346%6%60%
2319
September1st to 15thDay
4213325%36%5%61%
1980
16th to endDay
2112222478%
1980
October1st to 15thDay
211221223475%
1929
16th to endDay
112211245%76%
1920
November1st to 15thDay
2212213345%69%
1801
16th to endDay
5%212212235%68%
1755
December1st to 15thDay
6%314423437%58%
1755
16th to endDay
9%314313346%57%
1872
January1st to 15thNight
5%413323345%63%
2522
16th to endNight
8%323213235%63%
2561
February1st to 15thNight
4313212245%67%
2135
16th to endNight
7%21342335%6%59%
1895
March1st to 15thNight
5%212212346%67%
2012
16th to endNight
4211214335%68%
2112
April1st to 15thNight
421332233468%
1978
16th to endNight
21111135%79%
1645
May1st to 15thNight
212111145%75%
1619
16th to endNight
1112123479%
1684
June1st to 15thNight
111211122380%
1620
16th to endNight
11123483%
1620
July1st to 15thNight
223325%45%9%61%
1620
16th to endNight
1214436%6%7%13%46%
1701
August1st to 15thNight
221332346%9%60%
1620
16th to endNight
32133245%5%8%59%
1881
September1st to 15thNight
21123345%6%6%62%
1980
16th to endNight
21111122480%
1980
October1st to 15thNight
31221224475%
2031
16th to endNight
1112212235%76%
2304
November1st to 15thNight
2312213235%70%
2387
16th to endNight
3212212235%72%
2535
December1st to 15thNight
6%21232334464%
2535
16th to endNight
8%323213346%59%
2704

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
22%2413%28%28%
1747
16th to endDay
23%15%16%25%27%
1766
February1st to 15thDay
20%25%15%27%27%
1715
16th to endDay
24%15%16%28%23%
1579
March1st to 15thDay
18%1312%30%33%
1947
16th to endDay
19%1411%32%29%
2112
April1st to 15thDay
16%1412%31%33%
1970
16th to endDay
10%129%30%44%
2311
May1st to 15thDay
12%1310%28%44%
2331
16th to endDay
10%128%27%49%
2432
June1st to 15thDay
7%15%20%63%
2340
16th to endDay
8%12411%72%
2340
July1st to 15thDay
19%5%8%13%17%35%
2201
16th to endDay
30%6%14%17%17%12%
2312
August1st to 15thDay
22%5%6%16%21%26%
2325
16th to endDay
20%5%7%14%28%23%
2319
September1st to 15thDay
21%26%15%25%28%
1980
16th to endDay
11%125%27%51%
1980
October1st to 15thDay
12%249%24%46%
1929
16th to endDay
11%148%26%46%
1920
November1st to 15thDay
15%1413%31%33%
1801
16th to endDay
17%1212%25%39%
1755
December1st to 15thDay
24%26%16%22%26%
1755
16th to endDay
26%36%16%28%18%
1872
January1st to 15thNight
23%3413%26%29%
2522
16th to endNight
25%1315%24%28%
2561
February1st to 15thNight
19%15%15%25%32%
2146
16th to endNight
24%2414%26%27%
1895
March1st to 15thNight
18%1310%29%36%
2012
16th to endNight
16%2413%30%31%
2112
April1st to 15thNight
18%2310%30%34%
1978
16th to endNight
8%1210%28%48%
1645
May1st to 15thNight
11%1210%30%43%
1620
16th to endNight
9%127%27%50%
1685
June1st to 15thNight
9%115%17%65%
1620
16th to endNight
6%11310%75%
1620
July1st to 15thNight
17%39%15%17%36%
1530
16th to endNight
22%7%12%23%17%16%
1593
August1st to 15thNight
16%47%19%21%29%
1611
16th to endNight
20%48%15%24%26%
1881
September1st to 15thNight
18%5%7%17%21%28%
1980
16th to endNight
9%126%24%55%
1980
October1st to 15thNight
12%1311%24%45%
2031
16th to endNight
12%148%20%52%
2304
November1st to 15thNight
16%1311%31%35%
2387
16th to endNight
17%1211%24%41%
2535
December1st to 15thNight
21%25%14%25%30%
2535
16th to endNight
25%25%17%29%19%
2704

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
23%118%29%20%6%
135
16th to endDay
7%7%21%26%23%13%
109
February1st to 15thDay
8%5%25%38%20%2
230
16th to endDay
12%12%35%25%12%1
238
March1st to 15thDay
412%25%36%16%4
270
16th to endDay
414%32%30%15%3
288
April1st to 15thDay
6%14%30%29%13%5%
269
16th to endDay
419%34%27%11%3
270
May1st to 15thDay
211%33%33%14%4
288
16th to endDay
19%31%37%16%3
330
June1st to 15thDay
2428%42%17%4
315
16th to endDay
1112%42%33%8%
315
July1st to 15thDay
1111%50%28%7%
305
16th to endDay
5%5%33%42%13%
327
August1st to 15thDay
48%40%33%12%
315
16th to endDay
35%41%37%10%
332
September1st to 15thDay
319%39%30%6%
315
16th to endDay
4323%39%24%4
315
October1st to 15thDay
4426%40%21%3
264
16th to endDay
418%29%38%9%
144
November1st to 15thDay
2117%34%37%6%
135
16th to endDay
8%222%28%29%8%
135
December1st to 15thDay
4317%38%30%5%
135
16th to endDay
10%314%32%30%8%
144
January1st to 15thNight
7%111%39%27%12%
780
16th to endNight
9%114%36%29%8%
788
February1st to 15thNight
7%213%37%31%7%
704
16th to endNight
8%115%44%23%6%
632
March1st to 15thNight
5%217%37%28%7%
720
16th to endNight
5%312%40%31%7%
768
April1st to 15thNight
4319%38%28%5%
719
16th to endNight
2322%39%25%6%
562
May1st to 15thNight
2313%40%31%7%
540
16th to endNight
2112%40%36%6%
563
June1st to 15thNight
2110%40%42%4
540
16th to endNight
1430%53%9%
540
July1st to 15thNight
3319%64%9%
510
16th to endNight
2113%65%15%
564
August1st to 15thNight
2215%63%15%
539
16th to endNight
4216%54%21%
699
September1st to 15thNight
25%26%51%14%
720
16th to endNight
317%33%41%12%
716
October1st to 15thNight
4111%36%38%6%
720
16th to endNight
28%33%38%15%
768
November1st to 15thNight
418%40%34%11%
760
16th to endNight
5%110%35%34%12%
780
December1st to 15thNight
6%111%39%32%7%
780
16th to endNight
10%113%36%30%8%
832
Page generated at 2018-01-21 10:19:21. Version ac04

Copyright 2018 A. Danko


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