TIMPA
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the TIMPA clear sky chart from 2005-11-05 to 2017-04-08.

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
78%
15111
37%
45405
33%
15073
82%
15073
56%
21140

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
75%
718
34%
2327
36%
716
78%
716
53%
1055
January16th to endNight
71%
768
36%
2496
36%
768
78%
768
44%
1251
February1st to 15thNight
75%
700
37%
2187
37%
700
81%
700
53%
1022
February16th to endNight
69%
632
38%
1850
37%
632
75%
632
51%
925
March1st to 15thNight
71%
720
40%
1980
33%
720
78%
720
60%
956
March16th to endNight
74%
768
40%
2112
30%
768
83%
768
64%
991
April1st to 15thNight
70%
672
37%
1882
27%
672
77%
672
59%
889
April16th to endNight
74%
495
44%
1616
39%
495
82%
495
73%
596
May1st to 15thNight
75%
494
43%
1484
33%
494
83%
494
74%
587
May16th to endNight
80%
513
40%
1540
34%
513
83%
513
73%
613
June1st to 15thNight
82%
495
37%
1485
31%
495
84%
495
72%
608
June16th to endNight
86%
495
31%
1485
27%
495
87%
495
66%
641
July1st to 15thNight
83%
465
23%
1395
20%
465
83%
465
43%
745
July16th to endNight
84%
522
22%
1467
19%
489
84%
489
37%
831
August1st to 15thNight
86%
494
30%
1476
28%
491
86%
491
50%
740
August16th to endNight
85%
572
30%
1729
29%
572
85%
572
43%
926
September1st to 15thNight
80%
660
33%
1815
28%
660
81%
660
47%
1005
September16th to endNight
82%
656
44%
1815
34%
656
86%
656
69%
813
October1st to 15thNight
83%
660
42%
1906
36%
660
86%
660
67%
836
October16th to endNight
87%
704
45%
2112
41%
704
90%
704
71%
869
November1st to 15thNight
84%
700
44%
2100
40%
700
88%
700
69%
879
November16th to endNight
76%
720
40%
2310
38%
720
81%
720
54%
1045
December1st to 15thNight
74%
720
39%
2340
41%
720
77%
720
51%
1067
December16th to endNight
69%
768
36%
2496
37%
768
74%
768
43%
1250

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
3212323346%67%
45851
Night
3212212336%69%
45601
TransparencyDay
18%3411%23%38%
45546
Night
16%25%13%24%37%
45407
SeeingDay
5%6%20%33%24%9%
4799
Night
4111%41%35%5%
15120

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
423214336%66%
1611
16th to endDay
5%313323336%63%
1728
February1st to 15thDay
5%31221213470%
1674
16th to endDay
7%312312245%65%
1624
March1st to 15thDay
322212345%69%
1980
16th to endDay
211213225%74%
2112
April1st to 15thDay
211212335%74%
1904
16th to endDay
11111112482%
2010
May1st to 15thDay
121122480%
2136
16th to endDay
111212284%
2221
June1st to 15thDay
2111112482%
2145
16th to endDay
21221223475%
2145
July1st to 15thDay
42136%46%6%7%10%45%
2145
16th to endDay
6%425%6%46%6%9%10%35%
2285
August1st to 15thDay
6%3246%36%5%8%7%45%
2145
16th to endDay
4215%5%46%6%6%7%50%
2117
September1st to 15thDay
5%313425%6%5%7%54%
1815
16th to endDay
321222335%73%
1815
October1st to 15thDay
112122225%76%
1724
16th to endDay
1111113480%
1760
November1st to 15thDay
11111236%78%
1759
16th to endDay
321122224472%
1648
December1st to 15thDay
6%212322245%66%
1620
16th to endDay
6%213223247%64%
1728
January1st to 15thNight
5%2221233470%
2327
16th to endNight
5%214324435%62%
2496
February1st to 15thNight
3212312235%68%
2176
16th to endNight
5%312223445%64%
1850
March1st to 15thNight
4111213335%71%
1980
16th to endNight
22121223475%
2112
April1st to 15thNight
312213335%71%
1882
16th to endNight
21111286%
1616
May1st to 15thNight
112335%80%
1484
16th to endNight
1111111384%
1540
June1st to 15thNight
212222381%
1485
16th to endNight
111211222478%
1485
July1st to 15thNight
23143345%8%11%51%
1485
16th to endNight
32145%46%7%9%15%41%
1575
August1st to 15thNight
3143235%6%10%58%
1485
16th to endNight
42124246%6%10%53%
1729
September1st to 15thNight
421442445%7%58%
1815
16th to endNight
21121213477%
1815
October1st to 15thNight
11111223378%
1906
16th to endNight
11111122481%
2112
November1st to 15thNight
111112235%77%
2100
16th to endNight
421212335%70%
2310
December1st to 15thNight
6%312212246%67%
2340
16th to endNight
6%313413245%62%
2496

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
19%2413%26%32%
1612
16th to endDay
22%2314%24%30%
1728
February1st to 15thDay
19%1312%27%35%
1674
16th to endDay
22%1313%30%28%
1624
March1st to 15thDay
16%235%29%41%
1980
16th to endDay
14%227%28%44%
2112
April1st to 15thDay
13%115%34%44%
1904
16th to endDay
9%115%22%59%
2010
May1st to 15thDay
9%116%20%60%
2136
16th to endDay
8%115%23%59%
2224
June1st to 15thDay
9%216%69%
2145
16th to endDay
12%22414%62%
2145
July1st to 15thDay
30%6%12%14%15%21%
2006
16th to endDay
38%8%15%21%12%3
2130
August1st to 15thDay
32%6%11%15%16%17%
2130
16th to endDay
29%7%10%18%18%15%
2117
September1st to 15thDay
25%6%7%19%17%23%
1815
16th to endDay
15%128%30%41%
1815
October1st to 15thDay
12%2410%25%44%
1724
16th to endDay
9%138%25%51%
1760
November1st to 15thDay
9%1110%33%42%
1759
16th to endDay
15%229%28%40%
1648
December1st to 15thDay
20%2415%31%25%
1620
16th to endDay
20%35%18%32%18%
1728
January1st to 15thNight
18%25%13%26%32%
2327
16th to endNight
24%3413%29%25%
2496
February1st to 15thNight
19%2315%24%34%
2187
16th to endNight
21%2313%31%28%
1850
March1st to 15thNight
16%229%25%43%
1980
16th to endNight
13%2210%29%41%
2112
April1st to 15thNight
16%128%32%38%
1882
16th to endNight
8%6%23%59%
1616
May1st to 15thNight
7%228%23%57%
1485
16th to endNight
8%115%21%61%
1541
June1st to 15thNight
9%12316%66%
1485
16th to endNight
12%12315%64%
1485
July1st to 15thNight
22%7%14%16%16%22%
1395
16th to endNight
26%8%21%24%14%4
1467
August1st to 15thNight
18%5%15%22%17%20%
1476
16th to endNight
24%6%11%22%20%15%
1729
September1st to 15thNight
23%5%8%22%19%20%
1815
16th to endNight
11%1310%31%41%
1815
October1st to 15thNight
11%2314%24%44%
1906
16th to endNight
9%1210%23%51%
2112
November1st to 15thNight
10%2210%32%41%
2100
16th to endNight
18%2210%24%41%
2310
December1st to 15thNight
19%2316%29%28%
2340
16th to endNight
25%25%17%28%19%
2496

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
13%320%38%21%3
90
16th to endDay
4413%36%31%10%
96
February1st to 15thDay
5%8%14%40%27%2
189
16th to endDay
8%11%31%28%15%4
238
March1st to 15thDay
5%11%27%27%18%9%
270
16th to endDay
311%31%25%18%10%
288
April1st to 15thDay
5%14%31%25%15%6%
239
16th to endDay
120%33%31%9%4
210
May1st to 15thDay
311%35%34%10%4
228
16th to endDay
26%28%37%21%3
266
June1st to 15thDay
6%225%41%16%8%
255
16th to endDay
314%44%23%13%
255
July1st to 15thDay
6%27%36%35%11%
245
16th to endDay
5%28%31%30%21%
271
August1st to 15thDay
8%6%29%39%15%
255
16th to endDay
425%30%36%20%
268
September1st to 15thDay
11%12%37%26%11%
255
16th to endDay
6%319%34%24%10%
255
October1st to 15thDay
15%25%31%23%12%
164
16th to endDay
26%22%53%15%
96
November1st to 15thDay
38%12%35%28%11%
90
16th to endDay
35%23%36%27%3
90
December1st to 15thDay
316%30%52%6%
90
16th to endDay
12%220%36%25%3
96
January1st to 15thNight
6%111%48%27%4
720
16th to endNight
8%113%45%26%4
768
February1st to 15thNight
5%211%46%28%5%
704
16th to endNight
6%217%51%19%2
632
March1st to 15thNight
4218%43%27%3
720
16th to endNight
2215%45%29%4
768
April1st to 15thNight
4418%50%21%1
672
16th to endNight
2317%52%21%2
495
May1st to 15thNight
319%49%25%1
495
16th to endNight
1213%49%30%1
515
June1st to 15thNight
1111%50%33%2
495
16th to endNight
27%37%50%2
495
July1st to 15thNight
3425%59%6%
465
16th to endNight
3319%60%13%
522
August1st to 15thNight
3217%63%13%
494
16th to endNight
3320%61%10%
572
September1st to 15thNight
5%1427%50%11%
660
16th to endNight
39%36%42%7%
656
October1st to 15thNight
1110%44%38%4
660
16th to endNight
16%42%41%7%
704
November1st to 15thNight
210%44%37%5%
700
16th to endNight
6%113%42%32%4
720
December1st to 15thNight
7%210%44%31%4
720
16th to endNight
8%211%49%23%4
768
Page generated at 2017-04-09 03:54:10. Version ac04

Copyright 2017 A. Danko


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