Howe Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Howe Observatory clear sky chart from 2005-11-05 to 2017-09-16.

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
24%
14893
17%
46813
7%
14861
36%
14861
18%
31018

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
11%
720
19%
2506
5%
716
29%
716
15%
1610
January16th to endNight
12%
768
18%
2688
3%
768
31%
768
12%
1761
February1st to 15thNight
10%
704
15%
2192
3%
701
26%
701
14%
1495
February16th to endNight
12%
631
21%
1893
5%
631
32%
631
15%
1268
March1st to 15thNight
14%
720
16%
2160
5%
720
27%
720
14%
1505
March16th to endNight
18%
768
22%
2016
6%
768
31%
768
19%
1382
April1st to 15thNight
16%
718
16%
1796
2%
718
24%
718
17%
1307
April16th to endNight
19%
618
17%
1698
3%
618
29%
618
20%
1167
May1st to 15thNight
18%
540
16%
1620
6%
540
28%
540
15%
1153
May16th to endNight
27%
383
11%
1505
7%
382
35%
382
15%
994
June1st to 15thNight
27%
360
12%
1440
7%
360
40%
360
14%
958
June16th to endNight
35%
360
11%
1440
11%
360
43%
360
20%
892
July1st to 15thNight
45%
340
12%
1360
13%
340
51%
340
21%
847
July16th to endNight
46%
376
13%
1418
14%
354
52%
354
21%
868
August1st to 15thNight
43%
478
16%
1549
10%
476
49%
476
25%
964
August16th to endNight
51%
759
20%
1905
10%
759
54%
759
33%
1240
September1st to 15thNight
35%
720
19%
1842
8%
720
41%
720
30%
1226
September16th to endNight
43%
658
25%
1818
16%
658
50%
658
33%
1123
October1st to 15thNight
31%
660
22%
1862
10%
660
43%
660
23%
1241
October16th to endNight
21%
704
15%
2271
5%
704
34%
704
18%
1513
November1st to 15thNight
25%
700
21%
2277
7%
700
42%
700
20%
1466
November16th to endNight
20%
720
18%
2349
7%
720
34%
720
16%
1552
December1st to 15thNight
18%
720
16%
2520
5%
720
31%
720
14%
1669
December16th to endNight
13%
768
18%
2688
4%
768
30%
768
12%
1817

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
16%6%25%5%3445%6%38%
47937
Night
16%6%25%424446%39%
46983
Cloud CoverDay
16%6%25%43445%6%38%
47947
Night
16%7%25%424446%39%
46988
TransparencyDay
44%6%12%21%13%2
47625
Night
44%6%12%21%14%1
46813
SeeingDay
21%15%30%20%8%2
5837
Night
21%16%34%21%6%
14893

By Month

Percentage Cloud Cover NE (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
15%7%246%35%5%6%6%37%
1432
16th to endDay
13%7%35%5%35%5%5%6%40%
1536
February1st to 15thDay
15%6%36%6%46%5%5%7%31%
1669
16th to endDay
15%8%45%5%24445%39%
1580
March1st to 15thDay
19%9%25%434447%35%
1790
16th to endDay
17%7%245%24335%41%
2205
April1st to 15thDay
19%8%35%5%34346%37%
2152
16th to endDay
17%5%15%424448%40%
2262
May1st to 15thDay
24%8%26%424435%31%
2332
16th to endDay
18%5%345%3435%7%38%
2618
June1st to 15thDay
23%7%25%43335%8%32%
2520
16th to endDay
15%5%25%5%45%6%6%8%33%
2520
July1st to 15thDay
13%6%35%5%35%5%6%8%36%
2520
16th to endDay
13%5%25%426%5%6%9%37%
2654
August1st to 15thDay
13%5%25%6%45%5%6%7%37%
2388
16th to endDay
11%5%25%5%3445%8%43%
2294
September1st to 15thDay
13%5%246%25%35%6%44%
2118
16th to endDay
15%5%2331335%5%50%
1815
October1st to 15thDay
18%6%25%424346%40%
1766
16th to endDay
17%6%245%23445%40%
1601
November1st to 15thDay
17%8%24323335%42%
1581
16th to endDay
18%5%34333336%43%
1608
December1st to 15thDay
19%5%25%5%2425%6%38%
1440
16th to endDay
20%9%334345%5%5%32%
1536
January1st to 15thNight
16%7%25%5%24347%39%
2506
16th to endNight
14%9%35%5%3445%5%38%
2688
February1st to 15thNight
14%8%35%5%35%45%6%36%
2191
16th to endNight
16%8%25%5%34445%38%
1893
March1st to 15thNight
18%8%24435%45%6%35%
2147
16th to endNight
15%7%34434346%41%
2016
April1st to 15thNight
19%6%26%6%25%5%35%35%
1796
16th to endNight
22%6%25%423335%40%
1698
May1st to 15thNight
20%8%36%424446%34%
1620
16th to endNight
17%5%26%6%2436%8%34%
1503
June1st to 15thNight
22%6%35%5%2445%6%34%
1440
16th to endNight
15%5%244245%5%8%41%
1440
July1st to 15thNight
13%5%245%25%5%6%8%39%
1440
16th to endNight
11%426%5%26%6%5%8%40%
1514
August1st to 15thNight
10%325%6%345%48%44%
1559
16th to endNight
11%3245%25%45%8%45%
1905
September1st to 15thNight
13%6%25%32345%6%45%
1842
16th to endNight
14%5%23413346%50%
1818
October1st to 15thNight
17%7%25%423345%43%
1862
16th to endNight
18%7%25%43345%5%38%
2271
November1st to 15thNight
16%5%26%423345%44%
2277
16th to endNight
17%6%35%435%446%39%
2349
December1st to 15thNight
20%7%25%424345%37%
2520
16th to endNight
19%8%345%3445%6%34%
2688

Percentage Cloud Cover SE (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
14%7%245%36%45%7%37%
1432
16th to endDay
13%6%25%5%25%5%5%6%40%
1536
February1st to 15thDay
15%6%36%6%35%6%5%7%32%
1669
16th to endDay
15%9%36%5%24345%39%
1580
March1st to 15thDay
19%9%25%434446%34%
1800
16th to endDay
17%6%25%435%246%40%
2205
April1st to 15thDay
18%8%35%5%34346%37%
2152
16th to endDay
17%5%25%425%447%40%
2262
May1st to 15thDay
24%8%36%5%35%345%31%
2332
16th to endDay
18%6%245%24347%38%
2618
June1st to 15thDay
23%6%35%33345%8%32%
2520
16th to endDay
15%5%25%5%45%6%6%8%33%
2520
July1st to 15thDay
13%6%25%6%35%5%6%9%35%
2520
16th to endDay
13%6%35%435%5%7%8%37%
2654
August1st to 15thDay
13%5%25%5%45%6%6%7%36%
2388
16th to endDay
11%5%26%4345%48%42%
2294
September1st to 15thDay
13%6%245%34445%44%
2118
16th to endDay
15%6%13314346%50%
1815
October1st to 15thDay
19%6%24324346%41%
1766
16th to endDay
15%6%35%5%2345%5%41%
1601
November1st to 15thDay
17%8%24424345%42%
1581
16th to endDay
17%6%34433345%43%
1608
December1st to 15thDay
20%5%25%5%24346%38%
1440
16th to endDay
20%9%24425%5%5%5%33%
1536
January1st to 15thNight
17%7%35%433346%39%
2506
16th to endNight
14%9%35%5%24446%39%
2688
February1st to 15thNight
14%8%35%436%45%6%37%
2184
16th to endNight
16%8%345%335%45%39%
1893
March1st to 15thNight
18%8%34435%45%6%35%
2160
16th to endNight
14%7%36%5%24346%42%
2015
April1st to 15thNight
18%7%25%6%35%5%45%34%
1796
16th to endNight
21%7%245%13335%40%
1698
May1st to 15thNight
19%8%36%4245%45%35%
1620
16th to endNight
18%5%36%5%2436%8%35%
1503
June1st to 15thNight
21%6%35%425%45%6%34%
1440
16th to endNight
15%5%2432445%8%41%
1440
July1st to 15thNight
14%5%25%5%245%7%8%39%
1440
16th to endNight
11%435%5%35%6%5%8%40%
1514
August1st to 15thNight
10%316%5%35%5%5%8%44%
1559
16th to endNight
11%42443445%8%45%
1905
September1st to 15thNight
13%6%25%424445%45%
1842
16th to endNight
14%5%2331335%5%51%
1818
October1st to 15thNight
17%6%2443343444%
1862
16th to endNight
18%6%25%43445%5%38%
2271
November1st to 15thNight
16%6%25%42334444%
2277
16th to endNight
17%6%25%425%445%39%
2349
December1st to 15thNight
19%8%34424445%37%
2520
16th to endNight
19%8%34434447%35%
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
45%5%12%24%9%2
1433
16th to endDay
42%6%14%23%12%1
1536
February1st to 15thDay
49%7%14%17%11%
1672
16th to endDay
47%410%21%13%2
1580
March1st to 15thDay
49%412%20%10%2
1800
16th to endDay
45%411%19%15%4
2205
April1st to 15thDay
48%310%20%14%2
2152
16th to endDay
43%5%9%20%17%3
2262
May1st to 15thDay
54%47%18%12%1
2332
16th to endDay
45%6%13%20%11%2
2622
June1st to 15thDay
50%7%12%20%8%
2520
16th to endDay
45%9%13%19%11%
2520
July1st to 15thDay
43%8%11%21%12%1
2371
16th to endDay
40%8%16%20%12%2
2487
August1st to 15thDay
43%8%14%21%11%1
2374
16th to endDay
38%6%10%26%15%1
2294
September1st to 15thDay
40%6%11%21%18%2
2118
16th to endDay
35%48%24%25%2
1815
October1st to 15thDay
43%6%10%23%12%3
1766
16th to endDay
43%6%13%21%13%2
1601
November1st to 15thDay
44%5%13%21%13%1
1581
16th to endDay
43%412%23%15%1
1608
December1st to 15thDay
45%5%15%18%13%
1440
16th to endDay
50%5%15%17%10%
1536
January1st to 15thNight
45%414%21%12%1
2506
16th to endNight
45%6%11%20%13%2
2688
February1st to 15thNight
47%6%13%20%10%1
2192
16th to endNight
45%5%11%20%14%2
1893
March1st to 15thNight
47%6%11%19%12%2
2160
16th to endNight
43%5%10%18%16%5%
2016
April1st to 15thNight
49%5%9%17%15%1
1796
16th to endNight
47%48%19%16%4
1698
May1st to 15thNight
49%7%8%17%13%2
1620
16th to endNight
46%7%16%18%9%1
1505
June1st to 15thNight
49%6%13%20%9%
1440
16th to endNight
39%9%13%22%14%
1440
July1st to 15thNight
39%9%13%24%12%
1360
16th to endNight
39%7%15%23%11%1
1418
August1st to 15thNight
36%9%14%22%14%1
1549
16th to endNight
35%7%12%27%16%
1905
September1st to 15thNight
39%6%12%23%18%
1842
16th to endNight
35%47%24%26%2
1818
October1st to 15thNight
43%5%11%21%15%3
1862
16th to endNight
45%5%14%21%11%
2271
November1st to 15thNight
42%6%11%19%17%3
2277
16th to endNight
45%5%14%19%13%1
2349
December1st to 15thNight
47%6%14%20%10%
2520
16th to endNight
48%5%12%21%11%
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
18%35%28%13%5%
60
16th to endDay
28%21%34%15%
64
February1st to 15thDay
25%26%34%11%2
197
16th to endDay
22%27%31%15%2
239
March1st to 15thDay
31%21%30%12%3
270
16th to endDay
23%26%32%10%6%1
288
April1st to 15thDay
27%17%34%12%7%
270
16th to endDay
24%15%33%18%5%3
270
May1st to 15thDay
35%17%25%13%7%1
288
16th to endDay
22%11%35%21%8%1
331
June1st to 15thDay
23%14%29%22%9%
315
16th to endDay
15%14%37%21%8%1
315
July1st to 15thDay
20%10%30%25%11%1
305
16th to endDay
13%8%29%31%13%3
326
August1st to 15thDay
15%7%28%32%12%4
313
16th to endDay
12%7%29%24%18%7%
332
September1st to 15thDay
17%10%32%20%13%6%
315
16th to endDay
17%10%26%20%12%12%
254
October1st to 15thDay
21%11%25%24%11%5%
255
16th to endDay
17%22%32%22%4
243
November1st to 15thDay
24%12%32%18%8%2
235
16th to endDay
23%21%28%17%7%2
228
December1st to 15thDay
23%26%35%10%5%
60
16th to endDay
39%26%26%6%1
64
January1st to 15thNight
23%22%37%13%1
720
16th to endNight
24%22%35%14%1
768
February1st to 15thNight
20%24%40%13%1
704
16th to endNight
25%22%35%14%1
631
March1st to 15thNight
25%23%34%15%1
720
16th to endNight
22%22%32%18%3
768
April1st to 15thNight
22%20%37%15%3
718
16th to endNight
24%18%33%18%4
618
May1st to 15thNight
25%16%35%18%3
540
16th to endNight
18%10%38%26%6%
383
June1st to 15thNight
23%8%34%26%6%
360
16th to endNight
16%440%32%6%
360
July1st to 15thNight
15%430%41%9%
340
16th to endNight
11%5%31%38%13%
376
August1st to 15thNight
11%333%39%11%
478
16th to endNight
13%325%38%16%1
759
September1st to 15thNight
17%6%35%29%10%
720
16th to endNight
17%6%28%27%16%3
658
October1st to 15thNight
22%12%31%22%9%1
660
16th to endNight
24%17%32%20%4
704
November1st to 15thNight
19%19%32%19%7%1
700
16th to endNight
21%19%33%16%6%
720
December1st to 15thNight
26%18%34%16%4
720
16th to endNight
26%23%35%13%1
768
Page generated at 2017-09-16 17:06:58. Version ac04

Copyright 2017 A. Danko


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