Hammond
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Hammond 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
35%
14221
13%
45464
9%
14189
40%
14189
17%
32692

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
21%
720
6%
2506
5%
716
24%
716
8%
2026
January16th to endNight
26%
768
10%
2661
7%
768
32%
768
12%
1998
February1st to 15thNight
23%
704
10%
2287
6%
701
28%
701
11%
1782
February16th to endNight
29%
631
14%
1934
8%
631
37%
631
15%
1461
March1st to 15thNight
26%
720
13%
2121
9%
720
32%
720
15%
1600
March16th to endNight
36%
768
20%
2019
11%
768
43%
768
24%
1411
April1st to 15thNight
30%
690
16%
1726
7%
690
33%
690
21%
1288
April16th to endNight
34%
594
17%
1584
8%
594
39%
594
25%
1104
May1st to 15thNight
37%
330
18%
1320
16%
330
46%
330
17%
859
May16th to endNight
42%
343
13%
1369
13%
342
51%
342
19%
872
June1st to 15thNight
40%
330
10%
1320
10%
330
48%
330
14%
927
June16th to endNight
47%
330
9%
1320
13%
330
51%
330
20%
825
July1st to 15thNight
60%
310
14%
1240
23%
310
64%
310
27%
697
July16th to endNight
58%
348
12%
1306
15%
326
60%
326
24%
766
August1st to 15thNight
55%
381
14%
1362
14%
379
59%
379
24%
844
August16th to endNight
57%
665
17%
1715
10%
665
60%
665
35%
1087
September1st to 15thNight
52%
660
14%
1650
8%
660
53%
660
28%
1148
September16th to endNight
50%
657
21%
1787
14%
657
54%
657
31%
1156
October1st to 15thNight
37%
660
17%
1980
12%
660
45%
660
21%
1383
October16th to endNight
30%
704
11%
2216
8%
704
35%
704
14%
1686
November1st to 15thNight
33%
700
17%
2313
13%
700
40%
700
17%
1650
November16th to endNight
24%
720
10%
2520
7%
720
29%
720
11%
1925
December1st to 15thNight
21%
720
7%
2520
4%
720
25%
720
9%
2028
December16th to endNight
18%
768
9%
2688
5%
768
24%
768
8%
2169

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%36%5%3445%6%32%
45804
Night
18%9%36%5%24445%32%
45633
Cloud CoverDay
18%8%36%5%3445%6%32%
45813
Night
18%9%36%5%34445%32%
45639
TransparencyDay
51%6%12%18%9%1
45491
Night
52%6%11%18%9%1
45464
SeeingDay
21%6%24%26%15%5%
4862
Night
22%6%27%30%11%
14221

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
23%14%6%8%6%33335%20%
1432
16th to endDay
14%16%5%8%7%34445%24%
1560
February1st to 15thDay
14%14%5%10%8%35%345%24%
1575
16th to endDay
20%12%5%8%6%35%345%25%
1539
March1st to 15thDay
18%10%49%6%35%34427%
1828
16th to endDay
17%7%35%424346%39%
2205
April1st to 15thDay
23%10%35%5%23335%33%
2062
16th to endDay
20%7%26%5%24345%35%
2056
May1st to 15thDay
19%6%25%6%34446%34%
2301
16th to endDay
18%6%35%5%3445%6%35%
2394
June1st to 15thDay
23%6%35%5%45%45%7%29%
2310
16th to endDay
18%5%25%435%6%6%8%31%
2310
July1st to 15thDay
13%5%245%35%47%9%37%
2310
16th to endDay
11%5%25%5%36%6%7%9%36%
2458
August1st to 15thDay
12%6%25%6%45%45%7%38%
2255
16th to endDay
10%425%435%46%9%43%
2124
September1st to 15thDay
17%42442445%7%41%
1980
16th to endDay
16%6%23324347%46%
1841
October1st to 15thDay
21%7%35%4235%46%34%
1650
16th to endDay
27%9%37%7%3334425%
1656
November1st to 15thDay
16%7%45%6%345%47%32%
1542
16th to endDay
22%13%48%5%2334427%
1440
December1st to 15thDay
24%14%5%7%5%45%5%45%19%
1440
16th to endDay
24%15%6%8%6%3333420%
1536
January1st to 15thNight
20%15%6%10%6%35%33420%
2506
16th to endNight
15%15%5%7%6%35%445%26%
2661
February1st to 15thNight
13%12%7%11%8%46%44422%
2285
16th to endNight
17%11%47%6%35%345%28%
1934
March1st to 15thNight
19%11%47%7%2434429%
2108
16th to endNight
16%8%36%5%2433441%
2019
April1st to 15thNight
26%8%34424345%34%
1726
16th to endNight
19%7%26%423336%39%
1584
May1st to 15thNight
21%6%34324445%38%
1320
16th to endNight
18%6%244245%5%6%39%
1367
June1st to 15thNight
21%7%35%5%35%36%6%31%
1320
16th to endNight
17%425%4245%6%8%38%
1320
July1st to 15thNight
10%424435%46%8%46%
1320
16th to endNight
9%4245%25%6%5%9%43%
1402
August1st to 15thNight
10%6%25%5%2446%10%40%
1372
16th to endNight
10%42442445%7%48%
1715
September1st to 15thNight
14%5%26%6%25%447%41%
1650
16th to endNight
17%424423335%49%
1787
October1st to 15thNight
19%8%25%434446%36%
1980
16th to endNight
25%8%27%6%24445%28%
2216
November1st to 15thNight
21%8%26%6%23345%33%
2313
16th to endNight
22%11%48%5%34445%25%
2520
December1st to 15thNight
23%14%5%6%5%35%44421%
2520
16th to endNight
25%15%5%7%6%2444420%
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
23%14%6%9%5%2434420%
1432
16th to endDay
13%16%5%9%6%45%446%24%
1560
February1st to 15thDay
14%13%6%10%7%34445%24%
1575
16th to endDay
19%11%5%8%6%35%445%25%
1539
March1st to 15thDay
18%10%5%9%7%35%445%26%
1838
16th to endDay
17%7%35%5%24335%39%
2204
April1st to 15thDay
23%10%36%423335%33%
2062
16th to endDay
20%7%36%5%24345%36%
2056
May1st to 15thDay
19%7%26%6%3445%5%35%
2301
16th to endDay
18%7%345%3445%7%35%
2394
June1st to 15thDay
22%5%35%6%3445%7%29%
2310
16th to endDay
18%5%25%435%6%6%8%31%
2310
July1st to 15thDay
13%5%245%35%5%7%9%38%
2310
16th to endDay
10%5%26%6%45%6%8%8%35%
2458
August1st to 15thDay
12%6%36%5%36%46%8%37%
2255
16th to endDay
9%425%435%46%9%44%
2124
September1st to 15thDay
17%42442445%7%41%
1980
16th to endDay
16%5%33323347%46%
1841
October1st to 15thDay
20%8%35%424447%34%
1650
16th to endDay
26%9%47%6%4433425%
1656
November1st to 15thDay
15%7%36%6%445%5%7%32%
1542
16th to endDay
22%12%47%6%23345%27%
1440
December1st to 15thDay
24%13%47%6%35%5%45%18%
1440
16th to endDay
24%15%5%8%6%2433420%
1536
January1st to 15thNight
20%15%6%10%6%35%33420%
2506
16th to endNight
15%15%5%8%6%35%345%26%
2661
February1st to 15thNight
13%12%6%12%7%36%5%4422%
2278
16th to endNight
17%12%5%7%5%35%45%428%
1934
March1st to 15thNight
20%10%5%7%6%2433429%
2121
16th to endNight
15%9%36%5%2433442%
2019
April1st to 15thNight
26%8%24423345%34%
1726
16th to endNight
18%8%26%5%23236%39%
1584
May1st to 15thNight
21%6%15%4245%5%5%38%
1320
16th to endNight
17%7%244335%5%5%39%
1367
June1st to 15thNight
21%7%35%425%45%7%30%
1320
16th to endNight
16%5%244245%6%9%37%
1320
July1st to 15thNight
9%4234345%5%9%45%
1320
16th to endNight
8%4346%345%6%8%44%
1402
August1st to 15thNight
10%6%25%5%245%6%10%40%
1372
16th to endNight
10%42442446%6%48%
1715
September1st to 15thNight
14%5%25%6%34446%40%
1650
16th to endNight
17%414423345%48%
1787
October1st to 15thNight
19%8%35%434446%36%
1980
16th to endNight
24%9%26%6%33446%27%
2216
November1st to 15thNight
20%9%27%5%24346%33%
2313
16th to endNight
21%11%48%5%3444426%
2520
December1st to 15thNight
22%15%5%7%5%3444421%
2520
16th to endNight
25%14%5%7%6%2443420%
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
67%48%13%5%
1433
16th to endDay
60%5%11%13%7%
1560
February1st to 15thDay
61%5%11%17%3
1577
16th to endDay
60%410%13%9%1
1539
March1st to 15thDay
59%5%11%13%7%1
1838
16th to endDay
46%5%9%18%15%5%
2205
April1st to 15thDay
54%37%19%12%2
2062
16th to endDay
50%37%18%14%4
2056
May1st to 15thDay
50%5%7%19%14%2
2301
16th to endDay
47%7%12%19%11%1
2398
June1st to 15thDay
53%6%11%18%9%
2310
16th to endDay
47%8%14%18%10%
2310
July1st to 15thDay
39%7%16%24%11%
2161
16th to endDay
41%11%16%20%9%
2291
August1st to 15thDay
43%9%15%21%9%
2241
16th to endDay
35%9%18%25%10%
2124
September1st to 15thDay
40%7%14%26%11%
1980
16th to endDay
39%6%12%31%9%
1841
October1st to 15thDay
50%5%13%20%10%
1650
16th to endDay
62%5%12%13%5%
1656
November1st to 15thDay
49%7%16%17%8%
1542
16th to endDay
60%6%12%15%5%
1440
December1st to 15thDay
66%8%12%10%2
1440
16th to endDay
68%5%9%11%5%
1536
January1st to 15thNight
68%5%10%10%4
2506
16th to endNight
59%5%11%15%6%
2661
February1st to 15thNight
63%5%10%16%4
2287
16th to endNight
58%5%8%18%9%
1934
March1st to 15thNight
57%5%10%17%8%1
2121
16th to endNight
47%49%19%15%4
2019
April1st to 15thNight
52%5%7%18%14%1
1726
16th to endNight
47%48%18%17%3
1584
May1st to 15thNight
46%6%7%18%15%5%
1320
16th to endNight
44%7%11%20%14%2
1369
June1st to 15thNight
51%7%11%18%9%
1320
16th to endNight
41%8%14%19%15%
1320
July1st to 15thNight
32%8%15%29%14%
1240
16th to endNight
35%8%16%23%15%
1306
August1st to 15thNight
37%8%19%22%11%
1362
16th to endNight
32%8%17%30%11%
1715
September1st to 15thNight
43%6%12%25%11%
1650
16th to endNight
38%6%12%32%10%
1787
October1st to 15thNight
48%5%11%23%10%
1980
16th to endNight
57%6%12%16%6%
2216
November1st to 15thNight
52%5%13%17%9%1
2313
16th to endNight
60%6%12%15%4
2520
December1st to 15thNight
65%6%12%12%2
2520
16th to endNight
67%5%9%11%5%
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
30%11%21%26%6%3
60
16th to endDay
35%127%29%41
68
February1st to 15thDay
31%8%43%15%1
90
16th to endDay
34%6%29%25%5%
198
March1st to 15thDay
24%11%29%26%8%
270
16th to endDay
22%9%25%27%10%4
288
April1st to 15thDay
29%11%27%19%10%1
240
16th to endDay
18%8%24%25%18%5%
210
May1st to 15thDay
24%428%24%10%7%
228
16th to endDay
17%9%30%22%15%3
267
June1st to 15thDay
23%7%26%25%12%4
255
16th to endDay
17%420%34%20%2
255
July1st to 15thDay
13%220%34%20%8%
245
16th to endDay
12%220%34%22%7%
270
August1st to 15thDay
16%315%33%24%7%
253
16th to endDay
12%217%33%20%14%
268
September1st to 15thDay
17%419%18%23%17%
255
16th to endDay
20%5%21%21%18%12%
254
October1st to 15thDay
22%7%25%23%18%2
255
16th to endDay
31%8%24%25%10%
253
November1st to 15thDay
20%8%25%28%16%1
196
16th to endDay
28%13%20%26%11%
60
December1st to 15thDay
23%6%38%23%8%
60
16th to endDay
42%10%34%12%
64
January1st to 15thNight
26%9%30%28%5%
720
16th to endNight
22%8%31%29%7%
768
February1st to 15thNight
19%7%38%28%6%
704
16th to endNight
25%6%33%28%6%
631
March1st to 15thNight
26%9%30%28%5%
720
16th to endNight
19%7%30%31%10%
768
April1st to 15thNight
28%7%29%30%4
690
16th to endNight
23%9%27%30%8%1
594
May1st to 15thNight
23%428%30%10%2
330
16th to endNight
18%6%26%32%14%1
343
June1st to 15thNight
21%326%38%9%
330
16th to endNight
16%226%36%16%1
330
July1st to 15thNight
8%223%44%20%
310
16th to endNight
10%118%45%21%1
348
August1st to 15thNight
14%317%38%23%3
381
16th to endNight
12%319%38%24%1
665
September1st to 15thNight
17%321%36%19%1
660
16th to endNight
19%421%29%22%2
657
October1st to 15thNight
22%5%30%27%13%
660
16th to endNight
28%7%26%27%8%
704
November1st to 15thNight
25%7%27%27%12%
700
16th to endNight
26%11%28%22%10%
720
December1st to 15thNight
32%9%30%22%5%
720
16th to endNight
32%9%29%22%41
768
Page generated at 2017-04-09 06:54:12. Version ac04

Copyright 2017 A. Danko


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