Northfield
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Northfield clear sky chart from 2005-11-05 to 2017-03-19.

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
31%
15573
15%
45281
8%
15526
37%
15526
24%
30444

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
26%
900
12%
2506
5%
895
31%
895
19%
1834
January16th to endNight
18%
960
11%
2535
3%
960
24%
960
16%
1942
February1st to 15thNight
23%
879
13%
2288
4%
875
30%
875
22%
1662
February16th to endNight
27%
746
14%
2008
5%
746
33%
746
23%
1413
March1st to 15thNight
29%
581
14%
2021
10%
581
35%
581
21%
1299
March16th to endNight
27%
540
14%
1966
12%
540
33%
540
16%
1341
April1st to 15thNight
27%
494
15%
1647
10%
494
36%
494
21%
1078
April16th to endNight
22%
495
11%
1543
6%
495
30%
495
17%
1114
May1st to 15thNight
27%
495
14%
1378
7%
495
33%
495
23%
959
May16th to endNight
34%
515
12%
1370
4%
513
39%
513
30%
900
June1st to 15thNight
35%
495
10%
1320
3%
495
38%
495
29%
872
June16th to endNight
43%
495
11%
1320
4%
495
45%
495
41%
779
July1st to 15thNight
52%
465
15%
1240
7%
465
54%
465
44%
706
July16th to endNight
55%
522
16%
1329
10%
489
62%
489
46%
747
August1st to 15thNight
59%
494
22%
1475
19%
491
62%
491
37%
851
August16th to endNight
53%
525
21%
1649
19%
525
60%
525
37%
917
September1st to 15thNight
54%
495
24%
1650
23%
495
61%
495
34%
906
September16th to endNight
40%
536
19%
1815
12%
536
50%
536
30%
1045
October1st to 15thNight
34%
660
23%
1980
14%
660
42%
660
31%
1197
October16th to endNight
32%
704
16%
2120
9%
704
38%
704
22%
1416
November1st to 15thNight
26%
817
20%
2393
9%
817
36%
817
25%
1564
November16th to endNight
23%
900
14%
2520
7%
900
29%
900
19%
1841
December1st to 15thNight
18%
900
9%
2520
3%
900
24%
900
15%
1912
December16th to endNight
17%
960
10%
2688
4%
960
23%
960
12%
2149

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
13%8%36%5%3445%7%36%
45546
Night
12%8%36%5%24446%40%
45452
Cloud CoverDay
26%7%25%423446%31%
45557
Night
25%7%25%423345%35%
45456
Cloud CoverDay
13%8%36%5%3445%7%36%
45555
Night
12%8%36%5%24446%40%
45456
TransparencyDay
46%6%13%22%9%
45235
Night
44%5%13%23%11%1
45281
SeeingDay
16%8%29%28%14%3
5283
Night
16%8%32%30%11%1
15574

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
9%10%8%8%9%47%446%25%
1432
16th to endDay
9%15%5%11%8%36%5%6%6%21%
1686
February1st to 15thDay
9%12%6%10%8%445%5%6%26%
1575
16th to endDay
13%9%47%6%36%5%5%6%31%
1464
March1st to 15thDay
15%11%5%7%4235%5%7%31%
1939
16th to endDay
18%9%37%5%35%35%7%31%
1988
April1st to 15thDay
17%8%46%42436%6%36%
1971
16th to endDay
21%12%36%425%435%28%
2084
May1st to 15thDay
20%8%37%5%35%446%30%
2243
16th to endDay
15%5%245%3445%8%39%
2393
June1st to 15thDay
16%6%25%5%2445%9%37%
2310
16th to endDay
9%5%25%5%445%6%10%40%
2310
July1st to 15thDay
7%314425%46%10%49%
2310
16th to endDay
7%314435%5%7%9%46%
2432
August1st to 15thDay
8%4245%35%6%7%9%41%
2145
16th to endDay
10%424324447%48%
2201
September1st to 15thDay
11%5%14425%5%5%8%45%
1980
16th to endDay
14%6%33444446%42%
1801
October1st to 15thDay
15%6%2442335%5%45%
1650
16th to endDay
18%9%36%423347%37%
1752
November1st to 15thDay
11%9%46%5%24446%41%
1464
16th to endDay
13%11%36%425%447%34%
1440
December1st to 15thDay
15%11%6%8%9%43446%25%
1440
16th to endDay
19%16%6%10%6%3333421%
1536
January1st to 15thNight
10%9%6%7%6%45%5%46%32%
2506
16th to endNight
11%12%5%10%6%35%5%5%5%28%
2535
February1st to 15thNight
8%13%6%8%6%34435%36%
2285
16th to endNight
10%8%47%7%35%45%6%37%
2008
March1st to 15thNight
12%9%36%43435%6%40%
2009
16th to endNight
14%8%47%6%2445%6%34%
1966
April1st to 15thNight
15%9%35%424445%40%
1647
16th to endNight
22%8%35%5%24345%32%
1543
May1st to 15thNight
20%5%15%42435%6%38%
1378
16th to endNight
11%5%25%425%448%44%
1368
June1st to 15thNight
12%5%25%5%3445%8%43%
1320
16th to endNight
8%314423448%55%
1320
July1st to 15thNight
3312315%5%6%9%55%
1320
16th to endNight
5%21242446%9%56%
1427
August1st to 15thNight
5%4244245%5%8%51%
1485
16th to endNight
9%314322347%56%
1649
September1st to 15thNight
10%314413346%55%
1650
16th to endNight
12%5%2432335%6%51%
1815
October1st to 15thNight
16%5%13422345%50%
1980
16th to endNight
18%10%33423337%40%
2120
November1st to 15thNight
12%8%35%42344444%
2393
16th to endNight
13%11%47%7%24346%34%
2520
December1st to 15thNight
12%11%5%8%7%35%447%29%
2520
16th to endNight
18%14%5%9%6%44345%23%
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
23%7%5%7%8%36%445%22%
1432
16th to endDay
23%14%49%7%3445%5%17%
1686
February1st to 15thDay
23%10%48%7%23445%24%
1575
16th to endDay
26%8%37%434445%27%
1464
March1st to 15thDay
28%9%46%322446%27%
1950
16th to endDay
31%8%25%5%24336%25%
1988
April1st to 15thDay
31%7%25%32325%5%30%
1971
16th to endDay
36%11%3442333421%
2084
May1st to 15thDay
35%6%26%42444424%
2243
16th to endDay
32%5%14423346%32%
2393
June1st to 15thDay
33%5%14423446%29%
2310
16th to endDay
26%5%14433447%32%
2310
July1st to 15thDay
24%31332345%7%39%
2310
16th to endDay
24%21433445%7%37%
2432
August1st to 15thDay
16%4145%35%5%6%8%38%
2145
16th to endDay
17%424323446%46%
2201
September1st to 15thDay
18%5%1442345%7%42%
1980
16th to endDay
21%5%23434446%39%
1801
October1st to 15thDay
23%5%1442333442%
1650
16th to endDay
25%8%26%413336%34%
1752
November1st to 15thDay
23%7%25%31334437%
1464
16th to endDay
28%8%35%323335%31%
1440
December1st to 15thDay
29%9%47%7%32435%21%
1440
16th to endDay
31%14%410%5%2223318%
1536
January1st to 15thNight
23%7%36%6%3444429%
2506
16th to endNight
26%11%38%5%3444423%
2535
February1st to 15thNight
23%12%46%43223432%
2278
16th to endNight
23%7%36%6%34345%32%
2008
March1st to 15thNight
25%8%25%423235%36%
2021
16th to endNight
29%6%36%5%2235%430%
1966
April1st to 15thNight
30%7%2432233334%
1647
16th to endNight
37%7%2442334425%
1543
May1st to 15thNight
35%413322345%32%
1377
16th to endNight
29%5%14422346%35%
1368
June1st to 15thNight
28%424434435%34%
1320
16th to endNight
24%313412326%45%
1320
July1st to 15thNight
21%213213448%45%
1320
16th to endNight
22%2231336%7%46%
1427
August1st to 15thNight
14%413424448%47%
1485
16th to endNight
17%313212246%54%
1649
September1st to 15thNight
17%323322345%51%
1650
16th to endNight
18%5%23313345%49%
1815
October1st to 15thNight
23%41342233446%
1980
16th to endNight
25%9%23322235%37%
2120
November1st to 15thNight
24%8%2432233439%
2393
16th to endNight
26%9%36%5%22235%31%
2520
December1st to 15thNight
27%10%37%6%23335%24%
2520
16th to endNight
30%12%39%5%3233420%
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
10%10%8%8%9%47%45%6%25%
1432
16th to endDay
9%15%5%11%8%45%5%6%6%21%
1686
February1st to 15thDay
9%11%6%10%8%345%5%6%26%
1575
16th to endDay
14%9%47%6%36%5%46%31%
1464
March1st to 15thDay
15%11%5%7%42345%7%31%
1950
16th to endDay
18%9%36%6%35%347%31%
1986
April1st to 15thDay
17%8%46%43436%6%36%
1971
16th to endDay
21%12%45%435%435%28%
2084
May1st to 15thDay
20%8%36%5%35%5%5%6%29%
2243
16th to endDay
15%5%25%5%3445%8%39%
2393
June1st to 15thDay
16%6%25%42445%9%37%
2310
16th to endDay
9%5%245%445%6%10%40%
2310
July1st to 15thDay
7%314435%46%9%49%
2310
16th to endDay
7%3145%35%6%6%9%46%
2432
August1st to 15thDay
8%4245%35%6%7%8%41%
2145
16th to endDay
10%42432445%7%48%
2201
September1st to 15thDay
11%5%1442445%8%45%
1980
16th to endDay
14%6%3344445%6%42%
1801
October1st to 15thDay
14%7%2342435%5%45%
1650
16th to endDay
18%9%36%413336%37%
1752
November1st to 15thDay
11%9%46%424446%41%
1464
16th to endDay
13%11%36%425%447%34%
1440
December1st to 15thDay
15%11%6%7%9%44446%25%
1440
16th to endDay
19%16%6%9%7%3433421%
1536
January1st to 15thNight
10%9%6%7%6%45%5%46%31%
2506
16th to endNight
11%12%5%10%6%345%5%5%27%
2535
February1st to 15thNight
8%13%6%8%6%34335%36%
2278
16th to endNight
10%8%47%7%35%446%37%
2008
March1st to 15thNight
12%9%36%43435%6%40%
2021
16th to endNight
15%8%47%6%3345%6%34%
1966
April1st to 15thNight
15%9%35%424445%40%
1647
16th to endNight
22%8%35%434445%32%
1543
May1st to 15thNight
20%5%2442435%6%38%
1377
16th to endNight
11%5%25%5%24448%44%
1368
June1st to 15thNight
12%426%5%35%448%42%
1320
16th to endNight
7%314423448%55%
1320
July1st to 15thNight
33223145%6%10%55%
1320
16th to endNight
5%21242436%8%57%
1427
August1st to 15thNight
5%4244245%5%8%51%
1485
16th to endNight
9%314312347%57%
1649
September1st to 15thNight
10%314323346%55%
1650
16th to endNight
12%6%24323346%51%
1815
October1st to 15thNight
16%5%13422345%50%
1980
16th to endNight
18%10%33422346%40%
2120
November1st to 15thNight
12%8%35%43345%444%
2393
16th to endNight
13%11%47%7%24346%34%
2520
December1st to 15thNight
13%11%5%8%7%35%447%28%
2520
16th to endNight
18%14%5%9%6%44345%23%
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
58%5%10%16%8%
1433
16th to endDay
60%6%13%14%4
1686
February1st to 15thDay
56%6%13%16%6%
1576
16th to endDay
53%6%11%21%6%
1464
March1st to 15thDay
52%6%14%19%6%
1950
16th to endDay
53%7%13%21%3
1988
April1st to 15thDay
47%5%13%22%10%1
1971
16th to endDay
56%6%12%16%6%1
2084
May1st to 15thDay
54%6%12%20%5%
2243
16th to endDay
43%7%12%23%12%1
2397
June1st to 15thDay
43%7%14%26%8%
2310
16th to endDay
37%8%16%25%11%1
2310
July1st to 15thDay
30%8%15%30%12%2
2161
16th to endDay
31%9%17%24%14%1
2267
August1st to 15thDay
36%8%13%28%11%1
2131
16th to endDay
33%7%15%27%15%1
2201
September1st to 15thDay
36%6%13%29%13%
1980
16th to endDay
40%7%12%29%9%
1801
October1st to 15thDay
40%412%28%14%
1650
16th to endDay
48%414%23%7%
1752
November1st to 15thDay
43%5%13%21%15%1
1464
16th to endDay
49%6%18%16%8%
1440
December1st to 15thDay
60%6%14%12%5%
1440
16th to endDay
67%5%9%12%4
1536
January1st to 15thNight
51%6%13%20%7%
2506
16th to endNight
56%5%14%16%5%
2535
February1st to 15thNight
50%413%22%8%
2288
16th to endNight
47%411%24%10%
2008
March1st to 15thNight
45%415%23%9%1
2021
16th to endNight
49%6%12%24%5%
1966
April1st to 15thNight
45%49%23%14%1
1647
16th to endNight
53%5%9%16%12%2
1543
May1st to 15thNight
45%6%14%19%11%2
1378
16th to endNight
37%6%11%24%16%1
1370
June1st to 15thNight
39%6%12%29%11%
1320
16th to endNight
28%5%15%27%18%3
1320
July1st to 15thNight
23%7%14%33%18%2
1240
16th to endNight
23%6%16%31%17%4
1329
August1st to 15thNight
29%6%12%29%18%3
1475
16th to endNight
27%6%14%29%18%3
1649
September1st to 15thNight
30%5%11%29%22%
1650
16th to endNight
34%413%30%15%
1815
October1st to 15thNight
36%411%28%15%3
1980
16th to endNight
45%414%21%13%
2120
November1st to 15thNight
42%411%23%16%1
2393
16th to endNight
51%5%14%19%8%1
2520
December1st to 15thNight
55%7%13%18%5%
2520
16th to endNight
64%410%14%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
15%6%38%31%5%2
90
16th to endDay
17%14%34%28%41
96
February1st to 15thDay
15%21%34%24%4
90
16th to endDay
23%9%27%32%7%
81
March1st to 15thDay
23%8%43%21%3
90
16th to endDay
31%8%34%20%4
72
April1st to 15thDay
17%13%34%22%11%
210
16th to endDay
30%9%29%19%10%1
314
May1st to 15thDay
22%18%28%21%7%2
393
16th to endDay
18%8%28%24%15%4
437
June1st to 15thDay
18%7%26%32%11%3
420
16th to endDay
10%7%34%28%14%4
420
July1st to 15thDay
8%428%29%19%10%
400
16th to endDay
8%424%34%21%5%
445
August1st to 15thDay
9%224%36%22%4
418
16th to endDay
14%421%35%17%7%
369
September1st to 15thDay
12%6%24%30%20%5%
255
16th to endDay
20%6%29%22%15%6%
131
October1st to 15thDay
7%8%33%28%15%5%
90
16th to endDay
27%9%32%21%9%
96
November1st to 15thDay
45%37%35%15%1
90
16th to endDay
38%8%34%15%2
90
December1st to 15thDay
18%13%28%35%3
90
16th to endDay
35%12%38%11%2
96
January1st to 15thNight
14%11%36%27%8%1
900
16th to endNight
18%10%39%27%4
960
February1st to 15thNight
14%10%38%27%7%1
880
16th to endNight
14%9%39%26%9%
746
March1st to 15thNight
15%10%33%29%9%1
581
16th to endNight
16%10%33%26%11%1
540
April1st to 15thNight
19%9%34%28%7%
494
16th to endNight
27%7%29%26%8%
495
May1st to 15thNight
22%9%31%28%6%
495
16th to endNight
15%5%30%32%15%
515
June1st to 15thNight
15%429%39%11%
495
16th to endNight
9%326%46%13%
495
July1st to 15thNight
5%224%43%21%2
465
16th to endNight
5%21%49%21%1
522
August1st to 15thNight
5%221%43%24%3
494
16th to endNight
10%224%36%24%2
525
September1st to 15thNight
12%322%36%19%5%
495
16th to endNight
14%6%31%26%19%1
536
October1st to 15thNight
18%7%32%25%13%1
660
16th to endNight
24%9%26%29%10%
704
November1st to 15thNight
17%11%36%25%8%
817
16th to endNight
17%14%35%24%8%
900
December1st to 15thNight
19%8%40%25%5%
900
16th to endNight
24%9%32%27%5%
960
Page generated at 2017-03-20 07:18:35. Version ac04

Copyright 2017 A. Danko


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