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 2017-12-04.

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
36%
16445
17%
47874
9%
16398
43%
16398
24%
32019

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
28%
900
12%
2506
5%
895
33%
895
19%
1834
January16th to endNight
21%
960
12%
2535
4%
960
28%
960
16%
1942
February1st to 15thNight
27%
879
14%
2288
4%
875
34%
875
22%
1662
February16th to endNight
28%
746
16%
2008
6%
746
36%
746
23%
1413
March1st to 15thNight
33%
581
15%
2021
11%
581
39%
581
21%
1299
March16th to endNight
32%
576
15%
2097
12%
576
39%
576
16%
1435
April1st to 15thNight
32%
539
17%
1797
11%
539
42%
539
21%
1188
April16th to endNight
29%
540
16%
1683
10%
540
38%
540
18%
1211
May1st to 15thNight
34%
540
15%
1503
8%
540
40%
540
24%
1033
May16th to endNight
42%
563
16%
1498
6%
561
49%
561
29%
988
June1st to 15thNight
47%
540
13%
1440
5%
540
49%
540
31%
934
June16th to endNight
54%
540
16%
1440
7%
540
57%
540
41%
853
July1st to 15thNight
62%
510
16%
1360
7%
510
65%
510
45%
765
July16th to endNight
67%
564
21%
1444
13%
531
70%
531
46%
808
August1st to 15thNight
64%
539
22%
1610
20%
536
67%
536
36%
929
August16th to endNight
58%
573
22%
1800
21%
573
65%
573
36%
1012
September1st to 15thNight
59%
540
24%
1800
24%
540
66%
540
36%
969
September16th to endNight
43%
585
22%
1980
14%
585
53%
585
30%
1139
October1st to 15thNight
36%
720
23%
2160
14%
720
44%
720
30%
1317
October16th to endNight
33%
768
19%
2313
10%
768
40%
768
22%
1536
November1st to 15thNight
30%
887
19%
2598
9%
887
40%
887
24%
1712
November16th to endNight
26%
975
17%
2730
8%
975
34%
975
20%
1945
December1st to 15thNight
23%
920
10%
2575
3%
920
29%
920
16%
1946
December16th to endNight
20%
960
12%
2688
4%
960
28%
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%
48628
Night
12%8%36%5%24446%41%
48045
Cloud CoverDay
25%7%25%423446%32%
48639
Night
24%7%25%423345%36%
48049
Cloud CoverDay
13%8%36%5%3445%7%36%
48637
Night
12%8%36%5%24446%41%
48049
TransparencyDay
46%6%13%22%9%
48317
Night
43%5%13%23%12%1
47874
SeeingDay
16%7%29%28%13%3
6352
Night
16%8%32%30%11%1
16446

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%10%37%6%35%347%30%
2127
April1st to 15thDay
17%8%46%42436%6%35%
2151
16th to endDay
22%12%36%425%435%28%
2274
May1st to 15thDay
19%7%36%435%446%32%
2448
16th to endDay
16%5%25%5%3445%8%37%
2617
June1st to 15thDay
15%5%25%42445%9%39%
2520
16th to endDay
9%5%25%5%445%6%10%39%
2520
July1st to 15thDay
6%314425%46%10%50%
2520
16th to endDay
7%314435%6%7%9%46%
2625
August1st to 15thDay
8%4245%35%6%7%8%41%
2340
16th to endDay
11%5%24324447%47%
2402
September1st to 15thDay
10%5%1442445%8%46%
2160
16th to endDay
15%6%33434447%42%
1965
October1st to 15thDay
16%7%2442335%5%44%
1800
16th to endDay
17%10%36%413346%37%
1911
November1st to 15thDay
11%10%46%5%24446%40%
1589
16th to endDay
13%10%36%425%448%35%
1560
December1st to 15thDay
15%11%5%8%9%44446%25%
1467
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
15%8%47%6%2445%6%34%
2097
April1st to 15thNight
16%9%35%424445%38%
1797
16th to endNight
22%8%35%5%24345%32%
1683
May1st to 15thNight
19%5%15%42435%6%40%
1503
16th to endNight
12%5%25%425%448%43%
1496
June1st to 15thNight
11%5%25%5%2445%8%45%
1440
16th to endNight
7%3145%23448%55%
1440
July1st to 15thNight
33123145%6%10%56%
1440
16th to endNight
5%21242346%8%57%
1542
August1st to 15thNight
44244245%5%8%51%
1620
16th to endNight
9%314422347%56%
1800
September1st to 15thNight
10%314313346%57%
1800
16th to endNight
12%5%2432335%6%51%
1980
October1st to 15thNight
16%5%13422335%50%
2160
16th to endNight
17%10%33413337%40%
2313
November1st to 15thNight
13%8%35%42344443%
2598
16th to endNight
13%10%47%6%24336%37%
2730
December1st to 15thNight
12%11%5%8%7%35%447%29%
2575
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
30%8%25%5%33336%25%
2127
April1st to 15thDay
31%7%25%323245%29%
2151
16th to endDay
35%11%3442333422%
2274
May1st to 15thDay
33%6%25%424445%27%
2448
16th to endDay
31%5%14423346%31%
2617
June1st to 15thDay
30%5%14423446%32%
2520
16th to endDay
25%415%434447%32%
2520
July1st to 15thDay
22%31332345%8%41%
2520
16th to endDay
23%31442445%7%38%
2625
August1st to 15thDay
16%4145%35%5%7%8%38%
2340
16th to endDay
18%424323446%45%
2402
September1st to 15thDay
17%41342345%7%44%
2160
16th to endDay
21%5%23424446%40%
1965
October1st to 15thDay
23%6%14423335%41%
1800
16th to endDay
24%8%25%413336%35%
1911
November1st to 15thDay
22%9%35%42334436%
1589
16th to endDay
27%8%35%423336%33%
1560
December1st to 15thDay
29%10%47%7%32435%20%
1467
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%7%36%5%2235%5%30%
2097
April1st to 15thNight
29%7%25%42333433%
1797
16th to endNight
35%8%245%2334425%
1683
May1st to 15thNight
33%413322245%34%
1502
16th to endNight
27%5%14423346%35%
1496
June1st to 15thNight
26%324423445%37%
1440
16th to endNight
23%313422336%46%
1440
July1st to 15thNight
20%213213448%47%
1440
16th to endNight
21%2231335%7%48%
1542
August1st to 15thNight
13%41442445%8%47%
1620
16th to endNight
16%313322246%53%
1800
September1st to 15thNight
16%313322345%53%
1800
16th to endNight
18%5%24313345%49%
1980
October1st to 15thNight
23%41342233445%
2160
16th to endNight
24%9%23322336%37%
2313
November1st to 15thNight
24%8%2432233439%
2598
16th to endNight
24%9%36%5%2223434%
2730
December1st to 15thNight
27%10%37%6%23336%25%
2575
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%30%
2125
April1st to 15thDay
17%8%36%43435%6%34%
2151
16th to endDay
22%12%45%434435%28%
2274
May1st to 15thDay
19%7%36%5%345%5%6%32%
2448
16th to endDay
16%5%25%5%3445%8%37%
2617
June1st to 15thDay
15%5%25%42445%9%39%
2520
16th to endDay
9%5%25%5%445%6%10%39%
2520
July1st to 15thDay
6%314425%46%9%50%
2520
16th to endDay
7%3145%35%6%6%9%46%
2625
August1st to 15thDay
8%4245%35%6%7%8%41%
2340
16th to endDay
11%5%2442445%7%48%
2402
September1st to 15thDay
10%5%1442445%8%46%
2160
16th to endDay
15%6%3343445%7%42%
1965
October1st to 15thDay
15%7%2442435%5%44%
1800
16th to endDay
17%9%36%413336%37%
1911
November1st to 15thDay
11%10%46%5%24446%39%
1589
16th to endDay
13%10%36%425%448%36%
1560
December1st to 15thDay
15%11%6%7%9%44446%25%
1467
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%2345%6%34%
2097
April1st to 15thNight
15%9%35%424445%38%
1797
16th to endNight
22%8%35%5%34445%32%
1683
May1st to 15thNight
20%5%25%42435%6%40%
1502
16th to endNight
12%5%25%5%24448%43%
1496
June1st to 15thNight
11%425%5%3445%8%44%
1440
16th to endNight
7%3135%23448%55%
1440
July1st to 15thNight
33123145%6%10%56%
1440
16th to endNight
5%21242436%8%58%
1542
August1st to 15thNight
5%4145%245%5%8%51%
1620
16th to endNight
9%31441235%7%56%
1800
September1st to 15thNight
10%314323346%57%
1800
16th to endNight
12%6%2432335%6%51%
1980
October1st to 15thNight
16%5%14422345%49%
2160
16th to endNight
17%10%33423347%40%
2313
November1st to 15thNight
13%8%35%43345%5%42%
2598
16th to endNight
13%10%46%6%23346%37%
2730
December1st to 15thNight
13%11%5%8%7%35%447%29%
2575
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
2127
April1st to 15thDay
48%5%12%21%10%1
2151
16th to endDay
57%6%11%16%6%1
2274
May1st to 15thDay
51%6%12%22%6%
2448
16th to endDay
44%7%11%22%11%1
2621
June1st to 15thDay
40%7%13%26%10%
2520
16th to endDay
37%8%16%25%10%1
2520
July1st to 15thDay
29%8%15%30%13%1
2371
16th to endDay
31%9%16%24%15%1
2460
August1st to 15thDay
36%8%13%29%10%1
2326
16th to endDay
34%6%15%27%14%1
2402
September1st to 15thDay
34%6%14%30%12%
2160
16th to endDay
40%6%12%30%8%
1965
October1st to 15thDay
41%412%27%13%
1800
16th to endDay
48%413%23%8%
1911
November1st to 15thDay
45%413%20%14%1
1589
16th to endDay
47%6%19%17%8%
1560
December1st to 15thDay
60%6%14%12%5%
1467
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
50%6%12%23%5%
2097
April1st to 15thNight
46%49%23%13%1
1797
16th to endNight
53%5%9%16%13%2
1683
May1st to 15thNight
44%6%14%20%11%2
1503
16th to endNight
38%6%12%24%16%1
1498
June1st to 15thNight
36%6%12%28%13%1
1440
16th to endNight
28%5%15%28%19%3
1440
July1st to 15thNight
22%7%14%34%18%3
1360
16th to endNight
23%6%15%31%18%4
1444
August1st to 15thNight
29%7%12%30%17%2
1610
16th to endNight
28%6%15%28%17%3
1800
September1st to 15thNight
28%5%11%32%21%
1800
16th to endNight
34%413%30%16%
1980
October1st to 15thNight
37%411%28%15%2
2160
16th to endNight
45%413%21%13%
2313
November1st to 15thNight
43%412%22%15%1
2598
16th to endNight
49%5%14%21%8%1
2730
December1st to 15thNight
55%7%13%18%5%
2575
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
34%8%30%19%7%
111
April1st to 15thDay
21%11%32%23%11%
270
16th to endDay
30%10%29%18%9%1
384
May1st to 15thDay
20%15%29%23%9%1
468
16th to endDay
19%8%29%25%13%3
517
June1st to 15thDay
15%6%27%32%14%3
495
16th to endDay
10%7%34%29%13%4
495
July1st to 15thDay
7%428%29%21%9%
475
16th to endDay
8%424%35%21%5%
515
August1st to 15thDay
10%223%36%23%3
493
16th to endDay
16%420%33%16%7%
442
September1st to 15thDay
10%6%26%32%19%5%
315
16th to endDay
20%5%33%25%11%4
180
October1st to 15thDay
17%8%35%22%11%3
135
16th to endDay
22%13%35%18%10%
144
November1st to 15thDay
9%9%38%30%11%
135
16th to endDay
29%11%39%17%2
135
December1st to 15thDay
20%12%29%36%3
100
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
17%10%32%26%11%1
576
April1st to 15thNight
20%9%33%29%7%
539
16th to endNight
26%6%30%26%8%
540
May1st to 15thNight
21%9%31%30%6%
540
16th to endNight
15%5%30%34%14%
563
June1st to 15thNight
14%429%39%12%
540
16th to endNight
9%226%47%13%
540
July1st to 15thNight
5%223%43%23%2
510
16th to endNight
5%21%49%21%1
564
August1st to 15thNight
5%121%42%25%3
539
16th to endNight
10%223%36%23%2
573
September1st to 15thNight
11%323%37%19%5%
540
16th to endNight
14%6%31%27%18%1
585
October1st to 15thNight
19%7%32%25%13%1
720
16th to endNight
23%10%27%29%9%
768
November1st to 15thNight
18%11%35%26%8%
887
16th to endNight
16%14%35%23%8%
975
December1st to 15thNight
19%8%40%25%5%
920
16th to endNight
24%9%32%27%5%
960
Page generated at 2017-12-05 09:19:04. Version ac04

Copyright 2017 A. Danko


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