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Downeast Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Downeast Observatory clear sky chart from 2005-11-05 to 2019-01-28.

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
28%
16738
15%
52465
7%
16698
37%
16698
17%
36546

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
18%
866
15%
3016
3%
862
33%
862
13%
2093
January16th to endNight
15%
882
14%
2987
2%
882
29%
882
12%
2116
February1st to 15thNight
16%
764
13%
2481
3%
761
28%
761
13%
1764
February16th to endNight
19%
683
15%
2106
4%
683
33%
683
13%
1495
March1st to 15thNight
19%
780
15%
2222
5%
780
30%
780
15%
1670
March16th to endNight
23%
832
17%
2288
7%
832
32%
832
19%
1618
April1st to 15thNight
21%
678
16%
1924
5%
678
30%
678
17%
1409
April16th to endNight
25%
578
14%
1734
7%
578
32%
578
19%
1231
May1st to 15thNight
31%
585
14%
1755
8%
585
38%
585
18%
1272
May16th to endNight
31%
567
11%
1613
7%
566
36%
566
18%
1186
June1st to 15thNight
33%
390
9%
1365
7%
390
38%
390
15%
990
June16th to endNight
37%
390
9%
1365
8%
390
42%
390
16%
979
July1st to 15thNight
48%
370
11%
1305
12%
370
52%
370
19%
859
July16th to endNight
44%
486
9%
1618
8%
458
47%
458
16%
1154
August1st to 15thNight
51%
574
10%
1713
9%
570
52%
570
21%
1203
August16th to endNight
52%
621
18%
1863
12%
621
55%
621
28%
1180
September1st to 15thNight
46%
706
17%
2048
12%
706
51%
706
27%
1336
September16th to endNight
44%
777
25%
2145
15%
777
52%
777
34%
1307
October1st to 15thNight
36%
780
21%
2294
10%
780
44%
780
25%
1499
October16th to endNight
24%
832
17%
2588
5%
832
36%
832
20%
1750
November1st to 15thNight
28%
837
18%
2725
8%
837
40%
837
17%
1853
November16th to endNight
23%
900
16%
2940
5%
900
35%
900
14%
2020
December1st to 15thNight
16%
900
16%
3010
3%
900
30%
900
13%
2160
December16th to endNight
13%
960
14%
3360
2%
960
27%
960
11%
2402

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
19%7%25%424447%36%
53120
Night
20%7%25%424446%35%
52634
TransparencyDay
46%6%12%21%11%1
52807
Night
49%5%11%20%12%1
52465
SeeingDay
24%9%28%25%10%1
8413
Night
24%10%29%25%8%
16738

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
16%9%46%42335%6%36%
1578
16th to endDay
17%9%35%5%2445%6%34%
1854
February1st to 15thDay
17%9%47%5%35%5%47%30%
1710
16th to endDay
14%11%36%5%35%438%33%
1653
March1st to 15thDay
22%11%35%423346%31%
2056
16th to endDay
17%9%35%434336%38%
2288
April1st to 15thDay
20%9%35%5%24345%34%
2353
16th to endDay
22%8%15%423435%36%
2501
May1st to 15thDay
24%8%36%423346%31%
2527
16th to endDay
23%6%25%4245%5%7%32%
2860
June1st to 15thDay
26%7%36%424346%30%
2925
16th to endDay
22%6%245%35%447%32%
2925
July1st to 15thDay
15%424435%449%40%
2913
16th to endDay
16%6%25%5%345%5%7%36%
2785
August1st to 15thDay
17%6%246%3436%8%36%
2488
16th to endDay
13%314425%45%7%46%
2691
September1st to 15thDay
14%424313446%49%
2239
16th to endDay
17%323323346%49%
2145
October1st to 15thDay
20%6%24424336%42%
1996
16th to endDay
21%6%15%434446%37%
1986
November1st to 15thDay
24%6%24323347%38%
1792
16th to endDay
21%8%2442435%6%35%
1680
December1st to 15thDay
24%8%3442335%7%32%
1607
16th to endDay
23%9%35%324337%32%
1568
January1st to 15thNight
16%9%36%43445%6%35%
3016
16th to endNight
15%11%36%5%345%5%7%31%
2987
February1st to 15thNight
17%10%25%436%5%46%32%
2480
16th to endNight
17%11%36%5%23445%34%
2106
March1st to 15thNight
20%10%46%5%34445%30%
2210
16th to endNight
18%9%25%5%24446%36%
2288
April1st to 15thNight
22%8%36%5%25%345%31%
1924
16th to endNight
26%7%2432445%5%33%
1734
May1st to 15thNight
23%7%35%5%34446%32%
1755
16th to endNight
23%7%35%6%2445%6%30%
1611
June1st to 15thNight
28%7%26%32445%7%27%
1365
16th to endNight
23%7%345%34447%30%
1365
July1st to 15thNight
14%8%345%25%5%6%10%34%
1375
16th to endNight
20%8%26%435%46%6%31%
1720
August1st to 15thNight
17%6%35%5%245%5%8%34%
1725
16th to endNight
14%5%2442445%8%44%
1863
September1st to 15thNight
17%5%2442345%6%42%
2048
16th to endNight
15%423323346%51%
2145
October1st to 15thNight
20%5%15%42345%6%41%
2294
16th to endNight
21%6%24423445%40%
2588
November1st to 15thNight
21%6%245%24346%38%
2725
16th to endNight
21%6%25%5%25%447%35%
2940
December1st to 15thNight
23%8%35%423346%33%
3010
16th to endNight
22%8%25%424446%33%
3360

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
48%7%14%18%9%1
1579
16th to endDay
50%7%11%18%10%1
1854
February1st to 15thDay
53%6%11%17%10%1
1713
16th to endDay
49%6%12%20%9%1
1653
March1st to 15thDay
53%410%18%10%1
2067
16th to endDay
46%410%19%16%3
2288
April1st to 15thDay
49%49%18%14%2
2353
16th to endDay
48%410%18%13%3
2501
May1st to 15thDay
52%5%10%18%11%2
2527
16th to endDay
49%6%13%20%7%1
2864
June1st to 15thDay
53%5%12%16%10%1
2925
16th to endDay
50%7%10%18%11%
2925
July1st to 15thDay
38%7%16%23%12%1
2754
16th to endDay
44%7%16%20%9%1
2625
August1st to 15thDay
43%7%15%23%9%
2475
16th to endDay
34%6%15%27%14%
2691
September1st to 15thDay
34%6%12%26%18%2
2239
16th to endDay
36%410%30%17%1
2145
October1st to 15thDay
43%412%26%12%
1996
16th to endDay
46%5%12%23%10%
1986
November1st to 15thDay
46%414%20%13%1
1792
16th to endDay
49%6%13%19%10%1
1680
December1st to 15thDay
53%6%12%19%8%
1607
16th to endDay
53%7%10%16%10%1
1568
January1st to 15thNight
49%7%11%19%10%1
3016
16th to endNight
51%6%11%19%9%
2987
February1st to 15thNight
51%6%13%17%9%1
2481
16th to endNight
52%5%10%16%13%1
2106
March1st to 15thNight
56%48%16%12%1
2222
16th to endNight
48%49%19%15%1
2288
April1st to 15thNight
54%48%15%14%3
1924
16th to endNight
52%49%16%14%2
1734
May1st to 15thNight
53%5%9%17%12%1
1755
16th to endNight
54%5%12%18%8%1
1613
June1st to 15thNight
55%6%12%17%7%1
1365
16th to endNight
55%5%10%18%10%
1365
July1st to 15thNight
43%8%13%19%13%
1305
16th to endNight
52%7%11%18%8%1
1618
August1st to 15thNight
46%8%14%20%10%
1713
16th to endNight
38%6%13%27%13%
1863
September1st to 15thNight
41%5%10%24%16%1
2048
16th to endNight
35%310%30%19%
2145
October1st to 15thNight
42%5%10%25%14%1
2294
16th to endNight
47%411%23%12%
2588
November1st to 15thNight
47%5%12%19%13%1
2725
16th to endNight
48%6%12%18%12%
2940
December1st to 15thNight
53%5%9%21%9%
3010
16th to endNight
53%6%10%18%11%
3360

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
24%20%36%14%3
120
16th to endDay
23%20%36%16%2
214
February1st to 15thDay
23%19%34%18%4
281
16th to endDay
22%14%36%22%4
278
March1st to 15thDay
27%19%33%16%3
330
16th to endDay
22%17%31%20%6%1
352
April1st to 15thDay
26%14%33%19%41
330
16th to endDay
27%7%31%24%7%1
319
May1st to 15thDay
28%8%33%21%7%1
348
16th to endDay
27%7%27%25%10%1
565
June1st to 15thDay
28%5%27%28%9%
570
16th to endDay
27%425%27%12%1
570
July1st to 15thDay
22%222%33%17%2
538
16th to endDay
21%225%32%16%2
390
August1st to 15thDay
19%324%34%17%1
358
16th to endDay
15%221%33%23%3
396
September1st to 15thDay
16%324%36%16%3
375
16th to endDay
21%426%26%16%3
374
October1st to 15thDay
22%10%24%24%14%3
329
16th to endDay
24%13%33%21%6%
336
November1st to 15thDay
27%16%25%20%7%2
325
16th to endDay
26%16%30%20%6%
330
December1st to 15thDay
29%12%33%18%5%
257
16th to endDay
27%28%30%10%2
128
January1st to 15thNight
22%18%33%22%3
866
16th to endNight
21%20%35%18%3
882
February1st to 15thNight
23%15%39%18%3
764
16th to endNight
25%17%32%19%41
683
March1st to 15thNight
26%12%34%22%2
780
16th to endNight
22%14%32%22%6%1
832
April1st to 15thNight
27%9%34%21%6%
678
16th to endNight
28%5%33%24%8%
578
May1st to 15thNight
24%5%29%30%8%1
585
16th to endNight
25%6%30%29%7%1
567
June1st to 15thNight
31%322%31%9%1
390
16th to endNight
28%322%31%12%1
390
July1st to 15thNight
20%416%41%16%
370
16th to endNight
24%218%38%15%1
486
August1st to 15thNight
20%314%42%17%1
574
16th to endNight
17%119%38%20%2
621
September1st to 15thNight
20%223%33%17%1
706
16th to endNight
17%427%32%15%2
777
October1st to 15thNight
23%429%28%12%2
780
16th to endNight
24%12%33%20%8%
832
November1st to 15thNight
24%12%29%23%9%1
837
16th to endNight
25%16%30%19%8%
900
December1st to 15thNight
29%14%33%17%4
900
16th to endNight
29%18%33%14%2
960
Page generated at 2019-01-28 21:54:04. Version ac04

Copyright 2019 A. Danko


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