May River Road Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the May River Road Observatory clear sky chart from 2005-11-05 to 2018-01-20.

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
46%
16392
21%
48440
14%
16350
54%
16350
24%
30657

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%
778
21%
2522
9%
776
44%
776
20%
1548
January16th to endNight
31%
788
24%
2560
14%
788
45%
788
22%
1552
February1st to 15thNight
33%
704
21%
2189
12%
700
45%
700
22%
1360
February16th to endNight
33%
631
24%
1832
11%
631
46%
631
23%
1143
March1st to 15thNight
40%
720
27%
1980
16%
720
49%
720
28%
1195
March16th to endNight
43%
768
21%
2112
11%
768
51%
768
28%
1305
April1st to 15thNight
43%
718
23%
1941
13%
718
50%
718
29%
1190
April16th to endNight
47%
710
27%
1790
13%
710
54%
710
34%
1070
May1st to 15thNight
51%
539
23%
1620
14%
539
56%
539
30%
948
May16th to endNight
53%
561
20%
1683
11%
561
58%
561
24%
1045
June1st to 15thNight
62%
540
13%
1620
11%
540
63%
540
23%
1050
June16th to endNight
62%
540
12%
1620
9%
540
63%
540
22%
1081
July1st to 15thNight
59%
510
12%
1530
10%
510
60%
510
23%
992
July16th to endNight
60%
564
10%
1595
9%
531
65%
531
21%
1089
August1st to 15thNight
64%
539
14%
1609
12%
536
66%
536
19%
1121
August16th to endNight
54%
705
13%
1872
10%
705
54%
705
16%
1441
September1st to 15thNight
61%
720
15%
1980
13%
720
62%
720
22%
1388
September16th to endNight
50%
717
14%
1980
9%
717
56%
717
17%
1458
October1st to 15thNight
50%
720
26%
2103
24%
720
56%
720
28%
1308
October16th to endNight
54%
768
33%
2304
26%
768
65%
768
33%
1299
November1st to 15thNight
49%
760
30%
2281
22%
760
60%
760
33%
1269
November16th to endNight
42%
780
26%
2478
17%
780
54%
780
26%
1454
December1st to 15thNight
37%
780
22%
2535
14%
780
48%
780
20%
1594
December16th to endNight
34%
832
22%
2704
13%
832
46%
832
18%
1757

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
11%5%24435%5%6%8%43%
49075
Night
11%5%25%43445%8%44%
48642
TransparencyDay
36%9%14%20%15%5%
48776
Night
36%7%13%18%16%6%
48445
SeeingDay
11%10%14%25%27%10%
6172
Night
11%18%16%26%22%4
16397

By Month

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
13%6%2342345%7%45%
1746
16th to endDay
15%424323446%46%
1768
February1st to 15thDay
14%7%2432445%5%45%
1666
16th to endDay
13%5%24422246%50%
1640
March1st to 15thDay
12%423313447%51%
1980
16th to endDay
11%5%24325%447%48%
2111
April1st to 15thDay
10%413223447%53%
2005
16th to endDay
6%32433345%8%54%
2179
May1st to 15thDay
7%3145%246%6%8%48%
2331
16th to endDay
9%425%435%5%6%8%43%
2431
June1st to 15thDay
7%325%6%37%7%8%11%36%
2340
16th to endDay
8%425%5%47%6%9%10%35%
2340
July1st to 15thDay
9%4245%37%6%9%12%32%
2340
16th to endDay
8%5%25%6%47%7%9%12%29%
2465
August1st to 15thDay
9%426%6%47%8%9%12%28%
2340
16th to endDay
13%7%36%5%36%7%8%11%25%
2312
September1st to 15thDay
12%5%25%6%45%6%6%8%35%
1980
16th to endDay
14%7%26%7%45%5%6%8%32%
1980
October1st to 15thDay
11%6%25%323445%50%
1857
16th to endDay
10%413223346%58%
1920
November1st to 15thDay
8%424324346%56%
1907
16th to endDay
11%423323445%55%
1810
December1st to 15thDay
13%6%245%2345%6%45%
1755
16th to endDay
15%6%25%5%23336%45%
1872
January1st to 15thNight
11%6%25%434446%45%
2522
16th to endNight
14%5%24423446%47%
2560
February1st to 15thNight
14%5%25%42444447%
2184
16th to endNight
10%5%25%5%34445%47%
1832
March1st to 15thNight
8%42442446%7%50%
1980
16th to endNight
11%5%15%32335%7%50%
2112
April1st to 15thNight
11%224323447%52%
1941
16th to endNight
8%32242435%8%53%
1790
May1st to 15thNight
7%415%33445%8%51%
1619
16th to endNight
8%424435%6%7%8%45%
1682
June1st to 15thNight
8%425%445%6%9%12%35%
1620
16th to endNight
5%325%5%36%7%8%15%35%
1620
July1st to 15thNight
8%426%5%35%7%7%13%35%
1620
16th to endNight
6%436%7%36%9%7%12%32%
1703
August1st to 15thNight
6%436%6%5%6%7%8%14%29%
1620
16th to endNight
12%7%27%7%5%6%6%6%10%27%
1872
September1st to 15thNight
11%5%45%5%35%5%7%10%34%
1980
16th to endNight
13%6%37%6%45%5%6%7%32%
1980
October1st to 15thNight
12%5%25%323346%49%
2103
16th to endNight
8%324323445%57%
2304
November1st to 15thNight
8%414423346%56%
2281
16th to endNight
12%5%23323445%51%
2478
December1st to 15thNight
14%6%245%2335%6%44%
2535
16th to endNight
16%6%35%42335%7%40%
2704

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
38%6%9%18%21%6%
1747
16th to endDay
38%48%19%20%8%
1768
February1st to 15thDay
40%47%16%21%9%
1668
16th to endDay
36%47%19%23%8%
1640
March1st to 15thDay
32%5%11%22%20%7%
1980
16th to endDay
35%6%12%20%17%6%
2112
April1st to 15thDay
30%5%12%25%18%7%
2005
16th to endDay
26%5%14%23%20%8%
2179
May1st to 15thDay
30%8%14%24%17%4
2331
16th to endDay
34%10%17%23%13%1
2435
June1st to 15thDay
34%14%19%22%9%
2340
16th to endDay
36%15%18%21%7%
2340
July1st to 15thDay
35%15%23%19%41
2201
16th to endDay
39%16%23%16%3
2310
August1st to 15thDay
40%16%20%16%6%
2327
16th to endDay
46%16%16%15%4
2312
September1st to 15thDay
42%11%17%16%10%1
1980
16th to endDay
46%10%13%14%11%2
1980
October1st to 15thDay
34%7%11%17%21%8%
1857
16th to endDay
28%47%19%25%13%
1920
November1st to 15thDay
29%5%9%21%23%10%
1907
16th to endDay
31%6%8%21%21%10%
1810
December1st to 15thDay
39%6%10%20%14%7%
1755
16th to endDay
40%6%9%23%13%6%
1872
January1st to 15thNight
38%5%10%17%20%7%
2522
16th to endNight
38%5%8%14%22%11%
2560
February1st to 15thNight
39%48%17%18%12%
2193
16th to endNight
37%5%9%16%20%10%
1832
March1st to 15thNight
32%5%12%20%18%10%
1980
16th to endNight
34%5%12%19%19%8%
2112
April1st to 15thNight
31%6%9%22%20%8%
1941
16th to endNight
27%6%13%21%22%8%
1790
May1st to 15thNight
31%6%14%22%20%4
1620
16th to endNight
33%9%16%26%11%2
1684
June1st to 15thNight
36%10%21%22%8%
1620
16th to endNight
33%15%21%21%6%
1620
July1st to 15thNight
35%11%25%22%31
1530
16th to endNight
37%15%23%19%4
1595
August1st to 15thNight
40%14%20%20%4
1609
16th to endNight
50%12%16%16%2
1872
September1st to 15thNight
41%11%17%17%10%1
1980
16th to endNight
49%9%13%14%11%1
1980
October1st to 15thNight
35%6%10%19%19%8%
2103
16th to endNight
30%48%15%25%15%
2304
November1st to 15thNight
29%410%20%24%11%
2281
16th to endNight
35%49%16%23%10%
2478
December1st to 15thNight
39%6%12%17%17%6%
2535
16th to endNight
43%6%9%20%13%7%
2704

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
22%8%35%19%8%5%
135
16th to endDay
16%9%40%24%9%
109
February1st to 15thDay
8%17%30%35%7%
90
16th to endDay
9%14%39%31%4
141
March1st to 15thDay
11%17%28%25%15%1
270
16th to endDay
10%17%23%30%13%4
288
April1st to 15thDay
10%17%22%24%20%3
270
16th to endDay
5%13%16%31%22%10%
270
May1st to 15thDay
5%14%19%33%21%5%
288
16th to endDay
11%11%9%21%33%13%
331
June1st to 15thDay
8%9%423%33%19%
315
16th to endDay
9%10%424%37%12%
315
July1st to 15thDay
6%6%317%45%20%
305
16th to endDay
8%10%317%45%15%
326
August1st to 15thDay
10%5%5%18%45%14%
313
16th to endDay
16%6%315%34%25%
332
September1st to 15thDay
14%6%6%24%37%11%
315
16th to endDay
15%6%7%20%37%12%
314
October1st to 15thDay
18%8%13%27%22%9%
315
16th to endDay
8%8%19%27%26%8%
336
November1st to 15thDay
10%13%18%30%21%5%
325
16th to endDay
7%7%24%36%17%6%
190
December1st to 15thDay
19%331%33%11%1
135
16th to endDay
26%422%31%13%1
144
January1st to 15thNight
12%25%28%23%8%1
780
16th to endNight
12%25%27%26%7%
788
February1st to 15thNight
15%23%23%28%8%
704
16th to endNight
10%24%26%32%5%
631
March1st to 15thNight
11%22%21%32%11%
720
16th to endNight
10%21%19%32%14%1
768
April1st to 15thNight
10%21%20%28%17%2
718
16th to endNight
9%20%19%25%22%2
710
May1st to 15thNight
8%18%15%32%21%3
540
16th to endNight
9%18%9%22%28%11%
563
June1st to 15thNight
7%17%226%35%10%
540
16th to endNight
7%16%327%33%10%
540
July1st to 15thNight
9%12%6%19%41%10%
510
16th to endNight
7%16%319%45%7%
564
August1st to 15thNight
8%9%421%43%11%
539
16th to endNight
14%9%6%17%38%13%
705
September1st to 15thNight
11%9%5%20%44%8%
720
16th to endNight
18%9%8%23%31%7%
717
October1st to 15thNight
16%10%15%24%25%7%
720
16th to endNight
7%14%18%27%26%5%
768
November1st to 15thNight
10%18%17%29%21%2
760
16th to endNight
10%21%20%28%16%2
780
December1st to 15thNight
13%23%20%24%15%2
780
16th to endNight
16%21%22%27%11%
832
Page generated at 2018-01-21 12:19:22. Version ac04

Copyright 2018 A. Danko


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