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Rappahanock Astronomy Club...

Mark Slade Remote Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Mark Slade Remote Observatory clear sky chart from 2005-11-05 to 2017-03-26.

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
39%
14796
21%
45333
12%
14760
49%
14760
26%
28623

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
25%
716
23%
2365
9%
716
42%
716
20%
1468
January16th to endNight
24%
768
23%
2496
10%
768
41%
768
23%
1546
February1st to 15thNight
24%
701
21%
2287
8%
701
41%
701
23%
1393
February16th to endNight
20%
631
25%
1922
8%
631
41%
631
23%
1188
March1st to 15thNight
25%
720
23%
1980
9%
720
39%
720
26%
1276
March16th to endNight
25%
748
21%
2052
9%
748
36%
748
25%
1358
April1st to 15thNight
27%
658
21%
1646
5%
658
36%
658
29%
1092
April16th to endNight
41%
660
20%
1650
8%
660
46%
660
31%
1090
May1st to 15thNight
38%
521
16%
1511
8%
521
43%
521
22%
1052
May16th to endNight
52%
371
17%
1398
14%
371
57%
371
24%
830
June1st to 15thNight
58%
330
20%
1320
21%
330
64%
330
24%
765
June16th to endNight
64%
330
15%
1320
18%
330
68%
330
25%
775
July1st to 15thNight
56%
353
14%
1283
15%
353
58%
353
22%
806
July16th to endNight
70%
522
15%
1469
12%
489
73%
489
35%
888
August1st to 15thNight
68%
494
18%
1474
15%
491
69%
491
29%
969
August16th to endNight
63%
684
16%
1734
10%
684
63%
684
29%
1194
September1st to 15thNight
60%
660
25%
1650
16%
660
63%
660
33%
1096
September16th to endNight
50%
657
19%
1820
16%
657
53%
657
26%
1242
October1st to 15thNight
46%
660
24%
1980
21%
660
53%
660
26%
1289
October16th to endNight
38%
704
29%
2112
18%
704
54%
704
32%
1247
November1st to 15thNight
38%
700
26%
2181
15%
700
52%
700
29%
1293
November16th to endNight
36%
720
22%
2475
13%
720
49%
720
25%
1449
December1st to 15thNight
29%
720
19%
2520
10%
720
42%
720
20%
1600
December16th to endNight
27%
768
22%
2688
10%
768
43%
768
20%
1717

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
14%5%244345%5%7%42%
45627
Night
14%5%2442445%7%44%
45520
Cloud CoverDay
14%5%2443445%7%42%
45637
Night
14%5%2442445%7%44%
45524
TransparencyDay
39%6%11%22%16%3
45332
Night
38%6%11%22%17%3
45333
SeeingDay
17%7%23%24%18%7%
4983
Night
17%8%28%29%14%1
14804

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%6%35%324446%42%
1570
16th to endDay
15%7%25%434345%42%
1728
February1st to 15thDay
13%7%26%5%2345%6%41%
1575
16th to endDay
13%6%35%5%35%45%7%39%
1548
March1st to 15thDay
16%415%425%445%44%
1969
16th to endDay
16%6%25%4245%45%40%
2058
April1st to 15thDay
13%5%25%324446%47%
1972
16th to endDay
15%5%35%323446%44%
1980
May1st to 15thDay
17%6%24425%5%5%7%38%
2119
16th to endDay
14%4134345%6%8%43%
2363
June1st to 15thDay
11%4245%35%5%5%10%40%
2310
16th to endDay
7%3245%36%5%7%9%43%
2310
July1st to 15thDay
11%415%5%46%6%7%9%37%
2261
16th to endDay
6%415%6%37%6%8%10%38%
2283
August1st to 15thDay
10%5%36%6%36%6%6%9%34%
2145
16th to endDay
13%4146%36%5%6%8%39%
2105
September1st to 15thDay
11%3144445%5%7%46%
1980
16th to endDay
18%6%15%4245%6%7%37%
1807
October1st to 15thDay
19%424423336%46%
1650
16th to endDay
14%5%24423435%49%
1760
November1st to 15thDay
14%423423346%49%
1676
16th to endDay
17%323324446%47%
1482
December1st to 15thDay
15%6%1442345%7%44%
1440
16th to endDay
19%6%35%323335%41%
1536
January1st to 15thNight
17%5%24423346%44%
2365
16th to endNight
16%6%25%324346%44%
2496
February1st to 15thNight
14%6%2442445%6%45%
2285
16th to endNight
13%6%25%4235%5%6%45%
1922
March1st to 15thNight
17%42442435%6%45%
1968
16th to endNight
17%5%2442435%5%44%
2052
April1st to 15thNight
12%6%3442345%7%44%
1646
16th to endNight
14%424434446%46%
1650
May1st to 15thNight
18%6%245%34449%36%
1511
16th to endNight
12%413425%45%10%43%
1396
June1st to 15thNight
9%5%335%345%6%9%44%
1320
16th to endNight
8%4235%35%5%7%10%43%
1320
July1st to 15thNight
7%6%25%7%345%6%10%39%
1367
16th to endNight
5%324436%7%7%11%42%
1577
August1st to 15thNight
8%426%5%46%6%5%9%41%
1485
16th to endNight
11%6%25%6%35%5%6%9%38%
1734
September1st to 15thNight
11%415%4245%5%8%46%
1650
16th to endNight
15%7%25%42345%7%40%
1820
October1st to 15thNight
18%5%14324445%43%
1980
16th to endNight
14%313424445%51%
2112
November1st to 15thNight
14%5%24323335%51%
2181
16th to endNight
15%41432445%7%47%
2475
December1st to 15thNight
16%5%35%5%34446%41%
2520
16th to endNight
17%5%25%424447%40%
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
16%6%25%323446%41%
1570
16th to endDay
15%7%25%424445%42%
1728
February1st to 15thDay
13%8%26%5%33446%41%
1575
16th to endDay
13%6%35%5%35%45%7%39%
1548
March1st to 15thDay
15%424435%445%44%
1980
16th to endDay
17%5%35%425%45%6%39%
2057
April1st to 15thDay
13%6%25%324446%47%
1972
16th to endDay
15%5%35%42335%5%45%
1980
May1st to 15thDay
17%6%23425%45%7%39%
2119
16th to endDay
14%4133345%5%9%42%
2363
June1st to 15thDay
11%4235%25%5%6%10%41%
2310
16th to endDay
7%3246%36%5%6%9%43%
2310
July1st to 15thDay
11%425%5%46%5%7%9%37%
2261
16th to endDay
6%415%6%47%6%9%9%39%
2283
August1st to 15thDay
10%5%36%6%45%6%6%9%34%
2145
16th to endDay
13%4146%35%5%6%8%39%
2105
September1st to 15thDay
12%314435%5%5%7%46%
1980
16th to endDay
18%6%15%4245%6%7%37%
1807
October1st to 15thDay
19%424423336%45%
1650
16th to endDay
14%5%24423435%49%
1760
November1st to 15thDay
14%423423346%49%
1676
16th to endDay
17%32332445%5%47%
1482
December1st to 15thDay
15%6%1442345%7%44%
1440
16th to endDay
19%6%35%323335%41%
1536
January1st to 15thNight
17%6%24423346%44%
2365
16th to endNight
16%6%24323446%44%
2496
February1st to 15thNight
14%5%2442445%6%46%
2278
16th to endNight
13%6%25%423446%45%
1922
March1st to 15thNight
17%41442435%7%44%
1980
16th to endNight
17%5%34423345%44%
2052
April1st to 15thNight
12%5%35%42435%7%44%
1646
16th to endNight
15%424424446%47%
1650
May1st to 15thNight
18%6%25%5%3445%8%36%
1510
16th to endNight
12%423425%46%9%43%
1396
June1st to 15thNight
9%424425%5%6%8%44%
1320
16th to endNight
8%4234346%7%9%43%
1320
July1st to 15thNight
7%6%247%346%6%9%39%
1367
16th to endNight
5%313436%7%7%12%42%
1577
August1st to 15thNight
8%426%446%6%6%9%41%
1485
16th to endNight
11%5%25%5%445%6%9%38%
1734
September1st to 15thNight
11%415%425%5%5%7%46%
1650
16th to endNight
16%6%25%423446%40%
1820
October1st to 15thNight
18%6%14424445%43%
1980
16th to endNight
14%31342345%5%51%
2112
November1st to 15thNight
13%5%24323335%51%
2181
16th to endNight
15%314324446%47%
2475
December1st to 15thNight
15%5%35%5%3445%5%41%
2520
16th to endNight
18%5%25%324447%40%
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
41%6%13%19%15%3
1571
16th to endDay
42%49%22%16%4
1728
February1st to 15thDay
43%410%23%15%3
1577
16th to endDay
42%5%11%20%17%2
1548
March1st to 15thDay
41%5%9%23%15%4
1980
16th to endDay
44%5%10%18%17%4
2058
April1st to 15thDay
38%5%10%22%18%5%
1972
16th to endDay
39%6%8%19%18%7%
1980
May1st to 15thDay
43%7%12%20%14%
2119
16th to endDay
37%7%15%25%12%1
2367
June1st to 15thDay
36%8%15%24%13%1
2310
16th to endDay
34%9%15%22%16%1
2310
July1st to 15thDay
40%9%12%19%14%3
2116
16th to endDay
35%10%14%22%14%1
2128
August1st to 15thDay
42%9%12%21%13%
2132
16th to endDay
39%8%12%23%13%1
2105
September1st to 15thDay
36%8%11%18%21%3
1980
16th to endDay
43%7%9%20%18%1
1807
October1st to 15thDay
40%48%27%15%3
1650
16th to endDay
37%48%24%22%3
1760
November1st to 15thDay
36%310%21%20%6%
1676
16th to endDay
37%5%9%23%20%3
1482
December1st to 15thDay
38%6%11%24%14%5%
1440
16th to endDay
45%5%9%22%15%1
1536
January1st to 15thNight
41%410%18%18%6%
2365
16th to endNight
40%410%24%17%2
2496
February1st to 15thNight
38%49%24%17%4
2287
16th to endNight
38%49%24%19%3
1922
March1st to 15thNight
38%5%10%26%15%3
1980
16th to endNight
41%5%10%21%18%2
2052
April1st to 15thNight
38%5%9%19%21%5%
1646
16th to endNight
37%5%9%20%17%8%
1650
May1st to 15thNight
45%8%12%19%13%2
1511
16th to endNight
36%8%14%24%13%2
1398
June1st to 15thNight
34%8%14%26%14%2
1320
16th to endNight
33%10%16%18%19%2
1320
July1st to 15thNight
39%9%16%17%13%3
1283
16th to endNight
29%9%19%25%15%1
1469
August1st to 15thNight
36%9%12%22%16%1
1474
16th to endNight
40%7%13%21%14%1
1734
September1st to 15thNight
35%8%11%20%19%4
1650
16th to endNight
42%6%9%17%19%3
1820
October1st to 15thNight
42%48%22%17%4
1980
16th to endNight
33%47%25%22%5%
2112
November1st to 15thNight
36%37%21%22%7%
2181
16th to endNight
36%49%23%20%4
2475
December1st to 15thNight
43%5%10%20%15%3
2520
16th to endNight
42%6%10%21%15%3
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
24%26%30%15%3
83
16th to endDay
26%25%30%15%3
96
February1st to 15thDay
25%22%40%10%2
90
16th to endDay
17%18%36%26%1
202
March1st to 15thDay
17%16%32%25%7%
270
16th to endDay
19%15%35%19%7%1
267
April1st to 15thDay
19%14%25%23%15%1
210
16th to endDay
20%5%27%22%18%6%
210
May1st to 15thDay
25%9%29%15%14%5%
228
16th to endDay
18%223%21%26%7%
267
June1st to 15thDay
12%328%23%23%7%
255
16th to endDay
8%321%35%23%7%
255
July1st to 15thDay
14%217%28%28%7%
245
16th to endDay
7%111%34%30%15%
270
August1st to 15thDay
11%113%25%32%14%
253
16th to endDay
14%19%28%26%19%
268
September1st to 15thDay
10%315%24%21%24%
255
16th to endDay
29%115%23%16%12%
254
October1st to 15thDay
25%318%22%23%7%
255
16th to endDay
14%9%30%26%15%3
272
November1st to 15thDay
19%6%26%23%19%4
252
16th to endDay
21%10%28%22%16%
102
December1st to 15thDay
21%13%33%13%15%3
60
16th to endDay
40%9%29%17%3
64
January1st to 15thNight
20%15%34%24%5%
720
16th to endNight
20%13%37%27%1
768
February1st to 15thNight
19%13%40%25%1
704
16th to endNight
17%17%40%21%2
631
March1st to 15thNight
20%12%37%24%4
720
16th to endNight
18%12%39%22%6%
748
April1st to 15thNight
15%15%40%23%5%
658
16th to endNight
17%8%27%30%14%
660
May1st to 15thNight
20%5%29%29%13%1
521
16th to endNight
15%320%36%23%1
372
June1st to 15thNight
11%220%42%22%1
330
16th to endNight
9%115%49%23%
330
July1st to 15thNight
12%118%33%32%1
353
16th to endNight
6%13%36%36%6%
522
August1st to 15thNight
10%110%43%32%2
494
16th to endNight
14%19%37%31%5%
684
September1st to 15thNight
12%215%30%34%3
660
16th to endNight
19%216%31%26%2
657
October1st to 15thNight
22%420%28%22%2
660
16th to endNight
16%8%33%26%13%
704
November1st to 15thNight
16%8%30%27%14%1
700
16th to endNight
18%11%31%25%12%
720
December1st to 15thNight
20%8%36%24%10%
720
16th to endNight
21%9%36%27%3
768
Page generated at 2017-03-27 11:15:18. Version ac04

Copyright 2017 A. Danko


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