Baltimore
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Baltimore clear sky chart from 2005-11-05 to 2017-08-12.

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%
15051
21%
46519
9%
15011
44%
15011
21%
29153

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%
718
22%
2455
9%
716
36%
716
15%
1540
January16th to endNight
15%
768
23%
2496
6%
768
37%
768
18%
1545
February1st to 15thNight
17%
704
18%
2287
5%
701
34%
701
16%
1432
February16th to endNight
17%
631
25%
1901
5%
631
40%
631
18%
1188
March1st to 15thNight
21%
720
21%
2031
8%
720
36%
720
21%
1298
March16th to endNight
19%
768
20%
2070
7%
768
31%
768
21%
1384
April1st to 15thNight
19%
718
20%
1796
4%
718
29%
718
23%
1191
April16th to endNight
29%
720
19%
1800
4%
720
37%
720
24%
1200
May1st to 15thNight
28%
545
17%
1625
8%
545
36%
545
19%
1094
May16th to endNight
40%
374
17%
1497
12%
374
50%
374
17%
896
June1st to 15thNight
44%
360
19%
1440
15%
360
55%
360
20%
829
June16th to endNight
46%
360
17%
1440
14%
360
57%
360
22%
826
July1st to 15thNight
48%
340
12%
1360
13%
340
52%
340
17%
868
July16th to endNight
58%
503
16%
1535
12%
471
65%
471
31%
869
August1st to 15thNight
54%
533
18%
1581
11%
530
58%
530
27%
989
August16th to endNight
56%
700
19%
1750
9%
700
58%
700
32%
1148
September1st to 15thNight
52%
660
26%
1650
15%
660
57%
660
33%
1071
September16th to endNight
48%
657
23%
1799
16%
657
54%
657
28%
1171
October1st to 15thNight
39%
660
23%
1980
19%
660
48%
660
25%
1266
October16th to endNight
32%
704
27%
2112
13%
704
51%
704
28%
1226
November1st to 15thNight
29%
700
25%
2252
12%
700
46%
700
23%
1360
November16th to endNight
24%
720
21%
2454
9%
720
40%
720
17%
1479
December1st to 15thNight
23%
720
18%
2520
6%
720
38%
720
13%
1598
December16th to endNight
17%
768
22%
2688
6%
768
37%
768
15%
1685

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%24435%5%5%7%41%
47451
Night
14%5%2442445%7%43%
46700
Cloud CoverDay
14%5%244345%5%7%41%
47461
Night
14%5%2442445%7%43%
46704
TransparencyDay
39%6%12%22%16%2
47151
Night
39%5%11%23%17%3
46519
SeeingDay
16%18%23%22%13%5%
5554
Night
15%23%23%23%11%1
15054

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%23435%46%6%41%
1483
16th to endDay
14%6%345%3445%5%42%
1728
February1st to 15thDay
14%6%25%5%245%5%6%41%
1575
16th to endDay
14%6%25%4245%46%41%
1572
March1st to 15thDay
14%6%34423446%44%
1915
16th to endDay
17%6%24424345%41%
2154
April1st to 15thDay
15%424435%35%7%43%
2152
16th to endDay
16%5%235%24347%44%
2160
May1st to 15thDay
18%6%24435%46%8%37%
2335
16th to endDay
15%4245%35%6%6%8%38%
2618
June1st to 15thDay
11%424436%5%6%9%40%
2520
16th to endDay
11%4235%35%5%6%9%42%
2520
July1st to 15thDay
9%425%5%35%6%7%9%39%
2520
16th to endDay
6%325%5%47%7%8%12%37%
2524
August1st to 15thDay
10%325%6%37%6%7%8%37%
2269
16th to endDay
11%4245%36%5%6%8%41%
2100
September1st to 15thDay
13%4245%2445%6%45%
1980
16th to endDay
16%5%26%43435%7%40%
1829
October1st to 15thDay
18%414323347%45%
1650
16th to endDay
16%5%14323446%46%
1760
November1st to 15thDay
15%6%14224446%46%
1605
16th to endDay
17%5%2432435%6%43%
1506
December1st to 15thDay
16%5%243145%5%7%42%
1440
16th to endDay
18%6%2433445%6%39%
1536
January1st to 15thNight
17%5%25%424447%41%
2455
16th to endNight
16%6%2342345%5%44%
2496
February1st to 15thNight
14%6%345%24347%42%
2285
16th to endNight
14%6%24424346%45%
1901
March1st to 15thNight
15%6%2432435%6%45%
2019
16th to endNight
15%5%25%6%24445%43%
2070
April1st to 15thNight
14%5%34425%35%6%43%
1796
16th to endNight
17%5%23324447%44%
1800
May1st to 15thNight
21%5%14423347%39%
1625
16th to endNight
14%5%245%34448%43%
1495
June1st to 15thNight
11%323435%46%9%45%
1440
16th to endNight
9%4245%35%5%5%12%42%
1440
July1st to 15thNight
9%437%6%47%6%7%9%35%
1440
16th to endNight
5%313435%5%7%12%46%
1641
August1st to 15thNight
9%425%435%5%6%8%44%
1592
16th to endNight
12%5%2442446%8%45%
1750
September1st to 15thNight
12%6%24424447%46%
1650
16th to endNight
14%5%25%42435%7%43%
1799
October1st to 15thNight
19%5%24324345%44%
1980
16th to endNight
15%413323347%51%
2112
November1st to 15thNight
13%6%3442333450%
2252
16th to endNight
16%425%32345%7%43%
2454
December1st to 15thNight
17%5%245%35%45%5%39%
2520
16th to endNight
17%5%345%2335%7%41%
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%24325%46%6%41%
1483
16th to endDay
14%6%25%43435%6%43%
1728
February1st to 15thDay
14%5%25%5%3445%7%41%
1575
16th to endDay
14%7%34434446%41%
1572
March1st to 15thDay
14%6%345%33346%44%
1926
16th to endDay
17%6%24425%436%41%
2153
April1st to 15thDay
14%4245%2445%7%43%
2152
16th to endDay
16%5%24424447%43%
2160
May1st to 15thDay
17%5%245%3445%8%37%
2335
16th to endDay
14%425%5%25%5%6%8%38%
2618
June1st to 15thDay
11%324435%5%7%10%41%
2520
16th to endDay
10%4145%35%5%6%9%42%
2520
July1st to 15thDay
8%425%5%35%7%7%8%40%
2520
16th to endDay
6%3245%36%8%9%11%38%
2524
August1st to 15thDay
11%325%6%35%7%7%8%37%
2269
16th to endDay
11%424435%5%6%8%41%
2100
September1st to 15thDay
12%41443446%7%45%
1980
16th to endDay
15%5%35%43435%8%40%
1829
October1st to 15thDay
18%414323337%46%
1650
16th to endDay
15%5%1432345%6%47%
1760
November1st to 15thDay
15%6%2322445%6%46%
1605
16th to endDay
17%6%2333345%6%44%
1506
December1st to 15thDay
16%5%243145%48%42%
1440
16th to endDay
18%5%244335%5%6%39%
1536
January1st to 15thNight
17%425%5%23447%41%
2455
16th to endNight
16%6%2342435%6%44%
2496
February1st to 15thNight
14%5%25%43435%6%43%
2278
16th to endNight
15%5%23424446%45%
1901
March1st to 15thNight
15%5%2442345%6%45%
2031
16th to endNight
14%6%25%5%2345%6%41%
2070
April1st to 15thNight
14%5%2443445%5%44%
1796
16th to endNight
17%5%2332345%6%45%
1800
May1st to 15thNight
20%6%24424347%38%
1624
16th to endNight
14%42443445%9%42%
1495
June1st to 15thNight
11%32342446%10%45%
1440
16th to endNight
9%325%5%35%6%5%11%41%
1440
July1st to 15thNight
8%5%36%6%47%6%6%8%36%
1440
16th to endNight
5%323435%7%6%12%46%
1641
August1st to 15thNight
9%4145%25%5%6%9%44%
1592
16th to endNight
12%5%2442446%8%44%
1750
September1st to 15thNight
11%6%34333447%46%
1650
16th to endNight
14%6%25%433449%42%
1799
October1st to 15thNight
19%5%23423346%44%
1980
16th to endNight
15%412333347%51%
2112
November1st to 15thNight
14%6%3431333451%
2252
16th to endNight
16%42442445%7%43%
2454
December1st to 15thNight
17%5%25%5%35%45%5%40%
2520
16th to endNight
16%5%25%42445%7%41%
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%5%13%22%13%3
1484
16th to endDay
41%5%11%23%13%3
1728
February1st to 15thDay
41%5%11%25%12%2
1577
16th to endDay
41%411%26%13%2
1572
March1st to 15thDay
40%5%11%24%15%2
1926
16th to endDay
44%5%9%18%18%3
2154
April1st to 15thDay
40%5%10%21%18%4
2152
16th to endDay
39%5%9%18%21%5%
2160
May1st to 15thDay
43%7%11%20%14%2
2335
16th to endDay
40%7%14%22%13%2
2622
June1st to 15thDay
38%7%13%25%13%1
2520
16th to endDay
35%8%13%21%18%1
2520
July1st to 15thDay
36%8%13%22%15%3
2371
16th to endDay
32%10%16%24%13%1
2368
August1st to 15thDay
39%8%12%21%17%1
2256
16th to endDay
36%8%11%23%17%3
2100
September1st to 15thDay
36%6%12%19%21%3
1980
16th to endDay
41%48%21%21%2
1829
October1st to 15thDay
38%5%11%23%18%3
1650
16th to endDay
37%310%27%19%1
1760
November1st to 15thDay
37%412%21%19%4
1605
16th to endDay
41%39%26%16%2
1506
December1st to 15thDay
40%5%15%23%11%2
1440
16th to endDay
45%5%11%23%13%
1536
January1st to 15thNight
42%410%21%17%3
2455
16th to endNight
40%410%26%16%1
2496
February1st to 15thNight
42%311%23%15%2
2287
16th to endNight
39%49%24%19%2
1901
March1st to 15thNight
38%5%12%26%14%2
2031
16th to endNight
42%411%20%17%3
2070
April1st to 15thNight
39%410%21%19%3
1796
16th to endNight
38%5%9%19%19%6%
1800
May1st to 15thNight
44%5%11%20%15%2
1625
16th to endNight
38%7%15%19%14%3
1497
June1st to 15thNight
35%7%11%27%16%1
1440
16th to endNight
36%6%12%25%17%2
1440
July1st to 15thNight
41%9%14%17%12%4
1360
16th to endNight
27%9%18%24%18%1
1535
August1st to 15thNight
34%8%13%22%18%2
1581
16th to endNight
36%6%10%24%18%3
1750
September1st to 15thNight
36%5%11%22%20%3
1650
16th to endNight
38%5%8%20%22%4
1799
October1st to 15thNight
41%49%23%18%3
1980
16th to endNight
33%310%28%21%2
2112
November1st to 15thNight
37%37%23%19%7%
2252
16th to endNight
39%410%23%17%3
2454
December1st to 15thNight
44%411%23%14%1
2520
16th to endNight
42%5%13%23%13%2
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
28%30%26%11%11
69
16th to endDay
16%34%29%17%2
96
February1st to 15thDay
22%30%35%12%
90
16th to endDay
17%27%36%15%3
231
March1st to 15thDay
15%31%26%21%4
270
16th to endDay
20%26%31%13%42
288
April1st to 15thDay
17%25%30%18%6%1
270
16th to endDay
19%19%27%16%12%5%
270
May1st to 15thDay
26%27%22%12%8%3
288
16th to endDay
19%14%21%25%16%2
331
June1st to 15thDay
14%16%24%22%17%4
315
16th to endDay
13%17%24%29%11%4
315
July1st to 15thDay
10%10%20%33%19%5%
305
16th to endDay
7%11%18%30%24%8%
326
August1st to 15thDay
12%7%18%31%19%11%
297
16th to endDay
8%7%13%30%22%17%
268
September1st to 15thDay
11%12%16%21%21%16%
255
16th to endDay
23%8%15%27%13%10%
254
October1st to 15thDay
21%10%18%24%19%4
255
16th to endDay
13%18%30%23%13%1
272
November1st to 15thDay
16%21%25%17%15%3
239
16th to endDay
17%26%27%17%8%1
126
December1st to 15thDay
18%28%25%20%5%3
60
16th to endDay
34%12%31%17%4
64
January1st to 15thNight
16%31%27%20%4
720
16th to endNight
17%29%33%17%1
768
February1st to 15thNight
16%30%31%19%2
704
16th to endNight
16%34%28%18%1
631
March1st to 15thNight
18%30%27%20%4
720
16th to endNight
15%28%32%17%5%1
768
April1st to 15thNight
16%31%28%18%4
718
16th to endNight
17%25%24%22%10%
720
May1st to 15thNight
23%23%21%24%6%
545
16th to endNight
17%23%13%28%16%
375
June1st to 15thNight
11%19%18%30%18%
360
16th to endNight
7%18%19%40%14%
360
July1st to 15thNight
10%14%15%33%25%
340
16th to endNight
5%17%14%32%25%4
503
August1st to 15thNight
12%10%12%36%24%2
533
16th to endNight
12%11%13%32%26%5%
700
September1st to 15thNight
11%11%19%26%27%3
660
16th to endNight
17%11%14%29%23%4
657
October1st to 15thNight
20%14%19%25%16%2
660
16th to endNight
16%19%27%24%11%
704
November1st to 15thNight
14%25%25%21%10%2
700
16th to endNight
14%31%26%19%6%
720
December1st to 15thNight
18%29%24%18%8%
720
16th to endNight
17%31%29%19%2
768
Page generated at 2017-08-13 14:16:48. Version ac04

Copyright 2017 A. Danko


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