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 2018-02-22.

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
32%
15828
21%
48923
10%
15788
44%
15788
22%
30610

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
19%
778
22%
2661
8%
776
37%
776
16%
1649
January16th to endNight
16%
832
24%
2704
7%
832
37%
832
18%
1670
February1st to 15thNight
17%
764
18%
2482
5%
761
34%
761
16%
1575
February16th to endNight
17%
659
25%
1984
5%
659
40%
659
19%
1245
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
20%
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
27%
545
17%
1625
8%
545
35%
545
19%
1094
May16th to endNight
40%
374
17%
1497
12%
374
50%
374
17%
896
June1st to 15thNight
46%
360
19%
1440
15%
360
57%
360
20%
829
June16th to endNight
46%
360
17%
1440
14%
360
57%
360
22%
826
July1st to 15thNight
49%
340
12%
1360
13%
340
52%
340
17%
868
July16th to endNight
57%
503
16%
1535
12%
471
64%
471
31%
869
August1st to 15thNight
54%
546
18%
1616
11%
543
57%
543
27%
1014
August16th to endNight
57%
764
20%
1910
11%
764
59%
764
33%
1248
September1st to 15thNight
50%
720
25%
1800
14%
720
54%
720
33%
1171
September16th to endNight
50%
717
26%
1962
18%
717
57%
717
29%
1253
October1st to 15thNight
40%
720
22%
2160
18%
720
49%
720
25%
1386
October16th to endNight
33%
768
30%
2304
15%
768
52%
768
30%
1324
November1st to 15thNight
30%
760
24%
2445
12%
760
46%
760
23%
1481
November16th to endNight
25%
780
24%
2659
11%
780
42%
780
19%
1572
December1st to 15thNight
23%
780
18%
2730
6%
780
38%
780
13%
1745
December16th to endNight
18%
832
22%
2912
6%
832
37%
832
15%
1822

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%
49324
Night
14%5%2442445%7%44%
49104
Cloud CoverDay
14%5%244345%5%7%42%
49334
Night
14%5%2442445%7%44%
49108
TransparencyDay
39%6%12%22%16%2
49024
Night
39%5%11%23%17%3
48923
SeeingDay
16%17%24%22%13%5%
6174
Night
15%23%23%24%11%1
15831

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%
1607
16th to endDay
13%6%345%3445%5%43%
1872
February1st to 15thDay
15%6%25%5%24446%40%
1710
16th to endDay
14%6%25%4245%46%41%
1635
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
11%326%6%36%6%7%8%36%
2319
16th to endDay
11%425%5%36%6%6%8%40%
2292
September1st to 15thDay
13%4245%25%45%6%45%
2160
16th to endDay
14%5%25%42445%7%41%
1994
October1st to 15thDay
19%414323347%44%
1800
16th to endDay
15%414323445%48%
1920
November1st to 15thDay
15%6%243245%46%45%
1742
16th to endDay
16%5%24323346%46%
1631
December1st to 15thDay
16%5%343135%5%7%42%
1560
16th to endDay
17%6%25%335%45%6%39%
1664
January1st to 15thNight
17%5%25%424447%42%
2661
16th to endNight
16%6%24423445%44%
2704
February1st to 15thNight
14%6%345%24347%41%
2480
16th to endNight
14%6%24424346%45%
1984
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
10%424435%5%6%8%44%
1627
16th to endNight
11%5%2442446%8%45%
1910
September1st to 15thNight
12%6%24424447%46%
1800
16th to endNight
13%5%25%42435%7%45%
1962
October1st to 15thNight
19%5%14324345%44%
2160
16th to endNight
15%413323347%52%
2304
November1st to 15thNight
14%6%34423345%49%
2445
16th to endNight
15%42432345%7%45%
2659
December1st to 15thNight
17%5%25%5%35%45%5%39%
2730
16th to endNight
16%5%345%2445%6%41%
2912

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%24425%45%7%41%
1607
16th to endDay
14%6%24435%35%5%43%
1872
February1st to 15thDay
15%5%25%5%2445%7%40%
1710
16th to endDay
14%7%3443435%6%41%
1635
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%425%6%35%7%7%8%36%
2319
16th to endDay
11%424435%5%7%8%41%
2292
September1st to 15thDay
13%41443446%7%44%
2160
16th to endDay
14%5%35%43435%7%42%
1994
October1st to 15thDay
19%414323346%46%
1800
16th to endDay
15%5%14323446%48%
1920
November1st to 15thDay
15%6%233245%5%6%45%
1742
16th to endDay
15%6%23333345%47%
1631
December1st to 15thDay
16%5%25%3135%48%42%
1560
16th to endDay
18%5%244345%5%6%39%
1664
January1st to 15thNight
17%42442335%6%43%
2661
16th to endNight
16%6%2342435%6%44%
2704
February1st to 15thNight
15%6%25%43435%6%42%
2473
16th to endNight
15%5%23424447%45%
1984
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%5%145%25%5%6%9%43%
1627
16th to endNight
11%5%24425%5%5%8%44%
1910
September1st to 15thNight
12%6%34333447%46%
1800
16th to endNight
13%5%25%433449%44%
1962
October1st to 15thNight
19%5%14423345%44%
2160
16th to endNight
15%412233347%51%
2304
November1st to 15thNight
14%6%2442334449%
2445
16th to endNight
15%41442445%6%46%
2659
December1st to 15thNight
16%5%25%5%35%45%5%39%
2730
16th to endNight
16%5%25%424447%41%
2912

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%21%13%3
1608
16th to endDay
41%411%23%13%3
1872
February1st to 15thDay
43%5%11%24%12%3
1712
16th to endDay
41%411%26%12%2
1635
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
40%7%12%20%16%1
2306
16th to endDay
36%7%12%23%16%3
2292
September1st to 15thDay
37%5%11%20%20%3
2160
16th to endDay
40%47%23%21%2
1994
October1st to 15thDay
39%5%11%22%18%2
1800
16th to endDay
36%39%28%20%1
1920
November1st to 15thDay
38%412%21%18%4
1742
16th to endDay
39%39%27%17%2
1631
December1st to 15thDay
41%5%15%24%11%2
1560
16th to endDay
45%5%12%23%12%
1664
January1st to 15thNight
41%49%21%17%4
2661
16th to endNight
40%410%26%16%1
2704
February1st to 15thNight
43%312%23%14%2
2482
16th to endNight
39%49%24%19%2
1984
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
35%7%13%22%18%2
1616
16th to endNight
35%6%10%24%19%3
1910
September1st to 15thNight
37%410%23%20%3
1800
16th to endNight
36%5%8%22%22%4
1962
October1st to 15thNight
41%49%23%18%3
2160
16th to endNight
32%39%30%21%2
2304
November1st to 15thNight
38%38%23%18%6%
2445
16th to endNight
37%49%24%19%3
2659
December1st to 15thNight
45%5%11%23%13%1
2730
16th to endNight
42%5%13%23%13%1
2912

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
26%28%26%14%3
103
16th to endDay
16%31%31%18%2
144
February1st to 15thDay
25%25%39%8%
135
16th to endDay
18%25%37%15%3
256
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
13%7%17%31%18%10%
313
16th to endDay
9%6%15%31%22%15%
332
September1st to 15thDay
13%13%18%22%19%13%
315
16th to endDay
19%9%13%30%15%10%
314
October1st to 15thDay
23%9%16%22%21%5%
315
16th to endDay
13%17%30%21%15%2
336
November1st to 15thDay
16%18%27%20%14%2
286
16th to endDay
13%26%32%16%8%1
161
December1st to 15thDay
17%28%24%20%6%2
90
16th to endDay
26%19%34%14%5%
96
January1st to 15thNight
16%30%28%20%4
780
16th to endNight
18%28%32%18%2
832
February1st to 15thNight
17%29%31%20%1
764
16th to endNight
16%33%29%18%1
659
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
13%10%12%36%24%2
546
16th to endNight
12%10%13%33%26%4
764
September1st to 15thNight
12%10%20%26%26%3
720
16th to endNight
16%10%14%29%24%5%
717
October1st to 15thNight
20%13%18%26%17%3
720
16th to endNight
16%18%28%22%13%
768
November1st to 15thNight
15%24%25%23%10%2
760
16th to endNight
14%29%27%20%6%
780
December1st to 15thNight
18%28%24%18%9%
780
16th to endNight
17%29%30%19%2
832
Page generated at 2018-02-23 11:21:27. Version ac04

Copyright 2018 A. Danko


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