Fort Washington Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Fort Washington Park clear sky chart from 2005-11-05 to 2017-09-21.

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
38%
15284
21%
46936
11%
15246
49%
15246
25%
29431

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
22%
717
23%
2415
9%
716
39%
716
20%
1495
January16th to endNight
21%
768
23%
2496
8%
768
39%
768
21%
1567
February1st to 15thNight
22%
702
20%
2287
7%
701
39%
701
22%
1392
February16th to endNight
18%
631
25%
1907
6%
631
41%
631
23%
1189
March1st to 15thNight
24%
720
22%
2007
8%
720
39%
720
26%
1296
March16th to endNight
23%
768
21%
2085
8%
768
34%
768
24%
1406
April1st to 15thNight
26%
718
19%
1796
5%
718
35%
718
29%
1188
April16th to endNight
39%
720
20%
1800
8%
720
44%
720
31%
1189
May1st to 15thNight
36%
576
18%
1656
8%
576
42%
576
23%
1119
May16th to endNight
52%
374
17%
1497
15%
374
58%
374
23%
891
June1st to 15thNight
57%
360
20%
1440
20%
360
65%
360
26%
824
June16th to endNight
56%
360
17%
1440
16%
360
64%
360
25%
828
July1st to 15thNight
57%
340
13%
1360
14%
340
61%
340
20%
859
July16th to endNight
68%
553
17%
1584
13%
520
73%
520
37%
908
August1st to 15thNight
66%
540
17%
1610
13%
537
67%
537
30%
1019
August16th to endNight
60%
764
18%
1910
11%
764
61%
764
32%
1266
September1st to 15thNight
57%
720
25%
1800
15%
720
61%
720
34%
1198
September16th to endNight
54%
681
22%
1867
17%
681
57%
681
29%
1242
October1st to 15thNight
46%
660
24%
1980
21%
660
54%
660
27%
1253
October16th to endNight
37%
704
29%
2112
17%
704
52%
704
31%
1244
November1st to 15thNight
37%
700
25%
2224
14%
700
52%
700
27%
1323
November16th to endNight
33%
720
22%
2455
12%
720
47%
720
23%
1443
December1st to 15thNight
28%
720
19%
2520
8%
720
42%
720
18%
1591
December16th to endNight
21%
768
22%
2688
8%
768
39%
768
19%
1701

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
13%5%2442445%7%42%
47917
Night
14%5%2442445%7%44%
47118
Cloud CoverDay
13%5%2442445%7%42%
47927
Night
14%5%2442445%7%43%
47122
TransparencyDay
39%6%11%23%16%2
47617
Night
38%5%11%23%17%3
46936
SeeingDay
17%8%24%26%16%6%
5714
Night
17%9%29%28%13%1
15290

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
17%5%34415%35%7%41%
1522
16th to endDay
15%6%25%424346%42%
1728
February1st to 15thDay
15%7%25%435%45%6%41%
1575
16th to endDay
14%6%35%6%23446%41%
1563
March1st to 15thDay
15%6%25%424335%45%
1939
16th to endDay
16%6%35%5%24445%41%
2139
April1st to 15thDay
13%5%15%334447%45%
2152
16th to endDay
16%5%24324445%44%
2160
May1st to 15thDay
16%6%345%245%6%8%37%
2304
16th to endDay
14%4245%35%5%5%8%40%
2618
June1st to 15thDay
11%4245%245%6%10%41%
2520
16th to endDay
8%425%435%6%7%9%42%
2520
July1st to 15thDay
10%425%5%35%6%7%10%39%
2520
16th to endDay
6%3245%46%7%8%11%38%
2474
August1st to 15thDay
11%6%25%5%36%7%6%9%35%
2325
16th to endDay
11%4245%36%5%6%9%39%
2292
September1st to 15thDay
12%42442445%8%45%
2160
16th to endDay
14%7%24435%5%5%8%38%
1883
October1st to 15thDay
17%5%24323446%46%
1650
16th to endDay
15%5%14413345%49%
1760
November1st to 15thDay
14%5%12324347%49%
1634
16th to endDay
15%5%24313447%46%
1503
December1st to 15thDay
15%425%424446%44%
1440
16th to endDay
19%6%25%41445%5%40%
1536
January1st to 15thNight
16%6%25%413346%43%
2415
16th to endNight
16%7%24424346%44%
2496
February1st to 15thNight
15%5%2341435%6%45%
2285
16th to endNight
14%7%24313347%45%
1907
March1st to 15thNight
17%42442345%6%44%
1995
16th to endNight
16%5%35%423446%42%
2085
April1st to 15thNight
13%415%42445%6%44%
1796
16th to endNight
16%5%1432445%7%45%
1800
May1st to 15thNight
16%7%35%42445%7%38%
1656
16th to endNight
13%5%14425%5%7%10%40%
1495
June1st to 15thNight
9%324335%5%7%9%44%
1440
16th to endNight
9%335%5%345%7%10%42%
1440
July1st to 15thNight
7%6%36%5%45%6%7%9%38%
1440
16th to endNight
6%224335%5%8%12%44%
1691
August1st to 15thNight
9%315%5%36%6%6%8%43%
1621
16th to endNight
10%5%26%425%6%5%9%41%
1910
September1st to 15thNight
11%5%2442446%7%45%
1800
16th to endNight
12%6%26%42446%8%41%
1867
October1st to 15thNight
17%5%24423335%45%
1980
16th to endNight
14%314323346%52%
2112
November1st to 15thNight
14%5%24422335%51%
2224
16th to endNight
15%42342345%7%45%
2455
December1st to 15thNight
16%6%25%5%2445%6%40%
2520
16th to endNight
17%6%25%424446%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%5%3441435%6%42%
1522
16th to endDay
15%6%25%5%34346%42%
1728
February1st to 15thDay
15%7%25%425%35%5%41%
1575
16th to endDay
14%6%25%6%3335%6%41%
1563
March1st to 15thDay
15%6%24424345%45%
1950
16th to endDay
16%6%35%424436%41%
2138
April1st to 15thDay
13%5%2443445%6%45%
2152
16th to endDay
16%5%24424346%44%
2160
May1st to 15thDay
16%6%244245%6%7%38%
2304
16th to endDay
14%4245%345%5%8%40%
2618
June1st to 15thDay
11%4245%2446%9%42%
2520
16th to endDay
9%324436%6%7%9%42%
2520
July1st to 15thDay
10%426%5%345%7%10%39%
2520
16th to endDay
6%425%5%37%7%8%10%39%
2474
August1st to 15thDay
11%5%25%5%46%7%6%8%36%
2325
16th to endDay
10%4245%36%6%7%8%39%
2292
September1st to 15thDay
12%5%2442346%8%45%
2160
16th to endDay
14%7%24436%5%5%8%38%
1883
October1st to 15thDay
17%5%24313346%46%
1650
16th to endDay
14%5%24413345%49%
1760
November1st to 15thDay
14%5%13223337%49%
1634
16th to endDay
15%5%14313446%46%
1503
December1st to 15thDay
16%415%42445%6%44%
1440
16th to endDay
18%7%25%323446%40%
1536
January1st to 15thNight
16%6%24423447%43%
2415
16th to endNight
16%7%23423336%44%
2496
February1st to 15thNight
15%5%23424447%45%
2278
16th to endNight
14%7%24323346%45%
1907
March1st to 15thNight
17%41442335%7%44%
2007
16th to endNight
16%5%25%423447%41%
2085
April1st to 15thNight
13%5%145%3445%6%44%
1796
16th to endNight
16%5%2432435%7%45%
1800
May1st to 15thNight
15%7%35%5%2445%7%39%
1655
16th to endNight
12%6%234245%7%9%41%
1495
June1st to 15thNight
8%424425%5%8%10%43%
1440
16th to endNight
9%425%5%345%8%9%42%
1440
July1st to 15thNight
7%5%45%6%45%6%6%9%38%
1440
16th to endNight
6%224325%6%8%13%43%
1691
August1st to 15thNight
8%325%5%36%6%6%8%43%
1621
16th to endNight
10%5%36%425%6%5%8%41%
1910
September1st to 15thNight
11%5%2442446%7%45%
1800
16th to endNight
13%5%26%43446%8%40%
1867
October1st to 15thNight
17%5%15%423436%45%
1980
16th to endNight
14%323323346%51%
2112
November1st to 15thNight
14%5%24413335%50%
2224
16th to endNight
15%41442345%7%45%
2455
December1st to 15thNight
16%5%25%5%24446%40%
2520
16th to endNight
17%6%24424346%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%413%22%13%4
1523
16th to endDay
43%310%24%14%3
1728
February1st to 15thDay
42%410%25%14%2
1577
16th to endDay
42%5%10%24%15%1
1563
March1st to 15thDay
41%410%23%16%3
1950
16th to endDay
44%49%19%17%3
2139
April1st to 15thDay
39%49%23%18%4
2152
16th to endDay
40%5%9%18%19%6%
2160
May1st to 15thDay
43%6%11%21%15%1
2304
16th to endDay
40%7%12%24%13%1
2622
June1st to 15thDay
36%7%14%26%14%1
2520
16th to endDay
34%8%15%22%16%2
2520
July1st to 15thDay
38%8%13%20%15%3
2371
16th to endDay
35%8%15%23%15%1
2318
August1st to 15thDay
42%8%12%21%14%1
2312
16th to endDay
38%7%14%22%15%2
2292
September1st to 15thDay
35%6%14%19%20%3
2160
16th to endDay
42%5%10%20%18%1
1883
October1st to 15thDay
39%5%9%26%16%3
1650
16th to endDay
36%38%26%21%2
1760
November1st to 15thDay
35%412%23%18%5%
1634
16th to endDay
37%49%26%18%2
1503
December1st to 15thDay
39%5%13%24%13%3
1440
16th to endDay
44%5%10%24%13%1
1536
January1st to 15thNight
41%410%20%18%4
2415
16th to endNight
41%49%25%17%1
2496
February1st to 15thNight
39%310%24%17%3
2287
16th to endNight
39%39%26%18%2
1907
March1st to 15thNight
39%5%11%26%14%2
2007
16th to endNight
41%6%9%21%17%3
2085
April1st to 15thNight
38%5%9%20%21%3
1796
16th to endNight
38%5%10%20%17%7%
1800
May1st to 15thNight
44%6%11%20%14%3
1656
16th to endNight
36%8%16%22%14%2
1497
June1st to 15thNight
33%8%12%27%15%1
1440
16th to endNight
35%7%15%20%18%2
1440
July1st to 15thNight
41%8%14%18%12%4
1360
16th to endNight
27%8%18%27%16%1
1584
August1st to 15thNight
34%9%13%22%18%1
1610
16th to endNight
37%7%13%22%16%2
1910
September1st to 15thNight
35%7%10%21%20%4
1800
16th to endNight
40%6%9%20%19%4
1867
October1st to 15thNight
41%48%23%18%3
1980
16th to endNight
33%5%8%26%22%4
2112
November1st to 15thNight
37%38%22%20%7%
2224
16th to endNight
37%410%24%19%4
2455
December1st to 15thNight
43%5%10%22%14%2
2520
16th to endNight
43%411%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
26%14%42%14%1
75
16th to endDay
21%26%31%19%1
96
February1st to 15thDay
27%23%37%7%3
90
16th to endDay
20%18%37%23%
222
March1st to 15thDay
19%16%32%25%5%
270
16th to endDay
19%12%36%23%43
288
April1st to 15thDay
17%15%26%27%12%1
270
16th to endDay
20%8%25%27%12%4
270
May1st to 15thDay
28%13%26%16%12%3
288
16th to endDay
20%422%24%21%6%
331
June1st to 15thDay
14%6%24%21%22%9%
315
16th to endDay
12%326%35%17%4
315
July1st to 15thDay
15%18%36%22%7%
305
16th to endDay
6%113%36%30%12%
326
August1st to 15thDay
13%316%28%27%10%
313
16th to endDay
9%111%32%29%15%
332
September1st to 15thDay
14%322%23%17%18%
315
16th to endDay
23%315%26%17%13%
275
October1st to 15thDay
21%5%20%22%23%5%
255
16th to endDay
13%10%30%27%14%2
272
November1st to 15thDay
20%8%26%25%15%3
244
16th to endDay
19%13%30%21%12%3
123
December1st to 15thDay
16%23%23%18%15%3
60
16th to endDay
39%10%28%20%1
64
January1st to 15thNight
21%15%35%22%5%
720
16th to endNight
21%14%38%23%2
768
February1st to 15thNight
20%14%37%25%1
704
16th to endNight
21%18%37%21%1
631
March1st to 15thNight
22%10%39%24%3
720
16th to endNight
19%12%41%20%5%1
768
April1st to 15thNight
16%15%38%24%4
718
16th to endNight
19%6%30%30%11%
720
May1st to 15thNight
18%8%31%29%10%
576
16th to endNight
14%422%36%20%1
375
June1st to 15thNight
10%123%38%23%1
360
16th to endNight
9%321%45%18%
360
July1st to 15thNight
9%221%38%27%
340
16th to endNight
7%15%39%32%4
553
August1st to 15thNight
10%112%45%27%2
540
16th to endNight
13%114%37%30%3
764
September1st to 15thNight
14%118%33%29%2
720
16th to endNight
15%318%32%26%3
681
October1st to 15thNight
19%6%20%29%20%3
660
16th to endNight
16%10%31%25%15%
704
November1st to 15thNight
16%9%31%27%13%2
700
16th to endNight
18%15%28%26%10%
720
December1st to 15thNight
19%11%34%24%8%
720
16th to endNight
22%13%38%22%3
768
Page generated at 2017-09-22 07:35:38. Version ac04

Copyright 2017 A. Danko


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