Leominster
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Leominster clear sky chart from 2005-11-05 to 2018-04-23.

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
25%
15745
18%
49500
7%
15713
38%
15713
20%
32319

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
13%
780
19%
2716
5%
776
31%
776
15%
1740
January16th to endNight
12%
832
19%
2912
3%
832
33%
832
14%
1863
February1st to 15thNight
12%
764
16%
2384
3%
761
28%
761
15%
1613
February16th to endNight
14%
683
21%
2049
5%
683
33%
683
16%
1375
March1st to 15thNight
15%
780
16%
2340
5%
780
28%
780
15%
1640
March16th to endNight
20%
832
23%
2190
6%
832
33%
832
20%
1487
April1st to 15thNight
20%
778
17%
1946
3%
778
29%
778
19%
1390
April16th to endNight
22%
623
18%
1737
4%
623
33%
623
20%
1178
May1st to 15thNight
21%
540
15%
1620
6%
540
31%
540
17%
1123
May16th to endNight
26%
394
11%
1516
7%
393
35%
393
14%
1014
June1st to 15thNight
30%
360
12%
1440
7%
360
42%
360
15%
957
June16th to endNight
33%
360
12%
1440
11%
360
43%
360
20%
898
July1st to 15thNight
45%
340
12%
1360
15%
340
51%
340
22%
826
July16th to endNight
46%
376
14%
1418
14%
354
53%
354
22%
841
August1st to 15thNight
44%
488
16%
1559
10%
486
50%
486
26%
961
August16th to endNight
50%
738
20%
1884
10%
738
54%
738
34%
1215
September1st to 15thNight
37%
720
20%
1851
8%
720
44%
720
32%
1191
September16th to endNight
45%
717
27%
1980
17%
717
52%
717
34%
1213
October1st to 15thNight
34%
720
22%
2019
11%
720
44%
720
26%
1286
October16th to endNight
23%
768
18%
2490
6%
768
38%
768
19%
1629
November1st to 15thNight
28%
760
20%
2472
10%
760
42%
760
21%
1586
November16th to endNight
22%
780
22%
2535
8%
780
39%
780
18%
1604
December1st to 15thNight
19%
780
16%
2730
4%
780
34%
780
15%
1777
December16th to endNight
13%
832
19%
2912
4%
832
31%
832
15%
1912

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
16%6%25%5%3445%7%39%
50024
Night
16%6%2442445%6%41%
49670
Cloud CoverDay
16%6%245%3445%6%39%
50034
Night
16%6%2442445%6%41%
49675
TransparencyDay
43%6%11%21%14%2
49712
Night
42%6%11%21%15%2
49500
SeeingDay
22%15%31%20%8%2
6542
Night
21%15%34%22%6%
15745

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
13%7%25%5%35%35%6%40%
1552
16th to endDay
14%6%25%43445%6%42%
1664
February1st to 15thDay
16%5%26%5%36%5%5%7%33%
1804
16th to endDay
14%8%25%6%25%35%6%38%
1710
March1st to 15thDay
20%8%245%34446%34%
1940
16th to endDay
16%6%35%5%34436%41%
2382
April1st to 15thDay
16%7%25%6%35%5%46%36%
2332
16th to endDay
17%5%25%43345%7%41%
2338
May1st to 15thDay
24%7%36%433345%32%
2332
16th to endDay
17%5%25%5%345%48%37%
2608
June1st to 15thDay
25%5%2442445%8%32%
2520
16th to endDay
15%5%25%5%35%6%7%7%34%
2520
July1st to 15thDay
12%5%25%6%36%6%6%8%36%
2520
16th to endDay
13%426%5%35%6%5%8%37%
2654
August1st to 15thDay
12%5%25%6%45%5%5%8%38%
2379
16th to endDay
11%5%25%5%345%5%9%42%
2315
September1st to 15thDay
13%5%14435%35%7%44%
2109
16th to endDay
14%5%24323336%50%
1980
October1st to 15thDay
20%5%23424446%41%
1939
16th to endDay
17%4245%24446%42%
1734
November1st to 15thDay
18%6%2342344344%
1716
16th to endDay
16%5%23434335%45%
1752
December1st to 15thDay
17%6%25%5%34446%39%
1560
16th to endDay
20%6%3442445%6%36%
1664
January1st to 15thNight
14%7%35%434446%42%
2716
16th to endNight
13%8%35%425%446%40%
2912
February1st to 15thNight
14%8%35%425%45%6%38%
2383
16th to endNight
15%8%35%42445%6%39%
2049
March1st to 15thNight
18%7%3442445%6%36%
2327
16th to endNight
14%7%25%5%24345%44%
2190
April1st to 15thNight
16%6%26%5%3445%7%37%
1946
16th to endNight
21%5%15%5%23345%41%
1737
May1st to 15thNight
22%6%25%43345%6%36%
1620
16th to endNight
20%6%25%4345%5%7%35%
1514
June1st to 15thNight
24%435%42235%7%35%
1440
16th to endNight
16%423425%45%8%41%
1440
July1st to 15thNight
13%4245%35%5%6%8%41%
1440
16th to endNight
11%4245%35%5%5%9%42%
1514
August1st to 15thNight
10%425%425%5%7%8%43%
1569
16th to endNight
13%31442447%8%45%
1884
September1st to 15thNight
14%5%1342336%7%48%
1851
16th to endNight
13%413323346%52%
1980
October1st to 15thNight
18%41431335%5%47%
2019
16th to endNight
19%6%24423346%40%
2490
November1st to 15thNight
16%6%25%424345%45%
2472
16th to endNight
16%6%24424446%43%
2535
December1st to 15thNight
18%6%25%424447%38%
2730
16th to endNight
17%7%35%32346%6%39%
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
14%7%25%435%446%41%
1552
16th to endDay
14%6%245%25%35%5%44%
1664
February1st to 15thDay
16%6%36%5%35%6%5%7%33%
1804
16th to endDay
15%8%26%425%345%39%
1710
March1st to 15thDay
21%7%34424446%34%
1950
16th to endDay
16%7%345%24345%41%
2382
April1st to 15thDay
17%7%25%6%34446%36%
2332
16th to endDay
17%424434447%42%
2338
May1st to 15thDay
23%9%36%43335%5%32%
2332
16th to endDay
16%5%25%5%2445%8%37%
2608
June1st to 15thDay
24%5%2442445%8%32%
2520
16th to endDay
15%5%246%446%6%8%34%
2520
July1st to 15thDay
12%5%35%5%36%6%5%8%36%
2520
16th to endDay
12%425%5%35%5%6%8%38%
2654
August1st to 15thDay
11%5%25%5%46%5%5%8%38%
2379
16th to endDay
11%425%5%245%5%7%44%
2315
September1st to 15thDay
14%5%144245%47%45%
2109
16th to endDay
13%5%24423335%50%
1980
October1st to 15thDay
19%424324446%41%
1939
16th to endDay
16%5%24424446%43%
1734
November1st to 15thDay
19%6%2342344444%
1716
16th to endDay
17%5%244245%35%45%
1752
December1st to 15thDay
17%6%246%2345%6%39%
1560
16th to endDay
21%7%244245%5%436%
1664
January1st to 15thNight
15%7%25%424445%42%
2716
16th to endNight
14%9%35%43435%6%40%
2912
February1st to 15thNight
14%8%36%5%2435%6%38%
2376
16th to endNight
16%8%25%424446%39%
2049
March1st to 15thNight
19%7%35%424446%36%
2340
16th to endNight
13%8%36%433245%44%
2189
April1st to 15thNight
16%6%26%6%3445%6%37%
1946
16th to endNight
20%425%5%33335%41%
1737
May1st to 15thNight
22%6%2443345%5%36%
1620
16th to endNight
19%6%25%43446%7%36%
1514
June1st to 15thNight
23%5%3442335%8%34%
1440
16th to endNight
15%4245%3446%8%41%
1440
July1st to 15thNight
13%4235%36%45%8%41%
1440
16th to endNight
11%4245%25%5%5%8%43%
1514
August1st to 15thNight
9%4146%35%5%7%8%43%
1569
16th to endNight
13%313425%45%9%46%
1884
September1st to 15thNight
14%5%1432335%7%47%
1851
16th to endNight
13%413323346%52%
1980
October1st to 15thNight
18%42331335%5%46%
2019
16th to endNight
19%7%24423346%40%
2490
November1st to 15thNight
16%5%35%424345%44%
2472
16th to endNight
17%6%23424445%43%
2535
December1st to 15thNight
18%7%24434346%39%
2730
16th to endNight
17%7%35%3235%5%6%38%
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
42%6%9%24%12%3
1553
16th to endDay
40%5%14%24%13%1
1664
February1st to 15thDay
47%7%12%19%11%1
1807
16th to endDay
46%5%9%20%14%2
1710
March1st to 15thDay
50%411%18%11%3
1950
16th to endDay
45%5%9%19%15%5%
2382
April1st to 15thDay
48%5%10%18%14%3
2332
16th to endDay
42%5%8%20%19%4
2338
May1st to 15thDay
53%5%7%18%12%2
2332
16th to endDay
44%6%13%20%13%1
2612
June1st to 15thDay
49%7%12%20%9%
2520
16th to endDay
44%9%12%19%13%
2520
July1st to 15thDay
42%9%11%21%13%1
2371
16th to endDay
40%7%14%21%12%2
2487
August1st to 15thDay
42%7%14%22%12%1
2365
16th to endDay
37%6%11%26%15%2
2315
September1st to 15thDay
37%7%10%21%19%2
2109
16th to endDay
36%38%24%24%2
1980
October1st to 15thDay
43%5%10%24%13%3
1939
16th to endDay
41%6%12%23%14%1
1734
November1st to 15thDay
43%5%12%23%13%1
1716
16th to endDay
40%5%12%22%16%2
1752
December1st to 15thDay
45%5%15%16%15%
1560
16th to endDay
48%6%12%18%12%1
1664
January1st to 15thNight
44%5%12%21%14%2
2716
16th to endNight
44%412%20%15%2
2912
February1st to 15thNight
46%6%13%19%12%1
2384
16th to endNight
45%5%10%21%14%3
2049
March1st to 15thNight
48%6%10%20%11%2
2340
16th to endNight
43%48%18%19%5%
2190
April1st to 15thNight
45%6%10%18%16%2
1946
16th to endNight
45%48%19%16%5%
1737
May1st to 15thNight
48%6%10%18%14%2
1620
16th to endNight
46%8%13%17%11%1
1516
June1st to 15thNight
48%6%12%21%9%1
1440
16th to endNight
39%9%12%22%14%1
1440
July1st to 15thNight
38%8%13%25%14%
1360
16th to endNight
38%7%15%26%9%2
1418
August1st to 15thNight
35%9%15%22%16%1
1559
16th to endNight
33%8%12%27%17%
1884
September1st to 15thNight
36%6%13%24%18%1
1851
16th to endNight
34%47%25%25%2
1980
October1st to 15thNight
39%5%12%24%15%3
2019
16th to endNight
44%5%12%23%13%
2490
November1st to 15thNight
42%5%11%19%17%3
2472
16th to endNight
42%5%12%22%14%2
2535
December1st to 15thNight
45%5%13%22%11%
2730
16th to endNight
45%6%12%21%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
20%31%30%15%3
90
16th to endDay
29%20%36%13%
96
February1st to 15thDay
26%23%35%11%2
258
16th to endDay
24%24%34%13%3
291
March1st to 15thDay
33%19%33%12%2
330
16th to endDay
22%23%34%12%6%
352
April1st to 15thDay
25%19%35%12%7%
330
16th to endDay
22%14%35%17%6%2
289
May1st to 15thDay
33%19%24%15%6%1
288
16th to endDay
19%13%35%23%6%1
331
June1st to 15thDay
25%13%30%21%8%
315
16th to endDay
17%12%38%24%5%2
315
July1st to 15thDay
18%9%29%29%11%1
305
16th to endDay
12%7%31%31%12%3
326
August1st to 15thDay
12%9%31%28%15%2
313
16th to endDay
12%6%30%26%18%5%
332
September1st to 15thDay
17%10%29%23%12%6%
315
16th to endDay
18%8%24%20%13%14%
314
October1st to 15thDay
20%9%26%24%14%4
315
16th to endDay
23%16%30%22%7%
289
November1st to 15thDay
24%15%29%20%9%1
280
16th to endDay
25%20%25%18%8%1
282
December1st to 15thDay
27%27%25%11%7%
90
16th to endDay
37%27%27%7%1
96
January1st to 15thNight
22%19%40%15%1
780
16th to endNight
23%20%38%15%1
832
February1st to 15thNight
20%21%40%15%1
764
16th to endNight
24%21%36%15%2
683
March1st to 15thNight
26%20%35%16%1
780
16th to endNight
20%21%33%19%4
832
April1st to 15thNight
23%21%33%19%3
778
16th to endNight
23%17%33%19%5%
623
May1st to 15thNight
25%15%34%20%3
540
16th to endNight
21%11%35%26%5%
394
June1st to 15thNight
23%8%32%28%6%
360
16th to endNight
16%242%33%4
360
July1st to 15thNight
12%433%39%9%
340
16th to endNight
10%333%38%13%
376
August1st to 15thNight
11%233%40%10%
488
16th to endNight
14%225%38%16%1
738
September1st to 15thNight
16%6%34%29%12%
720
16th to endNight
16%7%27%25%19%2
717
October1st to 15thNight
20%11%29%24%11%2
720
16th to endNight
24%16%31%19%7%
768
November1st to 15thNight
20%14%32%21%9%1
760
16th to endNight
22%18%32%18%6%1
780
December1st to 15thNight
25%19%33%17%4
780
16th to endNight
25%19%37%14%1
832
Page generated at 2018-04-24 10:02:59. Version ac04

Copyright 2018 A. Danko


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