Saint Petersburg
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Saint Petersburg clear sky chart from 2005-11-05 to 2018-02-14.

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
63%
16449
20%
48807
17%
16411
66%
16411
30%
30401

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
48%
777
19%
2522
14%
776
55%
776
24%
1579
January16th to endNight
47%
832
25%
2574
19%
832
54%
832
28%
1591
February1st to 15thNight
51%
756
22%
2273
17%
755
57%
755
32%
1373
February16th to endNight
53%
631
24%
1871
14%
631
62%
631
34%
1103
March1st to 15thNight
55%
720
28%
1980
17%
720
64%
720
41%
1141
March16th to endNight
60%
768
26%
2112
21%
768
64%
768
39%
1224
April1st to 15thNight
65%
718
22%
1976
17%
718
69%
718
43%
1114
April16th to endNight
64%
693
26%
1872
20%
693
68%
693
40%
1112
May1st to 15thNight
78%
539
28%
1619
25%
539
81%
539
46%
850
May16th to endNight
76%
561
24%
1683
20%
561
78%
561
38%
985
June1st to 15thNight
69%
540
12%
1620
11%
540
69%
540
25%
1097
June16th to endNight
77%
540
9%
1620
8%
540
78%
540
24%
1127
July1st to 15thNight
74%
510
6%
1530
5%
510
74%
510
20%
1120
July16th to endNight
73%
564
7%
1595
7%
531
74%
531
21%
1131
August1st to 15thNight
78%
539
4%
1702
5%
536
78%
536
23%
1166
August16th to endNight
68%
684
9%
2021
9%
684
68%
684
20%
1456
September1st to 15thNight
66%
720
6%
1980
7%
720
66%
720
18%
1470
September16th to endNight
62%
717
13%
1980
13%
717
63%
717
21%
1433
October1st to 15thNight
70%
720
25%
2000
23%
720
73%
720
35%
1236
October16th to endNight
57%
768
27%
2304
24%
768
63%
768
33%
1368
November1st to 15thNight
64%
760
29%
2281
26%
760
70%
760
40%
1262
November16th to endNight
56%
780
28%
2453
25%
780
64%
780
34%
1418
December1st to 15thNight
55%
780
24%
2535
22%
780
61%
780
30%
1485
December16th to endNight
60%
832
24%
2704
25%
832
63%
832
31%
1560

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
7%425%5%35%6%7%10%41%
49253
Night
7%425%5%35%5%6%9%44%
49013
TransparencyDay
34%11%16%18%14%4
48954
Night
33%8%17%20%14%5%
48816
SeeingDay
9%211%24%30%23%
6232
Night
8%215%32%29%11%
16459

By Month

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
10%7%35%4345%6%9%39%
1746
16th to endDay
10%5%24425%35%7%47%
2000
February1st to 15thDay
11%4343345%5%7%46%
1883
16th to endDay
7%415%323448%54%
1601
March1st to 15thDay
42133245%5%9%57%
1980
16th to endDay
7%32332445%8%53%
2111
April1st to 15thDay
6%21432447%10%51%
1972
16th to endDay
5%31442446%8%54%
2095
May1st to 15thDay
421331446%9%57%
2331
16th to endDay
6%3235%35%6%8%10%45%
2431
June1st to 15thDay
10%5%26%5%46%6%8%11%31%
2340
16th to endDay
6%5%26%5%5%8%8%10%12%28%
2340
July1st to 15thDay
7%326%8%5%8%9%11%12%23%
2340
16th to endDay
7%5%27%8%5%9%9%10%12%22%
2465
August1st to 15thDay
6%325%8%6%9%9%11%13%23%
2244
16th to endDay
9%5%35%7%48%9%9%12%24%
2167
September1st to 15thDay
9%426%7%48%8%9%12%27%
1980
16th to endDay
8%6%36%8%46%6%8%10%28%
1980
October1st to 15thDay
5%415%6%36%5%7%9%43%
1959
16th to endDay
9%4243225%5%8%50%
1920
November1st to 15thDay
5%3134345%5%7%54%
1907
16th to endDay
8%32442445%8%51%
1834
December1st to 15thDay
8%5%245%345%6%9%46%
1755
16th to endDay
6%3245%3445%9%49%
1872
January1st to 15thNight
9%7%26%5%36%45%8%40%
2522
16th to endNight
11%5%25%5%245%5%8%43%
2574
February1st to 15thNight
11%5%25%4235%47%48%
2271
16th to endNight
7%42443446%8%48%
1871
March1st to 15thNight
431442445%7%55%
1980
16th to endNight
6%31443445%7%55%
2112
April1st to 15thNight
6%31242446%10%53%
1976
16th to endNight
5%31443445%8%54%
1872
May1st to 15thNight
321332446%10%58%
1619
16th to endNight
5%3234245%7%7%52%
1682
June1st to 15thNight
10%5%26%5%35%5%7%9%38%
1620
16th to endNight
5%4236%37%6%9%12%36%
1620
July1st to 15thNight
6%426%6%37%7%8%12%32%
1620
16th to endNight
5%425%8%5%7%6%10%12%30%
1703
August1st to 15thNight
5%315%6%46%7%9%13%35%
1713
16th to endNight
8%5%27%6%36%7%8%12%32%
2021
September1st to 15thNight
7%5%36%8%47%8%9%10%28%
1980
16th to endNight
7%6%37%8%37%5%7%11%30%
1980
October1st to 15thNight
6%3245%35%5%6%9%48%
2000
16th to endNight
9%5%245%3346%7%49%
2304
November1st to 15thNight
4324425%5%5%7%53%
2281
16th to endNight
7%4245%35%448%49%
2453
December1st to 15thNight
8%425%5%3445%8%47%
2535
16th to endNight
6%415%435%6%6%8%46%
2704

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
38%6%12%23%15%3
1747
16th to endDay
35%48%19%24%7%
2000
February1st to 15thDay
34%6%10%16%19%11%
1885
16th to endDay
28%5%14%17%22%10%
1601
March1st to 15thDay
22%7%13%27%21%7%
1980
16th to endDay
27%6%12%23%21%7%
2112
April1st to 15thDay
26%7%17%21%21%6%
1972
16th to endDay
26%7%12%21%26%5%
2095
May1st to 15thDay
21%7%15%26%20%7%
2331
16th to endDay
29%11%16%24%16%1
2435
June1st to 15thDay
40%13%21%19%4
2340
16th to endDay
39%16%24%15%3
2340
July1st to 15thDay
45%20%25%6%2
2201
16th to endDay
45%18%24%10%1
2310
August1st to 15thDay
41%21%28%8%
2231
16th to endDay
45%18%23%11%
2167
September1st to 15thDay
43%19%22%11%2
1980
16th to endDay
44%12%17%18%5%1
1980
October1st to 15thDay
32%12%12%17%16%8%
1959
16th to endDay
30%6%11%16%21%12%
1920
November1st to 15thDay
27%5%10%26%23%7%
1907
16th to endDay
29%8%10%21%19%10%
1834
December1st to 15thDay
33%7%14%22%17%4
1755
16th to endDay
30%6%14%23%18%5%
1872
January1st to 15thNight
40%5%12%22%15%3
2522
16th to endNight
37%6%10%18%19%7%
2574
February1st to 15thNight
34%5%10%16%21%11%
2280
16th to endNight
31%6%15%17%21%7%
1871
March1st to 15thNight
27%5%12%27%20%6%
1980
16th to endNight
28%6%11%25%20%8%
2112
April1st to 15thNight
24%6%18%24%20%5%
1976
16th to endNight
28%6%12%23%24%5%
1872
May1st to 15thNight
22%6%15%30%19%6%
1620
16th to endNight
26%9%18%25%17%1
1684
June1st to 15thNight
39%11%21%20%6%
1620
16th to endNight
36%15%25%17%5%
1620
July1st to 15thNight
40%18%30%9%1
1530
16th to endNight
37%17%30%13%
1595
August1st to 15thNight
34%17%36%10%
1702
16th to endNight
41%15%26%14%1
2021
September1st to 15thNight
44%15%24%12%1
1980
16th to endNight
44%11%19%17%42
1980
October1st to 15thNight
30%9%14%20%18%6%
2000
16th to endNight
33%5%10%16%23%10%
2304
November1st to 15thNight
28%411%23%23%8%
2281
16th to endNight
31%6%11%22%17%11%
2453
December1st to 15thNight
34%5%12%26%16%4
2535
16th to endNight
31%7%14%23%16%5%
2704

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
18%7%23%30%17%2
135
16th to endDay
9%13%29%34%11%1
144
February1st to 15thDay
8%9%20%32%25%4
130
16th to endDay
9%135%36%15%
102
March1st to 15thDay
4333%37%18%2
270
16th to endDay
9%5%19%35%26%3
288
April1st to 15thDay
8%122%31%29%5%
270
16th to endDay
7%212%39%27%10%
270
May1st to 15thDay
6%111%34%31%14%
288
16th to endDay
6%6%21%36%28%
331
June1st to 15thDay
16%215%34%30%
315
16th to endDay
6%110%30%49%
315
July1st to 15thDay
5%1429%58%
305
16th to endDay
12%210%28%45%
326
August1st to 15thDay
8%16%32%49%
313
16th to endDay
12%310%31%42%
332
September1st to 15thDay
12%5%13%29%39%
315
16th to endDay
8%414%40%32%
314
October1st to 15thDay
7%111%28%37%13%
315
16th to endDay
11%216%33%28%6%
336
November1st to 15thDay
7%112%31%36%10%
325
16th to endDay
8%116%37%30%4
214
December1st to 15thDay
7%321%39%25%2
135
16th to endDay
28%5%36%38%9%
144
January1st to 15thNight
10%7%25%35%20%1
780
16th to endNight
12%7%27%36%16%
832
February1st to 15thNight
14%423%39%16%
760
16th to endNight
10%425%43%16%
631
March1st to 15thNight
6%428%44%15%1
720
16th to endNight
7%322%43%20%2
768
April1st to 15thNight
6%317%46%24%1
718
16th to endNight
7%319%43%25%
693
May1st to 15thNight
4110%44%34%4
540
16th to endNight
6%17%36%39%9%
563
June1st to 15thNight
10%1420%43%19%
540
16th to endNight
6%211%42%36%
540
July1st to 15thNight
8%15%39%45%
510
16th to endNight
6%27%39%43%
564
August1st to 15thNight
6%17%38%45%
539
16th to endNight
8%1314%39%32%
684
September1st to 15thNight
9%1419%43%22%
720
16th to endNight
11%5%26%41%13%
717
October1st to 15thNight
7%110%37%36%6%
720
16th to endNight
11%219%34%29%3
768
November1st to 15thNight
5%219%41%27%3
760
16th to endNight
8%322%41%21%2
780
December1st to 15thNight
9%421%38%24%1
780
16th to endNight
8%419%38%27%2
832
Page generated at 2018-02-15 10:58:38. Version ac04

Copyright 2018 A. Danko


Saint Petersburg Clear Sky Chart |Charts Home