Prince George Centre Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Prince George Centre Observatory clear sky chart from 2005-11-06 to 2024-11-05.

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 Type	Minimum conditions for hour to be usable				Out of hours
	Clear of Clouds	Transparency	Seeing	Sky Brightness
Planetary:	50%	(no limit)	Average	(no limit)	Nighttime Hours
Deep Sky:	70%	Average	(no limit)	5.9	Nighttime Hours
CCD Imaging:	70%	Below Average	Poor	(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

By Month

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 Forecast	Data Points
Cloud Cover	Day	9% 10% 4 9% 6% 6% 6% 5% 6% 8% 32%	105650
	Night	10% 13% 4 9% 6% 6% 6% 4 6% 7% 29%	101958
Transparency	Day	47% 10% 16% 19% 7%	105386
	Night	51% 10% 14% 17% 7% 1	101868
Seeing	Day	14% 12% 27% 26% 17% 4	16410
	Night	17% 11% 24% 29% 17% 2	24198

By Month

Percentage Cloud Cover NW (2006-)
Color Meanings: Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	6% 17% 7% 15% 8% 7% 7% 5% 7% 6% 17%	2095
	11th to 20th	Day	9% 17% 5% 10% 6% 4 4 4 6% 7% 28%	2199
	21st to end	Day	9% 19% 6% 13% 8% 7% 6% 4 7% 7% 15%	2442
February	1st to 10th	Day	14% 16% 4 11% 5% 6% 5% 3 5% 7% 23%	1545
	11th to 20th	Day	9% 17% 4 10% 7% 5% 6% 5% 6% 6% 26%	1665
	21st to end	Day	5% 17% 5% 11% 7% 6% 4 4 5% 7% 30%	1413
March	1st to 10th	Day	4 13% 5% 13% 8% 6% 6% 4 7% 8% 28%	3121
	11th to 20th	Day	6% 12% 4 9% 6% 5% 7% 6% 8% 9% 27%	3490
	21st to end	Day	5% 12% 4 9% 5% 5% 5% 4 6% 7% 38%	3969
April	1st to 10th	Day	5% 12% 6% 13% 8% 7% 6% 6% 6% 6% 24%	2280
	11th to 20th	Day	9% 14% 5% 11% 8% 6% 6% 5% 6% 6% 25%	2428
	21st to end	Day	11% 12% 4 10% 6% 6% 6% 4 5% 7% 28%	2641
May	1st to 10th	Day	7% 10% 4 10% 6% 5% 5% 5% 7% 10% 32%	4420
	11th to 20th	Day	9% 10% 4 11% 8% 7% 7% 5% 8% 8% 24%	4567
	21st to end	Day	12% 11% 4 10% 7% 7% 7% 5% 6% 7% 24%	5374
June	1st to 10th	Day	10% 9% 4 9% 8% 7% 6% 5% 6% 9% 28%	3040
	11th to 20th	Day	13% 9% 4 9% 6% 7% 5% 6% 7% 8% 26%	3040
	21st to end	Day	10% 9% 4 8% 6% 6% 6% 5% 6% 9% 31%	3040
July	1st to 10th	Day	8% 5% 2 5% 4 4 5% 4 6% 7% 49%	5060
	11th to 20th	Day	6% 5% 2 5% 4 4 5% 4 6% 9% 51%	4742
	21st to end	Day	8% 5% 2 8% 6% 6% 7% 5% 7% 9% 36%	5138
August	1st to 10th	Day	4 4 2 4 3 3 4 3 5% 8% 60%	4502
	11th to 20th	Day	8% 5% 2 8% 4 5% 5% 5% 7% 10% 42%	4247
	21st to end	Day	10% 7% 3 9% 6% 5% 7% 5% 6% 8% 33%	4521
September	1st to 10th	Day	9% 6% 3 7% 6% 6% 5% 4 6% 8% 39%	2284
	11th to 20th	Day	9% 7% 3 6% 4 6% 5% 5% 7% 9% 38%	2280
	21st to end	Day	14% 9% 3 10% 6% 5% 5% 5% 6% 7% 29%	2003
October	1st to 10th	Day	14% 12% 4 9% 6% 6% 6% 5% 6% 7% 26%	3180
	11th to 20th	Day	15% 11% 3 8% 6% 6% 6% 5% 6% 7% 27%	3145
	21st to end	Day	10% 11% 3 9% 6% 5% 5% 4 5% 7% 33%	2853
November	1st to 10th	Day	16% 15% 4 10% 6% 5% 5% 4 5% 6% 24%	1520
	11th to 20th	Day	9% 16% 6% 14% 7% 6% 7% 4 6% 7% 19%	1520
	21st to end	Day	11% 20% 7% 9% 7% 6% 6% 4 5% 6% 18%	1214
December	1st to 10th	Day	11% 14% 4 12% 7% 7% 6% 4 7% 7% 20%	1140
	11th to 20th	Day	13% 21% 5% 13% 8% 5% 4 4 5% 6% 18%	1442
	21st to end	Day	6% 16% 5% 13% 7% 6% 6% 5% 6% 7% 24%	2090
January	1st to 10th	Night	9% 17% 5% 13% 8% 7% 7% 4 5% 8% 17%	4878
	11th to 20th	Night	10% 16% 4 11% 7% 6% 5% 3 4 6% 28%	4699
	21st to end	Night	12% 21% 6% 12% 7% 6% 6% 5% 5% 6% 14%	5214
February	1st to 10th	Night	13% 19% 6% 11% 6% 5% 5% 4 4 5% 22%	2632
	11th to 20th	Night	10% 17% 6% 10% 6% 5% 5% 4 5% 6% 27%	2402
	21st to end	Night	8% 14% 4 11% 7% 5% 5% 3 5% 6% 31%	2041
March	1st to 10th	Night	4 14% 5% 11% 7% 6% 7% 5% 8% 7% 27%	3748
	11th to 20th	Night	6% 13% 4 9% 7% 7% 6% 5% 8% 8% 27%	3489
	21st to end	Night	5% 11% 3 7% 5% 5% 5% 4 6% 8% 41%	3684
April	1st to 10th	Night	8% 13% 4 10% 7% 6% 6% 5% 7% 8% 27%	1900
	11th to 20th	Night	8% 14% 4 9% 7% 7% 6% 5% 8% 7% 27%	1700
	21st to end	Night	9% 13% 3 9% 7% 5% 7% 5% 6% 6% 31%	1539
May	1st to 10th	Night	9% 11% 4 9% 7% 5% 6% 4 7% 7% 32%	2540
	11th to 20th	Night	12% 12% 4 8% 6% 6% 7% 5% 7% 9% 23%	2313
	21st to end	Night	14% 15% 4 9% 6% 6% 5% 4 5% 6% 26%	2198
June	1st to 10th	Night	14% 8% 4 8% 7% 7% 6% 5% 8% 8% 27%	1140
	11th to 20th	Night	13% 10% 3 9% 7% 6% 6% 6% 6% 7% 27%	1140
	21st to end	Night	10% 8% 4 8% 7% 6% 8% 5% 7% 9% 28%	1140
July	1st to 10th	Night	5% 6% 2 6% 4 5% 4 4 6% 8% 51%	1900
	11th to 20th	Night	5% 5% 2 5% 4 3 4 4 5% 7% 55%	2215
	21st to end	Night	13% 6% 2 6% 5% 5% 5% 4 6% 9% 39%	2414
August	1st to 10th	Night	4 3 1 3 4 3 3 3 4 7% 67%	2426
	11th to 20th	Night	6% 5% 2 5% 4 4 5% 4 6% 10% 48%	2582
	21st to end	Night	12% 9% 4 9% 5% 5% 5% 5% 6% 8% 33%	3146
September	1st to 10th	Night	11% 8% 3 8% 5% 4 5% 5% 6% 9% 38%	1896
	11th to 20th	Night	10% 8% 2 6% 5% 4 6% 3 6% 6% 43%	1900
	21st to end	Night	14% 11% 3 9% 5% 5% 5% 4 6% 7% 31%	2176
October	1st to 10th	Night	13% 14% 5% 10% 6% 5% 6% 4 6% 7% 24%	3800
	11th to 20th	Night	9% 8% 3 9% 7% 7% 7% 5% 8% 8% 29%	3792
	21st to end	Night	11% 11% 4 8% 6% 6% 6% 4 6% 7% 30%	4697
November	1st to 10th	Night	15% 14% 5% 9% 7% 5% 6% 4 6% 6% 23%	2658
	11th to 20th	Night	10% 15% 4 12% 7% 6% 5% 4 6% 6% 24%	2660
	21st to end	Night	9% 19% 5% 11% 7% 5% 6% 4 6% 7% 19%	2943
December	1st to 10th	Night	10% 15% 5% 10% 6% 7% 6% 4 5% 6% 25%	3040
	11th to 20th	Night	13% 20% 5% 12% 6% 6% 4 4 6% 6% 18%	3750
	21st to end	Night	5% 15% 5% 12% 8% 8% 7% 5% 7% 7% 22%	5566

Transparency (when cloud cover <= 30%)
Color Meanings: Too cloudy to forecast Poor Below Average Average Above average Transparent
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	60% 12% 14% 12% 2	2095
	11th to 20th	Day	55% 9% 13% 8% 11% 4	2220
	21st to end	Day	65% 12% 11% 9% 3	2442
February	1st to 10th	Day	60% 8% 12% 10% 10% 1	1545
	11th to 20th	Day	57% 8% 17% 12% 5%	1674
	21st to end	Day	52% 9% 14% 15% 8% 2	1413
March	1st to 10th	Day	49% 12% 11% 17% 11% 1	3121
	11th to 20th	Day	45% 14% 16% 20% 5%	3490
	21st to end	Day	43% 10% 16% 19% 12% 1	3969
April	1st to 10th	Day	56% 11% 12% 15% 5% 1	2280
	11th to 20th	Day	56% 8% 11% 19% 6%	2428
	21st to end	Day	53% 8% 14% 17% 8%	2641
May	1st to 10th	Day	42% 11% 20% 21% 5% 1	4420
	11th to 20th	Day	49% 14% 14% 16% 7%	4570
	21st to end	Day	52% 12% 14% 17% 4	5375
June	1st to 10th	Day	49% 12% 13% 17% 8%	3040
	11th to 20th	Day	52% 11% 15% 19% 4	3040
	21st to end	Day	46% 12% 17% 19% 6%	3040
July	1st to 10th	Day	32% 8% 12% 25% 22% 2	4981
	11th to 20th	Day	28% 8% 21% 31% 12%	4660
	21st to end	Day	40% 9% 19% 19% 12% 1	4976
August	1st to 10th	Day	23% 7% 17% 38% 15%	4484
	11th to 20th	Day	36% 9% 21% 28% 6%	4289
	21st to end	Day	47% 9% 24% 18% 2	4520
September	1st to 10th	Day	41% 11% 23% 20% 5%	2284
	11th to 20th	Day	41% 11% 18% 24% 6%	2280
	21st to end	Day	51% 12% 16% 16% 4 1	2003
October	1st to 10th	Day	55% 8% 19% 12% 6%	3180
	11th to 20th	Day	52% 10% 17% 19% 2	3145
	21st to end	Day	47% 10% 22% 15% 5%	2853
November	1st to 10th	Day	59% 9% 13% 13% 5% 1	1520
	11th to 20th	Day	61% 11% 13% 11% 4	1520
	21st to end	Day	66% 11% 10% 10% 3	1214
December	1st to 10th	Day	59% 12% 15% 11% 3	1140
	11th to 20th	Day	68% 9% 10% 8% 5%	1444
	21st to end	Day	55% 11% 15% 13% 5%	2090
January	1st to 10th	Night	60% 12% 13% 13% 2	4878
	11th to 20th	Night	58% 7% 11% 6% 13% 6%	4740
	21st to end	Night	69% 12% 8% 8% 3	5214
February	1st to 10th	Night	63% 8% 11% 10% 8% 1	2632
	11th to 20th	Night	57% 9% 14% 14% 6%	2404
	21st to end	Night	52% 7% 14% 17% 8% 2	2041
March	1st to 10th	Night	50% 11% 12% 15% 11% 1	3748
	11th to 20th	Night	47% 12% 11% 23% 6%	3490
	21st to end	Night	37% 10% 13% 23% 16%	3684
April	1st to 10th	Night	50% 11% 13% 19% 7%	1900
	11th to 20th	Night	52% 9% 12% 19% 8%	1700
	21st to end	Night	50% 9% 10% 20% 10% 1	1539
May	1st to 10th	Night	45% 10% 16% 22% 6%	2540
	11th to 20th	Night	47% 14% 15% 18% 6%	2313
	21st to end	Night	55% 11% 11% 20% 4	2198
June	1st to 10th	Night	50% 11% 12% 17% 9% 1	1140
	11th to 20th	Night	52% 11% 12% 19% 5%	1140
	21st to end	Night	47% 12% 17% 19% 5%	1140
July	1st to 10th	Night	30% 7% 12% 27% 23% 1	1870
	11th to 20th	Night	27% 7% 17% 39% 9%	2174
	21st to end	Night	38% 8% 24% 15% 13% 1	2337
August	1st to 10th	Night	19% 6% 15% 42% 17% 1	2419
	11th to 20th	Night	31% 7% 19% 35% 9%	2606
	21st to end	Night	47% 9% 23% 17% 3	3146
September	1st to 10th	Night	40% 11% 19% 23% 6% 1	1896
	11th to 20th	Night	38% 10% 16% 27% 9%	1900
	21st to end	Night	50% 10% 14% 18% 8%	2176
October	1st to 10th	Night	57% 9% 15% 15% 4	3800
	11th to 20th	Night	49% 9% 17% 21% 4	3792
	21st to end	Night	51% 9% 17% 18% 4	4697
November	1st to 10th	Night	59% 11% 12% 13% 5%	2658
	11th to 20th	Night	59% 11% 12% 12% 5%	2660
	21st to end	Night	62% 11% 12% 11% 4	2943
December	1st to 10th	Night	57% 11% 13% 14% 5%	3040
	11th to 20th	Night	66% 11% 10% 9% 4	3747
	21st to end	Night	55% 12% 14% 13% 5%	5566

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
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	13% 16% 29% 26% 13% 3	180
	11th to 20th	Day	14% 21% 27% 25% 11% 2	180
	21st to end	Day	22% 20% 27% 18% 12% 2	198
February	1st to 10th	Day	24% 22% 24% 19% 8% 3	235
	11th to 20th	Day	15% 15% 34% 25% 9% 2	365
	21st to end	Day	15% 22% 30% 22% 8% 3	307
March	1st to 10th	Day	14% 16% 29% 24% 13% 3	445
	11th to 20th	Day	14% 18% 32% 23% 12% 2	460
	21st to end	Day	15% 22% 25% 20% 14% 4	506
April	1st to 10th	Day	12% 18% 32% 25% 11% 2	460
	11th to 20th	Day	15% 17% 30% 19% 15% 4	452
	21st to end	Day	13% 17% 31% 24% 13% 3	460
May	1st to 10th	Day	15% 14% 29% 26% 12% 3	463
	11th to 20th	Day	12% 9% 27% 30% 18% 4	598
	21st to end	Day	13% 10% 25% 27% 22% 4	857
June	1st to 10th	Day	14% 11% 27% 28% 17% 2	870
	11th to 20th	Day	17% 9% 25% 27% 18% 4	870
	21st to end	Day	12% 6% 25% 29% 24% 4	870
July	1st to 10th	Day	13% 7% 19% 31% 26% 4	856
	11th to 20th	Day	11% 9% 22% 27% 25% 6%	669
	21st to end	Day	9% 6% 22% 33% 26% 5%	739
August	1st to 10th	Day	6% 6% 22% 31% 28% 7%	550
	11th to 20th	Day	8% 9% 25% 30% 22% 7%	477
	21st to end	Day	11% 12% 28% 29% 16% 4	539
September	1st to 10th	Day	14% 10% 25% 28% 19% 4	490
	11th to 20th	Day	12% 11% 27% 25% 20% 5%	490
	21st to end	Day	19% 17% 33% 18% 11% 2	490
October	1st to 10th	Day	24% 11% 23% 24% 14% 3	490
	11th to 20th	Day	22% 14% 30% 22% 12% 1	486
	21st to end	Day	20% 17% 27% 24% 10% 2	252
November	1st to 10th	Day	31% 16% 24% 19% 8% 3	188
	11th to 20th	Day	17% 19% 29% 22% 8% 5%	180
	21st to end	Day	22% 15% 32% 18% 10% 3	180
December	1st to 10th	Day	17% 8% 28% 27% 16% 3	180
	11th to 20th	Day	14% 12% 28% 29% 16% 2	180
	21st to end	Day	21% 12% 25% 26% 15% 2	198
January	1st to 10th	Night	22% 15% 28% 25% 8% 2	937
	11th to 20th	Night	21% 13% 28% 25% 12%	850
	21st to end	Night	20% 16% 30% 22% 11% 1	935
February	1st to 10th	Night	24% 16% 21% 25% 12% 1	774
	11th to 20th	Night	18% 11% 26% 31% 13% 1	744
	21st to end	Night	15% 13% 25% 31% 14% 3	628
March	1st to 10th	Night	15% 13% 26% 29% 15% 2	760
	11th to 20th	Night	14% 13% 29% 29% 14% 1	760
	21st to end	Night	12% 11% 21% 30% 23% 4	836
April	1st to 10th	Night	14% 11% 20% 33% 19% 3	760
	11th to 20th	Night	13% 8% 27% 31% 18% 4	572
	21st to end	Night	12% 11% 28% 31% 18% 1	399
May	1st to 10th	Night	14% 9% 21% 37% 16% 3	380
	11th to 20th	Night	13% 3 22% 35% 23% 3	374
	21st to end	Night	13% 8% 19% 32% 25% 2	411
June	1st to 10th	Night	16% 6% 24% 34% 18% 3	380
	11th to 20th	Night	18% 4 19% 33% 22% 3	380
	21st to end	Night	12% 4 19% 36% 28% 1	380
July	1st to 10th	Night	10% 3 16% 40% 29% 1	370
	11th to 20th	Night	12% 3 16% 36% 30% 3	368
	21st to end	Night	13% 3 14% 36% 28% 6%	416
August	1st to 10th	Night	8% 3 14% 30% 38% 7%	378
	11th to 20th	Night	8% 3 15% 37% 35% 4	422
	21st to end	Night	17% 4 19% 33% 23% 4	627
September	1st to 10th	Night	14% 5% 17% 34% 27% 2	756
	11th to 20th	Night	13% 6% 16% 30% 28% 6%	760
	21st to end	Night	20% 11% 25% 26% 16% 2	760
October	1st to 10th	Night	21% 9% 20% 31% 16% 3	760
	11th to 20th	Night	21% 9% 25% 28% 15% 1	760
	21st to end	Night	21% 14% 29% 25% 11% 1	836
November	1st to 10th	Night	24% 16% 23% 27% 8% 2	760
	11th to 20th	Night	19% 17% 29% 25% 9% 1	760
	21st to end	Night	20% 16% 29% 25% 8% 2	981
December	1st to 10th	Night	17% 13% 25% 31% 13% 2	1040
	11th to 20th	Night	22% 12% 27% 27% 11% 1	1040
	21st to end	Night	17% 13% 30% 28% 11% 1	1144

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