Prince Albert
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Prince Albert 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	10% 9% 3 8% 5% 5% 5% 4 6% 8% 36%	105661
	Night	8% 9% 4 9% 6% 5% 5% 4 6% 7% 36%	101957
Transparency	Day	43% 8% 18% 23% 7%	105397
	Night	44% 8% 16% 23% 8% 1	101867
Seeing	Day	13% 9% 28% 29% 16% 4	15850
	Night	13% 6% 28% 36% 15% 2	25066

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% 8% 16% 8% 6% 5% 4 5% 5% 19%	1969
	11th to 20th	Day	5% 10% 5% 15% 10% 12% 7% 3 6% 7% 19%	2199
	21st to end	Day	6% 14% 6% 11% 6% 5% 5% 4 5% 7% 30%	2601
February	1st to 10th	Day	8% 9% 5% 11% 8% 7% 6% 7% 7% 8% 24%	1529
	11th to 20th	Day	6% 13% 5% 10% 6% 5% 5% 5% 6% 8% 31%	1665
	21st to end	Day	5% 11% 5% 13% 7% 6% 5% 6% 6% 8% 29%	1456
March	1st to 10th	Day	6% 13% 6% 10% 7% 8% 6% 5% 5% 7% 26%	3130
	11th to 20th	Day	6% 10% 3 9% 6% 5% 5% 4 6% 10% 34%	3383
	21st to end	Day	6% 9% 3 8% 5% 5% 6% 5% 6% 8% 39%	4067
April	1st to 10th	Day	6% 10% 3 8% 5% 5% 5% 4 6% 9% 38%	2280
	11th to 20th	Day	12% 12% 4 8% 6% 4 6% 4 7% 7% 31%	2372
	21st to end	Day	12% 9% 3 8% 6% 5% 5% 4 7% 8% 33%	2660
May	1st to 10th	Day	14% 10% 3 7% 5% 5% 5% 3 7% 7% 34%	4430
	11th to 20th	Day	12% 8% 3 8% 6% 5% 6% 4 6% 7% 34%	4388
	21st to end	Day	18% 10% 3 8% 5% 4 4 4 6% 7% 31%	5476
June	1st to 10th	Day	16% 8% 3 7% 5% 5% 5% 4 7% 8% 32%	3040
	11th to 20th	Day	22% 8% 3 7% 5% 5% 5% 4 7% 7% 26%	3040
	21st to end	Day	15% 6% 2 7% 5% 5% 6% 5% 6% 8% 35%	3040
July	1st to 10th	Day	9% 4 2 5% 4 4 5% 4 7% 10% 47%	5060
	11th to 20th	Day	7% 4 2 5% 3 4 4 4 7% 10% 51%	4878
	21st to end	Day	6% 4 1 5% 4 5% 5% 5% 7% 10% 47%	5051
August	1st to 10th	Day	11% 4 2 5% 4 4 5% 4 7% 9% 44%	4412
	11th to 20th	Day	9% 6% 2 7% 5% 5% 4 3 6% 8% 45%	4343
	21st to end	Day	12% 6% 2 6% 3 4 4 3 6% 8% 46%	4442
September	1st to 10th	Day	10% 6% 2 7% 4 4 4 4 5% 9% 45%	2280
	11th to 20th	Day	13% 8% 3 7% 6% 5% 5% 4 6% 8% 37%	2280
	21st to end	Day	10% 6% 2 5% 5% 4 4 4 5% 8% 47%	2029
October	1st to 10th	Day	10% 7% 3 6% 4 4 5% 3 6% 8% 45%	3170
	11th to 20th	Day	7% 6% 2 7% 5% 6% 5% 5% 8% 12% 37%	3004
	21st to end	Day	8% 10% 4 9% 6% 6% 6% 5% 7% 7% 32%	3009
November	1st to 10th	Day	15% 17% 5% 9% 6% 5% 4 3 6% 6% 25%	1520
	11th to 20th	Day	11% 14% 5% 14% 7% 7% 5% 3 4 6% 24%	1444
	21st to end	Day	9% 16% 7% 12% 7% 5% 5% 3 6% 6% 25%	1330
December	1st to 10th	Day	5% 12% 4 12% 10% 7% 7% 6% 4 6% 27%	1155
	11th to 20th	Day	8% 15% 6% 14% 6% 5% 6% 5% 5% 7% 22%	1439
	21st to end	Day	5% 8% 4 10% 6% 5% 5% 3 6% 5% 44%	2090
January	1st to 10th	Night	5% 12% 6% 19% 11% 6% 5% 4 6% 6% 19%	4973
	11th to 20th	Night	4 9% 5% 15% 11% 11% 7% 5% 6% 7% 19%	4699
	21st to end	Night	6% 13% 5% 12% 7% 6% 6% 4 6% 6% 29%	5059
February	1st to 10th	Night	6% 11% 5% 11% 8% 5% 5% 6% 7% 7% 27%	2660
	11th to 20th	Night	4 11% 4 12% 6% 7% 6% 4 7% 7% 32%	2410
	21st to end	Night	4 9% 4 11% 7% 5% 6% 5% 7% 7% 35%	1998
March	1st to 10th	Night	7% 12% 5% 10% 6% 6% 6% 5% 8% 9% 25%	3734
	11th to 20th	Night	7% 10% 3 7% 5% 6% 7% 4 7% 9% 33%	3593
	21st to end	Night	6% 8% 3 7% 4 5% 4 5% 6% 10% 41%	3577
April	1st to 10th	Night	5% 10% 2 7% 5% 5% 5% 5% 6% 9% 39%	1900
	11th to 20th	Night	12% 11% 4 8% 3 4 4 4 6% 8% 35%	1757
	21st to end	Night	14% 8% 3 7% 5% 5% 5% 4 6% 7% 35%	1520
May	1st to 10th	Night	16% 9% 3 8% 5% 6% 5% 3 6% 7% 31%	2540
	11th to 20th	Night	11% 9% 3 7% 5% 5% 6% 4 6% 8% 37%	2518
	21st to end	Night	16% 8% 3 8% 5% 6% 5% 4 5% 7% 32%	2097
June	1st to 10th	Night	14% 6% 2 5% 4 4 5% 5% 7% 7% 41%	1140
	11th to 20th	Night	20% 7% 3 7% 4 4 4 4 8% 7% 32%	1140
	21st to end	Night	12% 8% 1 5% 4 4 4 4 6% 9% 43%	1140
July	1st to 10th	Night	9% 4 2 5% 4 5% 6% 5% 8% 10% 43%	1900
	11th to 20th	Night	8% 3 1 4 3 3 4 4 6% 8% 56%	2078
	21st to end	Night	4 3 1 4 3 3 5% 3 6% 8% 60%	2502
August	1st to 10th	Night	9% 3 1 4 4 4 5% 4 6% 9% 52%	2528
	11th to 20th	Night	9% 4 2 5% 4 4 5% 4 7% 9% 47%	2496
	21st to end	Night	11% 4 2 5% 3 3 4 3 5% 8% 52%	3222
September	1st to 10th	Night	10% 5% 2 6% 4 4 4 4 5% 7% 50%	1900
	11th to 20th	Night	14% 6% 2 5% 4 4 4 4 6% 7% 45%	1900
	21st to end	Night	8% 5% 2 5% 4 4 5% 4 6% 9% 48%	2147
October	1st to 10th	Night	11% 7% 2 5% 4 3 4 3 6% 7% 48%	3800
	11th to 20th	Night	7% 7% 2 7% 5% 6% 5% 4 6% 6% 46%	3893
	21st to end	Night	10% 11% 4 9% 5% 4 4 3 5% 8% 37%	4547
November	1st to 10th	Night	15% 16% 5% 9% 6% 4 4 4 5% 7% 24%	2659
	11th to 20th	Night	9% 12% 6% 15% 7% 5% 5% 4 6% 7% 23%	2736
	21st to end	Night	8% 14% 5% 11% 7% 6% 6% 4 4 7% 28%	2850
December	1st to 10th	Night	6% 12% 5% 12% 8% 6% 6% 5% 6% 7% 27%	3025
	11th to 20th	Night	8% 13% 5% 14% 8% 7% 6% 4 6% 7% 22%	3753
	21st to end	Night	4 8% 3 8% 5% 4 5% 4 6% 6% 47%	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	63% 6% 12% 14% 5%	1969
	11th to 20th	Day	62% 8% 13% 12% 4	2220
	21st to end	Day	52% 8% 17% 18% 6%	2601
February	1st to 10th	Day	52% 9% 17% 14% 8%	1529
	11th to 20th	Day	48% 7% 14% 22% 10%	1674
	21st to end	Day	51% 7% 14% 18% 9%	1456
March	1st to 10th	Day	52% 9% 16% 16% 7%	3130
	11th to 20th	Day	43% 11% 20% 21% 6%	3384
	21st to end	Day	39% 7% 13% 25% 16%	4067
April	1st to 10th	Day	41% 8% 18% 22% 11% 1	2280
	11th to 20th	Day	50% 7% 15% 20% 8% 2	2372
	21st to end	Day	46% 8% 15% 23% 7% 1	2660
May	1st to 10th	Day	47% 8% 14% 22% 9%	4430
	11th to 20th	Day	42% 11% 12% 24% 9% 1	4392
	21st to end	Day	49% 9% 15% 19% 8%	5476
June	1st to 10th	Day	48% 8% 16% 20% 8% 1	3040
	11th to 20th	Day	54% 9% 13% 17% 7% 1	3040
	21st to end	Day	43% 9% 17% 24% 6%	3040
July	1st to 10th	Day	30% 9% 27% 30% 4	4981
	11th to 20th	Day	28% 8% 18% 42% 4	4792
	21st to end	Day	29% 9% 26% 32% 4	4891
August	1st to 10th	Day	34% 9% 26% 27% 4	4396
	11th to 20th	Day	36% 8% 22% 27% 7%	4385
	21st to end	Day	36% 7% 22% 31% 4	4441
September	1st to 10th	Day	37% 8% 17% 25% 11% 1	2280
	11th to 20th	Day	44% 9% 17% 24% 5%	2280
	21st to end	Day	35% 7% 19% 27% 11% 1	2029
October	1st to 10th	Day	38% 5% 20% 27% 9%	3170
	11th to 20th	Day	39% 6% 23% 26% 5% 1	3004
	21st to end	Day	50% 7% 19% 22% 3	3009
November	1st to 10th	Day	59% 8% 13% 16% 4	1520
	11th to 20th	Day	61% 8% 14% 13% 3	1444
	21st to end	Day	60% 5% 15% 14% 5%	1330
December	1st to 10th	Day	56% 8% 12% 16% 7% 1	1155
	11th to 20th	Day	58% 8% 17% 12% 4	1440
	21st to end	Day	41% 7% 12% 17% 21% 2	2090
January	1st to 10th	Night	62% 8% 11% 14% 5%	4973
	11th to 20th	Night	61% 8% 13% 14% 4	4740
	21st to end	Night	54% 9% 16% 16% 6%	5059
February	1st to 10th	Night	51% 8% 14% 17% 9%	2660
	11th to 20th	Night	49% 7% 14% 21% 9%	2411
	21st to end	Night	44% 7% 14% 23% 12%	1998
March	1st to 10th	Night	49% 10% 16% 21% 4	3734
	11th to 20th	Night	42% 11% 18% 20% 8% 1	3593
	21st to end	Night	36% 7% 10% 24% 23% 1	3577
April	1st to 10th	Night	38% 8% 16% 23% 13% 1	1900
	11th to 20th	Night	46% 6% 13% 19% 13% 2	1757
	21st to end	Night	46% 7% 14% 22% 10% 1	1520
May	1st to 10th	Night	48% 8% 12% 21% 9% 1	2540
	11th to 20th	Night	39% 10% 13% 21% 14% 2	2518
	21st to end	Night	48% 10% 12% 22% 8%	2097
June	1st to 10th	Night	37% 8% 17% 26% 9% 2	1140
	11th to 20th	Night	48% 9% 17% 16% 9%	1140
	21st to end	Night	36% 9% 19% 26% 9% 1	1140
July	1st to 10th	Night	32% 10% 25% 28% 5%	1870
	11th to 20th	Night	25% 7% 15% 43% 9%	2041
	21st to end	Night	22% 7% 25% 39% 7%	2423
August	1st to 10th	Night	28% 6% 25% 33% 7%	2520
	11th to 20th	Night	31% 7% 21% 34% 7%	2520
	21st to end	Night	30% 6% 22% 33% 9%	3222
September	1st to 10th	Night	33% 7% 17% 28% 12% 3	1900
	11th to 20th	Night	37% 7% 17% 30% 9%	1900
	21st to end	Night	31% 8% 16% 29% 15% 1	2147
October	1st to 10th	Night	36% 5% 20% 31% 8%	3800
	11th to 20th	Night	39% 5% 15% 30% 10%	3893
	21st to end	Night	46% 6% 21% 23% 5%	4547
November	1st to 10th	Night	59% 8% 12% 15% 5% 1	2659
	11th to 20th	Night	59% 8% 15% 14% 3	2736
	21st to end	Night	55% 8% 17% 16% 3	2850
December	1st to 10th	Night	54% 9% 14% 18% 5%	3025
	11th to 20th	Night	59% 8% 14% 15% 5%	3751
	21st to end	Night	35% 7% 14% 26% 16% 2	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	14% 5% 33% 28% 14% 6%	180
	11th to 20th	Day	11% 6% 31% 37% 15% 2	180
	21st to end	Day	12% 7% 31% 34% 15% 1	243
February	1st to 10th	Day	11% 6% 30% 36% 15% 2	270
	11th to 20th	Day	8% 5% 29% 37% 21% 1	270
	21st to end	Day	7% 5% 32% 33% 16% 7%	225
March	1st to 10th	Day	10% 9% 29% 36% 15% 1	270
	11th to 20th	Day	10% 7% 37% 30% 13% 4	393
	21st to end	Day	12% 9% 31% 30% 16% 2	506
April	1st to 10th	Day	10% 10% 33% 29% 12% 5%	460
	11th to 20th	Day	17% 12% 30% 27% 11% 4	493
	21st to end	Day	12% 10% 34% 27% 14% 2	650
May	1st to 10th	Day	15% 9% 26% 31% 16% 4	653
	11th to 20th	Day	12% 11% 26% 28% 19% 4	675
	21st to end	Day	17% 9% 24% 26% 20% 4	734
June	1st to 10th	Day	19% 10% 28% 26% 13% 3	680
	11th to 20th	Day	23% 12% 26% 22% 14% 4	680
	21st to end	Day	17% 8% 22% 29% 19% 6%	680
July	1st to 10th	Day	10% 5% 25% 28% 25% 7%	671
	11th to 20th	Day	10% 9% 26% 30% 19% 7%	668
	21st to end	Day	8% 7% 23% 30% 24% 8%	739
August	1st to 10th	Day	12% 6% 22% 31% 22% 7%	676
	11th to 20th	Day	9% 9% 21% 33% 21% 8%	665
	21st to end	Day	17% 8% 25% 32% 14% 4	568
September	1st to 10th	Day	14% 13% 30% 27% 15% 1	490
	11th to 20th	Day	17% 8% 30% 32% 12% 2	490
	21st to end	Day	11% 14% 28% 29% 15% 2	324
October	1st to 10th	Day	16% 9% 30% 27% 16% 2	300
	11th to 20th	Day	14% 10% 36% 27% 10% 4	300
	21st to end	Day	15% 12% 32% 26% 13% 1	330
November	1st to 10th	Day	21% 8% 29% 29% 10% 3	282
	11th to 20th	Day	13% 11% 43% 25% 8%	270
	21st to end	Day	16% 7% 40% 25% 9% 3	270
December	1st to 10th	Day	10% 7% 27% 32% 18% 5%	187
	11th to 20th	Day	14% 6% 34% 36% 10% 1	180
	21st to end	Day	9% 3 33% 27% 19% 10%	198
January	1st to 10th	Night	13% 5% 30% 37% 14% 1	950
	11th to 20th	Night	13% 6% 31% 38% 10% 1	950
	21st to end	Night	14% 7% 33% 36% 9% 1	1045
February	1st to 10th	Night	11% 4 30% 39% 15% 2	950
	11th to 20th	Night	9% 5% 29% 36% 18% 3	752
	21st to end	Night	8% 5% 23% 39% 23% 2	628
March	1st to 10th	Night	13% 5% 27% 36% 18% 2	760
	11th to 20th	Night	12% 7% 31% 36% 13% 1	760
	21st to end	Night	12% 4 27% 37% 16% 3	688
April	1st to 10th	Night	9% 6% 30% 38% 16% 2	570
	11th to 20th	Night	18% 8% 30% 29% 14% 1	563
	21st to end	Night	16% 5% 28% 38% 11% 1	570
May	1st to 10th	Night	14% 6% 31% 35% 13% 1	570
	11th to 20th	Night	11% 8% 28% 36% 16% 1	561
	21st to end	Night	19% 7% 20% 36% 17% 2	429
June	1st to 10th	Night	17% 4 28% 35% 14% 1	380
	11th to 20th	Night	20% 6% 22% 32% 19% 2	380
	21st to end	Night	16% 3 22% 40% 17% 2	380
July	1st to 10th	Night	9% 4 20% 42% 24% 1	370
	11th to 20th	Night	15% 4 21% 35% 22% 3	368
	21st to end	Night	6% 4 21% 37% 29% 3	468
August	1st to 10th	Night	7% 4 22% 37% 27% 3	567
	11th to 20th	Night	10% 3 20% 38% 25% 4	564
	21st to end	Night	12% 4 27% 36% 20% 1	627
September	1st to 10th	Night	12% 5% 25% 37% 19% 2	570
	11th to 20th	Night	18% 5% 22% 40% 15% 1	570
	21st to end	Night	9% 6% 33% 39% 12%	652
October	1st to 10th	Night	18% 5% 30% 35% 10% 2	760
	11th to 20th	Night	14% 6% 30% 36% 13% 1	824
	21st to end	Night	18% 8% 31% 31% 11% 1	1045
November	1st to 10th	Night	22% 6% 31% 32% 8% 2	950
	11th to 20th	Night	14% 7% 33% 32% 12% 2	950
	21st to end	Night	12% 8% 36% 33% 9% 1	950
December	1st to 10th	Night	11% 5% 30% 35% 17% 3	950
	11th to 20th	Night	13% 7% 32% 31% 14% 2	950
	21st to end	Night	12% 4 26% 36% 18% 4	1045

Page generated at 2024-11-03 00:11:09. Version ac07

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