The Pas
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the The Pas clear sky chart from 2005-11-06 to 2024-11-25.

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	11% 10% 4 9% 6% 5% 5% 4 6% 7% 33%	105982
	Night	9% 11% 4 10% 6% 6% 5% 4 6% 7% 33%	102050
Transparency	Day	49% 4 15% 24% 8%	105717
	Night	51% 3 15% 22% 8%	101963
Seeing	Day	18% 10% 31% 26% 12% 3	16165
	Night	17% 8% 30% 30% 13% 2	25577

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	5% 16% 9% 21% 9% 7% 6% 4 7% 4 11%	1899
	11th to 20th	Day	4 11% 6% 26% 11% 10% 7% 4 6% 4 12%	2071
	21st to end	Day	8% 18% 6% 11% 7% 6% 7% 5% 7% 7% 19%	2776
February	1st to 10th	Day	7% 10% 4 13% 7% 7% 9% 8% 8% 8% 19%	1520
	11th to 20th	Day	5% 10% 4 10% 8% 6% 9% 7% 7% 6% 26%	1520
	21st to end	Day	4 9% 5% 12% 10% 8% 7% 5% 6% 7% 26%	1570
March	1st to 10th	Day	6% 11% 4 10% 7% 7% 5% 4 6% 8% 32%	3130
	11th to 20th	Day	6% 11% 5% 14% 5% 5% 5% 4 5% 7% 34%	3309
	21st to end	Day	5% 8% 4 8% 5% 4 5% 3 5% 6% 47%	4062
April	1st to 10th	Day	8% 10% 3 8% 5% 5% 5% 4 6% 7% 38%	2289
	11th to 20th	Day	11% 13% 3 8% 6% 5% 5% 3 5% 6% 35%	2442
	21st to end	Day	8% 8% 4 8% 7% 5% 5% 4 6% 7% 37%	2565
May	1st to 10th	Day	15% 11% 3 7% 5% 5% 5% 4 6% 7% 32%	4520
	11th to 20th	Day	19% 9% 3 6% 5% 4 4 3 5% 6% 36%	4705
	21st to end	Day	20% 12% 4 8% 5% 4 4 3 5% 5% 31%	5173
June	1st to 10th	Day	17% 10% 3 7% 5% 5% 5% 4 5% 7% 30%	3017
	11th to 20th	Day	19% 8% 3 8% 5% 5% 5% 5% 7% 7% 29%	3040
	21st to end	Day	15% 8% 3 6% 6% 5% 5% 5% 7% 7% 34%	3040
July	1st to 10th	Day	12% 6% 2 8% 5% 5% 5% 5% 7% 8% 38%	5060
	11th to 20th	Day	8% 4 2 5% 4 4 4 5% 6% 8% 49%	4978
	21st to end	Day	9% 6% 2 6% 5% 4 5% 4 8% 11% 40%	5075
August	1st to 10th	Day	11% 5% 2 7% 5% 5% 5% 3 6% 8% 43%	4412
	11th to 20th	Day	10% 5% 2 6% 4 4 5% 5% 7% 9% 43%	4326
	21st to end	Day	14% 7% 2 7% 5% 4 4 4 6% 9% 38%	4532
September	1st to 10th	Day	14% 6% 2 7% 5% 6% 5% 4 6% 9% 37%	2312
	11th to 20th	Day	17% 8% 3 8% 4 4 4 4 5% 8% 34%	2166
	21st to end	Day	12% 8% 3 8% 5% 3 4 3 5% 8% 40%	2090
October	1st to 10th	Day	15% 10% 3 6% 4 4 5% 4 8% 8% 33%	3247
	11th to 20th	Day	9% 12% 4 8% 6% 6% 5% 5% 6% 8% 31%	2832
	21st to end	Day	12% 16% 5% 10% 6% 5% 6% 5% 5% 6% 22%	3091
November	1st to 10th	Day	15% 19% 7% 13% 7% 5% 5% 3 4 5% 17%	1553
	11th to 20th	Day	12% 16% 5% 15% 9% 6% 5% 4 4 6% 19%	1400
	21st to end	Day	8% 16% 7% 15% 9% 5% 6% 5% 4 6% 20%	1358
December	1st to 10th	Day	5% 13% 6% 15% 11% 8% 9% 5% 6% 7% 16%	1330
	11th to 20th	Day	10% 18% 6% 13% 8% 6% 6% 4 5% 5% 19%	1482
	21st to end	Day	5% 8% 3 12% 7% 6% 5% 4 7% 7% 37%	2090
January	1st to 10th	Night	5% 13% 6% 17% 10% 8% 8% 5% 6% 6% 16%	5046
	11th to 20th	Night	4 10% 6% 25% 12% 7% 8% 5% 7% 4 12%	4831
	21st to end	Night	8% 17% 5% 13% 6% 6% 6% 5% 5% 6% 21%	4876
February	1st to 10th	Night	6% 12% 4 11% 7% 10% 7% 5% 7% 6% 25%	2660
	11th to 20th	Night	4 10% 4 11% 8% 7% 7% 6% 6% 7% 29%	2559
	21st to end	Night	4 9% 4 11% 8% 5% 7% 5% 5% 9% 32%	1889
March	1st to 10th	Night	8% 13% 4 9% 4 4 4 3 5% 7% 38%	3734
	11th to 20th	Night	7% 10% 4 12% 6% 5% 4 3 5% 7% 36%	3654
	21st to end	Night	5% 8% 3 5% 4 4 4 3 5% 6% 52%	3575
April	1st to 10th	Night	9% 10% 3 8% 5% 5% 4 4 6% 7% 40%	1891
	11th to 20th	Night	11% 11% 4 8% 5% 4 4 4 6% 6% 36%	1689
	21st to end	Night	8% 9% 4 9% 6% 6% 5% 4 5% 6% 40%	1611
May	1st to 10th	Night	16% 9% 3 7% 5% 5% 4 4 6% 7% 34%	2449
	11th to 20th	Night	17% 9% 3 7% 5% 5% 5% 4 7% 6% 33%	2201
	21st to end	Night	20% 11% 3 9% 4 4 3 3 3 5% 35%	2414
June	1st to 10th	Night	17% 7% 3 6% 4 4 4 4 6% 7% 38%	1159
	11th to 20th	Night	17% 7% 3 7% 5% 5% 5% 4 6% 8% 34%	1140
	21st to end	Night	13% 7% 3 6% 4 4 5% 5% 7% 7% 37%	1140
July	1st to 10th	Night	9% 6% 2 5% 5% 6% 7% 5% 8% 8% 39%	1900
	11th to 20th	Night	7% 4 2 4 4 3 4 4 7% 9% 53%	1982
	21st to end	Night	7% 4 2 5% 4 5% 4 5% 9% 11% 45%	2475
August	1st to 10th	Night	8% 4 2 4 3 4 4 4 6% 8% 54%	2528
	11th to 20th	Night	10% 4 2 5% 4 5% 4 4 7% 10% 45%	2512
	21st to end	Night	14% 5% 2 6% 4 4 4 4 6% 8% 44%	3135
September	1st to 10th	Night	12% 7% 2 6% 3 5% 4 3 6% 8% 46%	1867
	11th to 20th	Night	16% 7% 2 7% 4 4 4 4 6% 7% 39%	2013
	21st to end	Night	13% 8% 3 6% 4 5% 4 4 6% 6% 41%	2090
October	1st to 10th	Night	10% 8% 3 7% 4 5% 4 4 5% 7% 44%	3684
	11th to 20th	Night	9% 11% 4 9% 5% 5% 5% 4 6% 8% 35%	4097
	21st to end	Night	15% 15% 4 10% 5% 5% 5% 4 5% 6% 26%	4467
November	1st to 10th	Night	14% 20% 6% 13% 7% 6% 4 4 4 5% 19%	2744
	11th to 20th	Night	12% 15% 6% 12% 10% 7% 4 3 6% 6% 21%	3000
	21st to end	Night	8% 18% 6% 14% 9% 7% 4 3 5% 5% 20%	2917
December	1st to 10th	Night	5% 15% 7% 16% 9% 9% 7% 4 6% 5% 18%	2850
	11th to 20th	Night	8% 15% 6% 13% 8% 6% 5% 4 5% 5% 23%	3705
	21st to end	Night	6% 10% 4 10% 7% 6% 6% 4 5% 5% 37%	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	74% 3 11% 10% 2	1899
	11th to 20th	Day	75% 2 8% 12% 2	2092
	21st to end	Day	63% 3 17% 13% 4	2776
February	1st to 10th	Day	59% 5% 13% 16% 7% 1	1520
	11th to 20th	Day	54% 5% 12% 20% 9%	1528
	21st to end	Day	56% 4 11% 21% 9%	1570
March	1st to 10th	Day	50% 4 16% 22% 7% 1	3130
	11th to 20th	Day	50% 5% 14% 18% 13%	3311
	21st to end	Day	38% 3 10% 25% 22% 2	4062
April	1st to 10th	Day	45% 3 13% 24% 14% 1	2289
	11th to 20th	Day	50% 3 10% 22% 15% 1	2442
	21st to end	Day	45% 4 12% 26% 13%	2565
May	1st to 10th	Day	52% 3 10% 26% 9% 1	4520
	11th to 20th	Day	49% 3 12% 24% 10% 2	4709
	21st to end	Day	55% 3 11% 23% 8%	5173
June	1st to 10th	Day	53% 4 11% 19% 13%	3017
	11th to 20th	Day	52% 5% 12% 20% 10% 1	3040
	21st to end	Day	47% 4 14% 26% 8% 1	3040
July	1st to 10th	Day	42% 5% 18% 28% 7%	4981
	11th to 20th	Day	31% 4 17% 41% 7%	4891
	21st to end	Day	37% 4 26% 28% 5%	4915
August	1st to 10th	Day	39% 4 21% 31% 5%	4396
	11th to 20th	Day	36% 4 21% 34% 4	4368
	21st to end	Day	43% 4 23% 25% 6%	4531
September	1st to 10th	Day	44% 4 20% 23% 8% 1	2312
	11th to 20th	Day	49% 4 20% 23% 4	2166
	21st to end	Day	44% 3 18% 28% 7% 1	2090
October	1st to 10th	Day	46% 3 18% 27% 4	3247
	11th to 20th	Day	51% 3 15% 24% 8%	2832
	21st to end	Day	62% 4 16% 16% 2	3091
November	1st to 10th	Day	71% 3 12% 10% 4	1553
	11th to 20th	Day	68% 3 15% 13% 2	1400
	21st to end	Day	67% 4 14% 13% 2	1358
December	1st to 10th	Day	67% 4 15% 10% 4	1330
	11th to 20th	Day	68% 3 14% 11% 3	1483
	21st to end	Day	46% 3 13% 23% 13% 2	2090
January	1st to 10th	Night	68% 3 14% 12% 2	5046
	11th to 20th	Night	73% 2 10% 13% 3	4872
	21st to end	Night	63% 3 15% 14% 4	4876
February	1st to 10th	Night	58% 3 12% 17% 9% 1	2660
	11th to 20th	Night	53% 4 13% 22% 8%	2561
	21st to end	Night	49% 4 15% 23% 10%	1889
March	1st to 10th	Night	46% 3 16% 25% 10% 1	3734
	11th to 20th	Night	48% 3 12% 26% 10%	3654
	21st to end	Night	32% 4 10% 26% 27% 1	3575
April	1st to 10th	Night	44% 2 12% 23% 16% 3	1891
	11th to 20th	Night	49% 3 9% 21% 17% 2	1689
	21st to end	Night	45% 3 8% 25% 17% 2	1611
May	1st to 10th	Night	49% 3 12% 24% 12% 1	2449
	11th to 20th	Night	50% 3 11% 20% 12% 3	2201
	21st to end	Night	53% 3 14% 20% 9%	2414
June	1st to 10th	Night	44% 3 12% 25% 14% 1	1159
	11th to 20th	Night	47% 6% 13% 21% 13% 1	1140
	21st to end	Night	42% 6% 17% 23% 11%	1140
July	1st to 10th	Night	41% 4 22% 25% 8%	1870
	11th to 20th	Night	27% 4 18% 43% 8%	1946
	21st to end	Night	32% 4 29% 30% 5%	2397
August	1st to 10th	Night	27% 4 22% 39% 8%	2520
	11th to 20th	Night	34% 3 22% 33% 7%	2536
	21st to end	Night	38% 4 20% 32% 6%	3135
September	1st to 10th	Night	37% 4 18% 31% 11% 1	1867
	11th to 20th	Night	44% 4 16% 29% 6%	2013
	21st to end	Night	43% 3 14% 28% 11% 1	2090
October	1st to 10th	Night	42% 3 16% 33% 7%	3684
	11th to 20th	Night	47% 2 15% 27% 8%	4097
	21st to end	Night	59% 5% 13% 20% 3	4467
November	1st to 10th	Night	69% 3 12% 12% 4	2744
	11th to 20th	Night	65% 3 15% 14% 3	3000
	21st to end	Night	67% 3 13% 14% 3	2917
December	1st to 10th	Night	66% 4 12% 14% 4	2850
	11th to 20th	Night	62% 3 15% 13% 6%	3703
	21st to end	Night	49% 3 11% 23% 14%	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% 11% 35% 30% 9% 1	180
	11th to 20th	Day	9% 6% 38% 35% 11% 2	234
	21st to end	Day	22% 6% 26% 35% 10% 1	297
February	1st to 10th	Day	13% 9% 36% 29% 11% 2	270
	11th to 20th	Day	11% 9% 33% 30% 14% 2	270
	21st to end	Day	6% 16% 37% 25% 14% 2	225
March	1st to 10th	Day	14% 6% 39% 27% 12% 2	270
	11th to 20th	Day	11% 9% 34% 31% 11% 4	270
	21st to end	Day	14% 13% 30% 27% 14% 2	442
April	1st to 10th	Day	18% 10% 33% 27% 8% 4	469
	11th to 20th	Day	20% 12% 30% 23% 12% 3	640
	21st to end	Day	14% 12% 36% 25% 12% 2	650
May	1st to 10th	Day	20% 12% 30% 25% 11% 1	653
	11th to 20th	Day	17% 12% 33% 24% 12% 3	675
	21st to end	Day	25% 7% 29% 26% 10% 3	734
June	1st to 10th	Day	24% 11% 29% 21% 12% 3	680
	11th to 20th	Day	23% 12% 26% 24% 10% 5%	680
	21st to end	Day	20% 10% 26% 27% 13% 4	680
July	1st to 10th	Day	13% 10% 30% 28% 16% 4	671
	11th to 20th	Day	16% 7% 27% 31% 13% 6%	668
	21st to end	Day	14% 7% 27% 29% 17% 6%	739
August	1st to 10th	Day	14% 9% 27% 26% 18% 5%	676
	11th to 20th	Day	14% 8% 26% 30% 17% 6%	665
	21st to end	Day	22% 7% 29% 26% 13% 2	748
September	1st to 10th	Day	21% 13% 34% 23% 8% 2	522
	11th to 20th	Day	24% 10% 32% 23% 10% 2	376
	21st to end	Day	19% 15% 29% 26% 10% 1	300
October	1st to 10th	Day	24% 11% 31% 25% 8% 2	300
	11th to 20th	Day	24% 15% 37% 14% 9% 2	300
	21st to end	Day	25% 14% 28% 25% 7% 1	330
November	1st to 10th	Day	23% 10% 30% 24% 10% 3	300
	11th to 20th	Day	19% 11% 35% 29% 5% 1	300
	21st to end	Day	16% 13% 41% 22% 6% 2	282
December	1st to 10th	Day	9% 10% 34% 30% 14% 3	270
	11th to 20th	Day	18% 11% 35% 30% 5%	201
	21st to end	Day	8% 9% 27% 36% 16% 4	198
January	1st to 10th	Night	15% 9% 32% 31% 11% 1	950
	11th to 20th	Night	14% 8% 38% 30% 10% 1	950
	21st to end	Night	20% 9% 33% 29% 9% 1	1045
February	1st to 10th	Night	13% 8% 34% 31% 12% 1	950
	11th to 20th	Night	10% 7% 33% 33% 15% 3	929
	21st to end	Night	7% 8% 35% 32% 16% 1	633
March	1st to 10th	Night	13% 7% 26% 35% 18% 1	760
	11th to 20th	Night	13% 10% 33% 29% 14% 2	679
	21st to end	Night	12% 6% 30% 33% 16% 4	627
April	1st to 10th	Night	15% 7% 23% 35% 17% 2	570
	11th to 20th	Night	18% 5% 32% 30% 13% 2	563
	21st to end	Night	14% 9% 33% 36% 8% 1	570
May	1st to 10th	Night	20% 7% 30% 30% 12% 1	570
	11th to 20th	Night	18% 10% 29% 29% 12% 2	561
	21st to end	Night	23% 7% 29% 31% 11%	617
June	1st to 10th	Night	21% 6% 26% 30% 15% 3	399
	11th to 20th	Night	22% 6% 24% 36% 11% 2	380
	21st to end	Night	20% 5% 21% 40% 14% 1	380
July	1st to 10th	Night	14% 5% 26% 37% 17% 1	370
	11th to 20th	Night	12% 5% 25% 37% 19% 2	411
	21st to end	Night	13% 4 25% 35% 19% 4	624
August	1st to 10th	Night	14% 5% 26% 32% 22% 2	567
	11th to 20th	Night	14% 6% 23% 29% 25% 3	564
	21st to end	Night	20% 4 27% 33% 13% 1	627
September	1st to 10th	Night	16% 6% 29% 29% 17% 1	570
	11th to 20th	Night	22% 6% 27% 32% 12%	570
	21st to end	Night	19% 10% 27% 33% 10% 1	570
October	1st to 10th	Night	24% 5% 29% 31% 10% 1	683
	11th to 20th	Night	21% 11% 28% 29% 9% 1	950
	21st to end	Night	27% 11% 27% 23% 10% 1	1045
November	1st to 10th	Night	23% 10% 29% 28% 10% 1	975
	11th to 20th	Night	21% 10% 33% 26% 9% 1	1000
	21st to end	Night	17% 14% 33% 27% 8% 1	973
December	1st to 10th	Night	13% 10% 33% 28% 12% 4	950
	11th to 20th	Night	18% 12% 33% 24% 11% 3	950
	21st to end	Night	17% 7% 29% 29% 15% 3	1045

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