Agassiz
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Agassiz clear sky chart from 2005-11-06 to 2026-05-17.

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	20% 12% 3 7% 4 4 4 3 4 5% 33%	135706
	Night	22% 13% 3 7% 4 4 4 3 4 5% 30%	135831
Transparency	Day	55% 7% 12% 16% 9% 1	135419
	Night	57% 7% 11% 15% 8% 1	135696
Seeing	Day	31% 16% 27% 19% 6% 1	17015
	Night	32% 11% 26% 22% 8%	25427

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	32% 21% 4 8% 5% 4 4 2 3 4 13%	4125
	11th to 20th	Day	17% 12% 4 7% 3 3 2 2 4 5% 42%	4392
	21st to end	Day	24% 13% 4 8% 5% 4 3 2 3 4 29%	5186
February	1st to 10th	Day	30% 15% 4 7% 5% 4 3 2 4 5% 19%	1853
	11th to 20th	Day	23% 17% 4 7% 5% 4 4 3 5% 5% 22%	1845
	21st to end	Day	22% 22% 4 9% 4 6% 4 3 4 4 19%	1625
March	1st to 10th	Day	20% 16% 4 9% 6% 5% 5% 4 5% 5% 22%	4634
	11th to 20th	Day	16% 19% 5% 12% 6% 5% 4 3 4 4 23%	5110
	21st to end	Day	22% 16% 5% 9% 6% 5% 5% 4 5% 6% 17%	5863
April	1st to 10th	Day	22% 19% 4 10% 5% 5% 4 4 6% 5% 16%	2520
	11th to 20th	Day	20% 15% 4 9% 5% 5% 6% 4 5% 5% 21%	2529
	21st to end	Day	24% 17% 3 8% 4 4 5% 3 5% 6% 22%	2849
May	1st to 10th	Day	15% 12% 4 8% 4 4 4 3 4 5% 38%	6460
	11th to 20th	Day	24% 12% 4 9% 4 5% 5% 4 5% 7% 22%	6362
	21st to end	Day	26% 11% 3 8% 4 4 4 3 5% 7% 24%	6903
June	1st to 10th	Day	26% 11% 4 7% 6% 4 4 3 4 5% 26%	2962
	11th to 20th	Day	31% 12% 3 10% 5% 4 3 3 5% 4 19%	3000
	21st to end	Day	20% 10% 2 7% 5% 5% 4 3 5% 6% 34%	3000
July	1st to 10th	Day	11% 3 1 3 2 3 3 2 5% 6% 61%	6780
	11th to 20th	Day	7% 4 1 3 2 2 2 2 3 5% 68%	6698
	21st to end	Day	13% 4 1 3 2 3 3 3 5% 6% 58%	6874
August	1st to 10th	Day	8% 4 1 3 2 3 3 2 4 6% 63%	4541
	11th to 20th	Day	17% 6% 2 6% 3 3 4 3 6% 8% 42%	4225
	21st to end	Day	19% 7% 2 7% 5% 4 4 2 4 6% 40%	4481
September	1st to 10th	Day	13% 7% 2 5% 4 3 3 3 5% 7% 48%	2400
	11th to 20th	Day	18% 8% 2 8% 4 4 4 3 4 5% 39%	2400
	21st to end	Day	24% 7% 3 5% 5% 3 4 3 5% 6% 36%	2124
October	1st to 10th	Day	21% 9% 3 8% 4 5% 5% 4 5% 6% 30%	3280
	11th to 20th	Day	31% 11% 3 8% 4 3 4 3 4 5% 24%	3261
	21st to end	Day	26% 14% 6% 10% 5% 3 4 3 4 6% 18%	3264
November	1st to 10th	Day	33% 14% 4 8% 4 4 2 3 5% 4 19%	1668
	11th to 20th	Day	34% 16% 5% 8% 3 3 4 2 3 3 20%	1680
	21st to end	Day	31% 16% 3 7% 5% 3 4 3 5% 5% 18%	1680
December	1st to 10th	Day	20% 13% 4 8% 5% 4 5% 3 4 4 29%	2700
	11th to 20th	Day	25% 19% 5% 11% 5% 5% 4 3 4 4 15%	2857
	21st to end	Day	27% 18% 5% 11% 5% 6% 4 3 5% 5% 11%	3575
January	1st to 10th	Night	27% 21% 5% 10% 5% 4 4 3 3 3 14%	8770
	11th to 20th	Night	20% 13% 2 4 3 2 3 2 4 6% 40%	8503
	21st to end	Night	21% 12% 4 8% 5% 4 4 3 4 4 32%	8994
February	1st to 10th	Night	28% 15% 4 8% 5% 4 4 3 5% 5% 20%	2765
	11th to 20th	Night	23% 21% 3 8% 5% 4 3 2 3 4 24%	2662
	21st to end	Night	24% 19% 4 7% 6% 4 3 3 4 4 22%	2180
March	1st to 10th	Night	18% 18% 4 9% 5% 4 4 4 5% 6% 23%	5479
	11th to 20th	Night	18% 20% 5% 9% 5% 3 3 3 4 5% 25%	5109
	21st to end	Night	28% 17% 4 9% 4 5% 4 3 4 5% 18%	5353
April	1st to 10th	Night	22% 18% 3 10% 5% 5% 4 4 5% 4 21%	2100
	11th to 20th	Night	21% 14% 4 8% 5% 5% 4 4 5% 6% 25%	2038
	21st to end	Night	27% 14% 4 8% 5% 5% 4 4 4 6% 22%	1769
May	1st to 10th	Night	17% 10% 4 7% 5% 4 3 3 3 4 41%	3720
	11th to 20th	Night	22% 13% 4 7% 5% 4 4 4 5% 6% 28%	3664
	21st to end	Night	21% 12% 3 7% 5% 4 5% 4 6% 6% 27%	3972
June	1st to 10th	Night	21% 12% 3 7% 6% 4 4 4 5% 4 29%	1434
	11th to 20th	Night	23% 11% 4 8% 6% 4 5% 5% 5% 6% 22%	1400
	21st to end	Night	19% 8% 3 5% 4 4 3 3 5% 7% 39%	1400
July	1st to 10th	Night	10% 4 1 4 3 2 2 2 4 6% 64%	3180
	11th to 20th	Night	5% 3 1 3 2 2 2 2 3 5% 74%	3262
	21st to end	Night	10% 3 1 3 2 3 3 2 4 6% 63%	3969
August	1st to 10th	Night	6% 2 1 2 2 2 3 3 6% 8% 65%	2609
	11th to 20th	Night	15% 6% 2 6% 2 2 3 3 5% 7% 49%	2829
	21st to end	Night	18% 7% 2 6% 4 3 4 3 5% 7% 40%	3433
September	1st to 10th	Night	12% 5% 2 6% 4 4 4 4 5% 6% 48%	2000
	11th to 20th	Night	19% 8% 3 6% 4 4 3 2 3 6% 41%	2000
	21st to end	Night	20% 8% 3 7% 4 4 4 3 4 6% 36%	2271
October	1st to 10th	Night	20% 9% 3 9% 5% 4 5% 4 5% 7% 28%	3920
	11th to 20th	Night	33% 9% 3 5% 3 4 3 3 4 5% 28%	3897
	21st to end	Night	28% 13% 3 8% 4 4 4 3 4 4 24%	4537
November	1st to 10th	Night	34% 14% 3 7% 4 5% 4 3 4 5% 18%	2846
	11th to 20th	Night	34% 15% 3 7% 4 4 4 3 3 4 20%	2940
	21st to end	Night	31% 17% 3 7% 4 4 4 3 3 4 19%	2940
December	1st to 10th	Night	21% 13% 4 7% 5% 4 4 3 4 6% 31%	4700
	11th to 20th	Night	30% 18% 4 9% 6% 4 4 3 4 4 14%	5563
	21st to end	Night	27% 20% 5% 10% 6% 5% 5% 3 4 4 12%	7623

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	77% 5% 6% 9% 3	4125
	11th to 20th	Day	48% 5% 10% 19% 15% 3	4414
	21st to end	Day	62% 5% 6% 17% 11%	5187
February	1st to 10th	Day	70% 6% 7% 9% 7% 2	1853
	11th to 20th	Day	67% 6% 7% 11% 8% 2	1854
	21st to end	Day	73% 6% 6% 10% 4 2	1625
March	1st to 10th	Day	63% 8% 7% 13% 8%	4634
	11th to 20th	Day	67% 7% 8% 14% 4	5110
	21st to end	Day	69% 10% 8% 8% 4	5863
April	1st to 10th	Day	72% 8% 10% 9% 1	2520
	11th to 20th	Day	67% 8% 7% 9% 8% 2	2529
	21st to end	Day	67% 8% 9% 9% 7% 1	2849
May	1st to 10th	Day	51% 9% 13% 20% 8%	6460
	11th to 20th	Day	62% 12% 14% 10% 2	6365
	21st to end	Day	61% 11% 15% 13% 1	6904
June	1st to 10th	Day	63% 7% 12% 11% 4 2	2962
	11th to 20th	Day	71% 7% 10% 10% 2	3000
	21st to end	Day	54% 7% 14% 17% 6% 1	3000
July	1st to 10th	Day	27% 7% 19% 21% 19% 8%	6706
	11th to 20th	Day	22% 5% 17% 30% 24% 3	6617
	21st to end	Day	27% 7% 26% 28% 10% 2	6681
August	1st to 10th	Day	25% 5% 12% 34% 23% 1	4524
	11th to 20th	Day	42% 10% 20% 17% 9% 2	4266
	21st to end	Day	49% 6% 12% 21% 10% 1	4480
September	1st to 10th	Day	39% 7% 13% 23% 13% 5%	2400
	11th to 20th	Day	49% 6% 9% 18% 16% 2	2400
	21st to end	Day	51% 7% 15% 16% 9% 2	2124
October	1st to 10th	Day	56% 7% 11% 19% 7%	3280
	11th to 20th	Day	66% 5% 9% 13% 7% 1	3261
	21st to end	Day	69% 7% 8% 9% 6%	3264
November	1st to 10th	Day	71% 6% 8% 10% 3 1	1668
	11th to 20th	Day	72% 5% 6% 9% 6% 2	1680
	21st to end	Day	68% 7% 5% 10% 7% 2	1680
December	1st to 10th	Day	60% 7% 11% 11% 11%	2700
	11th to 20th	Day	74% 6% 8% 8% 3 1	2859
	21st to end	Day	75% 7% 8% 7% 3	3575
January	1st to 10th	Night	76% 5% 6% 9% 4 1	8770
	11th to 20th	Night	48% 7% 9% 14% 19% 4	8543
	21st to end	Night	57% 5% 9% 15% 13% 1	8994
February	1st to 10th	Night	68% 6% 7% 10% 7% 1	2765
	11th to 20th	Night	67% 6% 6% 11% 7% 2	2664
	21st to end	Night	69% 6% 6% 13% 6% 1	2180
March	1st to 10th	Night	59% 8% 10% 13% 9% 1	5479
	11th to 20th	Night	63% 6% 11% 16% 4	5110
	21st to end	Night	69% 7% 12% 10% 2	5353
April	1st to 10th	Night	68% 7% 12% 10% 2	2100
	11th to 20th	Night	62% 6% 10% 12% 8% 2	2038
	21st to end	Night	65% 7% 10% 11% 5% 1	1769
May	1st to 10th	Night	48% 9% 13% 21% 9%	3717
	11th to 20th	Night	58% 12% 15% 12% 3	3664
	21st to end	Night	57% 12% 17% 13% 1	3972
June	1st to 10th	Night	57% 8% 14% 13% 6% 2	1434
	11th to 20th	Night	62% 9% 13% 13% 3	1400
	21st to end	Night	47% 9% 20% 17% 6% 2	1400
July	1st to 10th	Night	25% 6% 19% 25% 17% 8%	3145
	11th to 20th	Night	16% 5% 19% 29% 27% 3	3220
	21st to end	Night	26% 5% 24% 27% 15% 3	3857
August	1st to 10th	Night	20% 6% 15% 34% 23% 1	2601
	11th to 20th	Night	36% 9% 26% 16% 10% 2	2854
	21st to end	Night	45% 8% 14% 23% 8% 2	3433
September	1st to 10th	Night	37% 8% 15% 21% 15% 4	2000
	11th to 20th	Night	47% 7% 11% 17% 15% 4	2000
	21st to end	Night	51% 7% 14% 17% 8% 2	2271
October	1st to 10th	Night	56% 7% 15% 17% 5%	3920
	11th to 20th	Night	61% 5% 9% 16% 9% 1	3897
	21st to end	Night	64% 7% 9% 13% 7%	4537
November	1st to 10th	Night	71% 7% 8% 10% 4 1	2846
	11th to 20th	Night	71% 5% 8% 9% 6% 2	2940
	21st to end	Night	70% 6% 5% 9% 8% 2	2940
December	1st to 10th	Night	56% 7% 12% 16% 8% 1	4700
	11th to 20th	Night	75% 5% 7% 10% 2 1	5560
	21st to end	Night	75% 8% 7% 7% 3	7623

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	38% 23% 21% 11% 7%	220
	11th to 20th	Day	32% 16% 28% 17% 6%	220
	21st to end	Day	35% 13% 28% 20% 5%	242
February	1st to 10th	Day	40% 19% 23% 15% 3 1	393
	11th to 20th	Day	35% 20% 26% 14% 4	425
	21st to end	Day	38% 19% 27% 13% 3	391
March	1st to 10th	Day	33% 20% 29% 16% 3	540
	11th to 20th	Day	38% 17% 21% 18% 5% 1	540
	21st to end	Day	38% 21% 23% 14% 3	594
April	1st to 10th	Day	37% 20% 24% 14% 4 1	540
	11th to 20th	Day	33% 20% 24% 16% 5% 1	532
	21st to end	Day	41% 19% 19% 16% 5% 1	540
May	1st to 10th	Day	27% 17% 32% 20% 3	543
	11th to 20th	Day	33% 13% 26% 18% 8% 1	553
	21st to end	Day	36% 18% 20% 18% 6% 2	573
June	1st to 10th	Day	31% 18% 28% 18% 4	692
	11th to 20th	Day	38% 21% 24% 13% 3 1	730
	21st to end	Day	29% 15% 26% 21% 7% 1	730
July	1st to 10th	Day	22% 13% 34% 25% 6% 1	721
	11th to 20th	Day	18% 14% 38% 22% 7% 2	688
	21st to end	Day	13% 11% 36% 27% 9% 3	575
August	1st to 10th	Day	16% 10% 32% 27% 11% 4	527
	11th to 20th	Day	15% 11% 33% 27% 11% 3	517
	21st to end	Day	19% 15% 32% 23% 11% 1	583
September	1st to 10th	Day	19% 13% 33% 23% 9% 2	530
	11th to 20th	Day	27% 15% 28% 23% 7% 1	530
	21st to end	Day	30% 17% 25% 20% 7% 1	530
October	1st to 10th	Day	30% 15% 25% 21% 8% 1	530
	11th to 20th	Day	37% 15% 21% 19% 7% 1	530
	21st to end	Day	37% 15% 30% 14% 4	403
November	1st to 10th	Day	40% 12% 31% 14% 3	231
	11th to 20th	Day	43% 16% 21% 14% 5% 1	220
	21st to end	Day	42% 16% 22% 12% 6% 1	220
December	1st to 10th	Day	37% 15% 21% 20% 8%	220
	11th to 20th	Day	44% 13% 29% 11% 3	220
	21st to end	Day	40% 14% 29% 15% 2	242
January	1st to 10th	Night	44% 16% 26% 13% 1	950
	11th to 20th	Night	38% 13% 30% 17% 2	900
	21st to end	Night	34% 12% 34% 18% 2	924
February	1st to 10th	Night	35% 16% 34% 12% 3	840
	11th to 20th	Night	35% 12% 33% 18% 2	824
	21st to end	Night	36% 15% 28% 18% 2	692
March	1st to 10th	Night	32% 11% 28% 23% 6%	840
	11th to 20th	Night	37% 13% 27% 18% 5%	840
	21st to end	Night	35% 13% 30% 16% 5%	924
April	1st to 10th	Night	34% 11% 25% 24% 5% 1	840
	11th to 20th	Night	31% 11% 29% 24% 4	790
	21st to end	Night	36% 9% 27% 21% 7%	509
May	1st to 10th	Night	26% 7% 25% 30% 12%	420
	11th to 20th	Night	26% 7% 19% 32% 15%	406
	21st to end	Night	29% 7% 18% 31% 14%	433
June	1st to 10th	Night	30% 6% 23% 28% 12% 1	400
	11th to 20th	Night	31% 9% 19% 28% 13% 1	400
	21st to end	Night	25% 6% 18% 35% 16% 1	400
July	1st to 10th	Night	17% 3 17% 36% 26% 1	390
	11th to 20th	Night	14% 5% 14% 41% 24% 1	388
	21st to end	Night	10% 2 13% 41% 33% 2	438
August	1st to 10th	Night	11% 3 10% 37% 37% 3	398
	11th to 20th	Night	12% 4 15% 39% 29% 1	545
	21st to end	Night	17% 5% 20% 40% 19%	770
September	1st to 10th	Night	16% 5% 26% 32% 21%	800
	11th to 20th	Night	24% 7% 19% 28% 21% 2	800
	21st to end	Night	26% 11% 22% 32% 10%	800
October	1st to 10th	Night	28% 8% 25% 29% 10%	800
	11th to 20th	Night	37% 9% 26% 22% 6%	800
	21st to end	Night	39% 13% 29% 16% 4	880
November	1st to 10th	Night	44% 11% 33% 11% 1	820
	11th to 20th	Night	45% 12% 26% 15% 2	840
	21st to end	Night	43% 15% 25% 14% 3	840
December	1st to 10th	Night	33% 13% 34% 18% 2	840
	11th to 20th	Night	43% 15% 31% 11% 1	901
	21st to end	Night	40% 16% 34% 10%	1045

Page generated at 2026-05-13 22:58:55. Version ac07

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