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 2024-01-31.

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	23% 12% 4 6% 5% 3 4 4 4 5% 29%	74928
	Night	25% 13% 3 6% 5% 3 4 4 4 5% 28%	75211
Transparency	Day	60% 7% 10% 15% 7% 1	74619
	Night	61% 7% 10% 14% 7% 1	75038
Seeing	Day	31% 16% 27% 19% 6% 1	14039
	Night	33% 10% 26% 22% 9%	22545

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	35% 18% 4 6% 5% 3 4 3 3 4 16%	1329
	11th to 20th	Day	27% 15% 5% 8% 6% 3 4 4 4 4 21%	1412
	21st to end	Day	30% 15% 4 6% 5% 2 3 3 4 4 22%	1664
February	1st to 10th	Day	33% 14% 5% 6% 5% 3 3 3 4 5% 18%	1588
	11th to 20th	Day	26% 17% 4 6% 6% 3 4 3 5% 5% 21%	1575
	21st to end	Day	21% 22% 4 7% 5% 4 5% 4 4 4 20%	1390
March	1st to 10th	Day	23% 17% 6% 7% 7% 4 5% 5% 4 4 19%	1803
	11th to 20th	Day	24% 19% 5% 8% 6% 3 4 4 4 5% 18%	1980
	21st to end	Day	26% 17% 5% 8% 6% 4 5% 4 5% 4 16%	2274
April	1st to 10th	Day	25% 19% 5% 9% 5% 3 4 5% 4 6% 16%	2160
	11th to 20th	Day	23% 15% 5% 9% 6% 4 6% 5% 4 5% 18%	2163
	21st to end	Day	26% 17% 4 7% 5% 3 5% 4 4 6% 19%	2441
May	1st to 10th	Day	21% 13% 5% 7% 6% 3 5% 4 5% 5% 27%	2520
	11th to 20th	Day	20% 9% 3 6% 6% 3 5% 5% 6% 8% 28%	2477
	21st to end	Day	26% 11% 5% 7% 6% 3 4 4 3 6% 25%	2723
June	1st to 10th	Day	27% 10% 4 7% 6% 3 4 4 4 6% 24%	2665
	11th to 20th	Day	33% 12% 4 9% 6% 3 4 4 4 4 18%	2700
	21st to end	Day	20% 9% 3 6% 6% 3 4 4 5% 6% 34%	2700
July	1st to 10th	Day	16% 6% 3 6% 4 3 4 4 5% 5% 46%	2700
	11th to 20th	Day	13% 6% 3 5% 4 2 4 5% 4 6% 49%	2674
	21st to end	Day	10% 5% 2 4 3 2 2 4 4 5% 60%	2741
August	1st to 10th	Day	13% 6% 2 4 4 2 4 3 4 5% 53%	2507
	11th to 20th	Day	11% 4 1 3 4 2 3 3 6% 8% 55%	2341
	21st to end	Day	17% 6% 2 5% 6% 3 4 4 4 8% 41%	2475
September	1st to 10th	Day	14% 7% 2 5% 5% 2 3 4 4 7% 46%	2160
	11th to 20th	Day	19% 8% 3 6% 6% 3 5% 4 4 4 39%	2160
	21st to end	Day	25% 6% 3 4 5% 2 4 4 4 5% 37%	1913
October	1st to 10th	Day	23% 11% 3 5% 4 3 4 4 4 6% 35%	1800
	11th to 20th	Day	27% 10% 3 6% 5% 3 4 4 5% 6% 27%	1800
	21st to end	Day	30% 10% 4 7% 5% 2 3 4 4 6% 25%	1818
November	1st to 10th	Day	34% 13% 4 7% 6% 3 3 3 5% 4 19%	1506
	11th to 20th	Day	34% 14% 5% 7% 5% 2 3 2 3 3 22%	1520
	21st to end	Day	33% 15% 4 5% 6% 2 3 4 5% 5% 19%	1520
December	1st to 10th	Day	26% 15% 4 7% 5% 3 4 4 3 3 27%	1520
	11th to 20th	Day	24% 17% 5% 9% 7% 4 4 4 4 4 19%	1767
	21st to end	Day	27% 17% 5% 9% 6% 4 4 5% 5% 5% 12%	2442
January	1st to 10th	Night	34% 17% 4 6% 5% 3 4 3 3 4 18%	2836
	11th to 20th	Night	31% 14% 4 5% 5% 2 4 4 4 7% 21%	2765
	21st to end	Night	27% 16% 4 7% 6% 2 4 4 3 5% 22%	2918
February	1st to 10th	Night	31% 14% 4 6% 5% 3 4 4 4 5% 19%	2371
	11th to 20th	Night	24% 22% 4 7% 5% 3 4 2 3 4 22%	2272
	21st to end	Night	23% 18% 5% 6% 6% 3 4 4 3 5% 24%	1866
March	1st to 10th	Night	24% 14% 4 6% 6% 3 4 4 4 5% 24%	2156
	11th to 20th	Night	26% 16% 4 7% 6% 2 4 4 4 6% 21%	1979
	21st to end	Night	28% 16% 4 7% 4 3 6% 4 4 5% 19%	2081
April	1st to 10th	Night	23% 17% 4 8% 6% 3 5% 4 4 5% 20%	1800
	11th to 20th	Night	22% 14% 5% 7% 6% 4 5% 5% 5% 5% 23%	1744
	21st to end	Night	28% 13% 4 8% 5% 3 5% 5% 4 6% 20%	1517
May	1st to 10th	Night	22% 9% 3 6% 6% 4 4 5% 4 5% 33%	1440
	11th to 20th	Night	17% 10% 3 6% 6% 3 5% 5% 6% 8% 31%	1416
	21st to end	Night	23% 9% 2 6% 5% 4 4 4 5% 5% 32%	1552
June	1st to 10th	Night	22% 11% 4 6% 7% 3 4 5% 5% 4 27%	1292
	11th to 20th	Night	24% 11% 5% 7% 8% 3 5% 6% 5% 6% 21%	1260
	21st to end	Night	17% 7% 3 4 5% 2 4 4 5% 8% 41%	1260
July	1st to 10th	Night	14% 6% 2 5% 5% 2 3 4 5% 5% 48%	1260
	11th to 20th	Night	12% 6% 2 4 4 2 3 4 3 7% 54%	1286
	21st to end	Night	8% 3 1 2 3 2 4 3 4 5% 64%	1576
August	1st to 10th	Night	11% 3 1 2 3 2 3 3 5% 7% 59%	1432
	11th to 20th	Night	7% 4 2 4 3 1 3 3 4 8% 62%	1557
	21st to end	Night	12% 6% 2 4 6% 3 4 4 5% 9% 43%	1880
September	1st to 10th	Night	12% 5% 2 5% 5% 3 4 5% 5% 6% 48%	1800
	11th to 20th	Night	19% 8% 3 5% 5% 3 4 3 3 7% 41%	1800
	21st to end	Night	20% 8% 3 6% 5% 4 4 4 4 6% 36%	2043
October	1st to 10th	Night	22% 8% 3 6% 6% 3 4 4 4 6% 34%	2160
	11th to 20th	Night	29% 10% 3 5% 5% 3 4 4 4 6% 28%	2160
	21st to end	Night	30% 11% 3 6% 5% 2 4 4 4 5% 26%	2537
November	1st to 10th	Night	34% 13% 3 6% 5% 4 5% 3 4 5% 19%	2568
	11th to 20th	Night	35% 13% 3 5% 5% 3 4 3 3 4 21%	2660
	21st to end	Night	33% 16% 3 6% 5% 3 4 4 3 4 20%	2660
December	1st to 10th	Night	25% 12% 4 6% 5% 3 4 4 4 5% 28%	2660
	11th to 20th	Night	31% 16% 5% 8% 7% 3 4 4 4 4 15%	3433
	21st to end	Night	28% 19% 5% 9% 7% 3 5% 4 4 4 13%	5214

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	75% 4 6% 9% 5% 1	1329
	11th to 20th	Day	69% 5% 9% 11% 4 3	1412
	21st to end	Day	66% 5% 8% 13% 7%	1664
February	1st to 10th	Day	72% 5% 6% 9% 6% 1	1588
	11th to 20th	Day	69% 6% 7% 10% 7% 1	1584
	21st to end	Day	72% 6% 6% 11% 4 2	1390
March	1st to 10th	Day	71% 6% 6% 11% 5% 1	1803
	11th to 20th	Day	72% 6% 7% 10% 4 1	1980
	21st to end	Day	75% 7% 8% 8% 2	2274
April	1st to 10th	Day	75% 8% 9% 8% 1	2160
	11th to 20th	Day	71% 8% 5% 8% 8% 1	2163
	21st to end	Day	71% 8% 8% 7% 6% 1	2441
May	1st to 10th	Day	62% 9% 10% 14% 5%	2520
	11th to 20th	Day	58% 10% 13% 15% 4	2480
	21st to end	Day	65% 8% 12% 14% 2	2724
June	1st to 10th	Day	66% 7% 11% 10% 3 3	2665
	11th to 20th	Day	73% 7% 10% 9% 2	2700
	21st to end	Day	54% 7% 14% 18% 6% 1	2700
July	1st to 10th	Day	44% 7% 11% 24% 11% 2	2626
	11th to 20th	Day	39% 8% 14% 26% 11% 2	2593
	21st to end	Day	27% 5% 14% 34% 15% 5%	2589
August	1st to 10th	Day	36% 7% 16% 25% 14% 2	2490
	11th to 20th	Day	31% 8% 18% 26% 16% 3	2341
	21st to end	Day	44% 8% 14% 25% 7% 2	2475
September	1st to 10th	Day	42% 7% 12% 23% 12% 5%	2160
	11th to 20th	Day	51% 5% 8% 17% 17% 3	2160
	21st to end	Day	51% 7% 14% 16% 10% 2	1913
October	1st to 10th	Day	54% 7% 11% 18% 10%	1800
	11th to 20th	Day	60% 7% 9% 15% 8% 2	1800
	21st to end	Day	63% 5% 10% 13% 8%	1818
November	1st to 10th	Day	72% 6% 8% 10% 3 1	1506
	11th to 20th	Day	71% 4 7% 10% 6% 2	1520
	21st to end	Day	68% 7% 5% 10% 8% 3	1520
December	1st to 10th	Day	65% 7% 9% 9% 11% 1	1520
	11th to 20th	Day	69% 5% 9% 11% 5% 1	1769
	21st to end	Day	72% 8% 7% 9% 4	2442
January	1st to 10th	Night	74% 4 4 13% 4 2	2836
	11th to 20th	Night	66% 6% 8% 11% 6% 3	2765
	21st to end	Night	66% 6% 8% 11% 8% 1	2918
February	1st to 10th	Night	69% 6% 8% 10% 6% 1	2371
	11th to 20th	Night	70% 6% 7% 10% 6% 2	2274
	21st to end	Night	66% 6% 7% 13% 6% 1	1866
March	1st to 10th	Night	63% 7% 11% 11% 7% 1	2156
	11th to 20th	Night	67% 5% 10% 12% 5%	1980
	21st to end	Night	71% 8% 12% 8% 1	2081
April	1st to 10th	Night	69% 7% 12% 10% 2	1800
	11th to 20th	Night	65% 6% 9% 12% 8% 1	1744
	21st to end	Night	68% 7% 8% 10% 5% 1	1517
May	1st to 10th	Night	56% 11% 13% 15% 5% 1	1440
	11th to 20th	Night	54% 10% 16% 15% 5%	1416
	21st to end	Night	55% 11% 14% 17% 2	1552
June	1st to 10th	Night	59% 8% 13% 13% 4 2	1292
	11th to 20th	Night	64% 9% 14% 10% 2	1260
	21st to end	Night	45% 9% 21% 17% 6% 2	1260
July	1st to 10th	Night	39% 10% 16% 20% 13% 2	1225
	11th to 20th	Night	34% 9% 16% 28% 11% 2	1244
	21st to end	Night	24% 5% 14% 32% 20% 5%	1488
August	1st to 10th	Night	28% 8% 18% 26% 17% 2	1424
	11th to 20th	Night	26% 8% 20% 24% 18% 3	1557
	21st to end	Night	40% 8% 16% 26% 8% 2	1880
September	1st to 10th	Night	39% 8% 14% 22% 14% 3	1800
	11th to 20th	Night	47% 7% 9% 17% 16% 4	1800
	21st to end	Night	51% 7% 13% 17% 9% 2	2043
October	1st to 10th	Night	53% 6% 12% 21% 8%	2160
	11th to 20th	Night	61% 5% 9% 14% 10% 1	2160
	21st to end	Night	63% 6% 7% 14% 9%	2537
November	1st to 10th	Night	71% 6% 8% 10% 4 1	2568
	11th to 20th	Night	69% 6% 8% 9% 7% 2	2660
	21st to end	Night	70% 5% 4 9% 9% 2	2660
December	1st to 10th	Night	61% 7% 10% 12% 9% 1	2660
	11th to 20th	Night	74% 6% 8% 7% 4 1	3430
	21st to end	Night	73% 8% 6% 7% 5% 1	5214

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	37% 24% 19% 11% 8% 1	180
	11th to 20th	Day	35% 16% 26% 17% 7% 1	180
	21st to end	Day	38% 11% 28% 20% 4	196
February	1st to 10th	Day	46% 19% 19% 13% 3	308
	11th to 20th	Day	39% 20% 23% 14% 3	335
	21st to end	Day	35% 18% 28% 15% 3	306
March	1st to 10th	Day	33% 21% 28% 15% 3	420
	11th to 20th	Day	36% 17% 24% 18% 6%	420
	21st to end	Day	39% 19% 22% 15% 4	462
April	1st to 10th	Day	41% 18% 22% 15% 3 1	420
	11th to 20th	Day	35% 20% 21% 16% 6% 1	412
	21st to end	Day	43% 17% 19% 15% 4 1	420
May	1st to 10th	Day	28% 16% 31% 21% 3	423
	11th to 20th	Day	31% 12% 25% 21% 9% 1	448
	21st to end	Day	36% 17% 20% 18% 7% 2	485
June	1st to 10th	Day	33% 18% 26% 18% 5%	595
	11th to 20th	Day	39% 20% 24% 13% 3 1	630
	21st to end	Day	28% 14% 27% 22% 8% 1	630
July	1st to 10th	Day	23% 13% 31% 26% 6% 1	621
	11th to 20th	Day	19% 15% 36% 23% 6% 2	592
	21st to end	Day	12% 11% 35% 29% 9% 3	487
August	1st to 10th	Day	17% 10% 32% 28% 10% 4	447
	11th to 20th	Day	13% 9% 33% 29% 12% 3	437
	21st to end	Day	19% 15% 33% 21% 11%	495
September	1st to 10th	Day	21% 15% 36% 22% 5% 1	450
	11th to 20th	Day	29% 13% 28% 22% 8% 1	450
	21st to end	Day	30% 16% 24% 21% 8% 1	450
October	1st to 10th	Day	30% 15% 24% 22% 9% 1	450
	11th to 20th	Day	34% 15% 22% 19% 8% 1	450
	21st to end	Day	36% 13% 30% 16% 5% 1	333
November	1st to 10th	Day	40% 11% 31% 15% 3 1	189
	11th to 20th	Day	41% 16% 20% 17% 6% 1	180
	21st to end	Day	43% 16% 19% 13% 7% 1	180
December	1st to 10th	Day	37% 14% 22% 18% 8% 1	180
	11th to 20th	Day	39% 12% 32% 13% 4 1	180
	21st to end	Day	41% 15% 28% 15% 2	198
January	1st to 10th	Night	44% 14% 26% 13% 2	850
	11th to 20th	Night	41% 10% 29% 17% 2	810
	21st to end	Night	35% 11% 34% 17% 2	834
February	1st to 10th	Night	38% 14% 33% 12% 3	720
	11th to 20th	Night	38% 11% 33% 17% 2	704
	21st to end	Night	35% 14% 29% 19% 3	592
March	1st to 10th	Night	33% 11% 27% 23% 6%	720
	11th to 20th	Night	37% 12% 28% 17% 5%	720
	21st to end	Night	36% 11% 29% 17% 6%	792
April	1st to 10th	Night	35% 10% 24% 23% 6% 1	720
	11th to 20th	Night	33% 11% 27% 24% 5%	676
	21st to end	Night	38% 8% 27% 19% 7%	437
May	1st to 10th	Night	28% 7% 24% 28% 13%	360
	11th to 20th	Night	25% 5% 19% 34% 16%	354
	21st to end	Night	30% 6% 17% 31% 15%	389
June	1st to 10th	Night	31% 6% 22% 26% 13% 1	360
	11th to 20th	Night	31% 9% 18% 28% 13% 1	360
	21st to end	Night	23% 5% 18% 37% 17% 1	360
July	1st to 10th	Night	19% 3 15% 35% 28% 1	350
	11th to 20th	Night	16% 5% 14% 39% 25% 1	348
	21st to end	Night	10% 2 13% 40% 32% 2	394
August	1st to 10th	Night	11% 4 10% 34% 39% 3	358
	11th to 20th	Night	9% 4 15% 40% 30% 2	489
	21st to end	Night	16% 4 21% 39% 20%	692
September	1st to 10th	Night	16% 5% 28% 32% 19%	720
	11th to 20th	Night	24% 6% 19% 27% 21% 2	720
	21st to end	Night	26% 10% 20% 33% 11%	720
October	1st to 10th	Night	29% 7% 23% 30% 11%	720
	11th to 20th	Night	36% 8% 26% 24% 7%	720
	21st to end	Night	39% 11% 29% 17% 4	792
November	1st to 10th	Night	44% 10% 33% 12% 1	740
	11th to 20th	Night	45% 12% 26% 15% 2	760
	21st to end	Night	44% 14% 25% 14% 3	760
December	1st to 10th	Night	32% 13% 35% 17% 3	760
	11th to 20th	Night	41% 14% 33% 12% 1	809
	21st to end	Night	42% 15% 32% 10%	935

Page generated at 2024-01-28 02:26:35. Version ac07

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