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 2025-01-22.

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	21% 12% 3 7% 4 4 4 3 4 5% 31%	109046
	Night	23% 14% 3 7% 4 4 4 3 4 5% 29%	108916
Transparency	Day	57% 7% 10% 15% 9% 2	108800
	Night	59% 7% 10% 14% 8% 2	108808
Seeing	Day	31% 16% 27% 19% 6% 1	15313
	Night	32% 10% 26% 22% 9%	23764

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% 23% 4 7% 4 3 4 2 3 4 14%	2289
	11th to 20th	Day	22% 15% 6% 10% 4 3 3 2 3 4 28%	2407
	21st to end	Day	34% 17% 5% 9% 5% 4 3 2 3 3 14%	2802
February	1st to 10th	Day	32% 16% 4 7% 5% 4 3 2 4 5% 18%	1676
	11th to 20th	Day	24% 18% 4 7% 5% 3 4 3 5% 5% 21%	1665
	21st to end	Day	21% 23% 4 8% 4 6% 4 3 4 4 19%	1475
March	1st to 10th	Day	17% 19% 5% 10% 7% 5% 5% 4 5% 4 20%	3154
	11th to 20th	Day	16% 16% 4 8% 5% 4 4 3 3 4 32%	3490
	21st to end	Day	22% 18% 5% 9% 5% 5% 5% 4 5% 4 19%	3998
April	1st to 10th	Day	24% 20% 4 10% 4 4 4 4 5% 5% 15%	2280
	11th to 20th	Day	21% 16% 4 10% 5% 5% 5% 4 5% 5% 20%	2285
	21st to end	Day	26% 18% 3 8% 4 4 4 3 5% 5% 19%	2577
May	1st to 10th	Day	18% 14% 4 8% 5% 4 4 3 4 4 33%	4420
	11th to 20th	Day	18% 9% 2 7% 4 5% 5% 4 6% 8% 31%	4377
	21st to end	Day	32% 15% 4 9% 5% 4 4 3 4 5% 16%	4813
June	1st to 10th	Day	27% 11% 4 7% 6% 4 4 3 4 5% 23%	2814
	11th to 20th	Day	32% 13% 3 10% 5% 4 3 3 4 4 18%	2850
	21st to end	Day	20% 10% 2 7% 5% 5% 4 3 5% 6% 34%	2850
July	1st to 10th	Day	10% 4 1 4 2 3 3 2 4 5% 63%	4740
	11th to 20th	Day	7% 4 1 3 2 2 2 3 3 5% 67%	4686
	21st to end	Day	16% 4 1 4 2 3 3 2 5% 6% 54%	4790
August	1st to 10th	Day	8% 4 1 3 2 3 3 2 4 6% 64%	4401
	11th to 20th	Day	17% 6% 2 6% 3 3 4 3 6% 8% 42%	4093
	21st to end	Day	19% 7% 2 7% 5% 4 4 2 4 6% 39%	4344
September	1st to 10th	Day	14% 7% 2 5% 4 3 4 3 5% 7% 47%	2280
	11th to 20th	Day	18% 9% 2 8% 4 4 5% 3 4 5% 38%	2280
	21st to end	Day	25% 7% 3 5% 5% 3 4 3 4 5% 36%	2018
October	1st to 10th	Day	21% 9% 3 8% 4 5% 5% 4 5% 6% 30%	3180
	11th to 20th	Day	31% 11% 3 8% 4 3 4 3 4 5% 24%	3161
	21st to end	Day	26% 14% 6% 10% 5% 3 4 3 4 6% 18%	3163
November	1st to 10th	Day	33% 14% 4 8% 5% 4 2 3 5% 4 19%	1587
	11th to 20th	Day	33% 16% 5% 8% 3 2 4 2 3 3 21%	1600
	21st to end	Day	31% 17% 3 7% 5% 3 4 3 5% 5% 18%	1600
December	1st to 10th	Day	19% 13% 4 8% 5% 4 5% 4 4 4 29%	2620
	11th to 20th	Day	25% 19% 5% 11% 5% 6% 4 3 4 4 15%	2783
	21st to end	Day	27% 18% 5% 11% 5% 6% 4 3 5% 4 11%	3498
January	1st to 10th	Night	30% 23% 5% 8% 4 4 3 2 3 3 15%	4876
	11th to 20th	Night	25% 15% 3 5% 3 3 3 2 4 7% 29%	4708
	21st to end	Night	30% 17% 5% 10% 6% 5% 4 3 3 4 14%	4876
February	1st to 10th	Night	30% 15% 3 8% 5% 4 4 3 5% 5% 19%	2503
	11th to 20th	Night	23% 22% 3 8% 5% 4 3 2 3 4 23%	2402
	21st to end	Night	23% 19% 4 7% 5% 3 3 3 3 4 24%	1979
March	1st to 10th	Night	18% 18% 5% 9% 6% 5% 4 4 5% 6% 22%	3719
	11th to 20th	Night	19% 16% 3 6% 4 3 3 3 4 6% 34%	3489
	21st to end	Night	25% 17% 3 9% 4 5% 4 4 4 4 21%	3654
April	1st to 10th	Night	22% 19% 4 10% 5% 5% 4 4 4 4 20%	1900
	11th to 20th	Night	21% 15% 4 8% 5% 5% 4 4 4 5% 25%	1842
	21st to end	Night	27% 15% 4 8% 5% 5% 4 4 4 6% 19%	1601
May	1st to 10th	Night	19% 12% 4 6% 4 4 3 3 3 4 40%	2540
	11th to 20th	Night	16% 11% 3 7% 5% 3 4 4 5% 7% 36%	2516
	21st to end	Night	28% 16% 3 8% 4 4 3 3 4 4 22%	2762
June	1st to 10th	Night	22% 12% 3 7% 6% 4 4 4 6% 4 27%	1363
	11th to 20th	Night	24% 12% 4 8% 6% 4 5% 5% 5% 6% 21%	1330
	21st to end	Night	18% 8% 3 5% 4 3 3 3 5% 8% 40%	1330
July	1st to 10th	Night	8% 4 1 4 3 2 2 2 4 5% 65%	2220
	11th to 20th	Night	6% 4 1 3 2 1 2 2 3 4 72%	2274
	21st to end	Night	13% 4 2 3 2 3 3 2 4 5% 61%	2762
August	1st to 10th	Night	6% 2 1 2 2 2 3 3 6% 8% 66%	2529
	11th to 20th	Night	14% 6% 2 6% 2 2 3 3 5% 7% 49%	2741
	21st to end	Night	19% 7% 2 6% 4 4 4 3 5% 7% 40%	3328
September	1st to 10th	Night	12% 5% 2 6% 4 4 4 4 5% 6% 49%	1900
	11th to 20th	Night	19% 8% 3 6% 4 4 3 2 3 6% 40%	1900
	21st to end	Night	20% 8% 3 7% 4 4 4 3 4 6% 36%	2157
October	1st to 10th	Night	21% 9% 3 9% 5% 4 5% 4 5% 7% 27%	3800
	11th to 20th	Night	33% 9% 2 5% 3 3 4 3 4 5% 28%	3777
	21st to end	Night	28% 13% 4 8% 4 4 4 3 4 4 24%	4396
November	1st to 10th	Night	33% 14% 3 7% 4 5% 4 3 4 5% 18%	2707
	11th to 20th	Night	34% 15% 3 7% 4 3 4 2 3 4 20%	2800
	21st to end	Night	31% 17% 3 7% 4 4 4 3 3 4 19%	2800
December	1st to 10th	Night	19% 13% 4 7% 5% 4 4 3 4 6% 32%	4560
	11th to 20th	Night	30% 18% 4 9% 6% 4 4 3 4 4 15%	5417
	21st to end	Night	27% 20% 5% 10% 6% 5% 5% 3 4 4 11%	7458

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	76% 5% 5% 9% 4 1	2289
	11th to 20th	Day	63% 5% 9% 11% 7% 5%	2429
	21st to end	Day	76% 5% 6% 8% 4	2802
February	1st to 10th	Day	72% 6% 6% 9% 6% 1	1676
	11th to 20th	Day	69% 6% 7% 10% 8% 2	1674
	21st to end	Day	72% 6% 6% 11% 4 2	1475
March	1st to 10th	Day	65% 9% 7% 11% 7% 1	3154
	11th to 20th	Day	58% 6% 10% 20% 5%	3490
	21st to end	Day	69% 9% 8% 7% 6%	3998
April	1st to 10th	Day	74% 8% 9% 8% 1	2280
	11th to 20th	Day	69% 8% 5% 8% 8% 2	2285
	21st to end	Day	71% 8% 7% 8% 6% 1	2577
May	1st to 10th	Day	55% 10% 8% 18% 8%	4420
	11th to 20th	Day	51% 14% 18% 14% 3	4380
	21st to end	Day	71% 11% 10% 8% 1	4814
June	1st to 10th	Day	66% 7% 11% 10% 4 2	2814
	11th to 20th	Day	72% 7% 10% 9% 2	2850
	21st to end	Day	54% 7% 14% 17% 6% 1	2850
July	1st to 10th	Day	27% 6% 9% 25% 22% 11%	4666
	11th to 20th	Day	24% 5% 8% 34% 26% 3	4605
	21st to end	Day	31% 7% 19% 28% 11% 3	4639
August	1st to 10th	Day	24% 5% 12% 34% 23% 1	4384
	11th to 20th	Day	42% 10% 21% 17% 9% 1	4134
	21st to end	Day	50% 7% 12% 21% 10% 1	4343
September	1st to 10th	Day	40% 7% 13% 23% 13% 5%	2280
	11th to 20th	Day	51% 6% 8% 16% 16% 2	2280
	21st to end	Day	52% 7% 14% 15% 10% 2	2018
October	1st to 10th	Day	56% 7% 11% 19% 7%	3180
	11th to 20th	Day	66% 5% 9% 13% 7% 1	3161
	21st to end	Day	68% 7% 8% 9% 6%	3163
November	1st to 10th	Day	72% 6% 8% 10% 3 1	1587
	11th to 20th	Day	72% 4 7% 10% 6% 2	1600
	21st to end	Day	68% 7% 5% 10% 7% 2	1600
December	1st to 10th	Day	59% 7% 11% 11% 11%	2620
	11th to 20th	Day	74% 6% 8% 8% 3 1	2785
	21st to end	Day	75% 7% 8% 7% 3	3498
January	1st to 10th	Night	76% 5% 5% 10% 4 1	4876
	11th to 20th	Night	57% 7% 9% 12% 9% 6%	4748
	21st to end	Night	74% 7% 7% 7% 5% 1	4876
February	1st to 10th	Night	69% 6% 8% 10% 6% 1	2503
	11th to 20th	Night	68% 6% 7% 10% 7% 2	2404
	21st to end	Night	67% 6% 7% 13% 6% 1	1979
March	1st to 10th	Night	60% 8% 9% 12% 9% 2	3719
	11th to 20th	Night	54% 6% 13% 22% 6%	3490
	21st to end	Night	66% 8% 13% 10% 3	3654
April	1st to 10th	Night	69% 7% 12% 10% 2	1900
	11th to 20th	Night	63% 6% 9% 12% 8% 2	1842
	21st to end	Night	69% 8% 8% 10% 5% 1	1601
May	1st to 10th	Night	49% 11% 9% 22% 8%	2540
	11th to 20th	Night	47% 13% 19% 17% 4	2516
	21st to end	Night	65% 13% 11% 10% 1	2762
June	1st to 10th	Night	59% 8% 13% 13% 4 2	1363
	11th to 20th	Night	64% 9% 14% 12% 2	1330
	21st to end	Night	46% 9% 20% 17% 6% 2	1330
July	1st to 10th	Night	24% 7% 10% 28% 19% 12%	2185
	11th to 20th	Night	19% 5% 10% 29% 32% 5%	2232
	21st to end	Night	30% 5% 16% 24% 20% 4	2674
August	1st to 10th	Night	19% 6% 15% 35% 24% 1	2521
	11th to 20th	Night	36% 9% 27% 17% 10% 2	2766
	21st to end	Night	45% 9% 14% 23% 8% 2	3328
September	1st to 10th	Night	38% 8% 14% 21% 14% 5%	1900
	11th to 20th	Night	47% 7% 10% 17% 15% 4	1900
	21st to end	Night	51% 8% 13% 17% 9% 2	2157
October	1st to 10th	Night	57% 7% 15% 17% 5%	3800
	11th to 20th	Night	61% 5% 9% 16% 9% 1	3777
	21st to end	Night	64% 7% 9% 13% 7%	4396
November	1st to 10th	Night	70% 7% 8% 10% 4 1	2707
	11th to 20th	Night	70% 6% 8% 9% 6% 2	2800
	21st to end	Night	70% 5% 5% 9% 9% 2	2800
December	1st to 10th	Night	55% 7% 12% 17% 8% 1	4560
	11th to 20th	Night	74% 5% 7% 10% 2 1	5414
	21st to end	Night	75% 8% 7% 7% 3	7458

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	36% 24% 21% 12% 7% 1	200
	11th to 20th	Day	33% 16% 27% 18% 7% 1	200
	21st to end	Day	38% 13% 27% 20% 4	200
February	1st to 10th	Day	43% 19% 21% 14% 3	336
	11th to 20th	Day	37% 21% 25% 13% 3	365
	21st to end	Day	36% 19% 27% 14% 3	337
March	1st to 10th	Day	31% 21% 28% 17% 3	460
	11th to 20th	Day	34% 17% 23% 20% 6% 1	460
	21st to end	Day	38% 19% 22% 16% 4	506
April	1st to 10th	Day	39% 20% 23% 14% 3 1	460
	11th to 20th	Day	34% 20% 23% 16% 5% 1	452
	21st to end	Day	44% 17% 19% 15% 4 1	460
May	1st to 10th	Day	28% 16% 31% 22% 3	463
	11th to 20th	Day	31% 12% 27% 20% 9% 1	488
	21st to end	Day	38% 17% 20% 18% 6% 2	529
June	1st to 10th	Day	33% 18% 26% 18% 4	644
	11th to 20th	Day	39% 20% 23% 14% 3 1	680
	21st to end	Day	28% 15% 27% 21% 8% 1	680
July	1st to 10th	Day	22% 13% 32% 25% 6% 1	671
	11th to 20th	Day	18% 13% 37% 23% 7% 2	640
	21st to end	Day	14% 12% 35% 28% 9% 3	531
August	1st to 10th	Day	16% 10% 32% 28% 11% 4	487
	11th to 20th	Day	14% 10% 33% 29% 11% 3	477
	21st to end	Day	20% 16% 32% 22% 10%	539
September	1st to 10th	Day	20% 14% 34% 22% 8% 1	490
	11th to 20th	Day	28% 14% 28% 22% 7% 1	490
	21st to end	Day	30% 17% 25% 20% 7% 1	490
October	1st to 10th	Day	31% 14% 23% 22% 8% 1	490
	11th to 20th	Day	35% 15% 22% 19% 8% 1	490
	21st to end	Day	36% 13% 30% 15% 4 1	368
November	1st to 10th	Day	40% 11% 30% 15% 3	210
	11th to 20th	Day	42% 17% 20% 15% 6% 1	200
	21st to end	Day	42% 15% 23% 13% 7% 2	200
December	1st to 10th	Day	35% 14% 22% 22% 9% 1	200
	11th to 20th	Day	40% 14% 31% 12% 4 1	200
	21st to end	Day	40% 15% 28% 15% 2	220
January	1st to 10th	Night	43% 16% 26% 13% 1	900
	11th to 20th	Night	39% 11% 30% 17% 2	855
	21st to end	Night	35% 11% 34% 17% 2	840
February	1st to 10th	Night	36% 15% 33% 12% 3	760
	11th to 20th	Night	37% 11% 33% 17% 2	744
	21st to end	Night	36% 14% 29% 18% 3	628
March	1st to 10th	Night	31% 12% 27% 24% 7%	760
	11th to 20th	Night	36% 12% 28% 19% 5%	760
	21st to end	Night	35% 12% 30% 17% 6%	836
April	1st to 10th	Night	34% 11% 25% 23% 6% 1	760
	11th to 20th	Night	32% 11% 28% 25% 4	714
	21st to end	Night	37% 9% 27% 20% 7%	461
May	1st to 10th	Night	27% 7% 24% 28% 13%	380
	11th to 20th	Night	24% 6% 20% 34% 16%	374
	21st to end	Night	30% 7% 17% 30% 15%	411
June	1st to 10th	Night	31% 6% 23% 27% 12% 1	380
	11th to 20th	Night	32% 8% 18% 28% 13% 1	380
	21st to end	Night	24% 6% 18% 35% 16% 1	380
July	1st to 10th	Night	18% 3 17% 35% 26% 1	370
	11th to 20th	Night	15% 5% 14% 40% 25% 1	368
	21st to end	Night	11% 2 13% 41% 32% 2	416
August	1st to 10th	Night	10% 3 9% 37% 38% 2	378
	11th to 20th	Night	10% 4 15% 39% 31% 2	517
	21st to end	Night	17% 5% 21% 38% 19%	731
September	1st to 10th	Night	16% 5% 26% 33% 19%	760
	11th to 20th	Night	25% 7% 19% 26% 21% 2	760
	21st to end	Night	26% 11% 21% 33% 10%	760
October	1st to 10th	Night	29% 8% 24% 29% 10%	760
	11th to 20th	Night	36% 8% 26% 23% 6%	760
	21st to end	Night	39% 12% 29% 17% 4	836
November	1st to 10th	Night	43% 11% 34% 12% 1	780
	11th to 20th	Night	45% 12% 26% 15% 2	800
	21st to end	Night	43% 15% 25% 14% 3	800
December	1st to 10th	Night	31% 13% 35% 18% 2	800
	11th to 20th	Night	41% 15% 33% 11% 1	855
	21st to end	Night	42% 15% 33% 10%	990

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