Loowit Imaging Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Loowit Imaging Observatory clear sky chart from 2005-11-06 to 2025-09-19.

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	16% 9% 3 8% 5% 5% 5% 4 5% 7% 33%	130768
	Night	19% 9% 3 8% 5% 4 4 4 5% 6% 33%	126991
Transparency	Day	50% 8% 15% 18% 8% 1	130481
	Night	52% 8% 14% 18% 7% 1	126855
Seeing	Day	21% 13% 23% 24% 15% 4	16360
	Night	24% 9% 20% 28% 17% 2	24624

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	33% 11% 5% 11% 7% 5% 5% 4 4 5% 11%	3179
	11th to 20th	Day	18% 9% 5% 12% 7% 5% 5% 4 6% 8% 22%	3524
	21st to end	Day	33% 10% 3 8% 6% 5% 4 3 4 3 20%	4252
February	1st to 10th	Day	23% 11% 4 12% 7% 6% 6% 4 7% 7% 15%	1800
	11th to 20th	Day	26% 13% 5% 10% 5% 5% 4 4 5% 4 21%	1755
	21st to end	Day	23% 12% 3 9% 6% 6% 4 4 5% 6% 21%	1525
March	1st to 10th	Day	19% 13% 4 11% 7% 7% 7% 4 5% 5% 16%	4728
	11th to 20th	Day	22% 12% 4 9% 5% 4 4 3 5% 5% 27%	5000
	21st to end	Day	24% 13% 4 11% 7% 6% 6% 5% 6% 5% 14%	5607
April	1st to 10th	Day	23% 11% 3 9% 6% 6% 5% 4 7% 6% 20%	2400
	11th to 20th	Day	19% 11% 3 9% 6% 5% 5% 4 5% 6% 27%	2428
	21st to end	Day	17% 10% 4 8% 6% 6% 5% 4 6% 8% 27%	2600
May	1st to 10th	Day	13% 7% 3 7% 5% 4 6% 4 6% 7% 38%	6319
	11th to 20th	Day	11% 8% 3 8% 5% 6% 6% 5% 7% 10% 32%	6277
	21st to end	Day	14% 8% 3 8% 5% 5% 5% 4 7% 10% 31%	6903
June	1st to 10th	Day	16% 8% 4 8% 5% 5% 5% 4 7% 8% 31%	2886
	11th to 20th	Day	10% 8% 3 10% 7% 7% 6% 6% 7% 9% 26%	3000
	21st to end	Day	9% 7% 3 7% 5% 5% 5% 5% 7% 9% 38%	3000
July	1st to 10th	Day	4 5% 2 5% 3 3 3 3 5% 6% 63%	6780
	11th to 20th	Day	3 3 1 4 3 3 3 3 4 5% 68%	6562
	21st to end	Day	5% 6% 3 6% 4 4 4 3 5% 7% 54%	6874
August	1st to 10th	Day	4 4 2 5% 3 4 4 4 6% 8% 56%	4362
	11th to 20th	Day	8% 6% 3 9% 5% 5% 5% 4 6% 8% 41%	4156
	21st to end	Day	11% 7% 3 7% 4 4 5% 3 5% 6% 44%	4510
September	1st to 10th	Day	8% 6% 2 7% 5% 4 5% 3 5% 6% 48%	2400
	11th to 20th	Day	11% 7% 4 8% 5% 5% 5% 4 5% 8% 38%	2368
	21st to end	Day	16% 6% 2 7% 5% 4 6% 3 5% 7% 39%	2005
October	1st to 10th	Day	13% 7% 3 6% 4 4 5% 4 8% 10% 36%	3180
	11th to 20th	Day	25% 9% 3 7% 5% 4 4 3 6% 7% 28%	3161
	21st to end	Day	24% 10% 3 9% 5% 5% 5% 4 5% 6% 23%	3324
November	1st to 10th	Day	30% 13% 4 8% 7% 6% 5% 3 4 5% 17%	1583
	11th to 20th	Day	29% 13% 3 9% 6% 5% 4 3 5% 6% 19%	1600
	21st to end	Day	29% 10% 3 9% 6% 5% 4 3 5% 6% 19%	1600
December	1st to 10th	Day	20% 9% 3 14% 9% 7% 6% 4 5% 5% 18%	2620
	11th to 20th	Day	37% 12% 4 10% 6% 6% 5% 3 4 4 8%	3002
	21st to end	Day	31% 14% 6% 12% 6% 6% 4 3 4 4 11%	3498
January	1st to 10th	Night	32% 14% 5% 11% 6% 5% 4 3 4 4 12%	6766
	11th to 20th	Night	19% 8% 3 8% 5% 4 4 4 5% 7% 31%	6356
	21st to end	Night	30% 9% 3 8% 5% 4 4 4 5% 5% 24%	6715
February	1st to 10th	Night	22% 13% 4 9% 6% 5% 5% 4 5% 6% 20%	2600
	11th to 20th	Night	21% 13% 3 8% 6% 5% 4 3 5% 6% 25%	2532
	21st to end	Night	21% 12% 3 9% 5% 5% 4 4 6% 6% 25%	2105
March	1st to 10th	Night	16% 13% 4 10% 7% 5% 6% 5% 7% 6% 20%	5163
	11th to 20th	Night	23% 10% 3 7% 4 4 4 3 5% 6% 33%	4999
	21st to end	Night	29% 13% 4 9% 5% 4 5% 4 5% 6% 16%	5368
April	1st to 10th	Night	20% 9% 3 9% 6% 4 6% 4 7% 7% 25%	2000
	11th to 20th	Night	15% 7% 3 7% 6% 5% 5% 4 5% 8% 34%	1919
	21st to end	Night	16% 8% 2 7% 6% 5% 4 4 5% 8% 33%	1800
May	1st to 10th	Night	12% 8% 3 6% 4 4 4 3 4 5% 46%	3640
	11th to 20th	Night	9% 7% 3 7% 5% 5% 5% 4 7% 7% 42%	3616
	21st to end	Night	7% 7% 2 7% 5% 5% 6% 6% 8% 10% 37%	3972
June	1st to 10th	Night	11% 7% 3 6% 4 5% 4 4 6% 8% 40%	1510
	11th to 20th	Night	8% 6% 2 7% 4 6% 6% 4 8% 10% 39%	1400
	21st to end	Night	6% 4 2 6% 5% 4 4 4 6% 6% 54%	1400
July	1st to 10th	Night	2 2 1 4 3 3 3 3 4 6% 70%	3180
	11th to 20th	Night	1 2 1 2 1 2 2 2 4 6% 77%	3382
	21st to end	Night	3 3 1 3 3 3 4 3 6% 8% 64%	3969
August	1st to 10th	Night	2 2 1 2 2 2 3 3 4 8% 71%	2791
	11th to 20th	Night	9% 4 2 5% 3 3 3 4 5% 8% 55%	2902
	21st to end	Night	12% 4 2 4 3 4 4 3 4 8% 51%	3402
September	1st to 10th	Night	5% 5% 1 5% 3 3 3 3 6% 7% 59%	2000
	11th to 20th	Night	11% 7% 2 6% 4 4 4 3 6% 7% 46%	1986
	21st to end	Night	13% 6% 2 7% 5% 5% 3 3 5% 6% 44%	2175
October	1st to 10th	Night	11% 7% 2 7% 4 4 4 3 6% 8% 43%	3800
	11th to 20th	Night	22% 8% 3 7% 5% 4 5% 4 5% 7% 31%	3777
	21st to end	Night	26% 10% 3 8% 4 5% 4 3 5% 6% 27%	4239
November	1st to 10th	Night	31% 9% 3 7% 5% 4 4 4 6% 5% 23%	2711
	11th to 20th	Night	29% 10% 3 9% 6% 5% 4 4 4 5% 22%	2800
	21st to end	Night	26% 10% 3 8% 6% 5% 5% 4 4 6% 23%	2800
December	1st to 10th	Night	20% 10% 3 13% 8% 6% 5% 3 4 5% 20%	4560
	11th to 20th	Night	37% 13% 5% 10% 6% 5% 4 3 4 3 11%	5198
	21st to end	Night	33% 16% 5% 10% 5% 5% 3 3 3 3 13%	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	75% 8% 5% 7% 4	3179
	11th to 20th	Day	61% 6% 12% 17% 3 1	3548
	21st to end	Day	68% 7% 6% 13% 6%	4252
February	1st to 10th	Day	66% 12% 10% 7% 4	1800
	11th to 20th	Day	65% 11% 9% 9% 6% 1	1764
	21st to end	Day	63% 9% 11% 10% 6%	1525
March	1st to 10th	Day	65% 10% 12% 11% 2	4728
	11th to 20th	Day	58% 7% 11% 22% 3	5000
	21st to end	Day	70% 8% 12% 8% 1	5607
April	1st to 10th	Day	62% 11% 15% 10% 2	2400
	11th to 20th	Day	57% 11% 12% 14% 6% 1	2428
	21st to end	Day	54% 11% 15% 15% 4	2600
May	1st to 10th	Day	43% 9% 16% 22% 10%	6319
	11th to 20th	Day	44% 11% 23% 19% 3	6280
	21st to end	Day	46% 12% 21% 18% 3	6904
June	1st to 10th	Day	49% 12% 20% 14% 5%	2886
	11th to 20th	Day	52% 15% 17% 14% 3	3000
	21st to end	Day	41% 11% 21% 19% 6% 2	3000
July	1st to 10th	Day	25% 5% 19% 22% 21% 8%	6706
	11th to 20th	Day	19% 5% 15% 30% 28% 2	6481
	21st to end	Day	31% 4 22% 32% 11% 1	6681
August	1st to 10th	Day	27% 6% 13% 36% 17% 2	4345
	11th to 20th	Day	41% 5% 23% 21% 8% 2	4195
	21st to end	Day	41% 6% 14% 26% 13% 1	4509
September	1st to 10th	Day	36% 8% 16% 21% 14% 5%	2400
	11th to 20th	Day	43% 10% 13% 17% 15% 2	2368
	21st to end	Day	45% 10% 15% 18% 11% 2	2005
October	1st to 10th	Day	42% 5% 18% 29% 6%	3180
	11th to 20th	Day	56% 7% 12% 16% 9%	3161
	21st to end	Day	61% 6% 11% 13% 8% 1	3324
November	1st to 10th	Day	69% 8% 10% 8% 4	1583
	11th to 20th	Day	68% 8% 8% 9% 6% 1	1600
	21st to end	Day	65% 8% 9% 11% 6%	1600
December	1st to 10th	Day	67% 5% 5% 15% 7%	2620
	11th to 20th	Day	79% 6% 7% 7% 1	3005
	21st to end	Day	76% 7% 9% 6% 2	3498
January	1st to 10th	Night	76% 7% 7% 8% 2	6766
	11th to 20th	Night	53% 7% 12% 22% 6% 1	6394
	21st to end	Night	63% 7% 8% 15% 6%	6715
February	1st to 10th	Night	64% 11% 12% 8% 6%	2600
	11th to 20th	Night	60% 11% 11% 10% 8% 1	2534
	21st to end	Night	58% 10% 13% 12% 6%	2105
March	1st to 10th	Night	59% 10% 14% 12% 4	5163
	11th to 20th	Night	53% 7% 12% 24% 4 1	5000
	21st to end	Night	68% 9% 11% 9% 2	5368
April	1st to 10th	Night	56% 12% 16% 14% 3	2000
	11th to 20th	Night	46% 10% 16% 17% 9% 1	1919
	21st to end	Night	48% 10% 18% 17% 6% 1	1800
May	1st to 10th	Night	39% 7% 13% 30% 10% 1	3637
	11th to 20th	Night	38% 8% 26% 22% 6%	3616
	21st to end	Night	40% 14% 23% 21% 2	3972
June	1st to 10th	Night	41% 8% 24% 21% 6% 1	1510
	11th to 20th	Night	37% 13% 28% 20% 2	1400
	21st to end	Night	30% 10% 29% 21% 7% 3	1400
July	1st to 10th	Night	18% 5% 24% 28% 19% 7%	3145
	11th to 20th	Night	11% 4 18% 36% 30% 1	3340
	21st to end	Night	19% 4 28% 35% 13% 2	3857
August	1st to 10th	Night	14% 6% 15% 41% 22% 2	2783
	11th to 20th	Night	30% 4 32% 22% 10% 3	2929
	21st to end	Night	33% 5% 19% 28% 13% 1	3402
September	1st to 10th	Night	24% 9% 20% 27% 16% 5%	2000
	11th to 20th	Night	37% 9% 17% 17% 16% 4	1986
	21st to end	Night	41% 9% 13% 21% 13% 2	2175
October	1st to 10th	Night	40% 5% 14% 34% 7%	3800
	11th to 20th	Night	53% 6% 14% 21% 5%	3777
	21st to end	Night	58% 5% 10% 17% 9% 1	4239
November	1st to 10th	Night	62% 9% 11% 13% 4 1	2711
	11th to 20th	Night	64% 9% 11% 9% 6% 2	2800
	21st to end	Night	62% 9% 12% 9% 7% 1	2800
December	1st to 10th	Night	67% 5% 7% 15% 5%	4560
	11th to 20th	Night	77% 8% 8% 6% 2	5194
	21st to end	Night	76% 6% 7% 8% 2	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	41% 13% 20% 17% 8% 3	200
	11th to 20th	Day	33% 15% 20% 18% 13% 2	200
	21st to end	Day	38% 12% 18% 20% 10% 2	325
February	1st to 10th	Day	31% 21% 20% 18% 9% 2	400
	11th to 20th	Day	37% 17% 24% 18% 4	395
	21st to end	Day	37% 16% 24% 16% 6% 1	351
March	1st to 10th	Day	31% 16% 24% 20% 7%	500
	11th to 20th	Day	29% 15% 23% 18% 11% 4	500
	21st to end	Day	30% 16% 28% 17% 7% 2	550
April	1st to 10th	Day	31% 16% 22% 20% 9% 2	500
	11th to 20th	Day	26% 17% 28% 16% 9% 4	492
	21st to end	Day	21% 17% 28% 21% 10% 2	500
May	1st to 10th	Day	16% 14% 27% 26% 14% 2	503
	11th to 20th	Day	25% 12% 21% 24% 14% 5%	528
	21st to end	Day	17% 13% 25% 27% 14% 5%	573
June	1st to 10th	Day	19% 11% 28% 23% 15% 4	616
	11th to 20th	Day	15% 17% 31% 25% 10% 2	730
	21st to end	Day	10% 13% 26% 29% 18% 4	730
July	1st to 10th	Day	8% 8% 24% 35% 20% 5%	721
	11th to 20th	Day	5% 6% 22% 36% 24% 7%	630
	21st to end	Day	8% 5% 18% 29% 31% 9%	575
August	1st to 10th	Day	6% 9% 17% 32% 29% 7%	527
	11th to 20th	Day	10% 3 18% 33% 27% 9%	517
	21st to end	Day	14% 9% 23% 28% 20% 7%	583
September	1st to 10th	Day	12% 8% 25% 32% 16% 7%	530
	11th to 20th	Day	15% 11% 21% 29% 20% 5%	523
	21st to end	Day	19% 12% 21% 29% 16% 3	490
October	1st to 10th	Day	23% 11% 23% 22% 17% 4	490
	11th to 20th	Day	27% 11% 20% 23% 15% 3	490
	21st to end	Day	33% 18% 19% 18% 11% 2	464
November	1st to 10th	Day	34% 18% 21% 15% 11% 1	207
	11th to 20th	Day	40% 13% 22% 13% 10% 3	200
	21st to end	Day	29% 17% 19% 20% 13% 5%	200
December	1st to 10th	Day	38% 15% 15% 16% 15% 3	200
	11th to 20th	Day	44% 15% 19% 17% 5% 1	200
	21st to end	Day	38% 16% 23% 15% 7%	220
January	1st to 10th	Night	43% 13% 16% 17% 10% 1	900
	11th to 20th	Night	34% 10% 15% 24% 15% 1	817
	21st to end	Night	29% 12% 16% 25% 15% 2	880
February	1st to 10th	Night	30% 15% 21% 23% 10% 2	800
	11th to 20th	Night	27% 16% 22% 23% 12% 1	784
	21st to end	Night	30% 14% 24% 20% 11% 1	660
March	1st to 10th	Night	26% 13% 23% 25% 12% 2	800
	11th to 20th	Night	28% 13% 22% 23% 12% 2	800
	21st to end	Night	31% 13% 23% 24% 9% 1	880
April	1st to 10th	Night	24% 12% 25% 25% 13% 1	800
	11th to 20th	Night	18% 13% 26% 28% 14% 2	731
	21st to end	Night	18% 9% 26% 33% 13% 1	600
May	1st to 10th	Night	13% 10% 25% 37% 15% 1	400
	11th to 20th	Night	15% 6% 26% 31% 20% 1	394
	21st to end	Night	12% 7% 24% 36% 20% 1	433
June	1st to 10th	Night	13% 8% 25% 36% 19% 1	400
	11th to 20th	Night	11% 10% 29% 36% 15%	400
	21st to end	Night	7% 6% 27% 34% 25% 1	400
July	1st to 10th	Night	6% 1 19% 44% 28% 2	390
	11th to 20th	Night	4 4 16% 47% 28% 2	388
	21st to end	Night	4 2 14% 48% 30% 3	438
August	1st to 10th	Night	4 3 15% 33% 40% 5%	502
	11th to 20th	Night	8% 2 10% 32% 43% 5%	594
	21st to end	Night	11% 3 18% 36% 29% 3	752
September	1st to 10th	Night	8% 4 20% 35% 28% 5%	800
	11th to 20th	Night	14% 5% 19% 30% 28% 5%	792
	21st to end	Night	16% 7% 20% 32% 21% 3	760
October	1st to 10th	Night	20% 7% 16% 29% 24% 3	760
	11th to 20th	Night	26% 8% 16% 27% 20% 4	760
	21st to end	Night	31% 9% 21% 22% 15% 2	836
November	1st to 10th	Night	34% 9% 22% 25% 9% 1	780
	11th to 20th	Night	34% 12% 21% 20% 11% 1	800
	21st to end	Night	29% 9% 23% 23% 14% 2	800
December	1st to 10th	Night	30% 9% 18% 26% 15% 2	800
	11th to 20th	Night	38% 11% 19% 22% 8% 1	803
	21st to end	Night	40% 13% 21% 18% 8% 1	990

Page generated at 2025-09-15 22:49:11. Version ac07

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