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 2024-01-12.

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	18% 8% 4 7% 6% 4 5% 5% 5% 7% 31%	74865
	Night	20% 8% 3 6% 6% 3 4 5% 5% 6% 33%	74854
Transparency	Day	52% 11% 14% 15% 7% 1	74557
	Night	51% 10% 14% 16% 7% 1	74680
Seeing	Day	21% 13% 23% 24% 15% 3	14085
	Night	24% 9% 20% 27% 17% 2	22594

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	37% 10% 5% 8% 7% 3 4 4 4 4 13%	1329
	11th to 20th	Day	27% 12% 6% 9% 6% 4 4 4 5% 5% 17%	1411
	21st to end	Day	28% 11% 4 10% 8% 4 6% 5% 5% 4 15%	1678
February	1st to 10th	Day	25% 10% 5% 11% 7% 4 6% 5% 6% 7% 15%	1620
	11th to 20th	Day	25% 12% 5% 9% 6% 4 5% 5% 5% 4 22%	1575
	21st to end	Day	23% 11% 4 8% 6% 4 5% 5% 5% 6% 22%	1368
March	1st to 10th	Day	24% 11% 4 8% 7% 4 6% 6% 5% 5% 19%	1880
	11th to 20th	Day	28% 10% 4 9% 8% 4 4 4 4 5% 19%	1980
	21st to end	Day	24% 11% 4 9% 9% 5% 6% 7% 6% 5% 15%	2222
April	1st to 10th	Day	24% 9% 4 8% 7% 4 5% 5% 7% 6% 21%	2160
	11th to 20th	Day	22% 10% 5% 8% 7% 3 6% 5% 4 5% 24%	2182
	21st to end	Day	17% 10% 4 8% 7% 4 5% 6% 6% 8% 26%	2340
May	1st to 10th	Day	14% 7% 3 7% 8% 3 7% 6% 6% 8% 31%	2519
	11th to 20th	Day	15% 8% 4 6% 7% 4 7% 6% 7% 8% 26%	2477
	21st to end	Day	16% 9% 3 7% 7% 4 6% 6% 6% 7% 28%	2723
June	1st to 10th	Day	16% 7% 4 7% 6% 4 5% 6% 7% 8% 29%	2596
	11th to 20th	Day	11% 8% 4 9% 9% 5% 6% 8% 7% 9% 25%	2700
	21st to end	Day	9% 6% 3 6% 5% 4 5% 5% 6% 9% 40%	2700
July	1st to 10th	Day	7% 6% 2 5% 5% 3 4 4 5% 7% 51%	2700
	11th to 20th	Day	7% 4 2 5% 5% 3 6% 5% 6% 7% 51%	2622
	21st to end	Day	5% 3 2 4 4 3 4 4 5% 7% 61%	2741
August	1st to 10th	Day	5% 4 2 5% 4 3 5% 5% 6% 8% 53%	2412
	11th to 20th	Day	6% 3 1 5% 4 2 4 4 5% 7% 57%	2298
	21st to end	Day	8% 5% 2 6% 5% 3 5% 5% 6% 8% 47%	2490
September	1st to 10th	Day	8% 6% 2 5% 6% 3 5% 4 4 7% 50%	2160
	11th to 20th	Day	11% 6% 3 7% 6% 4 5% 5% 5% 8% 39%	2152
	21st to end	Day	17% 6% 2 7% 6% 3 5% 4 5% 7% 39%	1900
October	1st to 10th	Day	19% 9% 5% 6% 5% 3 4 4 5% 7% 33%	1800
	11th to 20th	Day	21% 8% 3 6% 7% 4 5% 4 6% 7% 29%	1800
	21st to end	Day	26% 10% 4 7% 6% 4 4 4 5% 5% 26%	1909
November	1st to 10th	Day	30% 13% 4 7% 7% 3 6% 4 4 5% 17%	1503
	11th to 20th	Day	30% 12% 3 7% 6% 3 4 4 4 6% 20%	1520
	21st to end	Day	29% 9% 3 8% 7% 4 5% 4 5% 6% 20%	1520
December	1st to 10th	Day	28% 11% 3 8% 7% 4 5% 4 4 5% 22%	1520
	11th to 20th	Day	34% 11% 4 10% 8% 5% 6% 4 4 5% 9%	1916
	21st to end	Day	28% 13% 6% 11% 8% 4 5% 4 3 4 13%	2442
January	1st to 10th	Night	38% 10% 4 7% 5% 4 4 4 4 4 16%	2836
	11th to 20th	Night	31% 10% 5% 6% 6% 4 4 5% 5% 7% 19%	2573
	21st to end	Night	25% 10% 5% 7% 7% 3 5% 5% 5% 7% 21%	2678
February	1st to 10th	Night	23% 11% 4 8% 7% 4 6% 5% 6% 6% 21%	2340
	11th to 20th	Night	20% 12% 4 7% 6% 4 5% 4 5% 6% 26%	2272
	21st to end	Night	20% 11% 4 8% 6% 4 5% 6% 5% 6% 26%	1888
March	1st to 10th	Night	24% 9% 4 7% 6% 4 5% 6% 5% 5% 24%	2077
	11th to 20th	Night	26% 9% 4 7% 5% 3 6% 5% 5% 7% 23%	1979
	21st to end	Night	26% 10% 4 8% 7% 3 5% 6% 4 7% 20%	2134
April	1st to 10th	Night	21% 8% 3 8% 7% 3 5% 6% 6% 7% 26%	1800
	11th to 20th	Night	16% 6% 3 7% 7% 4 5% 5% 5% 9% 32%	1726
	21st to end	Night	16% 8% 3 6% 7% 4 5% 5% 5% 9% 32%	1620
May	1st to 10th	Night	12% 7% 4 5% 6% 3 5% 5% 5% 8% 40%	1440
	11th to 20th	Night	13% 6% 3 6% 5% 4 6% 6% 8% 7% 37%	1416
	21st to end	Night	10% 5% 3 7% 6% 5% 5% 5% 6% 8% 39%	1552
June	1st to 10th	Night	11% 6% 5% 6% 6% 4 4 6% 6% 9% 38%	1360
	11th to 20th	Night	9% 6% 2 7% 5% 4 6% 6% 8% 10% 37%	1260
	21st to end	Night	6% 4 2 4 4 3 5% 5% 5% 6% 56%	1260
July	1st to 10th	Night	5% 3 1 4 4 3 4 4 5% 7% 59%	1260
	11th to 20th	Night	3 3 2 4 2 2 3 4 5% 9% 63%	1336
	21st to end	Night	3 1 1 2 2 1 3 4 4 8% 72%	1576
August	1st to 10th	Night	3 2 1 3 3 2 4 5% 5% 10% 63%	1525
	11th to 20th	Night	4 2 1 3 2 2 2 3 4 8% 69%	1602
	21st to end	Night	8% 4 2 3 4 3 4 4 4 8% 55%	1864
September	1st to 10th	Night	5% 4 1 4 4 2 3 3 5% 7% 61%	1800
	11th to 20th	Night	10% 6% 3 5% 4 3 4 4 6% 8% 47%	1805
	21st to end	Night	14% 5% 2 6% 6% 4 4 4 5% 6% 44%	2060
October	1st to 10th	Night	17% 7% 3 5% 4 3 4 4 5% 6% 41%	2160
	11th to 20th	Night	22% 8% 2 6% 6% 3 4 5% 4 7% 33%	2160
	21st to end	Night	26% 8% 3 6% 5% 3 3 4 5% 6% 32%	2445
November	1st to 10th	Night	31% 9% 3 6% 5% 3 4 5% 6% 6% 23%	2572
	11th to 20th	Night	28% 9% 4 8% 6% 4 4 5% 4 6% 23%	2660
	21st to end	Night	26% 8% 3 7% 7% 4 5% 5% 4 6% 24%	2660
December	1st to 10th	Night	26% 11% 3 7% 6% 4 6% 4 4 7% 23%	2660
	11th to 20th	Night	30% 10% 5% 9% 8% 4 5% 5% 4 4 16%	3284
	21st to end	Night	31% 15% 5% 8% 6% 3 4 3 4 4 17%	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% 8% 5% 7% 4 1	1329
	11th to 20th	Day	70% 8% 11% 6% 4 2	1411
	21st to end	Day	68% 11% 9% 9% 3	1678
February	1st to 10th	Day	67% 12% 10% 6% 4	1620
	11th to 20th	Day	64% 11% 9% 10% 6% 1	1584
	21st to end	Day	62% 10% 11% 10% 6%	1368
March	1st to 10th	Day	64% 11% 11% 12% 3	1880
	11th to 20th	Day	67% 9% 9% 12% 2 1	1980
	21st to end	Day	68% 12% 10% 9% 1	2222
April	1st to 10th	Day	62% 11% 15% 10% 2	2160
	11th to 20th	Day	60% 11% 10% 13% 5% 1	2182
	21st to end	Day	56% 11% 14% 14% 5% 1	2340
May	1st to 10th	Day	48% 13% 18% 16% 5%	2519
	11th to 20th	Day	51% 14% 17% 14% 4 1	2480
	21st to end	Day	53% 14% 17% 15% 2	2724
June	1st to 10th	Day	51% 13% 19% 12% 5%	2596
	11th to 20th	Day	53% 16% 17% 11% 2	2700
	21st to end	Day	40% 12% 21% 18% 7% 2	2700
July	1st to 10th	Day	34% 11% 15% 25% 13% 2	2626
	11th to 20th	Day	30% 11% 18% 26% 14% 1	2541
	21st to end	Day	21% 9% 16% 36% 16% 3	2589
August	1st to 10th	Day	28% 10% 20% 26% 13% 2	2395
	11th to 20th	Day	27% 9% 21% 27% 14% 3	2298
	21st to end	Day	33% 10% 16% 29% 10% 1	2490
September	1st to 10th	Day	34% 9% 16% 21% 14% 5%	2160
	11th to 20th	Day	42% 11% 13% 17% 15% 2	2152
	21st to end	Day	45% 11% 14% 18% 11% 2	1900
October	1st to 10th	Day	49% 9% 14% 18% 9%	1800
	11th to 20th	Day	53% 10% 15% 15% 6% 1	1800
	21st to end	Day	60% 9% 10% 12% 8%	1909
November	1st to 10th	Day	69% 9% 10% 8% 4	1503
	11th to 20th	Day	67% 8% 8% 9% 6% 1	1520
	21st to end	Day	64% 8% 9% 12% 7%	1520
December	1st to 10th	Day	65% 8% 7% 12% 8%	1520
	11th to 20th	Day	76% 9% 7% 6% 2	1919
	21st to end	Day	74% 9% 8% 6% 3	2442
January	1st to 10th	Night	71% 8% 8% 8% 4 1	2836
	11th to 20th	Night	65% 9% 12% 9% 4 1	2573
	21st to end	Night	61% 11% 11% 12% 5% 1	2678
February	1st to 10th	Night	63% 11% 12% 8% 5%	2340
	11th to 20th	Night	59% 11% 11% 10% 8% 1	2274
	21st to end	Night	58% 11% 13% 13% 6%	1888
March	1st to 10th	Night	59% 9% 12% 15% 5%	2077
	11th to 20th	Night	59% 10% 11% 14% 4 1	1980
	21st to end	Night	63% 12% 14% 10% 2	2134
April	1st to 10th	Night	56% 11% 16% 14% 3	1800
	11th to 20th	Night	49% 11% 15% 16% 7% 1	1726
	21st to end	Night	49% 11% 17% 16% 7% 1	1620
May	1st to 10th	Night	40% 12% 20% 20% 7% 1	1440
	11th to 20th	Night	43% 11% 20% 19% 6% 1	1416
	21st to end	Night	42% 14% 21% 19% 4	1552
June	1st to 10th	Night	42% 9% 23% 19% 6% 1	1360
	11th to 20th	Night	39% 15% 29% 16% 2	1260
	21st to end	Night	28% 12% 29% 21% 7% 3	1260
July	1st to 10th	Night	24% 12% 21% 28% 11% 4	1225
	11th to 20th	Night	18% 10% 20% 34% 15% 2	1294
	21st to end	Night	10% 8% 19% 38% 19% 5%	1488
August	1st to 10th	Night	18% 10% 21% 30% 18% 3	1517
	11th to 20th	Night	16% 8% 24% 31% 16% 4	1602
	21st to end	Night	28% 9% 19% 30% 13% 2	1864
September	1st to 10th	Night	23% 9% 19% 27% 16% 5%	1800
	11th to 20th	Night	34% 10% 16% 18% 17% 4	1805
	21st to end	Night	42% 9% 13% 21% 13% 2	2060
October	1st to 10th	Night	43% 9% 13% 23% 11% 1	2160
	11th to 20th	Night	50% 10% 13% 19% 8%	2160
	21st to end	Night	53% 8% 11% 16% 11%	2445
November	1st to 10th	Night	61% 10% 12% 13% 4 1	2572
	11th to 20th	Night	63% 9% 11% 9% 6% 2	2660
	21st to end	Night	60% 9% 12% 9% 8% 1	2660
December	1st to 10th	Night	63% 7% 10% 13% 7% 1	2660
	11th to 20th	Night	69% 12% 10% 7% 3	3280
	21st to end	Night	71% 9% 8% 9% 3	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	41% 12% 19% 16% 10% 3	180
	11th to 20th	Day	38% 15% 21% 13% 11% 2	162
	21st to end	Day	38% 13% 17% 21% 9% 1	270
February	1st to 10th	Day	34% 20% 19% 18% 9% 1	340
	11th to 20th	Day	36% 17% 23% 19% 4	335
	21st to end	Day	36% 16% 25% 16% 6% 1	296
March	1st to 10th	Day	32% 17% 25% 20% 6%	420
	11th to 20th	Day	28% 15% 25% 17% 11% 4	420
	21st to end	Day	31% 16% 28% 16% 8% 2	462
April	1st to 10th	Day	31% 17% 22% 18% 9% 2	420
	11th to 20th	Day	29% 17% 27% 14% 8% 4	412
	21st to end	Day	22% 18% 28% 22% 8% 1	420
May	1st to 10th	Day	16% 15% 26% 26% 14% 2	423
	11th to 20th	Day	25% 10% 21% 25% 14% 5%	448
	21st to end	Day	16% 11% 25% 28% 14% 5%	485
June	1st to 10th	Day	20% 12% 30% 20% 15% 3	526
	11th to 20th	Day	15% 19% 31% 25% 9% 2	630
	21st to end	Day	9% 14% 26% 30% 18% 3	630
July	1st to 10th	Day	9% 9% 24% 36% 20% 2	621
	11th to 20th	Day	6% 7% 24% 36% 24% 5%	540
	21st to end	Day	6% 5% 18% 29% 34% 8%	487
August	1st to 10th	Day	6% 10% 17% 31% 30% 7%	447
	11th to 20th	Day	8% 3 18% 34% 30% 8%	437
	21st to end	Day	12% 9% 25% 29% 19% 5%	495
September	1st to 10th	Day	12% 9% 27% 33% 15% 5%	450
	11th to 20th	Day	14% 11% 21% 29% 20% 4	450
	21st to end	Day	20% 12% 20% 30% 16% 2	450
October	1st to 10th	Day	24% 11% 23% 21% 17% 4	450
	11th to 20th	Day	26% 12% 20% 23% 16% 4	450
	21st to end	Day	32% 19% 18% 19% 10% 2	424
November	1st to 10th	Day	33% 20% 20% 16% 11% 1	187
	11th to 20th	Day	38% 14% 21% 13% 11% 3	180
	21st to end	Day	28% 18% 20% 18% 12% 4	180
December	1st to 10th	Day	39% 16% 16% 16% 11% 2	180
	11th to 20th	Day	40% 16% 20% 18% 6% 1	180
	21st to end	Day	35% 17% 25% 15% 8% 1	198
January	1st to 10th	Night	43% 14% 16% 17% 11% 1	850
	11th to 20th	Night	36% 10% 15% 22% 16% 1	741
	21st to end	Night	29% 12% 17% 25% 16% 2	792
February	1st to 10th	Night	30% 16% 20% 23% 10% 2	720
	11th to 20th	Night	26% 16% 22% 23% 13% 1	704
	21st to end	Night	29% 15% 24% 20% 11% 1	592
March	1st to 10th	Night	27% 13% 22% 24% 13% 2	720
	11th to 20th	Night	28% 13% 22% 23% 12% 2	720
	21st to end	Night	30% 12% 22% 24% 10% 1	792
April	1st to 10th	Night	25% 12% 24% 25% 13% 1	720
	11th to 20th	Night	18% 13% 26% 27% 14% 2	658
	21st to end	Night	19% 8% 26% 34% 12% 1	540
May	1st to 10th	Night	13% 10% 24% 36% 16% 1	360
	11th to 20th	Night	16% 5% 24% 33% 21% 1	354
	21st to end	Night	11% 7% 23% 38% 20% 2	389
June	1st to 10th	Night	12% 8% 26% 35% 19% 1	360
	11th to 20th	Night	11% 9% 29% 35% 16%	360
	21st to end	Night	7% 5% 28% 34% 25% 1	360
July	1st to 10th	Night	6% 1 19% 45% 27% 1	350
	11th to 20th	Night	4 4 15% 47% 28% 2	348
	21st to end	Night	3 2 13% 47% 32% 2	394
August	1st to 10th	Night	4 3 14% 33% 41% 5%	451
	11th to 20th	Night	6% 2 10% 32% 46% 5%	534
	21st to end	Night	10% 3 19% 37% 27% 3	676
September	1st to 10th	Night	8% 4 21% 34% 28% 4	720
	11th to 20th	Night	12% 4 19% 30% 29% 5%	720
	21st to end	Night	16% 7% 20% 33% 21% 3	720
October	1st to 10th	Night	21% 7% 16% 29% 24% 3	720
	11th to 20th	Night	25% 8% 16% 27% 20% 4	720
	21st to end	Night	30% 10% 21% 22% 15% 2	792
November	1st to 10th	Night	33% 9% 22% 25% 10% 1	740
	11th to 20th	Night	33% 13% 22% 20% 11% 1	760
	21st to end	Night	29% 9% 24% 23% 13% 2	760
December	1st to 10th	Night	31% 9% 19% 26% 14% 1	760
	11th to 20th	Night	37% 11% 20% 22% 9% 1	762
	21st to end	Night	39% 14% 21% 18% 8% 1	935

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